超声波振动下花岗岩裂纹变化特性的研究

发布时间：2018-08-09 19:22

【摘要】：世界经济的迅猛发展使得人类对矿产资源的需求量越来越大,矿产资源的勘探深度越来越大,勘探地层越来越硬。硬岩具有致密、研磨性强、强度高、破碎功大等特点,使得其很难被破坏。为解决硬岩钻进的基本问题,应进行碎岩新方法及碎岩机理的研究,降低岩石的破碎强度,实现大体积破碎。完整致密硬岩的固有频率一般为20KHz~40KHz,在岩石受到合理地共振时,内部会快速产生裂纹,导致其强度急剧下降,这种情况下,岩石会很容易被破坏,进而提高了钻头使用寿命与钻进速度。因此,采用超声波振动配合切削钻进的方法来解决硬岩钻进的难题,具有一定的可行性。岩石是一种含有多种细观缺陷的混合物质,岩石的破坏过程受控于这些细观结构,在载荷作用下,这些细观缺陷会产生不可逆的演化,从而导致岩石强度的降低。研究岩石在超声波振动下其内部细观裂纹的变化特性,能够从根本上揭示超声波作用下岩石强度下降规律的内在机理,为超声波振动辅助钻进技术提供理论指导,这对解决硬岩钻进的技术难题具有非常重要的战略性意义。本文从超声波振动下花岗岩裂纹的开裂条件、扩展特性及静载荷对花岗岩损伤的影响规律三个方面,采用有限单元法与室内实验相结合的方法,对超声波振动下花岗岩裂纹的变化特性进行了研究。介绍了花岗岩的物理力学参数,并以此为基础,通过联合强度理论推导出了超声波振动下花岗岩裂纹起裂的数学模型,应用岩石损伤力学,获取了以推导出的联合强度准则为基础的超声波振动下花岗岩的损伤模型。利用ANSYS软件与MATLAB软件建立了可以体现花岗岩非均匀程度的数值模拟模型,并以此模型为基础,对超声波振动下花岗岩裂纹的变化过程进行了数值模拟计算,得到以下结论:花岗岩固有频率随静载荷的增大而逐渐增大,静载荷-固有频率曲线近似呈对数型,固有频率的增加幅度随静载荷的增大逐渐减缓;当振动频率与花岗岩一阶固有频率相近时,花岗岩内应力、应变远远高于其他振动频率下花岗岩内部应力、应变值,振动频率对应力、应变变化速率的影响作用十分明显,当振动频率与花岗岩一阶固有频率相同时,应力、应变达到最大值;只有当花岗岩裂纹尖端处局部微单元体满足强度准则时,花岗岩裂纹开始扩展,其扩展过程分为萌生、扩展、贯通3个阶段,在萌生阶段,岩石内某些节点上产生应力集中,这些节点开裂形成微孔隙,缓和了应力集中并使得岩石内部应力重新分布,在扩展阶段,微孔隙不断向四周缓慢扩展,最终沿某一方向形成主裂纹,主裂纹继续延伸,在主裂纹上出现随机分布的次裂纹,在贯通阶段,微孔隙、微裂纹之间开始相互贯通,形成新的裂纹。设计了超声波动静组合加载装置,对超声波振动下花岗岩裂纹变化特性进行实验研究,实验结果与数值模拟结果基本一致。对比实验结果与数值模拟结果,发现采用以联合强度理论为基础的花岗岩裂纹起裂条件的数学模型进行数值模拟得到的结果要比单独采用第二或者第三强度理论进行数值模拟更加接近实验结果。对超声波振动实验数据进行整理,研究静载荷对花岗岩损伤程度的影响规律,得到以下结论:超声波振动过程中,静载荷存在阈值,当施加的静载荷小于阈值时,静载荷的变化并不引起花岗岩弹性模量的变化,静载荷的变化对花岗岩损伤没有影响,当施加的静载荷大于阈值时,改变静载荷值将直接影响对花岗岩造成的损伤程度;在施加的静载荷大于阈值的前提下,静载荷对花岗岩造成损伤的过程可分为缓冲阶段和损伤阶段,在缓冲阶段,花岗岩弹性模量下降不明显,在损伤阶段,花岗岩弹性模量急剧下降;在其他条件不变的情况下,超声波振动下存在最优的静载荷值使得花岗岩损伤程度最大,本实验中最优静载荷值为400N。进行CT扫描实验,获取了不同振动条件下花岗岩的CT图像,根据CT图像对超声波振动下花岗岩裂纹扩展过程进行分析,将花岗岩裂纹扩展过程分为萌生、扩展、贯通三个阶段,与数值模拟结果基本一致。振动过程中,随着振动时间的增加,裂纹逐渐向轴心处汇聚。
[Abstract]:With the rapid development of the world economy, the demand for mineral resources is becoming more and more large, the exploration depth of mineral resources is increasing, and the exploration strata are becoming harder and harder. Hard rock has the characteristics of tight, strong abrasive, high strength and great crushing work, which makes it difficult to destroy. In order to solve the basic problem of hard rock drilling, a new method of rock breaking and a new method of rock breaking should be carried out. The study of rock breaking mechanism reduces the crushing strength of rock and realizes large volume crushing. The natural frequency of the complete and dense hard rock is generally 20KHz~40KHz. When the rock is reasonably resonant, it will quickly produce cracks and lead to a sharp decline in its strength. In this case, the rock will be easily destroyed, thus improving the service life and drilling of the drill. Therefore, it is feasible to use the method of ultrasonic vibration and cutting drilling to solve the difficult problem of hard rock drilling. The rock is a kind of mixture containing a variety of mesoscopic defects. The failure process of the rock is controlled by these mesoscopic structures. Under the load, these fine defects will produce irreversible evolution and thus lead to the irreversible evolution. The reduction of rock strength. The study of the change characteristics of the meso crack in the rock under ultrasonic vibration can reveal the inherent mechanism of the law of rock strength decreasing under ultrasonic wave, and provide theoretical guidance for the ultrasonic vibration assisted drilling technology. It has a very important strategy to solve the technical problems of hard rock drilling. In this paper, the characteristics of granite crack under ultrasonic vibration, the propagation characteristics and the effect of static load on the damage of granite are three aspects. The method of combining the finite element method with the laboratory experiment is used to study the change characteristics of the granite crack under ultrasonic vibration. The physical and mechanical parameters of the granite are introduced. On the basis of this, the mathematical model of granite crack initiation under ultrasonic vibration is derived through the joint strength theory, and the damage model of granite under ultrasonic vibration is obtained by using the rock damage mechanics, which is based on the combined strength criterion derived from the ultrasonic vibration. The ANSYS soft parts and the MATLAB software can be used to reflect the granitoid. The numerical simulation model of uniform degree is used to simulate the change process of granite crack under ultrasonic vibration. The following conclusion is obtained: the inherent frequency of granite increases gradually with the increase of static load, and the static load natural frequency curve is approximate to logarithmic type, and the increase of natural frequency is with static load. When the vibration frequency is similar to the first natural frequency of granite, the internal stress of granite is much higher than that of the internal stress of granite under other vibration frequencies, the strain value, the vibration frequency correspond to the force, the change rate of strain change is very obvious, when the frequency of the vibration is the same as the first natural frequency of the granite, the stress is the same. The strain reaches the maximum. Only when the local microelement meets the strength criterion at the tip of the granite crack, the granite crack begins to expand, and its expansion process is divided into 3 stages: germination, expansion and penetration. In the initiation stage, the stress concentration is produced on some nodes in the rock, and these joints crack down to form micro pores and ease the stress concentration and make it possible. The internal stress of the rock is redistributed. In the expansion stage, the pore gap expands slowly around the surrounding area, and eventually forms the main crack along a certain direction. The main crack continues to extend, and the secondary crack is randomly distributed on the main crack. In the penetration stage, the micro pores and the micro cracks begin to interconnect with each other to form a new crack. The ultrasonic dynamic combination is designed. The experimental results are basically the same with the numerical simulation results. Compared with the results of the experimental and numerical simulation, it is found that the numerical simulation results of the cracking conditions of the granite crack based on the joint strength theory are compared with the results of the numerical simulation. The numerical simulation is closer to the experimental results with the second or third strength theory. The experimental data of ultrasonic vibration are arranged and the influence of static load on the damage degree of granite is studied. The following conclusion is drawn: the static load has a threshold in the process of ultrasonic vibration, and the static load changes when the applied static load is less than the threshold. It does not cause the change of the elastic modulus of granite, and the change of static load does not affect the damage of granite. When the static load is greater than the threshold, the change of static load will directly affect the damage degree of granite. Under the precondition that the static load is greater than the threshold, the process of damage caused by static load on granite can be divided into buffer. In the stage and the stage of damage, the modulus of granite's elastic modulus decreases not obviously in the buffer stage, and the elastic modulus of granite decreases sharply in the stage of damage. Under the condition of other conditions, the optimal static load value under ultrasonic vibration makes the maximum damage degree of granite. The optimal static load value in this experiment is 400N. CT scanning experiment. The CT images of granite under different vibration conditions are obtained. According to the CT image, the crack propagation process of granite under ultrasonic vibration is analyzed. The crack propagation process of the granite is divided into three stages: germination, expansion and penetration, which is basically consistent with the numerical simulation results. In the process of vibration, the crack gradually goes to the axis of the axis with the increase of vibration time Gather together.
【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P634.1

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