DETERMINATION OF TEMPERATURE RISE DURING HIGH-STRAIN RATE DEFORMATION

The energy converted to heat during high strain rate plastic deformati on is measured directly using an infra-red method for Ta-2.5% W alloy and, indirectly, using UCSD's recovery Hopkinson bar technique for the same alloy, as well as for commercially pure Ti, 1018 steel, 6061 Al and OFHC Cu. The infra-red measurement yields a 70% conversion of work to heat for Ta-2.5% W and generally underestimates this factor for al l tested materials. The final temperature at a given strain can be det ermined indirectly, based on the calculated plastic work. For this, th ree separate measurements are made: First, a sample is deformed at a h igh strain rate to a total strain of, say, 60%; this is essentially an adiabatic test. Then a second sample is deformed at the same strain r ate to about 30% strain; this should reproduce the first half of the p revious adiabatic stress-strain curve and in our test it does. This sa mple is then allowed to cool down to the initial room temperature. Thi s sample may then be heated to the temperature as was measured by the infra-red detectors and then deformed at the same strain rate to check if the adiabatic curve is traced. It is observed that only when the s ample temperature is increased based on 100% conversion of the plastic work to heat, that the original adiabatic stress-strain curve is trac ed. It is thus concluded that the infra-red detection system records a lower (surface) temperature than the actual temperature of the sample . (C) 1998 Elsevier Science Ltd.