Page 158 - Handbook of Adhesives and Sealants

128 Chapter Four

the adhesive or sealant will be suggested. This chapter will conclude
with a discussion regarding a methodology that can be used for estab-
lishing the service life of the adhesive or sealant joint. The next chap-
ter will address tests that are generally used for quality control and
for nondestructive evaluation of the finished joint.

4.2 Reasons to Test and Basic Principles
Adhesive and sealant tests are conducted for a variety of reasons.
They are used to either:

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; or
4. Investigate parameters or process variables that may lead to mea-
sured differences in the performance of the bond.

There are two general categories of tests for adhesives and sealants:
fundamental property tests and end-use tests. End-use tests, such as
T-peel and lap shear, are those which try to simulate the type of load-
ing and service conditions to which a joint will be subjected. These
tests are relatively straight-forward, but experience is required to es-
tablish the correct specimen type and testing procedures, judge the
reliability of the resulting data, and interpret the results and apply
them to a practical application.
The measurement of a fundamental or bulk property, such as vis-
cosity, hardness, or setting rate, is usually simpler and more repro-
ducible than end-use tests. However, a correlation between fundamen-
tal properties and the results of end-use testing is difficult.
Fundamental property tests are usually employed to assess the con-
sistency of the incoming adhesive or substrate once the joint system
is verified as suitable in a specific application. Often fundamental
property testing is undertaken after there is a failure or unexplained
occurrence to determine if a change in the incoming material may
have been the possible culprit.
A number of standard tests for adhesives and sealants have been
specified by the American Society for Testing and Materials (ASTM)
and other professional organizations such as the U.S. Department of
Defense and the Society of Automotive Engineers. By far, ASTM stan-
dards are the most commonly referenced test methods. Selected ASTM