Fatigue and fracture properties of nanostructured carbon and hierarchical polymer-matrix composites

Abstract

This thesis presents the results of an experimental study of two application-limiting properties of polymer-matrix composites: fatigue and fracture toughness. Two matrix dispersed nanostructured fillers (helical-ribbon carbon nanofibers and graphene oxide) were used to fabricate epoxy nanocomposites and hierarchical carbon fiber laminates based on them. There were three chief focus areas designed to evaluate the nanofiller's influence on bulk matrix properties in the nanocomposites and matrix-dominated laminates: standard quasi-static mechanical testing to assess stiffness and strength, in-plane fatigue performance represented by stress-life curves and constant life diagrams and fracture toughness via mode I crack opening and delamination. Experimental data indicate that at low weight fractions (¿ 1 wt.%) the unmodified nanofillers have little impact of stiffness and strength but function well to statically toughen the matrix and dynamically retard crack growth within it. These data correlate well with other novel studies in the field and offer insight into the toughening mechanisms that develop either ahead or behind the crack tip. Evidence suggests that toughness and resistance to fatigue developed predominately in the course of crack growth and not for crack initiation.