Effect of specimen thickness on Mode II fracture toughness of rock |
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Authors: | Rao Qiu-hua Sun Zong-qi Wang Gui-yao Xu Ji-cheng and Zhang Jing-yi |
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Affiliation: | (1) College of Resources, Environment and Civil Engineering, Central South University, 410083 Changsha, China;(2) River and Sea Department, Changsha Communications University, 410076 Changsha, China;(3) Open Lab of Mechanics, Central South University, 410083 Changsha, China |
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Abstract: | Anti-symmetric four-point bending specimens with different thickness, without and with guiding grooves, were used to conduct
Mode II fracture test and study the effect of specimen thickness on Mode II fracture toughness of rock. Numerical calculations
show that the occurrence of Mode II fracture in the specimens without guiding grooves (when the inner and outer loading points
are moved close to the notch plane) and with guiding grooves is attributed to a favorable stress condition created for Mode
II fracture, i.e. tensile stress at the notch tip is depressed to be lower than the tensile strength or to be compressive
stress, and the ratio of shear stress to tensile stress at notch tip is very high. The measured value of Mode II fracture
toughness K
II C decreases with the increase of the specimen thickness or the net thickness of specimen. This is because a thick specimen
promotes a plane strain state and thus results in a relatively small fracture toughness.
Foundation item: The National Natural Science Foundation of China (No: 49672164)
Biography of the first author: RAO Qiu-hua, doctor of engineering, born in 1965, majoring in rock fracture mechanics. |
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Keywords: | Mode II fracture toughness rock fracture stress analysis specimen thickness |
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