Mode I Fracture Toughness of Nanorubber Modified Epoxy under Wide loading Rate Ying-Gang Miao1,2, Hong-Yuan Liu 2*, Yu-Long Li 1*, Hsiu Hsien Wu 2, and Yiu-Wing Mai 2 1 School of Aeronautics, Northwestern Polytechnical University, Xi’an, Shaanxi Province, 710072, P.R.China 2 Center for Advanced Materials Technology (CAMT), School of Aeronautics, Mechanical & Mechatronic Engineering J07, The University of Sydney, Sydney, NSW 2006, Australia Corresponding Authors: hong-yuan.liu@sydney.edu.au (H-Y Liu); liyulong@nwpu.edu.cn (Y-L Li) Abstract Dynamic mode I fracture toughness of nano-rubber modified epoxy were investigated using the split Hopkinson tension bar (SHTB) facility, with loading rates up to 3×104 MPa·√m/s. The quasi-static toughness of those nanocomposites were also measured with an Instron machine at two loading rates of ~0.04 MPa·√m/s and 5 MPa·√m/s, respectively. The materials tested are: neat epoxy; and 2, 6 and 10 wt.% nano-rubber particles, respectively, in epoxy. Special specimens with a single-edge crack in the finite width direction were designed for mode I toughness testing with the SHTB. In addition, pulse shaping technique was used to optimize the loading stress wave for accurate measurements with the SHTB. The results indicated that the presence of nano-rubber could improve the fracture toughness of the bulk composites in the range of loading rates studied. However, high loading rates might have degraded the cavitation capability of the nano-rubber and hence decreased the toughness of the rubber-modified epoxies compared to low loading rates. Keywords Nano-rubber modified epoxy, fracture toughness, high strain rate, Hopkinson bar 1. Introduction Epoxies have gained growing attention from industries for its specific properties, such as high modulus and strength. Epoxy products have also been widely used as structural materials, e.g., window of vehicles and helmet to resist impact and explosion. However, the low toughness of epoxy is always the disadvantage in its applications. The advent of nanoparticles has offered one excellent candidate for toughening epoxy to satisfy specific engineering requirements. To add soft or rigid nano-fillers to epoxy can significantly enhance the toughness of epoxy with no serious loss in strength and elastic modulus [1-2]. Owing to the expanded applications of epoxy products, their dynamic responses have drawn increasing attention from both industry and scientific communities, though some polymers have been investigated extensively under quasi-static loading. Sahraoui [3] studied the fracture behaviors of a modified epoxy resin by three different testing machines with loading rates in the range from 5×103 to 104 MPa·√m/s. Evora [4] measured dynamic fracture
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