Quality Assurance of Composite Bonding Processes

Surface energy is potentially the most critical predictor of performance for composite/composite adhesive bonds. It is straightforward to measure the surface energy of a planar composite using, for example, contact angle measurements obtained from a range of probe liquids. However, once a surface has been roughened on a microscopic scale by a process such as grit blasting, quantifying the surface energy becomes a much more difficult task. In Phase I it was demonstrated that the wetting behavior of a single carefully chosen probe liquid is an excellent predictor of subsequent adhesive bond performance, even on a highly roughened surface. It was further demonstrated that the probe liquid wetting behavior was well quantified by measuring the diameter of a small drop of known volume. This technique provides fundamental information about the relationship between contamination, surface energy and performance for adhesively bonded composites. Phase II will use this technique to evaluate a wide range of substrates, adhesives, and contaminants. A practical prototype measuring tool for evaluating surface energy using this technique will be constructed and evaluated in a manufacturing environment.