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In this paper an analytical approach for determining load distribution in single-column multi-bolt composite joints by considering elastic nonlinear behavior of the composite materials is presented. Load distribution was calculated by writing the governing equations of the motion. This closed form solution is an integration of spring-based models with nonlinear behavior of composite plate materials. Developed method is capable to calculate taken load by each bolt and its displacement by simultaneous solving of governing equilibrium equations of the system. This manuscript specifically focused on the influence of composite material nonlinearity on the load distribution of single bolted composite joints. For this purpose, load changes versus displacement are plotted by taking into account both the linear and nonlinear material behavior. The achieved results via suggested solution revealed that displacements were increased upto 2.5-5 percent in comparison with the results of linear method available in the literature. In addition, due to the manufacturing tolerances, bolt–hole clearances can vary within allowable limits and fits. Therefore the effect of bolt hole-clearance on the composite joints with linear and nonlinear material properties was also investigated.

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Mechanical properties of polymeric materials are significantly sensitive to the loading rate. Therefore, it is necessary to develop a dynamic constitutive model to investigate their strain rate dependent mechanical behavior. In this study, first by conducting torsion experiments the shear behavior of neat and reinforced epoxy with carbon nano-fibers (CNFs) was studied experimentally. Then, the Johnson-Cook (J-C) model has been modified to be able to model the shear behavior of neat polymers. The strain rate effects on elastic behavior of polymers were considered by introducing a material equation. Then, by combining the modified Johnson-Cook (MJ-C) model with a micromechanical model (Halpin-Tsai model) and using pure polymer experimental tesults and mechanical properties of carbon nano fiber, the strain rate dependent mechanical behavior of polymers reinforced with CNFs at arbitrary strain rates and volume farction of carbon nanofiber has been predicted. The new model presented in this research is called as the dynamic-micromechanical constitutive model. The predicted results for the neat and nano-phased polymers were compared with conducted and available experimental results. It has been shown that the present dynamic constitutive model can predict the strain rate dependent mechanical behavior of polymeric materials with a good accuracy.