bluuebunny/crossref_metadata_2025 huggingface dataset:
Simple Two- and Three-Dimension Adhesive Finite Elements for Stress Analysis and Energy Release Rate Calculations in Adhesively Bonded Joints
Authors: Dillard DA , Taylor MW , Andruet R , Holzer SM
Published: March 2009

Special two- and three-dimensional adhesive elements have been developed for determining “mechanics of materials” level stresses in adhesively bonded joints. For two- dimensional analysis, the adherends are modeled as simple beam-truss elements connected by special adhesive elements that utilize offset nodes located at the mid-plane of the respective adherends. The technique has been extended to three-dimensional geometries by modeling the adhesive as a single element through the thickness with offset nodes located at the mid-plane of the adherends. The adherends are modeled as conventional plate elements. The simple models permitted by these elements provide good convergence to closed-form solutions for peel and shear stresses in 2-D lap joints. The 3-D elements offer significant computational efficiencies over more widely utilized three-dimensional element formulations. Although the results obtained using these elements are not sufficient to detect singular stress fields, or certain other details, they have proved to be very useful in understanding the overall stress states in bonded structures. Preliminary determination of strain energy release rates using the 2-D elements also appears to be quite promising.
The Need for Standardization of Fire Resistance Testing of Industrial Fluids (First Keynote Address)
Authors: Brandao AV
Published: March 2009

This presentation will address the need for global standardization of fire resistance criteria to promote free trade and to maximize the purchasing power of users facing increasingly tight budgets. The current proliferation of standards, both from various jurisdictions and specific to different industries, increases the number of overlapping tests that producers must perform to bring a new fluid to market.

Relative fire resistance is but one of the properties that must be established for any new or reformulated fluid. However, there is little agreement on test methodology among various jurisdictions and industries. This is a result of the largely empirical nature of fire research until very recent times. While still embracing much empirically-derived technology, in the past several decades fire research has increasingly made use of a more scientific approach. Developments in combustion science have led to a better understanding of the underlying phenomena. These new insights are now available to facilitate the design of tests that are more universally applicable to a wide variety of potential fire scenarios.
Combustion Fire Chemistry of Industrial Fluids
Authors: Newman JS
Published: March 2009

Fires generate two types of fire products in an uncontrolled fashion: heat and chemical compounds. Fires involving industrial fluids vary in the production of heat and chemical compounds due to 1) the chemical structure of the fluid, such as an aliphatic versus an aromatic hydrocarbon, and 2) the geometry or configuration of the fluid fire, such as a spray fire versus a pool fire. This paper illustrates the impact of both chemical structure and configuration on the production of heat and chemical compounds from fires.
Characteristics of Pool Fire Burning
Authors: Hamins A , Kashiwagi T , Buch RR
Published: March 2009

The structure and energetics of hydrocarbons burning in a pool fire configuration are reviewed. Examples of non-hydrocarbons are also presented. The character and structure of pool fires are discussed with special regard to the flame shape, flame pulsation frequency, flame height, and the detailed flame structure. An enthalpy balance about the flame considers enthalpy losses to the surroundings due to radiation, convection of sensible heat, and combustion efficiency considerations. The power radiated from a flame as a function of burner diameter is discussed. An enthalpy balance about the pool surface partitions the heat feedback into conduction, convection, and radiation. This enthalpy is part of a positive feedback loop which goes to vaporize the fuel. Differences between field and zone models are discussed.
Fire Resistance Testing Procedures: A Review and Analysis
Authors: Totten GE , Webster GM
Published: March 2009

Numerous tests have been developed to measure fire resistance of industrial fluids. However, few of these tests have been adopted as industry or national standards. Furthermore, little reference information is available illustrating how these tests correlate with specific fire-risk situations. This paper will provide an overview of the various tests that have been reported to quantify the relative fire-resistance of industrial fluids. This information will provide guidance in the future development of fire-resistance specifications for various types of industrial fluids.
Fire Resistance Tests for Fluids and Lubricants — Their Limitations and Misapplication
Authors: Phillips WD
Published: March 2009

A large number of tests are currently available for assessing the fire resistance of functional fluids and lubricants. Since it is extremely difficult to simulate fire conditions for fluids in laboratory tests, the main use for the different methods is a comparative assessment of the various fluids.

The fluids in commercial use, where fire resistance is a critical feature, can be divided into those which depend on water for their performance and non-aqueous fluids, where the fire resistance depends on the chemical composition. Ideally a fire resistance test should be capable of assessing the behaviour of all candidate fluids on an equal basis, but because the two groups of fluids behave in totally different ways comparison in most tests is not valid.

Although some tests suffer from indifferent precision or are unable to satisfactorily discriminate one type of fluid from another (within the same group), many rank the fluids in approximately the same order and therefore do not provide any additional information.

The introduction of two new spray ignition tests which enable all the different fluids to be compared under similar conditions is a major step forward. These tests, however, cannot simulate a condition where the water content of aqueous fluids can volatilise and leave behind a flammable residue. As a result, for the minimum assessment of the behaviour of both groups of fluid it is advisable to obtain both spray ignition test performance and performance in a ‘hot surface’ test.
General View and Critical Considerations of Spray Ignition Tests in Fire-Resistance Evaluation of Hydraulic Fluids
Authors: Heyn W
Published: March 2009

The need for a spray-ignition test method for hydraulic fluids to be used in underground mining is described. The current spray-ignition testing method as recommended by the European Commission and a proposed “heat release of a stabilised flame”testing method are discussed. The limitations of laboratory spray ignition fire-resistance testing methods, especially for non-aqueous fluids is considered. Additional measures for minimising the fire hazards in the workplace and the potential use of jet spray ignition testing for hydraulic fluids used in non-mining applications are also included in this discussion.
Spray Flammability of Hydraulic Fluids
Authors: Khan MM
Published: March 2009

The spray flammability characteristics of several hydraulic fluids, and mineral oil, methanol, ethanol, and n-heptane, sprayed vertically upward in the open through a pressure-jet hollow cone nozzle and stabilized by a propane-air ring burner, have been evaluated using the Factory Mutual Research Corporation (FMRC) Fire Products Collector. A spray flammability parameter (SFP) has been defined, which combines the combustion intensity of spray fires in terms of chemical heat release rate with the fluid volatility described by the critical heat flux for ignition. An SFP value has een identified at or below which a range of hydraulic fluids cannot be stabilized as spray flames using a standard flame stabilization test. Mineral oil, some hydraulic fluids, and highly volatile fluids such as n-heptane, methanol and ethanol, have high SFP values and are easy to stabilize as spray flames. SFP appears to be useful in discriminating between flammable and less flammable fluids.

Experimentally, it was found that the burning of multi-component fluids, such as water-in-oil emulsion and polyglycol-in-water on a wick (porous ceramic disc), does not simulate burning of such fluids in an atomized spray. Thus, a spray fire test appears to be a much better method for characterizing the flammability of all types of hydraulic fluids.
Implementation of Revised Evaluations of Less Flammable Hydraulic Fluids
Authors: Brandao AV
Published: March 2009

Factory Mutual Research Corporation (FMRC) has evaluated and certified (“Approved”) less flammable hydraulic fluids since the 1950s. This Approval is widely recognized among users, insurance interests, and regulators. However, the two traditionally used flammability tests (ignition of specifically defined sprays by open flame and a heated steel channel) have been shown to lack consistent repeatability. Consequently, the development of a new test methodology has been undertaken. The new protocol involves separate measurements of ease of ignition and heat release of the same spray discharge. These two measurements are then combined mathematically into a dimensionless “spray flammability parameter” (SFP), which becomes a unitary measure of the flammability hazard of the fluid. The revised methodology has been incorporated in the first significant revision to the Approval Standard for less flammable hydraulic fluids since the 1970s.
Ease of Extinction — An Alternative Approach to Liquid Flammability
Authors: Nelson GL
Published: March 2009

Traditionally fluid fire resistance testing has focused on ignitability under specific test conditions. It is well known, however, that fluids of similar flashpoint can differ substantially in their abilities to sustain fire. One technique which has been used extensively to measure ease of extinction of solid plastic strips is oxygen index. This simple test has also been applied to 1000 compounds including hydraulic fluids, lubricating oils, and silicone fluids. This paper reviews data on fluids and powders and discusses how oxygen index can be used to provide additional insight into the flammability behavior of fluids.
Structural Silicone Performance Testing on 2 cm Polished Granite
Authors: Carbary LD , Fulton JR
Published: March 2009

Polished granite panels, 91 cm (36 in.) x 152 cm (60 in.) x 2 cm (3/4 in.) were structurally attached with silicone adhesives to anodized aluminum frames and pressure tested to destruction after 21 days of cure and after six winters of exposed aging in Cold Spring, Minnesota. Silicone adhesives were tested for physical properties using an ASTM C1135 method both initially and after aging. Polished red granite samples were tested to a modified ASTM C880 dry and wet initially and after aging. Adhesive deflection was studied and reported along with ultimate loads required for destruction of the silicone attached granite panel. The structural silicone adhesives were found to be unaffected by the freeze-thaw cycling experienced by the panels. Ultimate performance of the aged composite panels were essentially unchanged from the initial performance. Flexural strength of the granite was found to have decreased over the test period.
A Case Study of the Use of Preformed, Surface-Applied Silicone Sealant Joints
Authors: Piper RS , Kenney RJ
Published: March 2009

Field-applied bridge or band-aid joints have had limited use for many years, and shop molded, preformed silicone sealants have been used on a very limited basis in the U.S. for less than 10 years, primarily in remedial work. Two major sealant manufacturers have recently introduced preformed silicone sealant tape for application as bridge joints. These materials, though relatively expensive compared to typical wet-applied sealant joints, are well suited for use on many remedial projects. Several recent applications are discussed, and specific joint configurations are described. Advantages and disadvantages are presented, and recommendations for use and application are made.
Movement During Cure of Latex Building Joint Sealants
Authors: Lacasse MA , Margeson JC
Published: March 2009

The level of performance of high performance building joint sealants clearly diminishes if during cure, the joint in which sealant is placed, undergoes cyclic movement. However, it is less well known the degree to which the movement capability is adversely affected. A preliminary study was undertaken to ascertain the change in performance of a series of water-based sealants and a chemical cured product subjected to movement during cure. Model sealant specimens were subjected to cyclic movement during cure at rates of 12.7mm and 3.2mm / hour such that complete cycles were achieved in 1 and 4 hours respectively. Specimens were evaluated over a single movement cycle having undergone various intervals of cure starting with those cured for 1 day and thereafter cured at 2, 3, 4, 7, 14, 21, 28, 50 and 100 days. Failure was recorded if the sealant bead ruptured or became detached from the substrate. Also, a series of specimens was continuously cycled for 4 days and the change in mechanical response was recorded with time such mat the increase in modulus during cure could readily be determined. Standard tests were also conducted as to the tack free time of these products.
Minnesota's Quality Management Program “A Process for Continuous Improvement”
Authors: Wegman DE
Published: March 2009

Minnesota's Quality Management Program began in 1986 when the Minnesota Department of Transportation (Mn/DOT) and the Minnesota Asphalt Pavement Association (MAPA) formed a partnership to develop a process for improving the quality of asphalt pavements within the state. A Quality Management Task Force was formed with members representing Mn/DOT Construction and Materials, Counties, Cities, Consultants, FHWA, Hot Mix Asphalt (HMA) Contractors and a Consultant hired as a technical advisor. The Task Force was charged with the goal to “Develop and Implement a Quality Management Program to Assure Construction of Quality Asphalt Pavements”. This was the beginning of a continuous evolution which has and will continue to guide the production and placement of HMA Mixtures.

Today the key components of the program are: 1. Volumetric Quality Control(QC), Quality Assurance (QA) and Independent Assurance Sampling and Testing (IAST) 2. Technical Certification 3. Plant Certification 4. Incentives/ Disincentives 5. Program Evaluation through Data Analysis 6. An Issue Resolution Policy
Design and Implementation of a Dynamic Quality Management System for HMA: A Case Study
Authors: Weigel JJ , Cominsky RJ , Moulthrop JS
Published: March 2009

One of the items identified during the AASHO Road Test, constructed in Ottawa, Illinois in the late 1950's, was the variability of materials, the effects of this variation on material properties and, subsequently, the performance of various construction items. These activities had a marked influence on the development of assurance specifications during the last 30 years. These specifications, while recognizing variability in sampling and testing and establishing means to evaluate their effects, also clearly delineate the quality management responsibilities of the contractor during the construction process and the acceptance procedures of the agency.

The objective of this paper is to document an effective quality management system for an HMA contractor that has been used since 1989 on numerous projects and the steps taken to design and implement such a program.

This paper discusses the essential aspects of the QM Program and the actions required by the contractor's key management personnel in implementing the program. These include planning, budgeting, equipment acquisition and training. The program was intentionally designed to be dynamic so that changes that occur because of job conditions can be easily handled.

Specific attention is given to the unit costs associated with the implementation process and the elements of an effective company-wide training effort.
The Use of Falling Weight Deflectometer in Asphalt Pavement Construction Quality Control
Authors: Zaghloul SM , Saeed NA
Published: March 2009

Good quality control (QC) practices are essential to obtain satisfactory pavements. Typical QC tests for asphalt pavements include: asphalt content, mixture properties of laboratory samples, density, …, etc. Results of these tests are used to ensure that the constructed pavements comply to specifications. However, quality of compliance to specifications and quality performance are two different things and are not always directly related to each other. The ultimate goal of QC is to have high quality of performance. However, efforts are made to achieve this goal by using laboratory based specifications, which are empirically related to field performance.

Current specifications are based on standard conditions which can be easily controlled in the laboratory but never exist in the field. Also, laboratory tests are run on samples representing individual layers (such as surface, base, etc.). In real life, a pavement structure performs as one unit and failure in one layer could happen because of another layer. Therefore, a performance-based specification that describes how a pavement must perform under the actual field conditions should be considered.

A study is underway in the Dubai Municipality (DM), U.A.E., to develop a procedure in which the falling weight deflectometer (FWD) is used to evaluate the in situ structural capacity of new pavements. FWD testing is conducted on each layer before constructing the next layer. Comparisons between the FWD test results and target deflection values are made to evaluate the construction quality of layers, as well as to identify weak spots. In this paper, the outline of this procedure is presented. Also, the results of a pilot study conducted to evaluate the procedure are presented.
Quality Management in Asphalt Pavement Construction
Authors: Davis RL
Published: March 2009

The concept of identifying and controlling the processes that are essential to quality is at the heart of Total Quality Management (TQM) The best path to quality lies in making the product right the first time. Not by sorting out and rejecting the bad, but by reducing the bad by concentrating on the control of the core process where quality is obtained at minimum cost to both the buyer and the seller. The buyer is not protected from loss by inspection and rejection. In the long run he pays for the bad material as well as the good for he has to pay for the entire cost of manufacture. There will be no suppliers or contractors if there is no profit. The cooperation of buyer and seller in the control of the process has been shown to be the optimum method of realizing the benefits of TQM in numerous instances in the revolution in quality in the private sector. While there has been much enthusiasm for Quality, Quality Assurance, and even for Total Quality Management in the construction field, the changes necessary to achieve real progress are so difficult that most transportation agencies will not even give serious consideration to them. Transportation agencies are not faced with decisions that mean life or death to their organizations that is part of everyday life in the private sector and can afford a more relaxed attitude toward their problems. The benefits and cost reductions which have been shown to follow the introduction of Total Quality Management in the private sector should be an incentive to transportation agencies to undertake the difficult organizational changes required to realize TQM.
Consideration of Hot Mix Asphalt Thermal Properties During Compaction
Authors: Chadbourn BA , Luoma JA , Newcomb DE , Voller VR
Published: March 2009

A computer program was developed at the University of Minnesota to predict asphalt concrete cooling times for road construction during adverse weather conditions. Cooling models require extensive experimental data on the thermal properties of hot-mix paving materials. A sensitivity analysis was performed to determine which thermal properties affect pavement cooling times significantly. The results indicated that more information on asphalt thermal conductivity and thermal diffusivity is required. Two suitable test methods for determining these properties at typical paving temperatures and densities were developed, and preliminary results for dense-graded and stone-matrix asphalt (SMA) mixes agreed well with values reported in the literature.
Creep Crack Growth Behavior of Aluminum Alloy 2519: Part II—Numerical Analysis
Authors: Hall DE , Hamilton BC , McDowell DL , Saxena A
Published: March 2009

The experimental analysis of high temperature fracture in Aluminum Alloy 2519-T87 presented in Part I of this paper highlighted the creep-brittle fracture characteristics of the material and showed reasonable correlation of crack growth rates with the stress intensity factor K. Part II continues this investigation numerically using growing crack finite element analyses. Experimentally observed crack growth histories of four aluminum 2519-T87 compact specimens are enforced by controlling the rate of release of finite element nodes along the crack growth path to gain insight into the relation of the crack tip fields to far field fracture parameters and to crack growth rates. A variable time-step, nodal-release algorithm is presented to model the high strain rates that occur during the initial stages of crack growth. The numerical results indicate an initial transient period of crack growth followed by a quasi-steady-state crack growth regime in which the crack tip fields change slowly with increasing crack length. Transition of crack growth to the quasi-steady-state regime, where similitude and small-scale creep conditions roughly exist, is given by a transition time tg that depends on the crack growth history and material properties. Excellent correlation of the stress intensity factor K with the crack growth rates is observed after time tg. Experimental difficulties in measuring the creep component of the load-line deflection rate are also discussed.
A Micromechanical Model for Creep Damage and Its Application to Crack Growth in a 12% Cr Steel
Authors: Sester M , Mohrmann R , Riedel H
Published: March 2009

If creep cavities on grain boundaries grow by the constrained diffusive mechanism, partly cavitated boundary facets act mechanically like microcracks. Two cell models, one based on a cylindrical cell and the other on a regular tetrakaidekahedron, are worked out numerically to explore the influence of a distribution of microcracks on the constitutive response of a creeping solid. The results confirm the predictions of analytical estimates based on the differential self-consistent method of Rodin and Parks [5]. The Rodin and Parks model is then combined with the Robinson model [9] to provide a comprehensive model covering primary, secondary, and tertiary creep under arbitrary loading conditions. The combined model is implemented in the finite element code ABAQUS. The model is adjusted to a set of creep curves for a 12% Cr steel (X 20 CrMoV 12 1), and tests on compact specimens are successfully modeled.
Environmentally Enhanced Crack Growth in Nickel-Based Alloys at Elevated Temperatures
Authors: Gao M , Chen S-F , Chen GS , Wei RP
Published: March 2009

A recent understanding of environmentally enhanced sustained-load crack growth in nickel-based superalloys at elevated temperatures is presented. This understanding is based on the results of coordinated studies of crack growth kinetics, surface chemistry, and microstructure in a commercial Inconel 718. The results suggest that environmental enhancement of sustained-load crack growth in Inconel 718 is associated with the formation and rupture of niobium oxides at grain boundary surfaces and is controlled mainly by the rate of oxidation and decomposition of niobium carbides at the grain boundaries. Data on other nickel-based alloys in the literature appear to support this suggested role of niobium. Initial results from a study of a niobium-free Ni-18Cr-18Fe alloy (its base composition is identical to Inconel 718) confirm the possible influence of niobium and the proposed mechanism. Some open issues for further investigation are discussed.
Analysis of the Intergranular Cracking Process Inside Polycrystalline Heat-Resistant Materials Under Creep-Fatigue Conditions
Authors: Tada N , Zhou W , Kitamura T , Ohtani R
Published: March 2009

In order to investigate the intergranular failure process in polycrystalline materials under creep-dominant fatigue, numerical simulation of inner small cracks was conducted on the basis of a simple probabilistic model. Although the simulation condition is determined from experimental observation of the cross section of specimens interrupted at different fatigue cycles, the simulation is carried out continuously and reproduces inner cracking behavior throughout the fatigue life. This enables us not only to extract the spatial distribution of inner cracks at arbitrary creep-fatigue cycles, but also to calculate the propagation rate of each inner crack.
Effects of Loading Rate on Creep Crack Growth During the Succeeding Load-Hold Period Under Trapezoidal Fatigue Waveshapes
Authors: Yoon KB , Baek UB , Suh CM
Published: March 2009

When turbines are started up in power plants, the procedures recommended by the manufacturer should be carefully followed. However, many utilities often start turbines so fast that they accelerate the crack growth of existing cracks. Hence, in order to accurately predict the crack growth life of a turbine rotor, a crack growth prediction model is needed in which the effects of load increase time on the crack growth rate during the succeeding load hold period are considered.

In this study, creep-fatigue crack growth tests were performed at 538°C using C(T) specimens of 1Cr-1Mo-0.25V rotor steel. Triangular and trapezoidal fatigue waveshapes with 0.5, 1, 10, and 100-s load rise times and 100-s load hold times were employed. The time-dependent crack growth rate during the load hold period, (da/dt)avg, was correlated with estimated (Ct)avg. Large data scatter was observed due to the effect of various load increase rates reaching the hold load. A new Ct, estimation equation was proposed in which the effects of load increase rate are considered. The effectiveness of the proposed equation is argued by showing that the scatter of the measured (da/dt)avg data was reduced when the new equation was adopted. Also, characteristics of the initial transient crack growth behavior are studied and show that the cause is the oxidation-dominated crack growth mechanism during the transient period.
Atmospheric Influence on Fatigue Crack Propagation in Titanium Alloys at Elevated Temperature
Authors: Sarrazin-Baudoux C , Lesterlin S , Petit J
Published: March 2009

The fatigue crack propagation behavior of a Ti-6Al-4V alloy has been investigated at room temperature and at 300°C. Tests were run in air, high vacuum, and some other environments with controlled partial pressure of water vapor and oxygen. The enhancement of the fatigue crack growth rates observed in air in comparison to high vacuum, considered as an inert environment, is clearly attributed to the presence of water vapor. Tests in a controlled environment demonstrate that very low partial pressure can accelerate crack propagation. On the basis of previous studies on Al alloys and steels, two controlling mechanisms are considered and discussed, namely, a propagation-assisted water vapor adsorption and a hydrogen-assisted propagation.
Micromechanical Modeling of Temperature-Dependent Initiation Fracture Toughness in Advanced Aluminum Alloys
Authors: Haynes MJ , Somerday BP , Lach CL , Gangloff RP
Published: March 2009

The temperature dependence of the plane-strain initiation fracture toughness (KJICi) is modeled micromechanically for a variety of advanced aluminum alloys that fail by microvoid processes. Materials include precipitation-hardened ingot metallurgy, spray formed, submicron-grain-size powder metallurgy, and metal-matrix composite alloys. A critical-plasticstrain-controlled model, employing tensile yield strength, elastic modulus, work hardening, and reduction of area measurements, successfully predicts KJICi versus temperature for eight alloys, providing a strong confirmation of this approach. Modeling shows that KJICi is controlled by the interplay between the temperature dependencies of the intrinsic failure locus εfp (σmσfl) and the crack-tip stress/strain fields governed by alloy flow properties. Uncertainties in εfp (σmσfl), as well as the critical distance (volume) for crack-tip damage evolution, hinder absolute predictions of KJICi. Critical distance (calculated from the model) correlates with the nearest-neighbor spacing of void-nucleating particles and with the extent of primary void growth determined from quantitative fractography. These correlations suggest a means to predict absolute plane-strain fracture toughness.
Oxidation and Mechanical Damage in a Unidirectional SiC/Si3N4 Composite at Elevated Temperature
Authors: Yang F , Saxena A , Starr TL
Published: March 2009

The results of a study on the high-temperature damage mechanisms in a unidirectional Nicalon fiber-reinforced reaction-bonded silicon nitride (RBSN) composite are presented in this paper. The microstructure of the as-manufactured and tested specimens were characterized using a variety of techniques including: X-ray diffraction; optical, scanning, and transmission microscopy; and dilatometry. Single-edge notch specimens under three-point bend loading were tested under a constant displacement-rate condition as well as under a sustained loading condition at 1000°C in air. The load-line displacement was used as the in situ indicator of damage accumulation. The fracture surface and the damage zone around the main crack were characterized in the fractured specimens to investigate the high-temperature fracture mechanisms. Under constant displacement rate, the composite showed extensive nonlinear load versus displacement behavior, indicating that the presence of the fiber has indeed toughened the composite. Cracks propagated nominally along the notch plane, though some delaminations were also observed. The substantial bulk oxidation occurred even at test temperatures as low as 800°C and resulted in significant changes in the dimension of the composite specimens. The fiber pullout, fracture surface morphology, and delamination were all strongly influenced by the high temperature oxidation.
Assessing Crack Growth Behavior Under Continuous Temperature Gradients
Authors: Cunningham SE , DeLuca DP
Published: March 2009

A process for automated temperature gradient crack growth testing has been developed and shown to be effective in characterizing crack growth properties which vary as a function of temperature. This method, which controls temperature while correcting for measurable temperature dependent material properties, has been used with DC electric potential drop and compliance techniques for a variety of specimen configurations. Its development has led to varied approaches for temperature dependent crack growth models used in life predictions and has enabled the investigation of temperature dependent fracture modes. Benefits to the aircraft engine industry include better understanding of temperature dependent material behavior, novel temperature-crack growth based design strategies, and reductions in material characterization costs.
Thermal Fatigue Testing System for the Study of Gamma Titanium Aluminides in Gaseous Environments
Authors: Gao M , Dunfee W , Miller C , Wei RP , Wei W
Published: March 2009

To critically assess the thermal fatigue resistance of γ-titanium aluminides in hydrogen and other gases, a thermal fatigue test system and associated procedures were developed. The test equipment consisted of an environmental chamber, a rigid test fixture with fixed grips, and a thermal controller. Direct electrical resistance heating was used to heat the specimen, and cooling was accomplished by a chilled gas jet. Characterization of the thermal-mechanical features of the equipment showed that the system allows for rapid heating and cooling rates with acceptable control of the thermal stresses and has excellent repeatability between cycles.

Proof tests were performed on a Ti-48Al-2Cr alloy in helium, hydrogen, and air, with temperature cycling between 25 and 900°C and a preload equal to 50% of the material's yield strength. The results showed that the equipment and test method developed here are an effective tool for material evaluation, specifically for the critical assessment of materials for high temperature applications in hydrogen and hydrogenous gases.
Thermal Mechanical Fatigue Crack Growth in Titanium Alloys: Experiments and Modelling
Authors: Dai J , Marchand NJ , Hongoh M
Published: March 2009

Strain controlled thermal-mechanical fatigue crack growth (TMFCG) tests were conducted on two titanium alloys, namely Ti-6A1-4V and Ti-6Al-2Sn-4Zr-6Mo, to evaluate the effect of phase angle between strain and temperature on the TMFCG rates. Three fracture mechanics parameters were used to correlate the data: the ΔK, ΔKe and ΔKeff. A fractographic study of the specimens tested under TMF was carried-out to identify the mechanisms responsible for cracking in these two titanium alloys. Hence, specimens tested under in-phase (εmax at Tmax), out-of-phase (εmin at Tmax) and counter-clockwise diamond (90° out-of-phase) conditions were compared to specimens tested under isothermal conditions (Tmin and Tmax) for different ΔKeff levels. The dominant TMF cracking mechanisms were mechanical fatigue (crack tip plasticity) and oxygen-induced embrittlement. The ΔKeff was found to be the only parameter to properly correlate all the data obtained under various testing conditions. A model is developed to predict the TMFCG rates based solely on isothermal data. The model uses a linear summation of the contributions to crack growth of the two dominant mechanisms which are active at the minimum and maximum temperature of the cycle. A discussion on the applicability of the model to predict the fatigue lives of actual components is discussed.
Analysis of the Thermoviscoplastic Behavior of [0/90] SCS-6/TIMETAL®21S Composites
Authors: Coker D , Neu RW , Nicholas T
Published: March 2009

Micromechanical modeling is used to determine the stresses and strains due to both mechanical and thermal loads in [0/90] titanium matrix composites (TMCs) subjected to cooldown from the processing temperature and subsequent thermomechanical fatigue (TMF) loading conditions. The [0/90] composite is treated as a material system composed of three constituents: fiber and matrix in the [0] ply, and a [90] ply. The [0/90]S layup is modeled by a uniaxial stress rule of mixtures model for the [0] ply and adding a parallel element to the [0] model and invoking strain compatibility and stress equilibrium in the loading direction. The fiber in the [0] ply is treated as elastic and the matrix in the [0] ply is treated as viscoplastic with temperature dependent mechanical properties. The [90] ply is characterized as a viscoplastic material including damage from fiber/matrix interface separation. Computations are made for isothermal fatigue as well as in-phase and out-of-phase TMF conditions for the crossply SCS-6/Timetal®21S composite. Effects of frequency and maximum temperature on the composite and constituent stress-strain behavior are evaluated. Fiber/matrix separation and strain ratchetting are found to be important factors in describing the response. Fiber stresses are shown to be dominant in isothermal fatigue at low frequencies as well as under in-phase TMF conditions. Matrix stresses dominate the behavior under high frequency isothermal fatigue and out-of-phase TMF. The use of tenth cycle constituent stresses is shown to be a good compromise between capturing the fully relaxed behavior and computational efficiency.
Damage Accumulation in Titanium Matrix Composites Under Generic Hypersonic Vehicle Flight Simulation and Sustained Loads
Authors: Johnson WS , Mirdamadi M , Bakuckas JG
Published: March 2009

The damage accumulation behavior of a [0/90]2s laminate made of Ti-15V-3Cr-3Al-3Sn (Ti-15-3) reinforced with continuous silicon-carbide fibers (SCS-6) subjected to a simulated generic hypersonic flight profile, portions of the flight profile, and sustained loads was evaluated experimentally. Portions of the flight profile were used separately to isolate combinations of load and time at temperature that influenced the fatigue behavior of the composite. Sustained load tests were also conducted and the results were compared with the fatigue results under the flight profile and its portions. The test results indicated that the fatigue strength of this materials system is considerably reduced by a combination of load and time at temperature.
Fatigue Behavior of [0]8 SCS-6/Ti-6Al-4V Composite Subjected to High Temperature Turboshaft Design Cycles
Authors: Aksoy SZ , Gayda J , Gabb TP
Published: March 2009

Mission cycle fatigue testing of a [0]8 SCS-6/Ti-6A1-4V composite was performed. The mission cycle simulates the stress-temperature-time profile in a ring-reinforced impeller of a turboshaft engine. The cycle has a fourteen minute period and attains a peak stress and temperature of 1100 MPa and 427‡C respectively. A fatigue life of 9,528 cycles was achieved. While this life was less than the design goal, 15,000 cycles, a moderate increase in fiber content coupled with a small decrease in peak stress or temperature would probably achieve the stated design goal.
An Experimental and Analytical Investigation of Titanium Matrix Composite Thermomechanical Fatigue
Authors: Ball D
Published: March 2009

The results of complementary experimental and analytical investigations of thermomechanical fatigue of both unidirectional and crossply titanium matrix composite laminates are presented. Experimental results are given for both isothermal and thermomechanical fatigue tests which were based on simple, constant amplitude mechanical and thermal loading profiles. The discussion of analytical methods includes the development of titanium matrix composite laminate constitutive relationships, the development of damage models and the integration of both into a thermomechanical fatigue analysis algorithm. The technical approach begins with a micro-mechanical formulation of lamina response. Material behavior at the ply level is based on a mechanics of materials approach using thermo-elastic fibers and an elasto-thermo-viscoplastic matrix. The effects of several types of distributed damage are included in the material constitutive relationships at the ply level in the manner of continuum damage mechanics. The modified ply constitutive relationships are then used in an otherwise unmodified classical lamination theory treatment of laminate response. Finally, simple models for damage progression are utilized in an analytical framework which recalculates response and increments damage sizes at every load point in an applied thermal/mechanical load history. The model is used for the prediction of isothermal fatigue and thermomechanical fatigue life of unnotched, crossply [0‡/90‡]s titanium matrix composite laminates. The results of corresponding isothermal and thermomechanical fatigue tests are presented in detail and the correlation between experimental and analytical results is established in certain cases.
Mechanisms Controlling the Composition Influence on Radiation Hardening and Embrittlement of Iron-Base Alloys
Authors: Nikolaev VA , Rybin VV
Published: March 2009

Classification and ranking of the solid solution on thier reaction to the irradiation is suggested on the basis of binary system structure controlling by mixing enthalpy sign, melting temperatures relation of components and solidus curves slope. Several combinations of these characteristics permit to pick out three groups of substitutional elements capable to form the vacancy-solute atom complexes either low-mobile or fast-mobile ones as compared to monovacancies migration. The radiation hardening (and embrittlement) of binary alloys should be intensified respectively either due to heterogeneous point defect clusters nucleation on solute traps or due to solute atom clusters/precipitate formation. A local cohesion decrease may also occur especially if low-melting elements (characterized by low surface energy) are segregating on internal sinks or grain boundaries. The predicted specifics of different alloy group under irradiation and during post-irradiation annealing were experimentally examined using a wide set of Fe-base alloys. A good agreement was find between expected and really observed behaviour of alloys.
Pressure Vessel Embrittlement Predictions Based on a Composite Model of Copper Precipitation and Point Defect Clustering
Authors: Stoller RE
Published: March 2009

A theoretical model is used to investigate the relative importance of point defect clusters (PDC) and copper-rich precipitates CRP) in reactor pressure vessel (RPV) embrittlement and to examine the influence of a broad range of irradiation and material parameters on predicted yield strength changes. The results indicate that there are temperature and displacement rate regimes wherein either CRP or PDC can dominate the material's response to irradiation, with both interstitial and vacancy type defects contributing to the PDC component. The different dependencies of the CRP and PDC on temperature and displacement rate indicate that simple data extrapolations could lead to poor predictions of RPV embrittlement. It is significant that the yield strength changes predicted by the composite PDC/CRP model exhibit very little dependence on displacement rate below about 10−9 dpa/s. If this result is confirmed, concerns about accelerated displacement rates in power reactor surveillance programs should be minimized. The sensitivity of the model to microstructural parameters highlights the need for more detailed microstructural characterization of RPV steels.
The B&W Owners Group Program for Microstructural Characterization and Radiation Embrittlement Modelling of Linde 80 Reactor Vessel Welds
Authors: Pavinich WA , Harbison LS
Published: March 2009

The Babcock and Wilcox Owners Group (B&WOG) is sponsoring an on-going study to develop an understanding of radiation embrittlement of Linde 80 reactor vessel welds from a micro-mechanical viewpoint. Previous work that focused on characterizing the large microstructural features indicated that a large portion of the bulk copper content is in precipitate/inclusion/carbide form. This result indicates that copper in solid solution is considerably less than the bulk composition. Field-ion microscope atom probe investigations on unirradiated weld metals with bulk copper contents ranging from 0.22 to 0.38 wt%, also indicate significant amount of copper are tied up in precipitate/inclusion/carbide form. This results is significant since the bulk copper content (which includes both copper in solid solution and copper contained in precipitates, inclusions, and carbides) is used in Regulatory Guide 1.99, Revision 2 to determine radiation damage. This paper reviews these results.

Existing radiation embrittlement models superpose the changes in yield strength due to defect clusters and copper-rich precipitates induced by neutron irradiation. Low-copper Linde 80 welds display little or no increase in the 41 joule (30 ft-lb) transition temperature as a result of neutron irradiation which indicates that precipitation is the dominant component of radiation embrittlement for Linde 80 welds. Future work will include further microstructural characterizations of Linde 80 reactor vessel welds and applying the existing radiation embrittlement models to Linde 80 welds. This paper describes the detailed plans for future work.
Modeling of Irradiation Embrittlement and Annealing/Recovery in Pressure Vessel Steels
Authors: Lott RG , Freyer PD
Published: March 2009

The results of reactor pressure vessel (RPV) annealing studies are interpreted in light of the current understanding of radiation embrittlement phenomena in RPV steels. An extensive RPV irradiation embrittlement and annealing database has been compiled and the data reveal that the majority of annealing studies completed to date have employed test reactor irradiated weldments. Although test reactor and power reactor irradiations result in similar embrittlement trends, subtle differences between these two damage states can become important in the interpretation of annealing results. Microstructural studies of irradiated steels suggest that there are several different irradiation-induced microstructural features that contribute to embrittlement. The amount of annealing recovery and the post-anneal re-embrittlement behavior of a steel are determined by the annealing response of these microstructural defects. The active embrittlement mechanisms are determined largely by the irradiation temperature and the material composition. Interpretation and thorough understanding of annealing results require a model that considers the underlying physical mechanisms of embrittlement. This paper presents a framework for the construction of a physically based mechanistic model of irradiation embrittlement and annealing behavior.
The Modelling of Irradiation Embrittlement in Submerged-Arc Welds
Authors: Bolton CJ , Buswell JT , Jones RB , Moskovic R , Priest RH
Published: March 2009

Until very recently, the irradiation embrittlement behaviour of submerged-arc welds has been interpreted in terms of two mechanisms, namely a matrix damage component and an additional component due to the irradiation-enhanced production of copper-rich precipitates.

However, some of the weld specimens from a recent accelerated re-irradiation experiment have shown high Charpy shifts which exceeded the values expected from the measured shift in yield stress. Microstructural examination has revealed the occurrence of intergranular fracture (IGF) in these specimens, accompanied by grain boundary segregation of phosphorus.

Theoretical models were developed to predict the parametric dependence of irradiation-enhanced phosphorus segregation on experimental variables. Using these parametric forms, along with the concept of a critical level of segregation for the onset of IGF instead of cleavage, a three mechanism trend curve has been developed. The form of this trend curve, taking into account IGF as well as matrix and copper embrittlement, is thus mechanistically based. The constants in the equation, however, are obtained by a statistical fit to the actual Charpy shift database.