Development of Strain-Rate Testing and Its Implications
SourceThe application of slow dynamic straining to specimens to facilitate stress corrosion cracking (SCC) now has been in use for more than a decade, and the test is beginning to emerge as one that has much more relevance than the rapid sorting test to which its early use was related. The importance of creep effects in constant load testing is considered, and it is shown that reasonable predictions of threshold stresses for SCC can be made from relevant creep data and that the effects of prior creep upon the incidence of cracking and of the phenomenon of nonpropagating cracks below the threshold stress are all in agreement with the concept of the crack tip strain rate playing a major role, even under constant load conditions. The reasonable correlation between appropriate strain rate and constant load tests is therefore not surprising, nor is the reduction in threshold stress by dynamic straining, with or without cyclic loading, over that observed for constant loads.