Mechanical response and crack propagation of oil well cement under dynamic and static loads

摘要

The dynamic mechanical properties and fracture mechanism of three types of oil well cement with different formulations were investigated using a phi 50 mm split Hopkinson pressure bar (SHPB) and quasi-static mechanical tests were conducted with a hydraulic universal testing machine. The stress-strain diagram, time-stress diagram, total energy absorption diagram, and the dynamic growth factor (DIF) under different strain rates were obtained. The crack propagation process of the oil well cement under dynamic loading is evaluated using high-speed photography to determine the fracture mechanism. The test results show that the strength of the cement increases under a dynamic impact. The compressive strength of the pure cement increases from 37 MPa to 184.80 MPa under static loading. However, the peak stress of the cement stone strengthened with cellulose fiber is lower under a dynamic load than a static load. Under dynamic loading, the absorption energy is higher for the pure cement stone than for the cement stone reinforced with whiskers and cellulose. Furthermore, the crack initiation, crack propagation, and fracture characteristics of the oil well cement are different under dynamic and static loads. Under a static load, the rupture of the cement is the result of the propagation of the tensile cracks. Under dynamic loading, there are fewer micro cracks on the cement surface and a composite fracture results from tensile and shear cracks.