13th International Conference on Fracture June 16–21, 2013, Beijing, China -9- toughness of PMMA increases. A comparison of methods to determine SIF evolution was examined. One method using the applied load up to the point of fracture, another method, measuring strain directly on the sample close to the crack tip and a third through the use of an impact response curve. It was shown that strain measurements directly on the sample greatly underestimate the SIF. This is due to the strain measurements being erroneous as they were taken outside the singular zone. The impact response curve yielded apparent dynamic fracture toughness very similar to that of the load-point method. The strain used to calculate the IRC was measured directly on the crack tip in the model, which should lead to a more accurate calculation of SIF even when using static formula. Future testing will focus on detailed experimental work concurrent with numerical analysis to investigate the validity of these methods with emphasis on the use of impact response curves to determine dynamic fracture toughness. No attempt has been made to explain the observed increase in apparent fracture toughness at this stage, although it is in the scope for future testing. The dynamic SIF evolution of two grades of advanced ceramic was investigated. At high rates of loading the fracture toughness of these grades was shown to decrease from their static values. A numerical model of the one-point bend set up has also been developed and excellent agreement between experimental and numerical results has been achieved. Future work will focus on further development of the model to determine the fracture time, a vital fracture parameter for accurate determination of dynamic fracture toughness. Acknowledgements The authors would like to thank Element Six Ltd., Enterprise Ireland and the Irish Research Council for providing financial support for this research. References [1] M.G. Charpy, On testing metals by the bending of notched bars. Int. J. Frac. 25 (1984) 287-305. [2] D.R. Ireland, Critical Review of Instrumental Impact Testing Dynamic Fracture Toughness. The Welding Institute of American Society for Metals, Technical Report (1976) No. 79-55. [3] W.L. Server, Impact three-point bend testing for notched and precracked specimens. J. Test. Eval., 6.1 (1978) 29-34. [4] W. Bohme, The influence of stress wave on the dynamic crack tip loading in three- point bend impact. DGM Informationsgesellschaft mbH, Impact Loading and Dynamic Behaviour of Materials, 1 (1988) 305-311. [5] C. Bacon, J. Farm, J.L. Lataillade, Dynamic fracture toughness determination from load-point displacement. Exp. Mech. 34.3 (1994) 217-223. [6] G. Weisbrod, D. Rittel, A method for dynamic fracture toughness using short beams. Int. J. Frac., 104.1 (2000) 89-103. [7] A. Belenky, I. Bar-On, D. Rittel, Static and dynamic fracture of transparent nano-grained alumina. Journal of the Mechanics and Physics of Solids, 58.4 (2010) 484-501. [8] J. Fengchun, K.S. Vecchio, Hopkinson Bar Loaded Fracture Experimental Technique: A Critical Review of Dynamic Fracture Toughness Tests. Applied Mechanics Review, 62 (2009) 060802. [9] J.G. Williams and J.M. Hodgkinson, Crack-blunting mechanisms in impact tests on polymers. Proc. R. Soc. Lond. A, 375 (1981) 231-248. [10] H. Kolsky, An Investigation of the mechanical properties of materials at very high rates of loading. Proc. Phys. Soc Lond, 62.11 (1949) 676.
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