Quantitative evaluation of mechanical properties of machined surface layer using automated ball indentation technique

Machining-induced microstructure alteration in the machined surface layer possibly tends to result in the change of mechanical properties in this area that are different from the bulk material. It is very important to evaluate quantitatively mechanical properties of machined surface layer. In the present research, the nondestructive automated ball indentation (ABI) technique equipped with stress-strain microprobe system was employed to evaluate the mechanical properties of the machined surface layer generated by hard milling of AISI H13 steel. Through performing ABI tests, the mechanical properties including the true stress-strain curve, yield strength, ultimate tensile strength (UTS), strain hardening exponent and Brinell hardness were quantitatively acquired before and after hard milling. In addition, the fracture toughness can be determined by analyzing the continuous loading and unloading curves on the basis of the continuum damage mechanics (CDM). It indicates that the ABI technique can be exploited as a nondestructive technique for mechanical property evaluation of machined surface layer.