Modelling and analysis of the CRTM-2 process

Initial reinforcement layup, followed by compaction and resin injection, are phases common to RTM. The volume of literature devoted to RTM can thus be applied directly to these phases (e.g., references 14,15). Once the resin has been injected and the gates have been closed, wet compression is initiated. The first theoretical analyses on the compression of saturated fibrous materials were carried out by Dave et and Gutowski et in the context of autoclave processing and bleeder ply moulding. Therein it was noted the similarity between these processes and the classic geomechanics consolidation problem, that is, the compression of a water-saturated soil or clay. i The theory can be formulated in terms of Lagrangian coordinates, but is more conveniently presented for the present purposes, as in what follows, in terms of an Eulerian description.  

For composite parts which are relatively thin and saturated through the thickness, one can reasonably neglect fluid-flow in the thickness direction, particularly when the transverse permeability is very much smaller than the in-plane permeability. For this case, one can derive the fluid mass conservation equation in general three-dimensional form and then specialise it to 

It is generally accepted that Darcy s law is valid for the low-Reynold s number flow of resin through a fibrous material  

From conservation of mass for the solid component,/iVy.is constant, equal to A N/ps, where is the areal mass, p, is the fibre density and N is the number of layers. Thus, with j) = l -Vp 

In this equation, the thickness h, pressure p and permeability K are in general coupled. To relate these, one must consider equilibrium of forces within the preform. At the foundation of such an analysis is Terzaghi s principle of effective stress, which states that the effective stress 7j carried by the solid skeleton is the difference between the total applied stress a and the pore fluid pressure p  

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