Investigating the Anisotropy of Mechanical Parameters of Schist Rock with Practical Numerical Methods

The anisotropy of deformation and strength behavior in quartz mica schist is fundamental to rock mechanics. Here, we concentrated on the practical application of the numerical simulation of the anisotropy of schist rock. First, the existence of the anisotropy of the schist rock in engineering application was reported, tested in situ, and analyzed. Then, a set of specially designed multi-angle uniaxial compression tests was conducted. Based on these, two numerical simulation methods (explicit and implicit) for anisotropy were demonstrated and discussed. Between the two methods, the implicit method was more practical. Ultimately, the implicit method was adopted to perform an excavation simulation of the exploratory tunnel CPD-1. Our findings demonstrated the feasibility of the implicit method as a practical numerical method to determine the anisotropy of schist rock.

Characterizing the Asymmetric/Anisotropic Deformation Response and Forming Behaviour of Wrought Magnesium and Titanium Alloys

There is the requirement to describe the asymmetric and anisotropic deformation behaviour of hexagonal closed packed (hcp) alloys, including wrought magnesium and titanium. Magnesium and to limited extent, titanium, alloys are candidate materials for weight and emission reduction in the automotive industry. Predicting the deformation response of hcp alloys is challenging to the complexity and number of potentially operative deformation mechanisms which can drastically change with temperature, deformation rate, and chemistry. In this work, the constitutive material response is described using various asymmetric/anisotropic yield criteria, specifically designed to describe the deformation response of hexagonal close packed (hcp) materials. These models allow the size and shape of the yield surface to evolve with plastic strain. The Marciniak-Kuczynski (M-K) approach is utilized to predict the forming limit in the form of forming limit diagrams (FLD). The degree of asymmetry and anisotropy is varied in the predictions to quantify their effects on the forming limit response. The numerical FLD predictions are compared to FLD which have been experimentally determined for AZ31B magnesium and Grade 1 CP titanium sheet alloys. For CP titanium alloys, it was found that it was important to capture the asymmetry and anisotropy of deformation to capture the forming limit response. For AZ31B formed at 200 °C, it was important to capture the strain-rate sensitivity of the material, more so than the asymmetry and anisotropy of deformation, for predicting the forming limit behaviour. The combination of experimental data and predictive models developed in this work are intended to characterize the forming behaviour of various lightweight sheet alloys without the requirement for excessive experimental data, and to ultimately aid in the selection of lightweight sheet metals for multi-material vehicle design.

Anisotropy of Deformation Behavior of AZ31 Magnesium Alloy Sheets

In order to develop magnesium alloy sheets with high formability at room temperature, the anisotropy of deformation behavior of AZ31 magnesium alloy sheets produced by equal channel angular rolling were examined, which were compared with that of the sheets produced by the unidirectional hot rolling. The differences in the deformation behavior of the sheets at the rolling direction (0°), 45° and the transverse direction (90°) were discussed in term of the texture and microstructure. Compared with the as-received specimens, the anisotropy of deformation behavior of AZ31 magnesium alloy sheet produced by equal channel angular rolling was enhanced, which was following with an improved ductility and a large work hardening phenomenon. These could be due to the non-basal texture, which was induced by the continuous shearing deformation during equal channel angular rolling procedure. The fracture mechanism transferred from the cleavage fracture for the unidirectional rolling to the quasi-cleavage fracture for the sheets produced by equal channel angular rolling, which proved that the non-basal texture was in favor of the ductility of magnesium alloy.