Analyse des surfaces grenaillées : fissuration, rugosité et contraintes résiduelles

Shot peened surfaces analysis : cracks, roughness and residual stresses

¹ PSA, centre Citroën, Vélizy
² Dépt. Structures, ENSAM, Paris
³ Dépt. Matériaux (U.A. CNRS 1219), ENSAM, Paris.

Abstract

The study of superficial cracks of shot peened surfaces in terms of coverage rate, material nature and ball diameter shows the relation between cracks and dynamic behaviour of the sample surface during the impact. The shot peened layers are not deformed quickly enough under the shock.

For the different shot peened steels, the fracture of superficial layers appears for materials such as 35CD4 (SAE 4135) and E460 which are more sensitive than others of high mechanical strength. The roughness of E460 and its cracks increase with coverage rate. In case of a long shot peening exposition, the cracks are deeper and the superficial residual stresses decrease, hence the exterior loading to enable the propagation of the surface default is small.

The classical fracture mechanics could not be applied for short cracks (10 ìm) and the mechanical characteristics of the hammered layer are unknown. We shall describe how difficult is the prediction of noxiousness of cracks using our actual knowledges.