Two rail shear test

Specimen configuration for the crack rail shear test is identical to the ASTM D4255 standard [15.5] specimen for the two-rail shear test. Analytical expressions for strain energy release rate determination are derived by a strength of materials approach [1.54]. 

Figure 17.46 Two-rail shear test, Source Reprinted from Course on Mechanical Testing of Advanced Fibre Composites, University of London, Imperial College, Sep 1995.

The two-rail shear test is only suitable for the determination of shear moduli. The three-rail shear does give a better approximation to pure shear as the compressive load is applied parallel to the clamped edges of the specimen. 

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