INSTRUMENTED DART IMPACT EVALUATION OF LINEAR LOW-DENSITY POLYETHYLENE AT CONTROLLED IMPACT ENERGY

Instrumented impact testing of linear low density polyethylene (LLDPE I) (ethylene and 1-octene copolymer) was carried out using a Rheometrics Drop-Weight Tester (RDT-5000). A method of partial penetration at controlled impact energy was used and developed. The set impact speed was raised step by step in small intervals of 0.25 m/s over a range of 0.76 m/s to 9.14 m/s. The impact deformation profiles of LLDPE I were obtained for a series of specimens impacted at different speeds. The stress states of the LLDPE I during the corresponding impact events were obtained with the instrumented impact tup. By comparing the observed impact profile with the force-displacement trace, the yield point and the initial failure point of LLDPE I were assessed. The point of 100 percent of the maximum load on the force-displacement trace of a total penetration impact was shown to be the yield point. On the basis of the determination of the yield point, a parameter, ductile ratio (D.R.), was redefined to characterize the ductility of polymers. The initial break point of LLDPE I was determined. The effect of specimen thickness and test temperature on the impact properties was investigated.