Uniformity of Stress Distributions in Rock Cylinder Specimen under Uniaxial Compression

This paper presents an axial symmetric finite element analysis of rock cylinder under uniaxial compression and gives the new results which are more reasonable than early ones of other workers. Because the joint elements have been applied in this analysis for simulating the interfaces, the relative sliding along the interfaces can be considered. It is demonstrated that the experimental method of making a specimen keep direct touch with the platens of the testing machine must induce to an ununiform stress distribution for this specimen even if the friction on the end surfaces of specimen is reduced. It is proved that stress distribution in specimen could get much more uniform by inserting stiff inserters of height-to-diameter ratio of 1.0 between the specimen and the platens. If the tengential stiffness coefficient Ks at the interfaces between the end surfaces of specimen and the inserters should reaches 10~4kg/cm3, deviation of axial stress is less than 1%, the ratio of radial stress to axial stress is less than 3%, and the ratio of shear stress to axial stress is less than 1%. Finally, the technical way to obtain these indications and the part of testing results are given.