Volume 20, Issue 6 (November 1992)
An Evaluation of the Impression Test for Estimating the Tensile Properties of Metallic Materials
The load versus displacement response of a flat-ended cylindrical indenter when pushed into a material at a constant displacement rate, termed the “impression test,” and originally used as a measure of the compressive flow curve of metals, has also been used for estimating the tensile properties of metallic materials. The validity of this test method for determining tensile properties has been studied for five different materials of widely differing tensile flow behaviors. It is demonstrated that the impression test, like all indentation or hardness tests, can be used for the estimation of tensile properties of metallic materials only under very restrictive circumstances. In particular, the test cannot be relied upon alone without calibration and verification by actual tension tests, as it is insensitive to variations in tensile ductility. It was possible, with empirically defined relationships, to obtain reasonable estimates of the tensile yield stress for most of the materials studied. For true tensile strengths of metallic materials the method was less successful. In the case of heterogeneous materials of limited tensile ductility, such as gray cast iron or some particulate reinforced metal matrix composites, the test failed to give a valid characterization of tensile properties. Additionally, it was found to be insensitive to the upper and lower yield point associated with the initiation and propagation of a Luders band which is commonly observed in annealed low-carbon steels.