Process robustness and defect formation mechanisms in unidirectional semipreg

Abstract

Out-of-autoclave/vacuum-bag-only (OoA/VBO) composite processing has emerged as an alternative to autoclave cure, addressing economic, environmental, and production flexibility limitations associated with autoclave production. VBO processing can produce defect-free components under ideal processing conditions; however, adverse process conditions (e.g. poor vacuum) commonly encountered in manufacturing environments result in unacceptably high scrap rates, preventing more widespread adoption of such techniques. This work explores how modifications to prepreg format can increase process robustness. A unidirectional (UD) prepreg was produced with a customized, discontinuous resin distribution, henceforth referred to as semipreg. The semipreg exhibited through-thickness permeability orders of magnitude greater than conventional hot-melt VBO prepregs. The semipreg also was less sensitive to variations in process conditions than conventional VBO prepreg. In situ process monitoring allowed observation and identification of two defect formation mechanisms arising during cure of the custom prepreg. Resin feature topography played a critical role in these mechanisms, indicating its importance to the design of next generation VBO semipregs.

Keywords

• prepreg
• semipreg
• through-thickness permeability
• robust manufacturing
• prepreg format design
• defect formation mechanism