红砂岩受高压电脉冲击穿作用下的破裂行为试验研究

Experimental Study on Fracture Behavior of Red Sandstone Subjected to Breakdown Effect of High Voltage Electric Pulse

高压脉冲放电破岩具有绿色环保、能量可控的特色,是一种应用前景广阔的新兴岩石破碎技术。通过电击穿试验分析了高压脉冲作用下红砂岩的破裂机制,研究了不同试件尺寸和放电电压下红砂岩的破裂模式及破裂程度。结果表明:高温和冲击波是导致试件破裂的内在机制。高压电脉冲作用下,红砂岩在电极附近由于等离子通道贯通后的迅速膨胀作用形成击穿区,损伤最为严重。击穿区外侧受冲击波的影响出现径向裂纹,冲击波强度足够时可继续诱发试件边界附近出现剥落裂纹。击穿区、径向裂纹及剥落裂纹的形成与试件的尺寸和放电电压密切相关。采用裂纹密度和分形维数两个指标量化分析了高压脉冲作用后试件的破裂程度。随着试件尺寸增加,试件由块状破碎转变成穿孔破坏模式,试件的裂纹密度、裂纹的复杂程度以及分形维数呈现出降低趋势。随着放电电压的增加,试件由穿孔破坏模式转变成块状破碎,其裂纹密度、裂纹的复杂程度和分形维数呈现增加趋势。

Rock breaking by high voltage pulse has the characteristics of environmental protection and energy controllable,which is an emergent rock fragmentation technology with broad application prospect.The fracture mechanism of red sandstone specimens under high voltage pulse was analyzed by electric breakdown experiment,and the fracture modes and fracture degrees of red sandstone specimen under different size and discharge voltages were studied.The results show that high temperature and shock wave are the internal mechanisms leading to the fracture of the specimen.Under the action of high voltage pulse,a breakdown zone near the electrodes is formed in the sandstone specimen due to the rapid expansion of plasma channel,and the damage is the most serious.Radial cracks appear on the outside of the breakdown zone under the action of shock wave.When the shock wave is strong enough,it can induce spalling cracks near the boundary.The formation of breakdown zone,radial cracks and spalling cracks is closely related to the specimen size and discharge voltage.The crack density and fractal dimension are selected to quantitatively analyze the fracture degree of the specimen after high voltage pulse.With the increase of specimen size,the failure mode of specimen changes from fragmentations to perforation failure,the fracture density,the complexity and the fractal dimension of the specimen decrease continuously.With the increase of discharge voltage,the failure mode of specimen changes from perforation failure to fragmentations,the fracture density,the complexity of crack and the fractal dimension of the specimen are increased.