چكيده به لاتين
In this study, the effect of fiber angle orientation, in delamination interface, on the initiation and propagation fracture toughness of plain woven composites with stacking sequences of [012//012], [011/30//0/011], [011/45//0/011] and [011/30//-30/011] under mode I loading was investigated. These stacking sequences were chosen to eliminate the effects of the remote ply orientation on the delamination behavior of double cantilever beam (DCB) specimens. The samples were manufactured using the wet hand lay-up method and the fracture tests were conducted on specimens using the universal testing machine, SANTAM STM-150. The experimental results show that the interface ply orientation has a negligible effect on the magnitude of initiation and propagation fracture toughness of plain woven composites due to the delamination propagation in the resin-fiber interface of delamination. Experimental investigations of fracture surface demonstrate the existance of different mechanisms on the delamination propagation, where the crack propagation in the resin-fiber interface proves to be one of the primary mechanisms for increasing the fracture toughness of such specimens. In addition, the experimental observations reveal that the fiber bridging is not an influential mechanism for increasing the fracture toughness during delamination propagation unlike unidirectional DCB specimens. The VCCT method was used to predict the amount of initiation fracture toughness using the numerical simulation. In order to predict the experimental load-displacement curve, the traction-separation curve was obtained using the J-integral approach and experimental data. Then, using the resulting curve, the crack propagation in DCB specimens was simulated in Abaqus finite element package. The experimental results show that the change in the delamination interface angle has an insignificant effect on the initiation and propagation fracture toughness as well as the length of the fracture process zone. Therefore, in order to obtain the R-curve of a certain specimen with different interface angles, only a single test on the specimen with the 0//0 interface angle is sufficient, followed by the use the resulting R-curve for other interfaces
