Effects of laser ablation coating removal (LACR) on a steel substrate: Part 2: Residual stress and fatigue

The effects of laser ablation coating removal (LACR), from high strength shipbuilding steel, on fatigue performance have been investigated relative to abrasive blasted specimens. It was shown that the fatigue behavior of the steel subjected to LACR is statistically unchanged from those of the baseline material. Residual stress, surface roughness and fractographic analyses were employed to rationalize the fatigue performance. X-ray measurements revealed that tensile residual stress was induced in the surface by LACR. However, depth-resolved residual stress measurement showed that the tensile residual stress is limited to a shallow depth below which there is a deep case of balancing compressive residual stress. Finally, scanning electron microscopic (SEM) analysis of fracture surfaces showed that cracks initiated from valleys in the roughness profile. Thus, the observed fatigue performance is attributed to the combined effects of residual stress and surface roughness.