Fig. 7 Crack growth rates in rubber toughened epoxy resin. a) in terms of ΔK and b) in terms of Kmax. c) ΔK –R plots for selected crack growth rates showing two mechanisms. d) ΔK-Kmax plots showing two L-shaped curves. e) Crack growth trajectory maps for the two mechanisms. The results are compared with the trajectory of Epoxy material tested by Osorio.
7b. From the data, ΔK-R plots are made as shown in Fig. 7c. Only one line can be drawn through the data at low crack growth rates. On the other hand, at high Rs, the data diverges into two levels indicating two possible mechanisms operating at high R values. Thus, both mechanisms seem to have the same Kmax limiting value but different ΔK limiting values. It is the first time we are observing this type of behavior. Fig. 7e shows the crack growth trajectories for