PSI - Issue 18

V. Dattoma et al. / Procedia Structural Integrity 18 (2019) 719–730 Author name / Structural Integrity Procedia 00 (2019) 000–000

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The influence of parameters of r and q is shown in Fig. 5. the maximum shear traction T t * can become negative, when r ˃ q and Δ n ˃ 0 and for r ˂ q, unrealistic results are observed, when there is large normal compression: T t * reduces with increasing normal compression and eventually can become smaller or equal to zero. Only when r = q the required tangential traction increases with increasing normal compression, yielding a phenomenological description of friction. And for r = q the influence of the value of “r” on the required normal traction after a certain amount of shear separation is scrutinized. The results are shown in Fig. 5a-b. The maximum normal traction T t * after complete shear separation is given by equation 2. � � �� � �� ����� � � (2) This yields unrealistic results for r ≠ 1 since T n * can never decrease to zero, therefore only r = q =1 is a realistic coupling behavior; the required normal traction reduces to zero at complete shear separation. In this work, the energy release of the material was estimated to be 279 [J m -2 ] and the normal (δ n) and tangential -6 m and 1,74×10 -6 m respectively, after several numerical trials. In the numerical software the cohesive zone is modelled by interface elements between plies, to which the properties of the cohesive zone were attribute (Fig. 6a) and the area in which the cohesive zone is defined is highlighted in Fig. 6b. The cohesive area was limited around the hole, since the experimental results show delamination starting from hole boundary. (δ t ) opening shifts were evaluated in 2.29×10

(a) (b) Fig. 5. (a) Shear traction and (b) normal traction varying coupling parameter (M. Van den Bosch et al., 2006).

(a)

(b)

Fig. 6. (a) Cohesive zone and (b) Cohesive zone area.

3.4. Constraints and loads The composite plate was loaded with an in-plane uniform tensile displacement at its end. At the other end all the movements have been blocked by imposing a fixed support. In order to prevent secondary bending of the joint, zero displacement in the z-direction was applied in various zone of the model (Fig. 7a); such areas include the entire