Comparison of mode I and mode II elastic-plastic fracture toughness for two 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 specimen and JII-integral vs. crack growth resistance curve technique were used for determining the mode II elastic-plastic fracture toughness, JIIc· JII-integral expression of the specimen was calibrated by finite element method. The results indicate that the present procedure for determining the JIIcvalues is easy to use. Moreover, the mode I fracture toughness JIcis very sensitive to the rolling direction of the test steels, but the mode II fracture toughness JIIcis completely insensitive to the rolling direction of the steels, and the JIIc/JIcratio is not a constant for the two steels, including the same steel with different orientations. Finally, the difference of the fracture toughness between the mode I and mode II is discussed with consideration of the different fracture mechanisms.