Papers by Keyword: Deformation Mechanism

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Authors: Wei Neng Tang, Hong Yan, Rong Shi Chen, En Hou Han
Abstract: Superplastic deformation (SPD) behaviors of two fine-grained materials produced by ECAE and hot rolling methods have been contrastively studied in this paper. It is found that the optimum superplastic condition in as-ECAEed material was at 350°C and 1.7×10-3s-1 with elongation to failure about 800%; while in as-rolled material, the largest elongation to failure about 1000% was obtained at 480°C and 5.02×10-4s-1. Microstructure observation showed that grain evolution and cavitation behavior were different in these two materials during superplastic deformation. The controlled mechanisms for superplasticity, i.e. grain boundary sliding (GBS), dislocation creep and diffusional creep, at different deformation conditions were discussed in terms of strain rate sensitivity coefficient, stress exponent and activity energy.
Authors: Yuan Tong Gu, Prasad K.D.V. Yarlagadda
Abstract: This paper presents a concurrent multiscale study for the deformation mechanism of monocrystalline copper under dynamic uniaxial tension. The multiscale simulation is based on the coupled meshless and molecular dynamic (MD) method. Using it, the size of computational model can be extended to a large dimension (in micrometer) with an atomistic resolution. The pure MD simulation is difficult to reach this microscopic dimension because the number of atoms will be too large. In this study, it has been revealed that the deformation behavior and mechanism of the copper is sensitive to its size, geometry, and loading strain rate. In addition, the Young’s modulus is found to be independent of the cross-sectional size and the strain rate range considered in this study. On the other hand, the yield stress decreases with specimen length and increases with the loading strain rate.
Authors: Takuya Uehara
Abstract: Molecular dynamics simulations were carried out to investigate the plastic deformation mechanism of fcc crystalline materials using the conventional Lennard-Jones potential. An fcc structure with square cross-section was prepared, and a tensile load was applied in the longitudinal direction. A weak potential was assigned to a specific (111) plane to induce a slip on the specified plane. Accordingly, a slip was initiated in the weak plane following an elastic deformation. The step-by-step motion of the atoms on the slip plane was studied, and a detailed trajectory is presented. The slip then expanded to other planes, and plastic deformation progressed in the whole model. The weak plane was also set as (110) or (100) plane, where different deformation modes were observed: not only slip but also gradual distortion or brittle fracture occurred.
Authors: Marie Kvapilová, Vaclav Sklenička, Jiří Dvořák, Petr Král
Abstract: Our earlier published creep data are analyzed for ultrafine-grained pure aluminium and copper processed by equal-channel angular pressing (ECAP). The analysis demonstrates conclusively that creep occurs in the investigated materials after ECAP by the same mechanism as in conventional coarse-grained materials with intergranular dislocation glide and climb as the dominant rate-controlling flow process. Under creep conditions examined in this work diffusion creep is not important in pure aluminium and copper because the ultrafine grains are unstable at elevated and/or high temperature creep and the grains grow sufficiently to preclude any significant contribution from Nabarro-Herring or Coble creep.
Authors: Li Meng, Ping Yang, Zude Zhao, Wei Min Mao
Abstract: Orientation mapping based on EBSD technique was applied to analyze the rules of orientation evolution of grains in AZ31 magnesium alloy. Results show that not only under deformation strain rate of 1×10-2s-1, but under 4×10-4s-1(the superplastic deformation condition), grains in all samples with initial textures rotate gradually to near basal orientation ({0002} || compression plane) at different ways, and basal texture becomes stronger with increasing strain, which indicates plastic slip plays an important role during hot deformation. Otherwise, no evident non-basal pyramidal slip of as some studies mentioned was observed in the sample with the initial basal texture, and the basal orientation is kept unchanged during the deformation process, which suggests that basal slip is the uppermost plastic slip mechanism in this sample. In addition, the phenomenon of viscous laminar flow was observed in the sample with initial basal texture.
Authors: Eric M. Taleff
Abstract: Al-Mg alloys exhibit remarkable hot and warm ductilities, which have made the 5000-series alloys a critical part of commercial hot gas-pressure forming operations for the transportation industry. A review of the metallurgical and practical engineering reasons for this success is presented, and new understanding for behaviors in these materials, expected to impact future advances in hot- and warm-forming technology, are described. The excellent formabilities in this material class are fundamentally attributable to two deformation mechanisms, grain-boundary-sliding and solute-drag creep. However, a number of failure mechanisms ultimately limit final ductility and formability. These include cavitation, flow localization and microstructure evolution. The interplay of these mechanisms is discussed in terms of the potential to improve processing windows in forming operations.
Authors: Fei Pan, Sheng Guo Cheng
Abstract: With the development of transportation construction, soft rock tunnel with high geostress construction has become a key problem to overcome of traffic engineering construction. In order to explore the deformation mechanism and control technology of soft rock tunnel with high geostress, Xiakou tunnel engineering as an example, the geological characteristics and deformation characteristics of the tunnel were analyzed, to obtain the deformation mechanism of soft rock tunnels with high geostress, and to develop deformation control technology, the results provide a basis and reference for the domestic and foreign the similar engineering construction.
Authors: L. Guétaz, Jean-Michel Pénisson
Authors: Fei Zhang, Jing Cao, Hui Min Zhao
Abstract: Taken an open-pit landslide as an example, the cause of formation and the factors inducing the slope to failure are analyzed. According to deformation characteristic of the landslide, the deformation has been exacerbating with the deep mining in depth, and the deformation has close relationship with the rainfall. Rainwater infiltration, which soften the rock mass and induce the pore water pressure to increase, induce envoke landslides. Through analysis on the factors of landslides, the formation lithology(FL) and precipitation are main factors triggering generation and reactivation of landslides. Meanwhile, the deformation failure mechanism and instability mode of the landslide is obtained, which is the sliding and bending deformation model.
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