The Effect of Primer Thickness and Cure on the Bond Strength of a Nitrile-Phenolic Adhesive System

The growing application of bonded structure in aircraft, aerospace, and other industries emphasizes the importance of achieving reliable, high-strength bondments, particularly in multiple-stage bonding. As the result of variations in the bond strength and failure mode of quality control coupons representing production parts that undergo multiple cure cycles using a nitrile-phenolic adhesive system, an investigation was conducted to determine possible causes. Results were twofold. First, the optimum blending of primer thickness and cure time increases bond strength and reliability. As primer thickness is increased and the primer is subjected to extended cures, bond strength decreases. Second, the most accurate method of measurement is the beta backscatter method, measuring the thickness of primer layers as thin as 0.00001 inch.