Experimental investigation of shear fatigue behavior of composite stiffened panels with impact damage

Abstract

Shear fatigue experiments were performed to investigate the fatigue behavior and failure mechanism of composite stiffened panels. Low-velocity impact was conducted on the stiffener flange from the smooth side. Barely visible impact damage was introduced and it decreased the buckling and failure loads of the stiffened panels by 13.5% and 14.4%, respectively. The delamination and residual strength did not exhibit noticeable changes when the fatigue load level was set at 40% of shear strength after impact (SSAI). However, when it was increased to 67% of SSAI, delamination grew steadily and stiffener damage caused the delamination growth rate to temporarily increase by approximately 5-fold. A clear correlation was observed between the delamination growth and sublaminate buckling. Delamination grew over the entire web of the stiffener, resulting in the ultimate failure of the stiffened panels.