39.4 Results and Discussion 39.4.1 Finite Element Results Figure 39.5a shows strain vs. percent wall loss for the full encircle and patch repairs. As expected, as the wall loss increases, the maximum strain also increases. This trend continues in the repair, as shown in Fig. 39.5b, with the composite repair strain increasing as percent wall loss increases. However, we see that the maximum strain levels in the composite repair and substrate are nearly the same regardless of the repair approach, at least for the lower wall loss values. Figure 39.6 shows the maximum strain values for a full encirclement repair subjected to a simulated pressure ramp from 0 to 14.6 MPa (2130 psi). From this simulation, the substrate begins to yield at approximately 10.3 MPa (1500 psi). Figure 39.6 also indicates that the substrate yields significantly before the repair begins to respond to the increased strains. Fig. 39.5 (a) Strain vs. wall loss for the substrate only (left), (b) strain vs. wall loss for composite material (right) Fig. 39.6 Strain response during pressure loading cycle 340 C.W. Burnworth and M.W. Keller
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