The single and double shear test fixtures are designed to test the ability of a fastener to withstand load applied transversely to the axis of the fastener. ASTM F 606 provides guidance for single shear testing of tower bolts, but refers to MIL-STD-1312 Test 13 for double shear and Test 20 for other single shear applications.
The single shear fixture is made of a ultrahigh strength, heat treated alloy steel for durability. It is a tension type fixture using a closed hole design to capture the fastener. This design requires a nut to be used on the bolt or stud being tested to prevent the fixture from separating. A separate fixture must be purchased for each size fastener being tested.
The double shear fixture is made of a high strength tool steel to accommodate the high stress involved in a double shear test. It is a compression type fixture, consisting of a mandrel and an anvil, both with U-shaped cutouts. The anvil supports the fastener during the test and the mandrel applies the compressive force. The mandrel and anvil of the fixture are precision machined as a matched set for a specific size fastener. A separate fixture must be purchased for each size fastener being tested.
Principle of Operation
The single shear fixture is designed for mounting to spherical tension rods. The fixture can be adapted to frames without tension rods provided a spherical alignment device is utilized as part of the load train.
The fastener is passed through both halves of the fixture, the nut maintains both halves of the fixture in contact with one another. Applying a tensile force to the fixture causes a shear force to be applied to the fastener.
The double shear fixture is designed so that the lower half (anvil and base) rests on the machine table. The mandrel is mounted to the test frame adjustable crosshead with a mounting plate that is matched to the frame being used.
The fastener is placed in the U-shaped cutouts of the anvil and base. The mandrel fits between the sides of the anvil with a very close tolerance, and has a corresponding U-shaped cutout. A compressive force is applied to the fixture which induces a shear force at two different points on the fastener.