Authors

Yunqui Liu

Publication Date

2015

Abstract

Nanoindentation has been reported as an effective tool for realizing the strength and stiffness (modulus of elasticity) of different materials including thin film materials, cementitious composites and rock or clay mineral materials. However, to the best of the authors’ knowledge, nanoscale fracture of shale materials has rarely been examined. Fracture toughness property of shale has been typically studied by observing crack growth of notched macroscale specimens subjected to flexural or tension loads. This research discusses the possible characterization of fracture toughness of shale using contact mechanics at the nanoscale. The analysis method is based on two traditional fracture toughness measurement methods which are used for some different materials. One is the radial crack length measurement method and the other one is based on evaluating the energy absorbed by radial cracks propagating from the indentation imprint in brittle materials. Nanoindentation experiments performed using Berkovich and Cube corner nanoindenter are reported. The Young’s Modulus, Hardness and fracture toughness of shale are extracted from nanoindentation experiments. Fracture toughness for different types of shale are evaluated using both crack length measurement and an equivalent elastic crack energy approach and are compared to macroscale fracturetoughness of different types of shale from the literature. Mechanical properties for different types of shale are calculated from nanoindentation tests and mineralogy is found to play an important role in controlling mechanical properties of shales. An increase in organic content and clay minerals content decreases both Young’s Modulus and Hardness of shale. But the deviation of fracture toughness calculation results in this project cannot be ignored comparing with results from macroscale tests. There is some influence for fracture toughness measurement by size effect and shale heterogeneity. Shale heterogeneity and compositional variability should be considered as serious challenges in quantifying the mechanical properties of shale in the future work.

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