MODELING THE DEFORMATION OF THERMOFORMABLE RANDOM FIBER REINFORCEMENTS DURING PREFORM MANUFACTURE

Liquid molding processes have been identified by the automotive and ae rospace industries as having potential for structural and semistructur al applications. Of the several obstacles to their more widespread use , the major drawback is the lack of an automated and reliable technolo gy for producing reinforcement preforms. Current preform technology is usually based on the forming of continuous fiber mats or fabrics betw een matched molds. This can result in defects within the fiber structu re including wrinkling, thinning, and, in extreme cases, tearing. To u nderstand and eliminate these defects, it is necessary to develop a si mulation of the preforming process. This paper is aimed at developing a mathematical model of the deformation of thermoformable continuous f ilament random mat. The analysis presented is based on plasticity theo ry, suitably modified to describe the behavior of fiber reinforcements , This is demonstrated for the stretch-forming of reinforcement using arbitrary axisymmetric punch and die profiles. Experimental work is in cluded to demonstrate the effect of varying a range of process paramet ers, including rate of forming, reinforcement temperature, and stack t hickness. The validity of the model is demonstrated for a number of pu nch geometries.