Thick-walled parts manufactured from thermosetting prepreg material can develop unacceptable voids, residual stresses, warpage, resin gradients and resin degradation during cure. These defects are caused by cure shrinkage, debulking, void nucleation, low resin viscosity, and exothermic energy release.
A method for prestaging thermosetting towpreg material is developed to address these concerns. This method entails an in-line manufacturing process, whereby as-received thermosetting towpreg is heated in a tunnel oven and subsequently compacted in a roller apparatus.
This process initiates cure advancement and shrinkage, raises the resin viscosity, and reduces the voids and bulk inherent in towpreg. Furthermore, moisture and volatiles are reduced in the towpreg, which can nucleate voids in a part during cure.
The goals of this thesis are to determine the feasibility of using prestaged towpreg to produce parts, and if feasible, to determine the optimum amount of prestaging. Prestaged towpreg must have sufficient drape to pass through the rollers of lay-up equipment. Reductions in towpreg “tack” and bulk also are considered.
The quality and mechanical properties of subsequently manufactured parts are desired to be equal or better than those of as-received towpreg parts. Based on these analyses, feasibility is determined, and a processing window is developed for optimal towpreg characteristics.