MICRORADIOGRAPHIC STRAIN-MEASUREMENT USING MARKERS

A method for measuring strain on interior planes of some real structur al materials is presented. X-ray images are formed of small (10-40 mic ron) gold markers placed on selected interior planes of optically opaq ue X-ray transparent materials. The use of well collimated monochromat ic synchrotron radiation makes possible high contrast images of the sm all markers. Images of the particles before and after straining are re corded photographically. Photographs are enlarged 33X and measured usi ng a simple electro-optical setup. In calibration experiments using ap proximately a 300-micron gage length, the strain measured by this meth od agreed with extensometer measured strains to within 100 microstrain . Example applications in a graphite-epoxy composite are presented, in cluding measurement of the strain drop off near the free edge, strain concentration around a hole, and the strain field on a particular plan e near a hole after local delamination. The technique is currently lim ited to materials no less X-ray transparent than titanium.