Floating roller method
The floating roller peel test has been developed to determine the relative peel strength of adhesive bonds between one rigid adherend and one flexible adherend. This test method is considered suitable for acceptance and process control testing. The asymmetric specimen is typically 25 mm wide and consists of a 250 mm long flexible adherend bonded to a 200 mm long rigid adherend. The unbonded end of the flexible adherend is bent perpendicular to the rigid adherend and clamped in the grip of the testing machine. The applied load peels the flexible adherend from the rigid substrate. ASTM D 3167 [16] specifies 0.63 mm thick flexible adherend and 1.63 mm thick rigid adherend, whereas the British Standards Institution (BSI) [17] recommends corresponding values of 0.5 mm and 1.6 mm.
Tests are normally conducted at displacement rates of 100 mm/min or higher. As with the T-peel test, the average peeling load per unit area is used to define the peel strength. This is taken from the force-displacement curve after the initial peak reading. Failure analysis does not allow for deformation of the flexible adherend. It is recommended that at least five specimens be tested from each batch of material [17].
The BSI standard [17] was developed to assess surface treatments for aluminium (e.g. chromic acid anodisation (CAA) and phosphoric acid anodisation (PAA)). In the wet peel test, several drops of water containing a wetting agent (e.g. 0.5 to 1.0% detergent) is applied to the crack opening after peeling 75 mm of the bonded length. The introduction of the liquid changes the mode of failure from cohesive (dry joint) to quasi-adhesive failure. The test is not suitable for long-term durability prediction.
Specimen preparation and testing is relatively straightforward. Associated costs of specimen fabrication and preparation can be considered reasonable. A relatively high cost fixture is required to test specimens. Commercial fixtures are available. The floating roller test is considered the more reliable method of the three techniques. The floating roller method is not particularly suited to operating in hostile environments, and is definitely incompatible with cyclic loading conditions.
| Advantages | Disadvantages |
|
Yields peel strength Compatible with metals and PMCs Straightforward/economic DD ENV 1967: 1996/ASTM D 3167 |
Special test fixture required Limited to rigid-to-flexible adherends No allowance for large adherend deformation Comparative data/service correlation unknown Unsuitable for fatigue testing Unsuitable for in-situ environmental testing |
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