残余应力对Oliver-Pharr方法测量弹性模量的影响

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

Oliver-Pharr方法是利用纳米压痕测量材料弹性模量最常用的方法。选用石英和铝合金两种材料,采用数值模拟法研究材料内部残余应力对Oliver-Pharr方法测量弹性模量的影响。结果表明:由于铝合金在压入过程容易产生pile-up突起现象,Oliver-Pharr方法测量铝合金材料的弹性模量在无残余应力状态下误差较大,当有残余压应力时误差高达41.3%;对于石英材料,Oliver-Pharr方法测量石英材料弹性模量在无残余应力时误差为0.9%,残余拉、压应力都会产生较大的误差。Oliver-Pharr方法在无残余应力时测量类似石英这种较硬材料的弹性模量具有更好的识别精度,而对铝合金这类较软的材料则不适用。在利用纳米压痕法测量材料弹性模量时应充分考虑残余应力的影响。

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when measuring the elastic modulus of harder materials like fused silica when there was no residual stress,but it was no longer applicable to softer materials such as aluminum alloy.It was advised that the effect of residual stress should be fully considered when measuring elastic modulus of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.