L. Zhang
Liberty University, Virginia, United States
Keywords: intermediate strain rate, dynamic material characterization, Split Hopkinson pressure bar, digital image correlation, material model calibration
The Center for Engineering Research and Education at Liberty University provides dynamic mechanical characterization of defense materials, from armor and structural metals to polymers, across the strain rate spectrum from quasi-static to high rate impact. Its reconfigurable direct loading platform reaches the intermediate strain rate regime, roughly 50 to 500 per second, that most laboratories cannot access. This is exactly the regime where analysts otherwise extrapolate, so closing it directly improves the accuracy of the material models behind armor, platform survivability, and structural performance. Strain is measured directly on the specimen by digital image correlation, removing the systematic error that wave theory inference introduces for ductile metals. A validated linescan extensometry method, developed by the principal investigator, is ready to deploy as a higher throughput, lower cost alternative with the same accuracy: Bland-Altman analysis shows it matches 2D DIC to within about 0.03% mean difference, while wave theory deviates by roughly 30%. Testing pairs with field emission electron microscopy, with Zeiss In Situ Lab, linking how a material is loaded to how it deforms and fails. Each engagement delivers traceable stress strain data across strain rate and temperature, plus a calibrated Johnson-Cook model ready for finite element simulation.