(b) Bulk specimen tests
We can acquire information on the interfacial strength using bulk composite specimens and modifications to conventional mechanical property tests such s torsion, tensile and three-point bend tests. For present purposes it is inappropriate to discuss all of these and the three-point bend and the losipescu tests have been selected as commonly used examples of this type of test.
Of these the three-point bend is the simplest and the most widely employed. The three-point bend geometry and the variation in the shear and stresses in the loaded specimen are illustrated in Figure 2.24. At a given load P, the maximum tensile stress a, which is parallel to the specimen length, lies on a line on the surface below the centre loading point (Figure 224(b) and is given by