INFLUENCES OF STRESS ON THE MEASUREMENT OF MECHANICAL-PROPERTIES USING NANOINDENTATION .1. EXPERIMENTAL STUDIES IN AN ALUMINUM-ALLOY

The influence of applied stress on the measurement of hardness and ela stic modulus using nanoindentation methods has been experimentally inv estigated using special specimens of aluminum alloy 8009 to which cont rolled stresses could be applied by bending, When analyzed according t o standard methods, the nanoindentation data reveal changes in hardnes s with stress similar to those observed in conventional hardness tests . However, the same analysis shows that the elastic modulus changes wi th stress by as much as 10%, thus suggesting that the analysis procedu re is somehow deficient. Comparison of the real indentation contact ar eas measured optically to those determined from the nanoindentation da ta shows that the apparent stress dependence of the modulus results fr om an underestimation of the contact area by the nanoindentation analy sis procedures.