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Folding of coated paper is examined numerically using the finite element method. Particular emphasis is put on the behaviour of field variables relevant for cracking of the coating layers. In the numerical analysis, the basepaper is modelled as an anisotropic elastic–plastic material (both elastic and plastic anisotropy is accounted for) while the constitutive behaviour of the coating layers are approximated by classical (Mises) elastoplasticity. The numerical results suggest, among other things, that particular forms of plastic anisotropy can substantially reduce the maximum strain levels in the coating. It is also shown that delamination buckling, in the present circumstances, will have a very small influence on the strain levels in the coating layer subjected to high tensile loading. [Copyright &y& Elsevier]

Abstract: The creep of paper is accelerated by moisture cycling. This effect is known as mechano-sorptive creep. It is assumed that this is an effect of transient stresses produced during moisture content changes in combination with non-linear creep behaviour of the fibres. The stresses produced by the moisture content changes are often much larger than the applied mechanical loads. If this is the case, the mechanical loads are only a perturbation to the internal stress state, and it will appear as if the mechano-sorptive creep is linear in stress. It is possible to take advantage of this feature. In the present report the pure moisture problem is first solved. The mechanical load is then treated as a perturbation of the solution to the moisture problem. Using this strategy, it is possible to linearize a non-linear network model for mechano-sorptive creep and to formulate a continuum model. As a result, the number of variables in the model is reduced. This is a significant improvement as it will be possible to use the linearized model to describe the material in a finite element program and solve problems with complicated geometries. [Copyright &y& Elsevier]

• A complex variable EFG method for hyperelastic large deformation under non-conservative loads was proposed. • Deformation and stress of hyperelastic materials under non-conservative loads were analysed. • The approximation function of the displacement field was established by the complex variable moving least-squares method. • The complex variable EFG method has a great advantage in efficiency and accuracy than other methods. The finite element method is extremely popular in almost all fields of engineering and scientific research due to its powerful and accessible industrial software for computational modelling. However, alternatives including the meshless methods, have received increasing attention on the large deformation problems of hyperelastic materials that need to avoid mesh distortion. In this paper, based on the complex variable moving least-squares approximation, the complex variable element-free Galerkin (CVEFG) method for the large deformation problem of hyperelastic materials under non-conservative loads is established. In the present method, the Newton-Raphson method is used for solving the nonlinear equations. The algorithm for hyperelastic large deformation problems under non-conservative loads are established. Three numerical examples are used to verify the effectiveness of the CVEFG method in this paper. Numerical results show that the solution obtained using the CVEFG method is closer to that obtained by ABAQUS and is more efficient than the element-free Galerkin method. [ABSTRACT FROM AUTHOR]

In this paper we introduce and analyze a Banach spaces-based approach yielding a fully-mixed finite element method for numerically solving the stationary chemotaxis-Navier-Stokes problem. This is a nonlinear coupled model representing the biological process given by the cell movement, driven by either an internal or an external chemical signal, within an incompressible fluid. In addition to the velocity and pressure of the fluid, the velocity gradient and the Bernouilli-type stress tensor are introduced as further unknowns, which allows to eliminate the pressure from the equations and compute it afterwards via a postprocessing formula. In turn, besides the cell density and the chemical signal concentration, the pseudostress associated with the former and the gradient of the latter are introduced as auxiliary unknowns as well. The resulting continuous formulation, posed in suitable Banach spaces, consists of a coupled system of three saddle point-type problems, each one of them perturbed with trilinear forms that depend on data and the unknowns of the other two. The well-posedness of it is analyzed by means of a fixed-point strategy, so that the classical Banach theorem, along with the Babuška-Brezzi theory in Banach spaces, allow to conclude, under a smallness assumption on the data, the existence of a unique solution. Adopting an analogue approach for the associated Galerkin scheme, and under suitable hypotheses on arbitrary finite element subspaces employed, we apply the Brouwer and Banach theorems to show existence and then uniqueness of the discrete solution. General a priori error estimates, including those for the postprocessed pressure, are also derived. Next, a specific set of finite element subspaces satisfying the required stability conditions, and yielding approximate local conservation of momentum, is introduced, which, given an integer k ≥ 0 , is defined in terms of Raviart-Thomas spaces of order k and piecewise polynomials of degree ≤ k only. The respective rates of convergence of the resulting Galerkin method are then provided. Finally, several numerical experiments confirming the latter and illustrating the good performance of the method, are reported. [ABSTRACT FROM AUTHOR]

This paper describes an advanced coupling method of finite element and discrete element called the Continuum-Discontinuum Element Method (CDEM). In this study, the Barton-Bandis model(BB model) for joint non-linear deformation is introduced into the CDEM to investigate the propagation of stress waves in jointed rock masses. The paper provides a detailed account of the development process of the BB model. Then, the developed model is utilized to simulate several representative cases of stress wave propagation in jointed rock masses, revealing the principles of stress wave propagation in jointed rock masses. The findings of this study demonstrate that the simulation results of the CDEM exhibit favorable consistency with experimental and theoretical results. This confirms the capability of the CDEM to accurately and effectively simulate stress wave propagation in jointed rock masses, thereby expanding the applicability of the CDEM. This research provides powerful support for further understanding and analysis of stress wave propagation problems in jointed rock masses. [ABSTRACT FROM AUTHOR]

• An atomistic–continuum multi-scale method is developed for nonlinear behavior of hetrogenous nano-materials. • The nucleation, migration, and elimination of dislocation as well as the dislocation-vacancy interaction are captured. • Effect of nano-scale void defects is modeled using the stress tensor and tangent modulus derived from atomistic RVE. • A statistical study is exerted to investigate the effect of influential parameters on the RVE mechanical behavior. • The mechanical behavior of nano-porous gold foam is studied during the compaction process. In this paper, an atomistic–continuum homogenization multiscale method is developed to study the nonlinear behavior of heterogeneous nanomaterials. The atomistic representative volume element (RVE) with vacancy and/or void defects are analyzed by employing the fully atomistic method, in which the nucleation, migration, and elimination of dislocation, as well as the dislocation-vacancy interaction, are captured. The coarse-scale material domain is modeled within the framework of the nonlinear finite element method, and the impression of nanoscale material defects is investigated by upscaling the stress tensor and tangent modulus from the atomistic RVE based on the Hill-Mandel principle. The principle of inter-scale kinematic compatibility is implemented using the periodic boundary condition. The mechanical behavior of atomistic RVE under various deformation modes is elucidated through stress – strain and dislocation density – strain curves. Due to the random nature of defects on the atomistic scale, a statistical procedure is exerted to numerically investigate the effect of influential parameters on the RVE mechanical behavior. Finally, the impression of vacancy and/or nanoscale void defects on the multiscale simulation of coarse-scale materials is illustrated in several numerical examples. The obtained results of the multiscale analysis is also verified with experimental data. Moreover, the compaction behavior of nanoporous gold foam is studied through the proposed multiscale method that highlights a good agreement with the fully atomistic analysis. [ABSTRACT FROM AUTHOR]

As studies on the damage behaviors of composites during screw type blind riveting are notably absent, this paper seeks to fill this gap by combining experimental tests and numerical simulation methods. A three-dimensional finite element model was proposed, and the simulation results were obtained and validated by experimental data. The light microscope and scanning electron microscope were used to observe the stress state, axial deformation, damage modes, and damage distribution in two load-bearing regions at the initial contact and after installation. The results demonstrated that the preload showed a four-step "zero -steep rise -decline -steep rise" development during installation. The stress and deformation were concentrated in two circular zones, with the maximum axial stress component and deformation of 321 MPa and 0.046 mm, respectively. In two pressed zones, there were three failure modes, with out-plane matrix crushing being the most severe. In-plane matrix cracking damage is seen at a 45° direction in the first layer, with a damage index of 0.745. In addition, the effect of two geometric parameters of the sleeve on the blind head shape, load-bearing regions, and CFRP damage was investigated. The results would build confidence in reducing CFRP damage and enhancing joint integrity. [ABSTRACT FROM AUTHOR]

In this paper, the finite element method is utilized to evaluate the behavior of the armchair phosphorene nanotubes under the compressive loading. The energy equations of the molecular and structural mechanics are used to obtain the elemental properties. The critical compressive forces of various armchair phosphorene nanotubes are computed with clamped-clamped and clamped-free boundary conditions. Results show that the stability of armchair phosphorene nanotubes increases with increasing nanotube aspect ratio, particularly under clamped-clamped boundary conditions. Finally, the buckling mode shapes of armchair phosphorene nanotubes under different boundary conditions are compared. Our work offers valuable insights into how these nanotubes respond to mechanical stress, helps determine elemental properties, and investigates the effects of nanotube geometry and different boundary conditions on their stability. This knowledge has broad applications in fields like nanotechnology, materials science, and nanomechanics, advancing the understanding of nanoscale materials and their potential for various practical uses. The finite element method is utilized to evaluate the behavior of the armchair phosphorene nanotubes under the compressive loading. [Display omitted] • FE method is utilized to evaluate the behavior of the armchair PNTs under the compressive loading. • The elemental properties are obtained by the energy equations of the molecular and structural mechanics. • The buckling forces of the armchair PNTs with different radii and lengths are computed. • The stability of armchair PNTs increases by increasing the nanotube aspect ratio. • The clamped-clamped nanotubes are more stable than clamped-free ones. [ABSTRACT FROM AUTHOR]

• A train-cracked track slab coupled dynamic model is newly established by co-simulation technology. • The reliability of the proposed model is demonstrated by comparison with field measurement results. • The dynamic characteristic differences of the entire system with or without side cracks are revealed. • Several new insights into the dynamic stress of the slab with side-crack. The Ballastless track have been extensively implemented in high-speed railways. However, during the long-term operational process, degradation, such as side crack or defect phenomena produced on the slab inevitably, poses a threat to the stability and the durability of the track structure. Consequently, it is imperative to propose a dynamic approach that can effectively predict the impact of side-cracked slab (SCS) on the vehicle-track coupled system. This paper utilizes co-simulation technology to investigate the dynamic behavior of the slab with and without side crack. Firstly, the dynamic substructure of the finite element model of the SCS is obtained by eigenvalue analysis. Secondly, the SCS model has been applied to the classical vehicle-track coupled dynamic system, and the coupled dynamic model of the train-side cracked slab (TSCS) is established, which considers the multi-rigid-body vehicle subsystem, the flexible rail subsystem, the flexible SCS and subgrade foundation subsystem, and the wheel-rail nonlinear contact model. Later, the accuracy and reliability of the proposed model are verified by the comparison with field tests. Finally, the differences in the vibration characteristics of the vehicle and track structure with and without a side crack are compared and analyzed, and its dynamic stress of the slab as variable train speeds is revealed. The results indicate that the existence of a side crack will reduce the natural frequency of the slab, with a maximum decrease of 22.31%. Although the SCS has a minor effect on the vehicle responses, the existence of a side crack has a significant impact on the slab, especially on the root mean square (RMS) of the vibration acceleration of the slab, with a maximum difference of 74.10% laterally and an increase of 55.16% vertically. Meanwhile, the train speed remarkably affects the crack tip dynamic stress of the SCS, with a maximum increase of 76.07% in the longitudinal direction, 50.34% in the lateral direction and 49.09% in the vertical direction. Higher train speeds will further exacerbate crack propagation under long-term train loading. This study may contribute to the dynamic modeling of TSCS systems and the maintenance of the slab ballastless track. [ABSTRACT FROM AUTHOR]

• Establish a relationship between bite depth and residual collapse strength. • Determine the critical depth of slip bite by calculating the extrusion force. • Propose a new simulation methodology to test slip ultimate bearing capacity. • Carry out indoor tests to test the ultimate load-bearing capacity of the slip. • Optimal design of slip structure based on casing damage and ultimate bearing capacity. The packer's slips indent the inner wall of the casing, leaving a series of marks between the teeth of the slips and the inner wall of the casing. Excessive bite depth can result in damage to the inner wall of the casing, potentially leading to failure. To minimize damage to the inner wall of the casing and improve the ultimate bearing capacity of the slip, a three-dimensional finite element analysis model of the slips is developed and validated through laboratory experiments. The optimization objective is to minimize casing damage and maximize bearing capacity. This paper examines the correlation between the residual collapse strength of the casing and the maximum depth of slips penetrating the inner wall. It determines the critical depth value by calculating the extrusion force endured by the inner wall of the casing as an optimization evaluation index. At the same time, the optimal structural parameters of the slips were determined through numerical simulation and orthogonal experiments. These parameters include a 90° dental angle, a 21° inner cone angle, a 219 mm outer diameter, and a 6.5 mm tooth pitch. The research results indicate that the equivalent stress of the improved slip has decreased by 8.66 %. The equivalent stress on the inner wall of the casing has been reduced by 9.34 %, and the maximum tooth mark depth of the casing has decreased by 30.48 %. Furthermore, the ultimate bearing capacity of the slip has increased by 2.24 times. Research has shown that the improved slip not only reduces damage to the inner wall of the casing and minimizes stress concentration on the slip, but also increases the ultimate bearing capacity of the slip. The research results can serve as a reference for the study and application of packers. [ABSTRACT FROM AUTHOR]

In this paper, a novel numerical simulation approach based on the finite element method for dynamically modeling the excavation process of shield tunneling is proposed, with the shield-ground interactions well captured. This method is capable of mimicking the alternating modes of advancing and stopping of a shield boring machine during underground construction, with the important effects of the cutterhead rotation and slurry support pressure considered. Under the cutting action, the soil at the excavation face would experience irreversible deformation and damage, such that additional support needs to be provided by the cutterhead blades and slurry to maintain stability. The impacts of key construction parameters are examined, including cutterhead rotary speed, advance rate, and slurry support pressure, on shield tunneling operations and ground responses. The numerical model is rigorously validated against physical model experiments. This work provides useful insights into the mechanistic processes in the stratum during shield tunneling, including the spatiotemporal evolution of ground deformation patterns and stress redistributions. The results offer valuable guidance for optimizing shield tunneling operations and enhancing tunneling safety and efficiency. [ABSTRACT FROM AUTHOR]

Non-directional rafting of γ' phases in high generation nickel-based single crystal superalloys happens when the alloys are thermally exposed at high temperatures, but so far the reason remains unclear. The microstructures and internal stress fields of a 4th generation single crystal superalloy during thermal exposure at 1100 ℃ and 950 ℃ are investigated using transmission electron microscopy and finite element analysis. It is found that the non-directional rafting of γ' phases occurs after 1100 ℃/200 h and 950 ℃/500 h thermal exposures. The γ' phases are mainly rodlike shape in the space after thermal exposures and a small quantity of γ' rafts exist as well. The elastic strain energy gradient in γ matrix caused by the inhomogeneity of matrix channel width in the alloy is most likely the driving force for the non-directional rafting. Additionally, dislocations are observed only after the thermal exposure process at 1100 ℃. The effect of dislocations on non-directional rafting during thermal exposure is discussed in detail in the paper. • TEM and finite element analysis are used to study non-directional rafting of γ'. • γ' phases are mainly rodlike spatially after thermal exposure at high temperature. • It is found that dislocations are unnecessary for the non-directional rafting. • Elastic strain energy is larger in narrower γ matrix channel at high temperature. • Elastic strain energy gradient in matrix probably causes non-directional rafting. [ABSTRACT FROM AUTHOR]

The battery-pack system of electric vehicles is prone to collide with low obstacles on the road, causing battery short circuits and even explosions. It poses a great safety threat to passengers and drivers. The honeycomb structure's high energy absorption and lightweight properties have made it a popular choice in the automotive industry. This paper designs different bio-inspired honeycomb structures to a battery-pack system of electric vehicles to improve the crashworthiness performance. The effects of different bio-inspired honeycomb structures on the crashworthiness of a battery-pack system during frontal impact are analyzed based on a nonlinear finite element model. First, the geometric parameters of seven different bio-inspired honeycomb individual units are described. The overall structure of the honeycomb is applied to a battery-pack system. Second, the nonlinear finite element model of a battery-pack system and honeycomb structures are established and verified. Then, collision simulations are conducted. The deformation and the maximum stress of a battery-pack's bottom shell are computed. The energy absorbed by the honeycomb structures during frontal impact are investigated. The results indicate that the proposed bio-inspired honeycomb structure mimicking grass stems improves the safety performance of battery-pack systems most. Finally, a parametric design is carried out on the bio-inspired honeycomb structure. The effects of wall thicknesses and the number of replacement hexagons on the crashworthiness performance are analyzed. The honeycomb structure preforms best when thickness is 1 mm and the number of replacement hexagons is 2 and 4. The optimized bio-inspired honeycomb structure reduces the deformation of the battery-pack' bottom shell by up to 30%, and maximum stress by 10%. • The deformation, maximum stress, and energy absorption are investigated. • The effects of seven bio-inspired honeycomb structures are analyzed. • Parametric design is carried out to further improve the crashworthiness performance. • The deformation of the bottom shell can be reduced by up to 30%. [ABSTRACT FROM AUTHOR]

Due to the multi-functional requirements, more and more multi-dimensional functionally graded structures are reported, while their thermo-mechanical performances are still unclear. This paper aims at theoretically examining the thermo-mechanical behaviors of two-dimensional functionally graded (2D-FG) microbeam excited by a moving load. The formulation is established in the framework of the modified couple stress theory in combination with Hamilton's principle, and this problem is numerically solved through the finite element method (FEM). The material properties of the 2D-FG microbeam are treated as temperature-dependent parameters that vary smoothly along with both the axial and thickness directions, and three different thermal loads including the uniform, linear, and nonlinear temperature rises are taken into account. Both the fundamental frequency and the dynamic transverse deflection are analyzed with consideration of different axial and thickness gradient indexes, thermal load types, temperature rise amplitudes, and small scale parameters. The conclusion obtained in this paper can serve as a guideline for assessing the thermal performance of microstructures subjected to a moving load. • A two-dimensional functionally graded (2D-FG) microbeam under moving load is modeled. • 2D-FG material properties are treated as temperature-dependent parameters. • Influences of uniform, linear and nonlinear temperature rises are compared. • Coupling effect of temperature rise and moving load on the dynamic deflection is analyzed. [ABSTRACT FROM AUTHOR]

• The heterogeneous aggregate expansion rooted from fast neutron was considered. • Radiation-induced damage yields significant stiffness degradation. • Combined effect of neutron radiation, lateral stress ratio and strain rate was investigated. • Failure mechanism of radiation-induced concrete under biaxial compression was revealed. • Formulas of biaxial compression strength for radiation-induced concretes were derived. As a good shielding material, heavyweight concrete is largely utilized for building the Concrete Biological Shielding (CBS) wall of the commercial nuclear power plant, and is often subjected to the biaxial loadings with a strain rate possibly varying from 10−5s−1 to 10−2s−1. This paper assesses the combined effects of the lateral stress and the strain rate on the compressive strength of radiation-induced heavyweight concrete on the example of serpentine concrete. For this goal, a 3-dimensional rectangular numerical concrete specimen containing special aggregates and ITZs was firstly established. Exposed to neutrons of different fluences, the initial damages caused by the fast neutron were assessed by a thermal-mechanical approach. Then, a series of static and dynamic biaxial compressive tests on the rectangular specimens having initial damages of different degrees were carried out by finite element analysis via ABAQUS. The failure modes, the crack patterns, and the ultimate compressive strengths of the pre-irradiated serpentine concrete were obtained numerically. Finally, based on the numerical results and the classical "Kupfer-Gerstle" ("K-G") criterion, this paper derives the biaxial strength criterion of the radiation-induced heavyweight concrete undergoing both lateral stress and strain rate. Through the formula, it was found that the fast neutron fluence of high level reduces significantly the biaxial compressive strength of the heavyweight concrete. Besides, if the heavyweight concrete undergoes additionally lateral stress and the strain rate, the biaxial compressive strength could be enhanced. The enhancement effect was maximized at the lateral stress ratio of 0.5 and the strain rate of 10−2s−1. The current numerical approach was developed with a potential application to the lifetime extension of the heavyweight concrete infrastructures used in commercial nuclear reactors. [Display omitted] [ABSTRACT FROM AUTHOR]

• A stress-based evolutionary topology optimization framework via XIGA is proposed. • Geometric boundaries of optimized design explicitly expressed as B-spline. • Satisfactory stress accuracy along the structural boundaries is guaranteed by XIGA. • No need for fine meshing to achieve clear strength design with smooth boundaries. • Structural boundary control points of the strength design can be directly edited to further improve strength performance. This paper presents a novel approach to stress-based topology optimization that employs NURBS representations of explicit geometric boundaries to address stress minimization and stress-constrained problems. The proposed methodology is compatible with CAD systems and utilizes Extended IsoGeometric Analysis (XIGA) to ensure an accurate representation of stress field in the evolving structure. A p -norm aggregation scheme is used to measure global stress levels, and the aggregated stress constraint is augmented to the objective (compliance) via a Lagrange multiplier in stress-constrained problems. The proposed approach introduces a novel and efficient Lagrange multiplier trail strategy aimed at reducing computational costs. Additionally, a normalization scheme and a partial differential equation filter are presented to stabilize the highly nonlinear stress-based optimization. Validation studies demonstrate the effectiveness and characteristics of the proposed approach. Moreover, control points of the structural design can be directly edited to further improve strength performance. Comparative studies show clear advantages of the proposed methodology in terms of computational efficiency compared to other Finite element analysis (FEA)-based optimization methods. Overall, this paper presents a practical and novel approach that addresses the limitations of existing FEA-based optimization methods in terms of accuracy, flexibility, and degree of freedom (DOF) cost, and makes a significant contribution to the field of stress-based topology optimization. Graphical abstract [Display omitted] [ABSTRACT FROM AUTHOR]

• Level-set method is applied for stress-based topology optimization of plate problems. • Solving optimization problems with arbitrarily complex geometries and boundaries. • A stabilized least-squares method is applied for solving level-set-based equations. • The shape derivatives, adjoint method, and p -norm aggregation function are used. In this paper, we present a stress-based topology optimization of plate structures by using a finite element level-set (LS) method. Since stress constraints are independent with LS-based design variables, the singularity phenomenon arising in topology optimization under stress constraints can be resolved without using any relaxation technique. The finite element method is used for solving LS-based equations of design variables and the state and adjoint equations of plate structures with arbitrary complex geometries and boundaries of the design domain. To obtain stable finite element solutions without any oscillation, both unsteady LS convection-diffusion equation and LS re-initialization convection-reaction equation are solved using a stabilized least-squares finite element method. [ABSTRACT FROM AUTHOR]

Although extensive experimental and numerical studies have been conducted on the axial performance of steel tube and sandwiched concrete jacketed CFST columns, contableurations with outer square tubes and inner circular CFST components are rarely found. This paper investigates the axial performance of square steel tube and sandwiched concrete jacketed circular CFST columns, examining the effects of outer steel ratio and sandwiched concrete strength on failure patterns, relative load-strain curves, and load-bearing capacity. The analysis of ultimate compressive capacity confirmed the effective confinement provided by the outer square steel tube. Based on the experimental results, a finite element model was established to further study the working mechanism of retrofitted columns. The load on components, distribution of longitudinal stress and transverse constraint stress on concrete revealed that the inner concrete experiences dual confinement effects from both inner and outer steel tubes, with the constraint of the outer square steel tube becoming significant only during the load dropping phase. Furthermore, a simple equation was proposed for predicting the axial compressive load-bearing capacity of retrofitted columns using superposition methods and design codes. Comparison results demonstrated good agreement between experimental and calculated values. • The axial performance of circular CFST columns strengthened with square steel tube and sandwiched concrete jackets was investigated. • The outer tube thickness had a greater impact on the compressive strength of retrofitted columns compared to the sandwiched concrete strength. • A finite element model was established to study the force mechanism of axially-loaded circular CFST columns strengthened with square STSCJ. • An equation was proposed to calculate the axial compressive capacity of retrofitted columns based on the superposition methods and design codes. [ABSTRACT FROM AUTHOR]

This paper presents the experimental and numerical results of an ongoing research project on the use of thermal break systems (TBSs) in internally insulated reinforced concrete (RC) structures. A new TBS, which combines steel profiles and U-shaped steel bars, is introduced and tested under monotonic loading to determine its horizontal and vertical shear capacities. The test results confirmed the appropriateness of SLABE-TBS for use in exterior wall–slab joints that demand high ductility or energy absorption despite the failure mode by concrete punching. The tested joints exhibited load-carrying capacities of 190.2 and 120.5 kN/m under horizontal and vertical loading, respectively. On the other hand, the finite element analysis performed using LS-DYNA software confirmed the significance of the U-shaped steel bars of the SLABE-TBS in improving the joint's shear capacity. However, incorporating the steel bars in the SLABE unit can reduce the equivalent stresses in the adjacent steel profiles by 33 %. • A new thermal break system (SLABE-ZN) for exterior wall–slab joints was proposed. • The tested exterior joints equipped with SLABE-ZN exhibited stable behavior under horizontal and vertical loading. • Incorporating steel bars in the SLABE unit can reduce the equivalent stresses in adjacent steel profiles by 33 %. • The contribution of the U-steel bars was approximately 30 % and 21 % under horizontal and vertical loading, respectively. • Decreasing the insulation thickness by 10 mm accounts for a 7 % increase in the load-carrying capacity of the SLABE system. [ABSTRACT FROM AUTHOR]

In this paper, a composite column using carbon fibre reinforced plastics and polyvinyl chloride composite tube (CFRP-PVC) to constrain coral aggregate seawater sea-sand concrete (CSSC) was proposed, and CFRP was pasted on the inner and outer walls of the PVC tube. To investigate the effects of the number of CFRP layers and void defects on the axial compression performance of PVC tubes, six specimens were made for axial compression loading tests and finite element parameter analysis. The results indicate that due to PVC improving the integrity of CFRP, PVC tube provide a stress transfer path for CFRP, placing CSSC in a triaxial compression state. When both the inner and outer walls of the tube are pasted with CFRP, brittle failure of CFRP-PVC tube can be effectively avoided and have relatively superior mechanical properties. In the same situation, when one layer of CFRP is pasted on the inner wall of the tube, it has better ductility and bearing capacity. When two layers of CFRP are pasted on the outer wall of the tube, the coefficient of constraint stress increase is as high as 121.5%, and the void defect only has a significant impact on ductility. A finite element model of CFRP-PVC confined CSSC columns considering Hashin damage criterion was established based on ABAQUS, accurately predicting the failure process and CFRP damage morphology of test columns under axial load. Parameter analysis shows that when the confinement coefficient of CFRP-PVC confined CSSC columns is less than 0.3 and the height-diameter ratio is greater than 15, the load-displacement curve will lose the strengthening stage, and increasing the number of outer CFRP layers will slightly increase the stiffness of the strengthening stage. A bearing capacity calculation method suitable for CFRP-PVC confined CSSC was proposed based on the model of steel tube confined concrete, with an error of 1.2%. ● CFRP-PVC tube confined coral aggregate seawater sea-sand concrete (CSSC) column was proposed. ● The axial compression test was conducted to explore the mechanical properties of CFRP-PVC confined CSSC columns. ● The finite element models of the CFRP-PVC confined CSSC column were established to conduct parametric investigation. ● The axial strength calculation method of CFRP-PVC confined CSSC columns was proposed considering the CFRP-PVC tube restraint efficiency. [ABSTRACT FROM AUTHOR]

The working environment of industrial fields where the Particulate Reinforced Composites (PRCs) are commonly used is complex. In these harsh environments, PRCs produce some nonlinear strains, such as plastic, thermal, and creep strains, which affect the performance of PRCs to some extent. In addition, the actual structure of PRCs contains a massive amount of inclusions, and the number of inclusions could reach the magnitude of millions or even tens of millions. For the large-scale numerical simulation of PRCs, ordinary displacement finite element requires a large number of meshes, which increases their computational complexity and unsolvability. For real PRCs with random particle distribution, homogenisation theory does not accurately capture the true state of stress concentration in PRCs. The Voronoi cell finite element method (VCFEM) can be a good solution to the drawbacks of the above two numerical simulation methods. The subject of the present work explores a modified complementary energy generalized function that takes the constitutive relationship of nonlinear strain into account, proposing a two-dimensional VCFEM, formulated with plastic, thermal, and creep strain. The simulation results are compared with the computed results of a commercial finite element software Marc to verify the validity and accuracy of the VCFEM. Results of the comparison show that the VCFEM has the advantages of simple meshing and faster computation under the same precision. The VCFEM, considering plastic, thermal, and creep strains proposed in this paper, lays the foundation for future large-scale numerical simulations of PRCs containing a large quantity of inclusion structures and can realistically capture the stress concentration state of PRCs. At the end of the article, the impact of the order of stress function on the calculation results is discussed. [ABSTRACT FROM AUTHOR]

With the advancement of 3D printing technology, manufacturing metamaterials with extreme mechanical properties is becoming more feasible. Hierarchical lattices appear to be ideal candidates for obtaining desirable lightweight, high specific stiffness, and enhanced specific energy absorption. They can be constructed by architected substructures at multiple length scales. The interpretations of the underlying deformation mechanisms are necessary in order to manipulate with expected mechanical properties. In this paper, experiments were conducted to examine the effective mechanical behaviors of hierarchical lattice metamaterials. A strain gradient homogenization approach has been employed to correlate their morphological characteristics to the resulting material properties. The effective stiffness tensors are identified including the fourth-, fifth-, and sixth-order stiffness tensors. The higher-order inertial parameters are determined by a fitting procedure. Comparisons between direct finite element analyses and the homogenized strain gradient continua have been made for hierarchical lattice materials under static and dynamic loads. It is found that strain gradient homogenization approach can be an accurate, efficient and reliable way of predicting the mechanical behaviors of hierarchical lattice. A systematic analysis of geometrical parameters was conducted to uncover the underlying mechanisms responsible for the enhancement of effective properties. This work offers a novel approach for designing the mechanical properties of hierarchical metamaterials through precise control of secondary structure types and distributions. • Experimental compression tests reveal the relevance of the shape of lattice microstructure. • Detailed homogenization and iterative homogenization methods are compared. • Hierarchical lattices are investigated by means of parameters determined by strain gradient homogenization. • The high accuracy and necessity of strain gradient homogenization is revealed by a method comparison. [Display omitted] [ABSTRACT FROM AUTHOR]

In this paper, the flexoelectric effect in flexoelectric semiconductors (FSs) is studied via a second-order collocation mixed finite element method (MFEM) with the consideration of the strain gradient, electric field gradient, and drift-diffusion motion of carriers. In the present second-order collocation MFEM, the mechanical strain is assumed to be an independent quadratic polynomial function of local coordinates, and the kinematic constraint between the mechanical strain and displacement is approximately satisfied through a collocation method at 9 Gaussian quadrature points in each element. The setup for the electric field and electric potential also follows similar collocation strategy. Thus, except for the fundamental field variables, no additional DOFs are introduced. The accuracy of the proposed second-order collocation MFEM is verified by comparing numerical results with analytical solutions for a cantilever beam example. By performing the numerical experiments using the second-order collocation MFEM, the flexoelectric effect in FSs is simulated. Besides, we propose a novel mechanism for the converse flexoelectric effect in FSs which is induced by the diffusion motion of electrons. Numerical results indicate that by intensifying the diffusion motion of electrons, the converse flexoelectric effect, associated with the electric field gradient, could be enhanced. [Display omitted] • Flexoelectricity in semiconductors is studied via a second-order collocation MFEM. • The mechanical strain is assumed to be an independent quadratic polynomial function. • The kinematic constraint is approximately satisfied at Gaussian points. • The converse flexoelectric effect can be induced by the diffusion motion of electrons. [ABSTRACT FROM AUTHOR]

The meshless numerical manifold method (MNMM) inherits the advantages of handling continuous and discontinuous problems uniformly, improving interpolation precision, and avoiding linear dependence issues. This paper refines the MNMM method for slope stability analysis to overcome the dependence and sensitivity of the strength reduction method of the finite element method on the number of finite element meshes and the algorithm for solving the nonlinear equations when calculating slopes with soft and weak interlayers. First, the strength reduction method (SRM) was incorporated into MNMM to create the numerical model called MNMM-SRM. Based on the MNMM-SRM, a complementary Mohr-Coulomb (M−C) control equation compliant with Koiter's rule of multi-yielding surfaces was established. In the principal stress space, the subspace tracking method was used to track the eigenvalues and eigenvectors of the stress tensor, thereby addressing the corner problem of M−C multi-yield surfaces. Combining the k-means clustering algorithm with wavelet transformation and employing the slope's total nodal displacement field as an input variable, an intelligent and efficient critical slip surface (CSS) automatic extraction method was developed. Three typical cases were used to validate the accuracy of the numerical model. This numerical model has a wide range of potential applications in slope stability research. [ABSTRACT FROM AUTHOR]

In this paper, an efficient formulation for the topology optimization of extruded beams is developed considering linearized buckling, displacement, and stress constraints. The proposed method relies on a computationally efficient extended\generalized finite element (XFEM\GFEM) formulation for the forward problem, recently developed for the analysis of beams. In this method, a coarse 3D finite element (FE) mesh is enhanced with global enrichment functions, enabling a substantial reduction in the number of degrees of freedom with comparable accuracy to a traditional 3D FE fine mesh. The material distribution at the cross-section is optimized utilizing the material density approach with the Solid Isotropic Material with Penalization (SIMP) method. Our objective is to minimize the total weight of the beam, subject to performance constraints including buckling, displacement, and stress. The forward problem enables the application of general loading and boundary conditions. Thus, both buckling and lateral–torsional buckling are automatically considered. The optimization problem is solved using a gradient-based optimization approach, with analytical gradients derived by using the adjoint variable method. Several numerical examples are presented to investigate the accuracy and efficiency of the proposed formulation. A parametric study showed that the optimized cross-section is strongly dependent on the length and permissible buckling load. In addition, it is shown that a simultaneous formulation leads to significantly different designs, with different structural behavior, compared to results obtained by considering only a subset of the performance constraints. Finally, we verify the model on a beam warping problem under pure torsion, in which the cross-section optimization converges to a known analytical solution. Compared with traditional FEM, two orders of magnitude in terms of execution time are reported in favor of the proposed XFEM\GFEM approach. • A new approach for the topology optimization of extruded beams is proposed. • The forward problem is solved using an efficient numerical scheme relying on the extended finite element method. • The approach simultaneously considers buckling, stress, and displacement constraints. • We show that the beam's length significantly affects the optimal shape. • The proposed XFEM\GFEM approach shows significant time savings compared with 3D FE. [ABSTRACT FROM AUTHOR]

• Innovative Methodology: The research introduces a novel hybrid approach that combines analytical and numerical methods., • Relevance to "Engineering Failure Analysis": The article aligns with the journal and fosters discussions in the field. • Practical Implications : The study's findings contribute to improving safety, and performance in the gas pipe industry. • Contribution to Research : My inovation exposes traditional methods limits in engineeringanalysis. The present paper presents findings from a case study of a buried gas pipeline that ruptured, causing a gas cloud explosion and subsequent fire. The study aimed to identify the incident's cause and improve the pipeline's strength under specific conditions. The study measured the pipe's actual wall thickness and conducted stress analysis using analytical and finite element methods to assess its integrity under corrosion. It evaluated if the 20-inch pipeline near road crossings could withstand external forces. In conclusion, the research underscores the importance of accurately assessing the structural integrity of buried pipelines, especially under conditions of corrosion. It highlights the utility of finite element analysis in providing a more precise understanding of stress distribution and can aid in designing pipelines that are better equipped to withstand various external pressures. The investigation illustrates the importance of increasing the strength of buried natural gas pipelines, in the crossing road area and, for this purpose, it was proposed (in terms of novelty associated with the study) a solution consisting in introduction of the pipeline in protective sleeves fitted with spacer rings. [ABSTRACT FROM AUTHOR]

• This paper presents the fracture model calibration of SS275 hot-rolled thin plates, which involved quasi-static tests and finite element analysis. • The hardening model parameters were determined using the Swift law, while the ductile fracture model parameters were calibrated using the Hosford-Coulomb model within the linear damage framework. • The accuracy of the model was validated by comparing the results with the test data, and it was found that the highest fracture strain occurred in the uniaxial tension state. • The calibrated model was then used to predict the cycle life to failure in an extreme low cycle fatigue test, which was found to be 70 cycles. • The results indicate that the ductile fracture model performed well in predicting extremely low-cycle fatigue. • The paper's findings can be useful in predicting the fracture initniaon of engineering structures and components under multiaxial stress states, which can ultimately lead to improved designs and increased safety. The complexity of the loading conditions makes it challenging to accurately predict the damage evolution and resulting ductile fracture in materials and structures. This paper presents an application method to predict fracture initiation for low cycle fatigue of 4-point bending in structural steel SS275. The swift isotropic hardening law was used in the numerical simulation to account for large strain deformation. The damage indicator framework with the Hosford-Coulomb (HC) model was adopted to characterize the damage accumulation and fracture behavior. Uniaxial tension tests on specimens with various fracture modes were conducted to determine the material properties required for calibration of the plasticity model and fracture model param1eters. Non-linear finite element analyses were performed to identify fracture model parameters based on the loading path of fracture initiation. The presented HC model was applied to an extremely low fatigue test (less than 100 cycles) and demonstrated good accuracy in predicting fracture initiation for complex loading scenarios. [ABSTRACT FROM AUTHOR]

Prediction of the deformation during shape casting by FEM (finite element method) thermal stress analysis has been desired. For such prediction, validated constitutive models are essential for both the casting alloy and the mold. In this paper, two fatal defects in the modified Cam-Clay (MCC) model, which has conventionally been employed for a green sand mold, are clarified. The aim of this paper is to concurrently resolve these defects by a new yield criterion. The defects were those that cause an unreal distinct yielding and dilatancy peak on the stress-strain curve, which was clarified by comparing the true stress-strain curves obtained in the experiment and the FEM stress analysis of a triaxial compression test. A device capable of measuring the true stress during vertical compression was newly developed for the triaxial experiment. These defects inevitably led the MCC model to overestimate the mold strength by approximately 200% of the experimental value. This paper provides a new yield criterion, which employs an additional yield surface with the Drucker-Prager inherent surface, to rectify these defects of the MCC model. As a result of the stress analysis of the triaxial test with the new criterion, the smooth stress-strain curve with neither a peak nor a distinct yielding was reproduced. The calculated compressive stress traced the experimental value with less than a 15% error. Therefore, the new criterion should remarkably improve the accuracy of calculating the mold strength in the FEM thermal stress analyses during casting when compared to the MCC model. [Display omitted] • Modified Cam-Clay model of a green sand mold is constructed and validated. • An original triaxial test device is developed to validate the model experimentally. • Defects of the model that cause overestimation of the mold strength are clarified. • The defects are distinct yielding and dilatancy regardless of sand filling degree. • To resolve both of the two defects, a new yield criterion is proposed and validated. [ABSTRACT FROM AUTHOR]

To promote the analysis/design of high-strength steel (HSS) Q690E/Q960E structures, this paper firstly developed stress-strain (σ-ε) constitutive models of HSS Q690E/Q960E at different low temperatures (T) of −80, −60, −30, and 20 °C. The prediction equations on key parameters in the σ-ε constitutive models (e.g., yield/ultimate/fracture strength and their corresponding strains, and elastic modulus) of HSS Q690E/Q960E at varying low temperatures were developed. Validations against 39 test results confirmed that proposed constitutive models offered reasonable estimations on the low-temperature σ-ε constitutive models of HSS Q690E/Q960E. Finite element models (FEMs) with the continuum damage plasticity model (CDPM) and proposed σ-ε models were developed for HSS Q690E/Q960E materials at ambient/low temperatures. Validations of FEM simulations against 39 tensile tests on HSS coupons proved that the FEMs with CDPM predict well σ-ε behaviours of HSS Q690E/Q960E at −80–20 °C. This paper also developed FEMs with CDPM to simulate the low-temperature compression behaviour of HSS Q690E/Q960E tubular columns. Validations against six compression tests confirmed that the FEMs with the CDPM and proposed σ-ε constitutive models were capable of simulating the HSS Q690E/Q960E structural members. • Stress-strain (σ-ε) constitutive models of HSS Q690E and Q960E at low temperatures (T) are developed. • FEMs with proposed σ-ε models are developed for HSS Q690E and Q960E materials at low temperatures. • FEMs with CDPM predict well σ-ε behaviours of HSS Q690E and Q960E at −80–20 °C. • FEMs with the CDPM and proposed σ-ε constitutive models predict well behaviours of HSS Q690E and Q960E structural members. [ABSTRACT FROM AUTHOR]

• A new method for deformations and stresses of multi-angle FW pipes/vessels is for the first time presented in this paper. • More complex working conditions are taken into consideration. • Finite element method is used to compare with experimental and numeric results. • Results verify the effectiveness and accuracy of the proposed method. An multi-angle filament wound(FW) model is proposed under pressure, torsion and axial loads (multiple combined loads), which can calculate stresses and displacements of arbitrary multi-layers and bring more uniform strength though FW wall thickness. Based on orthotropic constitutive relation and axisymmetric thick-walled cylinder theory, a three-dimensional (3D) analytical solution for deformations and stresses of multi-angle FW pipes/vessels is presented. First, the stresses of fiber layer in cylindrical coordinate are obtained. Then, the deformations and stresses of each orthotropic winding layers, including longitudinal stresses σ 1 , transverse stresses σ 2 , σ 3 and shear stresses τ 12 are obtained, respectively. Moreover, the effect of shear extension coupling is taken into consideration because it is impossible for the ± ϕ winding angles to exist in the same radius. Subsequently, the proposed formulae are verified by numerical and experimental examples with finite element method (FEM). Results show that our new method calculates accurate stresses of FW pipes/vessels under multiple combined loads, which provides a theoretical foundation for damage analysis and optimization for FW structures. [ABSTRACT FROM AUTHOR]

Abstract Intelligent morphing wings have become a research hotspot due to their potential value. This paper is also an innovative basic research work to study it. The deformation performances of the GFRP(glass fiber reinforced polymer) composite beams embedded different pre-strained indented SMA wires were experimentally and numerically studied. The indentation SMA wire made by mechanical indentation method has better interface bonding strength than normal SMA wire. In this paper, the indented SMA wires acting as actuators, were embedded in a symmetrically GFRP laminated composite beam and located at the eccentric position of the laminate. The layering scheme of the laminated plate is as follows: [90°(4:1 fabric)/SMA/0°/0°/90°(4:1)]. The 0° direction is consistent with the direction of the axis of the SMA wire. The Finite element method is adopted to simulate the deformation of the beam with indented SMA wire in which the linear constitutive model of fully constrained SMA wires, together with considering their thermally-induced strain response, is used to describe the recoverable properties of SMA. The prediction from the numerical simulation agrees well with experimental measurements. [ABSTRACT FROM AUTHOR]

Abstract ASME B31 and EN 13480-3 piping design codes are considered as the state-of-the-art codes for many piping engineers. However, as shown in this paper, there seem to be inconsistencies between ASME B31 code and more elaborate calculation codes, such as ASME Section III. In fact, it is shown in the paper that the ASME B31 approach can produce potentially non-conservative results. This seemingly important flaw in the B31 (and other major) piping codes is based on the allowable stress calculation based on equation (1b) of both ASME B31.1 and B31.3 and has been shown in detail in the paper. Finally, the stated flaw is verified by means of a finite element analysis which corroborates the stated concerns. Highlights • Paper presents an overview and comparison of various piping Code philosophies. • Critical overview of verification criteria is provided. • New acceptance criteria which guarantee conservative design are proposed. • Validation of the statements given in form of FEA verification. [ABSTRACT FROM AUTHOR]

Highlights • An improved geometrical conception of the DEMO Divertor Cassette has been considered and a suitable finite element mesh has been adopted. • The loads really acting on this component have been evaluated detailly and applied overcoming the early hypothesis of uniform distribution: so the load spatial gradients have been reprioduced with more precision. • The obtained results confirm the previous deductions: the main role has been carried out by the thermal loads, and moreover the electric-magnetic loads determine a state of stress far lower than that caused by the thermal loads. • These thermal loads are the results of a dedicated thermal-fluid–dynamic numerical code properly developed for this aim. • Also in this case, an early application of RCC-MRx design rule have been applied: the Divertor Cassette results to be safe in nominal conditions while the same assessment states that the knuckle stress state is above faliure. Abstract This paper presents the enhancements related to the structural analyses of DEMO Divertor in the framework of the EUROfusion Power Plant Physics & Technology (PPPT) program. This activity started two years ago and its preliminary results were published in previous papers. It has been divided in some areas defined by the similarity of the matters they contain: the structural analysis, of utmost importance, has been preceded by a preliminary phase, like the geometry definition or the thermal and the electric-magnetic analysis for loads evaluation; then the structural analysis has been finally confirmed with further evaluations related to excessive deformation or plastic instability. This paper discusses the improvements adopted either in the preliminary analysis or in the main structural analysis. Specifically it highlights the introduction of the thermal and electro-magnetic loads application in terms of a detailed spatial distribution that is now available. More the supports have been introduced in the model and their structural behavior has been investigated considering their interaction with the cassette. The structural assessment, according to the Design and Construction Rules for Mechanical Components of Nuclear Installation (RCC-MRx), has been performed either for the cassette or for the attachments: for the former it is positive while for the latter case serious limitations have been found. [ABSTRACT FROM AUTHOR]

Abstract A concept for using snap-fit connectors in sandwich pipes is investigated numerically in two companion papers using a combination of 2D axisymmetric and 3D finite element models in Abaqus. In the Part 1 paper, results of key parametric studies related to the installation analysis of sandwich pipes in deepwater are reported. The modification of the nib groove to include variable radii, the use of an elastomeric seal coupled with compressive pre-stress and an optimum resin-to-core ratio all proved to enhance the performance of the sandwich pipe snap-fit connectors. The influence of the interlayer adhesion configuration on the stress concentration experienced in the connector is also studied. Furthermore, a comparative study is performed to investigate the mechanical behaviour of the snap-fit connector concept in sandwich pipes and conventional pipe-in-pipe. In the Part 2 paper, an optimisation study is carried out for the stress relief groove (SRG) in the pin of the snap-fit connector. A combined parameter is proposed to capture the relationship between the investigated geometric properties and the stress concentration factor at the SRG. It is established that the fillet radius could indeed be used to offset the drop in performance associated with increasing the SRG depth while improving the fatigue characteristics of the connector threads. Highlights • A snap-fit connector between sandwich pipes is analysed under installation loads. • Stress relief groove is optimised using a series of FE models. • A relationship between stress concentration and groove geometry is quantified. • Existence of optimal groove length is established. • Ways to offset drop in performance due to increased groove depth are suggested. [ABSTRACT FROM AUTHOR]

Over the past 5 years, a substantial research effort aimed at optimising the design of offshore wind turbines has led to significant reductions in the projected cost of developing offshore wind. Optimising the geotechnical design of these structures, through modern analysis techniques such as 3D Finite Element Modelling (FEM), has played a key role in helping to reduce costs. This paper presents a methodology for accurately modelling monopile behaviour using Cone Penetration Test (CPT) data to calibrate the non-linear stress dependent Hardening Soil (HS) model. The methodology is validated by comparing the modelled behaviour to field tests on a range of pile geometries. The paper also demonstrates how the soil-pile reaction response curves can be extracted from the FE model by isolating the stresses on each element of the pile. The contribution of each component to the overall lateral resistance is shown to vary with the pile geometry and is examined using the extracted soil reaction curves. [ABSTRACT FROM AUTHOR]

An enriched finite element procedure is proposed for formulating interaction of rock bolts with multiple intersecting/ non-intersecting joints in a rock mass. The numerical method involves analysis of reinforced rock mass having arbitrary joint dip angle, bolt angle and joint-bolt-grout properties in extended finite element (XFEM) platform. Shifted Heaviside and junction enrichment is incorporated for the intersecting jointed element. The paper presents procedures and formulation of stiffness matrices of a bolt crossing multiple joints (BCMJ) which may or may not intersect each other. Hence an element may contain two intersecting joints and a bolt. In that case for a 2D element, each node is enhanced to eleven degrees of freedom, 2 for rock displacements, 2 each for displacements of rock joints, 2 for displacements of the junction of joint intersection and 3 for displacements and rotation of bolt. The procedure also allows traction to be applied to a side of an enhanced element and to be transformed as nodal forces at enhanced degrees of freedom. The paper considers elastoplastic behaviour of joint surface and bolt-grout interface using Mohr-Coulomb criterion. For yielding of bolt rod unified tensile and bending criterion is adopted. The proposed method is implemented using 3-noded triangular elements and can be upgraded for higher order elements. The efficacy of the proposed procedure is evaluated by analyzing behaviour of a bolt reinforced jointed sample under direct shear test. The method is also applied to analyze displacements and stresses around a circular tunnel made in rock mass having multiple intersecting joints at different orientations, reinforced by bolts along the periphery of the tunnel. The results in terms of displacements and stresses are compared with those of unbolted rock mass model. The proposed method shows that effect of an individual joint, bolt and their interaction can be analyzed to understand the stability of excavation under given loading conditions and can be applied in wide variety of applications. [ABSTRACT FROM AUTHOR]

• Shell substrate with axisymmetric distribution thickness is investigated. • Different curvatures on upper and lower surfaces of substrate are involved. • Axisymmetric distribution film stress resultant is considered in the model. • Analytical formulas between shell deformation and film stress are provided. Axisymmetric film/substrate systems are irreplaceable for many applications, owing to special structural requirements. Stoney's formula is widely used to analyze the thin plate film/substrate system. Many researches have been presented to relax limitations of Stoney's formula, which considered the substrate as a thin plate without any curvature. For the optical lens, the axisymmetric thin shell substrate with different curvatures on its upper and lower surfaces is common due to the need of optical focusing. The film stress of the optical lens needs to be optimized and measured due to its effects on system deformations and optical performances. However, the optical lens cannot be solved by Stoney's formula and its extensions due to the curvatures. In this paper, analytical solutions for the thin shell optical lens with different curvatures on upper and lower substrate surfaces are developed by the thin shell theory with the axisymmetric distribution film stress resultant (FSR) in consideration. The FSR is modeled by thermal stress equivalent method, which allows the calculation for the axisymmetric distribution FSR induced by many factors. The forward and inverse solutions between the FSR and the bending deformation are provided in the form of simple formulas with correction coefficient vectors depending on the global substrate thickness, which enables its feasibility in practical applications. Moreover, the two solutions are verified by the finite element method considering the deformation normal to the substrate surface measured by the interferometer in inverse solution, and small errors are found when the optical lens conforms to the assumptions of the method in this paper. The proposed method is efficient to predict the optical lens' bending deformations, and extends the usage of curvature-based techniques from plates to shells with different curvatures on upper and lower surfaces in the film stress measurement, which makes great significance to the thin film/substrate application. [Display omitted] [ABSTRACT FROM AUTHOR]

In this paper we propose and analyze a fully-mixed finite element method for the steady-state model of fluidized beds. This numerical technique, which arises from the use of a dual-mixed approach in each phase, is motivated by a methodology previously applied to the stationary Navier–Stokes equations and related models. More precisely, we modify the stress tensors of the fluid and solid phases by defining pseudostresses as phasic stresses that include shear, pressure, and convective effects. Next, we eliminate the pressures from the equations and derive constitutive relations depending only on the aforementioned pseudostresses and the velocities of the fluid and the particles. In this way, these variables, together with the skew-symmetric parts of the velocity gradients, also named vorticities, become the only unknowns of our variational formulation. As usual, the latter is obtained by testing against suitable functions, and then integrating and integrating by parts, respectively, the equilibrium and the constitutive equations. The particle pressure, a known function of the concentration, is given as a datum, and the fluid pressure is computed afterwards via a postprocessing formula. The continuous setting, lying in a Banach spaces framework rather than in a Hilbertian one, is rewritten as an equivalent fixed-point equation, and hence the well-posedness analysis is carried out by combining the Babu s ˇ ka–Brezzi theory, the Banach–Ne c ˇ as–Babu s ˇ ka Theorem, and the classical Banach fixed-point Theorem. Thus, existence of a unique solution in a closed ball is guaranteed for sufficiently small data. In turn, the associated Galerkin scheme is introduced and analyzed analogously, so that, under suitable assumptions on generic finite element subspaces, and for sufficiently small data as well, the Brouwer and Banach fixed-point Theorems allow to conclude existence and uniqueness of solution, respectively. Specific finite element subspaces satisfying the required hypotheses are described, and optimal a priori error estimates are derived. Finally, several numerical examples illustrating the performance of the method and confirming the theoretical rates of convergence, are reported. [ABSTRACT FROM AUTHOR]

The necessary conditions for fabricating plasma sprayed self-healing MgO coating with excellent performance is to find an optimized coating structure with suitable thickness of each layer, self-healing agent content and low residual stress. This paper discusses the design and optimization of a suitable coating structure for the self-healing MgO coating prepared by atmospheric plasma spraying (APS) using the finite element method (FEM). Through the stress analysis of the special points of the coating and interface, a suitable coating structure is designed. The optimization of the coating structure mainly includes the thickness of the coating, the analysis of the composition of the coating and the analysis of the effect of convective heat transfer coefficient (CHTC) on the residual stress of the coating. The failure modes are predicted. The spray thickness of each layer and the fabrication method in the coating cooling process are optimized. [ABSTRACT FROM AUTHOR]

• LC sheet is characterised by a rounded stress–strain response with two "knee" regions. • A simplified full-range engineering stress–strain model for LC sheets is proposed. • An average weight method is used to determine post-necking true stress–strain curves. • Recommended values of weight factor and toughness coefficient for LC sheets are obtained. Laser cladding (LC) is being used increasingly in civil engineering owing to its high efficiency and minimal distortion since requiring little heat input; especially for repairing or strengthening damaged metal structures. LC stainless steel sheets are characterised by a rounded stress–strain response, with two "knee" regions and no sharply defined yield point. Such behaviour cannot be accurately represented by using previous stress–strain models. Moreover, determining the true stress–strain curve and toughness coefficient for the fracture model is essential to carry out a non-linear finite element analysis for solving elastoplastic problems. In the present study, one simplified full-range engineering stress–strain model for LC 316L stainless steel sheets is proposed based on the three-stage Hradil model and is validated against the experimental results of thirty tensile coupon tests. The proposed model redefines the second and third stages of the stress–strain curve following the experimental observations. All parameters in this simplified model can be derived directly from only four basic material property parameters: the initial elastic modulus, 0.2 % proof stress, ultimate stress and the strain corresponding to the ultimate stress. For defining the fracture model of LC stainless steel sheets, an average weight method is employed to determine the post-necking true stress–strain curves. The recommended values of the weight factor and toughness coefficient for the LC sheets are also obtained based on the available tensile coupon test results. The comparisons between the experimental force–displacement curves of the tensile coupons and the finite element analysis results using the proposed stress–strain relationship and fracture model for the LC sheets shows both results to be in good agreement. Therefore, the stress–strain relationship and fracture model proposed in this paper is suitable for use in the analytical and numerical modelling of structures having LC 316L stainless steel sheets. [ABSTRACT FROM AUTHOR]

The study of wave propagation in the periodic nano-waveguides is of importance to advance the development of energy and wave controlling systems. In this paper, firstly, the element discretization of nano structures is introduced based on the second strain gradient theory. The displacement field is determined through the utilization of six quintic Hermite polynomial interpolating functions. By applying Hamilton's principle, the weak form, which incorporates the element matrices, is determined and the global dynamic stiffness matrix of a unit cell is assembled. Then, the wave finite element method, based on the inverse form, direct form and contour integral solution, is used to analyze the two-dimensional free wave propagation properties of complex nano structures by solving the eigenvalue problems. The interpretation of the frequency spectrum is confined to the irreducible first Brillouin zone, encompassing both the dispersion relation and band structure. Furthermore, the slowness surfaces and energy flow vector fields are discussed via the second strain gradient theory. The novel work, which utilizes the second strain gradient theory equipped with the wave finite element method to investigate two-dimensional complex nano structures, has revealed significant potential in elucidating the two-dimensional wave propagation characteristics of the complex nano-waveguides. [Display omitted] • Second strain gradient theory is used for the modeling of 3D nano-sized structures. • Constitutive relation and weak form are calculated through the Hamilton's principle. • Eigenvalue problems are analyzed within the wave finite element method framework. • Wave propagation properties are illustrated through three complex nano-sized structures. [ABSTRACT FROM AUTHOR]

• The microstructure of 3rd GEN AHSS exhibits a complex phase of ferrite (46.2 %), bainite (36.1 %), martensite (9.4 %) and austenite (8.3 %) with excellent strength and ductility. • Macroscopic stress-strain relationships and microscopic hardening properties of the individual constituent phases are successfully determined. • The presence of bainite with a relatively high volume fraction induces the localization of plastic strain in the ferrite. • High strain, strain gradient and stress are concentrated in ferrite grains, ferrite/bainite grain boundaries and bainite grains, respectively, as fracture site initiation. This paper investigated the micromechanical properties and deformation behavior of the constituent phases in 3rd generation (GEN) complex phase advanced high-strength steel (AHSS). The hybrid method was a comprehensive combination of uniaxial tensile test with digital image correlation (DIC), electron backscatter diffraction (EBSD), in-situ neutron diffraction (NED) and crystal plasticity finite element method (CPFEM). Results reveal that the microstructure of 3rd GEN AHSS exhibits a complex phase of ferrite (46.2 %), bainite (36.1 %), martensite (9.4 %) and austenite (8.3 %), which would be promising microstructure in the development of new-generation complex phase AHSS. The significant findings are: (1) excellent ductility is obtained while high strength is preserved despite small martensite volume fraction, which can reduce the tendency of martensite cracking; (2) macroscopic stress-strain relationships and microscopic hardening properties of constituent phases are successfully determined, which are very important for predicting the overall performance of complex phase AHSS; (3) presence of bainite with high volume fraction plays a critical role in inducing plastic strain localization in ferrite, resulting in the heterogeneous stress/strain distribution. It is disclosed that pronounced strain localization is mostly initiated in ferrite grains while the deformation bands are mainly located in ferrite/bainite grain boundaries. Furthermore, strain partitioning between ferrite and bainite results in the high-stress concentration in bainite grains. As a result, these "hot zones", i.e., ferrite grains, ferrite/bainite grain boundaries and bainite grains, experience high strain, strain gradient and stress, respectively, which can be a primary origin of ductile fracture initiation in the 3rd GEN complex phase AHSS. The findings reported in the present investigation would be of great interest in the development of new-generation complex phase automotive steels. [Display omitted] [ABSTRACT FROM AUTHOR]

This paper presents a validated finite element modeling approach for simulating shear cutting, needing a minimal amount of experimental characterization. Only one uniaxial tensile test and one force–displacement relationship from a punching experiment are needed for calibration, with maintained prediction accuracy compared to more experimentally demanding approaches. A key ingredient is the observation that the Lode angle parameter is close to zero in the fracture region, postulating that the fracture strain only depends on stress triaxiality, with one free calibration parameter. The true stress–strain behavior is provided from inverse modeling of the tensile test, whereas the fracture model is calibrated using the punching test. The model is verified for different materials by comparing force–displacement curves for punching experiments not used in the calibration. The prediction error for the intrusion is below 4%. A validation is made for two setups. The local residual stresses are measured using Focused Ion-Beam Digital Image Correlation (FIB-DIC). The simulated values are within the experimental bounds. Cut edge morphology and plastic strains obtained by nano-indentation mappings are compared to simulation results, showing a decent agreement. For trimming, the cut edge morphology prediction performance decreases at 17% cutting clearance while it is maintained over the whole range for punching. The predicted hardness values have a mean absolute percentage error below 7.5%. Finally, the effect of element size and remeshing is discussed and quantified. The minimal experimental characterization and simulation effort needed, enables an efficient optimization of the cutting process in the industry. [ABSTRACT FROM AUTHOR]

• A proposed cavity expansion method considers dynamic hardening, which includes plastic strain, plastic strain rate, and temperature. • This study proposes an analytical approach based on the gradients of plastic strain and temperature under self-similarity transformation. • It is considered the behavior of the expanding cavity problem for thermal softening and strain rate sensitivity. • The Johnson-Cook (JC) hardening model is used to analyze the behavior of the cavity expansion for AISI 4340 steel. This paper presents a spherical cavity expansion method based on the self-similar field considering dynamic hardening, which includes plastic strain, plastic strain rate, and temperature for an infinite compressible medium under J2 plasticity. This study proposes an approach based on the gradients of plastic strain and temperature under self-similarity transformation to deal with dynamic hardening models such as the Johnson-Cook (JC) and the modified Johnson-Cook (mJC) models. A theoretical model shows that the effective and radial stresses are reduced near the cavity surface and increased away from the cavity under the mutual influence of hardening and thermal softening. The JC hardening model is used to analyze the behavior of the cavity expansion for AISI 4340 steel. The proposed theoretical model was validated by comparing the result of the explicit finite element method (FEM). This study discusses the behavior of the expanding cavity problem for thermal softening and strain rate sensitivities. In addition, rigid penetration problems are simulated to analyze the application of the presented method. FEM and the proposed cavity expansion method were compared with the penetration depth of AA6061-T651 target using the mJC hardening model for a hemispherical-nosed penetrator. A comparison is made for the performance of the penetration depth with an ogive-nose projectile for AA7075-T651 and AA6061-T651 materials using the mJC hardening model. This study concludes that the proposed method can be applied without modifying the hardening models to spherical cavity expansion problems that involve dynamic hardening models dependent on strain, strain rate, and temperature under adiabatic heat. [ABSTRACT FROM AUTHOR]

In this paper, a nonlinear finite element formulation for a hyperelastic, modified Timoshenko–Ehrenfest beam with geometrical and material nonlinearities is developed for the first time. A new five-parameter beam element is introduced. The parameters contain displacement, values of difference vector and a through-the-thickness scalar value. Moreover, a new procedure is employed to apply the moment to the beam. The constitutive formulation is derived for Saint Venant–Kirchhoff (SVK) as well as the compressible neo-Hookean (n-H) hyperelastic model. The beam is subjected to different loads such as dead load, point and distributed loads, and follower pressure. To demonstrate the applicability of the formulations, several examples are solved. The results reveal that this formulation can capture the previous results reported in the literature. Furthermore, a comparative study is done between two hyperelastic models. It is demonstrated that in the case of large rotation of the beam, both Saint Venant–Kirchhoff and neo-Hookean models show the same behavior. However, in case of large deformation with large strains of the beam, the Saint Venant–Kirchhoff model behaves stiffer than the neo-Hookean hyperelastic model. [ABSTRACT FROM AUTHOR]

• Non-linear finite element analyses were used to evaluate slabs in transition between one-way shear and punching shear failure mechanisms. • A sensibility study evaluated the influence of different modeling choices on the numerical results. • Different damage models, stress–strain behavior models in compression and tension were evaluated. • Recommendations to assess the shear and punching capacity of slabs under concentrated loads are provided for using NLFEA. Several studies investigated the precision of non-linear finite element analyses (NLFEA) to predict the shear capacity of beams or the punching capacity of slab-column connections. However, in the literature, there is little discussion regarding the results of NLFEA to predict the ultimate capacity and failure mechanism of slabs susceptible to different failure mechanisms. In this study, a set of tests from literature that developed different shear failure mechanisms was evaluated by NLFEA. A total of thirteen slabs were modeled, where slab's width and shear span varied. A coupled damaged-plasticity model was employed to simulate the concrete behavior. The proposed model was calibrated to simulate specimens that failed as wide beams in one-way shear and specimens that failed by punching shear. Besides, the effect of different modeling choices was investigated: (i) the assumed stress–strain behavior in compression; (ii) tensile stress–strain behavior; (iii) the inclusion or not of damage parameters and (iv) the viscosity parameter. The results indicated that, on average, the proposed modeling strategy represented the failure mechanism and ultimate loads well. Also, the same calibrated model was found capable of representing one-way shear failure and punching shear failure or mixed modes. The sensitivity study demonstrated that the tensile stress–strain behavior and viscosity parameter influences the results of the numerical models more significantly than the assumed stress–strain behavior in compression or including/not including the damage parameters. This paper concludes that modeling strategies during the calibration process shall be checked carefully before performing any parametric analyses to identify the accuracy of the numerical models to represent the different failure mechanisms. Moreover, the validation step of the modeling strategy shall identify possible limits of the numerical model to be considered in the parametric analyses. [ABSTRACT FROM AUTHOR]

[Display omitted] • Adhesion strength of dental ceramic to milled and SLM Ti6Al4V alloy is studied. • The novelty is that experimental load–strain graphs are used in FEM simulations. • Normal, tangential and equivalent von Mises stresses are determined. • Greatest values of normal stresses perpendicular to porcelain/bond/metal interface. • They are primary reason for adhesive delamination of porcelain coating. The aim of the present paper is to investigate the adhesion strength of dental ceramic to milled and selective laser melted (SLM) Ti6Al4V alloy by experiment and finite element method (FEM). The experimental study was done by three-point bending test. Before applying the porcelain, the metal surface was treated by sandblasting, application of bonding agent and a combination of sandblasting and bonding layer. The novelty is that FEM simulations of individual samples from each group were conducted using the experimental load–strain graphs. The normal, tangential and equivalent von Mises stresses at endpoint of the edge of porcelain coating and bonding agent sublayer were determined. It was found that the distribution of the equivalent stresses along the porcelain edge on the porcelain/metal interface is uneven: low stresses at both ends and maximum value in the central part. The Y-axis normal stresses, acting perpendicular to the porcelain/metal, bond/metal, or porcelain/bond interface, have greatest values which is primary reason the coating to be adhesively delaminated by peeling the porcelain off the metal or bonding agent. For the milled specimens, the stress trend follows the adhesion strength trend. In the combined treatment, the highest equivalent and normal stresses are generated in the bond sublayer. If they are higher than the cohesive strength of the ceramic, the porcelain coating is destroyed cohesively by cracking. For the SLM fabricated specimens, the bond treatment increased the stresses at the bond/metal interface, and the stresses at the bond/porcelain interface were commensurate with the experimental adhesion strength. This causes the destruction of the coating to occur by peeling the porcelain off the bonding agent. [ABSTRACT FROM AUTHOR]