COMPARISON OF MODE-I AND MODE-II ELASTIC-PLASTIC FRACTURE-TOUGHNESS FOR 2 LOW-ALLOYED HIGH-STRENGTH STEELS

In the present work, mode I and mode II tests were carried out on two low alloyed high strength steels. An asymmetrical four point bend spec imen and J(II)-integral vs. crack growth resistance curve technique we re used for determining the mode II elastic-plastic fracture toughness , J(IIc).J(II)-integral expression of the specimen was calibrated by f inite element method. The results indicate that the present procedure for determining the J(IIc) values is easy to use. Moreover, the mode I fracture toughness J(Ic) is very sensitive to the rolling direction o f the test steels, but the mode II fracture toughness J(IIc) is comple tely insensitive to the rolling direction of the steels, and the J(IIc )/J(Ic) ratio is not a constant for the two steels, including the same steel with different orientations. Finally, the difference of the fra cture toughness between the mode I and mode II is discussed with consi deration of the different fracture mechanisms.