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Mechanical Engineering Faculty Publications

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Articles 391 - 420 of 618

Full-Text Articles in Mechanical Engineering

Production Of Β-Silicon Carbide Nanofibers Using The Forcespinning® Method, Alfonso Salinas, Aleksey Altecor, Maricela Lizcano, Karen Lozano Jan 2016

Production Of Β-Silicon Carbide Nanofibers Using The Forcespinning® Method, Alfonso Salinas, Aleksey Altecor, Maricela Lizcano, Karen Lozano

Mechanical Engineering Faculty Publications

Silicon carbide (SiC) nanofibers were produced on a large scale using the Forcespinning® method. Non-oxide ceramics such as SiC are known for their low density, oxidation resistance, thermal stability, and wear resistance. The nanofibers were prepared using a solution-based method with polystyrene and polycarbomethylsilane as the precursor materials. Fiber spinning was performed under different parameters to obtain high yield, fiber homogeneity, and small diameters. The fibers were spun under a controlled nitrogen environment to prevent fiber oxidation. The resultant nonwoven nanofiber mats were then subjected to different heat treatments to evaluate the effect of these on the crystalline structure. Characterization …

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Knee Internal Forces In Moderate Squat Exercise, Dumitru I. Caruntu, Jose Mario Salinas Jan 2016

Knee Internal Forces In Moderate Squat Exercise, Dumitru I. Caruntu, Jose Mario Salinas

Mechanical Engineering Faculty Publications

This paper deals with internal forces of human knee during moderate squat exercise. The moderate squat exercise consists of a descending phase from standing to the lowest position (largest flexion angle) in which no significant contact between thigh and calf occurs, and an ascending phase back to standing position. This research predicts the internal forces such as muscle forces, contact forces, and ligamentous forces. The ligamentous structures in this research consist of Anterior Cruciate Ligament (ACL), Posterior Cruciate Ligament (PCL), Lateral Collateral Ligament (LCL), and Medial Collateral Ligament (MCL). The ligaments are modeled as nonlinear elastic strips (they do not …

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Direct Numerical Simulation Of Cylindrical Particle-Laden Gravity Currents, ‪Nadim Zgheib, Thomas Bonometti, S. Balachandar Dec 2015

Direct Numerical Simulation Of Cylindrical Particle-Laden Gravity Currents, ‪Nadim Zgheib, Thomas Bonometti, S. Balachandar

Mechanical Engineering Faculty Publications

We present results from direct numerical simulations (DNS) of cylindrical particle-laden gravity currents. We consider the case of a full depth release with monodisperse particles at a dilute concentration where particle–particle interactions may be neglected. The disperse phase is treated as a continuum and a two-fluid formulation is adopted. We present results from two simulations at Reynolds numbers of 3450 and 10,000. Our results are in good agreement with previously reported experiments and theoretical models. At early times in the simulations, we observe a set of rolled up vortices that advance at varying speeds. These Kelvin–Helmholtz (K–H) vortex tubes are …

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An Experimental Investigation Of Microalgal Dewatering Efficiency Of Belt Filter System, Anjali Sandip, Val H. Smith, Terry N. Faddis Nov 2015

An Experimental Investigation Of Microalgal Dewatering Efficiency Of Belt Filter System, Anjali Sandip, Val H. Smith, Terry N. Faddis

Mechanical Engineering Faculty Publications

The objective of this study was to investigate the microalgal dewatering efficiency of a belt filter system for feed concentrations below 10 g dry wt./L. A prototype belt filtration system designed for 50 g dry wt./L microalgal feed concentration was used for this investigation. The highest concentration of microalgal suspension available for testing on the prototype belt filtration system was 6 g dry wt./L obtained from biomass settling tanks at the Lawrence, Kansas domestic wastewater treatment plant. For preparation of feed suspension with concentrations below 10 g dry wt./L, microalgal cultivation was followed by flocculation. A mixed laboratory culture of …

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Dynamics Of Non-Circular Finite-Release Gravity Currents, ‪Nadim Zgheib, T. Bonometti, S. Balachandar Oct 2015

Dynamics Of Non-Circular Finite-Release Gravity Currents, ‪Nadim Zgheib, T. Bonometti, S. Balachandar

Mechanical Engineering Faculty Publications

The present work reports some new aspects of non-axisymmetric gravity currents obtained from laboratory experiments, fully resolved simulations and box models. Following the earlier work of Zgheib et al. (Theor. Comput. Fluid Dyn., vol. 28, 2014, pp. 521–529) which demonstrated that gravity currents initiating from non-axisymmetric cross-sectional geometries do not become axisymmetric, nor do they retain their initial shape during the slumping and inertial phases of spreading, we show that such non-axisymmetric currents eventually reach a self-similar regime during which (i) the local front propagation scales as t1/2 as in circular releases and (ii) the non-axisymmetric front has a self-similar …

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Propagation And Deposition Of Non-Circular Finite Release Particle-Laden Currents, ‪Nadim Zgheib, Thomas Bonometti, S. Balachandar Aug 2015

Propagation And Deposition Of Non-Circular Finite Release Particle-Laden Currents, ‪Nadim Zgheib, Thomas Bonometti, S. Balachandar

Mechanical Engineering Faculty Publications

The dynamics of non-axisymmetric turbidity currents is considered here for a range of Reynolds numbers of O (104) when based on the initial height of the release. The study comprises a series of experiments and highly resolved simulations for which a finite volume of particle-laden solution is released into fresh water. A mixture of water and polystyrene particles of mean diameter 𝑑̃𝑝=300𝜇m and mixture density 𝜌̃𝑐=1012kg/m3 is initially confined in a hollow cylinder at the centre of a large tank filled with fresh water. Cylinders with two different cross-sectional shapes, but equal cross-sectional areas, are examined: a circle and a …

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Fabrication Of Cellulose Fine Fiber Based Membranes Embedded With Silver Nanoparticles Via Forcespinning, Fenghua Xu, Baicheng Weng, Luis A. Materon, Anxiu Kuang, Jorge A. Trujillo, Karen Lozano Aug 2015

Fabrication Of Cellulose Fine Fiber Based Membranes Embedded With Silver Nanoparticles Via Forcespinning, Fenghua Xu, Baicheng Weng, Luis A. Materon, Anxiu Kuang, Jorge A. Trujillo, Karen Lozano

Mechanical Engineering Faculty Publications

This study presents the successful development of cellulose fiber based membranes embedded with silver nanoparticles. These fine fiber membranes were developed utilizing the Forcespinning (FS) technique followed by alkaline hydrolysis treatment. The fiber morphology, homogeneity and yield were optimized by varying spinning parameters such as polymer concentration and angular velocity of the spinnerets. The structure, thermal and mechanical properties, and water absorption capability of the developed membranes were investigated. The cellulose acetate (CA) present in the membrane was converted to cellulose in the presence of embedded silver nanoparticles by alkaline hydrolysis. The silver nanoparticles embedded cellulose membrane exhibits outstanding water …

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Contours For Planar Cracks Growing In Three Dimensions: Illustration For Transversely Isotropic Solid, Louis Milton Brock Jul 2015

Contours For Planar Cracks Growing In Three Dimensions: Illustration For Transversely Isotropic Solid, Louis Milton Brock

Mechanical Engineering Faculty Publications

Three-dimensional dynamic steady state growth of a semi-infinite plane crack in a transversely isotropic solid is considered. Growth takes place on a principal plane with the material symmetry axis as one tangent. Fracture is brittle, and driven by compressive loads that translate on the crack surfaces. Translation speed is constant and subcritical, but direction with respect to the principal axes is arbitrary. An analytical solution is obtained, and examined in light of the dynamic energy release rate criterion for the case of a translating compressive point force. Introduction of quasipolar coordinates leads to a nonlinear first-order differential equation for the …

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Tracking Of Spall Deterioration On Tapered Roller Bearings, Amy Gonzalez, Constantine Tarawneh, Ping Hu, Joseph A. Turner, Brent Wilson Jun 2015

Tracking Of Spall Deterioration On Tapered Roller Bearings, Amy Gonzalez, Constantine Tarawneh, Ping Hu, Joseph A. Turner, Brent Wilson

Mechanical Engineering Faculty Publications

Fatigue spall initiation is one of the major modes of premature bearing failure. The spall initiation is often exacerbated by the presence of impurities in the near-surface region (∼400 μm) of the bearing raceways. Once a spall initiates, it can propagate rapidly, leading to abnormal bearing operation and possible catastrophic failure if not detected early. Testing performed at the University of Texas-Pan American (UTPA) has focused on ultrasonically scanned tapered roller bearings found to have inclusion content within 400 μm of the surface of the raceways. These bearings undergo accelerated service life tests in which spall initiation is detected and …

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Fatigue Life Estimation Of Modified Railroad Bearing Adapters For Onboard Monitoring Applications, Alexis Trevino, Arturo A. Fuentes, Constantine Tarawneh, Joseph Montalvo Jun 2015

Fatigue Life Estimation Of Modified Railroad Bearing Adapters For Onboard Monitoring Applications, Alexis Trevino, Arturo A. Fuentes, Constantine Tarawneh, Joseph Montalvo

Mechanical Engineering Faculty Publications

This paper presents a study of the fatigue life (i.e. number of stress cycles before failure) of Class K cast iron conventional and modified railroad bearing adapters for onboard monitoring applications under different operational conditions based on experimentally validated Finite Element Analysis (FEA) stress results. Currently, freight railcars rely heavily on wayside hot-box detectors (HBDs) at strategic intervals to record bearing cup temperatures as the train passes at specified velocities. Hence, most temperature measurements are limited to certain physical railroad locations. This limitation gave way for an optimized sensor that could potentially deliver significant insight on continuous bearing temperature conditions. …

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Nanofiber-Based Membrane Separators For Lithium-Ion Batteries, Mataz Alcoutlabi, Hun Lee, Xiangwu Zhang Jun 2015

Nanofiber-Based Membrane Separators For Lithium-Ion Batteries, Mataz Alcoutlabi, Hun Lee, Xiangwu Zhang

Mechanical Engineering Faculty Publications

Nanofiber-based membranes were prepared by two different methods for use as separators for Lithium-ion batteries (LIBs). In the first method, Electrospinning was used for the fabrication of Polyvinylidene fluoride PVDF nanofiber coatings on polyolefin microporous membrane separators to improve their electrolyte uptake and electrochemical performance. The nanofiber-coated membrane separators show better electrolyte uptake and ionic conductivity than that for the uncoated membranes. In the second method, Forcespinning® (FS) was used to fabricate fibrous cellulose membranes as separators for LIBs. The cellulose fibrous membranes were made by the Forcespinning® of a cellulose acetate solution precursor followed by a subsequent alkaline hydrolysis …

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An Elaborate Data Set On Human Gait And The Effect Of Mechanical Perturbations, Jason K. Moore, Sandra K. Hnat, Antonie J. Van Den Bogert Apr 2015

An Elaborate Data Set On Human Gait And The Effect Of Mechanical Perturbations, Jason K. Moore, Sandra K. Hnat, Antonie J. Van Den Bogert

Mechanical Engineering Faculty Publications

Here we share a rich gait data set collected from fifteen subjects walking at three speeds on an instrumented treadmill. Each trial consists of 120 s of normal walking and 480 s of walking while being longitudinally perturbed during each stance phase with pseudo-random fluctuations in the speed of the treadmill belt. A total of approximately 1.5 h of normal walking (>5000 gait cycles) and 6 h of perturbed walking (>20,000 gait cycles) is included in the data set. We provide full body marker trajectories and ground reaction loads in addition to a presentation of processed data that …

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Structural Integrity Of Conventional And Modified Railroad Bearing Adapters For Onboard Monitoring, Joseph Montalvo, Alexis Trevino, Arturo A. Fuentes, Constantine Tarawneh Mar 2015

Structural Integrity Of Conventional And Modified Railroad Bearing Adapters For Onboard Monitoring, Joseph Montalvo, Alexis Trevino, Arturo A. Fuentes, Constantine Tarawneh

Mechanical Engineering Faculty Publications

This paper presents a detailed study of the structural integrity of conventional and modified railroad bearing adapters for onboard monitoring applications. Freight railcars rely heavily on weigh bridges and stations to determine cargo load. As a consequence, most load measurements are limited to certain physical railroad locations. This limitation provided an opportunity for an optimized sensor that could potentially deliver significant insight on bearing condition monitoring as well as load information. Bearing adapter modifications (e.g. cut outs) were necessary to house the sensor and, thus, it is imperative to determine the reliability of the modified railroad bearing adapter, which will …

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Contours For Planar Cracks Growing In Three Dimensions, Louis Milton Brock Jan 2015

Contours For Planar Cracks Growing In Three Dimensions, Louis Milton Brock

Mechanical Engineering Faculty Publications

A three-dimensional dynamic steady state analysis for extension of a semi-infinite plane crack is considered. Fracture is brittle and driven by loads applied to the crack surfaces. An analytical solution is obtained, and examined in light of two criteria: energy release (rate) and strain energy density. Introduction of a quasipolar coordinate system allows, for each criterion, generation of a nonlinear first-order differential equation for the distance from the origin to any point on the crack edge. These in turn give insight into the crack contour generated by the crack edge. In particular, for loading by compressive point forces, the equation …

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Direct Numerical Simulation Of Three-Dimensional Gravity Current On A Uniform Slope, A. Ooi, ‪Nadim Zgheib, S. Balachandar Jan 2015

Direct Numerical Simulation Of Three-Dimensional Gravity Current On A Uniform Slope, A. Ooi, ‪Nadim Zgheib, S. Balachandar

Mechanical Engineering Faculty Publications

Gravity currents occur when fluids of different density are brought together. When gravity currents travel down a uniform slope, buoyancy effects become more important and changes the physical dynamics of its motion. In the present paper, we report data from full three-dimensional direct numerical simulation of gravity currents propagating down a uniform slope. Our data shows that in most cases, the gravity current evolve to a shape that is similar to a triangular wedge. The physical mechanisms leading to formation of this triangular shape and the dynamics of such a structure is presented

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Fabrication And Characterization Of Silver- And Copper-Coated Nylon 6 Forcespun Nanofibers By Thermal Evaporation, Dorina M. Mihut, Karen Lozano, Heinrich D. Foltz Oct 2014

Fabrication And Characterization Of Silver- And Copper-Coated Nylon 6 Forcespun Nanofibers By Thermal Evaporation, Dorina M. Mihut, Karen Lozano, Heinrich D. Foltz

Mechanical Engineering Faculty Publications

Silver and copper nanoparticles were deposited as thin films onto substrates consisting of Nylon 6 nanofibers manufactured using forcespinningR equipment. Different rotational speeds were used to obtain continuous nanofibers of various diameters arranged as nonwoven mats. The Nylon 6 nanofibers were collected as successive layers on frames, and a high-vacuum thermal evaporation method was used to deposit the silver and copper thin films on the nanofibers. The structures were investigated using scanning electron microscopy–scanning transmission electron microscopy, atomic force microscopy, x-ray diffraction, and electrical resistance measurements. The results indicate that evaporated silver and copper nanoparticles were successfully deposited on Nylon …

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Long-Lasting Effect Of Initial Configuration In Gravitational Spreading Of Material Fronts, ‪Nadim Zgheib, Thomas Bonometti, S. Balachandar Sep 2014

Long-Lasting Effect Of Initial Configuration In Gravitational Spreading Of Material Fronts, ‪Nadim Zgheib, Thomas Bonometti, S. Balachandar

Mechanical Engineering Faculty Publications

We present the results from laboratory experiments and fully resolved simulations pertaining to finite-release turbulent density flows with a non-axisymmetric initial shape. First, we demonstrate that the effects of the initial shape influence the current’s evolution well into the long-time phase which would corresponds to the inertial self-similar phase in the case of planar or axisymmetric configurations. Then, we identify the physical mechanisms responsible for this dependence and propose a new model capable of capturing the dynamics of such releases. Finally, we show that this dependence on the initial configuration is robust for various types of gravity currents over a …

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Real-Time Simulation Of Three-Dimensional Shoulder Girdle And Arm Dynamics, Edward K. Chadwick, Dimitra Blana, Robert F. Kirsch, Antonie J. Van Den Bogert Jul 2014

Real-Time Simulation Of Three-Dimensional Shoulder Girdle And Arm Dynamics, Edward K. Chadwick, Dimitra Blana, Robert F. Kirsch, Antonie J. Van Den Bogert

Mechanical Engineering Faculty Publications

Electrical stimulation is a promising technology for the restoration of arm function in paralyzed individuals. Control of the paralyzed arm under electrical stimulation, however, is a challenging problem that requires advanced controllers and command interfaces for the user. A real-time model describing the complex dynamics of the arm would allow user-in-the-loop type experiments where the command interface and controller could be assessed. Real-time models of the arm previously described have not included the ability tomodel the independently controlled scapula and clavicle, limiting their utility for clinical applications of this nature. The goal of this study therefore was to evaluate the …

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Numerical Evaluation Of Paris-Regime Crack Growth Rate Based On Plastically Dissipated Energy, Parag G. Nittur, Anette M. Karlsson, Leif A. Carlsson Jul 2014

Numerical Evaluation Of Paris-Regime Crack Growth Rate Based On Plastically Dissipated Energy, Parag G. Nittur, Anette M. Karlsson, Leif A. Carlsson

Mechanical Engineering Faculty Publications

The crack growth rate during cyclic loading is investigated via numerical simulations. The crack advancement is governed by a propagation criterion that relates the increment in plastically dissipated energy ahead of the crack tip to a critical value. Once this critical value is satisfied, crack propagation is modeled via a node release scheme. Thus, the crack growth rate is an output from the numerical simulation. The crack growth rate predicted by the proposed scheme is compared with published experimental crack growth data in the Paris-regime for selected metals. A good match is found between the experimentally observed crack growth rates …

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Relationship Between Jump Landing Kinematics And Peak Acl Force During A Jump In Downhill Skiing: A Simulation Study, D. Heinrich, Antonie J. Van Den Bogert, W. Nachbauer Jun 2014

Relationship Between Jump Landing Kinematics And Peak Acl Force During A Jump In Downhill Skiing: A Simulation Study, D. Heinrich, Antonie J. Van Den Bogert, W. Nachbauer

Mechanical Engineering Faculty Publications

Recent data highlight that competitive skiers face a high risk of injuries especially during off-balance jump landing maneuvers in downhill skiing. The purpose of the present study was to develop a musculo-skeletal modeling and simulation approach to investigate the cause-and-effect relationship between a perturbed landing position, i.e., joint angles and trunk orientation, and the peak force in the anterior cruciate ligament (ACL) during jump landing. A two-dimensional musculo-skeletal model was developed and a baseline simulation was obtained reproducing measurement data of a reference landing movement. Based on the baseline simulation, a series of perturbed landing simulations (n=1000) was generated. Multiple …

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Multi-Muscle Fes Force Control Of The Human Arm For Arbitrary Goals, Eric M. Schearer, Yu-Wei Liao, Eric J. Perreault, Matthew C. Tresch, William D. Memberg, Robert F. Kirsch, Kevin M. Lynch May 2014

Multi-Muscle Fes Force Control Of The Human Arm For Arbitrary Goals, Eric M. Schearer, Yu-Wei Liao, Eric J. Perreault, Matthew C. Tresch, William D. Memberg, Robert F. Kirsch, Kevin M. Lynch

Mechanical Engineering Faculty Publications

We present a method for controlling a neuroprosthesis for a paralyzed human arm using functional electrical stimulation (FES) and characterize the errors of the controller. The subject has surgically implanted electrodes for stimulating muscles in her shoulder and arm. Using input/output data, a model mapping muscle stimulations to isometric endpoint forces measured at the subject’s hand was identified. We inverted the model of this redundant and coupled multiple-input multiple-output system by minimizing muscle activations and used this inverse for feedforward control. The magnitude of the total root mean square error over a grid in the volume of achievable isometric endpoint …

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Bifurcation Type Change Of Ac Electrostatically Actuated Mems Resonators Due To Dc Bias, Dumitru Caruntu, Kyle N. Taylor Apr 2014

Bifurcation Type Change Of Ac Electrostatically Actuated Mems Resonators Due To Dc Bias, Dumitru Caruntu, Kyle N. Taylor

Mechanical Engineering Faculty Publications

This paper investigates the nonlinear response of microelectromechanical system (MEMS) cantilever resonator electrostatically actuated by applying a soft alternating current (AC) voltage and an even softer direct current (DC) voltage between the resonators and a parallel fixed ground plate. The AC frequency is near natural frequency. This drives the resonator into nonlinear parametric resonance. The method ofmultiple scales (MMS) is used to solve the dimensionless differential equation of motion of the resonator and find the steady-state solutions.The reduced order model (ROM) method is used to validate the results obtained using MMS. The effect of the soft DC voltage (bias) component …

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Expressing The Joint Moments Of Drop Jumps And Sidestep Cutting In Different Reference Frames – Does It Matter?, Eirik Kristianslunda, Tron Krosshauga, Kam-Ming Mok, Scott Mclean, Antonie J. Van Den Bogert Jan 2014

Expressing The Joint Moments Of Drop Jumps And Sidestep Cutting In Different Reference Frames – Does It Matter?, Eirik Kristianslunda, Tron Krosshauga, Kam-Ming Mok, Scott Mclean, Antonie J. Van Den Bogert

Mechanical Engineering Faculty Publications

Joint moments help us understand joint loading and muscle function during movement. However, the interpretation depends on the choice of reference frame, but the different reference frames have not been compared in dynamic, high-impact sporting movements. We have compared the magnitude and the resulting ranking of hip and knee joint moments expressed in the laboratory coordinate system, the local system of the distal segment and projected or decomposed to the Joint Coordinate System (JCS) axes. Hip and knee joint moments of drop jumps and sidestep cutting in 70 elite female handball players were calculated based on recordings from an eight-camera …

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Semiactive Virtual Control Method For Robots With Regenerative Energy-Storing Joints, Hanz Richter, Daniel J. Simon, Antonie J. Van Den Bogert Jan 2014

Semiactive Virtual Control Method For Robots With Regenerative Energy-Storing Joints, Hanz Richter, Daniel J. Simon, Antonie J. Van Den Bogert

Mechanical Engineering Faculty Publications

A framework for modeling and control is introduced for robotic manipulators with a number of energetically self-contained semiactive joints. The control approach consists of three steps. First, a virtual control design is conducted by any suitable means, assuming a fully-actuated system. Then, virtual control inputs are matched by a parameter modulation law. Finally, the storage dynamics are shaped using design parameters. Storage dynamics coincide with the system's internal dynamics under exact virtual control matching. An internal energy balance equation and associated self-powered operation condition are given for the semiactive joints. This condition is a structural characteristic of the system and …

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Time-Dependent Mechanical Behavior Of Proton Exchange Membrane Fuel Cell Electrodes, Zongwen Lu, Michael H. Santare, Anette M. Karlsson, F. Colin Busby, Peter Walsh Jan 2014

Time-Dependent Mechanical Behavior Of Proton Exchange Membrane Fuel Cell Electrodes, Zongwen Lu, Michael H. Santare, Anette M. Karlsson, F. Colin Busby, Peter Walsh

Mechanical Engineering Faculty Publications

The electrodes used for Proton Exchange Membrane Fuel Cells (PEMFCs) are typically painted or sprayed onto the membrane during manufacturing, making it difficult to directly characterize their mechanical behavior as a stand-alone material. An experimental-numerical hybrid technique is devised to extract the electrode properties from the experimentally measured properties of Nafion® 211 membrane1 and a membrane electrode assembly (MEA) based on Nafion® 211 membrane at various temperatures, humidities, and strain rates. Within the linear regime, the rule-of-mixtures assuming an iso-strain condition is used to calculate the rate-dependent Young's modulus of the electrodes. Beyond the linear regime, reverse …

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Unidirectional Rotary Tendency Of A Wave-Driven Rotor, Yingchen Yang Jan 2014

Unidirectional Rotary Tendency Of A Wave-Driven Rotor, Yingchen Yang

Mechanical Engineering Faculty Publications

Ocean waves can directly drive WECs (wave energy converters) to perform two types of motion—reciprocating motion and unidirectional rotary motion. In general, the efficiency of a reciprocating WEC is strongly wave-frequency dependent, whereas the efficiency of a rotary WEC can be somewhat wave-frequency independent. To date, a huge majority of WEC technologies under development in industry belong to the reciprocating class, and only a few WEC concepts fall in the unidirectional rotary class. In the present work, a wave-driven rotor for unidirectional rotary motion was proposed and characterized. A numerical tool has been developed for characterization of the rotor’s unidirectional …

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On The Uniqueness And Sensitivity Of Indentation Testing Of Isotropic Materials, J. K. Phadikar, T. A. Bogetti, Anette M. Karlsson Oct 2013

On The Uniqueness And Sensitivity Of Indentation Testing Of Isotropic Materials, J. K. Phadikar, T. A. Bogetti, Anette M. Karlsson

Mechanical Engineering Faculty Publications

Instrumented indentation is a popular technique to extract the material properties of small scale structures. The uniqueness and sensitivity to experimental errors determine the practical usefulness of such experiments. Here, a method to identify test techniques that minimizes sensitivity to experimental erros is in indentation experiments developed. The methods are based on considering “shape functions,” which are sets of functions that describe the force–displacement relationship obtained during the indentation test. The concept of condition number is used to investigate the relative reliability of various possible dual indentation techniques. Interestingly, it was found that many dual indentation techniques can be as …

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Implementation Of A Plastically Dissipated Energy Criterion For Three Dimensional Modeling Of Fatigue Crack Growth, Parag G. Nittur, Anette M. Karlsson, Leif A. Carlsson Sep 2013

Implementation Of A Plastically Dissipated Energy Criterion For Three Dimensional Modeling Of Fatigue Crack Growth, Parag G. Nittur, Anette M. Karlsson, Leif A. Carlsson

Mechanical Engineering Faculty Publications

Fatigue crack growth is simulated using three dimensional elastic-plastic finite element analysis. The crack extension per load cycle, da/dN, as well as crack front profile changes (crack tunneling) under cyclic loading is not specified as an input but evaluated based on a condition that relates plastically dissipated energy to a critical value. Simulation of cyclic crack propagation in a middle-crack tension M(T) specimen using this implementation captures the well established, experimentally obtained crack growth rate reduction accompanying a single overload event. The analysis predicts that the single overload also affects the crack front profile, where a tunneling crack propagates with …

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Conical Indentation Of A Viscoelastic Sphere, J. K. Phadikar, T. A. Bogetti, V. N. Kaliakin, Anette M. Karlsson Jun 2013

Conical Indentation Of A Viscoelastic Sphere, J. K. Phadikar, T. A. Bogetti, V. N. Kaliakin, Anette M. Karlsson

Mechanical Engineering Faculty Publications

Instrumented indentation is commonly used for determining mechanical properties of a range of materials, including viscoelastic materials. However, most—if not all—studies are limited to a flat substrate being indented by various shaped indenters (e.g., conical or spherical). This work investigates the possibility of extending instrumented indentation to nonflat viscoelastic substrates. In particular, conical indentation of a sphere is investigated where a semi-analytical approach based on “the method of functional equations” has been developed to obtain the force–displacement relationship. To verify the accuracy of the proposed methodology selected numerical experiments have been performed and good agreement was obtained. Since it takes …

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Compressive Response Of Polycrystalline Nicomnga High-Temperature Meta-Magnetic Shape Memory Alloys, H. E. Karaca, A. S. Turabi, B. Basaran, A. K. Pathak, I. Dubenko, N. Ali, Y. I. Chumlyakov, P. Li May 2013

Compressive Response Of Polycrystalline Nicomnga High-Temperature Meta-Magnetic Shape Memory Alloys, H. E. Karaca, A. S. Turabi, B. Basaran, A. K. Pathak, I. Dubenko, N. Ali, Y. I. Chumlyakov, P. Li

Mechanical Engineering Faculty Publications

The effects of the addition of quaternary element, Co, to polycrystalline NiMnGa alloys on their magnetic and shape memory properties have been investigated. NiCoMnGa polycrystalline alloys have been found to demonstrate good shape memory and superelasticity behavior under compression at temperatures greater than 100 °C with about 3% transformation strain and low-temperature hysteresis. It is also possible to train the material to demonstrate a large two-way shape memory effect.

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