bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Minor Alloying Elements and Stress on Microstructural Evolution and Void Swelling of Austenitic Steels Under Neutron Irradiation
Authors: Hübner R , Ehrlich K
Published: April 2008

A pressurized tube experiment was carried out in the British Prototype Fast Reactor (PFR) at Dounreay, U.K. in order to determine swelling and stress-induced swelling of four heats of the commercial German austenitic steel DIN 1.4970, with different contents of the minor alloying elements Si, Ti and Ti/C ratio. The maximum doses achieved are 106 dpaNRT at 420°C, 81 dpaNRT at 500°C and 61 dpaNRT at 600°C. The hoop stresses of the pressurized tubes were 0, 60 and 120 MPa at all irradiation temperatures. TEM-examinations have been carried out to determine the influence of the minor alloying elements and the stress on the void swelling and the microstructural evolution. All alloys exhibited the highest swelling values at 420°C and no swelling at 600°C. The measurements show the large effect of the minor alloying elements upon swelling and in-pile creep. The maximum swelling suppression is achieved by a high Si-content and an understoichiometric Ti/C ratio (understabilization). The analysis of the microstructural evolution shows that the swelling resistance is correlated to the formation and stability of very fine γ'-precipitates. For the alloy with the highest swelling resistance these precipitates can be found up to 106 dpaNRT at 420°C, whereas they dissolve in the course of irradiation for the alloys with lower swelling resistance.

The estimates of the stress-induced swelling using the Soderberg theorem and the length measurements are compared with immersion density measurements and results of void structure analysis by TEM. All methods yield the same order of magnitude for the stress-induced linear swelling.
On the Formation of α-Ferrite in Stainless Steel Alloys
Authors: Schüle W
Published: April 2008

Results of investigations on the microstructure of nickel-containing and of manganese-containing stainless steel alloys by means of the electrical resistivity are reported. These investigations were completed by X-ray diffractometry, by measurements of the magnetic response and of the stored energy. The investigations were performed on AMCR- and 316-type materials and on model stainless steel alloys varying slightly in the composition of the main components of the alloys and the concentrations of the additions.

The following phases were identified: α-ferrite, γ-austenite, α'-martensite, α'def.-martensite, ε-martensite, εdef.-martensite, α-Mn and σ-phase. Small amounts of α-ferrite, α-Mn and σ-phase in stainless steel alloys cause brittleness.

It was found that α-ferrite is always formed when nucleation sites, e.g. α'-martensite and dislocations, are provided, α-ferrite is readily formed by annealing at e.g. 356°C and is dissolved again after annealing for one month at the same temperature, when the nucleation sites are dissolved or recovered.

During irradiation with high energy particles α-ferrite is formed below about 600°C in AMCR- and 316-type stainless steel alloys. The amount of α-ferrite formed at 100°C is so large that many of the stainless steel specimens broke before a dose of 0.11 dpa was obtained.

These findings require a modification of the phase diagrams of stainless steel alloys.
Neutron-Induced Evolution of Mechanical Properties of 20% Cold-Worked 316 Stainless Steel as Observed in Both Miniature Tensile and TEM Shear Punch Specimens
Authors: Hamilton ML , Garner FA , Hankin GL , Faulkner RG , Toloczko MB
Published: April 2008

Three heats of 20% cold worked 316 stainless steel were irradiated in the Materials Open Test Assembly of the Fast Flux Test Facility producing data at three or four irradiation increments to doses ranging from 12 to 88 dpa. There were five irradiation temperatures ranging from 400 to 730°C. The specimens were in two forms, standard TEM microscopy disks and miniature tensile specimens, irradiated side by side. The tensile specimens were tested at room temperature, and the TEM disks were subjected to a shear punch test, also at room temperature. Both methods yielded very similar results, showing that the mechanical properties of these steels quickly approached and then maintained saturation levels of yield strength. The saturation levels were only slightly dependent on heat identity, but were strongly dependent on irradiation temperature. Ductility decreased with increasing exposure, however.

It was shown that the tensile and shear punch data can be well-correlated with simple expressions that reflect the differences in stress state and physical constraints of the two techniques. This allows the application of the shear punch technique to situations where steep neutron flux or gamma heating gradients, insufficient irradiated material or insufficient reactor volume prevent the use of even small tensile specimens.
Effect Of Irradiation On Structural Materials In Fusion Reactors
Authors: Tavassoli F , Burlet H , Lind A , Singh BN , Tähtinen S , van Osch E
Published: April 2008

The ITER R&D program on the structural design criteria includes the effects of irradiation on material's properties. The work has started with the design rules for stainless steels at low temperatures (< 350°C) and at moderate irradiation doses (3 – 10 dpa), where degradation of ductility and toughness are of primary concern. It is now extended to copper alloys and multi-layer components, as well as to rules for high temperature properties. A similar work has also been initiated on ferritic / martensitic steels for the future Demonstration reactor, where the operating temperature range is 250–550°C and anticipated irradiation doses are well over 70 dpa.

This paper presents an overview of the above work. It details some of the recent irradiation data obtained for stainless steel type 316LN, precipitation strengthened CuCrZr alloy, oxide dispersion strengthened Cu-A125 alloy, and commercial and low activation grades of 7–10%Cr ferritic / martensitic steels. Since most of the fusion invessel components have to be fabricated using advanced manufacturing techniques, e.g. high temperature isostatic pressing (HIP) of steel/copper/beryllium layers in ITER primary modules, the paper also analyzes effects of such processes on the materials properties and design data.
Effect of Ion-Irradiation on Phase Transformation in TiNi Shape Memory Alloys
Authors: Matsukawa Y , Sumita Y , Ohnuki S , Watanabe S , Namba C , Takahashi H
Published: April 2008

Ion-irradiation induced amorphization and crystallization processes in TiNi shape memory alloys have been investigated. The primary concern is to clarify the relationship between the critical temperature for irradiation-induced amorphization and the thermal crystallization temperature. The critical temperature for irradiation-induced amorphization was 673K, however, the edge of the foil specimen crystallized during the irradiation at a lower temperature. The crystallization temperature of the specimen edge during irradiation decreased with increasing of incident ion energy. Thermal annealing experiments revealed that the thermal crystallization preferentially occurred at the specimen edge and the crystalline-amorphous (C-A) interface; The crystallization temperature of the preferential sites were 573K and 623K, respectively. These preferential nucleation indicate that the nucleation barrier dominates the thermal crystallization temperature; the critical temperature for amorphization is higher than the thermal crystallization temperature with no nucleation barrier.
Irradiation Growth of Zirconium Alloys at High Neutron Fluences
Authors: Shamardin VK , Kobylyansky GP , Kosenkov VM
Published: April 2008

The effect of high dose irradiation on irradiation growth in zirconium commercial Zr-1%Nb, Zr-2.5%Nb, Zr-1%Nb-1.3%Sn-0.4%Fe alloys at temperatures of ∼80 and 320–360°C has been investigated.

It is shown that the irradiation growth strain in Zirconium and Zr-Nb alloys as a function of neutron fluence sharply increases at fluences higher than (2–3)×1026 m-2 (E>0.1 MeV). Zr-1%Nb-1,3%Sn-0,4%Fe alloy was observed to exhibit radiation growth at high neutron fluences.

One of the methods to reduce anisotropy of properties and dimensional changes under irradiation is fast high-frequency treatment (FHF) consisting in quenching from beta-phase following quick heating with exposure.
Geotechnical Characterization of a Clayey Soil Stabilized with Polypropylene Fiber Using Unconfined Compression and Resilient Modulus Testing Data
Authors: Iasbik I , de Lima DC , Carvalho CAB , Silva CHC , Minette E , Barbosa PSA
Published: April 2008

This paper focuses on the geotechnical characterization of a clayey soil and its mixture with polypropylene fiber. The laboratory testing program was directed to: (i) analysis of the influence of fiber content and fiber length on the unconfined compression strength of a clayey soil in order to determine optimum parameters to be used in repeated-loading triaxial tests, and (ii) analysis of the influence of fiber on the resilient modulus of the clayey soil, according to the Brazilian Standard DNER-ME 131/94. The laboratory testing data support that: (i) the mechanical response of the composite is fiber content and fiber length dependent; (ii) addition of fiber to the soil improves substantially its unconfined compression strength; and (iii) addition of fiber to the soil is also responsible for substantial decrease in its MR values, and produces a composite that can be useful in road engineering practice.
Resilient Modulus Testing Using Conventional Geotechnical Triaxial Equipment
Authors: Konrad JM , Robert C
Published: April 2008

This paper presents the results of a comprehensive laboratory investigation program on the mechanical properties of an unbound aggregate used in pavement base courses. Repeated load triaxial tests were used to assess the influence of test conditions (specimen size, degree of saturation, pulse loading and loading sequence) on resilient modulus. A conventional triaxial setup, used by most geotechnical laboratories, was adapted for the testing of 100-mm-diameter and 200-mm-high specimens. The material response under a sinusoidal variation of load was compared with the AASHTO procedure on larger samples and different pulse loading. The test program showed that the resilient modulus obtained from the different loading sequences agreed well for given density and moisture content conditions. Conventional triaxial equipment can be used to determine the resilient modulus of unbound aggregates provided accurate displacement gauges are used in the middle-third of the specimen.
A Case History: Refutation of Alleged Floor Maintenance Malpractice by the Application of Forensic Biomechanics
Authors: Sacher A
Published: April 2008

This paper is based upon the author's liability expert report prepared for the defendant's attorney who represented a general maintenance contractor. The author was retained to evaluate the technical aspects and merits of the case, and to render an opinion, which would meet the criteria of the Supreme Court's “Daubert” decision.

The complaint charged that the subject (unwittnessed) slip and fall accident was the result of negligent floor maintenance in an office building where the plaintiff was employed. And more specifically, it was due to the defendant's negligent spraying of furniture polish onto a carpeted floor, the accident situs.

A brief review of the circumstances surrounding the accident is presented, followed by: (a) select portions of the plaintiffs “remarkable” (medical terminology for significant and relevant) prior and post accident medical history; (b) the more salient aspects of the plaintiff's deposition testimony and that of the defendant's maintenance supervisor; (c) an inspection of the accident site; (d) coefficient of friction measurements of the subject carpet (before and after application of the plaintiff identified furniture polish) by two independent test laboratories retained by both the defendant and plaintiff; (e) technical considerations (the biomechanics of walking mishaps, the pathophysiologic consequences of injuries and surgeries, et al); and (f) the author's opinion, to wit, that the plaintiffs detailed description of the alleged incident was exquisitely inconsistent with the biomechanics of a slip and fall accident. But instead, it is suggested that the accident was actually the result of a stumble, the sequela of the plaintiffs prior chronic locomotor deficiencies.
Structural Glazing Failure — Five Case Studies
Authors: Baker ME
Published: April 2008

Silicone sealant manufacturers produce extensive amounts of information instructing users of silicone structural glazing material on proper use of their material, including design guidelines, compatibility analysis, material storage, handling and application, including surface preparation and installation instructions. What are usually not shared are the results of not following the manufacturers' instructions. The following five case studies are examples of actual projects where structural silicone sealant failure occurred as a result of improper use of the material. The case studies are followed by commentary on what might be done to prevent failure in the future.
Application of a Sublaminate Method to the Analysis of Bonded Joints
Authors: Flanagan GV , Chatterjee S
Published: April 2008

The sublaminate method consists of using stacked and interconnected plates to evaluate interfacial tractions. A high-order plate theory that includes shear and through-thickness stretching is used for each layer. For composites, the stacking sequence information is included. Because the method is an accurate and convenient way to evaluate debond between layers, it is natural to apply the technique to bonded joints. Previous work had focused on exact solutions of these systems. To create a practical tool for bonded joints, nonlinear material properties had to be included. This was accomplished with an approximate method using the P-element technique. One unusual feature is that the material property distribution is approximated using the same functions. The paper outlines the method, and gives examples that highlight the capability of the code. In particular, the bending behavior of joggled joints can be evaluated. The code can also be used to determine strain-energy-release rate for an existing crack between layers.
Adhesive Nonlinearity and the Prediction of Failure in Bonded Composite Lap Joints
Authors: Kim H , Lee J
Published: April 2008

A theoretical model is derived that predicts failure in adhesively bonded lap joints loaded by in-plane shear. This model is based on shear lag assumptions and accounts for a nonlinear adhesive shear stress-strain relationship so that the development of plastic strain is tracked. Failure of the joint is determined when the plastic strain reaches its ultimate value. By accounting for adhesive plasticity, this model permits the design of joints with higher load-carrying efficiency than designs based on simple elastic-to-failure adhesive constitutive behavior. Example calculations presented in this paper show that the theoretical model predicts failure load accurately for a carbon/epoxy adherend joint (within 6%), in comparison with finite element analysis (FEA) predictions, for joints with adhesive bondlines of 0.33 mm or less. For the thicker bondlines studied, a severe strain localization effect was observed in the FEA models to occur at the joint interface corners, and therefore the theoretical model over-predicted failure load by up to 22% for 2.08 mm bondline carbon/epoxy adherends.
Box Beam Lap Shear Torsion Testing for Evaluating Structural Performance of Adhesive Bonded Joints
Authors: Tomblin JS , Seneviratne WP , Kim H , Lee J
Published: April 2008

In this study, failure strengths of in-plane shear loaded bonded joints were compared with analytical predictions of Shear Loaded Bonded Joint (SLBJ) theory. The investigation was carried out in two phases. Phase I was conducted with a particular focus placed on the effect of bondline thickness on joint strength. These specimens were fabricated using E-glass/epoxy cloth and PTM&W ES6292 two-component paste adhesive. A box beam torsion test fixture was used to apply a shear loading. Phase II was carried out to investigate adhesive and/or adherend variability in SLBJ predictions. These specimens were fabricated using aluminum and carbon adherends with Loctite and Hysol EA9360 paste adhesives. Several joggle (production-style) joints were tested to investigate the effects of joggle adherend on strength of the adhesive joint. Furthermore, a failure analysis was conducted to study the failure mechanism of these joints. Experimental data and SLBJ predictions indicated a decrease in strength as the bondline thickness was increased. SLBJ predictions for thin bondlines were comparable with experimental data, but for thick bondlines SLBJ predictions were lower than the experimental data. Substrate failure of EA9360 specimens resulted in significantly lower experimental data than SLBJ predictions. An accumulation of large plastic strains in thin bondlines resulted in high adherend interlaminar strains and caused substrate failure. The unstable damage development of thick bondlines resulted in adhesive cracking in multiple locations with a cohesive type failure and lower failure strengths than that of the thin bondlines.
Performance of a Composite Double Strap Joint with Attachments
Authors: Qian H , Sun CT
Published: April 2008

Thin composite laminate attachments were designed and added onto the conventional double-strap joints so that additional load transfer paths were created and localized interfacial stress concentrations near the joint edge were reduced. Experiments were performed and the result revealed that the new double-strap joint with attachments had significantly greater strengths than the conventional double-strap joint. Joints with attachments having different angular configurations and lay-ups were tested and different failure modes were observed. Interfacial stresses along the bondlines were analyzed in order to understand the increase in joint strength and the change of failure modes in joints with attachments.
Ski Injury Epidemiology: A Short-Term Epidemiology Study of Injuries with Skiboards
Authors: Greenwald RM , Nesshoever M , Boynton MD
Published: April 2008

A one-season epidemiology study of skiing injuries at a large Eastern ski resort was conducted for the 1998–99 season to compare injury rates and injury severity for various mountain sports, including alpine skiing, snowboarding, and, particularly, the new sport of skiboarding. Ski patrol reports and follow-up medical injury diagnosis data at the mountain clinic were compiled along with demographic information about the injured skiers and their equipment. The population at risk for each sport was determined by collecting parking lot surveys of typical skiers using previously published methodologies. The overall injury rate for all sports at the mountain was consistent with rates reported in the literature at other ski resorts. Injury rates for skiboards represented 1.1% of the total injury population, while participation in this sport was 2.7% of the entire mountain population. Skiboard users were younger than skiers, and were predominantly male. Lower leg fractures and shoulder injuries represented 56% of the total skiboard injuries (n = 24). Tibia fractures occurred much more frequently in the skiboard population than in the alpine skiing population, while knee sprains were significantly lower in the skiboard population. This study represents one of the first studies of skiboard use, and is limited to one mountain and one season. The study will be continued in subsequent years to determine significant injury trends and implications for prevention of injuries in skiboarding.
Elastic-Plastic Fracture Mechanics: Where Has it Been? Where is it Going?
Authors: Landes JD
Published: April 2008

Elastic-plastic fracture mechanics (EPFM) is the name given to a body of fracture technology that includes parameters, test methods, and analysis techniques. EPFM began in the 1960s, soon after it was recognized that the linear elastic approach to fracture mechanics was too limited to cover many engineering applications. It began in response to real engineering problems and continues to develop in the same application-driven mode. The development of EPFM spans more than three decades. It involved many people and a multitude of good ideas. Some of the people have gone on to other pursuits, and many of the ideas have been set aside or discarded in the never-ending debate about which is the best approach. The development of EPFM is not complete, nor is the controversy ended. It is important to look back at the factors that influenced such a vast development of technology before trying to forge ahead.

This paper takes a look at the area of fracture mechanics called EPFM. It considers the development of a technology that involved people, places, and a seemingly inexhaustible supply of technical ideas. It considers what happened in the past, what is going on in the present, and speculates about what will happen for the future. Its purpose is to stop for a moment and consider for EPFM: Where has it been? Where is it going?
J-Q-M
Approach for Failure Assessment of Fusion Line Cracks: Two-Material and Three-Material Models
Authors: Thaulow C , Zhang ZL , Ranestad Ø , Hauge M
Published: April 2008

The theoretical background for the J-Q-M approach for quantifying the constraint in weldments for fusion line cracks is presented. In this model, Q quantifies the geometry effects and M the material mismatch effects. Initially the approach was developed for a two-material modified boundary level (MBL) model, but later was extended to include three materials: weld metal, heat-affected zone and base material, and more realistic specimen geometries. The analysis with MBL models showed that the effect of mismatch was rather independent of the T-stress for both bi- and tri-material models, indicating that Q and M could be treated independently. However, analysis of fracture mechanics tension specimens made of three materials revealed that the mismatch effect in some cases could depend on the geometry effects. New calculations have demonstrated that the dependence/independence is related to load level, ratio of mismatch, and the local geometry.
The Fracture and Fatigue Crack Growth Behavior of Forged Damage-Tolerant Niobium Aluminide Intermetallics
Authors: Ye F , Mercer C , Farkas D , Soboyejo WO
Published: April 2008

The micromechanisms of fracture and fatigue crack growth are elucidated for a new class of damage-tolerant niobium aluminide Nb3Al-xTi intermetallics. Fatigue crack growth in alloys containing 10 and 25 at% Ti is shown to occur primarily by cleavage, while alloys containing ∼40 at% Ti are shown to exhibit similar fracture and fatigue crack growth behavior to ductile metals and their alloys. Slower elevated-temperature (750°C) crack growth rates in the Nb3Al-40Ti alloy are attributed largely to the effects of oxide-induced crack closure. The transition from cleavage fracture (in the Nb3Al-10Ti and Nb3Al-25Ti alloys) to ductile fracture in the Nb3Al-40Ti is correlated with the onset of significant levels of crack-tip plasticity, which is predicted using atomistic simulations.
Prediction of S-N Fatigue Curves Using Various Long-Crack-Derived ΔKeff Fatigue Crack Growth Curves and a Small Crack Life Prediction Model
Authors: Brockenbrough JR , Bray GH
Published: April 2008

In this study, stress-life (S-N) fatigue curves are predicted for high-strength aluminum alloy 7055 for open-hole specimens at two stress ratios, R = 0.1 and 0.5, and smooth specimens at R = 0.1 using the small-crack growth model of Brockenbrough et al. [1,2] and closure-free FCG curves obtained from long-crack tests by the following methods: (1) high R testing at R = 0.7; (2) constant Kmax testing at Kmax of 11 and 24.7 MPa√m; (3) a ΔKeff curve obtained at the appropriate stress ratio (R = 0.1 or 0.5) by the ASTM method; and (4) a ΔKeff curve obtained at the appropriate stress ratio by the adjusted compliance ratio (ACR) method. The predictions were compared to experimental S-N fatigue data. The objective of the study was to determine which method of obtaining closure-free FCG curves from long-crack tests provided the best estimates of fatigue life for the three combinations of specimen type and stress ratio in conjunction with the small-crack growth model employed. The ΔKeff curves obtained by the ACR method yielded the closest and most consistent fatigue predictions for all three conditions. This was attributed to this method being able to account for Kmax sensitivity of fatigue crack growth rates in aluminum alloys that could not be accounted for by the other methods.
Early Stage Fatigue Damage Characterization in Aluminum Alloys and Stainless Steels with Meandering Winding Magnetometer Technology
Authors: Weiss V , Goldfine N , Natishan M
Published: April 2008

It is shown that pre-crack and early stage fatigue damage can be characterized by a new sensor technology, the Meandering Winding Magnetometer (MWM™). This new technology consists of a conformable sensor, the MWM, and associated measurement grids that are model based.

Measurements on type 304 stainless steel indicated that damage is readily detectable at 20% of life (N/NF = 0.2) and causes a 1.5% conductivity loss. Near failure the conductivity loss in the crack-free region was approximately 4%. In 2024 aluminum the onset of detectable fatigue damage was observed at approximately 50% of total life. For the probe geometry employed, the conductivity loss in the microcrack region just prior to failure was 7%; in the macrocrack region it reached 13%.
Finite-Element Fracture Analyses of Welded Beam-Column Connections
Authors: Chi W-M , Deierlein GG , Ingraffea AR
Published: April 2008

Unexpected brittle cracking of welded beam-column connections during the 1994 Northridge earthquake has raised serious concerns about standards and practice for the seismic design and construction of steel moment resisting frames. As part of a nationally coordinated program to investigate the connection damage, finite-element fracture analyses are used to quantify fracture toughness demands in welded beam-column connections as influenced by various detailing parameters. Toughness demands at weld root defects in the beam flange groove welds are quantified in terms of KI, CTOD, and CTOA. Summarized are insights concerning the role of finite-element fracture analyses to investigate fracture behavior and the influence of factors such as flaw sizes, weld strengths, inelastic crack growth, and other parameters affecting fracture toughness demands.
A Plate Element-Based Model for Mixed-Mode Debonding of Composite Stitched Stiffened Panels
Authors: Glaessgen EH , Raju IS , Poe CC
Published: April 2008

An analysis based on plate finite elements and the virtual crack closure technique is used to study the effect of stitching on Mode I and Mode II strain energy release rates for a stitched warpknit composite debond configuration. The stitches were modeled as discrete nonlinear fastener elements with a compliance determined by experiment. The axial and shear behavior of the stitches was considered with both the compliances and failure loads assumed to be independent. The effect of model slenderness ratio on the accuracy of the strain energy release rates determined with the plate element models for configurations without stitching was determined by comparison with similar plane strain models. The analysis showed that stitches are very effective in reducing Mode I strain energy release rate, GI by closing the debond faces near the debond front; however, they are less effective in reducing the Mode II strain energy release rate, GII.
The Significance of the Intrinsic Threshold — What Is New?
Authors: Hadrboletz A , Weiss B , Stickler R
Published: April 2008

Numerous investigations in the past decades have shown that the fatigue threshold is influenced by several external and internal parameters. The effect of closure as one of the dominating factors indicates the existence of ΔKth,eff as a material property. Due to the fact that the determination of closure is controversial a modified closure evaluation procedure was used in this investigation.

Using selected materials (dual phase steel, particulate reinforced Al-alloy) this modified closure procedure resulted in ΔKth,eff values of reduced scatter in comparison to conventional evaluation procedures.

An alternative concept to describe threshold conditions was suggested by introducing characteristic plastic strain contours. The dislocation configuration in the vicinity of a crack tip, revealed by the electron channeling contrast imaging (ECCI) technique in the scanning electron microscope, allowed to deduce such plastic strain values in poly crystalline Cu selected as model material.

The ECCI technique was also applied to quasi two-dimensional structures (thin foils) which may be of interest in microelectronic systems. Results show that for foils of the thickness in the magnitude of the grain size a crack growth behavior is observed which appears not to be affected by closure.
Near-Threshold Fatigue Strength of a Welded Steel Bridge Detail
Authors: Albrecht P , Wright WJ
Published: April 2008

This paper consists or three parts. First, fatigue test data are presented for a tensile specimen with transverse stiffeners, a typical steel bridge detail. The specimens were tested under variable-amplitude fatigue for up to 250,000,000 cycles of loading proportional to the gross vehicle weight distribution of 27,000 trucks weighed on highways. Few and, in some cases, no stress ranges exceeded the endurance limit in the longest life tests. It took up to nine months to test the longest-life specimens.

Second, the variable-amplitude S-N life is predicted with an equivalent stress range model in which stress ranges smaller than the fatigue limit are assumed not to contribute to fatigue damage. A simplified S-N model is proposed for determining the fatigue life of existing bridges. The variable-amplitude fatigue limit is shown, both experimentally and analytically, to be a function of the constant-amplitude fatigue limit and the ratio of root-mean-cube stress range to maximum stress range of the variable-amplitude load spectrum.

In the third part of the paper, the variable-amplitude fatigue lives of the transverse stiffener specimens are predicted with a fracture mechanics model of crack growth.
Endurance Limit Design of Spheroidal Graphite Cast Iron Components Based on Natural Defects
Authors: Marquis G , Rabb R , Siivonen L
Published: April 2008

Cast irons are used extensively in the production of large diesel engines for power generation or oceangoing ships. One current trend is to replace grey iron with spheroidal graphite (SG) iron for fatigue critical components. In order to take advantage of the higher fatigue strength of SG iron and ensure the reliability of a design, better understanding of the typical defects for these large castings and the relationship between these defects and the endurance limit fatigue strength have been studied. Testing included uniaxial constant amplitude, constant amplitude torsion, and simple variable amplitude loading sequences in the long-life regime. Defects in several thick wall castings have been statistically evaluated. A fracture mechanics based model involving matrix hardness and √area successfully related the defect size to the experimentally observed fatigue limit. For ferritic-pearlitic SG iron, the hardness of the tougher pearlite phase was used in the model. The model also correlated the torsion and tension endurance limits. Endurance limit as a function of mean stress is presented in the form of Haigh diagrams.
Current Structure and Activities of ASTM Committee D09
Authors: Baker DK
Published: April 2008

Over the last 14 years, the span of my direct involvement with ASTM, many changes have occurred not only in the membership and goals of Committee D09, but also in ASTM itself. This paper will highlight the various Subcommittees within Committee D09 and some of the activities that have been completed over the past several years. In addition, the current topics of discussion within these Subcommittees will be pointed out. Committee D09 has a working relationship with other ASTM committees and standards organizations and some of these activities will be covered as well.

D09 membership is made up of approximately 160 individuals representing users, manufacturers, and general interest groups. Members may participate in as many subcommittees as they desire. In D09 the 160 members are responsible for 194 standards.

The scope of D09 is to develop test methods, practices, terminology, specifications, and promote knowledge and research relating to solid and solidifying fluid electrical insulating materials.

The principal materials included are grades designed primarily for electrical insulating or dielectric purposes of the following: • Varnishes and resins • Reinforced, laminated, filled and unfilled themoplastic and thermosetting plastics • Metal-clad dielectrics • Glass and Mica • Embedment resins, compounds, and waxes
NEMA Activities and Their Relation to ASTM Committee D09
Authors: Strachan DJ
Published: April 2008

This paper details the history of the National Electrical Manufacturers Association. It discusses the three core competencies of NEMA. It also goes into detail of the NEMA Committee structure and the process of getting a document published as a NEMA standard. Also discussed is NEMA's ongoing relationship with the U.S. Department of Defense and the working relationship that various NEMA product sections have had with ASTM D09 over the years. The paper concludes with a presentation of current working projects in NEMA that might be of interest to ASTM D09 members.
Specification Issues Associated with the Development of an Agriculturally Based Biodegradable Dielectric Fluid
Authors: Claiborne CC , Oommen TV , Walsh EJ
Published: April 2008

A fully biodegradable dielectric fluid based on high oleic acid vegetable oil has been developed for use in electrical equipment. The development of such a fluid for use in equipment such as electrical transformers has naturally caused it to be compared to more conventional mineral oil based insulating fluids and to high-temperature hydrocarbons and silicones for which specifications already exist. The selection of the base oil and its modifications relied heavily on preexisting standards such as ASTM D 3487 and ASTM D 5222. Because such a vegetable based fluid in practical terms does not completely match any of these fluids exactly in its characteristics, commercial implementation may lead to a desire for a standard specification describing its unique set of properties.

In addition, the biodegradable nature of the fluid has required that standard tests not used in the electrical industry, such as CEC L-33-A-94, developed for two-stroke-cycle outboard engine oils, be applied to the material in question. ASTM has subsequently developed a standard guide, ASTM D 6006 for hydraulic fluids, but relatively little work was performed on dielectric fluids at the time of the development of the biodegradable fluid discussed in this paper. Comparisons with other potential tests will be discussed and a discussion of the relative merits of these tests for dielectric fluids will be presented.
Electrical Insulating Mineral Oils: Specifications and Products
Authors: Griffin PJ , Rouse TO , Kelly JJ
Published: April 2008

This paper provides a review of two specifications for electrical insulating mineral oils by ASTM and the International Electrotechnical Commission (IEC). The physical, electrical, and chemical properties of these fluids are specified for use in electric apparatus such as transformers. The specified test methods are compared and their differences are presented. Some properties of commercial oils are shown.
Long-Term Endurance Determinations Using Traditional Accelerated Aging in Combination with Oxidative Stability Testing Resorting to Isothermal DSC Measurements of Oxidation Induction and Maximum Times
Authors: Giannoni SG , Montanari GC , Motori A , Hasan O
Published: April 2008

During the service life of electrical equipment, organic electrical insulating materials used at elevated service temperatures can degrade as a result of progressive chemical reactivity. It is therefore essential that normal operating temperature limits be established for such materials. The traditional approach is to accelerate the degradation process with simultaneous testing at moderately elevated temperatures above the intended service temperatures of both the candidate material and a control reference material. With proper application of a chemical kinetic model, a service limit is established for the candidate material based on the comparative test performance, with the control having known long-term thermal service capabilities. There are practical limits on the maximum test temperatures and corresponding minimum test times to ensure an accurate representation of the service degradation mechanism during the test program. This results in an onerous, unavoidably protracted test time for these thermal aging studies. A number of relatively rapid analytical techniques have been proposed to reduce the test times without compromising the accuracy of the determined service limit. The most successful of these often involve hybrid testing, as a combination of a rapid analytical technique and part of the traditional program at the higher test temperatures and shorter test times, to result in a desirable and substantial reduction in test program times. This paper will review the principles of the traditional program, and the theory and initial results of a proposed hybrid technique based on oxidative stability testing using oxidation induction.
Voltage Step Stress for 10 nm Oxides
Authors: Strong A
Published: April 2008

The advantages and challenges of a voltage step stress technique using time dependent dielectric breakdown (TDDB) as the metric are discussed for oxides in the range of 10 nm. A brief comparison is given between life stress and step stress results for oxides on the order of 10 nm. Reference is made to a more complete comparison between life stress and step stress as well as to some of the literature in which step stress changed the outcome of the life stress. Some of the challenges for thinner oxides are discussed, especially oxides of thickness less than 5 nm. An example of the step stress analysis technique is discussed on a point-by-point basis.
Multiaxial Stress-Strain Notch Analysis
Authors: Buczynski A , Glinka G
Published: April 2008

Fatigue and durability analyses require the use of analytical and/or numerical methods for calculating elastic-plastic notch tip stresses and strains in bodies subjected to nonproportional loading sequences. The method discussed in the paper is based on the incremental relationships, which relate the elastic and elastic-plastic strain energy densities at the notch tip and the material stress-strain behavior, simulated according to the Mroz-Garud cyclic plasticity model. The formulation described below is based on the equivalence of the total distortional strain energy density, which appears to give the upper-bound estimations for the elastic-plastic notch tip strains and stresses. The formulation consists of a set of algebraic incremental equations that can easily be solved for elastic plastic stress and strain increments, based on the increments of the hypothetical elastic notch tip stress history and the material stress-strain curve. The validation of the proposed model against the experimental and numerical data includes several nonproportional loading histories. The basic equations involving the equivalence of the strain energy density are carefully examined and discussed. Finally, the numerical procedure for solving the two sets of equations is briefly described. The method is particularly suitable for fatigue life analyses of notched bodies subjected to cyclic multiaxial loading paths.
A Newton Algorithm for Solving Non-Linear Problems in Mechanics of Structures Under Complex Loading Histories
Authors: Arzt M , Brocks W , Mohr T
Published: April 2008

A Newton algorithm is discussed. This algorithm allows for studying nonlinear material behavior, such as plasticity and viscoplasticity. The material behavior is described by so-called internal variables. The model applied in this paper was developed by Lemaitre and Chaboche. The Newton algorithm is implemented as a user-subroutine in the commercial finite-element method package ABAQUS. The results of a numerical analysis of the rotation of an aircraft turbine disk are presented. Cyclic loading conditions are studied, and the results are compared with numerical results in the literature.
A Numerical Approach for High-Cycle Fatigue Life Prediction with Multiaxial Loading
Authors: de Freitas M , Li B , Santos JLT
Published: April 2008

This paper presents an efficient approach for predicting high-cycle fatigue crack initiation life under general multiaxial fatigue loadings. A minimum circumscribed ellipse approach is proposed for evaluating the effective shear stress amplitude and mean value throughout a complex loading cycle. The idea of this approach is to construct a minimum circumscribed ellipse enclosing the loading path in the transformed deviatoric stress space. The new definition of the effective shear stress amplitude is the root mean square of the major semi-axis and the minor semi-axis of the minimum circumscribed ellipse. In this way, the out-of-phase loading effects are taken into account and improvement is made over the previous approaches such as the longest projection, the longest chord, and the minimum circumscribed circle methods. By using mathematical programming techniques, an efficient numerical algorithm is proposed for solving the min-max problem of finding the minimum circumscribed ellipse that can enclose the whole loading path. This new approach allows extension of the Sines or Crossland fatigue criteria to fatigue life prediction under general multiaxial loading with arbitrary stress-time histories. Multiaxial fatigue test results collected from literature, which include complex stress histories with different waveforms, frequencies, out-of-phase angles and mean stresses, were used to validate the approach here proposed.
Cumulative Axial and Torsional Fatigue: An Investigation of Load-Type Sequencing Effects
Authors: Kalluri S , Bonacuse PJ
Published: April 2008

Cumulative fatigue behavior of a wrought cobalt-base superalloy, Haynes 188, was investigated at 538°C under various single-step sequences of axial and torsional loading conditions. Initially, fully-reversed, axial and torsional fatigue tests were conducted under strain control at 538°C on thin-walled tubular specimens to establish baseline fatigue life relationships. Subsequently, four sequences (axial/axial, torsional/torsional, axial/torsional, and torsional/axial) of two load-level fatigue tests were conducted to characterize both the load-order (high/low) and load-type sequencing effects. For the two load-level tests, summations of life fractions and the remaining fatigue lives at the second load level were computed by the Miner's linear damage rule (LDR) and a nonlinear damage curve approach (DCA). In general, for all four cases predictions by LDR were unconservative. Predictions by the DCA were within a factor of two of the experimentally observed fatigue lives for a majority of the cumulative axial and torsional fatigue tests.
Micro-Crack Growth Modes and Their Propagation Rate under Multiaxial Low-Cycle Fatigue at High Temperature
Authors: Isobe N , Sakurai S
Published: April 2008

Crack growth behavior and propagation rates in SUS316L steel, 1CrMoV steel, and Hastelloy-X in multiaxial low-cycle fatigue tests at high temperature were investigated. Crack growth mode in pure torsion tests changed from the principal strain plane to the maximum shear plane with increasing temperature or strain range. The dominant mechanism of micro-crack initiation, however, differed among the three materials. The dominant process of micro-cracking was considered to be slip in grains for SUS316L steel, whereas oxidation film cracking and grain boundary cracking were the mechanisms for 1CrMoV steel and Hastelloy-X, respectively. The appropriate parameter for evaluating the crack growth rate under multiaxial conditions is discussed in relation to the micro-crack growth mechanisms. Good correlation was obtained between the crack growth rate and the strain parameter based on the micro-cracking mechanism of each material.
Development of a True Triaxial Testing Facility for Composite Materials
Authors: Welsh JS , Adams DF
Published: April 2008

An electromechanical testing facility capable of applying any combination of tensile and/or compressive forces to three mutually orthogonal axes of a thickness-tapered composite cruciform specimen was designed, fabricated, assembled, and evaluated. Any stress ratio in biaxial (σ1 - σ2) or triaxial (σ1 - σ2 - σ3) stress space can be explored using this computer-controlled test facility. A brief description of the testing machine and its capabilities as well as the present test specimen design is included. Once fully assembled, uniaxial and biaxial tests were performed on 6061-T6 aluminum using this facility. The excellent agreement between the uniaxial and biaxial results obtained in the present study for this material, with accepted handbook values and applicable failure theories, confirmed the performance of several aspects of the testing facility. These aspects included the intra-axis alignment, machine compliance, specimen fabrication and testing procedures, automated computer testing algorithms, data acquisition algorithms, and calibration values. In addition, biaxial and triaxial tests were performed on an AS4/3501-6 carbon/epoxy cross-ply laminate. While most of these tests are considered valid, they revealed aspects of the present thickness-tapered cruciform specimen design that could be improved. More specifically, an undesirable failure mode was encountered in some biaxial tension tests, and triaxial tension tests were not performed successfully. Nevertheless, the overall acceptable performance of the triaxial testing facility is believed to have been demonstrated.
Spectral Unfolding of Mixed Proton/Neutron Fluences in the LANSCE Irradiation Environment
Authors: James MR , Maloy SA , Sommer WF , Ferguson PD , Fowler MM , Mueller GE , Corzine RK
Published: April 2008

An analysis of activation foils from irradiations at the Los Alamos Neutron Science Center (LANSCE) was used to provide a basis for determination of combined proton and neutron fluxes. Materials samples were irradiated in the A-6 target area at LANSCE to explore the mechanical property changes in a high-energy proton/spallation neutron environment. Proper assessment of the effects of irradiation required quantifying the proton and neutron fluences. Foil stacks consisting of disks of Co, Ni, Fe, Al, Nb and Cu, were irradiated concurrently with mechanical property samples. The irradiation consisted of an 800 MeV, 1 mA proton beam, and a W target in the beam provided a source of spallation neutrons. The maximum proton fluence was 4×1021 p/cm2 and the maximum neutron fluence was approximately 1×1021 n/cm2. After irradiation, the foils were withdrawn and the radioactive isotopes sampled with gamma spectroscopy. Initial calculated estimates of the fluences we made with the Los Alamos High-Energy Transport (LAHET) Code System (LCS). The LCS code is a coupling of LAHET and MCNP (Monte Carlo N-Particle) to calculate transport of the high-energy protons, neutrons and photons. From the initial estimates and the measured activation products, STAYSL2 was used to produced a revised spectra of proton and neutron fluences. STAYSL2 is an extension of the STAY'SL code normally used for neutron activation analysis. STAYSL2 has been modified to include proton fluences in the analysis of activation to account for the mixed proton/neutron fluence in the target area. This methodology was applied to multiple foil stacks from different regions of the target in order to profile the spatial dependencies of the fluences.