平面压痕断裂型破岩理论及其应用

When a substrate in half-plane of the brittle material is indented by a relatively rigid, square-ended punch, a singular stress field and K-dominant region will arise at the near-surface adjacent to the punch corners. By the same way, when a flat-ended cylindrical rigid indenter is pressed on the surface of the half-space substrate, a cylindrical singular stress field will arise also. Similar to cracked solids, as the load reaches its critical value, the surface of the substrate should fracture and a shallow and small crack should be formed. Rock is a typical quasi-brittle material. When a rigid and flat-ended indenter is pressed on the rock substrate, fracture-based damage will be induced on the surface of the rock, which should form a new fracture-based mechanism of the rock breakage. In present research project, by using mechanical model of singular stress field induced by indentation, a new fracture-based theory for rock breaking will be formulated from the theorem of the energy release rate. Firstly, the mathematical model and fracture-based model for indentation will be investigated; fracture-based damage mechanism for the indentation cracking will be discussed; the critical value for energy release rate of indentation cracking and cracking angle will be formulized. The Kind-based cracking criterion will be proposed; then the applications of the fracture-based theory for rock breakage in rock cutting, petroleum drilling and shield tunnelling will be researched also. Its theoretical significances cover: ①Propose a new fundamental theory on the fracture-based rock breakage; ②Establish the theoretical basis for rock like materials cutting and the design method of oil and gas drill bit.

当矩形刚性压头作用在二维弹性基体的表面时，形成一个平面压痕，在压痕的边界处会出现I型或复合型渐近奇异应力场；同样,当圆柱平端刚性压头作用在三维弹性基体的表面时，在压痕的周边也会形成I型或复合型渐近奇异压应力场。与裂纹情形类似,当载荷达到临界值时，在应力奇异点处开裂，形成一个新的浅裂纹。岩石是典型的脆性材料,若将刚性平端压头作用在岩石的表面，将导致岩石断裂型损伤，表现出断裂型的破岩过程。本项目将利用平面压痕诱生奇异应力场的原理以及能量释放率原理构造一个平面压痕断裂型破岩理论。首先研究岩石基体表面平面压痕开裂的数学和断裂力学模型；研究压痕边界断裂型开裂机理；导出压痕开裂能量释放率的临界值和理论预计的边界开裂方向,给出Kind-型开裂准则，同时研究断裂型破岩机理在岩石切割、石油钻井和隧道盾构中的应用。其理论意义在于：①建立平面压痕断裂型破岩理论；②为岩石类材料加工、钻头设计等建立新的理论基础。

项目背景: 当矩形刚性压头作用在二维弹性基体的表面时，形成一个平面压痕，在压痕的边界处会出现I型或I-II复合型渐近奇异应力场；同样,当圆柱平端刚性压头作用在三维弹性基体的表面时，在压痕的周边也会形成I型或复合型渐近奇异压应力场。与裂纹情形类似,当载荷达到临界值时，在应力奇异点处开裂，形成一个新的浅裂纹。岩石是典型的脆性材料,若将刚性平端压头作用在岩石的表面，将导致岩石断裂型损伤，表现出断裂型的破岩过程。本项目利用平面压痕诱生奇异应力场的原理以及能量释放率原理构造了一个平面压痕断裂型破岩理论。.主要研究内容:①建立岩石平面压痕周边开裂分析的数学模型和断裂力学模型。②压痕边界临界开裂条件，包括Kind-型边界单裂纹开裂和多裂纹开裂的破岩准则。③研究压痕应力强度因子-Kind通用的计算方法。④岩石I-型平面压痕开裂韧性Kind-IC的标准实验测试技术研究。⑤平面压痕开裂理论在岩石切割中的应用，给出工程应用案例。.重要结果及其科学意义: 传统观点认为，r-1/2渐近奇异应力场仅与裂纹问题相关，然而平面压痕的应力状态分析表明，该r-1/2渐近奇异应力场也存在于平面压痕的边界。断裂力学的发展史表明，几乎全部的研究聚焦在裂纹的断裂行为上。所形成的断裂理论均基于裂纹问题，也决定了断裂力学理论仅适用于裂纹问题。对于处于同类应力状态的平面压痕边界的开裂，经典断裂力学无法适用。如经典J积分理论等，不能应用于I-型平面压痕边界的开裂研究。平面压痕诱生的r-1/2奇异应力边界开裂问题，对经典断裂力学提出了深层次的检验和挑战，促使人们必须重新审视经典断裂理论的严谨性、完整性、通用性和系统性。如何秉持断裂力学基本原理，为平面压痕边界断裂型开裂研究打造新型的断裂理论，具有重要的科学意义。也为用新的视角审视经典裂纹开裂问题提供了新的方法。