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March 2012

Volume 2, Issue 2, Articles (02xxxx)

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Achieving high strength and high ductility in nanostructured metals: Experiment and modelling

Linli Zhu, Aiying Chen, and Jian Lu

Theor. Appl. Mech. Lett. 2, 021001 (2012); http://dx.doi.org/10.1063/2.1202101 (9 pages)

Online Publication Date: March 10, 2012

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Engineering nanostructures in metallic materials such as nanograins and nanotwins can promote plastic performance significantly. Nano/ultrafine-grained metals embedded in coarse grains called bimodal metals and nanotwinned polycrystalline metals have been proved to possess extensively improved yield strength whilst keeping good ductility. This paper will present an experimental study on nanostructured stainless steel prepared by surface mechanical attrition treatment (SMAT) with surface impacts of lower strain rate (10 s−1–103 s−1) and higher strain rate (104 s−1–105 s−1). Microstructure transition has been observed from the original γ-austenite coarse grains to α′-martensite nanograins with bimodal grain size distribution for lower strain rates to nanotwins in the ultrafine/coarse grained austenite phase for higher strain rates. Meanwhile, we will further address the mechanism-based plastic models to describe the yield strength, strain hardening and ductility in nanostructured metals with bimodal grain size distribution and nanotwinned polycrystalline metals. The proposed theoretical models can comprehensively describe the plastic deformation in these two kinds of nanostructured metals and excellent agreement is achieved between the numerical and experimental results. These models can be utilized to optimize the strength and ductility in nanostructured metals by controlling the size and distribution of nanostructures.
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Entropy productions in granular materials

Qicheng Sun, Shixiong Song, Feng Jin, and Yimin Jiang

Theor. Appl. Mech. Lett. 2, 021002 (2012); http://dx.doi.org/10.1063/2.1202102 (5 pages) | Cited 1 time

Online Publication Date: March 10, 2012

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Granular materials display more abundant dissipation phenomena than ordinary materials. In this paper, a brief energy flow path with irreversible processes is illustrated, where the concept of granular temperature Tg, initially proposed for dilute systems, is extended to dense systems in order to quantify disordered force chain configurations. Additionally, we develop the concept of conjugate granular entropy sg and its production equation. Our analyses find out that the granular entropy significantly undermined the elastic contact between particles, seriously affecting the transport coefficients in granular materials and creating new transport processes.

Coupling between finite element method and material point method for problems with extreme deformation

Yanping Lian, Xiong Zhang, and Yan Liu

Theor. Appl. Mech. Lett. 2, 021003 (2012); http://dx.doi.org/10.1063/2.1202103 (4 pages)

Online Publication Date: March 10, 2012

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As a Lagrangian meshless method, the material point method (MPM) is suitable for dynamic problems with extreme deformation, but its efficiency and accuracy are not as good as that of the finite element method (FEM) for small deformation problems. Therefore, an algorithm for the coupling of FEM and MPM is proposed to take advantages of both methods. Furthermore, a conversion scheme of elements to particles is developed. Hence, the material domain is firstly discretized by finite elements, and then the distorted elements are automatically converted into MPM particles to avoid element entanglement. The interaction between finite elements and MPM particles is implemented based on the background grid in MPM framework. Numerical results are in good agreement with experimental data and the efficiency of this method is higher than that of both FEM and MPM.

Deflection of transient thermoelastic circular plate by Marchi-Zgrablich and Laplace integral transform technique

Badrinath E. Ghonge and Kirtiwant P. Ghadle

Theor. Appl. Mech. Lett. 2, 021004 (2012); http://dx.doi.org/10.1063/2.1202104 (4 pages)

Online Publication Date: March 10, 2012

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This paper deals with the determination of temperature distribution and thermal deflection function of a thin circular plate with the stated conditions. The transient heat conduction equation is solved by using Marchi-Zgrablich transform and Laplace transform simultaneously and the results of temperature distribution and thermal deflection function are obtained in terms of infinite series of Bessel function and it is solved for special case by using Mathcad 2007 software and represented graphically by using Microsoft excel 2007.

Uncoupled thermoelastic analysis for a thick cylinder with radiation

Navneet Kumar Lamba and N. W. Khobragade

Theor. Appl. Mech. Lett. 2, 021005 (2012); http://dx.doi.org/10.1063/2.1202105 (6 pages)

Online Publication Date: March 10, 2012

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An attempt has been made to study the uncoupled thermoelastic response of thick cylinder of length 2h in which heat sources are generated according to the linear function of the temperature, with boundary conditions of the radiation type. This approach is based upon integral transform techniques, to find out the thermoelastic solution. The results are obtained in terms of Bessel functions in the form of infinite series.

Simulation of shape variation of projectile nose during high-speed penetration into concrete

Liling He and Xiaowei Chen

Theor. Appl. Mech. Lett. 2, 021006 (2012); http://dx.doi.org/10.1063/2.1202106 (4 pages)

Online Publication Date: March 10, 2012

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A formula is developed to estimate the total mass loss of projectile, based on the assumptions that the peeling of molten surface layer in projectile nose is the primary cause of mass loss, and the frictional heat is totally absorbed by the projectile. Extrapolating this formula to predict the mass loss of local area of projectile, the receding displacement on projectile surface is obtained, which is vertical to the symmetry axis of projectile. Thereby, a finite difference method model is constructed to simulate the variation of projectile shape. The shape of residual projectile, depth of penetration of projectile and its mass loss obtained by calculation are found in good consistency with respective experimental data.

Friction coefficient and error test via micro-rotation mechanics model

Zhitong Chen, Guang Li, and Yuan Xia

Theor. Appl. Mech. Lett. 2, 021007 (2012); http://dx.doi.org/10.1063/2.1202107 (4 pages)

Online Publication Date: March 10, 2012

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An air pressure-loading mode incorporated into the friction apparatus is firstly applied to coatings tribology involving large load, automation, stepless and continuous loading processes. A novel measurement principle is proposed and a micro-rotation mechanics model was developed for high precision measurement of friction coefficient. By properly designing and locating two sensors real-time monitoring the normal and friction forces, the troublesome influences in friction measurement is considerably relieved which come from surface characteristics of coatings of the samples in traditional friction test processes. By calculation and analysis, the max rotation angle θmax = 0.0018° is gained, which indicates that the measurement error of the apparatus is greatly reduced. The whole system error is about 1.15% given by finite element method and indication error of the least square fitting of measurements.

Characterization of the arrangement feature of copper interconnects by Moiré inversion method

Qinghua Wang, Satoshi Kishimoto, Huimin Xie, Kewei Xu, and Jianfeng Wang

Theor. Appl. Mech. Lett. 2, 021008 (2012); http://dx.doi.org/10.1063/2.1202108 (4 pages)

Online Publication Date: March 10, 2012

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This paper explores the planar arrangement feature of the copper interconnects in a view field of several millimeters by the focused ion-beam (FIB) Moiré inversion method quantitatively. The curved FIB Moiré patterns indicate that the copper interconnects are a series of curves with continuous variations instead of beelines. The control equation set of the copper interconnects central lines is attained through the Moiré inversion method. This work can be extended to inspect the structural defects and provide a reliable support for the interconnects structure fabrication.
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Planar collisionless jet impingement on a specular reflective plate

Chunpei Cai and Chun Zou

Theor. Appl. Mech. Lett. 2, 022001 (2012); http://dx.doi.org/10.1063/2.1202201 (5 pages)

Online Publication Date: March 10, 2012

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This paper presents a fundamental gas-kinetic study on a high speed planar rarefied jet impinging on a flat plate of specular reflections. Based on previous collisionless planar free jet results, it is straightforward to obtain jet impingement flowfield solutions, and jet impingement for specular reflective plate surface properties. Several direct simulation Monte Carlo simulation results are provided and they validate these analytical solutions of rarefied planar jet flows. The results can find applications in many disciplines, such as materials processing, molecular beams, and space engineering.

Evolution of three-dimensional cavitation following water entry of an inclined cylinder

Zhaoyu Wei and Xiuhua Shi

Theor. Appl. Mech. Lett. 2, 022002 (2012); http://dx.doi.org/10.1063/2.1202202 (3 pages)

Online Publication Date: March 10, 2012

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The water entry of an inclined cylinder is firstly studied experimentally for low Froude number. The cylinder is 50 mm in diameter and 200 mm in length, with a moderate length to diameter ratio. As it is submerged below the water surface, the cavity is fully three-dimensional. Due to the rotation of the cylinder caused by the initial inclined impact, the cavity evolution is quite complicated and a new phenomenon is revealed. The cylinder moves along a curved trajectory in water, which greatly affects the evolution of the cavities. The cavity breaks up into two sub-cavities, and finally collapses because of hydrostatic pressure.

Simulation of flow through porous anode in MFC at higher power density

Weiwei Su, Weiwei Yan, Zhongdi Su, Yang Liu, and Yousheng Xu

Theor. Appl. Mech. Lett. 2, 022003 (2012); http://dx.doi.org/10.1063/2.1202203 (5 pages)

Online Publication Date: March 10, 2012

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Microbial fuel cell (MFC) is a novel environmental friendly energy device which has received great attention due to its technology for producing electricity directly from organic or inorganic matter by using bacteria as catalyst. To date, many experiments have been carried out to achieve the maximum power output with advective flow through porous anode to the cathode in the MFC. However, the precise mechanical mechanism of flow through anode and the quantified relationship between electrode spacing and MFC performance are not yet clearly understood. It has been found experimentally that the power output can be increased apparently at certain electrode spacing configuration. Based on these available experimental data, this paper investigates the effect of spacing between electrodes, the Darcy number of porous anode and the Reynolds number on the power production performance of MFC by using lattice Boltzmann method. The numerical simulation results present that the distance between electrodes significantly influences the flow velocity and residence time of the organic matter attached to the anode in the MFC. Moreover, it is found that the Darcy number of porous anode and the Reynolds number can regulate the output efficiency of MFC. These results perform better understanding of the complex phenomena of MFC and will be helpful to optimize MFC design.

Numerical simulations for gas-structure interaction in inflated deployment of folded membrane boom

Jianzheng Wei, Huifeng Tan, Jianxin Yu, and Xingwen Du

Theor. Appl. Mech. Lett. 2, 022004 (2012); http://dx.doi.org/10.1063/2.1202204 (5 pages)

Online Publication Date: March 10, 2012

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It is very important for gas-structure interaction between compressible ideal gas and elastic structure of space folded membrane booms during the inflatable deployment. In order to study this gas-structure interaction problem, Arbitrary Lagrangian-Eulerian (ALE) finite element method was employed. Gas-structure interaction equation was built based on equilibrium integration relationship, and solved by operator split method. In addition, numerical analysis of V-shape folded membrane booms inflated by gas was given, the variation of inner pressure as well as deployment velocities of inflatable boom at different stage were simulated. Moreover, these results are consistent with the experiment of the same boom, which shows that both ALE method and operator split method are feasible and reliable methods to study gas-structure interaction problem.

Onset of instability of a flag in uniform flow

Fangbao Tian, Xiyun Lu, and Haoxiang Luo

Theor. Appl. Mech. Lett. 2, 022005 (2012); http://dx.doi.org/10.1063/2.1202205 (5 pages)

Online Publication Date: March 10, 2012

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This paper numerically and analytically studies the onset of instability of a flag in uniform flow. The three-dimensional (3D) simulation is performed by using an immersed-boundary method coupled with a nonlinear finite element method. The global stability, bistability and instability are identified in the 3D simulations. The Squire's theorem is extended to analyze the stability of the fluid-flag system with 3D initial perturbations. It is found that if a parallel flow around the flag admits an unstable 3D disturbance for a certain value of the flutter speed, then a two-dimensional (2D) disturbance at a lower flutter speed is also admitted. In addition, the growth rate of 2D disturbance is larger than that of the 3D disturbance.

Vortex-induced vibration of pipes conveying fluid using the method of multiple scales

Huliang Dai and Lin Wang

Theor. Appl. Mech. Lett. 2, 022006 (2012); http://dx.doi.org/10.1063/2.1202206 (4 pages)

Online Publication Date: March 10, 2012

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The nonlinear dynamics of supported pipes conveying fluid subjected to vortex-induced vibration is evaluated using the method of multiple scales. Frequency response portraits for different internal fluid velocities under lock-in conditions are obtained and the stability of steady-state responses is discussed. Results show that the internal fluid velocity has a prominent effect on the oscillation amplitude and that the steady-state responses incorporating unstable solutions in the lock-in region are also obtained. In addition, the effects of two kinds of fluctuating lift coefficients on the steady-state responses are compared with each other.
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Nonlinear dynamic analysis on rigid-flexible coupling system of an elastic beam

Feiyun Zhao, Jinyang Liu, and Jiazhen Hong

Theor. Appl. Mech. Lett. 2, 023001 (2012); http://dx.doi.org/10.1063/2.1202301 (4 pages)

Online Publication Date: March 10, 2012

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Previous work examined the effect of the attached stiffness matrix terms on stability of an elastic beam undergoing prescribed large overall motion. The aim of the present work is to extend the nonlinear formulations to an elastic beam with free large overall motion. Based on initial stress method, the nonlinear coupling equations of elastic beams are obtained with free large overall motion and the attached stiffness matrix is derived by solving sub-static formulation. The angular velocity and the tip deformation of the elastic pendulum are calculated. The analytical results show that the simulation results of the present model are tabled and coincide with the one-order approximate model. It is shown that the simulation results accord with energy conservation principle.

An improved HSFR method for natural vibration analysis of an immersed cylinder pile with a tip mass

Kai Wei, Wancheng Yuan, Najib Bouaanani, and Chih-Chen Chang

Theor. Appl. Mech. Lett. 2, 023002 (2012); http://dx.doi.org/10.1063/2.1202302 (4 pages)

Online Publication Date: March 10, 2012

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Immersed cylinder piles are usually modelled as immersed cantilever cylinder columns carrying a tip mass and rotary moment of inertia. In this paper, the equations of motion of an immersed cylinder pile along transversal modes of vibration are developed. Compressibility of water and structural damping are included in the formulation. Natural frequencies of the immersed pile are obtained from the developed equations using harmonic sweep frequency response analyses. The proposed method is applied to numerical examples, and the results obtained are shown satisfactory when compared to other numerical solutions in the literature, or to finite element solutions and experimental data.
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Red blood cell partitioning and blood flux redistribution in microvascular bifurcation

Yuanqing Xu, Fangbao Tian, Hanjun Li, and Yulin Deng

Theor. Appl. Mech. Lett. 2, 024001 (2012); http://dx.doi.org/10.1063/2.1202401 (5 pages)

Online Publication Date: March 10, 2012

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This paper studies red blood cell (RBC) partitioning and blood flux redistribution in microvascular bifurcation by immersed boundary and lattice Boltzmann method. The effects of the initial position of RBC at low Reynolds number regime on the RBC deformation, RBC partitioning, blood flux redistribution and pressure distribution are discussed in detail. It is shown that the blood flux in the daughter branches and the initial position of RBC are important for RBC partitioning. RBC tends to enter the higher-flux-rate branch if the initial position of RBC is near the center of the mother vessel. The RBC may enter the lower-flux-rate branch if it is located near the wall of mother vessel on the lower-flux-rate branch side. Moreover, the blood flux is redistributed when an RBC presents in the daughter branch. Such redistribution is caused by the pressure distribution and reduces the superiority of RBC entering the same branch. The results obtained in the present work may provide a physical insight into the understanding of RBC partitioning and blood flux redistribution in microvascular bifurcation.
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