Fastener Double Shear Test Fixtures (MIL-STD-1312-13 / NASM 1312-13)

Model No. WTF-DS (hardened tool steel inserts)

fastener double shear testfixtures_0

Fig. 1: Set of six Fastener Double Shear Test Fixtures (one shown disassembled).

These fixtures are used to test, in double shear, fasteners (typically metallic) of various types and sizes.  Six fixtures of various sizes are shown in Fig. 1.

A hardened tool steel blade (lower left in the photograph of Fig. 2, having an accurately toleranced cutout of the diameter of the fastener to be tested is inserted in a fastener support fork (lower right) having similar cutouts.  These two components are mounted in a steel holder (top) for stability.  The fastener to be tested rests on the fork and a compressive force is applied directly to the top of the blade to double-shear the fastener.

The three components of the fixture are shown individually in Fig. 2.

IMG_3156

Fig. 2: Components of a typical fixture

These fixtures are sold either individually or in sets such as indicated in Fig. 1 since a fixture of specific dimensions is required for each fastener size to be tested, either English or metric. Thus, these fixtures are normally supplied in sets of various numbers of sizes as specified by the customer. Custom sizes for testing special fasteners can be fabricated, since each fastener diameter requires an individual fixture.

As indicated in Fig. 3, sets of as many as 52 individual fixtures have been fabricated for customers, with sizes ranging from 0.112" diameter to 1.250" diameter.  The smallest of these fixtures weigh on the order of only one ounce, while the largest weigh nearly 50 lbs. For those who need to test to a MIL-STD with fasteners considered too short to be used in this method MIL-STD-1312-20 (Model No. WTF-SS) is recommended.
IMG_3952

Fig. 3: Set of 35 fixtures ranging in size from 0.131" to 0.330" fastener diameter.

Special, non-standard double-shear test fixtures can also be supplied, such as those shown in Fig. 4.

fastener double shear testfixtures_3

Fig. 4: Custom Double Shear Test Fixtures

Another option for testing cylinders in double shear is ASTM B769 (Model No. WTF-AS), which can be seen below. The benefit of this fixture is it modular as the dies used for loading can be swapped out to accommodate different diameters as opposed to the MIL-STD which requires a new fixture for each size.

Amsler

Fig. 5: Amsler Double Shear ASTM B769 (Model No. WTF-AS)

Source of Additional Information:
1) "Fastener Test Methods, Method 13, Double Shear Test (Method 113, Metric Sizes)," Military Standard MIL-STD-1312-13A, August 1991, also National Aerospace Standard NASM 1312-13, August 1997.