J integral and COD fracture criteria in 40CrNiMo steel under mixed mode I+II loading

AbstractBy defining the J integral and crack opening displacement (COD) under mixed mode I + II loading, a mixed J integral fracture criterion is proposed and the relationship between the J integral and COD in 40CrNiMo steel is discussed. The mixed J integral J M and its mode I and II components J I and J II were calculated by the finite element method, while the mixed COD and its mode I and II components CTOD and CTSD were measured using a duplicated grid. The critical values J Mc and CODc for mixed crack initiation were determined by a resistance curve. The results show that mode II loading lowers both J Mc and CODc for 40CrNiMo steel. The variation of J Mcfrommode I tomode II loading is found to be in accordance with the linked equations J Mc=J Ii+J IIi;(J Ii/J Ic)+(J IIi/J IIc)=1, where J Icand J IIcare the critical J integrals of pure mode I and II cracks,and J Iiand J IIiare the mode I and II components of J Mc at arbitrary mixed KI/KII ratio respectively; the J Mc value for a given KI/KII ratio can...