静-动态加载条件下岩石断裂特性及断口形貌特征研究

Research on fracture surface morphology of rock with static and dynamic fracture toughness

采用直切槽半圆盘弯曲型试件,对北京房山花岗岩样品进行静态断裂韧性和动态断裂韧性试验,获得其静态断裂韧度与动态断裂韧度的定量关系;采用不同表面形貌刻画技术,对破坏岩样的表面形貌进行观测与表征,获得岩石表面的三维重构及其粗糙度。研究结果表明:在中高应变率条件下,动态断裂韧度一般为静态断裂韧度的1.3~2.6倍,动态传播韧度为动态起裂韧度的3~4倍,静态断裂韧度的8~10倍;其静态和动态断裂都呈Ⅰ型裂纹拉伸破坏模式。同时,在静态韧性测试中,裂纹断裂模式主要为沿晶断裂,穿晶断裂相对较少;而在动态韧性测试中,裂纹断裂模式主要为沿晶和穿晶耦合断裂。裂纹传播过程均经历了加速阶段和减速阶段,裂纹传播速度与其表面三维形貌重构的相对高度变化趋势一致,同样与表面粗糙度变化规律相吻合。岩石静态行为与动态行为的本质区别是,材料在动态加载时所表现出来的率效应(惯性效应)与材料自身由物理、几何引起的结构效应存在相互抵消、此消彼长的本质属性。

Based on the notched semi-circle bend(NSCB) specimen and its fracture toughness test method, static fracture toughness and dynamic fracture toughness tests were carried out for Beijing Fangshan granite samples.Meantime, the quantitative relationship between static fracture toughness and dynamic fracture toughness was obtained. Furthermore, kinds of surface morphology characterization techniques were used to observe and judge the surface morphology of the damaged rock samples, and the three-dimensional reconstruction and roughness of the rock surface were obtained. The results show that the dynamic fracture toughness is generally 1.3-2.6 times of the static fracture toughness under the medium and high strain rate conditions, the dynamic propagation toughness is 3-4 times of the dynamic initiation toughness and 8-10 times of the static fracture toughness. The static and dynamic fracture modes are mode Ⅰ crack tensile failure. During the rock static toughness test, the crack fracture mode is mainly inter-granular fracture while the trans-granular fracture is relatively less. However, for the rock dynamic toughness test, the crack fracture mode is mainly inter-granular and trans-granular coupling fracture. The crack propagation processes undergone acceleration and deceleration stages. The change trend of rock crack propagation speed is consistent with the relative height of rock surface three-dimensional morphology reconstruction, which also corresponds to the rock surface roughness variation. The essential performance between the rock static and dynamic behavior is that the rate effect(inertia effect) under dynamic loading and the structural effect caused by the physical and geometric properties of the rock material itself have the counteracting feature.