Modeling the deformation of thermoformable random fiber reinforcements during preform manufacture

Abstract Liquid molding processes have been identified by the automotive and aerospace industries as having potential for structural and semistructural applications. Of the several obstacles to their more widespread use, the major drawback is the lack of an automated and reliable technology for producing reinforcement preforms. Current preform technology is usually based on the forming of continuous fiber mats or fabrics between matched molds. This can result in defects within the fiber structure including wrinkling, thinning, and, in extreme cases, tearing. To understand and eliminate these defects, it is necessary to develop a simulation of the preforming process. This paper is aimed at developing a mathematical model of the deformation of thermoformable continuous filament random mat. The analysis presented is based on plasticity theory, 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 included to demonstrate the effect of varying a range of process parameters, including rate of forming, reinforcement temperature, and stack thickness. The Validity of the model is demonstrated for a number of punch geometries.