PSI - Issue 5

Nikolai Kashaev et al. / Procedia Structural Integrity 5 (2017) 263–270 Jin Lu et al. / Structural Integrity Procedia 00 (2017) 000 – 000

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The crack propagation rates calculated based on Fig. 3(a) with a 5-points-polynominal fitting method according to ASTM E647 were plotted against the corresponding stress intensity factor ranges from the FEM simulations (Lu et al., 2015b) under double logarithm (Fig. 3(b)). The data points of both flat and crenellated panels of AA2139 fall into the same linear band as characterized by Paris Law whereas the data points for panels of AA2198 are located in a lower and broader scatter band. The crenellated panel of AA2198 generally has lower crack propagation rates at the same  K compared to the flat panel. At low  K range (< 15MPa ⋅ m 1/2 ), the da/dN values of AA2198 panel tend to be the same as those of the panels of AA2139. The same trend was also found at high  K range (> 35MPa ⋅ m 1/2 ), where the da / dN values of all the panels tend to be the same.

Fig. 1. (a) Flat and crenellated structure with the same weight, (b) geometries of crenellation patterns in this study, (c) experimental set-up and (d) mounting of  5 clip gauge at the crack tip.

Fig. 2. Microstructures of (a) AA2139 and (b) AA2198; Pole figures of (c) AA2139 (sheet center), (d) AA2198 (sheet center) and (e) AA2198 (sheet surface). During the fatigue tests, the crack opening load was measured every time when the crack extended by another 2 mm. Average crack opening load, S op , in major loading axis was calculated for the four tested specimens: F op = 46 kN (flat AA2139), F op = 46 kN (crenellated AA2139), F op = 50 kN (flat AA2198) and F op = 57 kN (crenellated AA2198). Both the flat panel and crenellated panels of AA2139 have the same averaged crack opening load, whereas for the case of AA2198 alloy the averaged F op is significantly higher in the crenellated panel compared to the flat panel.