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| 1 | Cold spray additive manufacturing of Invar 36 alloy:microstructure,thermal expansion and mechanical properties显示文摘In this work,the Invar 36 alloys were manufactured using cold spray(CS)additive manufacturing technique.The systematic investigations were made on the microstructural evolution,thermal expansion and mechanical properties under as-sprayed(AS)and heat-treated(HT)conditions.XRD(X-ray diffraction)and ICP-AES(inductively coupled plasma atomic emission spectroscopy)analyses show that no phase transformation,oxidation,nor element content change have occurred.The X-ray computed tomography(XCT)exhibited a near fully dense structure with a porosity of 0.025%in the helium-produced sample under as-sprayed condition,whereas the nitrogen-produced samples produced at 5 MPa and 800℃show more irregular pore defects.He-AS sample shows a more prominent grain refinement than that of nitrogen samples due to the more extensive plastic deformation.The post heat-treatment exhibited a promoted grain growth,inter-particle diffusion,as well as the formation of annealing twins.Between25℃and 200℃,the nitrogen samples possessed lower CTE(coefficient of thermal expansion)values(1.53×10^(-6)/℃)compared with those produced by casting and laser additive manufacturing.The He-AS samples exhibited a noticeable negative CTE value between 25℃and 200℃,which may due to the significant compressive residual stress(-272 MPa)compensating its displacement with temperature increase during CTE test.The N2-HT and He-HT Invar 36 samples present a notable balance between strength and ductility.In conclusion,the CS technique can be considered as a potential method to produce the Invar36 component with high thermal and mechanical performance. | Chaoyue Chen Yingchun Xie Longtao Liu Ruixin Zhao Xiaoli Jin Shanqing Li Renzhong Huang Jiang Wang Hanlin Liao Zhongming Ren | 2021 | Journal of Materials Science & Technology2021，，13： | 4 |
| 2 | Variational bounds of the effective moduli of piezoelectric composites显示文摘The classical Hashin-Shtrikman variational principle was re-generalized to the heterogeneous piezoelectric materials.The auxiliary problem is very much simplified by selecting the reference medium as a linearly isotropic elastic medium.The electromechanical fields in the inhomogeneous piezoelectrics are simulated by introducing into the homogeneous reference medium certain eigenstresses and eigen electric fields.A closed-form solution can be obtained for the disturbance fields,which is convenient for the manipulation of the energy functional.As an application,a two-phase piezoelectric composite with nonpiezoelectric matrix is considered.Expressions of upper and lower bounds for the overall electromechanical moduli of the composite can be developed.These bounds are shown better than the Voigt-Reuss type ones. | WAN YongPing XIE LongTao ZHONG Zheng | 2012 | Science China(Physics,Mechanics & Astronomy)2012，55，11： | 0 |
| 3 | Correction Factors of the Approximate Theories for Axisymmetric Modes of Longitudinal Waves in Circular Rods显示文摘The longitudinal waves guided by rods are widely used in broad engineering fields.Approximate theories are required to improve the understanding of the longitudinal wave propagation in finite rods in particular.The correction factors are commonly used in the vibration analyses of beams and plates,but are seldom adopted to the longitudinal wave propagation in rods in a similar manner.In this paper,the longitudinal and radial displacements in axisymmetric problems of circular rods are expanded in infinite power series of the radial coordinate.By using Hamilton’s principle,an infinite one-dimensional system of equations of motion is established.The high-order components of stress and strain,and their relations are introduced to obtain the infinite one-dimensional system for the axisymmetric wave propagation in elastic rods.A proper truncation of the infinite equations leads to an approximate theory of a specific order.To improve the truncated equations,some high-order components of strain are multiplied by the correction factors.The correction factors for the first-to fourth-order approximations are systematically determined to ensure that the cutoff frequencies are the same as the exact values calculated by the Pochhmammer–Chree equation.The frequency spectra,via the well-known Pochhmammer–Chree equation and the approximate theories of order one to four,are presented for comparison in a region where the longitudinal wave is not attenuating and the wavelength in the axial direction is longer than the diameter of the rod.Compared to the approximate theories without correction factors,the approximate theories with correction factors show some advantages in accuracy when the branches are high. | Longtao Xie Chunlei Bian Ji Wang | 2022 | Acta Mechanica Solida Sinica2022，35，5： | 0 |
| 4 | The axisymmetric Rayleigh waves in a semi-infinite elastic solid显示文摘It is well-known that Rayleigh wave,also known as surface acoustic wave(SAW),solutions in semiinfinite solids are plane waves with signatory properties like the distinct velocity and exponentially decaying deformation in the depth.Applications of Rayleigh waves are focused on the deformation and energy in the vicinity of surface of solids and less loss in the propagation.A generalized model of Rayleigh waves in axisymmetric mode is established and solutions are obtained with cylindrical coordinates.It is found that the Rayleigh waves also propagate in the axisymmetric mode with slow decay in radius,confirming the existence of surface acoustic waves is irrelevant to coordinate system.On the other hand,the solutions can be treated as plane waves in regions far away from the source.Furthermore,the particle trajectory of axisymmetric SAW is a line with constant slope rather than the signatory ellipse in Cartesian coordinate case. | Ji Wang Shaoyun Wang Longtao Xie Yangyang Zhang Lili Yuan Jianke Du Han Zhang | 2020 | Theoretical & Applied Mechanics Letters2020，10，2： | 0 |
| 5 | Nonlinear thickness-shear vibration of an infinite piezoelectric plate with flexoelectricity based on the method of multiple scales显示文摘This paper presents a nonlinear thickness-shear vibration model for onedimensional infinite piezoelectric plate with flexoelectricity and geometric nonlinearity.The constitutive equations with flexoelectricity and governing equations are derived from the Gibbs energy density function and variational principle.The displacement adopted here is assumed to be antisymmetric through the thickness due to the thickness-shear vibration mode.Only the shear strain gradient through the thickness is considered in the present model.With geometric nonlinearity,the governing equations are converted into differential equations as the function of time by the Galerkin method.The method of multiple scales is employed to obtain the solution to the nonlinear governing equation with first order approximation.Numerical results show that the nonlinear thickness-shear vibration of piezoelectric plate is size dependent,and the flexoelectric effect has significant influence on the nonlinear thickness-shear vibration frequencies of micro-size thin plates.The geometric nonlinearity also affects the thickness-shear vibration frequencies greatly.The results show that flexoelectricity and geometric nonlinearity cannot be ignored in design of accurate high-frequency piezoelectric devices. | Yang ZHENG Bin HUANG Lijun YI Tingfeng MA Longtao XIE Ji WANG | 2022 | Applied Mathematics and Mechanics(English Edition)2022，43，5： | 0 |
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