Ⅰ型断裂韧度模拟方法及细观影响因素研究

既有离散元参数敏感性分析大多集中在压缩试验及巴西劈裂试验,对Ⅰ型断裂韧度K_Ic试验细观影响因素及3D破裂过程系统分析的报道较少。采用三维平节理模型(FJM3D)研究微观结构参数及黏结细观参数对不同切槽形状的Ⅰ型断裂韧度试验的影响。微观结构参数包括晶粒平均半径的平方根R^1/2、模型分辨率Ψ和最大/最小晶粒直径d_max/d_min。黏结细观参数包括平均配位数CN、S类型单元比例φ_s、黏结抗拉强度σ_b、黏结内聚力c_b、摩擦系数μ和摩擦角φ。参数敏感性分析结果表明,K_Ic与R^1/2、CN及σ_b正相关,与d_max/d_min 、φ_s负相关,而与Ψ、c_b、μ和φ无明显的线性关系,此外为获得较低的K_Ic波动水平,给出了参数Ψ和d_max/d_min

Study on simulation method of mode I fracture toughness and its meso-influencing factors

The discrete element numerical method has been usually used for some parameter sensitivity analysis of geo-materials in the compression test and the Brazilian splitting test. However, there have been limited studies systematically focusing on mesoscopic influencing factors and 3D fracture process in mode I fracture toughness tests. The 2D discrete element methods cannot reflect the real mechanical behavior of a 3D model. Therefore, a three-dimensional flat joint model (FJM3D) is used in this paper to investigate the effects of microstructure parameters and bond mesoscopic parameters on mode I fracture toughness tests with different notch shapes. The microstructure parameters include the square root of average particle radius ( ), model resolution ( ), and maximum/minimum particle diameter ( ). Bond meso-parameters include average coordination number (CN), slit element fraction ( ), bond tensile strength ( ), bond cohesion ( ), friction coefficient ( ) and friction angle ( ). Results of parameter sensitivity analysis show that the mode I fracture toughness ( ) is positively correlated with , CN, and , and negatively correlated with and . There are no obvious linear relationships between and , , , . In addition, suitable ranges of and are recommended to obtain an appropriate mode I fracture toughness with a low level of variation. Based on the results of parameter sensitivity analysis, the mechanical behaviors of the Kowloon granite with notched semi-circular bend (SCB) and cracked chevron notched semi-circular bend (CCNSCB) specimens are calibrated. The failure process of mode I fracture toughness tests with different notch shapes indicates that the pre-peak and post-peak behaviors of the SCB test is more consistent with the laboratory test.