Influence of Residual Stress on Measurement of Elastic Modulus by Oliver-Pharr Method

It is common to use the Oliver-Pharr method to measure the elastic modulus of materials by nanoindentation. Numerical simulation methods were used to study the influence of the residual stress on the measurement of the elastic modulus when using the Oliver-Pharr method. Fused silica material and aluminum alloy material were selected in this study. The results show that due to the pile-up effect of aluminum alloy material during the indentation process, it had large error when measuring the elastic modulus of aluminum alloy material without the residual stress. Especially, the error caused by compressive residual stress was as high as 41. 3%. On the contrary, it had an error of 0. 9% when measuring the elastic modulus of the fused silica material without the residual stress. However, the stress state of tensile and compressive residual stress will both caused large error when using the Oliver-Pharr method. The Oliver-Pharr method had better recognition accuracy when measuring the elastic modulus of harder materials like fused silica when there was no residual stress, but it was no longer applicable to softer materials such as aluminum alloy. It was advised that the effect of residual stress should be fully considered when measuring elastic modulus of materials by the nanoindentation method.