Abstract:
In this thesis, high strain rate properties of isotropic material (a copper alloy) and anisotropic material (2195-T8 aluminum-lithium alloy) are investigated using Taylor impact tests. Coordinate measuring machines (CMMs) are used to measure the shape of specimens after the deformation. The geometrical data enables us to determine the plastic distributions and the dynamic yield stresses of specimens. A raise in yield strength is found in the copper alloy during the impact. It means that material properties of the copper alloy are sensitive to high strain rate. Yet such phenomenon is not found in the 2195-T8 aluminum-lithium alloy. Based on the uniaxial compression strain state in the barreling regions of the specimens, the dynamic yield stresses in the rolling, transverse and short transverse directions are obtained for the 2195-T8 aluminum-lithium alloy. This enables us to determine the anisotropic coefficients in Hill's criterion and carry out the finite element analysis. The dependencies of fracture are also investigated. It is found that the fracture is sensitive to maximum shear stress, equivalent plastic strain and stress triaxiality.
