Stresswave® Fatigue Life Improvement Process

A new method for improving the fatigue lives of holes in metal structures has been developed. The StressWave® process provides compressive residual stresses and fatigue life improvement factors that are similar to or exceed those produced by legacy mandrel cold working processes. StressWave creates the stresses prior to machining the hole, without any pre- or extra post-processing operations. The process has been applied in a variety of alloys (aluminum, steel, titanium and cast iron) and section thickness (0.8 to 25 mm). Fatigue testing has shown life improvement factors typically five to twenty times greater than untreated open-hole specimens. Residual stress distributions have been measured by neutron diffraction and photo-elastic techniques and compared with FEA analysis to verify process parameters. Crack growth measurements and fractography have revealed the beneficial compressive residual stresses extend fatigue crack growth life. Results from experiments have validated the effectiveness of the StressWave process in improving the fatigue life of structures with holes or cutouts. Recent fatigue test results on ASTM grade 40 cast iron samples with straight and threaded holes treated by the single side StressWave™ method showed life improvement factors from 8 to 25.