Autoclave Processing AP

Autoclave processing is a process in which individual prepreg plies are laid up in a prescribed orientation to form a laminate (Fig. 5.9). The process involves consolidation of the laminate, which generally results in a three-dimensional flow field. Similar to the IP process the fiber bed is not stationary in the AP process hence, its movement has to be specifically considered when the appropriate conservation equation for this process are developed. If it is assumed that the resin has a relatively constant density (i.e., the excess resin is squeezed out before the gel point is reached) then the appropriate conservation of mass equation for this consolidating system is Equation 5.12. 

An energy balance equation for this system can be obtained by simplifying Equation 5.41 using the same assumptions used earlier (i.e., (Uf) = 0, V (Ur) = —dsr/dt and V (Uf) = der/dt). 

In summary, the appropriate governing equations for transport of mass, momentum, and energy in the AP process are  

The viscosity fi can be described by Equations 5.42 or 5.43, depending on whether a Newtonian or a generalized Newtonian viscosity model is required to describe the resin rheology. 

To solve the preceding set of equations, Equation 5.62 is plugged into Equation 5.60. By separately determining the compaction properties of the fiber bed [32] an evolution equation for the pressure can be obtained. Because this is a moving boundary problem the derivative in the thickness direction can be rewritten [32] in terms of an instantaneous thickness. The pressure field can then be solved for by finite difference or finite element techniques. Once the pressure is obtained and the velocity computed, the energy and cured species conservation equations can be solved using the methodology outlined in Section 5.4.1. 

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