Autoclave flow compaction

Key words autoclave processing, process modelling, flow, compaction, heat transfer, cure, dimensional control, residual stresses, cure cycle. 

The boundary conditions that may be simulated with the flow-compaction module are autoclave pressure, impermeability or permeability with prescribed bag pressure, no displacement or no normal displacement (tangent sliding condition). The governing equations (Eqs [13.3] and [13.4]) are coupled during individual time-steps of the transient solution. A Newton-Raphson iterative procedure is used to solve the resulting nonlinear system of equations. Details in the solution of the flow-compaction for autoclave processing can be found in reference 17. 

Very briefly, the Dave model considers a force balance on a porous medium (the fiber bed). The total force from the autoclave pressure acting on the medium is countered by both the force due to the spring-like behavior of the fiber network and the hydrostatic force due to the liquid resin pressure within the porous fiber bed. Borrowing from consolidation theories developed for the compaction of soils 22 23), the Dave model describes one-dimensional consolidation with three-dimensional Darcy s Law flow. Numerical solutions were in excellent agreement with closed-form solutions for one- and two-dimensional resin flow cases in which the fiber bed permeabilities and compressibility, as well as the autoclave pressure, are all held constant21). 

Resin Flow Submodel. Resin flow analysis in a manufacturing process provides estimates of resin flow, and fiber and resin distribution and compaction. In the early stage of the autoclave process, after the prepregs are staked and vacuum hagged, the system is pressurized while the temperature is increased in order to minimize the resin viscosity. In this way the resin flow removes the excess resin from adjacent plies and makes uniform the fiber distribution. In the RTM process the dry fibers inside the mold can be considered as a porous medium through which the resin is injected from a single or multiple inlets Darc/s law can he used to perform a two-dimensional flow analysis. Darcy s law can he written as... 

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