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Investigation of the Thermomechanical Coupling Strength in High-Rate Plastic Deformation Processes

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Final rept. 15 Jun 2006-14 Jun 2010

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An advanced understanding of thermoplastic heating process in dynamic deformation events is one of the key steps which not only enhances design and analysis capabilities but also may lead to development of new material systems with unprecedented impact and blast protection performance. The main objective of this project is to develop reliable and repeatable experimental data to serve this purpose and develop predictive models for the fraction of plastic work converted into heat i.e., thermo-mechanical coupling strength in dynamically deforming metals. This objective has been achieved by integrating high-strain-rate split Hopkinson pressure bar SHPB experiments with high-speed IR thermometry measurements, and by establishing repeatable calibration procedures. The results of experiments conducted on a series of alloys, including CP-Ti, OF HC copper FCC, 1018 cold rolled steel and Al 2139-T8 alloy, have shown that thermo-mechanical coupling strength may evolve as a complex function of strain, strain rate, and deformation history. We have established that dislocation density based strain hardening models lend themselves to satisfactory prediction of thermo-mechanical coupling strength factor for most material systems with the exception of 2139-T8 aluminum alloy. The alloy 2139-T8, which is a newly developed aluminum alloy with promising properties to use in armor applications, has repeatedly showed that fraction of plastic work converted to heat is smaller than other alloy systems, and unlike other alloys this fraction does not reach to 0.9-1 interval but rather stays below 0.6 even at large plastic strains.

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  • Thermodynamics

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