Compliance calibration

Another approach developed on the basis of an empirical compliance calibration, which was designed originally for isotropic brittle materials (Berry 1963), appears to avoid certain problems associated with correction factors. The compliance is given in the form of empirical equation... 

There are, of course, an infinite number of m values that can be chosen to satisfy Equation 13.46. The determination of m is governed by a basic assumption that the entire energy supplied to the specimen is concentrated on the crack line for crack extension. Thus the choice of m is such that the bending stresses on the adherend are minimized. This, in turn, depends on the modulus of the adherends relative to the adhesive. This necessitates an empirical determination of the appropriate m value through a procedure known as compliance calibration. Figure 13.37 is a schematic of the specimen geometries of TDCB for the determination of Gj, for bulk adhesives and adhesive joints. 

Of course, the correction function Y is another way of expressing the compliance calibrations given in equation (4) for a three-point bend test (Fig. 12b), for example, is... 

TABLE 2—Calculated crack mouth opening and load-line compliance calibrations for modified compact bolt-loaded specimen [30]. 

Dynamic mechanical analysis (DMA) was performed to determine the influence of the polymer constitution on tensile modulus and mechanical relaxation behavior. For this purpose, a Perkin Elmer DMA-7 was run in tensile mode at an oscillation frequency of 1 Hz with a static stress level of 5 x lO Pa and a superposed oscillatory stress of 4 x 10 Pa. With this stress controlled instrument, the strain and phase difference between stress and strain are the measured outputs. Typically, the resulting strain levels ranged from 0.05% to 0.2% when the sample dimensions were 8 mm x 2 mm x 0.1 mm. A gaseous helium purge and a heating rate of 3°C min" were employed. The temperature scale was calibrated with indium, and the force and compliance calibrations were performed according to conventional methods. 

Varadarajan R, Rimnac CM. Compliance calibration for fatigue crack propagation testing of ultra high molecular weight polyethylene. Biomaterials 2006 September 27(27) 4693-7. 

The notched pipe bend configuration has not previously been studied and ite geometry correction functions C (a), and P(a) had to be computed. The scheme for doing so has been outlined elsewhere [3] and will not be repeated here. The starting point, as for conventional linear-elastic fracture mechanics, was a compliance calibration... 

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