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Skin doubler test
A number of factors render most of the test methods unsuitable for fatigue testing of structural adhesives, particularly when combined with prolonged exposure to a hostile environment. The tendency is for engineers to conduct fatigue tests on actual components or on complex specimens related to a specific design. The data generated by loading a skin-doubler specimen in tension may possibly be more pertinent to actual engineering structures, providing static, fatigue and creep design limits.
Testing can be conducted using standard tension/compression mechanical test equipment. Specimen fabrication is relatively straightforward and economic. Stress-strain response can be measured in both the linear and non-linear regions of the stress-strain curve using a KGR-1 extensometer [6]. Unfortunately, there is insufficient comparative data to support the use of this technique for determining design limits for adhesives.
| Advantages | Disadvantages |
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Yields shear strength and shear modulus Compatible with all metals, plastics and PMCs Stress state relatively uniform over bondline Straightforward/economic Representative of actual structures Suitable for environmental and fatigue testing |
Complex/expensive extensometers (2 off) required Geometry dependent Large specimens required Limited to rigid adherends Stress concentrations present at bondline ends Elevated shear and peel stresses at bondline No existing national or international standards |
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