Crack propagation in porous polymer sheets with different pore sizes

2019

Polymer

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It has long been known for elastomers that the velocity of crack propagation jumps as a function of strain. On the other hand, such a jump has not been reported in the literature for polymers which do not exhibit a rubbery plateau in the storage-modulus plot. Here, we report observation of jumps in crack propagation for semi-crystalline polymer sheets without the rubbery plateau, as a result of pulling the sheets at a constant speed. We discuss the advantages of this crack-propagation test under constant-speed stretching and provide physical interpretation of the velocity jump observed for non-elastomer sheets on the basis of a recently proposed theory for the velocity jump in crack propagation.

Section: Crack Propagation Test Under a Fixed-grip Conditionmentioning

confidence: 77%

Velocity jump in the crack propagation induced on a semi-crystalline polymer sheet by constant-speed stretching

Tomizawa

2019

Polymer

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“…Considering that the velocity jump has been utilized effectively for developing tough elastomers in the industry, the results of the present study are useful for developing tough polymers in general. This is especially because the previous study [5] suggests theoretically that the velocity jump is expected be observed universally for variety of materials and the previous studies [9] and [8] demonstrate experimentally that the dynamic test is more sensitive for detecting the velocity jump.…”

Section: Discussionmentioning

confidence: 89%

“…Recently, it is reported that the velocity jump is not observed for a semi-crystalline polymer [8] as a result of performing the crack-propagation test under the static boundary condition. However, more recently, the velocity jump is successfully observed for the same semi-crystalline polymer when the crack-propagation test is performed under a dynamic boundary condition [9].…”

Section: Introductionmentioning

confidence: 99%

Crack propagation under static and dynamic boundary conditions

Aoyanagi

2019

Polymer

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Velocity jumps observed for crack propagation under a static boundary condition have been used as a controlling factor in developing tough rubbers. However, the static test requires many samples to detect the velocity jump. On the contrary, crack propagation performed under a dynamic boundary condition is timesaving and cost-effective in that it requires only a single sample to monitor the jump. In addition, recent experiments show that velocity jump occurs only in the dynamic test for certain materials, for which the velocity jump is hidden in the static test because of the effect of stress relaxation. Although the dynamic test is promising because of these advantages, the interrelation between the dynamic test and the more established static test has not been explored in the literature. Here, by using two simulation models, we elucidate this interrelation and clarify a universal condition for obtaining the same results from the two tests, which will be useful for designing the dynamic test. arXiv:1907.06825v1 [cond-mat.soft]

“…As a result, we did not observe crack propagation in the velocity range studied in the present study. However, in the previous study [33], from a technical reason, the constant-speed crack propagation with a fixed-grip condition was initiated some time after 9 we set a given strain to samples and we consider that the effect of stress relaxation due to this preparation time could tend to suppress crack propagation. This point will be further discussed elsewhere.…”

Section: Discussionmentioning

confidence: 99%

Visco- and plastoelastic fracture of nanoporous polymer sheets

Tomizawa

2019

Polym J

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We study the dependence of the fracture surface energy on the pulling velocity for nano-porous polypropylene (PP) sheets to find two components: the static and dynamic ones. We show that these terms can be interpreted respectively as plastoelastic and viscoelastic components, as has been shown for soft polyethylene (PE) foams in a previous work. Considering significant differences in the pore size, volume fraction and Young's modulus of the present PP and previous PE sheets, the present results suggest a universal physical mechanism for fracture of porous polymer sheets. The simple physical interpretation emerging from the mechanism could be useful for developing tough polymers. Equivalence of Griffith's energy balance in fracture mechanics to a stress criterion is also discussed and demonstrated using the present experimental data.