Mechanical Engineering Commons^™

The Displacement Of The Thermally Grown Oxide In Thermal Barrier Systems Upon Temperature Cycling, Anette M. Karlsson, J. W. Hutchinson, A. G. Evans

Mechanical Engineering Faculty Publications

Models that characterize the displacement instability of the thermally grown oxide (TGO) found in some thermal barrier systems are reviewed, consolidated and extended. It is demonstrated that the simulations are only consistent with the observations whenever the bond coat and TGO both undergo plastic deformation. The TGO yields at the peak temperature, during growth, while the bond coat yields on thermal cycling. The trends oppose. Namely, the TGO displacement is diminished by increasing the high temperature strength of the bond coat, but is increased upon increasing the TGO strength. The model rationalizes certain experimental trends, particularly the decrease in durability …

Near-Field Calculations For A Rigid Spheroid With An Arbitrary Incident Acoustic Field, John P. Barton, Nicholas L. Wolff, Haifeng Zhang, Constantine Tarawneh

Mechanical Engineering Faculty Publications

A general spheroidal coordinate separation-of-variables solution is developed for the determination of the acoustic pressure distribution near the surface of a rigid spheroid for a monofrequency incident acoustic field of arbitrary character. Calculations are presented, for both the prolate and oblate geometries, demonstrating the effects of incident field orientation and character (plane-wave, spherical wave, cylindrical wave, and focused beam) on the resultant acoustic pressure distribution.

Thermomechanical Behavior Of Rotor With Rubbing, Jerzy T. Sawicki, Alberto Montilla-Bravo, Zdzislaw Gosiewski

Mechanical Engineering Faculty Publications

This article presents an analytical study of the dynamics and stability of rotors subjected to rubbing due to contact with seals, taking account of associated thermal effects. The seal interaction force acting on the shaft gives rise to a friction force, which is a source of heating and can induce so-called spiral vibrations. A mathematical model that has been developed couples the heat-conduction equation with the equations for motion of the rotor. Numerical simulations have been conducted that show the thermomechanical behavior of the rotor at various operating conditions. A procedure for analyzing the stability of multibearing rotors based on …

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

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 …

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 …

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 …

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 …

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 and …

Horses Damp The Spring In Their Step, Alan M. Wilson, M. Polly Mcguigan, Anne Su, Antonie J. Van Den Bogert

Mechanical Engineering Faculty Publications

The muscular work of galloping in horses is halved by storing and returning elastic strain energy in spring-like muscle–tendon units^{1, 2}.These make the legs act like a child's pogo stick that is tuned to stretch and recoil at 2.5 strides per second. This mechanism is optimized by unique musculoskeletal adaptations: the digital flexor muscles have extremely short fibres and significant passive properties, whereas the tendons are very long and span several joints^{3, 4}. Length change occurs by a stretching of the spring-like digital flexor tendons rather than through energetically expensive length changes in the muscle^{5 …}

Modal Uncoupling Of Damped Gyroscopic Systems, Jerzy T. Sawicki, G. Genta

Mechanical Engineering Faculty Publications

A new approach for uncoupling the equations of motion typical for rotordynamical systems is presented. The method does not neglect the speed-dependent e!ects, such as gyroscopic e!ects, and can be particularly valuable in the controller design of actively controlled rotors. In the presence of hysteretic type of damping, the resulting uncoupled gyroscopic systems come with an equivalent viscous damping, equivalent in a sense of yielding the same natural frequency and decay rate. The approach is illustrated through three examples of technical interest: a Je!cott rotor with hysteretic damping, a Stodola}Green rotor, and a rotor of a small gas turbine. The …

A Numerical Model For The Cyclic Instability Of Thermally Grown Oxides In Thermal Barrier Systems, Anette M. Karlsson, A. G. Evans

Mechanical Engineering Faculty Publications

Morphological instability of the thermally grown oxide (TGO) is a fundamental source of failure in some thermal barrier systems. The instabilities occur when initial non-planarity in the TGO grows in amplitude as the system experiences thermal cycling. By numerical means, this study explores how these instabilities are linked to constituent properties. The associated phenomena involve oxidation of the TGO, plastic flow of the bond coat, thermal expansion misfit between the TGO, bond coat and substrate, and stress relaxation in the TGO at high temperature. A key implication of the simulations is that the incidence of reverse yielding upon reheating differentiates …

Modeling Nonlinear Behavior In A Piezoelectric Actuator, Hanz Richter, Eduardo A. Misawa, D. A. Lucca, H. Lu

Mechanical Engineering Faculty Publications

A piezoelectric tube actuator is employed as a sample positioning device in Nanocut, a cutting instrument conceived to study the mechanics of nanometric cutting. Extension of functionality of the instrument as a nanometric machine tool motivates the search for an accurate model of the actuator for implementing feedback control. A simple nonlinear model describing longitudinal expansion of the piezoelectric tube actuator is presented in this paper. The model derivation is based on a non-formal analogy with nonlinear viscoelastic materials under uniaxial extension, for which the responses to a step input are similar to the piezoelectric tube. Suitability of the …

Tibiocalcaneal Kinematics Of Barefoot Versus Shod Running, Alex Stacoff, Benno M. Nigg, Christoph Reinschmidt, Antonie J. Van Den Bogert, Arne Lundberg

Mechanical Engineering Faculty Publications

Barefoot running kinematics has been described to vary considerably from shod running. However, previous investigations were typically based on externally mounted shoe and/or skin markers, which have been shown to overestimate skeletal movements. Thus, the purpose of this study was to compare calcaneal and tibial movements of barefoot versus shod running using skeletal markers. Intracortical bone pins with reflective marker triads were inserted under standard local anesthetic into the calcaneus and tibia of five healthy male subjects. The subjects ran barefoot, with a normal shoe, with three shoe soles and two orthotic modifications. The three-dimensional tibiocalcaneal rotations were determined using …

Contributions Of Proximal And Distal Moments To Axial Tibial Rotation During Walking And Running, T. L. Bellchamber, Antonie J. Van Den Bogert

Mechanical Engineering Faculty Publications

The purpose of this study was to determine the cause and effect relationship between tibial internal rotation and pronation of the foot during walking and heel–toe running. This would allow predictions of orthotic effectiveness in reducing knee pain related to excessive internal tibial rotation. Kinematic and force plate data were collected from twenty subjects performing ten running and ten walking trials across a force plate. Using a least-squares algorithm, attitude matrices for each segment in each frame were obtained and the angular velocity vector of the tibia was calculated. The intersegmental moment at the ankle was calculated from ground reaction …

The Effects Of Patch Properties On The Debonding Behavior Of Patched Beam-Plates, Anette M. Karlsson

Mechanical Engineering Faculty Publications

The debonding characteristics of patched structures are investigated in this study by means of an analytical model. In particular, the effects the lay-up sequence and edge tapering of a carbon-reinforced epoxy patch, as well as the beveling of an aluminum patch, have on the initiation, stability, and extent of the debonding are considered. The results presented show that both the degree of edge-tapering and the patch properties must be carefully selected in order to optimize the patched structure. It is also shown that when designing a patched system, it is important to model the correct boundary and load conditions to …

The Influence Of Orthotic Devices And Vastus Medialis Strength And Timing On Patellofemoral Loads During Running, R. R. Neptune, I. C. Wright, Antonie J. Van Den Bogert

Mechanical Engineering Faculty Publications

Objective. To use a musculoskeletal model and simulation of running to examine: (1) the influence of two commonly prescribed treatments for patellofemoral pain (vastus medialis oblique strengthening and orthoses) and (2) the functional significance of timing differences between vastus medialis oblique and vastus lateralis on lateral patellofemoral joint loads.

Design. A three-dimensional musculoskeletal model of the lower extremity was used to simulate running at 4 m/s.

Background. Repetitive and excessive joint loading is often associated with overuse injuries that require clinical treatments to reduce pain and restore function. Affecting one in four runners, patellofemoral pain is one …

On Thermal Buckling Of Patched Beam-Plates, Anette M. Karlsson, W. J. Bottega

Mechanical Engineering Faculty Publications

The behavior of uniformly heated plates is considered for the situation where a patch is adhered over a region of the structure. A variational formulation results in a self-consistent set of equations and conditions, which governs the response of the system. The nonlinear problems are solved analytically, yielding exact results within the context of the mathematical model employed. A stability criterion is established for the class of problems considered, based on the second variation of the potential energy of the composite structure, and issues of stability are assessed in this context. Three non-dimensional parameters that characterize the response of the …

On The Behavior Of A Class Of Patched Plates During Cooling, Anette M. Karlsson, W. J. Bottega

Mechanical Engineering Faculty Publications

The behavior of patched beam-plates during uniform cooling is considered. A non-linear formulation is adopted and the problems of interest are solved analytically yielding exact results within the context of the mathematical model employed. Three non-dimensional parameters corresponding to (i) a loading parameter, (ii) a critical temperature and (iii) a critical membrane force, are seen to characterize the response of the composite structure. Stability is considered and critical behavior includes bifurcation and asymptotic buckling, non-trivial “groundstates”, and demarcation and transition in deflection direction. Extensive numerical simulations based on analytical solutions are performed. Results are presented for various loading and support …

The Influence Of Foot Positioning On Ankle Sprains, I. C. Wright, R. R. Neptune, Antonie J. Van Den Bogert, B. M. Nigg

Mechanical Engineering Faculty Publications

The goal of this study was to examine the influence of changes in foot positioning at touch-down on ankle sprain occurrence. Muscle model driven computer simulations of 10 subjects performing the landing phase of a side-shuffle movement were performed. The relative subtalar joint and talocural joint angles at touchdown were varied, and each subject-specific simulation was exposed to a set of perturbed floor conditions. The touchdown subtalar joint angle was not found to have a considerable influence on sprain occurrence, while increased touchdown plantar flexion caused increased ankle sprain occurrences. Increased touchdown plantar flexion may be the mechanism which causes …

Quantification Of In Vivo Acl Elongation During Dynamic Joint Movements: A New Methodology, Scott G. Mclean, Antonie J. Van Den Bogert

Mechanical Engineering Faculty Publications

Anterior cruciate ligament (ACL) injuries are common in movement tasks incorporating sudden changes in velocity, such as sidtestepping. Current techniques adopted to quantify ACL strain are invasive as well as limited to slow, quasi-static move- ments. This paper presents a method for non-invasive measurement of ACL elongation during dynamic movement tasks, validation of the method, and demonstrates its applicability to the analysis of sidestep movements

Movement Coupling At The Ankle During The Stance Phase Of Running, Alex Stacoff, Benno M. Nigg, Christoph Reinschmidt, Antonie J. Van Den Bogert, Arne Lundberg, Edgar Stüssi, Jachen Denoth

Mechanical Engineering Faculty Publications

The purpose of this study was to quantify movement coupling at the ankle during the stance phase of running using bone-mounted markers. Intracortical bone pins with reflective marker triads were inserted under standard local anaesthesia into the calcaneus and the tibia of five healthy male subjects. The three-dimensional rotations were determined using a joint coordinate system approach. Movement coupling was observed in all test subjects and occurred in phases with considerable individual differences. Between the shoe and the calcaneus coupling increased after midstance which suggested that the test shoes provided more coupling for inversion than for eversion. Movement coupling between …

Structural Damage Detection Using Modal Norms, W. Gawronski, Jerzy T. Sawicki

Mechanical Engineering Faculty Publications

No abstract provided.

Effects Of Foot Orthoses On Skeletal Motion During Running, A. Stacoff, C. Reinschmidt, B. M. Nigg, Antonie J. Van Den Bogert, A. Lundberg, J. Denoth, E. Stüssi

Mechanical Engineering Faculty Publications

Objective. To quantify the effects of medial foot orthoses on skeletal movements of the calcaneus and tibia during the stance phase in running.

Design. Kinematic effects of medial foot orthoses (anterior, posterior, no support) were tested using skeletal (and shoe) markers at the calcaneus and tibia.

Background. Previous studies using shoe and skin markers concluded that medially placed orthoses control/reduce foot eversion and tibial rotation. However, it is currently unknown if such orthoses also affect skeletal motion at the lower extremities.

Methods. Intracortical Hofman pins with reflective marker triads were inserted under standard local anesthetic into the calcaneus …

On The Detachment Of Step-Tapered Doublers: Part 2—Evolution Of Pressure Loaded Structures, Anette M. Karlsson, W. J. Bottega

Mechanical Engineering Faculty Publications

One-dimensional edge debonding of layerwise step-tapered patches from both flat and cylindrical structures subjected to applied pressure is studied in the context of the general formulation presented in Part 1. Numerical simulations based on analytical solutions of the problems of interest are performed and intricate results presented in the form of threshold curves/delamination paths for various taper angles and support conditions. Configurations corresponding to full contact of the debonded segments, edge contact of the debonded segments and no contact of the debonded segments of the evolving composite structure are included in the model and found to significantly affect the predicted …

On The Detachment Of Step-Tapered Doublers : Part 1—Foundations, W. J. Bottega, Anette M. Karlsson

Mechanical Engineering Faculty Publications

One-dimensional edge debonding of layerwise step-tapered patches from both flat and cylindrical structures is examined. The problems are approach from a unified point of view, as propagating boundary problems in the calculus of variations, with the models for both flat and curved structures being formulated simultaneously. The effects of a contact zone adjacent to the bonded region are incorporated as is the phenomenon of edge-point contact. The formulation results in a selfconsistent representation of the various intact and debonded segments of the composite structure comprised of a multilayer patch and a base structure. It concurrently yields the conditions which establish …

On-Line Free Form Surface Measurement Via A Fuzzy-Logic Controlled Scanning Probe, Ming Chang, Paul P. Lin

Mechanical Engineering Faculty Publications

This paper presents a system and methodology for on-line free form surface measurement via a scanning contact probe installed on a CNC (computer numerical control) machine. The scanning probe provides more sampling points than any traditional touch trigger type of probes used on CNC machines, and better measuring accuracy than laser displacement sensing or structured lighting. The presented measuring system's main advantage is that the number of measured points can vary with the change of surface curvature. To improve the measuring stability and continuity, fuzzy logic control, in lieu of traditional PID control, is employed. As a result, the …

Frequency Driven Phasic Shifting And Elastic-Hysteretic Partitioning Properties Of Fractional Mechanical System Representation Schemes, Jerzy T. Sawicki, Joe Padovan

Mechanical Engineering Faculty Publications

Based on the Louiville–Riemann fractional formulation of lumped hysteretic mechanical system simulations, asymptotic-type relationships are derived. These are employed to determine how such operators, which act as viscoelastic elements, partition system energy into conservative and nonconservative components. Special emphasis is given to: (a) determine how operator order serves to weigh such a splitting, (b) determine how partitioning affects system phasing and amplitude response, and (c) to establish how conservative and nonconservative effects modulate during a given system cycle. The generality of the undertaken approach is such that multi-element fractional Kelvin Voigt formulations subject to spectrally rich inputs can be handled, …

The Presence Of Edge Contact And Its Influence On The Debonding Of Patched Panels, Anette M. Karlsson, W. J. Bottega

Mechanical Engineering Faculty Publications

A formulation is presented which accounts for configurations of debonding patched cylindrical panels for which the edge of the debonded segment of the patch maintains sliding contact with the corresponding base structure. The formulation is incorporated with that which accounts for configurations for which a contact zone is present and for which no contact between the debonded segments of the patch and base structure occurs during debonding. Analyses are performed for two types of loading conditions: Applied circumferential tension and applied internal pressure. Results of numerical simulations based on analytical solutions of the problems of interest are presented in the …

The Dynamics Of Rotor With Rubbing, Jerzy T. Sawicki, Joe Padovan, Rabih Al-Khatib

Mechanical Engineering Faculty Publications

This paper presents the description of some phenomena associated with dynamic behavior of rotors interacting with stationary components. Numerical simulations show rotor vibration spectrum rich in subharmonic, quasi-periodic, and chaotic vibrations. The nonlinear calculation techniques are applied to demonstrate the changes of the vibration patterns for different operating conditions. Some conclusions are discussed with regard to unique characteristics of rub-induced rotor response, initial conditions, as well as appropriate ranges of system parameters. Of special interest are the changes in the apparent nonlinearity of the system dynamics as rubs are induced at different rotor speeds. In particular, starting with 2nd order …