岩石试样围压下直接拉伸试验

Direct Tensile Experiment of Rock Specimens Under Confining Pressure

圆盘试样巴西劈裂是在拉压应力联合作用下破裂的,Griffith准则认为压应力小于3倍抗拉强度则对岩石拉伸破坏没有影响,这些问题都需要直接的试验验证.在50 mm×100mm试样两端粘结80 mm的拉头,置入液压缸中施加围压,拉头承受轴向载荷引起岩样拉伸;同时利用伺服试验机对拉头施加轴向压缩载荷,平衡其承受的部分拉伸载荷.通过改变轴向压缩载荷的数值,就可以得到不同围压下岩样的拉伸强度.尽管试验结果具有相当的离散性,但完全可以确认岩样拉伸强度随围压增大而减小,巴西劈裂强度低于岩石单向拉伸强度.岩石在压拉应力作用下发生的拉伸破坏可以利用应力之间的线性关系描述.

Rock disc is fractured under tensile and compression stresses in Brazilian split test. Griffith criterion shows that the compression stress which less than 3 times of uniaxial tensile strength has no influence on the tensile fracture. All of these need the experimental results to verify. Specimens of φ50 mm × 100 mm in size were glued with joints 80 mm in diameter and put in hollow cylinder in which hydraulic oil was pumped. The joints were compressed in axial direction by servo-control testing machine to balance tensile force produced by hydraulic oil in the hollow cylinder. The tensile strengths under different confining pressure can get by changing the axial compression force. Although the experimental results were diverse, conclusions can be demonstrated as follows： the tensile strength decreases with confining pressure, and the Brazilian split strength is lower than the uniaxial tensile strength. The strength criterion of rock loaded by compression stress and tensile stress can be described with linear relation of stresses.