Issue 29

M. Scafè et alii, Frattura ed Integrità Strutturale, 29 (2014) 399-409; DOI: 10.3221/IGF-ESIS.29.35 401 L max = maximum load applied to the specimen; A = cross-sectional area of the specimen. The BF values used in this paper are given by the following equation [3]: 0 0 11 22 12 12 2 11 22 12 ( ) ( ) t Q A Q A BF A A A    (2) where: o ij Q is the ij element in the transformed plane stress stiffness matrix for a unidirectional lamina ij A is the ij element in the laminate extensional matrix t is the total laminate thickness In this study the cross-ply laminate is defined as a composite with plies oriented at 0° or 90° [5] and the angle-ply laminate is defined as a composite with plies oriented at 0°, ±45°, and 90°. The BF for symmetric and cross-ply laminate is given by the following equation [6]:               2 0 0 2 0 0 0 0 1 1 1 x y x xy y x y y x xy y E V E V E E BF V E V E V E V E E                         (3) where: V 0 = fraction of 0° plies in the cross-ply laminate; E x = axial compressive stiffness of the 0° plies; E y = transverse compressive stiffness of the 0° plies; ν xy = Poisson’s ratio of 0° plies. The BF for symmetric and angle-ply laminate is given by the following equation:     2 x y xy E B E C BF N A B C         (4) with: 2 2 2 1 4 y x y x y y xy xy xy x E q k A nE pE E E E G E                                     (5) 2 2 2 1 4 y y x x y y xy xy xy x E q k B nE pE E E E G E                                     (6)   2 2 2 1 4 y y xy x y y xy xy xy x E q k C n p E E E E G E                                      (7) where: E x , E y , and ν xy have the same meaning of Eq. (3); G xy = in plain shear modulus of elasticity; N = total number of plies; n = total number of 0° plies; p = total number of 90° plies; q = total number of +45° plies; k = total number of – 45° plies;