چكيده به لاتين
Crack propagation specially under spatial mixed mode loadings is a complicated phenomenon. On the other hand, most of the cracked components are subjected to different combinations of mixed mode I/II/III loading. Experimental studies help us better understand this phenomenon and present new fracture criteria that can better estimate fracture toughness and fracture initiation angles under different mixed mode loadings and for different materials. Until now, many fracture test configurations have been presented for different mixed mode loading cases. Among them, the number of spatial mixed mode configurations specially those dedicated to mixed mode II/III loading, are really limited and they have some serious defects like inducing considerable mode I deformation. The mixed mode I/II/III configurations can be utilized in order to investigate mixed mode II/III loading, but their loading fixtures are complicated. So in this study, a new configuration for mixed mode II/III fracture test is introduced. This new configuration does not have the defects of previous mixed mode II/III configurations and also has some advantages like simple geometry, ease of set up and negligible T-stress value. At first, this configuration is used to conduct mixed mode II/III experiments on a brittle polymer called PMMA. According to the comparison between the experimental results and the estimations of some existing fracture criteria, the best consistency is found with the Richard and the maximum effective stress fracture criteria. In the next step, the new configuration is used to conduct mode II and mode III fracture experiments on nanocomposite reinforced by carbon nanotubes. The nanocomposite test specimens are made of an epoxy resin commonly used in aerospace industry. To reinforce this polymer, different contents of multi-walled carbon nanotube (0.1%, 0.5% and 1% weight percentage) are used. It was observed that by increasing the nanoparticle content, the mode II and mode III fracture toughness is improved with an increasing trend. To justify the observed improvement, the test specimens fracture surfaces are investigated by means of a scanning electron microscope (SEM).
Keywords: spatial mixed mode loading, mixed mode II/III loading, nanocomposite fracture toughness, brittle fracture
