10.1 Introduction

Adhesive bonds must withstand the mechanical forces acting on them, but must also resist the service environment. Adhesive strength is affected by many common environments, including temperature, moisture, chemical fluids, and outdoor weathering.[1]

In applications where possible degrading elements are present, candidate adhesives should be tested under simulated service conditions. Common ASTM environmental test methods often reported in the literature include the following, described in Chapter 12:

The service environments to which adhesive-bonded assemblies are exposed vary from highly protected sealed systems to exterior unprotected systems. The latter may include semi-arid sites, such as New Mexico or Arizona, and highly corrosive tropical jungle or marine locations. Durability must always be linked with the service environment. The durability of an adhesive bond to extreme environmental conditions is very much dependent on the surface treatment of the adherends. Another factor that must be considered is the durability of bonds under stress. This is of particular concern in primary structures in aircraft applications. Most other types of bonds are not subject to high loads for prolonged periods. In laboratory ambient storage, no degradation was found in bond strengths of epoxy/aluminum bonds stored for periods as long as 11 years, nor for elastomeric adhesive sealant bonds to aluminum and cold-rolled steel stored for up to 5 years.[1]

Applied stress will, however, cause an adhesive bond to degrade at a faster rate than an...