Heterogeneously Tempered Martensitic Stainless Steel by Selective Laser Melting: Microstructure Evolution, Mechanical Performance, and Mechanisms

Z. Y. Duan(돤쯔양),J. Suhr(서종환) Korean Society for Precision Engineering 2021 한국정밀공학회 학술발표대회 논문집 Vol.2021 No.11월

Martensitic stainless steels have gained renewed interest recently for their use in automotive, aerospace, and defense applications due to their ultra-high yield strengths and reasonable ductility. Herein, by using optimized process parameters, we report the successfully manufactured 410 martensitic stainless steel using Selective Laser Melting (SLM). Bulk 410 was printed to high part qualities with an excellent combination of tensile properties of 1,100 ± 20 Mpa yield strength, 1,280 ± 5 Mpa ultimate tensile strength, and 13.5% ± 0.6% fracture elongation. This unique performance is attributed to the alternating distribution of ferrite, ultra-fine tempered martensite, nano-sized austenite, and retained martensite produced by the SLM process. Moreover, due to the inherent heat treatment phenomenon in the SLM process, the distribution of ultrafine and heterogeneous grains is formed, which is believed to promote good ductility. This work proved that the high-performance martensitic stainless steel parts could be prepared through SLM by using appropriate processing parameters.

Damping BGP Route Flaps

Z. Duan,J. Chandrashekar,J. Krasky,K. Xu,Z.-L. Zhang 한국통신학회 2007 Journal of communications and networks Vol.9 No.4

The Influence of Cryogenic Deformation on Bi2223 Superconducting Tapes

Y. Wang,W. Z. Luan,Z. Z. Duan,R. B. Feng,Q. Zhou,Y. N. Li,Y. X. Yao,F. Z. Du 대한금속학회 2005 METALS AND MATERIALS International Vol.11 No.1

Stochastic micro-vibration response characteristics of a sandwich plate with MR visco-elastomer core and mass

Z. G. Ying,Y. Q. Ni,Y.F. Duan 국제구조공학회 2015 Smart Structures and Systems, An International Jou Vol.16 No.1

The magneto-rheological visco-elastomer (MRVE) is used as a smart core to control the stochastic micro-vibration of a sandwich plate with supported mass. The micro-vibration response of the sandwich plate with MRVE core and supported mass under stochastic support motion excitations is studied and compared to evaluate the vibration suppression capability. The effects of the supported mass and localized magnetic field on the stochastic micro-vibration response of the MRVE sandwich plate are taken into account. The dynamic characteristics of the MRVE core in micro-vibration are described by a non-homogeneous complex modulus dependent on vibration frequency and controllable by applied magnetic fields. The partial differential equations for the coupled transverse and longitudinal motions of the MRVE sandwich plate with supported mass are derived from the dynamic equilibrium, constitutive and geometric relations. The simplified ordinary differential equations are obtained for the transverse vibration of the MRVE sandwich plate under localized magnetic fields. A frequency-domain solution method for the stochastic micro-vibration response of sandwich plates with supported mass is developed based on the Galerkin method and random vibration theory. The expressions of frequency-response functions, response power spectral densities and root-mean-square velocity responses of the plate in terms of the one-third octave frequency band are obtained for micro-vibration evaluation. Finally, numerical results are given to illustrate the large response reduction capacity of the MRVE sandwich plate with supported mass under stochastic support motion excitations, and the influences of MRVE parameters, supported mass and localized magnetic field placement on the micro-vibration response.

Stochastic vibration response of a sandwich beam with nonlinear adjustable visco-elastomer core and supported mass

Z. G. Ying,Y. Q. Ni,Y. F. Duan 국제구조공학회 2017 Structural Engineering and Mechanics, An Int'l Jou Vol.64 No.2

The stochastic vibration response of the sandwich beam with the nonlinear adjustable visco-elastomer core and supported mass under stochastic support motion excitations is studied. The nonlinear dynamic properties of the visco-elastomer core are considered. The nonlinear partial differential equations for the horizontal and vertical coupling motions of the sandwich beam are derived. An analytical solution method for the stochastic vibration response of the nonlinear sandwich beam is developed. The nonlinear partial differential equations are converted into the nonlinear ordinary differential equations representing the nonlinear stochastic multi-degree-of-freedom system by using the Galerkin method. The nonlinear stochastic system is converted further into the equivalent quasi-linear system by using the statistic linearization method. The frequencyresponse function, response spectral density and mean square response expressions of the nonlinear sandwich beam are obtained. Numerical results are given to illustrate new stochastic vibration response characteristics and response reduction capability of the sandwich beam with the nonlinear visco-elastomer core and supported mass under stochastic support motion excitations. The influences of geometric and physical parameters on the stochastic response of the nonlinear sandwich beam are discussed, and the numerical results of the nonlinear sandwich beam are compared with those of the sandwich beam with linear visco-elastomer core.

Three-dimensional full Euler flows in axisymmetric nozzles

Duan, B.,Luo, Z. Academic Press 2013 Journal of differential equations Vol.254 No.7

In this paper, we consider global subsonic compressible flows through general infinitely long nozzles. The flow is governed by the steady full Euler equations. We find a new invariant along streamline. Take advantages of this, we reformulate the full Euler system into quasilinear second order equations of stream function. With the upstream condition and the solid wall boundary condition, we obtain the existence, uniqueness, asymptotic behavior and the critical mass flux.

Stochastic vibration suppression analysis of an optimal bounded controlled sandwich beam with MR visco-elastomer core

Z.G. Ying,Y.Q. Ni,Y.F. Duan 국제구조공학회 2017 Smart Structures and Systems, An International Jou Vol.19 No.1

To control the stochastic vibration of a vibration-sensitive instrument supported on a beam, the beam is designed as a sandwich structure with magneto-rheological visco-elastomer (MRVE) core. The MRVE has dynamic properties such as stiffness and damping adjustable by applied magnetic fields. To achieve better vibration control effectiveness, the optimal bounded parametric control for the MRVE sandwich beam with supported mass under stochastic and deterministic support motion excitations is proposed, and the stochastic and shock vibration suppression capability of the optimally controlled beam with multi-mode coupling is studied. The dynamic behavior of MRVE core is described by the visco-elastic Kelvin-Voigt model with a controllable parameter dependent on applied magnetic fields, and the parameter is considered as an active bounded control. The partial differential equations for horizontal and vertical coupling motions of the sandwich beam are obtained and converted into the multi-mode coupling vibration equations with the bounded nonlinear parametric control according to the Galerkin method. The vibration equations and corresponding performance index construct the optimal bounded parametric control problem. Then the dynamical programming equation for the control problem is derived based on the dynamical programming principle. The optimal bounded parametric control law is obtained by solving the programming equation with the bounded control constraint. The controlled vibration responses of the MRVE sandwich beam under stochastic and shock excitations are obtained by substituting the optimal bounded control into the vibration equations and solving them. The further remarkable vibration suppression capability of the optimal bounded control compared with the passive control and the influence of the control parameters on the stochastic vibration suppression effectiveness are illustrated with numerical results. The proposed optimal bounded parametric control strategy is applicable to smart visco-elastic composite structures under deterministic and stochastic excitations for improving vibration control effectiveness.

Stochastic stability control analysis of an inclined stay cable under random and periodic support motion excitations

Z.G. Ying,Y.Q. Ni,Y.F. Duan 국제구조공학회 2019 Smart Structures and Systems, An International Jou Vol.23 No.6

The stochastic stability control of the parameter-excited vibration of an inclined stay cable with multiple modes coupling under random and periodic combined support disturbances is studied by using the direct eigenvalue analysis approach based on the response moment stability, Floquet theorem, Fourier series and matrix eigenvalue analysis. The differential equation with time-varying parameters for the transverse vibration of the inclined cable with control under random and deterministic support disturbances is derived and converted into the randomly and deterministically parameter-excited multi-degree-of-freedom vibration equations. As the stochastic stability of the parameter-excited vibration is mainly determined by the characteristics of perturbation moment, the differential equation with only deterministic parameters for the perturbation second moment is derived based on the Itô stochastic differential rule. The stochastically and deterministically parameter-excited vibration stability is then determined by the deterministic parameter-varying response moment stability. Based on the Floquet theorem, expanding the periodic parameters of the perturbation moment equation and the periodic component of the characteristic perturbation moment expression into the Fourier series yields the eigenvalue equation which determines the perturbation moment behavior. Thus the stochastic stability of the parameter-excited cable vibration under the random and periodic combined support disturbances is determined directly by the matrix eigenvalues. The direct eigenvalue analysis approach is applicable to the stochastic stability of the control cable with multiple modes coupling under various periodic and/or random support disturbances. Numerical results illustrate that the multiple cable modes need to be considered for the stochastic stability of the parameter-excited cable vibration under the random and periodic support disturbances, and the increase of the control damping rather than control stiffness can greatly enhance the stochastic stability of the parameter-excited cable vibration including the frequency width increase of the periodic disturbance and the critical value increase of the random disturbance amplitude.

Microstructural evolution and flow behaviour during hot compression of twin roll cast ZK60 magnesium alloy

Liu, Z.Y.,Duan, A.J.,Hou, Y.H.,Kang, S.,Cho, J. Maney Publishing 2010 Materials Science and Technology Vol.26 No.12

Efficient Electrochemical Potentiostatic Activation Method for GaN-Based Green Vertical-LEDs

Tawfik, Wael Z.,Cho, Sung Oh,Ha, Jun-Seok,Ryu, Sang-Wan,Cai, Duan-Jun,Lee, June Key The Electrochemical Society 2018 ECS journal of solid state science and technology Vol.7 No.4

<P>An efficient electrochemical potentiostatic activation (EPA) method was designed and performed for hydrogen atoms removal from inside a Mg-doped gallium nitride (GaN) layer of green vertical light-emitting diodes (V-LEDs). The EPA method was conducted at the potentiostatic conditions of 2, 3, and 5 V for 5 mins. The role of the applied voltage value in the breaking of the Mg-H complexes and in increasing the holes concentration inside the p-GaN layer in terms of LED device performances was investigated. The internal quantum efficiency (IQE) of the green V-LEDs behaved inversely with the applied voltage. The IQE of green V-LEDs EPA processed with a low voltage of 2 V realized an improvement of about 6% and only about 2.5% for green V-LEDs EPA processed with a high voltage of 5 V at an injection current of 100 mA compared to the conventional rapid thermal annealing method. The light output power achieved the highest enhancement of about 10.5% at 100 mA when applying the lowest voltage of 2 V, which originated from an improvement of the IQE. The forward voltage was also reduced after the EPA process. The developed EPA method was proven to effectively improve the external quantum efficiency of green V-LEDs. (C) 2018 The Electrochemical Society.</P>