Revolutionary Materials Research Technology for High-Strain-Rate Ordnance Research

Air Force weapons designers require in-depth knowledge of high strain rate response of ductile materials so they can tailor the performance of multi-mode warheads. The Split Hopkinson Bar technique (SHB) is the most commonly used technique for measuring the mechanical properties of materials (stress-strain curves) at strain rates ranging from 200 to 5000 s-1. A critical requirement for obtaining the correct stress, strain rate, and strain in the specimen from the recorded stress waves in a SHB test is that the specimen is in equilibrium and the state of stress and deformation in the specimen is uniaxial and uniform. The objective of this project is development, performance testing and delivery of a 3D image correlation system using digital high speed cameras that obtains full-field strain maps at data acquisition rates of up to 250,000 frames per second. In Phase I, strain concentrations around a 0.0625” diameter hole in a copper specimen were clearly visualized and quantified, and necking evolution was profiled at 10 microsecond increments on a dogbone specimen. Phase II will include standard benchmark performance tests and standards, examples of model to experiment validation techniques and results, and measurements of material behavior under various loading conditions and geometries.