Objective:
Verify fatigue disbound propogation models developed for constant amplitude mode I stress state to a block loading. the material is woven glass/vinyl ester composite.
Approach and Results:
Previously we developed two fatigue disbound propogation models for the opening mode stress-state under constant amplitude displacement loading (Fig. a). The models covered all the three regimes of fatigue propagation, namely threshold Paris' linear, and unstable regimes. The two equations best described the experimental data plotted in log-log and log linear scales. These equations are verified here. The block loading test was performed by stepped (interval 10k cycles) constant amplitude displacement loading. Figure b shows the intended and actual loading in terms of mode I energy release rate (GImax) normalized by mode I fracture toughness (GIc = 1.97 lb/in). For each interval of loading, there are three GImax values associated with initial, final and average crack lengths.
Significance:
Figure c shows a comparison of two equations with experimental data for 300 k cycles. All computations were done for GImax (initial). Both equations predict the experimental data very well, but Eq (2) had the best fit. Final crack length from Eqs 1 and 2 were 2.13 in and 2.15 in while the experiment had 2.13 in
