Dynamic Split Tensile Strength of Basalt, Granite, Marble and Sandstone: Strain rate dependency and Fragmentation

The scope of this study is to understand the strength behaviour and fragment size of rocks during indirect, quasi-static, and dynamic tensile tests. Four rocks with different lithological characteristics namely, basalt, granite, sandstone and marble are selected. The Brazilian disc experiments are performed over a range of strain rates from 10-5 /s to 2.7x101 /s using a hydraulic loading frame and a split-Hopkinson bar. Over the range of strain rates, our measurements of dynamic strength increase are in good agreement with the universal theoretical scaling relationship of Kimberley et al. (2013). Dynamic fragmentation during a split tension mode receives very little attention and not much information is available about the generated fragment size distributions. The fragments fall into two distinct groups based on the nature of failure, coarser primary fragments and finer secondary fragments. The degree of fragmentation is assessed in terms of characteristic strain rate and is compared with existing theoretical tensile fragmentation models. The primary fragment size are less sensitive to strain rate, particularly at lower strain rates. The size of secondary fragment has a strong strain rate dependency over the entire testing range. Marble and sandstone are found to generate more pulverized secondary debris when compared to basalt and granite. Further, it is shown that the mean fragment sizes of primary and secondary fragments are well described by a power law function of strain rate.