Dynamic Brazilian Split Tests on Gypsum as a Model Material for Soft Rocks

Understanding the deformation behaviour of rocks under dynamic loads is crucial in rock mechanics. This study investigates the rate-dependent tensile strength and fracture response of gypsum, a model material for soft rocks, across two different sample porosities. Quasi-static Brazilian disc tests were conducted using a servo-controlled universal testing machine, revealing that tensile strength decreases with increasing porosity. However, in the quasi-static regime, strength remains relatively constant across different strain rates. Dynamic tests were performed using a Split Hopkinson Pressure Bar (SHPB) setup, showing that dynamic tensile strength is consistently higher than quasi-static strength, regardless of porosity. Furthermore, as the dynamic strain rate increases, strength values further rise, indicating a strong rate dependency. Also, due to gypsum’s brittle nature and low tensile strength, fracture resulted in significant powder formation. To capture real-time fracture evolution, high-speed imaging was employed. Full-field strain distribution and fracture evolution has been studied using Digital Image Correlation (DIC). The findings demonstrate a strong correlation between porosity, tensile strength, and fracture behaviour, offering valuable insights into the dynamic response of soft rocks.