Measurement of Residual Stresses in Difficult Locations

Beneficial residual stress concentrations in aircraft structures and systems are altered by service loading and temperature changes, and it is necessary to identify detrimental residual stresses. Life cycle costs are high because structural integrity andsafety concerns lead to reliance on overly conservative estimates of life cycles. Some structures and systems are difficult to access, making it impossible to inspect parts and quantitatively identify those needing repair or replacement. X-raydiffraction (XRD) is a proven and accepted method for quantitatively and nondestructively measuring residual stresses in the materials of concern. However, accessing these locations requires a much smaller instrument than those currently available. TECproposes in Phase I to (1) identify the conceptual efforts and technologies required to miniaturize an XRD measurement system, (2) quantitatively micro measure residual stresses in one material of concern, and (3) target difficult locations. A conceptualprototype will be assembled for performing proof-of-concept measurements on aluminum. Successful completion of demonstration measurements will advance the design to a prototype field usuable instrument during Phase II. This miniaturized XRD system forquantitatively and nondestructively measuring residual stresses in a variety of materials has many applications in industry, government, and research.The proposed miniaturized x-ray diffraction system will be ideal for nondestructively quantifying residualstresses caused by service loading and temperature effects and for production-line inspections to monitor quality control. It can be a reliable and affordable tool for detecting faulty components in field situations and for inspecting and maintainingaircraft, land transport vehicles, ships, rails, pipelines, vessels, tanks, process systems, utility infrastructures, and many kinds of welds.