Fracture mechanics test specimens

Fig. 5.1 Geometries of quasi-static fracture mechanics test specimen a) SENB and b) CT [13Gre].

See also articles on Fracture-mechanics test specimens, Biister test, Peei tests, adhesion - fundamental and practicai. 

Although for many straightforward comparative purposes it is often adequate to record the results as a peel force/width, it is easy to derive an expression for the peel energy from basic mechanical principles by equating the work done by the test machine to the work done on the sample. The result forms a basis for understanding and interpreting peel tests (see also Fracture-mechanics test specimens). 

Many widely used Tests of adhesion can be applied to the rubber to metal bonds Blister test. Fracture-mechanics test specimens. Non-destructive testing of adhesively-bonded structures. Peel tests. Shear tests. Tensile tests and Wedge test. This particular article is concerned with those aspects that are of practical concern in the rubber-processing industry. 

The optimal adhesive layer thickness depends on a number of factors. Some bonds, notably Tensile test specimens, are stronger when the adhesive layer thickness is redn-ced. For fracture specimens, including double cantilever beam specimens bonded with structural adhesives (see Fracture mechanics test specimens), optimal bond thicknesses have been identified, although the optimal thickness depends on the loading rate and test temperature. " Enhanced ductility plays a role in this process, and a sufficient quantity of adhesive is desired to dissipate energy (see Peel tests). This latter mechanism is also important in the peel energy of Pressure-sensitive adhesives and other systems. 

In treating adhesives as polymeric materials, it is possible to use Fracture-mechanics test specimens to determine material properties independent of geometry. A typical sample would be the compact tension test-piece, where a sheet of material, typically 6-mm thick and 100-mm square, has a sharp crack inserted in one edge. The sample is then loaded perpendicular to the plane of the crack and the load at which crack propagation... 

Fracture-mechanics test specimens A J KINLOCH Test methods for flexible and rigid joints... 

Conventional fracture mechanics testing specimens, such as the compact, cantilever beam, modified bolt-load compact previously referred to as wedge-opening load (WOL), and contoured double-cantilever beam specimens, have been adapted for testing in both aqueous environments and in a high-pressure gaseous hydrogen environment. 

Another basic major advantage is that the cyclic-fatigue fracture-mechanics data may be gathered in a relatively short time-period, but may be applied to other designs of bonded joints and components, whose lifetime may then be predicted over a far longer time-span. Obviously, the fracture-mechanics tests need to be conducted under similar test conditions and environments as the joints, or components, whose service-life is to be predicted. This is important since the fracture-mechanics test specimens do need to exhibit a similar mechanism and locus of failure (e.g. cohesively through the adhesive layer, or interfacially between the adhesive and substrate, or through the oxide layer on the metallic substrate, etc.) as observed in the joints, or components, whose lifetime is to be ranked and predicted. 

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