Study on the composite strengthening with laser shock processing and ultrasonic extrusion strengthening for small hole components

As a method of strengthening small-holes components, laser shock processing (LSP) exhibits thickness effect and uncertainties in the strengthening effectiveness when applied to thicker materials. To overcome this disadvantage, in this study, ultrasonic extrusion strengthening (UES) and laser shock processing (LSP) were combined to form a new composite strengthening method - laser shock processing and ultrasonic extrusion (LUE). Under certain process conditions, a comparative analysis was conducted on the fatigue life benefits and strengthening mechanisms of three strengthening methods. The results demonstrated that, under the process parameters of this study, compared to single-process treatments, LUE specimens showed 3-4 times higher average fatigue life gain. The residual stress distribution in the LUE specimens was more reasonable, and the morphology of fatigue fracture differed completely from that of a single LSP or UES specimen. The main crack source was located far away from the hole, with a radial crack source zone. The stable crack propagation rate of fatigue cracks was significantly lower than that of single-process treatments, effectively suppressing the initiation and propagation of fatigue cracks. This study proposed the method of combining LSP and UES, revealing the mechanism through which LUE improves the fatigue life of small-hole components.