Search

Numerous empirical and numerical studies have been carried out on the mechanical characterization of ductile materials. The application of digital image correlation (DIC) equipped with three-dimensional measurement analysis was used to examine the mechanical characteristics of aluminum alloy (AL 7075). Then, the DIC outcome with finite element simulation results will be compared with the experimental results to measure the performance of the DIC. A tensile specimen of AL 7075 is tested under constant loading with a 2 mm/min displacement rate until fracture. Strain gauge and extensometer are used along with DIC monitoring technique to capture the structural deformation of the specimens. The specimen and test are simulated in ABAQUS software, in which the results are compared with experiment and DIC data, indicating a good correlation between the results. Limited data in the form of average deformation and strain of the experiments are not applicable to the plastic and necking process. In this respect, the 3D DIC results are used to analyze the strain field throughout the test, including specimen necking, and predict fracture location. Moreover, the outcome of DIC and finite element simulation are employed to examine the characteristics of AL 7075 about the large plastic deformation and mechanical behavior. The proposed 3D DIC methodology in providing insight into the characteristic mechanical behavior of ductile materials is highlighted in this paper. [ABSTRACT FROM AUTHOR]

The paper determines the actual stress-strain state of a vertical steel tank RVS-20000's bottom considering the subsoil base inhomogeneity zones of various sizes. Using the ANSYS software a finite element model of the RVS-20000's bottom has been developed. A design scheme proposed in the article takes into account the impact of the out-contour space. Analysis of the test calculation results has shown that the area of maximum stress acting on the vertical steel tank bottom is located along the perimeter of the base subsidence area. There are dependences that characterize tank bottom sags at maximum operating stress occurring in the metalwork of the tank bottom and concentrated on the border of the subsidence area out-contour zone in the paper end. It is found that Russian regulatory documents require harmonization with international standards. [ABSTRACT FROM AUTHOR]

The paper presents the innovative process with possibility of predict the state of deformation and stresses in a two-stage metal forming process. In the first stage, regular surface roughness with arched outlines are embossed. In the second stage, these inequalities are flat burnished to obtain the required dimensions, roughness of the surface, and state of deformation and stresses in the surface layer of the workpiece. The process are considered as a geometrical and physical non-linear boundary and initial value problem, with unknown boundary conditions in the contact zone. The applications were developed in the Ansys/LS-Dyna system, which makes possible a complex time analysis of the states of displacements, strains and stresses, in the workpiece in the two-stage cold metal forming processes. Application of this method were showed for examples the modelling and the analysis of the regular asperities with arched outlines. In the simulations, the material as well as the geometrical parameters of surface asperities were changed. The simulation results were verified experimentally. [ABSTRACT FROM AUTHOR]

The paper deals with the development of the technique for J-integral computation using the vector fields obtained by digital image correlation method. The proposed computing algorithm includes several steps following each other: (i) construction of displacement vector field; (ii) calculation of deformations and stresses; (iii) calculation of the J-integral value. A comparative study of the results obtained by the proposed technique and by finite element simulation was carried out. The errors of the data modeled in the ANSYS from the computed J-integral values were estimated at various tensile loads. [ABSTRACT FROM AUTHOR]

Over the past 60 years, the finite element method has been very successful in modelling deformation in engineering structures. However the method requires the definition of constitutive models that represent the response of the material to applied loads. There are two issues. Firstly, the models are often difficult to define. Secondly, there is often no physical connection between the models and the mechanisms that accommodate deformation. In this paper, we present a potentially disruptive two-level strategy which couples the finite element method at the macroscale with cellular automata at the mesoscale. The cellular automata are used to simulate mechanisms, such as crack propagation. The stress-strain relationship emerges as a continuum mechanics scale interpretation of changes at the micro- and meso-scales. Iterative two-way updating between the cellular automata and finite elements drives the simulation forward as the material undergoes progressive damage at high strain rates. The strategy is particularly attractive on large-scale computing platforms as both methods scale well on tens of thousands of CPUs. [ABSTRACT FROM AUTHOR]

The paper deals with the problem of identification of microstructure evolution model on the basis of two-step compression test. This test is characterized by non-uniform fields of strains, stresses and temperatures in the deformation zone. Therefore, the inverse approach with finite element model for the experiment - direct problem, was applied to eliminate the influence of these inhomogeneities. Inverse solution for two-step compression test is time consuming. Thus, sensitivity analysis was performed and an influence of the parameters of the microstructure model on the goal function defined in the inverse solution was evaluated. Data generated for sensitivity analysis was reused in the inverse approach to reduce the computation costs of identification. [ABSTRACT FROM AUTHOR]

This paper presents a simplified finite element method called "Pseudo Inverse Approach" (PIA) for tool shape design and optimization in multi-step cold forging processes. The approach is based on the knowledge of the final part shape. Some intermediate configurations are introduced and corrected by using a free surface method to consider the deformation paths without contact treatment. A robust direct algorithm of plasticity is implemented by using the equivalent stress notion and tensile curve. Numerical tests have shown that the PIA is very fast compared to the incremental approach. The PIA is used in an optimization procedure to automatically design the shapes of the preform tools. Our objective is to find the optimal preforms which minimize the equivalent plastic strain and punch force. The preform shapes are defined by B-Spline curves. A simulated annealing algorithm is adopted for the optimization procedure. The forging results obtained by the PIA are compared to those obtained by the incremental approach to show the efficiency and accuracy of the PIA. [ABSTRACT FROM AUTHOR]

A novel flexible roll forming method is proposed for manufacturing of large curved metal plates. By adjusting the position of three rows of staggered arranged rollers, a large curved metal plate is formed in an incremental way. In this paper, FE (finite element) model is established to analyze the stress-strain distribution of the deformed plates in the forming process. Based on the numerical simulation, the influence of the relative position between upper rollers and lower rollers on the dimensional accuracy of the large curved metal plate is studied. Comparison results show that roller arrangement has great influence on the dimensional accuracy of deformed plates, and process with staggered arranged rollers has the best dimensional accuracy. [ABSTRACT FROM AUTHOR]

The aim of this paper is to introduce a method to reduce the weight in structures which are subjected to multiple restrictions like deformation, max allowable stress, natural frequency, etc.... The method is shown through the analysis of an aluminum bracket, whose maximum stress and deformation is well defined. The analysis is done using the Structural and Design of Experiments modules of Ansys Workbench v12.1. As result of the method a weight reduction of 50,2% is achieved. [ABSTRACT FROM AUTHOR]

The study of the mechanical components on the micro/nano-scale requires the investigation on stress, contact pressure and deformation of the contacting components particularly. On the micro/nano-scale, the discussion on the rolling contact between two mechanical components takes place not only on the general surface but also covers the asperity level on the rough surface scale. During rolling contact of the mechanical components, the model can be simplified to the contact between a roller on a rough surface. This model is occupied in finite element analysis to observe the steady state phase during rolling contact. The steady state phase is the second phase of the new components life-cycle where the plastic deformation, contact stress and contact pressure found their stabilized form and the optimal condition on the contact loading is reached. The steady state phase takes place after running-in phase where the aforementioned parameters still occur in the transient mode and still vary with time. In this paper, two-dimensional model of a cylinder rolls over a surface are employed in the simulation by considering the elastic-plastic material with strain hardening behavior. The contact stress and residual stress of the rough surface due to rolling contact are observed to determine the steady state phase. The results show that the steady state of the contact stress and residual stress has been obtained on the second repeated rolling contact. The stability of the contact and residual stress on the second cycle is not only influenced by the strain hardening behavior but it is also influenced by the flattening of the asperity which produces larger contact area such that the contact load is homogenously distributed on the truncated asperity. [ABSTRACT FROM AUTHOR]

The paper presents an approach that combines the simulation of technological processes on two levels. One of them is the finite element model that predicts material flow and temperature distribution in the workpiece during any multi-stage deformation where forming steps can be separated by heating/cooling of the billet. The second level is a semi-empirical microstructural model that simulates static and dynamic recrystallisation and grain growth during deformation or dwelling time. The background of the microstructural model is Sellars formulation. The model parameters are derived by parameterization of the experiments done with the material specimens for a wide range of strain, strain-rate, temperature variation and pause time. This model has been integrated in QForm3D software and tested for several practical cases of open and closed die forging. The case studies have shown good agreement between the simulation results and practice that have opened the way for its implementation in industry. [ABSTRACT FROM AUTHOR]

Machining is the most common manufacturing process. A good behaviour law is necessary in the simulation of machining processes (analytical and finite element modeling). Usually, commonly used behaviour laws such as Jonhson-Cook can bring unsatisfactory results especially for high strain and large deformation processes. Significant differences can appear between experimental and simulation results. The aim of this paper is to present the choices made regarding the behaviour law in this context. This study develops a large deformation strain-gradient theoretical framework with hypothesis linked to metal cutting processes. The theoretical framework has the potential of expressing moments at the tool tip as they were observed in experiments. It will be shown that the theory has the capability of interpreting the complex phenomena found in machining and more particularly in high speed machining. [ABSTRACT FROM AUTHOR]

The paper is focused on application of multi-scale 2D method. Model approach consists of Cellular Automata (CA) model of microstructure development and the finite element code to solve thermo-mechanical problem. Dynamic recrystallization phenomenon is taken into account in 2D CA model which takes advantage of explicit representation of microstructure, including individual grains and grain boundaries. Flow stress is the main material parameter in mechanical part of FE and is calculated on the basis of average dislocation density obtained from CA model. The results attained from the model were validated with the experimental data. In the present study, austenitic steel X3CrNi18-10 was investigated. The examination of microstructure for the initial and final microstructures was carried out, using light microscopy and transmission electron microscopy. [ABSTRACT FROM AUTHOR]

Modeling of collision processes of colliding bodies with different properties is of particular theoretical and practical interest e.g. for modeling of plastic deformation processes. Best results regarding the parameters of the collision processes (forces, stress, strain, duration of contact, etc.) are obtained using the finite elements method (FEM). This paper presents the results of FEM modeling of the collision process after a free fall of a sphere on an elastic-plastic plate of specific dimensions under the additional application of an external force. Two cases are described: the application of an external force during the time of contact of the colliding bodies, and without application of an external force. Correlations were obtained for the change of the strength of the impact, the stress and strain as function of time for the sphere and the plate. The strain of the plate were defined for various values of the external force. These results allow us to define the conditions, necessary to perform the so called 'Combined Impact' leading to significant change of the deformation processes conditions. [ABSTRACT FROM AUTHOR]

During forming, the deep drawing press and tools undergo large loads, and even though they are extremely sturdy structures, deformations occur. This causes changes in the geometry of the tool surface and the gap width between the tools. The deep drawing process can be very sensitive to these deformations. Tool and press deformations can be split into two categories. The deflection of the press bed-plate or slide and global deformation in the deep drawing tools are referred to as macro press deformation. Micro-deformation occurs directly at the surfaces of the forming tools and is one or two orders lower in magnitude. The goal is to include tool deformation in a FE forming simulation. This is not principally problematic, however, the FE meshes become very large, causing an extremely large increase in numerical effort. In this paper, various methods are discussed to include tool elasticity phenomena with acceptable cost. For macro deformation, modal methods or ‘deformable rigid bodies’ provide interesting possibilities. Static condensation is also a well known method to reduce the number of DOFs, however the increasing bandwidth of the stiffness matrix limits this method severely, and decreased calculation times are not expected. At the moment, modeling Micro-deformation remains unfeasible. Theoretically, it can be taken into account, but the results may not be reliable due to the limited size of the tool meshes and due to approximations in the contact algorithms. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

The main purpose of the “Numisheet’05 Benchmark[sharp/mesh/hash_synonym]3: Channel Draw/Cylindrical Cup” was to evaluate the forming characteristics of materials in multi-stage processes. The concept was to verify the strain fields achieved during the two stage forming process and also to test the ability of numerical models to predict both strain and stress fields. The first stage consisted of forming channel sections in an industrial-scale channel draw die. The material that flows through the drawbead and over the die radii into the channel sidewalls is prestrained by cyclic bending and unbending. The prestrained channel sidewalls are subsequently cut and subjected to near plane-strain Marciniak-style cup test. This study emphasizes the analysis of the first stage process, the Channel Draw, since accurate numerical results for the first stage forming and springback are essential to guarantee proper initial state variables for the subsequent stage simulation. Four different sheet materials were selected: mild steel AKDQ-HDG, high strength steel HSLA-HDG, dual phase steel DP600-HDG and an aluminium alloy AA6022-T43. The four sheet materials were formed in the same channel draw die, but with drawbead penetrations of 25%, 50% and 100%. This paper describes the testing and measurement procedures for the numerical simulation of these conditions with DD3IMP FE code. A comparison between experimental and numerical simulation results for the first stage is presented. The experimental results indicate that an increase in drawbead penetration is accompanied by a general decrease in springback, with both sidewall radius of curvature and the sidewall angle increasing with increasing drawbead penetration. An exception to this trend occurs at the shallowest bead penetration: the radius of curvature in the sidewall is larger than expected. The sequence of cyclic tension and compression is numerically studied for each drawbead penetration in order to investigate this phenomenon. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

In this paper, a new computational technique is presented based on the eXtended Arbitrary Lagrangian-Eulerian Finite Element Model (X-ALE-FEM) in large plasticity deformations. An arbitrary Lagrangian-Eulerian (ALE) technique is employed to capture the advantages of both Lagrangian and Eulerian methods and alleviate the drawbacks of the mesh distortion in Lagrangian formulation. In order to remove the limitation of the mesh conforming to the boundary conditions in the simulation, the extended finite element method (X-FEM) is implemented by incorporating discontinuous fields through a partition of unity method. The implementation of X-FEM technique in the framework of ALE model is finally presented in modeling of free-die pressing with flexible central core. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

The analysis of mechanical structures using the Finite Element Method, in the framework of large elastoplastic strains, needs frequent remeshing of the deformed domain during computation. Remeshing is necessary for two main reasons, the large geometric distortion of finite elements and the adaptation of the mesh size to the physical behavior of the solution. This paper presents an adaptive remeshing method to remesh a mechanical structure in two dimensions subjected to large elastoplastic deformations with damage. The proposed remeshing technique includes adaptive refinement and coarsening procedures, based on geometrical and physical criteria. The proposed method has been integrated in a computational environment using the ABAQUS solver. Numerical examples show the efficiency of the proposed approach. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

The critical issue during finite element analysis of tailor welded blank is the handling of the weld region — either the weld may be treated just as a weld line (without imposing mechanical properties) or as a weld zone (by imposing separate mechanical properties to the weld zone). The formability of TWB will be affected not only by the weld characteristics but also by the relative mechanical properties of the weld zone and the base metal. The above effects will be discussed in this paper by considering the tensile and Limiting Dome Height (LDH) testing of the TWB. Tensile testing will be modeled using standard tensile specimen. In LDH simulations, samples deforming near plane strain and balanced biaxial stretching will be modeled. Load-progression behavior will be monitored. Throughout this study , simulations will be performed by finite element analysis. By analyzing the simulation results, the specific conditions where the weld zone assumption should be followed will be identified. It is found from the analysis that modeling weld region as weld line is not accurate for all the weld conditions. Also the domain of weld conditions wherein weld line assumption breaks down depends on the deformation mode or part shape. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

A new non-finite element friction model for tube hydroforming corner fill analysis has been introduced. The proposed model, which is applicable to 90-degree die corners, is based upon geometric considerations and does not require an incremental solution scheme. Hoop strain distributions are evaluated using both FEA and the proposed theory. Overall correlation between the FEA and proposed solutions is quite respectable in light of the fact that the proposed friction model is based upon a non-finite element theory which does not account for the intermediate deformation. This paper helps lay the groundwork for improvements in numerical modeling of friction effects on the hoop strain distribution in tubular hydroforming corner fill analysis when closed form solutions are required. The long term-intent of this effort is to mold the proposed theory into a form that is accommodating to a more global contact model. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]