Local and Effective Mechanical Properties of Polymer Nanocomposites

116 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2009.The study on the effect of nanospheres on the mechanical property improvement of epoxies pointed to the fact that nanostructured materials provide improvements mainly on the toughness of an epoxy. In this regard, local information of the interfacial properties of embedded nanoparticles can be the key in developing calibrated hierarchical damage models. To this effect, a new methodology was developed to quantify the average interfacial shear strength (IFSS) of individual vapor grown carbon nanofibers (VGCNFs) embedded in an aerospace grade epoxy. The IFSS from several experiments with as-grown and non-functionalized VGCNFs was 111+/-32 MPa. This value is up to 24% higher than that of the IFSS of multi-wall carbon nanotubes in epoxy matrices and twice the IFSS of high temperature heat-treated VGCNFs. The measured IFSS values were independent of the nanofiber embedded length. Post-mortem images of the embedded section of the nanofibers after the pull-out experiments showed no traces of the matrix on the fiber surface, which indicates that cracks initiated and propagated along the fiber-matrix interface causing adhesive failure, rather than shearing of the epoxy. (Abstract shortened by UMI.).U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD