Fatigue crack growth in epoxy polymer nanocomposites

The present paper describes detailed analyses of experimental data for the cyclic-fatigue behaviour of epoxy nanocomposite polymers. It has been shown that the data may be interpreted using the Hartman-Schijve relationship to yield a unique, 'master', linear relationship for each epoxy nanocomposite polymer. By fitting the experimental data to the Hartman-Schijve relationship, two key materials parameters may be deduced: (i) the term A, which may be thought of as the fatigue equivalent to the quasi-static value of the fracture energy, G, and (ii) the fatigue threshold value, [Formula: see text], below which no significant fatigue crack growth (FCG) occurs. It has then been established that the values of these parameters, together with the slope, n, and intercept, D, of the Hartman-Schijve master relationship, may be used (i) to compute the experimental results measured for the fatigue behaviour of the epoxy nanocomposite polymers, (ii) to understand the observed fracture and fatigue behaviour of these materials with respect to the structure of the epoxy nanocomposite polymers, and (iii) to deduce the 'upper-bound', i.e. 'worst-case', FCG rate curve which may be used by industry as a material development, material selection, design and service-life prediction tool when these epoxy nanocomposite polymers are used in engineering applications such as structural adhesives and/or as matrices in fibre-reinforced composites. This article is part of a discussion meeting issue 'A cracking approach to inventing new tough materials: fracture stranger than friction'.