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Zhu H.,Tianjin University | Ding Q.,Tianjin Key Laboratory of Nonlinear Dynamics and Chaos Control
Applied Mechanics and Materials | Year: 2012

By means of the finite differential method, the Reynolds equation is solved and the static characteristics of herringbone grooved hydrodynamic journal bearing are numerically analyzed by presenting the circumferential and axial pressures. The influences of parameters such as the eccentricity, width-diameter ratio of bearing, spiral angle, depth and number of grooves, on the static characteristics of herringbone grooved bearing are discussed. The results indicate that the normal pressure of oil film and the load carrying capacity as well, of herringbone grooved bearing will decrease with the increase of groove number and depth. On the other hand, as the pressure distributes in wider area in the circumferential direction, the stability of bearing can be improved. In consideration of these two aspects, the optimal groove number is 8-12, and the selection of depth and screw angle of grooves should also be chosen carefully to obtain the significant performance of herringbone grooved bearing. © (2012) Trans Tech Publications. Source


Guo X.,Tianjin University | Guo X.,Tianjin Key Laboratory of Nonlinear Dynamics and Chaos Control | Dai X.Y.,Tianjin University | Zhu L.L.,Zhejiang University | Lu J.,City University of Hong Kong
Acta Mechanica | Year: 2014

Nanostructured metals with bimodal grain size distribution, composed of coarse grain (CG) and nanograin (NG) regions, have proved to have high strength and good ductility. Here, numerical investigation, based on the mechanism-based strain gradient plasticity theory and the Johnson-Cook failure model, focuses on effects of (1) distribution characteristics of the CG regions and (2) the constitutive relation of the NG with different grain sizes on fracture behavior in a center-cracked tension specimen of bimodal nanostructured Cu. High strain rate simulations show that both of them directly influence load response and energy history, and importantly, they are closely related to the fracture pattern. This study shows that both CG region bridging and crack deflection toughen the bimodal nanostructured Cu significantly, while debonding enhances the overall ductility moderately. Simulations also show that with volume fraction of the CG regions increasing, both structural strength and ductility of the bimodal nanostructured Cu specimen can be improved. © 2014 Springer-Verlag Wien. Source


Guo X.,Tianjin University | Guo X.,Tianjin Key Laboratory of Nonlinear Dynamics and Chaos Control | Zhang W.J.,Tianjin University | Zhu L.L.,Zhejiang University | Lu J.,City University of Hong Kong
Engineering Fracture Mechanics | Year: 2013

Combination of surface mechanical attrition treatment (SMAT) and co-rolling can produce large-scale laminated nanostructured metals with both high strength and high ductility. For the co-rolled SMATed metals with nanograined interface layers, numerical investigation based on the cohesive finite element method focuses on effects of shape of the cohesive law and mesh size. Simulations show that the shape of the bilinear cohesive law varies peak stress and normal opening displacement significantly and that larger thickness of brittle phase allows use of coarser meshes while not to consider lower bound of the mesh size may lead to unreasonable results. © 2013 Elsevier Ltd. Source


Guo X.,Tianjin University | Guo X.,Tianjin Key Laboratory of Nonlinear Dynamics and Chaos Control | Chang K.,Pennsylvania State University | Chen L.Q.,Pennsylvania State University | Zhou M.,Georgia Institute of Technology
Engineering Fracture Mechanics | Year: 2012

The objective of this study is to develop a micromechanical approach for determining the fracture toughness. A phase-field model for grain growth is employed to generate microstructures with varying attributes and the cohesive finite element method is employed to quantify the interaction between a propagating crack and microstructures of an AZ31 Mg alloy. Simulations show that fracture toughness increases as the average grain size decreases and that the local crack tip environment significantly affects the fracture behavior. Dramatically different dependences of fracture toughness on overall strain rate are seen when two different types of cohesive laws are employed. © 2012 Elsevier Ltd. Source


Zhu Z.-W.,Tianjin University | Xie W.-Y.,Hainan University | Xu J.,Tianjin Key Laboratory of Nonlinear Dynamics and Chaos Control
Journal of Vibroengineering | Year: 2012

In this paper, nonlinear dynamic characteristics of shape memory alloy (SMA) simply supported beam in axial stochastic excitation were studied. Von del Pol nonlinear difference item was introduced to interpret the hysteresis phenomenon of the strain-stress curve of SMA, and the hysteretic nonlinear dynamic model of SMA simply supported beam in axial stochastic excitation was developed. The local stochastic stability of the system was analyzed according to the largest Lyapunov exponent, and the global stochastic stability of the system was discussed in singular boundary theory. The steady-state probability density function and the joint probability density function of the system were obtained in quasi-nonintegrable Hamiltonian system theory. The result of simulation shows that the stability of the trivial solution varies with bifurcation parameter, and stochastic Hopf bifurcation appears in the process. The result is helpful to stochastic bifurcation control to SMA simply supported beam. © Vibroengineering. Journal Of Vibroengineering. Source

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