PSI - Issue 28

Mohamed Khodjet Kesba et al. / Procedia Structural Integrity 28 (2020) 864–872 KHODJET KESBA Mohamed/ Structural Integrity Procedia 00 (2019) 000–000

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and Hashin (2010)). General off-axis laminas behave differently in the sense that cracks are developed in a more stable manner with applied load and time. Crack density depends on laminate stacking sequence, ply thickness, layer orientation with respect to the load direction, mechanical properties and fracture toughness in particular, loading direction, variation of moisture and temperature and number of cycles in fatigue.

Nomenclature E fx

Young modulus of fiber in longitudinal direction Young modulus fiber in transverse direction

E fy E m f(z)

Young modulus of the matrix Function of displacement

υ fx υ m

Poisson's ratio in the direction of the fiber

Poisson's ratio of the matrix G fx Shear modulus of the fibre G m Shear modulus of the matrix g

Ration temperature concentration

E β Young modulus of β°-layer E 0 Young modulus of 0°-layer η t Transfer parameter of mechanical loading across the thickness c Moisture concentration G xz β Shear modulus of the cracked β°-layer G xz 0 Shear modulus of 0°-layer

R(a) Modified stress perturbation function g(l 0 ) Function depend on variationnel model

In polymer composite material, the matrix is very sensitive to the variation of moisture and temperature. Indeed, at high temperature and moisture concentration, we have a more degradation of the matrix which reduces the mechanical characteristics of the composite laminate (Shen and Springer (1981)). The hygrothermal effect in cross-ply composite laminates was studied by Tounsi et al. (2006), where theoretically they examined the relative longitudinal Young’s modulus by taking into account the decrease in mechanical properties by the variation of temperature and moisture. The results show that the hygrothermal environment has a significant effect on the reduction of the relative longitudinal Young’s modulus at high crack density. The modified shear-lag model and variational approach were used to predict the effect of transverse cracks on the stiffness degradation of transient hygrothermal aged off-axis [0 m /β n ] s composite laminates. The obtained results show a good agreement comparing with experimental data (Katerelos et al. (2008)) without taking into account the hygrothermal effect. On the other hand, the off-axis laminates is initially exposed to the hygrothermal aging. The obtained results illustrate well the dependence of the stiffness degradation on fibre angle orientation of the cracked layer, cracks density and transient hygrothermal conditions for desorption case. 2. Theoretical analysis 2.1 Shear-lag model We consider a symmetric off-axis [0/β] s composite laminate which is subjected to uniaxial loads. It is assumed that the β° ply has developed continuous intralaminar cracks in fiber direction which extend from edge to edge in z direction. The angle-ply laminate is characterized by 2.t β the width of β° ply, t 0 the width of 0° ply and the spacing between two cracks is 2.l 0 (Fig. 1).