Void stability map

Figure 6.5 Equilibrium void stability map for a typical epoxy resin system. Curves indicate stable void equilibrium states for liquid-resin pressures indicated. Growth takes place above the lines and dissolution occurs below the lines for any given resin pressure...

A plot of Equation 6.32 for two relative humidities (50 and 100%) yields a void stability map, which is shown in Figure 6.10. It is evident from this map that vacuum can be applied... 

Figure 6.10 Void stability map for pure water void formation in epoxy matrixes. Note the significant effect of initial relative humidity exposure of the resin...

A plot of Eq. (32) for two relative humidities (50 and 100%) yields a void stability map which is shown in Fig. 10. It is evident from this map that vacuum can be applied without encouraging void growth if such application is coordinated with the temperature of the system. Brown and McKague 14) have experimentally observed that the void content is reduced significantly when pressure is applied to the prepreg early in the cycle, which is in accordance with the stability map. 

A pressure-temperature stability map can be constructed as a function of humidity exposure, which identifies the resin pressure values for each temperature below which void growth is possible and above which voids cannot grow but rather tend to collapse via dissolution. 

Based strictly on equilibrium considerations, bounds can be set on the stability of voids as a function of temperature and pressure. Although this type of phase map does not depict the time dependency of an actual process, it does provide a limiting scenario toward which the actual process would be heading at any point in the curing cycle. It is surprising that high void pressures are possible if sufficient moisture is present in the resin. 

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