ASTM E238-17a measures bearing ultimate and yield strength to determine the load-carrying capacity and bearing properties of a material’s edge. Bearing properties are useful in the comparison of materials and the design of structures under conditions where the pin is not restricted.
The bearing load is applied to the specimen by a cylindrical pin. The pin is harder and stronger than the material being tested. The pin is uniform in diameter, hardness, and surface roughness. The pin is checked carefully after each test to ensure that no metallic residue adheres to it and that it is both straight and undeformed. The dimensions of the specimen and the pin are measured. The specimen, pin, and machine are cleaned for all foreign matters. The specimen is positioned on the test machine, and a load is applied by the cylindrical pin. The data is recorded.
The specimen should be a flat sheet with the thickness of the intended product, if possible. If the specimen is too thick compared to the pin diameter, the pin might bend or break before the bearing strength is measured. If a specimen is too thin, the pin may buckle. A ratio of pin diameter to specimen thickness of 2 to 4 is used to avoid both conditions.
The diameter of the hole should be the same as the diameter of the hole in the intended product. The width of the specimen should be 4 to 8 times the hole diameter.
Edge distance ratios of 1.50 and 2.00 are commonly used. There is a close fit between the specimen and the pin. A loose fit gives lower results. The diameter of the hole must not exceed the pin diameter by more than 0.001 inches.
The bearing yield strength is determined from the graph of the bearing load versus bearing deformation.
The yield strength is calculated from the load at an offset from the initial straight-line portion of the graph equal to 2 % of the pin diameter. The stress is calculated by dividing the load by the bearing area.
The bearing strength is calculated by dividing the maximum load carried by the specimen by the bearing area.