Joint tests for fracture

A major feature of the fracture mechanics argument is that the fracture energy, Cc, for a given joint, tested at a stated rate and temperature, is independent of the test geometry employed. In principle therefore, and with appropriate modifications, almost any test configuration could be used. In practice, certain geometries lend themselves particularly to analysis and experimental convenience, and are depicted in Fig. 4.14. 

Tapered double cantilever beam (TDCB). The TDCB, or more accurately the contoured DCB, specimen as developed by Mostovoy 

Major limitations of this test include the initial requirement for a numerically controlled milling machine to achieve the cubically curved specimen shape (for constant m ), the configuration is not 

The behaviour of specimens constructed with either soft or stiff adhesives may be quite different(64). For instance, for the same value of f and a in each specimen, Gic will be the same but the stiffer adhesive will be resisting a higher tensile stress. Clearly, creep effects with ductile adhesives will redistribute stress concentrations. There may also be a rate-dependent effect on (7 c (initial) when displacing the adherends with bolts. 

The success of the test in discriminating between variations in adherend surface preparation and adhesive environmental durability has led to its widespread use in an R D role(60, 66-69). In general, the test results are viewed only as qualitative because the fracture energies of many adhesives are high enough to cause inelastic deformation of the adherends. Thus crack lengths, rather than 

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