The fracture strength σR of the materials was measured on beams having all the same dimensions of W= 2 mm, B = 2 mm and L = 15 mm (2x2x15mm 3 geometry) in order to be able to compare the strength between them without any fracture probabilistic effect. The surfaces in contact with the spans have been mirror-polished. The samples were monotonically loaded at a constant displacement rate of 50 µm/min, and the strength was calculated by linear-elastic relationships by taking the maximum load measured during the test.