12.1 Introduction

Industrial processing of adhesives has made considerable progress from the crude processes of the past. Unfortunately, one of the disadvantages of adhesive bonding as an assembly method is that a bond area cannot be inspected visually. Inspection must be carried out by two methods: destructive and non-destructive. Destructive inspection may be carried out on process-control test specimens prepared from the same adherend and adhesive materials as the production parts. The process-control specimen, as the name implies, accompanies the production parts throughout the stages of cleaning, assembly, and cure. The adhesives and adherends are all assembled at the same time and cured in the same press or autoclave. As an additional control, each part may be designed with an expendable tab as an integral part of the assembly. After the cure, the tab is removed and subjected to the same tests as the control test specimens. The results are checked against the specification requirements and the part is accepted or rejected based on these results. The rejected parts may subsequently be inspected non-destructively for final acceptance or rejection. Final rejection would result in systematic destruction to learn how good or bad the parts really were. In initial production of critical parts, such as primary bonded structures for aircraft, where human lives are dependent on reliability, a sampling and destructive analysis of actual production parts may be included in the test program.[1]

A flow chart of a quality-control system for a major aircraft manufacturer is shown in Figure 12.1. This...