Dr. Lauren K. Stewart

Project Information

PI: Karagozian & Case and Lauren Stewart

Dates: March 15, 2017 - September 15, 2017

Funding: $150,000 with $30,000 to GT

Summary

First-principles codes, used for analysis of structural response to energetic events such as explosions or high-velocity impacts, require material characterization data for high strain and high strain rate loading. Materials characterization data is needed at high strains and high strain rates: 10^5 to 10^7 s^-1 to support first-principles computational tools used for prediction of fracture and fragmentation. The methods may include sensor development, instrumentation and data collection, data analysis and characterization, and/or test and experimental design. Characterization of ductile structural materials (e.g., steel and aluminum) is straight-forward when quasi-static material properties are needed, but characterizing dynamic properties it is more involved, requiring specialized testing such as a Hopkinson bar test. The technical literature indicates that Hopkinson bar tests will achieve strain rates up to 10^3 to 10^4 s^-1. Achieving the strain rates of interest in energetic events (10^5 to 10^7 s^-1) requires a light gas gun facility. Some other specialized facility may be required, the cost may be significant, and direct measurement of the material response may be challenging. Material properties of interest for first-principles modeling include elastic modulus, critical fracture tension, the Taylor-Quinney parameter, flow stress as a function of strain rate, and the plastic strain rate as a function of shear stress (which relates to the development of adiabatic shear bands). However, the basic challenge is to develop low-cost test and instrumentation methodologies that will result in empirical measurements of global and local strain and strain-rate dependence of the material properties as well as material failure limits under high strain-rate loadings.

PHASE I: Develop an innovative and cost-effective solution to the test and measurement of material properties under high strain-rate loading and large strains, including the plastic strain as well as stress and strain at failure. This may include commercially available sensor and instrumentation hardware and data analysis software in new applications and combinations, as well as new approaches and measurement devices. Approaches could involve innovative methodologies for use of existing test facilities, as well as new test designs. In order to show feasibility, demonstrate the utility of the proposed approach to measure material properties at high strain rates through modeling, simulation, and analysis.