Papers by Keyword: Large Strain

Abstract: An efficient numerical framework suitable for three-dimensional analyses of brittle material failure is presented. The proposed model is based on an (embedded) Strong Discontinuity Approach (SDA). Hence, the deformation mapping is elementwise additively decomposed into a conforming, continuous part and an enhanced part associated with the kinematics induced by material failure. To overcome locking effects and to provide a continuous crack path approximation, the approach is extended and combined with advantages known from classical interface elements. More precisely, several discontinuities each of them being parallel to a facet of the respective finite element are considered. By doing so, crack path continuity is automatically fulfilled and no tracking algorithm is necessary. However, though this idea is similar to that of interface elements, the novel SDA is strictly local (finite element level) and thus, it does not require any modification of the global data structure, e.g., no duplication of nodes. An additional positive feature of the advocated finite element formulation is that it leads to a symmetric tangent matrix. It is shown that several simultaneously active discontinuities in each finite element are required to capture highly localized material failure. The performance and predictive ability of the model are demonstrated by means of two benchmark examples.

Abstract: Based on thermodynamics and phase transformation driving force, we apply a SMA constitutive model to analyze the large and small deformation of SMA materials. Simulations under different loading, uniaxial tension and shear conditions, illustrate the characteristics of the model in large strain deformation and small strain deformation. The results indicate that the difference between the two methods is small under the uniaxial tension case, while the large deformation and the small deformation results are very different under shear deformation case. It lays a foundation for the further studies of the constitutive model of SMA, especially in the multiaxial non-proportional loading aspects.

Abstract: The consolidation of frozen soil is a coupled action of temperature and deformation. Using moving boundary method and taking the void ratio as a variable, the large strain thaw consolidation mathematical model is built according to Gibson’s large strain consolidation theory and thermal conductivity equation with consideration of phase change. In order to verify the model, a simple example is simulated by FEM software. The result shows that the consolidation range and consolidation rate are decided by the temperature boundary; the change of void and deformation are influenced by pore pressure dissipation and the thaw process in permafrost are delayed by consolidation process.

Abstract: Recently, our research team has been considering to applying shape memory alloys (SMA) constitutive model to analyze the large and small deformation about the SMA materials because of the thermo-dynamics and phase transformation driving force. Accordingly, our team use simulations method to illustrate the characteristics of the model in large strain deformation and small strain deformation when different loading, uniaxial tension, and shear conditions involve in the situations. Furthermore, the simulation result unveils that the difference is nuance concerning the two method based on the uniaxial tension case, while the large deformation and the small deformation results have huge difference based on shear deformation case. This research gives the way to the further research about the constitutive model of SMA, especially in the multitiaxial non-proportional loading aspects.

Abstract: In order to provide scientific basis for design and application of cast steel joint, this paper researches on mechanical properties of tubular-plate combined cast steel joint and tubular cast steel joint, which work in International Expo Center in the most unfavorable load condition. Finite Element Method (FEM) is employed to analysis the mechanical properties of the complex cast steel joint and an optimize solution is given. FEM based on large deformation theory and material nonlinearity obtained ultimate load and failure mode of the joints. The results show that, force transmission path of combined cast steel joint is complex for its cross-section shape of branch changes much; stress concentration is very obvious on the branch. In contrast, the force transmission path of tubular cast steel joint is clear and concise; the phenomenon of stress concentration alleviated effectively, the efficiency of material improved greatly; in the same amount of material, the ultimate bearing capacity of tubular cast steel joint increased by 9.5%. The joint design should follow the principle of simple and practical in premise of mechanical requirements.

Abstract: A challenge in the design of functional parts in metal forming processes is the determination of the initial, undeformed shape such that under a given load a part will obtain the desired deformed shape. An inverse mechanical or a shape optimization formulation might be used to solve this problem, which is inverse to the standard kinematic analysis in which the undeformed shape is known and the deformed shape unknown. The objective of the inverse mechanical formulation aims in the inverse deformation map that determines the (undeformed) material configuration, where the spatial (deformed) configuration and the mechanical loads are given. The shape optimization formulation predicts the initial shape in the sense of an inverse problem via successive iterations of the direct problem. In this paper, both methods are presented using a formulation in the logarithmic strain space. An update of the reference configuration of the sheet of metal during the optimization process is proposed in order to avoid mesh distortions. A first example showed the results obtained with both methods in isotropic hyperelasticity. A second example illustrated a simplified deep drawing computed with the shape optimization formulation in isotropic elastoplasticity. From the undeformed shapes obtained with both methods the deformed shapes are acquired with the direct mechanical formulation. Compared to the target deformed shape a minor difference in node coordinates is found. The computation time is lower with the inverse mechanical formulation in hyperelasticity. The update of the reference configuration in the shape optimization formulation allowed to avoid mesh distortions but increased the computational costs.

Abstract: The formation of Cube oriented elements in plane strain compressed aluminium has been studied by EBSD for both hot and cold deformations. By following the orientation changes of the same set of 176 grains deformed at 400 °C up to a strain of 1.2 using a split sample, it is shown that about 15% of the grains can break up into several regions of very different orientations, characterized by very large orientation gradients. In particular those grains oriented within about 30° of Cube develop Cube oriented zones in contact with other rolling texture components. Finite element crystal plasticity simulations confirm this mechanism of creation of Cube by plastic deformation. The same type of microstructure can also be observed after heavy cold rolling (strain of 2.3), but at a scale that is much finer by at least an order of magnitude. In this case the micron-sized Cube fragments are located along many grain boundaries or in some particular grains. When the cold deformed sample is annealed, EBSD observations of the same areas reveal that the intergranular Cube fragments are very efficient recrystallization nucleation sites, apparently since they possess mobile high angle boundaries with the local environment.

Abstract: The development of orientation spreads within individual grains of a polycrystal submitted to large deformations is analysed by both experiment and simulation. In the experiment, 176 grains on an internal surface of a split sample were followed by detailed EBSD measurements, at successive strains up to 1.2. In parallel, a high-resolution finite element simulation has been carried out on the same polycrystal configuration. For both experiment and simulation, hundreds to thousands of orientation values were obtained in each grain. Most grains showed a “unimodal” rotation, composed of an average rotation and an orientation spread. The experimental and simulated orientation spreads were compared through different statistical metrics. The average lattice disorientations are found to increase rapidly at the beginning of the deformation and to saturate at high strains. The orientation spreads are also analysed in terms of anisotropy along the sample axes. It is shown that the orientation spreads are aligned preferably along TD at the beginning of the deformation, then tend to move to RD in the experiment, and RD or ND in the simulation.

Abstract: A simplified method called “Pseudo Inverse Approach” (PIA) has been developed for the axi-symmetrical cold forging modeling in this paper. The traditional “Inverse Approach” (IA) based on the assumptions of the proportional loading and simplified tool actions may quickly give a fairly good strain distribution, but poor stress estimation. Meanwhile the PIA proposed in this paper not only keeps the advantages of the Inverse Approach but also gives good stress estimation by taking into account the loading history. To fulfill this aim, some kinematically admissible intermediate configurations represented by the free surface are used to consider the deformation paths without classical contact treatment. A new direct algorithm of plasticity integration has been used by using the notion of equivalent stress and the tensile curve, leading to a very fast and robust plastic integration procedure. An axi-symmetrical forging has been taken as an example to validate the PIA.

Abstract: Anti-seepage reinforcement technology of splitting grouting to improve the stability of dam, has been an effective reinforcement method in the field of dam reinforcement. Based on the extended SMP criterion and stress-dilatancy relation considering large strain, the governing equations of axisymmetric problem in the plane strain condition and the partial differential equations for the boundary-value problem of cavity expansion in frictional cohesive soils were established. Then, the early phase of splitting grouting is regarded as the plane strain question of cylindrical expansion infinite soil. Under initial grouting pressure, the soil body was supposed as ideal elastic mass. However, the soil body was supposed to generate plastic damage considering large strain with the increase of grouting pressure and submit the extended spatial mobilization plane theory. Solutions of radial and hoop stresses and strains around the grouting cavity were obtained by recursive computations. Furthermore, the influence of damage softening parameter, cohesion and friction angle was examined by a parametric study.