【摘要】 为了研究裂缝长度和角度对红砂岩Ⅰ型和Ⅰ/Ⅱ型断裂特性的影响，对含有3种角度和3种长度预制裂缝的半圆红砂岩试样组进行静态三点弯曲试验，分析裂缝角度和长度对红砂岩试样Ⅰ型和Ⅰ/Ⅱ型断裂韧度和裂纹路径等断裂特性的影响规律。试验结果表明：红砂岩试样在Ⅰ型和Ⅰ/Ⅱ型断裂时均表现出脆性破坏特征；红砂岩纯Ⅰ型断裂韧度K_ⅠC=7.179 MPa·mm^1/2；在Ⅰ/Ⅱ型复合断裂中，裂缝长度较小时，红砂岩复合型等效断裂韧度随裂缝角度的增加而减小，当裂缝长度增加至一定值时，复合型等效断裂韧度随裂缝角度的增加呈现出先减后增的变化趋势，并不是简单的随裂缝角度增加而减小的变化规律。更多还原

【Abstract】 The internal structure of rock masses is characterized by the presence of various cracks,and the inherent uncertainty in crack angle and loading direction often results in brittle rock masses undergoing mixedmode fractures,which combine mode Ⅰ（tensile mode） and mode Ⅱ（shear mode）. To examine the effects of crack length and angle on the modeⅠand mixed-mode Ⅰ/Ⅱ fracture properties of red sandstone,semi-circular bend（SCB） specimens of red sandstone were prepared with three distinct crack angles and three varying crack lengths,resulting in a total of nine experimental groups.Static three-point bending tests were performed on these specimens to obtain load-displacement curves and peak load data. Subsequently,the fracture toughness and fracture energy for each group were calculated.The study analyzed the impact of crack angle and length on the mode Ⅰ and mixed-mode Ⅰ/Ⅱ fracture toughness,fracture energy,and crack propagation paths in red sandstone specimens.Furthermore,the extended finite element method（XFEM） was utilized to develop models corresponding to each group of specimens. This approach facilitated the calculation of dimensionless stress intensity factors for mode Ⅰ and mode Ⅱ fractures,thereby providing a foundation for determining fracture toughness.The numerical results were instrumental in analyzing the proportion of modeⅠand mode Ⅱ fracture types present in the specimens. Experimental findings reveal that red sandstone specimens exhibit pronounced brittle failure characteristics under both mode Ⅰ and mixed mode Ⅰ/Ⅱ fracture conditions. The crack path during specimen fracture adheres to the shortest trajectory from the tip of the prefabricated crack to the loading point at the top. Specifically,when the crack inclination angle is 0°,the specimen experiences pure mode Ⅰfracture,with the calculated pure mode Ⅰ fracture toughness of red sandstone being 7.179 MPa·mm^1/2.Additionally,as the crack length increases,the peak fracture load of the specimen decreases. For mixed-mode（Ⅰ/Ⅱ） fractures occurring within a specific range of crack lengths,the equivalent fracture toughness,denoted as K_eff,exhibits a decreasing trend as the crack inclination angle increases.Nonetheless,when the crack length surpasses a critical threshold,K_eff no longer adheres to a straightforward decreasing pattern with respect to the inclination angle. Both the crack length and the inclination angle play significant roles in modulating the interplay between mode Ⅰ and mode Ⅱ fracture mechanisms,consequently influencing the overall equivalent fracture toughness of the composite.更多还原