PSI - Issue 13

Mor Mega et al. / Procedia Structural Integrity 13 (2018) 123–130 M. Mega et al. / Structural Integrity Procedia 00 (2018) 000–000

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Fig. 3: Critical interface toughness G ic as a function of the phase angle ψ representing the mode mixity for a delamination along an interface between a transversely isotropic UD fabric with fibers oriented in the 0 ◦ -direction and a balanced plain tetragonal woven fabric with fibers oriented in the + 45 ◦ / − 45 ◦ -directions.

each specimen was calculated as

1 H 1 (

2 )

1 H 2

2

2

K ( T ) III

K ( T ) 1

( T ) 2

(2)

+ K

G ic =

+

where

1 H 1 1 H 2

D 22 4 cosh 2 πε

=

(3)

D 33 4

.

=

In eqs. (3), D 22 and D 33 are diagonal members of the matrix D (see [33] p. 344) which contains values related to the mechanical properties of the upper and lower plies of the investigated interface. The oscillating parameter ε is given by

ln (

1 + β 1 − β )

1 2 π

(4)

ε =

where the parameter β is also a function of the mechanical properties of the two materials of the specific interface investigated here. The oscillatory parameter was found to be ε = 0 . 02257. In addition, the phase angle ψ was computed for each specimen. This phase angle represents the in-plane mode mixity and is defined as ψ ≡ arctan   K ( T ) 2 K ( T ) 1   . (5) In Fig. 3, the critical energy release rate G ic , found for each test using eq. (2) with K ( T ) III = 0, is presented as a function of ψ . A best fit through the data is shown. In the future, after additional tests are carried out, a failure criterion will be sought. Use will also be made of statistics for predicting failure. A three-dimensional criterion including the stress intensity factor K ( T ) III with an additional phase angle will also be examined.