Crack propagation in porous polymer sheets with different pore sizes
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Crack propagation in porous polymer sheets with different pore sizes Atsushi Takei *, Center for Soft Matter Physics, Ochanomizu University, 2-1-1 Otsuka, Bunkyo, Tokyo 112-8610, Japan Ko Okumura , Department of Physics and Center for Soft Matter Physics, Ochanomizu University, 2-1-1 Otsuka, Bunkyo, Tokyo 112-8610, Japan Address all correspondence to Takei Atsushi at [email protected] and Ko Okumura at [email protected] (Received 15 July 2018; accepted 31 October 2018)
Abstract Physical understanding of crack propagation is a fundamental issue in the industry. In the literature, crack velocities of polymer materials are strongly dependent on their visco-elastic properties and energy release rates. Recently, numerical and theoretical studies have proposed that structural sizes in polymers also influence on crack propagation. Here, using polymer sheets with similar visco-elastic properties but with different pore sizes, we vary explicitly the representative structural size and examine the effect of the size on crack propagation. Findings in this work help us to understand crack propagation in polymer materials and bio-inspired materials which have porous structures.
Introduction Physical understanding of crack propagation plays an essential role in the industry, and mechanical properties of materials with cracks have been studied for a wide range of materials such as metal, glass, and polymer. Recently, polymer materials attract considerable attention as a low-weight, tough, and inexpensive material for a new era. For example, recent polymer science has provided high toughness,[1] self-healing properties,[2] and high stretchablility[3, 4] with polymer materials. The polymer is a promising material, but an understanding of its fracture mechanism is still a challenging issue partially because both of its visco-elastic property and molecular-network structure are complex. In the literature, crack behavior in polymer sheets has been studied with various methods, which include tensile,[5, 6] trouser,[7] cutting,[8] tearing,[9] and fixed-grip methods.[10] Most of the previous studies conclude that the energy for tearing a polymer sheet correlates with the propagation velocity of a crack. Among these experimental methods, the fixed-grip method is a unique method to explore the behavior of crack propagation in polymer sheets. With this method, the so-called energy release rate G, which corresponds to tearing energy, takes a constant value during crack propagation, and the relationship between the energy release rate G and the crack-propagation velocity V can be clearly quantified. With the fixed-grip method, interesting characteristics of crack propagation on rubber sheets have been found: (1) power laws between energy release rate and crack velocity, and (2) a drastic velocity jump from a slow
* Present address: National Institute of Advanced Industrial Science and Technology, Central 5-2, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan.
mode (∼1 mm/s) to a fast mode (∼1000 mm/s) at a critical rele
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