Strain energy density method for estimating fracture toughness from indentation test of 0Cr12Mn5Ni4Mo3Al steel with Berkovich indenter

A non-destructive indentation technique is proposed to estimate fracture toughness of 0Cr12Mn5Ni4Mo3Al high strength stainless steel with different heat treatment conditions (RH520 and TH560) with a Berkovich indenter based on strain energy density. The material damage is represented by the effective elastic modulus Ẽ, and the relations of indentation load P and effective elastic modulus Ẽ with the plastic indentation depth h _p are extracted from its given experimental indentation P-h curves. The critical damage value D ^* can be determined by the critical void volume fraction f ^*, then critical effective elastic modulus Ẽ* corresponding to D ^* can be obtained. The curves of logarithmic effective elastic modulus lnẼ and logarithmic plastic indentation depth lnh _p show approximate linear relationship. Thus the values of lnhp* corresponding to lnẼ* are determined. And the strain energy density factor S is calculated according to the equations of indentation load P, plastic indentation depth h _p and effective elastic modulus Ẽ. Finally, the values of fracture toughness K _IC of 0Cr12Mn5Ni4Mo3Al steel used in the present work are calculated based on the predicted critical value of strain energy density factor S _c by indentation tests. The computational results are compared well with experimental dates, which show the prediction of fracture toughness by microindentation is accurate.