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 E∼, and the relations of indentation load P   and effective elastic modulus E∼ with the plastic indentation depth hp 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 E∼∗ corresponding to D* can be obtained. The curves of logarithmic effective elastic modulus lnE∼ and logarithmic plastic indentation depth ln hp   show approximate linear relationship. Thus the values of lnhp∗ corresponding to lnE∼∗ are determined. And the strain energy density factor S is calculated according to the equations of indentation load P, plastic indentation depth hp   and effective elastic modulus E∼. Finally, the values of fracture toughness KIC of 0Cr12Mn5Ni4Mo3Al steel used in the present work are calculated based on the predicted critical value of strain energy density factor Sc by indentation tests. The computational results are compared well with experimental dates, which show the prediction of fracture toughness by microindentation is accurate.