Interfacial characterization of carbon fiber/epoxy composites

The interfacial characteristics of carbon fiber/epoxy composites have been characterized using several experimental methods. In order to guarantee a wide variation in the fiber/matrix bond strength, composites were fabricated using surface treated PAN-based fibers and compared to composites fabricated with the same fibers which had not been surface treated. Additionally, composites fabricated with PAN-based fibers were compared to composites formed with pitch-based fibers. Also, in a separate series of evaluations the influence of fiber sizing on both composite formation and standard measurements of interfacial bonding was evaluated.; Physical characterization techniques such as a wetting test and a water absorption test were performed to evaluate the work of adhesion and the water absorption characteristics of the different carbon fiber/epoxy composite systems. Conventional mechanical characterization techniques such as the longitudinal tensile test, transverse tensile test, short beam shear test, and double cantilever beam test were conducted on the carbon fiber/epoxy composites to evaluate longitudinal tensile strength, transverse tensile strength, interlaminar shear strength and critical strain energy release rate, G{dollar}sb{lcub}rm 1c{rcub}{dollar}. Dynamic mechanical characterization tests were also conducted to measure, (i) the storage shear modulus, loss shear modulus, and tan {dollar}delta{dollar} as a function of frequency and temperature and, (ii) tan {dollar}delta{dollar} values at T{dollar}sb{lcub}rm g{rcub}{dollar} of the different fiber/matrix systems.; The results of the work indicated that the water absorption test and the wetting test may be used to differentiate between sized and unsized carbon fiber. It was also concluded that the transverse tensile test and the double cantilever beam test can be used to distinguish between surface treated carbon fiber and carbon fiber without surface treatment. The short beam shear test can only differentiate between fibers having widely different surface characteristics. The longitudinal tensile test may be used to qualitatively differentiate between sized and unsized fibers. However, the results from these conventional techniques for characterizing fiber/matrix interfaces, tend to have high standard deviation and are sensitive to the composite fabrication technique. The dynamic mechanical characterization technique can clearly differentiate between surface treated fiber and fiber without surface treatment. Compared to the conventional characterization techniques, the results of the dynamic mechanical technique tend to have less standard deviation and are less sensitive to the composite fabrication technique. Thus, the most significant result of this dissertation is the development of a new non-destructive technique for characterizing the fiber/matrix interface in composite specimens. The results from this dynamic mechanical technique can be used to evaluate a viscosity term for the composite and, thus, estimate the energy dissipation occurring at the fiber/matrix interfaces.