雷电作为自然界一种极端天气的表现形式,常给地基、地面、高耸建筑等造成严重破坏。工程防雷措施依赖于土体雷电冲击特性。现阶段,研究人员大多从电气工程角度探究雷电冲击土体造成的危害,但因学科间的差异与局限,雷电作用下岩土工程与...雷电作为自然界一种极端天气的表现形式,常给地基、地面、高耸建筑等造成严重破坏。工程防雷措施依赖于土体雷电冲击特性。现阶段,研究人员大多从电气工程角度探究雷电冲击土体造成的危害,但因学科间的差异与局限,雷电作用下岩土工程与电气工程的交叉融合方面的研究十分欠缺。本文构建土体雷电冲击模型,基于电弧通道能量平衡方程计算雷电放电产生的冲击波压力,将冲击波压力作为外加荷载作用在土体中,并通过修正Mohr-Coulomb屈服准则考虑动荷载下土体应变硬化,利用土体的理想锁定状态方程(Idealized Locked Equation of State)和动态扩孔方法考虑冲击波非稳态加载,探究雷电冲击下土体的弹塑性界面及应力时程变化规律。研究表明:在雷电冲击下,土体应力随时间变化呈现先陡增后迅速衰减的趋势,应力突变点表明土体此时正处于弹塑性交界面;在应力突变点之前,土体附加应力趋于0,处于弹性状态。任一时刻下,随着逐渐远离雷电冲击点,土体应力呈现迅速衰减的趋势,应力发生突变骤降表明此处土体正处于弹塑性交界面;在突变点之后土体附加应力趋于0,处于弹性状态。土体压缩系数对土体的弹塑性界面变化具有显著影响,随着压缩指标增大,土体塑性区半径逐渐减小;随着土体黏聚力逐渐增大,土体塑性区半径逐渐减小;增大土体弹性模量可以增大土体塑性区半径,但变化幅度相对较小;电流波形对土体塑性区中的应力会产生较大影响,而对土体弹性区影响较小。展开更多
A three-dimensional discrete element model of the connective type is presented. Moreover,a three-dimensional numerical analysis code,which can carry out the transitional pro- cess from connective model(for continuum)t...A three-dimensional discrete element model of the connective type is presented. Moreover,a three-dimensional numerical analysis code,which can carry out the transitional pro- cess from connective model(for continuum)to contact model(for non-continuum),is developed for simulating the mechanical process from continuum to non-continuum.The wave propagation process in a concrete block(as continuum)made of cement grout under impact loading is numer- ically simulated with this code.By comparing its numerical results with those by LS-DYNA,the calculation accuracy of the model and algorithm is proved.Furthermore,the failure process of the concrete block under quasi-static loading is demonstrated,showing the basic dynamic tran- sitional process from continuum to non-continuum.The results of calculation can be displayed by animation.The damage modes are similar to the experimental results.The two numerical examples above prove that our model and its code are powerful and efficient in simulating the dynamic failure problems accompanying the transition from continuum to non-continuum.It also shows that the discrete element method(DEM)will have broad prospects for development and application.展开更多
The impact buckling of a laminated composite bar is investigated in case of one of its ends moving due to axial impact compression. The governing equations considering the first- order shear deformation effect are der...The impact buckling of a laminated composite bar is investigated in case of one of its ends moving due to axial impact compression. The governing equations considering the first- order shear deformation effect are derived by the Hamilton principle and solved by the finite difference method. The critical axial shortness is determined by the B - R cirterion. The given example is used to highlight the influences of initial imperfection, impact velocity, stress wave and coupled stiffness. It is found that the unsymmetrically laminated bar has a quite different dynamic buckling behaviour from that of the symmetrically laminated bar.展开更多
An experiment of impact between 450 m/s water jets and polymethylme- thacrylate (PMMA) materials with complex surface geometry was conducted. The testing surfaces were a corner, step change, surface-breaking notch, in...An experiment of impact between 450 m/s water jets and polymethylme- thacrylate (PMMA) materials with complex surface geometry was conducted. The testing surfaces were a corner, step change, surface-breaking notch, inclined surface, etc. Stress waves propagation in the solid such as reflection, interference and diffraction was observed using polarized optics and an Imacon high speed camera (operating at both of 106 and 5×105 framing rates per second, fps). A damage test by the impact of the side jetting of an 850 m/s water jet was also carried out. It was found that stress waves propagation in solids depends not only on the surface geometry but also on the contact situation between liquid and solid. It was shown that the side jetting has sufficient damage potential although its head may consist of finer droplets. The results of this paper are useful to further analyze the dynamic stress state of solids under high-speed liquid impact.展开更多
文摘雷电作为自然界一种极端天气的表现形式,常给地基、地面、高耸建筑等造成严重破坏。工程防雷措施依赖于土体雷电冲击特性。现阶段,研究人员大多从电气工程角度探究雷电冲击土体造成的危害,但因学科间的差异与局限,雷电作用下岩土工程与电气工程的交叉融合方面的研究十分欠缺。本文构建土体雷电冲击模型,基于电弧通道能量平衡方程计算雷电放电产生的冲击波压力,将冲击波压力作为外加荷载作用在土体中,并通过修正Mohr-Coulomb屈服准则考虑动荷载下土体应变硬化,利用土体的理想锁定状态方程(Idealized Locked Equation of State)和动态扩孔方法考虑冲击波非稳态加载,探究雷电冲击下土体的弹塑性界面及应力时程变化规律。研究表明:在雷电冲击下,土体应力随时间变化呈现先陡增后迅速衰减的趋势,应力突变点表明土体此时正处于弹塑性交界面;在应力突变点之前,土体附加应力趋于0,处于弹性状态。任一时刻下,随着逐渐远离雷电冲击点,土体应力呈现迅速衰减的趋势,应力发生突变骤降表明此处土体正处于弹塑性交界面;在突变点之后土体附加应力趋于0,处于弹性状态。土体压缩系数对土体的弹塑性界面变化具有显著影响,随着压缩指标增大,土体塑性区半径逐渐减小;随着土体黏聚力逐渐增大,土体塑性区半径逐渐减小;增大土体弹性模量可以增大土体塑性区半径,但变化幅度相对较小;电流波形对土体塑性区中的应力会产生较大影响,而对土体弹性区影响较小。
基金Project supported by the National Natural Science Foundation of China(Nos.59978005 and 10232024)the National Distinguished Youth Fund of China(No.10025212).
文摘A three-dimensional discrete element model of the connective type is presented. Moreover,a three-dimensional numerical analysis code,which can carry out the transitional pro- cess from connective model(for continuum)to contact model(for non-continuum),is developed for simulating the mechanical process from continuum to non-continuum.The wave propagation process in a concrete block(as continuum)made of cement grout under impact loading is numer- ically simulated with this code.By comparing its numerical results with those by LS-DYNA,the calculation accuracy of the model and algorithm is proved.Furthermore,the failure process of the concrete block under quasi-static loading is demonstrated,showing the basic dynamic tran- sitional process from continuum to non-continuum.The results of calculation can be displayed by animation.The damage modes are similar to the experimental results.The two numerical examples above prove that our model and its code are powerful and efficient in simulating the dynamic failure problems accompanying the transition from continuum to non-continuum.It also shows that the discrete element method(DEM)will have broad prospects for development and application.
基金The present research work was financially supported by the National Natural Science Foundation of China.(No.19472042)
文摘The impact buckling of a laminated composite bar is investigated in case of one of its ends moving due to axial impact compression. The governing equations considering the first- order shear deformation effect are derived by the Hamilton principle and solved by the finite difference method. The critical axial shortness is determined by the B - R cirterion. The given example is used to highlight the influences of initial imperfection, impact velocity, stress wave and coupled stiffness. It is found that the unsymmetrically laminated bar has a quite different dynamic buckling behaviour from that of the symmetrically laminated bar.
文摘An experiment of impact between 450 m/s water jets and polymethylme- thacrylate (PMMA) materials with complex surface geometry was conducted. The testing surfaces were a corner, step change, surface-breaking notch, inclined surface, etc. Stress waves propagation in the solid such as reflection, interference and diffraction was observed using polarized optics and an Imacon high speed camera (operating at both of 106 and 5×105 framing rates per second, fps). A damage test by the impact of the side jetting of an 850 m/s water jet was also carried out. It was found that stress waves propagation in solids depends not only on the surface geometry but also on the contact situation between liquid and solid. It was shown that the side jetting has sufficient damage potential although its head may consist of finer droplets. The results of this paper are useful to further analyze the dynamic stress state of solids under high-speed liquid impact.
