Numerical Analysis of Load Transfer Mechanism in Fiber-Reinforced Composites Enhanced by Zinc Oxide Nanowires

Composite reinforced structures have high strength and high stiffness to weight ratio because of the outstanding properties of the fiber reinforcement. The load transferring mechanism from the matrix to the fiber is very crucial since the fibers carry most of the applied load and protect the whole structure from the early damages. The interfacial bonding between fiber and matrix plays a critical role in this procedure. In this regard, studying the ways to enhance the fiber interface has attracted a lot of attention recently. Experimental investigations show that growing nanoparticles directly on the fiber can improve the interface. It is reported that Zinc Oxide (ZnO) nanowires grown on the fiber result in fewer defects on the fiber surface compare to other nanoparticles due to the methods of growth. Single fiber fragmentation test (SFFT) is widely used to evaluate the load transfer mechanism by applying the tensile load and tracking the number of fragments.

In this study, three-dimensional (3D) single carbon-fiber enhanced with radially grown ZnO reinforced epoxy matrix is investigated numerically. Multi-scale analysis is employed to simulate the behavior of the enhanced fiber composite due to the different length scale of the material, and the theories used in each scale. Since the strength of ZnO nanowires are much higher than the shear force on the fiber, the ZnO is not fractured during the loading. Hence, the nanowires grown in the fiber and embedded in the epoxy create a domain called the enhancement layer. The effective material properties of the enhancement layer are extracted at micro-scale by the homogenization analysis of an appropriate representative volume element (RVE). The fiber interface is modeled at the meso-scale utilizing the cohesive zone method (CZM). A very thin layer (close to zero) of interface with the cohesive element is modeled around the fiber. The material properties of the interface are evaluated based on the properties of fiber and the enhancement layer. The macro-scale damage behavior of fiber is defined by user-defined mechanical material behavior (UMAT) based on the Tsai-Wu failure criterion. Single fiber fragmentation test (SFFT) is simulated in ABAQUS by applying the tensile loads on the enhanced SFC. The load transferring mechanism is evaluated by capturing the number of fiber fragmentation and calculating the interfacial shear strength (ISS). The effect of different volume fraction of ZnO is also investigated. The results show the improvement of the interface due to the increasing number of fragments and the ISS in the enhanced composite compared to the bare composite.