Void submodel

For a spherical void of diameter d, the surface tension T at the void composite interface is a function of the pressure inside the void Pv and the pressure surrounding the void P (Eq. 13.19) 

The surface tension is found from an empirical formula and is a function of temperature (determined in the thermochemical submodel). The surrounding pressure P is determined in the resin flow or compaction submodels. The pressure within the void is determined by the partial pressures of the water vapor and air within the void. The mass of water vapor within the void changes during processing and can be described by Fickian diffusion across the void-composite interface [29], Once the mass of vapor inside the void and the pressure at the location are known, the change in void size can readily be calculated from Equation 13.19. Changes in void size are halted when the resin has solidified. 

If the initial void volume fraction and average initial diameter d0 are known, the final void volume fraction vv can be calculated [34]. 

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Void Submodel Changes in void size associated with processing conditions are quantified in this submodel. 

Solutions to these equations yield the temperature distribution inside the mandrel and inside the composite as a function of time. Degree of cure or crystallinity and matrix viscosity in the composite as a function of time are also determined. This model is the building block for the other submodels. Viscosity calculations are input to the fiber motion submodel. Temperature and cure calculations are input to the stress submodel. Temperature data are also input to the void submodel. 

In process modeling of filament winding, regardless of matrix material, the process is considered to consist of several simultaneously occurring subprocesses winding, application of heat and/or pressure, consolidation, and void evolution [16], The process model is consequently broken down into several submodels, each with a distinct function, and each coupled to one another ... 

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