A portable X-ray diffraction system was used to measure strain in 7039-T6, 6061-T6, and 2014-T6 aluminum alloy sheet stock, with X-ray elastic constants determined for these alloys. Residual stress estimates have been made as a contribution to the failure analysis of cracking in production parts.
The procedure used to make the stress estimates involves surface preparation by electropolishing, the preparation of three focused, back reflection photographs, data collection by microphotometer, and interpretation of the data by the “sin2 Ψ method.” A computer program has been written to calculate the slope of the line, Δd/d0 versus sin2 Ψ, from the positions of the lines on the films.
The crystalline structure of 2014-T6 aluminum alloy sheet stock is such that a large specimen sampling is required to obtain suitable strain measurements. The peculiarities of this material and the resulting effects are discussed, as well as the contribution of X-ray stress measurements to a stress corrosion study involving a launch vehicle part.