Study On Fracture Behaviours Of Epoxy Resin Modified With Nanoparticles And The Fiber/Matrix Interfacial Properites

Over the past few decades, due to high specific strength, stiffness and toughness, fiber-reinforced polymer composite materials (FRPs) have found broad application in the aerospace, maritime and automobile and sport industries. Epoxy resin is widely used as a structural matrix material in FRPs because of their advantageous properties, e.g. ease in processing, recyclability, and good chemical resistance. The widespread use of the epoxy resin, however, is limited because of their inherent brittleness limitations. Therefore, to reinforce and/or toughen epoxy resin without significantly sacrificing other important characteristics such as thermo-mechanical properties and modulus is desired and required in many applications. Recently, due to the nano-scale dispersion of nanofillers in epoxy resin, a small amount of nanoparticles can significantly improve the mechanical properties of the resulting nanocomposites, which offers a new way to design and produce the epoxy-based nanocomposites with low cost, high performance and multi-function.In this thesis, the high shear mechanical mixing methods were used to disperse different nanoparticles and their combination; and the preparation, characterization and performance of nanoparticle-filled epoxy composites were systematically investigated. The effect of different size, type and modification of nanoparticles on the mechanical properties of epoxy composites and the related fracture mechanisms were discussed. We also tried to tailor the mechanical properties of epoxy resin through adjusting the content ratio of rigid and soft particles. Moreover, the influence of nanoparticles on interfacial adhesion between fiber and epoxy was further studied. The detail work is shown as following:1. Effect of ozone modification of MWCNTs on the performance of epoxy compositeBased on the environmental friendship and convenient process, a mild gaseous ozonolysis treatment was used to functionalize the pristine MWCNTs. After ozone functionalization, the MWCNTs reached better dispersion level and stronger interfacial bonding with the epoxy polymer, which in turn significantly improved the basic mechanical properties as well as the fracture toughness of the composites samples. We used a new method to ascertain and contrast the failure modes from one pair of homologous fracture surfaces of MWCNTs/epoxy composites. The result suggested that the MWCNT/epoxy composites showed complicated failure modes than the conventional fibrous composites. Based on this method, we quantified these failure modes of MWCNTs and correlated them with the fracture toughness of the composites studied.2. Mechanical properties and fracture mechanisms of epoxy nanocomposites with rigid or soft nanoparticlesSubmicron rubber particles resulted in remarkable improvement in fracture toughness of epoxy resin; however, other desirable properties of the rubber-toughened epoxy resin such as the elastic modulus and glass transition temperature (Tg) depress significantly; while the nano-rubber particles increased dramatically the fracture toughness of epoxy without impairing the strength and Tg of epoxy matrix. Comparatively, the rigid inorganic nanoparticles could improve the fracture toughness, stiffness and even strength simultaneously, while their toughening efficiency to epoxy was much lower than that of rubber particles. The major toughening mechanisms in rubber-filled epoxy composites involved rubber particle debonding/cavitation and localized shear banding of matrix. The rigid nanoparticles exhibited the similar toughening mechanisms as the soft rubber particles did. The nanoparticles debonding, and the subsequent plastic void growth as well as the matrix shear band likely played the key role in toughening.3. Tailoring the mechanical properties of epoxy resin with hybrid particlesThe aggregate-free distribution of silica and different rubber hybrid particles was achieved in epoxy matrix with improved dispersion techniques. As compared to the single-type particles, the silica/rubber hybrid particles filled composite performs an excellent balance among stiffness, strength and fracture toughness, which have the prominent advantages in tailoring the mechanical properties of epoxy resin. The complicated interactions between the silica/rubber hybrid particles took place in the ternary composites during both curing and fracture processes, which led to some specific morphological features that were not observable in the binary counterparts. Moreover, it was found that the combination of rubber nanoparticles and submicron particles shows a synergistic effect on toughening epoxy resin, which could be attributed to the improved matrix plastic deformation facilitated by the increased debonding ability of rubber particles to consume considerable fracture energy.4. Influence of nanoparticles on interfacial adhesion between fiber and epoxy matrixVia a convenient and intensive mixing procedure, almost uniform dispersion of rigid nanoparticles was obtained in epoxy matrix. It was found that the presence of nanoparticles improved not only simultaneously the stiffness and toughness of bulk nanocomposites but also significantly the interface strength between fiber (including carbon and glass fibers) and matrix. The improved quality of the fiber/matrix interface after addition of rigid nanoparticles could be a likely consequence of the increased toughness of bulk nanocomposites and the reduced thermal residual stress caused by mismatch in the coefficient of thermal expansion between fiber and matrix.