剪切盒加载下岩石剪切(Ⅱ型)断裂韧度K_ⅡC的测定

来源期刊：中南大学学报(自然科学版)2001年第6期

论文作者：饶秋华 孙宗颀 LI Chun-lin B.Stillborg

文章页码：563 - 567

关键词：剪切(Ⅱ型)断裂;Ⅱ型断裂韧度;岩石;剪切盒试验;有限单元法

Key words：shear (ModeⅡ) fracture; ModeⅡfracture toughness; rock; shear-box test; finite element method

摘    要：采用剪切盒实验获得了岩石的Ⅱ型断裂并测定了岩石的Ⅱ型断裂韧度K_ⅡC,通过有限单元法中的位移法推导出剪切盒加载下双切口试样的Ⅱ型应力强度因子K_Ⅱ的一般计算公式,并探讨了K_ⅡC的尺寸效应和Ⅱ型断裂机理.实验及数值计算结果表明:在剪切盒加载下,裂纹尖端最大拉应力始终低于岩石的拉伸强度,最大剪应力大于其对应压应力下的剪切强度,且Ⅱ型最大应力强度因子K_Ⅱmax为Ⅰ型最大应力强度因子K_Ⅰmax的2~4倍,从而导致产生Ⅱ型断裂;测得的K_ⅡC值随无量纲切口长度(2a/W)的增加而降低,当2a/W≥0.7,且B≥W,α为65°~75°时,K_ⅡC趋近于一个常数,该常数为Ⅰ型断裂韧度K_ⅠC的2~3倍,可认为是较合理的岩石Ⅱ型断裂韧度值;剪切盒实验是一种测定岩石K_ⅡC的行之有效的方法.

Abstract: Shear-box test was used to conduct ModeⅡfracture of rock and to determine ModeⅡfracture toughness K_ⅡC. Under shear-box loading the formula for calculating the shear stress intensity factor K_Ⅱof double-notched specimen was obtained by finite element method through displacement approach. The effects of the dimensionless notch length (2a/W) on K_ⅡC and ModeⅡfracture mechanism were studied. Test and numerical results showthatundershear-box loading the major principal stressσ1at the notch tip is smaller than the tensile strength σ tand the maximum shear stress τ maxis larger than the shear strengthσc in the presence of the compressive stress. Furthermore, the maximum ModeⅡstress intensity factor K_Ⅱmax is 2-4 times as large as the maximum ModeⅠstress intensity factor K_Ⅰmax. Therefore ModeⅡfracture occurs. The measured value of K_ⅡC decreases with the dimensionless notch length (2a/W) and becomes a constant when 2a/W≥0.7 and B≥Win the range ofα=65°~75°.K_ⅡC is 2~3 times K_ⅠC and can be regarded as a reliable and reasonable value of ModeⅡfracture toughness of rock. Shear-box test is a potential method for determining K_ⅡC of rock.