High-Rate Micro-Compression Using an Elastic Half-Space Loading Configuration

Abstract

Recent developments in high rate micro-mechanical testing have used miniaturized Kolsky (Split-Hopkinson) Bars as the basic loading technique. These methods, which employ optical instrumentation instead of strain gages, have been used to test samples in the 20–50 μm size range at rates as high as 1 M/s. However, difficulties attributed to machining and alignment of such small systems make higher strain-rates difficult to achieve. In this work, we investigate an alternate method in which a small compression sample will be loaded rapidly against a transparent elastic half space. As the specimen deforms, it exerts what is essentially a point load on the half space, resulting in an indentation at the contact point. This indentation is measured with a displacement interferometer and in principle can be used to calculate the force applied to the sample. This can then be used to determine the stress–strain response of the specimen. Because loading plates can be made and aligned to great precision, this method has the potential to reach strain-rates as high as 3 M/s provided the force can be correlated to measured displacement with sufficient accuracy. This paper presents preliminary experimental and numerical results that illustrate the challenges in implementing such an approach.