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ADVANCED MANUFACTURING: POLYMER & COMPOSITES SCIENCE 2020, VOL. 6, NO. 1, 38–47 https://doi.org/10.1080/20550340.2020.1728476 Effects of debulk temperature on air evacuation during vacuum bag-only prepreg processing Wei Hu and Steven Nutt M.C. Gill Composites Center, University of Southern California, Los Angeles, CA, USA ABSTRACT Air removal prior to cure is critical for limiting porosity during vacuum bag-only (VBO) proc- essing of prepregs. In this study, the effects of pre-cure dwell temperature (debulk) on air evacuation were investigated for both plain weave (PW) and unidirectional (UD) prepregs. In situ observations revealed that increasing dwell temperature promoted inter-ply air evacu- ation (by as much as 2x for UD prepregs). Through-thickness gas permeability increased with increasing temperature and decreased with increasing number of plies. The decrease in in-plane permeability during heated debulk was attributed to increased tow impregnation. The findings provide guidelines for cure cycle optimization. Heated debulk enhanced air evacuation in PW laminates, particularly as laminate width/thickness ratios exceed a threshold value. However, warm debulks were less effective, particularly for thicker laminates (>8 plies). GRAPHICAL ABSTRACT 1. Introduction Vacuum bag-only (VBO) processing of prepreg offers advantages over conventional autoclave proc- essing, including reduction of capital and oper- ational costs, a greater energy efficiency, increased throughput, and relaxation of size limits [1]. However, the maximum pressure in VBO processing is limited to 0.1 MPa (1 atm), unlike autoclaves, where the pressure can be 0.5 MPa 0.6 MPa or greater. Consequently, resin pressure and vacuum can be insufficient to collapse/remove entrapped air bubbles, and these can remain after gelation, result- ing in voids detrimental to mechanical properties [2, 3]. Thus, air evacuation prior to gelation is critical to achieve low porosity in laminates produced by VBO processing of prepregs. VBO prepregs are only partially impregnated by design to facilitate air evacuation, and typically feature dry fiber tows sandwiched between resin films. Because of this format, air is initially present within tows (intra- tow dry fiber regions), as well as between plies (inter- ply resin-rich regions) [4]. Dry fiber regions provide high-permeability pathways for gas transport within the plane of the plies, promoting air evacuation via edge breathing [5]. However, when air is trapped between plies during lay-up, air bubbles must migrate in the through-thickness direction (for a short distance) to reach in-plane evacuation pathways within the tows [6]. KEYWORDS Vacuum bag-only (VBO) prepreg; heated debulk; permeability; air evacuation CONTACT Wei Hu weihu@usc.edu M.C. Gill Composites Center, University of Southern California, 3651 Watt Way, VHE 602, Los Angeles, CA 90089, USA " 2020 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.PDF Image | VACUUM BAGGING SUPPLIES Peel Ply Fabric
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