Laser peening induced stress forming and dislocation evolution of the integral stiffened plate: fatigue crack growth behavior under three-point bending cyclic loading

Abstract

A comprehensive process of forming manufacturing and fatigue performance enhancement by laser peening (LP/LPF) was proposed for integral skin structure. The forming law for integral stiffened plate was explored, and the dislocation features of typical positions after LPF was characterized. The inhibition mechanism of crack propagation by grain refinement, dislocation evolution, and compressive residual stress (CRS) implantation in typical positions induced by LP and deformation was analyzed. The fatigue crack growth behavior and fatigue life extension mechanism under three-point bending cyclic loading mode were revealed. Results revealed that the stiffener decrease the bending curvature by 17.3 times. LP causes a fine-grained layer containing high-density dislocations, accompanied by increased and coarsened second phase. The dislocation density and second phase precipitation in the compressed region only affected by CRS decrease, and many subgrains appear. Under three-point bending cyclic loading mode, the fatigue life of LPFed samples increase by 8.6, 10.6, and 11.3 times. The compressed stiffener perpendicular to crack increase the distance and area to inhibit propagation, and overlapping spots induced rough surface “guides” the deviated crack return. High-density dislocations and compressed fine grain layers implanted by LP and deformation have dislocation strengthening, fine grain strengthening, and compression toughening effects.