Creep lifetime prediction of polypropylene/clay nanocomposites based on a critical failure strain criterion

This work presents a new approach for the creep lifetime prediction of polypropylene (PP)/organoclay nanocomposites. The creep failure of PP and its nanocomposites with and without PP grafted maleic anhydride (PP-g-MAH) is found to occur at a critical strain independent of the stress level investigated. This peculiar critical strain is combined with a time-strain superposition method to predict the creep failure lifetime of PP nanocomposites. In this method, a generalized creep compliance curves followed a relatively simple power law are generated from nonlinear creep data obtained by accelerated tests at high stresses. The creep lifetime under lower stresses is then predicted successfully by using the critical strain as the failure criterion. The lifetime predictions for the PP materials considered based on this approach are satisfactory compared with the experimental results. The approach proposed is intuitive and convenient, and has the potential to be extended to other polymeric materials which possess a critical failure strain behavior.