Microhardness Testing, Its Possibilities and Limitations
Abstract The need to test small awkwardly shaped rubber articles, which cannot be tested by normal methods, has led to the development of a scaled-down micro test for hardness. Attention is drawn to the mechanical problems that arise in devising such a micro test, especially those associated with friction in the moving parts and with the measurement of the very small movements of the indentor; the various ways in which these problems have been solved are described. The results of experimental work are presented to show the substantial equivalence in readings between the micro and the normal (macro) test, the good reproducibility of micro test results, the influence of testpiece dimensions, and the advantage of using a foot on the instrument as specified in ISO Recommendation R48 for the normal hardness test. Attention is drawn in particular to the influence of the dimensions of the rubber tested, showing on the one hand that reliable hardness measurements can be made, as expected theoretically, on much thinner and smaller specimens than in the standard test, though on the other hand there are minimum dimensions below which even the micro test cannot be expected to give results agreeing strictly with those of the macro test.