The role of nano-sized calcium carbonate on tearing behaviour of a medium density polyethylene during a perforation experiment was investigated in this study. Several composite samples with different amounts of CaCO3 nanoparticles were fabricated. The results of perforation tests showed that the tearing behaviour of MDPE/CaCO3 nanocomposites depends on their relative amount of CaCO3 particles. Addition of CaCO3 nanoparticles to pure PE increased both the applied force for the first penetration of the indenter in the sample and the peak force (perforation force). However, the nanocomposite sample with 5 wt.% CaCO3 exhibited the highest values of the mentioned forces. In addition, this nanocomposite sample consumed the greatest energy for the whole perforation test. Images obtained from optical microscope were used to closely examine the damaged and plastic zone regions around the perforated area in all materials investigated. The plastic zone areas in tested specimens were measured using an image analyzing technique. The results of image analysis confirmed the formation of considerable expended plastic zone areas in nanocomoposite samples. The mechanical response of composite samples containing CaCO3 nanoparticles greater than 5 wt.% in a perforation test was found to be different. This was mainly due to the fact that the probability of crack formation becomes greater when higher weight percent particles are used in composites with greater possibility for agglomeration as a result of the presence of stress concentration sites within the matrix at locations where the particles are present.

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