13th International Conference on Fracture June 16–21, 2013, Beijing, China -9- significant factors, when we use this material as cellphone bumper. However, it is not easy to measure the dynamic stress or strain rate accurately at the notch root by experiment. In this study, therefore, dynamically and elastic FEM is applied to the high-speed tensile test for notched specimens. Then, the dynamic stress and strain rate concentrations have been discussed under various tensile speeds. The conclusions can be made the following way. (1) It may be concluded that the strain rate concentration factor ( ) ( ) max t nom K t t ε ε ε = , which is defined by the maximum strain rate ( ) max t ε at the notch root over the average strain rate ( ) nom t ε at the minimum section at each time, is always constant and controlled by the notch shape alone independent of the tensile speed. (2) It is found that the difference between the static and dynamic maximum stress concentration ( max st σ σ− ) at the notch root increases is proportional to the tensile speed when 5000 u t mm s ≤ . (3) It is found that the strain rate of the notch root increases is proportional to the tensile speed when 5000 u t mm s ≤ . References [1] J. Radin, W. Goldsmith, Normal missile penetration and perforation of layered plates. Int. J. Impact Engng, 7, (1988) 229-259. [2] T. Aya, T. Nakayama, Influence of Strain Rate on Elastic Modulus of Polymers. Journal of the Japan Society for Technology of Plasticity, Sosei-to-Kako, 36, 413 (1995) 665-670. [3] S. Honma, Practical strength and durability of plastics (in Japanese). Plastics, 55, 1, (2004) 174-182. [4] A. Chatani, S. Uchiyama, Dynamic stress concentration of notched strips. Material, 21, 226 (1972) 636-640. [5] W. Altenhof, N. Zamani, W. North, B. Arnold, Dynamic stress concentrations for an axially loaded strut at discontinuities due to an elliptical hole or double circular notches. International Journal of Impact Engineering, 30, 3 (2004) 255-274. [6] K. Kawata, S. Hashimoto, Dynamic stress concentration for notched elastic bar under dynamic load. University of Tokyo Institute of Space Aeronautical Report (in Japanese), 8, 2 (1972) 377-384. [7] H. Matsumoto, I. Nakahara, Dynamic stresses in a hollow cylinder or a disc with a hole due to axially symmetric pressure variations. Transactions of the Japan Society of Mechanical Engineers, 32, 237 (1966) 709-717. [8] H.G.. Georgiadis, A.P. Rigatos, N.C. Charalambakis, Dynamic stress concentration around a hole in a viscoelastic plate. Acta Mechanica, 111, 1-2 (1995) 1-12. [9] S. Tanimura, Dynamic problems of materials and structures review of the studies. Transactions of the Japan Society of Mechanical Engineers, Series A, 63, 616 (1997) 2466-2471.
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