VICKERS INDENTATIONS IN GLASS .1. RESIDUAL-STRESS FIELDS AND ISO-STRESS CONTOUR MAPS

This paper describes an experimental approach to measure the residual stress field around Vickers indentations in soda-lime glass. The method uses a small indentation as a microprobe to measure the residual stress at a specific position near a large indentation. Extensive experiments have been performed and the residual stresses field around a 45 N Vickers indentation were mapped. The relation between the residual stress and the distance from the indentation was determined along several specific directions from the indentation based on numerical regression. The residual stress field around the Vickers indentation is a non-equal bi-axial stress field. Both residual tensile stress and compressive stress show a power law relation with distance from the indentation. These relations are angle dependent. The iso-stress contours of both residual tensile and compressive stresses are then determined from the experiments. A self-calibration experiment, i.e. indentation on pre-stressed glass bending bars, was specially designed to confirm the accuracy of the experiments and the analysis. The present experiments and the analysis are accurate as long as the residual stress is larger than 10 MPa.