Plastic deformation of metals will broaden the x-ray diffraction line. The diffraction line around its peak can he approximated by a Gaussian function. The broadness of the diffraction line can be evaluated by the standard deviation, called Gaussian curve parameter (GCP), of a Gaussian function approximating the diffraction peak. Plastic strains applied to mild steels by simple and combined tension, compression, and tortion were correlated with GCP. Two kinds of GCP's were determined; the one, GCP α', was determined from the diffraction line corrected for the background counts, and the other, GCP α, was from the line uncorrected for the background, The GCP α' can be obtained from the GCP α as

α' = 0.936α + 0.011

This equation shows that the background subtraction can be omitted in determining GCP. The equivalent plastic strain ɛeq can be evaluated from the GCP a as

ɛeq - 0.000108 x 103.97α

This x-ray method allows rapid measurement of complex plastic strain without touching specimens.