Micromechanics-based characterization of mechanical properties of fuzzy fiber-reinforced composites containing carbon nanotubes

General off-axis mechanical behavior of fuzzy fiber-reinforced composites (FFRCs) is investigated using a 3-dimensional unit cell micromechanics model. In the FFRCs studied herein, uniformly aligned carbon nanotubes (CNTs) are radially grown on the circumferential surfaces of carbon fibers. The effects of orientation and volume fraction of carbon fiber, volume fraction of CNT, stiffness and thickness of the interphase region created due to non-boned interaction between the CNT and polymer matrix on the elastic response of the FFRCs are studied. The results reveal that the mechanical properties of the FFRCs are strongly dependent on the off-axis angle of carbon fiber. With the increase of off-axis angle from 0° up to 90°, the elastic modulus of FFRC sharply decreases up to 45° and then its value increases, whereas without considering CNTs on the surface of carbon fiber, the elastic modulus continuously decreases. It is shown that the growth of CNTs on the surface of carbon fiber can lead to the highest enhancement for the elastic modulus of 90° on-axis coupon. Poisson's ratio of the FFRC rises with the increase of off-axis angle from 0° up to about 35° and then its value decreases. Also, the increase of CNT volume fraction yields a significant increase for the elastic modulus of 90° on-axis coupon, while rising carbon fiber volume fraction can substantially enhance the elastic modulus of 0° coupon. According to the obtained results, increasing both stiffness and thickness of the interphase can improve the elastic modulus of FFRC over the range of 0-90°, especially for 90° on-axis coupon. The results predicted by the present model are much closer to the experiment than those predicted by the numerical simulations available in the literature.