Experimental Study For Dynamic Mechanical Properties Of Marble Using Split Hopkinson Pressure Bar

Brazilian disc (BD) specimens were prepared according to the test method for split tensile strength which was suggested by International Society for Rock Mechanics (ISRM) in 1978. Furthermore, two parallel flat ends were introduced in the original Brazilian disc in order to avoid the high stress concentration near the loading area, thus the specimen becomes flattened Brazilian disc (FBD). The specimens have different diameter and thickness, the loading angle of all the FBD specimens is 20°. In addition, cracked chevron notched Brazilian discs (CCNBD) were made according to the new type of rock fracture toughness specimen proposed by ISRM in 1995. For the same reason, two parallel flat ends were made in the specimen for the benefit of loading.More importantly, these two ISRM suggested methods used in static testing were extended to dynamic situation. The BD and FBD specimens were subjected to diametral impact by the projectile with different speed using the split Hopkinson pressure bar (SHPB) of 100mm diameter with a thin aluminum circular plate as pulse shaper. First, the dynamic stress distribution in the BD and FBD specimens was obtained by using the finite element software ANSYS, and the validity of the tests was affirmed according to the qualifications which a complete dynamic split tension test should have. The performance of BD and FBD specimens under the dynamic impact was compared, then the repetitive of tests was validated and the influence of stress nonuniformness near two flattened ends of specimen to the results was taken into account. The strain rate, failure time, failure pattern and the relationship betweenstress and strain during the failure process were analyzed to get some conclusions about the elastic modulus, tensile strength and its sensitivity of marble at high strain rate. Finally, the influence of the geometry and strain rate to the results of the test was also analyzed.Finally, using the same equipment, the cracked chevron notched Brazilian disc specimens were subjected to diametral impact, the fracture initiation time for the specimen was studied, which laid a foundation for dynamic fracture toughness test in the future.