剪切断裂韧度(K_(Ⅱc))确定的研究

STUDY ON DETERMINATION OF SHEAR FRACTURE TOUGHNESS(K_(Ⅱc))

对含裂纹的试件施加单纯剪应力时，裂纹将偏离原裂纹面扩展，测得的ＫⅠｃ小于ＫⅠｃ。理论分析证明，在剪切载荷作用下裂纹扩展是由于拉伸应力引起的，并非剪切破坏。为了抑制或消除剪切力引起裂纹尖端的拉应力，在给试件剪切力的同时，还必须给试件施加一定方向的压应力，从而在剪应力作用下．获得了剪切断裂。在此条件下测得岩石的剪切断裂韧度 ＫⅡｃ都大于 ＫⅠｃ。研究表明，产生Ⅱ型断裂是有前提条件的，即：裂纹尖端最大无因次剪应力强度因子ｆｒθｍａｘ与裂纹尖端最大无因次拉应力强度因子ｆｒθｍａｘ的比值ｆｒθｍａｘ／ｆｒθｍａｘ＞１和ｆｒθｍａｘ／ｆｒθｍａｘ＞ＫⅡｃ／ＫⅠｃ。

As shear force is applied to the specimen with a crack, the crack extends and deviates from original crack plane. Measured and calculated shear fracture toughness, K_(Ⅱc) is less than K_(Ⅰc). Theoretical study shows that the crack extension under shear loading is caused by tensile stress, and it does not belong to shear fracture. To restrain or eliminate tensile stress, compressive stress should be applied to the specimen. Thus pure shear fracture caused by shear stress is obtained. Calculated shear fracture toughness K_(Ⅱc) is larger than K_(Ⅰc). The study shows that the occurrence of mode II fracture requires its prerequisite. A prerequisite for mode Ⅱ fracture is f_(rθmax)/ f_(rθmax)＞1 and f_(rθmax) / f_(rθmax)> K_(Ⅱc) / K_(Ⅰc), where f_(rθmax) is the maximum dimensionless shear stress intensity factor, f_(rθmax) is the maximum dimensionless circumferential tensile stress intensity factor.