A comparison between the total Lagrangian scheme (TLS) and the predominat twin reorientation (PTR) methods to analyze the twinning deformations in a rate dependent crystal plasticity model

Materials with Hexagonal-Closed Pack (HCP) crystal structures, as for example the magnesium and titanium alloys, have a small number of active slip systems at room temperature. This fact makes twinning as a predominant deformation mechanism and thus essential for the accurate prediction of plastic deformations and texture evolution. Also, because of the directional property of the twinning mechanism, different responses are obtained for tension and compression, explaining the asymmetric behaviour of HCP metals. As reported by Van Houtte [1], the twinning mechanism is also important for low stacking fault energy Face Centred Cubic (FCC) metals. In this work, we developed two types of a finite element analysis code, based on the crystal plasticity theory, including twinning as a dominant deformation mechanism. The first twinning model is based on the Predominat Twin Reorientation (PTR) scheme, suggested initially by Van Houtte [1], and the second one is based on the Total Lagragian Scheme (TLS), suggested by Kalidindi [2]. The PTR model has the advantage of being simple and computationally efficient. On the other hand, the TLS model has some advantages when compared with the PTR model that are: i) the possibility of continuously consider the texture's evolution from both slip and twinning deformations; ii) the consideration of slip in the twinned regions. In the present paper, the two models are compared for a tension and a compression simulation for a FCC material

Effect of Texture of AZ31 Magnesium Alloy Sheet on Mechanical Properties and Formability at High Strain Rate

The mechanical properties and formability of AZ31 magnesium alloy strips having different textures were investigated at a high strain rate based on that occuring in mass production by press forming. Forming at a high strain rate on the order of 10 0 s À1 requires a high temperature of over 473 K. To obtain accurate stress-strain curves, a high-speed testing machine that can maintain a constant true strain rate was used, and the change in gauge length on a test piece in a furnace was measured during the testing time of about 0.5 s. For the specimens, rolled strips consisting of fine grains (about 10 mm) and an extruded strip consisting of coarse grains (about 40 mm) were used. The {0001} textures of the extruded strip and one of the rolled strips were strongly oriented parallel to the rolled surface, but the texture of another rolling strip had two peaks that were inclined at 5 $15 deg in front of and behind the rolling direction. At the high strain rate of 10 0 s À1 , elongation decreased for every specimen. Nevertheless, a limiting drawing ratio (LDR) of 2:1$ 2:2 was obtained under uniform heating above 503 K in all the specimens except for the extruded strip. The high LDR of the rolled strip having a two-peak texture was maintained in forming at temperatures down to 473 K, in contrast to the LDR of the strongly oriented rolled strip, which reduced rapidly when formed at temperatures less than 503 K

Identification of Viscoplastic Properties of Individual Phases in Lead-Free Solder Alloy by Depth-Sensing Microindentation

The viscoplastic properties of the Sn-rich phase and Sn-Ag-Cu eutectic constituent in a Sn-3.5Ag-0.75Cu lead-free solder were determined by performing microindentation tests on these individual phases. Material parameters in Norton's law for each phase were successfully identified by fitting the experimentally obtained rate-dependent indentation load (P) vs penetration-depth (h) curves, as well as indentation-creep data, with the corresponding Finite Element (FE) simulation results. For this material parameter identification, an appropriate indenter-penetration depth for a given size of a phase, where the P-h response is not affected by the other neighboring phases, was determined by FE simulation

Identification of Material Parameters in Constitutive Models for Metal and Metal/Polymer Composite Sheets by Elastic-Plastic Inverse Analyses

研究期間:平成9-10年度 ; 研究種目:基盤研究C2 ; 課題番号: 09650105原著には既発表論文の別刷を含む