Revolutionary Impact of the Oliver and Pharr Method
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In 1992, Warren Oliver and George Pharr published an article in the Journal of Materials Research that revolutionized hardness testing [1]. According to Thomas Reuters Web of Knowledge, this article has been cited more than 8,500 times, making it one of the most cited works in all of material science. The genius of Oliver and Pharr was this: they devised a way to know the size of a hardness indentation without imaging it. This development disrupted Vickers and Knoop microhardness testing which required direct measurement of the lengths of the indentation diagonals [2]. Not having to image the indentation paved the way for fully automated hardness testing. Not only was automated testing independent of human bias, it was also much faster, because multiple tests on multiple samples could be prescribed and executed with no human intervention. Further, the Oliver-Pharr method extended hardness testing to much smaller scales, because one could determine the size of even sub-micron indentations with incredible accuracy. This note explains the theory of the Oliver-Pharr method and shows how it can be used to obtain an equivalent Vickers hardness number (HVc ).