Effect of prepreg format on defect control in out-of-autoclave processing

Abstract

Prepreg format plays a key role in part quality for composites produced using vacuum bag only (VBO) techniques. To date, however, VBO prepregs have been produced by modifying existing autoclave formats. In this work, we introduce USCpreg, a prepreg format designed specifically for out-of-autoclave cure, featuring through-thickness permeability. We describe the fabrication and analysis of laminates processed with USCpreg, as well as laminates fabricated from traditional VBO prepreg formats. The through-thickness pathways for air transport in USCpreg result in near-zero internal porosity and defect-free surfaces in parts cured under VBO conditions, even under challenging processing conditions. Results highlight the fact that surface and internal porosity depend on prepreg format, and that through-thickness permeability is critical to achieving high quality parts in non-ideal manufacturing scenarios.

Defect reduction strategies for the manufacture of contoured laminates using vacuum BAG-only prepregs

“…More complex OoA/VBO composite structures were also evaluated in previous studies. For example, Grunenfelder et al studied the void content in embedded doublers that consisted of a local build‐up of additional plies in regions of laminates and hat‐stiffeners. Results showed that voids within the embedded plies could be reduced by fostering air evacuation through prepreg plies impregnated on only one side and longer vacuum hold times before cure.…”

Effects of debulk temperature on air evacuation during vacuum bag-only prepreg processing

“…However, for most laminates comprised of UD prepregs, heated debulk is not an effective means to achieve air evacuation prior to cure. To increase transverse air evacuation efficiency in UD prepregs, prepreg formats with discontinuous resin distributions can be a more effective approach [22,23].…”

Design and application of discontinuous resin distribution patterns for semi-pregs

“…Anisotropic patterns such as stripes must be intelligently applied to ensure proper placement with reference to the fiber orientation. However, stripes may be simpler and more convenient to produce relative to other pattern designs, such as islands or grid, depending on the production method of the discontinuous resin distribution [6,7,10].…”

“…Previous work has shown that use of OoA/VBO prepregs with a discontinuous resin pattern (semi-pregs) virtually eliminates porosity caused by entrapped air or moisture, without an autoclave cure [6]. For example, Grunenfelder [7][8][9] showed that even under adverse process conditions, parts cured using semi-preg contained near-zero internal porosity and no surface defects. In contrast, conventional VBO prepreg (with continuous resin films) yielded unacceptable levels of porosity (3-8%).…”