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Qi H.,The University of Michigan - Shanghai Jiao Tong University Joint Institute
Cailiao Gongcheng/Journal of Materials Engineering | Year: 2012

Since its invention and initial application in gas turbine components in the early 60's of 20th century at INCO Huntington Alloys (now called Special Metals Co.), INCONEL 718 alloy (IN718) has become the most widely used nickel based superalloy in the aircraft engine industry. It was used in many critical aircraft engine components, accounting for over 30% of the total finished component mass of a modern aircraft engine. This article reviews IN718 alloy development history, its mechanical properties, long-term thermal stabilities, industrial processing methods, and current developing substitute alloys for enhanced thermal stability. Source

Dugnani R.,The University of Michigan - Shanghai Jiao Tong University Joint Institute | Zednik R.,Santa Clara University
Journal of the American Ceramic Society | Year: 2013

Thin components made from advanced brittle glasses or ceramics are becoming increasingly important due to the widespread adoption of portable consumer products as well as other modern electronic and medical devices. The strength of these brittle materials is traditionally estimated from empirical relationships relating the stress at failure to characteristic lengths derived from the fracture surface's topography. One example is Orr's relationship, σf·Rm 1/2 = Am, which correlates the material strength, σf, to the radius of the "mirror-mist boundary region," Rm, through the empirical constant, Am. Although various studies have shown that, for flexural fractures (failed in bending), Am depends on the specimen's geometry, this effect has been generally neglected by arguing that the magnitude of Am is almost constant for thicker specimens. However, we show that this argument cannot be applied to thin geometries, and that by not accounting for the thickness of the sample, the flexural strength will be grossly underestimated. In this work, we introduce an expression based on an iterative fracture mechanics algorithm which yields more accurate estimates of flexural strength for thin brittle components in bending. The accuracy of the model is validated both through flexural strength tests on glass and by comparing our predictions to an extensive literature survey of experimental results. © 2013 The American Ceramic Society. Source

Muller A.,The University of Michigan - Shanghai Jiao Tong University Joint Institute
Proceedings - IEEE International Conference on Robotics and Automation | Year: 2014

This paper addresses the sensitivity of dexterity measures w.r.t. The posture of a manipulator, with given design parameters, as well as w.r.t. The manipulator's geometric parameters. These are required for placing a manipulator so to maximize dexterity and for the optimal layout of the link geometry, respectively. Explicit expressions are derived for first and second partial derivatives of dexterity measures w.r.t. to joint angles and w.r.t. geometric link parameters. The latter is obtained using a virtual joint method extending the product of exponentials formula for the forward kinematics. The approach applies to serial and parallel manipulators. © 2014 IEEE. Source

Ahmed M.,Assiut University | Eslamian M.,The University of Michigan - Shanghai Jiao Tong University Joint Institute
Applied Thermal Engineering | Year: 2015

The multi-phase Lattice Boltzmann Method (LBM) is used to explore some unprecedented aspects of laminar forced convection in a bottom heated rectangular microchannel. Important physical parameters, such as forces exerted on fluid parcels as well as on the dispersed nanoparticle phase are studied, in an attempt to elucidate the mechanism that results in establishment of a relative velocity between nanoparticles and the continuous fluid phase (slip velocity). The significance of the external forces, such as the gravitational, thermophoresis and Brownian forces is investigated. A recently established expression for the estimation of thermophoresis force in nanofluids is employed to study the true effect of thermophoresis, as other studies either neglect this effect, or are parametric or employ expressions that overestimate this effect. The results indicate that in laminar forced convection, the Brownian force has a significant effect on flow and heat transfer characteristics for low Re number flows (Re∼1-10), but thermophoresis may be safely neglected for all flow conditions. At low Re number flows, the nanofluid flow is heterogeneous, and heat transfer characteristics of nanofluid compared to the base fluid, such as Nu and convection heat transfer coefficient, significantly increase, while at higher Re numbers, such as Re = 100, flow behaves homogeneously and therefore the application of a nanofluid may not be justified. © 2015 Elsevier Ltd. All rights reserved. Source

Wang L.,The University of Michigan - Shanghai Jiao Tong University Joint Institute
Physics of Fluids | Year: 2012

To address the geometrical properties of the turbulent velocity vector field, a new concept named streamtube segment has been developed recently [L. Wang, "On properties of fluid turbulence along streamlines," J. Fluid Mech.648, 183-203 (2010)10.1017/S0022112009993041]. According to the vectorial topology, the entire velocity field can be partitioned into the so-called streamtube segments, which are organized in a non-overlapping and space-filling manner. In principle, properties of turbulent fields can be reproduced from those of the decomposed geometrical units with relatively simple structures. A similar idea is implemented to study the turbulent vorticity vector field using the vorticity tube segment structure. Differently from the conventional vortex tubes, vorticity tube segments are space-filling and can be characterized by non-arbitrary parameters, which enables a more quantitative description rather than just an illustrative explanation of turbulence behaviors. From analyzing the direct numerical simulation data, the topological and dynamical properties of vorticity tube segments are explored. The characteristic parameters have strong influence on some conditional statistics, such as the enstrophy production and the probability density function of vorticity stretching. Consequently the common knowledge in turbulence dynamics that vorticity are more stretched than compressed need to be rectified in the vorticity tube segment context. © 2012 American Institute of Physics. Source

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