SBIR-STTR Award

The development of aerospace technology is in part limited by the development and implementation of advanced materials. The challenge is to accelerate the maturation and insertion times of advanced materials to support the delivery of technically advanced systems. The precise modeling of these advanced materials and structures is only possible with accurate measurements of their real dynamic response. High-strain-rate testing of these advanced materials is limited by existing methods. Non-contact, high-speed, optical strain measurement looks to broadly extend the capabilities of the split-Hopkinson bar high-strain-rate test method, currently applicable for homogeneous, ductile materials, to be valid for the study of advanced brittle and composite materials. This capability will offer broad abilities to measure the high-strain-rate material properties at the sample, rather than inferring these properties from remote gages, reducing the limitations on materials, geometries and environments, producing better material data for the advancement of aerospace and ordinance technologies. Modern ordinace systems are operating at higher temperatures and using brittle and composite materials. This work is corner stone to the further development of these advanced materials

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 0.0625î 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.

Keywords:
Hopkinson Bar, Image Correlation, High Speed, Strain, Localization, Stress Concentration, Dyna