Climbing test with sandwich specimen
The climbing drum peel test was developed to determine the peel resistance of adhesive bonds between [14, 15]:
The test consists of peeling a thin strip of metal from a thick strip by winding the thin strip around a drum. Torque is applied to the drum by pulling down on straps wrapped around the drum. The thin strip of metal is wound on the drum at a smaller radius than the straps. The difference in radius (i.e. moment arm) results in a large torque being applied to the drum compared with that applied on the thin strip. The resultant upward motion causes the thin strip to peel from the thicker strip. The average peel torque T can be calculated as follows [15]:
where RO is the flange radius, RI is the drum radius, FP is the average load required to bend and peel adherend (including load required to overcome the torque resistance of the drum), FO is the load required to overcome the torque resistance of the drum and b is the specimen width. Both RO and RI account for one half the loading strap thickness. Additional tests are required to determine the resisting torque of the drum, clamp and counterweight, and to compensate for the bending of the adherend.
The upward motion of the drum causes the thin strip to be peeled from the thicker adherend resulting in bond failure. This test can be used for qualifying skin-to-core bond strength of sandwich structures, and is particularly sensitive to adherend surface preparation. This method provides comparative data of adhesion and is particularly suited to process control. Direct comparison of different adhesive systems and processes is only applicable for identical specimen configurations and test conditions.
The climbing drum peel test is applicable to the testing of joints between an outer metal sheet and the core of sandwich assemblies (e.g. honeycomb). The test specimen for a sheet metal assembly consists of two 25 mm wide adherends, one 300 mm long and the other 240 mm long [14]. The longer adherend has a 30 mm tail at either end. BSI recommends that the thickness for the longer adherend and shorter adherend be 0.5 mm and ³ 5 mm, respectively. The test specimen for honeycomb structures should be 75 mm wide. The skins (facings or adherends) of the sandwich structure should be 0.5 mm thick, and the core separating the skins should be at least 12 mm thick. The adherend lengths should be 300 mm and 240 mm. When testing laminated assemblies, the test specimens are typically 25 mm wide. The short adherend should be 240 mm long and the long adherend at least 254 mm long [15]. BSI recommends that sandwich structures be 75 mm wide and 300 mm long, including a 25 mm overhang of one skin at each end of the specimen.
It is important to ensure that the core thickness/stiffness is high enough to prevent bending of the sandwich specimen. For aluminium alloy 2024-T3, an adherend thickness of 0.51 mm and core thickness of 12.7 mm has been found to produce satisfactory results [14]. Tests are conducted at 25 mm/min. Specimen preparation and testing is relatively straightforward, although the cost of specimen preparation can be expensive, particularly for honeycomb sandwich structures. A special fixture is required, which can be purchased from a test machine manufacturer or produced in-house, but at a substantial cost. Commercial fixtures are available. The climbing drum test is not particularly suited to operating in hostile environments, and is definitely incompatible with cyclic loading conditions.
| Advantages | Disadvantages |
|
Yields Laminated or honeycomb sandwich structures Straightforward/economic BS 5350: Part C13/ASTM D 3167 |
Special test fixture required Limited to Large and expensive specimens Comparative data/service correlation unknown Unsuitable for in-situ environmental testing Unsuitable for fatigue testing |
Next: Floating Roller Method
