Page 183 - Handbook of Adhesives and Sealants

Standard Test Methods 153

Figure 4.8 Peel strength of 3 mil aluminum foil bonded
with DETA cured DGEBA epoxy adhesive. 9

will generally result in higher peel strengths. The elongation charac-
teristics of these adhesives permit a greater area of the bond to absorb
the applied load. With more rigid adhesives, the thicker bond-line low-
ers the peel strength (as shown in Fig. 4.9 for an epoxy adhesive)
because of stresses at the edge of the bond. Peel strength is also a
function of the stiffness or modulus of the substrates and of the ad-
hesive, and it is also a function of the thickness of the two substrates
being peeled. 7,8
The T-peel test is described in ASTM D 1876 and is the most popular
of all peel tests. The T-peel specimen is shown in Fig. 4.10. Generally,
this test method is used when both adherends are flexible. Because
the angle of peel is uncontrolled and dependent on the properties of
the adherends and the adhesive, the test is less reproducible than
other peel tests. A sample population of at least ten is required,
whereas most other ASTM tests require a minimum of five.
The floating roller peel test is used when one adherend is flexible
and the other is rigid. The flexible member is peeled through a spool
arrangement to maintain a constant angle of peel. Thus, the values
obtained are generally more reproducible than the T-peel test method.
The floating roller peel resistance test is designated ASTM D 3167.
The climbing-drum peel specimen is described in ASTM D 1781.
This test method is intended primarily for determining peel strength
of thin metal facings on honeycomb cores, although it can be used for
joints where at least one member is flexible. The fixtures of the float-
ing roller peel and drum peel tests help control the angle of peel so
that they generally provide more reproducible peel values for a given
adhesive than the T-peel method. 10,11
A variation of the T-peel test is a 180 deg stripping test illustrated
in Fig. 4.11 and described in ASTM D 903. This method is commonly