DYNAMIC FRACTURE-TOUGHNESS (DFT) OF BANDED HSLA STEELS

Dynamic fracture toughness (DFT) evaluation by instrumented impact ana lysis 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 pearlit e in microstructure. The banded microstructure has given rise to an ir regular stable crack front which shows spikes and splits. Three approa ches to evaluate DFT, namely, premaximum energy, compliance changing r ate (CCR), and the low blow test method, have been analyzed and compar ed to assess applicability in the case of irregular crack front. The c urve fitting analysis of data justifies the power law fit to give cons ervative DFT values. The effects of a/w and impact velocity have been investigated. Attempts have also been made to calculate dynamic CTOD f rom load-displacement curves. Single specimen CCR technique obviates t he need for stable crack growth (Delta a) measurements and predicts co nservative DFT values comparable to DFT values obtained from the low b low test method.