平行双裂缝圆盘试样裂纹扩展过程的尺寸效应试验研究

Experimental study on the size effect of crack propagation process of disk samples containing parallel double pre-existing flaws

针对含多条裂缝不同尺寸的岩石受载时内部裂纹扩展及贯通存在尺寸效应的问题,制作了直径分别为50,100,150和200 mm的平行双裂缝砂岩圆盘试样,其厚度、裂缝长度和裂缝间距随直径等比变化。在GCTS RTX–3000试验机上对圆盘试样进行静态加载试验,采用声发射(acoustic emission,AE)和数字图像相关(digital image correlation,DIC)技术对试样的裂纹扩展过程进行监测。结果表明:随试样尺寸的增加,破坏载荷呈线性增长趋势,预制裂缝对试样承载能力的削弱作用增强,试样破坏单位体积消耗的能量逐渐减小;多裂纹扩展存在相互竞争机制,裂纹的起裂顺序决定着扩展方向,直径50,100和200 mm的试样裂纹扩展具有同方向性,直径150 mm的试样裂纹相向扩展;通过AE准确反映了试样内部的损伤演化过程,运用DIC技术将裂纹扩展过程数值化,能够精确分析裂纹的张开位移和扩展速度;不同尺寸试样裂纹扩展速度的变化规律相似,即裂纹以一个较低的初速度开始扩展,并在很短的距离内达到峰值速度,之后扩展速度急剧下降,末段裂纹扩展速度缓慢减小并趋于稳定。

In view of the size effect of internal crack propagation and penetration when rocks of different sizes containing multiple flaws are loaded,sandstone disk samples with diameters of 50,100,150 and 200 mm containing parallel double flaws were made.Their thickness,flaw length and flaw spacing change in proportion to the diameter.Static loading tests were carried out on disc samples on GCTS RTX–3000 testing machine,and the crack propagation process of the samples was monitored by comprehensively using acoustic emission(AE)and digital image correlation(DIC)technology.The results show that with the increase of the sample size,the failure load increases linearly,the weakening effect of prefabricated flaws on the bearing capacity of the samples is enhanced,and the energy consumed per unit volume of sample failure decreases gradually.There is a competitive relationship between multiple crack propagation.The crack initiation sequence determines the propagation direction.The crack propagation of samples with diameters of 50,100 and 200 mm has the same direction.Cracks expand in opposite directions of samples with diameter of 150 mm.AE can accurately reflect the damage evolution process inside the sample.Using DIC technology to digitize the crack propagation process,the crack opening displacement and propagation speed can be accurately analyzed.The variation law of crack propagation speed of samples with different sizes is similar,that is,the crack starts to grow at a low initial speed and reaches a peak speed within a short distance,then the propagation speed drops sharply,and the final crack propagation speed decreases slowly and tends to be stable.