Development of Impact Micro-Indentation Testing Machine for Evaluation of Surface Fracture

Abstract

We developed an impact-micro-indentation testing machine and measurement system on the basis of electromagnetic phenomena to measure histories of the impact load and indentation depth as well as the impact load-indentation depth curve for evaluating surface fractures. Four indenters consisting of tungsten-carbide cylindrical cones with different tip shapes and neodymium magnets were prepared. The total masses of the indenters ranged from 1 to 2 g. We conducted impact-microindentation tests on soda-lime glass plates by freely dropping an indenter onto a plate. We evaluated the effectiveness of the developed machine and measurement system based on the fact that the maximum measured indentation depths by the machine and system agreed with the maximum indentation depths on the glass plates observed after the tests when the sharp-tipped indenter collided with little fragmentation in the vicinity of the impact point. Comparing the results of the indenters with the same tip curvature, the indentation work-indentation depth curves were approximately the same up to an initial indentation stage. However, the curve slope was found to be affected by the tip angle of the indenter. These results indicate that the developed machine and measurement system are effective for evaluating surface fractures.