20.1 INTRODUCTION

Adhesive tests are of interest to both the formulator and the end user. They are generally used to do the following:

1. Choose among materials or processes, such as adhesive, adherend, or joint design.

2. Monitor the quality of production materials to make certain that they have not changed since the last time they were verified for use in the bonding process.

3. Confirm the effectiveness of a bonding process, such as surface cleaning or curing.

4. Investigate parameters or process variables that may lead to measured differences in the performance of the bond.

There are two categories of common tests for adhesives: fundamental property tests and end-use tests. End-use tests, such as peel and shear, are those that try to simulate the type of loading and service conditions to which a joint will be subjected. These tests are relatively straightforward, but experience is required to establish the correct sample type and testing procedures, judge the reliability of the resulting data, and interpret the results and apply them to a practical application.

The determination of a fundamental or bulk property, such as viscosity, hardness, or settling rate, is usually simpler and more reproducible than end-use tests. However, a correlation between fundamental properties and the results of end-use testing is very difficult. Fundamental property tests are usually employed to assess the consistency of the incoming raw materials, adhesive formulation, or substrates. Often fundamental property testing is done after there is a failure or unexplained occurrence to determine if a change in the incoming...