FATIGUE PERFORMANCE ENHANCEMENT OF AWJ-MACHINED AIRCRAFT ALUMINUM WITH DRY-GRIT BLASTING

The effects of dry-grit 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 subsequently with dry-grit and AWJ blasting, decreases with the increase in Ra. Removal of the striations with dry-grit blasting only reduces the surface roughness somewhat and the resulted Ra is still higher than that of the conventionally machined edges. 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 specimens by more than three times. Similar trend is observed for AWJ-machined specimens followed by AWJ blasting. The extraordinary boost in the fatigue performance could be attributed to the induction of residual compressive stresses by dry-grit and AWJ blasting and was subsequently confirmed experimentally. Dry-grit blasting could be carried out efficiently and cost effectively by stacking and the benefits gained from this secondary process simply outweigh the marginal cost increase. Therefore, waterjet technology combined with dry-grit blasting has the potential of not only lowering the costs for manufacturing aircraft aluminum but also significantly enhancing the fatigue performance.