Flow during consolidation

An important research need is to systematise ways of characterising the topology and geometry of these complex fibre assemblies. This is a prerequisite for a scientifically based engineering approach to the control of manufacture of the preform, the flow of matrix during consolidation, the design procedures and visualisation of the structure, and the prediction of mechanical performance. 

As already shown by Roberts [5], the parameter y depends only on the material and P as well on the normal stress level during consolidation pre-history. With regard to the yield locus model, Eq. (2), this consolidation stress level can be expressed by the centre stress crM.s of cohesive steady-state flow. It could be observed, that the ratio P/gm.si remains nearly constant in the whole consolidation stress range investigated, see Fig. 6. That means, the vibrated shear strength can be characterised by two parameters, the characteristic velocity y and the ratio P/ctm,s(, see Table 2. 

Fig. 9 shows the unconfined yield strength for various vibration velocities versus the major principle stress during consolidation oi. The dashed lines show the range of effective wall stresses 0 = 0]/ff of a cohesive powder arch for common values of the flow factor ff. The intersection point of Oc and oT delivers the so-called critical unconfined yield strength ac.crii-Eventually, the minimum outlet diameter to avoid bridging in a mass flow hopper bmin is directly proportional to Cc,crit- In the example, shown in Fig. 9, the critical unconfined yield strength (and hence bmin) can be strongly reduced in presence of vibrations. 

The final consolidation of the sediment is the slowest part of the process because the displaced fluid has to flow through the small spaces between the particles. As consolidation occurs, the rate falls off because the resistance to the flow of liquid progressively increases. The porosity of the sediment is smallest at the bottom because the compressive force due to the weight of particles is greatest and because the lower portion was formed at an earlier stage in the sedimentation process. The rate of sedimentation during this period is... 

In overcoming the shortcomings of the earlier models, Dave et al. [21,22] proposed a comprehensive three-dimensional consolidation and resin flow model that can be used to predict the following parameters during cure (1) the resin pressure and velocity profiles inside the composite as a function of position and time, (2) the consolidation profile of the laminate as a function of position and time, and (3) resin content profile as a function of position and time. 

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