PNNL

Abstract

The effects of dry-grid blasting of AWJ-machined dog-bone specimens of aircraft aluminum with aluminum oxide abrasives were investigated in terms of enhancement in fatigue performance and mitigating concerns of abrasive contamination. Results obtained from fatigue tests have indicated that the surface roughness, Ra, of AWJ-induced striations is inversely proportional to the fatigue life. The fatigue life of AWJ-machined and baseline specimens, excluding those processed with dry-grit blasting, decreases with the increase in Ra. Removal of the striations with dry-grit blasting until they disappear visually only reduces Ra from 3.5 to 2.4 ?m and is still higher than that of the conventionally machined edges with Ra = 1.6 ?m. From the surface roughness point of view, the fatigue life of the dry-grit blasted specimens should not have exceeded that of the baseline counterparts. Yet the dry-grit blasting process has extended the fatigue life of the AWJ-machined specimens and the baseline counterparts by more than four and three times, respectively. The extraordinary boost in the fatigue performance is believed to be attributed to the induction of residual compressive stresses by dry-grit blasting. Such a belief was subsequent confirmed quantitatively through measurements of residual compressive stresses. Dry-grid blasting can be carried out efficiently and cost effectively by stacking AWJ-machined parts together. The benefits gained from dry-grit blasting simply outweigh the marginal cost increase.