Interferometric 45° and 60° strain rosettes measuring.
A laser-based technique, referred to as interferometric strain rosettes for measuring three in-plane strains, is presented. The strain rosette consists of three microindentations produced on a specimen surface and can be of two separate forms. The two forms are 45° and 60° rosettes for indentations located at the vertices of a 45° right triangle and an equilateral triangle, respectively. The three indentations for either form can be grouped into three pairs. When the indentations are illuminated with laser light, each pair of indentations acts like a two-point source generating a pair of Young's interference fringe patterns. The fringe spacing is inversely proportional to the separation of the indentations. Because strains cause the separation to change, the fringe spacing also changes. The fringe change is monitored with linear-array diodes and collected real time through a microcomputer system. The three strain components in the directions of the indentation pairs can then be obtained.
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