Page 175 - Handbook of Adhesives and Sealants

Standard Test Methods 145

4.4 Standard Test Methods for
Adhesive Joints
The physical testing of standard adhesive joints provides a method of
comparison for materials and processes that are being evaluated.
Standard tests also provide a means to control the adequacy of the
bonding process, once it is established, and of assessing its confor-
mance to specification.
Standard test methods are only useful if they can be reproduced. It
is important that the same results can be measured by both the ad-
hesive developer and the end-user. It is also important that the results
are reproducible with time and with different testing personnel. The
accuracy and reproducibility of test results depend on the conditions
under which the bonding process is performed. The following variables
must be strictly controlled.

1. Procedures for cleaning, etching, and drying the surface of the sub-
strates prior to application of adhesive.
2. The time between surface preparation and application of adhesive
and the environmental conditions present during this period. This
includes the temperature and percent relative humidity. Usually
standard atmospheric conditions are specified (73.5 2 F and 50
4% relative humidity).
3. Complete procedures for mixing the adhesive components.
4. Conditions and methods for application of the adhesive to the sub-
strate surface.
5. Curing conditions, including the pressure, temperature, and time
of the curing cycle. It should be specified whether or not the tem-
perature is measured within the glue line, or on some other point
on the substrate, or at some location within the curing oven. The
temperatures could vary significantly at these different locations
depending on the weight and size of the assembly. When an ad-
hesive producer specifies a temperature and time for cure, it refers
to the conditions of the actual adhesive within the bond-line.
6. Conditioning procedures for specimens after curing and prior to
testing.
7. The rate at which the sample is loaded during test. Peel and impact
tests especially are dependent on the speed at which the sample is
tested.

A standard test report usually documents the resulting measurements
such as tensile shear strength, peel strength, etc. It should also indi-