This is indicated by the delay between the onset of yielding in the substrate and the slope change in the repair strain response. Factors impacting the efficiency of load transfer between the substrate and repair are still being studied. Based on the function of the dimensional restoration putty as central to efficient load transfer from the substrate to the repair, a set of simulations were performed to investigate the impact of bulk modulus on repair strain. The hypothesis being that a load transfer material that is nearly incompressible would lead to more efficient load transfer. For these simulations, bulk modulus was varied by fixing the elastic modulus and varying the Poisson ratio from 0.25 to 0.48. As shown in Fig. 39.7, increasing bulk modulus leads to increasing repair strain, however the variation in strain is very small, only 1.26 % from a Poisson ratio of 0.25 to a Poisson ratio of 0.48. However, a comparison of a pressurization simulation for a system with a Poisson ratio of 0.25 and a system with a Poisson ration of 0.48 indicates that the Poisson ratio has very little impact on the onset of significant load transfer. Studies are ongoing to determine the critical parameter that governs the efficiency of the load transfer (Fig. 39.8). Fig. 39.8 Comparison of Poisson ratio and strain during a pressure cycle Fig. 39.7 bulk modulus vs. strain plotted for both repair types 39 Performance of Patch and Full-Encirclement Bonded Composite Repairs 341
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