Specimen Geometry Effect on the Deformation Mechanisms of Polypropylene-Based Composites Under Impact Loading at Different Temperatures

Abstract

Dynamic behaviors of polypropylene (PP), PPethylene propylene rubber (PP-EPR) and PP-nanoclay (PP-Nanocor) composites were studied by using split Hopkinson pressure bar at different temperatures and under different strain rates. Samples with two different geometries and with or without petroleum jelly lubricant were tested under identical testing conditions to compare the dynamic responses with underlying deformation mechanisms. For all the test temperatures and strain rates, the dynamic responses of neat PP and PP-Nanocor showed post-yield strain-softening, whereas those of PP-EPR showed strain-hardening after the yield point. PP-Nanocor showed more strain-softening compared with neat PP at room temperature due to the more important localized shearing deformation at the nanofiller/matrix interfaces. Friction between the sample and the bars affected the dynamic response of the materials at room temperature as well as high temperatures seen as differences in behavior between the dynamic behaviors of the non-lubricated thin samples and the non-lubricated thick samples under the same testing conditions. At room temperature and without lubrication, the thicker specimens of neat PP and PPNanocor failed during dynamic testing due to the barrelinginduced crack that propagated in the specimen and led to the formation of a peripheral fragment. Although petroleum jelly provided a satisfactory lubrication condition for both neat PP and PP-based composites at room temperature and at high temperatures, by reducing the friction effect on the yield behavior, the lubrication did not have a significant effect on the post-yield behavior of neat PP and PPNanocor, particularly for the room temperature testing and with the thick specimens.

Elastic and yield behaviors of recycled polypropylene-based composites: Experimental and modeling study

“…Cylindrical samples with a diameter of 8 mm and a thickness of 3 mm were cut from the center of the injected tensile samples and were placed between the input bar and output bar to determine the dynamical responses. Petroleum jelly was used as lubricant for the dynamic testing [28,29]. A furnace with two symmetrical resistance heaters was installed for high-temperature testing, while liquid nitrogen was used for low temperature testing.…”

“…Once the master curve was built, the parameters DH eff and s i (0) could be determined in line with Equation (29). KnowingDH eff , the parameters DH Amorphous and DH Crystalline could be calculated through Equation (22) for a given crystallinity content.…”