Quality Assurance of Composite Bonding Processes

Adhesive bonding of composite materials is a critical component of modern aircraft construction. Adhesive bonding of metals such as aluminum is well understood, and the processes currently used for manufacture of adhesively bonded metal aircraft components are robust and controllable. However, the factors responsible for obtaining strong and durable adhesive bonds to fiber reinforced composite materials are only poorly understood. Current practice usually involves abrasive blasting of the adherend surface. This is believed to improve adhesive bond strength through improved wetting of the substrate by the adhesive and by providing for mechanical interlocking of the adhesive and the substrate. While this process can result in strong and durable bonds, variations in bond performance can occur unexpectedly. Quality control techniques for ensuring reproducibility of the bond performance are needed. Our previous work has shown that surface energy of a prepared composite correlates well with the adhesive joint performance, and can potentially serve as the basis for a shop floor-level quality assurance tool. The goal of Phase I of the proposed research is to develop and evaluate at least two techniques for predicting wettability of a composite surface by a room-temperature paste curing adhesive.