Test Research On The Fracture Mechanics For The Britlle Materials Under Compressing

In this paper, Based on the theory analysis and test, the fracture mechanism and fracture direction of brittle materials are studied. Firstly, from studing the error of the former literature, the existing of internal friction on the inclined section of the samples is discussed, when the samples are breaking. And analyse the influence of the endface friction, slanting press, pressure head of testing machine and characteristic of materials to the frature direction; Secondly, the quasi-static uniaxial compression test on massively cast iron samples of TH200 is analysed and the SEM photo of different position on the fracture section is studied. The position of crack initiation and fracture direction are observed macroscopically. While, different fracture mechanics on the fracture section is analysed microcosmicly; Thirdly, fracture mechanism of different cast irion samples are observed by uniaxial compression, and the reason why the uniaxial compression strength is different for different size samples is discussed theoryly; Finally, fracture mechanism is studied by fracture SEM vision and test on marble, granite and sandstone. And then, stress states parameter of stress tri-axility is bringed to differentiate different fracture mechanism; while the fracture strength criterions which are popular in engineering project are discussed.The result shows, the position of crack initiation is at the place of maximum stress triaxiality; the direction of crack initiation is the direction of maximal shear stress at the dangerous point; the fracture of cast iron is complex process, the same fracture section occur different fracture mechanics: the middle fracture section occurs shear fracture, but the end fracture section occur tensile fracture; The reason why the compression strength is different for different size samples is different influence zone of endface friction; For rock materials, affecting by different material characteristic and strss status, brittle material can take place traction fracture, shear fracture, plastic flow fracture; the transition of shear fracture and plastic flow fracture is consecutive, but the transition of traction fracture and shear fracture is unconsecutive, while existing diverge zone which is affected by material characteristic; for the same materials, there is a critical value of stress tri-ality between different fracture mechanism; for the different materials, here is also a critical value of stress tri-ality.