Fig. 1 FCG in PVC pipe grade material tested at 1Hz at 20oC. a) rates as a function of ΔK and b) Kmax. c) ΔK-R plots for selected crack growth rates and d) ΔK-Kmax plots showing an L-shaped type of behavior with limiting values of ΔK* and Kmax*. e). The crack growth trajectory map in terms of ΔK* and Kmax*.
Fig.2a. The data spread is more extensive in terms of Kmax than in terms of ΔK. The ΔK-R plots at low crack growth rates, Fig. 2c, seem to indicate two mechanisms governing the behavior, one at low R and the other at high R. The corresponding ΔK-Kmax plots, Fig. 2d, indicate the possible two L-shaped curves corresponding to the two mechanisms involved. Fig. 2e shows the crack growth trajectories at both test frequencies. The two mechanisms operating at a higher frequency are shown, one following the pure fatigue behavior with ΔK=Kmax, and the other deviating from