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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]

In this paper, a nonlinear finite element analysis of slab-beam-column connection in precast concrete structures is presented. The detailed experimental results of the full-scale connection have been discussed in a different paper. However, due to the complexity of slab-beam-column connection and the unique features of the tested specimen, the numerical study was carried out to better understand the structural behavior. The internal connection was comprised by corbels, dowels and a continuity bars passing though the column. The FE model was validated using the experimental results of the precast concrete connection and it showed good capacity to represent the behavior observed in laboratory. A parametric analysis was conducted with the variation of the diameter of the continuity bars and the properties of the cast in place concrete. As a result of this study, some information about stresses, strains and displacements not obtained experimentally was determined in the numerical simulation and, with the parametric analysis it was concluded that the diameter of the continuity bars had more influence in the precast concrete connection capacity than the concrete compressive strength. [ABSTRACT FROM AUTHOR]

Abstract In this paper, analytical and numerical solutions are presented for computing the displacements and stresses in a FGM thick-walled cylinder under a uniform internal and external pressure. An analytical and a finite element (FE) model of the pressurized vessel were constructed, where the radial continuous varying of elastic modulus along the thickness was assumed and implemented in a FE code. It has been assumed that the elastic modulus is varying through thickness of the FGM material according to a nonlinear general expression. The analytical solutions of distribution of displacements and stresses were obtained and illustrated in radial direction for pressurized FGM cylinder. The results are checked with FE results. Thus, the inhomogeneity in material properties can be exploited to optimize stress distribution. Highlights • Exact solutions are obtained for thick wall pressurized functionally graded cylinder. • A more general form for the spatial variation of the stiffness was used. • A finite element (FE) model was constructed and validated. • Displacements and stresses are examined and compared with the homogeneous cylinder. • Material inhomogeneity has a great effect on stresses and radial displacement distribution. [ABSTRACT FROM AUTHOR]

This paper develops a novel and simple analytical model to investigate the bending response of superelastic shape memory alloy (SMA) laminated composite cantilever beam during a complete loading/unloading cycle based on ZM's three-dimensional (3D) thermomechanical model for SMAs and Timoshenko beam theory. The laminated composite beam configuration is formed by two SMA layers bonded to one elastic core layer. The results show a superelastic behavior of the composite. The moment-curvature response, martensite distribution along vertical direction, stress distribution along vertical and axial direction, tip deflection of the composite are revealed. The effects of temperature, thickness ratio and stiffness ratio on the moment-curvature response are also investigated. 3D finite element analysis (FEA) is carried out in parallel to validate against results obtained from analytical and exact numerical models. A good agreement is obtained. Whereby the maximum observed difference in terms of curvature is 7% between analytical and 3D FEA data, and 0.5% between analytical and accurate numerical solutions at moment M e = 0.181 N . m during the loading cases. This novel work sheds light on the fundamental and deep knowledge of SMA composite's static bending behavior. That will be very helpful and significant for other researchers to furtherly investigate on dynamical behavior of this and other SMA laminated composite configurations. [ABSTRACT FROM AUTHOR]

Abstract: This research paper describes the development of NURBS Isogeometric finite element analysis and post-processor for interlaminar stress calculation in composite and sandwich plates. First-order, shear-deformable laminate composite plate theory is utilized in deriving the governing equations using a variational formulation. Linear, quadratic, higher order and k-refined NURBS elements are constructed and numerical validation is performed for laminated composite and sandwich plates. Lagrange finite element suffers from higher order stress gradient oscillations due to Gibbs phenomenon and require alternative stress recovery procedures for accurate interlaminar stress calculations, especially interlaminar normal stress. In this paper, direct post-processing is performed which computes interlaminar shear and normal stresses from higher order gradients of NURBS basis in a single step procedure. Interlaminar stresses are found to be in an excellent agreement with 3D elasticity solution and FSDT along with k-refinement procedure of NURBS basis is found to compute equivalent or better interlaminar normal stress than higher-order shear deformation theory. [Copyright &y& Elsevier]

Abstract: A method based on the Refined Zigzag Theory (RZT) to model delamination in composite laminated beam structures is presented. The novelty of this method is the use of one-dimensional finite elements to discretize the geometry of the beam. The key property of this beam element, named LRZ [1], is the possibility to capture the relative displacement between consecutive layers which occurs during delamination. The fracture mode that the LRZ element is capable to predict is mode II. In order to capture the relative displacement using the LRZ element it is necessary to adapt the RZT theory as presented in this paper. The mechanical properties of the layers are modeled using a continuum isotropic damage model [2]. The modified Newton–Raphson method is used for solving the non-linear problem. The RZT theory, the LRZ finite element and the isotropic damage model are described in the paper. Also, the implicit integrations algorithm is presented. The performance of the LRZ element is analyzed by studying the delamination in a beam for two different laminates, using the plane stress solution as a reference. [Copyright &y& Elsevier]

The development of all-steel tube-in-tube buckling controlled brace (TinT-BCB) is presented. The efficiency of the TinT-BCBs is evaluated experimentally and numerically. The cyclic behavior and fracture life of TinT-BCBs was first investigated through physical testing, followed by FE-based simulations revealing the inherent correlation between fracture and peak cyclic strain in load-bearing braces. The cyclic strain in plastic zones was recorded up to 0.02 strain range during the cyclic tests, enabling the study to use the recorded strain in verifying the FE simulation models. The strain response of plastic zones was captured by the FE simulation up to fracture in conventional large-size braces. The paper concludes that (1) the TinT-BCB, developed based on the buckling-controlling concept, has demonstrated stable and symmetrical cyclic response, with global and local buckling controlled up to 0.035–0.04 story drift ratio; (2) the TinT-BCB is proven to be effective in elongating cyclic fracture life of conventional CBF from 2% SDR to 3.5–4% SDR by adding simple buckling controller. The cost for adding the buckling controller is low in comparison with the substantially increased lateral strength and energy dissipation capacity; and (3) the efficiency of the TinT-BCB in improving overall cyclic behavior in general and elongating fracture life of braces in particular is attributed to its ability in controlling highly concentrated strain in plastic zones of conventional braces. By spreading the concentrated strain demand throughout the entire length, the buckling controller is shown to reduce excessive peak strains in conventional braces by 7–8 times. [ABSTRACT FROM AUTHOR]

Foundation settlement is a common issue for bridges, which not only generates additional static stresses in continuous bridge members but also may affect the dynamic interaction between the bridge and vehicle traveling over it. In this paper, a new bridge-vehicle model with consideration of foundation settlement effect is created through the principle of virtual works to investigate the settled bridge and vehicle interaction responses. The correctness and accuracy of the model are validated with theoretical and numerical results. Based on the proposed model, numerical simulations have been conducted using the Newmark’s β method to investigate the effects of settlement mode, vehicle traveling speed, road surface roughness and boundary condition. It is shown that foundation settlement has a significant effect on impact factors of the bridge at high vehicle speeds, and road surface roughness may act together with the settlement to have a coupling effect, which needs special attentions in bridge design. [ABSTRACT FROM AUTHOR]

A wide range of parameters is available in the literature for the Johnson-Cook constitutive model, the most used flow stress in metal cutting modelling. This strength of the Johnson-Cook model is also a weakness as it is therefore difficult to choose the set that will provide the most accurate results. Indeed, for a given material, several parameters are available due to different identification conditions (strain, strain rates and temperature range). This paper gathers the sets of Johnson-Cook parameters from the literature for Ti6Al4V before comparing them based on their stress-strain curves. The twenty identified sets are then introduced in a Coupled Eulerian-Lagrangian (CEL) finite element orthogonal cutting model and their results are compared at fixed cutting conditions. This comparison is then extended for the three most characteristic sets to two other uncut chip thicknesses. All the numerical results are compared to an experimental reference in the same cutting conditions. Links between the parameters of the Johnson-Cook flow stress and outputs of the model are then highlighted; they are still valid when the uncut chip value is modified. A set is finally recommended to obtain an accurate estimation of the cutting force and average feed force and chip thickness values. [ABSTRACT FROM AUTHOR]

Cross wedge rolling-forging (CWR-forging) is an innovative process for local plastic deformation that is suitable for forming hollow valves. This paper presents the numerical and experimental results of hollow valve production using this new method. The most popular production methods are described. Then, this study examines the formation of such valves through CWR-forging. A numerical model of CWR-forging using the finite element method (FEM) is developed to estimate the technological viability of this process. The distributions of effective strain, temperature, metal flow, force, and torque are analyzed as well. In this study, changing the stretching angle (β) can effectively avoid swollen holes. therefore, the forming quality of the workpiece can be greatly improved when the forming angle (α) is equal to 35° and the stretching angle (β) is equal to 5° and 4° in the knifing and stretching zones and the mandrel diameter is 4 mm, respectively. Numerical results are then verified under laboratory conditions. Experimental results are consistent with the FEM results, thus confirming that hollow valves can be produced through CWR-forging. [ABSTRACT FROM AUTHOR]

Abstract: Shape optimization in connection with numerical modelling is used to reduce bending and associated flexural stresses in buried concrete arches. Modelling of the arch is carried out via a nonlinear finite element model that accounts for soil constitutive relations, soil–structure interactions, sequential construction stages and soil compaction. Centre line of the arch is parameterized by Bézier curve with three degrees of freedom that are subjected to optimization by genetic and Levenberg–Marquardt algorithm. The paper presents a parametric study which aims to determine the optimal shapes for buried arches of various span/rise ratios, backfill depths and foundation soil types. In the second part of the paper it shows a theoretical reduction in tensile stresses obtained by shape optimization of concrete arch culvert with a 9.4m span tested at the University of Massachusetts at Amherst. [Copyright &y& Elsevier]

In this paper, a meso-scale analysis is performed (1) to study the size effect on the nominal stress at failure and, (2) to quantify the evolution of the fracture process zone (FPZ) in the context of the tensile splitting test. The meso-structure is based on a two-phase 3D representation of heterogeneous materials, such as concrete, where stiff aggregates are embedded into a mortar matrix. In order to take into account these heterogeneities without any mesh adaptation, a weak discontinuity is introduced into the strain field. In addition, a strong discontinuity is also added to take into account micro-cracking. This model is cast into the framework of the Enhanced Finite Element Method (E-FEM). Based on the Finite Element simulations, size effect on the nominal stress at failure is numerically investigated and then compared to the so-called Bažant size effect law. In addition, an analysis based on the spatial distribution of the fracture energy is also regarded, leading to the 3D representation of the FPZ and to its volume value estimation. [ABSTRACT FROM AUTHOR]

Shape-memory polymers (SMPs) represent a class of smart materials able to store a temporary shape and to recover the original shape upon an external stimulus, such as temperature. The present paper proposes a three-dimensional finite-strain phenomenological model for thermo-responsive SMPs, which distinguishes between two material phases presenting different properties and is based on a rule of mixtures. The proposed model is motivated by the earlier work of Reese et al. (2010) and it considers several significant material features that had not been addressed in previous phenomenological approaches. Specifically, the model reproduces both heating-stretching-cooling and cold drawing shape-fixing procedures and it takes into account the non-ideal behavior of realistic SMPs (i.e. imperfect shape-fixing and incomplete shape-recovery). Several numerical tests are reported to assess model performances, from simple uniaxial and biaxial tests to complex simulations of biomedical devices. Comparisons with experimental data taken from the literature are also provided to validate the model. The proposed improvements increase the model applicability over a wide range of polymer types and operating conditions. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a numerical study on the short-term bearing capacity of preloaded footings on soft clay. In practice, this situation needs to be addressed when re-using an existing foundation for a new building or when extra load is to be transmitted to an existing foundation. Previous studies have estimated the bearing capacity in this situation, allowing simply for the increase in the soil undrained strength due to the increase in effective stresses imposed by the preload. However, field and laboratory observations corroborate that there is a continuous increase in the stiffness and strength soil properties with time, even after the dissipation of the excess pore water pressures generated during the initial loading is complete. This paper quantifies the short-term bearing capacity of existing foundations allowing for the occurrence of creep deformations and associated soil hardening. The problem is investigated by means of a series of plane-strain coupled finite element analyses of a 2m wide rough strip footing, in which the foundation soil is modelled using an overstress based elastic-viscoplastic model. The study investigates the effect of the level of preload, the applied loading rate, the creep characteristics of the foundation soil (magnitude and creep law type) and the footing geometry. It is shown that the time dependent nature of soil (e.g. occurrence of creep) accounts for a significant increase in bearing capacity. [Copyright &y& Elsevier]

Abstract: This paper reports experimental results of the debonding propagation of bundled-fibers specimens subjected to a tensile stress wave. In addition, the paper also presents a dynamic debonding model for the problem on the basis of the cohesive zone model, and verifies the model by comparing the predicted debonding to the experimental data. The established numerical model is used to study the propagation mode of the debonding, and the result suggests that in this particular specimen design and loading condition, the debonding initiated in a mixed mode condition. However, the mode II quickly increased and dominated the mode I during an early debonding propagation up to certain extend where the mode mixity became constant. [Copyright &y& Elsevier]

Abstract: The yield vertex non-coaxial model is different from classical elastoplastic models, in that there is an additional plastic strain rate tangential to yield surfaces, as well as the plastic strain rate normal to yield surfaces, when orientations of principal stress change. This feature raises concerns on its finite element implementations. In nonlinear finite element numerical iterations, a large tangential plastic strain rate is likely to make the trial total strain rate direct inside a yield surface, which entails convergence difficulty. Some modifications are introduced on the non-coaxial model itself to make numerical convergence easier in the work published in Yang and Yu (2010) . This paper is an extension of the previous work. Instead of modifying the non-coaxial model itself, this paper concerns the use of finite element explicit procedure, which is suitable for highly discontinuous problems. The simulations of shallow foundation load-settlement responses indicate that the finite element explicit procedure, assisted with a robust and explicit automatic substepping integration scheme of the non-coaxial model, does not encounter numerical difficulty. In addition, the overall trends of implicit and explicit simulations are similar. [Copyright &y& Elsevier]

Abstract: This paper presents a model test and numerical finite element analysis (FEA) on the mechanical behavior of a composite joint in a truss cable-stayed bridge. The model test with the scale of 1:2.5 for the truss joint was conduct to fully understand the safety and serviceability. In the experiment, stress distribution, crack resistance ability and shear resistance of headed studs were carefully measured to investigate the mechanical performance, force transmission of the joint part. The maximum strain of the steel plate and concrete chord remained in the linear elastic region until 1.7 times the design load, which means there is a significant safety margin for such composites. On the basis of the experimental results of composite truss joints, three-dimensional finite element models are established. The results of the finite element analysis are in good agreement with those of the tests in terms of strength and stiffness. It is also expected that the results presented in this paper would be useful as references for the further research and the design of composite truss bridges and composite joints. [Copyright &y& Elsevier]

Abstract: Modeling shot peening process is very complex as it involves the interaction of metallic surfaces with a large number of shots of very small diameter. Conventionally such problems are solved using the finite element software (such as ABAQUS) to predict the stresses and strains. However, the number of shots involved and the number of elements required in a real-life components for a 100% coverage that lasts a considerable duration of peening make such an approach impracticable. Ideally, a method that is suitable for obtaining residual compressive stresses (RCS) and the amount of plastic deformations with the least computational effort seems a dire need. In this paper, an attempt has been made to address this issue by using the discrete element method (DEM) in combination with the finite element method (FEM) to obtain reasonably accurate predictions of the residual stresses and plastic strains. In the proposed approach, the spatial information of force versus time from the DEM simulation is utilized in the FE Model to solve the shot peening problem as a transient problem. The results show that the RCS distribution obtained closely matches with that of the computationally intensive direct FEM simulation. It has also been established, in this paper, that this method works well even in the situations where the robust unit cell approaches are found to be difficult to handle. [ABSTRACT FROM AUTHOR]

Abstract: This paper introduces a recovery-type error estimator yielding upper bounds of the error in energy norm for linear elastic fracture mechanics problems solved using the extended finite element method (XFEM). The paper can be considered as an extension and enhancement of a previous work in which the upper bounds of the error were developed in a FEM framework. The upper bound property requires the recovered solution to be equilibrated and continuous. The proposed technique consists of using a recovery technique, especially adapted to the XFEM framework that yields equilibrium at a local level (patch by patch). Then a postprocess based on the partition of unity concept is used to obtain continuity. The result is a very accurate but only nearly-statically admissible recovered stress field, with small equilibrium defaults introduced by the postprocess. Sharp upper bounds are obtained using a new methodology accounting for the equilibrium defaults, as demonstrated by the numerical tests. [Copyright &y& Elsevier]

Abstract: This paper considers the analysis and numerical simulation of strong discontinuities in partially saturated solids. The goal is to study observed localized failures in such media like shear bands and similar. The developments consider a fully coupled partially saturated elastoplastic model for the (continuum) bulk response of the solid formulated in effective stresses, identifying the necessary mathematical conditions for the appearance of strong discontinuities (that is, discontinuities in the displacement field leading to singular strains) as well as the proper treatment for the fields characterizing the flow of the different fluid phases, namely, the fluid contents of these phases and their individual pore pressures. The geometrically linear range of infinitesimal strains is considered. These developments allow the formulation of multiphase cohesive laws along the strong discontinuity, capturing in this way the coupled localized dissipation observed in the aforementioned failures. Furthermore, the paper also presents the formulation of enhanced finite elements capturing all these discontinuous solutions in general unstructured meshes. In particular, the finite elements capture the strong discontinuity through the proper enhancements of the discrete element strains, allowing for a complete local resolution of these effects. This results in a particularly efficient computational approach, easily accommodated in an existing finite element code. Different representative numerical simulations are presented illustrating the performance of the proposed formulation, as well as its use in practical applications like the modeling of the excavation of tunnels in variably saturated media. [Copyright &y& Elsevier]

Abstract: This paper, in parallel to the investigation on axially embedded cracks reported in the companion paper, presents a numerical study on the linear-elastic KI and T-stress values over the front of elliptical cracks circumferentially embedded in the wall of a pipe/cylindrical structure, under a uniform pressure applied on the inner surface of the pipe. The numerical procedure employs the interaction-integral approach to compute the linear-elastic stress-intensity factor (SIF) KI and T-stress values for embedded cracks with practical sizes at different locations in the wall of the pipe. The parametric study covers a wide range of geometric parameters for embedded cracks in the pipe, including: the wall thickness to the inner radius ratio (t/Ri ), the crack depth over the wall thickness ratio (a/t), the crack aspect ratio (a/c) and the ratio of the distance from the centerline of the crack to the outer surface of the pipe over the pipe wall thickness (eM /t). The parametric investigation identifies a significant effect of the remaining ligament length on both the T-stress and KI values at the crack-front location (denoted by point O) nearest to the outer surface of the pipe and at the crack-front location (denoted by point I) nearest to the inner surface of the pipe. The numerical investigation establishes the database to derive approximate functions from a nonlinear curve-fitting procedure to predict the T-stress and KI values at three critical front locations of the circumferentially embedded crack in a pipe: points O, I and M. The proposed T-stress and KI functions utilize a combined second-order polynomial and a power-law expression, which presents a close agreement with the T-stress and KI values computed from the very detailed finite element models. The comparison between the circumferentially embedded crack and the axially embedded crack indicates that both the T-stress and KI values at crack-front points O and I in a circumferential crack equal approximately 50% the T-stress and KI values at the corresponding front locations in an axial crack with the same crack depth ratio, the same crack aspect ratio and the same pipe wall thickness to the inner radius ratio. [Copyright &y& Elsevier]

Abstract: This paper first presents a critical review and assessment of the ability of the existing Drucker–Prager (D–P) type concrete plasticity models to predict the behavior of confined concrete using both experimental observations and numerical results. This assessment shows that for a D–P plasticity model to succeed in predicting the behavior of FRP-confined and other passively-confined concrete, it needs to be modified to possess the following three features: (a) a yield criterion including the third deviatoric stress invariant; (b) a hardening/softening rule which is dependent on the confining pressure; and (c) a flow rule which is dependent not only on the confining pressure but also on the rate of confinement increment. None of the existing D–P type models includes all three features, so they cannot be expected to lead to accurate predictions for both actively-confined and passively-confined (e.g. FRP-confined) concrete. A modified D–P type model, which includes all three features mentioned above, is then presented in this paper. The capability of the proposed model in providing close predictions of the behavior of both actively-confined and FRP-confined concrete is next demonstrated through comparisons between numerical predictions obtained using this modified D–P type model and available test results. Finally, the limitations of the proposed plasticity model are discussed. These limitations are addressed in the companion paper through the development of a plastic-damage model. [Copyright &y& Elsevier]

Abstract: This paper addresses finite element evaluation of the non-singular T-stress and mixed-mode stress intensity factors in functionally graded materials (FGMs) under steady-state thermal loads by means of interaction integral. Interaction integral provides an accurate and efficient numerical framework in evaluating these fracture parameters in FGMs under thermal as well as mechanical loads. We use a non-equilibrium formulation and the corresponding auxiliary (secondary) fields tailored for FGMs. Graded finite elements have been developed to account for the spatial gradation of thermomechanical properties. This paper presents various numerical examples in which the accuracy of the present method is verified. [Copyright &y& Elsevier]

Abstract: This paper investigates the large deformations of an extended thick cylindrical tube under internal pressure, with emphasis on the static nonlinear behavior and instabilities of the shell. Thick elastic tubes that undergo large elastic deformations under internal pressure can exhibit novel instabilities. After some deformation, part of the tube becomes highly deformed taking the form of a bulge, while the remainder appears almost unchanged. This local instability phenomenon corresponds to a limit point along the nonlinear equilibrium path. After the onset of these highly nonuniform deformations, the local bulge initially grows with a marked decrease in internal pressure while the rest of the tube unloads. First, a detailed experimental analysis is carried out involving different geometries and initial axial forces and the influence of the axial force and of the internal pressure on the critical pressure is investigated. The shell used in the experiments is composed of an isotropic, homogeneous and hyperelastic rubber, which is modeled as a Mooney–Rivlin incompressible material, described by two elastic constants. These constants are obtained by comparing the experimental and numerical solutions for the shell under axial tension. The governing shell equations are solved numerically using the finite-element method, using the program ABAQUS. The experimental results are, as shown in the paper, in satisfactory agreement with the numerical analysis. [Copyright &y& Elsevier]

One-step finite element method (also called inverse approach) is more and more widely used in the automobile industry because of its unique advantages. Initial solution is an essential issue to ensure the success of the non-linear resolution in the implicit static one-step finite element solver. In order to speed up the convergence of the Newton–Raphson iterations, different kinds of initial solution methods are known. These are studied and compared in this paper. Several examples are followed to show their performance and efficiency. However most of these methods are based on geometric considerations like the geometric mapping method or the radial length development method. This kind of geometry based mapping methods could not reflect all aspects of the actual forming process. Therefore, an energy based mapping algorithm was implemented and coupled with the reverse deformation method which is based on the assumption of linear elastic deformation. This novel algorithm is proposed to provide the initial solution of one-step finite element method. For a complicated sheet forming modeling initial solutions obtained by different energy based algorithms coupled with the reverse deformation method are then compared in this paper. The results show that the Desbrun quadratic energy method and the accordant parameterization method combined with the inverse deformation method respectively are universal, efficient and robust initial solution schemes for the one-step finite element method. [Copyright &y& Elsevier]

Abstract: The buckling behavior of several simple tri-axial woven composite structures is studied. These structures include basic tri-axial structure, modified tri-axial structure and enlarged tri-axial structure. The structure is subjected to bi-directional loading. Approximate analytical method using equivalent anisotropic plate theory is presented in this paper. Its confirmation is obtained by non-linear finite element solution. Approximate analytical method provides a simpler way to obtain the buckling load, while the non-linear finite element method gives the numerical results and detailed analysis of buckling behavior of the tri-axial structures. The non-linear finite element analysis results reveal that the structures investigated in the paper approximately have the same buckling behavior, but with different values of buckling load. When more X-crossovers are involved in the tri-axial structures, their buckling loads increase and tend to approach a certain value. The results show that techniques used for approximate analytical solution can be used to obtain the buckling load of a real life tri-axial structure. The sensitivity of the buckling behavior of the basic tri-axial structure to the change in the boundary conditions and to the imperfection due to initial configuration is investigated. [Copyright &y& Elsevier]

Abstract: The dynamic buckling of thin isotropic thermoviscoplastic cylindrical shells compressed with a uniform axial velocity prescribed at the end faces is investigated analytically and numerically. In the first part of the paper, the stressed/deformed state of a shell is assumed to have buckled if infinitesimal perturbations superimposed upon it grow. Cubic algebraic equations are derived for both the initial growth rate of the perturbation and its wavenumber. The wavenumber corresponding to the maximum initial growth rate of a perturbation introduced at an axial strain of 0.1 is taken to determine the buckling mode. The computed buckling modes are found to match well with those listed in the available experimental data. A thermoviscoplastic constitutive relation is used to delineate the influence of material parameters on the buckling behavior. In the second part of the paper, the finite element method is used to analyze the collapse of an imperfect circular cylindrical tube with axial velocity prescribed at one of its flat end faces with the other end face kept fixed. The influence of initial randomly located imperfections on the buckling behavior is investigated and discussed. [Copyright &y& Elsevier]

The paper presents a feature-based approach for design of extrusion dies. Part drawing of given shape to be extruded is drawn using line, arc, circle, polyline and ellipse entities of AutoCAD Rel-12 and corresponding DXF file is created. Treating shape as a feature, DXF file is processed and necessary data are separated for feature recognition according to Kumar et al. (Int. J. Prod. Res. 37 (1999) 2519). An upper-bound model with strain hardening for die design of non-re-entry cold extrudable shapes as proposed by Kumar et al. (Trans. ASME J. Manuf. Sci. Eng. 126 (1) (2002) 71) is extended for re-entry shapes. Rounded square and clover sections are taken to test and validate the proposed procedure for re-entry shapes. The paper has been combined with a rigid plastic finite element (RPFE) model (Kumar and Prasad; J. Prod. Eng. (2003)) for steady state axisymmetric hot extrusion using the kinematically admissible velocity field obtained from the upper-bound model as proposed in Kumar et al. (Trans. ASME J. Manuf. Sci. Eng. 126 (1) (2002) 71). Based on the optimal power obtained from the upper-bound method (Int. J. Prod. Res. 37 (1999) 2519) the temperature distribution in cold as well as hot extrusion process has been determined to study the effect of process parameters such as ram velocity, reduction, friction between die–billet interface, die length and temperatures (initial billet, die and container and surrounding). The result obtained agrees well with the experiment and the theoretical analysis. [Copyright &y& Elsevier]

The paper gives a bibliographical review of finite element methods applied to creep and creep fracture/damage of engineering materials and structures from the theoretical as well as practical points of view. It is a continuation of the author''s bibliography published in Int. J. Pressure Vessels Piping 2000; 77: 53–77, where 964 references were listed for the period 1980–1999. This addendum lists more than 400 references to papers, conference proceedings and theses/dissertations on the subject that were published between 1999 and 2003. These references are classified in the following categories: materials, topics, and areas of applications. Each category is further divided into specific subcategories for a more effective and faster reference retrieval. [Copyright &y& Elsevier]

This paper presents a residual-based a posteriori error estimator for the Arnold–Winther mixed finite element that utilises a post-processing for the skew-symmetric part of the strain. Numerical experiments verify the proven reliability and efficiency for suitable approximation of the skew-symmetric deformation gradient. Numerical evidence supports that the L 2 -stress error estimator is robust in the Poisson ratio and allows stable error control even in the incompressible limit. [ABSTRACT FROM AUTHOR]

This paper presents a new numerical model for a static and dynamic analysis of thin plate structures based on the combined finite–discrete element method (FDEM). The model uses three-noded triangular finite elements taking into account linear-elastic material behaviour, finite rotations, finite displacements and small strains. The model is implemented into the open source FDEM package ‘Yfdem’. Performance of the new numerical model was demonstrated on simple benchmark tests by a comparison with known analytical and numerical results. [ABSTRACT FROM AUTHOR]

Analytical solutions for tunnel design are widely used in practical engineering, as they allow a quick analysis of design issues such as estimation of support requirement. In recent years, several papers analyzing the behavior of rock masses that obey the conventional or generalized Hoek–Brown criterion have been published. This article presents a complementary analysis that includes a new normalization of the generalized Hoek–Brown failure criterion, complete solutions for associated and non-associated flow rules, with some new closed-form solutions in the latter case, and in-depth considerations regarding intermediate stresses and edge effects. The results obtained show full agreement with existing solutions in the literature, when possible, and with numerical finite element models in cases that had not been treated previously. [ABSTRACT FROM AUTHOR]

The present paper considers a non-prismatic beam i.e., a beam with a cross-section varying along the beam axis. In particular, we derive and discuss a model of a 2D linear-elastic non-prismatic beam and the corresponding finite element. To derive the beam model, we use the so-called dimensional reduction approach: from a suitable weak formulation of the 2D linear elastic problem, we introduce a variable cross-section approximation and perform a cross-section integration. The satisfaction of the boundary equilibrium on lateral surfaces is crucial in determining the model accuracy since it leads to consider correct stress-distribution and coupling terms (i.e., equation terms that allow to model the interaction between axial-stretch and bending). Therefore, we assume as a starting point the Hellinger–Reissner functional in a formulation that privileges the satisfaction of equilibrium equations and we use a cross-section approximation that exactly enforces the boundary equilibrium. The obtained beam-model is governed by linear Ordinary Differential Equations (ODEs) with non-constant coefficients for which an analytical solution cannot be found, in general. As a consequence, starting from the beam model, we develop the corresponding beam finite element approximation. Numerical results show that the proposed beam model and the corresponding finite element are capable to correctly predict displacement and stress distributions in non-trivial cases like tapered and arch-shaped beams. [ABSTRACT FROM AUTHOR]

This paper focuses on the effects of stud and hole configurations on weld defects in friction hydro-pillar processing (FHPP). Various configurations of the stud and hole are designed and all welds are performed by using a self-developed high-performance platform with the same welding parameters. The experimental results indicate that the defects usually appear at the bottom of the hole, but the upper region bonds well. The quality of welded joints is deeply affected by the bottom filling which is called initial stage. Therefore, the finite-element method (FEM) is employed to simulate the initial stage of FHPP. The simulated results agree well with those of the experiments. The results indicate that the geometry of the hole influences the welding quality more strongly than the shape of the stud and that weld samples with a rounded corner at the bottom of the hole bond well. Moreover, different shapes of the studs cause different stress states and temperature distributions, which also influence the quality of welded joints. [ABSTRACT FROM AUTHOR]

A technique for evaluating the (steady-state) creep stress exponent ( n ) from indentation data has come into common use over recent years. It involves monitoring the indenter displacement history under constant load and assuming that, once its velocity has stabilized, the system is in a quasi-steady state, with Stage II creep dominating the behaviour. The stress field under the indenter, and the way in which the creep strain field is changing there, are then represented by “equivalent stress” and “equivalent strain rate” values. These are manipulated in a similar manner to that conventionally employed with (uniaxial) creep test data, allowing the stress exponent, n , to be obtained as the gradient of a plot of the logarithm of the equivalent strain rate against the logarithm of the equivalent stress. The procedure is therefore a very simple one, often carried out over relatively short timescales (of the order of 1 h or less). However, concerns have been expressed about its reliability, regarding the neglect of primary creep (after a very short initial transient) and about the validity of representing the stress and strain rate via these “equivalent” values. In this paper, comprehensive experimental data (both from a conventional, uniaxial loading set-up and from instrumented indentation over a range of conditions) are presented for two materials, focusing entirely on ambient temperature testing. This is supplemented by predictions from numerical (finite element method) modelling. It is shown that the methodology is fundamentally flawed, commonly giving unreliable (and often very high) values for n . The reasons for this are outlined in some detail. An attempt is made to identify measures that might improve the reliability of the procedure, although it is concluded that there is no simple analysis of this type that can be recommended. [ABSTRACT FROM AUTHOR]

Abstract: This paper deals with the treatment of incompressibility in solid mechanics in finite-strain elastoplasticity. A finite-strain model proposed by Miehe, Apel and Lambrecht, which is based on a logarithmic strain measure and its work-conjugate stress tensor is chosen. Its main interest is that it allows for the adoption of standard constitutive models established in a small-strain framework. This model is extended to take into account the plastic incompressibility constraint intrinsically. In that purpose, an extension of this model to a three-field mixed finite element formulation is proposed, involving displacements, a strain variable and pressure as nodal variables with respect to standard finite element. Numerical examples of finite-strain problems are presented to assess the performance of the formulation. To conclude, an industrial case for which the classical under-integrated elements fail is considered. [Copyright &y& Elsevier]

Abstract: Failure in ductile sheet metal structures is usually caused by one, or a combination of, ductile tensile fractures, ductile shear fractures or localised instability. In this paper the failure characteristics of the high strength steel Docol 600DP are explored. The study includes both experimental and numerical sections. In the experimental sections, the fracture surface of the sheet subjected to Nakajima tests is studied under the microscope with the aim of finding which failure mechanism causes the fracture. In the numerical sections, finite element (FE) simulations have been conducted using solid elements. From these simulations, local stresses and strains have been extracted and analysed with the aim of identifying the fracture dependency of the stress triaxiality and Lode parameter. [Copyright &y& Elsevier]

Abstract: Joints play an important role in resisting impact loading in Tubular structures. In this paper, a finite element model validated by experimental results is developed to numerically study the failure modes and energy dissipation mechanism of tubular T-joint impacted by a drop hammer with the initial velocity of 7–10 m/s. The resistant mechanism is investigated based on the dynamic responses of the joints under impact loading. Strain, displacement and the failure modes of the T-joints are also predicted. Global and local deformations of the tubular joints are distinguished using an equal area axis method, which helps to discover the failure mechanism of the joints. Using the yield line theory, an equivalent impact force estimation method is also proposed based on the impact load versus displacement relationship. The numerical analysis and the simplified method provide a basis for impact resistance evaluation and progressive collapse mitigation of steel tubular structures in design practice in the future. [Copyright &y& Elsevier]

Abstract: Bone modeling and remodeling have been extensively studied in many fields of research. The process of adaptive bone remodeling can be described mathematically and simulated in a computer model, integrated with the finite element method (FEM). The FEM can determine the long-term behavior of bone and the impact on bone biomechanics produced by prosthetic models. As whole bone remodeling simulations are time consuming, the aim of this paper is to combine FE analyses with numerical extrapolation techniques to accelerate bone remodeling simulations. Two vector extrapolation methods, reduce ranked extrapolation (RRE) and minimal polynomial extrapolation (MPE), are used to reduce the simulation time. These extrapolation techniques are illustrated by numerical examples of 2D and 3D models based on a strain-adaptive bone remodeling theory. [Copyright &y& Elsevier]

Abstract: In this paper several currently available bond stress-slip models for steel and FRP reinforcing bars in concrete are firstly reviewed, and both merits and demerits of these models are discussed. The models which are promising to be used for describing the bond-slip behaviour of FRP reinforcing bars in numerical analysis are evaluated through finite element analysis of FRP-reinforced concrete beams with bond-slip effect taken into account. A newly developed composite beam element with bond-slip is employed for finite element analysis of a GFRP-reinforced concrete beam and a CFRP-reinforced concrete beam with the selected bond stress-slip models built in the finite element model. The suitability and capability of the bond stress-slip models informed from the finite element analyses are summarised and concluded. Finally, parametric study is carried out on the most appropriate bond stress-slip model to investigate the effect of different surface conditions of reinforcing bars on the structural behaviour. [Copyright &y& Elsevier]

Abstract: Steel Reinforced Polymers (SRPs) and Steel Reinforced Grout (SRG) strengthening systems have been recently introduced as an alternative solution to the traditional systems based on the use of fiber reinforced polymers materials (FRPs). Few studies on SRP/SRG are available in the current literature and all have shown the potentialities of SRP/SRG in improving structural performances of masonry and concrete elements and, at the same time, their difference with respect to FRPs particularly in terms of bond behavior. Aim of the present paper is to propose a simple approach devoted to study the bond behavior of masonry structures strengthened with SRP/SRG systems. The approach, based on experimental evidences and theoretical considerations mainly consists of deriving approximate bond stress-slip laws for the strengthening/support interface layer, able to reproduce the local bond stresses transferring mechanism. Finite Element (FE) analyses are then developed with reference to the experimental tests available in the current literature by adopting the bond stress-slip laws obtained through the proposed approach. The deduced results show the reliability of the proposed approach in simulating the bond behavior of masonry elements strengthened with SRP/SRG and the possibility to investigate further peculiarities characterizing this kind of strengthening systems. [Copyright &y& Elsevier]

Abstract: The paper is aimed at investigating the effects of stitching or tufting on displacement and stress fields of sandwiches, whose homogenised mechanical properties are computed through virtual material tests with 3D finite element analysis. After that, structural analysis is carried out using the adaptive model by the authors, which has variable representation of displacements across the thickness and fixed degrees of freedom. This choice is done considering its accuracy and computational efficiency. Numerical applications show that using these technical skills it is possible to considerably reduce stresses and displacements in sandwiches. [Copyright &y& Elsevier]

Abstract: A robust reduced integration solid-shell finite element in irreducible variational formulation is demonstrated in this paper. To enable shell element-like performance using a single through-shell-thickness element layer, we apply element technologies isotropically, introducing local tri-quadratic hierarchical displacement modes thereafter systematically projected to the global coordinate frame. We also enforce uniform, bilinear and linear ANS interpolations to all local normal and shear strains respectively, imposing identical in-plane and out-of-plane element response for robust 3D thin shell deformation behaviour in non-regular, trapezoidal-shaped meshes. The hierarchical strains realised improve the element performance by complementing the locking alleviating actions of the ANS-modified membrane and shear strain fields in reduced numerical integration scheme performed along the designated shell thickness. We restrict our initial numerical investigations to geometrically linear beams, plates and shell problems solely for preliminary assessment of the element's in-plane and out-of-plane behaviour in response to the uniform modification of strains and hierarchical displacement modes introduced. To this end, the results indicate robust behaviour and comparable accuracy in comparison to mixed variational, enhanced assumed strain elements in full and in reduced integration in all structural problem classes undertaken. [Copyright &y& Elsevier]

Abstract: This paper presents a new finite-element formulation for the dynamic analysis of three-dimensional beams. The formulation is based on the geometrically exact three-dimensional beam theory in which the strain vectors are the only unknown functions of the arc-length parameter. The classical Newmark time integration scheme extended to the multiplicative group of spatial rotations is used and properly adapted for the strain-based formulation. The Generalized- method is used to enforce a numerical dissipation of higher modes. The update procedure needed in the iteration process is discussed in detail. The exact linearization of the governing equations is also presented. The performance of the formulation is demonstrated with numerical examples. [Copyright &y& Elsevier]

Abstract: In this paper, the ductile fracture of Al-alloy 5052 is studied by experiments and simulations using a modified Rousselier model. Although tension failure has been successfully predicted by the classical Rousselier model, its predictive capability on shear failure was seldom discussed. A modified Rousselier model was proposed by incorporating the recent extended damage evolution model by Nahshon and Hutchinson. The modified Rousselier model can capture both tension and shear failure. A stress integration algorithm based on the general backward-Euler return algorithm for this constitutive model was developed and implemented into finite element model by the user defined material subroutine VUMAT in the ABAQUS/Explicit. The tensile tests of smooth round bar and notched round bars with different sizes were carried out to investigate the mechanical behavior of Al-alloy 5052. Consequently, the material parameters of the classical Rousselier model were identified by an inverse method using these experimental data. A shear test was also performed to calibrate the new shear damage coefficient in the modified Rousselier model. For the shear test, the simulations show that although shear failure can be predicted by the Rousselier model, the ductility was over-estimated. However, the modified Rousselier model can give more accurate results. The simulations on uniaxial tension of the round bars also confirm that the modified Rousselier model can well predict the cup-cone fracture mode. The results indicate that the Lode parameter in the new damage evolution model is important to capture the cup-cone fracture mode transition. [Copyright &y& Elsevier]

Abstract: The helical-wedge rolling (HWR) process is a new metal forming technique for producing spherical parts of various dimensions. In this paper, the overall details of the HWR process are described and the important process parameters that control the HWR process are systematically discussed. A new experimental method, developed under laboratory conditions, showed that the HWR process can produce spherical steel parts (balls) with high manufacturing quality. Numerical simulations of the HWR process were carried out using a commercially available FEM software (Simufact) to show the stress, strain, and temperature distributions in the rolled balls. In addition, the variation of forces and rolling moments during the process are analyzed. Based on the experimental and numerical investigations, the HWR technique has been found to be a viable process for enhancing the quality and productivity of formed spherical products. [Copyright &y& Elsevier]

Abstract: This paper presents the constitutive aspects and a finite element application for an energetic damage criterion within Cristescu’s viscoplastic constitutive law. The numerical model is implemented in finite element code LCPC-CESAR [1] by the author. The numerical solution is used to perform an analysis of the evolution of the damage zones around a circular lined cavity in a viscoplastic material subjected to a far field stress. Two important factors regarding the opening stability, namely the lining mounting time and the tunnel face influence, are analyzed. The initial stress of rock mass varies with the depth at which the tunnel is excavated and this fact determines a bigger displacement of the tunnel bottom than the tunnel ceiling. The time emphasizes this asymmetry. The results obtained are in completely accordance with the practical observations. [Copyright &y& Elsevier]

Abstract: The construction of tunnels in soft ground causes short and long term ground deformations resulting from the disturbance of the virgin stress state of the soil and the changing pore water conditions. In particular in urban tunneling, in each stage of the construction process, interactions between the construction process, the soil and existing building infrastructure need to be evaluated to limit the risk of damage on existing buildings and to decide on appropriate mitigation measures. Besides conventional tunneling, mechanized tunneling is a well established and flexible technology in particular in urban areas, which allows for tunnel advances in a wide range of soils and difficult conditions. The paper presents a finite element model for the simulation of interactions between mechanized tunnel construction, the surrounding soil and existing buildings resting on pile foundations in the framework of a process-oriented simulation model for mechanized tunneling. The performance of the model is demonstrated by means of selected prototype analyses. As a consequence of the high computational demand connected with this type of spatio-temporal simulations, problem specific parallelization techniques are investigated to increase the numerical efficiency of the numerical analyses. [Copyright &y& Elsevier]