Experimental Device for the Determination of Fracture Toughness at High Pressure

Abstract

Mode I fracture toughness (K_IC) is a relevant property in many applications involving rock mechanics. However, the conventional methods for its determination only consider ambient pressure conditions. Although the available experimentation on high pressure fracture toughness shows that K_IC tends to increase with confining pressure not all the published results provide with the same evidence. Among the available methodologies for K_IC testing, the pseudo-compact tension (pCT) test approach provides with a number of operational advantages over other alternatives and makes it a good candidate for its extension to high pressure research. Based on it, we have designed and constructed a simple high-pressure cell that may be easily installed in any conventional compression frame without modifications to test pCT specimens. The cell may accommodate either a gas or liquid as confining fluids and work with samples of up to 50 mm (~2”) diameter. In order to verify the expected performance, we have conducted different calibration tests, including leak rate and the assessment of axial friction. For the demonstration and validation of the experimental approach presented, we have selected virtually impervious poly-methacrylate (PMMA) and Corvio sandstone samples. Results obtained at room conditions and at high pressure are compared and discussed.