The fracture toughness of glass is increased by the introduction of reinforced platelets made of a second constituent with high modulus, strength and/or ductility. In such composites different toughening mechanisms appear. In particular, the borosilicate glass/Al 2 O 3 platelet composite introduced in 1996 is a very atractive solution for industrial proposes, since it is a environmentally friendly and low-cost material. In this paper the toughening mechanisms that correspond to a change in the crack path due to the presence of platelets is analysed from the point of view of the Coupled Criterion, together with the Matched Asymptotic approach.