冲击荷载作用下岩石动态损伤特性研究

【作者】 张华；

【导师】 程赫明；

【作者基本信息】 昆明理工大学 ， 工程力学， 2009， 博士

【摘要】 冲击载荷作用下岩石动态损伤力学特征问题一直是岩石动力学研究的热点问题。近几十年来,研究者在岩石动态冲击特性、本构模型、数值模拟计算等方面取得了丰硕的研究成果,但还有很多问题未能完善解决。本文简要回顾了岩石材料动态力学性能在实验和理论研究方面取得的成果和不足,主要就岩石材料动态力学特性的两个方面展开研究：一方面研究了一维应力条件下,岩石材料的动态响应特性；另一个方面研究一维应变条件下,岩石材料的动态响应特性。研究采用试验结果与理论分析相结合的方法,并对冲击荷载作用下岩石动态损伤模型进行了详细研究。具体工作内容和研究成果如下：(1)采用SHPB实验装置对岩石材料一维应力条件动态冲击实验进行了研究。结果表明：动态冲击加载条件下,岩石材料抗压强度和杨氏模量具有明显应变率敏感性,而初始切线模量是率无关的,它们又在一定程度上受实验装置和加载波形的影响；岩石材料抗压强度和杨氏模量与应变率表现出率敏感性更为明显,随着冲击速度增大,岩石材料杨氏模量明显增大,整体上表现为尺寸硬化效应,而其应变率变化效应更为敏感,只要很小的应变率变化就能引起抗压强度的显著增大,岩石损伤破坏形式主要是由侧向的拉伸应变引起的。(2)采用一级轻气炮实验装置对一维应变条件下的动态试验进行了研究。研究采用了符合实际工程背景的岩石材料,采用主动围压的方式来模拟地应力条件下的岩石受力情况。对岩石试件分别进行了无围压作用和有围压作用下冲击速度在200-400m/s范围内的平板撞击实验。利用锰铜压阻传感器测得靶板内不同位置处的应力时间曲线,采用拉氏分析方法中的路径线法对应力时间曲线进行分析,得到了其它力学参量如应变、应变率、比容、密度、质点速度等随时间的变化过程。结果表明：岩石和围压作用岩石在某些方面具有相似的力学性质,比如材料的率敏感性、应力波的弥散性和衰减性,以及应力应变关系的滞徊、流变性等,但围压的存在使得岩石材料的非线性变得不明显；强冲击载荷作用下,围压载荷的加入提高了岩石材料的刚度和延展性,使得材料的抗冲击能力得以提高。(3)基于岩石材料损伤机理和破坏形态的分析,构造了描述岩石材料在不同加载形式下动态损伤的本构模型。模型主要建立在以下的假设：1)假设岩石材料宏观上是一个均匀连续体,而细观上其内部包含了大量随机分布的微损伤缺陷；2)材料的损伤演化是由其内部拉应力作用下微裂纹的扩展引起的,导致材料强度和刚度的弱化；3)随着微孔洞的塌陷,材料内部产生了不可恢复的塑性变形,体积模量也相应增加,将这一过程视为微孔洞缺陷的演化发展；4)当微裂纹被激活、成核并扩展,且累积裂纹密度到某一阈值时,材料发生破坏。通过对模型预测曲线与实验曲线的比较,发现该模型能很好地描述岩石材料的本构特性。(4)基于复合材料力学的观点,将围压作用岩石视为一种增强型岩石复合材料,通过简化分析,提出了一个适于工程实践分析的动态本构方程。方程包括两个方面：1)围压对岩石本构特性的影响通过损伤演化方程表征；2)岩石在动态冲击过程中的力学参量突变通过应力松弛时间描述。(5)利用VISC2D及VISC3D计算程序,对飞片撞击多层岩石靶板的碰撞过程进行模拟,很好地分析了岩石试件的动态破坏作用机理。更多还原

【Abstract】 The dynamic damage mechanics character of rock under impact loading is always on the focus of rock mechanics research. In the last few decades, Some scholars have achieved a series of result of the fields of rock dynamic characteristic, constructive relation model and calculation of numerical simulation, but there are still many problems unsolved. The text simply reviewed the findings and shortages about rock-material dynamic mechanic behavior on the aspects of experimental and theoretical research. The questions about it are be researched On the side of one-dimensional stress and the other side of one-dimensional strain. At the same time, the dynamic damage model of rock under impact loading is also researched in the result of experiment and theory analysis. The following is the content and the result.(1) The equipment of a split Hopkinson pressure bar(SHPB) is utilized in the dynamic impact loading experiment of one-dimension stress. The test result indicates that both compression strength and the young’s modulus are strain rate-sensitivity, but the initial tangent modulus is strain rate-insensitivity, they are also affected by the test equipments and the mode of loading in a certain extent. The young’s modulus increased obviously with growing-up impact speed. The whole material represents as a size harden effect. A little variety of strain rate can increase compression strength obviously. The cause of damnification breakage is the side direction stretch.(2)The research of dynamic mechanics experiment of one-dimension strain condition is investigated by single-stage-gun. The rock materials which accorded with engineering background is simulated as the ground stress conditions by the active confining pressure. The experiments of planner impact were performed to the rocks material included confining pressure and non-confining pressure with the speed of 200-400m/s, and Manganin gauges between the rock targets were used to record the stress-time curves at the different locations of target. With the measured stress histories, the complete histories of strain, strain rate, specific volume, density and particle velocity are gained by using path line principle of Lagrange Analysis. The results indicate that rock and confining pressure rock have some similar response behavior in some respects, such as the rate-sensitivity, the dispersion and attenuation effect of pressure pulse, and the stagnant-return and flow-deformation phenomena of stress-strain curves and so on, but the confining pressure decrease the nonlinear of stress-strain curves. Confining pressure can also raise the shock resistance ability, the stiffness and ductility of rock targets.(3) Based on the analysis of damage mechanism and failure model for material, a dynamic damage constitutive model is constructed to describe the constitutive response of rock material. The model is described briefly as the following hypothesis:1) Rock is assumed in a macroscopic view as homogenous continuum with a mass of stochastically distributed micro-damage; 2) Damage evolution is considered to be the accumulation of micro-crack growth due to the interior tension stress, which leads to a decrease of strength and stiffness of rock; 3) Compaction of rock is essence a collapse of the material voids, which produces the plastic strain and the increasing of the bulk modulus in the rock, so this process is considered as the evolution development of void damage; 4) When crack density reaches a critical value, the rock material destroy tack place. The comparison of model curves and experimental curves indicate that this model can describe the constitutive properties excellently.(4)Base on the point of composite material mechanics, the confining pressure rock is considered as a enhanced composite material, a dynamic constitutive equation which is suitable for engineering analysis is briefly proposed. The equation include in two aspects: 1) The effect of confining pressure on constitutive property is characterized by the damage evolution equation; 2) The mutation of mechanics parameters in the dynamic impact process is described by stress relaxation time.(5) Adopting VISC2D and VISC3D, the dynamic collision process of rock target impacted by flyer are simulated, and the dynamic failure mechanism is analyzed excellently.更多还原