Factors Affecting Nanoindentation Test Data
In conventional indentation tests, the area of contact between the indenter and the specimen at maximum load is usually calculated from the diameter or size of the residual impression after the load has been removed. The size of the residual impression is usually considered to be identical to the contact area at full load, although the depth of penetration may of course be significantly reduced by elastic recovery. Direct imaging of residual impressions made in the submicron regime are usually only possible using inconvenient means and, for this reason, it is usual to measure the load and depth of penetration directly during loading and unloading of the indenter. These measurements are then used to determine the projected area of contact for the purpose of calculating hardness and elastic modulus. In practice, various errors are associated with this procedure. The most serious of these errors manifests themselves as offsets to the depth measurements. Others arise from environmental changes during the test and the non-ideal shape of the indenter. In addition to the above, there are a number of materials related issues that also affect the validity of the results. The most serious of these are an indentation size effect and the phenomenon of piling-up and sinking-in. The sensitivity of nanoindentation tests to these phenomena and others is a subject of continuing research.1 In this chapter, some of the most commonly encountered sources of error and methods of accounting for them are reviewed.
KeywordsResidual Stress Strain Gradient Indentation Test Specimen Material Indentation Size Effect
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