A study of a micro-indentation technique for estimating the fracture toughness of Al6061-T6

Abstract

An indentation test is a non-destructive and easy to implement test studied in this paper to estimate the fracture toughness of ductile materials, specifically the Al6061-T6 aluminium alloy. The Berkovich indenter is adopted to generate a crack-like indent; this established technique is based on the principal concept of continuum damage mechanics (CDM) and the model of indentation energy to fracture. It is found that the relation between the effective elastic modulus and the indentation plastic depth hp during the indentation process can be exponentially fitted. Thus the critical plastic indentation depth hp* is evaluated based on the elastic modulus degradation technique and the effective elastic modulus behaviour. Consequently, the critical indentation energy per unit area γ* is determined by using the power law behaviour between the applied load and the plastic indentation depth hp. Considering the stress intensity approach and the Griffith theory, this energy per unit area value is used to calculate the fracture toughness KIC of the ductile material. The fracture toughness of Al6061-T6 is evaluated by indentation tests. Traditional compact tension (CT) tests are performed to attest the accuracy of the indentation energy approach and a numerical analysis is adopted to investigate the stress state in the indentation test. The fracture toughness obtained by the indentation test stands in good agreement with the experimental CT tests.