Mixed-mode I-II crack-based fatigue crack propagation(FCPⅠ-Ⅱ)usually occurs in engineering structures;however,no theoretical formula or effective compliance test methods have been established for FCPI-IIto date.For ...Mixed-mode I-II crack-based fatigue crack propagation(FCPⅠ-Ⅱ)usually occurs in engineering structures;however,no theoretical formula or effective compliance test methods have been established for FCPI-IIto date.For mixed-mode I-II flawed components,based on the principle of mean-value energy equivalence,we propose a theoretical method to describe the relationship between material elastic parameters,geometrical dimensions,load(or displacement),and energy.Based on the maximum circumferential stress criterion,we propose a uniform compliance model for compact tensile shear(CTS)specimens with horizontal cracks deflecting and propagating(flat-folding propagation)under different loading angles,geometries,and materials.Along with an innovative design of the fixture of CTS specimens used for FCPI-IItests,we develop a new compliancebased testing method for FCPⅠ-Ⅱ.For the 30Cr2Ni4MoV rotor steel,the FCP rates of modeⅠ,modeⅡ,and mixed-modeⅠ-Ⅱcracks were obtained via FCP tests using compact tension,Arcan,and CTS specimens,respectively.The obtained da/d N versusΔJ curves of the FCP rates are close.The loading angleαand dimensionless initial crack length a0/W demonstrated negligible effects on the FCP rates.Hence,the FCP rates of mode I crack can be used to predict the residual life of structural crack propagation.展开更多
Cohesive element is developed from the Dugdal-Barenblatt model in the field of fracture mechanics. The mechanical constitutive relation of cohesive element can be artificially assumed depending on the specific applica...Cohesive element is developed from the Dugdal-Barenblatt model in the field of fracture mechanics. The mechanical constitutive relation of cohesive element can be artificially assumed depending on the specific applications. It has been successfully applied in the study of crystal plasticity/brittle fracture process and decohesion between delaminations. In this paper, tensile experiments of large steel plate with different length of pre-existing cracks are conducted. Based on commercial software ABAQUS, cohesive element is adopted to simulate the tensile tests, and appropriate parameter values are obtained by fitting displacement-force curves. Using these parameters, a numerical method is presented by applying cohesive element to thermo-elastic-plastic finite element method （TEP-FEM） to simulate plate rigid restraint cracking （PRRC） tests. By changing constitutive relation of cohesive element, dimensions of the model and welding conditions, the influence of welding restraint intensity and welding conditions on the crack propagation are discussed, respectively. Three types of welding cold cracking are simulated. Significant influence of welding cold cracking on resistant stress in welding line is captured by this numerical method.展开更多
为研究冻胀荷载对双裂隙岩体裂纹扩展及贯通机制的影响,文章基于扩展有限元法(extended finite element method,XFEM),分析冻胀力作用下不同岩桥参数双裂隙试样的裂纹扩展特征和破坏形式,探究在冻胀力和侧向卸荷共同作用下双裂隙试样的...为研究冻胀荷载对双裂隙岩体裂纹扩展及贯通机制的影响,文章基于扩展有限元法(extended finite element method,XFEM),分析冻胀力作用下不同岩桥参数双裂隙试样的裂纹扩展特征和破坏形式,探究在冻胀力和侧向卸荷共同作用下双裂隙试样的裂纹扩展贯通规律。结果表明:基于XFEM的数值模拟结果与试验中的裂纹扩展路径基本吻合,验证了XFEM能够有效地应用于双裂隙岩体的裂纹扩展模拟;非岩桥区冻胀裂纹的扩展方向与预制裂隙走向相同,而岩桥区裂纹的扩展方向受到冻胀应力的影响,裂纹扩展方向偏向于另一条预制裂隙位置;冻胀裂纹的扩展模式受到围压的影响,随着围压增加,侧向卸荷过程中裂纹扩展模式由拉张模式变成拉剪混合模式,裂纹扩展方向也发生偏转。研究方法和结果可为低温裂隙岩体裂纹扩展相关研究提供参考。展开更多
The mechanical properties and fracturing mechanism of shale containing beddings are critically important in shale gas exploitation and wellbore stability.To investigate the effects of shale bedding on crack behavior a...The mechanical properties and fracturing mechanism of shale containing beddings are critically important in shale gas exploitation and wellbore stability.To investigate the effects of shale bedding on crack behavior and fracturing mechanism,scanning electron microscope(SEM)with a loading system was employed to carry out three-point bending tests on Longmaxi outcrop shale.The crack initiation and propagation of Longmaxi shale were observed and recorded by taking photos during loading.The cracking paths were extracted to calculate the crack length through a MATLAB program.The peak load,fracture toughness and fracture energy all increase with the bedding angle from 0°to 90°.The crack length and energy were also found to increase with the bedding angle in the range of 0°-600 and then drop slightly.The fracturing mechanism of shale includes the main crack affected by the bedding angle and disturbed by randomly distributed particles.The main cracking path was accompanied by several microcrack branches which could form an interconnected crack system.When the main crack encounters larger sedimentary particles,it will deflect around the particles and then restore to the initial direction.A numerical technique using extended finite element method(XFEM)coupled with anisotropic cohesive damage criteria was developed,which is able to capture the dependence of crack propagations on bedding angle and sedimentary particles.This study sheds light on understanding and predicting mesoscale fracture behavior of shale with different bedding angles.展开更多
为了研究Ⅰ-Ⅱ复合型裂纹动态扩展问题及裂纹止裂问题,侧开单裂纹半孔板(single cleavage semi circle compression,SCSCC)试样采用分离式霍普金森压杆(SHPB)实验系统进行冲击,完成SCSCC试样I–II复合型裂纹动态断裂实验,并针对实验进...为了研究Ⅰ-Ⅱ复合型裂纹动态扩展问题及裂纹止裂问题,侧开单裂纹半孔板(single cleavage semi circle compression,SCSCC)试样采用分离式霍普金森压杆(SHPB)实验系统进行冲击,完成SCSCC试样I–II复合型裂纹动态断裂实验,并针对实验进行数值分析,研究其扩展路径。为了验证数值模拟的可靠性,不仅进行有限尺寸中心裂纹板受冲击拉伸作用的动态有限差分法分析,而且在对SHPB实验进行数值分析后,将模拟监测点应变值与实验中入射杆应变片测得的应变值进行比较。结果表明:(1)验证分析中应力强度因子结果与其他测试的结果比较吻合,同时,模拟监测点记录下的应变值与SHPB实验中入射杆应变片记录下的应变数据相比较,两者吻合程度很高,说明使用数值方法模拟SHPB实验的可行性;(2)数值模拟的裂纹扩展路径与SHPB实验裂纹扩展路径基本吻合;(3)SCSCC试件在扩展过程中,裂纹尖端存在短暂停留现象,并最终朝着试件中轴线方向(最大应力区)移动;(4)SCSCC试件是一种便于研究裂纹动态扩展问题的构型,可以有效地求解不同复合程度的I–II复合型裂纹问题,为后续的止裂研究提供基础。展开更多
基金the National Key Research and Development Program of China(Grant No.2017YFB0702200)the National Natural Science Foundation of China(Grant No.11872320)the Policy Guidance Program of Jiangsu Province(Grant No.BZ2020057)。
文摘Mixed-mode I-II crack-based fatigue crack propagation(FCPⅠ-Ⅱ)usually occurs in engineering structures;however,no theoretical formula or effective compliance test methods have been established for FCPI-IIto date.For mixed-mode I-II flawed components,based on the principle of mean-value energy equivalence,we propose a theoretical method to describe the relationship between material elastic parameters,geometrical dimensions,load(or displacement),and energy.Based on the maximum circumferential stress criterion,we propose a uniform compliance model for compact tensile shear(CTS)specimens with horizontal cracks deflecting and propagating(flat-folding propagation)under different loading angles,geometries,and materials.Along with an innovative design of the fixture of CTS specimens used for FCPI-IItests,we develop a new compliancebased testing method for FCPⅠ-Ⅱ.For the 30Cr2Ni4MoV rotor steel,the FCP rates of modeⅠ,modeⅡ,and mixed-modeⅠ-Ⅱcracks were obtained via FCP tests using compact tension,Arcan,and CTS specimens,respectively.The obtained da/d N versusΔJ curves of the FCP rates are close.The loading angleαand dimensionless initial crack length a0/W demonstrated negligible effects on the FCP rates.Hence,the FCP rates of mode I crack can be used to predict the residual life of structural crack propagation.
文摘Cohesive element is developed from the Dugdal-Barenblatt model in the field of fracture mechanics. The mechanical constitutive relation of cohesive element can be artificially assumed depending on the specific applications. It has been successfully applied in the study of crystal plasticity/brittle fracture process and decohesion between delaminations. In this paper, tensile experiments of large steel plate with different length of pre-existing cracks are conducted. Based on commercial software ABAQUS, cohesive element is adopted to simulate the tensile tests, and appropriate parameter values are obtained by fitting displacement-force curves. Using these parameters, a numerical method is presented by applying cohesive element to thermo-elastic-plastic finite element method （TEP-FEM） to simulate plate rigid restraint cracking （PRRC） tests. By changing constitutive relation of cohesive element, dimensions of the model and welding conditions, the influence of welding restraint intensity and welding conditions on the crack propagation are discussed, respectively. Three types of welding cold cracking are simulated. Significant influence of welding cold cracking on resistant stress in welding line is captured by this numerical method.
文摘为研究冻胀荷载对双裂隙岩体裂纹扩展及贯通机制的影响,文章基于扩展有限元法(extended finite element method,XFEM),分析冻胀力作用下不同岩桥参数双裂隙试样的裂纹扩展特征和破坏形式,探究在冻胀力和侧向卸荷共同作用下双裂隙试样的裂纹扩展贯通规律。结果表明:基于XFEM的数值模拟结果与试验中的裂纹扩展路径基本吻合,验证了XFEM能够有效地应用于双裂隙岩体的裂纹扩展模拟;非岩桥区冻胀裂纹的扩展方向与预制裂隙走向相同,而岩桥区裂纹的扩展方向受到冻胀应力的影响,裂纹扩展方向偏向于另一条预制裂隙位置;冻胀裂纹的扩展模式受到围压的影响,随着围压增加,侧向卸荷过程中裂纹扩展模式由拉张模式变成拉剪混合模式,裂纹扩展方向也发生偏转。研究方法和结果可为低温裂隙岩体裂纹扩展相关研究提供参考。
基金financially supported by National Natural Science Foundation of China(grant No.41877257)Beijing OutstandingYoung Scientist Program(Grant No.BJJWZYJH01201911413037)+1 种基金Shaanxi Coal Group Key Project(Grant No.2018SMHKJA-J-03)Yueqi outstanding scholar Award Program by China University of Mining and Technology(Beijing),China。
文摘The mechanical properties and fracturing mechanism of shale containing beddings are critically important in shale gas exploitation and wellbore stability.To investigate the effects of shale bedding on crack behavior and fracturing mechanism,scanning electron microscope(SEM)with a loading system was employed to carry out three-point bending tests on Longmaxi outcrop shale.The crack initiation and propagation of Longmaxi shale were observed and recorded by taking photos during loading.The cracking paths were extracted to calculate the crack length through a MATLAB program.The peak load,fracture toughness and fracture energy all increase with the bedding angle from 0°to 90°.The crack length and energy were also found to increase with the bedding angle in the range of 0°-600 and then drop slightly.The fracturing mechanism of shale includes the main crack affected by the bedding angle and disturbed by randomly distributed particles.The main cracking path was accompanied by several microcrack branches which could form an interconnected crack system.When the main crack encounters larger sedimentary particles,it will deflect around the particles and then restore to the initial direction.A numerical technique using extended finite element method(XFEM)coupled with anisotropic cohesive damage criteria was developed,which is able to capture the dependence of crack propagations on bedding angle and sedimentary particles.This study sheds light on understanding and predicting mesoscale fracture behavior of shale with different bedding angles.
文摘为了研究Ⅰ-Ⅱ复合型裂纹动态扩展问题及裂纹止裂问题,侧开单裂纹半孔板(single cleavage semi circle compression,SCSCC)试样采用分离式霍普金森压杆(SHPB)实验系统进行冲击,完成SCSCC试样I–II复合型裂纹动态断裂实验,并针对实验进行数值分析,研究其扩展路径。为了验证数值模拟的可靠性,不仅进行有限尺寸中心裂纹板受冲击拉伸作用的动态有限差分法分析,而且在对SHPB实验进行数值分析后,将模拟监测点应变值与实验中入射杆应变片测得的应变值进行比较。结果表明:(1)验证分析中应力强度因子结果与其他测试的结果比较吻合,同时,模拟监测点记录下的应变值与SHPB实验中入射杆应变片记录下的应变数据相比较,两者吻合程度很高,说明使用数值方法模拟SHPB实验的可行性;(2)数值模拟的裂纹扩展路径与SHPB实验裂纹扩展路径基本吻合;(3)SCSCC试件在扩展过程中,裂纹尖端存在短暂停留现象,并最终朝着试件中轴线方向(最大应力区)移动;(4)SCSCC试件是一种便于研究裂纹动态扩展问题的构型,可以有效地求解不同复合程度的I–II复合型裂纹问题,为后续的止裂研究提供基础。
