چكيده به لاتين
In the present research, delamination initiation and growth of the end notch flexure (ENF) specimens at different interface fiber angles (0//θ), under mode II loading was investigated. To this end, ENF specimens with stacking sequences of [011/θ//012] were manufactured by the hand lay-up method and θ=0, 15, 45, 60 and 90 are selected in order to eliminate the effect of the remote ply orientation on the R-curve behavior of delaminated beams. The initiation and propagation fracture toughness and R-curves were extracted based on the ASTM standard. In addition, the crack length and the crack slipping were extracted by the image-processing method. The experimental results showed that the ENF specimens with 0//0 and 0//15 interfaces, due to the suddenly crack propagation, did not show any R-curve behavior. In the other words, the initiation and propagation of interlaminar fracture toughness of these specimens were the same. Also, it was observed that by increasing θ of [011/θ//012], the initiation load and the initiation interlaminar fracture toughness were significantly reduced. Moreover, the fiber bridging and constitutive laws for specimens were derived experimentally. The obtained results indicated that, by increasing of θ from zero of [011/θ//012] staking sequences, the bilinear cohesive law could not predict the load-displacement curves for ENF specimens. Therefore, two modified cohesive models were introduced to consider the fiber bridging zone. Moreover, the capabilities of each model were examined. Finally, for a more accurate understanding of the influence of interface fiber orientation on the delamination initiation and growth, the stress components of the interlaminar zone were evaluated. The results showed that by changing the interface angles, the shear stress components have a greater effect on the initiation and steady-state interlaminar fracture toughness.
Keywords: Delamination Initiation and Growth, Mode II, Strain Energy Release Rate, Cohesive Zone Model, Fiber Bridging Law.
