Indentation technique for estimating the fracture toughness of 7050 aluminum alloy with the Berkovich indenter

A nondestructive and convenient technique was proposed to estimate the fracture toughness for 7050 aluminum alloy using an indentation system equipped with a Berkovich indenter based on the continuum damage mechanics. With the increase of indentation loads P, the material damage was exhibited on the effective elastic modulus E*. It was found that natural logarithms of the effective elastic modulus E* versus them of plastic indentation depth hp   approximated great linear relationship, the critical effective elastic modulus Ec∗ can be obtained based on the basic concepts of continuum damage mechanics using the elongation δ   of the standard uniaxial tensile tests, subsequently the critical plastic indentation depth hp∗ can be obtained using the extrapolation method. Consequently the critical indentation energy per unit area γ* can be obtained based on the quadratic polynomial fitting between the indentation load P and the plastic indentation depth hp, and then the value of the fracture toughness Kc can be obtained. Both indentation tests and conventional compact tensile tests were conducted to verify the agreement of the results.

► The fracture toughness of 7050 aluminum alloy was indicated using indentations.
► hp∗ and γ* were obtained using the extrapolation and quadratic polynomial fitting.
► The avoidance from defects during the indentation tests enhanced the Kc values.