Fatigue crack propagation in mica‐filled polyolefins

Abstract Edge notched samples of polypropylene (PP) and high‐density polyethylene (HDPE) containing different mica concentrations were tested in mode I tensile loading. Crack growth was approximated by a non‐linear regression of exponential form using statistical software (SAS). Characterization of fatigue crack propagation (FCP) was made using the Paris‐Erdogan law. The crack front in PP was preceded by a wide plastic zone in which craze developed, leading to a discontinuous crack growth. Using spline functions, a margin between maximum and minimum FCP rates, recorded during the crack progression, is presented along with the average FCP rates. It is shown that mica‐reinforced PP samples exhibit higher FCP rates than unfilled PP. In HDPE, mica reduces FCP rates resulting in a higher resistance to fatigue crack propagation. Effect of test frequency is presented for unfilled polymers and 10 percent mica concentration by weight in both matrices. An increase in the test frequency has no significant effect on FCP rates for both raw and mica‐reinforced PP. Unfilled and mica‐filled HDPE show noticeable decrease in FCP rates with increasing frequency.