PSI - Issue 13

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

183

3

work, we have used two models developed by Berthelot et al. (1996). This latter is modified by introducing the stress perturbation function. The stress perturbation function   0 R l is found as : cosh( ) 2 ( ) tanh( ) cosh( ) a a x R a d x a a          (4) where,  is the shear-lag parameter :

90 90 90 90 ( ) t t E t E t E E     

2

(5)

G





3. Results and discussion In this section we will validate the results of the present program without taking into account the hygrothermal effect on the material properties. The results are compared with experimental data for glass/epoxy laminate (joffe et al. 2001). The material properties of the chosen composite as well as their geometrical characteristics are summarized in Table 1.

Table 1. Material properties of glass/epoxy laminate used in calculations (Joffe et al. 2001). Material properties E L (GPa) E T (GPa) G LT (GPa) G TT’ (GPa) υ LT υ TT’

t 90 (mm) 0.144

44.73

12.76

5.8

4.49

0.297

0.42

Glass/epoxy

3.1. Reduction of longitudinal Young’s modulus Figure 2 shows the degradation of longitudinal Young’s modulus due to transverse cracks for glass/epoxy composite laminates. These figures exhibit the prediction on stiffness reduction by shear-lag model and the experimental data published by Joffe et al. (2001). It can be seen that good agreement is obtained between the parabolic analysis and the experimental data (Joffe and al. 2001). When fibre angle θ° is greater than 0° the two analytical models (parabolic analysis and progressive shear) give the same results.

1,0

Parabolic analysis Progressive shear Experimental data

0,9

0,8

0,6 Ex / Ex 0 0,7

0,5

0,4

0,0

0,2

0,4

0,6

0,8

Crack density (1/mm)

Fig. 2. Longitudinal Young’s modulus degradation due to transverse cracks in a [±30/90 4 ] s glass/epoxy laminate.