Euan Wielewski

On the shock response of the magnesium alloy elektron 675

Alloying elements such as aluminum, zinc or rare-earths allow precipitation hardening of magnesium (Mg). The low densities of such strengthened Mg alloys have led to their adoption as aerospace materials and (more recently) they are being considered as armor materials. Consequently, understanding their response to high strain-rate loading is becoming increasingly important. Here, the plate-impact technique was employed to measure longitudinal stress evolution in armor-grade wrought Mg-alloy Elektron 675 under 1D shock loading. The spall behavior was interrogated using a Heterodyne velocimeter (Het-v) system, with an estimate made of the materials Hugoniot elastic limit for both aged and un-aged materials.

Increasing data from high rate characterization experiments using optical reconstruction

Uniaxial characterization experiments in tension and compression are widely used to evaluate the mechanical response of materials to applied deformation over a wide range of strain rates. By taking photographs of the specimen as it deforms, it is possible to more fully characterize materials by reconstructing the specimen shape during the deformation process. This allows us to better evaluate the stress and strain in the specimen during deformation, and also provides a more rigorous validation of material models. For many materials, specimens with initially circular cross sections will evolve to a different shape; in particular, hcp metals become elliptical. We have developed a technique whereby images of a specimen during deformation (for example, from a high speed camera) from three different angles are used to reconstruct elliptical cross sections during an experiment. The technique has been applied to tensile Hopkinson bar experiments and Taylor Impact experiments on Zirconium. This paper presents an ...

On the influence of texture on spall evolution in the HCP materials Ti-6Al-4V and Zr

Dynamic tensile failure (spall) is known to be a highly microstructure-dependant phenomena. In particular, spall is greatly influenced by the availability of plastic deformation modes such as slip systems. Significant effort has been put into understanding spall in the common engineering BCC and FCC materials, however there is a relative paucity of data on such behaviour in the highly anisotropic HCP class of materials. Here, preliminary results pertaining to the dynamic behaviour of two important HCP materials, Ti-6Al-4V and Zr, are presented, with the aim of enhancing understanding of this complex class of materials.

Electron backscatter diffraction of a pre- and post-deformation Ti-6Al-4V Taylor impact specimen

Titanium alloys have seen wide spread, and ever increasing, use in the aerospace industry, due to a high specific strength and good resistance to corrosion. However, current understanding of the deformation mechanisms of Titanium alloys under complex high strain rate loading is limited. In order to improve understanding in this area, post-deformation microstructural analyses of Titanium alloys loaded under well controlled, but complex, high strain rate loading conditions, such as the Taylor impact test, are required. This paper presents the initial results of a program of Taylor impact experiments carried out on heavily textured Ti-6Al-4V plate. An optical measurement technique was used to provide data on the anisotropic deformation of the specimen, providing a full strain path history along the axial length of the specimen. Electron backscatter diffraction analysis was performed on the pre and post-deformation specimen with comparisons made between the deformed and undeformed microstructures.