Using cavitation peening to enhance the fatigue strength of duralumin plate containing a hole with rounded edges

• The fatigue life of Duralumin plates (made of JIS A2017-T3) containing holes with rounded edges was investigated.
• The specimens were treated by cavitation peening or shot peening.
• Cavitation peening extended the life by 2 times and shot peening did opposite.
• Roll over caused by shot peening around the hole assisted crack initiation.

The purpose of this study is to examine the effect of peening on the fatigue life of a duralumin plate containing a hole with rounded edges. To this end, duralumin plates containing holes with rounded edges with a radius of 0.5 mm were treated by cavitation peening (CP) and shot peening (SP). Fatigue tests under uniaxial tensile loading were carried out to obtain the lifetime versus applied stress curves, i.e., the S-N curves. Then, the fractured surfaces were examined using SEM. Also, a combination of residual stress measurements with electro-chemical polishing was carried out to evaluate the compressive residual stress profile with respect to the depth into the wall surrounding the hole. The results showed that the lifetime of the CP specimen was almost 25 times larger than that of the as-machined one. The fatigue strength, also, was increased by 18% by cavitation peening. In contrast, shot peening reduced the lifetime, since this caused the formation of a roll over layer at the rounded edges, from which cracks due to high stress can initiate. The effect on the fatigue strength of a plate with a hole can be explained on the basis of whether or not roll over occurs and on the residual stress profile with respect to the depth from the surface surrounding the hole.