Issue 29

M. Scafè et alii, Frattura ed Integrità Strutturale, 29 (2014) 399-409; DOI: 10.3221/IGF-ESIS.29.35

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 ) t Q A Q A BF A A A    12 12 2 11 22 12 ( (

)

(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:

   

    

   

   

E E

 

  

4 

q k

y

2

2 E E E G    y xy x y



   

2 1 xy    

A nE pE 

(5)

x

y

xy

x

   

    

   

   

E E

 

  

4 

q k

y

2

B nE pE     

2 E E E G    y xy x y

2 1 xy    



(6)

y

x

xy

x

   

    

   

   

E E

 

  

4 

q k  





y

2

C n p E    



2 E E E G     y xy x y





(7)

2 1 xy 

y xy

xy

x

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;

401