Search

A method is proposed and the results of calculations are discussed in the coupled problem of the theory of large deformations on the deformation of the material of a cylindrical layer between rigid cylindrical surfaces. The layer material is assumed to be elastoviscoplastic, and its contact with the rough boundaries when the outer one is rotated is accompanied by friction, which generates heat; irreversible deformation is also considered to be calorific. The total cycle of the process of quasi-static deformation is calculated from its beginning to complete unloading and cooling of the material layer. The time points of the beginning and end of the sliding of the material along its rigid boundary surface and the beginning and end of its near-wall viscoplastic flow are indicated. [ABSTRACT FROM AUTHOR]

A solution for a coupled thermomechanical boundary value problem of the theory of large deformations that simultaneously takes into account the intense deformation of an elastoviscoplastic material and its heating due to such deformation and near-wall friction is constructed. The conditions for the emergence and development of a viscoplastic flow in the material of a cylindrical layer enclosed between rigid surfaces, one of which has the ability to rotate under the action of a changing given load relative to the axis of the viscometer, are calculated. At all stages of the process from its start to stop, the stress-strain state and temperature distributions in the areas of flow and reversible deformation are calculated, including flow stop, unloading and cooling, with the calculation of residual stresses and deformations. The yield strength is assumed to be temperature dependent. [ABSTRACT FROM AUTHOR]

A mathematical model of large deformations is used to solve a coupled boundary-value problem about the deformation of an elastoviscoplastic material in a cylindrical viscometer with account for its heating due to wall friction. The deformation of a material enclosed between rigid surfaces due to the rotation of an inner cylindrical surface at a variable velocity is investigated. It is taken into account that a yield point depends on temperature. The motion of elastoplastic boundaries is described. Stresses, strains, and temperature in a thermoelastic deformation region and in a flow region both during the development of the flow and during its deceleration, including stopping, unloading, and cooling, are calculated. Residual stresses and deformations are determined. [ABSTRACT FROM AUTHOR]

The theory of large deformations is used to solve the problem of deformation of an elastoviscoplastic material placed in a gap between two coaxial cylindrical surfaces, with one of them rotating with an alternating rate and the other one at rest. It is shown that an increase in the stresses in a cylindrical layer due to a mechanical influence on it initially causes irreversible creep strains because of viscosity of the material and then the accumulation of plastic strains because of the arrival of stress states at the loading surface. The unloading is accompanied by a plastic strain and then a viscous one. The stress-strain parameters of the medium with a varying rotation rate of the cylinder are calculated. Stress relaxation after the complete stop of a cylinder is described. [ABSTRACT FROM AUTHOR]

The methodology to extract in-plane shear properties has been standardised for polymer-based composite materials. However, no standards have been designed to extract reliable test data that can be used to calibrate material models in numerical simulations for non-fibre reinforced polymers. The quality of the results from three widely used experimental techniques was examined in this study for mineral-filled polypropylene in terms of shear strain distribution, out-of-plane deformations and shear stress-strain curves with the aid of the digital image correlation method. The V-Notched Rail test (ASTM D7078 ) exhibited ultimate fracture of the specimen, but valid shear strain was only obtained for small deformations. For relatively large strains, more reliable shear test data were obtained from a modified version of ASTM B831 : a standard test designed for aluminium but modified and implemented for polymers. Although out-of-plane deformations were avoided using aluminium holders, large variability was found in the strain distribution along the shear path. In contrast, the modified Wyoming Iosipescu test (ASTM D5379 ) exhibited the most robust shear stress-strain results due to consistent shear strain uniformity and low variability during the entire duration of the test. [ABSTRACT FROM AUTHOR]

Summary: This paper presents a high fidelity homogenization method for periodically layered composite structures that accounts for plasticity in the matrix material and quasi‐brittle damage in the reinforcing layers, combined with strong geometrical nonlinearities. A set of deliberately chosen internal kinematic variables results in a rigorous representation of the kinematics of the 2 constituents, which in turn allows for complex constitutive laws per constituent to be used directly in the formulation. The model accounts for hyper‐elastoplastic behavior in the matrix phase and hyper‐elastic behavior in the reinforcement as well as for the bending stiffness of the reinforcement layers. Additionally to previously proposed models, the present method includes Lemaitre‐type damage for the reinforcement, making it applicable to a wider range of engineering applications. The capability of the proposed method in representing the combined effect of plasticity, damage, and buckling at microlevel within a homogenized setting is demonstrated by means of direct comparisons to a reference discrete model. [ABSTRACT FROM AUTHOR]

This work shows a sequence of numerical models for the simulation of the Presta joining process: a well-established industrial process for manufacturing assembled camshafts. The operation is divided into two sub-steps: the rolling of the shaft to widen the cam seat and the joining of the cam onto the shaft. When manufactured, the connection is tested randomly by loading it with a static torque. Subsequently, there are three numerical models using the finite element method. Additionally, a material model of finite strain viscoplasticity with nonlinear kinematic hardening is used throughout the whole simulation process, which allows a realistic representation of the material behavior even for large deformations. In addition, it enables a transfer of the deformation history and of the internal stresses between different submodels. This work also shows the required parameter identification and the associated material tests. After comparing the numerical results with experimental studies of the manufacturing process for steel-steel connections, the models are used to extend the joining process to the utilization of aluminum shafts. [ABSTRACT FROM AUTHOR]

Within the framework of the model of large deformations, the deformation of a material exhibiting elastic, viscous, and plastic properties and placed between two rigid cylinders is investigated when turning the internal cylinder. The accumulation of irreversible deformations prior to the onset of plastic flow and upon its termination is associated with creep. Reversible and irreversible deformations according to the model in question are determined by differential transport equations. To calculate the displacement fields, stresses, and reversible, irreversible, and complete deformations, a system of partial differential equations is obtained, for which a finite-difference scheme is constructed. [ABSTRACT FROM AUTHOR]

Within the framework of the theory of large elastoplastic deformations generalized to the case of viscous and thermophysical properties of materials, we give a solution of a sequence of coupled problems on the onset and development of a flow in a material layer filling the gap between two rigid coaxial cylindrical surfaces under increasing pressure drop and on the subsequent flow deceleration under decreasing pressure gradient. Here the thermophysical and deformation processes are coupled, and the yield stress depends on temperature. Heat production due to the layer material friction against the rough cylindrical boundary surfaces is taken for an additional heat source. [ABSTRACT FROM AUTHOR]

In the framework of the theory of large deformations, we obtain the solution of a boundary value problem on the flow of an elastoviscoplastic material in a gap between two rigid coaxial cylindrical surfaces under pressure drop changing with time. It is assumed that slip of the material is possible on both surfaces. We consider reversible deformation, the development of viscoplastic flow under the increasing and constant pressure drop, deceleration of the flow under the decreasing pressure drop, and the unloading of the medium. [ABSTRACT FROM AUTHOR]

A large deformation thermomechanical model is developed for shock loading of a material that can exhibit elastic and inelastic anisotropy. Use is made of evolution equations for a triad of microstructural vectors $$\mathbf{m}_{\mathrm{i}}\,(\hbox {i}=1,2,3)$$ which model elastic deformations and directions of anisotropy. Specific constitutive equations are presented for a material with orthotropic elastic response. The rate of inelasticity depends on an orthotropic yield function that can be used to model weak fault planes with failure in shear and which exhibits a smooth transition to isotropic response at high compression. Moreover, a robust, strongly objective numerical algorithm is proposed for both rate-independent and rate-dependent response. The predictions of the continuum model are examined by comparison with exact steady-state solutions. Also, the constitutive equations are used to obtain a simplified continuum model of jointed rock which is compared with high fidelity numerical solutions that model a persistent system of joints explicitly in the rock medium. [ABSTRACT FROM AUTHOR]

This work shows a sequence of numerical models for the simulation of the Presta joining process: a well-established industrial process for manufacturing assembled camshafts. The operation is divided into two sub-steps: the rolling of the shaft to widen the cam seat and the joining of the cam onto the shaft. When manufactured, the connection is tested randomly by loading it with a static torque. Subsequently, there are three numerical models using the finite element method. Additionally, a material model of finite strain viscoplasticity with nonlinear kinematic hardening is used throughout the whole simulation process, which allows a realistic representation of the material behavior even for large deformations. In addition, it enables a transfer of the deformation history and of the internal stresses between different submodels. This work also shows the required parameter identification and the associated material tests. After comparing the numerical results with experimental studies of the manufacturing process for steel-steel connections, the models are used to extend the joining process to the utilization of aluminum shafts.

While the deleterious effects of hydrogen on metals and alloys are well known, the precise role of hydrogen in the underlying microscopic mechanisms is still not well understood and as of yet, the modeling attempts on hydrogen embrittlement and hydrogen induced cracking have not led to a proper method for life-time prediction. This work aims at the development of a robust numerical strategy in order to solve the non-linear coupled problem presented in the work of Anand [1]. The numerical implementation is performed for finite element method and the analysis are done to address the issue of hydrogen transport and hydrogen-embrittlement-related failures in metals. Specifically, problems related to the mechanism of hydrogen enhanced localized plasticity (HELP) is studied and macroscale shear localization phenomenon resulting from hydrogen induced material softening is considered at the phenomenological level. [ABSTRACT FROM AUTHOR]

A method of investigating the stressed-strained state of elasto-plastic bodies subjected to large deformations is presented. [ABSTRACT FROM AUTHOR]

This paper presents a solution of a sequence of coupled problems of thermoelastoplasticity which study the occurrence and development of flow in a material layer under pure shear conditions, and its subsequent deceleration by slowly removing the load. The homogeneity of the stress state of the layer is excluded due to the coupling of thermal and deformation processes in the presence of a temperature dependence of the yield point. An additional source of heat is taken to be its production by friction of the material layer on a rough plane. The conditions for the occurrence of viscoplastic flow in the deformable material layer and the laws of motion of the boundaries between the elastic and plastic regions in this layer are determined, and the flow velocities and large irreversible and reversible deformations are calculated. It is shown that reversible deformations cause stresses in the flow region and the moving elastically deformed core. [ABSTRACT FROM AUTHOR]

At the beginning of the last century two different types of constitutive relations to describe the complex behavior of elasto-plastic material were presented. These were the deformation theory originally developed by Hencky and the Prandtl-Reuss theory. Whereas the former provides a direct solid-like relation of stress as function of strain, the latter has been based on an additive composition of elastic and plastic parts of the increments of strains. These in turn were taken as a solid- and fluid-like combination of the de Saint-Venant/Lévy theory with an incremental form of Hooke's law. Even nowadays this Prandtl-Reuss theory is still accepted - within the restriction of small elastic deformations, i.e. it is generally stated in most textbooks on plasticity that this theory due to a number of defects can not be applied to large deformations. In the present article it is shown that this restrictive statement may be no longer true. Introducing a specific objective time derivative it could be shown that these defects disappear. [ABSTRACT FROM AUTHOR]

We give a solution to the thermoplasticity problem on the slide of a heavy layer from an inclined plane under heating. The reason for the creep effect is the development of a viscoplastic flow due to the dependence of the yield strength of the layer material on temperature. In the framework of large deformation theory we indicate a law of propagation for the elastoplastic boundary, calculate stresses, deformations, and deformation velocities both in the thermoplastic deformation region and the flow region. [ABSTRACT FROM AUTHOR]

The article discusses the simulation of acceleration and deceleration of a liner in a magnetic compressor. Two-dimensional approximations are considered, corresponding to the sections of the initial spatial area of transversal and longitudinal planes. The models are presented where the liner is considered as an elastic body, elastic-plastic body, and viscous liquid. The calculated results are presented and a comparative analysis of liner motion in various models is given. [ABSTRACT FROM AUTHOR]

We propose a mathematical model of large elastoviscoplastic deformations where intensive deformation results in temperature increasing and heat transfer processes. As an example of applying the model relations, we present a solution of the boundary-value problem on rectilinear motion and heating of a medium located in the gap between coaxial rigid cylindrical surfaces. [ABSTRACT FROM AUTHOR]

Abstract: This paper deals with the development of a mechanism-based two-scale constitutive model for thick-walled metallic honeycombs in sandwich applications. The mechanical response of metallic honeycomb sandwich sheets subject to large in-plane normal loading and out-of-plane shear loading is investigated using a detailed finite element model of the honeycomb microstructure. Based on the simulation results, a simple micro-mechanical system is proposed and used to develop the macroscopic constitutive model. The finite-strain constitutive model accounts for microstructural evolution due to geometrical changes and strain hardening at the microscale. The macroscopic model has been validated for various loading conditions. Furthermore, the evolution of the macroscopic yield surface for pure out-of-plane shear is discussed in detail. [Copyright &y& Elsevier]

Abstract: This paper presents an implementation in C++ of an explicit parallel finite element code dedicated to the simulation of impacts. We first present a brief overview of the kinematics and the explicit integration scheme with details concerning some particular points. Then we present the OpenMP parallelization toolkit used in order to parallelize our FEM code, and we focus on how the parallelization of the DynELA FEM code has been conducted for a shared memory system using OpenMP. Some examples are then presented to demonstrate the efficiency and accuracy of the proposed implementations concerning the Speedup of the code. Finally, an impact simulation application is presented and results are compared with the ones obtained by the commercial Abaqus explicit FEM code. [Copyright &y& Elsevier]

Abstract: The mechanical behavior of ideal truss lattice materials is controlled by the so-called direct action mechanism at the microscale which involves the uniform stretching and compressing of individual truss members. Standard homogenization techniques have been employed to develop a general micromechanics-based finite-strain constitutive model for truss lattice materials. Furthermore, a specialized small-strain plasticity model has been derived. Both models have been implemented in a finite-element program and used to simulate the anisotropic plastic behavior of the octet-truss lattice material in various applications including cyclic uniaxial loading, pure shear, and three-point bending. The constitutive model predictions agree well with the results obtained from discrete finite element models. Regarding the plasticity of the octet-truss lattice material, it has been found that the elastic domain is constrained by twelve pairwise parallel hyperplanes in the six-dimensional stress space. Moreover, the mechanism-based small-strain formulation reveals that the direction of plastic flow is normal to the pressure-dependent macroscopic yield surfaces. [Copyright &y& Elsevier]

This paper deals with the development of a phenomenological, orthotropic, rate-independent constitutive model of metallic honeycombs guided by earlier experimental investigations. Previous physical and virtual experiments have shown that under large out-of-plane deformation, the cellular microstructure of a honeycomb is progressively folded while the macroscopic normal and shear stress–strain curves exhibit pronounced stress plateaus. Furthermore, it follows from the experimental results that in a monolithic hexagonal honeycomb, the direction of macroscopic plastic flow during crushing under combined out-of-plane loading is coaxial with the direction of the compressive principal stress. Based on these experimental observations, a constitutive model is formulated that describes the out-of-plane mechanical behavior of a metallic honeycomb in the crushing and densification regimes. The model is incorporated into a commercial finite element code and successfully utilized to simulate several biaxial experiments on a hexagonal aluminum honeycomb. A universal procedure to calibrate the model for other types of metallic honeycombs is provided. [Copyright &y& Elsevier]

During the last 50 years, the development of better numerical methods and more powerful computers has been a major enterprise for the scientific community. In the same time, the finite element method has become a widely used tool for researchers and engineers. Recent advances in computational software have made possible to solve more physical and complex problems such as coupled problems, nonlinearities, high strain and high-strain rate problems. In this field, an accurate analysis of large deformation inelastic problems occurring in metal-forming or impact simulations is extremely important as a consequence of high amount of plastic flow.In this presentation, the object-oriented implementation, using the C++ language, of an explicit finite element code called DynELA is presented. The object-oriented programming (OOP) leads to better-structured codes for the finite element method and facilitates the development, the maintainability and the expandability of such codes. The most significant advantage of OOP is in the modeling of complex physical systems such as deformation processing where the overall complex problem is partitioned in individual sub-problems based on physical, mathematical or geometric reasoning.We first focus on the advantages of OOP for the development of scientific programs. Specific aspects of OOP, such as the inheritance mechanism, the operators overload procedure or the use of template classes are detailed. Then we present the approach used for the development of our finite element code through the presentation of the kinematics, conservative and constitutive laws and their respective implementation in C++. Finally, the efficiency and accuracy of our finite element program are investigated using a number of benchmark tests relative to metal forming and impact simulations. [Copyright &y& Elsevier]

During the last fifty years, the development of better numerical methods and more powerful computers has been a major enterprise for the scientific community. Recent advances in computational softwares have lead to the possibility of solving more physical and complex problems (coupled problems, nonlinearities, high strain and high strain rate problems, etc.). The development of object-oriented programming leads to better structured codes for the finite element method and facilitates the development, the maintainability and the expandability of such codes.This paper presents an implementation in C++ of an explicit finite element program dedicated to the simulation of impacts. We first present a brief overview of the kinematics, the conservative and constitutive laws related to large deformation inelasticity. Then we present the design and the numerical implementation of some aspects developed with an emphasis on the object-oriented programming adopted. Finally, the efficiency and accuracy of the program are investigated through some benchmark tests. [Copyright &y& Elsevier]

• Nonlinear analysis of membrane shells by three distinct spring cell models. • Stiffness-, flexibility-, and complete substitutes of the finite element triangle. • Substantially large deformations in elasticity, plasticity, visco-plastic damage. • Comparison with the finite element solutions and discussion on performance. • Remarks on stress and strain representation, mesh dependency and nonlinearity. Following the accomplishment of fundamental research on- and the development of improved spring models, this work investigates the utility of spring lattice models in representing actual structures. The study explores the applicability of spring lattice models for the analysis of nonlinear shell structures. Of importance the limits of the approximation of defective bar-spring models, on the one hand, and the attempt of a rigorous representation of the continuum by introducing additional spring elements, on the other hand. Preliminary investigations indicate appropriateness for membrane shells, but reveal weakness in modelling shells with bending stiffness by axial bar elements despite three-dimensional cell arrangements. Therefore the focus here is on membrane structures. A direct insight to the employed triangular spring cells is offered by the approach based on the natural description of the continuum suiting the individual geometry. The investigations address specifically the performance of the spring models when applied to problems involving geometrical and material non-linearity. For this purpose the spring models have been tested against the continuum finite element distinctly in elasticity and in plasticity in the context of large deformations. In addition, the effect of damage is simulated by means of a regularized constitutive model of softening plasticity. [ABSTRACT FROM AUTHOR]