Search

The effect of grain orientation distribution on the dynamic strength of highly textured magnesium alloy AZ31B has been studied in a series of plate-impact experiments. Specimens with thicknesses between 0.45 mm and 2 mm were cut parallel and perpendicular to the material extrusion direction and shock loaded to impact stresses between 1.4 GPa and 3.4 GPa. The dynamic strength is found to be highly dependent on the loading direction, with loading along the extrusion direction exhibiting significantly higher Hugoniot elastic limits than the transverse direction, including a much slower precursor decay rate. Application of an orientation-based analysis framework shows that the yield point of the polycrystalline material can be predicted reasonably well from its grain orientation distribution, predicated upon the use of dynamic critical resolved shear stress values from single-crystal data modified by a fitted strengthening factor. It is shown that the strong dependence on loading orientation in Mg AZ31 is caused by the relative differences in slip system activity and the slip anisotropies inherent to the hexagonal close packed crystal structure. [ABSTRACT FROM AUTHOR]

Extraordinary states of highly localised pressure and temperature can be generated upon the collapse of impulsively driven cavities. Direct observation of this phenomenon in solids has proved challenging, but recent advances in high-speed synchrotron radiography now permit the study of highly transient, subsurface events in real time. We present a study on the shock-induced collapse of spherical cavities in a solid polymethyl methacrylate medium, driven to shock states between 0.49 and 16.60 GPa. Utilising multi-MHz phase contrast radiography, extended sequences of the collapse process have been captured, revealing new details of interface motion, material failure and jet instability formation. Results reveal a rich array of collapse characteristics dominated by strength effects at low shock pressures and leading to a hydrodynamic response at the highest loading conditions. [ABSTRACT FROM AUTHOR]

Taylor impact experiments in the classic and symmetric configurations were used to study the plastic deformation and void nucleation in Al-6082-T6 rods. Deformation histories during impact were recorded using high-speed photography. X-ray computed tomography was used to visualize the extent of damage in recovered specimens. Above threshold velocities, void nucleation was observed along the central axis of the specimens, and reconstructed images from the tomography provide a 3-D mapping of the damaged region. The use of X-ray tomography is the first step in developing a method to characterise the damage process during impact using in-situ flash X-rays, which is also attempted in this study. Finite element simulations of these experiments are in good agreement with the experimental measurements, and confirm that void nucleation is due to the coalescence of lateral release waves at the centre of the specimen. The simulations also revealed that the time to failure is velocity dependent, and that the threshold velocity for void nucleation is sensitive to the properties and geometry of the target. [ABSTRACT FROM AUTHOR]