Strain rate dependence of Ti64: Characterisation of mechanical properties up to failure using novel optical techniques

Two methods for the improved characterisation of anisotropic materials are presented. One method utilises three optical videos of cylindrical specimens undergoing uniaxial loading to reconstruct elliptical cross-sectional contours. This information can be used to improve knowledge of anisotropic plastic deformation behaviour. A second method uses digital images of specimens to perform the task of a video extensometer. Through the high resolution imaging of specimens, the undulations due to machining can be seen in edges detected to sub-pixel accuracy. These edges have unique variations along their length that may be tracked to provide high density strain data without occlusions due to the marking required by other methods. The cross-section reconstruction has been applied to rolled Ti64 at strain rates of ~10-3 s -1 , ~1s-1 and ~103 s -1 in compression and tension experiments. Three views have been obtained using both multiple camera rigs and mirrors. The strain measurement through edge tracking has been applied to specimens loaded at ~10-3 s -1 using high resolution imaging

Strain rate dependence of a super-elastic NiTi alloy

The response of a super-elastic NiTi alloy to mechanical deformation has been investigated in tension and compression at strain rates of 10−3 and 103 s−1. The effect of loading direction has been understood through the nature of the phase transformation in the material, whilst comparison of quasi-static experiments at elevated temperatures to the response of the material at high strain rates provides better understanding of the importance of adiabatic heating in high strain rate loading

Experimental characterisation of the strain rate dependent failure and damage behaviour of 3D composites

Two through-thickness angle-interlock (TTAIL) 3D weaves especially designed to minimise crimp and with different binder volume fraction (3% and 6%), but otherwise identical architecture, have been characterised at quasi-static and dynamic loading. The aim of this work was to assess the suitability of different experimental techniques to investigate the effect of through thickness reinforcement on failure and damage behaviour of thin 3D reinforced composite plates, providing data that ultimately can be used to validate a numerical modelling strategy. It was found that there was little difference between the materials in terms of in-plane properties; however, the impact resistance of the 6% material was significantly increased. Furthermore, a noticeable difference between the interlaminar shear behaviour in warp and weft direction was observed. Therefore, it can be concluded that for a given weave architecture, a higher binder tow size (in this case 6%) can be used without compromising the in-plane response

Taylor impact experiments on Ti-6Al-4V specimens using 3D geometry reconstruction and instrumented target rods

This paper describes results from Taylor impact experiments on specimens cut from a Ti-6Al-4V plate. High-speed photography and a mirror arrangement are used to obtain images of the specimen from three views. The positions of the edges of the specimen in these images are then used to fully reconstruct the specimen surface in 3D, allowing the real-time anisotropic deformation of the specimen to be studied. Further to this, the traditional anvil used in Taylor impact experiments has been replaced with an instrumented target bar, which enables the force at the end of the specimen to be calculated over the duration of the experiment. The results from these Taylor impact experiments are compared to Finite Element simulations using an anisotropic material model