Evaluation of fracture toughness of thin sheet of interstitial free high strength steel through critical crack tip opening angle (CTOA $$_\mathrm{c}$$ ) 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 $$(\hbox {CTOA}_\mathrm{c})$$ 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 $$\hbox {CTOA}_\mathrm{c}$$ 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 $$_\mathrm{c}$$ measured from these photographs found to be $$12^{\circ }\,\pm \,1.5^{\circ }$$ . In these experiments, the crack tip velocity was also varied from 1.9 to 960 mm/min and no changes in the $$\hbox {CTOA}_\mathrm{c}$$ value were observed. The high ductility of IFHS steel along with prevailing plane stress condition might be the reason of appreciably large $$\hbox {CTOA}_\mathrm{c}$$ value. [ABSTRACT FROM AUTHOR]