bluuebunny/crossref_metadata_2025 huggingface dataset:
Collapse Resistance Modeling of Encased Pipes
Authors: Lo KH , Zhang JQ
Published: March 2009

Two different collapse models are developed for predicting the collapse resistance of encased pipes for pipe rehabilitation applications. One model corresponds to an unsymmetrical collapse mode and the other one corresponds to a symmetrical collapse mode. Attention is focused here on modeling the effect of the small radial gap between the encased pipe and the host pipe on encased pipe collapse resistance. This small radial gap is assumed to have developed when installing the encased pipe into the host pipe. It increases in size when subjected to temperature change, swelling, and application of external hydrostatic pressure. The predictions by the models correlate well with some collapse test results on encased pipes.
Compressive Buckling of Hollow Cylinders: Implications for Pressure Testing of Plastic Pipe
Authors: Woods DW , Ferry SR
Published: March 2009

Compressive buckling of hollow cylinders due to internal pressure is a little-known phenomenon that can affect pressure testing of plastic pipe. High strength pipe materials with large dimension ratios particularly exhibit the phenomenon, but it can also occur in pipe with low dimension ratios (relatively thick walls) when the material is highly elastic or plastic at the test conditions. To successfully test such materials may require special constraints on test geometry and end closures. Specific examples of the phenomenon observed in the laboratory are discussed along with an analytical treatment from the literature.
Analysis of The Factors in Earth Pressure and Deformation of Buried Flexible Pipes Through Centrifuge Model Tests
Authors: Tohda J , Li L , Yoshimura H
Published: March 2009

A series of centrifuge model tests was conducted to estimate parametrically effects of the following factors on earth pressure and deformation of buried flexible pipes: pipe flexibility, pipe installation type, ground condition, and three burial dimensions (cover height, ditch width and bedding thickness). The tests yielded accurate measured data of circumferential distributions of normal and tangential earth pressures on the model pipes, circumferential distributions of bending strains in the pipe wall, and vertical pipe deflection, fully quantifying the effects of the investigated factors. It was found that Japanese current design standards, based on Marston-Spangler theory, do not conform to the test results by ignoring the effects of almost all the factors on the earth pressures, and, as a result, they specify definitely unsafe design values of bending moment and pipe deflection for the case when the pipes are buried by the open excavation method using sheet-piling.
Pressure Vessel Steel Embrittlement Monitoring by Magnetic Properties Measurements
Authors: Stubbins JF , Shong W-J , Giacobbe M , Ougouag AM , Williams JG
Published: March 2009

The magnetic properties of specimens of one heat of A533B nuclear pressure vessel grade steel have been examined in the as-received condition and after neutron irradiation to various fluence levels up to 4 × 1018 cm-2 (E > 0.1 MeV) in the University of Illinois advanced TRIGA reactor core at two temperatures, approximately 120 and 260°C. The effect of certain heat treatments was also investigated. The magnetic properties were measured by an automated hysteresis curve-tracing method using a miniature transformer which incorporated the specimens in its core. Changes in magnetic hysteresis energy loss were correlated with neutron fluence in the case of certain irradiated specimens and with microhardness measurements in the case of heat-treated specimens. At the higher irradiation temperatures, no significant changes in either the magnetic hysteresis properties or the microhardness were noted for the present fluences. The relationship between the observed magnetic properties response and irradiation-induced embrittlement is discussed.
Electrochemical Evaluation of Thermal Aging Embrittlement of 2 1/4Cr-1Mo Steel for a Nuclear Pressure Vessel
Authors: Nishiyama Y , Fukaya K , Suzuki M , Eto M , Shoji T
Published: March 2009

A nondestructive test technique using an electrochemical method was investigated for evaluating thermal aging embrittlement of 21/4Cr-lMo steel for a nuclear pressure vessel. Agings were conducted at temperatures ranging from 400 to 500°C for up to 50 000 h. In the anodic polarization curve measured in calcium nitrate solution, a secondary peak, which is higher for embrittled materials than for the deembrittled ones, was observed in the passive potential region. Changes in the secondary peak can be correlated with the degree of the embrittlement evaluated by the shift in Charpy ductile-to-brittle transition temperature (ΔDBTT).
In-Situ Measurements of Mechanical Properties Using Novel Automated Ball Indentation System
Authors: Haggag FM
Published: March 2009

Determination of the integrity of any metallic structure is required either to ensure that failure will not occur during the service life of the components (particularly following any weld repair) or to evaluate the lifetime extension of the structure. A portable/insitu stress-strain microprobe system was developed to evaluate nondestructively in situ the integrity of metallic components [including base metal, welds, and heat-affected zones (HAZs)]. The microprobe system utilizes an innovative automated ball indentation (ABI) technique to determine several key mechanical properties (yield strength, true-stress/trueplastic-strain curve, strain-hardening exponent, Lüders strain, elastic modulus, and an estimate of the local fracture toughness). This paper presents ABI test results from several metallic samples. The microprobe system was used successfully to nondestructively test in-situ a circumferentially welded Type 347 stainless steel pipe. Four V-blocks were used to mount the testing head of the microprobe system, allowing a 360° inspection of property gradients in the weld and its HAZ.
Laser Weld Reconstitution of Conventional Charpy and Miniaturized Notch Test (MNT) Specimens
Authors: Manahan MP , Williams J , Martukanitz RP
Published: March 2009

As nuclear power plants approach end-of-license (EOL) and consideration is given to license renewal, there is an ever increasing need to expand the amount of data obtainable from the original surveillance specimens. A laser welding technique to reconstitute broken Charpy specimens is being developed to produce both conventional and miniaturized Charpy specimens. This paper reports on early laser welding development efforts and summarizes previous proof-of-principle experiments on a 1/16 scale miniaturized Charpy test. In order to benchmark the laser welding procedure, the laser-reconstituted specimen data have been compared with the original specimen data. In addition, the microstructure after welding has been examined to ensure that the material in the vicinity of the notch is essentially unchanged after the welding process. Data which characterize the thermal transient during welding are obtained by attaching thermocouples to the specimens. Other important considerations include perturbation of the stress field near the notch, dynamic stress waves, and contact of the weld region with the tup.

Precise control of welding parameters has been demonstrated, heat-affected zones as small as 0.25 mm can be achieved, and sufficient penetration depth can be obtained to enable welding thick sections (1T or greater) to yield conventional Charpy specimens or fracture toughness specimens and thin sections (̃5 mm) to yield Miniaturized Notch test (MNT) specimens.
Application of Micromechanical Material Models for the Evaluation of the Fracture Toughness of Primary Circuit Steel Components
Authors: Schmitt W , Blauel JG
Published: March 2009

The safety assessment of nuclear components requires that fracture mechanics material data or curves are available. These data must be measured with suitable specimens of the original material for the given condition, i.e., temperature and irradiation. Especially for reactor pressure vessel (RPV) weld material, fracture mechanics specimens are not available within the irradiation surveillance programs in sufficient number, or, if available, the performance of accurate fracture mechanics tests in hot cell facilities is extremely difficult.

New developments in the field of micromechanical material models taking into account the ductile damage process characterized by nucleation, growth, and coalescence of voids make it possible to determine micromechanical material parameters from tension tests and finite element analyses of notched and smooth specimens. If, in addition, a characteristic length, lc,is considered, the ductile fracture resistance behavior of fracture mechanics specimens and, hence, J-resistance curves may be predicted.

Here, the modified Gurson model is applied to calculate a static J-resistance curve for irradiated weld material from the results of smooth static tension tests out of the irradiation surveillance program of a specific nuclear power plant. Since original material was not available in sufficient quantity for fracture mechanics tests, a verification program was conducted comprising tests and analyses of smooth tension specimens and side-grooved compact (CT) and wedge opening loading (WOL) X-type specimens of two unirradiated and one irradiated weld materials. In every case, the predicted resistance curves are in good agreement with the measured curves.

Following the successful evaluation of static material tests, the first experimental and numerical steps are presented towards the evaluation of dynamic J-R curves from the results of instrumented Charpy tests.
On the Development of a Fracture Toughness Test Procedure Using a Notched Disk Specimen
Authors: Bernard M , Provan JW , Lakshminarayana HV
Published: March 2009

The research reported in this paper provides validation of a notched disk M(N) specimen geometry for both static and dynamic fracture toughness testing. More specifically, the work verifies the proposed procedure for the determination of the fracture toughness of materials most commonly used in plate-like configurations and extends its application to the dynamic case. The notched disk M(N) specimen has an axisymmetric notch machined on one of its faces, is clamped on its periphery, and is loaded axisymmetrically in a direction normal to its plane for both the precracking and loading-to-failure portions of the test. The advantage of this specimen geometry is that it is free from the adverse edge effects that exist in the standard C(T) specimen. Furthermore, a uniform plane strain state along the crack front induces a triaxial tensile stress and a small plastic zone. Finally, the specimens may be manufactured without difficulty.

Also reported in this paper are the findings of finite element analyses of both the 3-mm and 4-mm notch specimen geometries. Parametric studies emphasize the influence on the stress intensity factors of the notch location with respect to the clamped boundary. Stress intensity factors are evaluated for different crack lengths and orientations by the crack opening displacement method, the modified crack closure integral approach, and the virtual crack extension technique. The results, presented as normalized stress intensity factors, are essential for a reliable reduction of the test data.

Fracture toughness testing of an A17075-T651 aluminum alloy was performed using 3-mm notch depth M(N) plate specimens. For dynamic fracture toughness testing, the 4-mm notch depth specimens, manufactured from polystyrene resins, were used.

Using the procedure fully detailed in the body of this_paper, the static fracture toughness of A17075-T651 was determined as KIc = 31.4 MPa √m, while the dynamic fracture toughnesses of polystyrene using the M(N) specimen geometry were between 0.73 and 0.99 MPa √m. These values indicate that the M(N) specimen geometry testing capabilities are substantiated.
Miniaturized Fracture Toughness Testing During the Plant Life Extension Period
Authors: Manahan MP
Published: March 2009

It is desirable to obtain plane strain fracture toughness data in support of plant refurbishment and plant life extension (PLEX) efforts. These data may be needed for pressurized thermal shock (PTS) analyses, low upper shelf energy analyses, and to verify shifts in the KIR curve. A major impediment to the development of plant-specific fracture toughness data is the specimen size requirement and the fact that many surveillance capsule programs do not include fracture toughness specimens.

A new test has been developed to resolve these difficulties. An experimental modification, referred to as stress field modification, enables testing using specimens substantially thinner than those currently required by ASTM. Examination of the stress field modified specimen fracture surface demonstrates that plane strain conditions were achieved in the miniature specimens. The miniature specimens were machined from a nuclear-grade ASTM A508 steel used in the Oak Ridge National Laboratory pressurized thermal shock study. The miniature specimen data lie within the experimental scatter of the 6-in. (15.24 cm) vessel data. The development of this new fracture test enables plane strain testing of materials from surveillance programs (broken Charpy specimens) and from material cut from in-service components.
Estimation of Toughness Degradation by Microhardness and Small Punch Tests
Authors: Suzuki M , Eto M , Nishiyama Y , Fukaya K , Isozaki T
Published: March 2009

Microhardness and small punch (SP) tests were conducted to improve the reliability of evaluating the ductile-to-brittle transition temperature (DBTT) shift caused by aging (thermal aging, neutron irradiation, cold rolling) using several model alloys (Fe-0.15C alloys and 2¼Cr-1Mo steels). Although evaluation of DBTT by the SP test was good overall, intergranular brittleness could not be detected by SP-DBTT measurement only. By combining other measurements like fractographic observation, however, material degradation can be better evaluated.
Hardening Characteristics of Ion-Irradiated Iron-Based Model Alloys
Authors: Iwai T , Kawanishi H , Arai Y , Kato Y , Sekimura N , Ishino S
Published: March 2009

Fe-C-Cu, Fe-C-Ni, and Fe-C-Cu-Ni model alloys were prepared in order to investigate the effects of copper and nickel on radiation embrittlement. They were irradiated with 4 MeV Ni3+ ions at 563 K to introduce displacement damage, followed by a micro-Vickers hardness test employing low load (0.5 g). It was observed that greater hardening occurred for samples of larger copper content, and that hardening of the samples containing both copper and nickel was greater than hardening of the ones containing copper or nickel solely for samples irradiated to 10-2 and 10-1 dpa. Increased hardness after annealing occurred for Fe-0.1C-0.2Cu and Fe-0.lC-0.4Cu. Small defect clusters of approximately 3 nm in diameter were observed by transmission electron microscopy (TEM) of the irradiated Fe-0.1C and Fe-0.1C-0.4Cu samples, which cause hardening.
Development of a Miniature-Disk Bending Fatigue Specimen
Authors: Rao GR , Chin BA
Published: March 2009

A miniature-disk bending fatigue specimen was earlier developed for testing materials to be used for fusion reactor applications. The specimen is based on a 3-mm-diameter transmission electron microscope disk. A second larger rectangular specimen was also developed, with dimensions of 30.16 by 4.76 by 0.76 mm. The specimens, made from annealed type 316 stainless steel, were tested using a specialized bending fatigue machine at temperatures of 25, 550, and 650°C. In the current study, the results are compared against standard full-size specimen results.

Strain ranges were calculated using an analytical technique based on specimen geometry and material properties. For the rectangular specimen, strains were also measured using strain gauges attached to the gauge region. The calculated strains were then modified using a calibration factor based on the measurement. The rectangular specimen results were in good agreement with ASTM full-size specimen results. The miniature-disk specimen data fell below the other results, indicating that the analytical technique underestimates strain values. No clear temperature dependence was evident for the miniature-disk specimen, unlike larger specimens which show a degradation of fatigue properties with increasing temperature. The miniature-disk specimen results also show a greater scatter about the best-fit curve, which was attributed to greater sensitivity to misalignment.
Two Micro Fatigue Test Methods for Irradiated Materials
Authors: Nunomura S , Noguchi S , Okamura Y , Kumai S , Jitsukawa S
Published: March 2009

This paper demonstrates two miniature fatigue test methods in response to the requirements of the fusion reactor wall materials development program. It is known that the fatigue strength evaluated by the axial loading test is independent of the specimen size, while that evaluated by the bend test or torsion test is dependent upon the size of specimen. The new type of gripping system for the axial, tension-tension, fatigue testing of TEM disk5-size specimens that has been developed is described in this paper. An alignment tool assists in gripping the miniature specimen. The miniature tension-tension fatigue test method seems to provide reliable S-N curves for SUS304 and SUS316L stainless steels.

An indentation method has also been developed to determine fatigue properties. A hard steel ball or ceramic ball was used for cyclically loading the specimen, and an S-N curve was subsequently obtained. The merit of this method is primarily simple handling. S-N curves obtained from four materials by this indentation method compared well with those obtained from the rotary bend fatigue test employing a standard-size specimen.
Evaluating a Service-Exposed Component's Mechanical Properties by Means of Subsized and Miniature Specimens
Authors: Lucon E , Bicego V , D'Angelo D , Fossati C
Published: March 2009

Estimating the mechanical properties of a service-exposed component in a quasinondestructive manner implies sampling as little material as possible from the component itself. Different subsized or miniature specimens to be employed in the various fields of mechanical testing are presented and discussed: 1. Cylindrical specimens with circumferential crack for fracture toughness testing in the brittle regime and miniature disk-shaped specimens for the upper-shelf ductile regime. 2. Miniature reconstructed specimens for residual creep strength evaluation by means of isostress temperature-accelerated tests. 3. Small-size specimens for low-cycle fatigue testing with enhanced cycle frequency.

Data significance and transferability to actual components, as well as accuracy of results, are discussed. Particular emphasis is devoted to usually favorable comparisons obtained with respect to larger, conventional specimens considered by ASTM test standards.
Application of Miniature Tension Specimens to Studies of Radiation Damage in Metals
Authors: Garner FA , Hamilton ML , Heinisch HL , Kumar AS
Published: March 2009

Miniature sheet-type tension specimens are currently being used in a variety of radiation damage studies conducted in a number of different reactors. Although these specimens are very small (12.7 mm long, 0.25 mm thick, 1.0 mm gage width), they have proven successful in addressing issues encountered in both thermal reactors and anticipated fusion reactors. This paper reviews the results of a number of recent studies that illustrate the range of applicability of these small specimens. When combined with other types of specimens and other types of measurements made prior to tension testing, miniature tension specimens have been found to serve as very useful tools for application to both fundamental studies and alloy screening studies.
Evaluation of Miniature Tension Specimen Fabrication Techniques and Performance
Authors: Hamilton ML , Blotter MA , Edwards DJ
Published: March 2009

The confident application of miniature tensile specimens requires adequate control over their fabrication and is facilitated by automated test and analysis techniques. Three fabrication processes—punching, chemical milling, and electrical discharge machining (EDM)—were recently evaluated, leading to the replacement of the previously used punching technique with a wire EDM technique. The automated data acquisition system was upgraded, and an interactive data analysis program was developed.
A Novel Miniature Tension Test Machine
Authors: Sharpe WN , Fowler RO
Published: March 2009

Tensile stress-strain curves can be measured on specimens with an overall length of 3 mm using this new approach. The square test section of the specimens is 0.2 mm on each side.

The load frame is made from stainless steel by electrical discharge machining (EDM) and is 20 mm wide by 12 mm high and 3 mm thick. Load is applied and measured with an external translation stage and the load cell connected to the load frame with a fine wire. The load frame has wedge-shaped grips into which the ends of the specimen fit. The specimens have a “dog-bone” shape and are also manufactured by EDM.

Strain is measured directly on the specimen with laser-based interferometry from two tiny indentations placed in the specimen with a Vickers microhardness tester. Motion of the interference fringes emanating from the indentations is measured with two linear diode arrays and a microcomputer to enable real time strain measurement.

Preliminary tests have been conducted on brass samples to demonstrate the test technique. The relative uncertainty in stress measurement is high in these tests, but that arises from lack of precision in measuring the area. The relative uncertainty of strain is also high because of the crude mounts for the diodes. This paper demonstrates that the approach is feasible; straightforward refinements in the procedures will reduce the uncertainties.
Investigation of Material Behavior Under Reirradiation after Annealing Using Subsize Specimens
Authors: Kryukov AM , Sokolov MA
Published: March 2009

Experimental results are presented from a study of changes in the ductile-to-brittle transition temperature of VVER-440 base and weld metals under cyclic irradiation and recovery. The transition temperatures were determined from the results of subsize V-notch impact specimens measuring 5 by 5 by 27.5 mm. Specimen irradiation was carried out in a commercial reactor at a temperature of 270°C in three irradiation and recovery cycles. Annealing of specimens was performed at 340, 420, and 460°C. The shift in the transition temperature of subsize specimen data in the first irradiation cycle was compared to the transition temperature shift determined from tests using standard Charpy specimens.
Use of Subsize Specimens for Determination of Radiation Embrittlement of Operating Reactor Pressure Vessels
Authors: Amayev AD , Badanin VI , Kryukov AM , Nikolayev VA , Rogov MF , Sokolov MA
Published: March 2009

This paper presents groundwork for determining the ductile-to-brittle transition temperature (DBTT) from subsize specimens (5 by 5 by 27.5 and 3 by 4 by 27.0 mm) and describes the correlation between the DBTT obtained from tests of standard Charpy specimens and subsize specimens. A method for taking samples from the inside surface of reactor pressure vessels and fabricating small specimens from them was developed in the USSR. This method is used to assess the effectiveness of pressure vessel recovery by annealing. Some results of the DBTT evaluation for the base and weld metal before and after recovery are given.
Application of Reconstitution Welding Technique for Studying Base Metal of a Novovoronesh Unit-1 Trepan Sample
Authors: Valo M , Ahlstrand R
Published: March 2009

The toughness of a through-wall trepan sample cutout from the shut-down Novovoronesh Unit-1 was characterized with reconstituted specimens. The trepan sample was taken from the core weld and also contained base metal from the upper and lower forged rings. Because the sample is relatively small, with a diameter of 110 mm and a height of 120 mm, effective use of the material is of vital importance. Standard Charpy specimen size was chosen to be used throughout the sample. All the specimens were reconstituted from 10 by 10 by 16-mm unit volumes. Both Charpy-V impact and Charpy-size three-point bending (3-PB) specimens were used. The validation of specimen preparation technique includes Charpy-V impact and static 3-PB tests with reference and irradiated materials and is described in detail. The results for one base metal, including the vessel wall condition and annealed conditions at 470°C/168 h and 650°C/2 h, are reported and discussed.
Slow Strain Rate Testing—25 Years Experience
Authors: Parkins RN
Published: March 2009

The development of slow strain rate testing for environment sensitive cracking over the last 25 years is reviewed. In its original form, in which specimens are continuously strained to total failure, the method is still valuable, especially as a rapid sorting approach to the effects of metallurgical or environmental changes in systems, and examples are given of such. The importance of employing an appropriate strain rate for the particular system being studied is emphasized, after which consideration is given to applying variations on the method to determining threshold stresses for cracking.
Status of Standardization Activities on Slow Strain Rate Testing Techniques
Authors: Kane RD , Wilhelm SM
Published: March 2009

A brief review of current test method standardization activities for slow strain rate testing will be given. This presentation will include activities involving ASTM Committee G-l .06.05 (Corrosion of Metals/SCC Test Methods/Dynamic Testing) and NACE Task Group T-1F-9 (Metallic Materials Testing Techniques for Sulfide Corrosion Cracking).
Applications of Slow Strain Rate Testing in the Nuclear Power Industry
Authors: Miglin MT , Miglin BP
Published: March 2009

Slow strain rate (SSR) tests are widely used to evaluate materials for service in the nuclear power industry. The slow strain rate method is used to select new materials and to qualify heats of existing materials for use in components exposed to reactor coolant.

Several different modifications of the SSR test have been developed over the years to meet the demands of specific reactor applications. For testing the nickel-base superalloys used in reactor core internals, tensile bars may be notched or fatigue-precracked to accelerate crack initiation. A precracked fracture mechanics specimen may be substituted for a tensile bar. Three-point-bend loading, rather than tensile loading, is used for evaluating material resistance to cracking during the intermediate temperatures associated with reactor heat-up and cool-down transients.

for testing thin-walled steam generator tubing, tube tensile specimens or single-ligament tensile bars are used. Rather than testing in a typical steam generator environment, a high-temperature caustic environment may be chosen, with an anodic potential applied to the specimen to accelerate cracking.

The SSR test method is also applied to reactor pressure vessel steels and weldments. Tests conducted in reactor coolant environment have established the importance of maintaining low oxygen levels in preventing stress corrosion cracking (SCC).
Measurement of the Deformability of Austenitic Stainless Steels and Nickel-Base Alloys in Light Water Reactor Cores
Authors: Dewes P , Alter D , Garzarolli F , Hahn R , Nelson JL
Published: March 2009

The deformability of austenitic stainless steels and nickel-base alloys was studied in an experimental program combining the influence of irradiation in a light water reactor (LWR) core environment and high stresses and strains. Tubular specimens filled with ceramic mandrels were inserted into fuel elements of both a BWR and a PWR where they were exposed to the neutron flux and coolant water of the core. The ceramic mandrels swelled under irradiation and applied high stresses to the cladding tube specimens; hence, in case of sensitive material, this led to intergranular stress corrosion cracking. The strain was varied by choosing different ceramic materials and by the axial position of the specimens in the reactor core. During the refueling shutdown of the reactor, the specimens were examined by integrity testing and diameter measurements.

The experimental setup, irradiation conditions, examination methods, and deduced stresses will be described and the status of the experiments outlined. Many materials failed by brittle cracking under the conditions applied. In the first program phase only a low phosphorus and silicon stainless steel and an Inconel alloy 718 with a special heat treatment were found to be resistant. In the second phase, when other material charges were used to verify the first results, the good performance of alloy 718 was confirmed. High purity austenitic stainless steels, however, failed during Phase 2 at the same low strain level as commercial purity material. In the case of alloy X-750, it was found that the material surface condition had a significant influence on the resistance to stress corrosion cracking.
Slow Strain Rate Fracture of High-Strength Steel at Controlled Electrochemical Potentials in Ammonium Chloride, Potassium Chloride, and Ammonium Nitrate Solutions
Authors: Nguyen DT , Nichols DE , Daniels RD
Published: March 2009

Earlier investigations using slow strain rate fracture tests at controlled electrochemical potentials demonstrated the susceptibility of AISI 4340 high-strength steel to stress corrosion cracking (SCC) in the combustion product residues of jet engine cartridge ignition starters. X-ray diffraction analyses of the residues revealed significant concentrations of ammonium chloride, potassium chloride, and ammonium nitrate. In the present investigation, slow strain rate testing was conducted to determine the effects of each of these chemical compounds on the fracture process. Test environments included ammonium chloride, potassium chloride, and ammonium nitrate solutions at concentrations of 100, 1000, and 10 000 parts per million by weight and at a pH of 5. The tests were performed at a constant extension rate of 1 × 10-7 m/s (strain rate of approximately 2.7 × 10-6/s). Tests were performed at controlled electrochemical potentials, both anodic and cathodic with respect to the open-circuit corrosion potential, to delineate the potential ranges for SCC and hydrogen-induced cracking.

Of the three compounds studied, only ammonium chloride caused SCC of the AISI 4340 high-strength steel. The corrosion potential of about -620 mV versus saturated calomel electrode (SCE) is at the brink of the potential range for stress corrosion cracking. The most severe embrittlement was observed at a potential of -450 mV and at a solution concentration of 1000 ppm ammonium chloride. Hydrogen-induced cracking was observed at -850 mV in the ammonium chloride and ammonium nitrate solutions, but not in the potassium chloride solutions.
Slow Strain Rate Testing of Precracked Titanium Alloys in Salt Water and Inert Environments
Authors: Meyn DA , Pao PS
Published: March 2009

The stress corrosion cracking (SCC) propagation kinetics of fatigue-precracked Ti-6Al-4V (an α-β alloy) and Ti-15V-3Al-3Cr-3Sn (a β-α alloy) were studied in neutral 3.5% NaCl solution and in inert environments. The slow strain rate method was used instead of the constant load method. This was pursued in an effort to minimize the number of specimens normally required and reduce the time required to determine the stress intensity threshold for SCC. The results were encouraging, but some anomalies in the crack growth kinetics were noted. At a relatively low extension rate, crack rates in both alloys alternated between high Stage II rates and very low rates during the test. At a higher extension rate, crack rates in the Ti-15-3 alloy behaved as previously described, whereas in the Ti-6-4 alloy crack growth remained at Stage II rates continuously above the threshold. No traces of crack arrest could be found on the fracture surfaces.
Case Histories Using the Slow Strain Rate Test
Authors: Baumert KL , Watkins WR
Published: March 2009

The slow strain rate test (SSRT) has been used at Air Products and Chemicals for a number of different environments. It was used to estimate the propensity of various amines to stress crack storage tanks; it was used to determine if existing equipment could be used in amine manufacture. Several tests were conducted to duplicate conditions that produced cracking in process equipment. The results of some tests were inconclusive.
Use of Slow Strain Rate Tests to Evaluate the Embrittlement of Aluminum and Stainless Alloys in Process Environments Containing Mercury
Authors: Kane RD , Wu D , Wilhelm SM
Published: March 2009

As a process contaminant, mercury is a significant problem due to its ability to induce liquid metal attack (LMA) and embrittlement (LME) in some alloys of construction. Aluminum alloys are particularly susceptible to LME. Several test methods (i.e., constant load tensile tests, fracture mechanics crack growth tests, and slow strain rate tests) were used to evaluate LME in aluminum alloys along with AISI 304 stainless steel. Additionally, the effect of various surface treatments on LME of aluminum alloys was also examined. This paper evaluates the effectiveness of the various testing techniques and results obtained in laboratory studies conducted in elemental mercury.
Effect of Heat Treatment on Liquid Metal-Induced Cracking of Austenitic Alloys
Authors: Krupowicz JJ
Published: March 2009

Slow strain rate tests were used to rank the liquid metal embrittlcment (LME) susceptibility of Types 304 (UNS S30400), 304L (UNS S30403), 316 (UNS S31600), 316L (UNS S31603), and 321 (UNS S32100) stainless steel, as well as alloys 600 (UNS N06600) and 800 (UNS N08800). Testing revealed that LME susceptibility was influenced significantly by heat-treated condition. Sensitized materials were consistently more susceptible to cracking in liquid mercury at ambient conditions. Cracking was predominantly intergranular for the sensitized materials and was analogous to stress corrosion cracking in high temperature aqueous solutions. These results suggest that low-carbon or stabilized materials are inherently more resistant to LME and are preferable for applications in environments where mercury may exist.
Hydrogen Cracking Initiation of a High-Strength Steel Weldment
Authors: Klein PA , Hays RA , Moran PJ , Scully JR
Published: March 2009

The hydrogen assisted crack initiation susceptibility of 5-Ni-Cr-Mo-V (MIL-S-24371A) quenched and tempered steel plate, weldment, and Gleeble thermal cycled materials representative of tempered and untempered weld metal was investigated in 3.5% NaCl solution. The conjoint role of steady state diffusible hydrogen content and maximum principal stress was quantitatively characterized by: (1) Devanathan-Stachurski hydrogen permeation tests, and (2) slow strain rate tests conducted under various cathodic protection levels.

For the four material conditions studied, the threshold maximum principal stress decreased with increasing hydrogen concentration. The base plate was less susceptible to hydrogen assisted crack initiation than the weld metal and thermal cycled weld metals. The tempered and untempered thermal cycled weld materials defined the upper and lower bounds of the aswelded material cracking susceptibility respectively.
Relationship of Localized Corrosion and SCC in Oil and Gas Production Environments
Authors: Wilhelm SM , Currie DM
Published: March 2009

Laboratory corrosion tests consisting of electrochemical cyclic polarization, critical pitting temperature (CPT), and slow strain rate (SSR) tests were performed on a group of candidate nickel base alloys. The objective of the test program was to predict service performance in deep sour gas well applications. Of particular interest were localized corrosion resistance and stress corrosion cracking (SCC).

The test data indicated that localized corrosion can occur at intermediate temperatures (110 to 170°C) and that SCC may also occur in this temperature region. The temperature region of susceptibility coincides with the transition from a stable chromium oxide surface film to a predominantly sulfide surface film. The localized loss of chromium oxide protectiveness at 150 to 180°C is manifested by crevice corrosion, pitting, and ductility loss. Elemental sulfur in the test environment lowers the region of susceptibility to 100 to 150°C.

From the information provided by this experimental program (and others), procedures and criteria were established for purchase specifications for tubular products. SSR test methods were used to predict service performance.
Elevated Temperature Behavior of Sintered Silicon Nitride Under Pure Tension, Creep, and Fatigue
Authors: Sankar J , Krishnaraj S , Vaidyanathan R , Kelkar AD
Published: March 2009

Pure tensile fast fracture, tensile creep, and tensile cyclic fatigue/creep interaction data are reported for GTE SNW-1000 sintered silicon nitride (Si3N4) which is being investigated as a candidate material for advanced heat engine applications.

Pure uniaxial tensile tests conducted at room temperature and at elevated temperatures indicate that the tensile strength of this material was retained to 1100°C, above which there was a sharp decrease in strength.

Tensile creep tests performed at 1100°C and 1200°C showed that the steady state creep rate was dependent on both the temperature and the applied stress, the effect of temperature being more dominant than the applied stress. Further, creep induced deformation by linking of small pores, and changes in the chemical contents were observed.

The effect of cyclic loading on creep, and residual tensile strength were also studied at 1200°C. Test results showed that precycling can dramatically increase creep resistance. Cyclic loading at 1200°C also increases the strength of the material.
Fracture Mechanism Maps: Their Applicability to Silicon Nitride
Authors: Wiederhorn SM , Quinn GD , Krause R
Published: March 2009

Fracture mechanism maps provide a means of assessing the structural reliability of ceramics at elevated temperatures. They can be used to summarize large quantities of data dealing with effects of load, temperature and environment on component lifetime. They also can be used to generate a design envelope that defines stress allowables for a given application. In this paper, we review the history and philosophy behind fracture mechanism maps and then discuss methods of obtaining such maps in an efficient manner. Based on data obtained in simple tensile tests, these methods are illustrated for one of the newer grades of silicon nitride. The map is then used to compare this material with a high temperature structural alloy, and another, older grade of silicon nitride. Finally, we discuss the use of fracture mechanism maps for design.
A Comparative Study of Existing and Newly Proposed Models for Creep Deformation and Life Prediction of Si3N4
Authors: Ding J-L , Liu KC , Brinkman CR
Published: March 2009

This paper summarizes recent experimental results, obtained at Oak Ridge National Laboratory (ORNL), on creep behavior and creep rupture of a commercial grade of Si3N4 ceramic in the temperature range of 1150°C to 1300°C. A uniaxial model capable of describing the behavior under general thermomechanical loading is introduced and compared with existing models. An exploratory extension of the new model to a multiaxial form is then discussed. Issues are also discussed concerning the standardization of data analysis methodology and future research needs in the area related to development of creep database and life prediction methodology for high temperature structural ceramics.
Creep Behavior of Silicon Nitride Determined From Curvature and Neutral Axis Shift Measurements in Flexure Tests
Authors: Salem JA , Choi SR
Published: March 2009

The creep behavior of a hot-pressed silicon nitride was determined in flexure in air at 1200 and 1300°C by monitoring the creep deflection, the specimen curvature and the position of the neutral axis. The resulting data was used to evaluate the steady-state creep rate from the conventional elastic solution, curvature-moment relations and a model accounting for neutral axis shift. Fractography and measurements of specimen compliance before and after testing indicated bulk cracking and a loss of stiffness. The validity of flexural data to determine creep life parameters was considered.
Comparison of Tension and Flexure to Determine Fatigue Life Prediction Parameters at Elevated Temperatures
Authors: Choi SR , Salem JA , Palko JL
Published: March 2009

High temperature slow crack growth of a hot-pressed silicon nitride (NCX 34) was determined at temperatures of 1200 and 1300°C in air. Three different testing methods were utilized: dynamic and static fatigue with bend specimens, and static fatigue with dog-bone-shaped tensile specimens. Good agreement exists between the dynamic and static fatigue results under bending. However, fatigue susceptibility in uniaxial tensile loading was greater than in bending. This result suggests that high temperature fatigue behavior should be measured with a variety of specimen configuration and loading cycles so that adequate lifetime prediction parameters are obtained.
Monotonic and Cyclic Rupture of a Silicon Nitride Ceramic
Authors: Hild F , Marquis D
Published: March 2009

A testing system was developed to perform tensile tests on monolithic ceramics. Tensile tests under monotonic and cyclic conditions were carried out on a silicon nitride ceramic. Fractographic observations were made to identify the causes of failure. The monotonie tensile tests are compared with three different kinds of monotonie flexural tests. A size effect analysis is performed using a Weibull-type of modeling. An expression of the cumulative failure probability, which takes account of the initial flaw distribution, is derived in the framework of the weakest link assumption and the independent events hypothesis.
The Numerical Evaluation of Failure Theories for Brittle Materials
Authors: Smart J , Fok SL
Published: March 2009

Many laws have been proposed for the failure of brittle materials. These divide into two main categories — volume and surface integrals. To evaluate these for a complex body requires an initial finite element analysis followed by postprocessing to evaluate the integrals. How this can be achieved efficiently and effectively so that the errors are similar to those associated with the initial finite element analysis is discussed.
Lifetime Prediction for Ceramic Materials Under Constant and Cyclic Load
Authors: Fett T , Munz D
Published: March 2009

Subcritical crack growth under static and cyclic loads is an important failure mode and often responsible for delayed failure. At least for subcritical crack extension under constant load it is a well-known fact that the crack growth behaviour of natural cracks differs significantly from that of macroscopic cracks, especially for such materials exhibiting a pronounced R-curve behaviour. The influence of bridging surface interactions — responsible for R-curves in alumina (Al2O3) — will be discussed with respect to strength and static lifetimes. Experimental results obtained for both loading cases are presented for alumina. Measured lifetimes are significantly shorter than the predictions and a reduction of lifetimes is found for increasing frequencies. From these results an effect of cycles becomes obvious and it can be concluded that a real cyclic fatigue effect occurs.
Probabilistic Failure Predictions in Ceramics and Ceramic Matrix Fiber Reinforced Composites
Authors: Lamon JL
Published: March 2009

An approach to predictions of failure in ceramics and of failure damage in Ceramic Matrix Composites (CMC) is discussed. For ceramics, particular emphasis was placed upon the populations of fracture inducing flaws. The flaw strength parameters, that are used to infer the failure of various loading geometries were estimated in view of fracture origins identified by scanning electron microscopy, using analytical as well as computerized methods. The proposed approach for CMC considers the microcomposite geometry. The Weibull model as well as a more fundamental model based upon the elemental strength concept were used.
A Methodology to Predict Creep Life for Advanced Ceramics Using Continuum Damage Mechanics
Authors: Chuang J , Duffy SF
Published: March 2009

A methodology is proposed to estimate creep rupture life for advanced ceramics such as continuous fiber reinforced ceramic matrix composites (CFCMC). Based on the premise that the damage pattern takes the form of a heterogeneous distribution of grain boundary cavities in the majority of creep life, a damage parameter is incorporated in various creep strain rate equations. The resulting constitutive equations for creep strain and accumulated damage are cast in terms of stress, and other affinities. It is pointed out that these affinities can be derived from a scalar creep potential in nonequilibrium thermodynamics. The evolutionary laws are formulated based on many micro-mechanical models. The time-dependent reliability or hazard rate for a Sic is then established by damage mechanics with Weibull analysis. A unit cell model is presented for predicting life of a uni-directional CFCMC subjected to a constant far-field stress. A system of coupled first order ordinary differential equations is derived from which the evolution of creep damage can be solved giving the rupture life. It is shown that the stress dependence on the lifetime is very sensitive to the type of damage mechanisms active at the microstructural level.
Weibull Estimators for Pooled Fracture Data
Authors: Johnson CA , Tucker WT
Published: March 2009

An estimator is a method or algorithm to analyze fracture data and estimate useful quantities such as distribution parameters and predicted component strengths. There are advantages in efficiency and model validation that typically result from combining or pooling of fracture data from multiple specimen sizes and geometries. Three types of information are contained in pooled data sets: variability in strength within subgroups, dependence of strength on specimen size, and dependence of strength on loading geometry. Efficient pooled estimators extract information of all three types from the data to yield the best overall estimates of distribution parameters and fracture strengths. Two Weibull estimators for pooled fracture data are derived and discussed. One is based on linear regression and the other on the maximum likelihood technique. The pooled estimators are extensions of conventional linear regression and maximum likelihood estimators. The estimators are derived for the two-parameter, size-scaled, uniaxial Weibull distribution function. It has been shown, however, that these estimators are also valid for multiaxial Weibull models. The pooled estimators are demonstrated using strength data from sintered SiC tested in six different combinations of specimen size and bending configuration.