The effects of welded clips on fatigue crack growth in AA6156 T6 panels

Abstract

Fatigue crack growth in different panels, made of AA6156 T6, was investigated experimentally and numerically. Three different types of panels were used, simple one, so-called base metal (BM), panel with 4 welded stringers and panel with 4 welded stringers and 3 welded clips. Experimental investigation indicated benefits of stringers, especially in respect to residual life, since the number of cycles were more than doubled (420 Kcyc vs 195 Kcyc for initial crack length 14 mm), but that was not the case for panels with clips (220 Kcyc). Experimental investigation was also performed on panels with longer cracks (75 mm) to check the effect of initial crack length in the case of BM and panels with 4 stringers, showing practically the same effect of stringers on residual life (95 Kcyc vs 50 Kcyc). Then, fatigue crack growth in panels was simulated numerically using xFEM. Numerical simulation indicated the same trend and effectiveness of stringers, with sufficient agreement with experimental results for BM and panels with stringers only. Anyhow in the case of clips panels with 4 stringers and 3 clips, number of cycles for panel with additional 3-clips was higher than for panel with just 4-stringer, (278 Kcyc vs 265 Kcyc), improving fatigue life for cca 5 %, contrary to experimental results.