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

An indentation test is a non-destructive and easy to implement test studied in this paper to estimatethe fracture toughness of ductile materials, specifically the Al6061-T6 aluminium alloy. The Berkovichindenter is adopted to generate a crack-like indent; this established technique is based on the principalconcept of continuum damage mechanics (CDM) and the model of indentation energy to fracture. Itis found that the relation between the effective elastic modulus and the indentation plastic depth hpduring the indentation process can be exponentially fitted. Thus the critical plastic indentation depthh∗pis evaluated based on the elastic modulus degradation technique and the effective elastic modulusbehaviour. Consequently, the critical indentation energy per unit area * is determined by using thepower law behaviour between the applied load and the plastic indentation depth hp. Considering thestress intensity approach and the Griffith theory, this energy per unit area value is used to calculatethe fracture toughness KICof the ductile material. The fracture toughness of Al6061-T6 is evaluated byindentation tests. Traditional compact tension (CT) tests are performed to attest the accuracy of theindentation energy approach and a numerical analysis is adopted to investigate the stress state in theindentation test. The fracture toughness obtained by the indentation test stands in good agreement withthe experimental CT tests.