PSI - Issue 13

M. Khodjet-kesba et al. / Procedia Structural Integrity 13 (2018) 181–186 KHODJET KESBA Mohamed/ Structural Integrity Procedia 00 (2018) 000–000

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3.2. Reduction of Poisson’s ratio modulus In Fig. 3 the degradation of the normalized effective Poisson’s ratio are shown against crack density and compared with experimental data published by Joffe et al. (2001). The results show good agreement between the experimental results and those predicted using the analytical models. Always the parabolic analysis gives the best prediction compared to experimental data. The present models give less accurate predictions of the degraded Poisson’s ration as a function of crack density.

1,0

Parabolic analysis Progressive shear Experimental data

0,9

0,8

0,7

 xy /  xy 0

0,6

0,5

0,4

0,0

0,2

0,4

0,6

0,8

Crack density (1/mm)

Fig. 3. Poisson’s ratio degradation due to transverse cracks in [±15/90 4 ] s GF/EP laminate.

3.3. Influence of hygrothermal conditions on mechanical properties Tsai (1988) proposes the adimensional temperature T*, which is the essential parameter for evaluation of the hygrothermal effect in stress distribution:

T T T T 

g opr g rm 

*

(6)

T



Where T g is the glass transition temperature, T opr is the operating temperature and T rm is the room temperature. We further assume that moisture suppresses the glass transition temperature T g by simple temperature shift. 0 g g T T gc   (7) Let us consider a laminated plate of thickness h made of polymer matrix composite, submitted on it two sides to the same dry environment. The plate is considered to be infinite in both x and y directions and the moisture vary only in the z direction. The initial moisture concentration C=0 at t=0. Both sides of the plate are suddenly exposed to a Cint moist environment. The moisture concentration inside the plate is described by Fick equation (Shen and Springer 1981, Benkhedda et al. 2008) with diffusivity Dz. 2 2 z C D C t z      (8) With the initial conditions: C=0 pour -h/2 ≤ z ≤ h/2 et t = 0, C=Ci pour z=-h/2 ; z= h/2 et t >0