PSI - Issue 5

Khodjet-Kesba Mohamed et al. / Procedia Structural Integrity 5 (2017) 271–278 Khodjet-Kesba Mohamed et al/ Structural Integrity Procedia 00 (2017) 000 – 000

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The interlaminar shear stress at the interface between the 0° and 90° layers is shown as a function of the longitudinal coordinate in Fig. 3. It can be observed that the results of interlaminar shear stress at the interface deduced from the complete parabolic model is similar to the finite element model in large range 0 ≤ x / l ≤ 0.6. The results differ in the crack plane, where only the finite element analysis satisfies the stress free boundary condition at the crack tip.

4. Moisture absorption effect

The study here has been focussed on the axial and flexural stiffness properties reduction due to transverse cracking in [0/90] 2s composite laminate when this latter is initially exposed to different environmental conditions. The model which will enable us to introduce ageing and to see its development on the fibre and matrix scales is Chamis model (1983). The matrix mechanical property retention ratio is expressed as (27) Where T gw and T go are the glass transition temperature for wet and reference dry conditions, T opr is the operating temperature and T rm is the room temperature. The glass transition temperature for wet material is determined as : (28) Where C is the weight percent of moisture in the matrix material. Let us consider a laminated plate of thickness h made of polymer matrix composite, submitted on it two sides to the different dry environment. Provided that the laminate has a uniform moisture concentration C I for t=0. The moisture concentration inside the plate is described by Fick equation ( Rezoug et al. 2011, Khodjet kesba et al. 2015, Khodjet kesba et al. 2016a,b ) with diffusivity D z . 1/ 2            go rm opr gw m T T T T F   go gw C C T T 0.1 1 0.005 2   

Fig. 4. The one-dimensional problem of moisture diffusion in plates

2 z D C z   2

t C



(29)





With

C I = C init at t = 0 for 0

(30)

C = C 0 at t = 0 for z = 0 and z = h (31) For the case when the moisture environment instantly reach the crack surfaces in the interior of the laminate the model becomes (32) μ is the moisture transfer coefficient which is related to the crack density, ρ, according to Lundgren and Gudmundson (1999) as : (33)                  h z n e n C z C C C e n n I       sin (2 1) (2 1) 4 ) ( ( , ) 2 2 (2 1) 1 0 0 b N a      2