bluuebunny/crossref_metadata_2025 huggingface dataset:
Applicability of the KIScc Concept to Very Small Defects
Authors: Clark WG
Published: March 2009

Stress corrosion threshold (KIscc) data were generated for 180 and 215-ksi yield strength Type 4340 steel exposed to a 5 psig hydrogen sulfide gas environment. Tests were conducted with three-point-bend specimens containing both edge cracks and surface cracks ranging from 0.010 to 0.200 in. deep. The effect of defect size on KIscc was evaluated and the results compared to KIscc data generated with 1-in.-thick compact toughness specimens. Results show that absolute defect size (to as small as 0.010 in. deep) does not impose a limitation on the applicability of linear-elastic fracture mechanics concepts to small defect problems.
Notch-Yield Ratio as a Quality Control Index for Plane-Strain Fracture Toughness
Authors: Kaufman JG , Sha GT , Kohm RF , Bucci RJ
Published: March 2009

The ratio of notch-tensile strength to tensile-yield strength (the notch-yield ratio) is correlatable with plane-strain fracture toughness, KIc. As a result of that fact and relative simplicity of notch-tension testing, it is suitable for plant quality control testing for fracture toughness. The test procedures and quality control testing practices are described, and data showing the correlation between KIc and notch-yield ratio from both ½ and 1 1/16-in.-diameter notched tension specimens for several aluminum alloys are presented. The 1 1/16-in.-diameter specimen provides a more discriminating correlation at high toughness levels than does the ½-in.-diameter specimen. It is emphasized that this is not a procedure for estimating KIc directly, but for providing assurance that KIc equals or exceeds a stated value.
Note on the Dependence of Crack Velocity on Driving Force for an Epoxy Adhesive
Authors: Mostovoy S , Crosley PB , Ripling EJ
Published: March 2009

The dependence of crack velocity, ˙a, on driving force for an adhesive system was shown to be described by a curve having the shape of an inverted L. That is, at high values of ˙a, large increases in G caused small increases in ˙a while at low velocities, small increases in G cause large increases in ˙a. Since the data in the literature on polymethylmethacrylate (PMMA) and mild steel can also be represented by such a curve shape, the inverted L may represent the general dependence of ˙a on driving force.

The high velocity branch appears to be associated with rough fracture surfaces and the low velocity branch, with smooth fracture surfaces.
Fracture Toughness Testing of Glassy Plastics
Authors: Margolis RD , Dunlap RW , Markovitz H
Published: March 2009

Despite widespread use of linear elastic fracture mechanics to describe brittle fracture in glassy plastics, prior work has not established a valid fracture toughness criterion based on the unique aspects of polymer mechanical behavior. In this study, fracture toughness tests on poly(methyl methacrylate) (PMMA) were correlated with crack-tip crazing and fracture surface morphology in order to assess the influence of dissipative processes and crack growth modes on standard toughness test variables. Various Kc criteria were examined for their relevance to PMMA, a material with a velocity dependence of fracture typical of glassy plastics. Since crack-tip crazing is restricted in this material, crack extension is essentially elastic for all normal specimen dimensions and precrack conditions. The load instability at the maximum of the load-displacement record is distinguished from the point of intrinsic instability, which is indicated by the K versus ˙a relationship. The load instability leads to a geometry-dependent Kc criterion which can be described analytically, and procedures for measuring a Kc based on intrinsic instability are defined for a standard fracture test. Measured values are in reasonable agreement with estimates derived from K versus ˙a in the literature. The implications of the geometric effects on instability are discussed for other materials and specimen geometries.
Brittle Fracture (KIc) Behavior of Cracks Emanating from Notches
Authors: Novak SR , Barsom JM
Published: March 2009

Experimental and analytical studies were conducted under AISI sponsorship to determine the influence of short cracks emanating from notches on fracture behavior. All studies were conducted by using concepts of linear-elastic fracture mechanics (LEFM). The experimental studies were conducted on AISI 4340 steel at a high strength level (σys = 215 ksi = 1480 MN/m2) under plane-strain (KIc) conditions by using various types of fatigue-cracked as well as notched and fatigue-cracked specimens. The analytical studies were conducted by using recently developed theoretical KI analyses for notched and fatigue-cracked specimens.

The experimental results obtained by using various types of standard fatigue-cracked specimens demonstrated that the basic fracture-toughness behavior of 4340 steel is repeatable and reproducible within a relatively narrow range (KIc = 70±5 ksi √in. = 77±5.5 MNm−3|2). Limited experimental results on notched and fatigue-cracked double-edge-notched tension (DENT) specimens verified the accuracy of a recent theoretical KI analysis by Tada. Results for these notched and cracked DENT specimens exhibited good agreement with the baseline KIc behavior, but two to three times the amount of scatter usually observed in standard KIc tests (±5 to 10 percent). Tests demonstrated no significant differences in the basic fracture behavior (apparent KIc) of either pure-tension (DENT) specimens or essentially pure-bending (three-point-bend) specimens when tested with cracks emanating from notches. Apparent KIc results calculated by using traditional equations, in which the presence of the notch is ignored (treated as a crack of equivalent length), were elevated above the intrisic KIc level by less than 30 percent for all investigated combinations of specimen type, notch type, and the length of the fatigue crack beyond the notch tip (ΔaF).

The theoretical studies were conducted to develop an analytical criterion [(ΔaFaNρ)=¼] that predicts the depth beyond which a notch with an emanating crack can be treated as a crack of equivalent length. The engineering significance of this criterion is discussed. For values of the parameter that are greater than the criterion, traditional KI equations are accurate within ±5 to ±10 percent. For values less than the criterion, the stress-intensity (KI) at the tip of a short fatigue crack (of length ΔaF) emanating from a dull notch (of length, aN, and radius ρ) is always less severe than a crack of equivalent length, and the use of traditional KI equations can grossly overestimate the actual KI at the crack tip. For this short crack-length range, KI values must be calculated by using appropriate theoretical analyses that account for notch effects in order to minimize the conservative results of traditional analyses.

Included in the present work is a state-of-the-art summary of currently available theoretical KI analyses for cracks in the near vicinity of notches.
Theoretical and Experimental Analysis of Crack Extension at Nozzle Junctions
Authors: Broekhoven MJG
Published: March 2009

Due to the complexity of both geometry and stress distribution, the analysis of cracks in the transition region of nozzle-to-cylinder junctions, where local peak stresses promote crack extension, constitutes one of the most complicated problems in a fracture mechanics based design procedure as adopted in the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (Section III, Appendix G) for nuclear pressure vessels. Results of studies on this subject are scarce. This paper reviews results obtained in the last two years within a Netherlands cooperative research program mainly directed at the nozzle corner crack problem and covers both theoretical and experimental investigations. Significant conclusions from these studies are also presented.
Stress-Intensity Dependence of Stress-Corrosion Crack-Growth Rate in 7079-T651 Aluminum
Authors: Finnegan JE , Hartt WH
Published: March 2009

Stress-corrosion cracking experiments have been performed on double-cantilever-beam specimens of 7079-T651 aluminum in 3 percent sodium chloride in distilled water and in seawater. At relatively low-stress intensities (Region I of the crack-growth rate/stress-intensity plot) crack length versus exposure time curves were comprised of steps, plateaus, and straight-line segments. These could not be related to any variations in the stress-intensity parameter; so, where such behavior was encountered, no unique relationship between stress intensity and crack-growth rate was apparent. On the other hand, crack-growth rate did vary inversely with exposure time for the range 25 to 200 h. Such an observation was interpreted to mean that properties of the local environment within a crack control extension rate.
Learning from Experience of the Stress-Corrosion Failure of High-Strength Aluminum Alloy Forgings
Authors: Cina B , Kaatz T
Published: March 2009

Despite the extensive literature on the subject and the known methods for preventing stress corrosion, the users of high-strength aluminum alloys are still on occasion faced with this problem particularly in wrought components. Examples from actual experience with aircraft forgings are cited to emphasize the susceptibility of the transverse direction, particularly at parting lines, and the complex and often unpredictable role of residual stresses. Despite the absence of a specific short transverse direction, cylindrical forgings can show considerable susceptibility in their single transverse direction. Attention is drawn to the possibly dangerous combination of stresses resulting from heat treatment, machining, and interference assemblies.

It is shown that the mere presence at the surface of a forging of residual compressive stresses resulting from heat treatment is no guarantee that stress-corrosion failure will not initiate from such a surface.

Residual stresses developed along the inside diameter of a blind hole on quenching are a major unknown, and methods for obviating such difficulties are discussed.

In addition to the factors known to affect stress-corrosion susceptibility, there would also seem to be a batch factor whereby some apparently small and temporary modification in manufacturing procedure can increase the susceptibility to stress corrosion significantly.

An example is quoted of the minute amount of moisture found sufficient to initiate a stress-corrosion failure.

The necessity is discussed and emphasized for determining the nature and gradient of residual stresses adjacent to potentially critical surfaces as a stage in the qualification of prototype forgings.
Crack Growth in Heavy Section Titanium
Authors: Judy RW , Goode RJ
Published: March 2009

The integrity of structures that operate in the marine environment depends on both the resistance to the propagation of cracks and the resistance to fracture that are inherent to the structural material. Diagrammatic procedures have been established to analyze systematically the material thickness-stress level-defect size interactions that are implied by the basic characterizations and their relation to various types of structures. In the case of titanium alloys, the extremely rapid growth of stress-corrosion cracks in salt water effectively precludes the possibility of design use of the crack-growth rates; for this reason the design problem reduces to selection of materials to prevent stress-corrosion cracking (SCC) and to minimize corrosion-fatigue crack growth. In this paper, the results of experiments conducted for structural integrity analyses of two 2-in.-thick titanium alloys are presented to illustrate the procedures currently used to measure the basic properties of structural titanium alloys and to interpret these characterizations for structural behavior. One of the test materials was highly sensitive to salt water SCC and the other was immune. Use of the SCC Ratio Analysis Diagram concept as a framework for interpretation of the fracture resistance and SCC resistance of these materials is also illustrated.
Constant Strain Rate Technique for Assessing Stress-Corrosion Susceptibility
Authors: Payer JH , Berry WE , Boyd WK
Published: March 2009

The constant strain rate technique is a rapid laboratory method to assess susceptibility of metals and alloys to stress-corrosion cracking (SCC). Positive results are obtained since specimen failure occurs, either in a ductile manner or prematurely in a brittle mode if SCC occurs. Experimental apparatus, methods to interpret results, and important experimental parameters are discussed.
An Automated Method for Evaluating Resistance to Stress-Corrosion Cracking with Ring-Loaded Precracked Specimens
Authors: Kaufman JG , Coursen JW , Sprowls DO
Published: March 2009

This paper describes a ring-loading method for evaluating stress-corrosion resistance with precracked specimens and presents representative data for compact specimens of some high-strength aluminum alloys. The deflection of the ring was large relative to that of the specimen, simulating deadweight loading. This method provides several advantages over techniques previously used. Unlike most constant-displacement loading systems, the load and crack length and thus the stress intensity are known accurately throughout the life of each test, and the initiation and growth of stress-corrosion cracking (SCC) lead to a definitive end point (failure). Also, the effects of corrosion product wedging are minimal. The ring loading system is more compact than most deadweight systems, and because it is readily automated, data can be collected with the expenditure of few manhours.
Stress-Corrosion Crack Growth in Surface-Cracked Panels of High-Strength Steels
Authors: Shahinian P , Judy RW
Published: March 2009

Stress-corrosion crack growth in 17-4PH and 4340 steels in 3.5 percent sodium chloride solution was examined over a wide range of KIscc/σys values by electrochemically coupling the 17-4PH steel to aluminum, zinc, magnesium, and open circuit and by testing the 4340 steel at three strength levels in open circuit.

It was demonstrated that the parameter, KIscc, determined from small cantilever bend specimens can be used to predict the flaw size/stress level combinations required for the onset of crack growth in large surface-cracked tensile panels. For this purpose the stress-intensity values for the surface-cracked panels were calculated from the basic surface-flaw equation.

The microfracture processes in the stress-corrosion cracking included intergranular, cleavage, and microvoid coalescence, the proportion of intergranular became greater with increase in negative electrochemical potential.
Activation Energy Dependence on Stress Intensity in Stress-Corrosion Cracking and Corrosion Fatigue
Authors: Bania PJ , Antolovich SD
Published: March 2009

The phenomena of stress-corrosion cracking and corrosion fatigue have been investigated assuming that a thermally activated process (diffusion) acts in conjunction with mechanical energy to produce subcritical extension of a flaw. Associated with this diffusion process is an apparent activation energy which is shown to be dependent on the stress-intensity level indicating that the rate limiting diffusion step is associated with the material rather than the environment. A characteristic activation energy associated with the diffusion process is obtained by plotting apparent activation energy versus mechanical energy input required for crack extension and extrapolating to zero mechanical energy input. The characteristic activation energy associated with the stress-corrosion differs fram that associated with the corrosion-fatigue process. Thus, a linear superposition model for corrosion fatigue employing stress-corrosion data is not valid for the material studied. Also from this plot it can be seen that the toughness of the material at the crack tip is inherently degraded by the diffusion process.
Effects of Composition on Stress-Corrosion Cracking Resistance of Ultrahigh-Strength Steels
Authors: Waid GM , Ault RT
Published: March 2009

An investigation was made to evaluate the effects of various alloying and impurity elements on the stress-corrosion cracking (SCC) resistance of ultrahigh-strength steels. The influence of phosphorus and sulfur on the SCC threshold parameter, KIscc, of HP 9-4-45 steel heat treated to both bainitic and martensitic microstructures was measured. The bainitic microstructure was consistently more resistant to SCC than was the martensitic structure, and neither phosphorus nor sulfur had a pronounced effect on the KIscc value. However, impurities, especially sulfur, had an adverse effect on fracture toughness. A systematic examination of silicon, chromium, and molybdenum compositional effects on the SCC behavior of 0.40C low-alloy martensitic steels also was included in this study. SCC as measured by the KIscc parameter of these low-alloy steels heat treated to strength levels in the neighborhood of 300 000 psi was, essentially, independent of composition; however, increasing amounts of silicon and possibly chromium decreased the crack-growth rates. The fracture-toughness levels of these alloy steels, however, were highly dependent on compositional variations.
Stress-Corrosion Cracking Evaluation of Aerospace Bolting Alloys
Authors: Taylor E
Published: March 2009

The susceptibility of aerospace bolting alloys to stress-corrosion cracking has been of continuing interest especially since strength levels have by far exceeded 200 000 psi, the threshold above which failures are much more common. The search for a stress corrosion resistant material has progressed through a number of alloys with strength levels up to 300 000 psi.

All of the high-strength steel alloys exhibted a similar trend where time to failure decreases as strength level increases. However, different levels of immunity were observed for the different alloys. Martensitic stainless steels were found to be much more resistant to stress-corrosion cracking but were very sensitive to hydrogen embrittlement from plating or galvanic corrosion reactions.

The use of a MIL-STD-1312 test procedure to evaluate coated or plated alloy steel bolts is sanctioned because of the short time to failure required, the reproducibility of results, and the duplication of service failures. The same is not true for the more resistant alloys where times to failure are in thousands of hours and results are scattered. A more aggressive test is warranted.

Crevice corrosion and pitting at interfaces are the most common initiators of stress-corrosion cracking failures for high-strength fasteners. Since this is unavoidable with fastened joints, it behooves the consumer to realize all of the advantages and disadvantages of various materials so that he may select the best one for his needs.
Corrosion Thresholds for Interference Fit Fasteners and Cold-Worked Holes
Authors: Kaneko RS , Simenz RF
Published: March 2009

Empirical relationships were obtained between fastener interference or hole expansion and the stress-corrosion thresholds of aluminum alloys. Tensile and stress-corrosion threshold properties were determined for single heats of 2024-T3, 7075-T6, 7075-T76, and 7050-T76 extruded bar used in the studies. The various fastener and hole expansion systems, with a range of interference levels to over 10 mils, were installed in the principal grain directions of each alloy. Specimens were subjected to 3.5 percent sodium chloride alternate immersion and seacoast exposures, then analyzed by visual and metallographic techniques.

The residual tensile stresses created around the holes appeared to rise sharply with increasing amounts of interference, approaching a theoretical limit. Even low interference fits of a few mils caused stress corrosion under the more susceptible conditions. Crack initiation tended to occur further from the hole as interference increased; wet sealant installation helped to reduce galvanic reactions in the vicinity of the hole. Estimated stress corrosion potential over a range of interference fits in aluminum alloys is presented.
Interference Fits and Stress-Corrosion Failure
Authors: Hanagud S , Carter AE
Published: March 2009

Service failure analysis and theoretical and experimental investigations have been carried out to investigate the stress-corrosion susceptibility of the aluminum alloy structures due to the use of interference fit sleeves and mandrel-coining procedures. A methodology has been discussed for the design of interference fits so that maximum improvement of fatigue life can be attained while the stress-corrosion susceptibility is kept to a minimum.
Stress-Corrosion Cracking of Stainless Steels in Hydrogen Sulfide Solutions
Authors: Takemura S , Onoyama M , Ooka T
Published: March 2009

The environment causing stress-corrosion cracking (SCC) at the top of a distillation tower in a crude oil refinery was reproduced in the laboratory. It was an acidified hydrogen sulfide solution with a pH value up to 3.5 at 80°C. In the solution, austenitic stainless steels such as AISI Type 304 or 316 failed because of SCC; however, modified ferritic stainless steels showed good corrosion resistance.
Removal of Iron-Sulfide Deposits from Fracture Surfaces
Authors: Interrante CG , Hicho GE
Published: March 2009

Steels are most commonly used at moderate strength levels at which they have high ductility and resistance to subcritical crack growth due to hydrogen. Thus, in testing the susceptibility to hydrogen damage of these steels, severe charging conditions are commonly used, and hydrogen sulfide is often used in low-pH solutions to obtain the desired high fugacity for the test. The fracture faces of specimens tested in this type of solution become covered with iron and other sulfides that are difficult to remove without affecting the underlying metal as well. The removal of these sulfide deposits from the fracture surfaces is a prerequisite to fractographic analysis of the failure mode, and it was attempted by various methods. Hydrogen reduction of the sulfides at elevated temperatures followed by ultrasonic cleaning in alcohol was found to be much more successful than the other methods studied. This is true principally because the hydrogen-reduction treatment did not attack the fracture surface. Procedures for four different cleaning treatments are described, and they are rated in terms of their relative capability for cleaning sulfide-contaminated fracture surfaces without affecting the underlying metal. Evaluations of these methods for double-cantilever-beam and Charpy V-notch specimens of a 2¼Cr-1Mo steel with fracture surfaces that were created at various stress-intensity levels provides information needed for studying the cracking mechanism under severe sulfide exposure conditions.
Effects of Ferrite and Sensitization on Intergranular and Stress-Corrosion Behavior of Cast Stainless Steels
Authors: Beck FH , Juppenlatz J , Wieser PF
Published: March 2009

Cast stainless steels of the CF grades (19Cr, 9Ni), which find widespread application in the chemical, petrochemical, and power generating industry, were subjected to intergranular corrosion tests (Huey) and stress-corrosion tests (vapor phase of aqueous 875-ppm sodium chloride (NaCl) solution at 477 K [400°F]) to evaluate the effect of ferrite in the range of 0 to 40 ferrite numbers, in the solution-annealed and in the sensitized condition.

The intergranular corrosion tests demonstrated beneficial effects of ferrite for all the alloys tested in the solution-annealed condition and for the molybdenum-free cast steel grades in the sensitized condition. Ferrite increased the sensitization effects on intergranular corrosion for the molybdenum-bearing grades. Highest corrosion rates in Huey tests, based upon weight loss measurements, do not necessarily mean deepest intergranular attack. Intergranular attack was found to terminate at ferrite-austenite grain boundaries. The intergranular corrosion test results would indicate that ferrite numbers exceeding 10 offer greater operating safety for cast, corrosion resistant grades, CF-3, CF-3M, CF-8, and CF-8M in the solution-annealed condition and also, in the event of sensitization, for cast corrosion-resistant grades CF-3 and CF-8.

Significantly increased resistance to stress-corrosion cracking with increasing ferrite content was observed for cast steels in the solution-annealed and in the sensitized condition. These stress-corrosion cracking tests would indicate that ferrite numbers of 10 or more offer greater operating safety for cast corrosion-resistant CF grades in the solution-annealed as well as in the sensitized condition.
Effect of Inclusions on Sulfide Stress Cracking
Authors: Ohki T , Tanimura M , Kinoshita K , Tenmyo G
Published: March 2009

Sulfur was taken as a residual element in steel for investigating the sulfide stress-cracking characteristics. The tests were performed by controlling the shape and the amount of the sulfide inclusions by adding rare earth metal (REM) and varying the sulfur content from 0.002 to 0.019 percent. Susceptibility to sulfide stress cracking was found to be correlated to the sulfur content and also to the shape of the inclusions.

Detailed observation of crack nucleation showed that though precracks nucleate and grow from elongated sulfide inclusions to form large cracks in conventional steels, the nucleation can be suppressed by controlling the shape of sulfide inclusions to the globular type.

The results of this work suggest that controlling the shape of sulfide inclusions by adding an optimum amount of REM is so effective that it would completely minimize the detrimental effect of sulfur against hydrogen sulfide stress cracking.
Experience in Plane-Strain Fracture Toughness Testing Per ASTM Method E 399
Authors: Kaufman JG
Published: March 2009

A review of data generated utilizing ASTM Method E 399 since its last substantial revision in 1971 illustrates the importance of most of the major provisions and criteria for validity, but also that some technical revisions of the criteria are justified. For the standard geometry of specimen (a = B), the Pmax/PQ criterion is a useful indicator of plane-strain crack resistance curve characteristics and should not be “stretched” or ignored in establishing the validity of test data. Alternative geometries are also useful in measuring KIc so long as B >¯ 2.5 (KIc/σys)2, but the present Pmax/PQ limit is too severe for W/B > 2; there is a need to establish alternative limiting values of Pmax/PQ to go with the alternative geometries. With regard to fatigue precracking, the Kfmax during fatigue precracking could be increased from 0.6 to 0.8 KIc, and the limits on fatigue crack front straightness could be modified to permit differences of as much as 10 percent among the middle three measurements.
Fracture Toughness Testing Using the C-Shaped Specimen
Authors: Underwood JH , Kendall DP
Published: March 2009

Fracture toughness testing of material with cylindrical geometry is discussed, and the inherent advantages of the C-shaped specimen in this situation are given. A K calibration equation for the C-shaped specimen is presented which is based on boundary value collocation results. The C-shaped specimen K calibration is compared with those for the standard compact specimen and the single-edge-notched bar specimen.

Guidelines for measuring plane-strain fracture toughness (KIc) using the C-shaped specimen are described, including (a) a KI calibration which applies over a wide range of diameter ratios and to two load point locations in segments of hollow cylinders, as well as over a range of crack lengths, (b) compliance and crack-mouth-displacement analyses and their use to obtain critical value of KI in a fracture toughness test, and (c) suggested specimen geometries to be used in performing KIc tests with C-shaped specimens.

The use of C-shaped specimens for performing J-integral fracture toughness tests and fatigue crack growth tests is described, and some preliminary testing guidelines are offered. Included are suggested methods of load-point-displacement measurement for J-integral tests and suggestions for the geometry and K calibration which could be used in fatigue tests.
Recent Developments in JIc Testing
Authors: Landes JD , Begley JA
Published: March 2009

The J-integral, as proposed by Rice, has been shown to characterize the crack-tip stress and strain field under both elastic and plastic stress-strain conditions. The parameter offers a logical extension of linear elastic fracture mechanics concepts to include cases of large-scale plastic behavior. Begley and Landes proposed the J-integral (labeled JIc) as a measure of material fracture toughness under plane-strain conditions ranging from linear elasticity to large-scale plasticity. Data originally presented by Begley and Landes on two steels showed that JIc characterized fracture toughness under fully plastic conditions and was compatible with KIc in the linear elastic range. Subsequent work has shown that this approach is successful in a variety of metal alloy systems.

In this paper the basis for the JIc approach to fracture toughness characterization is discussed. The recent developments in the method for determining JIc experimentally are explained as well as the future trends in the development of the test method. The present test method relies on the development of a fracture resistance curve where J is plotted as a function of stable crack extension. The present method employs multiple specimens where each specimen supplies one point on the fracture resistance curve. New test methods have been developed which allow this curve to be developed from a single specimen.

Sample data are presented to illustrate the method. The relationship between KIc and JIc is illustrated in regions where both test methods apply. The present work directed at establishing the limitations of the JIc test method is presented, A brief description of the extension of the J-integral approach to other areas of cracking behavior is also included.
Heavy-Section Fracture Toughness Screening Specimen
Authors: Shannon JL , Donald JK , Brown WF
Published: March 2009

Size requirements for a pin-loaded double-edge notch plus crack tension specimen proposed for fracture toughness screening heavy-section alloys were studied. Ranking of eight selected alloys based on the specimen's net strength was compared with that based on the valid plane-strain fracture toughness separately determined. Performance of the specimen was judged on the basis of that comparison.

The specimen's net strength was influenced by three critical specimen dimensions: distance between the crack plane and the loading hole, specimen width, and specimen thickness. Interaction between the stress fields of the crack and the loading holes reduced the net strength, but this effect disappeared as the separation reached a dimension equal to the specimen width. The effects of specimen width and thickness are interrelated and affect the net strength through their influence on the development of the crack-tip plastic zone. Correlation between the net strength of the screening specimen and the plane-strain fracture toughness was enhanced by increasing thickness and decreasing width of the screening specimen.

The work described is intended to form the technical base for the development of a standard fracture toughness screening test method for heavy sections to supplement ASTM E 338 Standard Method of Sharp Notch Tension Testing of High-Strength Sheet Materials. Development of the test method is the responsibility of the ASTM E24.01.02 Task Group on Revision of E 338.
Investigation of Some Problems In Developing Standards for Precracked Charpy Slow Bend Tests
Authors: Succop G , Bubsey RT , Jones MH , Brown WF
Published: March 2009

Precracked Charpy slow bend tests and plane-strain fracture toughness (KIc) tests were made on the following alloys: (1) 4340 and 18Ni maraging steels heat treated to a wide range of strength levels; (2) several 2000 and 7000 series aluminum alloys; and (3) a metastable beta titanium alloy, Ti-8Mo-8V-2Fe-3Al. Load-deflection records for the precracked Charpy specimens were obtained from measurements of tensile machine screw rotation and directly from the specimen deflection. It was shown that records obtained from screw motion measurements contained large extraneous components of deflection arising primarily from elastic strains in the tensile machine. The magnitude of these components will be a function of the compliance of the testing machine and, depending on the method of record analysis, can have a substantial influence on the derived W̄/A values. Load-deflection record analysis procedures are presented which minimize the effects of these extraneous deflections. If the deflections are obtained from measurements made directly on the specimen, the influence of the tensile machine compliance for practical purposes may be neglected, and a simplified method of record analysis can be used which does not involve graphical integration of the load-deflection trace.

Relations between W¯E/Aσ ys2 and the crack size factor KIc2/σ ys2 are presented for the alloy conditions investigated. In all but a few cases there was a general upward trend in the Charpy energy values with increasing crack size factor. In some cases, excellent correlation was obtained. Where relatively large scatter was observed, the Charpy derived values in a few cases did not follow the trend of the crack size factor. Apparently no generalizations can be made concerning the degree of correlation that can be expected between precracked Charpy energies and plane-strain fracture toughness. Correlations can be useful but should be established carefully over the complete range of toughness of interest.

The authors recommend that an ASTM test method be developed for the slow bend precracked Charpy test and believe there is sufficient information available to do this now. Some suggestions along these lines are presented in this paper.
Solution Chemistry Modification within Corrosion-Fatigue Cracks
Authors: Hartt WH , Tennant JS , Hooper WC
Published: March 2009

There exists in the literature several observations indicating that the electrolyte within corrosion-fatigue cracks can become modified relative to the bulk solution. Since the rate of fatigue-crack growth should depend upon electrolyte chemistry near the crack tip, it is important that the conditions under which such modification occurs and the role of influential variables be recognized. This paper represents an initial analysis of how fatigue variables might influence mixing between the crack and bulk solutions. The rationale considers that such mixing is governed primarily by net momentum of the periodically exhausted and ingested electrolyte. It is shown that this momentum should be directly proportional to the crack opening angle, cyclic frequency, and the cube of crack length. Decreasing mean stress also contributes to a momentum increase, with the latter becoming large for stress functions that result in crack closure during a portion of each cycle. Other factors which are considered include temperature, stress-wave form, specimen geometry, test method, and applied current density. The significance of the projected trends is discussed within the frame of commonly employed corrosion-fatigue test procedures.
Investigation of Effects of Saltwater on Retardation Behavior of Aluminum Alloys
Authors: Chanani GR
Published: March 2009

The 2024-T8, 7075-T6, and 7075-T73 alloys were studied in laboratory air and 3.5 percent sodium chloride (NaCl) solution to investigate the effects of a corrosive environment on the retardation behavior of aluminum alloys. Single overload cycles at overload ratios of 1.5, 2.0, and 2.5 were used. The single overloads were found to cause a decrease in constant-amplitude crack-growth in saltwater just as they did in air. Also, the number of delay cycles increased with each increase in overload ratio (OLR) in saltwater just as they did in air. However, the number of delay cycles was larger in air than in 3½ percent saltwater, and the difference was greater for the 7075-T6 alloy than it was for the 2024-T8 and 7075-T73 alloys. The results indicated that a given microstructure and its susceptibility to environmental attack are important in determining its fatigue behavior under variable amplitude loading in a corrosive environment. An alloy which shows superior retardation behavior in air can be inferior in a corrosive environment such as saltwater as was found for the 7075-T6 and 2024-T8 alloys. The difference in the retardation behavior of these two alloys in air was small, while in saltwater, the 2024-T8 alloy was generally superior. Environmental attack similar to that which was observed in the constant-amplitude saltwater fatigue specimens was found by fractographic examination of selected retardation specimens. However, these observations indicated that the general nature of the fractographic features in relation to the OLR and the applied baseline stress-intensity factor is similar in both air and saltwater, except that, at the lower OLR and low K values, the overload markings were not visible in the specimens tested in saltwater. This lack of overload marking was more common in the 7075-T6 alloy because of its high susceptibility to environmental attack.
Influences of Secondary Stress Fluctuations of Small Amplitude on Low-Cycle Corrosion Fatigue
Authors: Endo K , Kormai K
Published: March 2009

The influences of small superimposed stress fluctuations on low-cycle corrosion fatigue under trapezoidal waveform are varied by the susceptibility of the test materials to stress corrosion cracking (SCC).

The corrosion-fatigue life of the materials which are insensitive to SCC is greatly diminished if small stress fluctuations are superimposed. The crack initiation is shortened somewhat by such a superposition.

In materials sensitive to SCC, the corrosion-fatigue life is almost occupied by the crack growth period, and the crack rate greatly decreases with the superposition of small stress fluctuations under Kmax higher than KISCC. Under low Kmax which is nearly equal to KISCC, the similar characteristics to that of the materials insensitive to SCC are obtained. The effects of stress change on corrosion fatigue component and SCC component have been discussed.
Corrosion-Fatigue Behavior of Some Special Stainless Steels
Authors: Amzallag C , Rabbe P , Desestret A
Published: March 2009

We have studied the corrosion-fatigue crack initiation and propagation of different types of steels: two austenitic, one austenitic-ferritic, and one ferritic. The testing program had been established in order to define, particularly, the part in corrosion fatigue of electrochemical effects and mechanical damage. Tests were carried out on smooth specimens in rotating bending and on precracked specimens in tension in air, and in a 3 percent aerated solution of sodium chloride.

The capacity of the metal for dissolution and repassivation seems largely responsible for the behavior of the metal in the corrosive solution. This capacity varies notably with the composition of the metal, the loading conditions of the specimens, and the characteristics of the corrosive medium.
Corrosion-Fatigue Behavior of Austenitic-Ferritic Stainless Steels
Authors: Moskovitz JA , Pelloux RM
Published: March 2009

The corrosion-fatigue behavior of austenitic-ferritic (duplex) stainless steels, which combine high strength, good fracture toughness, and excellent corrosion resistance, is described in detail. The physical metallurgy of this class of alloys is reviewed so that the microstructure of different cast and wrought alloys can be understood in terms of alloy content, heat treatment, and cooling rate. The corrosion and stress corrosion cracking behaviors of duplex stainless steels are discussed and related to their corrosion-fatigue resistance. The results of recent work investigating the effects of various microstructural variables on corrosion-fatigue crack initiation and crack propagation in acidic chloride solution are described. The main structural variables are: volume fraction of austenite and ferrite, microstructural orientation of the different phases, embrittling intermetallic precipitates, and grain boundary carbides. An attempt is made to describe the microstructural features which will give the best corrosion-fatigue resistance in austenitic-ferritic stainless steels.
Corrosion-Fatigue Properties of Recrystallization Annealed Ti-6A1-4V
Authors: Ryder JT , Krupp WE , Pettit DE , Hoeppner DW
Published: March 2009

The corrosion-fatigue crack growth properties of recrystallization annealed (RA) Ti-6A1-4V were studied in room-temperature laboratory air, dry air, high-humidity air, sump-tank water, and 3.5 percent sodium chloride (NaCl) solution environments. The alloy was characterized by chemical, microstructural, and tensile properties. Corrosion fatigue tests were conducted using wedge-opening-load (WOL), center-cracked-through (CCT) and part-through-cracked (PTC) specimens. Frequency and environmental interactions were studied as well as the effects of orientation and stress ratio. The effect of frequency was to increase the fatigue crack growth rate as the frequency was decreased. A severe effect of frequency was noted in sump-tank water and saltwater where at low frequencies, crack growth rates increased to such a high level that failure occurred at Kmax levels significantly below those expected. Fractographic studies showed no apparent cause of this phenomenon.
Influence of High Pressure Hydrogen on Cyclic Load Crack Growth in Metals
Authors: Jewett RP , Walter RJ , Chandler WT
Published: March 2009

The effect of high pressure hydrogen on the crack growth rate of various nickel-base alloys was studied at ambient temperature. Considerable enhancement of the cyclic flaw growth rate was observed for Inconel 718, wrought and cast, and Waspaloy, a nickel-base alloy similar to Inconel 718. Only slight enhancement of the flaw growth rate for Alloy 903 was observed.
Fatigue of Tantalum in Sulfuric Acid at 150°C
Authors: Seastrom CC
Published: March 2009

Tantalum is resistant to 80 percent sulfuric acid (H2SO4) at 150°C (302°F). However, data on fatigue of tantalum under these conditions were unavailable. To determine design criteria for a tantalum pump impeller, high frequency fatigue tests were conducted over a range from less than 106 to over 9 x 109 cycles, establishing approximate stress amplitudes which allow tantalum to achieve up to 8 × 109 cycles of loading without failure. These stresses were found to be about 11 ksi (7.7 kg/mm2) for unalloyed tantalum and about 12.4 ksi (8.7 kg/mm2) for Ta-2.5W. These two tantalum alloys were deliberately processed to create very soft materials with large grain sizes. Such materials may indicate behavior of these alloys in or near weld areas.

Case histories are presented on two Ta-2.5W pump impellers which failed in 80 percent H2SO4. The cracks were generally associated with welds. The crack surfaces show evidence of corrosion fatigue and cleavage fractures. The areas of cleavage fracture suggest an environmental effect such as hydrogen-assisted stress corrosion cracking.
Corrosion-Fatigue Behavior of Coated 4340 Steel for Blade Retention Bolts of the AH-1 Helicopter
Authors: Levy M , Morrossi JL
Published: March 2009

The main rotor blade bolt for the 540 helicopter rotor system of the AH-1G, UH-1C, and UH-1M helicopters is proposed to be improved by substituting a plasma-sprayed tungsten carbide coating on the outer shank of the 4340 steel bolt for the present cadmium or chromium plate. This study was undertaken to determine the effects of these coating systems on the fatigue behavior of 4340 steel in environments likely to be encountered in service. Both axial tension-tension and rotating bending fatigue testing of coated specimens were carried out in air and in 3.5 percent sodium chloride (NaCl) solution. The NaCl environment causes reductions in fatigue strength of bare and coated 4340 steel. The severity of the degradation depends on the coating applied and the type of fatigue test utilized.
Significance of Defects in Liquefied Natural Gas Tanks in Ships
Authors: Tenge P , Solli O , Förli O
Published: March 2009

The commonly encountered defects in welding of 9 percent nickel steel and aluminum alloy 5083-0 for liquefied natural gas tanks are described, and their significance with respect to fatigue crack propagation and fracture in ship tanks is discussed. Fracture mechanics testing and analysis have been applied. Diagrams describing the growth in depth and length of surface cracks in welded joints as a function of long term distribution of dynamic stresses for North Atlantic service are presented. The possibilities and limitations of the presently used nondestructive testing methods are treated.
Fatigue Crack Growth Rate of Thick 5083-O Plate at Room and Low Temperatures
Authors: Person NL , Wolfer GC
Published: March 2009

Thick aluminum alloy 5083-O has gained wide usage in liquefied natural gas (LNG) tank construction. Fatigue crack growth rate (FCGR) characteristics are described for specimens obtained from 5083-O plate in thickness from about ½ to 7.75 in. Data were obtained from crack propagation gages and compared with data obtained by an ultrasonic technique. Crack growth rate was measured at 75 and -320°F. At -320°F, FCGR appeared to be substantially lower than at 75 °F in the second stage of growth; however, in the accelerated third stage of growth, the FCGR for the two temperatures were similar. Data show that location of specimen in relation to plate thickness can affect crack growth rate, depending on the crack orientation. From crack propagation gage measurements, it was determined that thickness of compact specimens, per se, (1 to 2 in.) had no effect on growth rate.
Fracture Toughness and Fatigue Properties of 5083-0 Plate and 5183 Welds for Liquefied Natural Gas Applications
Authors: Kaufman JG , Kelsey RA
Published: March 2009

The results of a number of investigations on the properties of 5083-0 plate and weldments of various thicknesses have been summarized. The data show that the tensile properties and toughness of 5083-0 plate at room and subzero temperatures remain about constant or decrease modestly with an increase in thickness from 1 to 9 in. and that the properties of 5083-0 plate formed into a spherical contour by the Alcoa 570 process are essentially the same as those of asrolled 5083-0 plate. Both strength and toughness are higher at -260 and -320°F than at room temperature. The strength and toughness of 5183 welds at room temperature, -260, and -320°F are equivalent to those of the parent plate. The high toughness of these products at those temperatures has been demonstrated by tests of relatively large-scale specimens, all of which have fractured by ductile tearing; conservative engineering estimates of KIc and Kc have been made based upon these results and those published in the literature. The fatigue crack propagation characteristics of these materials have been established and found to be largely unaffected by temperature, thickness, orientation, or location in the weld. Crack growth rates are faster in moist air than in dry air.