Wedge
penetration, a type of crack opening test that is particularly
suitable to testing fruit and vegetables, cheese, stiff gels and cooked
meats, involves a wedge driven into a block of material. The dimensions of the test specimen affect the results and so it is important to use reproducible rectangular blocks. This test is similar to a tensile test but instead of the two halves of the specimen being pulled, they are pushed out by the penetrating wedge. The two halves bend outward storing strain energy.
At the point of fracture this energy is fed to the tip of the wedge where stress concentration is highest and a free running crack starts and propagates ahead of the wedge.
