bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of the Stress-Strain Behaviour of Large-Diameter X100 Linepipe in View of Strain-Based Design Requirements
Authors: Liessem Andreas , Schro¨der Jens , Pant Martin , Knauf Gerhard , Zimmermann Steffen , Stallybrass Charles , Erdelen-Peppler Marion
Published: July 2009

The use of high strength steels is considered as the best economical option to transport large gas volumes under high pressure from remote areas to the market. Exploration of new energy resources located in areas of complex ground and ambient climate imposes strict requirements on pipeline material and design. One of the major research issues in such areas is differential ground movement, which may be associated with large longitudinal straining in addition to plastic circumferential elongation. Hence, common design principles need thorough re-consideration, notably with respect to strain hardening properties of both base metal and girth welds. The present paper addresses several characteristics of axial and circumferential stress-strain behaviour as it is encountered in high-grade UOE line pipe. Two delivery states are taken into account, namely the “as expanded” as well as the “as coated” state. In a first experimental step, the effect of thermal cycle of the anti-corrosion coating process on stress-strain behaviour is simulated subjecting pipe material to temperatures in the range of 180° up to 250° C. In a second experimental step, stress-strain behaviour in both axial and transverse direction is mapped along the pipe production process in order to assess when and to what extent plastic strain capacity is lost during cold forming. The experimental work is complemented by instrumented ring expansion tests and instrumented burst tests. In a third future step, stress-strain information measured in both directions will be analyzed using a theoretical model based on Hill’s plasticity in order to clarify in which way circumferential stress-strain behaviour may impose constraints on strain capacity of axial direction. Within the scope of this paper, first and foremost, underlying principles are outlined and discussed and indications with respect to modelling implications given. Based upon these three sequential investigatory steps, it will be possible to draw conclusions with respect to stress-strain behaviour of parent material and the pipe forming process and to show that unfavourable effects triggered by coating do not show within the structure while they might do in material tests.
Deformation-Based Behavior of X65 Gas Pipeline in Rectangular Concrete Encasement
Authors: Won Jong Hwa , Kim Mi Seung , Kim Moon Kyum
Published: July 2009

The pipelines located in cold region, offshore and under riverbed are exposed and unpredictable loads and these pipelines should be protected by assistant structures. As one manner of protecting river crossing pipelines, a rectangular concrete encasement is generally used in Korea. This paper describes behavior characteristics of underground pipelines encased in rectangular concrete box in terms of deformed radius derived from occurred hoop stress. The solution for contact pressure between steel pipeline and concrete encasement is derived from the equation of Lame’s double walled cylinder. Every FEA model adopted in this study has same pipe diameter (762mm), internal pressure and cover depth. A variable is only the thickness of concrete encasement. This problem is formulated as a shrink-fit cylinder because of the inner steel pipe expanding by internal gas pressure. In order to get a deformed radius, the interface (contact) pressure was calculated, and the local deformed radius was determined based on obtained interface pressure and hoop stress. In this data processing, peculiar ovalized shape was developed in the section of the X65 steel pipeline covered with rectangular concrete encasement. The result in terms of the rate of local diameter change describes that shoulder (±45°, ±135°) part has the largest change rate over 120% and the smallest values occurred at a bottom (±180°). By using the relation of encasement size and deformed diameter, the results make stress design for the double layer pipeline be more precise and effective.
Strain Relief of a Buried Pipeline Due to Slope Movement
Authors: Martens Michael , Kania Richard , Kare Raymond , Topp David , Sander Frank
Published: July 2009

Pipelines constructed through geologically active areas, over time, can experience a significant amount of strain due to slope movement. Eventually may become necessary to strain relief the pipeline to ensure its integrity, which is the removal of the surrounding soil to allow for relaxation of the pipeline. This paper looks at the issue of pipeline strain relief due to gradual slope movement and quantifying the amount of relaxation. A non-contacting electromagnetic tool, the TSC StressProbe, that responds to material strain in ferromagnetic materials and a series of strain gauges were used to take in-situ pipeline strain measurements during the strain relieving excavation.
Towards a Validated Pipeline Dent Integrity Assessment Model
Authors: Bolton Brock , Semiga Vlado , Dinovitzer Aaron , Tiku Sanjay , Alexander Chris
Published: July 2009

Detectable dents in buried pipelines can occur due to a number of potential causes; the pipe resting on rock, third party machinery strike, rock strikes during backfilling. The integrity of a dented pipeline segment is a complex function of a variety of parameters, including pipe geometry, indenter shape, dent depth, indenter support and pressure history at and following indentation. In order to estimate the safe remaining operational life of a dented pipeline, all of these factors must be accounted for in the analysis. The following paper summarizes ongoing efforts to develop a validated pipeline dent integrity assessment model. The model under development makes use of experimental tests to validate a finite element model of the denting and re-rounding process for a variety of dent scenarios (i.e. depths, restraints, indenter sizes). The results of the finite element model are then used in conjunction with the estimated pressure-time history in an integrity assessment procedure to estimate the safe remaining operational life of the pipe segment. The paper presents a discussion of the full scale fatigue tests carried out on dented pipeline segments and the efforts under way to develop and validate a finite element model of the experimental specimens with the goal of estimating the experimental fatigue life.
A 3-Dimensional Continuum ALE Model for Soil-Pipe Interaction
Authors: Fredj Abdelfettah , Dinovitzer Aaron , Zhou Joe
Published: July 2009

Soil-pipe interactions when large ground movements occur are an important consideration in pipeline design, route selection, guide monitoring and reduce the risk of damage or failure. Large ground movement can be caused by slope failures, faulting, landslides and seismic activities. Such conditions induce large deformations of both the soil and pipe. Analyses of such behavior pose a significant challenge to capabilities of standard finite elements as the capability to analyze large deformations is required. This requirement is difficult to meet for Lagrangian-based code. New developments using ALE methods make it possible to determine soil and pipe deformation confidently for large displacements. This paper describes a study performed to investigate the mechanical behavior of a pipeline subjected to large soil movement. A 3D continuum modeling using an ALE (Arbitrary Eulerian Lagrangian) formulation was developed and run using LS-DYNA. The results are compared with published experimental data of large-scale test to verify the numerical analysis method. The analysis is further extended to analyze the soil-pipe interaction under permanent ground deformation such as those associated with surface fault rupture and landslides.
Research on the Critical Buckling Strain Criterion for Pipelines
Authors: Zhang Hua , Zhao Xinwei , Luo Jinheng , Zhang Guangli , Chen Zhixin
Published: July 2009

The local buckling of pipelines is regarded as a kind of failure. The critical buckling strain is an important parameter in strain-based design of pipelines. According to the grey system theory, the factors affecting the critical buckling strain were analyzed and the correlation between these factors and the critical buckling strain was quantitatively measured based on test data. According to the dimension analysis theory, the factors affecting the critical buckling strain were analyzed and the correlation between the factors and a new critical buckling strain equation was proposed based on test data. And some advice was provided for the improvement of critical buckling strain equations. Comparing the results with data from full scale tests, these as-obtained equations could provide a higher precision.
Significance of Splits and Pop-Ins Observed During Fracture Toughness Testing of Line Pipe Steel
Authors: Pisarski Henryk G. , Hammond Ruth , Watt Keith
Published: July 2009

The occurrence of pop-in on the test record of fracture toughness tests and appearance of splits on the fracture surface, coupled with failure to meet Charpy toughness requirements, raised doubts about the fracture integrity of a parent pipe to API 5L X65 for low temperature operation. The cause of pop-in was investigated using fractographic and metallographic methods and additional fracture mechanics testing was conducted using different notch orientations. In addition, fitness-for-service was assessed using a fracture mechanics assessment procedure. It is shown that for typical flaw orientations that might be present, the apparent fracture toughness at pop-in is not representative. Nevertheless, it is shown that for the stress levels considered, the pipeline is tolerant to flaws without risk of fracture initiation at low temperature.
Compositional Aspects of Cellulosic Electrodes Used for Welding Pipelines
Authors: Barbaro Frank J. , Linton Valerie M. , Gamboa Erwin , Fletcher Leigh
Published: July 2009

The mechanical properties and compositional limits of line pipe for all major pipeline projects are subject to stringent project specific specifications and have substantial user input. The standards for welding electrodes do not have the same level of user involvement and permit significant latitude in terms of alloy design despite the fact that it is known the original electrode design can be markedly altered by elemental transfer as a result of changes in welding parameters and also the condition of the electrodes prior to welding. Several commercially available E8010 consumables have been evaluated under simulated field welding conditions. In addition, the influence of welding arc length and electrode conditioning were investigated. Significant variations in microstructure, hardness and Charpy impact toughness were noted and appear to be primarily related to the final chemical composition of the deposited weld metal. The weld metal carbon equivalent values ranged from 0.20 to 0.42 and all consumables contained additions of Ti and B in the flux coating which resulted in significant levels of B in the final deposited weld metal. It is recommended that the appropriate standards relating to the production and performance of cellulosic consumables be addressed to ensure complete disclosure of consumable formulations to the end user.
Sub-Bituminous Coals Fired in Boiler Designed for Bituminous Coals
Authors: Korytnyi Efim , Chudnovsky Boris , Perelman Miron , Saveliev Roman , Talanker Alexander , Bar-Ziv Ezra
Published: July 2009

In the last two decades there has been little capacity added to coal-based power plants. However, much of the existing plants had to comply with the Clean Air Act amendments. Using sub-bituminous coals has become an important solution for emissions compliance due to their unique constituents and combustion characteristics; these coals are often referred to as enviro coals. The considerable advantages of these coals, like Melawan, Adaro or PRB coals, is their low sulfur compared to typical bituminous coals, which makes its burning more economic as scrubbers or other SO2 reduction technologies are not required. Low nitrogen and ash content as well as their high volatile matter are other advantages of these coals. Hence, firing sub-bituminous coals alone or as blends with bituminous coals is deemed economically attractive. Power generation plants were originally designed to operate on a particular bituminous coal. In order to fire sub-bituminous coals or their blends some modifications are required in the firing modes. These modifications may affect boiler reliability and as result to reduction of the power plant availability and hence increasing operation and maintenance cost. In order to prevent such undesirable effects we initiated a study to understand the influence of using sub-bituminous coals on the capacity, limitations of furnace size, heat transfer surfaces, firing systems, pulverizers, fans and airheaters. The present paper discusses issues connected with each of these issues on the combustion system. We also present recommendations for reliable burning of various sub-bituminous coals and their blends in a 575 MW tangentially-fired boiler. For example, we found that firing Indonesian sub-bituminous coals (Adaro and Melawan) considerably reduced NOx (30% reduction) and SOx (reduced to 200 mg/dNm3@6%O2) emissions without post combustion measures. We also tested various blends of sub-bituminous coals with bituminous coals and found positive and negative synergism in these blends with regard to NOx emissions. We used in the present study a series of experiments in a test facility and computational fluid dynamic codes.
Improving Plant Efficiency While Optimizing Water Use in Simple and Combined Cycle Power Plants
Authors: Demakos Peter G.
Published: July 2009

Closed-loop, evaporative cooling systems (Wet Surface Air Coolers) are a cost-effective heat transfer technology (for cooling and condensing) in simple and combined cycle power plants that also optimize use of scarce water resources. In addition to providing lower outlet temperatures and requiring less space and horsepower (HP), the WSAC can use poor quality water as spray makeup.
Mechanical Seal Efficiency Considerations for Pumps in Utilities: Economics of Seals vs. Packing, and Savings With Best Available Seal Flush Arrangements
Authors: Smith Richard , Roddis Alan , Bloch Heinz P.
Published: July 2009

Applicable industrial standards for centrifugal pumps endorse several different sealing options as “best practice.” However, the overall acceptance of best practice techniques seems slow and is linked to the fact that sealing devices account for only a small fraction of the energy consumed by pumps. Yet, regardless of perception, significant energy conservation has been achieved by thoughtful sealing practices, as this paper will show. It will highlight case studies that provide guidance on issues of increasing technical and societal concerns relating to fluid emissions. Special attention will be directed to barrier fluid circulation devices used in dual mechanical seal arrangements as described by API-682 (Ref.1), a Standard widely used in the oil refining and petrochemical industries. The applicability of these ciculation devices to the Power Industry will be explained. Comparisons of three of the most widely used conventional integral flow induction/pumping ring devices will be made and the results of extensive testing presented. The paper and presentation also quantifies the value of advanced sealing technologies for pumps and highlights configurational differences between the newer and the more traditional (older) devices. Without exception, international utilities and power producers know that both energy and maintenance expenditures are affected by availability and reliability considerations relating to power generators and their turbine drivers. But feed water pumps and cooling water issues play their part as well. Consequently, a measure of attention has been given to “other big ticket items”, such as cooling tower losses and the like. However, there is compelling evidence that additional, less prominent or less obvious opportunities exist and that these can no longer be overlooked. Pump sealing falls into that category, although sealing devices and seal cooling account for only a small fraction of the energy consumed by pumps. In can be readily shown that significant energy savings have been achieved by thoughtful sealing practices. The general narrative and the implications conveyed by our case studies give visibility to the issues and provide guidance to the user.
Performance Study on Coal Gasification by High Temperature Air
Authors: Tian Hong , Chen Donglin , Yan Xiaozhong , Liu Liang , Cai Jiuju
Published: July 2009

A kinetics model and an experimental rig for high temperature air coal gasification (HTAG) research were set up. The effects of important operation parameters, such as air temperature and air/coal ratio, on gasification indexes were studied through the kinetics model and gasifier. The results show that: the model can accurately predict the gas composition. And when air temperature increases from 823K to 1073K, carbon conversion increases from 82% to 95%, gasification efficiency increases from 71% to 83%, calorific value and yield of the syngas increase from 7052kJ/m3 and 2.56m3/kg to 7586kJ/m3 and 2.79m3/kg respectively. With air/coal ratio increasing from 1m3/kg to 1.25m3/kg, the syngas yield increases from 2.27m3/kg to 2.82m3/kg, carbon conversion increases from 73% to 94% and gasification efficiency increases from 68% to 82%, but the calorific value changes little. When air/coal ratio is larger than 1.25m3/kg, the combustion zone extends much because of the excessive air and as a result, the calorific value and gasification efficiency decrease a lot. Thus the proper air/coal ratio should be 1.25m3/kg.
Thermoeconomic Analysis of Integrated Systems for Electricity and Hydrogen Production
Authors: Franzoni A. , Galanti L. , Traverso A. , Massardo A. F.
Published: July 2009

This paper describes and compares the results of thermodynamic and economic modelling based on integrating an existing large size steam power plant (ENEL’s Brindisi power plant-660 MWe) with hydrogen production and purification plants. ENEL is one of the main Italian power utility. The high quality of the hydrogen produced would guarantee its usability for distributed generation (e.g. by micro gas turbine, Stirling engine, fuel cell, etc.) and also for public transport (using PEM fuel cells). The proximity of an hydrogen production and purification plant to an existing steam power plant can favour connections in terms of energy requirements exchanges; the integrated system, proposed here, can represent an attractive approach to a flexible hydrogen-electricity co-production. Two different technologies for the syngas production section are considered: the pyrolysis process and direct pressurised gasification. These technologies produce syngas with different characteristics in terms of temperature, pressure and composition: this has a profound effect on the layout of the complete systems proposed in this paper. The model for the pyrolysis process is based on an existing 800 kWt coal- and biomass-fed pyrolysis ENEL’s plant placed in Bastardo (Perugia, Italy): a detailed model of the plant was created. Different coals (Ashland, South Africa, Sulcis) and biomass (Poplar, Mischantus, Wood residuals, Husk) are considered in this study to explore the real potential of mixed-fuels in terms of thermodynamic performances and costs. The results were obtained using WTEMP software, developed by the TPG of the University of Genoa, showing the performance attainable by integrating a real steam power plant with systems for hydrogen production and purification for a novel vision of clean distributed hydrogen generation.
Thermodynamic Analysis and Comparison on Oxy-Fuel Power Generation Process
Authors: Deng Shimin , Hynes Rory
Published: July 2009

In this paper, pressurized oxy-fuel combustion power generation processes are modeled and analyzed based on a 350 MW subcritical reheat boiler associated with a condensing steam turbine. The performance results are obtained. Furthermore, the influences of slurry concentration and coal properties on power plant performance are investigated. An oxy-fuel configuration operating at ambient pressure is studied to compare the performance with pressurized oxy-fuel configuration. Thermodynamic analysis reveals the true potentials of the pressurized oxy-fuel process. Based on the system integration, an improved configuration is proposed in which plant efficiency of pressurized oxy-fuel process is increased by 1.36%.
H2 Cooled Generator Gas Monitoring System Upgrade: More Than a Dryer
Authors: Green Michael L. , McPhearson John F. , Ramirez Blanca A.
Published: July 2009

Hydrogen cooled generators have utilized dryers since 1935 to keep the generator cooling gas dry. The dryer and auxiliary skid of 2008 can do much more and can be an effective tool in managing and monitoring the generator gas system. SIPC (Southern Illinois Power Cooperative) started with the original OEM single tower dryer. Three changes in the new skids are noteworthy. The dual tower dryers we have now are automatic and provide drying continuously including turning gear operation without gas purging or venting. The dryers also continuously provide information on the gas dew point in the generator at operating pressure as well as documenting the dryer performance. The newest skid also includes a water discharge monitoring system that measures the water removed from the generator. This information has been very helpful in detecting potential problems or changes in the water infiltration rates which can be one of the earliest indicators of a serious problem. The last significant addition to the dryer skid is the purity monitoring system, which is scheduled to be installed shortly. It is fully integrated into the dryer skid and information is supplied on the operator interface of the control panel. All the pertinent information including alarms, dew points, water discharge and purity is available to the control room and can be trended on the plant DCS system. The plant experiences and benefits of the new drying skid will be fully detailed in this presentation.
A Review and Cost Comparison of Current Idle-Reduction Technology
Authors: Lust Ethan E. , Horton W. Travis , Radermacher Reinhard
Published: July 2009

As of January 1, 2008 idling of the main vehicle engine for the purpose of powering sleeper cabin amenities by any truck over 10,000 lbs (4,500 kg) within the borders of the state of California is prohibited unless strict emissions standards are met. Following California’s lead, a number of other states have also passed legislation restricting idling time and emissions. In anticipation of tighter idling legislation and rising fuel prices, idle-reduction technologies are garnering an increasing market share. These include auxiliary battery-electric power systems, primary vehicle battery systems, truck-stop electrification, diesel-fueled auxiliary power systems, and fuel-fired heaters. In this paper the current state of anti-idling technology is reviewed. Off the shelf systems are compared in an attempt to discern which is more advantageous in terms of factors such as lifetime cost, lifetime cost per hour, and payback period.
Increased Revenue Generation of Existing Assets Through a Systematic Approach to Improve Availability
Authors: Munisteri Anthony J.
Published: July 2009

Owners of existing generating units can increase revenue generation through the utilization of a systematic approach to improve availability, reduce unplanned outages and maintenance costs as well as improve system design. This approach yields a reduced unit cost of operation through higher dispatch rates and capacity factors. It is beneficial to generating units in both regulated and competitive markets. An underpinning of this approach includes benchmarking, which identifies whether maintenance spend and unit availability tracks that of similar populations. Benchmarking also uncovers unbalanced application of maintenance resources based upon historical and projected future equipment failure rates and their impact on EFOR and economic availability. This data is enhanced through a detailed FMECA, which pinpoints areas of focused investment based upon an equipment’s impact due to failure. Knowledge gained through benchmarking, FMECA and best practices is applied in adjusting maintenance strategies. The design of the generating unit is evaluated to determine if there are single points of failure or other similar constraints that contribute to increased outages or derates. Additionally, operating history is reviewed against original design criteria and then overlaid onto failure rates and equipment histories to identify operational changes that can improve availability. This paper discusses the process successfully utilized recently at generating facilities in the US.
Numerical Simulation of Freight Railcar Dynamic Clearance Envelopes
Authors: Shust William , Pasta Corey
Published: July 2009

The operating dynamic clearance envelope has historically been a sum of estimated dimensional tolerances, sometimes even called “black magic” [1]. These tolerances exist by design within the car and the track, as well as between the wheel flanges and the rail gage face. Field observations of operating clearance have augmented these estimates. Recently a review of such expectations was desired as related to wide and/or tall payloads, with particular respect to train speed and track roughness. This project reexamines the factors affecting car body envelopes, including track curvature and elevation, and car parameters such as length, center of gravity (CG), and side bearing type. A particular goal of this study was to gain a rough understanding of the behavior expected relative to wide loads in the speed range of 30–50 mph. Both static analyses and dynamic negotiation of typical revenue track have been predicted. The NUCARS® multibody simulation software has been used to examine the influence of operating speed and FRA track class on the dynamic envelope. A summary of results is presented along with a discussion of general guidelines and additional considerations.
Development and Fabrication of State-of-the-Art End Structures for Budd M1 Cars
Authors: Stringfellow Richard , Paetsch Christopher , Amar Gabriel
Published: July 2009

The Volpe Center and the Federal Railroad Administration are engaged in active research aimed at improving rail vehicle crashworthiness. One component of this research is focused on improving the performance of passenger train cab cars during collisions with heavy objects at grade crossings. New standards have been approved by the American Public Transportation Association that increase the strength requirements for cab car end structures and impose further requirements on their ability to absorb energy during a collision. The FRA has issued a notice of proposed rulemaking (NPRM) to include these new standards in 49CFR238.211. These standards include requirements for demonstration of energy absorption through either quasi-static or dynamic tests. The intent of each test method is to demonstrate a minimum level of energy absorption—120,000 ft-lbs for a corner post load and 135,000 ft-lbs for a collision post load—while limiting occupied volume intrusion to less than 10 inches. To aid in the development of these new standards, the FRA and Volpe Center are conducting a set of three tests: quasi-static loading of both the collision and corner posts, and dynamic loading of the collision post only. (A dynamic test of the corner post was conducted as part of an earlier program). These tests were developed to illustrate testing methodologies and to demonstrate the feasibility of the new energy absorption and large deformation requirements. In+ each test, the post is loaded 30 inches above the underframe by a proxy object that is 36-inches wide, with a 48-inch diameter cylindrical face. In support of this testing program, the research reported here focused on the design and fabrication of end frames suitable for retrofitting onto the cab end of a Budd M1 cab car. The design of an end frame for retrofit onto the cab end of a Budd Pioneer cab car was modified to account for differences between the two car designs. In addition, reinforcements to the M1 car body and connections from the end frame to the car body were designed and fabricated. An FEA model of the end frame retrofit onto the M1 cab car was developed based upon the detailed design. A series of linear and nonlinear static, quasi-static, and dynamic FEAs were performed to evaluate the performance of the design. Preliminary analyses revealed the need for a few minor modifications to the connections in order to meet design requirements; these were incorporated into the final design for manufacture. Components for the end frame, connections between the end frame and the car body, and reinforcements to the car body were fabricated based on detailed design drawings and then assembled and connected to the reinforced M1 Car, from which the original end frame had been cut off. A successful dynamic test was completed in April, 2008; quasi-static tests are scheduled for summer 2008. The results of FEA model predictions are compared with the results of the dynamic test.
Design, Fabrication and Mechanical Characterization of Pyramidal Periodic Cellular Metal/Polyurethane Foam Hybrid Materials
Authors: Campbell J. E. , Hibbard G. D. , Naguib H. E.
Published: July 2009

A new type of hybrid material was designed and fabricated by reinforcing periodic cellular metals (PCMs) with rigid polyurethane (PU) foams. A pyramidal PCM geometry and various densities of two-phase rigid polyurethane foam were used to fabricate three different hybrid materials. These novel hybrid materials may find useful application as cores in sandwich structures. By increasing the density of the polyurethane foam used in the PCM/PU foam hybrids, the stiffness of the hybrid increased allowing the stiffness to be tailored for a specific application. Furthermore, the strength of the hybrids was greater than that of the PCM or foam alone, and in most configurations the strength was greater than the sum of the strength of the PCM and the polyurethane foam. Next, the resilience of the hybrids was greater than that of the PCM or foam alone and was also greater than the sum of the resilience of the PCM and foam. Finally, the impact energy at which surface failure would occur was greater in the hybrid samples than the foams or the PCM and was found to increase with increasing foam density.
Fully-Coupled Model for 3-D Induction and Strain of Galfenol With Geometry Effects and Applied Currents
Authors: Evans Phillip , Dapino Marcelo
Published: July 2009

A fully-coupled and 3-D model for induction and strain of cubic magnetostrictive materials is presented which incorporates geometry dependent demagnetizing fields, current induced fields, and stress dependent permeability. Maxwell’s equations are coupled with a nonlinear constitutive model derived through thermodynamics. Discretization of the nonlinear problem with a known reference configuration yields a piecewise linear model ideal for transducer design.
Micromechanics Modeling of the Nonlinear Behavior of Electrostrictive Multiphase Composites
Authors: Tang Tian , Yu Wenbin
Published: July 2009

The micromechanics modeling of the nonlinear behavior of the electrostrictive multiphase composites is developed using an incremental formulation based on the variational asymptotic method for unit cell homogenization (VAMUCH), a recently developed micromechanics modeling scheme. The microstructure of composites is assumed to be periodic. Taking advantage of the small size of the microstructure, we formulate a variational statement of energy change of the unit cell through an asymptotic analysis of the functional by invoking only two essential assumptions within the concept of micromechanics. Finally, the expression of the effective instantaneous tangential electromechanical matrix of the composites are established. Several numerical examples will be used to demonstrate the capability of the present theory.
Performance Analysis of Magnetorheological Energy Absorbers Under Impact Conditions
Authors: Mao Min , Hu Wei , Choi Young-Tai , Wereley Norman M. , Browne Alan L. , Ulicny John
Published: July 2009

Magnetorheological energy absorbers (MREAs) can provide adaptive vibration and shock mitigation capabilities to adapt to varying payloads, vibration spectra, and shock pulses, as well as other environmental factors. To effectively utilize these adaptive capabilities, the dynamic range (defined as the ratio of the force at maximum field to the force in the absence of field) or turn-up ratio is a key issue. Previous studies found that the dynamic range of a MREA significantly degraded at velocities even as low as nominally 6 m/s. To improve understanding of MREA behavior and to enable effective MREA design, which implies maintaining sufficient dynamic range over its design speeds range, this study focuses on the design, fabrication, testing, and transient impact analysis of a MREA for which the primary design objective was a dynamic range, D≥2, for nominal impact speeds of up to 6.75 m/s. The MREA was tested using the drop tower facility at GM R&D Center under nominal drop speeds of up to 6 m/s. The drop test experimental results showed that the MREA achieved a dynamic range of ≥2 for nominal speeds up to 6 m/s. However, the design analysis, based primarily on a laminar Bingham-plastic model (Re < 2300) failed to properly account for passive viscous losses for drop speeds above 2 m/s. Suggestions for improving the design analysis are described. To accurately predict the transient MREA force response behavior in this impact speed range, a hydromechanical model was developed and experimentally validated using results from the drop tests for nominal speeds up to 6 m/s. It was concluded that: 1) maintaining a low Reynolds number is essential to achieve a useful dynamic range, where in our case, a Re<850 led to a predicted dynamic range of D≥2; and 2) the hydromechanical analysis is a useful and accurate tool for predicting this MREA transient force behavior for these drop test data.
Multifunctional Power Structures and Related Thermal Issues
Authors: Foster James A. , Roberts Samuel C. , Aglietti Guglielmo S.
Published: July 2009

Multifunctional spacecraft power structures are an incorporation of energy storage and generation into structures on a spacecraft. For the mass and volume saving benefits to be realised, the technology must be shown to be viable throughout the spacecraft’s lifetime. Firstly, commercially available batteries where built into a structural panel and tested to determine the battery’s capability to withstand the manufacturing cycle and the effect upon the mechanical characteristics of the panel. Secondly, a mathematical model was created to determine the temperatures a battery would experience in various earth orbits. It was found that spacecraft in most low earth orbits will require thermal control and that the addition of a phase change material is a feasible control solution.
A Modified Micromechanical Model of Ionic Polymer-Metal Composite Actuation
Authors: Davidson J. D. , Goulbourne N. C.
Published: July 2009

Recent ionic polymer-metal composite (IPMC) research efforts have been directed at developing optimized electrode configurations, using novel solvents and cations, and modeling the actuation response. A micromechanical model of IPMC actuation has been developed by Nemat-Nasser [1]. In this work a similar approach is taken to model the electrochemomechanical transduction mechanisms in IPMC’s, specifically IPMC’s with ionic liquid as the solvent. An analysis of the electrostatic interactions, which are dominant in determining actuation response, is conducted in order to gain further insight into the mechanisms behind actuation. The ultimate goal of this research is to model the underlying mechanisms of IPMC actuation in order to direct the development of new transducers consisting of novel polymers and solvents. Changes to the actuation model are also implemented to describe free air actuation and to account for the finite volume of the mobile cations. Results are presented from the different calculations and the implications are discussed.
Stress Relief in Contact-Aided Cellular Compliant Mechanisms
Authors: Mehta Vipul , Frecker Mary , Lesieutre George
Published: July 2009

Cellular structures with an internal contact-mechanism are investigated. These contact-aided compliant mechanisms are shown to reduce the local tensile stresses, thereby providing additional global strain before yielding or fracture failure compared to honeycomb or auxetic cellular structures. An analytical model for such structures is developed and it is validated using FEA simulations. Two different materials are considered for comparison. More than 100% improvement in global strain capability is possible using the contact. A high-strain morphing aircraft skin is examined as an application of these mechanisms. The contact-aided cellular compliant mechanisms are more advantageous in terms of both the structural mass as well as the global strain compared to a non-contact design. In the application considered the stress-relief mechanism increased the global strain capability by as high as 37%.
Mechanical and Acoustic Performance of Compression Molded Open Cell Polypropylene Foams
Authors: McRae Joe D. , Naguib Hani E. , Atalla Noureddine
Published: July 2009

The mechanical and acoustic performance of open cell polypropylene (PP) foam has been studied in this paper. The particulate leaching method was used to fabricate the open cell PP samples. Foaming parameters such as salt size and salt/polymer mass ratio were controlled to produce samples with different open cell morphologies. The study analyzes the effects cell size, cell density, and relative density have on mechanical and acoustic performance. Mechanical testing was conducted to quantify stiffness and strength of the open cell PP foams. Optimal cellular morphologies for acoustic absorption and mechanical performance were identified.
Numerically Implemented Constitutive Model for SMA Applications Experiencing General Loads Resulting in Plastic Deformation and Large Rotations
Authors: Hartl Darren , Mooney Jesse , Lagoudas Dimitris
Published: July 2009

As active structures become more prominent, the use of more capable numerical modeling has gained importance as an aid to the design process. The need to accurately account for the response of Shape Memory Alloys (SMAs) under complex loading paths has become increasingly important. Such paths are general in a stress-temperature space and may induce irreversible deformation (plasticity). In addition, the structural utilization of active SMA components often includes large deformations, specifically large rotations. This is especially important in beam bending and torsional applications. This work proposes a new method for implementing a phenomenological SMA model originally formulated using small strains into a numerical framework which preserves objectivity given large rigid body rotations. The implementation is shown to be straightforward, and example analyses are performed which demonstrate the usefulness of this capability. An extension of the model to include the generation of plastic strains is also discussed. Alterations to the numerical algorithms are addressed which allow the analysis of simultaneous transformation and yielding. Additional analyses are performed on structural members undergoing transformation and yielding while at the same time moving through large rotations.
Magneto-Mechanical Finite Element Analysis of Magnetic Shape Memory Alloys With Body Force and Body Couple
Authors: Lagoudas Dimitris C. , Kiefer Bjoern , Haldar Krishnendu
Published: July 2009

This work describes the coupling between the magnetostatic and mechanical problems. The aim is to investigate the influence of magnetic body force and magnetic body couple on the equilibrium equations. The magnetic body force and couple are computationally evaluated using finite element analysis over the domain of a magnetic shape memory alloy (MSMA) specimen with rectangular cross-section, subjected to applied magnetic and mechanical boundary conditions. The analysis presented in this paper studies the non uniform distribution of magnetic body force and body couple in the specimen and their impact on the Cauchy stress distribution.
Development of a Simple Morphing Wing Using Elastomeric Composites as Skins and Actuators
Authors: Peel Larry D. , Mejia James , Narvaez Ben , Thompson Kyle , Lingala Madhuri
Published: July 2009

Morphing wings are desired for their ability to reduce drag, change flight characteristics, and perhaps reduce weight by eliminating flap / aileron mechanisms. Development of two generations of a student morphing wing project is documented. The second wing was further developed by Peel. The work shows how a relatively low cost but realistic morphing wing test-bed can be fabricated. Wing skin, actuator, and actuator attachment development are discussed, as well as possible auxetic skin behavior. Aerodynamic characterization of the wing will be discussed in another paper. A very simple morphing wing was fabricated in phase one. The nose was able to elastically camber down ∼ 25° and the tail 20°. Actuation was provided by three pneumatic “Rubber Muscle Actuators” (RMA) that produce high contractive forces. Upper and lower wing skins were fabricated from carbon fiber / polyurethane elastomer laminates. Lower skin buckling, actuator air leaks and actuator attachment problems were resolved in the second phase. A finite element model of the generation II wing was developed and is being used to refine/ explore the morphing wing test-bed. The second generation wing fabrication methodology shows smooth elastic cambering and no buckling or waviness in the skins. The nose cambered down 23° and the tail cambered down to 15°. Improved leak-free biomimetic actuators and attach points now include no metal parts, have higher actuation forces due to new braided sheaths and functionally gradient matrix properties.
Magnetorheological Energy Absorbers Employing a Valve Filled With Porous Media
Authors: Robinson Ryan , Hu Wei , Wereley Norman M.
Published: July 2009

The effects of porous media selection on the performance of a porous-valve-based magnetorheological (MR) damper are evaluated. Important media parameters affecting the damper performance, i.e. porosity and morphology (shape), are identified using flow analysis. The relationship between the controllable force of the damper and the porous valve characteristics is studied for three types of porous media. Equivalent damping is determined, and damping performance is compared. Effects of piston-valve area ratio on damper performance are also evaluated. A nonlinear hysteretic biviscous model is applied to the damper and the experimental results are compared with predicted results.
Development and Validation of a Bidirectional Magneto-Mechanical Coupled Actuator Model
Authors: Graham Frank C. , Mudivarthi Chaitanya , Datta Supratik , Flatau Alison B.
Published: July 2009

The bidirectionally coupled magnetoelastic model (BCMEM) developed by [1] has been modified to include electric currents in its magnetic finite element formulation. This enables the model to capture the magnetoelastic behavior of magnetostrictive materials subjected to elastic stresses and magnetic fields applied not only by permanent magnets but also by current carrying coils used often in actuator applications. This model was implemented by combining COMSOL Multiphysics 3.4 (Finite Element Modeling software) with an energy-based non-linear magnetomechanical constitutive model. The coupling variables are magnetostriction and magnetic permeability that are dependent on both magnetic (magnetic flux density) and mechanical (stress) properties. In this research, the BCMEM was used to simulate actuator load lines for a magnetostrictive Fe84Ga16 alloy, which were then compared to experimental data [2]. Also, the ability of the model to capture the presence of the ΔE effect in Galfenol was demonstrated using the BCMEM. Finally, the use of the BCMEM to as a tool for transducer design optimization is demonstrated by using the model to visualize the influence of different magnetic circuit designs on transducer performance.
Experimental Investigation of Galfenol Elastic Properties and Auxetic Behavior
Authors: Schurter Holly M. , Flatau Alison B. , Petculescu Gabriela , Wun-Fogle Marilyn
Published: July 2009

Iron-gallium alloys (known as Galfenol) are one of only a few metal alloys known to exhibit large auxetic or negative Poisson’s ratio behavior. The mechanical properties of Galfenol, including the auxeticity, are strongly dependent on the composition of the alloy. This research seeks to measure the elastic properties of Galfenol through a range of practical compositions in order to create a database as well as present trends in the elastic properties. This is achieved through tensile testing of single-crystal Galfenol dog-bone-shaped specimens and through Resonant Ultrasound Spectroscopy (RUS) of small parallelepiped samples. The effects of heat treatment were also studied. This project will enable future researchers to refer to the elastic properties of the alloy measured using two different techniques, as well as enable them to select the alloy with optimum elastic properties for their applications.
Analysis of Clustering and Interphase Region Effects on the Electrical Conductivity of Carbon Nanotube-Polymer Nanocomposites via Computational Micromechanics
Authors: Seidel Gary D. , Boehringer Kelli L. , Lagoudas Dimitris C.
Published: July 2009

In the present work, computational micromechanics techniques are applied towards predicting the effective electrical conductivities of polymer nanocomposites containing aligned bundles of SWCNTs at wide range of volume fractions. Periodic arrangements of well-dispersed and clustered/bundled SWCNTs are studied using the commercially available finite element software COMSOL Multiphysics 3.4. The volume averaged electric field and electric flux obtained are used to calculate the effective electrical conductivity of nanocomposites in both cases, therefore indicating the influence of clustering on the effective electrical conductivity. In addition, the influence of the presence of an interphase region on the effective electrical conductivity is considered in a parametric study in terms of both interphase thickness and conductivity for both the well dispersed case and for the clustered arrangements. Comparing the well-dispersed case with an interphase layer to the same arrangement without the interphase layer allows for the assessment of the influence of the interphase layer on the effective electrical conductivities, while similar comparisons for the clustered arrangements yield information about the combined effects of clustering and interphase regions. Initial results indicate that there is very little influence of the interphase layer on the effective conductivity prior to what is identified as the interphase percolation concentration, and that there is an appreciable combined effect of clustering in the presence of interphase regions which leads to increases in conductivity larger than the sum of the two effects independently.