Different mechanical and cracking behaviors of single-flawed brittle gypsum specimens under dynamic and quasi-static loadings

• Strain rate affects the compressive strength of gypsum.
• Strain rate influences the cracking behaviours around the flaw.
• Different failure modes under different loading conditions
• The development of tensile cracks is suppressed in dynamic compression tests.
• Elastic modulus and failure strain are also strain rate-dependent for gypsum.

Besides the strength, other mechanical properties of rock and rock-like brittle materials are also loading-rate/strain-rate dependent over a wide range of strain rate, which in turn affect the cracking behaviors. In order to investigate the variation of the mechanical properties and cracking behaviors under both the dynamic and quasi-static strain rate conditions, rock-like artificially moulded gypsum specimens with and without pre-existing flaw(s) are loaded under different strain rates. A quasi-static loading is applied to the specimens by a uniaxial compression rig. The dynamic loading is produced by the split Hopkinson pressure bar (SHPB). It is found that the compressive strength, the nominal elastic modulus and the failure strain of the gypsum specimens increase apparently with the strain rate. Using the high speed video imaging system, the similarities and differences of the fracturing processes in specimens containing a pre-existing flaw under the quasi-static and dynamic loading conditions are studied. Shear cracks are observed to be the dominant crack types under dynamic loadings while tensile cracks are dominant under quasi-static loadings.