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Sayyed Mohammad Rad

Grade:  Master

 

Thesis Title:

Modeling of Short Fiber Composites Behavior under Tensile Loading by Damage Mechanics

Year: Sept. 2018 - Jun. 2021.

Abstract:

Nowadays, a variety of damage numerical models has been proposed to calculate and estimate the failure strength of short fiber composites. This study investigates and numerically simulates the failure strength of short fiber composites and aims to provide a comprehensive model for modeling the behavior of short fiber composites are used in different parts to the point of failure leading to reduction in the time and cost of analyzing them while increasing the accuracy. In this study. the behavior of short fiber composite including short glass fibers and thermoset resin is modeled. To model the resin behavior until the failure, a numerical elastic-viscoplastic-damage model was implemented together with a developed continuous damage model for thermoset polymers. To use this model as an applied one implemented on applied geometries, which in this research is the standard dumbbell shaped samples. numerical homogenization method was employed. In this homogenization method, due to the similarity of the resin and composite behavior, the same numerical model expressing the resin behavior is utilized to model the composite behavior. Furthermore. experimental tests were performed in different stages to extract the constants of the numerical model and to extract the data required for the validation of the model. The samples required for the experimental tests were fabricated according to the ASTM D638 standard and were analyzed. Composite samples filled with 3 wt% of fibers were prepared. By comparing the results obtained from numerical modeling approach with those from experimental tests, it was found that the numerical model was highly capable of modeling the performance of this composite with low error. The strain error of this model at the breaking point of the samples compared to the experimental results was found to be 0.45% and that in the case of strength was equal to 3.98%. The model further predicted the decrease in the fracture strength in specimens loaded with low filler content ascribed to the increase in the effect of fiber tip stress concentration relative to the fiber reinforcing effect, which in turn increases the damage and thus causes premature failure. For composites with the components introduced in this study, the critical percentage of fibers, under which the effect of loss in the strength is observed, is equal to approximately 16% by weight fraction of fibers. For composites with 40% by fibers weight fraction, the increase in strength at the breaking point compared to the pure resin is equal to 18.3%. In addition, the strain reduction at the breaking point is shown to be 60%.

 

Keywords:  Short fiber composite, Strength, Numerical simulation, Tensile test, Damage mechanics.

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