Papers by Keyword: Plasticity

Abstract: The cyclic deformation behaviors of 42CrMo steel with different heat treatments were observed by uniaxial cyclic straining and stressing tests at room temperature. The cyclic softening/ hardening features of the tempered or annealed 42CrMo steel and their effects on the uniaxial ratcheting produced in asymmetrical cyclic stressing were discussed. It is concluded that the tempered 42CrMo steel shows significantly cyclic softening feature, but the annealed one is cyclic stabilizing. Different ratcheting behaviors are also observed. For the tempered 42CrMo steel, a special tertiary ratcheting behavior is observed and the previous cyclic straining greatly accelerates the evolution of ratcheting strain in subsequent cyclic stressing. In contrast, the annealed sample presents a stabilized ratcheting with nearly constant ratcheting strain rate after certain cycles, and the previous cyclic straining slightly influences the ratcheting in subsequent cyclic stressing.

Abstract: The interface strength of low-dimensional nano-components such as films and islands formed on substrates has been investigated in this project, and the focus is put on the mechanics of crack initiation from the free interface edge and propagation along the interface. The series of experiments elucidates the applicability of fracture mechanics concept on the structures. We proposed experimental methods for evaluating the initiation strength of an interface crack in submicron films and islands deposited on substrates. The initiation is governed by the singular stress field, and the criterion is prescribed by the stress intensity parameter. Using special loading apparatus built in a TEM, we developed a crack initiation method for nano-components and the role of plasticity on the delamination is clarified. Subcritical crack growth along an interface between submicron films under fatigue was also investigated by modified four-point bend method.

Abstract: The stress-strain characteristics and plastic behavior of aluminum alloy were examined by tensile test and infrared thermo-viewer. This thermo viewer is a device for converting a thermal radiation pattern from an object into visible images. Al-Mg alloy plates with different crystal grain size subjected to a uni-axial tensile load were measured continuously by this thermo viewer. The strain concentration pattern was analyzed by the differential thermal image and the macroscopic estimation method by the thermal image processing was proposed and the propriety of FE simulation based on polycrystalline plasticity model was shown.

Abstract: This paper discusses ratchetting deformation of lead-free solder Sn/3Ag/0.5Cu and lead-containing solder alloy Sn/37Pb with several stress amplitudes and stress ratios of the maximum stress to the minimum stress. First the uniaxial ratchetting tests
are conducted with three maximum stresses and five stress ratios. The all tests are conducted using cylindrical bulk specimens of the solder alloys at 313 K. The test results show that there is the difference in the viscoplastic deformation behavior between two solder alloys. The relationship between ratchetting strain and time is estimated by Biley-Norton law to explain that the uniaxial ratchetting deformation is strongly dominated by the viscous deformation. Finally, the ratchetting deformation is simulated by the dislocation based constitutive model proposed by Estrin [1]. The simulations show that there is a possibility to simulate the uniaxial ratchetting by clarifying the dislocation mechanism of the solder alloys.

Abstract: A new approach is proposed for description of autowave processes responsible for plastic deformation localization in metals and alloys. It is postulated that to a localized flow autowave there corresponds a quasi-particle. The characteristics of the quasi-particle have been determined. A direct relationship has been established between the processes involved in the deformation on a macro- and a micro-scale level.

Abstract: Various polygonal tubes were compressed in the axial direction under quasi-static and dynamic loading conditions. The effect of the polygonal shape and the wall thickness on the crush behavior is investigated, in which the cyclic buckling takes place. The numbers of polygonal edges were 3, 4, 5, 6 and 7 in the experiment. A circular tube was also tested for comparison. The tubes were machined from aluminum alloy A5056 bar. Crush strength is estimated as an index of the energy absorption capacity of the tube. It increases with increasing the number of polygonal edges of the tube, although it almost saturates when the number of polygonal edges is more than 6. For the wider variety of polygonal tubes than that in the experiment, numerical simulation is performed using the dynamic explicit finite element code DYNA3D. The computed crush behavior well agrees with the corresponding experimental one, however, the difference in collapse mode arises due to the slight imperfections in experiment. The deformation pattern becomes more irregular for the thinner-walled tube. Further, it is presumed that the large hardening exponent in the plastic property of the material could prevent the buckling switching from the symmetric mode to asymmetric one in the crushing of circular tube.

Abstract: In this study, we focus on the modeling of solid structures that include microstructures observed in particle-dispersed composites. The finite element modeling can be used to clarify how the macroscopic behaviors of solid structures are influenced by the microstructures. In such a case, if the whole structure including the microstructures is modeled by the finite elements, an enormous number of finite elements and enormous amount of computational time are required. To overcome such difficulties, we propose a new method for modeling microstructures. In this method, an explicit form of the stress-strain relation covering both elastic and elastic-plastic regions is derived from the equivalent inclusion method proposed by Eshelby that provides mathematical solutions for stress and strain at an arbitrary point inside and outside the inclusion. The derived elastic-plastic constitutive equation takes account of the microstructures, so that the effect of microstructures on the macroscopic behaviors can be obtained from the conventional finite element method by using such a constitutive equation without modeling microstructures in the finite element analysis. The effectiveness of the proposed constitutive equation is verified for a simple problem by comparing the results of the one-element finite element analyses using the proposed constitutive equation with those of the detailed finite element analyses using multi-element finite element modeling.

Abstract: This paper presents a concurrent multiscale method for the stress analysis of solids using a coupled meshless and molecular dynamic analysis. A new transition algorithm using transition particles was employed to ensure the compatibility of both displacements and their gradients. The equivalent continuum strain energy density was obtained locally based on the atomic potential and Cauchy-Born rule, and hence plasticity can be easily handled in not only the atomic domain but also the continuum domain. Numerical examples demonstrated that the present multiscale technique has a promising potential of application to multiscale systems subjected to deformation.