Evaluation of fracture toughness of thin sheet of interstitial free high strength steel through critical crack tip opening angle (CTOAc) measurement

Conventional testing of fracture toughness measurement for thin metallic sheets is not possible owing to the large plastic zone ahead of the crack tip. Hence, the critical-crack tip opening angle has been considered to be the key parameter to evaluate resistance of a thin sheet against stable crack propagation. In the present work, attempt has been made to measure the of interstitial free high strength steel (IFHS) with 1 mm thickness using compact tension C(T) specimen. A high speed camera has been used for monitoring and imaging the progress of the crack length and crack tip angle during loading. The CTOA measured from these photographs found to be . In these experiments, the crack tip velocity was also varied from 1.9 to 960 mm/min and no changes in the value were observed. The high ductility of IFHS steel along with prevailing plane stress condition might be the reason of appreciably large value.