Composite material shear test fixture

Standard specimens (shown in front view in Figure 1) are 3 inches long, 0.75 inches wide, and up to 0.50 inches thick.Typically a specimen thickness of approximately 0.1 inch is used.The clamp can also accommodate shorter and narrower specimens if required.Each edge of the specimen is machined with a 90° notch, and a strain gauge can be installed on the specimen surface in the notch area to monitor shear strain.Standard ±45° biaxial strain gauges or special commonly used gages.When mounting the specimen, use your fingers to lift the small-diameter rod extending from the clamp below the notch at the lower end of the specimen (front view in Figure 1) so that the specimen is centered from left to right.The specimen is pushed onto the flat back side of the fixture, positioning it front and back.The tapered wedges are not intended for clamping; they can be adjusted with a finger knob to accommodate specimens of slightly different widths.Wedges of varying thicknesses can be supplied to accommodate specimens outside of this small range of thickness variations.

The moving portion of the clamp consists of a linear ball sleeve (see rear view photo in Figure 1) that travels on a hardened steel vertical post mounted on the bottom of the clamp.This ball bearing eliminates guide post binding and minimizes frictional resistance.The fit of the bearings can be adjusted using a screw and lock nut on the back of the moving part of the clamp.

When in use, the clamp is placed directly on the base of the testing machine without restraint.As shown for the standard-size clamp in Figure 2, the clamp has a standard 1.25-inch diameter stud with a locking ring and a 0.50-inch diameter cross-pin hole that threads to the moving half of the clamp.Any special adapters required are attached to this stud for the specific test machine being used, the adapter is nailed to the stud and secured by the locking ring provided with the clamp.

Figure 2 shows an example of a special fixture.The small jig on the left is essentially a quarter-scale model of a standard jig designed to test specimens 20 mm long, 5 mm wide, and 5 mm thick.On the right is a standard size clamp for comparison.We also make special jigs for customers that are larger than standard.

Figure 2: Quarter scale shear fixture (left).and standard clamp (right).

Figure 3 shows a special fixture designed for high temperature testing.This clamp is made of nickel.Superalloys can be used at temperatures up to 1500ºF (815ºC).Since there are no ball bushings capable of operating at such high temperatures, the right half of the fixture travels on a large diameter, tight-fitting calibration post.Additionally, since this clamp is typically used in high-temperature furnaces, the clamp has a threaded hole at the bottom for attachment to the support post and a threaded bolt at the top for attachment.

Figure 3: Nickel Superalloy Shear Test Fixture for 1500°F (815°C)