Evaluation of Peel Ply Surface Preparation of Composite Surfaces for Secondary Bonding

Because of the extensive costs associated with building composite laminates, the U.S. Army is exploring approaches to reducing process steps associated with hybridized structures. One area of focus is in surface preparation for secondary bonding. An important quality of an effective surface preparation method is its ability to consistently provide clean and highly chemically active substrates for bonding. In this report, we examine peel ply surface preparation methods for secondary bonding of composite substrates using FM 94K epoxy film adhesive by mechanical testing, elemental surface analysis, and high-resolution imaging of failure surfaces. Woven S2 fiberglass infused with SC-15 toughened epoxy resin composites laminates, were fabricated by the Vacuum Assisted Resin Transfer Molding process. Tool-side surfaces of the composites were prepared using nine commercial off-the-shelf peel plies, including dry and impregnated forms. Two preparation methods for bonding were investigated: peel ply only prepared surfaces and peel ply in combination with grit blast prepared surfaces. This report covers testing results concluded by a quantitative and qualitative analysis of the comparative effects of the preparation methods, technical challenges and influential factors controlling peel ply effectiveness in bond performance, and recommendations for future work. The original document contains color images. A reprint from the 2012 SAMPE Conference Proceedings, Baltimore, MD, 21 24 May 2012.