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Mechanical Engineering Faculty Publications

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Articles 421 - 450 of 618

Full-Text Articles in Mechanical Engineering

Time-Dependent Mechanical Response Of A Composite Pfsa Membrane, Narinder S. Khattra, Zongwen Lu, Anette M. Karlsson, Michael H. Santare, F. Colin Busby, Thomas Schmiedel Apr 2013

Time-Dependent Mechanical Response Of A Composite Pfsa Membrane, Narinder S. Khattra, Zongwen Lu, Anette M. Karlsson, Michael H. Santare, F. Colin Busby, Thomas Schmiedel

Mechanical Engineering Faculty Publications

The mechanical response of a composite fuel cell membrane, made from layers of reinforced and unreinforced PFSA material, is investigated via both experimental and numerical means. First, the time-dependent mechanical properties for the reinforced layers are measured for a range of environmental and loading conditions. A three-network, viscoelastic-plastic constitutive model is developed to characterize the mechanical response of this reinforced membrane material. This constitutive model is then used in finite element simulations of a fuel cell unit (consisting of composite membrane, electrodes, gas diffusion layer and bipolar plates) where the effect of relative humidity (RH) cycling on the stress response …

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In Situ Analysis Of Fatigue Crack Propagation In Polymer Foams, Elio E. Saenza, Leif A. Carlsson, Anette M. Karlsson Mar 2013

In Situ Analysis Of Fatigue Crack Propagation In Polymer Foams, Elio E. Saenza, Leif A. Carlsson, Anette M. Karlsson

Mechanical Engineering Faculty Publications

This paper presents an in situ SEM experimental study on cyclic crack propagation in closed-cell polymer foams. The microscopic failure mechanisms in precracked PVC and PES specimens of 60 and 90 kg/m3 densities were examined under low-cycle fatigue loading. In the PVC foam, crack propagation occurred incrementally by successive failure of cell boundaries in front of the crack tip. The crack occasionally jumped to cell boundaries above or below the main crack resulting in non-self similar growth. Crack propagation in the PES foam occurred incrementally by extensive plastic tearing and subsequent tensile failure of the cell edge in front …

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Experimental Study Of Nanofiber Production Through Forcespinning, Simon Padron, Arturo Fuentes, Dumitru Caruntu, Karen Lozano Jan 2013

Experimental Study Of Nanofiber Production Through Forcespinning, Simon Padron, Arturo Fuentes, Dumitru Caruntu, Karen Lozano

Mechanical Engineering Faculty Publications

A newly developed method of producing nanofibers, called forcespinning, has proven to be a viable alternative to mass produce nanofibers. Unlike electrospinning, the most common method currently being employed (which draws fibers through the use of electrostatic force), forcespinning utilizes centrifugal forces which allow for a host of new materials to be processed into nanofibers (given that electric fields are not required) while also providing a significant increase in yield and ease of production. This work presents a detailed explanation of the fiber formation process. The study is conducted using high speed photography to capture the jet initiation process at …

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Separation Control On High Lift Low-Pressure Turbine Airfoils Using Pulsed Vortex Generator Jets, Ralph J. Volino, Mounir B. Ibrahim Dec 2012

Separation Control On High Lift Low-Pressure Turbine Airfoils Using Pulsed Vortex Generator Jets, Ralph J. Volino, Mounir B. Ibrahim

Mechanical Engineering Faculty Publications

Boundary layer separation control has been studied using vortex generator jets (VGJs) on a very high lift, low-pressure turbine airfoil. Experiments were done under low (0.6%) freestream turbulence conditions on a linear cascade in a low speed wind tunnel. Pressure surveys on the airfoil surface and downstream total pressure loss surveys were documented. Instantaneous velocity profile measurements were acquired in the suction surface boundary layer. Cases were considered at Reynolds numbers (based on the suction surface length and the nominal exit velocity from the cascade) of 25000 and 50000. Jet pulsing frequency and duty cycle were varied. In cases without …

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Rotor Model Updating And Validation For An Active Magnetic Bearing Based High-Speed Machining Spindle, Adam C. Wroblewski, Jerzy T. Sawicki, Alexander H. Pesch Dec 2012

Rotor Model Updating And Validation For An Active Magnetic Bearing Based High-Speed Machining Spindle, Adam C. Wroblewski, Jerzy T. Sawicki, Alexander H. Pesch

Mechanical Engineering Faculty Publications

This paper presents an experimentally driven model updating approach to address the dynamic inaccuracy of the nominal finite element (FE) rotor model of a machining spindle supported on active magnetic bearings. Modeling error is minimized through the application of a numerical optimization algorithm to adjust appropriately selected FE model parameters. Minimizing the error of both resonance and antiresonance frequencies simultaneously accounts for rotor natural frequencies as well as for their mode shapes. Antiresonance frequencies, which are shown to heavily influence the model’s dynamic properties, are commonly disregarded in structural modeling. Evaluation of the updated rotor model is performed through comparison …

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An Experimental Investigation Of Strain Rate, Temperature And Humidity Effects On The Mechanical Behavior Of A Perfluorosulfonic Acid Membrane, Zongwen Lu, Melissa Lugo, Michael H. Santare, Anette M. Karlsson, F. Colin Busby, Peter Walsh Sep 2012

An Experimental Investigation Of Strain Rate, Temperature And Humidity Effects On The Mechanical Behavior Of A Perfluorosulfonic Acid Membrane, Zongwen Lu, Melissa Lugo, Michael H. Santare, Anette M. Karlsson, F. Colin Busby, Peter Walsh

Mechanical Engineering Faculty Publications

The time-dependent hygro-thermal mechanical behavior of a perfluorosulfonic acid (PFSA) membrane (Nafion® 211 membrane) commonly used in Proton Exchange Membrane Fuel Cells (PEMFCs) is investigated at selected strain rates for a broad range of temperatures and humidities. Tensile tests and relaxation tests are conducted to determine Young’s modulus and proportional limit stress as functions of strain rate, temperature and humidity. The results show that Young’s modulus and proportional limit stress increase as the strain rate increases, and decrease as the temperature or humidity increases. The results also show that the mechanical response of Nafion® 211 membrane is more …

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Effect Of Time-Dependent Material Properties On The Mechanical Behavior Of Pfsa Membranes Subjected To Humidity Cycling, Narinder S. Khattra, Anette M. Karlsson, Michael H. Santare, Peter Walsh, F. Colin Busby Sep 2012

Effect Of Time-Dependent Material Properties On The Mechanical Behavior Of Pfsa Membranes Subjected To Humidity Cycling, Narinder S. Khattra, Anette M. Karlsson, Michael H. Santare, Peter Walsh, F. Colin Busby

Mechanical Engineering Faculty Publications

A viscoelastic-plastic constitutive model is developed to characterize the time-dependent mechanical response of perfluorosulphonic acid (PFSA) membranes. This model is then used in finite element simulations of a representative fuel cell unit, (consisting of electrodes, gas diffusion layer and bipolar plates) subjected to standardized relative humidity (RH) cycling test conditions. The effects of hold times at constant RH, the feed rate of humidified air and sorption rate of water into the membrane on the stress response are investigated. While the longer hold times at high and low humidity lead to considerable redistribution of the stresses, the lower feed and sorption …

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Controlled Deflection Approach For Rotor Crack Detection, Zbigniew Kulesza, Jerzy T. Sawicki Sep 2012

Controlled Deflection Approach For Rotor Crack Detection, Zbigniew Kulesza, Jerzy T. Sawicki

Mechanical Engineering Faculty Publications

Atransverse shaft crack is a serious malfunction that can occurdue to cyclic loading, creep, stress corrosion, and other mechanismsto which rotating machines are subjected. Though studied for manyyears, the problems of early crack detection and warning arestill in the limelight of many researchers. This is dueto the fact that the crack has subtle influence onthe dynamic response of the machine and still there areno widely accepted, reliable methods of its early detection. Thispaper presents a new approach to these problems. The methodutilizes the coupling mechanism between the bending and torsional vibrationsof the cracked, nonrotating shaft. By applying an external lateralforce …

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Rigid Finite Element Model Of A Cracked Rotor, Zbigniew Kulesza, Jerzy T. Sawicki Aug 2012

Rigid Finite Element Model Of A Cracked Rotor, Zbigniew Kulesza, Jerzy T. Sawicki

Mechanical Engineering Faculty Publications

The article introduces a new mathematical model for the cracked rotating shaft. The model is based on the rigid finite element (RFE) method, which has previously been successfully applied for the dynamic analysis of many complicated, mechanical structures. In this article, the RFE method is extended and adopted for the modeling of rotating machines. An original concept of crack modeling utilizing the RFE method is developed. The crack is presented as a set of spring–damping elements of variable stiffness connecting two sections of the shaft. An alternative approach for approximating the breathing mechanism of the crack is introduced. The approach …

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Adding Autonomic Healing Capabilities To Polyethylene Oxide, Dorina M. Chipara, Maritza Flores, Alma Perez, Nancy Puente, Karen Lozano, Mircea Chipara Aug 2012

Adding Autonomic Healing Capabilities To Polyethylene Oxide, Dorina M. Chipara, Maritza Flores, Alma Perez, Nancy Puente, Karen Lozano, Mircea Chipara

Mechanical Engineering Faculty Publications

The addition of autonomic healing (frequently defined as self-healing) capabilities to a water-soluble polymer (polyethylene oxide, PEO) is for the first time reported. The self-healing system consists of urea-formaldehyde microcapsules filled with dicyclopentadiene and first-generation Grubbs catalyst, dispersed within polyethylene oxide. Raman spectroscopy, optical microscopy, electron microscopy, and thermogravimetric analysis were used to characterize this autonomic healing system. Self-healing capabilities were confirmed by mechanical testing (load–displacement, engineering stress–engineering strain, and true stress–true strain dependences) recorded at very slow elongation rates (0.01 mm/s). The testing fate was chosen to allow for the complete consumption of the monomer before fracture (the polymerization …

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On Establishing Elastic–Plastic Properties Of A Sphere By Indentation Testing, J. K. Phadikar, T. A. Bogetti, Anette M. Karlsson Jul 2012

On Establishing Elastic–Plastic Properties Of A Sphere By Indentation Testing, J. K. Phadikar, T. A. Bogetti, Anette M. Karlsson

Mechanical Engineering Faculty Publications

Instrumented indentation is a popular technique for determining mechanical properties of materials. Currently, the evaluation techniques of instrumented indentation are mostly 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 non-flat surfaces. To this end, conical indentation of a sphere is investigated where two methodologies for establishing mechanical properties are explored. In the first approach, a semi-analytical approach is employed to determine the elastic modulus of the sphere utilizing the elastic unloading response (the “unloading slope”). In the second method, reverse analysis based on …

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Predictive Musculoskeletal Simulation Using Optimal Control: Effects Of Added Limb Mass On Energy Cost And Kinematics Of Walking And Running, Antonie J. Van Den Bogert, Maarten Hupperets, Heiko Schlarb, Berthold Krabbe Jun 2012

Predictive Musculoskeletal Simulation Using Optimal Control: Effects Of Added Limb Mass On Energy Cost And Kinematics Of Walking And Running, Antonie J. Van Den Bogert, Maarten Hupperets, Heiko Schlarb, Berthold Krabbe

Mechanical Engineering Faculty Publications

When designing sports equipment, it is often desirable to predict how certain design parameters will affect human performance. In many instances, this requires a consideration of human musculoskeletal mechanics and adaptive neuromuscular control. Current computational methods do not represent these mechanisms, and design optimization typically requires several iterations of prototyping and human testing. This paper introduces a computational method based on musculoskeletal modeling and optimal control, which has the capability to predict the effect of mechanical equipment properties on human performance. The underlying assumption is that users will adapt their neuromuscular control according to an optimality principle, which balances task …

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A Double Cantilever Beam Specimen For Foam Core Fracture Characterization, Elio E. Saenz, Adrián Hernández-Pérez, Leif A. Carlsson, Anette M. Karlsson May 2012

A Double Cantilever Beam Specimen For Foam Core Fracture Characterization, Elio E. Saenz, Adrián Hernández-Pérez, Leif A. Carlsson, Anette M. Karlsson

Mechanical Engineering Faculty Publications

This article presents the analysis and test results for a new sandwich double cantilever beam specimen for foam fracture characterization. The foam is sandwiched between two stiff and strong aluminum adherends. The specimen is analyzed using a modified version of the classical Kanninen elastic foundation model. Finite element analysis is conducted to determine the stress state near the crack tip and compliance of the double cantilever beam sandwich specimen. Model predictions are compared to experimental compliance data and crack growth paths for double cantilever beam specimens with polyvinyl chloride and polyethersulfone foams. The elastic foundation model and finite element analysis …

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Predictive Simulation Of Gait At Low Gravity Reveals Skipping As The Preferred Locomotion Strategy, Marko Ackermann, Antonie J. Van Den Bogert Apr 2012

Predictive Simulation Of Gait At Low Gravity Reveals Skipping As The Preferred Locomotion Strategy, Marko Ackermann, Antonie J. Van Den Bogert

Mechanical Engineering Faculty Publications

The investigation of gait strategies at low gravity environments gained momentum recently as manned missions to the Moon and to Mars are reconsidered. Although reports by astronauts of the Apollo missions indicate alternative gait strategies might be favored on the Moon, computational simulations and experimental investigations have been almost exclusively limited to the study of either walking or running, the locomotion modes preferred under Earth's gravity. In order to investigate the gait strategies likely to be favored at low gravity a series of predictive, computational simulations of gait are performed using a physiological model of the musculoskeletal system, without assuming …

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Development And Testing Of An Actively Adjustable Stiffness Mechanism, Eleazar Marquez, Robert Freeman, Horacio Vasquez Apr 2012

Development And Testing Of An Actively Adjustable Stiffness Mechanism, Eleazar Marquez, Robert Freeman, Horacio Vasquez

Mechanical Engineering Faculty Publications

This study presents the comparison of the theoretical and experimental results of the performance of an adjustable stiffness mechanism. In particular, the use of redundant actuation is emphasized in the design of a one degree-of-freedom Watt II mechanism capable of independently controlling the effective stiffness without a change in equilibrium position. This approach is in contrast to spring mechanism designs unable to actively control the spring rate independent of deflection, and with potential applications in various types of suspension and assembly systems. Results indicate that two direct drive brush-type direct current motors are required to drive the redundantly actuated mechanism …

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A Three-Dimensional Inverse Finite Element Analysis Of The Heel Pad, Snehal Chokhandre, Jason P. Halloran, Antonie J. Van Den Bogert, Ahmet Erdemir Mar 2012

A Three-Dimensional Inverse Finite Element Analysis Of The Heel Pad, Snehal Chokhandre, Jason P. Halloran, Antonie J. Van Den Bogert, Ahmet Erdemir

Mechanical Engineering Faculty Publications

Quantification of plantar tissue behavior of the heel pad is essential in developing computational models for predictive analysis of preventive treatment options such as footwear for patients with diabetes. Simulation based studies in the past have generally adopted heel pad properties from the literature, in return using heel-specific geometry with material properties of a different heel. In exceptional cases, patient-specific material characterization was performed with simplified two-dimensional models, without further evaluation of a heel-specific response under different loading conditions. The aim of this study was to conduct an inverse finite element analysis of the heel in order to calculate heel-specific …

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Electrospun Carbon Nanofibers Decorated With Various Amounts Of Electrochemically-Inert Nickel Nanoparticles For Use As High-Performance Energy Storage Materials, Liwen Ji, Zhan Lin, Mataz Alcoutlabi, Ozan Toprakci, Yingfang Yao, Guanjie Xu, Shuli Li, Xiangwu Zhang Jan 2012

Electrospun Carbon Nanofibers Decorated With Various Amounts Of Electrochemically-Inert Nickel Nanoparticles For Use As High-Performance Energy Storage Materials, Liwen Ji, Zhan Lin, Mataz Alcoutlabi, Ozan Toprakci, Yingfang Yao, Guanjie Xu, Shuli Li, Xiangwu Zhang

Mechanical Engineering Faculty Publications

Carbon nanofibers decorated with various amounts of electrochemically-inert metallic nickel nanoparticles are synthesized through electrospinning and carbonization processes. The morphology and composition of Ni nanoparticles in carbon nanofibers are controlled by preparing different nanofiber precursors. The lithium-ion battery performance evaluations indicated that the content of electrochemically-inert Ni nanoparticles in carbon nanofibers has a great influence on the final electrochemical performance. For example, at certain Ni contents, these composite nanofibers display excellent electrochemical performance, such as high reversible capacities, good capacity retention, and excellent rate performance, when directly used as binder-free anodes for rechargeable lithium-ion batteries. However, when the Ni content …

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Accelerated Fatigue Crack Growth Simulation In A Bimaterial Interface, R. Moslemian, Anette M. Karlsson, C. Berggreen Dec 2011

Accelerated Fatigue Crack Growth Simulation In A Bimaterial Interface, R. Moslemian, Anette M. Karlsson, C. Berggreen

Mechanical Engineering Faculty Publications

A method for accelerated simulation of fatigue crack growth in a bimaterial interface (e.g. in a face/core sandwich interface) is proposed. To simulate fatigue crack growth, a routine is incorporated in the commercial finite element program ANSYS and a method to accelerate the simulation is implemented. The proposed method (the cycle jump technique) is based on conducting finite element analysis for a set of cycles to establish a trend line, extrapolating the trend line spanning many cycles, and use the extrapolated state as initial state for additional finite element simulations. A control criterion is utilized to ensure the accuracy of …

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Aspects Of Fatigue Failure Mechanisms In Polymer Fuel Cell Membranes, Ahmet Kusoglu, Michael H. Santare, Anette M. Karlsson Nov 2011

Aspects Of Fatigue Failure Mechanisms In Polymer Fuel Cell Membranes, Ahmet Kusoglu, Michael H. Santare, Anette M. Karlsson

Mechanical Engineering Faculty Publications

The swelling-driven fatigue behavior of polymer fuel cell membranes during relative humidity (RH) cycling is investigated. In particular, swelling-induced membrane stresses are obtained from a numerical model simulating fuel cell RH cycle tests, and compared to the lifetimes obtained experimentally from tests conducted in the absence of electrochemical effects. A strong correlation between the lifetimes of the membranes in the actual tests and model results is obtained. In general, higher RH (or swelling) amplitude results in larger stress amplitudes and shorter lifetime, that is, fewer cycles to failure. Tensile stresses are needed for forming local cavities in the membrane, which …

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A Multi-Regulator Sliding Mode Control Strategy For Output-Constrained Systems, Hanz Richter Oct 2011

A Multi-Regulator Sliding Mode Control Strategy For Output-Constrained Systems, Hanz Richter

Mechanical Engineering Faculty Publications

This paper proposes a multi-regulator control scheme for single-input systems, where the setpoint of a regulated output must be changed under the constraint that a set of minimum-phase outputs remain within prescribed bounds. The strategy is based on a max–min selector system frequently used in the aerospace field. The regulators used for the regulated and limited outputs are of the sliding mode type, where the sliding variable is defined as the difference between an output and its allowable limit. The paper establishes overall asymptotic stability, as well as invariance properties leading to limit protection. The design methodology is illustrated with …

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Exploration Of Nde Properties Of Amb Supported Rotors For Structural Damage Detection, Jerzy T. Sawicki, Dmitry L. Storozhev, John D. Lekki Oct 2011

Exploration Of Nde Properties Of Amb Supported Rotors For Structural Damage Detection, Jerzy T. Sawicki, Dmitry L. Storozhev, John D. Lekki

Mechanical Engineering Faculty Publications

Recent advancements in actuator technology, power electronics, sensors, and signal processing have created a rapid development of smart machine technologies for rotating machinery. Ranging from machine condition monitoring and diagnostics to full active control of machine behavior, the integration of electrical and computer systems has produced significant advances in machine performance and reliability. Magnetic bearings are a typical mechatronics product. The hardware is composed of mechanical components combined with electronic elements such as sensors and power amplifiers and an information processing part, usually in the form of a microprocessor. In addition, an increasingly important part is software, which specifies the …

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In Situ Analysis Of Crack Propagation In Polymer Foams, Elio E. Saenz, Leif A. Carlsson, Anette M. Karlsson Aug 2011

In Situ Analysis Of Crack Propagation In Polymer Foams, Elio E. Saenz, Leif A. Carlsson, Anette M. Karlsson

Mechanical Engineering Faculty Publications

This article presents an experimental study on the microscopic mechanisms associated with crack propagation in closed cell polymer foams. A brittle, slightly cross-linked polyvinyl chloride (PVC) foam of density 60 kg/m3 and a ductile thermoplastic polyether sulfone (PES) foam of density 90 kg/m3 were examined. The PVC and PES foams have similar cell size (≈0.7 mm) but the cell edges of the PES foam were much thicker than those in the PVC foam. Overall, it was observed that the elements of both foams fractured in an extensional mode. Crack propagation in the PVC foam was inter-cellular, where agglomerates …

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Polarization Sensitive Near-Complete Reflection From Photonic Crystal Slab In Centered Rectangular Lattice, Simon Padron, Kris Ohlinger, Karen Lozano, Yuankun Lin Jul 2011

Polarization Sensitive Near-Complete Reflection From Photonic Crystal Slab In Centered Rectangular Lattice, Simon Padron, Kris Ohlinger, Karen Lozano, Yuankun Lin

Mechanical Engineering Faculty Publications

In this study, reflective properties have been systematically calculated for two-dimensional photonic crystal slabs in centered rectangular lattices with elliptical patterns for transverse electric polarization along perpendicular x- and y-directions. The slab structures can be geometrically optimized for a near-complete reflection over a broad wavelength range. The reflection from the photonic crystal slabs is polarization selective, allowing a complete reflection for one polarization and complete transmission for the other polarization, which could be useful for a laser cavity mirror without using Brewster windows. The dependence of the reflection on the slab thickness and the structural parameters demonstrates the effect of …

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Artificial Lateral Line Canal For Hydrodynamic Detection, Yingchen Yang, Adrian Klein, Horst Bleckmann Jul 2011

Artificial Lateral Line Canal For Hydrodynamic Detection, Yingchen Yang, Adrian Klein, Horst Bleckmann

Mechanical Engineering Faculty Publications

Fish use their lateral line system to detect minute water motions. The lateral line consists of superficial neuromasts and canal neuromasts. The response properties of canal neuromasts differ from those of superficial ones. Here, we report the design, fabrication, and characterization of an artificial lateral line canal system. The characterization was done under various fluid conditions, including dipolar excitation and turbulent flow. The experimental results with dipole excitation match well with a mathematical model. Canal sensors also demonstrate significantly better noise immunity compared with superficial ones. Canal-type artificial lateral lines may become important for underwater flow sensing.

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Artificial Lateral Line Canal For Hydrodynamic Detection, Yingchen Yang, Adrian Klein, Horst Bleckmann, Chang Liu Jul 2011

Artificial Lateral Line Canal For Hydrodynamic Detection, Yingchen Yang, Adrian Klein, Horst Bleckmann, Chang Liu

Mechanical Engineering Faculty Publications

Fish use their lateral line system to detect minute water motions. The lateral line consists of superficial neuromasts and canal neuromasts. The response properties of canal neuromasts differ from those of superficial ones. Here, we report the design, fabrication, and characterization of an artificial lateral line canal system. The characterization was done under various fluid conditions, including dipolar excitation and turbulent flow. The experimental results with dipole excitation match well with a mathematical model. Canal sensors also demonstrate significantly better noise immunity compared with superficial ones. Canal-type artificial lateral lines may become important for underwater flow sensing.

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On The Opening Of A Class Of Fatigue Cracks Due To Thermo-Mechanical Fatigue Testing Of Thermal Barrier Coatings, M. T. Hernandez, D. Cojocaru, M. Bartsch, Anette M. Karlsson Jul 2011

On The Opening Of A Class Of Fatigue Cracks Due To Thermo-Mechanical Fatigue Testing Of Thermal Barrier Coatings, M. T. Hernandez, D. Cojocaru, M. Bartsch, Anette M. Karlsson

Mechanical Engineering Faculty Publications

The evolution of fatigue cracks observed in thermal barrier coatings (TBCs) subjected to an accelerated test scheme is investigated via numerical simulations. The TBC system consists of a NiCoCrAlY bond coat and partially yttria stabilized zirconia top coat with a thermally grown oxide (TGO) between these two coatings. The cracks of interest evolve in the bond coat parallel and near the interface with the TGO during thermo-mechanical fatigue testing. In their final stage, the cracks lead to partial spallation of the TBC. This study focuses on why the cracks open to their characteristic shape. To this end, finite element simulations …

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Characterization Of Fracture Toughness G (Sub C) Of Pvc And Pes Foams, Elio E. Saenz, Leif A. Carlsson, Anette M. Karlsson May 2011

Characterization Of Fracture Toughness G (Sub C) Of Pvc And Pes Foams, Elio E. Saenz, Leif A. Carlsson, Anette M. Karlsson

Mechanical Engineering Faculty Publications

The fracture behavior of polyvinyl chloride (PVC) and polyethersulfone (PES) foams has been examined using the single-edge notch bend and the double cantilever beam (DCB) tests. PVC foam densities ranging from 45 to 100 kg/m3 and PES foam densities ranging from 60 to 130 kg/m3 were examined. The PVC foams failed in a linear elastic brittle manner, whereas the PES foams displayed much more ductility and substantially larger toughness at a comparable foam density. The cell wall thickness of the PES foams was almost twice the thickness of the PVC foams which may have contributed to the high …

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Synthesis And Characterization Of Poly(Butylene Oxide) Grafted Carbon Nanofibers, Carlos Ramos, Ram Thapa, Karen Lozano, Mircea Chipara, Domingo Ferrer, Jose J. Gutierrez May 2011

Synthesis And Characterization Of Poly(Butylene Oxide) Grafted Carbon Nanofibers, Carlos Ramos, Ram Thapa, Karen Lozano, Mircea Chipara, Domingo Ferrer, Jose J. Gutierrez

Mechanical Engineering Faculty Publications

The grafting of polybutylene oxide onto purified and functionalized carbon nanofibers is reported. Grafting was possible after the insertion of 2-(formyloxy)ethyl 2-bromo-2-methylpropanoate onto the carbon nanofibers. The polymerization of tetrahydrofuran was mediated by copper(I) bromide and 1,1,4,7-pentamethyl diethylenetriamine. The polymer-grafted carbon nanofibers were characterized by Raman spectrsocopy, Transmission Electron Microscopy, and Thermogravimetric Analysis. TEM images of CNF-COOH (A), CNF-PBO (B), completely open tip of CNF-COOH, and coated tip of CNF-PBO (D) are shown in the left panel. The right panel depicts the distribution of bromine (blue), and carbon (red) atoms inside and in the vicinity of CNF-Br (as obtained by …

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Detecting Cracked Rotors Using Auxiliary Harmonic Excitation, Jerzy T. Sawicki, Michael I. Friswell, Zbigniew Kulesza, Adam C. Wroblewski, John D. Lekki Mar 2011

Detecting Cracked Rotors Using Auxiliary Harmonic Excitation, Jerzy T. Sawicki, Michael I. Friswell, Zbigniew Kulesza, Adam C. Wroblewski, John D. Lekki

Mechanical Engineering Faculty Publications

Cracked rotors are not only important from a practical and economic viewpoint, they also exhibit interesting dynamics. This paper investigates the modelling and analysis of machines with breathing cracks, which open and close due to the self-weight of the rotor, producing a parametric excitation. After reviewing the modelling of cracked rotors, the paper analyses the use of auxiliary excitation of the shaft, often implemented using active magnetic bearings to detect cracks. Applying a sinusoidal excitation generates response frequencies that are combinations of the rotor spin speed and excitation frequency. Previously this system was analysed using multiple scales analysis; this paper …

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Mechanical Behavior Of Bio-Inspired Laminated Composites, Liang Cheng, Adam Thomas, James L. Glancey, Anette M. Karlsson Feb 2011

Mechanical Behavior Of Bio-Inspired Laminated Composites, Liang Cheng, Adam Thomas, James L. Glancey, Anette M. Karlsson

Mechanical Engineering Faculty Publications

To investigate if the relative high strength and stiffness of biological composites can be translated into man-made materials, innovative bio-inspired laminated composites with commercial materials (glass epoxy prepreg) were designed and manufactured by incorporating the distinctive helicoidal morphology observed in the exoskeletons of crustaceans. The helicoidal structure is characterized by a stacking sequence consisting of a gradual rotation of each lamina in the multi-layered laminated composites. Variations of the helicoidal structure were designed and produced to address some important issues encountered in the practical composites manufacturing process, including mid-plane symmetry. In addition, composite structures with a general quasi-isotropic configuration were …

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