Analysis Of Load-Displacement Curves Of Ceramics Measured With Low-Load Hardness Test

The main aim of this paper is to analyze the load-displacement curves of ceramicsmeasured with low-load Vicerks hardness test. The samples was loaded and unloadedcontinuously to recode the load and displacement, so we need to use thenanoindentation theory to analyze experimental datas. The hardness and elastic modulusof the test materials could be acquired by analyzing and fitting the unloding portions ofthe load-displacement curves of the test materials gained under low-load continuousloading condition.The samples were also tested in nanoindentation experiment, microscopic-Vickers-indentation experiment and traditional low-load static Vickers experiment. Thereliability of test results of low-load continuous loading were examined by comparingwith that of three kinds of experiments. The true hardness of the test materials indifferent kinds of experiments were calculated based on the PSR model and themodified PSR model, respectively. It was found that the true hardness of low-loadindentation experiment was nearly close to that of nanoindentation andmicroscopic-Vickers-indentation experiments, so it was demonstrated that the testresults of low-load indentation experiment were reliable. It was also found that the truehardness of nanoindentation experiment was higher than that of another three kinds ofexperiments. Moreover, the larger difference of the true hardness for same materialbetween different kinds experiments based on the modified PSR model demonstratedthat the PSR model was more suitable to calculated the true hardness of the testmaterials in this paper.Indentation size effect (ISE) usually appears in the indentation experiment. It wasfound that the inverse ISE appeared in the low-load traditional-Vickers experiment, butthe ISE appeared in the other three kinds of indentation experiments. Three kinds ofmodels were used to describe the ISE of experiments. It was found that the Meyerempirical equation could describe the ISE of experiments perfectly. Meanwhile, thevalues of the Meyer exponent n of all materials in the low-load traditional-Vickersexperiment were larger than2, which proved to show the inverse ISE. On the contrary,the Meyer exponent n of all materials in the low-load indentation experiment were smaller than2, which prove to show the ISE. The results of analysis by Meyer empiricalequation were same as the experimental results. It was suitable enough for both the PSRmodel and the modified PSR model to describe the ISE of the test materials in differentkinds of experiments. It was considered that the ISE in the indentation experimentsunder the PSR model appeared because of the a1, which stands for the elastic resistanceof samples, the frictional resistance of sample surface and the energy consumed for theformation of the new surface. Under the modified PSR model, it was demonstrated thatthe ISE appeared because of P0, besides a1. The P0stands for the surface residual stressassociated with the surface machining and polishing. It was demonstrated that these twoexplanations about the ISE were reasonable.