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Abstract
Six fracture surfaces have been observed extending at velocities between cR (the Rayleigh wave velocity) and 1.3cR in high-speed photographs of four diamond specimens. The diamonds were embedded in a transparent polymer and shocked in plate impact experiments. The measured velocities exceed limiting velocities proposed in theoretical and practical studies of single mode I cracks in diamond. The fracture surfaces probably extend by initiation and coalescence of multiple tensile fractures along a single cleavage plane. This mechanism is dependent on the suppression of cracks branching from the {111} growth plane in diamond and considers the population of flaws near a propagating crack tip.
Acknowledgements
The authors thank Dr. Alan Guest and De Beers Consolidated Mines Ltd. for support of this research. Specimens were prepared by Ray Flaxman and Daniel Cross. High-speed photography at the Cavendish Laboratory is funded by the Engineering and Physical Sciences Research Council.