figure 2.25 Diagram of losipescu testing fixture and specimen
found to depend on the volume fraction of fibres and as a result cannot be considered as true values for the bond strengths.
A number of tests use specimens with a double-V-notch and the method attributed to losipescu falls into this category. The losipescu shear test (Figure 2.25) aims to achieve a state of pure shear in the mid-length of the specimen through the action of force couples which produce counteracting moments. The principle is that a constant shear force is induced through the mid-section of the specimen and that the moments exactly cancel at the mid-length of the specimen, thus producing a pure shear loading at that location. In practice however there is some non-uniformity of the shear stress distribution in the test section with probably small normal compres sive stresses. Nevertheless this test geometry has been found to yield reliable shear strength data.