Compressibility and relaxation of a new sandwich textile preform for liquid composite molding

Abstract In liquid composite molding, such as RTM or SRIM, the dry reinforcement is first compressed in the mold, and then the resin is injected into the mold cavity and cured. Knowledge of the compressibility of the reinforcement is important in order to estimate the mold closing force and the attainable range of fiber volume fraction. Moreover, in a lay‐up composed of several types of fabrics, the compressibility of each fabric should be known to predict the thickness of each fabric layer, which is a prerequisite for the mold filling simulation. In this work, the relaxation and compressibility of a new sandwich fabric, Multimat®, and its components (a weft knit and a random mat) were studied and compared with a woven fabric. The different fabric relaxation behavior is explained in terms of fabric stiffness and volumetric dissipation energy. Fabric compression tests were performed by taking the fabric relaxation behavior into account. Fabric compression curves are fitted with the power law equation and agree well with the clamping pressure experimentally measured with a pressure transducer in an RTM mold. The influence of the number of layers was also investigated. Finally the compressibility of the Multimat is correlated to its components with a simple model.