DYNAMIC FRACTURE-TOUGHNESS (DFT) OF BANDED HSLA STEELS

Dynamic fracture toughness (DFT) evaluation by instrumented impact analysis has been emerging as a time- and material-conservative technique. The present investigation attempts to assess DFT of a high strength low alloy (HSLA) steel showing alternate layers of ferrite and pearlite in microstructure. The banded microstructure has given rise to an irregular stable crack front which shows spikes and splits. Three approaches to evaluate DFT, namely, premaximum energy, compliance changing rate (CCR), and the low blow test method, have been analyzed and compared to assess applicability in the case of irregular crack front. The curve fitting analysis of data justifies the power law fit to give conservative DFT values. The effects of a/w and impact velocity have been investigated. Attempts have also been made to calculate dynamic CTOD from load-displacement curves. Single specimen CCR technique obviates the need for stable crack growth (Delta a) measurements and predicts conservative DFT values comparable to DFT values obtained from the low blow test method.