A DIFFRACTION GRATING METHOD FOR MEASURING ELASTIC-PLASTIC SURFACE STRAINS IN METAL SHEETS.

A procedure is developed for making strain measurements from small, separate, plane diffraction gratings ruled as integral parts of the surfaces of flat metal specimens. Choice of a particular diffraction-strain relationship and the use of master gratings in conjunction with diffraction gratings to be used as strain gages permits use of simple optical instrumentation. Strain measurements resolution and deviation from that of other techniques are examined. The optical diffraction technique in the form employed permits resolving strain increments of magnitude 0.0008 in the range 0.003 to 0.030. Strain measurements are recorded and analyzed from Mar-aging steel specimens containing centrally located notches subjected to axial tension.