Experimental analysis of core crushing and core movement in RTM and SRIM foam cored composite parts

摘要

In liquid composite molding, SRIM can typically achieve a higher pressure than the RTM process. When molding a foam cored composite part at high flow rates using an SRIM system, the following related effects can be observed: high molding pressures, core shifting, core crushing, variable permeability and reinforcement compaction. Because of the variable permeability in such conditions, the linear Darcy law does not apply for flow simulation. Finally, all this can easily result in dry spot defects. To study the various problems occurring in the molding of foam cored composite parts, two molds equipped with pressure transducers were used. The first one was a picture frame square plaque mold. To ease the measurement of reinforcement compaction and core crushing, flat panels were molded with reinforcement on one side only. The second part was a quasi-rectangular foam cored beam with braided reinforcement all around the foam core. In this paper, it is refered as the Small Core part. With this part, reinforcement compaction, core crushing and core shifting was measured. The picture frame plaque mold was used with the RTM and SRIM processing equipment. Continuous strand mat with a constant fiber volume fraction was used with polyurethane foam of variable density. For the RTM process, Vinyl Ester resin was injected at constant pressure while for SRIM, Polyurethane resin was injected at constant flow rate. Parts were cut to measure laminate thickness and core deformation. For the Small Core mold, only the SRIM system was used with a constant flow rate. In this case the core materials used were Polyurethane of various densities. All parts were braided with +/-45 and axial (0 degrees) glass filaments. For some parts, locators were placed on the core surface to prevent its shifting. Short shots were used to observe the resin flow progression. For the picture frame experiments, the RTM process gave no significant core deformation. With the SRIM system, results showed a non-negligible core deformation at some foam densities. The SRIM system was also used with the Small Core tool. The results revealed the dominance of the core shifting and fabric compaction over core crushing. The use of locators placed on the core surface led to a better flow progression and nearly eliminated the core shifting, resulting in a part without defects. The flow simulation software RTMFLOT developed in our laboratory and based on a linear Darcy Law was used with these complex cases. The simulation results gave a good approximation of the gate pressure during filling. [References: 13]