Rail Shear Test According To ASTM D7078 / ASTM D4255
In the Rail Shear test following ASTM D7078 and ASTM D4255, a composite specimen is gripped along each side of a long narrow central region by clampings and the two opposing sections of the apparatus are loaded, in opposite directions. The central region of the specimen is assumed to be in pure shear.
Among the benefits, the rail shear test is limited by the following:
- The method is limited to small deformations only. Large deformations lead to load shift for horizontal fibre orientation.
- There is no homogenious but parabolic stress distribution in the cross section.
- Specimen of multiaxial or parallel to load direction oriented fibres include fibres not connected to the clampings, which leads to unwanted effects.
- ASTM D7078 uses a notched specimen. The stress distribution is strongly influenced by the manufacturing of the specimen.
- For using ASTM D4255, several holes must be drilled into the specimen in the clamping region, which leads to stress concentration.
On the other hand, the rail shear test method is a system of low complexity which uses simple and flat specimen.