Fracture parameters of welded joints with different strength matching and crack depth in weld metal are investigated by using the methods of elastoplastic finite element analysis and three point bend specimen test. Th...Fracture parameters of welded joints with different strength matching and crack depth in weld metal are investigated by using the methods of elastoplastic finite element analysis and three point bend specimen test. The results show that for shallow crack, the plastic zone turns large in loading process, and the fracture toughness turns high. The extent of the plastic zone of overmatched joint is larger than that of undermatched joint because it will extends to parent metal from the weld metal in loading process for the same CTOD value. The plastic zone of undermatched joint is restricted within the weld, and the size of that is small. Overmatched joint shows the fracture behaviour of shallow crack may more easily than the undermatched joint, while the two sorts of joint specimens have the same crack depth. Therefore, the fracture-resistant capability of overmatched weld is better than that of undermatched weld. when the toughness of weld metals is similar for both overmatched and undermatched joints.展开更多
In order to meet the requirement of structural inspection,the crack spacing and crack width at various heights in the tensile zone of six large depth reinforced concrete beams were measured under several loading level...In order to meet the requirement of structural inspection,the crack spacing and crack width at various heights in the tensile zone of six large depth reinforced concrete beams were measured under several loading levels of serviceability state.The effects of the depth of normal section beams on the crack spacing and crack width were analyzed,and the modified model is proposed for calculating the average crack spacing by thinking about the depth of normal section,the reinforcement arrangement and the effective reinforcement ratio.The relationships of crack widths at any position in the tensile zone and at the reinforcement level on the side surface of beam were studied.By theoretical and statistical analysis,a method is proposed to calculate the ratios of crack widths between any position and the reinforcement level on the side surface of large depth reinforced concrete beams.展开更多
植物根系可以通过机械加固直接增加土壤强度,抑制其附近土壤开裂。基于三维土壤开裂模型,结合以趋势项和随机波动项为特征的非平稳随机场,建立了描述根系影响下三维土壤干缩开裂过程的数值模型。该模型通过引入三维根系密度分布函数,并...植物根系可以通过机械加固直接增加土壤强度,抑制其附近土壤开裂。基于三维土壤开裂模型,结合以趋势项和随机波动项为特征的非平稳随机场,建立了描述根系影响下三维土壤干缩开裂过程的数值模型。该模型通过引入三维根系密度分布函数,并利用临界应变与根密度的指数函数关系将根系对土壤的加固作用具现在非平稳随机场中。采用闵可夫斯基密度(即面积密度、长度密度和欧拉数密度)来量化裂纹模式。通过现场实验结果对模型参数进行率定和验证,并对模型的精度进行了评价。实验与模拟裂纹图像的闵可夫斯基密度及裂纹深度相对频率的决定系数在0.7697~0.9983之间,均方根误差在0.005~0.083之间,偏差在0.0148~0.0810之间,一致性指标大于0.9617,表明新构建的模型能够很好地模拟根系影响下的三维土壤干缩开裂。此外,敏感性分析表明,土壤表面裂纹分布随着根系三维径向分布密度函数(Radial Distribution Density Function,RDDF)的横向分布半径的增加而减少,裂纹深度相对频率则受极半径的影响更加明显。研究成果对于干旱条件下的土壤结构变化具有一定意义。展开更多
This paper investigates the mechanisms of rock failure related to axial splitting and shear failure due to hoop stresses in cylindrical specimens.The hoop stresses are caused by normal viscous stress.The rheological d...This paper investigates the mechanisms of rock failure related to axial splitting and shear failure due to hoop stresses in cylindrical specimens.The hoop stresses are caused by normal viscous stress.The rheological dynamics theory(RDT)is used,with the mechanical parameters being determined by P-and S-wave velocities.The angle of internal friction is determined by the ratio of Young's modulus and the dynamic modulus,while dynamic viscosity defines cohesion and normal viscous stress.The effect of frequency on cohesion is considered.The initial stress state is defined by the minimum cohesion at the elastic limit when axial splitting can occur.However,as radial cracks grow,the stress state becomes oblique and moves towards the shear plane.The maximum and nonlinear cohesions are defined by the rock parameters under compressive strength when the radial crack depth reaches a critical value.The efficacy and precision of RDT are validated through the presentation of ultrasonic measurements on sandstone and rock specimens sourced from the literature.The results presented in dimensionless diagrams can be utilized in microcrack zones in the absence of lateral pressure in rock masses that have undergone disintegration due to excavation.展开更多
文摘Fracture parameters of welded joints with different strength matching and crack depth in weld metal are investigated by using the methods of elastoplastic finite element analysis and three point bend specimen test. The results show that for shallow crack, the plastic zone turns large in loading process, and the fracture toughness turns high. The extent of the plastic zone of overmatched joint is larger than that of undermatched joint because it will extends to parent metal from the weld metal in loading process for the same CTOD value. The plastic zone of undermatched joint is restricted within the weld, and the size of that is small. Overmatched joint shows the fracture behaviour of shallow crack may more easily than the undermatched joint, while the two sorts of joint specimens have the same crack depth. Therefore, the fracture-resistant capability of overmatched weld is better than that of undermatched weld. when the toughness of weld metals is similar for both overmatched and undermatched joints.
基金Sponsored by the Outstanding Youth Scientific Fund of Henan Province(Grant No.04120002300)Program for Innovation in University of Henan Province(Grant No.[2004]294)
文摘In order to meet the requirement of structural inspection,the crack spacing and crack width at various heights in the tensile zone of six large depth reinforced concrete beams were measured under several loading levels of serviceability state.The effects of the depth of normal section beams on the crack spacing and crack width were analyzed,and the modified model is proposed for calculating the average crack spacing by thinking about the depth of normal section,the reinforcement arrangement and the effective reinforcement ratio.The relationships of crack widths at any position in the tensile zone and at the reinforcement level on the side surface of beam were studied.By theoretical and statistical analysis,a method is proposed to calculate the ratios of crack widths between any position and the reinforcement level on the side surface of large depth reinforced concrete beams.
文摘植物根系可以通过机械加固直接增加土壤强度,抑制其附近土壤开裂。基于三维土壤开裂模型,结合以趋势项和随机波动项为特征的非平稳随机场,建立了描述根系影响下三维土壤干缩开裂过程的数值模型。该模型通过引入三维根系密度分布函数,并利用临界应变与根密度的指数函数关系将根系对土壤的加固作用具现在非平稳随机场中。采用闵可夫斯基密度(即面积密度、长度密度和欧拉数密度)来量化裂纹模式。通过现场实验结果对模型参数进行率定和验证,并对模型的精度进行了评价。实验与模拟裂纹图像的闵可夫斯基密度及裂纹深度相对频率的决定系数在0.7697~0.9983之间,均方根误差在0.005~0.083之间,偏差在0.0148~0.0810之间,一致性指标大于0.9617,表明新构建的模型能够很好地模拟根系影响下的三维土壤干缩开裂。此外,敏感性分析表明,土壤表面裂纹分布随着根系三维径向分布密度函数(Radial Distribution Density Function,RDDF)的横向分布半径的增加而减少,裂纹深度相对频率则受极半径的影响更加明显。研究成果对于干旱条件下的土壤结构变化具有一定意义。
文摘This paper investigates the mechanisms of rock failure related to axial splitting and shear failure due to hoop stresses in cylindrical specimens.The hoop stresses are caused by normal viscous stress.The rheological dynamics theory(RDT)is used,with the mechanical parameters being determined by P-and S-wave velocities.The angle of internal friction is determined by the ratio of Young's modulus and the dynamic modulus,while dynamic viscosity defines cohesion and normal viscous stress.The effect of frequency on cohesion is considered.The initial stress state is defined by the minimum cohesion at the elastic limit when axial splitting can occur.However,as radial cracks grow,the stress state becomes oblique and moves towards the shear plane.The maximum and nonlinear cohesions are defined by the rock parameters under compressive strength when the radial crack depth reaches a critical value.The efficacy and precision of RDT are validated through the presentation of ultrasonic measurements on sandstone and rock specimens sourced from the literature.The results presented in dimensionless diagrams can be utilized in microcrack zones in the absence of lateral pressure in rock masses that have undergone disintegration due to excavation.
