In order to simultaneously measure the initiation toughness of pure mode Ⅰ and mode Ⅱ cracks in one specimen,a large-size double-cracked concave-convex plate(DCCP)specimen configuration was proposed.Impacting tests ...In order to simultaneously measure the initiation toughness of pure mode Ⅰ and mode Ⅱ cracks in one specimen,a large-size double-cracked concave-convex plate(DCCP)specimen configuration was proposed.Impacting tests were implemented in the drop plate impact device.Strain gauges were employed to measure impact loads and crack initiation time.The corresponding numerical model was established by using the dynamic finite difference program AUTODYN,and the experimental-numerical method and ABAQUS code were utilized to obtain the initial fracture toughness of the crack.Using experiments and numerical research,we concluded that the DCCP specimen is suitable for measuring the initial fracture toughness of pure mode Ⅰ and mode Ⅱ cracks at the same time;the dynamic initiation toughness increases with the increase of loading rate and the crack initiation time decreases with increasing loading rate;the initiation toughness of mode Ⅱ crack is 0.5 times that of mode Ⅰ crack when subjected to the same loading rate.For the pre-crack in the vicinity of the bottom of a sample,when its length increases from 20 to 100 mm,the dynamic initiation toughness of the pure mode Ⅰ crack gradually decreases,and the longer the lower crack length is,the easier the crack would initiate,but the dynamic initiation toughness of pure mode Ⅱ crack varies little.展开更多
以非线性断裂力学理论为基础，通过应力叠加原理，推导出了ⅠⅡ型复合水力裂缝起裂角的解析模型。利用该模型计算了裂缝与最大水平主应力方向夹角为0°、30°、60°和90°时的裂缝端部塑性区域范围，并将利用该模型计...以非线性断裂力学理论为基础，通过应力叠加原理，推导出了ⅠⅡ型复合水力裂缝起裂角的解析模型。利用该模型计算了裂缝与最大水平主应力方向夹角为0°、30°、60°和90°时的裂缝端部塑性区域范围，并将利用该模型计算出的起裂角与利用最大周向应力准则计算出的起裂角进行了对比。结果表明：裂缝与最大水平主应力方向夹角为0°、30°、60°和90°时的裂缝端部塑性区域的范围分别是0～0.18，0～0.45，0～0.45和0～0.18倍半缝长；裂缝与最大水平主应力方向夹角为0°时，裂缝的起裂角为180°；当裂缝与最大水平主应力方向夹角增大至90°时，起裂角降为0°；在裂缝与最大水平主应力方向夹角及缝内流体压力相同的情况下，利用该模型计算出的起裂角比利用最大周向应力准则计算出的大0°～20°；在裂缝与最大水平主应力方向夹角相同的情况下，缝内流体压力为55 M Pa时的起裂角比缝内流体压力为45 M Pa时的大0°～40°。研究表明，利用非线性断裂力学研究泥页岩地层起裂是可行的，研究结果可以为水平井分段压裂优化提供一定的理论指导。展开更多
基金Projects(U19A2098,1210021843)supported by the National Natural Science Foundation of ChinaProject(2021SCU12130)supported by Fundamental Research Funds for the Central Universities,China+1 种基金Project(2021YJ0511)supported by the Sichuan Science and Technology Program,ChinaProjects(DESEYU202205,DESE202005)supported by the Open Fund of Key Laboratory of Deep Earth Science and Engineering,China。
文摘In order to simultaneously measure the initiation toughness of pure mode Ⅰ and mode Ⅱ cracks in one specimen,a large-size double-cracked concave-convex plate(DCCP)specimen configuration was proposed.Impacting tests were implemented in the drop plate impact device.Strain gauges were employed to measure impact loads and crack initiation time.The corresponding numerical model was established by using the dynamic finite difference program AUTODYN,and the experimental-numerical method and ABAQUS code were utilized to obtain the initial fracture toughness of the crack.Using experiments and numerical research,we concluded that the DCCP specimen is suitable for measuring the initial fracture toughness of pure mode Ⅰ and mode Ⅱ cracks at the same time;the dynamic initiation toughness increases with the increase of loading rate and the crack initiation time decreases with increasing loading rate;the initiation toughness of mode Ⅱ crack is 0.5 times that of mode Ⅰ crack when subjected to the same loading rate.For the pre-crack in the vicinity of the bottom of a sample,when its length increases from 20 to 100 mm,the dynamic initiation toughness of the pure mode Ⅰ crack gradually decreases,and the longer the lower crack length is,the easier the crack would initiate,but the dynamic initiation toughness of pure mode Ⅱ crack varies little.
文摘以非线性断裂力学理论为基础，通过应力叠加原理，推导出了ⅠⅡ型复合水力裂缝起裂角的解析模型。利用该模型计算了裂缝与最大水平主应力方向夹角为0°、30°、60°和90°时的裂缝端部塑性区域范围，并将利用该模型计算出的起裂角与利用最大周向应力准则计算出的起裂角进行了对比。结果表明：裂缝与最大水平主应力方向夹角为0°、30°、60°和90°时的裂缝端部塑性区域的范围分别是0～0.18，0～0.45，0～0.45和0～0.18倍半缝长；裂缝与最大水平主应力方向夹角为0°时，裂缝的起裂角为180°；当裂缝与最大水平主应力方向夹角增大至90°时，起裂角降为0°；在裂缝与最大水平主应力方向夹角及缝内流体压力相同的情况下，利用该模型计算出的起裂角比利用最大周向应力准则计算出的大0°～20°；在裂缝与最大水平主应力方向夹角相同的情况下，缝内流体压力为55 M Pa时的起裂角比缝内流体压力为45 M Pa时的大0°～40°。研究表明，利用非线性断裂力学研究泥页岩地层起裂是可行的，研究结果可以为水平井分段压裂优化提供一定的理论指导。
