Rail Shear Test fixture are described as Method B in ASTM Standard D4255. 

The specimen is 6 in. long and 5 3/8 in. wide, and of the desired thickness. 

Details of specimen preparation and installation, and a complete test procedure, are included in ASTM Standard D4255. This standard also includes the two-rail shear test method, as Method A, this fixture also being available from Wyoming Test Fixtures, Inc. The two-rail version has the advantage of utilizing a smaller specimen, with only six rather than nine holes to prepare. However, the three-rail version is attractive because it loads the specimen symmetrically.

These shear tests are designed to produce in-plane shear property data for material specifications, research and development, and design.

Factors that influence the shear response and should therefore be reported include: material, methods of material preparation and lay-up, specimen stacking sequence, specimen preparation, specimen conditioning, environment of testing, specimen alignment and gripping, speed of testing, time at temperature, void content, and fiber volume reinforcement content.

Properties that may be measured by this test method include:

•  In-plane shear stress versus engineering shear strain response,

•  In-plane shear chord modulus of elasticity,

•  Offset shear stress, and

•  Maximum in-plane shear stress. 

In cases in which the engineering shear strain at failure is greater than 5 %, the shear stress corresponding to 5 % engineering shear strain should be reported.

ASTM Standard D4255-01 (2007), "Guide for Testing In-Plane Shear Properties of Composite Laminates," American Society for Testing and Materials, West Conshohocken, Pennsylvania (first published in 1983).