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.