13th International Conference on Fracture June 16–21, 2013, Beijing, China -8- Figure 7. Numerical and experimental incident and reflected wave for ceramic sample Figure 8(a). Experimental trace from tests on advanced ceramic A & B, (b) SIF evolution for advanced ceramic A & B from Eq. (5) The difference in the incident and reflected waves in the ceramic tests is much greater than that of the PMMA tests. This is due to the difference in mechanical impedance between the test specimens and the tungsten carbide bar where more of the incident wave was transmitted through the bar/specimen interface. It is desirable to test specimens with similar impedance to that of the bar. In the case of advanced ceramics the impedance difference is low and as a result there is a notable difference between the incident and reflected traces, which allows for the clearer data analysis. With PMMA its mechanical impedance is much lower then that of the tungsten carbide bars. In view of this fact it is not surprising that the reflected and incident signals are of similar amplitude as very little of the incident wave can be transferred to the specimen for fracture. For relatively low impedance materials it is recommended that a low impedance bar be used as the loading apparatus. 5. Conclusions A novel experimental method for determining the dynamic fracture toughness of super-hard materials where specimen dimensions are limited was presented. This was achieved using a miniaturized Kolsky bar in one-point fracture. Preliminary tests were undertaken to determine the dynamic fracture toughness of PMMA. It has been shown that at increased loading rates the fracture A B B A
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