High resolution optical measurements of specimen deformation in the split Hopkinson pressure bar

Abstract

The use of finite element modelling, coupled to an increased interest in the mechanical properties of inhomogeneous materials, such as composites, geological and biological materials, at high strain rates, requires an improvement in the quantity of data obtained from high strain rate mechanical testing. This paper discusses a method of providing these data through the application of speckle metrology to specimens in the split Hopkinson pressure bar (SHPB). The paper describes speckle metrology, and in particular the algorithm used for the current research. It then examines the experimental application of the technique to the SHPB, including issues relating to image acquisition and data analysis. The discussion is illustrated using a polymer specimen, allowing the relative magnitudes and sources of possible errors to be visualized. A separate paper presents, in more detail, results from applying this technique to various specimens.

Keywords:

• SPLIT HOPKINSON PRESSURE BAR
• SPECKLE METROLOGY
• HIGH-SPEED PHOTOGRAPHY