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The modern formulation of the Saint-Venant principle allows us to assert that the disturbance of the stress-strain state caused by statically equivalent loads attenuates quickly enough at some distance from the places of application of loads, which can be called the effect of static heterogeneity. This principle is widely used in the calculation and design of building structures, for example, rods operating under tension, compression and bending, since it allows, neglecting complex functions of stresses and deformations near the places of application of loads, to obtain more easily realizable results in practical terms. The article provides a historical overview of the Saint-Venant principle, its subsequent development, application, as well as its modern interpretation. Numerical experiments carried out within the framework of this paper made it possible to reveal the similarity in the behavior of the stress and strains functions under conditions of static inhomogeneity with other types of inhomogeneities, which we will divide into four groups: geometric, physical and mechanical, static and kinematic. Within the framework of this work, the application of the Saint-Venant principle to the kinematic inhomogeneities of the boundary conditions was generalized. Using numerical modeling techniques in the ANSYS Mechanical APDL software package, two options for the implementation of rigid anchoring, representing inhomogeneous kinematic boundary conditions, were considered. The reliability and correctness of the results of numerical experiments is justified by the mesh convergence carried out, as well as by comparison with solutions by strength of materials. As well as for static inhomogeneity, the stress distribution in the places of inhomogeneous kinematic boundary conditions can be represented as the sum of solutions by the methods of strength of materials and some self-balanced function, which rapidly decays with distance from the disturbance zone. The considered self-balanced function forms the stress-strain state near various kinds of inhomogeneities. [ABSTRACT FROM AUTHOR]

Application of confinement as repairing technique can improve the strength and ductility of concrete significantly. This paper compares the existing models of repaired concrete, and describes the differences between these models. Over recent years, a great number of studies have been done to develop the models to define the stress-strain behaviour of repaired structures. The considered variables are the cross-sectional area, types of confinement, types of materials used and type of the strength models. Subsequently, the limitations were discussed and significant conclusions on the strength and weakness of each existing models were highlighted. This paper presented the state of the art design strength models available for repaired concrete structures and indicated a direction for future development. [ABSTRACT FROM AUTHOR]

This paper presents a numerical study of a road barrier subjected to a bus crash test. The authors focus on the proper description of a barrier material model. Material model parameters are verified according to a simulated forming process. The solution uses modeling and simulation methods, as well as the finite elements method implemented with LS-DYNA software. The obtained results show that defining a proper road barrier model must consider the manufacturing process. Intensive plastic deformation leads to a significant increase in yield stress only in areas where the highest strain is observed during the forming process. The barrier model is divided into three zones, each of which have material properties characterized by different constants. The described construction, which uses homogenous material, is much more deformed and flatter than that of the improved model. Comparison with the experimental results shows that the new model better describes barrier deformation. In addition, deformation of the barrier under impact is evaluated according to European regulations (EN 1317). In comparison to the performed bus crash test, the crash test parameters obtained in the numerical simulation (static working width and normalized working width) gave more accurate results when the improved material model was utilized. [ABSTRACT FROM AUTHOR]

In this paper, we propose an algorithm for predicting the residual life of structures made of polymer composite materials (PCM) using a structured phenomenological model. In the developed algorithm for estimating the residual life of PCM structures under cyclic loading, it is proposed to use the explicit description of the process of destruction of adhesive layers. The implementation of the algorithm is accomplished in the APDL language in ANSYS Mechanical. The algorithm and the program are tested on a flange type design. Based on the results of numerical experiments, the area of damage is identified. The service life is determined, as well as the allowable value of the PCM flange stiffness drop under cyclic loading. [ABSTRACT FROM AUTHOR]

The paper presents a shear strength model used to evaluate information of interest from shock experiments aimed at studying the properties of the hardened 30KhGSA steel and the MA14 magnesium alloy subjected to low- and high-intensity loadings. The model parameters are adjusted by experimental deformation curves obtained from static and dynamic tests at different temperatures and the data from shock experiments to account for strength variation at high strain rates. The simulation of low-intensity loading tests helped to improve the description of elastic-plastic properties and to adjust our failure model. The data from the shock experiments with high-intensity loading of 30KhGSA steel samples and unloading of the shocked samples in window materials were used to verify the phase diagram and the kinetics of direct and inverse phase transitions, and to determine more exactly how the changed phase state influences the strength. The model presented here has allowed us to reproduce the complicated strength behavior of the MA14 alloy at different loading intensities. [ABSTRACT FROM AUTHOR]

Analysis of The cracking process of structural elements on The basis of fracture toughness characteristics determined according to standards - the stress intensity factor, J integral, crack tip opening displacement, assumes the occurrence of one crack front. In the case of a concentrated layered arrangement of non-metallic inclusions, delamination larnellar) is often caused. Depending on the configuration of the two cracks, i.e. the main and delamination, The real fracture and impact toughness may vary significantly, resulting in a reduction as well as an increase in characteristics. The use of the values of fracture toughness in The strength analysis of the element with delamination cracking obtained in the standard test will be misleading. This paper presents The results of experimental and numerical research performed in order to assess The impact of delamination crack on The parameters of the triaxial state of stress in front of the main crack. [ABSTRACT FROM AUTHOR]

This paper presents a proposition of a computational algorithm to be applied for the assessment of fatigue strength of notched elements using the concept of the fictitious radius. It has been demonstrated that the fictitious radius is significantly dependent on the forecasted fatigue life and specimen's geometry. The results of computations are compared with experimental results for notched specimens made from C45 steel. [ABSTRACT FROM AUTHOR]

The paper presents easy-to-use and accurate numerical procedures determining the level of damage to structures subjected to fatigue load. The main goal of the research was the implementation in the finite element analysis program of fatigue analysis procedures for selected multiaxial fatigue criteria, taking into account the exact fatigue characteristics of materials and the certain pattern of cumulative summation the fatigue damages. Selections of three types of criteria were selected for the study: invariant criterion, criterion using the mean values in the elementary volume and the criterion defined in the critical plane. Moreover, tests were carried out for Michell's problem of the topology optimization, which showed the impact of the criteria on the shape of optimal structures. [ABSTRACT FROM AUTHOR]

The chloride-induced corrosion of reinforcement used to be represented by Tuutti's model with initiation and propagation phases. During the initiation phase chlorides penetrate the concrete cover and accumulate around reinforcement bars. The chloride concentration in concrete increases until it reaches a chloride threshold value, causing deterioration of the passive layer of reinforcement. Then the propagation phase begins. During the propagation phase steel has no natural anti-corrosion protection, a corrosion current flows and this induces the production of rust. A growing volume of corrosion products generates stresses in concrete, which leads to cracking, splitting, delamination and loss of strength. The mechanical response of RC elements to reinforcement corrosion has mostly been examined on the basis of a 2D cross-section analysis. However, with this approach it is not possible to represent both corrosion and static loading. In the paper a 3D finite element model of an RC beam with the two actions applied is presented. Rust is represented as an interface between steel and concrete, considering the volumetric expansion of rust. [ABSTRACT FROM AUTHOR]

This paper deals with design values of safety factors for load-bearing reflector skeleton made of polymer composites. These safety factors characterize the strength, stability and geometry constancy of the reflector in a wide range of mechanical and thermal impacts. [ABSTRACT FROM AUTHOR]

Residual stresses induced in the component by previous thermal/mechanical processes are compressive or tensile stresses having a zero resultant. In particular, they arise as consequence of thermo-mechanical processes (e.g. ring-rolling process), casting and heat treatments. When machining stressed components, volume removal leads to a rearrangement of residual stresses, which inevitably causes distortions in the workpiece. If distortions are excessive, they can lead to a large number of scrap parts. This paper describes the development of a numerical procedure for the analysis of the distortions on a waspaloy turbine case, obtained by ring rolling process. A 3D model of ring rolling process has been set in the commercial software DEFORM 3D. Three different ring rolling strategies have been analyzed, in order to find the combination of process parameters which allows to obtain the best component in terms of geometrical precision. Then, the heat treatments (air cooling, solubilization, stabilization and aging) have been simulated to predict the bulk residual stresses distributions. Finally, the numerical distortions induced by machining have been simulated considering the material removal in some machining operations. [ABSTRACT FROM AUTHOR]

To achieve high accuracy in finite element simulation, it is beneficial to model forming limit curves (FLCs) for nonlinear strain paths, since FLCs based on linear strain paths inaccurately predict the failure of parts that undergo nonlinear strain paths. Standardized Nakajima or Marciniak tests are used to create a FLC for linear strain paths. For common strain paths, the shapes of the specimens are well-known. Only a limited set of nonlinear strain paths can be generated by using these tests. For example, a biaxial strain path can be generated, and then the test specimen can be cut to generate a uniaxial strain path. However, the other way around is not possible. Therefore, it is important to develop a new tool that can systematically investigate all kinds of nonlinear strain paths. This paper describes a newly developed deep drawing tool that exhibits these properties. Large specimens with homogeneous strain in the centre can be generated for any strain state. These specimens are sufficiently large that a second test specimen can be cut out to generate another strain path using Nakajima or Marciniak tests. The shape of blank for uniaxial, plane and biaxial strains are presented and analysed both numerically and experimentally. A nonlinear strain path consisting of a uniaxial strain path followed by a biaxial strain path is shown as an example. [ABSTRACT FROM AUTHOR]

As is known, the constraints (strength conditions) for the safety factor of elastic structures and design details of a particular class, e.g. aviation structures are established, i.e. the safety factor values of such structures should be within the given range. It should be noted that the constraints are set for the safety factors corresponding to analytical (exact) solutions of elasticity problems represented for the structures. Developing the analytical solutions for most structures, especially irregular shape ones, is associated with great difficulties. Approximate approaches to solve the elasticity problems, e.g. the technical theories of deformation of homogeneous and composite plates, beams and shells, are widely used for a great number of structures. Technical theories based on the hypotheses give rise to approximate (technical) solutions with an irreducible error, with the exact value being difficult to be determined. In static calculations of the structural strength with a specified small range for the safety factors application of technical (by the Theory of Strength of Materials) solutions is difficult. However, there are some numerical methods for developing the approximate solutions of elasticity problems with arbitrarily small errors. In present paper, the adjusted reference (specified) strength conditions for the structural safety factor corresponding to approximate solution of the elasticity problem have been proposed. The stress error estimation is taken into account using the proposed strength conditions. It has been shown that, to fulfill the specified strength conditions for the safety factor of the given structure corresponding to an exact solution, the adjusted strength conditions for the structural safety factor corresponding to an approximate solution are required. The stress error estimation which is the basis for developing the adjusted strength conditions has been determined for the specified strength conditions. The adjusted strength conditions presented by allowable stresses are suggested. Adjusted strength conditions make it possible to determine the set of approximate solutions, whereby meeting the specified strength conditions. Some examples of the specified strength conditions to be satisfied using the technical (by the Theory of Strength of Materials) solutions and strength conditions have been given, as well as the examples of stress conditions to be satisfied using approximate solutions with a small error. [ABSTRACT FROM AUTHOR]

The paper is devoted to the comparative analysis of features of some popular mechanical models of interphase boundaries in metal-ceramic composite materials. We have numerically studied the influence of the parameters of interface models on effective strength, strain-hardening coefficient and ultimate strain of a microscopic composite fragment including adjacent areas of the matrix, inclusions and the interface zone. We have shown that the most "powerful" and flexible mechanical model of an interphase boundary is the model of an "interface shell" with a gradient of mechanical properties. [ABSTRACT FROM AUTHOR]

This paper deals with the possibility of making alloys with the use of an oxidation-reduction reaction proceeding in thermite mixtures. The variation of the fraction composition of oxidizing and reducing agents provides a possibility to obtain alloys with different compositions and properties. It has been found that the ratio between oxidizer and reducer contents has an effect on reaction parameters, the properties of generating phases and residual aluminum content in the alloy. A fairly high content of aluminum dopes the alloy, eliminates the γ-area and makes it possible to obtain the ferritic structure of the alloy. This results in the increase of internal stresses and the occurrence of intergranular cracks, which significantly decrease the physical-mechanical properties. If aluminum content in the alloy is rather small, ultimate strength may reach 800 MPa. In these circumstances, the samples fail at about 5.2 % strain. The structures of such samples are ferrite-pearlite. All the investigated samples are characterized by brittle wavy fracture, and the stressstrain diagrams do not have a distinct yield plateau. [ABSTRACT FROM AUTHOR]

The paper presents the experimental results obtained to test the effect of nano-fillers on the aging performance of silicone rubber for outdoor applications and enamelled wire for motor insulation. The erosion resistance of silicone rubber (SIR) filled with 12 nm size fumed silica is compared to those filled with 5 μm size silica filler using the ASTM 2303 Inclined Plane Tracking and Erosion Test. The erosion resistance of the SIR materials increased with increasing percentage of the fillers, and it was observed that 10% by weight of nano-filled SIR gives a performance that is similar to that obtained with 50% by weight of micro-filled SIR. The paper discusses the possible reasons for the improvement in the erosion resistance of nano-filled silicone composites using different material analysis techniques like Thermo Gravimetric Analysis (TGA), and Scanning Electron Microscopy (SEM). Also, the effect of using different nano fillers like alumina, fumed silica and titanium oxide on the erosion resistance of enamel wire insulating material subjected to different electrical stresses will be addresses. Surface roughness is used to evaluate the effect of different nano-fillers on the erosion resistance of enamel wire insulation. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

This paper presents a brief review of Gurson’s damage model, employed to describes the strength degradation in ductile metals submitted to large plastic deformations. The damage model is applied using finite elements and an Arbitrary Lagrangian-Eulerian formulation (ALE), to ensure a better quality to the finite elements mesh. The study of the combined application of ALE and Gurson approach to damage modeling and strain localization is the object of this paper. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

Incremental sheet metal forming, which uses a CNC forming stylus, is new flexible forming process not requiring the use of any expensive dies. We have applied the incremental forming process to dental prosthesis. This new process, however, posed difficult problems. After removing the outer portion of the incremental formed sheet metal part, the inner part is distorted. In this paper, the residual stress in the sheet metal part obtained by incremental forward stretch forming operations has been examined. Numerical simulations were conducted for solid elements. When small rigid ball slides on the metal sheet with a certain vertical feed, tension residual stress is produced in the upper layer of the sheet and compression stress in the lower. Then, the resultant moments throughout the sheet cause negative spring-back when the outer portion is removed. A systematic study of the behavior was conducted in this paper. Parameters considered included the tool radius and the vertical tool feed rate. The tip radius of forming stylus has a significant influence on the residual stress. The smaller radius of forming stylus, the larger bending force becomes. And new process with double forming styluses is examined to reduce the bending force. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

Forming simulation technologies continues to develop at a rapid pace, to address formability, tolerance control, and product performance issues in an increasing range of processes, and in ever more detail. Springback prediction and compensation continue to evolve, with new concepts for improving the accuracy of the springback prediction for example by the incorporation of geometric drawbeads, and further refinement in compensation techniques. The paper highlights how the integration of simulation and geometry plays an ever more important role, in improving accuracy and reducing time. Other techniques which can help speed-up and improve simulation results for hydroforming, and tube bending are ‘classical’ and more recently ‘in-process’ optimization techniques. The paper will show the advantages on an industrial case, and the potential for the future. The paper will discuss how the PAM-STAMP 2G™ and PAM-TUBE 2G™ integrated solutions are successfully implemented to deliver a positive business impact, by providing virtual product quality assessment, tolerance control, and springback compensation. The paper will also discuss how new forming processes such as hot forming, superplastic forming, and tube hydroforming, can be accurately modeled using the new modules. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

Ceramic materials are commonly used as ballistic protection materials. The response of a ceramic to impact, perforation and penetration is complex and only limited physical instrumentation can be used in experiments. This paper demonstrates how a hydrocode, such as AUTODYN, can be used to aid in the understanding of the response of brittle materials to high pressure impact loading. While the penetration process is dominated by the material compressive thermodynamic and deviatoric response, the final damaged state of the material can be significantly influenced by the tensile behaviour. Modelling of the final damage state is important since this is often the only physical experimental information available. In this paper we present a unique implementation, in a hydrocode, of a tensile crack softening model for improved modelling of brittle materials in the tensile regime. Tensile failure initiation is based on principal stress while the post-failure tensile strength of the material is controlled through a damaging Rankine plasticity failure surface. The performance of the model is demonstrated with the relatively new meshless SPH technique; simulations of steel ball impacts onto alumina ceramic are presented and compared with experiments. [ABSTRACT FROM AUTHOR]

The aim of this paper is to evaluate the effects of various strain rates on the tensile properties of Al-6Si-0.5Mg cast alloys with Cu or/and Ni additions and to establish data on the stress-strain behavior of the alloys with applications in automotive engineering. Experimental alloys of the following composition were prepared by melt processing technique. Both microstructure and the mechanical properties were investigated. The uniaxial tension test was carried out at strain rates ranging from 10-4s-1 to 10-2s-1. Tensile strengths were found to increase with ageing temperature and the maximum being attained at peak age condition (1hr at 225°C). The additions of Cu or/and Ni resulted in an increase in tensile strength and 2wt% Cu content alloy (Al-6Si-0.5Mg-2Cu) showed maximum strength. Evaluation of tensile properties at three strain rates (10-4, 10-3 and 10-2s-1) showed that strain rates affected the tensile properties significantly. At higher strain rates the strength was better but ductility was poor. [ABSTRACT FROM AUTHOR]

The alignment of polymer chains is a well known microstructural evolution effect due to straining of polymers. This has a drastic influence on the macroscopic properties of the initially isotropic material, such as a pronounced strength in the loading direction of stretched films. For modeling the effect of strain induced anisotropy a macroscopic constitutive model is adopted in this paper. As a key idea, weighting functions are introduced to represent a strain-softening/hardening-effect to account for induced anisotropy. These weighting functions represent the ratio between the total strain rate (representing the actual loading direction) and a structural tensor (representing the stretched polymer chains). In this way, material parameters are used as a sum of weighted direction related quantities. In the finite element examples we simulate the cold-forming of amorphous thermoplastic films below the glass transition temperature subjected to different re-loading directions. [ABSTRACT FROM AUTHOR]

MP35N is a Nickel-Cobalt based superalloy that currently has numerous applications at both room and elevated temperatures due to its ultra high strength, high modulus and outstanding corrosion resistance. The National High Magnetic Field Laboratory (NHMFL) further explored the use of MP35N in cryogenic temperature applications. Currently, the material is used as a structural reinforcement component for high field pulsed magnets operating at 77 K. The NHMFL is also pursuing the application of MP35N below 77 K, such as either reinforcement or substrates for high-temperature superconducting (HTS) magnets operating at 4.2 K. This paper reports the tensile properties of cold-rolled and aged MP35N at room temperature, liquid nitrogen and liquid helium temperatures. Optimized fabrication methods developed by the NHMFL and H.C. Starck have improved the material's cryogenic properties with ultimate tensile strengths exceeding 2500 MPa and a modulus of elasticity higher than 200 GPa. Closer examination of the stress-strain curve reveals that the material exhibits internal stress which is attributed to the development of nanoplatelets during the fabrication process. [ABSTRACT FROM AUTHOR]

Typical aero engine alloys, such as IN718, can be surface-treated by shot peening to induce near-surface compressive strains. To calculate the remaining operation time for those critical aero engine components, a quantitative nondestructive determination of near-surface strain gradients has to be developed. We have demonstrated in the past, that it is possible to obtain a characteristic depth profile (surface and sub-surface) of the electrical conductivity of shot peened specimen by using high-frequency eddy current techniques. The measured conductivity profile is resulting from residual stresses, cold work, surface roughness, and the microstructure of the material. The objective is to measure residual stresses (separately from other material properties) in such components after a defined life time. It can be assumed, that surface roughness and microstructure remain unchanged in IN718 materials over their lifetime, but cold work and residual stresses can change independently. Consequently, there is a need to clearly separate the information from both material properties of received eddy current conductivity signals in order to obtain specific information related to residual stresses. This paper presents results acquired from different experiments, conducted to separate both effects by using the eddy current technique on shot peened IN718 materials. We present different physical approaches and illustrate the experiments to solve them. In addition, we will demonstrate that there is a need to use additional techniques, for example ultrasonic time-of-flight measurements, to separate the effects of residual stresses from compound (mixed) signals obtained on cold work samples. [ABSTRACT FROM AUTHOR]

In this paper, we carried out the true triaxial test simulation under plane strain condition with three dimensional DEM analyses (3D DEM) to study behavior and development of shear band. The maximum mobilized internal friction angle corresponds to the shape factor, FU, on a linear relationship, and the inclination of the linear relationship seems to become larger with the microscopic angularity of the grain. The thickness of the shear band increased with the grain size. Also the grain shape affects on the relationship of residual stress ratio to relative shear displacement along the shear band. [ABSTRACT FROM AUTHOR]

Experiments published by other workers, on the resistance change of manganin stress gauges embedded in a lateral orientation in tantalum targets shocked to a range of stresses, have been analysed using an adaptive mesh refinement hydrocode. It was found that for all of the four experiments the shape of the time profile of the computed lateral stress in the mounting layer closely matched the shape of the experimental lateral stress profiles. However, the calculated lateral stresses at the gauge location in the mounting layer are significantly less than the lateral stresses that would have been produced in the target if no gauge had been present. The perturbation caused by the gauge increased as the strength of the applied shock increased. When the perturbations are taken into account values of flow stress that are significantly smaller than those reported in the original research paper are derived. The work shows that the lateral gauge technique can give valuable information on strength provided high resolution simulation is used to compensate for the perturbations caused by the gauges. [ABSTRACT FROM AUTHOR]

A correct prediction of a possible sheet metal failure is essential to sheet metal forming simulations. The use of the conventional forming limit curve (FLC) is the standard approach on industrial level for this problem. The FLC concept is limited to the case of linear strain paths, however. The initial FLC is no longer valid in the case of nonlinear strain paths. The algorithm Crach allows for a transient prediction of the forming limit for localized necking in the case of arbitrary strain paths. For high strength steels and aluminium sheets there is also a risk of fracture without prior localized necking. This paper presents a fracture model that accounts for ductile fracture (caused by void nucleation, void growth and void coalescence) and shear fracture (caused by shear band localization). For both types of fracture, stress state parameters are introduced which can be applied for the plane stress state and for the general 3D stress state. The fracture limits are defined by the equivalent plastic strain at fracture as a function of the stress state parameter based on different experiments with nearly constant stress state parameter. These fracture limit curves are a basis for an integral damage accumulation in the sheet metal forming simulation for arbitrary nonlinear strain paths. The model Crach for the prediction of localized necking and the two fracture models for ductile and shear fracture are combined in the comprehensive failure model CrachFEM. CrachFEM can be linked via a user material model MF GenYld to different explicit FEM codes. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

This paper presents the effect of tool modelling accuracy on the simulation accuracy of springback in high strength steels. Simulations of a two-dimensional draw-bending process are carried out by using a polyhedral tool model whose surface is approximated by a polyhedron, and a model whose surface is smoothed by quadratic parametric surfaces proposed by Nagata [Nagata, Comput. Aided Geom. D, 22(2005), 55–59] (Nagata patch model). It is found that not only the shape accuracy but also the normal vector accuracy of tool models are of importance for accurate springback predictions. The use of the Nagata patch model is an efficient approach not only to improve the simulation accuracy but also to make the simulation be hardly influenced by the tool mesh, even for simulations of a high strength steel in which large amount of springback is involved. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

High performance composite materials have many well-known structural advantages. On the other hand, questions about durability and aging are still a subject of discussion and much needed research. As a consequence, in the last few years there have been available a growing amount of information on composites aging considering effects as temperature, oxidation, UV radiation, permanent loading etc. Much of this research is performed at the materials level, by materials scientists and it is not directly applicable to the design stage. In this paper, we use an analytical-numerical framework for the compilation, interpretation and application of experimental data to actual engineering analysis and design. The formulation includes elastic anisotropic relations; aging viscoelastic anisotropic constitutive equations in terms of state variables; age-adjusted failure and degradation criteria; all in a setting of large displacements with small strains. These equations are set in a form adequate for numerical analysis in a Finite Elements context, taking account of thermal and hygrometric effects and using an incremental-iterative solution procedure accounting for strain-softening post-critical effects. Case studies on ageing buckling analysis of thin-walled beam are presented. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

This paper presents a fatigue damage model, based on the continuum damage mechanics and general thermodynamic theory, proposed by Lemaitre and Chaboche, for rolling bearings under very numerous loading cycles. A flow surface of fatigue using the Sines criterion is adopted. The coupling between the hardening plasticity and damage effects is considered in the constitutive equations. An explicit algorithm of weak coupling leads to a calculation very fast. This fatigue damage model is implemented into Abaqus/Explicit using a Vumat user’s subroutine. Moreover, the damage variable in function of time is transformed into a function of number of cycles. An algorithm of cycle jump, with a criterion for choosing the number increment of cycles, is proposed, which allows to largely reduce the CPU time. The present damage simulation allows to determine the lifetime of mechanical parts under cyclic loading. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

Parts created by Tube Hydro-Forming (THF) are increasingly used in automobile bodies because of their high stiffness. THF parts have complex shape with varying cross-sections along its length, therefore, a multi-stage forming process such as bending, pre-forming and hydro-forming is generally necessary to produce them. To understand and to determine the forming conditions before production, simulation technology becomes indispensable. In this paper, firstly, the sheet metal simulation system JSTAMP/NV will be briefly introduced, and then its new function for THF simulation will be described in detail. JSTAMP/NV was released in 1996 on UNIX platforms and was re-developed on Windows in 2004. It is composed of a pre-post processor for stamping simulation, and uses solvers LS-DYNA, JOH/NIKE3D for analysis. The THF function was developed in 2006. It includes a specialized pre-post system for THF simulation and the faster computation program HYTUBE for tube bending, accurate FEM program LS-DYNA for both pre-forming and hydro-forming simulation. By using the THF function in JSTAMP/NV, the simulation can be performed much more efficiently and the design time for THF parts should become shorter. Lastly, application examples will be shown to demonstrate the accuracy and effectiveness of the system JSTAMP/NV. Furthermore, ductile damage parameters are applied to evaluate the formability of tube hydro-forming. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

There is currently much focus on the application of magnesium alloys to automotive structural components. This has arisen due to the positive environmental aspects associated with use of magnesium alloys such as weight reduction and recycling potential. In recent years many researchers have focused on the application of various forming processes to magnesium alloys. Magnesium alloys would seem highly suitable for sheet forming due to high N and r values, however, in application their formability has been inferior to, for example, aluminium alloys. It has thus been concluded that, when dealing with magnesium alloys, it is difficult to predict formability based on material properties. In order to improve formability and forming accuracy when using Mg alloys it is necessary to build a database and inference system which could decide the optimal forming parameters for complex automotive components. Currently not enough data is available to build such a database due to the limited number of studies available in literature. In this study an experimental analysis of hemispherical bulge forming at elevated temperature was undertaken in order to evaluate formability and hence build a database for forming process design. A finite element model based on the experiment has been built and validated against the experimental results. A ductile failure criterion has been integrated with the FE model and is used to predict the onset of failure. This paper discusses the development and validation of the finite element model with the ductile failure criterion and presents results from the experimental tests and FE simulations. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

In forging process, formability is limited by ductile fracture. In many cases forgeability is determined by the occurrence of ductile fracture and therefore limitations are set by the appearance of surface or internal cracks within regions that are highly strained due to extensive material flow. In this paper, the continuum damage mechanics framework for ductile materials developed by Lemaitre has been utilized numerically. A constitutive elastic-plastic-damage model has been implemented inside the finite element code ABAQUS. In forming process, crack closure effects have a strong influence on damage evolution. Therefore, it is necessary to split the tensile and compression stresses in damage evolution and deal with them separately. A modified version of Lemaitre model has been implemented and utilized through the study. The prediction of the surface cracks in forging is analyzed numerically. The results could correctly predict the location of surface cracks in the forging process. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

Finite element modeling of a prototype friction stir welded blank made of aluminum alloy 2024-T351 is considered in this paper. Feasibility of implementation of the experimentally-obtained mechanical properties of the weld nugget and heat-affected zones in FEM models is investigated. Limiting dome height test is considered as case of the study. Three different finite element models implementing different levels of the weld details are built and compared. It is shown that despite increased simulation time, implementation of the weld nugget and heat-affected zones is justified by significantly improved accuracy of the simulation results. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

A Tailor welded blank (TWB) technology gives automotive designers the ability to selectively vary body panel thickness and alloy to optimize the use of material. TWBs offer several notable benefits including decreased part weight, reduced manufacturing costs, increased environmental friendliness, and improved dimensional consistency. In order to take advantage of these benefits, however, designers need to overcome the formability of TWBs and be able to accurately predict unique characteristics related to TWB forming early in the design process. In this paper, a numerical model to predict the forming height dome and a specific forming curve of TWBs is presented. Finite element analyses of standard TWB forming tests (Nakazima) were performed in Arcelor Mittal Auto Application Research Center to determine the interaction between the weaker and the stronger materials. To measure the critical strain at necking a numerical method is used. A comparison of numerical and experimental results highlights a good agreement. The numerical approach offers a considerable gain to obtain specific FLC for all configurations. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

Within the scope of this article a decoupling algorithm to reduce computing time in Finite Element Analyses of incremental forming processes will be investigated. Based on the given position of the small forming zone, the presented algorithm aims at separating a Finite Element Model in an elastic and an elasto-plastic deformation zone. Including the elastic response of the structure by means of model simplifications, the costly iteration in the elasto-plastic zone can be restricted to the small forming zone and to few supporting elements in order to reduce computation time. Since the forming zone moves along the specimen, an update of both, forming zone with elastic boundary and supporting structure, is needed after several increments. The presented paper discusses the algorithmic implementation of the approach and introduces several strategies to implement the denoted elastic boundary condition at the boundary of the plastic forming zone. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

In metal forming processes especially in cold forming, elastic deformation of the tools has a big impact on the final shape of the work-piece. Computation of such processes considering the plastic effects of the work-piece and elastic deformations of the tools at a time in a single FE model complicates to manage the convergence criteria. This situation is even aggravated if the contact situations (between working and support rolls) have to be considered in the simulation, which requires a very fine discretization of the contact zones of both the tool and work piece. This paper presents recently developed concept which meets the above mentioned demands very effectively. Within this concept, the computation of the elastic effects of the tools is separated from the process simulation (which considers elastic-plastic effects of the work-piece). Both simulations are coupled via automatic data interchange, which is bi-directional, because both simulations influence each other. The advantages of this concept include a quite easy to handle contact situations in process simulation, smaller stiffness matrix compared to single model approach and good convergence of the computation. This concept is highly generalized and successfully applied to simulate rolling, drawing, extrusion and forging processes. The above mentioned concept is being implemented into the FE package PEP and LARSTRAN/SHAPE. Rolling experiments are conducted in duo and quarto configuration. Optical three-dimensional digitalizing system was used to measure the deformations within the machine and work-piece profile. These results are used for the validation of FE simulations. This work is being sponsored by the German Research Foundation (DFG) through the project “Interaction effects between processes and structures-SPP1180”. © 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]

In this paper we present a hybrid eXtended Finite Element/Level Set Method to simulate a two dimensional moving interfaces. The discrete discontinuity (material interfaces) is treated by the extended finite element method (X-FEM), in the partition of unity concept, whereby interface discontinuities are completely independent of the mesh. In this context, the discontinuity is represented without explicitly meshing its shape and the moving interface simulations are carried out without any re-meshing. Enriched approximations to the velocities and deformation fields are developed in the context of the eXtended Finite-Element Method, and the level-set representation of the interface was used to model the evolution of the discontinuity interface in time. The X-FEM utilizes the partition of unity property, of the finite element shape functions to incorporate arbitrary enrichment functions into the approximation. An explicit Newmark algorithm and one-point integration scheme with hourglass mode control is used to update the discontinuous fields. Material interface simulations as well as some free surface simulations, follow theoretical aspects presented in. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

This paper deals with the identification of material parameters using an inverse strategy. In the classical methods, the inverse technique is generally coupled with a finite element code which leads to a long computing time. In this work an inverse strategy coupled with an ANN procedure is proposed. This method has the advantage of being faster than the classical one. To validate this approach an experimental plane tensile and bulge tests are used in order to identify material behavior. The ANN model is trained from finite element simulations of the two tests. In order to reduce the gap between the experimental responses and the numerical ones, the proposed method is coupled with an optimization procedure to identify material parameters for the AISI304. The identified material parameters are the hardening curve and the anisotropic coefficients. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

Numerical modeling of engineering contact problems is one of the most difficult and demanding tasks in computational mechanics. In this paper, the extended finite element method is employed to simulate the presence of discontinuities caused by frictional contact based on the penalty approach. The FEM approximation is enriched by applying additional terms to simulate the frictional behavior of contact between two bodies. The penalty method, which is one of the most commonly used techniques for contact problems, is used to model the penetration between two contacting boundaries and the normal contact force is related to the penetration by a penalty parameter. Finally, numerical examples are presented to demonstrate the applicability of the XFEM in modeling of frictional contact behavior. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

The paper refers to the problem of parallel generation of 3D meshes for complex objects. Simulation of processes using finite element method (FEM) consists essentially of two phases: generation of finite element mesh and solving the appropriate set of algebraic equations. The parallel solving of such problems has been often reduced to sequential generation of a mesh and than decomposing of this mesh. The latter operation was usually performed sequentially as well. In such approach the only part being parallelized is the solver. In the recent years much attention has been directed to the task of parallelization of the mesh generation process. The need for considering this problem results mainly from the fact that the simulations are currently being run on meshes with very large number of elements. In such cases the sequential generation of meshes poses significant problems regarding both the amount of the required memory and the discretization time. In this work there is described the decomposition strategy of the initial surface 3D mesh for subsequent generation of the volume mesh. Surface meshes are the input data which are being decomposed into sub-domains by cutting them with separators. Next, the surface meshes are constructed for the separator, which are closing the new sub-domains. There is ensured the compatibility of the surface meshes at the interface. This procedure is being continued until the prescribed number of sub-domains is reached. Generation of volume meshes can then be performed for each closed sub-domain on the parallel computer. As a result, the whole volume mesh needn’t be stored in the memory of the single computational node. During the simulation phase there is interchanged only the information about the interface meshes, which stay compatible. Moreover, for single-processor unit, the method can give additional benefits. It’s possible to partition the domain depending on the amount of the available memory and then generate the volume meshes sequentially for each sub-domain. This approach allows to use the sequential mesh generator without any modifications. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

This paper presents an example of the application of a genetic algorithm to a 2-D design problem, which consists in the reconstruction of the function that describes the convective heat transfer coefficient, when the position of the moving interface of the phase change is well-known. In numerical calculations the Tikhonov regularization, the genetic algorithm and the alternating phase truncation method were used. The featured examples of calculations show a very good approximation of the exact solution and the stability of the procedure. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

Advances in the processing power of modern computer hardware and the availability of sophisticated simulation software have fostered the use of virtual prototyping techniques in the automotive industry. However, many engineering problems require simulation and optimization computations so complex that it is imperative to utilize parallel computing to solve these problems in reasonable time. In this paper, FETI-INDEED — a parallelized simulation code for sheet metal forming — as well as algorithms for distributed optimizations are examined. Because it is anticipated that increasingly large problems will need to be solved in the future, particular focus is put on scalability aspects of these components. Experimental results are provided for optimizations which were performed on a 300 CPU Opteron cluster. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

This paper deals with the construction of efficient algorithms for the solution of finite dimensional constrained minimization problem arising from the finite element discretization of contact problems. We present domain decomposition methods within framework of mortar techniques, which provide a more flexible approach than the standard formulations. The mortar finite element method formulations is applied to a variational inequality to carry out numerical experiments associated with theoretical results already obtained. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

Nowadays, functional gradient materials (FGM) are successfully used to manufacture parts and structures which are subject to strains and temperature loadings. Use of FGM as well as other advanced materials to develop and manufacture shock-resistant protective structures is conditioned by continuous upgrade of shock and explosive devices. In this paper, computational investigation of shockwave loading of barriers with strength gradient properties is presented. In particular, the effect of linear change in characteristics responsible for spallation and shear strains over the whole barrier thickness from the surface loaded through its back surface on strain and destruction processes was investigated. The effect on barriers was defined as plane shock wave loading, and as impact of compact steel oblong strikers against the barriers along the normal. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The paper presents results of studies of shear strength of copper having various grain sizes under quasi-isentropic and shock-wave loading up to pressures P»40 GPa and P»70 GPa. The studies were performed for copper M1; large-grain copper with grain size d»100 mm; and ultradispersed copper with grain size d»0.5 mm. Basing on results of the experiments, the relaxation models of shear strength were developed. The model of shear strength of large -grain copper takes account for deformation heterogeneity. The first experimental data on strength properties of copper at pressure up to P»300 GPa were obtained by the perturbation method. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

As more Advanced High-Strength Steels (AHSS) are heavily used for automotive body structures and closures panels, accurate springback prediction for these components becomes more challenging because of their rapid hardening characteristics and ability to sustain even higher stresses. In this paper, a modified Mroz hardening model is proposed to capture realistic Bauschinger effect at reverse loading, such as when material passes through die radii or drawbead during sheet metal forming process. This model accounts for material anisotropic yield surface and nonlinear isotropic/kinematic hardening behavior. Material tension/compression test data are used to accurately represent Bauschinger effect. The effectiveness of the model is demonstrated by comparison of numerical and experimental springback results for a DP600 straight U-channel test. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Tailor welded blanks (TWBs) are made by welding same or different materials having same/different properties into a single blank. They can be tailored to any specific shape and size. The formability of these blanks depend on material and geometric parameters like strength ratio and thickness ratio. This paper studies the effect of thickness ratio on the formability of tailor welded blanks by FE simulation. The formability is assessed by considering the Tensile and Limit Dome Height (LDH) tests. The weld region has been assumed as a line in all the simulations. While modeling tensile test, the ultimate tensile strength and the uniform elongation were monitored. In all LDH simulations, near plane strain condition is considered Uniaxial tensile testing shows that TWB formed will have lower elongation as compared to the base metal and the load bearing capacity will be comparable to that of thinner blank in case of transverse welded TWB. Thickness and thickness strain distribution along the blank show that the effective deforming area in a transversely welded TWB is that of the thinner blank. Both tests indicate that as the thickness ratio increases, the formability of TWB reduces. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

With advances in computer capabilities, cost of sheet metal forming has being reducing mainly due to the reduction of trial and error approaches. At the moment, a complete process can be simulated on computer and appropriate forming conditions optimized before actual industrial forming process is carried out. While formability predictions have improved, the problem of springback exhibited by most metal, including aluminum alloy AA6111-T4, after forming persist and often leads to significant part fit-up problems during assembly. There are a number of factors that affect springback and perhaps the most significant one is constitutive equation. In this paper springback predicted by six advanced kinematic models are evaluated. In addition an improved constitutive kinematic model is presented. It is shown that by adding stress correction term (SCT) to Armstrong-Frederick model a relatively simple and yet accurate stress prediction could be obtained. The SCT was developed with the assumption that the yield surface remains convex, yield center depends on translation, size and shape variations of the yield surface. The model is implemented in a commercial finite element code (ABAQUS/Standard) via its user material interface (UMAT). Numerical simulations of U-bending were performed using automotive aluminum sheet material (AA6111-T4). It was noted that springback has inverse relationship with residual stress. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]