Study On Mechanical Properties Of Rock-concrete Composite

This thesis focuses on the study of rock-cement mortar combinations with three different ratios and three different interface angles.Static compression tests were performed using a pressure testing machine,while dynamic impact tests were performed using a SHPB dynamic impact system.A photography system was used to obtain crack propagation patterns to investigate the influence of different ratios and interface angles on the mechanical properties and failure modes of the specimens.The main research content and conclusions are as follows:(1)Analysis of the static mechanical properties and fracture mode of the rock-cement mortar combination.A static uniaxial compression test was performed on the specimens using a pressure testing machine.During the compression process,crack propagation was observed using a camera and wave speed test system.The experimental results show that under the condition of uniaxial static compression,the uniaxial compressive strength and axial peak strain of the specimens decrease with increasing interface angle.At a 45 degree interface angle,the specimens also exhibit significant slip failure.The specimens show densification before approaching failure and the strain value at the interface will increase with the increase of the axial pressure,leading to the occurrence of a strain concentration zone.During the initial loading stage,the closure of internal pores has a greater impact on wave amplitude compared to wave speed.When cracks begin to propagate,the increase of axial stress has less impact on wave speed and wave amplitude due to the consistency of crack propagation with the direction of wave propagation.(2)Analysis of dynamic mechanical properties of the rock-cement mortar combination.Different dynamic impact tests were conducted on the specimens using a SHPB dynamic impact system at three different bullet launch gas pressures.The dynamic stress-strain curve and dynamic mechanical parameters under different bullet launch gas pressures were analyzed.The results showed that under the same bullet launch gas pressure,the dynamic compressive strength of the specimens increases with the increase of the cement mortar strength,and the axial peak strain also increases.As the interface angle of the specimens increases,the dynamic compressive strength decreases,and the axial peak strain also decreases.The dynamic compressive strength and axial peak strain of the specimens are linearly positively correlated with the bullet launch gas pressure but are linearly negatively correlated with the interface angle.(3)Analysis of the dynamic failure mode of the rock-cement mortar combination.High-speed cameras were used to record the failure process of the specimens under different bullet launch gas pressures.The strain field evolution during the cracking initiation and propagation process was analyzed,as well as the energy dissipation,crack type,and fracture mode of the specimens.The results showed that the specimens exhibit more complete fractures and diverse crack types at a bullet launch gas pressure of 0.085 MPa and 0.09 MPa.As the bullet launch gas pressure increases,the influence of the interface angle on the fracture energy and fracture energy density becomes more significant,with fracture energy and fracture energy density decreasing as the interface angle increases.Before reaching the stress peak,crack development and expansion are relatively slow,and the deformation of the specimen remains relatively uniform.When the stress peak is reached,the rapid expansion and penetration of cracks lead to an increase in localized deformation,resulting in more obvious and narrow localized deformation bands.