【摘要】 利用扫描电镜实时观测系统,研究了带预制割缝灰岩平板试件受单轴压缩时微裂纹的萌生、扩展和连通过程。实验所用灰岩平板试件尺寸为25 mm×13 mm×1.1 mm,试件中心预制一直径为3.0 mm的圆孔或一长轴与外载方向成不同角度(30°,45°或60°)的割缝,割缝长约6 mm,宽约1 mm。在扫描电镜的观察下,灰岩试样受到准静态单轴压缩。用照相的方法记录了试件受力产生变形和微裂纹扩展过程中的表面图像。将实验观测的微裂纹扩展结果与大理岩和砂岩中的裂纹扩展过程进行对比,发现次生裂纹的萌生部位与大理岩和砂岩中比较一致,但灰岩中的裂纹发育较单一。用NOLM程序中的低抗拉应变软化本构模型对实验结果进行了有限元模拟计算,将计算结果与实验观测结果进行对比,两者吻合较好。更多还原

【Abstract】 Testing study is made on the mini-crack development around a prefabricated fracture in a limestone plate specimen subject to uniaxial compression. The rock used for test is limestone,and direct SEM observation is used for testing. The elastic modulus of rock specimen is about 93.7 GPa,Poisson′s ratio 0.25 and uniaxial compressive strength 201 MPa. The specimen is a plate of 25 mm×13 mm×1.1 mm in size with a prefabricated central circular or a slot about 0.6 mm wide and 6.0 mm long. The major axis of the prefabricated slot is inclined to the loading direction at 30°,45°,60°,respectively. The tests are carried out in the vacuum chamber of a SEM using a vise-type loading frame. Its loading capacity is 2 000 N and the load on the specimen is measured by the piezoelectric transducer with an accuracy of 0.5 N. The development of mini-cracks in limestone specimen under uniaxial loading is photographed and analyzed. The test results are compared with those in marble and sandstone specimens from the previous study. It is shown from the comparison that the initiation points of cracks are similar in all three rock specimens,but there are less multiple mini-cracks development in limestone specimen. Finite element computation of the mini-crack process is performed using NOLM program with a strain-softening constitutive model of low tensile resistance. The computation result represents the experimental observation fairly well. The calculated results are compared with testing data,and they are agreed well with each other.更多还原