bluuebunny/crossref_metadata_2025 huggingface dataset:
Fatigue Pre-Cracking Curved Wide Plates in Bending
Authors: Richards Mark D. , Weeks Timothy S. , McColskey J. David , Wang Bo , Wang Yong-Yi
Published: April 2011

Curved wide plate (CWP) testing in tension, on API 5L X100 pipes of 36-inch (916-mm) diameter and 0.75-inch (19-mm) wall thickness, has been initiated in support of strain-based design using high strength steel for oil and gas pipeline applications. The CWP tests are being used to optimize and validate welding procedures and to determine the defect tolerance within the girth welds. A traditional pre-requisite for fracture mechanics testing is a final extension of a crack via fatigue pre-cracking to produce a representative flaw. A method of fatigue pre-cracking CWP specimens for final notch preparation in bending was developed to meet ASTM guidelines for fracture mechanics testing. Fatigue pre-cracking for the present specimen geometry was possible in bending due to lower requisite force capacity equipment which allowed for greater cyclic loading frequencies. In order to achieve sufficient stress levels for fatigue crack growth in the curved plate, a stress field analysis was performed to optimize the loading support configuration in four-point bending. In addition to the stress field analysis, a 3-D finite element model of the CWP specimen was generated to analyze the notched CWP specimen in four-point bending. Finite element analysis (FEA) results and experimental data were used to confirm the hypothesis that, under the proposed loading arrangement, the closed-form solutions for stress-intensity (K) of flat plates in bending can be used to approximate the K for CWP specimens in bending. Validation of a solution for stress-intensity factor subsequently allowed the determination of force amplitude levels for fatigue crack growth. Force and crack mouth opening displacement (CMOD) data were analyzed to correlate compliance with crack length measurements. From experimental results, a method was developed that enable the repeatable and well characterized extension of surface flaws by fatigue pre-cracking in curved wide plate specimens in bending.
Construction of the X100 Operational Trial Pipeline at Spadeadam, Cumbria, UK
Authors: Millwood N. A. , Johnson J. , Hudson M. , Armstrong K.
Published: April 2011

As part of an ongoing pipeline technology programme for BP Alaska, a 0.8 km, 48-inch diameter, X100 demonstration pipeline was constructed and operated for a period of two years. The pipeline was constructed using largely conventional techniques, with the exception of the mainline welding process, where a high productivity system was used. Mainline welding on X100 pipe was accomplished using a single tandem wire GMAW system offered by Serimax. Tie-in and fabrication welding was accomplished using vertical-down STT root pass and a vertical-up mechanised FCAW system. This paper discusses key features of the welding specification, presents key weld qualification results, reflects on the field welding experience and makes some general remarks about the construction experience.
Three-Dimensional Response of Buried Pipelines Subjected to Large Soil Deformation Effects: Part I—3D Continuum Modeling Using ALE and SPH Formulations
Authors: Fredj Abdelfettah , Dinovitzer Aaron
Published: April 2011

Understanding the effect of soil-pipeline interactions in the event of large ground movement is an important consideration for the pipeline designer. Both experimental investigation and computational analyses play significant roles in soil-pipeline research. As part of this effort, a framework incorporating continuum soil mechanics and advanced finite element approach (i.e., ALE and SPH method) for modeling soil pipe interaction was constructed. The overall objective of this work is to develop, validate and apply 3D continuum modeling techniques to assess the performance of pipeline systems subjected to large soil displacements. The numerical models produced may subsequently be used to predict the wrinkle formation and post formation behavior of the pipeline considering the effect of the soil confinement. The aim is to develop a comprehensive wrinkle integrity assessment process. This is the first paper (Part I) in a series of two papers. In this paper a three-dimensional Continuum models using MM-ALE (Multi-material Arbitrary Eulerian Lagrangian) and SPH (smooth particle hydrodynamics) approaches are developed and employed using LS-DYNA. The results are compared with published experimental data of large-scale tests to verify the numerical analysis methods. In the second paper (Part II) the effects of soil restraint on the response of the pipe/soil systems (e.g., pipeline wrinkle and buckle, strain demand) are discussed.
Research Progress on Friction Stir Welding of Pipeline Steels
Authors: Kumar A. , Fairchild D. P. , Macia M. L. , Anderson T. D. , Jin H. W. , Ayer R. , Ozekcin A.
Published: April 2011

Friction Stir Welding (FSW) has been widely commercialized to join aluminum alloys, but is yet to be broadly applied to structural steels. The primary difficulty in welding steels relates to severe loads and temperatures experienced at the interface between the FSW tool and the base material. These conditions are challenging even for the most advanced and expensive tool materials. However, within the last five years, tool advancements have begun to enable FSW of steels. Polycrystalline boron nitride (PCBN), tungsten-rhenium alloys, and mixtures thereof appear to be capable of producing sound welds in steel. This paper describes the results of a continuing study on the FSW of pipeline steels. Pipe grades from API X65 to X120 were subjected to FSW. Strength and toughness measurements using the crack tip opening displacement test were performed. The weld microstructure was evaluated using optical, scanning electron, and transmission electron microscopy. A computational fluid dynamics model was developed to better understand the effect of process parameters on thermal cycles, strain rates and strain experienced by material in the weld stir zone. The results indicate that the microstructure and properties of the welds have little dependence on the tool material, while significant variations in properties were observed between steels produced by different manufacturers. In general, obtaining high levels of toughness on par with gas metal arc mechanized girth welds appears difficult when using the FSW process. The results emphasize the need for a better understanding on the role of process parameters on microstructural evolution and weld quality during FSW of pipeline steels. As a full-scale demonstration of FSW on pipeline steels, several circumferential girth welds were produced in 762 mm (30 inch) diameter X80 pipe. The results of these efforts are discussed.
Root Causes for Failures in Flattening Test in High Frequency Induction Welded Steel Pipe Mill
Authors: Babakri Khalid Ali
Published: April 2011

The aim of the flattening test in a High Frequency Induction Welded (HFIW) steel pipe mill is to test the weld integrity. Failures in the flattening test may cause rejection of tested pipe and additional costs as result of retesting the other pipes from the same coil, scrapping and cutting the tested material, segregating and transporting of pipes required for flattening retest, and delaying the release of material. This paper presents the root causes for failures in the flattening test due to inadequate process control. The paper also discusses the failures in the flattening test associated with the severity and lack of clarity of the acceptance criteria in some of the pipeline international specifications. The targeted specifications are API 5L and ISO 3183. Specifically, the paper proposes, based on practical experience, changes of the acceptance criteria in the international specifications related to the first step of flattening test which is the test of weld ductility.
Evaluation of Composite Sleeve Repair in Kinked Dent in Natural Gas Pipeline
Authors: Souza Filho Byron G. , Frota Cristiane S. , Matsuo Fabio M. , Petry Gabriel , Schultz Neto Walter
Published: April 2011

The Code ASME B31.8 is well established as a safe Code for all life phases of Natural Gas Transmission and distribution pipelines, like: design, construction, operation and maintenance. In the case of mechanical damage, such as dents, the Code contains maintenance provisions for field acceptance or repair of dent and dents combined with other defects consisting of stresses raisers such as gouges, arc burns and welds. Dents, sometimes, are found in sensitive areas due to urban sprawl upon pipeline right-of-way or environmental concerns. In addition dents shapes, sometimes, are not smooth or plain like the code defines as criteria of acceptance. This paper presents and describes some full scale pipeline test’s results in samples containing kinked dents, reproduced in laboratory, in recent vintage pipelines. This type of defect is usually caused by rock puncturing, unauthorized excavation or soil-pipeline interaction in an inservice pipeline. The damaged pipeline samples were repaired by composite reinforcing sleeves before being submitted to the tests. The dimensions of the defects were detected and sized by Geometric and MFL PIG, and compared with field measurements. The studies were conducted concerning internal pressure fluctuations, which can be covered by fluctuations in the principal stresses in the pipe wall. The analyses also considered the plastic strain around the damaged area and effects of rerounding or spring back in case of the defects were generated in conditions of normal operation or in condition of out of service pipeline.
Experimental Strain Measurements on Large Diameter Mitered Pipe Joints
Authors: Feier Ioan I. , Leis Brian N. , Zhu Xian-Kui , Stonesifer Randall B. , Stavrakas John S. , D’Eletto Daniel
Published: April 2011

Historic pipeline construction utilized miter joints to enable small directional changes in pipeline routing, and this legacy construction remains in today’s pipelines. Current codes and regulations impose a limit on the maximum miter angle to less than three degrees of the total pipeline direction change, for pipeline operating with pressure over 30-percent SMYS (Specified Minimum Yield Stress). In anticipation of an operational pressure increase, an experimental and simulation effort was undertaken recently to determine the stress amplification due to miters in 30-inch diameter, 0.5-inch thick gas transmission pipelines. Experiments were conducted on six miter joints ranging in miter angle from 0° to 8° degrees of total pipeline direction change. Three of the miter joints were removed from the field (1950’s original installation), while the remaining three were specifically fabricated for the testing. All the miters considered were X42 pipeline steel. The miter pipe joint specimens were tested with pure pressurization, pure bending, and combined pressure and bending using a custom designed loading apparatus. Hoop and axial strains were measured using internally and externally mounted strain gauges. Pressure, as well as four point bending loads and deflections were recorded. One 3.8° field miter specimen was tested to burst. Experimental data, analytical solutions, and finite element results are compared at the miter joint section for the three loading cases. The study is limited to pipe radius to thickness ratio values of 30, and hence the results presented in this study are useful near this value. Results showed that miter joints increase stresses in the vicinity of the miter joint for pressure and/or bending loads. The peak stresses are on the exterior at the intrados. The pressure induced peak stress values increase proportional to the miter angle, and bending further increases the miter stress magnitudes. The ovalization effects significantly compromise the use of linear superposition of pressure and bending stresses even though material behavior remains elastic. Findings from this study demonstrate that in-situ miters on the pipeline in question do not compromise the integrity of the line, and stress additions for small angles over three degrees are comparable to stress risers occurring from normal pipeline features. The results of this work are important for performing structural integrity assessments and for making informed regulatory decisions for mitered pipeline operation.
Analysis of Bacterial Kill Versus Corrosion From Use of Common Oilfield Biocides
Authors: Keasler Vic , Bennett Brian , McGinley Heather
Published: April 2011

Bacterial proliferation is a severe problem in many oilfield systems, especially in aging systems with high water cuts. Depending on the types of microorganisms present, they can cause microbiologically influenced corrosion (MIC) or biofouling of filters, membranes, and metal surfaces. Common oilfield bacteria include sulfate-reducing bacteria (SRB) that can generate hydrogen sulfide (H2S) and iron sulfide (FeS) as a by-product (iron sulfide can occur in different structural forms), acid producing bacteria that can secrete organic acids that lower the pH within the microenvironment of a biofilm, as well as general heterotrophic bacteria that are often important in biofilm formation and maintenance, amongst others. To prevent corrosion or biofouling caused by these organisms, biocides are commonly added to the production fluids. Some concern has arisen that common oilfield biocides may be inherently corrosive at high end use concentrations and could cause general corrosion in the assets they are protecting from MIC. Accordingly, it is important to understand the risk of MIC, souring, and biofouling versus general corrosion from the biocides themselves. To examine the killing efficiency of oilfield biocides versus their corrosive potential, laboratory work was undertaken with five biocide products including: Tetrakis (hydroxymethyl) phosphonium sulfate (THPS), glutaraldehyde, glutaraldehyde / alkyldimethylbenzyl ammonium chloride (ADBAC) mixture, 5-chloro-2-methyl-4-isothiazolin-3-one/2-methyl-4-isothiazolin-3-one (CMIT/MIT), and a cocodiamine (quaternary amine). Each biocide was evaluated at four different concentrations ranging from 10–100,000 ppm of product. Killing efficiency was determined via bacterial kill studies, while wheelbox and bubble cell testing examined corrosion rates. Corrosion rates varied quite substantially from one biocide to the next, especially at high concentrations. Some biocides were found to be only mildly corrosive even at high dosages, while other biocides were much more corrosive at high concentrations. In general, it was observed that biocide corrosivity is directly related to the dosage of the biocide, with higher dosages correlating with higher corrosion rates. On the other hand, biocides were shown to be effective at killing common oilfield bacteria at relatively low dosages. This data suggests that biocides can be effective at killing bacteria at concentrations that do not cause significant amounts of general corrosion. Additionally, the common practice of batch treating biocides minimizes contact time between the biocide and the metal surface, which is in turn expected to minimize any corrosion that would otherwise be attributed to the biocides themselves. Taken together, this data would suggest that the benefit of biocide treatment to prevent MIC and biofouling substantially outweighs any potentially negative impact on corrosion.
South Arm Crossing Project: Navigating Through the Regulatory Environment and Stakeholder Communication in the Lower Fraser River Basin
Authors: MacKinnon Matthew T. , Dane Chris , Hennessy Amy
Published: April 2011

HDD projects in the Lower Mainland of British Columbia face a myriad of regulatory policies and community and stakeholder interests due to concerns associated with land use, zoning requirements, and sensitive archaeological, agricultural and environmental areas. As a result, the Terasen Gas Incorporated (TGI) Fraser River South Arm Crossing Upgrade Project aka “the South Arm Crossing” was subject to review by several regulatory agencies and local municipalities and underscores the importance of effective communication and collaboration with regulators, the community, and stakeholders. This paper provides an overview of the regulatory authorizations and permitting requirements of the South Arm Crossing and identifies key stakeholders affected by the project. The South Arm Crossing reveals the importance of effective communication with regulatory agencies, land owners, businesses, and communities in the early stages of a project. Furthermore, agency and stakeholder cooperation can be enhanced with increased responsiveness to regulatory issues, and by incorporating stakeholder concerns into the project’s development. The lessons learned from the South Arm Crossing will enhance the pipeline community’s understanding of the federal and provincial regulations required to complete HDD projects in the Lower Mainland and provide strategies for developing communications and relationships with community members and stakeholders.
The New CSA Standard for Leak Detection
Authors: Scott Don , Pietsch Ulli
Published: April 2011

Standards and Recommended Practices require periodic updating so they represent current technology and industry practices. Canadian Standards Association (CSA) Z662 “Oil and Gas Pipeline Systems” contains Annex E that covers software-based leak detection for liquid hydrocarbon pipelines. The CSA Technical Committee determined that is was time to update Annex E. A Task Force of industry experts and regulators met over a period of 18 month to draft a new Annex E. This paper outlines some of the significant features of the new Annex and where possible does a comparison with the similar section in American Petroleum Institute’s API 1130 which covers recommended practice for software based leak detection in the US. A pipeline operator should consider using both Annex E and API 1130 in the implementation and use of a software-based leak detection system. The CSA Task Force did not want to copy and modify API 1130 to provide a new Annex E, so both documents provide necessary information.
EPRG Tier 2 Guidelines for the Assessment of Defects in Transmission Pipeline Girth Welds
Authors: Denys Rudi , Andrews Robert Bob , Zarea Mures , Knauf Gerhard
Published: April 2011

This paper presents the proposed revisions of the EPRG guidelines for the assessment of defects in transmission pipeline girth welds. The revisions cover Tier 2 of the guidelines, in particular (a) the extension of the guidelines to include Grade L555 (X80) material, (b) the assessment of surface-breaking defects with heights up to 5mm and (c) the assessment of multiple co-planar defects. Since the welds should be, at least, matching the pipe material in yield strength, the paper also defines the required levels of weld metal yield strength for the safe application of the guidelines.
Offshore Installation of Welded Pipe: Local Buckling Evaluation
Authors: Mantovano Luciano , Bravo Richard E. , Cravero Sebastian , Ernst Hugo A.
Published: April 2011

Up to the present, most of the pipes used in offshore applications installed with methods introducing plastic deformation have been seamless pipes; however, welded pipes can also be used. Welded pipes offers benefits over seamless pipe in terms of improved lead times, lower project costs, tighter dimensional tolerance and good control of mechanical properties and chemistry resulting in excellent weldability. During installation of welded pipes, failure by fracture, plastic collapse and local buckling may occur. In this work, the occurrence of the local buckling phenomenon, produced during the installation method, was evaluated. Numerical models were developed to study the effect of materials and geometrical parameters on the local bucking of pipes subjected to bending. Specifically, the loads and strains at which the plastic instability occurs were determined for each particular condition. In addition, the influence of longitudinal and girth welds on the local bucking occurrence was assessed.
Corrosion of Pipeline Steel in the Presence of Alternating Current and the New CP Recommendation
Authors: Fu A. Q. , Cheng Y. F.
Published: April 2011

The alternating current (AC)-induced corrosion of a cathodically protected X65 pipeline steel was studied in a high pH, concentrated carbonate/bicarbonate solution. Results demonstrated that the corrosion rate of the steel increases with the AC current density, and AC interference could increase the pitting corrosion of the steel. In the absence of AC interference or at a low AC current density, i.e., 20 A/m2, a cathodic protection (CP) potential of −950 mV(Cu/CuSO4 electrode, CSE), which is 100 mV more cathodic than −850 mV(CSE) recommended by National Association of Corrosion Engineers (NACE), provides a full protection over the steel. When the AC current density is higher than 20 A/m2, the NACE-recommended CP is incapable of protecting the pipeline from corrosion. A new CP standard is thus developed for recommendation to industry to avoid AC corrosion of pipelines.
Track Health Monitoring Using Wavelets
Authors: Hopkins Brad M. , Taheri Saied
Published: April 2011

This paper presents a defect detection algorithm for rail health monitoring that could potentially be used with limited bogie. Current wheel and track monitoring requires expensive track instrumentation and/or time consuming operation of railway monitoring vehicles. The proposed health monitoring algorithm can potentially be used with a portable data acquisition system that can be relocated from train to train to monitor and diagnose the conditions of the track as a train is driven during typical day-to-day operation. The algorithm processes the data using wavelets and is able to locate defects and provide information that may help to distinguish between various types of rail defects. In recent years, wavelets have been used extensively in signal processing because of their ability to analyze a signal simultaneously in the time and frequency domains. The Fourier transform has been used traditionally in signal processing to locate dominant frequencies in a signal, but it is unable to provide time localization of those frequencies. Unlike the Fourier transform, the wavelet transform uses a set of basis functions with finite energy, which is advantageous for detecting the irregular events that may show up in a transient signal. The wavelets used in the proposed signal processing routine were chosen for optimal signal decomposition through consideration of the signals that are likely to be generated from common rail and wheel defects, including rail cracks, squats, corrugation, and, wheel out-of-rounds. A sample accelerometer signal was generated from information found in existing literature and was then processed using the proposed defect detection algorithm. Results show the potential of this algorithm to locate and diagnose defects from limited bogie vertical acceleration data. This study is intended to present a proof-of-concept for the proposed defect detection algorithm, providing a basis for which a more comprehensive defect detection and diagnosis algorithm can be developed.
NOx Reducing and Aftertreatment Technologies for EPA Tier 4 Locomotives: Railroad Perspective and Expectations
Authors: Iden Michael E. , Coles Mark A. , Kennedy Thomas A.
Published: April 2011

The year 2015 will be a landmark year in locomotive technology in the United States. Effective January 1st of that year, newly-manufactured U.S. line-haul and switch service (freight-and-passenger) locomotives must be manufactured to meet the fifth level of U.S. Environmental Protection Agency (EPA) emissions regulations since 2000. Achieving those emission levels will require aftertreatment technology in some form. Also effective December 31st of that year, U.S. railroads will be required to have in operation (on much of the rail network)1 a federally-mandated Positive Train Control (PTC) technology for collision avoidance. Class I U.S. freight railroads2 by the end of 2015 will have invested an estimated $5.8 billion in PTC technology, with a major emphasis on interoperability of PTC-equipped locomotives between different railroads. An estimated 17,000 locomotives will be retrofitted or equipped with PTC by the end of 2015 and most if not all newly-manufactured locomotives will be PTC equipped after 2015. For perspective, the U.S. freight railroad investment in PTC is roughly what the Class I railroads have spent the past 4–5 years combined on capital expenditures related to infrastructure expansion. This convergence of two new complex locomotive technologies in 2015 will create a large challenge, especially in locomotive maintainability, for freight railroads. Locomotive builders and aftertreatment suppliers must work together to provide Tier 4 locomotives with minimal impact on railroad operations. U.S. diesel locomotives share a common internal combustion engine technology with most Class 8 over-the-road diesel trucks, but the railroad and locomotive environment is very different from the highway truck environment, and a “cookie cutter” approach to replicating diesel truck aftertreatment on locomotives should be avoided. New EPA Tier 4 diesel locomotives should not be viewed as “Tier 2 or Tier 3 locomotives with truck-type exhaust aftertreatment added”. Baseline reliability of current locomotive designs must also be improved to compensate for the added complexities of both exhaust aftertreatment and PTC. This paper is focused toward educating (1) aftertreatment technology manufacturers and system integrators and (2) locomotive design engineers. The emphasis is on assisting them in understanding the operating and maintenance expectations for Tier 4 aftertreatment-equipped line-haul locomotives, from the perspective of a major freight railroad.
Stress-Induced Martensitic Phase Transformation in Nitinol Under Hard Cyclic Loading
Authors: Kim Kyubum , Juggernauth K. Anne , Daly Samantha H.
Published: April 2011

This paper describes an experimental study of stress-induced martensitic phase transformation in the shape memory alloy Nickel-Titanium, also known by the trade name Nitinol. The rich local thermo-mechanical interactions that underlie phase transformation are examined using three-dimensional Digital Image Correlation (to determine local strain fields) and infrared imaging (to determine local thermal fields). We quantify the complex local interactions between released/absorbed latent heat and the extent of transformation, and explore the characteristics of the phase fronts. There exists a remarkable amount of memory in the pattern of the martensitic formation from cycle to cycle. The initial pattern in which the martensite nucleates and propagates in the first cycle strongly dictates how the martensite nucleates and propagates in future cycles. The presence of this cycle-to-cycle strain pattern memory indicates that the local elastic stress fields in the martensite are driven by a dislocation structure and martensitic nuclei that largely stabilize during the first loading cycle.
Embedded Piezoresistive Thin Films for Monitoring GFRP Composites
Authors: Loyola Bryan R. , La Saponara Valeria , Loh Kenneth J.
Published: April 2011

The trend towards higher reliance on fiber-reinforced composites for structural components has led to the need to rethink current nondestructive evaluation (NDE) strategies. In principle, embeddable sensor schemes are desired for green-light/red-light structural health monitoring systems that do not negatively affect the properties and performance of the host structure. However, there are still numerous challenges that need to be overcome before these embedded sensing technologies can be realized for real-world structural systems. For example, some of these issues and challenges include the damage detection sensitivity/threshold, reliability of the system, transportability of the system to multiple configurations and different types of structural components, and signal processing/interpretation. The objective of this study is to develop a novel, embedded sensing system that can accurately quantify damage to composites without interfering with structural performance and functionality. In particular, this study will utilize multi-walled carbon nanotube (MWNT)-polyelectrolyte (PE) thin films deposited on a glass fiber substrate for in situ composite structural monitoring. A layer-by-layer (LbL) film fabrication methodology is employed for depositing piezoresistive nanocomposites directly onto glass fiber fabrics, and the resulting film exhibits excellent strain sensing performance, homogeneity, and exhibits no phase segregation. Specifically, the LbL fabrication process will employ polycationic poly(vinyl alcohol) (PVA) and polyanionic poly(sodium 4-styrene sulfonate) (PSS) doped with MWNTs for fabricating the electrically-conductive and piezoresistive thin films. Upon film deposition, the glass fiber substrates are infused with an epoxy matrix via wet-layup to fabricate self-sensing glass fiber-reinforced polymer (GFRP) composite specimens for testing. A frequency-domain approach, based on electrical impedance spectroscopy, is used to characterize the electromechanical response of the GFRP-MWNT-based thin film samples when subjected to complex uni-axial tensile load patterns. A resistor connected to a parallel resistor-capacitor circuit model is proposed for fitting experimental impedance spectroscopic measurements. It has been found that the series resistor models the bulk thin film piezoresistive performance accurately. In addition, these impedance measurements shed light on the glass fiber-thin film interaction electromechanical behavior. Bi-functional strain sensitivity is observed for all GFRP specimens, and the transition point of bilinear strain sensitivity is utilized as a possible metric for GFRP damage detection.
An Analysis of Composite Piezoelectric Actuators Incorporating Nonlinear Material Behavior
Authors: DeGiorgi Virginia G. , Qidwai M. A. Siddiq
Published: April 2011

Piezoelectric actuators of various composite designs have been proposed during the last few years including extension and shear bimorphs, tubular composites and multilayered actuators. These designs exploit the ability to define the actuation direction by varying the alignment between poling direction and applied electric field. Considerable research effort has been put to accurately model these actuators in order to attain predictive capability. The common factor in almost all of these studies is the assumption that the poled material behaves linearly under applied electric field. However, this assumption may only be accurate for the limited case of a homogenous actuator under relatively unconstrained environment, such as that of simply supported boundary conditions. In the case of composite structures, the actuation can potentially be restricted by non-actuating constituents resulting in multi-dimensional loading states, which may cause domain switching. The same argument can be made for most boundary conditions that are imposed in practical applications, such as when the actuator is clamped or fixed. Another point of concern is the presence of discontinuities and minor defects in the actuator. Both of these would promote non-uniform electric field causing domain switching, and hence, unexpected actuator output. Unless proven otherwise, these concerns directly affect the credibility of life cycle estimates based upon linear models. In this paper linear and nonlinear material models will be used to determine actuator performance using an established constitutive model in a commercial finite element code. Actuator performance for both material cases will be calculated and compared with existing analytical predictions under the same set of boundary conditions.
Design of a Passively Morphing Ornithopter Wing Using a Novel Compliant Spine
Authors: Tummala Yashwanth , Wissa Aimy , Frecker Mary , Hubbard James E.
Published: April 2011

A new scheme to design morphing ornithopter wings using a passive compliant spine is presented in this paper. The objective of this work is to optimize steady level flight performance of an ornithopter by passively implementing the Continuous Vortex Gait (CVG) which requires bending, twist and sweep coupling during the upstroke. An optimization problem is formulated to design a compliant spine for pre-specified bending, sweep, and twist deflections. As a first step to achieving these 3 DOF kinematics, a 1 DOF compliant spine is considered to produce a specified bending deflection during the upstroke for drag reduction while remaining stiff during the downstroke for increased lift. The effect of the relevant geometric design parameters, namely contact gap, angle, and hinge geometry, are considered and optimized to achieve the aforementioned kinematics for both single and multiple joints, which make up a compliant spine. Results presented include the spine design optimization procedure, as well as a complete analysis for a 1DOF compliant spine to illustrate the efficacy of the methodology. This compliant spine design methodology and optimization procedure will be used, in the future, to design the 3-DOF compliant spine for the passively morphing ornithopter.
Experiment Investigation of Magnetorheological Damper for High Impulsive Load
Authors: Li Zhaochun , Wang Jiong
Published: April 2011

In the past decade, magnetorheological (MR) damper, as a new type of smart damper, has gained significant findings which have led to good applications in the field of engineering. However, most of these work focused on low velocity and low frequency applications. This study provides an experimental investigation into a self-designed MR damper subject to high impulsive load. First of all, the active force of the recoil system in weapons is selected as an impulsive input of the MR damper. Then, a MR damper with long stroke of 440mm and single-ended construction especially for impact and high velocity is designed. The novel recoil apparatus is mainly composed of a MR damper and a series of springs. The measurement system includes transducers and the corresponding signal process equipments. Under the firing impulsive load, three currents including 1.0A, 1.5A and 2.0A are investigated. The results show that the peak force becomes larger when the current increases. On the other hand, the MR fluid is uncontrollable when velocity rises rapidly and it is not controllable until 0.026s.
Photoresponsive Azobenzene Liquid Crystal Polymer Networks: In Situ Photogenerated Stress Measurement
Authors: Torres Yanira , White Timothy , McClung Amber , Oates William
Published: April 2011

Azobenzene liquid crystal polymers and polymer networks are adaptive materials capable of converting light into mechanical work. Often, the photomechanical output of the azobenzene liquid crystal network (azo-LCN) is observed as a bending cantilever. The response of these materials can be either static (e.g. a simple bending cantilever) or dynamic (e.g. oscillating cantilever of 20–270 Hz). The resulting photomechanical output is dependent upon the domain orientation of the polymer network and the wavelength and polarization of the actinic light. Polydomain azobenzene liquid crystal polymer networks, which have the capability of bending both backwards and forwards with the change of polarization angle, are of particular interest. In the current study, three azo-LCNs are compared — two of them are equivalent in all respects except for one contains pendant azobenzene mesogens (1azo, azo-monoacrylate) and the other contains crosslinked azobenzene mesogens (2azo, azo-diacrylate). The third specimen has a combination of both mesogens. The mechanical behavior at different temperatures and examination of structure-property relationships in the polymerization process, including curing temperatures and liquid crystal cell alignment rubbing methods, were explored. Using dynamic mechanical analysis (DMA) the mechanical properties and the photogenerated stress and strain in the polymer are examined. It is found the differences in chemistry do correlate to small variation in the speed of photodirected bending, elastic modulus, and glass transition temperature. Despite these differences, all three azo-LCNs display nearly equivalent photogenerated stresses.
Thrust Modeling and Measurement for Clapping Wing Nano Air Vehicles Actuated by Piezoelectric T-Beams
Authors: Mateti Kiron , Zhang Zheqian , Tadigadapa Srinivas A. , Rahn Christopher D.
Published: April 2011

Insects that use a Weis-Fogh clap and fling mechanism, where their wings clap together and fling apart, show an increase in thrust per unit muscle mass compared to conventional flapping insects. This has motivated the development of macroscale clapping winged ornithopters with four wings. Most clapping wing ornithopters use electric motors with gears and linkages that are inefficient at the sub-millimeter (meso)scale. Piezoelectric actuators are attractive for Nano Air Vehicles (NAVs) because they have high power density, high efficiency, and new fabrication processes have been developed at this scale. Recently developed piezoelectric T-beam actuators are monolithically fabricated from bulk PZT and function like unimorph actuators without the need to bond passive layers. These bending actuators drive a novel four-winged clapping NAV that produces thrust. This paper studies thrust force generation of a clapping wing NAV using a model-based approach. A three degree of freedom dynamic model of the clapping wing nano air vehicle is derived including unsteady aerodynamic forces and torques. The model is validated using experimental data from a NAV prototype.
Singularities in Landau-Devonshire Potentials for Ferroelectric Phase-Transitions
Authors: Davi´ Fabrizio
Published: April 2011

Ferroelectrics phase transitions are studied in terms of fourth-order Landau potentials: a clever choice of the reference configuration allows for a complete description of all the possible transitions. The study of the stability conditions at the phase interface helps to explain the fairly complex nature of the observed twins.
Design of Extendable Chord Sections for Morphing Helicopter Rotor Blades
Authors: Barbarino Silvestro , Gandhi Farhan , Webster Steven D.
Published: April 2011

Chord extension in helicopter rotors allows for expansion of the flight envelope, with the helicopter capable of flying at higher gross weights, altitudes and maximum speeds. A fixed large chord, however, results in a penalty when the helicopter is well within the envelope (for example, at low to moderate gross weight, sea level, and at moderate speed cruise). Chord morphing allows the helicopter to perform optimally in these diverse conditions. In this paper, the authors present a morphing mechanism to extend the chord of a section of the helicopter rotor blade. The region aft of the leading-edge spar contains a morphing cellular structure. In the “compact” state the edge of the cellular structure aligns with the trailing-edge of the rest of the blade. When the morphing cellular structure is in the “extended” state the chord of that section of the blade is increased by close to 30% (with the trailing-edge extending beyond that of the rest of the blade). In transitioning from compact to extended states, the cellular structure slides along ribs which define the boundaries of the morphing section in the span-wise direction. The cellular section has mini-spars running along the span-wise direction to attach the flexible skin and provide stiffness against camber-like deformations due to aerodynamic loads. The paper presents a finite element analysis and a design study of the morphing cellular structure, ensuring that the local strains in the cellular structure do not exceed maximum allowables even as the section undergoes large global strain. On the other hand, the morphing cellular structure is required to be stiff enough so that the pre-stretched skin that is attached to the surfaces does not result in deformation. Another question that is considered in detail is various methods of attachment of the flexible skin to the morphing substructure, the levels of pre-strain required, and their ramifications. A model of a blade section is fabricated and shown to undergo chord morphing, as designed.
Thermal Robustness Assessment of a Rigidized Space Inflatable Boom via Experimental Modal Analysis and Finite Element Modeling
Authors: Daly Matthew , Salehian Armaghan , Doosthoseini Alireza
Published: April 2011

The following paper presents the results of a thermal robustness assessment of a rigidized space inflatable boom. Modal testing is performed at three different environmental temperatures; spanning a range of 38°C, with the purpose of characterizing dynamic behavior and assessing changes in bending frequencies. Experimental results show that the natural frequencies of the boom shift only marginally within the tested bandwidth. A finite element model is developed in parallel with experiments to determine compatibility with beam theory. The resulting simulation shows that linear beam theory can be used to predict bending frequencies and frequency response function magnitudes with very good accuracy.
Non-Contact Technique for Characterizing Full-Field Surface Deformation of Shape Memory Polymers
Authors: McClung A. J. W. , Tandon G. P. , Goecke K. E. , Baur J. W.
Published: April 2011

Thermally-actuated shape memory polymers (SMPs) typically display two phases separated by the glass transition temperature (Tg). At temperatures well below the Tg, the polymer exhibits a relatively high elastic modulus. Well above the Tg the elastic modulus drops by several orders of magnitude. In this high temperature region, SMP materials can achieve strain levels well above 100 %. The complex behavior of SMPs (stiffnesses dropping to the order of 1 GPa and extremely high strain levels) precludes the use of traditional strain gages and low-contact force extensometers. The present study presents a detailed expansion of state-of-the-art thermomechanical testing techniques used to characterize the material behavior of SMPs. An MTS environmental chamber with an observation window allows for non-contact optical measurements during testing. A laser extensometer is used for measurement and active control of axial strain. The upper limit on the strain rate capability of the laser extensometer is established. In addition, the photographic strain measurement method known as digital image correlation (DIC) is incorporated, allowing for full field measurement of axial and transverse strains of SMPs over a range of temperatures and strain rates. The strain measurements of the DIC and laser extensometer are compared to each other as well as to clip-on extensometers and strain gages. The comparisons provide insight into the limitations of the traditional strain measurement systems. A series of tensile tests are performed on a commercial SMP from 25 °C up to temperatures of 130 °C and strain levels above 100 %. The laser extensometer provides a robust method for controlling the strain in the gage section of the samples. In addition, results show that the full field measurements of both the axial and the transverse strain are essential for characterizing the constitutive response of SMPs at room and elevated temperatures.
Experimental and Numerical Analysis of Recovery Stress in Ni47Ti44Nb9 Shape Memory Alloys: Application to Tightening
Authors: Piotrowski Boris , Patoor Etienne , Ben-Zineb Tarak , Eberhardt Andre
Published: April 2011

Ni47Ti44Nb9 Shape Memory Alloys (SMAs) are widely considered for tightening applications. The alloy is composed of a NiTi SMA matrix containing niobium precipitates. A specific thermomechanical treatment strongly increases the transformation hysteresis in these alloys, what improves the tightening efficiency. Tightening pressures exhibited by Ni47Ti44Nb9 rings are experimentally investigated. Strain gage measurements allow to monitor the tightening pressure using a home test bed. Evolutions with temperature are recorded. A thermo-mechanical constitutive law, specific for Ni47Ti44Nb9, is proposed. It is based on the Mori-Tanaka scale transition technique by considering the precipitates as elastic-plastic inclusions embedded in the SMA matrix. The resulting effective law is implemented, and validated in ABAQUS via UMAT subroutine. Experimental tests are simulated by Finite Element Modeling, and comparisons are performed.
Modeling the Behavior of Crystallizable Shape Memory Polymers Subject to Inhomogeneous Deformations
Authors: Khanolkar Mahesh , Sodhi Jaskirat , Rao I. Joga
Published: April 2011

The constitutive model for the mechanics of crystallizable shape memory polymers (CSMP) has been developed in the past [1, 2]. The model was developed using the theory of multiple natural configurations and has been successful in addressing a diverse class of problems. In this research work, the efficacy of the developed CSMP model is tested by applying it to the torsion of a cylinder, which is an inhomogeneous deformation. The crystallization of the cylinder is studied under two different conditions i.e. crystallization under constant shear and crystallization under constant moment.
Degradation of Sensor Systems in Multifunctional Composites
Authors: Mehdizadeh Mohammad , John Sabu , Wang Chun , Bannister Michael , Verijenko Viktor
Published: April 2011

Structural health monitoring (SHM) systems are increasingly being considered for implementation in aerospace structures. As the application of SHM systems increase, it will be important to define standardized procedures to test durability, reliability, and longevity of the systems. The work presented in this paper is some preliminary work on the integrity of Piezoelectric sensors itself when used to monitor the strains in structures. This study involved the measurements of pertinent electrical properties of these sensors over 100,000 cycles of fatigue loading. Marked changes in the capacitance and inductance of these sensors highlighted deleterious structural changes in the sensor itself without any discernible change in the structure it is supposed to monitor. This might have significant implications in the reliability assessment of sensory data from SHM systems.
Flow Driven Vibration Energy Harvester
Authors: Bischur Enrico , Pobering Sebastian , Menacher Markus , Schwesinger Norbert
Published: April 2011

This paper describes an energy harvester working with the repeated deflection of a piezoelectric cantilever. The harvester works in flowing media like wind or water. The bending of the cantilever is driven by vortices traveling across it. The presented device is an easy solution for vibration energy harvesting without the need of external mechanical vibration. The working principle was determined with macroscopic models in wind and water channels. The harvester does not need in general a mechanical adaption to the external vibration frequency, because it oscillates always with its resonance frequency at different flow velocities. Furthermore a self synchronization of cantilevers arranged beside each other could be observed in water. A second system was able to supply a load of approximatly 2 mW in a wind channel at a flow velocity of 8 m/s.