The instability of functionally graded material(FGM)structures is one of the major threats to their service safety in engineering applications.This paper aims to clarify a long-standing controversy on the thermal inst...The instability of functionally graded material(FGM)structures is one of the major threats to their service safety in engineering applications.This paper aims to clarify a long-standing controversy on the thermal instability type of simply-supported FGM beams.First,based on the Euler-Bernoulli beam theory and von K′arm′an geometric nonlinearity,a nonlinear governing equation of simply-supported FGM beams under uniform thermal loads by Zhang’s two-variable method is formulated.Second,an approximate analytic solution to the nonlinear integro-differential boundary value problem under a thermal-induced inhomogeneous force boundary condition is obtained by using a semiinverse method when the coordinate axis is relocated to the bending axis(physical neutral plane),and then the analytical predictions are verified by the differential quadrature method(DQM).Finally,based on the free energy theorem,it is revealed that the symmetry breaking caused by the material inhomogeneity can make the simply-supported FGM beam under uniform thermal loads occur snap-through postbuckling only in odd modes;furthermore,the nonlinear critical load of thermal buckling varies non-monotonically with the functional gradient index due to the stretching-bending coupling effect.These results are expected to provide new ideas and references for the design and regulation of FGM structures.展开更多
The paper develops and examines the complete solutions for the elastic field induced by the point load vector in a general functionally graded material(FGM)model with transverse isotropy.The FGMs are approximated with...The paper develops and examines the complete solutions for the elastic field induced by the point load vector in a general functionally graded material(FGM)model with transverse isotropy.The FGMs are approximated with n-layered materials.Each of the n-layered materials is homogeneous and transversely isotropic.The complete solutions of the displacement and stress fields are explicitly expressed in the forms of fifteen classical Hankel transform integrals with ten kernel functions.The ten kernel functions are explicitly expressed in the forms of backward transfer matrices and have clear mathematical properties.The singular terms of the complete solutions are analytically isolated and expressed in exact closed forms in terms of elementary harmonic functions.Numerical results show that the computation of the complete solutions can be achieved with high accuracy and efficiency.展开更多
A functionally graded material-based actively water-cooled tungsten-copper mockup with a dimension of 30 mm×30 mm×25 mm was designed and fabricated by infiltration-brazing method.The thicknesses of the pure ...A functionally graded material-based actively water-cooled tungsten-copper mockup with a dimension of 30 mm×30 mm×25 mm was designed and fabricated by infiltration-brazing method.The thicknesses of the pure W layer and W/Cu graded layer were 2 and 3 mm,respectively.High heat flux tests were performed on the mockup using an e-beam device.There is no damage occurring on the joint after heat loading at 5 MW/m2.The temperature on the pure W surface is less than 500°C after irradiation for 100 s at 5 MW/m2,while the temperature on the brazing seam/copper surface is around 200°C.展开更多
为有效提升台风天气下主动配电网的韧性,提出同时考虑分级减载和同级负荷削减的主动配电网韧性提升方法。首先,综合考虑台风天气下强风和暴雨对配电网的影响,通过建立Batts台风风场模型和暴雨压强模型实现了对配电网元件故障率的量化分...为有效提升台风天气下主动配电网的韧性,提出同时考虑分级减载和同级负荷削减的主动配电网韧性提升方法。首先,综合考虑台风天气下强风和暴雨对配电网的影响,通过建立Batts台风风场模型和暴雨压强模型实现了对配电网元件故障率的量化分析,进而采用蒙特卡洛(MonteCarlo)法模拟台风天气下的主动配电网故障场景,并利用系统信息熵进行场景筛选,确定故障规模。其次,提出了同时考虑最大化一级负荷存活量与故障孤岛中同级负荷削减逻辑的主动配电网分级减载策略。然后,提出包括综合鲁棒性、一级负荷损失速度和损失率、总负荷曲线面积缺失比的4个主动配电网韧性评估指标,并通过遗传-粒子群融合算法(hybrid GA and PSO algorithm,GA-PSO)对配电网韧性评估模型进行高效求解。最后,基于Matlab2020a仿真平台建立某实际配电网和IEEE118节点测试系统算例,验证了提出的考虑分级减载的台风天气下主动配电网韧性评估方法的正确性和有效性。展开更多
文摘The instability of functionally graded material(FGM)structures is one of the major threats to their service safety in engineering applications.This paper aims to clarify a long-standing controversy on the thermal instability type of simply-supported FGM beams.First,based on the Euler-Bernoulli beam theory and von K′arm′an geometric nonlinearity,a nonlinear governing equation of simply-supported FGM beams under uniform thermal loads by Zhang’s two-variable method is formulated.Second,an approximate analytic solution to the nonlinear integro-differential boundary value problem under a thermal-induced inhomogeneous force boundary condition is obtained by using a semiinverse method when the coordinate axis is relocated to the bending axis(physical neutral plane),and then the analytical predictions are verified by the differential quadrature method(DQM).Finally,based on the free energy theorem,it is revealed that the symmetry breaking caused by the material inhomogeneity can make the simply-supported FGM beam under uniform thermal loads occur snap-through postbuckling only in odd modes;furthermore,the nonlinear critical load of thermal buckling varies non-monotonically with the functional gradient index due to the stretching-bending coupling effect.These results are expected to provide new ideas and references for the design and regulation of FGM structures.
基金Project supported by the National Natural Science Foundation of China(No.42207182)the Research Grants Council of the Hong Kong Special Administrative Region Government of China(Nos.HKU 17207518 and R5037-18)。
文摘The paper develops and examines the complete solutions for the elastic field induced by the point load vector in a general functionally graded material(FGM)model with transverse isotropy.The FGMs are approximated with n-layered materials.Each of the n-layered materials is homogeneous and transversely isotropic.The complete solutions of the displacement and stress fields are explicitly expressed in the forms of fifteen classical Hankel transform integrals with ten kernel functions.The ten kernel functions are explicitly expressed in the forms of backward transfer matrices and have clear mathematical properties.The singular terms of the complete solutions are analytically isolated and expressed in exact closed forms in terms of elementary harmonic functions.Numerical results show that the computation of the complete solutions can be achieved with high accuracy and efficiency.
基金supported by the National Natural Science Foundation of China (No.10805073)the National Magnetic Confinement Fusion Program of China (No.2010GB109000)
文摘A functionally graded material-based actively water-cooled tungsten-copper mockup with a dimension of 30 mm×30 mm×25 mm was designed and fabricated by infiltration-brazing method.The thicknesses of the pure W layer and W/Cu graded layer were 2 and 3 mm,respectively.High heat flux tests were performed on the mockup using an e-beam device.There is no damage occurring on the joint after heat loading at 5 MW/m2.The temperature on the pure W surface is less than 500°C after irradiation for 100 s at 5 MW/m2,while the temperature on the brazing seam/copper surface is around 200°C.
文摘为有效提升台风天气下主动配电网的韧性,提出同时考虑分级减载和同级负荷削减的主动配电网韧性提升方法。首先,综合考虑台风天气下强风和暴雨对配电网的影响,通过建立Batts台风风场模型和暴雨压强模型实现了对配电网元件故障率的量化分析,进而采用蒙特卡洛(MonteCarlo)法模拟台风天气下的主动配电网故障场景,并利用系统信息熵进行场景筛选,确定故障规模。其次,提出了同时考虑最大化一级负荷存活量与故障孤岛中同级负荷削减逻辑的主动配电网分级减载策略。然后,提出包括综合鲁棒性、一级负荷损失速度和损失率、总负荷曲线面积缺失比的4个主动配电网韧性评估指标,并通过遗传-粒子群融合算法(hybrid GA and PSO algorithm,GA-PSO)对配电网韧性评估模型进行高效求解。最后,基于Matlab2020a仿真平台建立某实际配电网和IEEE118节点测试系统算例,验证了提出的考虑分级减载的台风天气下主动配电网韧性评估方法的正确性和有效性。
