Using X-ray Diffraction to Assess Residual Stresses in Laser Peened and Welded Aluminum

摘要

This thesis examines the interplay of residual stress distributions caused by welding and laser peening of marine aluminum alloy 5083. Residual stresses at welds in this alloy can cause fatigue and stress corrosion cracking in ship superstructures. X-ray diffraction was used to measure the residual stress distributions across welded and laser peened areas of welded aluminum plate. Full strain and stress tensors were measured and calculated in order to develop a fuller picture of the residual stress distribution in this complex geometry. Electropolishing was used to take residual stresses from specified depth below the surface. The tensor analysis was found to be extremely sensitive to the exact choice of diffraction angles used in the experiment, and an algorithm was developed to optimize the design of the diffraction experiment. Bi-axial stress analysis did show an increase in compressive stress from the laser peening after a couple tenths of a millimeter followed by a gradual decrease in compressive stress as depth increases.