Round-robin programme

The double notch shear test consists of a notched specimen held in an anti-buckling fixture, which is based on the ASTM D 695 fixture. The proposed method is similar to that in ASTM D 3846-94, but has been modified to reduce the specimen width from 12.7 mm to 10 mm. This ensures equivalence with both the short beam shear and compressive test methods.

The exercise was conducted using six participating organisations and three materials. Each participant manufactured the specimens and sent them back to NPL for testing. Subsequent testing of all specimens was performed at NPL.

Materials investigated

1. Unidirectional carbon fibre/epoxy, autoclave moulded (CFRP)
2. Glass fibre/polyester, mixed format pultrusion (PUL)
3. Woven glass fibre/epoxy, press moulded

The new specimen dimensions are shown in Figure 1. This modified version is shown in Figure 2. The specimen is supported along its entire length, with the assembling screws secured finger-tight, 0.1 Nm, to allow free movement along the vertical axis. The specimen is then end-loaded in compression at a displacement rate of 1 mm/min whilst held in the fixture.

Figure 1: Double notch specimen design

Figure 2: Failure modes - (a) For more information (b) Acceptable ((c) Unacceptable