微波照射后磁铁矿石动力学性能及破碎特征研究

Experimental research on the dynamic mechanical properties and breakage behaviors of magnetite caused by microwave irradiation

以改善矿石破碎效率和能耗为目的,采用微波照射与霍普金森压杆(SHPB)相结合的试验方法,开展不同微波参数照射前、后磁铁矿石动力学性能及破碎特征研究,对比分析其宏观力学性能与微观结构特征,揭示微波弱化磁铁矿石力学性能的作用机制。结果表明:微波照射功率比照射时间对磁铁矿石的动力学性能的影响更为显著,只有当功率达到一定程度时,照射时间的影响才逐渐显著;随着照射功率的逐渐增大,磁铁矿石试样内部结构的损伤经历原有裂纹扩展、沿晶破裂及沿晶破裂伴随穿晶破裂3个阶段;应力﹣应变曲线弹性阶段的斜率逐渐变小,历时变短,屈服变形阶段逐渐变长,峰后阶段分别呈应变回弹、应力跌落及峰后塑性3种现象;微波对试样的P波波速和强度的弱化影响逐步显著;磁铁矿石试样经历拉伸破坏和拉伸剪切破坏2个阶段。分析认为微波对磁铁矿石力学性能的弱化主要是因为矿石中不同矿物晶粒对微波的敏感性不同而出现差异膨胀形成温度应力,最终导致试样内部发生沿晶体边界发生拉裂或晶体自身沿其内部缺陷发生破裂。因此,在利用微波辅助破岩时,需根据岩石的矿物组成、各矿物的升温特性及破碎块度要求设计微波加热参数,以提高微波辅助冲击破岩的能量利用率和破岩效率。

In order to improve rock crushing efficiency and to reduce energy consumption of ore,the dynamic properties and breakage behaviours of magnetite caused by microwave irradiation with different microwave parameters were studied by using microwave irradiation combined with Hopkinson pressure bar(SHPB). The weakening mechanisms of mechanical properties of magnetite ore by microwave were revealed by the comparative analysis of macroscopic mechanical properties and microscopic structure characteristics. The results show that the influence of the irradiation power on the dynamic performance of magnetite is more significant than that of the irradiation time,and only when the power reaches a certain level will the effect of the irradiation time become gradually significant. With increasing the irradiation power,the damage to the internal structure of the magnetite sample undergo three stages:original crack propagation,intergranular fracture and intergranular fracture accompanied by transgranular fracture,and the slope of the elastic stage of the stress-strain curve gradually decreases with a shorter duration. The yield deformation stage becomes longer,and the post-peak stage presents three phenomena:"strain resilience","stress drop" and "post-peak plasticity" respectively. It is concluded that the weakening effect of microwave on P wave velocity and strength is more and more significant with increasing the irradiation power,and the magnetite sample undergo tensile and shear failure stages. It is pointed out that the weakening effect of microwave on the mechanical behaviours of magnetite is attributed to that the different sensibility of magnetite components to microwave results in differential expansion and further leads to intergranular fracture or rupture of granular inner defects. Therefore,when using microwave-assisted rock fragmentation,microwave heating parameters should be designed according to the mineral composition of the rock,the heating characteristics of each mineral and the fragmentation requirements,so as to improve the energy utilization rate and rock fragmentation efficiency of microwave-assisted rock fragmentation.