Papers by Keyword: Local Deformation

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Authors: Mehdi Asadi, Heinz Palkowski
Abstract: The investigations deal with processes leading to local effects of strengthening in multiphase steels, being characterized by good formability, continuous yielding, high strength and a strong bake hardening and ageing effect. Dual phase and complex phase steels are under investigation to examine the effect of thermo-mechanical processing parameters on local ageing ability and its use for designed properties. For this purpose local heat treatment by laser are studied, as well as stability of local ageing on the adjusted strength. A remarkable increase of the hardness in the heat treated zone was observed. Stability of the local strengthening effect could be confirmed. Partial heat treatment of multiphase steels by laser can open a new field of application for the local use of the strengthening effect to influence only relevant areas, thus giving potential for energy saving.
Authors: Tomoaki Fukahori, Shinichi Suzuki, Naoya Yamada, Masatoshi Aramaki, Osamu Furukimi
Abstract: In recent years, high strength steel plates for building and pipelines have been required to improve ductile fracture properties, assuming ground deformation in earthquake-prone region. The ductile fracture is performed by the result from coalescence of micro-voids followed by the nucleation and growth [1]. Fractured surface morphology reflects the void coalescence process, so it is important to consider the relationship between the fracture surface morphology and the micro-voids formation beneath the fractured surface to consider the ductile fracture properties. The voids nucleate sites are mainly particles such as inclusions or precipitates, and grain boundries. These voids grow and coalesce according to three modes. The first mode is directly coalescence of voids followed by growth [2]. The second one is the coalescence of voids caused by shear deformation followed by internal necking between voids [3]. The third one is the coalescence of voids caused by micro-voids nucleation in shear band between two larger voids [4]. It is expected that these modes influence local elongation property which is one of the indices for ductile fracture property through the formation of fractured surface. In this study, local deformation energy which is measured by load-displacement curve in tensile test is examined by focusing the voids nucleation, growth and coalescence, for high tensile strength plates of TS480-830MPa which is controlled by the microstructure through the cooling rate of heat treatment. The deformation energy is useful to consider the ductile fracture property of steel plates which have a different tensile strength.
Authors: Xiao Ping Zhang, Wen Yu Yang, Miao Li
Abstract: The Fixture layout and clamping force are well known as important factors that influences the localization accuracy of the workpiece. Considering the unique characteristics of the Large-Scale workpiece in practice, we, in this paper, propose a unified method of optimizing an existing fixture configuration under heavy-duty condition based on Algmented Lagriangian Method (ALM). We fir- stly derived the models of localization error and static force equilibrium which describe the kinematic condition and quasi-static process of the fixture-workpiece system. Then, we introduce Hertz contact theory to better describe the nonlinear relationship of the local deformation and the contact force. Further, we define the minimum norm of the position error of critical points as the objective function and formulate a multi-constrained problem of solving the optimized fixture configuration. By using the ALM, the nonlinear constrained programming is transformed into an unconstrained one through which we obtain the optimal solution. Finally, a numerical example is presented and compared with the results of FEA simulation.
Authors: Roland Taillard, S. Guyot, Christophe Verwaerde
Abstract: Composites made of niobium filaments within an oversaturated α-CuSn bronze matrix were processed by restack bundle drawing. The differences in mechanical behaviour of the various components entail an heterogeneity of deformation. Such a feature is mostly unfavourable not only for the phase transformations that govern the microstructure and the electromagnetic properties but also for the composite mechanical integrity. The obtained results finally demonstrate the chief importance of the selection of both the design of the composite and the processing steps.
Authors: G. Sudarshan Rao, K. Saravanan, G Harikrishnan, V.M.J. Sharma, P. Ramesh Narayanan, K. Sreekumar, Parameshwar Prasad Sinha
Abstract: The weld portion will have different mechanical properties in weld bead, HAZ and fusion boundary due to variation in the microstructure, chemistry and internal stresses that arise in the welding process. Inconel 718 TIG welded samples are tested to study the deformation behavior of the weld constituents with the help of non contact laser extensometer. Stress-strain curves for the individual constituents of weld, parent, fusion boundary and HAZ are evaluated at room temperature and at 550°C. Test results show that the welded samples exhibited 50% lower tensile properties compared to the parent material. Parent metal remains elastic through out the test. The proof stress of the weld alone is 100 MPa lower than the average proof stress of the welded sample when considered standard gauge length.
Authors: Masayuki Kamaya, Joao Quinta da Fonseca, L.M. Li, Michael Preuss
Abstract: Work has been carried out recently, which demonstrates misorientation measurements recorded by using electron backscatter diffraction (EBSD) enables one to undertake local post mortem plastic strain quantification once the degree of misorientation is calibrated against plastic strain. The present paper builds on this work and investigates the possibility of determining strain in individual grains. Due to the anisotropy of crystalline grains, polycrystalline material deform inhomogeneously on a microstructural level. In this study, the local strain induced in a pure copper specimen during tensile loading measured using EBSD was compared to in-situ strain measurements using optical microscopy imaging in conjunction with image correlation technique. By applying an averaging procedure for improving the accuracy of the measured EBSD data, the distribution of the misorientation within grains was quantified, and, as one would expect, it tended to be highest near the grain boundaries.
Authors: H.D. Joo, J.S. Kim, C.W. Bark, J.Y. Kim, Yang Mo Koo, Nobumichi Tamura
Abstract: In-situ measurement of local orientation and strain Has Been carried out for a copperpolycrystals under a uniaxial loading using a synchrotron x-ray microdiffraction method at the Advanced Light Source. The heterogeneities of deformation-induced microstructure within single grains were observed. There were differences in the selection of simultaneously acting slip systems among neighboring volume elements within a grain.
Authors: T.X. Yu, A.J. Pontes, N.M. Neves, H.H. Ruan
Authors: R. Emre Erkmen
Abstract: Thin-walled members that have one dimension relatively large in comparison to the cross-sectional dimensions are usually modelled by using beam-column type finite element formulations. Beam-column elements however, are based on the assumption of rigid cross-section, thus they cannot consider the cross-sectional deformations such as local buckling and only allows considerations of the beam axis behaviour such as flexural or lateral-torsional buckling. Shell-type finite elements can be used to model the structure in order to consider these local deformation effects. Based on the Bridging multi-scale approach, this study proposes a numerical technique that is able to split the global analysis, which is performed by using simple beam-type elements, from the local analysis which is based on more sophisticated shell-type elements. As a result, the proposed multi-scale method allows the usage of shell elements in a local region to incorporate the local deformation effects on the overall behaviour of thin-walled members without necessitating a shell-type model for the whole member.
Authors: Chuan Yong Cui, Toshiyuki Hirano
Abstract: Notch effect on the fracture behavior of the Ni3Al foils has been investigated as a function of notch radius and depth. Tensile tests along the rolling direction showed that notch weakening occurred with introduce of notch. The effective stress concentration factor (ke) was much lower than the theoretical stress concentration factor (Kt), which was due to the local plastic deformation at the notch root. Cracks initiated along the shear band in the RD tension.
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