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Purpose: In this paper, the standard Peridynamic Timoshenko beam model accounting for the shear deformation is chosen to describe the thick beam kinematics. Unfortunately, when applied to very thin beam structures, the standard Peridynamics (PD) encounters the shear locking phenomenon, leading to incorrect solutions. Design/methodology/approach: PD differs from classical continuum mechanics and other nonlocal theories that do not involve spatial derivatives of the displacement field. PD is based on the integral equation instead of differential equations to handle discontinuities and other singularities. Findings: The shear locking can be successfully alleviated using the developed selective integration method. In particular, this technique has been implemented in the standard PD, which allows an accurate result for a wide range of slenderness from very thin to thick (10 < L/t < 103) structures. It can also accelerate the computational time for particular dynamic problems using fewer neighboring integration particles. Several numerical examples are solved to demonstrate the effectiveness of the proposed method for modeling beam structures. Originality/value: The paper highlights the severe shear locking phenomenon in the Peridynamic Timoshenko beam available in the literature, especially for very thin structures. A new alternative for the alleviation of shear locking in the Peridynamic Timoshenko beam, using selective integration. Hence the developed Peridynamic Timoshenko beam model is effective for thin and thick structures. A new peridynamic formulation for the low-velocity impact beam models is presented and validated. Highlights: The paper highlights the severe shear locking phenomenon in the Peridynamic Timoshenko beam proposed in the literature, especially for very thin structures. The developed Peridynamic Timoshenko beam model based on selective integration is effective for thin and thick structures. A new peridynamic formulation for the low-velocity impact beam models is presented and validated. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study is to develop an elasto-plastic multi-material shell model by which finite element analysis of laser welded joints is carried out at the interface of the heat-affected zone and base material. Design/methodology/approach: The multi-material shell model is implemented on the simple cantilever and double cantilever welded plates to examine the efficiency of the developed model. Findings: By reducing the computational time approximately 20 times with the developed model, the results obtained in the form of von Mises stress and equivalent plastic strain are found in good agreement as compared with the reference solid model. Originality/value: The accurate and fast prediction of the stresses and strains in the laser welded joints, and the developed multi-material model is helpful to simulate complex industrial welded structures. [ABSTRACT FROM AUTHOR]

Functionally graded (FG) composites reinforced by carbon nanotubes (CNTs) have received extensive attention due to their excellent mechanical properties. The impact responses of FG‐CNT nanocomposites are analyzed by the developed meshless method. The temperature‐dependent material properties are expressed by way of the extended rule of mixture. The kinematics of the composite plate is established on the basis of the first‐order shear deformation theory. The modified Hertzian contact law is adopted to evaluate the impact loading between the plate and the impactor. The dynamic balance equations of the plate are constructed and computed by the Systemic Smoothed Particle Hydrodynamics (SSPH) method with strengthened prediction ability. The impacting behaviors of the FG‐CNT nanocomposite plate, as well as the parametric effects, are analyzed by the developed model and the suitability is clearly demonstrated. Highlights: Impact of FG‐CNTRC is firstly solved by a self‐developed meshless SPH model.Strong capacity of the SPH impact model is clearly demonstrated.More CNTs close to the strike face would improve the impact resistance. [ABSTRACT FROM AUTHOR]

In a previous investigation (Bigerelle and Iost, 2004), the authors have proposed a physical interpretation of the instabilityλ = Δt/Δx² > 1/2 of the parabolic partial differential equations when solved by finite differences. However, our results were obtained using integration techniques based on erf functions meaning that no statistical fluctuation was introduced in the mathematical background. In this paper, we showed that the diffusive system can be divided into sub-systems onto which a Brownian motion is applied. Monte Carlo simulations are carried out to reproduce the macroscopic diffusive system. It is shown that the amount of information characterized by the compression ratio of information of the system is pertinent to quantify the entropy of the system according to some concepts introduced by the authors (Bigerelle and Iost, 2007). Thanks to this mesoscopic discretization, it is proved that information on each sub-cell of the diffusion map decreases with time before the unstable equality λ = 1/2 and increases after this threshold involving an increase in negentropy, i.e., a decrease in entropy contrarily to the second principle of thermodynamics. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to present an efficient smoothed particle hydrodynamics (SPH) method particularly adapted for the geometrically nonlinear analysis of structures. Design/methodology/approach – In order to resolve the inconsistency phenomenon which systematically occurs in the standard SPH method at the domain’s boundaries of the studied structure, the classical kernel function and its spatial derivatives were modified by the use of Taylor series expansion. The well-known tensile instabilities inherent to the Eulerian SPH formulation were attenuated by the use of the Total Lagrangian Formulation (TLF). Findings – In order to demonstrate the effectiveness of the present improved SPH method, several numerical applications involving geometrically nonlinear behaviors were carried out using the explicit dynamics scheme for the time integration of the PDEs. Comparisons of the obtained results using the present SPH model with analytical reference solutions and with those obtained using ABAQUS finite element (FE) commercial software, show its good accuracy and robustness. Practical implications – An additional application including a multilayered composite structure and involving buckling and delamination was investigated using the present improved SPH model and the results are compared to the FE results, they confirmed both the efficiency and the accuracy of the proposed method. Originality/value – An efficient 2D-continuum SPH model for the geometrically nonlinear analysis of thin and thick structures is proposed. Contrarily to the classical SPH approaches, here the constitutive material relations are used to link naturally the stresses and strains. The Total Lagrangian approach is investigated to alleviate the tensile instabilities problem, allowing at the same time to avoid the updating procedure of the neighboring particles search and therefore reducing CPU usage. The proposed approach is valid for isotropic and multilayered composites structures undergoing large transformations. CPU time savings and better results with the new 2D-continuum SPH formulation compared to the classical continuum SPH. The explicit dynamic scheme was used for time integration allowing a fast resolution algorithm even for highly nonlinear problems. [ABSTRACT FROM AUTHOR]

In the present investigation, a new modified smoothed particle hydrodynamics (SPH) method particularly adapted for the analysis of planar structures undergoing geometric nonlinearities is introduced and discussed. The problem of inconsistency which is often encountered in the classical SPH method is alleviated by introducing modifications of the kernel function and its derivatives using an explicit polynomial feature representation based on the Taylor series expansion. Tensile instabilities arising in the Eulerian-based SPH formulation which appear due to large deformations are attenuated by the introduction of a total Lagrangian formulation which is robust for large displacements/rotations. The resulting nonlinear problem is solved using the explicit dynamics time integration scheme. The validity of the proposed approach is demonstrated through two numerical applications involving geometrical nonlinearities, where the obtained results are compared to those obtained using the standard finite element method. [ABSTRACT FROM AUTHOR]

The objective of this paper is to present an extension of the Lagrangian Smoothed Particle Hydrodynamics (SPH) method to solve three-dimensional shell-like structures undergoing large deformations. The present method is an enhancement of the classical stabilized SPH commonly used for 3D continua, by introducing a Reissner-Mindlin shell formulation, allowing the modeling of moderately thin structure using only one layer of particles in the shell mid-surface. The proposed Shell-based SPH method is efficient and very fast compared to the classical continuum SPH method. The Total Lagrangian Formulation valid for large deformations is adopted using a strong formulation of the differential equilibrium equations based on the principle of collocation. The resulting non-linear dynamic problem is solved incrementally using the explicit time integration scheme, suited to highly dynamic applications. To validate the reliability and accuracy of the proposed Shell-based SPH method in solving shell-like structure problems, several numerical applications including geometrically non-linear behavior are performed and the results are compared with analytical solutions when available and also with numerical reference solutions available in the literature or obtained using the Finite Element method by means of ABAQUS© commercial software. [ABSTRACT FROM AUTHOR]

Peridynamics (PD) differs from classical continuum mechanics and other nonlocal theories that do not involve spatial derivatives of the displacement field. PD is based on the integral equation instead of differential equations to handle discontinuities and other singularities. In this paper, the standard peridynamic Reissner–Mindlin plate model (standard PD) accounting for the shear deformation is chosen to describe the thick plate kinematics. Unfortunately, when applied to very thin plate structures, the standard PD encounters shear locking phenomenon, leading to incorrect solutions. This shear locking can be successfully alleviated using the developed reduced or selective integration method. In particular, this technique has been implemented in the standard PD, which allows an accurate result for a wide range from very thin ( L / t > 10 3 ) to thick ( L / t ∼ 10 ) plate structures. It can also accelerate the computational time for particular dynamic problems using fewer neighboring integration particles. Several numerical examples are solved to demonstrate the effectiveness of the proposed method for modeling plate structures. [ABSTRACT FROM AUTHOR]

One of the vital parameters of the additive manufacturing (AM) process is the scanning strategy. In this article, advanced joint path strategies based on irregular hexahedrons instead of conventional regular elements are proposed, and the influences of advanced joint path strategies on the energy absorption capacity of Ti-6Al-4V Taylor bar are investigated. In particular, the thermomechanical results reveal that the zigzag loop path strategy has more influence on deformation than all advanced joint path strategies, among which the zigzag joint path strategy has the maximal effect, and the centrosymmetric joint path strategy has the minimal effect. Meanwhile, through the impact response of the Ti-6Al-4V Taylor bar with AM residual stress (AM RS), the centrosymmetric joint path strategy, which can better uniformly distribute the deformation, can maximize the energy absorption capacity of the structure. Advanced joint path strategies based on irregular hexahedrons instead of conventional regular elements are proposed. A fully coupled thermomechanical analysis between the AM process and the transient impact problem. Advanced joint path strategies and the generated RS on the impact response of the final workpieces (parts) are studied. A suitable joint path strategy for the generation of a formed part is identified, which allows a maximal energy absorption capacity. [ABSTRACT FROM AUTHOR]

Highlights: [•] New shell-based SPH model using only 1 layer of particles at the shell mid-surface. [•] SSPH model based on Reissner–Mindlin theory, accounting for transverse shearing. [•] Vector parameterization of rotations for the treatment of very large 3D rotations. [•] CPU time savings compared to the classical continuum SPH method. [•] Better results with the new SSPH model compared to the classical continuum SPH. [ABSTRACT FROM AUTHOR]

In this paper a general methodology for the modeling of material composite multilayered shell structures is proposed using a Hex-shell finite element modeling. The first part of the paper is devoted to the general FE formulation of the present composite 8-node Hex-shell element called SCH8, based only on displacement degrees of freedom. A particular attention is given to alleviate shear, trapezoidal and thickness locking, without resorting to the classical plane-stress assumption. The anisotropic material behavior of layered shells is modeled using a fully three dimensional elastic orthotropic material law in each layer, including the thickness stress component. Applications to laminate thick shell structures are studied to validate the methodology, and good results have been obtained in comparison with ABAQUS© commercial code. [ABSTRACT FROM AUTHOR]

Abstract: We focus on a successive response surface method for the optimization problems. The response surfaces are built using Moving Least Squares approximations constructed within a moving region of interest. Our first approach is an extension of pattern search algorithms with a fixed pattern panned and zoomed in a continuous manner across the design space. In the second one, the region of interest moves across a predefined discrete grid of authorized experimental designs. Two examples of the sheet metal forming process are used to demonstrate the robustness of the method. We use the one-step Inverse Approach as a surrogate model during the optimization. The final designs is validated with Stampack commercial code based on Explicit Dynamics Approach. [Copyright &y& Elsevier]

Abstract \nHIGHLIGHTS During the additive manufacturing, the shape of workpieces is influenced by printing parameters. To achieve the desired shape of the workpiece, an optimization algorithm is often used to determine an effective combination of printing parameters. Although multiparameter optimization can improve structure quality, they are very time-consuming. In this article, we propose a timesaving irregular element-based compensating approach, which allows a more precise fitting of the geometric boundaries without needing additional computing resources. Finally, we demonstrate that the proposed approach can accurately shape the workpiece to fulfill the expected computer-aided design geometry by experimental verification and error comparison analysis.The compensating approach based on the irregular hexahedron instead of the conventional regular discretization is proposed.The proposed technique compensates the deformation in advance on the original geometric model and avoids searching for the optimal combination of printing parameters.The compensating approach is theoretically no longer constrained by input printing parameters, and this method is suitable for selective laser melting and electron beam melting techniques.Experimental verification and error comparison analysis confirm that the proposed technique can accurately shape the workpiece to the user-designed form. [ABSTRACT FROM AUTHOR]

This work adapts the Q4γ s quadrilateral element to analyse three-layer FGM sandwich plates. Two types of FGM sandwich configurations are employed to assess the element performance in conducting static, free vibration, and thermal buckling analysis. The first configuration is a homogeneous core and FGM outer layers, while the second involves homogeneous top and bottom layers and an FGM core. Various problems have been run, and the results are compared with references to assess the accuracy of the element. Numerical results on the deflection, stresses, frequencies, and thermal buckling of symmetrical and non-symmetrical FGM sandwich plates are examined to evaluate the effectiveness of the current model. Furthermore, the influence of the power-law index and the length-to-thickness ratio on the analyses is also investigated. [ABSTRACT FROM AUTHOR]

Although the natural fiber composites are preferable for sustainable and green product due to the environmental friendliness, they suffer from the high flammability. In this study, the flame retardant ramie fiber reinforced poly(lactic acid) composites were prepared and the synergistic barrier effect of aluminum diethylphosphinate, melamine cyanurate and silica was investigated. When the mass ratio of each flame retardant was 10%, the composites reached UL‐94 V0 rating with the limiting oxygen index of 30.1%. The excellent flame retardancy was resulted from the formation of high‐quality char layers, the chain reaction of free radicals as well as the dilute effect of inert gases generated during the combustion process. Besides, the cone calorimeter test showed that the peak heat release rate and total heat release decreased by 22.5% and 15.0%, respectively. Importantly, the flame retardants did not deteriorate the mechanical properties, thanks to the fiber reinforcement and high‐adhesion work between the flame retardants and the matrix which was demonstrated by the contact angle test. [ABSTRACT FROM AUTHOR]

A smoothed finite element method formulation for the resultant eight-node solid-shell element is presented in this paper for geometrical linear analysis. The smoothing process is successfully performed on the element mid-surface to deal with the membrane and bending effects of the stiffness matrix. The strain smoothing process allows replacing the Cartesian derivatives of shape functions by the product of shape functions with normal vectors to the element mid-surface boundaries. The present formulation remains competitive when compared to the classical finite element formulations since no inverse of the Jacobian matrix is calculated. The three dimensional resultant shell theory allows the element kinematics to be defined only with the displacement degrees of freedom. The assumed natural strain method is used not only to eliminate the transverse shear locking problem encountered in thin-walled structures, but also to reduce trapezoidal effects. The efficiency of the present element is presented and compared with that of standard solid-shell elements through various benchmark problems including some with highly distorted meshes. [ABSTRACT FROM AUTHOR]

This paper deals with the analysis and design of tube hydroforming parameters in order to reduce defects which may occur at the end of the forming process, such as necking and wrinkling. We propose a specific methodology based on the coupling between an enhanced one-step method for the rapid simulation of tube hydroforming process and a surrogate model based on a metamodeling technique. The basic formulation of the one-step method has been modified and adapted for the modeling of 3D tube hydroforming problems in which the initial geometry is a circular tube expanded by internal pressure and submitted to axial feeding. In the surrogate model, approximate responses are built using moving least squares method and constructed within a moving region of interest which moves across a predefined discrete grid of authorized experimental designs. Two applications of tube hydroforming of aluminum alloy 6061-T6 have been utilized to validate our methodology. The final design is validated using experiments together with the classical explicit dynamic incremental approach using ABAQUS® commercial code. [ABSTRACT FROM AUTHOR]

Recently, natural fiber becomes an alternative to the synthetic fiber for the composites used in aerospace, automotive, sports, packaging and so on, due to its inherent characteristics like biodegradablity, renewablity, high‐specific strength and specific modulus. However, there are still many challenges in the fabrication of the natural fiber composites, including the poor compatibility between the nonpolar matrix and the polar natural fiber, relatively high‐moisture absorption and low‐thermal resistance of natural fibers, etc. Moreover, when manufacturing this type composite, the processing conditions, fiber loading and inherent properties of fiber not only affect the mechanical properties, but also cause products defects, such as warpage, volume shrinkage and weld lines, which needs a rapid numerical design for the mold and manufacturing parameters. Therefore, the properties of natural fiber composites have been widely investigated to satisfy the increasing demand in different applications. This paper intends to review the mechanical properties, flammability, durability, foaming behaviors and numerical simulation of injection molding process of natural fiber composites. [ABSTRACT FROM AUTHOR]

Path pattern is one of the most significant parameters in the additive manufacturing (AM) process because it influences the specimen's final shape and residual stress distribution. Generally, the optimal path pattern is a computationally expensive, high-dimensional, and black-box permutation optimization problem. In this paper, we propose a combinatorial radial basis function surrogate-assisted genetic algorithm (CRBF-GA) to effectively generate the optimal path pattern by integrating the combinatorial radial basis function surrogate model (CRBF) with the genetic algorithm (GA). To demonstrate the effectiveness of the proposed CRBF-GA, a Ti-6Al-4V thin rod, a component of lattice, is chosen as the research object. Through numerical simulation, experimental verification, and error comparison analysis, the RBF-GA pattern is demonstrated to be the best path pattern among the random forest-assisted evolutionary algorithm (RF-EA), GA, spiral, and zigzag patterns, and it excels in achieving a more precise rod shape compared to the other patterns examined. • Proposed irregular discretization enhances the fitting accuracy of structural boundaries. • Developed combinatorial surrogate-assisted genetic algorithm solves the expensive permutation optimization problem. • Results affirm the accuracy of the proposed method in forming Ti-6Al-4V thin rods. [ABSTRACT FROM AUTHOR]

Abstract Bi-directional Functionally Graded Materials (FGMs) is of more and more focus in special engineering application like aerospace craft at high altitude and speed. In this paper, bending analysis of this type Functionally Graded Beam (FGB) is performed by a proposed meshless Total Lagrangian (TL) Corrective Smoothed Particle Method (CSPM) which owns more capability in accuracy and stability than the classical Smoothed Particle Hydrodynamics (SPH) method. This method is validated by comparison of the bending deformation with analytical method, ABAQUS and a self-programmed finite element code. The influence of the gradient indexes and boundary conditions on the deformation behavior is also investigated. The method is proved to be more precise and stable than the semi-analytical and FE results when dealing with power-law bi-directional FGB. Highlights • Meshless SPH method is developed for the bending analysis of two-directional Functionally Graded Beam (FGB). • The convergence and accuracy of the proposed SPH model is validated by analyzing an exponentially varied bi-directional FGB. • For bi-directional FGB of power-law model, the proposed SPH model is proved more precise than the semi-analytical solution in literature. • The proposed SPH model shows better stability than FE solution by ABAQUS and a self-programmed code, where mesh is distorted. [ABSTRACT FROM AUTHOR]

Geometrically nonlinear bending deformation of Functionally Graded Beams (FGBs) with variable thickness is simulated by a meshless Smoothed Hydrodynamic Particle (SPH) method. The material properties of FGB is assumed to be varied smoothly in the thickness according to exponent-law distribution. To prevent the mesh-distortion in element-based numerical method, meshless SPH method is adopted, where corrective smoothed particle method and total-Lagrangian formulation are employed to improve its precision and stability. To validate the present SPH method, several numerical examples are performed and compared to analytical and finite element solutions. [ABSTRACT FROM AUTHOR]

The aim of this paper is to predict the low velocity impact damage in composite laminates through meshless Smoothed Particle Hydrodynamics (SPH) method. SPH shell model is developed based on the First-Order Shear Deformation Theory as well as explicit time integration using central difference method. The contact force is determined by the modified Hertzian contact model and the impact-induced damage is predicted by Tsai-Wu criterion. Several examples are investigated to demonstrate the accuracy of the present SPH model by comparing the results to those available in the literature. [ABSTRACT FROM AUTHOR]

A meshless Smoothed Hydrodynamic Particle (SPH) model is established to simulate the bending deformation of 2D structures made of Functionally Graded Materials (FGMs). The material property is assumed to be varied continuously through the thickness direction according to the power-law distribution. Problems in the classical SPH formulation, like inconsistency and tensile instability are solved by introducing several techniques. Several benchmarks are selected to estimate the performance of the proposed SPH model. [ABSTRACT FROM AUTHOR]

Abstract: Car manufacturers have to develop lightweight structures to limit the weight-increase induced by the new advanced powertrain systems for hybrid and electrical vehicles. Due to their draping, stiffness, improved ductility and damage tolerance properties woven composites are being increasingly used for the design of crash-relevant structural parts. Before an introduction of the strategies and the conditions set by industrial applications, the main current modeling techniques available for composites in the LS-DYNA finite element code featuring with explicit time integration will be discussed. A user defined composite material model (UMAT) characterized by a linear as well as non-linear behavior coupled with a plasticity definition will be then proposed. A maximal stress criterion is used to detect the failure on the ply. Four post-failure damage definitions have been investigated in order to account for the post-failure progressive material degradation. Finally, experimental results on coupons tests are used to identify the macroscopic behavior and the effective properties of the considered material. Experimental impact tests are then used to investigate the post-peak behavior. [Copyright &y& Elsevier]

For some shortcomings in the use of standard radial length development in the blank development for forming sheet metal parts, an improved radial length normal spreading approach considering outside normal direction is developed to resolve blank development in sheet metal forming. Moreover, a comprehensive spreading method, which combines radial length normal spreading and orthogonal length development method, is presented in this paper to avoid the overlapping problem which happens sometime in the spreading process related to severely curved sheet parts. To deal with holes and gaps which exist in some sheet metal parts, dummy elements are used to calculate the intercepting line's length precisely. Finally, a multistep spreading and merging strategy is adopted to handle some special sheet metal parts with vertical free edges that should be jointed or not. Through practical applications, the effectiveness and the usefulness of this approach are evaluated, and the unfolded result is more reasonable; meanwhile, the obtained blank shape should be a better initial guess in the application of the so-called one-step quick analysis for sheet metal forming simulation. [ABSTRACT FROM AUTHOR]

Abstract: Due to their draping, stiffness, improved ductility and damage tolerance properties woven composites are being increasingly used for the construction of crash-relevant structural parts. Textile composites may depict a nonlinear behavior along several directions. Moreover, considerably-thick composite structures are likely to be used in order to increase energy absorption and to comply with the crash validation criteria. Therefore, a nonlinear numerical material model for textile composite materials has been developed for shells and thick shells. The model has been implemented as a user-defined subroutine (UMAT) in the LS-DYNA finite element code featuring with explicit time integration. The nonlinear behavior until failure is modeled in each in-plane material direction by a user-defined load curve or the Ramberg–Osgood equation. A plasticity formulation coupled with the nonlinearity accounts for permanent deformations. The failure is predicted using either a maximal stress criterion or the quadratic Tsai–Wu criterion. In order to model damage propagation, different post-failure damage definitions have been developed and implemented for each main in-plane material direction. A smeared formulation ensures the mesh independence in the presence of strain localization. The model has been assessed using characterization tensile and compressive tests on plain-weave and twill-weave carbon fiber composites. [Copyright &y& Elsevier]

• Meshless SPH beam model is developed for the bending analysis of two-directional FGBs in consideration of the curved neutral plane. • The governing function is established based on Reddy-Bickford beam theory based on exact neutral surface position. • The convergence and accuracy of the proposed SPH beam model is validated by comparing the prediction results with the solution in literature. • Different aspect ratios, gradation exponents and boundary conditions on the deformation are considered and investigated. More and more attention has been paid on the two-directional functionally graded materials (FGMs) applied in harsh heat environment. A novel meshless model is established for the bending analysis, based on the Smoothed Particle Hydrodynamics (SPH) method. To improve the prediction accuracy, the conventional SPH method is improved by the symmetric SPH method starting from the Taylor series expansion. Moreover, the neutral surface position of the bi-directional FG beam is determined and the third order Reddy-Bickford beam theory based on this exact neutral surface is adopted. The governing equations are deduced for FGB composed by two or four different materials and then discretized by the proposed method. The present model is verified by comparison of the deflection with the solution obtained in literature and a self-programmed finite element code. The deformation of the beam with different gradient indexes and boundary conditions is also investigated. [ABSTRACT FROM AUTHOR]

The article presents a study which examines several neck tests on a child dummy Hybrid II and the effect of neck stiffness on the out-of-position (OoP) Nij Neck Injury Criteria. Quasit-static and dynamic analysis were conducted to compare the stiffness of four necks. Results show that the quasi-static and dynamic tests have the same classification of the neck. The study concludes that neck stiffness have an influence on Neck Injury Criteria.