In this article, the role of nano size calcium carbonate on resistant against penetration and perforation of MDPE was investigated through experiments. 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). In addition, this nanocomposite sample consumed the greatest energy for the whole perforation test. The plastic zone regions around the perforated area were inspected using scanning electron microscopy. The toughening mechanisms of shear yielding and massive shear yielding observed. The mechanical response of composite samples containing CaCO3 nanoparticles greater than 5 wt.% in a perforation test was found to be different. Fracture surface images showed when calcium carbonate content is higher than 5 weight percent, agglomeration of nano particles occured. Debonding stress relates on particle size inversely and debonding stress will be raised as particle size decreases. Therefore, as shown in the SEM micrograph of a nanocomposite sample with 10 wt.% CaCO3 nanoparticles, the crack has been nucleated and then propagated during different stages of the test.

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