Mechanics of bilayers: What soft matter physics can teach us about shot peen forming of aircraft wing skins*

Peening treatments (e.g., shot, laser, and cavitation peening) are ubiquitous when designing metallic parts against fatigue failure: by introducing compressive surface residual stresses that oppose crack initiation and growth, they can significantly increase the fatigue strength of treated parts. Peening induced stresses also cause distortions. Although usually seen as an unwanted side effect, these distortions can be controlled to form thin-walled structures into complex contours—a process referred to as peen forming. In this talk, we focus on modeling shot peen forming (a variant that consists in bombarding the parts with small hard shot). By analogy with thin bilayer actuated systems usually encountered in the fields of smart structures, soft robotics, and composite manufacturing, we investigate the shape and stability of peen formed parts. We also present a procedure to generate peening patterns required to form initially flat plates into a desired shape, alongside experimental validation.