A peel test is performed between two substrates bonded together with an adhesive. The substrates may be both flexible or one may be flexible while the other is rigid. The adhesive itself will generally take the form of a thin layer between the two substrates such as the adhesive located on the underside of a piece of tape that has been placed against a steel plate.

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Purpose of Peel Tests:

Generally the goal of a peel test is to determine the adhesive strength of the material or the strength of the adhesive bond between two materials. This adhesive strength may be referred to as the “stickiness” of a material as it is a measure of the samples resistance to separation from one another after the adhesive has been applied. This measured value may then be used to determine if the adhesive bond is strong enough or too strong for the application and whether a different adhesive or bonding process is needed.

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Common Peel Tests:

The most common types of peel tests for the measuring of adhesive strength are the T-peel, 90 degree peel, and the 180 degree peel. The T-peel test is a type of tensile test performed upon two flexible substrates that have been bonded together and placed into peel test grips such that one substrate sticks up and the other sticks down while the bonded area sticks out horizontally so that the entire setup forms a “T” shape. The 90 degree test requires a 90 degree peel test fixture to determine the adhesive strength between a flexible (tape) and rigid substrate (plate), where the plate lies horizontally with the gripped end of the tape sticking up perpendicular while the rest is bonded to the plate so that it forms an “L” shape. The 180 degree test is similar to the 90 degree peel test except that the bonded area between the tape and plate is placed vertically between the peel test grips while the free end of the of plate is gripped by the bottom and the free end of the tape is gripped by the top so that it forms a tight “U” shape.

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Types of Materials:

A peel test is commonly used to measure the adhesive strength between the bonded surface of two flexible substrates or a flexible and rigid substrate. The flexible substrate often consists of tape, film, thin plastic material, rubber, or other polymers, whereas the rigid substrate is commonly but not limited to a type of metal, rigid plastic or composite. The conditions under which these materials are tested are composed of various combinations of pretreatment, temperature and speed of testing depending upon the standard test method used to guide the testing process.

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