Application of Continuous Multiple Loading with Spherical- Tip Nanoindentation to Mechanical Property Evaluations of Industrial Materials

 There are increasing demands for measuring mechanical properties of small volumes of metal or smallsized materials used for Micro-Electro-Mechanical-Systems (MEMS). This is basically because such mechanical properties are closely related to the strength and reliability of the metal or systems. In this work, a nanoindentation technique with a spherical-tip is applied to the evaluation of elastic-plastic properties such as stress-strain relationship of industrial materials such as steel and aluminium. A continuous multiple loading method is employed to determine the stress-strain curve. A set of 21 times of loading/unloading sequences with increasing terminal load are made and load-displacement curves with the different terminal loads from 0.1 mN to 100 mN are then continuously obtained and converted to a stress-strain curve. The influence of measurement condition on the obtained stress-strain curve is examined and an appropriate condition is determined. Based on the examinations, stress-strain curves have been estimated for steels and aluminium. It has been found that the estimated stress-strain curves correlate closely with those measured by tensile or compression tests when the influence of the residual stress of the specimen surface is taken into account. In addition, some issues affecting the results are discussed.