This paper investigates the functionally graded coating bonded to an elastic strip with a crack under thermal- mechanical loading. Considering some new boundary conditions, it is assumed that the temperature drop acro...This paper investigates the functionally graded coating bonded to an elastic strip with a crack under thermal- mechanical loading. Considering some new boundary conditions, it is assumed that the temperature drop across the crack surface is the result of the thermal conductivity index which controls heat conduction through the crack region. By the Fourier transforms, the thermal-elastic mixed boundary value problems are reduced to a system of singular integral equations which can be approximately solved by applying the Chebyshev polynomials. The numerical computation methods for the temperature, the displacement field and the thermal stress intensity factors （TSIFs） are presented. The normal temperature distributions （NTD） with different parameters along the crack surface are analyzed by numerical examples. The influence of the crack position and the thermal-elastic non- homogeneous parameters on the TSIFs of modes I and 11 at the crack tip is presented. Results show that the variation of the thickness of the graded coating has a significant effect on the temperature jump across the crack surfaces when keeping the thickness of the substrate constant, and the thickness of functionally graded material （FGM） coating has a significant effect on the crack in the substrate. The results can be expected to be used for the purpose of gaining better understanding of the thermal-mechanical behavior of graded coatings.展开更多
A coordination control strategy is developed for 3-bearing swivel duct （3BSD） nozzles. A 3BSD nozzle＇s deflection angle and direction are changed through rotations of three revolute pairs. There is a nonlinear rela...A coordination control strategy is developed for 3-bearing swivel duct （3BSD） nozzles. A 3BSD nozzle＇s deflection angle and direction are changed through rotations of three revolute pairs. There is a nonlinear relationship between the deflection an- gle/direction and the rotation angles. The rotation speed of a revolute pair is limited by the power of the actuator. The moment of inertia and the aerodynamic load for each revolute pair are different and time-varying. A high-precision control system of 3BSD nozzles is required for applications on vertical and/or short take-off and landing （V/STOL） aircrafts. Difficulties of co- ordination control of 3BSD nozzles are distinct travel ranges, speed constraints, time^xarying dynamic models, and disturb- ances. The proposed control strategy is a combination of the characteristic model and tlF e dynamic control allocation method. A dynamic control allocation module is used as the coordination supervisor, which is aware of the kinematic model, the con- straints, and the dynamic models of the revolute pairs. Second-order characteristic models are used to represent the dynamic behavior of the revolute pairs. The gradient projection algorithm is modified for parameter estimation. A modified all-coefficient adaptive controller is developed to reject the disturbances. Experimental results of a scaled 3BSD nozzle indi- cate that the coordination control strategy is effective.展开更多
Inspired by the gradient structure of the nature,two gradient lattice structures,i.e.,unidirectional gradient lattice(UGL)and bidirectional gradient lattice(BGL),are proposed based on the body-centered cubic(BCC)latti...Inspired by the gradient structure of the nature,two gradient lattice structures,i.e.,unidirectional gradient lattice(UGL)and bidirectional gradient lattice(BGL),are proposed based on the body-centered cubic(BCC)lattice to obtain specially designed mechanical behaviors,such as load-bearing and energy absorption capacities.First,a theoretical model is proposed to predict the initial stiffness of the gradient lattice structure under compressive loading,and validated against quasi-static compression tests and finite element models(FEMs).The deformation and failure mechanisms of the two structures are further studied based on experiments and simulations.The UGL structure exhibits a layer-by-layer failure mode,which avoids structure-wise shear failure in uniform structures.The BGL structure presents a symmetry deformation pattern,and the failure initiates at the weakest part.Finally,the energy absorption behaviors are also discussed.This study demonstrates the potential application of gradient lattice structures in load-transfer-path modification and energy absorption by topology design.展开更多
基金The National Natural Science Foundation of China(No.10962008,51061015)Specialized Research Fund for the Doctoral Program of Higher Education of China(No.20116401110002)
文摘This paper investigates the functionally graded coating bonded to an elastic strip with a crack under thermal- mechanical loading. Considering some new boundary conditions, it is assumed that the temperature drop across the crack surface is the result of the thermal conductivity index which controls heat conduction through the crack region. By the Fourier transforms, the thermal-elastic mixed boundary value problems are reduced to a system of singular integral equations which can be approximately solved by applying the Chebyshev polynomials. The numerical computation methods for the temperature, the displacement field and the thermal stress intensity factors （TSIFs） are presented. The normal temperature distributions （NTD） with different parameters along the crack surface are analyzed by numerical examples. The influence of the crack position and the thermal-elastic non- homogeneous parameters on the TSIFs of modes I and 11 at the crack tip is presented. Results show that the variation of the thickness of the graded coating has a significant effect on the temperature jump across the crack surfaces when keeping the thickness of the substrate constant, and the thickness of functionally graded material （FGM） coating has a significant effect on the crack in the substrate. The results can be expected to be used for the purpose of gaining better understanding of the thermal-mechanical behavior of graded coatings.
基金supported by the National Natural Science Foundation of China(Grant Nos.60974339,61104082)
文摘A coordination control strategy is developed for 3-bearing swivel duct （3BSD） nozzles. A 3BSD nozzle＇s deflection angle and direction are changed through rotations of three revolute pairs. There is a nonlinear relationship between the deflection an- gle/direction and the rotation angles. The rotation speed of a revolute pair is limited by the power of the actuator. The moment of inertia and the aerodynamic load for each revolute pair are different and time-varying. A high-precision control system of 3BSD nozzles is required for applications on vertical and/or short take-off and landing （V/STOL） aircrafts. Difficulties of co- ordination control of 3BSD nozzles are distinct travel ranges, speed constraints, time^xarying dynamic models, and disturb- ances. The proposed control strategy is a combination of the characteristic model and tlF e dynamic control allocation method. A dynamic control allocation module is used as the coordination supervisor, which is aware of the kinematic model, the con- straints, and the dynamic models of the revolute pairs. Second-order characteristic models are used to represent the dynamic behavior of the revolute pairs. The gradient projection algorithm is modified for parameter estimation. A modified all-coefficient adaptive controller is developed to reject the disturbances. Experimental results of a scaled 3BSD nozzle indi- cate that the coordination control strategy is effective.
基金the National Natural Science Foundation of China(Grant Nos.11972049 and 12002050)National Key Laboratory Foundation of Science and Technology on Materials under Shock and Im-pact(Grant No.6142902200401)Opening Fund of State Key Laboratory of Nonlinear Mechanics.
文摘Inspired by the gradient structure of the nature,two gradient lattice structures,i.e.,unidirectional gradient lattice(UGL)and bidirectional gradient lattice(BGL),are proposed based on the body-centered cubic(BCC)lattice to obtain specially designed mechanical behaviors,such as load-bearing and energy absorption capacities.First,a theoretical model is proposed to predict the initial stiffness of the gradient lattice structure under compressive loading,and validated against quasi-static compression tests and finite element models(FEMs).The deformation and failure mechanisms of the two structures are further studied based on experiments and simulations.The UGL structure exhibits a layer-by-layer failure mode,which avoids structure-wise shear failure in uniform structures.The BGL structure presents a symmetry deformation pattern,and the failure initiates at the weakest part.Finally,the energy absorption behaviors are also discussed.This study demonstrates the potential application of gradient lattice structures in load-transfer-path modification and energy absorption by topology design.
