High strain rate properties of structural aluminium.
A number of theories and techniques have been used in the past to determine the stress-strain relationship of metals and alloys at high strain rates of up to 2.2 x 10 per second; some of these were approximate whilst others required expensive equipment. In the present study three aluminium alloys, HE15, HE30TF and DTD5044 have been investigated due to their importance in the aircraft, motor and construction industries. En-8 steel was also investigated for the purpose of comparison.A simple new approach using high velocity compression testing in conjunction with a finite-difference numerical technique was adopted, developed, used and modified to suit different situations. Incremental compression tests were conducted on the materials to obtain the quasi-static stress-strain properties and used in the high strain rate (dynamic) deformation theoretical analysis and calculations. The final dimensions of the dynamically deformed specimens (diameter and height) obtained experimentally were plotted against impact velocity. These parameters were also predicted theoretically for given values of material constants and compared with the experimental ones. The material constants were then varied in a systematic manner to obtain the optimum agreement between theoretical and experimental results.The temperature rise during deformation, specimen size and deformation history were investigated and found to alter the material constants and therefore affect the flow stress. However the radial inertia contribution to the flow stress was investigated and found negligible. Friction was investigated and its effect was minimised by using tallow-graphite lubricant, which proved to be adequate and effective.The new approach caters for material inertia, strain hardening, strain rate sensitivity, friction and temperature rise during deformation. This technique provides a simple, inexpensive method of obtaining the stress-strain characteristics of materials at high strain rates without sacrificing accuracy.
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Sheffield Hallam University (United Kingdom).