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Full-Text Articles in Mechanical Engineering

Comment On "Quadriceps Protects The Anterior Cruciate Ligament", Antonie J. Van Den Bogert Sep 2002

Comment On "Quadriceps Protects The Anterior Cruciate Ligament", Antonie J. Van Den Bogert

Mechanical Engineering Faculty Publications

No abstract provided.


A Fundamental Model Of Cyclic Instabilities In Thermal Barrier Systems, Anette M. Karlsson, J. W. Hutchinson, A. G. Evans Aug 2002

A Fundamental Model Of Cyclic Instabilities In Thermal Barrier Systems, Anette M. Karlsson, J. W. Hutchinson, A. G. Evans

Mechanical Engineering Faculty Publications

Cyclic morphological instabilities in the thermally grown oxide (TGO) represent a source of failure in some thermal barrier systems. Observations and simulations have indicated that several factors interact to cause these instabilities to propagate: (i) thermal cycling; (ii) thermal expansion misfit; (iii) oxidation strain; (iv) yielding in the TGO and the bond coat; and (v) initial geometric imperfections. This study explores a fundamental understanding of the propagation phenomenon by devising a spherically symmetric model that can be solved analytically. The applicability of this model is addressed through comparison with simulations conducted for representative geometric imperfections and by analogy with the ...


Die Soldering: Mechanism Of The Interface Reaction Between Molten Aluminum Alloy And Tool Steel, Sumanth Shankar, Diran Apelian Jun 2002

Die Soldering: Mechanism Of The Interface Reaction Between Molten Aluminum Alloy And Tool Steel, Sumanth Shankar, Diran Apelian

Mechanical Engineering Faculty Publications

Die soldering is the result when molten aluminum sticks to the surface of the die material and remains there after the ejection of the part; it results in considerable economic and production losses in the casting industry, and is a major quality detractor. In order to alleviate or mitigate die soldering, one must have a thorough understanding of the mechanism by which the aluminum sticks to the die material. A key question is whether the die soldering reaction is diffusion controlled or interface controlled. A set of diffusion couple experiments between molten aluminum alloy and the ferrous die was carried ...


Alternative Ways To Teaching Hvac And Related Subjects Through Actual Project Involvement-Three Case Studies, Samir F. Moujaes Jun 2002

Alternative Ways To Teaching Hvac And Related Subjects Through Actual Project Involvement-Three Case Studies, Samir F. Moujaes

Mechanical Engineering Faculty Publications

No abstract provided.


An Interactive Visual Environment For Scientific Problem Solving, Georg F. Mauer Jun 2002

An Interactive Visual Environment For Scientific Problem Solving, Georg F. Mauer

Mechanical Engineering Faculty Publications

Science and engineering students do not typically receive explicit training in scientific problem solving, i.e. applying science principles to specific situations. Students’ problem solving skills often show little improvement throughout their course of studies. This paper describes a structured, graphical, interactive (GUI) learning environment, which presents problems and tools for analysis in systematic and logical order, and encourages the student to develop the solution path in the manner of an experienced expert. The learning environment’s subject area is Engineering Dynamics, which was selected for its systematic structure and its early (usually sophomore) place in the undergraduate curriculum. The ...


A Model Study Of Displacement Instabilities During Cyclic Oxidation, Anette M. Karlsson, C. G. Levi, A. G. Evans Apr 2002

A Model Study Of Displacement Instabilities During Cyclic Oxidation, Anette M. Karlsson, C. G. Levi, A. G. Evans

Mechanical Engineering Faculty Publications

The shape changes that occur at imperfections on the surface of an alumina-forming alloy, subject to thermal cycling, have been simulated and measured. Observations have been made by emplacing a surface groove into a FeCrAlY material. Upon thermal cycling, large shape distortions have been observed: whereas, for comparable isothermal oxidation, the shape changes are minimal. The simulations predict similar responses. Upon cycling, upward displacements (pile-up) occur around the perimeter, accompanied by downward displacements at the center. Yet, minimal displacements arise upon isothermal oxidation. To realize cyclic displacements comparable in magnitude to those found experimentally, large values of the in-plane growth ...


Mathematical Modeling And Computer Simulation Of The Rotating Impeller Particle Flotation Process: Part I. Fluid Flow, Mohammed D. Maniruzzaman, Makhlouf M. Makhlouf Apr 2002

Mathematical Modeling And Computer Simulation Of The Rotating Impeller Particle Flotation Process: Part I. Fluid Flow, Mohammed D. Maniruzzaman, Makhlouf M. Makhlouf

Mechanical Engineering Faculty Publications

Removal of unwanted particles from molten metal by flotation is one of the most useful melt cleansing techniques used by the foundry industry. An effective way of flotation of particles in a melt relies on purging a gas into the molten metal through holes in a rotating impeller. Impeller rotation creates turbulence inside the melt, which helps agglomerate the impurity particles and. thereby, enhances their removal from the melt. In addition, turbulence increases the probability of particles attaching to the rising gas bubbles and, therefore, enhances the chance of their removal from the molten metal. A mathematical model has been ...


Mathematical Modeling And Computer Simulation Of The Rotating Impeller Particle Flotation Process: Part Ii. Particle Agglomeration And Flotation, Mohammed D. Maniruzzaman, Makhlouf M. Makhlouf Apr 2002

Mathematical Modeling And Computer Simulation Of The Rotating Impeller Particle Flotation Process: Part Ii. Particle Agglomeration And Flotation, Mohammed D. Maniruzzaman, Makhlouf M. Makhlouf

Mechanical Engineering Faculty Publications

Effective removal of unwanted particles from a molten metal alloy by flotation relies on purging a gas into the melt through a rotating impeller. This device is commonly known as a rotary degasser. Unwanted particles in the melt attach to the rising gas bubbles and rise to the slag layer where they are removed from the metal bulk. In addition, the turbulence created by the rotating impeller causes the randomly distributed solid particles to agglomerate into relatively large clusters. These clusters float up or settle down due to the difference between their density and that of the melt. A mathematical ...


Investigation Of Fatigue Crack Initiation In Ti-6al-4v During Tensile-Tensile Fatigue, Svetlana G. Ivanova, Ronald R. Biederman, Richard D. Sisson Jr. Apr 2002

Investigation Of Fatigue Crack Initiation In Ti-6al-4v During Tensile-Tensile Fatigue, Svetlana G. Ivanova, Ronald R. Biederman, Richard D. Sisson Jr.

Mechanical Engineering Faculty Publications

Fatigue crack initiation in Ti-6Al-4V has been investigated in high cycle fatigue (HCF) and low cycle fatigue (LCF) regimes at stress ratio R = 0.1 using the replication technique. In all four tested α/β microstructures, the crack was initiated by fracture of equiaxed alpha grain. Fractured alpha grains are seen on the fracture surface as flat facets with features characteristic of cleavage fracture. In the regime of low stress amplitudes and in the absence of reverse loading, cleavage fracture contributes to crack initiation and early stages of crack growth in Ti-6Al-4V. This mechanism is discussed in relation to the ...


The Effect Of The Thermal Barrier Coating On The Displacement Instability In Thermal Barrier Systems, Anette M. Karlsson, T. Xu, A. G. Evans Mar 2002

The Effect Of The Thermal Barrier Coating On The Displacement Instability In Thermal Barrier Systems, Anette M. Karlsson, T. Xu, A. G. Evans

Mechanical Engineering Faculty Publications

Thermal barrier systems are susceptible to instability of the thermally grown oxide (TGO) at the interface between the bond coat and the thermal barrier coating (TBC). The instabilities have been linked to thermal cycling and initial geometrical imperfections, as well as to misfit strains due to both oxide growth and thermal expansion misfit. Numerical simulations are used to investigate the role of the thermo-mechanical properties of the TBC in this instability. It is found that the TBC constrains the deformation, whereupon instabilities develop preferentially in regions where crack-like imperfections either pre-exist in the TBC or are created because of the ...


Lotka-Volterra System In A Random Environment, Mikhail F. Dimentberg Mar 2002

Lotka-Volterra System In A Random Environment, Mikhail F. Dimentberg

Mechanical Engineering Faculty Publications

Classical Lotka-Volterra (LV) model for oscillatory behavior of population sizes of two interacting species (predator-prey or parasite-host pairs) is conservative. This may imply unrealistically high sensitivity of the system's behavior to environmental variations. Thus, a generalized LV model is considered with the equation for preys' reproduction containing the following additional terms: quadratic "damping'' term that accounts for interspecies competition, and term with white-noise random variations of the preys' reproduction factor that simulates the environmental variations. An exact solution is obtained for the corresponding Fokker-Planck-Kolmogorov equation for stationary probability densities (PDF's) of the population sizes. It shows that both ...


Response Time Is More Important Than Walking Speed For The Ability Of Older Adults To Avoid A Fall After A Trip, Antonie J. Van Den Bogert, M. J. Pavol, M. D. Grabiner Feb 2002

Response Time Is More Important Than Walking Speed For The Ability Of Older Adults To Avoid A Fall After A Trip, Antonie J. Van Den Bogert, M. J. Pavol, M. D. Grabiner

Mechanical Engineering Faculty Publications

We previously reported that the probability of an older adult recovering from a forward trip and using a “lowering” strategy increases with decreased walking velocity and faster response time. To determine the within-subject interaction of these variables we asked three questions: (1) Is the body orientation at the time that the recovery foot is lowered to the ground (“tilt angle”) critical for successful recovery? (2) Can a simple inverted pendulum model, using subject-specific walking velocity and response time as input variables, predict this body orientation, and thus success of recovery? (3) Is slower walking velocity or faster response time more ...


A Model-Based Fault Detection And Diagnosis Scheme For Distributed Parameter Systems: A Learning Systems Approach, Michael A. Demetriou Jan 2002

A Model-Based Fault Detection And Diagnosis Scheme For Distributed Parameter Systems: A Learning Systems Approach, Michael A. Demetriou

Mechanical Engineering Faculty Publications

In this note, fault detection techniques based on finite dimensional results are extended and applied to a class of infinite dimensional dynamical systems. This special class of systems assumes linear plant dynamics having an abrupt additive perturbation as the fault. This fault is assumed to be linear in the (unknown) constant (and possibly functional) parameters. An observer-based model estimate is proposed which serves to monitor the system's dynamics for unanticipated failures, and its well posedness is summarized. Using a Lyapunov synthesis approach extended and applied to infinite dimensional systems, a stable adaptive fault diagnosis (fault parameter learning) scheme is ...


Comparison Of Mobility Method And Mass Conservation Method In A Study Of Dynamically Loaded Journal Bearings, Biao Yu, Jerzy T. Sawicki Jan 2002

Comparison Of Mobility Method And Mass Conservation Method In A Study Of Dynamically Loaded Journal Bearings, Biao Yu, Jerzy T. Sawicki

Mechanical Engineering Faculty Publications

The inverse problem of dynamically loaded journal bearings was solved using generalized Reynolds equation coupled with a complete mass conservative cavitation boundary conditions, as outlined by the Jacobsson-Floberg and Olsson (JFO) cavitation theory. In the course of solution, the modified Thomas algorithms was employed, instead of standard Gauss±Jordan reduction method, which fully utilizes the sparse character of the system matrix, and thus greatly reduces computational time. The developed model was tested against the well-known mobility method for the case of journal bearings in a commercial reciprocating air compressor. It was found that the mobility method overestimates minimum film thickness ...