Brittle deformation in rocks depends upon loading rate; with increasing rates, typically greater than~10 2 s −1 , rocks become significantly stronger and undergo increasingly severe fragmentation. Dynamic conditions required for rate-dependent brittle failure may be reached during impact events, seismogenic rupture, and landslides. Material characteristics and fragment characterization of specific geomaterials from dynamic loading are only approximately known. Here we determine the characteristic strain rate for dynamic behavior in felsic crystalline rocks, including anisotropy, and describe the resulting fragments. Regardless of the type of felsic crystalline rock or anisotropy, the characteristic strain rate is the same within uncertainties for all tested materials, with an average value of 229 ± 81 s −1. Despite the lack of variation of the critical strain rate with lithology, we find that the degree of fragmentation as a function of strain rate varies depending on material. Scaled or not, the fragmentation results are inconsistent with current theoretical models of fragmentation. Additionally, we demonstrate that conditions during impact cratering, where the impactor diameter is less than~100 m, are analogous to the experiments carried out here and therefore that dynamic strengthening and compressive fragmentation should be considered as important processes during impact cratering. Plain Language Summary When rocks deform quickly, they can behave with properties very different to the properties that would be measured when rocks are deformed slowly. In this study, we have measured the strength of rocks deformed at different rates to find how fast they must be deformed to cause substantial changes to their properties. We chose to look at granitic rocks and gneisses as they are broadly representative of the Earth's continental crust. We found that regardless of the exact rock type, the change from slow to fast deformation occurs at the same rate. When rocks break at fast rates, they break into many small fragments. We have measured the size of those fragments from our experiments to show how the average fragment size changes as a result of the deformation rate and the rock type. In addition, we show that the changes of properties that we see in our experiments is important for the formation of impact craters and potentially earthquake rupture and landslides. Rock strength can be investigated over a range of strain rate regimes (Zhang & Zhao, 2014): quasi-static (10 −5-10 −1 s −1), intermediate strain rate (10 −1-10 1 s −1), high strain rate (10 1-10 4 s −1), and very high strain rate (>10 4 s −1). Results across those regimes (

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The aim 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 were selected for this study. Brazilian disc experiments were performed over a range of strain rates from ~ 10–5 /s to 2.7 × 101 /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., Acta Mater 61:3509–3521, 2013). Dynamic fragmentation during split tension mode failure has received little attention, and in the present study, we determine the fragment size distribution based on the experimentally fragmented specimens. 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 average size of the secondary fragments has a strong strain rate dependency over the entire testing range, while the primary fragment size is less sensitive at lower strain rates. Marble and sandstone are found to generate more pulverised secondary debris when compared to basalt and granite. Furthermore, the mean fragment sizes of primary and secondary fragments are well described by a power-law function of strain rate.