Experimental study on tensile properties and crack propagation of dry and saturated tuff under different strain rates
Using an electro-hydraulic servo press and a split Hopkinson pressure bar(SHPB)with a 50 mm diameter,static and dynamic Brazilian disc splitting tensile tests were performed on tuff in order to study the impact of water saturation and strain rate on the tensile mechanical properties of tuff.The crack propagation process and fracture morphology of the specimen under high strain rate were obtain by a high-speed camera system,and the microstructure of the rock surface and fracture was observed with an electronic digital microscope with 1 000 times.The results show that there is an obvious strain rate effect on the tensile strength of the specimen;the higher the strain rate,the faster for the specimen to reach the peak stress.The average tensile strength of the saturated test piece under static load is 88.12％of the dry test piece,and the tensile strength of the saturated test piece under 0.2 MPa,0.3 MPa and 0.4 MPa air pressure is 99.89％,95.25％and 90.52％of the dry test piece.The saturated action degrades the rock mass and reduces its tensile strength.The average value of the dynamic enhancement factor(DIF)of the saturated specimen under the pressure of 0.2 MPa,0.3 MPa and 0.4 MPa is 1.14,1.08 and 1.05 times than that of the dry specimen.Due to the existence of cohesion and"stefen"effect,the DIF of saturated specimens is higher than that of dry ones.With the increase of strain rate,the crack propagation speed of the specimen increases,and the crack propagation is wider and speed of the saturated specimen is higher than that of the dry specimen.Under static load,the specimen is in the form of typical split tensile fail-ure,while the specimen is in the form of tensile and shear failure under dynamic load.The tuff itself has a large number of primary joints,pores and other structural weak surfaces.Under the action of stress waves,the cracks at the weak surface of the specimen expand and penetrate and eventually cause dam-age.The erosion effect of water makes the crack propagation degree of the saturated specimen signifi-cantly higher than that of the dry specimen.
full of waterstrain ratepeak stressDIFcrack propagationbroken formmesoscopic structure
万方数据
维普
