Abstract：The strain-based strength criteria are of increasing significance for brittle materials. In order to study the laws of failure strains under dynamic tension，a series of Brazilian disc and flattened Brazilian disc(FBD) samples of marble under the dynamic split tests are performed with a wide range of strain rates using split Hopkinson pressure bar(SHPB) of 100 mm in diameter. The relationship between the failure strain and the size of samples，the projectile speed，and the strain rate，are discussed；and some useful results are obtained. The failure strains of all types of samples in different projectile speeds are achieved with strain gauges stuck on the center of the samples；and the test results indicate that the failure strain increases with the increase of the projectile speed. In certain range of the projectile speed，the failure strain increases remarkably. But when it is out of this range，the failure strain increases slightly. The relationship between the failure strain and the size of samples is notably affected by the projectile speed. However，when the strain rate is low，the failure strain will increase remarkably，especially for FBD which has less scatter；when the strain rate is high，the failure strain increases slightly and results of all types of samples are scarcely scattered. Compared with Brazilian disc，the FBD has larger bearing capacity and higher failure strain in low projectile speed. With the increase of projectile speed，the trend of FBD vanishes gradually；and when the projectile speed is high，its failure strain is even less than that of the Brazilian disc.
