A Study on Stress-Strain Curve of Brittle Rock Under Compression

Rock compression testing is a universal laboratory testing method for determining rock elastic modulus, peak strength, Poisson's ratio, etc. For decades, the accuracy and applicability of the testing methods have been researchers’ great concern. In this study, uniaxial tests of brittle shale were conducted. Inclination induced by spherically/flatly seated upper loading platen was analyzed. Scanning Electron Microscope (SEM) was used to observe the micro crack tip induced by the non-uniform loading. Taking the inclination of loading platen into consideration, Particle Flow Code 2D was used to simulate non-uniform loading process. Typical post-peak failure was analyzed allowing for load train stiffness and servo response interval, which played a role in the uncontrolled failure process. Conclusion shows that slight inclination of loading platen would lead to highly non-uniform loading. Stress-strain curve of brittle rock post-peak failure showed characteristics of load train stiffness and servo response interval. Conclusion also showed that the insensitivity of axial strain to splitting in UCS testing was the main reason for axial strain rate control mode to give unsatisfactorily control in brittle rock UCS testing. The study here could give a better understanding on rock compression testing and corresponding machine design.