Effect of Loading Rate on Dynamic Fracture Toughness of Polycarbonate

Abstract

Accurate estimation of dynamic fracture properties of materials is important for component design under impact conditions. Amorphous glassy polymers have wide engineering applications. For Polymethyl methacrylate (PMMA), which is a brittle amorphous polymer, literature indicates that the fracture toughness increases at higher loading rates compared to that under static loading conditions. Motivated by this observation, in the present work, another amorphous polymer named Polycarbonate (PC), which is ductile in nature, is considered and effect of loading rate on fracture toughness of PC is investigated. Experiments using the single edge notched (SEN) specimen subjected to 3-point bending are performed at various loading rates. A UTM is used for low loading rate experiments. High loading rate experiments are conducted using Hopkinson pressure bar. Ultra high speed imaging (100,000 fps) is used to make accurate measurement of fracture initiation time in these experiments. Attempts are being made to investigate the near notch deformation in detail. A hybrid experimental and numerical approach is pursued in which finite element simulations are performed using the boundary conditions obtained from experiments. A rate and temperature dependant constitutive model is used for PC. Stress intensity factor (SIF), evaluated from simulation is correlated with experimentally measured SIF. Results show that that dynamic fracture initiation toughness of PC does not vary significantly at higher loading rates; values remain close to that obtained under quasi-static loading conditions.