bluuebunny/crossref_metadata_2025 huggingface dataset:
Pumpability — Past Accomplishments; Present and Future Challenges
Authors: Selby TW
Published: April 2008

The possible problem of inadequate low-temperature engine oil pumpability was considered in the early '60s and grew into prominence in the late '60s and early '70s with the success of the automotive industry in improving low-temperature engine startability. Reported incidents of field pumpability problems in the early '70s led to an extensive ASTM study using several cold-rooms and a number of reference oils. This study confirmed the previously anticipated existence of two forms of pumpability problems — flow-limited pumpability caused by higher viscosities and air-binding pumpability caused by engine oil gelation under certain cooling conditions.

Of these two forms of engine pumpability failure, air-binding was the primary threat to engine life. This was a consequence of the fact that some engine oil formulations could be induced to gelate at temperatures well above viscosity-limited temperatures. Despite these extensive cold-room studies and the development of a Mini-Rotary Viscometer bench test closely simulating the cold-room results, the work did not prepare those studying the problem area for the disastrous winter of 1980–81 when several million dollars of engines failed in the field as a result of air-binding oil effects.

In renewed efforts to develop viable bench tests correlating to these field-failing engine oils representing real world conditions, two instruments emerged: one in 1982 called the Scanning Brookfield Technique and the second, a further adaptation of the original MiniRotary Viscometer (called the MRV TP-1), in 1985.

Another recent ASTM cold-room study has confirmed improved startability and brought into question whether or not modern engines are less prone to air-binding.

At the same time, new pressures on both automotive and heavy-duty diesel engines have just come to attention as a consequence of long drain intervals and their effects on engine oil oxidation. It has been shown that such intervals can have serious effects on the engine through the coupling of both viscosity-limited and air-binding characteristics, In a similar manner, high soot loading in diesel engines recently redesigned to reduce oxides of nitrogen has produced further low-temperature pumpability problems and the associated needs to understand the chemistry and rheology of such oils at these temperatures and to find ways of reliably and repeatably measuring these phenomena.
Designing Low Temperature Performance for Diverse Basestocks
Authors: Girshick FW , Gaines LH , Martella DJ
Published: April 2008

A new class of Lubricant Oil Flow Improvers (LOFI) was developed using statistically-based molecular design techniques, employing model compound studies and fundamental mechanistic understanding. These LOFI's were designed to be effective in a broad range of solvent- and catalytically-dewaxed basestocks, including API Group II and III hydrocracked stocks.

Basestocks for crankcase oil formulations are changing in composition. The volume of hydrocracked basestocks is increasing, realtive to solvent extracted basestocks. New dewaxing processes have been successfully introduced, such as catalytic dewaxing and catalytic iso-dewaxing. These process changes, and increasingly varied crude sources, lead to significantly different types and distributions of wax in the basestock.

LOFI'S, also called pour point depressants, optimized for traditional solvent-extracted, solvent-dewaxed basestocks may not work efficiently in these newer stocks, or may not work at all. Conversely, LOFI's designed for the newer basestocks may be ineffective in the more traditional basestocks which still dominate the market. An ideal LOFI will be able to treat both types of basestock with a wide range of viscosity modifiers, to maximize formulators flexibility.

The traditional empirical approaches to selecting LOFI can require excessive time and test costs as the basestock slate becomes more complicated and new test requirements are introduced. The design and selection approach presented here is based on the use of model diagnostic compounds which maximize the response of oil formulations to the molecular parameters of the LOFI. These parameters include molecular weight, average carbon number of the side chains, and the distribution of side chain lengths.
Air Quality Measurements on Sixteen Commercial Aircraft
Authors: Lee SC , Poon CS , Li XD , Luk F , Chang M , Lam S
Published: April 2008

Indoor Air Quality Investigation on CPA aircrafts was investigated by the Cathay Pacific Airways Limited (CPA) and the Hong Kong Polytechnic University (HKPU). The parameters concerned were carbon dioxide (CO2), relative humidity, temperature, carbon monoxide (CO), ozone (O3), sulphur dioxide (SO2), nitrogen dioxide (NO2), bacteria, fungus, and respirable suspended particulate (RSP). This project covered 16 flights from June 1996 to August 1997. The overall air quality on CPA aircraft was satisfactory. CO2, CO and ozone levels on all flights were below the Federal Aviation Administration (FAA) standard. Peak levels of CO2 and RSP were observed during boarding and de-boarding periods. For smoking flights, the average RSP level (138μg/m3) was much higher when comparing with non-smoking flights (7.6 μg/m3). The minimum relative humidity (4.9%) during cruise was below the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) minimum relative humidity standard (20%). The average temperature was within the range of 20±2°C. The vertical temperature profile on aircraft was uniform and complied with the International Standard Organisation (ISO) 7730 standard.
A Proposed Indoor Air Quality Metric for Estimation of the Combined Effects of Gaseous Contaminants on Human Health and Comfort
Authors: Hollick HH , Sangiovanni JJ
Published: April 2008

An indoor air quality (IAQ) metric that generally accounts for the effects on health and comfort of the total combination of gaseous contaminants is described herein. Acceptable concentrations of individual contaminants are taken to be the most stringent of several established exposure limits. Individual measured concentrations are compared with those limits to determine their individual relative acceptability. These relative ratings are then combined in an overall summation, or index, to provide a means to compare air quality in different samples containing differing gaseous contaminants with varying levels of individual contaminants. Thus this IAQ metric accounts for the relative effect of individual compounds on overall health and comfort as well as synergistic effects of low-level individual concentrations on the total air quality. Moreover, the metric clearly identifies those contaminants that have an adverse effect on air quality and should be remediated. Use of the metric is demonstrated in both airliner and building applications. Evaluation based on actual measurements provides a quantitative, comparative metric based on objective data. The airliner model and metric assessment includes a prediction of the impact of reducing the fresh air ventilation rate on overall air quality. It indicates that as the fresh air rate is reduced, air quality deteriorates if air purification is not provided. In order to improve the usefulness of this approach in evaluation of indoor air quality, further work in establishing individual acceptable concentrations of contaminants is suggested.
Design of Air Purifiers for Aircraft Passenger Cabins Based on Photocatalytic Oxidation Technology
Authors: Hall RJ , Sangiovanni JJ , Hollick HH , Obee TN , Hay SO
Published: April 2008

An approach to airliner passenger cabin contaminant removal based on ultraviolet light (UV) illumination of the photoactive semiconductor, titania (T1O2), at room temperature is described. This technology is effective at conversion of harmful volatile organic compounds (VOC) to generally non-toxic compounds, and is also effective at killing bioaerosols. Factors unique to the airliner cabin environment make this a particularly promising application for this technology. This paper describes prototype test results and design methodologies needed for application of the technology to aircraft passenger cabins. The requirements of purifiers for airliners in terms of power consumption, size and weight, and life cycle costs will be compared to those for activated carbon adsorption. It will also be shown that photocatalytic oxidation (PCO) reactors designed for VOC control can supplant high efficiency particulate arresting (HEPA) filters for bioaerosol control. The design of compact purifiers for retrofitting existing airliners will be discussed.
Questionnaire Survey to Evaluate the Health and Comfort of Cabin Crew
Authors: Lee SC , Poon CS , Li XD , Luk F , Chang M
Published: April 2008

A questionnaire survey on evaluation of in-flight health and comfort of cabin crew was investigated between September 1996 to March 1997. One hundred eighty-five questionnaires were completed by the cabin crew. Overall comfort on the aircraft was acceptable and adequate. Important air quality issues were odour, cigarette smoke, and humidity. More than 60% of the cabin crew (especially for long haul flights) felt that the cabin humidity was low and caused discomfort; 80% felt that environmental tobacco smoke on smoking flights deteriorated the cabin air quality. The parameters most frequently complained about by passenger were humidity, temperature, odour, and noise. The three most frequently experienced symptoms were dry or irritated eyes, dry or stuffy nose, and skin dryness or irritation.
Passenger Comfort and the Effect of Air Quality
Authors: Rankin WL , Space DR , Nagda NL
Published: April 2008

A passenger comfort survey was conducted with a major U. S. airline with the objectives to determine: 1) the variables that affect passenger comfort, including air quality variables; 2) the level of passenger comfort during flight and whether passengers are experiencing specific types of health-related symptoms; 3) if passenger comfort is a function of the percent of bleed air vs. filtered, recirculated air, standard-body vs. wide-body aircraft, and flight length. Flight attendants distributed the self-administered questionnaires as part of their normal duty. Data from 3630 passengers on 71flights were collected in March, April, and June 1997. The response rate was approximately 43 percent. Conclusions from the study were that seat comfort, flight smoothness, and air quality were the important determinants of passenger comfort. The most frequent symptoms experienced by passengers included back/joint/muscle pain, dry/irritated/itchy eyes and dry/stuffy nose. These symptoms increased with flight length. On longer flights, seat discomfort became noticeable to passengers before eye and nasal symptoms. The percent of filtered recirculated air showed no direct relationship to passenger comfort ratings or reported symptoms.
A Method for Calculating Strain Energy Release Rates in Preliminary Design of Composite Skin/Stringer Debonding Under Multiaxial Loading
Authors: Krueger R , Minguet PJ , O'Brien TK
Published: April 2008

Three simple procedures were developed to determine strain energy release rates, G, in composite skin/stringer specimens for various combinations of uniaxial and biaxial (in-plane/out-of-plane) loading conditions. These procedures may be used for parametric design studies in such a way that only a few finite-element computations will be necessary for a study of many load combinations. The results were compared with mixed-mode strain energy release rates calculated directly from nonlinear two-dimensional plane-strain finite-element analyses using the virtual crack closure technique. The first procedure involved solving three unknown parameters needed to determine the energy release rates. Good agreement was obtained when the external loads were used in the expression derived. This superposition technique, however, is applicable only if the structure exhibits a linear load/deflection behavior. Consequently, a second modified technique was derived which was applicable in the case of nonlinear load/deformation behavior. The technique, however, involved calculating six unknown parameters from a set of six simultaneous linear equations with data from six nonlinear analyses to determine the energy release rates. This procedure was not time efficient, and hence, less appealing.

Finally, a third procedure was developed to calculate mixed-mode energy release rates as a function of delamination lengths. This procedure required only one nonlinear finite-element analysis of the specimen with a single delamination length to obtain a reference solution for the energy release rates and the scale factors. The delamination was subsequently extended in three separate linear models of the local area in the vicinity of the delamination subjected to unit loads to obtain the distribution of G with delamination lengths. This set of subproblems was solved using linear finite-element analyses, which resulted in a considerable reduction in CPU time compared to a series of nonlinear analyses. Although additional modeling effort is required to create the local submodel, this superposition technique is very efficient for large parametric studies, which may occur during preliminary design where multiple load combinations must be considered.
Fail-safe Approach for the V-22 Composite Proprotor Yoke
Authors: Altman LK , Reddy DJ , Moore H
Published: April 2008

The V-22 proprotor yoke is fabricated from filament-wound unidirectional glass/epoxy belts that react to centrifugal force (CF) loads and beam and chord bending loads. Fiberglass tape is laid up at off-axis orientation between the unidirectional belts to react shear loads. The structural criteria for both metallic and composite V-22 dynamically loaded rotor components specify that these components be fatigue tested and analyzed to show a “safe life” of 30 000 h. Based on the fatigue test results of prototype and production proprotor yokes, a safe life of 30 000 h for the composite proprotor yoke could not be substantiated. However, testing of the yoke was continued beyond delamination initiation. The V-22 proprotor yoke continued to carry load in the fatigue tests with significant delaminations within the composite structure. These results, in addition to similar test results produced by Bell Helicopter Textron on composite proprotor yokes for commercially produced aircraft, indicate that it will be possible to substantiate this component using a “fail-safe” methodology.
Structural Qualification of Composite Propeller Blades Fabricated by the Resin Transfer Molding Process
Authors: Smith SL , Mattavi JL
Published: April 2008

The unique challenges for developing design allowables for a resin transfer molded propeller blade are discussed. Preliminary allowables were determined based on coupon tests for the initial blade design. Nonstandard specimen geometries were investigated in order to provide valid failure modes and associated strength values for the spar, shell and adhesive bond joint in terms of static and fatigue strengths out to 108 cycles. Full-size blade component tests were performed to verify or substantiate the preliminary allowables. Analyses of failure modes on the full-size specimens directed the structural qualification process. This included follow-up coupon fatigue tests and expansion of the fullsize test matrix. The general conclusions are that coupon tests are necessary for determining elastic constants and for effects of batch variation, environment, and for shape of fatigue curves, but generally do not provide enough guidance to design a resin transfer molded (RTM) structure without some full-size test experience. This is due to the absence of edge, surface and width effects found in coupons and the inclusion of thermal, manufacturing and geometry effects found in the full-size specimens. These and other scale effect issues therefore dictate the need to test full-size specimens early on in the normal building block approach. The number of full-size tests is generally higher for an RTM blade or structure than for a metal blade or for a standard prepreg, thin composite structure, since statistical treatment of the full-size fatigue data is necessary for establishing final design allowables. This top-of-the-pyramid approach to structural qualification can make RTM unique from prepreg or metal structures.
Damage-Tolerance-Based Design of Bolted Composite Joints
Authors: Qing X , Sun H-T , Dagba L , Chang F-K
Published: April 2008

An approach based on damage tolerance is proposed for the design of bolted composite joints. The approach requires knowledge of failure processes and damage accumulation in composites under physical loading. Based on experimental observation, a progressive damage model was developed for predicting the accumulated damage and failure modes in composite joints.

In order to utilize the model for design, a computer code, 3DBOLT, has been developed. The code is based on the progressive damage model, and it interfaces with the commercial finite-element code ABAQUS to perform calculations of three-dimensional stresses, strains, and deformations of the joints for a given load. for a given joint configuration, ply orientation, and loading condition, the code can predict the response of the joint from the initial loading to final failure, estimate accumulated damage in the joint as a function of applied load, and predict the joint deformations. In order to verify the proposed damage model, the data obtained from the experiments were compared with the predictions from the 3DBOLT/ABAQUS code. Based on the code, a parametric study was performed to characterize several important factors that can significantly influence the design of bolted composite joints.
Characterizing Delamination Growth in a 0°/45° Interface
Authors: Martin RH , Rousseau CQ
Published: April 2008

Structural configurations in helicopter rotor systems often contain plies of 0° and 45° to resist centrifugal and torsional loads. Delaminations in test specimens that are tested to failure often experience delaminations between a 0°/45° ply interface. However, the standard methods to characterize delamination utilize a unidirectional 0° specimen. The reasons for using a unidirectional layup are that multidirectional beams suffer from ply cracks in the nonzero plies, increased anticlastic bending and other effects. This work investigated the issues for testing a nonunidirectional double cantilever beam (DCB) specimen with a delamination in a 0°/45° interface. Several criteria were developed to minimizethe effects noted above. These included reduction of bend twist coupling and residual thermal stresses, prevention of nonzero ply breakage, and minimized anticlastic bending. The resulting layup consisted of a 64-ply laminate of 0°, 45°, and -45° plies. Quasi-static and fatigue tests were conducted on unidirectional layups and the new configuration fabricated from S2/E773 glass/epoxy. For both the static and fatigue tests the delamination grew and remained in the 0°/45° interface for a significant portion of delamination growth. Crack branching was noted in some specimens as the delamination length became longer. The interlaminar fracture toughness, GIc, of the 0°/45° DCBs had more scatter and a 10% lower mean than the 0° DCB specimens. Both specimens experienced fiber bridging shown by an increase in GIc with delamination growth and observation of the delaminated surfaces. The influence of the fiber bridging was similar in the two specimen configurations. The fatigue delamination onset curves of the two specimen configurations were coincidentally not showing the scatter or lower values seen in the static tests. The static and fatigue results indicate that the use of 0° specimens for characterizing delamination in a 0°/45° interface is satisfactory for the materials tested in this work. However, the presence of fiber bridging in the 0°/45° specimens indicates that using the initiation value for predicting delamination growth may be overly conservative when fiber bridging is present. The same fiber bridging has also been observed in failure surfaces on structural components tested to failure. While the inclusion of fiber bridging in delamination growth predictive models is possible, further work should be conducted on the parameters that affect fiber bridging, such as thickness, processing and crack opening, to ensure that the properties from a DCB specimen are representative of that in the structures. Work on other material systems, other delamination modes and fatigue crack growth is also recommended.
Comparison of Designs of CFRP-Sandwich T-Joints for Surface-Effect Ships Based on Acoustic Emission Analysis from Load Tests
Authors: Brunner AJ , Paradies R
Published: April 2008

T-joints are typical structural elements in surface-effect ships. Seven different T-joint sandwich designs made of balsa wood cores and carbon fiber reinforced polymer (CFRP) facings have been compared under quasi-static tensile and compressive loading until failure. The T-joints differ in the details of the bond design between the horizontal and vertical plates. The performance of the designs is assessed based on failure loads and deformations, acoustic emission (AE) data and visual inspection. The design improvements yield an increase of the failure load from around 50 kN to at least 140 kN (corresponding to the failure of the horizontal plate). Preliminary results have been obtained for one repaired T-joint. AE monitoring indicates an early onset of damage and significant damage accumulation at loads around 70% of the ultimate failure load. For some T-joints there are indications for significant damage in zones outside that where final failure occurred.
What the Textbooks Won't Teach You About Interactive Composite Failure Criteria
Authors: Hart-Smith LJ
Published: April 2008

This paper exposes what really happens when interactive failure theories for fiber-polymer composites are combined with progressive-failure theories to justify discarding the predicted first-ply failure prediction in favor of a subsequent last-ply failure prediction. The procedure is shown to be far from the rational scientific process it is customarily presumed to be, even without any precise definition of the analytical procedure that is normally defined only in the associated computer codes, the source codes for which are not usually available. The paper shows how, and why, measured lamina properties are changed to others that cannot possibly be measured, and the theories changed, too, with no notice to that effect. The paper contains both qualitative and quantitative illustrations of the unacceptability of these theories, along with unresolved paradoxes that have bedeviled this process from the very start, but which have yet to be addressed. The never-justified simplifying assumptions made at the very first step of these analyses are explained, and a strong case is made that only mechanistic failure models, with separate equations for failures in the fibers, the matrix, and at the interface can be relied upon. An analogy can be drawn with reinforced concrete structures, the structural analysis of which requires the separate properties of steel and concrete, which are the “constituents” of this particular composite of materials. This does not imply that fiber-polymer composites can be characterized only at the micromechanical level; just that characterizations at the traditional macromechanical level must not be simplified (homogenized) to the point that they fail to adequately represent the dominant phenomena. Even for truly homogeneous materials, each mode of failure is completely defined by a single material reference property, be it a strength, a fracture toughness, or a modulus. It is noted that a need for multiple reference strengths should imply the presence of multiple independent failure mechanisms, not that there are interactions between them. A very strong recommendation is made that both the teaching and use of interactive composite failure theories cease forthwith, because the only applicability that any of these theories might have is to truly homogeneous anisotropic solids like rolled metallic plates and extrusions. Despite the fact that one of them, the Tsai-Wu theory, is the most widely taught theory for composites, not one of the many interactive theories for homogeneous anisotropic solids has ever been shown to have any relevance to inherently heterogeneous fiber-polymer composites. Progress towards simple reliable analysis tools for this task, to reduce the level of expensive testing that would be needed for entirely empirical characterizations, will not be achieved as long as these obstacles continue to stand in the way.
Compressive Strength of Production Parts Without Compression Testing
Authors: Barbero EJ , Wen EA
Published: April 2008

The purpose of this paper is to present a methodology to estimate the compressive strength of fiber-reinforced composite prototype and production parts. The procedure is based on test data that incorporate the effects of sample size and sample preparation but are simpler to obtain than compression test data. A simple formula is derived to relate the compressive strength to the shear stiffness, shear strength, and standard deviation of fiber misalignment. The formula is completely defined in terms of these three parameters, all of which can be measured by standard experimental procedures. It is proposed to use the shear stiffness and shear strength from coupon tests, usually available from the material supplier or from the characterization phase of the design/build project. Since these two parameters are relatively insensitive to part size and sample preparation, the coupon data are reliable and representative of the actual production part. Since fiber misalignment depends on the processing conditions, the third parameter used is the standard deviation of fiber misalignment, measured on samples from actual production parts. These three values characterize the compressive strength of the carbon/epoxy layups for which experimental data are found in the literature and those evaluated in this investigation. The predictions are then validated against data from a variety of specimens tested at high and low temperatures, as well as data from production prototype parts.
Flammability and Sensitivity of Materials in Oxygen-Enriched Atmospheres: 10th Volume
Authors: Steinberg TA , Newton BE , Beeson HD
Published: April 2008

Description

The tenth volume in this ongoing series provides 28 peer-reviewed papers written by experts in their field. This unique publication gives you the latest information available on flammability and sensitivity of materials in oxygen-enriched atmospheres, including oxygen compatibility and risk management concepts and practices. Topics include:

Ignition and Combustion of Nonmetals covers resistance of polymers to ignition by pneumatic impact; assessment of nonmetallic materials that are used in oxygen systems with a focus on toxicity; statistical evaluation of upward flammability testing (NASA STD 6001 Test 1 ) and ignition of materials exposed to liquid oxygen by mechanical impact.

Ignition and Combustion of Metals presents work evaluating metallic filters for use in oxygen systems; a unique ultrasonic system used to measure the melting rate of the metal rods while burning in oxygen in both normal gravity and reduced gravity; stainless steel promoted ignition tests under flowing conditions; a model for the ignition of rods and tubes in flowing oxygen; microanalysis of aluminum rods that were burned in oxygen and either quenched or self-extinguished; and several ignition-combustion test programs.

Failure/Hazard Analysis and Safety focuses on the documentation of failures and their causes; and techniques being used and developed to analyze systems or components operating in oxygen-enriched atmospheres to ensure system functionality and personnel safety. Papers cover a new technique for analyzing large systems based on prioritizing system components based on operating conditions; an analysis of the space shuttle external tank pressurization system; a failure analysis of fires that have been occurring in oxygen production process valves; a review of some incidents in oxygen systems that have occurred in Australia over a 30-year period; cause and origin analyses of fires; and an electronic database being used by NASA White Sands Test Facility to perform and archive oxygen system/component hazards analyses.

The final section discusses a diverse range of topics, including a parametric model examining nonmetallic materials that are contaminated or damaged being used in oxygen environments; and optical techniques used to view oxygen system fires.

This new publication is an invaluable source of new information and is highly relevant to individuals and organizations that own, operate, or in any way interface with oxygen systems or oxygen-enriched atmospheres.
Joining and Repair of Composite Structures
Authors: Kim H , Kedward KT
Published: April 2008

Description

Twelve peer-reviewed papers provide the latest information on the design, analysis, testing, and fabrication of structural joint and attachment configurations. Topics cover:

Adhesively Bonded Attachments includes two useful analysis techniques on closed-form model development and the development of a test specimen configuration suitable for the strength measurement of lap joints loaded under in plane shear. This section also investigates a new double-strap joint design configuration that makes use of extra attachments to improve significantly the joint strength; the correlation between analysis and testing of thick section thermoplastics composite-to-titanium for a marine application; and a "bondable" peel ply application for bonding fiberglass skins to a polyamide honeycomb core.

Adhesively Bonded Repair addresses the repair of new armor concepts that are to be used on advanced composite military vehicles, with particular focus on characterizing the dynamic response of the adhesive joints formed in scarf repairs; and the repair of thick steel structures used in earth excavation equipment.

Bolted Attachments discusses mechanically-fastened joints, as well as cover bolted and riveted composite joint analyses; the Strain Invariant Failure Theory (SIFTŕ bolted joint failure prediction; and the use of nonlinear finite element analyses for predicting failure in composite joints based on lamina-level failure criteria
Advances in Geosynthetic Clay Liner Technology: 2nd Symposium
Authors: Mackey RE , von Maubeuge K
Published: April 2008

Description

Ten-peer reviewed papers give you the latest information on geosynthetic clay liner (GCL) technology. Topics address the ability of the current ASTM standards to assess GCLs, and how they can be improved to better meet the needs of the industry; compatibility and longevity testing of GCLs; and new testing methods to advance the understanding of GCLs and their components.

Sections cover:

Assessment of Clay Component—examines various aspects of testing the clay component and what knowledge these test results generate for the user.

Durability of Clay Component—provides a better understanding of liquid/soil interactions with the bentonite and their possible effects on the durability of the clay component of the GCL.

Evaluation of Current and Proposed GCL Standards—discusses ASTM standards D 5889 Practice for Quality Control of Geosynthetic Clay Liners; D 6495 Guide for Acceptance Testing of Geosynthetic Clay Liners; and D6243 Test Method for Determining the Internal and Interface Shear Resistance of Geosynthetic Clay Liner by the Direct Shear Method

Movement of Compounds through the GCLs—details investigations on the behavior of GCLs subject to thermal gradients in a containment application; effect of freeze-thaw on the permeation of arctic diesel fuel through GCLs

STP 1456 is a valuable resource for regulators, engineers, and researchers.
Plastic Deformation in Fretting Processes — a Review
Authors: Waterhouse RB
Published: April 2008

In recent years, analytical treatments of contacting surfaces and resultant fretting, the initiation and early propagation of fatigue cracks, have been the subject of elastic stress analysis. However, direct observations of fretting damage in optical and scanning electron microscopes indicates that plastic deformation of the contacting surfaces is usually an important feature. In this respect it has some similarity with other surface deformation processes, such as shot-peening and surface rolling, in that residual stresses are developed or existing stresses are modified. Surface films which are there as a result of oxidation or applied as an anti-fretting palliative can be seriously disrupted by plastic deformations of the substrate, resulting in a “tribologically transformed layer” or third-body intervention. Consideration of these factors can play a role in the development of methods to counteract the effect of fretting, and is the basis of this review.
Fretting-Wear and Fretting-Fatigue: Relation Through a Mapping Concept
Authors: Fouvry S , Kapsa P , Vincent L
Published: April 2008

Developments in wear mapping recently described frontiers between partial and gross slip and between the main damages i.e. cracking and particle detachment both from experiences and from theoretical analysis. These maps, known as running condition fretting maps (RCFM) and material response fretting maps (MRFM), are powerful tools to analyze the contact and to predict failures. Especially MRFM is a major contribution for designers and engineers. Mapping concept enables a new approach of fretting-fatigue as it considers crack nucleation for ranges of contact conditions. Effects of displacement and normal load on cracking are now well admitted under fretting wear conditions. The question is still related to the effect of the cyclic external loading that it is superimposed to the contact loading. Theoretical and experimental results related to homogeneous metallic contacts are discussed to attempt an objective analysis on the interest of fretting fatigue tests.
High Temperature Fretting Fatigue Behavior in an XD™ γ-base TiAl
Authors: Hansson T , Kamaraj M , Mutoh Y , Pettersson B
Published: April 2008

The plain and fretting fatigue behavior was studied of a γ-base TiAl intermetallics at 675°C in air. he TiAl material was produced by the XD™ process and had a nominal composition of Ti-47Al-2Nb-2Mn+0.8vol%TiB2. The contact material was Inconel 718. The reduction of fatigue strength by fretting was very small (around 20%) compared to metallic materials (30̃60%). The plain and fretting fatigue S-N curves were flat, which resembled the behavior of ceramic materials. The flat S-N curves are corresponding to the very steep crack growth curve reported for TiAl-based materials containing TiB2. A fretting fatigue crack nucleated in the very late stage of fatigue life (later than 0.75Nf), while it is known to nucleate in the very early stage of fatigue life (less than few percent of Nf) for steels. The fatigue lifetimes of this material were suggested to be determined by the cycles needed for nucleation of a crack rather than by crack propagation.
Spectrum Load Effects on the Fretting Behavior of Ti-6Al-4V
Authors: Kinyon SE , Hoeppner DW
Published: April 2008

An investigation was performed to determine the effects of spectrum loading on the fretting fatigue life of titanium alloy Ti-6Al-4V. The research program consisted of a 10 Hz spectrum load cycle applied at six conditions of interest with a normal pressure of 31 MPa. Baseline tests were performed at three stress levels, 345, 310, and 286 MPa maximum load using a conventional haversine waveform. Tests were performed using a spectrum load waveform consisting of 2 cycles, one at 345 MPa, followed by another at 310 MPa, repeated to failure. Additional tests were performed using 345 and 286 MPa. The final condition of interest was investigated using a 345/310/286 MPa waveform. Miners rale was applied to each of the spectrum load cases to test the hypothesis that the titanium alloy followed Miners Rule under the loading conditions. The three conditions of interest varied from Miners Rule by 23, 47, and 62%. From these results it was concluded that Miners Rule was insufficient to predict failure lives of Ti-6Al-4V in fretting fatigue.
A Multiaxial Fatigue Analysis of Fretting Contact Taking Into Account the Size Effect
Authors: Fouvry S , Kapsa P , Vincent L
Published: April 2008

Fretting damage that consists of cracking or wear generated by debris formation is induced by very small alternated displacements between contacting surfaces. This paper focuses on the quantification of the fretting crack nucleation. Fretting experimental results obtained with a well defined quenched aeronautical steel are analyzed by means of a multiaxial fatigue approach. The plane/sphere configuration was studied under partial slip situations. Validated for classical fatigue conditions, the Dang Van's fatigue prediction is compared to fretting cracking mechanisms. The correlation is achieved according to some conditions : - The friction coefficient operating in the annular partial slip contact has to be identified.

It permits more accurate estimation of the stress loading path. - The loading states which are computed to determine the crack nucleation risk must be averaged on an elementary volume representative of the microstructure of the steel. It allows a convenient size effect consideration regarding the very small material volume stressed below the contact.
Effects of Contact Load and Contact Curvature Radius of Cylinder Pad on Fretting Fatigue in High Strength Steel
Authors: Lee SK , Nakazawa K , Sumita M , Maruyama N
Published: April 2008

Fretting fatigue of high strength steel was studied at various contact loads using bridge-type fretting cylindrical pads with various contact curvature radii. The fretting fatigue life showed a minimum at a certain contact load irrespective of the pad radius even though the frictional force increased monotonously with contact load. At a high contact load, the fretting fatigue life remained almost unchanged with a change in pad radius. At a low contact load, however, the fretting fatigue life increased with an increase in pad radius even though the frictional force was independent of the radius.
Fretting Fatigue of 8090-T7 and 7075-T651 Aluminum Alloys in Vacuum and Air Environments
Authors: Elliott CB , Georgeson AM
Published: April 2008

The fretting fatigue characteristics of 8090-T7 and 7075-T651 aluminum alloys were investigated. The purpose of this investigation was to determine the relative effects of wear and environmental degradation from laboratory air on the fretting fatigue process.

The fretting fatigue test system used in this experimentation enables testing either in air or a scanning electron microscope vacuum environment. Fretting fatigue damage in vacuum tests was considered as resulting predominantly from wear, whereas damage from tests in air results from the concurrent wear and oxidation mechanisms.

Based on this experimentation, it was concluded that: • Degradation of fatigue life in air due to fretting is caused primarily by wear mechanisms for 8090-T7 aluminum. • Fretting fatigue life in air was greater than fretting fatigue life in a vacuum for the 8090-T7 aluminum under the conditions of this experimentation. • Environmental mechanisms significantly decrease fatigue life due to fretting in air for 7075-T651 aluminum. • Fretting fatigue behavior is material dependent.
Influence of Ambient Air on Nucleation in Fretting Fatigue
Authors: Woodtli J , Trzebiatowski Ov , Roth M
Published: April 2008

Fretting damage often participates in failures caused by multiple site damage (MSD) as a nucleation process. Fretting itself is an extremely complex degradation process consisting of a combination of mechanical and chemical attacks. In order to avoid damage it is essential to understand which dominating parameter influences the crack nucleation.

The topography of the fracture surface, as well as changes in microstructure provide information about the dominant damage mechanism. An exact differentiation of the predominant damage mechanism can be established by microscopic and metallographic investigations.

Two service failures in axles for ski lifts, which suffered from fretting fatigue, are discussed. Though the macroscopic findings are very similar, the microscopic investigation indicates a completely different crack nucleation mechanism.
Experimental Study of Fretting Crack Nucleation in Aerospace Alloys with Emphasis on Life Prediction
Authors: Szolwinski MP , Harish G , McVeigh PA , Farris TN
Published: April 2008

A statistically-designed experimental program engendered to validate an analytical approach for the prediction of fretting crack nucleation in 2024-T351 aluminum alloy has been completed. The test results indicate that the near-surface cyclic contact stress and strain field can be juxtaposed with a multiaxial fatigue life parameter relying on uniaxial strain-life constants to predict crack nucleation for a wide range of load intensities and conditions representative of those experienced in riveted joints. With this approach validated, efforts have been initiated to predict fretting-induced fatigue failures in riveted single lap joint structures. Research was targeted at characterizing the conditions at and around the rivet/hole interface, including finite element modeling of both the mechanics of load transfer in riveted joints and the residual stress field introduced during the rivet installation process. Model results and an ancillary set of fatigue tests of single lap joint test articles have identified a strong correlation among riveting process parameters, the mechanics of load transfer, and the subsequent tribological and fatigue degradation of the joints. Final comments are offered regarding the ability of this integrated approach to predict the fatigue performance of riveted lap joint structures.
Fretting Fatigue Strengths of Forged and Cast Al-Si Aluminum Alloys
Authors: Nisida T , Mutoh Y , Yoshii K , Ebihara O
Published: April 2008

Plain fatigue and fretting fatigue tests were carried out using cast Al-Si aluminum alloy JIS AC4CH-T6 and forged aluminum alloy JIS 6061-T6. Plain fatigue strength of the cast aluminum alloy was lower than that of the forged alloy. The lower fatigue strength was attributed to casting defects such as pores in the cast aluminum alloy, which enhanced fatigue crack formation. On the other hand, fretting fatigue strength of the cast aluminum alloy almost coincided with that of the forged alloy. No difference of tangential force coefficient and then tangential force in fretting fatigue was observed between the two materials. From fatigue crack growth tests and fretting fatigue tests interrupted at various fatigue cycles, fatigue crack growth curves and fretting crack formation life for both materials were also found to coincide with each other. These phenomena and properties resulted in the agreement of fretting fatigue strengths between the cast and forged aluminum alloys.
Skiing Trauma and Safety: Sixteenth Volume
Authors: Johnson RJ , Shealy JE , Yamagishi T
Published: April 2008

Description

Ten peer-reviewed papers provide the latest information on winter sports safety, by identifying and reducing the risks in these activities, as well as identifying appropriate treatment when injuries are sustained. Topics include:

• Injuries in Norwegian Ski Resorts 2002—2004

• Observations study on fall trends in snowboarding

• On piste fatalities in recreational snow sports in the U.S.

• Arthroscopic treatment of the first anterior shoulder dislocation in young skiers

• Evaluation of the protective role of helmets in snowboarding

• Functional and release characteristics of Alpine ski equipment

• And more!
Analysis of Fretting Damage in Polymers by Means of Fretting Maps
Authors: Chateauminois A , Kharrat M , Krichen A
Published: April 2008

The features of the fretting-wear behavior of glassy polymers against rigid counterfaces are reviewed through fretting maps concepts. The suitability of an elastic analysis to describe the fretting conditions in Running Condition Fretting Maps is discussed on the basis of numerical and experimental investigations of the contact zone kinematics. Material response in terms of cracking is subsequently analyzed in relation to the contact loading and to the plain fatigue properties of the polymer.
Fretting Fatigue Testing Methodology Incorporating Independent Slip and Fatigue Stress Control
Authors: Favrow LH , Werner D , Pearson DD , Brown KW , Lutian MJ , Annigeri BS , Anton DL
Published: April 2008

A fretting fatigue apparatus was designed, built and tested incorporating independent computer control of fretting fatigue slip distance and fatigue stress. This was accomplished through the utilization of two coaxial servo-hydraulic test actuators controlled in real time by computer. The central hydraulic actuator applies the fatigue load to the test specimen, while the outer concentric hydraulic actuator moves the fretting pin carrier apparatus. Independent control of slip displacement is achieved with the use of a capacitance displacement gage attached to the specimen fret pin carrier in such a manner that relative displacements of <5μm can be controlled. Capacitance gage measurements indicate the relative motion of the fatigue specimen surface caused by loading with respect to the fret pins. The fret pin carrier is subsequently moved to accommodate this motion plus its own-programmed motion. Load cells are provided both above and below the fatigue specimen allowing for measurement, by difference, of the forces applied by the fretting pins. These forces can be used to calculate the dynamic coefficient of friction during test operation. Finally, a 3-D finite element analysis model was constructed of the fatigue specimen and the fret pins to determine analytically the slip occurring at the fatigue specimen surface within the bounds of the test operation.
Development of a High-Temperature-Steam Fretting Wear Test Apparatus
Authors: Blinn MP , Lipkin JM
Published: April 2008

Modern power generation technology requires the development and use of advanced materials to withstand aggressive environments. Candidate materials must be durable and provide resistance to fretting wear damage; this includes both coatings and the base materials used in the machinery. A prototypical, multi-specimen test apparatus was developed for use in this fretting wear test (FWT) program. The FWT apparatus was designed to generate and contain steam at temperatures up to 595 °C (1100 °F). Contact stresses over 3.45 MPa (500 psi), displacements of 0.1 mm (4 mil), and a frequency of 160 Hz are possible using this test machine.
The Effect of the Contact Conditions and Surface Treatments on the Fretting Fatigue Strength of Medium Carbon Steel
Authors: Kubota M , Tsutsui K , Makino T , Hirakawa K
Published: April 2008

Fretting fatigue tests characterized with employing a contact bridge pad clamped to a fatigue specimen were conducted to find the effect of shapes of contact pads. The shapes of the contact edge of the pad used in the test were sharp and round. The relative slip amplitude during fatigue testing was measured and the effect of the location of the displacement sensor was discussed with the result of the stress analysis around the contact area. The effect of molybdenum coating on the fretting fatigue strength was also investigated.

It was found that by using the round edge pad, reproducible fretting scars could be obtained and also the round edge pad prevented the fatigue failure at the contact edge. A remarkable difference of the measured slip amplitude was found by the location of the displacement sensor. The molybdenum coating increases the fretting fatigue limit about 1.5 times that of the fretting fatigue strength of uncoated specimens. Fretting fatigue cracks always initiate at the inner site of the contact area. The results were explained from the results of contact stress analysis where the maximum shear stress occurred at the inner surface of the contact area in both types of the pad.