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Damage in composites 1.1 A unidirectional E-glass/epoxy composite plate having a central through thickness crack of length 3a is subjected to a uniaxial stress o, as shown in the figure below. The unidirectional fibres are oriented at an angle a with respect to the direction of the crack, where a is in radians. The model fracture toughness of the composite Kıca, varies with the angle a according to the empirical equation. KKUIIIII = [0.739aa2+0.19aa + 1]KKIITTO, where KK1110 = 1.47 MPa m1/2 is the fracture toughness at the angle aa = 0 (i.e. when the crack is parallel to the fibre direction). The applied stress is oo = 150 MPa. IM Crack Elliptical zone assumed to be relaxed due to presence of crack Figure1: Griffith crack: A through-thickness crack in a uniaxially stressed plate of infinite width (Gibson 2016) Determine the critical size x for the cases, where the crack is (i) perpendicular to the fibres and (11) parallel to the fibres (10) 1.2 Discuss the interfacial sliding mechanisms in the following 1.2.1 PMC'S (2) 1.2.2 SFC's (2) (14) cil