The measurement of the Mode ΙΙ Fracture Toughness of Gypsum Using Shear-box Test

• Main Authors: Yi-Jiun Chuang, 莊翌君
• Other Authors: Chein-Lee Wang
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/31240170061906492137

碩士 === 國立成功大學 === 資源工程學系碩博士班 === 96 === It is observed that in most Mode II fracture toughness testings, it always exist shearing stress and tensile stress at the same time at the notch tips. Because the shear strength of brittle materials is always known to be larger than its tensile strength, this reults in Mode I fracture prior to Mode II fracture and it is difficult to obtain the Mode II fracture toughness. In order to obtain a pure Mode II fracture, we must apply a compressive stress to restrain tensile stress at the notch tips. This study proposes a shear-box test to measure the Mode II fracture toughness of gypsum. The size effect for double-notched specimens has been investigated for different specimen thicknesses and notch lengths. This study also utilizes the finite element program to evaluate the corresponding stress intensity factors. The study finds that the shear strength decreases when notch length increases. When notch length is equal to or larger than 0.6, Mode II fracture toughness becomes stationary. This study also finds that the variety of the thickness of the specimens has no influence on the Mode II fracture toughness. Three different scenarios of testing configurations are simulated by the finite element program ANSYS. The numerical results show that the scenario considering different material properties is the best fit for the realistic condition. Keyword：Mode II fracture toughness, shear-box.