It is highly expectable that a coupling of strain rate and temperature
also occurs under dynamic conditions, although its determination
requires further tests not available for this work. However, the overall
predominance of the temperature effects on the dynamic ones in affecting
the necking inception is ascertained here independently of the possible
further coupling above.
Failure strains under combined strain rate and temperature effects
Failure is a typically local phenomenon, so the local diameter-based
true strains at fracture should be much more appropriate than the
elongation-based engineering strains frequently adopted in the
literature, which only reflect a global volume-averaged strain
indicator.
Both types of fracture strains are reported in Table 4 for each test
family (average of two or three test repetitions), together with the
corresponding values of nominal strain rates and of estimated specimen
temperatures at fracture. In the same table are reported also the
effective / engineering strains ratio and the max postnecking true
strain (Fail – Neck).
Table
4 Strain-related variables at fracture