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Aiming at the problems of a large amount of material cutting waste or large forming load when large gear profile forming adopts overall cutting or precision forging process, this paper proposed a three-roller bending process (TRBP) for large gear teeth profile, and analyzed the deformation mechanism of the rack bending, meanwhile the gear chain for roll forming was designed. Finite element analysis (FEA) was carried out to numerically simulate the load effects of both the precision forging process and the TRBP for the large gear teeth profile in 17CrNiMo6. The effects of deformation force and strain of TRBP for large gear teeth profile were analyzed. The results showed that as the deformation temperature and speed increase, the deformation force and strain required by the gear profile gradually change. And the reasonable parameter of TRBP is around 750 ∘ C of deformation temperature and 0.5 mm · s - 1 of speed. Compared with the precision forging process under the same boundary conditions, the deformation force of the gear profile TRBP has decreased by about 99 % which could significantly reduce the tonnage requirement of deforming equipment. [ABSTRACT FROM AUTHOR]

This paper proposes a new sheet forming method that combines electromagnetic forming (EMF) with hydraulic forming called electromagnetic hydroforming (EMHF). Finite element models of both the EMF and EMHF processes were established using ANSYS and ABAQUS. Then, dynamic free bulging deformation of 5052 aluminum alloy during the forming processes was analyzed. The EMF process results in a deformed sheet profile with an uneven conical shape, whereas EMHF leads to a deformed profile with a regular circular shape. This is because during the EMHF process, electromagnetic impact energy is transformed into liquid pressure that is evenly distributed on the sheet surface. When the discharge voltage is 4.5 kV, the maximum deformation speed and strain rate reached 70.6 m/s and 2176.8 s−1, respectively. Thus, EMHF can be considered a high-speed forming method. The simulation results for both EMF and EMHF were verified by experiment at two different discharge voltages. The maximum error was less than 7.4%. [ABSTRACT FROM AUTHOR]

This paper presents a novel approach for removing out-of-plane deformation in stretched metal interconnects by adding a fractal structure to the original meander shape and using an optimized fabrication stack. In thermoformed electronics, in cases where copper is used as conductor, the twisting of meander-shaped structures caused by excessive mechanical stress can cause a non-uniform surface, delamination of the metal interconnect from the substrate, and in some cases, a short circuit to the adjacent tracks. Typically, designers of stretchable electronics use various shapes and widths of the copper interconnect to tackle this issue. Using conventional meander shapes such as horseshoes and U-shapes is not universally practical, especially when stretching is higher than 30 percent leading to significant out-of-plane buckling. Limiting this out-of-plane buckling by reducing the track width is not always applicable, as a minimum width is needed from a technology and conductivity perspective. The presented approach is inspired by computational and experimental studies of multiple meander shapes and fabrication methods. A geometry- and fabrication-based approach is presented, reducing the mechanical stress of almost all possible meander shapes by increasing the meander's path length to accommodate the metal track's produced torque during stretching. An analytical approach is provided for calculating the optimal meander parameters and the optimal fabrication stack is achieved based on simulation results. Experiments and finite element modeling for a case study show the improvement in the stress distribution and reduction of out-of-plane buckling. [ABSTRACT FROM AUTHOR]

Finite Element (FE) modeling of machining processes has received growing attention over the last two decades. Since machining processes operate at severe deformation conditions, involving very high strain, strain rate, stress, and temperature, the modeling procedure is still a challenging task even with new advanced software and computers. Therefore, most of the published research works were mainly performed for the simplest configuration of machining known as orthogonal cutting, in which a plane strain deformation state is assumed. This configuration leads to reducing the number of elements in the FE model and the computational time of the solution, compared to conventional machining processes (turning, milling, and drilling). Nevertheless, FE modeling of orthogonal turning is still considered as an open-ended subject as most of the phenomena involved in the orthogonal turning process, which also exist in other machining operations, are not fully well understood. The present review article deals with finite element modeling of orthogonal machining process. The paper consists of several related parts. First, the fundamentals of the FE simulation of orthogonal turning process are briefly described. Then, a detailed review on the FE prediction of machining characteristics including chip morphology, cutting forces, cutting temperature, tool wear, and burr formation is provided. Also, the FE prediction of surface integrity characteristics including residual stresses and microstructural changes is discussed. The influence of input model and parameters including thermal, material, and frictional models as well as size and arrangement of elements on machining and surface integrity characteristics are explained as well. Both technical and statistical aspects of the FE simulation of orthogonal turning are treated. Since there is no review paper thoroughly and specifically discussing the methods and findings of the finite element simulation of turning operations, the present article can be used as a reference for researchers who are active and/or interested in this filed. [ABSTRACT FROM AUTHOR]

The reduction in the number of coordinates for flexible multibody systems is necessary in order to achieve acceptable simulation times of real-life structures and machines. The conventional model order reduction technique for flexible multibody systems is based on the floating frame of reference formulation (FFRF), using a rigid body frame and superimposed small flexible deformations. The FFRF leads to strongly coupled terms in rigid body and flexible coordinates as well as to a non-constant mass matrix. As an alternative to the FFRF, a formulation based on absolute coordinates has been proposed which uses a co-rotational strain. In this way, a constant mass matrix and a co-rotational stiffness matrix are obtained. In order to perform a reduction in the number of coordinates, by means of the component mode synthesis, e.g., the number of modes needs to be increased, such that all modes are represented in every possible rotated configuration. This approach leads to the method of generalized component mode synthesis (GCMS). The present paper shows in detail how the equations of motion of the FFRF evolve from the ones of the GCMS by considering rigid body constraint conditions and subsequently eliminating them via an appropriate null-space projection. This approach allows a straightforward, term-by-term interpretation of the FFRF mass matrix and of the generalized gyroscopic forces, which, to the same extent, cannot be deduced from former publications on the FFRF. From a practical point of view, the resulting expressions allow to calculate all inertia coefficients from the constant finite element mass matrix together with standard input data of the finite element model in the course of a preprocessing step. Then, the repeated updates of the FFRF mass matrix and of the gyroscopic forces in the course of time integration involve only simple vector matrix operations of low dimensions. In contrast to previous implementations of the FFRF, no evaluations of extra inertia integrals are required. Consequently, the present formulation can be implemented entirely independent of the related finite element code. [ABSTRACT FROM AUTHOR]

Semi-analytical models have been developed to analyze the contact of inhomogeneous materials based on the equivalent inclusion method. It is important to pursue a higher efficiency in numerical implementation of the semi-analytical models. This paper reports the development of a dual-grid computational scheme for further improving the efficiency of the current semi-analytical modeling. Parametric studies show that the new method can save at least 50% of the execution time with respect to the original algorithm in a considerably wide range of conditions. The new method is applied to investigate the influence of inhomogeneities on contact pressure distributions. Data regression is performed to obtain the amplitudes of contact pressure disturbances as a function of inhomogeneitys elastic modulus, size and location. Then, a criterion is developed based on the values of contact pressure disturbances to determine the circumstances in which the coupling between inhomogeneities and surface contact be ignored. [ABSTRACT FROM AUTHOR]

Soil-filled gabion structures are widely used to protect against the effects of blast and fragmentation. It is known that moisture content significantly affects the capability of such structures, but the behaviour of partially-saturated soils is not well characterised at the strain rates and stresses experienced in these events. In particular, little data is available for loose soils, whose compaction behaviour can have a substantial impact on structural stability and ballistic performance. This paper describes the use of split Hopkinson pressure bar experiments to characterise the pre- and post-saturation compressibility of a loose quartz sand at moisture contents of up to 15.0%. In contrast to dense soils, increases in moisture content between 0.0% and 7.5% led to a decrease in the stiffness of the sand. Above 7.5% moisture content, specimens reached full saturation during the experiment: the additional water had no further effect on the pre-saturation stiffness, but post-saturation behaviour was dominated by the stiffness of the pore water. Full saturation occurred at lower dry densities as moisture content increased, leading to a decrease in particle breakage. [ABSTRACT FROM AUTHOR]

In order to improve the internal quality of cross wedge rolling (CWR) shaft, the floating-pressure method (FPM) using high-pressure gas to compact void in CWR shaft is adopted in this paper. Firstly, the theoretical relations between each influencing factor and flow stresses are deduced by establishing the mechanical model of void closure based on FPM. Then, the laws of stress variation, metal flow, void shape variation, and microstructure evolution are all analyzed by DEFORM-3D finite element software, and the mechanism of void closure based on FPM is clarified. By means of hot isostatic pressing equipment, the FPM experiments are conducted, and it is illustrated that the outer dimensions of CWR shaft are hardly affected and its internal void can be effectively eliminated. Finally, the tests of specimens’ mechanics performance show that the tensile strength of the specimen is improved and its surface hardness is slightly reduced. The research results provide a new way for improving the yield and mechanical properties of CWR shaft. [ABSTRACT FROM AUTHOR]

Stereo-DIC allows to track with a high accuracy the shape change and the surface displacement field of objects during deformation processes. When multiple camera arrangements are used, the shape and deformation measurement can be performed over the whole surface of the object. We submit that, in the case of intact specimens, with no internal defects and/or discontinuities, such boundary information can be used to estimate the internal displacement field by using proper interpolation functions. This calculation could serve, for instance, to evaluate the strain localization that occurs in metal specimens subjected to plastic deformation, hence allowing to get a better insight in the necking initiation and fracture propagation processes. In this paper, an interpolation method based on Bézier curves is developed and tested using simulated and real experiments on specimens with flat and cylindrical geometries. In particular, the deformation behaviour in the necking zone was investigated in the case of highly ductile and anisotropic materials. Numerical models were used to validate the method while the application to two real experiments demonstrated its feasibility in practical cases. The applicability of the method to more complex loading cases (e.g., bending, torsion, mixed-loads) or different initial shapes (e.g., curved beams, notches) will be investigated in future studies. [ABSTRACT FROM AUTHOR]

Instrumented indentation testing is widely used for the mechanical characterization of materials and phases. Among important mechanical parameters such as hardness and Young’s modulus the determination of yield stress and hardening behavior of metallic materials calculated from indentation results is a particular topical subject. This paper presents a methodology which allows for the reconstruction of the stress-strain curve from a single load-displacement curve measured by a spherical indenter. The method is based on the depth-dependent strain field induced by a spherical indenter. The loading part of the curve is discretised in single tuples of indentation depth and force. Since the mean strain induced by the spherical indenter is dependent on indentation depth, every depth can be assigned to a mean uniaxial strain value. The force is then used to calculate the associated uniaxial stress. The method was exemplarily applied to the carbon steel C45 in different heat treatment conditions. It could be shown that after a calibration procedure the stress-strain curves of the carbon steel can be calculated without the requirement of assuming a mathematical description of the curve (e.g. power-law material behavior). The method and its framework can easily be expanded and adjusted in order to be used as an easy and quick method for inverse determination of material parameters. [ABSTRACT FROM AUTHOR]

Analysis of the load distribution along raceways is fundamental for assessing dynamic and static capacity of the slewing bearings. In the literature, several finite element (FE) models have been proposed to estimate the load distribution and the deformation of slewing bearing. Although FE simulations are a useful tool for designers, there are a few experimental studies assessing accuracy and reliability of computations. In this paper, a FE model for a single-row four-point-contact slewing bearing is built in ABAQUS software. The key to the method is to simulate the balls under compression by traction-only nonlinear springs. Subsequently, the static loading experiment is designed: strain gauges are mounted on the inside circumference of the inner ring to obtain load distribution. The comparison between numerical and experimental results is discussed in detail. Remarkably, FE results are consistent with experimental data. [ABSTRACT FROM AUTHOR]

Springback in sheet metal forming is a deformation that occurs when a workpiece is released from dies after forming. Prediction of springback using the finite element method (FEM) has been used in the design of stamping dies. The present paper describes an effective approach by which to improve the accuracy of springback analysis, which can also suppress the increase in the calculation time. In general, FEM using the analysis condition to decrease discretization errors greatly increases the computation time. The proposed procedure is as follows: (1) Quick analysis using a large mesh size is performed. (2) Data mapping and morphology mapping for the forming results are then performed using the database based on a detailed partial analysis of the drawbead and the die shoulder. (3) Springback analysis is performed using the forming results modified by the data mapping and morphology mapping. A forming experiment was conducted to confirm that the proposed method using the database greatly improves the prediction accuracy of the shape after springback and also suppresses the increase in calculation time. [ABSTRACT FROM AUTHOR]

Shot peen forming is often used to form the aerodynamic configurations of aircraft integral wing panels. The component is traditionally regarded as perfectly constrained target in peen forming process. However, weak-stiffness of the component results in concomitant macroscopic bending and stretching deformations, and releasing of peening stresses. Subsequent peening stresses are induced by shot impacts based on the current released stresses. In this paper, a intermittently peening-releasing finite element simulation model is used to study peening stress evolution in lowrigidity plate. An algorithm is proposed to calculate the increment of subsequent peening stress by connecting current stresses to the peening stresses in perfectly constrained target.With the algorithm, the peen forming deformations of freely constrained plates are calculated by equivalently simulating the peen forming process. And strip peen forming deformations are calculated and compared with experimental data. The comparison shows the peening deformation of a low-rigidity component should be treated as an incremental process and the algorithm can be used to predict the deformation with good accuracy. [ABSTRACT FROM AUTHOR]

This paper presents a detailed literature review on the current research of incremental sheet forming relating to deformation mechanism, modelling techniques, forming force prediction and process investigations. First, a review of the fundamental deformation mechanism and formability in incremental sheet forming (ISF) is provided. Subsequently, the modelling techniques for ISF are reviewed and categorised into two approaches: analytical modelling and finite element modelling. Special interest is given to a critical review regarding the forming forces analysis and prediction during the process. Then, previous publications related to geometric accuracy, surface finish and forming efficiency in ISF are reviewed. Finally, several potential hybrid incremental sheet-forming strategies are discussed. This leads to a statement of conclusion which may act as an inspiration and reference for the researcher. [ABSTRACT FROM AUTHOR]

Laser shock forming (LSF) is a sheet plastic forming technology, which employs laser-induced shock waves to make sheet metal duplicate a desired shape of the mold. In this paper, a finite element analysis (FEA) model was developed to simulate dynamic forming process with the commercial finite element code ABAQUS/Explicit, and a series of dynamic deformation behaviors of the metal sheet shaped into conical cup at the end of different periods of time were displayed and discussed in detail. The springback of conical cup and the distribution of residual stress were analyzed with ABAQUS/Standard. All these investigations could provide insight into the physics process of the ultra-fast deformation. The LSF experiment was further conducted to verify the results predicted by FEA. The experiment results are well consistent with the numerical predicted data, which validates the FEA model. It indicates that FEA can be used to simulate the forming process and optimize its parameters. [ABSTRACT FROM AUTHOR]

Significance of application of metal matrix composites (MMCs) in various industries has already been demonstrated. In order to address the challenges faced during machining MMCs, development of novel modeling techniques for understanding the mechanics of the process is crucial. This paper presents a new approach towards finite element modeling of MMC machining process to facilitate the analysis of plastic deformations. Transient Lagrangian modeling is used with adaptive remeshing control in order to reduce the effects of mesh distortions on accurate estimation of plastic deformation during machining. The thorough understanding of MMC plastic deformations, which is achieved using the developed model, is an asset in analysis of MMC behavior during the process. [ABSTRACT FROM AUTHOR]

In this paper, a simulation model for two-roll cross wedge rolling (CWR) was presented to investigate the deformation mechanism for forming shafts without concavity by using the finite element method. Based on the simulation results, the reason for concavity in both sides of the rolled piece in the CWR process was analyzed in detail, and a method to implement the CWR process without loss of material was brought forward by billet compensation. In addition, the influence of the main process parameters on the concavity depth of the workpiece with a tapered or circular-arc end was compared and ascertained. The study results show that the concavity depth is in direct proportion to the cone angle, but in inverse proportion to the central angle, and the concavity can be improved with larger area reduction and mill length under the two profiled ends. Subsequently, the feasibility of using profiled billets to effectively control the concavity was verified via the rolling experiments. [ABSTRACT FROM AUTHOR]

Laser forming (LF) is a new die-less forming technique that employs the energy from a laser beam to modify and adjust the curvature of sheet metals. In order to advance the LF process further for realistic application industry, it is necessary to consider large scale three-dimensional laser forming (3DLF). The main problem of 3DLF is the understanding of the mechanism and the planning of laser scanning strategy. This paper illustrates the temperature field, stress-strain field, and deformation field in the process of 3DLF of square sheet to spherical dome with spider-lines strategy with a finite element method (FEM). The explicit dynamic integral is used in the work presented in the paper rather than implicit method for improving the computational efficiency and accuracy. The FEM results showed that the inner stress induced by the laser beam propagates through the sheet as a stress wave, and the thermal stress and the stress wave in the sheet are the main influence factors in 3DLF. Also, the FEM results have been verified against experimental data, and a reasonable correlation has been found. The work showed in the paper would be beneficial of the parameter optimization of laser scanning strategy and the control of the formed precision of the sheet in 3DLF. [ABSTRACT FROM AUTHOR]

Abstract  Inverse methods offer a powerful tool for the identification of the elasto-plastic material parameters. One of the advantages with respect to classical material testing is the fact that those inverse methods are able to deal with heterogeneous deformation fields. The basic principle of the inverse method that is presented in this paper, is the comparison between experimentally measured strain fields and those computed by the finite element (FE) method. The unknown material parameters in the FE model are iteratively tuned so as to match the experimentally measured and the numerically computed strain fields as closely as possible. This paper describes the application of an inverse method for the identification of the hardening behavior and the yield locus of DC06 steel, based on a biaxial tensile test on a perforated cruciform specimen. The hardening behavior is described by a Swift type hardening law and the yield locus is modeled with a Hill 1948 yield surface. [ABSTRACT FROM AUTHOR]

The present paper is concerned with an elastic body in a static intermediate configuration, the body being loaded by an additional distribution of transient eigenstrain. For the sake of convenience, we use the notion of actuation stress in the present paper in order to describe the action of eigenstrain. It is assumed that the incremental displacements produced by the additional actuation stress can be prescribed within the framework of the theory of infinitesimally small dynamic deformations superimposed upon a static strain. The intermediate configuration thus may represent a possibly large deformation from an undistorted state of the body. It is the scope of the present contribution to derive distributions of actuation stress, which do not produce any incremental displacements from the intermediate configuration. Solutions of this problem are not unique in general. In the present paper, we particularly seek for a displacement-free distribution of actuation stress that acts within a sub-region of the body only. We show that any statically admissible stress, which is produced in the sub-region by a possibly transient eigenstrain, and which satisfies appropriate dynamic boundary conditions, may be used as actuation stress in order that the incremental displacements vanish throughout the whole body. The body then remains in the static intermediate configuration for all times. Appropriate boundary-value problems are suggested for computing the statically admissible stress in the sub-domain. Other than elastic constitutive equations might be used for selecting a suitable boundary-value problem for the actuation stress. It is furthermore shown that the incremental first Piola-Kirchhoff stress of the elastic body is equal to the actuation stress inside the sub-region under consideration, and that it vanishes outside. As an example, we present successful Finite Element computations for the vibrations of a rectangular domain in a state of plane strain, where the rectangle is fixed at two adjacent edges, the sub-region also being taken as rectangular. [ABSTRACT FROM AUTHOR]

Damage models are widely used to describe the ductile damage and fracture of metals. This paper proposes a new approach to determine the damage parameters of the Gurson-Tveergard-Needleman model, which uses a load-displacement curve coupled with finite element method. The load-displacement curve was obtained from a tensile test of a smooth tensile specimen and contained information about the damage and fracture behavior of the tested material. The principle of damage parameters identification is to minimize the deviation between experimental and simulated load-displacement curves by a hybrid particle swarm optimization. As a combination of particle swarm optimization and simulated annealing, the hybrid particle swarm optimization is an economical and effective algorithm to identify damage parameters. The identified damage parameters are also verified by testing and simulating deformation shapes of the smooth tensile specimen which is used for parameters determination. Tests and simulations of notched tensile specimens were carried out to discuss the transformability of the identified damage parameters. It is observed that the value of critical void volume fraction of the Gurson-Tveergard-Needleman model decreases with the increase of stress triaxiality. [ABSTRACT FROM AUTHOR]

This paper describes the results of calculations and experiments on the torsion of plates made of isotropic and transversely isotropic VT-20 and 1163T alloys with low resistance to creep strain in the direction perpendicular to the median surface. The numerical simulation results for plates of different thicknesses related to the class of rigid and flexible plates are compared using the pure bending theory and the finite element method. It is found that the curvature values are smaller in the case of deformation of a plate made of anisotropic material into a sign-variable saddle surface than in the case of a plate of isotropic material. The calculation in the assumption of pure bending provides an upper bound of the curvature difference in the deformation of plates made of transversely isotropic and isotropic materials. [ABSTRACT FROM AUTHOR]

In this paper a purely phenomenological formulation and finite element numerical implementation for quasi-incompressible transversely isotropic and orthotropic materials is presented. The stored energy is composed of distinct anisotropic equilibrated and non-equilibrated parts. The nonequilibrated strains are obtained from the multiplicative decomposition of the deformation gradient. The procedure can be considered as an extension of the Reese and Govindjee framework to anisotropic materials and reduces to such formulation for isotropic materials. The stress-point algorithmic implementation is based on an elastic-predictor viscous-corrector algorithm similar to that employed in plasticity. The consistent tangent moduli for the general anisotropic case are also derived. Numerical examples explain the procedure to obtain the material parameters, show the quadratic convergence of the algorithm and usefulness in multiaxial loading. One example also highlights the importance of prescribing a complete set of stress-strain curves in orthotropic materials. [ABSTRACT FROM AUTHOR]

All the five independent elastic properties/constants of micro- and nano-structured hierarchical and self-similar random irregular honeycombs with different degrees of cell regularity are obtained by analysis and computer simulation in this paper. Cell wall bending, stretching, and transverse shearing are the main deformation mechanisms of hierarchical honeycombs. The strain gradient effects at the micro-meter scale, and the surface elasticity and initial stress effects at the nano-meter scale are incorporated into all the deformation mechanisms in the analysis and finite element simulations. The results show that the elastic properties of hierarchical random irregular honeycombs strongly depend on the thickness of the first-order cell walls if it is at the micro-meter scale, and that if the thickness of the first-order cell walls is at the nano-meter scale, the elastic properties of hierarchical random irregular honeycombs are not only size-dependent, but are also tunable and controllable over large ranges. In addition, the geometrical properties of nano-structured hierarchical random irregular honeycombs are also tunable and controllable. [ABSTRACT FROM AUTHOR]

This paper developed 3D elastoplastic finite element analysis (FEA) models to investigate non-axisymmetric tubes neck spinning. The three-roller mandreless neck spinning process was simulated by commercial FEA software, MSC. Marc. The distribution of the transient von Mises stresses in the contact zone between the roller and the blank, and the equivalent plastic strains after spinning were obtained. The locations and causes of fractures were analyzed. The thickness distribution of the spun workpiece was investigated numerically and experimentally. It shows that during 3D non-axisymmetric tubes spinning, diametral elongation and fractures mostly occur at the opening end of workpiece, which considered as the primary location of defects. Fractures may also occur easily at the initial spinning area, which may be considered a secondary location of defects. The distributions of equivalent stresses and strains are non-uniform during both offset and oblique 3D non-axisymmetric tubes spinning. The maximum stress and strain values occur at the location where the biggest offset or inclination is induced, while the minimum values occur at the opposite location of 180° away from the maximum values. For the oblique tube, however, the strain distribution changes gradually along the axial direction, which is different from that of the offset tube. Thinning occurs during forward path spinning and thickening occurs during backward path spinning. Therefore, for multipath neck spinning processes, forward and backward paths should be applied alternately to avoid excessive thinning or thickening of workpiece. [ABSTRACT FROM AUTHOR]

The aim of this paper is to provide a general procedure to extract the constitutive parameters of a plasticity model starting from displacement measurements and using the Virtual Fields Method. This is a classical inverse problem which has been already investigated in the literature, however several new features are developed here. First of all the procedure applies to a general three-dimensional displacement field which leads to large plastic deformations, no assumptions are made such as plane stress or plane strain although only pressure-independent plasticity is considered. Moreover the equilibrium equation is written in terms of the deviatoric stress tensor that can be directly computed from the strain field without iterations. Thanks to this, the identification routine is much faster compared to other inverse methods such as finite element updating. The proposed method can be a valid tool to study complex phenomena which involve severe plastic deformation and where the state of stress is completely triaxial, e.g. strain localization or necking occurrence. The procedure has been validated using a three dimensional displacement field obtained from a simulated experiment. The main potentialities as well as a first sensitivity study on the influence of measurement errors are illustrated. [ABSTRACT FROM AUTHOR]

This paper addresses the development of a hybrid-mixed finite element formulation for the quasi-static geometrically exact analysis of three-dimensional framed structures with linear elastic behavior. The formulation is based on a modified principle of stationary total complementary energy, involving, as independent variables, the generalized vectors of stress-resultants and displacements and, in addition, a set of Lagrange multipliers defined on the element boundaries. The finite element discretization scheme adopted within the framework of the proposed formulation leads to numerical solutions that strongly satisfy the equilibrium differential equations in the elements, as well as the equilibrium boundary conditions. This formulation consists, therefore, in a true equilibrium formulation for large displacements and rotations in space. Furthermore, this formulation is objective, as it ensures invariance of the strain measures under superposed rigid body rotations, and is not affected by the so-called shear-locking phenomenon. Also, the proposed formulation produces numerical solutions which are independent of the path of deformation. To validate and assess the accuracy of the proposed formulation, some benchmark problems are analyzed and their solutions compared with those obtained using the standard two-node displacement/ rotation-based formulation. [ABSTRACT FROM AUTHOR]

On the basis of continuum mechanics, a rate dependent directional damage model for fibred materials with application to soft biological tissues is presented. The structural model is formulated using the concept of internal variables that provides a very general description of materials involving irreversible effects. Continuum damage mechanics is used to describe the softening behavior of soft tissues under large deformation. To account for the rate dependency and to regularize the localization problems associated with strain-softening, a viscous damage mechanism is presented in this paper in decoupled form for matrix and fibers. The numerical implementation in the context of the finite element method is discussed in detail. In order to show the performance of the constitutive model and its algorithmic counterpart some simple examples are included. Results show that the model is able to capture the typical stress-strain behavior observed in fibrous soft tissues and appear to confirm the soundness of the proposed formulation. [ABSTRACT FROM AUTHOR]

This paper is an attempt to construct a computationally effective curved triangular finite element for geometrically nonlinear analysis of elastic shear deformable shells fabricated from functionally graded materials. The focus is on the concise finite-element formulation under the demand of accuracy-simplicity trade-off. To this end, a nonconventional approach based on the invariants of the natural strains of fibers parallel to the element edges is used. The approach allows one to obtain algorithmic formulas for computing the stiffness matrix, gradient, and Hessian of the total strain energy of the finite element. Transverse shear deformation effects are taken into account using the first order shear deformation theory with the shear correction factor dependent on the material property distribution across the shell thickness. The performance of the proposed finite element is demonstrated using problems of functionally graded plates and shells under mechanical and thermal loads. [ABSTRACT FROM AUTHOR]

The tooling design in the roll forming process plays a major role in the quality and successful mass production of a variety of complex profiled products, in many industrial sectors. The roll forming line is comprised of consecutive forming passes. Each roll forming pass consists of a set of rotating rollers able to bend the material as it passes through them. The roll forming pass design plays a major role in the production of profiles. The introduction of advanced high strength steels (AHSS), such as the DP-series and TRIP-series, has also posed new challenges for the design of the roll passes. The current paper exploits explicitly the finite elements (FE) method and investigates the effect of the roll forming passes design on main redundant deformations, such as longitudinal stains at the edge of the profile, shear strains on strips plane, thickness reduction, and final produced cross section with springback. The profiles discussed are symmetrical V- and U-sections from the AHSS Dual Phase series (DP780). The gradual lowering of the flower pattern design, known as 'downhill pass flow', is discussed. The calculated decrease in the peak longitudinal strains of up to 28%, and the decrease in thickness of up to 38% are also presented and discussed. [ABSTRACT FROM AUTHOR]

This paper introduces the application of micro-deep drawing of single and multicrystals of aluminium in order to identify parameters of micro-mechanical models. The information obtained experimentally is abundant: load-displacement curves of the punch, the evolution of grain orientation, mapping deformations throughout the test. All this experimental data was used to validate the multiscale models introduced in a finite element code for loading paths ranging from biaxial tensile to simple tensile. [ABSTRACT FROM AUTHOR]

In this paper, an accurate and efficient C-type third-order global-local model incorporating effects of the transverse normal strain is proposed to study the thermal/mechanical behaviors of thick multilayer cross-ply plates. Transverse displacement is assumed to be a linear distribution through the thickness direction, for which the normal strain could be readily computed. Based on the interlaminar continuity conditions of in-plane displacement and transverse shear stresses, layer-dependent variables could be reduced. Employing shear stress free condition at the upper and the lower surfaces, derivatives of transverse displacement are eliminated from the displacement field, so that C interpolation functions are only required for the finite element implementation. As a result, the number of variables is independent of the number of layers of the laminate. To assess the proposed model, the classical quadratic eight-node isoparametric element is used for the interpolation of all the displacement parameters defined at each nodal point on the composite plate. Comparing with various existing composite plate models, it is found that simple C finite elements with non-zero normal strain could produce accurate deformations and stresses of thick multilayer composite plates subjected to thermal and mechanical loads. [ABSTRACT FROM AUTHOR]

In this paper we address the application of recovery procedures in advanced problems in structural mechanics. The attention is focused on the recovery by compatibility in patches procedure (RCP) and shear deformable plate structures. The formulation of RCP procedure is extended to shear deformable plate problems (Reissner-Mindlin theory) and is applied to recover stresses from mixed and hybrid stress finite elements. These elements offer new possibilities, for recovery procedures in general, which deserve to be discussed. A comprehensive investigation on which finite element solution can be used as input for the recovery procedures is given through standard benchmark problems, obtained for several values of the thickness on structured and unstructured meshes. The numerical results confirm the effectiveness of the recovery procedure extended to plates problems. [ABSTRACT FROM AUTHOR]

Abstract  This paper deals with the identification of elasto-plastic constitutive parameters from deformation fields measured over the surface of thin flat specimens with the grid method. The approach for recovering the constitutive parameters is the virtual fields method. A dedicated algorithm is used for deriving the distribution of the 2D stress components from the measured deformation fields. A state of plane stress is assumed. Guesses of the constitutive parameters are input in the algorithm and updated until the stresses satisfy the principle of virtual work in the least squares sense. The advantage of this approach is that it can handle very heterogeneous plastic flows and it is much faster than classical finite element model updating approaches. An experimental application is provided to demonstrate it. Six mild steel double-notched specimens have been tested in a configuration combining tension and in-plane bending. The identified parameters are in good agreement with their reference counterparts. Stress fields are eventually reconstructed across the specimen all along the test for analyzing the evolution of the plastic flow. [ABSTRACT FROM AUTHOR]

This paper examines the application of kinematic hardening to modelling the behaviour of thinly surfaced pavements dominated by the clay subgrade. An existing three-surface kinematic hardening model has been found to predict too much shear strain and therefore too much settlement under repeated loading for certain stress conditions. Under some stress conditions, the model also predicts an accumulation of negative shear strain with increasing number of cycles of load, leading to a pavement rut depth which decreases with increasing numbers of cycles. Consequently, a new model has been developed by modifying the flow rule and hardening modulus. The new model requires 10 parameters, most of which can be determined directly from simple triaxial tests. The new model is validated against drained cyclic triaxial results in order to determine model parameters, and it is shown that the new model predicts better the accumulation of shear strain and the problem of accumulation of negative shear strain is eliminated. This new model is applied to the repeated loading of a thinly surfaced pavement and is seen to predict realistic resilient and permanent deformations. [ABSTRACT FROM AUTHOR]

The development of the formulation for a highly adaptable hexahedral shell finite element is presented in this paper. A basic 18-node isoparametric hexahedral element is adopted as the basis of the formulation. Potential strategies to alleviate transverse shear, trapezoidal, thickness and membrane locking are investigated, in several combinations, using a wide variety of geometrically linear benchmarks. The most promising approach is further assessed using geometrically non-linear shell and plate problems. The recommended ANS-formulation performs well against an extensive range of benchmarks, and continues to be accurate at an aspect ratio of 1:10,000. [ABSTRACT FROM AUTHOR]

In this paper, we provide a constitutive model for overall (macroscopic) plastic deformation behavior in a rubber-toughened polymer blend. A porous plasticity theory is employed as a basis for the constitutive modeling. In our investigation, the polycarbonate (PC) is chosen as a matrix material of polymer blend. First, the true uniaxial stress-strain relation for PC, which is an important part of the constitutive model, is carefully measured. Secondly, finite element analyses of neck propagation in a tensile specimen of PC are performed to test the efficiency of the introduction of the accurately measured true stress-strain relation into the model. Then, in order to investigate local and average deformation behavior of the matrix material (PC) around cavitated rubber particles in polymer blend, an axisymmetric unit cell analysis is carried out. Finally, finite element analyses of the neck propagation in a tensile specimen of a rubber-toughened PC are performed, and the numerical results are compared to experimental results. It is revealed that the present constitutive model has the ability to well reproduce the behavior of a rubber-toughened polymer blend with rather small volume fraction of rubber particles, which is up to about 10%. However, for blends with larger volume fraction of the rubber particles, the discrepancy between the computational and the experimental results increases. Several possibilities of enhancing the model are discussed. [ABSTRACT FROM AUTHOR]

In this paper, relative velocity at a given point on the wafer was first derived. The revolutions of wafer and pad are assumed the same and the axisymmetric uniformly distributed pressure form is given. Thus, a 2D axisymmetric quasic-static model for chemical-mechanical polishing process (CMP) was established. Based on the principle of minimum total potential energy and axisymmetric elastic stress-strain relations, a 2D axisymmetric quasic-static finite element model for CMP was thus established. In this model, the four-layer structures including wafer carrier, carrier film, wafer and pad are involved. The von Mises stress distributions on the wafer surface were analysed, the effects of axial, hoop, radial and shear stresses to von Mises stress and the effects of axial, hoop, radial and shear strains to deformation of the wafer were investigated. The findings indicate that near the wafer centre, von Mises stress distribution on the wafer surface was almost uniform, then increased gradually with a small amount. However, near the wafer edge, it would decrease in a large range. Finally, it would increase dramatically and peak significantly at the edge. Besides, the axial stress and strain are the dominant factors to the von Mises stress distributions on the wafer surface and the wafer deformation, respectively. [ABSTRACT FROM AUTHOR]