Possibility to Estimate Fracture Toughness of Ductile Steel Materials from Small Punch Test Data

This paper presents a procedure to predict fracture toughness of steel material using small punch test (or notched small punch test) and finite element (FE) damage analysis. Tensile property can be determined from setting the constitutive equations and can be validated by comparing the small punch (SP) test data with FE results applying the determined tensile property. FE damage analysis used in this paper is based on the strain-based fracture model. Material constants in the model are normally determined from analyzing notched bar tensile tests. To determine these material constants from SP test instead of notched bar tensile tests, simplified model (with only one material constant) can be introduced and used in the simulations. SP test and notched small punch (NSP) test are simulated via FE damage analyses using the tensile property and simplified strain-based fracture model. NSP simulation results are sensitive to element size. However, SP simulation results are not sensitive to element size. Compact tension (C(T)) test is also simulated and it can be found that the proper element size for C(T) simulation is four times of that for NSP simulation to predict cracking initiation toughness.