冲击载荷下松软煤力学特性及对煤与瓦斯突出的影响

发布时间：2018-05-26 17:41

本文选题：冲击载荷 + 动态力学特性　；参考：《安徽理工大学》2015年博士论文

【摘要】：随着煤炭开采向深部延伸,冲击地压、煤与瓦斯突出等煤岩动力灾害日趋严重,如何预防和减少灾害发生,保证煤炭开采安全、合理、高效显得更为迫切。根据对材料力学性能的研究发现,材料在静载与动载破坏时往往表现出不同的破坏形式和力学特征。现有文献对煤的力学特性的研究以准静态居多,但专门针对煤动态特性的研究较少,国内仅有几位学者对无烟煤在单轴冲击作用下的力学特性进行了少量研究。本论文以潘谢煤田13-1煤层气煤为主要研究对象,选取软硬程度不同的原煤制作成实体煤和型煤两种不同的煤样试件,进行准静态力学实验和单轴冲击压缩实验。采用实验室实验研究、理论分析、数值模拟和现场案例比对相结合的方法,对其动态力学特性、本构关系以及冲击破坏过程中的能量耗散规律进行了研究,并探索了动载荷对煤与瓦斯突出的影响。论文主要完成以下工作：采用分离式霍普金森压杆实验装置对两组试件进行了不同应变率条件下的单轴冲击压缩实验(以下简称SHPB实验),采集实验波形,并利用三波法进行分析处理,得到了两种煤样在不同应变率条件下的动态应力应变曲线和相关的动力学参数。实验结果分析表明：两种煤样在冲击载荷作用下的变形过程可概括为初始非线性阶段、屈服阶段、应变强化阶段和卸载破坏阶段四个阶段；煤体的动态强度、峰值应变、动态弹性模量等均具有显著的应变率相关性,表现出显著的应变硬化和应变率强化等动态力学特性。通过动、静态实验对比,得到了两种煤的动态应力增长因子DIF和动态应变增长因子DEIF,发现型煤的应变率强化效应较实体煤更为明显。对两种煤样在冲击载荷下变形特征分析的基础上,参考前人对岩石类材料和无烟煤本构关系的研究成果,根据粘弹性理论和损伤力学理论,对朱-王-唐模型本构方程进行了合理的简化,并引入一个依赖应变率和应变的损伤量,构建了适用于气煤的包含损伤效应和应变率效应的、能够较好地反映其峰值应力前应力应变关系的动态本构方程。结合SHPB实验数据,对本构方程的未知参数进行了拟合,得了到相应的再生动态应力-应变曲线。拟合结果表明：再生动态应力应变曲线与实验曲线能够较好地吻合,煤体材料具有高应变率响应敏感性,且在高应变率条件下气煤比无烟煤表征更明显的脆性特征。依照已建立的煤体动态本构方程,采用Fortran语言开发了VUMAT煤体材料子程序,同时结合有限元软件ABAQUS中的用户材料接口,将煤体动态本构方程进行嵌入,对不同应变率条件下煤体的动态力学行为进行了数值模拟。结果表明,该子程序能较好地模拟煤体在冲击载荷下的动态力学性能。论文在准静态实验和SHPB实验的基础上,分别计算得出了两种煤样在不同应变率条件下破碎功密度、总吸收能密度等,并进行了应变率相关性分析。结果表明：两种煤样的破碎吸收能量密度均随应变率的增大而指数提高,与准静态加载相比,型煤的能量密度提高更快,应变率效应更为显著。同时,采用0.5mm、 1mm、10mm、 20mm 和 30mm煤样筛对实验碎块进行了块度分形研究,结果表明：随着应变率的提高,碎块分形维数增大,试件破碎程度加剧,碎块粒径越小,分形维数与应变率之间呈对数增长关系；碎块的平均粒径与应变率之间基本满足负指数关系,说明使碎块进一步破碎,所需的能量越大。将已构建的煤体动态本构方程嵌入大型有限元分析软件,分别对峰值荷载Pmax=30MPa、50MPa、70MPa三种强度动荷载作用下的煤体损伤进行了数值模拟,结合煤与瓦斯突出过程的能量分析和现场案例解析,将突出过程分为临界突出和突出两个不同阶段,并提出了一个达到临界突出的煤体最小破坏能量标准范围(5-10)×104J/m3。通过数值分析,有效地研究了不同冲击荷载作用下煤体劈裂裂纹演化的过程。结果表明,煤体在动荷载作用下出现间隔劈裂的结构,具有两种劈裂损伤形式：强拉伸应力为主导的“跃升式”损伤和拉剪-压剪损伤累积为主导的“阶梯式”损伤。综合分析可知,煤与瓦斯突出是由瓦斯膨胀能和突加载荷(如采掘、放炮、构造应力、围岩应力等)输入能共同作用引起的。在某些低瓦斯、高应力或者强扰动条件下,突加载荷可以通过两种损伤方式造成煤体临界破坏,从而成为导致煤与瓦斯突出发生的主要动力。研究成果可以进一步认识深部开采过程中,低瓦斯、高应力、强扰动条件下的瓦斯动力现象发生的机理,为防治矿山爆破、采掘等引起的动力灾害事故提供了理论依据。
[Abstract]:With the extension of coal mining to the deep, rock burst and coal and gas outburst, coal and rock dynamic disasters are becoming more and more serious. How to prevent and reduce the occurrence of disasters and ensure the safety, rationality and efficiency of coal mining is more urgent. According to the study of the mechanical properties of materials, the material often shows different damage forms in the static and dynamic load damage. The research on mechanical properties of coal is mostly quasi-static, but the research on dynamic characteristics of coal is less. Only a few scholars have studied the mechanical properties of anthracite under Uniaxial Impact in China. In this paper, the 13-1 coal seam gas coal in Pan Xie coalfield is the main research object, and the soft and hard work is selected. Two different coal samples of different degree coal are made into solid coal and briquette sample, and the quasi static mechanical experiment and single axis impact compression test are carried out. The method of laboratory experiment, theoretical analysis, numerical simulation and case comparison is combined, and the dynamic mechanics, constitutive relation and energy in the process of impact failure are used. The dissipative law is studied and the influence of dynamic load on coal and gas outburst is explored. The following work is completed in this paper: a single axis impact compression test under the conditions of different strain rate (SHPB experiment) is carried out with a separate Hopkinson pressure bar experimental device. The experimental waveform is collected and the three wave method is used. The dynamic stress-strain curves and related dynamic parameters of two kinds of coal samples under different strain rate conditions are obtained by line analysis. The experimental results show that the deformation process of the two kinds of coal samples under the impact load can be summarized as the initial nonlinear stage, the yield stage, the stress-strain stage and the unloading failure stage in four stages. The dynamic strength, peak strain and dynamic elastic modulus of coal have significant strain rate correlation, showing significant dynamic mechanical properties such as strain hardening and strain rate strengthening. Through dynamic and static experiments, the dynamic stress growth factor DIF and dynamic strain growth factor DEIF of two kinds of coal are obtained, and the strain rate of briquette is strong. On the basis of the analysis of the deformation characteristics of two kinds of coal samples under the impact load, on the basis of the previous research results on the constitutive relation of rock materials and anthracite, according to the viscoelastic theory and the theory of damage mechanics, the constitutive equation of Zhu Wang Tang model is reasonably simplified, and a dependent strain rate is introduced. The damage effect and strain rate of the gas coal are constructed, which can reflect the dynamic constitutive equation of the stress-strain relationship before the peak stress. Combined with the SHPB experimental data, the unknown parameters of the constitutive equation are fitted, and the corresponding regenerated dynamic stress-strain curve is obtained. It is shown that the dynamic stress-strain curve of the regeneration is in good agreement with the experimental curve. The coal material has the sensitivity to the response of high strain rate, and the characteristics of the gas coal are more obvious than the anthracite under the high strain rate. According to the established dynamic constitutive equation of the coal body, the subprogram of the VUMAT coal material is developed by Fortran language. In conjunction with the user material interface in the finite element software ABAQUS, the dynamic constitutive equation of the coal body is embedded and the dynamic mechanical behavior of the coal body under different strain rates is simulated. The results show that the subprogram can better simulate the dynamic mechanical properties of the coal under the impact load. The paper is in the quasi static experiment and the SHPB experiment. On the basis of this, the work density and total absorption density of two kinds of coal samples under different strain rates were calculated, and the correlation analysis of strain rate was carried out. The results showed that the energy density of the two kinds of coal samples increased exponentially with the increase of the strain rate, and the energy density of the briquette increased more than that of the quasi-static loading. Fast, the strain rate effect is more significant. At the same time, the fractal dimension of 0.5mm, 1mm, 10mm, 20mm and 30mm coal samples is studied. The results show that the fractal dimension of the fragment increases with the increase of the strain rate, the fragmentation degree increases, the particle size is smaller, the fractal dimension and the strain rate are logarithmic growth relations; the fragments are broken. The relationship between the average particle size and the strain rate basically satisfies the negative exponential relation, indicating that the broken blocks are further broken and the energy required is greater. The coal body dynamic constitutive equations which have been constructed are embedded in the large finite element analysis software, and the numerical simulation of the coal body damage under three kinds of dynamic load loading of the peak load Pmax=30MPa, 50MPa and 70MPa is carried out respectively. The energy analysis and field case analysis of coal and gas outburst process are divided into two different stages of critical outburst and outburst, and a standard range of minimum failure energy of coal body (5-10) * 104J/m3. to reach critical outburst is proposed. Through numerical analysis, the splitting crack of coal under different impact loads is effectively studied. The process of evolution shows that the structure of the split split of the coal body under the action of dynamic load has two types of splitting damage: the "jump type" and the accumulation of shear and shear damage leading by the strong tensile stress and the leading "ladder type" damage. Load (such as mining, blasting, tectonic stress, surrounding rock stress, etc.) can be caused by the joint action. Under some low gas, high stress or strong disturbance conditions, the sudden loading can cause the critical failure of coal through two kinds of damage methods, thus becoming the main motive force of coal and gas outburst. The research results can further understand the deep part. In the process of mining, the mechanism of gas dynamic phenomenon occurring under the conditions of low gas, high stress and strong disturbance provides a theoretical basis for the prevention and control of dynamic disasters caused by mine blasting and mining.
【学位授予单位】：安徽理工大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TD713

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