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Interphase region in polymer based nanocomposites is a very thin layer that is created between the reinforcing phase and the matrix surface due to reaction forces between the nanoparticles and the matrix. The ability to determine the behavior of the interphase region can facilitate the understanding and prediction of the fracture toughness and fatigue behavior through multiscale modeling. In the present study, by using the fully analytical multiscale hierarchical modeling method, fracture toughness and also fatigue behavior of thermoset resins containing spherical fillers with consideration the influences of the main damage mechanisms and interphase properties (thickness and elastic modulus of the interphase region) were investigated. The novelty of this investigation is that it enables the application of a range of properties to the interphase zone and describes a technique for multiscale modeling based on this interphase zone. The present multiscale approach quantifies the dissipation energy due to main damage mechanisms at the nanoscale and accounts for the emergence of an interphase region as functionally graded (FG) properties surrounding nanofillers. Modeling of FG interphase power‐varying properties, the derivation of governing equations, and the evaluation of the findings, all are parts of the achievements of this research. In addition, multiscale analyses have been carried out on fracture energy and fatigue behavior in various fiber volume fractions with and without interphase properties. It was found that the fracture toughness and fatigue behavior are significantly dependent on the interphase elastic properties and thickness. Furthermore, the critical debonding stress and the fracture energy were assessed with various interfacial fracture energy, elastic modulus, and thickness of interphase. Finally, the accuracy of the utilized multiscale approach with consideration of interphase properties was verified by comparing the modeling results with experimental tests on thermoset resins containing spherical fillers. [ABSTRACT FROM AUTHOR]

In the present study, weight functions (WFs) of a subsurface crack were derived by proposing a new general form for approximate one‐dimensional WF. The WFs coefficients were considered as a function of crack length to depth ratio and were obtained using reference stress intensity factors (SIFs) of 16 cracks under uniform, linear, and parabolic normal and shearing loadings. The verification was performed by comparison of the straight and coupled SIFs calculated by WF and finite element modelling under some complicated loadings. In conclusion, the WFs can be simply and effectively employed for evaluating the cracks under any complex stress distributions. [ABSTRACT FROM AUTHOR]