Delamination properties of hierarchal structured carbon fiber composites with bio-inspired vertically aligned nano reinforcement

Abstract

Composites materials often provide the best solution for structural applications, offering a good combination of mechanical properties and low weight. Carbon fiber reinforced polymer (CFRPs) composites are commonly used wherever high strength-to-weight ratio and stiffness (rigidity) are required, such as aerospace, superstructure of ships, automotive, sports equipment etc... However, typically in epoxy based CFRPs composite laminates, debonding between the carbon fiber and polymer matrix, delamination between the CFRP sheets and generally the relatively low toughness of composite laminates are often limitations. Many researchers tried to overcome this limitation by mimicking nature principles, leading to a new class of composites with improved toughness. Understanding the hierarchical structural elements in biological materials can serve for systematizing the development of bio-inspired materials with improved mechanical properties. The tubular structural element that is found in hierarchically organized chitin-based crab exoskeleton provides ductile attachment that helps to stitch the layers together and improves fracture toughness. In a similar fashion, producing carbon fiber composites that contain well sorted and oriented nano reinforcement elements such as carbon nanotubes (CNTs) or carbon nanofibers (CNFs) has great importance in utilizing the capabilities and exceptional properties of CNTs and CNFs. In this thesis, first, functionalized CNT/CNF were dispersed in epoxy resin using a Three Roll Mill. Then, carbon fiber reinforced polymers (CFRPs) with a mixture of epoxy thermosets and CNTs/CNFs as a polymer matrix were fabricated using layer-by-layer deposition method. Finally, delamination properties of hierarchically structured CFRPs with and without CNTs/CNFs were investigated to assess the mechanical properties. The vertically aligned CNT/CNF structures are expected to improve fracture toughness and energy absorption.

Composites materials often provide the best solution for structural applications, offering a good combination of mechanical properties and low weight. Carbon fiber reinforced polymer (CFRPs) composites are commonly used wherever high strength-to-weight ratio and stiffness (rigidity) are required, such as aerospace, superstructure of ships, automotive, sports equipment etc... However, typically in epoxy based CFRPs composite laminates, debonding between the carbon fiber and polymer matrix, delamination between the CFRP sheets and generally the relatively low toughness of composite laminates are often limitations. Many researchers tried to overcome this limitation by mimicking nature principles, leading to a new class of composites with improved toughness. Understanding the hierarchical structural elements in biological materials can serve for systematizing the development of bio-inspired materials with improved mechanical properties. The tubular structural element that is found in hierarchically organized chitin-based crab exoskeleton provides ductile attachment that helps to stitch the layers together and improves fracture toughness. In a similar fashion, producing carbon fiber composites that contain well sorted and oriented nano reinforcement elements such as carbon nanotubes (CNTs) or carbon nanofibers (CNFs) has great importance in utilizing the capabilities and exceptional properties of CNTs and CNFs. In this thesis, first, functionalized CNT/CNF were dispersed in epoxy resin using a Three Roll Mill. Then, carbon fiber reinforced polymers (CFRPs) with a mixture of epoxy thermosets and CNTs/CNFs as a polymer matrix were fabricated using layer-by-layer deposition method. Finally, delamination properties of hierarchically structured CFRPs with and without CNTs/CNFs were investigated to assess the mechanical