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Sample records for environmental stress cracking

  1. Environmental stress cracking of polymers

    NASA Technical Reports Server (NTRS)

    Mahan, K. I.

    1980-01-01

    A two point bending method for use in studying the environmental stress cracking and crazing phenomena is described and demonstrated for a variety of polymer/solvent systems. Critical strain values obtained from these curves are reported for various polymer/solvent systems including a considerable number of systems for which critical strain values have not been previously reported. Polymers studied using this technique include polycarbonate (PC), ABS, high impact styrene (HIS), polyphenylene oxide (PPO), and polymethyl methacrylate (PMMA). Critical strain values obtained using this method compared favorably with available existing data. The major advantage of the technique is the ability to obtain time vs. strain curves over a short period of time. The data obtained suggests that over a short period of time the transition in most of the polymer solvent systems is more gradual than previously believed.

  2. Environment-induced embrittlement: Stress corrosion cracking and metal-induced embrittlement; Environmental embrittlement of iron aluminide alloys

    SciTech Connect

    Heldt, L.A.; Milligan, W.W.; White, C.L.

    1991-01-01

    This research program has included two thrusts. The first addressed environment-induced embrittlement in a parallel study of stress corrosion cracking and metal-induced embrittlement. This work has examined (1) mechanical properties as influenced by embrittling environments, (2) fractography and crystallography or transgranular cracking, (3) the mechanics of cracking, (4) the extent and role of local plastic flow, and (5) local chemistry within stress corrosion and metal-induced cracks. The embrittlement of iron aluminide alloys by air was addressed by determining the effect of water and hydrogen upon the mechanical properties. Slow strain rate testing in aqueous environments was carried out at controlled anodic and cathodic potentials. The effect of cathodically charged hydrogen and the effect of subsequent baking were measured. Environmental susceptibility was measured as affected by alloy composition, microstructure and degree of ordering.

  3. Environmental stress-corrosion cracking of fiberglass: lessons learned from failures in the chemical industry.

    PubMed

    Myers, T J; Kytömaa, H K; Smith, T R

    2007-04-11

    Fiberglass reinforced plastic (FRP) composite materials are often used to construct tanks, piping, scrubbers, beams, grating, and other components for use in corrosive environments. While FRP typically offers superior and cost effective corrosion resistance relative to other construction materials, the glass fibers traditionally used to provide the structural strength of the FRP can be susceptible to attack by the corrosive environment. The structural integrity of traditional FRP components in corrosive environments is usually dependent on the integrity of a corrosion-resistant barrier, such as a resin-rich layer containing corrosion resistant glass fibers. Without adequate protection, FRP components can fail under loads well below their design by an environmental stress-corrosion cracking (ESCC) mechanism when simultaneously exposed to mechanical stress and a corrosive chemical environment. Failure of these components can result in significant releases of hazardous substances into plants and the environment. In this paper, we present two case studies where fiberglass components failed due to ESCC at small chemical manufacturing facilities. As is often typical, the small chemical manufacturing facilities relied largely on FRP component suppliers to determine materials appropriate for the specific process environment and to repair damaged in-service components. We discuss the lessons learned from these incidents and precautions companies should take when interfacing with suppliers and other parties during the specification, design, construction, and repair of FRP components in order to prevent similar failures and chemical releases from occurring in the future. PMID:16950568

  4. Aqueous chloride stress corrosion cracking of titanium - A comparison with environmental hydrogen embrittlement

    NASA Technical Reports Server (NTRS)

    Nelson, H. G.

    1974-01-01

    The physical characteristics of stress corrosion cracking of titanium in an aqueous chloride environment are compared with those of embrittlement of titanium by a gaseous hydrogen environment in an effort to help contribute to the understanding of the possible role of hydrogen in the complex stress corrosion cracking process. Based on previous studies, the two forms of embrittlement are shown to be similar at low hydrogen pressures (100 N/sq m) but dissimilar at higher hydrogen pressures. In an effort to quantify this comparison, tests were conducted in an aqueous chloride solution using the same material and test techniques as had previously been employed in a gaseous hydrogen environment. The results of these tests strongly support models based on hydrogen as the embrittling species in an aqueous chloride environment.

  5. Environmentally assisted cracking of LWR materials

    SciTech Connect

    Chopra, O.K.; Chung, H.M.; Kassner, T.F.; Shack, W.J.

    1995-12-01

    Research on environmentally assisted cracking (EAC) of light water reactor materials has focused on (a) fatigue initiation in pressure vessel and piping steels, (b) crack growth in cast duplex and austenitic stainless steels (SSs), (c) irradiation-assisted stress corrosion cracking (IASCC) of austenitic SSs, and (d) EAC in high- nickel alloys. The effect of strain rate during different portions of the loading cycle on fatigue life of carbon and low-alloy steels in 289{degree}C water was determined. Crack growth studies on wrought and cast SSs have been completed. The effect of dissolved-oxygen concentration in high-purity water on IASCC of irradiated Type 304 SS was investigated and trace elements in the steel that increase susceptibility to intergranular cracking were identified. Preliminary results were obtained on crack growth rates of high-nickel alloys in water that contains a wide range of dissolved oxygen and hydrogen concentrations at 289 and 320{degree}C. The program on Environmentally Assisted Cracking of Light Water Reactor Materials is currently focused on four tasks: fatigue initiation in pressure vessel and piping steels, fatigue and environmentally assisted crack growth in cast duplex and austenitic SS, irradiation-assisted stress corrosion cracking of austenitic SSs, and environmentally assisted crack growth in high-nickel alloys. Measurements of corrosion-fatigue crack growth rates (CGRs) of wrought and cast stainless steels has been essentially completed. Recent progress in these areas is outlined in the following sections.

  6. Aqueous chloride stress corrosion cracking of titanium: A comparison with environmental hydrogen embrittlement

    NASA Technical Reports Server (NTRS)

    Nelson, H. G.

    1973-01-01

    The physical characteristics of stress corrosion cracking of titanium in an aqueous chloride environment are compared with those of embrittlement of titanium by a gaseous hydrogen environment in an effort to help contribute to the understanding of the possible role of hydrogen in the complex stress corrosion cracking process. Based on previous studies, the two forms of embrittlement are shown to be similar at low hydrogen pressures (100 N/sqm) but dissimilar at higher hydrogen pressures. In an effort to quantify this comparison, tests were conducted in an aqueous chloride solution using the same material and test techniques as had previously been employed in a gaseous hydrogen environment. The results of these tests strongly support models based on hydrogen as the embrittling species in an aqueous chloride environment. Further, it is shown that if hydrogen is the causal species, the effective hydrogen fugacity at the surface of titanium exposed to an aqueous chloride environment is equivalent to a molecular hydrogen pressure of approximately 10 N/sqm.

  7. Environmental Degradation of Materials: Surface Chemistry Related to Stress Corrosion Cracking

    NASA Technical Reports Server (NTRS)

    Schwarz, J. A.

    1985-01-01

    Parallel experiments have been performed in order to develop a comprehensive model for stress cracking (SCC) in structural materials. The central objective is to determine the relationship between the activity and selectivity of the microstructure of structural materials to their dissolution kinetics and experimentally measured SCC kinetics. Zinc was chosen as a prototype metal system. The SCC behavior of two oriented single-crystal disks of zinc in a chromic oxide/sodium sulfate solution (Palmerton solution) were determined. It was found that: (1) the dissolution rate is strongly (hkil)-dependent and proportional to the exposure time in the aggressive environment; and (2) a specific slip system is selectively active to dissolution under applied stress and this slip line controls crack initiation and propagation. As a precursor to potential microgrvity experiments, electrophoretic mobility measurements of zinc particles were obtained in solutions of sodium sulfate (0.0033 M) with concentrations of dissolved oxygen from 2 to 8 ppm. The equilibrium distribution of exposed oriented planes as well as their correlation will determine the particle mobility.

  8. Environment-induced embrittlement: Stress corrosion cracking and metal-induced embrittlement; Environmental embrittlement of iron aluminide alloys. Final report, September 1, 1986--August 31, 1991

    SciTech Connect

    Heldt, L.A.; Milligan, W.W.; White, C.L.

    1991-12-31

    This research program has included two thrusts. The first addressed environment-induced embrittlement in a parallel study of stress corrosion cracking and metal-induced embrittlement. This work has examined (1) mechanical properties as influenced by embrittling environments, (2) fractography and crystallography or transgranular cracking, (3) the mechanics of cracking, (4) the extent and role of local plastic flow, and (5) local chemistry within stress corrosion and metal-induced cracks. The embrittlement of iron aluminide alloys by air was addressed by determining the effect of water and hydrogen upon the mechanical properties. Slow strain rate testing in aqueous environments was carried out at controlled anodic and cathodic potentials. The effect of cathodically charged hydrogen and the effect of subsequent baking were measured. Environmental susceptibility was measured as affected by alloy composition, microstructure and degree of ordering.

  9. The effect of polymer blending on environmental stress cracking resistance: Role of polycarbonate blend morphology, miscibility, and crystallinity

    NASA Astrophysics Data System (ADS)

    Hopson, Peyton Lee

    The environmental stress cracking (ESC) of polymeric materials was investigated in order to elucidate the fundamental polymer properties leading to failure. In particular, the ESC of polymer blends was studied to gain a deeper understanding of the role of phase miscibility, blend morphology, and crystallinity on failure. Initial efforts to develop an ESC test method for polymer blends were based on failure induced by fabricated residual stresses utilizing a modified slow strain rate test. The modified slow strain rate test method was applied to a polycarbonate/polyamide and polycarbonate/polyester blend. Qualitative comparisons between industrially applied bent ESC test methods and the modified slow strain rate test were drawn. Further ESC test method development involved the determination of blend ESC resistance through tensile testing in a fluid environment utilizing an Eyring-type activated process to describe ESC. The validity of the test was confirmed through comparisons of the ESC resistance data to current theories describing the effect of polymer/fluid surface tension and fluid viscosity effects on ESC. It was found that the miscible blend, a polycarbonate/copolyester blend, displayed a rule of mixtures for ESC resistance to all fluids tested, except ether. In contrast, the immiscible blend, a polycarbonate/poly(butylenes terephthalate) blend, displayed a significant negative deviation from the rule of mixtures for ESC resistance. This behavior was attributed to the development of stress sites for craze initiation at the interface between the blend components on the surface of the test sample. The differences in ether resistance compared to the trends found for the fluid ESC resistance in this study were attributed to solvent/stress induced crystallization of the polycarbonate component. DSC traces indicated that significant crystallization of the polycarbonate component was observed for samples with low ether ESC resistance. These data suggest that

  10. Environmentally assisted cracking in light water reactors.

    SciTech Connect

    Chopra, O. K.; Chung, H. M.; Clark, R. W.; Gruber, E. E.; Shack, W. J.; Soppet, W. K.; Strain, R. V.

    2007-11-06

    This report summarizes work performed by Argonne National Laboratory on fatigue and environmentally assisted cracking (EAC) in light water reactors (LWRs) from January to December 2002. Topics that have been investigated include: (a) environmental effects on fatigue crack initiation in carbon and low-alloy steels and austenitic stainless steels (SSs), (b) irradiation-assisted stress corrosion cracking (IASCC) of austenitic SSs in BWRs, (c) evaluation of causes and mechanisms of irradiation-assisted cracking of austenitic SS in PWRs, and (d) cracking in Ni-alloys and welds. A critical review of the ASME Code fatigue design margins and an assessment of the conservation in the current choice of design margins are presented. The existing fatigue {var_epsilon}-N data have been evaluated to define the effects of key material, loading, and environmental parameters on the fatigue lives of carbon and low-alloy steels and austenitic SSs. Experimental data are presented on the effects of surface roughness on fatigue crack initiation in these materials in air and LWR environments. Crack growth tests were performed in BWR environments on SSs irradiated to 0.9 and 2.0 x 10{sup 21} n x cm{sup -2}. The crack growth rates (CGRs) of the irradiated steels are a factor of {approx}5 higher than the disposition curve proposed in NUREG-0313 for thermally sensitized materials. The CGRs decreased by an order of magnitude in low-dissolved oxygen (DO) environments. Slow-strain-rate tensile (SSRT) tests were conducted in high-purity 289 C water on steels irradiated to {approx}3 dpa. The bulk S content correlated well with the susceptibility to intergranular SCC in 289 C water. The IASCC susceptibility of SSs that contain >0.003 wt. % S increased drastically. bend tests in inert environments at 23 C were conducted on broken pieces of SSRT specimens and on unirradiated specimens of the same materials after hydrogen charging. The results of the tests and a review of other data in the literature

  11. Stress Corrosion Cracking of Carbon Steel Weldments

    SciTech Connect

    POH-SANG, LAM

    2005-01-13

    An experiment was conducted to investigate the role of weld residual stress on stress corrosion cracking in welded carbon steel plates prototypic to those used for nuclear waste storage tanks. Carbon steel specimen plates were butt-joined with Gas Metal Arc Welding technique. Initial cracks (seed cracks) were machined across the weld and in the heat affected zone. These specimen plates were then submerged in a simulated high level radioactive waste chemistry environment. Stress corrosion cracking occurred in the as-welded plate but not in the stress-relieved duplicate. A detailed finite element analysis to simulate exactly the welding process was carried out, and the resulting temperature history was used to calculate the residual stress distribution in the plate for characterizing the observed stress corrosion cracking. It was shown that the cracking can be predicted for the through-thickness cracks perpendicular to the weld by comparing the experimental KISCC to the calculated stress intensity factors due to the welding residual stress. The predicted crack lengths agree reasonably well with the test data. The final crack lengths appear to be dependent on the details of welding and the sequence of machining the seed cracks, consistent with the prediction.

  12. Stress-corrosion cracking in metals

    NASA Technical Reports Server (NTRS)

    1971-01-01

    Criteria and recommended practices for preventing stress-corrosion cracking from impairing the structural integrity and flightworthiness of space vehicles are presented. The important variables affecting stress-corrosion cracking are considered to be the environment, including time and temperature; metal composition, and structure; and sustained tensile stress. For designing spacecraft structures that are free of stress-corrosion cracking for the service life of the vehicle the following rules apply: (1) identification and control of the environments to which the structure will be exposed during construction, storage, transportation, and use; (2) selection of alloy compositions and tempers which are resistant to stress-corrosion cracking in the identified environment; (3) control of fabrication and other processes which may introduce residual tensile stresses or damage the material; (4) limitation of the combined residual and applied tensile stresses to below the threshold stress level for the onset of cracking throughout the service life of the vehicle; and (5) establishment of a thorough inspection program.

  13. Stress intensity and crack displacement for small edge cracks

    NASA Technical Reports Server (NTRS)

    Orange, Thomas W.

    1988-01-01

    The weight function method was used to derive stress intensity factors and crack mouth displacement coefficients for small edge cracks (less than 20 percent of the specimen width) in common fracture specimen configurations. Contact stresses due to point application of loads were found to be small but significant for three-point bending and insignificant for four-point bending. The results are compared with available equations and numerical solutions from the literature and with unpublished boundary collocation results.

  14. Stress analysis for structures with surface cracks

    NASA Technical Reports Server (NTRS)

    Bell, J. C.

    1978-01-01

    Two basic forms of analysis, one treating stresses around arbitrarily loaded circular cracks, the other treating stresses due to loads arbitrarily distributed on the surface of a half space, are united by a boundary-point least squares method to obtain analyses for stresses from surface cracks in places or bars. Calculations were for enough cases to show how effects from the crack vary with the depth-to-length ratio, the fractional penetration ratio, the obliquity of the load, and to some extent the fractional span ratio. The results include plots showing stress intensity factors, stress component distributions near the crack, and crack opening displacement patterns. Favorable comparisons are shown with two kinds of independent experiments, but the main method for confirming the results is by wide checking of overall satisfaction of boundary conditions, so that external confirmation is not essential. Principles involved in designing analyses which promote dependability of the results are proposed and illustrated.

  15. Environmentally Assisted Cracking of Nickel Alloys

    SciTech Connect

    Rebak, R B

    2004-02-06

    Environmentally Assisted Cracking (EAC) is a general term that includes phenomena such as stress corrosion cracking (SCC), hydrogen embrittlement (HE), sulfide stress cracking (SSC), liquid metal embrittlement (LME), etc. EAC refers to a phenomenon by which a normally ductile metal looses its toughness (e.g. elongation to rupture) when it is subjected to mechanical stresses in presence of a specific corroding environment. For EAC to occur, three affecting factors must be present simultaneously. These include: (1) Mechanical tensile stresses, (2) A susceptible metal microstructure and (3) A specific aggressive environment. If any of these three factors is removed, EAC will not occur. That is, to mitigate the occurrence of EAC, engineers may for example eliminate residual stresses in a component or limit its application to certain chemicals (environment). The term environment not only includes chemical composition of the solution in contact with the component but also other variables such as temperature and applied potential. Nickel alloys are in general more resistant than stainless steels to EAC. For example, austenitic stainless steels (such as S30400) suffer SCC in presence of hot aqueous solutions containing chloride ions. Since chloride ions are ubiquitous in most industrial applications, the use of stressed stainless steels parts is seriously limited. On the other hand, nickel alloys (such as N10276) are practically immune to SCC in presence of hot chloride solutions and therefore an excellent alternative to replace the troubled stainless steels. Nonetheless, nickel alloys are not immune to other types of EAC. There are several environments (such as hot caustic and hot hydrofluoric acid) that may produce embrittlement in nickel alloys (Crum et al, 2000) (Table 1). The conditions where nickel alloys suffer EAC are highly specific and therefore avoidable by the proper design of the industrial components.

  16. Environmentally assisted cracking in light water reactors

    SciTech Connect

    Chopra, O.K.; Chung, H.M.; Gruber, E.E.

    1996-07-01

    This report summarizes work performed by Argonne National Laboratory on fatigue and environmentally assisted cracking (EAC) in light water reactors (LWRs) from April 1995 to December 1995. Topics that have been investigated include fatigue of carbon and low-alloy steel used in reactor piping and pressure vessels, EAC of Alloy 600 and 690, and irradiation-assisted stress corrosion cracking (IASCC) of Type 304 SS. Fatigue tests were conducted on ferritic steels in water that contained various concentrations of dissolved oxygen (DO) to determine whether a slow strain rate applied during different portions of a tensile-loading cycle are equally effective in decreasing fatigue life. Crack-growth-rate tests were conducted on compact-tension specimens from several heats of Alloys 600 and 690 in simulated LWR environments. Effects of fluoride-ion contamination on susceptibility to intergranular cracking of high- and commercial- purity Type 304 SS specimens from control-tensile tests at 288 degrees Centigrade. Microchemical changes in the specimens were studied by Auger electron spectroscopy and scanning electron microscopy to determine whether trace impurity elements may contribute to IASCC of these materials.

  17. Sulfide stress corrosion cracking of line pipe

    SciTech Connect

    Kimuro, M.; Totsuka, N.; Kurisu, T.; Amano, K.; Matsuyama, J.; Nakai, Y. )

    1989-04-01

    This paper reports the sulfide stress corrosion cracking (SSC) behavior of line pipe steel investigated using the SSC test method in NACE Standard TMO177-77, Testing of Metals for Resistance to Sulfide Stress Cracking at Ambient Temperatures. SSC of base metal can be classified into two types, depending on microstructures. In ferrite-perlite steel, the first crack initiates parallel to the pipe surface and propagates perpendicularly to the axis of stress. In ferrite-bainite steel or low C-bainite steel, the crack initiates at the interface between the bainite particle and the ferrite. With decreasing carbon content, the threshold stress of SSC ({sigma}{sub th}) increases, but in low-carbon steel, the {sigma}{sub th} value of weld seam is lower than that of base metal. SSC of weld seams occurs at the softening zone in the heat-affected zone (HAZ) about 2 to 4 mm away from the fusion line.

  18. STRESS CORROSION CRACKING IN TEAR DROP SPECIMENS

    SciTech Connect

    Lam, P; Philip Zapp, P; Jonathan Duffey, J; Kerry Dunn, K

    2009-05-01

    Laboratory tests were conducted to investigate the stress corrosion cracking (SCC) of 304L stainless steel used to construct the containment vessels for the storage of plutonium-bearing materials. The tear drop corrosion specimens each with an autogenous weld in the center were placed in contact with moist plutonium oxide and chloride salt mixtures. Cracking was found in two of the specimens in the heat affected zone (HAZ) at the apex area. Finite element analysis was performed to simulate the specimen fabrication for determining the internal stress which caused SCC to occur. It was found that the tensile stress at the crack initiation site was about 30% lower than the highest stress which had been shifted to the shoulders of the specimen due to the specimen fabrication process. This finding appears to indicate that the SCC initiation took place in favor of the possibly weaker weld/base metal interface at a sufficiently high level of background stress. The base material, even subject to a higher tensile stress, was not cracked. The relieving of tensile stress due to SCC initiation and growth in the HAZ and the weld might have foreclosed the potential for cracking at the specimen shoulders where higher stress was found.

  19. STRESS CRACK TESTING OF POLYETHYLENE GEOMEMBRANES

    EPA Science Inventory

    The sensitivity of high density polyethylene (HDPE) geomembranes to stress cracking is evaluated under accelerated conditions at a constant stress. he test specimens are according to ASTM D-1822, and are of the dumbbell shape with a constant length in the central section. he acce...

  20. Seacoast stress corrosion cracking of aluminum alloys

    NASA Technical Reports Server (NTRS)

    Humphries, T. S.; Nelson, E. E.

    1981-01-01

    The stress corrosion cracking resistance of high strength, wrought aluminum alloys in a seacoast atmosphere was investigated and the results were compared with those obtained in laboratory tests. Round tensile specimens taken from the short transverse grain direction of aluminum plate and stressed up to 100 percent of their yield strengths were exposed to the seacoast and to alternate immersion in salt water and synthetic seawater. Maximum exposure periods of one year at the seacoast, 0.3 or 0.7 of a month for alternate immersion in salt water, and three months for synthetic seawater were indicated for aluminum alloys to avoid false indications of stress corrosion cracking failure resulting from pitting. Correlation of the results was very good among the three test media using the selected exposure periods. It is concluded that either of the laboratory test media is suitable for evaluating the stress corrosion cracking performance of aluminum alloys in seacoast atmosphere.

  1. Cause of stress-corrosion cracking in pipe

    SciTech Connect

    Christman, T.K.; Beavers, J.A.

    1987-01-05

    Carbonate-bicarbonate has been identified as the environmental species responsible for stress-corrosion cracking (SCC) in the majority of studied field failures of natural-gas pipelines. Battelle Columbus Division, Columbus, Ohio, studied approximately 30 SCC field failures of natural-gas pipelines form a 20-year period beginning in 1965. The results of the study also reject hydroxide (caustic) as a significant factor in these failures. Stress-corrosion cracking in natural-gas transmission pipelines has been recognized as a serious problem for a number of years. But there remains considerable controversy concerning the environmental species responsible for the cracking. One opinion has held that carbonate-bicarbonate promotes cracking, while another attributes the cracking to hydroxide (caustic). This issue is important because the feasibility of mitigation procedures based on potential control depend upon the chemical species responsible for the cracking. Moreover, it is important for the laboratory studies aimed at SCC mitigation to simulate closely the field failures. Both carbonate/bicarbonate and caustic environments can result from application of cathodic protection to a pipeline. The cathodic current applied to the pipeline accelerates the rate of the reduction reactions occurring on the pipe surface, promoting generation of hydroxide.

  2. Application of new experimental methods to pipeline stress corrosion cracking

    NASA Astrophysics Data System (ADS)

    Schmidt, C. G.; Kobayashi, T.; Crocker, J. E.; Kanazawa, C. H.; Kempf, J. A.

    1992-07-01

    The objective of the investigation is to develop a physically based understanding of the mechanisms of stress corrosion cracking (SCC) in pipeline steels by applying advanced fracture surface and electrochemical characterization techniques to samples taken from fielded pipeline and to laboratory corrosion test specimens. SCC is a well-known concern of the gas industry that occasionally affects natural gas treatment plants, gathering lines, and transmission lines. The research program is designed to increase the understanding of pipeline degradation by identifying the specific mechanisms that control SCC. From the results, the authors expect to improve the ability to identify features in the metallurgy of pipeline steel, the environmental conditions that affect the susceptibility to SCC. The effect of overloads (possibly from hydrotests or pressure fluctuations) on the propagation of stress corrosion cracks was readily evident from an analysis of the topographies of conjugate fracture surfaces. Crack branching usually resulted from overloads. Corrosion products were removed from the fracture surfaces of a stress corrosion crack in a pipeline specimen recovered from service. The topography of the underlying metal surface appears to be preserved with little corrosion damage after crack formation. This allowed the cracking process to be reconstructed and details to be investigated.

  3. Residual stress effects in stress-corrosion cracking

    SciTech Connect

    Toribio, J.

    1998-04-01

    This paper describes a wide variety of residual stress effects in stress-corrosion cracking (SCC) of metallic materials on the basis of previous research of the author on high-strength steel in the form of hot-rolled bars and cold-drawn wires for prestressed concrete. It is seen that internal residual stress fields in the material play a very important -- if not decisive -- role in the SCC behavior of any engineering material, especially residual stresses generated near the free surface or in the vicinity of a crack tip.

  4. Stress corrosion cracking of candidate waste container materials

    SciTech Connect

    Maiya, P.S.; Soppet, W.K.; Park, J.Y.; Kassner, T.F.; Shack, W.J.; Diercks, D.R.

    1990-11-01

    Six alloys have been selected as candidate container materials for the storage of high-level nuclear waste at the proposed Yucca Mountain site in Nevada. These materials are Type 304L stainless steel (SS), Type 316L SS, Incology 825, P-deoxidized Cu, Cu-30%Ni, and Cu-7% Al. The present program has been initiated to determine whether any of these materials can survive for 300 years in the site environment without developing through-wall stress corrosion cracks, and to assess the relative resistance of these materials to stress corrosion cracking (SCC). A series of slow-strain-rate tests (SSRTs) in simulated Well J-13 water which is representative of the groundwater present at the Yucca Mountain site has been completed, and crack-growth-rate (CGR) tests are also being conducted under the same environmental conditions. 13 refs., 60 figs., 22 tabs.

  5. Kinetic studies of stress-corrosion cracking

    NASA Technical Reports Server (NTRS)

    Noronha, P. J.

    1977-01-01

    Use of time-to-failure curves for stress-corrosion cracking processes may lead to incorrect estimates of structural life, if material is strongly dependent upon prestress levels. Technique characterizes kinetics of crackgrowth rates and intermediate arrest times by load-level changes.

  6. Stress Corrosion Cracking of Certain Aluminum Alloys

    NASA Technical Reports Server (NTRS)

    Hasse, K. R.; Dorward, R. C.

    1983-01-01

    SC resistance of new high-strength alloys tested. Research report describes progress in continuing investigation of stress corrosion (SC) cracking of some aluminum alloys. Objective of program is comparing SC behavior of newer high-strength alloys with established SC-resistant alloy.

  7. Stress corrosion cracking of duplex stainless steels in caustic solutions

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Ananya

    Duplex stainless steels (DSS) with roughly equal amount of austenite and ferrite phases are being used in industries such as petrochemical, nuclear, pulp and paper mills, de-salination plants, marine environments, and others. However, many DSS grades have been reported to undergo corrosion and stress corrosion cracking in some aggressive environments such as chlorides and sulfide-containing caustic solutions. Although stress corrosion cracking of duplex stainless steels in chloride solution has been investigated and well documented in the literature but the SCC mechanisms for DSS in caustic solutions were not known. Microstructural changes during fabrication processes affect the overall SCC susceptibility of these steels in caustic solutions. Other environmental factors, like pH of the solution, temperature, and resulting electrochemical potential also influence the SCC susceptibility of duplex stainless steels. In this study, the role of material and environmental parameters on corrosion and stress corrosion cracking of duplex stainless steels in caustic solutions were investigated. Changes in the DSS microstructure by different annealing and aging treatments were characterized in terms of changes in the ratio of austenite and ferrite phases, phase morphology and intermetallic precipitation using optical micrography, SEM, EDS, XRD, nano-indentation and microhardness methods. These samples were then tested for general and localized corrosion susceptibility and SCC to understand the underlying mechanisms of crack initiation and propagation in DSS in the above-mentioned environments. Results showed that the austenite phase in the DSS is more susceptible to crack initiation and propagation in caustic solutions, which is different from that in the low pH chloride environment where the ferrite phase is the more susceptible phase. This study also showed that microstructural changes in duplex stainless steels due to different heat treatments could affect their SCC

  8. Finite element microscopic stress analysis of cracked composite systems

    NASA Technical Reports Server (NTRS)

    Ko, W. L.

    1978-01-01

    This paper considers the stress concentration problems of two types of cracked composite systems: (1) a composite system with a broken fiber (a penny-shaped crack problem), and (2) a composite system with a cracked matrix (an annular crack problem). The cracked composite systems are modeled with triangular and trapezoidal ring finite elements. Using NASTRAN (NASA Structural Analysis) finite element computer program, the stress and deformation fields in the cracked composite systems are calculated. The effect of fiber-matrix material combination on the stress concentrations and on the crack opening displacements is studied.

  9. Environmentally assisted cracking in light water reactors

    SciTech Connect

    Shack, W.J.; Kassner, T.F.; Maiya, P.S.; Park, J.Y.; Ruther, W.E.

    1988-10-01

    Research during the past year focused on (1) stress corrosion cracking (SCC) of austentitic stainless steels (SS), (2) fatigue of Type 316NG SS, and (3) SCC of ferritic steels used in reactor piping, pressure vessels, and steam generators. Stress corrosion cracking studies on austentitic SS explored the critical strains required for crack initiation, the effects of crevice conditions on SCC susceptibility, heat-to-heat variations in SCC susceptibility of Type 316NG and modified Type 347 SS, the effect of heat treatment on the susceptibility of Type 347 SS, threshold stress intensity values for crack growth in Type 316NG SS, and the effects of cuprous ion and several organic salts on the SCC of sensitized Type 304 SS. Crevice conditions were observed to strongly promote SCC. Significant heat-to-heat variations were observed in SCC susceptibility of Types 316NG and 347 SS. No correlation was found between SCC behavior and minor variations in chemical composition. A significant effect of heat treatment was observed in Type 347 SS. A heat that was extremely resistant to SCC after heat treatment at 650/degree/C for 24 h was susceptible to transgranular stress corrosion cracking (TGSCC) in the solution-annealed condition. Although there was no sensitization in either condition, the presence or absence of precipitates and differences in precipitate morphology appear to influence the SCC behavior. 20 refs., 20 figs., 11 tabs.

  10. Propagation of stress corrosion cracks in Zr-1% Nb claddings

    NASA Astrophysics Data System (ADS)

    Bibilashvily, Yu. K.; Dolgov, Yu. N.; Nesterov, B. I.; Novikov, V. V.

    1995-09-01

    Experimental results on iodine induced stress corrosion cracking (SCC) are analyzed. The studies were performed at 350°C using Zr-1% Nb tubular specimens. Fatigue crack at internal surface served as an initial defect. The relationship was derived between crack propagation rate and stress intensity factor; the threshold stress intensity factor of 4.8 MPa m{1}/{2} was determined.

  11. Early stages in the development of stress corrosion cracks

    SciTech Connect

    Jones, R.H.; Simonen, E.P.

    1993-12-01

    Processes in growth of short cracks and stage I of long stress corrosion cracks were identified and evaluated. There is evidence that electrochemical effects can cause short stress corrosion cracks to grow at rates faster or slower than long cracks. Short cracks can grow at faster rates than long cracks for a salt film dissolution growth mechanism or from reduced oxygen inhibition of hydrolytic acidification. An increasing crack growth rate with increasing crack length could result from a process of increasing crack tip concentration of a critical anion, such as Cl{sup {minus}}, with increasing crack length in a system where the crack velocity is dependent on the Cl{sup {minus}} or some other anion concentration. An increasing potential drop between crack tip and mouth would result in an increased anion concentration at the crack tip and hence an increasing crack velocity. Stage I behavior of long cracks is another early development stage in the life of a stress corrosion crack which is poorly understood. This stage can be described by da/dt = AK{sup m} where da/dt is crack velocity, A is a constant, K is stress intensity and m ranges from 2 to 24 for a variety of materials and environments. Only the salt film dissolution model was found to quantitatively describe this stage; however, the model was only tested on one material and its general applicability is unknown.

  12. Corrosion Product Film-Induced Stress Facilitates Stress Corrosion Cracking.

    PubMed

    Wang, Wenwen; Zhang, Zhiliang; Ren, Xuechong; Guan, Yongjun; Su, Yanjing

    2015-01-01

    Finite element analyses were conducted to clarify the role of corrosion product films (CPFs) in stress corrosion cracking (SCC). Flat and U-shaped edge-notched specimens were investigated in terms of the CPF-induced stress in the metallic substrate and the stress in the CPF. For a U-shaped edge-notched specimen, the stress field in front of the notch tip is affected by the Young's modulus of the CPF and the CPF thickness and notch geometry. The CPF-induced tensile stress in the metallic substrate is superimposed on the applied load to increase the crack tip strain and facilitate localized plasticity deformation. In addition, the stress in the CPF surface contributes to the rupture of the CPFs. The results provide physical insights into the role of CPFs in SCC. PMID:26066367

  13. Corrosion Product Film-Induced Stress Facilitates Stress Corrosion Cracking

    PubMed Central

    Wang, Wenwen; Zhang, Zhiliang; Ren, Xuechong; Guan, Yongjun; Su, Yanjing

    2015-01-01

    Finite element analyses were conducted to clarify the role of corrosion product films (CPFs) in stress corrosion cracking (SCC). Flat and U-shaped edge-notched specimens were investigated in terms of the CPF-induced stress in the metallic substrate and the stress in the CPF. For a U-shaped edge-notched specimen, the stress field in front of the notch tip is affected by the Young’s modulus of the CPF and the CPF thickness and notch geometry. The CPF-induced tensile stress in the metallic substrate is superimposed on the applied load to increase the crack tip strain and facilitate localized plasticity deformation. In addition, the stress in the CPF surface contributes to the rupture of the CPFs. The results provide physical insights into the role of CPFs in SCC. PMID:26066367

  14. Environmentally assisted cracking of LWR materials.

    SciTech Connect

    Chopra, O. K.; Chung, H. M.; Kassner, T. F.; Park, J. H.; Shack, W. J.; Zhang, J.; Brust, F. W.; Dong, P.

    1997-12-05

    The effect of dissolved oxygen level on fatigue life of austenitic stainless steels is discussed and the results of a detailed study of the effect of the environment on the growth of cracks during fatigue initiation are presented. Initial test results are given for specimens irradiated in the Halden reactor. Impurities introduced by shielded metal arc welding that may affect susceptibility to stress corrosion cracking are described. Results of calculations of residual stresses in core shroud weldments are summarized. Crack growth rates of high-nickel alloys under cyclic loading with R ratios from 0.2-0.95 in water that contains a wide range of dissolved oxygen and hydrogen concentrations at 289 and 320 C are summarized.

  15. Environmentally assisted cracking in LWR materials

    SciTech Connect

    Chopra, O.K.; Chung, H.M.; Kassner, T.F.; Park, J.H.; Shack, W.J.; Zhang, J.; Brust, F.W.; Dong, P.

    1998-03-01

    The effect of dissolved oxygen level on fatigue life of austenitic stainless steels is discussed and the results of a detailed study of the effect of the environment on the growth of cracks during fatigue initiation are presented. Initial test results are given for specimens irradiated in the Halden reactor. Impurities introduced by shielded metal arc welding that may affect susceptibility to stress corrosion cracking are described. Results of calculations of residual stresses in core shroud weldments are summarized. Crack growth rates of high-nickel alloys under cyclic loading with R ratios from 0.2--0.95 in water that contains a wide range of dissolved oxygen and hydrogen concentrations at 289 and 320 C are summarized.

  16. Apollo experience report: The problem of stress-corrosion cracking

    NASA Technical Reports Server (NTRS)

    Johnson, R. E.

    1973-01-01

    Stress-corrosion cracking has been the most common cause of structural-material failures in the Apollo Program. The frequency of stress-corrosion cracking has been high and the magnitude of the problem, in terms of hardware lost and time and money expended, has been significant. In this report, the significant Apollo Program experiences with stress-corrosion cracking are discussed. The causes of stress-corrosion cracking and the corrective actions are discussed, in terminology familiar to design engineers and management personnel, to show how stress-corrosion cracking can be prevented.

  17. Stress-corrosion cracking of titanium alloys.

    NASA Technical Reports Server (NTRS)

    Blackburn, M. J.; Feeney, J. A.; Beck, T. R.

    1973-01-01

    In the light of research material published up to May 1970, the current understanding of the experimental variables involved in the stress-corrosion cracking (SCC) behavior of titanium and its alloys is reviewed. Following a brief summary of the metallurgy and electrochemistry of titanium alloys, the mechanical, electrochemical, and metallurgical parameters influencing SCC behavior are explored with emphasis on crack growth kinetics. Macro- and microfeatures of fractures are examined, and it is shown that many transgranular SCC failures exhibit morphological and crystallographic features similar to mechanical cleavage failures. Current SCC models are reviewed with respect to their ability to explain the observed SCC behavior of titanium and its alloys. Possible methods for eliminating or minimizing stress corrosion hazards in titanium or titanium alloy components are described.

  18. A probabilistic model of intergranular stress corrosion cracking

    SciTech Connect

    Bourcier, R.J.; Jones, W.B. ); Scully, J.R. )

    1991-01-01

    We have developed a model which utilizes a probabilistic failure criterion to describe intergranular stress corrosion cracking (IGSCC). A two-dimensional array of elements representing a section of a pipe wall is analyzed, with each element in the array representing a segment of grain boundary. The failure criterion is applied repetitively to each element of the array that is exposed to the interior of the pipe (i.e. the corrosive fluid) until that element dissolves, thereby exposing the next element. A number of environmental, mechanical, and materials factors have been incorporated into the model, including: (1) the macroscopic applied stress profile, (2) the stress history, (3) the extent and grain-to- grain distribution of carbide sensitization levels, which can be applied to a subset of elements comprising a grain boundary, and (4) a data set containing IGSCC crack growth rates as function of applied stress intensity and sensitization level averaged over a large population of grains. The latter information was obtained from the literature for AISI 304 stainless steel under light water nuclear reactor primary coolant environmental conditions. The resulting crack growth simulations are presented and discussed. 14 refs., 10 figs.

  19. Stress corrosion cracking evaluation of martensitic precipitation hardening stainless steels

    NASA Technical Reports Server (NTRS)

    Humphries, T. S.; Nelson, E. E.

    1980-01-01

    The resistance of the martensitic precipitation hardening stainless steels PH13-8Mo, 15-5PH, and 17-4PH to stress corrosion cracking was investigated. Round tensile and c-ring type specimens taken from several heats of the three alloys were stressed up to 100 percent of their yield strengths and exposed to alternate immersion in salt water, to salt spray, and to a seacoast environment. The results indicate that 15-5PH is highly resistant to stress corrosion cracking in conditions H1000 and H1050 and is moderately resistant in condition H900. The stress corrosion cracking resistance of PH13-8Mo and 17-4PH stainless steels in conditions H1000 and H1050 was sensitive to mill heats and ranged from low to high among the several heats included in the tests. Based on a comparison with data from seacoast environmental tests, it is apparent that alternate immersion in 3.5 percent salt water is not a suitable medium for accelerated stress corrosion testing of these pH stainless steels.

  20. Combined environmental stresses

    NASA Technical Reports Server (NTRS)

    Murray, R. H.; Mccally, M.

    1973-01-01

    Tolerance levels, physiological effects, and performance degradation during simultaneous or sequential exposures to two environmental stresses, and also three or more simultaneous stresses are described. Environmental stress combinations are characterized by four descriptors: order of occurrence, duration of exposure, severity of exposure, and type of interaction. Combined stress data and facilities for combined stress study are briefly mentioned.

  1. Optical methods of stress analysis applied to cracked components

    NASA Technical Reports Server (NTRS)

    Smith, C. W.

    1991-01-01

    After briefly describing the principles of frozen stress photoelastic and moire interferometric analyses, and the corresponding algorithms for converting optical data from each method into stress intensity factors (SIF), the methods are applied to the determination of crack shapes, SIF determination, crack closure displacement fields, and pre-crack damage mechanisms in typical aircraft component configurations.

  2. Role of environmental variables on the stress corrosion cracking of sensitized AISI type 304 stainless steel (SS304) in thiosulfate solutions

    NASA Astrophysics Data System (ADS)

    Roychowdhury, S.; Ghosal, S. K.; de, P. K.

    2004-10-01

    The stress corrosion cracking (SCC) behavior of sensitized AISI type 304 stainless steel (SS304) has been studied in dilute thiosulfate solutions as a function of thiosulfate concentrations and applied potentials. The susceptibility to SCC was observed to increase with thiosulfate concentrations and applied potentials. The addition of boric acid produced the reverse effect. A critical potential was found to exist, below which no SCC took place. Potential fluctuations, as recorded in the tests under open circuit conditions, appeared to be correlated with crack initiation and propagation during SCC. Current fluctuations observed in the controlled potential tests also gave indications of crack nucleation; however, at higher applied potentials such fluctuations were absent. The formation and presence of martensite in the specimens seemed to have a minor role in the overall SCC process. The aggressiveness of the thiosulfate concentration was also an important factor in determining the degree of susceptibility to SCC. The results obtained in the slow strain rate tests under open circuit as well as under potential-controlled conditions suggested a film ruptureanodic dissolution type of mechanism operative during SCC of sensitized SS304 in thiosulfate solutions.

  3. Computational modeling of the mechanism of hydrogen embrittlement (HE) and stress corrosion cracking (SCC) in metals

    NASA Astrophysics Data System (ADS)

    Cendales, E. D.; Orjuela, F. A.; Chamarraví, O.

    2016-02-01

    In this article theoretical models and some existing data sets were examined in order to model the two main causes (hydrogen embrittlement and corrosion-cracking under stress) of the called environmentally assisted cracking phenomenon (EAC). Additionally, a computer simulation of flat metal plate subject to mechanical stress and cracking due both to hydrogen embrittlement and corrosion was developed. The computational simulation was oriented to evaluate the effect on the stress-strain behavior, elongation percent and the crack growth rate of AISI SAE 1040 steel due to three corrosive enviroments (H2 @ 0.06MPa; HCl, pH=1.0; HCl, pH=2.5). From the computer simulation we conclude that cracking due to internal corrosion of the material near to the crack tip limits affects more the residual strength of the flat plate than hydrogen embrittlement and generates a failure condition almost imminent of the mechanical structural element.

  4. Stress corrosion cracking of Zircaloys. Final report

    SciTech Connect

    Cubicciotti, D.; Jones, R.L.; Syrett, B.C.

    1980-03-01

    The overall aim has been to develop an improved understanding of the stress corrosion cracking (SCC) mechanism considered to be responsible for pellet-cladding interaction (PCI) failures of nuclear fuel rods. The objective of the present phase of the project was to investigate the potential for improving the resistance of Zircaloy to iodine-induced SCC by modifying the manufacturing techniques used in the commercial production of fuel cladding. Several aspects of iodine SCC behavior of potential relevance to cladding performance were experimentally investigated. It was found that the SCC susceptibility of Zircaloy tubing is sensitive to crystallographic texture, surface condition, and residual stress distribution and that current specifications for Zircaloy tubing provide no assurance of an optimum resistance to SCC. Additional evidence was found that iodine-induced cracks initiate at local chemical inhomogeneities in the Zircaloy surface, but laser melting to produce a homogenized surface layer did not improve the SCC resistance. Several results were obtained that should be considered in models of PCI failure. The ratio of axial to hoop stress and the temperature were both shown to affect the SCC resistance whereas the difference in composition between Zircaloy-2 and Zircaloy-4 had no detectable effect. Damage accumulation during iodine SCC was found to be nonlinear: generally, a given life fraction at low stress was more damaging than the same life fraction at higher stress. Studies of the thermochemistry of the zirconium-iodine system (performed under US Department of Energy sponsorship) revealed many errors in the literature and provided important new insights into the mechanism of iodine SCC of Zircaloys.

  5. Experimental stress analysis of fatigue cracks by SPATE

    SciTech Connect

    Pang, H.L.J. )

    1993-04-01

    A computer-aided infrared detector and stress analyzer, called SPATE, was used to detect, monitor, and analyze interacting coplanar part-through surface cracks. It is concluded that thermoelastic stress analysis by the SPATE techique provides approximate stress intensity factors for interacting coplanar semielliptical surface cracks on the plate surface. 4 refs.

  6. Fatigue Crack Growth Analysis Under Spectrum Loading in Various Environmental Conditions

    NASA Astrophysics Data System (ADS)

    Mikheevskiy, S.; Glinka, G.; Lee, E.

    2013-03-01

    The fatigue process consists, from the engineering point of view, of three stages: crack initiation, fatigue crack growth, and the final failure. It is also known that the fatigue process near notches and cracks is governed by local strains and stresses in the regions of maximum stress and strain concentrations. Therefore, the fatigue crack growth can be considered as a process of successive crack increments, and the fatigue crack initiation and subsequent growth can be modeled as one repetitive process. The assumptions mentioned above were used to derive a fatigue crack growth model based, called later as the UniGrow model, on the analysis of cyclic elastic-plastic stresses-strains near the crack tip. The fatigue crack growth rate was determined by simulating the cyclic stress-strain response in the material volume adjacent to the crack tip and calculating the accumulated fatigue damage in a manner similar to fatigue analysis of stationary notches. The fatigue crack growth driving force was derived on the basis of the stress and strain history at the crack tip and the Smith-Watson-Topper (SWT) fatigue damage parameter, D = σmaxΔɛ/2. It was subsequently found that the fatigue crack growth was controlled by a two-parameter driving force in the form of a weighted product of the stress intensity range and the maximum stress intensity factor, Δ K p K {max/1- p }. The effect of the internal (residual) stress induced by the reversed cyclic plasticity has been accounted for and therefore the two-parameter driving force made it possible to predict the effect of the mean stress including the influence of the applied compressive stress, tensile overloads, and variable amplitude spectrum loading. It allows estimating the fatigue life under variable amplitude loading without using crack closure concepts. Several experimental fatigue crack growth datasets obtained for the Al 7075 aluminum alloy were used for the verification of the proposed unified fatigue crack growth

  7. Residual stresses and stress corrosion cracking in pipe fittings

    SciTech Connect

    Parrington, R.J.; Scott, J.J.; Torres, F.

    1994-06-01

    Residual stresses can play a key role in the SCC performance of susceptible materials in PWR primary water applications. Residual stresses are stresses stored within the metal that develop during deformation and persist in the absence of external forces or temperature gradients. Sources of residual stresses in pipe fittings include fabrication processes, installation and welding. There are a number of methods to characterize the magnitude and orientation of residual stresses. These include numerical analysis, chemical cracking tests, and measurement (e.g., X-ray diffraction, neutron diffraction, strain gage/hole drilling, strain gage/trepanning, strain gage/section and layer removal, and acoustics). This paper presents 400 C steam SCC test results demonstrating that residual stresses in as-fabricated Alloy 600 pipe fittings are sufficient to induce SCC. Residual stresses present in as-fabricated pipe fittings are characterized by chemical cracking tests (stainless steel fittings tested in boiling magnesium chloride solution) and by the sectioning and layer removal (SLR) technique.

  8. Mixed mode stress intensity factors for semielliptical surface cracks

    NASA Technical Reports Server (NTRS)

    Smith, F. W.; Sorensen, D. R.

    1974-01-01

    The three-dimensional equations of elasticity are solved for a flat elliptical crack which has nonuniform shear stresses applied to its surfaces. An alternating method is used to determine the mode two and mode three stress intensity factors for a semielliptical surface crack in the surface of a finite thickness solid. These stress intensity factors are presented as a function of position along the crack border for a number of crack shapes and crack depths. This same technique is followed to determine the mode one stress intensity factors for the semielliptical surface crack which has normal loading applied to its surface. Mode one stress intensity factors are presented and compared with the results obtained from previous work.

  9. The effects of crack surface friction and roughness on crack tip stress fields

    NASA Technical Reports Server (NTRS)

    Ballarini, Roberto; Plesha, Michael E.

    1987-01-01

    A model is presented which can be used to incorporate the effects of friction and tortuosity along crack surfaces through a constitutive law applied to the interface between opposing crack surfaces. The problem of a crack with a saw-tooth surface in an infinite medium subjected to a far-field shear stress is solved and the ratios of Mode-I stress intensity to Mode-II stress intensity are calculated for various coefficients of friction and material properties. The results show that tortuosity and friction lead to an increase in fracture loads and alter the direction of crack propagation.

  10. Surface aspects of pitting and stress corrosion cracking

    NASA Technical Reports Server (NTRS)

    Truhan, J. S., Jr.; Hehemann, R. F.

    1977-01-01

    The pitting and stress corrosion cracking of a stable austenitic stainless steel in aqueous chloride environments were investigated using a secondary ion mass spectrometer as the primary experimental technique. The surface concentration of hydrogen, oxygen, the hydroxide, and chloride ion, magnesium or sodium, chromium and nickel were measured as a function of potential in both aqueous sodium chloride and magnesium chloride environments at room temperature and boiling temperatures. It was found that, under anodic conditions, a sharp increase in the chloride concentration was observed to occur for all environmental conditions. The increase may be associated with the formation of an iron chloride complex. Higher localized chloride concentrations at pits and cracks were also detected with an electron microprobe.

  11. Aircraft crash caused by stress corrosion cracking

    SciTech Connect

    Kolkman, H.J.; Kool, G.A.; Wanhill, R.J.H.

    1996-01-01

    An aircraft crash in the Netherlands was caused by disintegration of a jet engine. Fractography showed that the chain of events started with stress corrosion cracking (SCC) of a pin attached to a lever arm of the compressor variable vane system. Such a lever arm-pin assembly costs only a few dollars. Investigation of hundreds of pins from the accident and a number of identical engines revealed that this was not an isolated case. Many pins exhibited various amounts of SCC. The failed pin in the accident engine happened to be the first fractured one. SCC requires the simultaneous presence of tensile stress, a corrosive environment, and a susceptible material. In this case the stress was a residual stress arising from the production method. There was a clear correlation between the presence of salt deposits on the levers and SCC of the pins. It was shown that these deposits were able to reach the internal space between the pin and lever arm, thereby initiating SCC in this space. The corrosive environment in Western Europe explains why the problem manifested itself in the Netherlands at a relatively early stage in engine life. The main point is, however, that the manufacturer selected an SCC-prone material in the design stage. The solution has been to change the pin material.

  12. Remote field eddy current detection of stress-corrosion cracks

    SciTech Connect

    Nestleroth, J.B. )

    1991-09-01

    This report describes experimental application of the RFEC technique for crack detection in gas transmission pipelines. Crack data from three pipe samples are presented. A total of eight stress corrosion cracks were detected ranging in depth from 25 percent of wall thickness to completely through-wall. An improved defect detection model is presented that explains the interaction of the remote electromagnetic field with axial cracks as well as other defects such as metal loss and circumferential cracks. The investigation of the through-wall crack helps illustrate this model and also indicates RFEC has potential for detection and location of leaks from cracks. Many regions with crack depths less than 25 percent and lengths less than one inch were investigated, but dejection was unsuccessful. Data from artificial defects are presented to describe the relative sensitivity and characterization capability of the RFEC technique to longitudinal and circumferential planar (crack-like) defects as well as volumetric (metal loss) defects.

  13. Influence of load interactions on crack growth as related to state of stress and crack closure

    NASA Technical Reports Server (NTRS)

    Telesman, J.

    1985-01-01

    Fatigue crack propagation (FCP) after an application of a low-high loading sequence was investigated as a function of specimen thickness and crack closure. No load interaction effects were detected for specimens in a predominant plane strain state. However, for the plane stress specimens, initially high FCP rates after transition to a higher stress intensity range were observed. The difference in observed behavior was explained by examining the effect of the resulting closure stress intensity values on the effective stress intensity range.

  14. Stress intensity factors for bonded orthotropic strips with cracks

    NASA Technical Reports Server (NTRS)

    Delale, F.; Erdogan, F.

    1978-01-01

    The elastostatic problem for a nonhomogeneous plane which consists of two sets of periodically arranged dissimilar orthotropic strips is considered. It is assumed that the plane contains a series of collinear cracks perpendicular to the interfaces and is loaded in tension away from and perpendicular to the cracks. Cracks fully imbedded into the homogenous strips were analyzed as well as the singular behavior of the stresses for two special crack geometries. The analysis of cracks crossing interfaces indicates that, for certain orthotropic material combinations, the stress state at the point of intersection of a crack and an interface may be bounded. A number of numerical examples are worked out in order to separate the primary material parameters influencing the stress intensity factors and the powers of stress singularity, and to determine the trends regarding the influence of the secondary parameters.

  15. The threshold stress intensity for hydrogen-induced crack growth

    NASA Astrophysics Data System (ADS)

    Akhurst, K. N.; Baker, T. J.

    1981-06-01

    The crack growth rates and threshold stress intensities, K TH, for a 3 1/2 NiCrMoV steel (0.2 pct proof stress 1200 MPa) have been measured in a hydrogen environment at various temperatures and hydrogen pressures. Fractographic evidence and the observation of alternating fast and slow crack growth near K TH suggests that the crack advances by the repeated nucleation of microcracks at microstructural features ahead of the main crack. Transient crack growth is observed following load increases just below K TH. Using the idea, from unstable cleavage fracture theory, that for fracture a critical stress must be exceeded over a critical distance ahead of the crack, and assuming that this critical stress is reduced in proportion to the local hydrogen concentration (in equilibrium with the external hydrogen at K TH), a theoretical dependence of K TH on hydrogen pressure is derived which compares well with the experimental evidence.

  16. A comparison of stress in cracked fibrous tissue specimens with varied crack location, loading, and orientation using finite element analysis.

    PubMed

    Peloquin, John M; Elliott, Dawn M

    2016-04-01

    Cracks in fibrous soft tissue, such as intervertebral disc annulus fibrosus and knee meniscus, cause pain and compromise joint mechanics. A crack concentrates stress at its tip, making further failure and crack extension (fracture) more likely. Ex vivo mechanical testing is an important tool for studying the loading conditions required for crack extension, but prior work has shown that it is difficult to reproduce crack extension. Most prior work used edge crack specimens in uniaxial tension, with the crack 90° to the edge of the specimen. This configuration does not necessarily represent the loading conditions that cause in vivo crack extension. To find a potentially better choice for experiments aiming to reproduce crack extension, we used finite element analysis to compare, in factorial combination, (1) center crack vs. edge crack location, (2) biaxial vs. uniaxial loading, and (3) crack-fiber angles ranging from 0° to 90°. The simulated material was annulus fibrosus fibrocartilage with a single fiber family. We hypothesized that one of the simulated test cases would produce a stronger stress concentration than the commonly used uniaxially loaded 90° crack-fiber angle edge crack case. Stress concentrations were compared between cases in terms of fiber-parallel stress (representing risk of fiber rupture), fiber-perpendicular stress (representing risk of matrix rupture), and fiber shear stress (representing risk of fiber sliding). Fiber-perpendicular stress and fiber shear stress concentrations were greatest in edge crack specimens (of any crack-fiber angle) and center crack specimens with a 90° crack-fiber angle. However, unless the crack is parallel to the fiber direction, these stress components alone are insufficient to cause crack opening and extension. Fiber-parallel stress concentrations were greatest in center crack specimens with a 45° crack-fiber angle, either biaxially or uniaxially loaded. We therefore recommend that the 45° center crack case be

  17. Stress corrosion cracking evaluation of precipitation-hardening stainless steel

    NASA Technical Reports Server (NTRS)

    Humphries, T. S.; Nelson, E. E.

    1970-01-01

    Accelerated test program results show which precipitation hardening stainless steels are resistant to stress corrosion cracking. In certain cases stress corrosion susceptibility was found to be associated with the process procedure.

  18. De-alloying and stress-corrosion cracking. Final report

    SciTech Connect

    Sieradzki, K.

    1998-09-01

    This research program has had two major areas of focus that are related: (1) alloy corrosion and (2) the role of selective dissolution in the stress corrosion cracking of alloy systems. These interrelated issues were examined using model systems such as Ag-Au and Cu-Au by conventional electrochemical techniques, in situ scanning tunneling microscopy (STM), in situ small angle neutron scattering (SANS), ultrahigh speed digital photography of fracture events, and computer simulations. The STM and SANS work were specifically aimed at addressing a roughening transition known to occur in alloy systems undergoing corrosion at electrochemical potentials greater than the so-called critical potential. Analytical models of de-alloying processes including the roughening transition were developed that specifically include curvature effects that are important in alloy corrosion processes. Stress-corrosion experiments were performed on the same model systems using rapid optical and electrochemical techniques on 50 {micro}m--250 {micro}m thick sheets and small diameter wires. The primary goal of this work was to develop a fundamental understanding of the corrosion and electrochemistry of alloys and the stress-corrosion cracking processes these alloys undergo. Computer simulations and analytical work identified surface stress and an important parameter in environmentally assisted fracture. The major results of the research on this program since the summer of 1993 are briefly summarized.

  19. Resistance of Some Steels to Stress Corrosion Cracking

    NASA Technical Reports Server (NTRS)

    Humphries, T. S.; Nelson, E. E.

    1982-01-01

    Evaluations of stress-corrosion cracking resistance of five high-strength low-alloy steels described in report now available. Steels were heat-treated to various tensile strengths and found to be highly resistant to stress-corrosion cracking.

  20. Cyclic stress effect on stress corrosion cracking of duplex stainless steel in chloride and caustic solutions

    NASA Astrophysics Data System (ADS)

    Yang, Di

    Duplex stainless steel (DSS) is a dual-phase material with approximately equal volume amount of austenite and ferrite. It has both great mechanical properties (good ductility and high tensile/fatigue strength) and excellent corrosion resistance due to the mixture of the two phases. Cyclic loadings with high stress level and low frequency are experienced by many structures. However, the existing study on corrosion fatigue (CF) study of various metallic materials has mainly concentrated on relatively high frequency range. No systematic study has been done to understand the ultra-low frequency (˜10-5 Hz) cyclic loading effect on stress corrosion cracking (SCC) of DSSs. In this study, the ultra-low frequency cyclic loading effect on SCC of DSS 2205 was studied in acidified sodium chloride and caustic white liquor (WL) solutions. The research work focused on the environmental effect on SCC of DSS 2205, the cyclic stress effect on strain accumulation behavior of DSS 2205, and the combined environmental and cyclic stress effect on the stress corrosion crack initiation of DSS 2205 in the above environments. Potentiodynamic polarization tests were performed to investigate the electrochemical behavior of DSS 2205 in acidic NaCl solution. Series of slow strain rate tests (SSRTs) at different applied potential values were conducted to reveal the optimum applied potential value for SCC to happen. Room temperature static and cyclic creep tests were performed in air to illustrate the strain accumulation effect of cyclic stresses. Test results showed that cyclic loading could enhance strain accumulation in DSS 2205 compared to static loading. Moreover, the strain accumulation behavior of DSS 2205 was found to be controlled by the two phases of DSS 2205 with different crystal structures. The B.C.C. ferrite phase enhanced strain accumulation due to extensive cross-slips of the dislocations, whereas the F.C.C. austenite phase resisted strain accumulation due to cyclic strain

  1. Mechanism of hydrogen generation in the stress corrosion crack

    SciTech Connect

    Li, R.; Ferreira, M.G.S.

    1995-10-01

    Based on the mass transport in the stress corrosion crack, a mathematical expression of potential distribution along the stress corrosion crack is deduced. From this mathematical expression and the E-pH diagram for H{sub 2}O, a new mechanism for hydrogen generation in the stress corrosion crack i.e. H{sup +} partial potential drop mechanism, is proposed. Following this mechanism, the relationship between hydrogen generation and affecting factors, such as current density of anodic dissolution inside the crack, pH value, partial resistivity of H{sup +} ion, dimension of the crack and potential of the metal, is discussed. The mechanism is verified by experimental measurement results of the H{sup +} partial potential drop with microelectrodes placed in an artificial crack on AISI 410 stainless steel in 3%NaCl solution.

  2. Propagation of stress corrosion cracks in alpha-brasses

    SciTech Connect

    Beggs, Dennis Vinton

    1981-01-01

    Transgranular and intergranular stress corrosion cracks were investigated in alpha-brasses in a tarnishing ammoniacal solution. Surface observation indicated that the transgranular cracks propagated discontinuously by the sudden appearance of a fine crack extending several microns ahead of the previous crack tip, often associated with the detection of a discrete acoustic emission (AE). By periodically increasing the deflection, crack front markings were produced on the resulting fracture surfaces, showing that the discontinuous propagation of the crack trace was representative of the subsurface cracking. The intergranular crack trace appeared to propagate continuously at a relatively blunt crack tip and was not associated with discrete AE. Under load pulsing tests with a time between pulses, ..delta..t greater than or equal to 3 s, the transgranular fracture surfaces always exhibited crack front markings which corresponded with the applied pulses. The spacing between crack front markings, ..delta..x, decreased linearly with ..delta..t. With ..delta..t less than or equal to 1.5 s, the crack front markings were in a one-to-one correspondence with applied pulses only at relatively long crack lengths. In this case, ..delta..x = ..delta..x* which approached a limiting value of 1 ..mu..m. No crack front markings were observed on intergranular fracture surfaces produced during these tests. It is concluded that transgranular cracking occurs by discontinuous mechanical fracture of an embrittled region around the crack tip, while intergranular cracking results from a different mechanism with cracking occurring via the film-rupture mechanism.

  3. Fatigue and environmentally assisted cracking in light water reactors

    SciTech Connect

    Kassner, T.F.; Ruther, W.E.; Chung, H.M.; Hicks, P.D.; Hins, A.G.; Park, J.Y.; Shack, W.J.

    1991-12-01

    Fatigue and environmentally assisted cracking of piping, pressure vessels, and core components in light water reactors (LWRs) are important concerns as extended reactor lifetimes are envisaged. The degradation processes include intergranular stress corrosion cracking (IGSCC) of austenitic stainless steel (SS) piping in boiling water reactors (BWRs), and propagation of fatigue or SCC cracks (which initiate in sensitized SS cladding) into low-alloy ferritic steels in BWR pressure vessels. Similar cracking has also occurred in upper shell-to-transition cone girth welds in pressurized water reactor (PWR) steam generator vessels. Another concern is failure of reactor-core internal components after accumulation of relatively high fluence, which has occurred in both BWRs and PWRs. Research during the past year focused on (1) fatigue and SCC of ferritic steels used in piping and in steam generator and reactor pressure vessels, (2) role of chromate and sulfate in simulated BWR water in SCC of sensitized Type 304 SS, and (3) irradiation-assisted SCC in high- and commercial-purity Type 304 SS specimens from control-blade absorber tubes used in two operating BWRs. Failure after accumulation of relatively high fluence has been attributed to radiation-induced segregation (RIS) of elements such as Si, P, Ni, and Cr. This document provides a summary of research progress in these areas.

  4. Insights into Stress Corrosion Cracking Mechanisms from High-Resolution Measurements of Crack-Tip Structures and Compositions

    SciTech Connect

    Bruemmer, Stephen M.; Thomas, Larry E.

    2010-04-05

    The fundamental basis for mechanistic understanding and modeling of SCC remains in question for many systems. Specific mechanisms controlling SCC can vary with changes in alloy characteristics, applied/residual stress or environmental conditions. The local crack electrochemistry, crack-tip mechanics and material metallurgy are the main factors controlling crack growth. These localized properties are difficult or impossible to measure in active cracks. Nevertheless, it is essential to quantitatively interrogate these crack-tip conditions if mechanistic understanding is to be obtained. A major recent advance has been the ability to investigate SCC cracks and crack tips using high-resolution ATEM techniques. ATEM enables the characterization of SCC cracks including trapped tip solution chemistries, corrosion product/film compositions and structures, and elemental composition gradients and defect microstructures along the crack walls and at the crack tip. A wide variety of methods for imaging and analyses at resolutions down to the atomic level can be used to examine the crack and corrosion film characteristics. Surface films and reaction layers have been examined by cross-sectional TEM techniques, but little work had been conducted on environmentally induced internal cracks until that of Lewis and co-workers [1-3] and the current authors [4-17]. This capability combined with modern ATEM techniques has enabled exciting new insights into corrosion processes occurring at buried interfaces and is being used to identify mechanisms controlling IGSCC in boiling water reactor (BWR) and pressurized water reactor (PWR) components. The objective of this paper is to summarize certain results focused on IGSCC of Fe- base and Ni-base stainless alloys in high-temperature water environments. Representative crack-tip examples will be shown to illustrate specific aspects that are characteristic of SCC in the material/environment combinations. Differences and similarities in crack

  5. Transient thermal stress problem for a circumferentially cracked hollow cylinder

    NASA Technical Reports Server (NTRS)

    Nied, H. F.; Erdogan, F.

    1982-01-01

    The transient thermal stress problem for a hollow elasticity cylinder containing an internal circumferential edge crack is considered. It is assumed that the problem is axisymmetric with regard to the crack geometry and the loading, and that the inertia effects are negligible. The problem is solved for a cylinder which is suddenly cooled from inside. First the transient temperature and stress distributions in an uncracked cylinder are calculated. By using the equal and opposite of this thermal stress as the crack surface traction in the isothermal cylinder the crack problem is then solved and the stress intensity factor is calculated. The numerical results are obtained as a function of the Fourier number tD/b(2) representing the time for various inner-to-outer radius ratios and relative crack depths, where D and b are respectively the coefficient of diffusivity and the outer radius of the cylinder.

  6. Sulfide stress cracking characteristics of high strength steels from the viewpoint of fracture mechanics

    SciTech Connect

    Asahi, H.; Ueno, M.

    1994-12-31

    Sulfide stress cracking (SSC) evaluation of high strength OCTG (oil country tubular goods) from the view point of environmental factors has been studied to some extent, but little research has been conducted from the view point of fracture mechanics. In the present study, SSC resistance was evaluated using threshold stress and K{sub 1ssc}. The same ranking of SSC resistance is obtained from both methods. However, SSC resistant steels show higher K{sub 1ssc} than conventional steels even if their respective threshold stresses are the same. For steel products bearing cracks and dents, SSC evaluation using both the threshold stress and the K{sub 1ssc} is suggested.

  7. Environmental Effects on Fatigue Crack Growth in 7075 Aluminum Alloy

    NASA Astrophysics Data System (ADS)

    Bonakdar, A.; Wang, F.; Williams, J. J.; Chawla, N.

    2012-08-01

    The fatigue behavior of aluminum alloys is greatly influenced by the environmental conditions. In this article, fatigue crack growth rates were measured for 7075-T651 Al alloy under ultrahigh vacuum (UHV, ~10-10 Torr), dry air, and water vapor. Standard compact tension (CT) specimens were tested along the L-T orientation under various load ratios of 0.1, 0.5, and 0.8. Fracture surfaces and crack morphologies were studied using scanning electron microscopy and crack deflection analysis. The crack growth behavior under vacuum was affected by friction and possible rewelding of crack surfaces, causing an asymmetry in the crack growth behavior, from load shedding to constant load. The enhancement of crack growth at higher moisture levels was observed and is discussed in terms of moisture decreasing friction between the crack faces. The effect of crack deflection as a function of R ratio and environment is also presented.

  8. Cracking of coated materials under transient thermal stresses

    NASA Technical Reports Server (NTRS)

    Rizk, A. A.; Erdogan, F.

    1989-01-01

    The crack problem for a relatively thin layer bonded to a very thick substrate under thermal shock conditions is considered. The effect of surface cooling rate is studied by assuming the temperature boundary condition to be a ramp function. Among the crack geometries considered are the edge crack in the coating layer, the broken layer, the edge crack going through the interface, the undercoat crack in the substrate and the embedded crack crossing the interface. The primary calculated quantity is the stress intensity factor at various singular points and the main variables are the relative sizes and locations of cracks, the time, and the duration of the cooling ramp. The problem is solved and rather extensive results are given for two material pairs, namely a stainless steel layer welded on a ferritic medium and a ceramic coating on a steel substrate.

  9. Cracking of coated materials under transient thermal stresses

    SciTech Connect

    Rizk, A.A.; Erdogan, F. )

    1989-01-01

    The crack problem for a relatively thin layer bonded to a very thick substrate under thermal shock conditions is considered. The effect of surface cooling rate is studied by assuming the temperature boundary condition to be a ramp function. Among the crack geometries considered are the edge crack in the coating layer, the broken layer, the edge crack going through the interface, the undercoat crack in the substrate and the embedded crack crossing the interface. The primary calculated quantity is the stress intensity factor at various singular points and the main variables are the relative sizes and locations of cracks, the time, and the duration of the cooling ramp. The problem is solved and rather extensive results are given for two material pairs, namely a stainless steel layer welded on a ferritic medium and a ceramic coating on a steel substrate. 12 refs.

  10. Cracking of coated materials under transient thermal stresses

    NASA Technical Reports Server (NTRS)

    Rizk, A. A.; Erdogan, Fazil

    1988-01-01

    The crack problem for a relatively thin layer bonded to a very thick substrate under thermal shock conditions is considered. The effect of surface cooling rate is studied by assuming the temperature boundary condition to be a ramp function. Among the crack geometries considered are the edge crack in the coating layer, the broken layer, the edge crack going through the interface, the undercoat crack in the substrate and the embedded crack crossing the interface. The primary calculated quantity is the stress intensity factor at various singular points and the main variables are the relative sizes and locations of cracks, the time, and the duration of the cooling ramp. The problem is solved and rather extensive results are given for two material pairs, namely a stainless steel layer welded on a ferritic medium and a ceramic coating on a steel substrate.

  11. Evaluation of Stress Corrosion Cracking Susceptibility Using Fracture Mechanics Techniques, Part 1. [environmental tests of aluminum alloys, stainless steels, and titanium alloys

    NASA Technical Reports Server (NTRS)

    Sprowls, D. O.; Shumaker, M. B.; Walsh, J. D.; Coursen, J. W.

    1973-01-01

    Stress corrosion cracking (SSC) tests were performed on 13 aluminum alloys, 13 precipitation hardening stainless steels, and two titanium 6Al-4V alloy forgings to compare fracture mechanics techniques with the conventional smooth specimen procedures. Commercially fabricated plate and rolled or forged bars 2 to 2.5-in. thick were tested. Exposures were conducted outdoors in a seacoast atmosphere and in an inland industrial atmosphere to relate the accelerated tests with service type environments. With the fracture mechanics technique tests were made chiefly on bolt loaded fatigue precracked compact tension specimens of the type used for plane-strain fracture toughness tests. Additional tests of the aluminum alloy were performed on ring loaded compact tension specimens and on bolt loaded double cantilever beams. For the smooth specimen procedure 0.125-in. dia. tensile specimens were loaded axially in constant deformation type frames. For both aluminum and steel alloys comparative SCC growth rates obtained from tests of precracked specimens provide an additional useful characterization of the SCC behavior of an alloy.

  12. Slow Crack Growth of Brittle Materials With Exponential Crack-Velocity Formulation. Part 3; Constant Stress and Cyclic Stress Experiments

    NASA Technical Reports Server (NTRS)

    Choi, Sung R.; Nemeth, Noel N.; Gyekenyesi, John P.

    2002-01-01

    The previously determined life prediction analysis based on an exponential crack-velocity formulation was examined using a variety of experimental data on advanced structural ceramics tested under constant stress and cyclic stress loading at ambient and elevated temperatures. The data fit to the relation between the time to failure and applied stress (or maximum applied stress in cyclic loading) was very reasonable for most of the materials studied. It was also found that life prediction for cyclic stress loading from data of constant stress loading in the exponential formulation was in good agreement with the experimental data, resulting in a similar degree of accuracy as compared with the power-law formulation. The major limitation in the exponential crack-velocity formulation, however, was that the inert strength of a material must be known a priori to evaluate the important slow-crack-growth (SCG) parameter n, a significant drawback as compared with the conventional power-law crack-velocity formulation.

  13. Fundamental understanding and life prediction of stress corrosion cracking in BWRs and energy systems

    SciTech Connect

    Andresen, P.L.; Ford, F.P.

    1998-03-01

    The objective of this paper is to present an approach for design and lifetime evaluation of environmental cracking based on experimental and fundamental modeling of the underlying processes operative in crack advance. In detailed this approach and its development and quantification for energy (hot water) systems, the requirements for a life prediction methodology will be highlighted and the shortcomings of the existing design and lifetime evaluation codes reviewed. Examples are identified of its use in a variety of cracking systems, such as stainless steels, low alloy steels, nickel base alloys, and irradiation assisted stress corrosion cracking in boiling water reactor (BWR) water, as well as preliminary use for low alloy steel and Alloy 600 in pressurized water reactors (PWRs) and turbine steels in steam turbines. Identification of the common aspects with environmental cracking in other hot water systems provides a secure basis for its extension to related energy systems. 166 refs., 49 figs.

  14. Fatigue crack closure behavior at high stress ratios

    NASA Technical Reports Server (NTRS)

    Turner, C. Christopher; Carman, C. Davis; Hillberry, Ben M.

    1988-01-01

    Fatigue crack delay behavior at high stress ratio caused by single peak overloads was investigated in two thicknesses of 7475-T731 aluminum alloy. Closure measurements indicated no closure occurred before or throughout the overload plastic zones following the overload. This was further substantiated by comparing the specimen compliance following the overload with the compliance of a low R ratio test when the crack was fully open. Scanning electron microscope studies revealed that crack tunneling and possibly reinitiation of the crack occurred, most likely a result of crack-tip blunting. The number of delay cycles was greater for the thinner mixed mode stress state specimen than for the thicker plane strain stress state specimen, which is similar to low R ratio test results and may be due to a larger plastic zone for the mixed mode cased.

  15. Stress corrosion crack tip microstructure in nickel-based alloys

    SciTech Connect

    Shei, S.A.; Yang, W.J.

    1994-04-01

    Stress corrosion cracking behavior of several nickel-base alloys in high temperature caustic environments has been evaluated. The crack tip and fracture surfaces were examined using Auger/ESCA and Analytical Electron Microscopy (AEM) to determine the near crack tip microstructure and microchemistry. Results showed formation of chromium-rich oxides at or near the crack tip and nickel-rich de-alloying layers away from the crack tip. The stress corrosion resistance of different nickel-base alloys in caustic may be explained by the preferential oxidation and dissolution of different alloying elements at the crack tip. Alloy 600 (UNS N06600) shows good general corrosion and intergranular attack resistance in caustic because of its high nickel content. Thermally treated Alloy 690 (UNS N06690) and Alloy 600 provide good stress corrosion cracking resistance because of high chromium contents along grain boundaries. Alloy 625 (UNS N06625) does not show as good stress corrosion cracking resistance as Alloy 690 or Alloy 600 because of its high molybdenum content.

  16. Environmentally assisted cracking of light-water reactor materials

    SciTech Connect

    Chopra, O.K.; Chung, H.M.; Kassner, T.F.; Shack, W.J.

    1996-02-01

    Environmentally assisted cracking (EAC) of lightwater reactor (LWR) materials has affected nuclear reactors from the very introduction of the technology. Corrosion problems have afflicted steam generators from the very introduction of pressurized water reactor (PWR) technology. Shippingport, the first commercial PWR operated in the United States, developed leaking cracks in two Type 304 stainless steel (SS) steam generator tubes as early as 1957, after only 150 h of operation. Stress corrosion cracks were observed in the heat-affected zones of welds in austenitic SS piping and associated components in boiling-water reactors (BRWs) as early as 1965. The degradation of steam generator tubing in PWRs and the stress corrosion cracking (SCC) of austenitic SS piping in BWRs have been the most visible and most expensive examples of EAC in LWRs, and the repair and replacement of steam generators and recirculation piping has cost hundreds of millions of dollars. However, other problems associated with the effects of the environment on reactor structures and components am important concerns in operating plants and for extended reactor lifetimes. Cast duplex austenitic-ferritic SSs are used extensively in the nuclear industry to fabricate pump casings and valve bodies for LWRs and primary coolant piping in many PWRs. Embrittlement of the ferrite phase in cast duplex SS may occur after 10 to 20 years at reactor operating temperatures, which could influence the mechanical response and integrity of pressure boundary components during high strain-rate loading (e.g., seismic events). The problem is of most concern in PWRs where slightly higher temperatures are typical and cast SS piping is widely used.

  17. Stress Ratio Effects on Crack Opening Loads and Crack Growth Rates in Aluminum Alloy 2024

    NASA Technical Reports Server (NTRS)

    Riddell, William T.; Piascik, Robert S.

    1998-01-01

    The effects of stress ratio (R) and crack opening behavior on fatigue crack growth rates (da/dN) for aluminum alloy (AA) 2024-T3 were investigated using constant-delta K testing, closure measurements, and fractography. Fatigue crack growth rates were obtained for a range of delta K and stress ratios. Results show that constant delta K fatigue crack growth for R ranging from near 0 to 1 is divided into three regions. In Region 1, at low R, da/dN increases with increasing R. In Region 2, at intermediate R, fatigue crack growth rates are relatively independent of R. In Region 3, at high R, further increases in da/dN are observed with increasing R.

  18. Influence of fatigue crack wake length and state of stress on crack closure

    NASA Technical Reports Server (NTRS)

    Telesman, J.; Fisher, D. M.

    1986-01-01

    The location of crack closure with respect to crack wake and specimen thickness under different loading conditions was determined. The rate of increase of K sub CL in the crack wake was found to be significantly higher for plasticity induced closure in comparison to roughness induced closure. Roughness induced closure was uniform throughout the thickness of the specimen while plasticity induced closure levels were 50 percent higher in the near surface region than in the midthickness. The influence of state of stress on low-high load interaction effects was also examined. Load interaction effects differed depending upon the state of stress and were explained in terms of delta K sub eff.

  19. Environmental Stress Screening 2000

    NASA Technical Reports Server (NTRS)

    Gibbel, Mark

    1997-01-01

    The following identifies the authors of this report and the organizations that sponsored the effort conducted under the National Center for Manufacturing Sciences (NCMS) Environmental Stress Screening (ESS) 2000 Project.

  20. Titanium alloy stress corrosion cracking in presence of dinitrogen tetroxide

    NASA Technical Reports Server (NTRS)

    Conner, A. Z.; Clarke, J. F. G., Jr.; Gailey, J. A.; Orr, A. A.

    1972-01-01

    Study resulting in a satisfactory stress corrosion cracking test with extremely consistent results produced six new analytical methods. Methods detect and determine differences in the minor constituent composition of different types of dinitrogen tetroxide.

  1. Stress-Corrosion Cracking in Martensitic PH Stainless Steels

    NASA Technical Reports Server (NTRS)

    Humphries, T.; Nelson, E.

    1984-01-01

    Precipitation-hardening alloys evaluated in marine environment tests. Report describes marine-environment stress-corrosion cracking (SCC) tests of three martensitic precipitation hardening (PH) stainless-steel alloys.

  2. Transient thermal stress problem for a circumferentially cracked hollow cylinder

    NASA Technical Reports Server (NTRS)

    Nied, H. F.; Erdogan, F.

    1983-01-01

    The paper is concerned with the transient thermal stress problem for a long hollow circular cylinder containing an internal axisymmetric circumferential edge crack that is suddenly cooled from inside. It is assumed that the transient thermal stress problem is quasi-static, i.e., the inertial effects are negligible. Also, all thermoelastic coupling effects and the possible temperature dependence of the thermoelastic constants are neglected. The problem is considered in two parts. The first part is the evaluation of transient thermal stresses in an uncracked cylinder; the second part is the isothermal perturbation problem for the cracked cylinder in which the crack surface tractions, equal and opposite to the thermal stresses obtained from the first problem, are the only external loads. The superposition of the two solutions gives results for the cracked cylinder.

  3. Stress corrosion cracking of zirconium in nitric acid

    SciTech Connect

    Beavers, J A; Griess, J C; Boyd, W K

    1980-01-01

    The susceptibility of zirconium and its common alloys to stress corrosion cracking (SCC) in nitric acid was investigated by slow strain-rate and constant deflection techniques. Cracking occurred at 25/sup 0/C over a wide range of acid concentrations and electrochemical potentials. The crack velocity increased slightly with increasing temperature. The failure mode was transgranular and the morphology was similar to SCC failures of zirconium alloys in other environments. The fracture was very orientation-dependent suggesting that it occurs on a single crystallographic plane in the material. The results of the study are not consistent with a hydrogen mechanism for cracking.

  4. Corrosion pitting and environmentally assisted small crack growth

    PubMed Central

    Turnbull, Alan

    2014-01-01

    In many applications, corrosion pits act as precursors to cracking, but qualitative and quantitative prediction of damage evolution has been hampered by lack of insights into the process by which a crack develops from a pit. An overview is given of recent breakthroughs in characterization and understanding of the pit-to-crack transition using advanced three-dimensional imaging techniques such as X-ray computed tomography and focused ion beam machining with scanning electron microscopy. These techniques provided novel insights with respect to the location of crack development from a pit, supported by finite-element analysis. This inspired a new concept for the role of pitting in stress corrosion cracking based on the growing pit inducing local dynamic plastic strain, a critical factor in the development of stress corrosion cracks. Challenges in quantifying the subsequent growth rate of the emerging small cracks are then outlined with the potential drop technique being the most viable. A comparison is made with the growth rate for short cracks (through-thickness crack in fracture mechanics specimen) and long cracks and an electrochemical crack size effect invoked to rationalize the data. PMID:25197249

  5. Corrosion pitting and environmentally assisted small crack growth.

    PubMed

    Turnbull, Alan

    2014-09-01

    In many applications, corrosion pits act as precursors to cracking, but qualitative and quantitative prediction of damage evolution has been hampered by lack of insights into the process by which a crack develops from a pit. An overview is given of recent breakthroughs in characterization and understanding of the pit-to-crack transition using advanced three-dimensional imaging techniques such as X-ray computed tomography and focused ion beam machining with scanning electron microscopy. These techniques provided novel insights with respect to the location of crack development from a pit, supported by finite-element analysis. This inspired a new concept for the role of pitting in stress corrosion cracking based on the growing pit inducing local dynamic plastic strain, a critical factor in the development of stress corrosion cracks. Challenges in quantifying the subsequent growth rate of the emerging small cracks are then outlined with the potential drop technique being the most viable. A comparison is made with the growth rate for short cracks (through-thickness crack in fracture mechanics specimen) and long cracks and an electrochemical crack size effect invoked to rationalize the data. PMID:25197249

  6. Stress intensity factor solutions for cracks in threaded fasteners

    SciTech Connect

    Oster, D.M.; Mills, W.J.

    1999-02-01

    Nondimensional stress intensity factor (K) solutions for continuous circumferential cracks in threaded fasteners were calculated using finite element methods that determined the energy release rate during virtual crack extension. Assumed loading conditions included both remote tension and nut loading, whereby the effects of applying the load to the thread flank were considered. In addition, K solutions were developed for axisymmetric surface cracks in notched and smooth round bars. Results showed that the stress concentration of a thread causes a considerable increase in K for shallow cracks, but has much less effect for longer cracks. In the latter case, values of K can be accurately estimated from K solutions for axisymmetric cracks in smooth round bars. Nut loading increased K by about 50% for shallow cracks, but this effect became negligible at crack depth-to-minor diameter ratios (a/d) greater than 0.2. An evaluation of thread root acuity effects showed that root radius has no effect on K when the crack depth exceeds 2% of the minor diameter. Closed-form K solutions were developed for both remote-loading and nut-loading conditions and for a wide range of thread root radii. The K solutions obtained in this study were compared with available literature solutions for threaded fasteners as well as notched and smooth round bars.

  7. Near tip stress and strain fields for short elastic cracks

    NASA Technical Reports Server (NTRS)

    Soediono, A. H.; Kardomateas, G. A.; Carlson, R. L.

    1994-01-01

    Recent experimental fatigue crack growth studies have concluded an apparent anomalous behavior of short cracks. To investigate the reasons for this unexpected behavior, the present paper focuses on identifying the crack length circumstances under which the requirements for a single parameter (K(sub I) or delta K(sub I) if cyclic loading is considered) characterization are violated. Furthermore, an additional quantity, the T stress, as introduced by Rice, and the related biaxiality ratio, B, are calculated for several crack lengths and two configurations, the single-edge-cracked and the centrally-cracked specimen. It is postulated that a two-parameter characterization by K and T (or B) is needed for the adequate description of the stress and strain field around a short crack. To further verify the validity of this postulate, the influence of the third term of the Williams series on the stress, strain and displacement fields around the crack tip and in particular on the B parameter is also examined. It is found that the biaxiality ratio would be more negative if the third term effects are included in both geometries. The study is conducted using the finite element method with linearly elastic material and isoparametric elements and axial (mode I) loading. Moreover, it is clearly shown that it is not proper to postulate the crack size limits for 'short crack' behavior as a normalized ratio with the specimen width, a/w; it should instead be stated as an absolute, or normalized with respect to a small characteristic dimension such as the grain size. Finally, implications regarding the prediction of cyclic (fatigue) growth of short cracks are discussed.

  8. Effect of Measured Welding Residual Stresses on Crack Growth

    NASA Technical Reports Server (NTRS)

    Hampton, Roy W.; Nelson, Drew; Doty, Laura W. (Technical Monitor)

    1998-01-01

    Welding residual stresses in thin plate A516-70 steel and 2219-T87 aluminum butt weldments were measured by the strain-gage hole drilling and X-ray diffraction methods. The residual stress data were used to construct 3D strain fields which were modeled as thermally induced strains. These 3D strain fields were then analyzed with the WARP31) FEM fracture analysis code in order to predict their effect on fatigue and on fracture. For analyses of fatigue crack advance and subsequent verification testing, fatigue crack growth increments were simulated by successive saw-cuts and incremental loading to generate, as a function of crack length, effects on crack growth of the interaction between residual stresses and load induced stresses. The specimen experimental response was characterized and compared to the WARM linear elastic and elastic-plastic fracture mechanics analysis predictions. To perform the fracture analysis, the plate material's crack tearing resistance was determined by tests of thin plate M(T) specimens. Fracture analyses of these specimen were performed using WARP31D to determine the critical Crack Tip Opening Angle [CTOA] of each material. These critical CTOA values were used to predict crack tearing and fracture in the weldments. To verify the fracture predictions, weldment M(T) specimen were tested in monotonic loading to fracture while characterizing the fracture process.

  9. Cohesive models of fatigue crack growth and stress-corrosion cracking

    NASA Astrophysics Data System (ADS)

    Nguyen, Olivier T.

    The aim of this dissertation was to develop models of fatigue crack growth and stress-corrosion cracking by investigating cohesive theories of fracture. These models were integrated in a finite-element framework embedding a contact algorithm and techniques of remeshing and adaptive meshing.For the fatigue model, we developed a phenomenological cohesive law which exhibits unloading-reloading hysteresis. This model qualitatively predicts fatigue crack growth rates in metals under constant amplitude regime for short and long cracks, as well as growth retardation due to overload. Quantitative predictions were obtained in the case of long cracks.We developed a chemistry-dependent cohesive law which serves as a basis for the stress-corrosion cracking model. In order to determine this cohesive law, two approaches, based on energy relaxation and the renormalization group, were used for coarse-graining interplanar potentials. We analyzed the cohesive behavior of a large--but finite--number of interatomic planes and found that the macroscopic cohesive law adopts a universal asymptotic form. The resulting stress-corrosion crack growth rates agreed well with those observed experimentally in 'static' fatigue tests given in the literature.

  10. Influence of precracked specimen configuration and starting stress intensity on the stress corrosion cracking of 4340 steel

    NASA Technical Reports Server (NTRS)

    Lisagor, W. B.

    1984-01-01

    Since the pioneer work of Brown (1966), precracked specimens and related fracture mechanics analyses have been extensively used to study stress corrosion cracking. Certain questions arose in connection with initial attempts to prepare standardized recommended practices by ASTM Committee G-1 on Corrosion of Metals. These questions were related to adequacy of test control as it pertains to acceptable limits of variability, and to validity of expressions for stress intensity and crack-surface displacements for both specimen configurations. An interlaboratory test program, was, therefore, planned with the objective to examine the validity of KIscc testing for selected specimen configurations, materials,and environmental systems. The results reported in the present paper include details of a single laboratory test program. The program was conducted to determine if the threshold value of stress intensity for onset and arrest of stress corrosion cracking was independent for the two specimen configurations examined.

  11. 2000-hour stress-corrosion cracking tests on 90-10 cupronickel in simulated Hanford groundwater

    SciTech Connect

    Mills, W.J.

    1987-02-01

    Self-loaded fracture mechanics specimens were tested in simulated groundwater at 150/degree/C to evaluate the susceptibility of 90-10 cupronickel to environmentally enhanced cracking. The test duration was 2000 hours. Electron fractographic evidence indicated that no stress corrosion cracking occurred during the test. Compliance methods demonstrated that a substantial amount of crack extension did not occur during the 2000-hour exposure, but this method was insensitive to detecting crack growth increments less than 0.030 inch. Conventional macroscopic examination of fracture surfaces could not be used to determine if any crack extension occurred during the test because stains were observed beyond the original precrack. The stains were attributed to artifacts associated with postcracking procedures. 7 refs., 11 figs., 3 tabs.

  12. Crack-tip chemistry modeling of stage I stress corrosion cracking

    SciTech Connect

    Jones, R.H.; Simonen, E.P.

    1991-10-01

    Stage I stress corrosion cracking usually exhibits a very strong K dependence with Paris law exponents of up to 30. 2 Model calculations indicate that the crack velocity in this regime is controlled by transport through a salt film and that the K dependence results from crack opening controlled salt film dissolution. An ionic transport model that accounts for both electromigration through the resistive salt film and Fickian diffusion through the aqueous solution was used for these predictions. Predicted crack growth rates are in excellent agreement with measured values for Ni with P segregated to the grain boundaries and tested in IN H{sub 2}SO{sub 4} at +900 mV. This salt film dissolution may be applicable to stage I cracking of other materials.

  13. Stress corrosion cracking of carbon steel in amine systems

    SciTech Connect

    Richert, J.P.; Bagdasarian, A.J.; Shargay, C.A.

    1988-01-01

    NACE Task Group T-8-14 was formed by Group Committee T-8 on Refining Industry Corrosion to conduct a survey on stress corrosion cracking (SCC) of existing amine units. The main purpose of the survey was to determine the extent of cracking problems in such units and to examine possible correlations between cracked and noncracked locations to establish possible cause(s) for cracking. A total of 294 completed survey forms were received and analyzed. Cracking was reported in monoethanolamine (MEA), diethanolamine, methyldiethanolamine, and diisopropanolamine solutions but was most prevalent in MEA units. Cracking occurs in all types of equipment and piping operating at all common temperatures. Cracking has been reported in all typical refinery streams containing H/sub 2/S, CO/sub 2/, or a combination of the two. The use of corrosion inhibitors, soda ash, caustic, filters, or reclaimers has no indicated effect on cracking tendencies. The survey results confirmed that stress relieving is a highly effective means of preventing amine SCC.

  14. Validation of Stress Corrosion Cracking Model for High Level Radioactive-Waste Packages

    SciTech Connect

    Lu, S; Gordon, G; Andresen, P

    2004-04-22

    A stress corrosion cracking (SCC) model has been adapted for performance prediction of high level radioactive-waste packages to be emplaced in the proposed Yucca Mountain radioactive-waste repository. SCC is one form of environmentally assisted cracking resulting from the presence of three factors: metallurgical susceptibility, critical environment, and tensile stresses. For waste packages of the proposed Yucca Mountain repository, the outer barrier material is the highly corrosion-resistant Alloy UNS-N06022, the environment is represented by the water film present on the surface of the waste package from dripping or deliquescence of soluble salts present in any surface deposits, and the stress is principally the weld induced residual stress. SCC has historically been separated into 'initiation' and 'propagation' phases. Initiation of SCC will not occur on a smooth surface if the surface stress is below a threshold value defined as the threshold stress. Cracks can also initiate at and propagate from flaws (or defects) resulting from manufacturing processes (such as welding). To account for crack propagation, the slip dissolution/film rupture (SDFR) model is adopted to provide mathematical formulae for prediction of the crack growth rate. Once the crack growth rate at an initiated SCC is determined, it can be used by the performance assessment (not in the scope of this paper) to determine the time to through-wall penetration for the waste package. This paper presents the development and validation of the SDFR crack growth rate model based on technical information in the literature as well as experimentally determined crack growth rates developed specifically for Alloy UNS- N06022 in environments relevant to high level radioactive-waste packages of the proposed Yucca Mountain radioactive-waste repository.

  15. Stress-corrosion fatigue-crack growth in a Zr-based bulk amorphousmetal

    SciTech Connect

    Schroeder, V.; Ritchie, R.O.

    2005-09-21

    Electrochemical and mechanical experiments were conducted to analyze the environmentally-influenced cracking behavior of a bulk amorphous metal, Zr41.2Ti13.8Cu12.5Ni10Be22.5. This study was motivated by a scientific interest in mechanisms of fatigue-crack propagation in an amorphous metal, and by a practical interest in the use of this amorphous metal in applications that take advantage of its unique properties, including high specific strength, large elastic strains and low damping. The objective of the work was to determine the rate and mechanisms of subcritical crack growth in this metallic glass in an aggressive environment. Specifically, fatigue-crack propagation behavior was investigated at a range of stress intensities in air and aqueous salt solutions by examining the effects of loading cycle, stress-intensity range, solution concentration, anion identity, solution de-aeration, and bulk electrochemical potential. Results indicate that crack growth in aqueous solution in this alloy is driven by a stress-assisted anodic reaction at the crack tip. Rate-determining steps for such behavior are reasoned to be electrochemical, stress-dependent reaction at near-threshold levels, and mass transport at higher (steady-state) growth rates.

  16. Stress corrosion cracking of zirconium used in the reprocessing plant

    SciTech Connect

    Kato, Chiaki; Motooka, Takafumi; Yamamoto, Masahiro

    2007-07-01

    We investigated stress corrosion cracking (SCC) of zirconium by constant load test and the small-scale mock-up test simulated the fuel dissolve. These tests operated in the simulated solution, which substituted non-radioactive elements, i.e. V with radioactive elements such as Pu and Np. From the results of constant load test, the cracks were not observed on 150 MPa after 908 hours in approximately 3 % strain. However a lot of cracks caused by SCC were observed over 20 % strain under high tensile stress in the simulated solution and the heat-transfer condition having more corrosive circumstance and noble potential accelerated the susceptibility of SCC. The cracking behavior would be caused by the creep phenomena. The small-scale mock-up test had been operated for about 50000 hours during 7 year. From the results, zirconium showed excellent corrosion resistance and no SCC was observed during these long-term operations. (authors)

  17. Elastostatic stress analysis of orthotropic rectangular center-cracked plates

    NASA Technical Reports Server (NTRS)

    Gyekenyesi, G. S.; Mendelson, A.

    1972-01-01

    A mapping-collocation method was developed for the elastostatic stress analysis of finite, anisotropic plates with centrally located traction-free cracks. The method essentially consists of mapping the crack into the unit circle and satisfying the crack boundary conditions exactly with the help of Muskhelishvili's function extension concept. The conditions on the outer boundary are satisfied approximately by applying the method of least-squares boundary collocation. A parametric study of finite-plate stress intensity factors, employing this mapping-collocation method, is presented. It shows the effects of varying material properties, orientation angle, and crack-length-to-plate-width and plate-height-to-plate-width ratios for rectangular orthotropic plates under constant tensile and shear loads.

  18. Stress analysis and stress-intensity factors for finite geometry solids containing rectangular surface cracks

    NASA Technical Reports Server (NTRS)

    Gyekenyesi, J. P.; Mendelson, A.

    1977-01-01

    The line method of analysis is applied to the Navier-Cauchy equations of elastic equilibrium to calculate the displacement field in a finite geometry bar containing a variable depth rectangular surface crack under extensionally applied uniform loading. The application of this method to these equations leads to coupled sets of simultaneous ordinary differential equations whose solutions are obtained along sets of lines in a discretized region. Using the obtained displacement field, normal stresses, and the stress-intensity factor variation along the crack periphery are calculated for different crack depth to bar thickness ratios. Crack opening displacements and stress-intensity factors are also obtained for a through-thickness, center-cracked bar with variable thickness. The reported results show a considerable potential for using this method in calculating stress-intensity factors for commonly encountered surface crack geometries in finite solids

  19. Stress analysis and stress intensity factors for finite geometry solids containing rectangular surface cracks

    NASA Technical Reports Server (NTRS)

    Gyekenyesi, J. P.; Mendelson, A.

    1975-01-01

    The line method of analysis is applied to the Navier-Cauchy equations of elastic equilibrium to calculate the displacement field in a finite geometry bar containing a variable depth rectangular surface crack under extensionally applied uniform loading. The application of this method to these equations leads to coupled sets of simultaneous ordinary differential equations whose solutions are obtained along sets of lines in a discretized region. Using the obtained displacement field, normal stresses and the stress intensity factor variation along the crack periphery are calculated for different crack depth to bar thickness ratios. Crack opening displacements and stress intensity factors are also obtained for a through-thickness, center cracked bar with variable thickness. The reported results show a considerable potential for using this method in calculating stress intensity factors for commonly encountered surface crack geometries in finite solids.

  20. Stress corrosion crack inhibiting method for titanium

    NASA Technical Reports Server (NTRS)

    Beck, T. R.

    1970-01-01

    Addition of oxyanions to liquid solvents in excess of the number of chloride, bromide, or iodide ions present prevents cracking of titanium-aluminum alloys under exposure to aqueous and other solvent environments. The molar concentration of oxyanion is set from 10 to 100 times higher than concentration of halide ions.

  1. An investigation of crack-tip stress field criteria of predicting cleavage-crack initiation

    SciTech Connect

    Keeney-Walker, J.; Bass, B.R.; Landes, J.D. )

    1991-09-01

    Cleavage-crack initiation in large-scale wide-plate (WP) specimens could not be accurately predicted from small, compact (CT) specimens by using a linear-elastic fracture-mechanics, K{sub Ic}, methodology. In the wide-plate tests conducted by the Heavy-Section Steel Technology Program at Oak Ridge National Laboratory, crack initiation has consistently occurred at stress-intensity (K{sub I}) values ranging from two to four times those predicted by the CT specimens. Studies were initiated to develop crack-tip stress field criteria incorporating effects of geometry, size, and constraint that will lead to improved predictions of cleavage initiation in WP specimens from CT specimens. The work centers around nonlinear two-and three-dimensional finite-element analyses of the crack-tip stress fields in these geometries. Analyses were conducted on CT and WP specimens for which cleavage initiation fracture had been measured in laboratory tests. The local crack-tip field generated for these specimens were then used in the evaluation of fracture correlation parameters to augment the K{sub I} parameter for predicting cleavage initiation. Parameters of hydrostatic constraint and of maximum principal stress, measured volumetrically, are included in these evaluations. The results suggest that the cleavage initiation process can be correlated with the local crack-tip fields via a maximum principal stress criterion based on achieving a critical area within a critical stress contour. This criterion has been successfully applied to correlate cleavage initiation in 2T-CT and WP specimen geometries. 23 refs., 16 figs., 5 tabs.

  2. Research on mechanisms of stress corrosion cracking in Zircaloy

    SciTech Connect

    Knorr, D.B.; Pelloux, R.M.

    1981-06-01

    The results of internal gas pressurization tests, primarily at 320/sup 0/C, on cladding tubes from two suppliers, Supplier A and Supplier B, are presented. The two lots show a substantial difference in iodine SCC susceptibility so a test matrix is used to resolve the relative contributions of surface condition, residual stress, and texture. Additional tests with constant deflection split-ring specimens and with unstressed cladding segments are used to understand crack initiation and the early crack growth stages of SCC. The difference in SCC susceptibility is due to crystallographic texture. Other variables such as surface finish, stress relief temperature, and residual stress have little or no effect. Mechanical properties, crack initiation, and crack propagation all depend on texture. Both initiation and propagation features are analyzed by scanning electron microscopy. A mechanism for crack initiation consistent with most observations in this study and with the work of other investigators is proposed. At 320/sup 0/C, lifetime is crack initiation limited while several tests at 390/sup 0/C indicate that lifetime is less initiation limited at higher temperature. 31 figures, 9 tables.

  3. Review of environmental effects on fatigue crack growth of austenitic stainless steels

    SciTech Connect

    Shack, W.J.; Kassner, T.F.

    1994-05-01

    Fatigue and environmentally assisted cracking of piping, pressure vessel cladding, and core components in light water reactors are potential concerns to the nuclear industry and regulatory agencies. The degradation processes include intergranular stress corrosion cracking of austenitic stainless steel (SS) piping in boiling water reactors (BWRs), and propagation of fatigue or stress corrosion cracks (which initiate in sensitized SS cladding) into low-alloy ferritic steels in BWR pressure vessels. Crack growth data for wrought and cast austenitic SSs in simulated BWR water, developed at Argonne National Laboratory under US Nuclear Regulatory Commission sponsorship over the past 10 years, have been compiled into a data base along with similar data obtained from the open literature. The data were analyzed to develop corrosion-fatigue curves for austenitic SSs in aqueous environments corresponding to normal BWR water chemistries, for BWRs that add hydrogen to the feedwater, and for pressurized water reactor primary-system-coolant chemistry.

  4. Crack growth in a welded microalloyed steel under sulfide stress cracking conditions

    SciTech Connect

    Albarran, J.L.; Martinez, L.; Lopez, H.F.

    1998-12-01

    In this work, the hydrogen sulfide stress-corrosion cracking (SSC) susceptibility of a welded API X-80 pipeline was investigated. For this purpose, steel welding was carried out normal to the rolling direction using a 60{degree} single V-joint design. After welding, compact modified-wedge opening loading (M-WOL) fracture mechanics specimens were machined and loaded to an applied stress intensity factor, K{sub 1}, of 27 to 53 MPa {radical}m. This was followed by specimen exposure to H{sub 2}S saturated synthetic seawater. Each of the M-WOL specimens contained the typical microstructures developed during welding, such as the weld metal (WM), base metal (BM), and heat affected zone (HAZ). No attempt was made to establish a unique K{sub ISCC} for crack arrest because its significance was not clear. Qualitatively, the experimental outcome indicated that in mode I loading under a K{sub 1} of 40.3 MPa {radical}m only the base metal region underwent SSC. Apparently, active anodic dissolution of the crack tip started the growth process, but it was followed by a transition to hydrogen induced cracking. At an applied K{sub 1} of 55 MPa {radical}m and under similar exposure times, crack growth in the base metal was discontinuous and tended to follow the grain boundaries. Moreover, the HAZ exhibited the least SSC susceptibility as inferred from the relatively short crack propagation lengths (0.829 mm). In this case, it was found that the crack lengths of up to 4.2 mm developed. In this case, the presence of a relatively coarse dendritic structure coupled with interdendritic segregation provided a weak path for crack propagation.

  5. Remote field eddy current detection of stress-corrosion cracks

    SciTech Connect

    Nestleroth, J.B.

    1990-02-01

    The feasibility of detecting stress-corrosion cracks (SSC) using the Remote Field Eddy Current (RFEC) technique was demonstrated. The RFEC technique interrogates the entire thickness of the pipe and is applicable for in-line inspection. If it can be shown that the RFEC technique is effective in detecting SSC, then the technique is an ideal method for detecting the defects of interest. A defect detection model is proposed for explaining the mechanism for crack detection. For axially oriented, closed cracks, such as SCC, the conventional defect detection model proved to be too simplistic and not applicable. Therefore, a new detection mode that examines the flow of circumferential eddy currents was developed based on experimental results. This model, though not rigorous, provides a general understanding of the applicability of the RFEC technique for finding SSC. The data from the cracks and various artificial defects is presented in three formats: isometric projections, pseudocolor images and line-of-sight data. Though only two cracks were found, the experimental results correlate well with the circumferential eddy current theory. A theoretical analysis of the effects of motion on the output signal of the receiver is presented. This analysis indicates that inspection speed of simple implementations may be limited to a few miles per hour. Remote field eddy current inspection has excellent potential for inspection of gas transmission lines for detecting stress corrosion cracks that should be further developed.

  6. Effect of material damage on the stress-strain state near a crack tip in creep

    NASA Astrophysics Data System (ADS)

    Astaf'ev, V. I.; Grigorova, T. V.; Pastukhov, V. A.

    1992-02-01

    The asymptotic stress and damage fields near the tip of a growing crack are determined for a creep-damaged material described by Rabotnov-Hayhurst-Leckie constitutive equations. It is found that the singular stress field, characteristic of the crack theory, is absent near the crack tip, which is consistent with the results of finite element solutions for tearing cracks. A crack growth law is obtained which provides a qualitative description of the crack growth process in stainless steels under constant loading.

  7. Primary Water Stress Corrosion Crack Morphology and Nondestructive Evaluation Reliability

    SciTech Connect

    Doctor, Steven R.; Schuster, George J.; Anderson, Michael T.

    2004-12-01

    A research program on primary stress corrosion crack (PWSCC) is being conducted by Pacific Northwest National Laboratory (PNNL). In this program, the material degradation problem in Alloys 600, 182, and 82 is being investigated with objectives that include compling a knowledge base on all cracking in nickel based materials at all degradation sites in nuclear power plants, assessing NDE methods using mockups to quantify the detection, sizing, and using mockups to quantify the detection sizing and characterization of tight cracks, and determining the role of welding processes in degradation. In this paper, the resuts of the initial literature searchs are presented. The relevant data on crack properties such as shape and orientation are presented and their impace on nondestructive evaluation (NDE) reliability is discussed.

  8. Laboratory stress corrosion cracking studies in polythionic acid

    SciTech Connect

    Baylor, V.B.; Newsome, J.F.

    1984-08-01

    Stress corrosion cracking caused by polythionic acid and/or chlorides is a problem in coal liquefaction pilot plants. This problem is also common in refineries and has been the subject of extensive research. This study examines (1) the relationship of the ASTM standard ferric sulfate-sulfuric acid test for determining sensitization to resistance to polythionic stress corrosion cracking, (2) the cracking resistance of higher-alloy Fe-Ni-Cr materials in addition to the common austenitic stainless steels, and (3) the effect of chloride concentrations up to 1% in polythionic acid solutions on cracking behavior. We found that the ferric sulfate-sulfuric acid test can be used as an acceptance test for materials resistant to polythionic acid stress corrosion cracking because of its severity. The more highly alloyed materials were more resistant to sensitization than most of the austenitic stainless steels and were virtually unattacked in polythionic acid solutions containing up to 1% chloride. Chloride increased the corrosion rate and caused localized pitting, but it did not affect significantly the number of failures or the failure mode.

  9. Stress corrosion cracking of austenitic stainless steel core internal welds.

    SciTech Connect

    Chung, H. M.; Park, J.-H.; Ruther, W. E.; Sanecki, J. E.; Strain, R. V.; Zaluzec, N. J.

    1999-04-14

    Microstructural analyses by several advanced metallographic techniques were conducted on austenitic stainless steel mockup and core shroud welds that had cracked in boiling water reactors. Contrary to previous beliefs, heat-affected zones of the cracked Type 304L, as well as 304 SS core shroud welds and mockup shielded-metal-arc welds, were free of grain-boundary carbides, which shows that core shroud failure cannot be explained by classical intergranular stress corrosion cracking. Neither martensite nor delta-ferrite films were present on the grain boundaries. However, as a result of exposure to welding fumes, the heat-affected zones of the core shroud welds were significantly contaminated by oxygen and fluorine, which migrate to grain boundaries. Significant oxygen contamination seems to promote fluorine contamination and suppress thermal sensitization. Results of slow-strain-rate tensile tests also indicate that fluorine exacerbates the susceptibility of irradiated steels to intergranular stress corrosion cracking. These observations, combined with previous reports on the strong influence of weld flux, indicate that oxygen and fluorine contamination and fluorine-catalyzed stress corrosion play a major role in cracking of core shroud welds.

  10. Stress-corrosion cracking in BWR and PWR piping

    SciTech Connect

    Weeks, R.W.

    1983-07-01

    Intergranular stress-corrosion cracking of weld-sensitized wrought stainless steel piping has been an increasingly ubiquitous and expensive problem in boiling-water reactors over the last decade. In recent months, numerous cracks have been found, even in large-diameter lines. A number of potential remedies have been developed. These are directed at providing more resistant materials, reducing weld-induced stresses, or improving the water chemistry. The potential remedies are discussed, along with the capabilities of ultrasonic testing to find and size the cracks and related safety issues. The problem has been much less severe to date in pressurized-water reactors, reflecting the use of different materials and much lower coolant oxygen levels.

  11. Crack Growth in First Wall by Cyclic Thermal Stress

    SciTech Connect

    Nishimura, T.; Hatano, T.; Honda, T.; Saito, M.

    2003-07-15

    The long pulse operation is assumed in ITER and future reactors. If the first wall has a defect, the crack may be propagated by cyclic thermal loads. In addition, flattop of more than 300 sec during plasma burning is expected, therefore, an effect of transient creep must be included. In order to simulate a severe temperature gradient in the first wall, an experimental facility was designed using an electron beam (EB) as a heat source, which has a distinct feature that the various plasma burning scenarios can be simulated by controlling the beam power so as to make surface temperature of the specimen to be fixed. To clarify the crack growth mechanism and the effects of transient creep, elastic-plastic stress analysis and creep analysis were performed. It is concluded that the creep effect during the operation duration period enlarges the residual tensile stress in the cooling period, and that consequently the crack propagation length increases.

  12. Stress-relief cracking of a new ferritic steel

    NASA Astrophysics Data System (ADS)

    Nawrocki, Jesse Gerald

    The mechanism of stress-relief cracking in the coarse-grained heat-affected zone (CGHAZ) of low-alloy ferritic steels was studied through a tempering study, stress-relaxation testing, and detailed microstructural characterization. A new ferritic alloy steel, HCM2S, was used as the model system. Common 2.25Cr-1 Mo steel, which is susceptible to stress-relief cracking, was used for comparison to HCM2S. The CGHAZ was simulated using Gleeble techniques. A dense distribution of small tungsten-rich carbides within the prior austenite grains induced secondary hardening in the CGHAZ of HCM2S. The CGHAZ of 2.25Cr-1 Mo steel exhibited secondary hardening due to the intragranular precipitation of many Fe-rich M3C carbides. The hardness of HCM2S was more stable at longer times and high temperatures than 2.25Cr-1 Mo steel due to the intragranular precipitation of small W and V-rich carbides. The CGHAZs of HCM2S and 2.25Cr-1 Mo steel were susceptible to stress-relief cracking between 575 and 725°C. HCM2S exhibited C-curve behavior with respect to the time to failure as a function of post-weld heat treatment (PWHT) temperature. No segregation of tramp elements to prior austenite grain boundaries was detected in HCM2S. Both intergranular and intragranular carbide precipitation controlled the stress-relief cracking behavior. The amount of intergranular failure increased with test temperature due to the increasing amounts of Fe-rich M3C carbides at the prior austenite grain boundaries. These carbides acted as cavity nucleation sites. The cavities coalesced to form microcracks along prior austenite grain boundaries. Eventually, the remaining uncracked areas could not support the load and failed by ductile rupture. The balance of intergranular and intragranular carbide precipitation resulted in the C-curve behavior. The nose of the C-curve occurred at 675°C. The intragranular regions were strong because of a dense distribution of W/Fe-rich carbides, but the prior austenite grain

  13. A demonstration of mitigation of environmentally-assisted cracking by the application of a tensile overload

    SciTech Connect

    James, L.A.

    1997-02-01

    Environmentally-assisted cracking (EAC) of low-alloy steels in high-temperature aqueous environments typical of those employed in light-water reactor (LWR) systems has been a subject of considerable interest since the pioneering work of Kondo et al demonstrated significantly higher fatigue crack propagation (FCP) rates in water than would be expected in an air environment under similar conditions. Here, environmentally-assisted cracking (EAC) of low-alloy steels in elevated temperature aqueous environments is readily observed in many laboratory experiments conducted in autoclaves, yet the observation of EAC in actual components operating in the same environments is quite rare. Mass transport of sulfides from the crack enclave by diffusion and convection occurring in operating components provides one plausible explanation to this apparent paradox. Another contribution to EAC mitigation may also arise from the non-constant stress amplitudes typical for many operating components. This paper provides a demonstration of how a single tensile overload to 40% above a steady-state maximum fatigue stress can retard subsequent crack growth at the steady-state level for a sufficient period of time that diffusion mass transport can reduce the crack-tip sulfide concentration to a level below that necessary to sustain EAC.

  14. Reducing Stress-Corrosion Cracking in Bearing Alloys

    NASA Technical Reports Server (NTRS)

    Paton, N. E.; Dennies, D. P.; Lumsden, I., J.b.

    1986-01-01

    Resistance to stress-corrosion cracking in some stainless-steel alloys increased by addition of small amounts of noble metals. 0.75 to 1.00 percent by weight of palladium or platinum added to alloy melt sufficient to improve properties of certain stainless steels so they could be used in manufacture of high-speed bearings.

  15. Grease Inhibits Stress-Corrosion Cracking In Bearing Race

    NASA Technical Reports Server (NTRS)

    Beatty, Robert F.; Mcvey, Scott E.

    1991-01-01

    Coating with suitable grease found to inhibit stress-corrosion cracking in bore of inner race of ball-bearing assembly operating in liquid oxygen. Protects bore and its corner radii from corrosion-initiating and -accelerating substances like moisture and contaminants, which enter during assembly. Operating life extended at low cost, and involves very little extra assembly time.

  16. STRESS CRACKING BEHAVIOR OF HDPE GEOMEMBRANES AND ITS PREVENTION

    EPA Science Inventory

    Geomembranes made from high density polyethylene (HOPE) have a high percent crystallinity and are therefore of concern with regard to stress cracking. A review of the literature plus our field exhuming of various sites-of-opportunity gave rise to twenty-five (25) situations wh...

  17. Chemical milling solution reveals stress corrosion cracks in titanium alloy

    NASA Technical Reports Server (NTRS)

    Braski, D. N.

    1967-01-01

    Solution of hydrogen flouride, hydrogen peroxide, and water reveals hot salt stress corrosion cracks in various titanium alloys. After the surface is rinsed in water, dried, and swabbed with the solution, it can be observed by the naked eye or at low magnification.

  18. Accelerated crack growth, residual stress, and a cracked zinc coated pressure shell

    NASA Technical Reports Server (NTRS)

    Dittman, Daniel L.; Hampton, Roy W.; Nelson, Howard G.

    1987-01-01

    During a partial inspection of a 42 year old, operating, pressurized wind tunnel at NASA-Ames Research Center, a surface connected defect 114 in. long having an indicated depth of a 0.7 in. was detected. The pressure shell, constructed of a medium carbon steel, contains approximately 10 miles of welds and is cooled by flowing water over its zinc coated external surface. Metallurgical and fractographic analysis showed that the actual detect was 1.7 in. deep, and originated from an area of lack of weld penetration. Crack growth studies were performed on the shell material in the laboratory under various loading rates, hold times, and R-ratios with a simulated shell environment. The combination of zinc, water with electrolyte, and steel formed an electrolytic cell which resulted in an increase in cyclic crack growth rate by as much as 500 times over that observed in air. It was concluded that slow crack growth occurred in the pressure shell by a combination of stress corrosion cracking due to the welding residual stress and corrosion fatigue due to the cyclic operating stress.

  19. Strengthening, Crack Arrest And Multiple Cracking In Brittle Materials Using Residual Stresses.

    DOEpatents

    Green, David J.; Sglavo, Vincenzo M.; Tandon, Rajan

    2003-02-11

    Embodiments include a method for forming a glass which displays visible cracking prior to failure when subjected to predetermined stress level that is greater than a predetermined minimum stress level and less than a failure stress level. The method includes determining a critical flaw size in the glass and introducing a residual stress profile to the glass so that a plurality of visible cracks are formed prior to failure when the glass is subjected to a stress that is greater than the minimum stress level and lower than the critical stress. One method for forming the residual stress profile includes performing a first ion exchange so that a first plurality of ions of a first element in the glass are exchanged with a second plurality of ions of a second element that have a larger volume than the first ions. A second ion exchange is also performed so that a plurality of the second ions in the glass are exchanged back to ions of the first element.

  20. Crack propagation and fracture in silicon wafers under thermal stress

    PubMed Central

    Danilewsky, Andreas; Wittge, Jochen; Kiefl, Konstantin; Allen, David; McNally, Patrick; Garagorri, Jorge; Elizalde, M. Reyes; Baumbach, Tilo; Tanner, Brian K.

    2013-01-01

    The behaviour of microcracks in silicon during thermal annealing has been studied using in situ X-ray diffraction imaging. Initial cracks are produced with an indenter at the edge of a conventional Si wafer, which was heated under temperature gradients to produce thermal stress. At temperatures where Si is still in the brittle regime, the strain may accumulate if a microcrack is pinned. If a critical value is exceeded either a new or a longer crack will be formed, which results with high probability in wafer breakage. The strain reduces most efficiently by forming (hhl) or (hkl) crack planes of high energy instead of the expected low-energy cleavage planes like {111}. Dangerous cracks, which become active during heat treatment and may shatter the whole wafer, can be identified from diffraction images simply by measuring the geometrical dimensions of the strain-related contrast around the crack tip. Once the plastic regime at higher temperature is reached, strain is reduced by generating dislocation loops and slip bands and no wafer breakage occurs. There is only a small temperature window within which crack propagation is possible during rapid annealing. PMID:24046487

  1. Environmental Fatigue-Crack Surface Crystallography for Al-Zn-Cu-Mg-Mn/Zr

    NASA Astrophysics Data System (ADS)

    Ro, Yunjo; Agnew, Sean R.; Gangloff, Richard P.

    2008-06-01

    The scanning electron microscope (SEM)-based electron backscattered diffraction (EBSD)/stereology technique quantitatively establishes distributions of the crystallographic characteristics of environmental-fatigue crack features for slightly overaged Al-Zn-Cu-Mg-X (X = Zr or Mn) alloys stressed in the low-growth-rate regime. Results for these homogeneous slip alloys conform to a substantial companion study of planar slip-prone Al-Cu-Mg/Li. Transgranular-crack characteristics are similar for the Mn and Zr variants, independent of grain size and recrystallization. Two morphologies of facetlike features exhibit a wide range of crystallographic orientations, change character at grain boundaries indicating an important role of grain orientation, and form in highly tensile-stressed spatial orientations about a crack tip. Similar characteristics for Al-Zn and Al-Cu suggest a common damage mechanism, speculatively attributed to hydrogen-environment embrittlement by decohesion. Slip-deformation band cracking resulting in facets near {111}, stimulated by H-enhanced localized plasticity, is not a viable mechanism for environmental fatigue. Repetitively stepped facets with surface curvature may involve H-enhanced cleavage along {100} or {110} planes subsequently distorted by plasticity. Broad-flat facets speculatively result from tensile stress-based cracking through dislocation cell structure, evolved by cyclic plasticity and containing trapped H.

  2. Stress Corrosion Cracking in Al-Zn-Mg-Cu Aluminum Alloys in Saline Environments

    NASA Astrophysics Data System (ADS)

    Holroyd, N. J. Henry; Scamans, G. M.

    2013-03-01

    Stress corrosion cracking of Al-Zn-Mg-Cu (AA7xxx) aluminum alloys exposed to saline environments at temperatures ranging from 293 K to 353 K (20 °C to 80 °C) has been reviewed with particular attention to the influences of alloy composition and temper, and bulk and local environmental conditions. Stress corrosion crack (SCC) growth rates at room temperature for peak- and over-aged tempers in saline environments are minimized for Al-Zn-Mg-Cu alloys containing less than ~8 wt pct Zn when Zn/Mg ratios are ranging from 2 to 3, excess magnesium levels are less than 1 wt pct, and copper content is either less than ~0.2 wt pct or ranging from 1.3 to 2 wt pct. A minimum chloride ion concentration of ~0.01 M is required for crack growth rates to exceed those in distilled water, which insures that the local solution pH in crack-tip regions can be maintained at less than 4. Crack growth rates in saline solution without other additions gradually increase with bulk chloride ion concentrations up to around 0.6 M NaCl, whereas in solutions with sufficiently low dichromate (or chromate), inhibitor additions are insensitive to the bulk chloride concentration and are typically at least double those observed without the additions. DCB specimens, fatigue pre-cracked in air before immersion in a saline environment, show an initial period with no detectible crack growth, followed by crack growth at the distilled water rate, and then transition to a higher crack growth rate typical of region 2 crack growth in the saline environment. Time spent in each stage depends on the type of pre-crack ("pop-in" vs fatigue), applied stress intensity factor, alloy chemistry, bulk environment, and, if applied, the external polarization. Apparent activation energies ( E a) for SCC growth in Al-Zn-Mg-Cu alloys exposed to 0.6 M NaCl over the temperatures ranging from 293 K to 353 K (20 °C to 80 °C) for under-, peak-, and over-aged low-copper-containing alloys (<0.2 wt pct) are typically ranging from

  3. Stress intensity factors in bonded half planes containing inclined cracks and subjected to antiplane shear loading

    NASA Technical Reports Server (NTRS)

    Bassani, J. L.; Erdogan, F.

    1979-01-01

    The antiplane shear problem for two bonded dissimilar half planes containing a semi-infinite crack or two arbitrarily located collinear cracks is considered. For the semi-infinite crack the problem is solved for a concentrated wedge load and the stress intensity factor and the angular distribution of stresses are calculated. For finite cracks the problem is reduced to a pair of integral equations. Numerical results are obtained for cracks fully imbedded in a homogeneous medium, one crack tip touching the interface, and a crack crossing the interface for various crack angles.

  4. Stress intensity factors in bonded half planes containing inclined cracks and subjected to antiplane shear loading

    NASA Technical Reports Server (NTRS)

    Bassani, J. L.; Erdogan, F.

    1978-01-01

    The antiplane shear problem for two bonded dissimilar half planes containing a semi-infinite crack or two arbitrarily located collinear cracks was considered. For the semi-infinite crack the problem was solved for a concentrated wedge load and the stress intensity factor and the angular distribution of stresses were calculated. For finite cracks the problem was reduced to a pair of integral equations. Numerical results were obtained for cracks fully imbedded in a homogeneous medium, one crack tip touching the interface, and a crack crossing the interface for various crack angles.

  5. Factors affecting stress assisted corrosion cracking of carbon steel under industrial boiler conditions

    NASA Astrophysics Data System (ADS)

    Yang, Dong

    Failure of carbon steel boiler tubes from waterside has been reported in the utility boilers and industrial boilers for a long time. In industrial boilers, most waterside tube cracks are found near heavy attachment welds on the outer surface and are typically blunt, with multiple bulbous features indicating a discontinuous growth. These types of tube failures are typically referred to as stress assisted corrosion (SAC). For recovery boilers in the pulp and paper industry, these failures are particularly important as any water leak inside the furnace can potentially lead to smelt-water explosion. Metal properties, environmental variables, and stress conditions are the major factors influencing SAC crack initation and propagation in carbon steel boiler tubes. Slow strain rate tests (SSRT) were conducted under boiler water conditions to study the effect of temperature, oxygen level, and stress conditions on crack initation and propagation on SA-210 carbon steel samples machined out of boiler tubes. Heat treatments were also performed to develop various grain size and carbon content on carbon steel samples, and SSRTs were conducted on these samples to examine the effect of microstructure features on SAC cracking. Mechanisms of SAC crack initation and propagation were proposed and validated based on interrupted slow strain tests (ISSRT). Water chemistry guidelines are provided to prevent SAC and fracture mechanics model is developed to predict SAC failure on industrial boiler tubes.

  6. Experimental evaluation of stress intensity factors for corner cracks in bolted joints

    SciTech Connect

    Guengoer, S.; Patterson, E.A.

    1994-12-31

    Stress freezing photoelasticity was used to measure mode one stress intensity factors of corner cracks in a double shear bolted joint. A model of the joint assembly was manufactured from a photoelastic material and three different corner cracks were introduced using a cutting wheel. After stress freezing process slices along the crack fronts were cut and analyzed using photoelastic procedures. Stress intensity factors of these cracks were found to be larger near the hole.

  7. Stress Corrosion Crack Detection on HU-25 Guardian Aircraft

    SciTech Connect

    Blackmon, R.; Huffman, J.; Mello, C.W.; Moore, D.G.; Walkington, P.D.

    1999-02-17

    Several ultrasonic inspection methods were developed at the Federal Aviation Administration's Airworthiness Assurance NDI Validation Center (AANC) to easily and rapidly detect hidden stress corrosion cracks in all vertical windshield posts on the US Coast Guard (USCG) HU-25 Guardian aircraft. The inspection procedure locates cracks as small as 2.0 millimeters emanating from internal fastener holes and determines their length. A test procedure was developed and a baseline assessment of the USCG fleet was conducted. Inspection results on twenty-five aircraft revealed a good correlation with results made during subsequent structural disassembly and visual inspection.

  8. Stress intensity, stress concentration and fatigue crack growth along evacuators of pressurized, autofrettaged tubes

    SciTech Connect

    Parker, A.P.; Underwood, J.H.

    1995-11-01

    The geometry analyzed consists of a thick-walled cylinder having a small diameter evacuator hole penetrating radially through the wall. The loading involves pressure acting on the ID of the tube and all or part of this pressure acting on the evacuator hole. In addition the tube may be fully or partially autofrettaged. Total hoop stress concentrations are determined for a range of radial locations along the evacuator, as are stress intensity factors along a crack emanating from the evacuator hole. Fatigue crack growth rates, and hence crack profiles, are predicted at each of the radial locations. These predictions indicate that the critical location for the crack in a non-autofrettaged tube is at the ID whereas in a fully autofrettaged tube it is located approximately half way through the wall thickness. Taking account of the influence of stress ratio, minimum value of direct stress/maximum value of direct stress has a significantly influence on crack shape in autofrettaged tubes, but a limited effect upon lifetime. The effect upon fatigue lifetime of axial residual stresses due to the autofrettage process is described and it is demonstrated that an insignificant reduction in lifetime results from the presence of such stresses. Finally the predicted profiles are compared with experimental observations of fatigue cracked evacuators and a limited comparison of predicted and actual lifetimes is presented. Agreement is considered good.

  9. Relationships between stress corrosion cracking tests and utility operating experience

    SciTech Connect

    Baum, Allen

    1999-10-22

    Several utility steam generator and stress corrosion cracking databases are synthesized with the view of identifying the crevice chemistry that is most consistent with the plant cracking data. Superheated steam and neutral solution environments are found to be inconsistent with the large variations in the observed SCC between different plants, different support plates within a plant, and different crevice locations. While the eddy current response of laboratory tests performed with caustic chemistries approximates the response of the most extensively affected steam generator tubes, the crack propagation kinetics in these tests differ horn plant experience. The observations suggest that there is a gradual conversion of the environment responsible for most steam generator ODSCC from a concentrated, alkaline-forming solution to a progressively more steam-enriched environment.

  10. Frequency domain stress intensity calibration of damped cracked panels

    NASA Technical Reports Server (NTRS)

    Doyle, James F.; Rizzi, Stephen A.

    1993-01-01

    This paper discusses two schemes for doing finite element K calibration in the frequency domain. The baseline scheme uses the definition of K as a limit toward the crack tip. The limiting process requires using a very fine mesh around the crack tip making the scheme computationally very expensive. It is shown that the behavior of K as a function of frequency is very similar to a modal response. Taking advantage of this, a more efficient scheme involves a modal analysis of the cracked sheet and scaling the response to that of the static stress intensity. In this way, only a static K calibration need be performed. All the examples shown are for a frequency range spanning multiple resonances and with two levels of damping.

  11. Environmentally assisted cracking in light water reactors. Semiannual report, July 1998-December 1998.

    SciTech Connect

    Chopra, O. K.; Chung, H. M.; Gruber, E. E.; Kassner, T. F.; Ruther, W. E.; Shack, W. J.; Smith, J. L.; Soppet, W. K.; Strain; R. V.

    1999-10-01

    This report summarizes work performed by Argonne National Laboratory on fatigue and environmentally assisted cracking (EAC) in light water reactors from July 1998 to December 1998. Topics that have been investigated include (a) environmental effects on fatigue S-N behavior of primary pressure boundary materials, (b) irradiation-assisted stress corrosion cracking of austenitic stainless steels (SSs), and (c) EAC of Alloys 600 and 690. Fatigue tests have been conducted to determine the crack initiation and crack growth characteristics of austenitic SSs in LWR environments. Procedures are presented for incorporating the effects of reactor coolant environments on the fatigue life of pressure vessel and piping steels. Slow-strain-rate tensile tests and posttest fractographic analyses were conducted on several model SS alloys irradiated to {approx}0.3 and 0.9 x 10{sup 21} n {center_dot} cm{sup -2} (E > 1 MeV) in helium at 289 C in the Halden reactor. The results have been used to determine the influence of alloying and impurity elements on the susceptibility of these steels to irradiation-assisted stress corrosion cracking. Fracture toughness J-R curve tests were also conducted on two heats of Type 304 SS that were irradiated to {approx}0.3 x 10{sup 21} n {center_dot} cm{sup -2} in the Halden reactor. Crack-growth-rate tests have been conducted on compact-tension specimens of Alloys 600 and 690 under constant load to evaluate the resistance of these alloys to stress corrosion cracking in LWR environments.

  12. Stress Intensity Factor Solutions for Multiple Edge Cracks in Ceramic Matrix Composites

    NASA Technical Reports Server (NTRS)

    Ghosn, Louis

    1997-01-01

    NASA Lewis Research Center conducted a study to determine the stress intensity factor solutions for periodic arrays of bridged cracks for various crack spacings and crack lengths. Initially, the stress intensity factor of an array of unbridged multiple edge cracks was determined under constant global displacement as well as at a point load along the crack wake. These solutions are expected to contribute toward the development of a damage-based life-prediction methodology for CMC engine components.

  13. Stress corrosion cracking of titanium alloys

    NASA Technical Reports Server (NTRS)

    Statler, G. R.; Spretnak, J. W.; Beck, F. H.; Fontana, M. G.

    1974-01-01

    The effect of hydrogen on the properties of metals, including titanium and its alloys, was investigated. The basic theories of stress corrosion of titanium alloys are reviewed along with the literature concerned with the effect of absorbed hydrogen on the mechanical properties of metals. Finally, the basic modes of metal fracture and their importance to this study is considered. The experimental work was designed to determine the effects of hydrogen concentration on the critical strain at which plastic instability along pure shear directions occurs. The materials used were titanium alloys Ti-8Al-lMo-lV and Ti-5Al-2.5Sn.

  14. Design Criteria for Controlling Stress Corrosion Cracking

    NASA Technical Reports Server (NTRS)

    Franklin, D. B.

    1987-01-01

    This document sets forth the criteria to be used in the selection of materials for space vehicles and associated equipment and facilities so that failure resulting from stress corrosion will be prevented. The requirements established herein apply to all metallic components proposed for use in space vehicles and other flight hardware, ground support equipment, and facilities for testing. These requirements are applicable not only to items designed and fabricated by MSFC (Marshall Space Flight Center) and its prime contractors, but also to items supplied to the prime contractor by subcontractors and vendors.

  15. Stress concentration, stress intensity, and fatigue crack growth along evacuators of pressurized, autofrettaged tubes

    NASA Astrophysics Data System (ADS)

    Parker, A. P.; Underwood, J. H.

    1994-12-01

    A stress analysis has been conducted on a pressurized, fully or partially autofrettaged cylinder with a small diameter evacuator hole penetrating radially through the wall. Pressure was applied on the inside diameter (ID) of the tube, and all or part of this pressure was applied on the evacuator hole surfaces. Total hoop stress concentrations have been determined for a range of radial locations along the evacuator and stress intensity factors have been determined along a crack emanating from the evacuator hole. Fatigue crack growth rates. and hence crack profiles, were predicted at each of the radial locations. These predictions indicate that the critical location for the crack in a non-autofrettaged tube is at the ID, whereas in a fully autofrettaged tube, it is located approximately halfway through the wall thickness. Stress ratio has a significant influence on crack shape in autofrettaged tubes, however, it has a limited effect upon lifetime. The effect of axial residual stresses upon fatigue lifetime due to the autofrettage process has been described and an insignificant reduction in lifetime was a result of such stresses. Finally, the predicted profiles are compared with experimental observations of fatigue crack evacuators, and a limited comparison of predicted and actual lifetimes is presented. Good agreement has been observed in both comparisons.

  16. Stress-corrosion cracking studies in coal-liquefaction systems

    SciTech Connect

    Baylor, V.B.; Keiser, J.R.

    1981-01-01

    Coal liquefaction plants with 6000 ton/d capacity are currently being planned by DOE as a step toward commercial production of synthetic fossil fuels. These plants will demonstrate the large-scale viability of the Solvent Refined Coal (SRC) process, which has been used since 1974 in two operating pilot plants: a 50-ton/d unit at Fort Lewis, Washington, and a 6-ton/d plant in Wilsonville, Alabama. Experience in these plants has shown that austenitic stainless steels are susceptible to stress corrosion cracking associated with residual stresses from cold working or welding. The corrodants responsible for the cracking have not yet been positively identified but are suspected to include polythionic acids and chlorides. To screen candidate materials of construction for resistance to stress corrosion cracking, racks of stressed U-bend specimens in welded and as-wrought conditions have been exposed at the Wilsonville and Fort Lewis SRC pilot plants. These studies have identified alloys that are suitable for critical plant applications.

  17. Separating the Influence of Environment from Stress Relaxation Effects on Dwell Fatigue Crack Growth in a Nickel-Base Disk Alloy

    NASA Technical Reports Server (NTRS)

    Telesman, J.; Gabb, T. P.; Ghosn, L. J.

    2016-01-01

    Both environmental embrittlement and crack tip visco-plastic stress relaxation play a significant role in determining the dwell fatigue crack growth (DFCG) resistance of nickel-based disk superalloys. In the current study performed on the Low Solvus High Refractory (LSHR) disk alloy, the influence of these two mechanisms were separated so that the effects of each could be quantified and modeled. Seven different microstructural variations of LSHR were produced by controlling the cooling rate and the subsequent aging and thermal exposure heat treatments. Through cyclic fatigue crack growth testing performed both in air and vacuum, it was established that four out of the seven LSHR heat treatments evaluated, possessed similar intrinsic environmental resistance to cyclic crack growth. For these four heat treatments, it was further shown that the large differences in dwell crack growth behavior which still persisted, were related to their measured stress relaxation behavior. The apparent differences in their dwell crack growth resistance were attributed to the inability of the standard linear elastic fracture mechanics (LEFM) stress intensity parameter to account for visco-plastic behavior. Crack tip stress relaxation controls the magnitude of the remaining local tensile stresses which are directly related to the measured dwell crack growth rates. It was hypothesized that the environmentally weakened grain boundary crack tip regions fail during the dwells when their strength is exceeded by the remaining local crack tip tensile stresses. It was shown that the classical creep crack growth mechanisms such as grain boundary sliding did not contribute to crack growth, but the local visco-plastic behavior still plays a very significant role by determining the crack tip tensile stress field which controls the dwell crack growth behavior. To account for the influence of the visco-plastic behavior on the crack tip stress field, an empirical modification to the LEFM stress

  18. Stress corrosion cracking in the earth

    NASA Technical Reports Server (NTRS)

    Das, S.; Scholz, C. H.

    1980-01-01

    Two fundamental concepts of fracture mechanics are used to develop a theory of the earthquake mechanism which specifically predicts observed time-dependent rupture phenomena such as slow earthquakes, postseismic rupture growth and afterslip, multiple events, foreshocks, and aftershocks. The theory also predicts that there must be a nucleation stage prior to an earthquake, and suggests a physical mechanism by which one earthquake may trigger another. Investigations show that all earthquakes must be preceded by a quasi-static slip over a portion of the rupture surfaces, although it may be difficult to detect in practice, and a study of delayed multiple events characterizes the strength of some barriers in the earth as having a stress corrosion index of about 24.

  19. Comparison of Stress Corrosion Cracking Susceptibility of Laser Machined and Milled 304 L Stainless Steel

    NASA Astrophysics Data System (ADS)

    Gupta, R. K.; Kumar, Aniruddha; Nagpure, D. C.; Rai, S. K.; Singh, M. K.; Khooha, Ajay; Singh, A. K.; Singh, Amrendra; Tiwari, M. K.; Ganesh, P.; Kaul, R.; Singh, B.

    2016-07-01

    Machining of austenitic stainless steel components is known to introduce significant enhancement in their susceptibility to stress corrosion cracking. The paper compares stress corrosion cracking susceptibility of laser machined 304 L stainless steel specimens with conventionally milled counterpart in chloride environment. With respect to conventionally milled specimens, laser machined specimens displayed more than 12 times longer crack initiation time in accelerated stress corrosion cracking test in boiling magnesium chloride as per ASTM G36. Reduced stress corrosion cracking susceptibility of laser machined surface is attributed to its predominantly ferritic duplex microstructure in which anodic ferrite phase was under compressive stress with respect to cathodic austenite.

  20. Controlling stress corrosion cracking in mechanism components of ground support equipment

    NASA Technical Reports Server (NTRS)

    Majid, W. A.

    1988-01-01

    The selection of materials for mechanism components used in ground support equipment so that failures resulting from stress corrosion cracking will be prevented is described. A general criteria to be used in designing for resistance to stress corrosion cracking is also provided. Stress corrosion can be defined as combined action of sustained tensile stress and corrosion to cause premature failure of materials. Various aluminum, steels, nickel, titanium and copper alloys, and tempers and corrosive environment are evaluated for stress corrosion cracking.

  1. Stress corrosion cracking of metal matrix composites: Modeling and experiment

    SciTech Connect

    Jones, R.H.

    1990-10-01

    The stress corrosion crack growth ate of metal matrix composites has been described by a model which is dependent on the length-to- diameter ({ell}/d) ratio and volume fraction of the reinforcing phase and matrix creep component. The model predicts a large dependence of the stress corrosion crack growth rate of a metal matrix composite on {ell}/d and matrix creep component and a small dependence on the volume fraction of reinforcement. Experimentally determined crack growth rates for 7090 Al/SiC tested in 3.5% NcCl solution, 6061 Al/SiC tested in moist air with NaCl and immersed in NaCl solution, and Mg/Al{sub 2}0{sub 3} tested in a chloride/chromate solution are all consistent with the model. The close correspondence between the model and experiment for a matrix creep stress exponent of 3 suggest that there is little corrosion damage to the reinforcing phase in these systems. 16 refs., 5 figs.

  2. Stress corrosion cracking of candidate waste container materials; Final report

    SciTech Connect

    Park, J.Y.; Maiya, P.S.; Soppet, W.K.; Diercks, D.R.; Shack, W.J.; Kassner, T.F.

    1992-06-01

    Six alloys have been selected as candidate container materials for the storage of high-level nuclear waste at the proposed Yucca mountain site in Nevada. These materials are Type 304L stainless steel (SS). Type 316L SS, Incoloy 825, phosphorus-deoxidized Cu, Cu-30%Ni, and Cu-7%Al. The present program has been initiated to determine whether any of these materials can survive for 300 years in the site environment without developing through-wall stress corrosion cracks. and to assess the relative resistance of these materials to stress corrosion cracking (SCC)- A series of slow-strain-rate tests (SSRTs) and fracture-mechanics crack-growth-rate (CGR) tests was performed at 93{degree}C and 1 atm of pressure in simulated J-13 well water. This water is representative, prior to the widespread availability of unsaturated-zone water, of the groundwater present at the Yucca Mountain site. Slow-strain-rate tests were conducted on 6.35-mm-diameter cylindrical specimens at strain rates of 10-{sup {minus}7} and 10{sup {minus}8} s{sup {minus}1} under crevice and noncrevice conditions. All tests were interrupted after nominal elongation strain of 1--4%. Scanning electron microscopy revealed some crack initiation in virtually all the materials, as well as weldments made from these materials. A stress- or strain-ratio cracking index ranks these materials, in order of increasing resistance to SCC, as follows: Type 304 SS < Type 316L SS < Incoloy 825 < Cu-30%Ni < Cu and Cu-7%Al. Fracture-mechanics CGR tests were conducted on 25.4-mm-thick compact tension specimens of Types 304L and 316L stainless steel (SS) and Incoloy 825. Crack-growth rates were measured under various load conditions: load ratios M of 0.5--1.0, frequencies of 10{sup {minus}3}-1 Hz, rise nines of 1--1000s, and peak stress intensities of 25--40 MPa{center_dot}m {sup l/2}.

  3. Stress corrosion cracking properties of 15-5PH steel

    NASA Technical Reports Server (NTRS)

    Rosa, Ferdinand

    1993-01-01

    Unexpected occurrence of failures, due to stress corrosion cracking (SCC) of structural components, indicate a need for improved characterization of materials and more advanced analytical procedures for reliably predicting structures performance. Accordingly, the purpose of this study was to determine the stress corrosion susceptibility of 15-5PH steel over a wide range of applied strain rates in a highly corrosive environment. The selected environment for this investigation was a highly acidified sodium chloride (NaCl) aqueous solution. The selected alloy for the study was a 15-5PH steel in the H900 condition. The slow strain rate technique was selected to test the metals specimens.

  4. An environmental cracking evaluation of fastener materials for seawater applications

    SciTech Connect

    Aylor, D.M.

    1994-12-31

    Slow strain rate tests (SSRT) were conducted on various nickel-base, titanium base, and copper-nickel (Cu-Ni) alloys in order to identify a replacement material for Alloy K-500 in seawater fastener applications. SSRT data and fracture surface analysis of the test specimens identified a susceptibility to environmental cracking in cathodically polarized environments for Alloy K-500, Alloy 625 Plus, and Alloy 625PH. Alloy 625 Plus exhibited slightly increased environmental cracking resistance-at {minus}850 mV vs. SCE over Alloy K-500 and Alloy 625PH. Ti-6Al-4V ELI, Beta C, and Beta 21S titanium displayed no susceptibility to environmental cracking in freely corroding 3.5% NaCl or cathodically polarized conditions. Precharging these titanium alloys for 8 weeks at {minus}1,250 mV vs. SCE did not adversely affect their environmental cracking resistance. The Cu-3Ni and Cu-15Ni-7Sn spray formed alloys exhibited extensive scatter and low measured maximum loads, presumably due to macroporosity present in the as-fabricated material.

  5. Role of Slip Mode on Stress Corrosion Cracking Behavior

    NASA Astrophysics Data System (ADS)

    Vasudevan, A. K.; Sadananda, K.

    2011-02-01

    In this article, we examine the effect of aging treatment and the role of planarity of slip on stress corrosion cracking (SCC) behavior in precipitation-hardened alloys. With aging, the slip mode can change from a planar slip in the underage (UA) to a wavy slip in the overage (OA) region. This, in turn, results in sharpening the crack tip in the UA compared to blunting in the OA condition. We propose that the planar slip enhances the stress concentration effects by making the alloys more susceptible to SCC. In addition, the planarity of slip enhances plateau velocities, reduces thresholds for SCC, and reduces component life. We show that the effect of slip planarity is somewhat similar to the effects of mechanically induced stress concentrations such as due to the presence of sharp notches. Aging treatment also causes variations in the matrix and grain boundary (GB) microstructures, along with typical mechanical and SCC properties. These properties include yield stress, work hardening rate, fracture toughness K IC , thresholds K Iscc, and steady-state plateau velocity ( da/ dt). The SCC data for a wide range of ductile alloys including 7050, 7075, 5083, 5456 Al, MAR M steels, and solid solution copper-base alloys are collected from the literature. Our assertion is that slip mode and the resulting stress concentration are important factors in SCC behavior. This is further supported by similar observations in many other systems including some steels, Al alloys, and Cu alloys.

  6. Grain-by-grain study of the mechanisms of crack propagation during iodine stress corrosion cracking of Zircaloy-4

    SciTech Connect

    Haddad, R.E.; Dorado, A.O.

    1994-12-31

    This paper describes the tests conducted to determine the conditions leading to cracking of a specified grain of metal, during the iodine stress corrosion cracking (SCC) of zirconium alloys, focusing on the crystallographic orientation of crack paths, the critical stress conditions, and the significance of the fractographic features encountered. In order to perform crystalline orientation of fracture surfaces, a specially heat-treated Zircaloy-4 having very large grains, grown up to the wall thickness, was used. Careful orientation work has proved that intracrystalline pseudo-cleavage occurs only along basal planes. the effects of anisotropy, plasticity, triaxiality, and residual stresses originated in thermal contraction have to be considered to account for the influence of the stress state. A grain-by-grain calculation led to the conclusion that transgranular cracking always takes place on those bearing the maximum resolved tensile stress perpendicular to basal planes. Propagation along twin boundaries has been identified among the different fracture modes encountered.

  7. Ultrasonic inspection reliability for intergranular stress corrosion cracks

    SciTech Connect

    Heasler, P G; Taylor, T T; Spanner, J C; Doctor, S R; Deffenbaugh, J D

    1990-07-01

    A pipe inspection round robin entitled Mini-Round Robin'' was conducted at Pacific Northwest Laboratory from May 1985 through October 1985. The research was sponsored by the US Nuclear Regulatory Commission, Office of Nuclear Regulatory Research under a program entitled Evaluation and Improvement of NDE Reliability for Inservice Inspection of Light Water Reactors.'' The Mini-Round Robin (MRR) measured the intergranular stress corrosion (GSC) crack detection and sizing capabilities of inservice inspection (ISI) inspectors that had passed the requirements of IEB 83-02 and the Electric Power Research Institute (EPRI) sizing training course. The MRR data base was compared with an earlier Pipe Inspection Round Robin (PIRR) that had measured the performance of inservice inspection prior to 1982. Comparison of the MRR and PIRR data bases indicates no significant change in the inspection capability for detecting IGSCC. Also, when comparing detection of long and short cracks, no difference in detection capability was measured. An improvement in the ability to differentiate between shallow and deeper IGSCC was found when the MRR sizing capability was compared with an earlier sizing round robin conducted by the EPRI. In addition to the pipe inspection round robin, a human factors study was conducted in conjunction with the Mini-Round Robin. The most important result of the human factors study is that the Relative Operating Characteristics (ROC) curves provide a better methodology for describing inspector performance than only probability of detection (POD) or single-point crack/no crack data. 6 refs., 55 figs., 18 tabs.

  8. Radiation enhancement of stress-corrosion cracking of Zircaloy

    SciTech Connect

    Shann, S.H.

    1981-09-01

    In order to examine the cause of the reactor fuel pin pellet-cladding interaction phenomenon (PCI), stress corrosion cracking (SCC) experiments of Zircaloy under iodine, iron iodide, aluminum iodide, cesium iodide, and cadmium were undertaken. Radiation enhancement tests with CsI were also performed. Iodine, iron iodide, and aluminum iodide can reduce the failure times. Fractography is of cleavage type and is completely different from the ductile dimple type failure for control specimens. There exists a critical stress of 379 MPa for iodine and iron iodide above which burst type failure occurs. Pinhole type failure predominates for lower stresses. Both types showed brittle fracture surfaces. The presence of CsI did not have any influence on failure time of zircaloy. The failure is burst-type, and the fractography is ductile. Radiation enhancement tests with cesium iodide did not cause reduction in failure time either. Failure times were decreased for the tests under cadmium. All specimens failed under cadmium vapor by a burst mode, and fractography showed cleavage brittle characteristics. Chemical parameters such as reaction order, activation energy, and minimum pressure required for SCC were determined. A crack propagation more originally designed for brittle solids for the SCC experimental data well. Variable stresses and surface roughness test results can be correlated quantitatively by the model. 80 figures.

  9. Variation of crack-opening stresses in three-dimensions - Finite thickness plate

    NASA Technical Reports Server (NTRS)

    Chermahini, R. G.; Blom, A. F.

    1991-01-01

    A 3D elastic-plastic finite-element analysis is conducted to study crack-growth behavior of thin and thick center-cracked specimens under constant-amplitude loading conditions. The numerical analysis and the specimen configuration and loading are described for both the thin and thick conditions. Stabilized crack-opening stresses of interior and exterior regions are given as are the closure and opening profiles of the crack-surface plane after the tenth cycle. The effect of thickness is discussed with respect to the crack-opening stress levels and the plastic zones of the interior and exterior regions. A load-reduced-displacement technique allows the calculation of the crack-opening stresses at three locations on the crack surface plane. The constraint effect related to thickness gives a lower stabilized crack-opening stress level for the thick specimens.

  10. A review of irradiation assisted stress corrosion cracking

    NASA Astrophysics Data System (ADS)

    Scott, P.

    1994-08-01

    The aim of this review is to assess from the available data whether irradiation in PWR primary water can adversely affect the properties of stainless steels due to irradiation assisted stress corrosion cracking (IASCC). The following aspects are examined: (i) Irradiation damage of the material, (ii) The influence of water radiolysis. Since the irradiation damage processes are similar for both PWR and BWR systems, differences observed in the intergranular cracking properties of core components of both systems must be attributable to differences in the synergistic interactions with the coolant chemistry. These aspects are analysed in detail to determine to what extent BWR experience can be used to predict IASCC in PWR core components. Several related potential failure mechanisms are also reviewed such as radiation hardening, radiation creep and helium or hydrogen embrittlement. The probable role of some or all of these failure mechanisms in core component failures observed to date, and in experiments ostensibly designed to observe IASCC, is critically examined.

  11. Quasi-static intergranular cracking in a Cu-Sn alloy: An analog of stress relief cracking of steels

    SciTech Connect

    Barrera, E.V.; Menyhard, M.; Bika, D.; Rothman, B.; McMahon, C.J. Jr.

    1991-01-01

    Intergranular cracking in a laboratory-made Cu-8wt%Sn alloy at 265 to 300{degree}C in vacuum was studied in order to explore the hypothesis that this could serve as an analog to the brittle mode of stress-relief cracking in steels and to test the mechanism proposed earlier to explain that phenomenon. This mechanism involves the stress-induced intergranular penetration along grain boundaries of a surface-adsorbed embrittling element. Sulfur is the active element in this regard in steels, and tin was envisioned as playing the same role in Cu-Sn alloys. Auger spectroscopy was used to confirm earlier reports of the surface activity of tin and to determine the segregation kinetics in the present polycrystals; no other elements were found to segregate to surfaces to any significant degree in the present alloy. Crack growth measurements showed that intergranular cracking occurs in an intermittent manner at an average rate on the order of 0.1 {mu}m/sec over a range of crack length. Crack initiation was found to be remarkably sensitive to the stress intensity, implying the existence of a threshold. The fracture appearance in the regions of slow crack growth was similar to that observed in steels undergoing stress-relief cracking at 500--600{degree}C. It was concluded that the quasi-static intergranular cracking in the steels and in the Cu-Sn alloy represent two aspects of the same generic phenomenon and that the proposed mechanism of stress-induced intergranular impurity penetration is valid. It is believed that liquid-and solid-metal embrittlement are closely related to the type of intergranular cracking described here.

  12. Quasi-static intergranular cracking in a Cu-Sn alloy: An analog of stress relief cracking of steels

    SciTech Connect

    Barrera, E.V.; Menyhard, M.; Bika, D.; Rothman, B.; McMahon, C.J. Jr.

    1991-12-31

    Intergranular cracking in a laboratory-made Cu-8wt%Sn alloy at 265 to 300{degree}C in vacuum was studied in order to explore the hypothesis that this could serve as an analog to the brittle mode of stress-relief cracking in steels and to test the mechanism proposed earlier to explain that phenomenon. This mechanism involves the stress-induced intergranular penetration along grain boundaries of a surface-adsorbed embrittling element. Sulfur is the active element in this regard in steels, and tin was envisioned as playing the same role in Cu-Sn alloys. Auger spectroscopy was used to confirm earlier reports of the surface activity of tin and to determine the segregation kinetics in the present polycrystals; no other elements were found to segregate to surfaces to any significant degree in the present alloy. Crack growth measurements showed that intergranular cracking occurs in an intermittent manner at an average rate on the order of 0.1 {mu}m/sec over a range of crack length. Crack initiation was found to be remarkably sensitive to the stress intensity, implying the existence of a threshold. The fracture appearance in the regions of slow crack growth was similar to that observed in steels undergoing stress-relief cracking at 500--600{degree}C. It was concluded that the quasi-static intergranular cracking in the steels and in the Cu-Sn alloy represent two aspects of the same generic phenomenon and that the proposed mechanism of stress-induced intergranular impurity penetration is valid. It is believed that liquid-and solid-metal embrittlement are closely related to the type of intergranular cracking described here.

  13. Surface Cracking and Interface Reaction Associated Delamination Failure of Thermal and Environmental Barrier Coatings

    NASA Technical Reports Server (NTRS)

    Zhu, Dong-Ming; Choi, Sung R.; Eldridge, Jeffrey I.; Lee, Kang N.; Miller, Robert A.

    2003-01-01

    In this paper, surface cracking and interface reactions of a BSAS coating and a multi-layer ZrO2-8wt%Y2O3 and mullite/BSAS/Si thermal and environmental barrier coating system on SiC/SiC ceramic matrix composites were characterized after long-term combined laser thermal gradient and furnace cyclic tests in a water vapor containing environment. The surface cracking was analyzed based on the coating thermal gradient sintering behavior and thermal expansion mismatch stress characteristics under the thermal cyclic conditions. The interface reactions, which were largely enhanced by the coating surface cracking in the water vapor environment, were investigated in detail, and the reaction phases were identified for the coating system after the long-term exposure. The accelerated coating delamination failure was attributed to the increased delamination driving force under the thermal gradient cyclic loading and the reduced interface adhesion due to the detrimental interface reactions.

  14. Surface Cracking and Interface Reaction Associated Delamination Failure of Thermal and Environmental Barrier Coatings

    NASA Technical Reports Server (NTRS)

    Zhu, Dongming; Choi, Sung R.; Eldridge, Jeffrey I.; Lee, Kang N.; Miller, Robert A.

    2003-01-01

    In this paper, surface cracking and interface reactions of a BSAS coating and a multi-layer ZTO2-8wt%Y2O3 and mullite/BSAS/Si thermal and environmental barrier coating system on SiC/SiC ceramic matrix composites were characterized after long-term combined laser thermal gradient and furnace cyclic tests in a water vapor containing environment. The surface cracking was analyzed based on the coating thermal gradient sintering behavior and thermal expansion mismatch stress characteristics under the thermal cyclic conditions. The interface reactions, which were largely enhanced by the coating surface cracking in the water vapor environment, were investigated in detail, and the reaction phases were identified for the coating system after the long- term exposure. The accelerated coating delamination failure was attributed to the increased delamination driving force under the thermal gradient cyclic loading and the reduced interface adhesion due to the detrimental interface reactions.

  15. Critical stress for stress corrosion cracking of duplex stainless steel in sour environments

    SciTech Connect

    Miyasaka, A.; Kanamaru, T.; Ogawa, H.

    1996-08-01

    The critical stress for initiation of stress corrosion cracking (SCC) of a duplex stainless steel (DSS) in a sour environment was investigated using three stress application techniques: constant-strain, constant-load, and slow strain rate testing (SSRT). The critical stresses for SCC initiation as determined by detailed observation of the alloy surface after the three tests were in good agreement when a newly proposed index was adopted to express the SSRT results combined with crack observations for each test. The effect of cold work (CW) on SCC and pitting resistance of the DSS also was studied. CW did not accelerate SCC when initiation was controlled by pitting. The critical stress for SCC initiation increased with increasing CW and the resultant increase in yield stress.

  16. Environmental fatigue of an Al-Li-Cu alloy. Part 3: Modeling of crack tip hydrogen damage

    NASA Technical Reports Server (NTRS)

    Piascik, Robert S.; Gangloff, Richard P.

    1992-01-01

    Environmental fatigue crack propagation rates and microscopic damage modes in Al-Li-Cu alloy 2090 (Parts 1 and 2) are described by a crack tip process zone model based on hydrogen embrittlement. Da/dN sub ENV equates to discontinuous crack advance over a distance, delta a, determined by dislocation transport of dissolved hydrogen at plastic strains above a critical value; and to the number of load cycles, delta N, required to hydrogenate process zone trap sites that fracture according to a local hydrogen concentration-tensile stress criterion. Transgranular (100) cracking occurs for process zones smaller than the subgrain size, and due to lattice decohesion or hydride formation. Intersubgranular cracking dominates when the process zone encompasses one or more subgrains so that dislocation transport provides hydrogen to strong boundary trapping sites. Multi-sloped log da/dN-log delta K behavior is produced by process zone plastic strain-hydrogen-microstructure interactions, and is determined by the DK dependent rates and proportions of each parallel cracking mode. Absolute values of the exponents and the preexponential coefficients are not predictable; however, fractographic measurements theta sub i coupled with fatigue crack propagation data for alloy 2090 established that the process zone model correctly describes fatigue crack propagation kinetics. Crack surface films hinder hydrogen uptake and reduce da/dN and alter the proportions of each fatigue crack propagation mode.

  17. Effect of corrosion and stress-corrosion cracking on pipe integrity and remaining life

    SciTech Connect

    Jaske, C.E.; Beavers, J.A.

    1996-07-01

    Process piping is often exposed to corrosive fluids. During service, such exposure may cause localized corrosion or stress-corrosion cracking that affects structural integrity. This paper presents a model that quantifies the effect of localized corrosion and stress-corrosion cracking on pipe failure stress. The model is an extension of those that have been developed for oil and gas pipelines. It accounts for both axial and hoop stress. Cracks are modeled using inelastic fracture mechanics. Both flow-stress and fracture-toughness dependent failure modes are addressed. Corrosion and crack-growth rates are used to predict remaining service life.

  18. Stress corrosion cracking of admiralty brass condenser tubes

    SciTech Connect

    Howell, A.G. ); Kendall, D. )

    1993-12-01

    Sodium sulfite is used routinely for removing traces of oxygen from the water in low- and moderate-pressure boilers. Sodium sulfite is unacceptable for use in higher pressure boilers because it will decompose, which will release acidic gases into the steam and increase corrosion of after-boiler components. However, even in moderate-pressure boilers, one of the products of sulfite decomposition, moist sulfur dioxide, can cause stress corrosion cracking (SCC) of copper alloys. Monitoring the degree of sulfite decomposition in a specific boiler and controlling the factors that promote decomposition will reduce the likelihood and severity of SCC.

  19. Low-pH stress corrosion crack propagation in API X-65 line pipe steel

    SciTech Connect

    Harle, B.A.; Beavers, J.A. )

    1993-10-01

    Preliminary results of ongoing crack growth studies being performed on an API X-65 line pipe steel in a low-pH cracking environment were reported. Objectives were to reproduce low-pH crack propagation in the laboratory, to identify a crack driving force parameter, and to evaluate the influence of environmental and mechanical parameters on crack growth. A J-integral test technique was used in the study. Significant crack growth was observed. The parameter J appeared to be a good driving force parameter to describe crack growth.

  20. FITNESS-FOR-SERVICE ASSESSMENT FOR A RADIOACTIVE WASTE TANK THAT CONTAINS STRESS CORROSION CRACKS

    SciTech Connect

    Wiersma, B; James Elder, J; Rodney Vandekamp, R; Charles Mckeel, C

    2009-04-23

    Radioactive wastes are confined in 49 underground storage tanks at the Savannah River Site. The tanks are examined by ultrasonic (UT) methods for thinning, pitting, and stress corrosion cracking in order to assess fitness-for-service. During an inspection in 2002, ten cracks were identified on one of the tanks. Given the location of the cracks (i.e., adjacent to welds, weld attachments, and weld repairs), fabrication details (e.g., this tank was not stress-relieved), and the service history the degradation mechanism was stress corrosion cracking. Crack instability calculations utilizing API-579 guidance were performed to show that the combination of expected future service condition hydrostatic and weld residual stresses do not drive any of the identified cracks to instability. The cracks were re-inspected in 2007 to determine if crack growth had occurred. During this re-examination, one indication that was initially reported as a 'possible perpendicular crack <25% through wall' in 2002, was clearly shown not to be a crack. Additionally, examination of a new area immediately adjacent to other cracks along a vertical weld revealed three new cracks. It is not known when these new cracks formed as they could very well have been present in 2002 as well. Therefore, a total of twelve cracks were evaluated during the re-examination. Comparison of the crack lengths measured in 2002 and 2007 revealed that crack growth had occurred in four of the nine previously measured cracks. The crack length extension ranged from 0.25 to 1.8 inches. However, in all cases the cracks still remained within the residual stress zone (i.e., within two to three inches of the weld). The impact of the cracks that grew on the future service of Tank 15 was re-assessed. API-579 crack instability calculations were again performed, based on expected future service conditions and trended crack growth rates for the future tank service cycle. The analysis showed that the combined hydrostatic and weld

  1. Effects of loading on the growth rates of deep stress-corrosion cracks

    SciTech Connect

    Beavers, J.A.; Christman, T.K.

    1990-08-01

    The goal of this research program was to determine the effects of loading on growth of stress-corrosion cracks (SCC) in line pipe steel and whether special loading procedures could actually inhibit crack growth. Of particular interest was the effect of hydrostatic retesting on the subsequent growth of existing cracks. The growth rate experiments showed that the slow-strain rate loading could successfully nucleate a group of fine cracks with depths up to 0.025 inches (0.64 mm). However, the subsequent cyclic loading at typical operating stress levels (lower than experienced during the slow- strain rate loading) produced minimal crack growth and stopped soon after the test was started. The limited growth is believed to be a real phenomenon which means this is not a suitable procedure for the measurement of average crack growth rates. These experiments indicate that cracks grown at high stress (as in the slow-strain rate phase) do not readily propagate at lower stress levels. This may be because of crack closure (compressive crack tip residual stress) induced by the initial higher stress level. If that is true, then hydrostatic retests could inhibit the growth of existing stress-corrosion cracks, especially if the hydrostatic tests are conducted at high stress levels. 15 figures, 3 tabs.

  2. Assessment of NDE methods for detecting cracks and damage in environmental barrier coated CMC tested under tension

    NASA Astrophysics Data System (ADS)

    Abdul-Aziz, Ali; Wroblewski, Adam C.; Bhatt, Ramakrishna T.; Jaskowiak, Martha H.; Gorican, Daniel; Rauser, Richard W.

    2015-03-01

    For validating physics based analytical models predicting spallation life of environmental barrier coating (EBC) on fiber reinforced ceramic matrix composites, the fracture strength of EBC and kinetics of crack growth in EBC layers need to be experimentally determined under engine operating conditions. In this study, a multi layered barium strontium aluminum silicate (BSAS) based EBC-coated, melt infiltrated silicon carbide fiber reinforced silicon carbide matrix composite (MI SiC/SiC) specimen was tensile tested at room temperature. Multiple tests were performed on a single specimen with increasing predetermined stress levels until final failure. During loading, the damage occurring in the EBC was monitored by digital image correlation (DIC). After unloading from the predetermined stress levels, the specimen was examined by optical microscopy and computed tomography (CT). Results indicate both optical microscopy and CT could not resolve the primary or secondary cracks developed during tensile loading until failure. On the other hand, DIC did show formation of a primary crack at ~ 50% of the ultimate tensile strength and this crack grew with increasing stress and eventually led to final failure of the specimen. Although some secondary cracks were seen in the DIC strain plots prior to final failure, the existence of these cracks were not confirmed by other methods. By using a higher resolution camera, it is possible to improve the capability of DIC in resolving secondary cracks and damage in coated specimen tested at room temperature, but use of DIC at high temperature requires significant development. Based on the current data, it appears that both optical microscopy and CT do not offer any hope for detecting crack initiation or determining crack growth in EBC coated CMC tested at room or high temperatures after the specimen has been unloaded. Other methods such as, thermography and optical/SEM of the polished cross section of EBC coated CMC specimens stressed to

  3. Stress corrosion cracking of several high strength ferrous and nickel alloys

    NASA Technical Reports Server (NTRS)

    Nelson, E. E.

    1971-01-01

    The stress corrosion cracking resistance of several high strength ferrous and nickel base alloys has been determined in a sodium chloride solution. Results indicate that under these test conditions Multiphase MP35N, Unitemp L605, Inconel 718, Carpenter 20Cb and 20Cb-3 are highly resistant to stress corrosion cracking. AISI 410 and 431 stainless steels, 18 Ni maraging steel (250 grade) and AISI 4130 steel are susceptible to stress corrosion cracking under some conditions.

  4. Fatigue Crack Growth Rate and Stress-Intensity Factor Corrections for Out-of-Plane Crack Growth

    NASA Technical Reports Server (NTRS)

    Forth, Scott C.; Herman, Dave J.; James, Mark A.

    2003-01-01

    Fatigue crack growth rate testing is performed by automated data collection systems that assume straight crack growth in the plane of symmetry and use standard polynomial solutions to compute crack length and stress-intensity factors from compliance or potential drop measurements. Visual measurements used to correct the collected data typically include only the horizontal crack length, which for cracks that propagate out-of-plane, under-estimates the crack growth rates and over-estimates the stress-intensity factors. The authors have devised an approach for correcting both the crack growth rates and stress-intensity factors based on two-dimensional mixed mode-I/II finite element analysis (FEA). The approach is used to correct out-of-plane data for 7050-T7451 and 2025-T6 aluminum alloys. Results indicate the correction process works well for high DeltaK levels but fails to capture the mixed-mode effects at DeltaK levels approaching threshold (da/dN approximately 10(exp -10) meter/cycle).

  5. Effects of weld residual stresses on crack-opening area analysis of pipes for LBB applications

    SciTech Connect

    Dong, P.; Rahman, S.; Wilkowski, G.

    1997-04-01

    This paper summarizes four different studies undertaken to evaluate the effects of weld residual stresses on the crack-opening behavior of a circumferential through-wall crack in the center of a girth weld. The effect of weld residual stress on the crack-opening-area and leak-rate analyses of a pipe is not well understood. There are no simple analyses to account for these effects, and, therefore, they are frequently neglected. The four studies involved the following efforts: (1) Full-field thermoplastic finite element residual stress analyses of a crack in the center of a girth weld, (2) A comparison of the crack-opening displacements from a full-field thermoplastic residual stress analysis with a crack-face pressure elastic stress analysis to determine the residual stress effects on the crack-opening displacement, (3) The effects of hydrostatic testing on the residual stresses and the resulting crack-opening displacement, and (4) The effect of residual stresses on crack-opening displacement with different normal operating stresses.

  6. Environmentally assisted cracking in light water reactors. Semiannual report July 1996--December 1996

    SciTech Connect

    Chopra, O.K.; Chung, H.M.; Gavenda, D.J.

    1997-10-01

    This report summarizes work performed by Argonne National Laboratory on fatigue and environmentally assisted cracking (EAC) in light water reactors from July 1996 to December 1996. Topics that have been investigated include (a) fatigue of carbon, low-alloy, and austenitic stainless steels (SSs) used in reactor piping and pressure vessels, (b) irradiation-assisted stress corrosion cracking of Type 304 SS, (c) EAC of Alloy 600, and (d) characterization of residual stresses in welds of boiling water reactor (BWR) core shrouds by numerical models. Fatigue tests were conducted on ferritic and austenitic SSs in water that contained various concentrations of dissolved oxygen to determine whether a slow strain rate applied during various portions of a tensile-loading cycle are equally effective in decreasing fatigue life. Slow-strain-rate-tensile tests were conducted in simulated BWR water at 288 C on SS specimens irradiated to a low fluence in the Halden reactor and the results were compared with similar data from a control-blade sheath and neutron-absorber tubes irradiated in BWRs to the same fluence level. Crack-growth-rate tests were conducted on compact-tension specimens from a low-carbon content heat of Alloy 600 in high-purity oxygenated water at 289 C. Residual stresses and stress intensity factors were calculated for BWR core shroud welds.

  7. Defenseive Structuring and Environmental Stress

    ERIC Educational Resources Information Center

    Siegel, Bernard J.

    1970-01-01

    This essay explores a kind of adaptation, referred to as defenseive structuring, that recurs with great regularity among groups that perceive themselves as exposed to environmental stress of long duration with which they cannot cope directly and aggressively." (Author)

  8. Susceptibility of Inconel X-750 to stress corrosion cracking

    SciTech Connect

    Mishra, B.

    1986-01-01

    High strength, age hardenable Ni-base superalloy Inconel X-750 in susceptible to severe intergranular stress corrosion cracking (IGSCC) when used in the triple heat treated condition. In this research, constant strain rate technique was employed to evaluate the stress corrosion cracking susceptibility of alloy X-750 under simulated pressurized water reactor conditions in a nuclear power plant using an automated autoclave system at 8 x 10/sup 6/ N/m/sup 2/ pressure and 289/sup 0/C temperature. The alloy produced via ESR and VAR processing routes containing .004% and .011% sulfur, respectively, were solution annealed at 1075 and 1240/sup 0/C for 2 hours and water quenched followed by aging in the 704 to 871/sup 0/C temperature range up to 200 hours and cooled in air as well as the furnace. Complete grain boundary chemistry and precipitation morphology was studied, supported by observations made using Charpy impact and modified Huey tests. Results showed Inconel X-750 processed through electroslag refining, solution annealed at 1240/sup 0/C for 2 hours and water quenched followed by aging at 871/sup 0/C for 200 hours and furnace cooling, provides the best combination of strength, ductility, and resistance to SCC.

  9. OBSERVATIONS AND IMPLICATIONS OF INTERGRANULAR STRESS CORROSION CRACK GROWTH OF ALLOY 152 WELD METALS IN SIMULATED PWR PRIMARY WATER

    SciTech Connect

    Toloczko, Mychailo B.; Olszta, Matthew J.; Overman, Nicole R.; Bruemmer, Stephen M.

    2013-08-15

    Significant intergranular (IG) crack growth during stress corrosion cracking (SCC) tests has been documented during tests in simulated PWR primary water on two alloy 152 specimens cut from a weldment produced by ANL. The cracking morphology was observed to change from transgranular (TG) to mixed mode (up to ~60% IG) during gentle cycling and cycle + hold loading conditions. Measured crack growth rates under these conditions often suggested a moderate degree of environmental enhancement consistent with faster growth on grain boundaries. However, overall SCC propagation rates at constant stress intensity (K) or constant load were very low in all cases. Initial SCC rates up to 6x10-9 mm/s were occasionally measured, but constant K/load growth rates dropped below ~1x10-9 mm/s with time even when significant IG engagement existed. Direct comparisons were made among loading conditions, measured crack growth response and cracking morphology during each test to assess IGSCC susceptibility of the alloy 152 specimens. These results were analyzed with respect to our previous SCC crack growth rate measurements on alloy 152/52 welds.

  10. Resolved shear stress intensity coefficient and fatigue crack growth in large crystals

    NASA Technical Reports Server (NTRS)

    Chen, QI; Liu, Hao-Wen

    1988-01-01

    Fatigue crack growth in large grain Al alloy was studied. Fatigue crack growth is caused primarily by shear decohesion due to dislocation motion in the crack tip region. The crack paths in the large crystals are very irregular and zigzag. The crack planes are often inclined to the loading axis both in the inplane direction and the thickness direction. The stress intensity factors of such inclined cracks are approximated from the two dimensional finite element calculations. The plastic deformation in a large crystal is highly anisotropic, and dislocation motion in such crystals are driven by the resolved shear stress. The resolved shear stress intensity coefficient in a crack solid, RSSIC, is defined, and the coefficients for the slip systems at a crack tip are evaluated from the calculated stress intensity factors. The orientations of the crack planes are closely related to the slip planes with the high RSSIC values. If a single slip system has a much higher RSSIC than all the others, the crack will follow the slip plane, and the slip plane becomes the crack plane. If two or more slip systems have a high RSSIC, the crack plane is the result of the decohesion processes on these active slip planes.

  11. Ambient temperature stress-corrosion cracking of sensitized stainless steels. [PWR

    SciTech Connect

    Sieradzki, K.; Isaacs, H.S.; Newman, R.C.

    1982-01-01

    Stress-corrosion cracking of sensitized Type 304 steel in low temperature borated water has been observed. The probable role of low levels of chloride ions or sulfur-containing ions is described, including the relationship of the phenomenon to polythionic acid cracking. The mechanism of the sulfur-induced cracking and its usefulness as a test for sensitization are outlined.

  12. Local delamination in laminates with angle ply matrix cracks. Part 1: Tension tests and stress analysis

    NASA Technical Reports Server (NTRS)

    Obrien, T. Kevin; Hooper, S. J.

    1991-01-01

    Quasi-static tension tests were conducted on AS4/3501-6 graphite epoxy laminates. Dye penetrant enhanced x-radiography was used to document the onset of matrix cracking and the onset of local delaminations at the intersection of the matrix cracks and the free edge. Edge micrographs taken after the onset of damage were used to verify the location of the matrix cracks and local delamination through the laminate thickness. A quasi-3D finite element analysis was conducted to calculate the stresses responsible for matrix cracking in the off-axis plies. Laminated plate theory indicated that the transverse normal stresses were compressive. However, the finite element analysis yielded tensile transverse normal stresses near the free edge. Matrix cracks formed in the off-axis plies near the free edge where in-plane transverse stresses were tensile and had their greatest magnitude. The influence of the matrix crack on interlaminar stresses is also discussed.

  13. Measuring Environmental Stress

    ERIC Educational Resources Information Center

    Walker, John E.; Dahm, Douglas B.

    1975-01-01

    Infrared remote sensors, plus photometric interpretation and digital data analysis are being used to record the stresses on air, water, vegetation and soil. Directly recorded photographic information has been the most effective recording media for remote sensing. (BT)

  14. Review of environmental effects on fatigue crack growth of austenitic stainless steels.

    SciTech Connect

    Shack, W. J.; Kassner, T. F.; Energy Technology

    1994-07-11

    Fatigue and environmentally assisted cracking of piping, pressure vessel cladding, and core components in light water reactors are potential concerns to the nuclear industry and regulatory agencies. The degradation processes include intergranular stress corrosion cracking of austenitic stainless steel (SS) piping in boiling water reactors (BWRs), and propagation of fatigue or stress corrosion cracks (which initiate in sensitized SS cladding) into low-alloy ferritic steels in BWR pressure vessels. Crack growth data for wrought and cast austenitic SSs in simulated BWR water, developed at Argonne National Laboratory under US Nuclear Regulatory Commission sponsorship over the past 10 years, have been compiled into a data base along with similar data obtained from the open literature. The data were analyzed to develop corrosion-fatigue curves for austenitic SSs in aqueous environments corresponding to normal BWR water chemistries, for BWRs that add hydrogen to the feedwater, and for pressurized water reactor primary-system-coolant chemistry. The corrosion-fatigue data and curves in water were compared with the air line in Section XI of the ASME Code.

  15. Environmental fatigue of an Al-Li-Cu alloy. Part 2: Microscopic hydrogen cracking processes

    NASA Technical Reports Server (NTRS)

    Piascik, Robert S.; Gangloff, Richard P.

    1992-01-01

    Based on a fractographic analysis of fatigue crack propagation (FCP) in Al-Li-Cu alloy 2090 stressed in a variety of inert and embrittling environments, microscopic crack paths are identified and correlated with intrinsic da/dN-delta K kinetics. FCP rates in 2090 are accelerated by hydrogen producing environments (pure water vapor, moist air, and aqueous NaCl), as defined in Part 1. For these cases, subgrain boundary fatigue cracking (SGC) dominates for delta K values where the crack tip process zone, a significant fraction of the cyclic plastic zone, is sufficiently large to envelop 5 micron subgrains in the unrecrystallized microstructure. SGC may be due to strong hydrogen trapping at T1 precipitates concentrated at sub-boundaries. At low delta K, the plastic zone diameter is smaller than the subgrain size and FCP progresses along (100) planes due to either local lattice decohesion or aluminum-lithium hydride cracking. For inert environments (vacuum, helium, and oxygen), or at high delta K where the hydrogen effect on da/dN is small, FCP is along (111) slip planes; this mode does not transition with increasing delta K and plastic zone size. The SGC and (100) crystallographic cracking modes, and the governing influence of the crack tip process zone volume (delta K), support hydrogen embrittlement rather than a surface film rupture and anodic dissolution mechanism for environmental FCP. Multi-sloped log da/dN-log delta K behavior is produced by changes in process zone hydrogen-microstructure interactions, and not by purely micromechanical-microstructure interactions, in contradiction to microstructural distance-based fatigue models.

  16. Role of Internal Stresses on the Incubation Times during Stress Corrosion Cracking

    NASA Astrophysics Data System (ADS)

    Vasudevan, A. K.; Sadananda, K.

    2011-02-01

    We have examined the incubation times in two alloys, 7075-T651 aluminum alloy and 4140 steel, as a function of applied K, using the published data in aqueous environment. The role of overloads was compared with the results from those without overloads, for a given environment. Effect of environment (NaCl vs deionized water) was also examined. The results show that in a constant K test, the incubation time increases with decreasing K. When a single overload cycle was applied, the time increased with percent overload for a constant background K, indicating that overload cycle affected the crack tip driving forces. These effects varied with the environment. The changes in the incubation times are analyzed considering one-to-one correspondence between the crack tip driving force and the times. Overloads contributed to compressive residual or internal stresses, thereby affecting the crack tip driving force. The stresses are related to changes in the plastic zone (PZ) sizes formed before and after the overloads. The effective stress intensity due to internal stress, K int, is defined and is shown to be a function of PZ size. Similarly, condition for crack initiation is expressed as K total = K app ± K int ≥ K Iscc. A detailed methodology for the determination of K int is outlined.

  17. STUDY OF GRAIN BOUNDARY CHARACTER ALONG INTERGRANULAR STRESS CORROSION CRACK PATHS IN AUSTENITIC ALLOYS

    SciTech Connect

    Guertsman, Valery Y.; Bruemmer, Stephen M.

    2001-05-25

    Samples of austenitic stainless alloys were examined by means of scanning and transmission electron microscopy. Misorientations were measured by electron backscattered diffraction. Grain boundary distributions were analyzed with special emphasis on the grain boundary character along intergranular stress-corrosion cracks and at crack arrest points. It was established that only coherent twin S3 boundaries could be considered as "special" ones with regard to crack resistance. However, it is possible that twin interactions with random grain boundaries may inhibit crack propagation. The results suggest that other factors besides geometrical ones play an important role in the intergranular stress-corrosion cracking of commercial alloys.

  18. Fatigue crack growth in 2024-T3 aluminum under tensile and transverse shear stresses

    NASA Technical Reports Server (NTRS)

    Viz, Mark J.; Zehnder, Alan T.

    1994-01-01

    The influence of transverse shear stresses on the fatigue crack growth rate in thin 2024-T3 aluminum alloy sheets is investigated experimentally. The tests are performed on double-edge cracked sheets in cyclic tensile and torsional loading. This loading generates crack tip stress intensity factors in the same ratio as the values computed for a crack lying along a lap joint in a pressurized aircraft fuselage. The relevant fracture mechanics of cracks in thin plates along with the details of the geometrically nonlinear finite element analyses used for the test specimen calibration are developed and discussed. Preliminary fatigue crack growth data correlated using the fully coupled stress intensity factor calibration are presented and compared with fatigue crack growth data from pure delta K(sub I)fatigue tests.

  19. Stress Corrosion Cracking Behavior of Alloy 22 in Multi-Ionic Aqueous Environments

    SciTech Connect

    K.J. King; J.C. Estill; R.B. Rebak

    2002-07-15

    The US Department of Energy is characterizing a potential repository site for nuclear waste in Yucca Mountain (NV). In its current design, the nuclear waste containers consist of a double metallic layer. The external layer would be made of NO6022 or Alloy 22 (Ni-22Cr-13Mo-3W-3Fe). Since over their lifetime, the containers may be exposed to multi-ionic aqueous environments, a potential degradation mode of the outer layer could be environmentally assisted cracking (EAC) or stress corrosion cracking (SCC). In general, Alloy 22 is extremely resistant to SCC, especially in concentrated chloride solutions. Current results obtained through slow strain rate testing (SSRT) shows that Alloy 22 may suffer SCC in simulated concentrated water (SCW) at applied potentials approximately 400 mV more anodic than the corrosion potential (E{sub rr}).

  20. Slow Crack Growth of Brittle Materials With Exponential Crack-Velocity Formulation. Part 2; Constant Stress Rate Experiments

    NASA Technical Reports Server (NTRS)

    Choi, Sung R.; Nemeth, Noel N.; Gyekenyesi, John P.

    2002-01-01

    The previously determined life prediction analysis based on an exponential crack-velocity formulation was examined using a variety of experimental data on glass and advanced structural ceramics in constant stress rate and preload testing at ambient and elevated temperatures. The data fit to the relation of strength versus the log of the stress rate was very reasonable for most of the materials. Also, the preloading technique was determined equally applicable to the case of slow-crack-growth (SCG) parameter n greater than 30 for both the power-law and exponential formulations. The major limitation in the exponential crack-velocity formulation, however, was that the inert strength of a material must be known a priori to evaluate the important SCG parameter n, a significant drawback as compared with the conventional power-law crack-velocity formulation.

  1. Stress Corrosion Cracking and Fatigue Crack Growth Studies Pertinent to Spacecraft and Booster Pressure Vessels

    NASA Technical Reports Server (NTRS)

    Hall, L. R.; Finger, R. W.

    1972-01-01

    This experimental program was divided into two parts. The first part evaluated stress corrosion cracking in 2219-T87 aluminum and 5Al-2.5Sn (ELI) titanium alloy plate and weld metal. Both uniform height double cantilever beam and surface flawed specimens were tested in environments normally encountered during the fabrication and operation of pressure vessels in spacecraft and booster systems. The second part studied compatibility of material-environment combinations suitable for high energy upper stage propulsion systems. Surface flawed specimens having thicknesses representative of minimum gage fuel and oxidizer tanks were tested. Titanium alloys 5Al-2.5Sn (ELI), 6Al-4V annealed, and 6Al-4V STA were tested in both liquid and gaseous methane. Aluminum alloy 2219 in the T87 and T6E46 condition was tested in fluorine, a fluorine-oxygen mixture, and methane. Results were evaluated using modified linear elastic fracture mechanics parameters.

  2. Environmentally Assisted Cracking of Nickel Alloys - A Review

    SciTech Connect

    Rebak, R

    2004-07-12

    Nickel can dissolve a large amount of alloying elements while still maintaining its austenitic structure. That is, nickel based alloys can be tailored for specific applications. The family of nickel alloys is large, from high temperature alloys (HTA) to corrosion resistant alloys (CRA). In general, CRA are less susceptible to environmentally assisted cracking (EAC) than stainless steels. The environments where nickel alloys suffer EAC are limited and generally avoidable by design. These environments include wet hydrofluoric acid and hot concentrated alkalis. Not all nickel alloys are equally susceptible to cracking in these environments. For example, commercially pure nickel is less susceptible to EAC in hot concentrated alkalis than nickel alloyed with chromium (Cr) and molybdenum (Mo). The susceptibility of nickel alloys to EAC is discussed by family of alloys.

  3. Revisiting Stress Corrosion Cracking of Steel in Caustic Solutions for Developing Cracking Susceptibility Diagrams for Improved Applicability

    NASA Astrophysics Data System (ADS)

    Pal, Sarvesh; Raman, R. K. Singh; Ibrahim, R. N.

    2012-06-01

    Stress corrosion cracking tests were conducted using Bayer solutions of different chemistry at different temperatures for extraction of alumina from bauxite ores. The validity of the commonly used caustic cracking susceptibility (CS) diagram for steels exposed to plain caustic solutions was assessed by testing the notched and precracked specimens. This study presents first results toward the development of a model susceptibility diagram for actual Bayer solutions, and for improved applicability of the traditional plain caustic diagram. For mechanistic understanding of caustic cracking, tests were also carried out under imposed electrochemical conditions.

  4. Self-crack-healing behavior under cyclic stress of silicon nitride composite at elevated temperature

    NASA Astrophysics Data System (ADS)

    Takahashi, Koji; Yoshida, Shoko; Ando, Kotoji; Saito, Shinji

    2004-02-01

    Si3N4/SiC composite ceramics were hot-pressed to investigate the crack-healing behavior under stress. Semi-elliptical surface cracks of 0.1 mm in surface length were made on each specimen. The pre-cracked specimens were crack-healed under cyclic or constant bending stress, and the resultant bending strength and cyclic fatigue strength were studied. The threshold stress for crack-healing was investigated at healing temperatures of 1000° and 1200°C. The cyclic fatigue strengths of crack-healed specimens were also investigated at healing temperatures of 900° and 1000°C. The main conclusions are as follows: (1) The threshold cyclic and constant stresses for crack-healing, below which pre-cracked specimens recovered their bending strength, were 300 MPa which was 75% of the bending strength of the pre-cracked specimens, and (2) The crack-healed specimens exhibited quite high cyclic fatigue strength at crack-healing temperatures of 900° and 1000°C.

  5. The stress corrosion cracking behavior of alloys 690 and 152 WELD in a PWR environment.

    SciTech Connect

    Alexandreanu, B.; Chopra, O. K.; Shack, W. J.

    2009-01-01

    Alloys 690 and 152 are the replacement materials of choice for Alloys 600 and 182, respectively. The latter two alloys are used as structural materials in pressurized water reactors (PWRs) and have been found to undergo stress corrosion cracking (SCC). The objective of this work is to determine the crack growth rates (CGRs) in a simulated PWR water environment for the replacement alloys. The study involved Alloy 690 cold-rolled by 26% and a laboratory-prepared Alloy 152 double-J weld in the as-welded condition. The experimental approach involved pre-cracking in a primary water environment and monitoring the cyclic CGRs to determine the optimum conditions for transitioning from the fatigue transgranular to intergranular SCC fracture mode. The cyclic CGRs of cold-rolled Alloy 690 showed significant environmental enhancement, while those for Alloy 152 were minimal. Both materials exhibited SCC of 10{sup -11} m/s under constant loading at moderate stress intensity factors. The paper also presents tensile property data for Alloy 690TT and Alloy 152 weld in the temperature range 25--870 C.

  6. 49 CFR 192.929 - What are the requirements for using Direct Assessment for Stress Corrosion Cracking (SCCDA)?

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... Assessment for Stress Corrosion Cracking (SCCDA)? 192.929 Section 192.929 Transportation Other Regulations... requirements for using Direct Assessment for Stress Corrosion Cracking (SCCDA)? (a) Definition. Stress... operator using direct assessment as an integrity assessment method to address stress corrosion cracking...

  7. 49 CFR 192.929 - What are the requirements for using Direct Assessment for Stress Corrosion Cracking (SCCDA)?

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... Assessment for Stress Corrosion Cracking (SCCDA)? 192.929 Section 192.929 Transportation Other Regulations... requirements for using Direct Assessment for Stress Corrosion Cracking (SCCDA)? (a) Definition. Stress... operator using direct assessment as an integrity assessment method to address stress corrosion cracking...

  8. 49 CFR 192.929 - What are the requirements for using Direct Assessment for Stress Corrosion Cracking (SCCDA)?

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... Assessment for Stress Corrosion Cracking (SCCDA)? 192.929 Section 192.929 Transportation Other Regulations... requirements for using Direct Assessment for Stress Corrosion Cracking (SCCDA)? (a) Definition. Stress... operator using direct assessment as an integrity assessment method to address stress corrosion cracking...

  9. 49 CFR 192.929 - What are the requirements for using Direct Assessment for Stress Corrosion Cracking (SCCDA)?

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... Assessment for Stress Corrosion Cracking (SCCDA)? 192.929 Section 192.929 Transportation Other Regulations... requirements for using Direct Assessment for Stress Corrosion Cracking (SCCDA)? (a) Definition. Stress... operator using direct assessment as an integrity assessment method to address stress corrosion cracking...

  10. 49 CFR 192.929 - What are the requirements for using Direct Assessment for Stress Corrosion Cracking (SCCDA)?

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... Assessment for Stress Corrosion Cracking (SCCDA)? 192.929 Section 192.929 Transportation Other Regulations... requirements for using Direct Assessment for Stress Corrosion Cracking (SCCDA)? (a) Definition. Stress... operator using direct assessment as an integrity assessment method to address stress corrosion cracking...

  11. Stress corrosion cracking on irradiated 316 stainless steel

    NASA Astrophysics Data System (ADS)

    Furutani, Gen; Nakajima, Nobuo; Konishi, Takao; Kodama, Mitsuhiro

    2001-02-01

    Tests on irradiation-assisted stress corrosion cracking (IASCC) were carried out by using cold-worked (CW) 316 stainless steel (SS) in-core flux thimble tubes which were irradiated up to 5×10 26 n/m 2 ( E>0.1 MeV) at 310°C in a Japanese PWR. Unirradiated thimble tube was also tested for comparison with irradiated tubes. Mechanical tests such as the tensile, hardness tests and metallographic observations were performed. The susceptibility to SCC was examined by the slow strain rate test (SSRT) under PWR primary water chemistry condition and compositional analysis on the grain boundary segregation was made. Significant changes in the mechanical properties due to irradiation such as a remarkable increase of strength and hardness, and a considerable reduction of elongation were seen. SSRT results revealed that the intergranular fracture ratio (%IGSCC) increased as dissolved hydrogen (DH) increased. In addition, SSRT results in argon gas atmosphere showed a small amount of intergranular cracking. The depletion of Fe, Cr, Mo and the enrichment of Ni and Si were observed in microchemical analyses on the grain boundary.

  12. Stress corrosion cracking of zirconium in hot nitric acid

    SciTech Connect

    Kajimura, H.; Nagano, H. )

    1992-05-01

    Zirconium (Zr) has excellent general corrosion resistance in nitric acid. However, stress corrosion cracking (SCC) has been reported in concentrated nitric acid. The purpose of this paper is to evaluate the SCC susceptibility of Zr as a function of HNO[sub 3] concentration, from 6 to 94%, and temperature. The SCC mechanism was also investigated in relation to the electrochemical behavior. The slow strain rate test technique, under constant potential conditions, was mainly adopted for SCC testing. SCC did not occur in the boiling HNO[sub 3] at concentrations less than 70% unless an anodic potential was applied. The critical SCC potential, which coincides with the transient potential from passive to transpassive behavior in the polarization curve, decreased with an increase in HNO[sub 3] concentration. In boiling 94% HNO[sub 3] Zr exhibited SCC even under open-circuit potential conditions.

  13. Stress corrosion cracking susceptibility of 18 Ni maraging steel

    NASA Technical Reports Server (NTRS)

    Humphries, T. S.; Nelson, E. E.

    1974-01-01

    The stress corrosion cracking (SCC) resistance of 18Ni maraging steel (grades 200, 250, 300, and 350) was determined in 3.5 percent salt (NaCl) solution, synthetic sea water, high humidity, and outside MSFC atmosphere. All grades of the maraging steel were found to be susceptible to SCC in varying degrees according to their strengths, with the lowest strength steel (grade 200) being the least susceptible and the highest strength steel (grade 350), the most susceptible to SCC. The SCC resistance of 250 grade maraging steel was also evaluated in salt and salt-chromate solutions using fracture mechanics techniques. The threshold value, K sub SCC, was found to be approximately 44 MN/sq m square root m, (40 ksi square root in.) or 40 percent of the K sub Q value.

  14. Stress Corrosion Cracking Issues in Light Metals for Automotive Applications

    SciTech Connect

    Jones, Russell H.; Danielson, Michael J.; Baer, Donald R.; Windisch, Charles F.; Vetrano, John S.; Edwards, Daniel J.

    2000-12-31

    The Partnership for New Generation Vehicle has the goal of producing lightweight automobiles that achieve 80 mpg. To accomplish this will require liberal use of Al and Mg alloys such as AA5083 and AZ91D. The corrosion and stress corrosion of alloy AA5083 is controlled by the precipitation of the b-phase (Al3Mg2) at grain boundaries and by the precipitation of the g-phase (Mg17Al12) in AZ91D. The b-phase is anodic to the Al matrix while the g-phase is cathodic to the Mg matrix. The effects of crack propagation along grain boundaries with electrochemically active particles is a key factor in the SCC performance of these materials.

  15. Corrosion and stress corrosion cracking in coal liquefaction processes

    SciTech Connect

    Baylor, V. B.; Keiser, J. R.

    1980-01-01

    The liquefaction of coal to produce clean-burning synthetic fuels has been demonstrated at the pilot plant level. However, some significant materials problems must be solved before scale-up to commercial levels of production can be completed. Failures due to inadequate materials performance have been reported in many plant areas: in particular, stress corrosion cracking has been found in austenitic stainless steels in the reaction and separation areas and several corrosion has been observed in fractionation components. In order to screen candidate materials of construction, racks of U-bend specimens in welded and as-wrought conditions and unstressed surveillance coupons were exposed in pilot plant vessels and evaluated. Failed components were analyzed on-site and by subsequent laboratory work. Laboratory tests were also performed. From these studies alloys have been identified that are suitable for critical plant locations. 19 figures, 7 tables.

  16. Correlation of the crack initiation stress with epoxy network topology

    SciTech Connect

    Adolf, D.; Weeks, T.; McCoy, J.

    1997-03-01

    Much controversy surrounds the dependence of stress intensity factor of glassy thermosets, epoxies in particular, with crosslink density. One could scan the literature and find references that claim K{sub Ic} increases with crosslink density, decreases with crosslink density, or is independent of crosslink density. The authors feel that two factors contribute to this confusion. First, a typical method for assessing this dependence relies on modifying the crosslink density by changing the precursor epoxy molecular weight. On the other hand, one could change stoichiometry or quench the reaction at intermediate extents of reaction to obtain large changes in crosslink density. However, most studies have not measured the resulting stress intensity factor of these partially cured systems at constant T-T{sub g}, where T{sub g} is the glass transition temperature of the epoxy. Since T{sub g} can change significantly with cure and since fracture processes at the crack tip are dissipative, they must work at constant T-T{sub g} to ensure that the nonlinear viscoelastic mechanisms are fairly compared. In this study, they quenched the reaction of the diglycidyl ether of bisphenol A (DGEBA) and diethanolamine (DEA) at various stages past the gel point and measured the three-point-bend stress intensity factor at a constant T-T{sub g} = {minus}50 C. The trend is clear and significant; increasing crosslink density directly increases the load-to-fail.

  17. Stress-induced martensitic transformation in metastable austenitic stainless steels: Effect on fatigue crack growth rate

    NASA Astrophysics Data System (ADS)

    Khan, Z.; Ahmed, M.

    1996-04-01

    This paper addresses the influence of cyclic stress-induced martensitic transformation on fatigue crack growth rates in metastable austenitic stainless steels. At low applied stress and mean stress values in AISI type 301 stainless steel, fatigue crack growth rate is substantially retarded due to a cyclic stress-induced γ-α' and γ-ɛ martensitic transformation occurring at the crack-tip plastic zone. It is suggested that the transformation products produce a compressive residual stress at the tip of the fatigue crack, which essentially lowers the effective stress intensity and hence retards the fatigue crack growth rate. At high applied stress or mean stress values, fatigue crack growth rates in AISI type 301 steels become almost equal to those of stable AISI type 302 alloy. As the amount of transformed products increases (with an increase in applied or mean stress), the strain-hardening effect brought about by the transformed martensite phase appears to accelerate fatigue crack growth, offsetting the contribution from the compressive residual stress produced by the positive volume change of γ → α' or ɛ transformation.

  18. Effects of stress ratio and fiber orientation on fatigue crack growth behavior in APAL

    SciTech Connect

    Oh, S.W.; Park, W.J.; Yoon, H.K.; Lee, K.G.; Cho, J.M.; Lee, K.B.

    1993-12-31

    A new hybrid composite (APAL; Aramid Patched Aluminum Alloy), consisting of 2024-T3 aluminum alloy plate sandwiched between aramid/epoxy prepregs (HK 285/RS 1222), was developed. Fatigue crack growth behavior was examined at stress ratios of R = 0.2, 0.5 using two kinds of APAL with different fiber orientation (0{degree}/90{degree} and {+-} 45{degree} for crack direction). The APAL showed superior fatigue crack growth resistance, which may be attributed to the crack bridging effect imposed by the intact fibers in the crack wave. The magnitude of crack bridging was estimated quantitatively and determined by a new technique on the basis of the compliances of 2024-T3 aluminum alloy and APAL specimens. The crack growth rate of the APAL specimens was reduced significantly as comparison to the monolithic aluminum alloy and was not adequately correlated with the conventional stress intensity factor range ({Delta}K). It was found that the crack growth rate was successfully correlated with the effective stress intensity factor range ( {Delta}K{sub eff} = K{sub br} {minus} K{sub cl}) allowing for the crack closure and the crack bridging. The relation between da/dN and {Delta}K{sub eff} was plotted within a narrow scatter band regardless at loading line of 2024-T3 aluminum alloy, two kinds of the APAL (APAL 0{degree}/90{degree}, APAL {+-} 45{degree}) and two kinds of stress ratios (R = 0.2, 0.5).

  19. Low-pH stress corrosion cracking of natural gas pipelines

    SciTech Connect

    Harle, B.A.; Beavers, J.A.; Jaske, C.E.

    1994-12-31

    Stress corrosion cracking of natural gas pipelines in low-pH environments is a serious problem for the gas transmission industry. To date, researchers have experienced significant difficulties in reproducing cracking in the laboratory. This paper describes results of an ongoing program investigating crack growth of an API X-65 line pipe steel in a low-pH cracking environment using a J-integral technique. The primary objectives of this research are to reproduce the cracking observed in the field and identify an appropriate crack driving force parameter. Significant crack growth has been observed in the testing and the J-integral appears to be a good parameter for characterizing crack growth behavior.

  20. Pacific Northwest National Laboratory Investigation of the Stress Corrosion Cracking in Nickel-Base Alloys, Volume 2

    SciTech Connect

    Bruemmer, Stephen M.; Toloczko, Mychailo B.; Olszta, Matthew J.

    2012-03-01

    The objective of this program is to evaluate the primary water stress corrosion cracking (PWSCC) susceptibility of high chromium alloy 690 and its weld metals, establish quantitative measurements of crack-growth rates and determine relationships among cracking susceptibility, environmental conditions and metallurgical characteristics. Stress-corrosion, crack-growth rates have been determined for 12 alloy 690 specimens, 11 alloy 152/52/52M weld metal specimens, 4 alloy 52M/182 overlay specimens and 2 alloy 52M/82 inlay specimens in simulated PWR primary water environments. The alloy 690 test materials included three different heats of extruded control-rod-drive mechanism (CRDM) tubing with variations in the initial material condition and degree of cold work for one heat. Two cold-rolled (CR) alloy 690 plate heats were also obtained and evaluated enabling comparisons to the CR CRDM materials. Weld metal, overlay and inlay specimens were machined from industry mock ups to provide plant-representative materials for testing. Specimens have been tested for one alloy 152 weld, two alloy 52 welds and three alloy 52M welds. The overlay and inlay specimens were prepared to propagate stress-corrosion cracks from the alloy 182 or 82 material into the more resistant alloy 52M. In all cases, crack extension was monitored in situ by direct current potential drop (DCPD) with length resolution of about +1 µm making it possible to measure extremely low growth rates approaching 5x10-10 mm/s. Most SCC tests were performed at 325-360°C with hydrogen concentrations from 11-29 cc/kg; however, environmental conditions were modified during a few experiments to evaluate the influence of temperature, water chemistry or electrochemical potential on propagation rates. In addition, low-temperature (~50°C) cracking behavior was examined for selected alloy 690 and weld metal specimens. Extensive characterizations have been performed on material microstructures and stress-corrosion cracks by

  1. Computational two-dimensional modeling of the stress intensity factor in a cracked metallic material

    NASA Astrophysics Data System (ADS)

    Rolón, J. E.; Cendales, E. D.; Cruz, I. M.

    2016-02-01

    Cracking of metallic engineering materials is of great importance due cost of replacing mechanical elements cracked and the danger of sudden structural failure of these elements. One of the most important parameters during consideration of the mechanical behavior of machine elements having cracking and that are subject to various stress conditions is the stress intensity factor near the crack tip called factor Kic. In this paper a computational model is developed for the direct assessment of stress concentration factor near to the crack tip and compared with the results obtained in the literature in which other models have been established, which consider continuity of the displacement of the crack tip (XBEM). Based on this numerical approximation can be establish that computational XBEM method has greater accuracy in Kic values obtained than the model implemented by the method of finite elements for the virtual nodal displacement through plateau function.

  2. A photoelastic determination of stress intensity factors for corner cracks in a bolted joint

    SciTech Connect

    Guengoer, S.; Patterson, E.A.

    1997-11-01

    Three-dimensional photoelasticity was used to measure mode I stress intensity factors of corner cracks in a double-shear bolted joint. A model of the joint assembly was manufactured from a photoelastic material and three different corner cracks were introduced using a cutting wheel. After the stress freezing process, slices along the crack fronts were cut and analyzed using three different photoelastic procedures. There was good correlation between the methods of analysis. Stress intensity factors of these cracks were found to vary along the crack front with a maximum at the bore of the hole and a minimum on the surface of the plate. This implies that the cracks are likely to grow more rapidly along the bore.

  3. Environmentally assisted cracking in Light Water Reactors: Semiannual report, April 1993--September 1993. Volume 17

    SciTech Connect

    Chopra, O.K.; Chung, H.M.; Karlsen, T.; Kassner, T.F.; Michaud, W.F.; Ruther, W.E.; Sanecki, J.E.; Shack, W.J.; Soppet, W.K.

    1994-06-01

    This report summarizes work performed by Argonne National Laboratory on fatigue and environmentally assisted cracking (EAC) in light water reactors (LWRS) during the six months from April 1993 to September 1993. EAC and fatigue of piping, pressure vessels, and core components in LWRs are important concerns as extended reactor lifetimes are envisaged. Topics that have been investigated include (a) fatigue of low-alloy steel used in piping, steam generators, and reactor pressure vessels; (b) EAC of cast stainless steels (SSs); and (c) radiation-induced segregation and irradiation-assisted stress corrosion cracking of Type 304 SS after accumulation of relatively high fluence. Fatigue tests were conducted on medium-sulfur-content A106-Gr B piping and A533-Gr B pressure vessel steels in simulated PWR water and in air. Additional crack growth data were obtained on fracture-mechanics specimens of cast austenitic SSs in the as-received and thermally aged conditions in simulated boiling-water reactor (BWR) water at 289{degree}C. The data were compared with predictions based on crack growth correlations for wrought austenitic SS in oxygenated water developed at ANL and rates in air from Section 11 of the ASME Code. Microchemical and microstructural changes in high- and commercial-purity Type 304 SS specimens from control-blade absorber tubes and a control-blade sheath from operating BWRs were studied by Auger electron spectroscopy and scanning electron microscopy.

  4. Environmentally assisted cracking in light water reactors : semiannual report, July 2000 - December 2000.

    SciTech Connect

    Chopra, O. K.; Chung, H. M.; Gruber, E. E.; Shack, W. J.; Soppet, W. K.; Strain, R. V.; Energy Technology

    2002-04-01

    This report summarizes work performed by Argonne National Laboratory on fatigue and environmentally assisted cracking (EAC) in light water reactors (LWRs) from July 2000 to December 2000. Topics that have been investigated include (a) environmental effects on fatigue S-N behavior of primary pressure boundary materials, (b) irradiation-assisted stress corrosion cracking (IASCC) of austenitic stainless steels (SSs), and (c) EAC of Alloys 600 and 690. The fatigue strain-vs.-life data are summarized for the effects of various material, loading, and environmental parameters on the fatigue lives of carbon and low-alloy steels and austenitic SSs. Effects of the reactor coolant environment on the mechanism of fatigue crack initiation are discussed. Two methods for incorporating the effects of LWR coolant environments into the ASME Code fatigue evaluations are presented. Slow-strain-rate tensile tests and posttest fractographic analyses were conducted on several model SS alloys irradiated to {approx}0.9 x 10{sup 21} n {center_dot} cm{sup -2} (E > 1 MeV) in He at 289 C in the Halden reactor. The results were used to determine the influence of alloying and impurity elements on the susceptibility of these steels to IASCC. A fracture toughness J-R curve test was conducted on a commercial heat of Type 304 SS that was irradiated to {approx}2.0 x 10{sup 21} n {center_dot} cm{sup -2} in the Halden reactor. The results were compared with the data obtained earlier on steels irradiated to 0.3 and 0.9 x 10{sup 21} n {center_dot} cm{sup -2} (E > 1 MeV) (0.45 and 1.35 dpa). Neutron irradiation at 288 C was found to decrease the fracture toughness of austenitic SSs. Tests were conducted on compact-tension specimens of Alloy 600 under cyclic loading to evaluate the enhancement of crack growth rates in LWR environments. Then, the existing fatigue crack growth data on Alloys 600 and 690 were analyzed to establish the effects of temperature, load ratio, frequency, and stress intensity range

  5. The influence of microstructure on environmentally assisted cracking of alloy 718. Final report

    SciTech Connect

    Ballinger, R.

    1996-03-01

    The goal of this project was to understand the effects of microstructure on the behavior of alloy 718 in aqueous environments. To achieve this goal the microstructure and resultant environmental properties of modified heat treatments were characterized. The role of grain boundary microstructure was emphasized. The performance of alloy 718, in both conventional and modified heat treatments, is also compared to existing data for the behavior of alloy X-750 in light water reactor environments. These comparisons were made with the goal of understanding the effects of alloy microstructure on performance. Four thermal treatments were investigated. Each condition was given an identical aging treatment (720 C/8h, furnace cool, 620 C/8h) to maintain equivalent precipitation of the strengthening precipitate, {gamma}{prime}. Annealing treatments were varied to control grain boundary precipitation. Stress corrosion cracking (SCC) resistance was determined using fatigue pre-cracked, bolt loaded specimens in high purity, deaerated water at 288 C. Reduced grain boundary precipitation substantially increases resistance to SCC for both grain sizes. The ADA condition showed no evidence of SCC for the environmental conditions studied. Alloy 718 direct aged (DA) also has superior SCC resistance relative to alloy X-750, an alloy more commonly used in light water reactor applications today. In corrosion fatigue crack growth experiments in high purity, deaerated water it was found that under all conditions studied the crack path was transgranular. Alloy 718 is not susceptible to accelerated, intergranular, corrosion fatigue crack growth at temperatures near 100 C as is alloy X-750 in some thermal treatments. This is most likely due to superior resistance to hydrogen embrittlement.

  6. A plane stress finite element model for elastic-plastic mode I/II crack growth

    NASA Astrophysics Data System (ADS)

    James, Mark Anthony

    A finite element program has been developed to perform quasi-static, elastic-plastic crack growth simulations. The model provides a general framework for mixed-mode I/II elastic-plastic fracture analysis using small strain assumptions and plane stress, plane strain, and axisymmetric finite elements. Cracks are modeled explicitly in the mesh. As the cracks propagate, automatic remeshing algorithms delete the mesh local to the crack tip, extend the crack, and build a new mesh around the new tip. State variable mapping algorithms transfer stresses and displacements from the old mesh to the new mesh. The von Mises material model is implemented in the context of a non-linear Newton solution scheme. The fracture criterion is the critical crack tip opening displacement, and crack direction is predicted by the maximum tensile stress criterion at the crack tip. The implementation can accommodate multiple curving and interacting cracks. An additional fracture algorithm based on nodal release can be used to simulate fracture along a horizontal plane of symmetry. A core of plane strain elements can be used with the nodal release algorithm to simulate the triaxial state of stress near the crack tip. Verification and validation studies compare analysis results with experimental data and published three-dimensional analysis results. Fracture predictions using nodal release for compact tension, middle-crack tension, and multi-site damage test specimens produced accurate results for residual strength and link-up loads. Curving crack predictions using remeshing/mapping were compared with experimental data for an Arcan mixed-mode specimen. Loading angles from 0 degrees to 90 degrees were analyzed. The maximum tensile stress criterion was able to predict the crack direction and path for all loading angles in which the material failed in tension. Residual strength was also accurately predicted for these cases.

  7. Stress Intensity Factors for Part-Through Surface Cracks in Hollow Cylinders

    NASA Technical Reports Server (NTRS)

    Mettu, Sambi R.; Raju, Ivatury S.; Forman, Royce G.

    1992-01-01

    Flaws resulting from improper welding and forging are usually modeled as cracks in flat plates, hollow cylinders or spheres. The stress intensity factor solutions for these crack cases are of great practical interest. This report describes some recent efforts at improving the stress intensity factor solutions for cracks in such geometries with emphasis on hollow cylinders. Specifically, two crack configurations for cylinders are documented. One is that of a surface crack in an axial plane and the other is a part-through thumb-nail crack in a circumferential plane. The case of a part-through surface crack in flat plates is used as a limiting case for very thin cylinders. A combination of the two cases for cylinders is used to derive a relation for the case of a surface crack in a sphere. Solutions were sought which cover the entire range of the geometrical parameters such as cylinder thickness, crack aspect ratio and crack depth. Both the internal and external position of the cracks are considered for cylinders and spheres. The finite element method was employed to obtain the basic solutions. Power-law form of loading was applied in the case of flat plates and axial cracks in cylinders and uniform tension and bending loads were applied in the case of circumferential (thumb-nail) cracks in cylinders. In the case of axial cracks, the results for tensile and bending loads were used as reference solutions in a weight function scheme so that the stress intensity factors could be computed for arbitrary stress gradients in the thickness direction. For circumferential cracks, since the crack front is not straight, the above technique could not be used. Hence for this case, only the tension and bending solutions are available at this time. The stress intensity factors from the finite element method were tabulated so that results for various geometric parameters such as crack depth-to-thickness ratio (a/t), crack aspect ratio (a/c) and internal radius-to-thickness ratio (R

  8. Effect of stress corrosion cracking on integrity and remaining life of natural gas pipelines

    SciTech Connect

    Jaske, C.E.; Beavers, J.A.; Harle, B.A.

    1996-08-01

    External stress-corrosion cracking of pipelines is a serious problem for the gas transmission industry. Longitudinal cracks initiate on the outside surface of the pipe and link up to form flaws that, in some cases, can lead to pipe rupture. This paper presents a model that quantifies the effect of stress-corrosion cracking on pipe failure stress. The model is an extension of those that have been developed for oil and gas pipelines and considers both flow-stress and fracture-toughness dependent failure modes. A methodology also is presented to calculate the remaining life of a pipeline containing flaws of known size.

  9. On the shape of stress corrosion cracks in sensitized Type 304 SS in Boiling Water Reactor primary coolant piping at 288 °C

    NASA Astrophysics Data System (ADS)

    Lee, Sang-Kwon; Kramer, Daniel; Macdonald, Digby D.

    2014-11-01

    Evolution of the shape of surface cracks in sensitized Type 304 SS in Boiling Water Reactor primary coolant circuit piping at the reactor operating temperature of 288 °C is explored as a function of various environmental variables, such as electrochemical potential (ECP), solution conductivity, flow velocity, and multiplier for the oxygen reduction reaction (ORR) standard exchange current density (SECD), using the coupled environment fracture model (CEFM). For this work, the CEFM was upgraded by incorporating Shoji's model for calculating the crack tip strain rate and more advanced expressions were used for estimating the stress intensity factor for semi-elliptical surface cracks. This revised CEFM accurately predicts the dependence of the crack growth rate on stress intensity factor and offers an alternative explanation for the development of semi-elliptical cracks than that provided by fracture mechanics alone. The evolution of surface crack semi-elliptical shape depends strongly upon various environmental variables identified above, and the CEFM predicts that the minor axis of the ellipse should be oriented perpendicular to the surface, in agreement with observation. The development of the observed semi-elliptical cracks with the minor axis perpendicular to the surface is therefore attributed to the dependence of the crack growth rate on the electrochemical crack length.

  10. Assessment of Cracks in Stress Concentration Regions with Localized Plastic Zones

    SciTech Connect

    Friedman, E.

    1998-11-25

    Marty brittle fracture evaluation procedures include plasticity corrections to elastically computed stress intensity factors. These corrections, which are based on the existence of a plastic zone in the vicinity of the crack tip, can overestimate the plasticity effect for a crack embedded in a stress concentration region in which the elastically computed stress exceeds the yield strength of the material in a localized zone. The interactions between the crack, which acts to relieve the high stresses driving the crack, plasticity effects in the stress concentration region, and the nature and source of the loading are examined by formulating explicit flaw finite element models for a crack emanating from the root of a notch located in a panel subject to an applied tensile stress. The results of these calculations provide conditions under which a crack-tip plasticity correction based on the Irwin plastic zone size overestimates the plasticity effect. A failure assessment diagram (FAD) curve is used to characterize the effect of plasticity on the crack driving force and to define a less restrictive plasticity correction for cracks at notch roots when load-controlled boundary conditions are imposed. The explicit flaw finite element results also demonstrate that stress intensity factors associated with load-controlled boundary conditions, such as those inherent in the ASME Boiler and Pressure Vessel Code as well as in most handbooks of stress intensity factors, can be much higher than those associated with displacement-controlled conditions, such as those that produce residual or thermal stresses. Under certain conditions, the inclusion of plasticity effects for cracks loaded by displacement-controlled boundary conditions reduces the crack driving force thus justifying the elimination of a plasticity correction for such loadings. The results of this study form the basis for removing unnecessary conservatism from flaw evaluation procedures that utilize plasticity

  11. Cracks in Martian boulders exhibit preferred orientations that point to solar-induced thermal stress.

    PubMed

    Eppes, Martha-Cary; Willis, Andrew; Molaro, Jamie; Abernathy, Stephen; Zhou, Beibei

    2015-01-01

    The origins of fractures in Martian boulders are unknown. Here, using Mars Exploration Rover 3D data products, we obtain orientation measurements for 1,857 cracks visible in 1,573 rocks along the Spirit traverse and find that Mars rock cracks are oriented in statistically preferred directions similar to those compiled herein for Earth rock cracks found in mid-latitude deserts. We suggest that Martian directional cracking occurs due to the preferential propagation of microfractures favourably oriented with respect to repeating geometries of diurnal peaks in sun-induced thermal stresses. A numerical model modified here with Mars parameters supports this hypothesis both with respect to the overall magnitude of stresses as well as to the times of day at which the stresses peak. These data provide the first direct field and numerical evidence that insolation-related thermal stress potentially plays a principle role in cracking rocks on portions of the Martian surface. PMID:25813699

  12. Publ 945, avoiding environmental cracking in amine units, first edition, August 1990

    SciTech Connect

    Not Available

    1990-01-01

    This publication covers problems with environmental cracking of carbon steel in amine units. It will provide guidelines for fabrication, inspection, and repair to help ensure safe, reliable operation.

  13. Environmentally assisted cracking in light water reactors annual report January - December 2005.

    SciTech Connect

    Alexandreanu, B.; Chen, Y.; Chopra, O. K.; Chung, H. M.; Gruber, E. E.; Shack, W. J.; Soppet, W. K.

    2007-08-31

    This report summarizes work performed from January to December 2005 by Argonne National Laboratory on fatigue and environmentally assisted cracking in light water reactors (LWRs). Existing statistical models for estimating the fatigue life of carbon and low-alloy steels and austenitic stainless steels (SSs) as a function of material, loading, and environmental conditions were updated. Also, the ASME Code fatigue adjustment factors of 2 on stress and 20 on life were critically reviewed to assess the possible conservatism in the current choice of the margins. An approach, based on an environmental fatigue correction factor, for incorporating the effects of LWR environments into ASME Section III fatigue evaluations is discussed. The susceptibility of austenitic stainless steels and their welds to irradiation-assisted stress corrosion cracking (IASCC) is being evaluated as a function of the fluence level, water chemistry, material chemistry, and fabrication history. For this task, crack growth rate (CGR) tests and slow strain rate tensile (SSRT) tests are being conducted on various austenitic SSs irradiated in the Halden boiling water reactor. The SSRT tests are currently focused on investigating the effects of the grain boundary engineering process on the IASCC of the austenitic SSs. The CGR tests were conducted on Type 316 SSs irradiated to 0.45-3.0 dpa, and on sensitized Type 304 SS and SS weld heat-affected-zone material irradiated to 2.16 dpa. The CGR tests on materials irradiated to 2.16 dpa were followed by a fracture toughness test in a water environment. The effects of material composition, irradiation, and water chemistry on growth rates are discussed. The susceptibility of austenitic SS core internals to IASCC and void swelling is also being evaluated for pressurized water reactors. Both SSRT tests and microstructural examinations are being conducted on specimens irradiated in the BOR-60 reactor in Russia to doses up to 20 dpa. Crack growth rate data

  14. Influence of stress intensity and loading mode on intergranular stress corrosion cracking of Alloy 600 in primary waters of pressurized water reactors

    SciTech Connect

    Rebak, R.B.; Szklarska-Smialowska, Z. . Fontana Corrosion Center)

    1994-05-01

    The steam generator in a pressurized water reactor (PWR) of a nuclear power plant consists mainly of a shell made of carbon (C) steel and tubes made of alloy 600 (UNS N06600). However, alloy 600 suffers environmentally induced cracking with exposure to high-temperature primary water. The susceptibility of alloy 600 to integranular stress corrosion cracking (IGSCC) was investigated as a function of the level of applied stresses and mode of loading. Constant load tests were conducted with specimens prepared from thin wall tubes, and constant deformation tests were conducted using specimens prepared from plates. With tubes exposed to primary water at 330 C, the crack propagation rate (CPR) was found to increase from 1 [times] 10[sup [minus]11] m/s at a stress intensity (K[sub i]) of 10 MPa[radical]m to 1 [times] 10[sup [minus]9] at K[sub i] = 60 MPa[radical]m. CPR obtained using compact specimens prepared from plates were 1 order of magnitude lower than values measured in tubes at the same temperature and in the same solution at each stress intensity. The corollary was that values of crack propagation and threshold stress intensities obtained using compact specimens could not be extrapolated to the behavior of thin wall tubes.

  15. Avalanche structural rearrangement through cracking-healing in weakly stressed cold dusty plasma liquids

    NASA Astrophysics Data System (ADS)

    Yang, Chi; Wang, Wen; I, Lin

    2016-01-01

    We experimentally investigate the spatiotemporal dynamical behaviors of the avalanche structural rearrangement through micro-cracking-healing in weakly stressed cold dusty plasma liquids, and the kinetic origins for their different spatial and temporal classifications. The crystalline ordered domains can be cracked or temporarily sustain and transfer the weak stress to remote regions for cracking-healing. It is found that cracking sites form a fractal network with cluster size following power law distribution in the x y t space. The histograms of the persistent times for sustaining regional ordered and disordered structure, the temporal cracking burst width, and quiescent time between two bursts all follow power law decays with fast descending tails. Cracking can be classified into a single temporal burst with simple line like spatial patterns and the successive cracking fluctuation with densely packed cracking clusters. For an ordered region, whether the Burgers vectors of the incoming dislocations from the boundary allow direct dislocation reduction is the key for the above two classifications through cracking a large ordered domain into medium scale corotating ordered domains or small patches. The low regional structural order at the end of a cracking burst can be regarded as an alarm for predicting the short quiescent period before the next cracking burst.

  16. EFFECT OF UNBROKEN LIGAMENTS ON STRESS CORROSION CRACKING BEHAVIOR OF ALLOY 82H WELDS

    SciTech Connect

    Mills, W.J. and Brown, C.M.

    2003-02-20

    Previously reported stress corrosion cracking (SCC) rates for Alloy 82H gas-tungsten-arc welds tested in 360 C water showed tremendous variability. The excessive data scatter was attributed to the variations in microstructure, mechanical properties and residual stresses that are common in welds. In the current study, however, re-evaluation of the SCC data revealed that the large data scatter was an anomaly due to erroneous crack growth rates inferred from crack mouth opening displacement (CMOD) measurements. Apparently, CMOD measurements provided reasonably accurate SCC rates for some specimens, but grossly overestimated rates in others. The overprediction was associated with large unbroken ligaments that often form in welds in the wake of advancing crack fronts. When ligaments were particularly large, they prevented crack mouth deflection, so apparent crack incubation times (i.e. period of time before crack advance commences) based on CMOD measurements were unrealistically long. During the final states of testing, ligaments began to separate allowing the crack mouth to open rather quickly. This behavior was interpreted as a rapid crack advance, but it actually reflects the ligament separation rate, not the SCC rate. Revised crack growth rates obtained in this study exhibit substantially less scatter than that previously reported. The effects of crack orientation and fatigue flutter loading on SCC rates in 82H welds are also discussed.

  17. Influence of precracked specimen configuration and starting stress intensity on the stress corrosion cracking of 4340 steel

    NASA Technical Reports Server (NTRS)

    Lisagor, W. B.

    1984-01-01

    Experimental results are presented from a study of the effects of precracked specimen configuration and initial starting stress intensity on crack growth rate and threshold stress intensity, for both onset of cracking and crack arrest. Attention is given to AISI 4340 steel in a 3.5-percent NaCl solution, for configurations of a single edge-cracked specimen tested in cantilever bending under constant load, and a modified compact specimen bolt loaded to a constant deflection. The threshold stress intensity value determined was independent of specimen configuration, if the stress intensity value associated with the compact specimen is taken where the discontinuous break occurs in the velocity-stress intensity curve.

  18. POTENTIAL FOR STRESS CORROSION CRACKING OF A537 CARBON STEEL NUCLEAR WASTE TANKS CONTAINING HIGHLY CAUSTIC SOLUTIONS

    SciTech Connect

    Lam, P.; Stripling, C.; Fisher, D.; Elder, J.

    2010-04-26

    The evaporator recycle streams of nuclear waste tanks may contain waste in a chemistry and temperature regime that exceeds the current corrosion control program, which imposes temperature limits to mitigate caustic stress corrosion cracking (CSCC). A review of the recent service history found that two of these A537 carbon steel tanks were operated in highly concentrated hydroxide solution at high temperature. Visual inspections, experimental testing, and a review of the tank service history have shown that CSCC has occurred in uncooled/un-stress relieved tanks of similar construction. Therefore, it appears that the efficacy of stress relief of welding residual stress is the primary corrosion-limiting mechanism. The objective of this experimental program is to test A537 carbon steel small scale welded U-bend specimens and large welded plates (30.48 x 30.38 x 2.54 cm) in a caustic solution with upper bound chemistry (12 M hydroxide and 1 M each of nitrate, nitrite, and aluminate) and temperature (125 C). These conditions simulate worst-case situations in these nuclear waste tanks. Both as-welded and stress-relieved specimens have been tested. No evidence of stress corrosion cracking was found in the U-bend specimens after 21 days of testing. The large plate test was completed after 12 weeks of immersion in a similar solution at 125 C except that the aluminate concentration was reduced to 0.3 M. Visual inspection of the plate revealed that stress corrosion cracking had not initiated from the machined crack tips in the weld or in the heat affected zone. NDE ultrasonic testing also confirmed subsurface cracking did not occur. Based on these results, it can be concluded that the environmental condition of these tests was unable to develop stress corrosion cracking within the test periods for the small welded U-bends and for the large plates, which were welded with an identical procedure as used in the construction of the actual nuclear waste tanks in the 1960s. The

  19. Study on stress intensity factors for cracks on the inner surface of thin spherical shells

    SciTech Connect

    Wang, D.F.; Huang, Z.Z.; Liu, W.M.; Chen, L.; Li, K.M.

    1995-11-01

    By using frozen stress photoelastic method, stress intensity factors of inner surface cracks in spherical shells and in spherical shells with geometric discontinuity (misalignment or angular distortion) are studied. In order to compare with the solutions of stress intensity factors of cracks in flat plates, a new definition of inner surface crack shape in spherical shells is proposed. In this paper, the variations of stress intensity magnification factors with the ratio of crack depth to crack length (a/c), the ratio of crack depth to wall thickness (a/t), the ratio of wall thickness to inner diameter (t/R) and the SIF along the crack front are analyzed. Mixed mode K1 and K2 at misalignment in spherical shells are discussed. The stress intensity factors of cracks in spherical shells are compared with the solutions of those in flat plates, and an empirical formula of modification factors is presented. These researches are very useful for assessment of the safety of spherical shells.

  20. Effect of electrode potential on stress corrosion cracking and crack chemistry of a nickel-base superalloy

    SciTech Connect

    Lillard, J.A.; Kelly, R.G.; Gangloff, R.P.

    1997-12-01

    The aqueous environment assisted cracking (EAC) resistance of a superalloy, Alloy 718 (Ni-19Fe-18Cr-5Nb-1Ti-0.6Al), was characterized by a rising displacement fracture mechanics methods. This precipitation-strengthened alloy was susceptible to room-temperature EAC in acidified sodium chloride at cathodic and anodic potentials. The threshold for stable crack growth in chloride (K{sub TH}) was as low as 47 MPa{radical}m, reduced from the laboratory air crack initiation toughness (K{sub ICi}) of 81--85 MPa{radical}m. The fracture morphology changed from ductile microvoids in air to a mixture of voids, transgranular facets, and intergranular facets in acidic chloride. Subcritical crack growth rates were on the order of 5 x 10{sup {minus}9} m/s for rising displacement at a stress intensity of 70 MPa{radical}m and were an order of magnitude slower for constant displacement conditions. The degree of reduction in K{sub TH} from K{sub ICi}, the amount and type of fracture surface features, and the crack growth rate depended on the applied electrode potential. Microstructure produced by sub- or super-{delta} solvus heat treatment affected these dependencies. Ion analysis indicated that alloy dissolution occurred at the crack tip even at cathodic polarizations.

  1. Stress intensity factors of eccentric cracks in bi-materials plate under mode I loading

    SciTech Connect

    Ismail, A. E.

    2015-05-15

    Bi-material plates were generally used to joint electronic devices or mechanical components requiring dissimilar materials to be attached. During services, mechanical failure can be occurred due to the formation of cracks at the interfacial joint or away from the centre. Generally, linear elastic fracture mechanics approach is used to characterize these cracks based on stress intensity factors (SIF). Based on the literature survey, the SIFs for the central cracks were easily available. However, the SIFs for eccentric cracks were difficult to obtain. Therefore, this paper presented the SIFs for eccentric cracks subjected to mode I tension loading. Three important parameters were used such as relative crack depth, a/L, relative offset distance, b/L and elastic mismatch, E{sub 1}/E{sub 2} or α. It was found that such parameters significantly affected the characteristic of SIFs and it was depend on the location of cracks.

  2. A metallurgical evaluation of stress corrosion cracking in large diameter stainless steel piping

    SciTech Connect

    Wheeler, D.A.; Rawl, D.E. Jr.; Louthan, M.R. Jr.

    1990-01-01

    Ultrasonic testing (UT) of the stainless steel piping in the primary coolant water system of SRS reactors indicates the presence of short, partly-through-wall stress corrosion cracks in the heat-affected zone of approximately 7% of the circumferential pipe welds. These cracks are thought to develop by intergranular nucleation and mixed mode propagation. Metallographic evaluations have confirmed the UT indications of crack size and provided evidence that crack growth involved the accumulation of chloride inside the growing crack. It is postulated that the development of an oxygen depletion cell inside the crack results in the migration of chloride ions to the crack tip to balance the accumulation of positively charged metallic ions. The results of this metallurgicial evaluation, combined with structural assessments of system integrity, support the existence of leak-before-break conditions in the SRS reactor piping system. 13 refs., 9 figs.

  3. The Evolution of Stress Intensity Factors and the Propagation of Cracks in Elastic Media

    NASA Astrophysics Data System (ADS)

    Friedman, Avner; Hu, Bei; Velazquez, Juan J. L.

    When a crack Γs propagates in an elastic medium the stress intensity factors evolve with the tip x(s) of Γs. In this paper we derive formulae which describe the evolution of these stress intensity factors for a homogeneous isotropic elastic medium under plane strain conditions. Denoting by ψ=ψ(x,s) the stress potential (ψ is biharmonic and has zero traction along the crack Γs) and by κ(s) the curvature of the crack at the tip x(s), we prove that the stress intensity factors A1(s), A2(s), as functions of s, satisfy: where , are stress intensity factors of the tangential derivative of in the polar coordinate system at x(s) with θ=0 in the direction of the crack at x(s). The case of antiplane shearing is also briefly considered; in this case ψ is harmonic.

  4. Transient thermal stresses in a reinforced hollow disk or cylinder containing a radial crack

    NASA Technical Reports Server (NTRS)

    Tang, R.; Erdogan, F.

    1983-01-01

    The transient thermal stress problem in a hollow cylinder or a disk containing a radial crack is considered. It is assumed that the cylinder is reinforced on its inner boundary by a membrane which has thermoelastic constants different than those of the base material. The transient temperature, thermal stresses and the crack tip stress intensity factors are calculated in a cylinder which is subjected to a sudden change of temperature on the inside surface. The results are obtained for various dimensionless parameters and material constants. The special cases of the crack terminating at the cylinder-membrane interface and of the broken membrane are separately considered and some examples are given.

  5. Transient thermal stresses in a reinforced hollow disk or cylinder containing a radial crack

    NASA Technical Reports Server (NTRS)

    Tang, R.; Erdogan, F.

    1984-01-01

    The transient thermal stress problem in a hollow cylinder or a disk containing a radial crack is considered. It is assumed that the cylinder is reinforced on its inner boundary by a membrane which has thermoelastic constants different than those of the base material. The transient temperature, thermal stresses and the crack tip stress intensity factors are calculated in a cylinder which is subjected to a sudden change of temperature on the inside surface. The results are obtained for various dimensionless parameters and material constants. The special cases of the crack terminating at the cylinder-membrane interface and of the broken membrane are separately considered and some examples are given.

  6. Three-dimensional elastic stress and displacement analysis of finite geometry solids containing cracks

    NASA Technical Reports Server (NTRS)

    Kring, J.; Gyekenyesi, J.; Mendelson, A.

    1977-01-01

    The line method of analysis is applied to the Navier-Cauchy equations of elastic equilibrium to calculate the displacement fields in finite geometry bars containing central, surface, and double-edge cracks under extensionally applied uniform loading. The application of this method to these equations leads to coupled sets of simultaneous ordinary differential equations whose solutions are obtained along sets of lines in a discretized region. Normal stresses and the stress intensity factor variation along the crack periphery are calculated using the obtained displacement field. The reported results demonstrate the usefulness of this method in calculating stress intensity factors for commonly encountered crack geometries in finite solids.

  7. Effect of Thermal Stresses Along Crack Surface on Ultrasonic Response

    SciTech Connect

    Virkkunen, I.; Haenninen, H.; Kemppainen, M.; Pitkaenen, J.

    2004-02-26

    Artificial flaws can be manufactured by controlled thermal fatigue loading. The produced cracks can be introduced to a wide variety of materials. This technology gives also a unique opportunity to monitor the ultrasonic response of a crack during thermal loading. This paper reports studies on the effects of different thermal load cycles on the ultrasonic response. The loads are analyzed with FEM. Two cracked samples were loaded with different thermal load cycles.

  8. Stress intensity factors in a cracked infinite elastic wedge loaded by a rigid punch

    NASA Technical Reports Server (NTRS)

    Erdogan, F.; Civelek, M. B.

    1978-01-01

    A plane elastic wedge-shaped solid was split through the application of a rigid punch. It was assumed that the coefficient of friction on the the contact area was constant, and the problem had a plane of symmetry with respect to loading and geometry, with the crack in the plane of symmetry. The problem was formulated in terms of a system of integral equations with the contact stress and the derivative of the crack surface displacement as the unknown functions. The solution was obtained for an internal crack and for an edge crack. The results include primarily the stress intensity factors at the crack tips, and the measure of the stress singularity at the wedge apex, and at the end points of the contact area.

  9. Cessation of environmentally-assisted cracking in a low-alloy steel: Theoretical analysis

    SciTech Connect

    Wire, G.L.

    1997-02-01

    Environmentally Assisted Cracking (EAC) can cause increases in fatigue crack growth rates of 40 to 100 times the rate in air for low alloy steels. The increased rates can lead to very large predicted crack growth. EAC is activated by a critical level of dissolved sulfides at the crack tip. Sulfide inclusions (MnS) in the steel produce corrosive sulfides in solution following exposure by a growing crack. In stagnant, low oxygen water conditions considered here, diffusion is the dominant mass transport mechanism acting to change the sulfide concentration within the crack. The average crack tip velocity is below the level required to produce the critical crack tip sulfide ion concentration required for EAC. Crack extension analyses also consider the breakthrough of large, hypothetical embedded defects with the attendant large freshly exposed sulfide inventory. Combrade et al. noted that a large inventory of undissolved metallurgical sulfides on crack flanks could trigger EAC, but did not quantify the effects. Diffusion analysis is extended herein to cover breakthrough of embedded defects with large sulfide inventories. The mass transport via diffusion is limited by the sulfide solubility. As a result, deep cracks in high sulfur steels are predicted to retain undissolved sulfides for extended but finite periods of time t{sub diss} which increase with the crack length and the metallurgical sulfide content in the steel. The analysis shows that the duration of EAC is limited to t{sub diss} providing V{sub eac}, the crack tip velocity associated with EAC is less than V{sub In}, the crack tip velocity below which EAC will not occur in an initially sulfide free crack. This condition on V{sub eac} need only be met for a short time following crack cleanup to turn off EAC. The predicted crack extension due to limited duration of EAC is a small fraction of the initial embedded defect size and would not greatly change calculated crack depths.

  10. Proceedings: 1987 EPRI Workshop on Mechanisms of Primary Water Intergranular Stress Corrosion Cracking

    SciTech Connect

    1988-09-01

    Representatives from utilities, vendors, universities, government agencies, and EPRI reviewed recent research on stress corrosion cracking of steam generator tubing in primary water. Participants agreed that, although the mechanism involved in cracking is uncertain, identifying the rate-limiting step is more important than understanding the complete mechanism.

  11. Proceedings: Workshop on Initiation of Stress Corrosion Cracking Under LWR Conditions

    SciTech Connect

    1988-05-01

    Participants at this 1986 workshop discussed methods, such as electrochemical monitoring, for determining stress corrosion crack (SCC) initiation and for identifying variables involved in initiation. A survey of field occurrences of SCC revealed a correlation between fabrication-related defects and crack initiation.

  12. Studies on explosively driven cracks under confining in-situ stresses

    SciTech Connect

    Simha, K.R.Y.; Fourney, W.L.; Dick, R.D.

    1984-01-01

    Successful explosive gas well stimulation requires a thorough understanding of explosively driven cracks under confining in-situ stresses. In a previous paper (Simha, et al 1983) the problem of explosively driven cracks was experimentally investigated to reveal the features of crack propagation. It was observed that the explosively driven crack propagation is the result of two different but overlapping phases. The first phase involving the initiation and early time crack propagation is entirely governed by the explosively generated stress transients. The rapidly decaying stress transients then lead to the second phase of crack propagation largely controlled by the in-situ stresses. The purpose of this paper is to more fully understand the characteristics of the first phase concerning the initiation and early time propagation of explosively driven cracks. Experiments are conducted with plastic models under biaxial compression and the dynamic event is observed with a high speed multiple spark gap camera of the Cranz-Schardin type. The experimental observations are utilized to propose analytical models of crack initiation under explosive loading to aid in the design of multiple fracturing necessary for successful application of modern well stimulation techniques. 8 references, 4 figures.

  13. Crack

    MedlinePlus

    ... sound the drug makes as it heats up. Short-Term Effects Crack is a stimulant that is absorbed through ... quickly, after about 5 or 10 minutes. Other short-term effects include: higher heart rate, breathing rate, blood pressure , ...

  14. The effect of non-singular stresses on crack-tip constraint

    NASA Astrophysics Data System (ADS)

    Du, Z.-Z.; Hancock, J. W.

    T HE EFFECT of the T-stress on the small-scale yielding field of a crack in plane strain conditions has been examined using modified boundary layer formulations. The numerically calculated stresses at the crack tip are represented by slip line fields for small-strain theory. Positive T-stresses cause plasticity to envelop the crack tip and exhibit a Prandtl field, corresponding to the limiting solution of the HRR field for a nonhardening material. Moderate compressive T-stresses reduce the direct stresses within the plastic zone by decreasing the hydrostatic stress by T. This causes a loss of J-dominance, and a stress distribution represented by an incomplete Prandtl field.

  15. High-Temperature Slow Crack Growth of Silicon Carbide Determined by Constant-Stress-Rate and Constant-Stress Testing

    NASA Technical Reports Server (NTRS)

    Choi, Sung H.; Salem, J. A.; Nemeth, N. N.

    1998-01-01

    High-temperature slow-crack-growth behaviour of hot-pressed silicon carbide was determined using both constant-stress-rate ("dynamic fatigue") and constant-stress ("static fatigue") testing in flexure at 1300 C in air. Slow crack growth was found to be a governing mechanism associated with failure of the material. Four estimation methods such as the individual data, the Weibull median, the arithmetic mean and the median deviation methods were used to determine the slow crack growth parameters. The four estimation methods were in good agreement for the constant-stress-rate testing with a small variation in the slow-crack-growth parameter, n, ranging from 28 to 36. By contrast, the variation in n between the four estimation methods was significant in the constant-stress testing with a somewhat wide range of n= 16 to 32.

  16. Hydrogen Cracking and Stress Corrosion of Pressure Vessel Steel ASTM A543

    NASA Astrophysics Data System (ADS)

    AlShawaf, Ali Hamad

    The purpose of conducting this research is to develop fundamental understanding of the weldability of the modern Quenched and Tempered High Strength Low Alloy (Q&T HSLA) steel, regarding the cracking behavior and susceptibility to environmental cracking in the base metal and in the heat affected zone (HAZ) when welded. A number of leaking cracks developed in the girth welds of the pressure vessel after a short time of upgrading the material from plain carbon steel to Q&T HSLA steel. The new vessels were constructed to increase the production of the plant and also to save weight for the larger pressure vessel. The results of this research study will be used to identify safe welding procedure and design more weldable material. A standardized weldability test known as implant test was constructed and used to study the susceptibility of the Q&T HSLA steel to hydrogen cracking. The charged hydrogen content for each weld was recorded against the applied load during weldability testing. The lack of understanding in detail of the interaction between hydrogen and each HAZ subzone in implant testing led to the need of developing the test to obtain more data about the weldability. The HAZ subzones were produced using two techniques: standard furnace and GleebleRTM machine. These produced subzones were pre-charged with hydrogen to different levels of concentration. The hydrogen charging on the samples simulates prior exposure of the material to high humidity environment during welding process. Fractographical and microstructural characterization of the HAZ subzones were conducted using techniques such as SEM (Scanning Electron Microscopy). A modified implant test using the mechanical tensile machine was also used to observe the effects of the hydrogen on the cracking behavior of each HAZ subzone. All the experimental weldability works were simulated and validated using a commercial computational software, SYSWELD. The computational simulation of implant testing of Q&T HSLA

  17. Development of a novel technique to assess the vulnerability of micro-mechanical system components to environmentally assisted cracking.

    SciTech Connect

    Enos, David George; Goods, Steven Howard

    2006-11-01

    Microelectromechanical systems (MEMS) will play an important functional role in future DOE weapon and Homeland Security applications. If these emerging technologies are to be applied successfully, it is imperative that the long-term degradation of the materials of construction be understood. Unlike electrical devices, MEMS devices have a mechanical aspect to their function. Some components (e.g., springs) will be subjected to stresses beyond whatever residual stresses exist from fabrication. These stresses, combined with possible abnormal exposure environments (e.g., humidity, contamination), introduce a vulnerability to environmentally assisted cracking (EAC). EAC is manifested as the nucleation and propagation of a stable crack at mechanical loads/stresses far below what would be expected based solely upon the materials mechanical properties. If not addressed, EAC can lead to sudden, catastrophic failure. Considering the materials of construction and the very small feature size, EAC represents a high-risk environmentally induced degradation mode for MEMS devices. Currently, the lack of applicable characterization techniques is preventing the needed vulnerability assessment. The objective of this work is to address this deficiency by developing techniques to detect and quantify EAC in MEMS materials and structures. Such techniques will allow real-time detection of crack initiation and propagation. The information gained will establish the appropriate combinations of environment (defining packaging requirements), local stress levels, and metallurgical factors (composition, grain size and orientation) that must be achieved to prevent EAC.

  18. Development of a Fatigue Crack Growth Coupon for Highly Plastic Stress Conditions

    NASA Technical Reports Server (NTRS)

    Allen, Phillip A.; Aggarwal, Pravin K.; Swanson, Gregory R.

    2003-01-01

    The analytical approach used to develop a novel fatigue crack growth coupon for highly plastic stress field condition is presented in this paper. The flight hardware investigated is a large separation bolt that has a deep notch, which produces a large plastic zone at the notch root when highly loaded. Four test specimen configurations are analyzed in an attempt to match the elastic-plastic stress field and crack constraint conditions present in the separation bolt. Elastic-plastic finite element analysis is used to compare the stress fields and critical fracture parameters. Of the four test specimens analyzed, the modified double-edge notch tension - 3 (MDENT-3) most closely approximates the stress field, J values, and crack constraint conditions found in the flight hardware. The MDENT-3 is also most insensitive to load misalignment and/or load redistribution during crack growth.

  19. Stress corrosion cracking of X-60 line pipe steel in a carbonate-bicarbonate solution

    SciTech Connect

    Pilkey, A.K.; Lambert, S.B.; Plumtree, A. . Dept. of Mechanical Engineering)

    1995-02-01

    An experimental system was developed to reproduce stress corrosion cracking (SCC) of API X-60 line pipe steels in highly alkaline (pH = 10) carbonate-bicarbonate (1 N sodium carbonate [Na[sub 2]CO[sub 3

  20. Calculation of Stress Intensity Factors for Interfacial Cracks in Fiber Metal Laminates

    NASA Technical Reports Server (NTRS)

    Wang, John T.

    2009-01-01

    Stress intensity factors for interfacial cracks in Fiber Metal Laminates (FML) are computed by using the displacement ratio method recently developed by Sun and Qian (1997, Int. J. Solids. Struct. 34, 2595-2609). Various FML configurations with single and multiple delaminations subjected to different loading conditions are investigated. The displacement ratio method requires the total energy release rate, bimaterial parameters, and relative crack surface displacements as input. Details of generating the energy release rates, defining bimaterial parameters with anisotropic elasticity, and selecting proper crack surface locations for obtaining relative crack surface displacements are discussed in the paper. Even though the individual energy release rates are nonconvergent, mesh-size-independent stress intensity factors can be obtained. This study also finds that the selection of reference length can affect the magnitudes and the mode mixity angles of the stress intensity factors; thus, it is important to report the reference length used with the calculated stress intensity factors.

  1. The mechanism of stress-corrosion cracking in 7075 aluminum alloy

    NASA Technical Reports Server (NTRS)

    Jacobs, A. J.

    1970-01-01

    Various aspects of stress-corrosion cracking in 7075 aluminum alloy are discussed. A model is proposed in which the continuous anodic path along which the metal is preferentially attacked consists of two phases which alternate as anodes.

  2. Estimation of crack closure stresses for in situ toughened silicon nitride with 8 wt pct scandia

    NASA Technical Reports Server (NTRS)

    Choi, Sung R.; Salem, Jonathan A.; Sanders, William A.

    1992-01-01

    An 8-wt pct-scandia silicon nitride with an elongated grain structure was fabricated. The material exhibited high fracture toughness and a rising R-curve as measured by the indentation strength technique. The 'toughening' exponent m was found to be m about 0.1. The high fracture toughness and R-curve behavior was attributed mainly to bridging of the crack faces by the elongated grains. The crack closure (bridging) stress distribution in the wake region of the crack tip was estimated as a function of crack size from the R-curve data, with an arbitrarily assumed distribution function.

  3. Stress corrosion cracking of Alloy 600 using the constant strain rate test

    SciTech Connect

    Bulischeck, T.S.; Van Rooyen, D.

    1981-10-01

    Nuclear grade production tubing of Alloy 600 was evaluated for stress corrosion cracking (SCC) susceptibility in high purity water at 365, 345, 325, and 290 C. Reverse tube U-bend specimens provided crack initiation data and constant extension rate tests were employed to determine the crack velocities experienced in th crack propagation stage. Initial results indicate that a linear extrapolation of data received from high temperature tests can be used to predict the service life of steam generator tubing that has been plastically deformed or is continually deforming by ''denting.''

  4. Surface Cracking and Interface Reaction Associated Delamination Failure of Thermal and Environmental Barrier

    NASA Technical Reports Server (NTRS)

    Zhu, Dongming; Choi, Sung R.; Eldridge, Jeffrey I.; Lee, Kang N.; Miller, Robert A.

    1990-01-01

    In this paper, surface cracking and interface reactions of a ZrO2-8wt%Y2O3 and mullite/BSAS/Si thermal and environmental barrier coating system on SiC/SiC ceramic matrix composites were characterized after long-term combined laser thermal gradient and furnace cyclic tests in a water vapor containing environment. The surface cracking was analyzed based on the coating thermal gradient sintering behavior and thermal expansion mismatch stress characteristics under the thermal cyclic conditions. The interface reactions that were largely enhanced by the coating surface cracking in the water vapor environment were investigated in detail, and the reaction phases were identified for the coating system after the long-term exposure. The accelerated coating delamination failure was attributed to the increased delamination driving force under the thermal gradient cyclic loading and the reduced interface adhesion due to the detrimental interface reactions. The coating design issues will also be discussed based on the observed failure mechanisms under the high-heat-flux test conditions.

  5. Effect of nitrogen content on the environmentally-assisted cracking susceptibility of duplex stainless steels

    NASA Astrophysics Data System (ADS)

    Tseng, Chuan-Ming; Tsai, Wen-Ta; Liou, Horng-Yih

    2003-01-01

    The effect of nitrogen content on the stress corrosion cracking (SCC) behavior of 22 pct Cr duplex stainless steel (DSS) in chloride solutions was investigated in this study. Slow strain rate testing (SSRT) was employed to evaluate the SCC susceptibility. The experimental results showed that the tensile strength and ductility of 22 pct Cr DSS increased with increasing amount of nitrogen (in the range of 0.103 to 0.195 wt pct). Slow strain rate testing results indicated that 22 pct Cr DSSs were resistant to SCC in 3.5 wt pct NaCl solution at 80 °C. However, environmentally assisted cracking occurred in 40 wt pct CaCl2 solution at 100 °C and in boiling 45 wt pct MgCl2 solution at 155 °C, respectively. The effects of environment and nitrogen content in DSS on the cracking susceptibility are discussed in this article. Selective dissolution of ferrite phase was found to participate in the SCC process for tests in CaCl2 solution. At temperatures above 80 °C, dynamic strain aging was found to occur in various environments at a strain beyond plastic deformation.

  6. Environmentally assisted cracking in light water reactors. Semiannual progress report, January 1996--June 1996

    SciTech Connect

    Chopra, O.K.; Chung, H.M.; Gruber, E.E.

    1997-05-01

    This report summarizes work performed by Argonne National Laboratory on fatigue and environmentally assisted cracking (EAC) in light water reactors from January 1996 to June 1996. Topics that have been investigated include (a) fatigue of carbon, low-alloy, and austenitic stainless steels (SSs) used in reactor piping and pressure vessels, (b) irradiation-assisted stress corrosion cracking of Type 304 SS, and (c) EAC of Alloys 600 and 690. Fatigue tests were conducted on ferritic and austenitic SSs in water that contained various concentrations of dissolved oxygen (DO) to determine whether a slow strain rate applied during various portions of a tensile-loading cycle are equally effective in decreasing fatigue life. Slow-strain-rate-tensile tests were conducted in simulated boiling water reactor (BWR) water at 288{degrees}C on SS specimens irradiated to a low fluence in the Halden reactor and the results were compared with similar data from a control-blade sheath and neutron-absorber tubes irradiated in BWRs to the same fluence level. Crack-growth-rate tests were conducted on compact-tension specimens from several heats of Alloys 600 and 690 in air and high-purity, low-DO water. 83 refs., 60 figs., 14 tabs.

  7. INVESTIGATION OF THE POTENTIAL FOR CAUSTIC STRESS CORROSION CRACKING OF A537 CARBON STEEL NUCLEAR WASTE TANKS

    SciTech Connect

    Lam, P.

    2009-10-15

    The evaporator recycle streams contain waste in a chemistry and temperature regime that may be outside of the current waste tank corrosion control program, which imposes temperature limits to mitigate caustic stress corrosion cracking (CSCC). A review of the recent service history (1998-2008) of Tanks 30 and 32 showed that these tanks were operated in highly concentrated hydroxide solution at high temperature. Visual inspections, experimental testing, and a review of the tank service history have shown that CSCC has occurred in uncooled/un-stress relieved F-Area tanks. Therefore, for the Type III/IIIA waste tanks the efficacy of the stress relief of welding residual stress is the only corrosion-limiting mechanism. The objective of this experimental program is to test carbon steel small scale welded U-bend specimens and large welded plates (12 x 12 x 1 in.) in a caustic solution with upper bound chemistry (12 M hydroxide and 1 M each of nitrate, nitrite, and aluminate) and temperature (125 C). These conditions simulate worst-case situations in Tanks 30 and 32. Both as-welded and stress-relieved specimens have been tested. No evidence of stress corrosion cracking was found in the U-bend specimens after 21 days of testing. The large plate test is currently in progress, but no cracking has been observed after 9 weeks of immersion. Based on the preliminary results, it appears that the environmental conditions of the tests are unable to develop stress corrosion cracking within the duration of these tests.

  8. Characterization of Residual Stress Effects on Fatigue Crack Growth of a Friction Stir Welded Aluminum Alloy

    NASA Technical Reports Server (NTRS)

    Newman, John A.; Smith, Stephen W.; Seshadri, Banavara R.; James, Mark A.; Brazill, Richard L.; Schultz, Robert W.; Donald, J. Keith; Blair, Amy

    2015-01-01

    An on-line compliance-based method to account for residual stress effects in stress-intensity factor and fatigue crack growth property determinations has been evaluated. Residual stress intensity factor results determined from specimens containing friction stir weld induced residual stresses are presented, and the on-line method results were found to be in excellent agreement with residual stress-intensity factor data obtained using the cut compliance method. Variable stress-intensity factor tests were designed to demonstrate that a simple superposition model, summing the applied stress-intensity factor with the residual stress-intensity factor, can be used to determine the total crack-tip stress-intensity factor. Finite element, VCCT (virtual crack closure technique), and J-integral analysis methods have been used to characterize weld-induced residual stress using thermal expansion/contraction in the form of an equivalent delta T (change in local temperature during welding) to simulate the welding process. This equivalent delta T was established and applied to analyze different specimen configurations to predict residual stress distributions and associated residual stress-intensity factor values. The predictions were found to agree well with experimental results obtained using the crack- and cut-compliance methods.

  9. The fatigue problems of cracks subjected to obliquely incident stress waves

    NASA Astrophysics Data System (ADS)

    Weng, I.-Chung

    Catastrophic failure of aircraft and other structures are often caused by undetected cracks. Fracture mechanics has been developed to augment traditional static and fatigue design. In the static theory of fracture mechanics, extensive treatment has been given to the stress distribution around sharp cracks and notches under various loading conditions. Previous works on the problems of dynamic loadings are not accurate in dealing with singularities at high frequencies. The numerical solutions become unrealistic at high frequencies in many practical applications. To address the need to obtain the stress intensity factor in high frequency dynamic loading situations, we studied the use of dislocation to represent a crack by a continuous distribution of dislocation singularities. This study focused on the configuration of finite crack located in an infinite isotropic elastic solid which is subjected to harmonic shear waves. The most important contribution of this thesis is a new approach which is based on the development of dynamic dislocation model to investigate the dynamic problems of cracks, particularly the dynamic interaction between a surface crack and screw dislocations; dynamic interaction between a free surface and an internal crack; crack propagation under dynamic loadings. With this approach, we are able to derive the exact analytical expression for stress intensity factor at any given frequencies. Results of the present investigation show the dynamic stress intensity factors will increase as the wave number (a measure of frequency of loadings) increases and the maximum value is about 25% more than the static stress intensity factor. At relatively high frequencies, the stress intensity factor drops rapidly beyond the first maximum value and exhibits oscillations of approximately constant period as wave number increases. This conclusion can be used to predict the useful life of a component at which consists of the crack propagation phase. The stress intensity

  10. The Stress-Strain Condition Estimation of Detail in Crack Tip by Integral Strain Gauges

    NASA Astrophysics Data System (ADS)

    Syzrantsev, V.; Syzrantseva, K.

    2016-04-01

    The paper considers the task of stress-strain condition calculation of experimental sample in fatigue crack tip on weld boundary at its cyclic deforming. For this task decision authors use the information obtained by original means of cyclic strains measurement: Integral Strain Gauges. The results of carried experimental researches are compared with data of stress-strain condition estimation of detail in crack tip calculated by Finish Element Method.

  11. Stress intensity factors for surface and corner cracks emanating from a wedge-loaded hole

    NASA Technical Reports Server (NTRS)

    Zhao, W.; Sutton, M. A.; Shivakumar, K. N.; Newman, J. C., Jr.

    1994-01-01

    To assist analysis of riveted lap joints, stress intensity factors are determined for surface and corner cracks emanating from a wedge-loaded hole by using a 3-D weight function method in conjunction with a 3-D finite element method. A stress intensity factor equation for surface cracks is also developed to provide a closed-form solution. The equation covers commonly-encountered geometrical ranges and retains high accuracy over the entire range.

  12. Susceptibility of carbon steel to stress corrosion cracking in sodium hydroxide

    SciTech Connect

    Ziomek-Moroz, Margaret; Flis, J.

    2005-01-01

    Stress corrosion cracking susceptibility of carbon steel and decarburized steel was studied in 8.5 M sodium hydroxide at 100 ?C. Potentiodynamic experiments were performed to determine the potential values to be applied in slow strain rate(ssr) experiments. Optical and scanning electron microscopy were used to investigate the surfaces of corroded samples. Severe intergranular stress corrosion cracking was observed on the carbon steel samples in comparison to the decarburized steel samples.

  13. Assessment of chances for external stress corrosion cracking in submarine pipelines

    SciTech Connect

    Mollan, R.; Eliassen, S.; Holt, T.; Ratkje, S.K.

    1982-11-08

    The possibility for stress corrosion cracking due to external environments to occur in submarine pipelines can not be excluded. The probability for stress corrosion to occur in submarine pipelines, however, considered to be for onshore pipelines mainly because calcareous deposits are expected to prevent buildup of the corrosive environment. Also the fact that the quality of surface preparation prior to coating for submarine pipelines normally is of a relatively high standard, contributes to reduce the probability for stresscorrosion cracking to occur.

  14. Free vibration analysis of size-dependent cracked microbeam based on the modified couple stress theory

    NASA Astrophysics Data System (ADS)

    Sourki, R.; Hoseini, S. A. H.

    2016-04-01

    This paper investigates the analysis for free transverse vibration of a cracked microbeam based on the modified couple stress theory within the framework of Euler-Bernoulli beam theory. The governing equation and the related boundary conditions are derived by using Hamilton's principle. The cracked beam is modeled by dividing the beam into two segments connected by a rotational spring located at the cracked section. This model invokes the consideration of the additional strain energy caused by the crack and promotes a discontinuity in the bending slope. In this investigation, the influence of diverse crack position, crack severity, material length scale parameter as well as various Poisson's ratio on natural frequencies is studied. A comparison with the previously published studies is made, in which a good agreement is observed. The results illustrate that the aforementioned parameters are playing a significant role on the dynamic behavior of the microbeam.

  15. Stress intensity factors for an inclined crack in an orthotropic strip

    NASA Technical Reports Server (NTRS)

    Delale, F.; Bakirtas, I.; Erdogan, F.

    1978-01-01

    The elastostatic problem for an infinite orthotropic strip containing a crack is considered. It is assumed that the orthogonal axes of material orthotropy may have an arbitrary angular orientation with respect to the orthogonal axes of geometric symmetry of the uncracked strip. The crack is located along an axis of orthotropy, hence at an arbitrary angle with respect to the sides of the strip. The general problem is formulated in terms of a system of singular integral equations for arbitrary crack surface tractions. As examples Modes I and II stress intensity factors are calculated for the strip having an internal or an edge crack with various lengths and angular orientations. In most calculations uniform tension or uniform bending away from the crack region is used as the external load. Limited results are also given for uniform normal or shear tractions on the crack surface.

  16. Stress-Intensity Factors for Corner Cracks at the Edge of a Hole

    NASA Technical Reports Server (NTRS)

    Raju, I. S.; Newman, J. C., Jr.

    1978-01-01

    Stress-intensity factors, calculated by a three-dimensional finite-element analysis, for shallow or deep quarter-elliptical corner cracks at the edge of a hole in a finite-thickness plate are presented. The plate was subjected to remote uniform tension, remote bending, or simulated pin loading in the hole. The crack depth-to-plate thickness ranged from 0.2 to 0.8, while the ratio of crack depth-to-plate crack length ranged from 0.2 to 2. The ratio of hole radius-to-plate thickness was held at 0.5. To verify the accuracy of the three-dimensional finite-element models empolyed, convergence studies were conducted (number of degrees of freedom ranged from 4400 to 9300). The stress-intensity factor variations along the crack front are presented and compared with other solutions from the literature.

  17. Effect of crack curvature on stress intensity factors for ASTM standard compact tension specimens

    NASA Technical Reports Server (NTRS)

    Alam, J.; Mendelson, A.

    1983-01-01

    The stress intensity factors (SIF) are calculated using the method of lines for the compact tension specimen in tensile and shear loading for curved crack fronts. For the purely elastic case, it was found that as the crack front curvature increases, the SIF value at the center of the specimen decreases while increasing at the surface. For the higher values of crack front curvatures, the maximum value of the SIF occurs at an interior point located adjacent to the surface. A thickness average SIF was computed for parabolically applied shear loading. These results were used to assess the requirements of ASTM standards E399-71 and E399-81 on the shape of crack fronts. The SIF is assumed to reflect the average stress environment near the crack edge.

  18. Role of Localized Deformation in Irradiation-Assisted Stress Corrosion Cracking Initiation

    NASA Astrophysics Data System (ADS)

    West, Elaine A.; McMurtrey, Michael D.; Jiao, Zhijie; Was, Gary S.

    2012-01-01

    Intergranular cracking of irradiated austenitic alloys depended on localized grain boundary stress and deformation in both high-temperature aqueous and argon environments. Tensile specimens were irradiated with protons to doses of 1 to 7 dpa and then strained in high-temperature argon, simulated boiling water reactor normal water chemistry, and supercritical water environments. Quantitative measurements confirmed that the initiation of intergranular cracks was promoted by (1) the formation of coarse dislocation channels, (2) discontinuous slip across grain boundaries, (3) a high inclination of the grain boundary to the tensile axis, and (4) low-deformation propensity of grains as characterized by their Schmid and Taylor factors. The first two correlations, as well as the formation of intergranular cracks at the precise locations of dislocation channel-grain boundary intersections are evidence that localized deformation drives crack initiation. The latter two correlations are evidence that intergranular cracking is promoted at grain boundaries experiencing elevated levels of normal stress.

  19. Analysis of Interface Properties of Hybrid Pre-stressed Strengthening RC Beams with Crack

    NASA Astrophysics Data System (ADS)

    zhihong, Xie; Peiyan, Huang; Yongchang, Guo; Jun, Deng; Genquan, Zhong

    2010-05-01

    A finite element (FE) analysis model of interface layer is established for the pre-stressed CFS-GFS hybrid strengthened beams. An elastic solution for the interfacial stress in the adhesive layer of the retrofitted beams is developed as well. The analytical results were compared with the FE results of interfacial stresses in the beams with different thickness of the adhesive and the fibre sheet. Different heights of Cracks in the interfacial layer of the concrete beam are considered in FE Model. Analysis results show the strengthening pattern is of excellent interface performance and the strength of the fiber sheet can be effectively utilized. The results also indicate the shear and normal stresses in the interfacial layer of the concrete beam release at the locations of the cracks and reach the maximal value before the concrete cracked. The shear and normal stresses in the adhesive layer increase abruptly, and the cracks in the adhesive layer then appear. The axial stresses of hybrid fiber sheet near the cracks decrease locally at the sites of the concrete cracks.

  20. Analysis of Interface Properties of Hybrid Pre-stressed Strengthening RC Beams with Crack

    SciTech Connect

    Xie Zhihong; Huang Peiyan; Guo Yongchang; Deng Jun; Zhong Genquan

    2010-05-21

    A finite element (FE) analysis model of interface layer is established for the pre-stressed CFS-GFS hybrid strengthened beams. An elastic solution for the interfacial stress in the adhesive layer of the retrofitted beams is developed as well. The analytical results were compared with the FE results of interfacial stresses in the beams with different thickness of the adhesive and the fibre sheet. Different heights of Cracks in the interfacial layer of the concrete beam are considered in FE Model. Analysis results show the strengthening pattern is of excellent interface performance and the strength of the fiber sheet can be effectively utilized. The results also indicate the shear and normal stresses in the interfacial layer of the concrete beam release at the locations of the cracks and reach the maximal value before the concrete cracked. The shear and normal stresses in the adhesive layer increase abruptly, and the cracks in the adhesive layer then appear. The axial stresses of hybrid fiber sheet near the cracks decrease locally at the sites of the concrete cracks.

  1. Nonlinear Rayleigh waves to detect initial damage leading to stress corrosion cracking in carbon steel

    NASA Astrophysics Data System (ADS)

    Matlack, K. H.; Kim, J.-Y..; Jacobs, L. J.; Qu, J.; Singh, P. M.

    2012-05-01

    This research experimentally investigates second harmonic generation of Rayleigh waves propagating through carbon steel samples damaged in a stress corrosion environment. Damage from stress corrosion cracking is of major concern in nuclear reactor tubes and in gas and fuel transport pipelines. For example, certain types of stress corrosion cracking (SCC) account for more failures in steam generator tubes than most other damage mechanisms, yet these cracks do not initiate until late in the structure's life. Thus, there is a need to be able to measure the damage state prior to crack initiation, and it has been shown that the acoustic nonlinearity parameter - the parameter associated with second harmonic generation - is sensitive to microstructural evolution. In this work, samples are immersed in a sodium carbonate-bicarbonate solution, which typically forms in the soil surrounding buried pipelines affected by SCC, and held at yield stress for 5-15 days to the onset of stress corrosion cracking. Measurements of second harmonic generation with Rayleigh waves are taken intermittently to relate cumulative damage prior to macroscopic cracking to nonlinear wave propagation. Experimental results showing changes in second harmonic generation due to stress corrosion damage are presented.

  2. Environmentally assisted cracking in light water reactors - annual report, January-December 2001.

    SciTech Connect

    Chopra, O. K.; Chung, H. M.; Clark, R. W.; Gruber, E. E; Hiller, R. W.; Shack, W. J.; Soppet, W. K.; Strain, R. V.; Energy Technology

    2003-06-01

    This report summarizes work performed by Argonne National Laboratory on fatigue and environmentally assisted cracking (EAC) in light water reactors (LWRs) from January to December 2001. Topics that have been investigated include (a) environmental effects on fatigue S-N behavior of austenitic stainless steels (SSs), (b) irradiation-assisted stress corrosion cracking (IASCC) of austenitic SSs, and (c) EAC of Alloy 600. The effects of key material and loading variables, such as strain amplitude, strain rate, temperature, dissolved oxygen (DO) level in water, and material heat treatment, on the fatigue lives of wrought and cast austenitic SSs in air and LWR environments have been evaluated. The mechanism of fatigue crack initiation in austenitic SSs in LWR environments has also been examined. The results indicate that the presence of a surface oxide film or difference in the characteristics of the oxide film has no effect on fatigue crack initiation in austenitic SSs in LWR environments. Slow-strain-rate tensile tests and post-test fractographic analyses were conducted on several model SS alloys irradiated to {approx}2 x 10{sup 21} n {center_dot} cm{sup -2} (E > 1 MeV) ({approx}3 dpa) in He at 289 C in the Halden reactor. The results were used to determine the influence of alloying and impurity elements on the susceptibility of these steels to IASCC. Corrosion fatigue tests were conducted on nonirradiated austenitic SSs in high-purity water at 289 C to establish the test procedure and conditions that will be used for the tests on irradiated materials. A comprehensive irradiation experiment was initiated to obtain many tensile and disk specimens irradiated under simulated pressurized water reactor conditions at {approx}325 C to 5, 10, 20, and 40 dpa. Crack growth tests were completed on 30% cold-worked Alloy 600 in high-purity water under various environmental and loading conditions. The results are compared with data obtained earlier on several heats of Alloy 600

  3. Chemical aspects of lodine-induced stress corrosion cracking of Zircaloys

    SciTech Connect

    Cubicciotti, D.; Jones, R.L.; Syrett, B.C.

    1982-01-01

    The thermodynamics of the zirconium-iodine system are summarized. Thermodynamic information for iodine chemisorbed on zirconium surfaces is also presented. These thermochemical results are used to analyze chemical behavior in situations related to stress corrosion cracking (SCC). Cracking initiation sites in commercial Zircaloy tubing were found to be associated with impurities (iron, aluminum, silicon, and chromium) in the Zircaloy surface in microsurface examination of failures produced in iodine-induced SCC tests. It is suggested that the impurity site may react with iodine to form a locally embrittled region that fails under stress and acts as a crack initiator.

  4. The shear-stress intensity factor for a centrally cracked stiff-flanged shear web

    NASA Technical Reports Server (NTRS)

    Fichter, W. B.

    1976-01-01

    By use of the principle of superposition the stiff-flanged shear web is modeled mathematically by an infinite elastic strip with fixed longitudinal edges. The shear-stress intensity factor for a central longitudinal crack is calculated for various values of the ratio of strip width to crack length, h/a, in the range 0.1-10. The interaction of the crack with the boundaries is illustrated by boundary shear-stress distributions for three values of h/a. Some implications of the results for the design of damage-tolerant shear webs are discussed briefly.

  5. A critical evaluation of the stress-corrosion cracking mechanism in high-strength aluminum alloys

    NASA Astrophysics Data System (ADS)

    Lee, Seong-Min; Pyun, Su-Il; Chun, Young-Gab

    1991-10-01

    Attempts have been made to elucidate the mechanism of stress-corrosion cracking (SCC) in high-strength Al-Zn-Mg and Al-Li-Zr alloys exposed to aqueous environments by considering the temperature dependence of SCC susceptibility based upon the anodic dissolution and hydrogen embrittlement models. A quantitative correlation which involves the change of threshold stress intensity, K ISCC, with temperature on the basis of anodic dissolution has been developed with the aid of linear elastic fracture mechanics. From the derived correlation, it is concluded that the threshold stress intensity decreases as the test temperature increases. This suggestion is inconsistent with that predicted on the basis of hydrogen embrittlement. It is experimentally observed from the Al-Zn-Mg and Al-Li-Zr alloys that the threshold stress intensity, K,ISCC, decreases and the crack propagation rate, da/dt, over the stress intensity increases with increasing test temperature. From considering the change in SCC susceptibility with temperature, it is suggested that a gradual transition in the mechanism for the stress-corrosion crack propagation occurs from anodic dissolution in stage I, where the crack propagation rate increases sharply with stress intensity, to hydrogen embrittlement in stage II, where the crack propagation rate is independent of stress intensity.

  6. Thermodynamic analysis on the role of hydrogen in anodic stress corrosion cracking

    SciTech Connect

    Qiao, L.; Mao, X.

    1995-11-01

    A synergistic effect of hydrogen and stress on a corrosion rate was analyzed with thermodynamics. The results showed that an interaction of stress and hydrogen could increase the corrosion rate remarkably. Stress corrosion cracking (SCC) of austenitic stainless steel (ASS) was investigated in boiling chloride solution to confirm the analysis. Hydrogen could be introduced into the specimen concentrated at the crack tip during SCC in boiling LiCl solution (143 C). The concentrating factor is about 3 which is consistent with calculated results according to stress induced diffusion.

  7. Use of Slow Strain Rate Tensile Testing to Assess the Ability of Several Superalloys to Resist Environmentally-Assisted Intergranular Cracking

    NASA Technical Reports Server (NTRS)

    Gabb, Timothy P.; Telesman, Jack; Banik, Anthony; McDevitt, Erin

    2014-01-01

    Intergranular fatigue crack initiation and growth due to environmental degradation, especially at notched features, can often limit the fatigue life of disk superalloys at high temperatures. For clear comparisons, the effects of alloy composition on cracking in air needs to be understood and compared separately from variables associated with notches and cracks such as effective stress concentration, plastic flow, stress relaxation, and stress redistribution. The objective of this study was to attempt using simple tensile tests of specimens with uniform gage sections to compare the effects of varied alloy composition on environment-assisted cracking of several powder metal and cast and wrought superalloys including ME3, LSHR, Udimet 720(TradeMark) ATI 718Plus(Registered TradeMark) alloy, Haynes 282(Trademark), and Inconel 740(TradeMark) Slow and fast strain-rate tensile tests were found to be a useful tool to compare propensities for intergranular surface crack initiation and growth. The effects of composition and heat treatment on tensile fracture strain and associated failure modes were compared. Environment interactions were determined to often limit ductility, by promoting intergranular surface cracking. The response of various superalloys and heat treatments to slow strain rate tensile testing varied substantially, showing that composition and microstructure can significantly influence environmental resistance to cracking.

  8. Corrosion cracking

    SciTech Connect

    Goel, V.S.

    1986-01-01

    Various papers on corrosion cracking are presented. The topics addressed include: unique case studies on hydrogen embrittlement failures in components used in aeronautical industry; analysis of subcritical cracking in a Ti-5Al-2.5Sn liquid hydrogen control valve; corrosion fatigue and stress corrosion cracking of 7475-T7351 aluminum alloy; effects of salt water environment and loading frequency on crack initiation in 7075-T7651 aluminum alloy and Ti-6Al-4V; stress corrosion cracking of 4340 steel in aircraft ignition starter residues. Also discussed are: stress corrosion cracking of a titanium alloy in a hydrogen-free environment; automation in corrosion fatigue crack growth rate measurements; the breaking load method, a new approach for assessing resistance to growth of early stage stress corrosion cracks; stress corrosion cracking properties of 2090 Al-Li alloy; repair welding of cracked free machining Invar 36; radial bore cracks in rotating disks.

  9. Environmentally assisted cracking in Light Water Reactors. Volume 16: Semiannual report, October 1992--March 1993

    SciTech Connect

    Chung, H.M.; Chopra, O.K.; Ruther, W.E.; Kassner, T.F.; Michaud, W.F.; Park, J.Y.; Sanecki, J.E.; Shack, W.J.

    1993-09-01

    This report summarizes work performed by Argonne National Laboratory on fatigue and environmentally assisted cracking (EAC) in light water reactors (LWRs) during the six months from October 1992 to March 1993. Fatigue and EAC of piping, pressure vessels, and core components in LWRs are important concerns as extended reactor lifetimes are envisaged. Topics that have been investigated include (1) fatigue of low-alloy steel used in piping, steam generators, and reactor pressure vessels. (2) EAC of cast stainless steels (SSs), (3) radiation-induced segregation and irradiation-assisted stress corrosion cracking of Type 304 SS after accumulation of relatively high fluence, and (4) EAC of low-alloy steels. Fatigue tests were conducted on medium-sulfur-content A106-Gr B piping and A533-Gr B pressure vessel steels in simulated PWR water and in air. Additional crack growth data were obtained on fracture-mechanics specimens of cast austenitic SSs in the as-received and thermally aged conditions and chromium-nickel-plated A533-Gr B steel in simulated boiling-water reactor (BWR) water at 289{degrees}C. The data were compared with predictions based on crack growth correlations for ferritic steels in oxygenated water and correlations for wrought austenitic SS in oxygenated water developed at ANL and rates in air from Section XI of the ASME Code. Microchemical and microstructural changes in high- and commercial-purity Type 304 SS specimens from control-blade absorber tubes and a control-blade sheath from operating BWRs were studied by Auger electron spectroscopy and scanning electron microscopy.

  10. EPRI-NASA Cooperative Project on Stress Corrosion Cracking of Zircaloys. [nuclear fuel failures

    NASA Technical Reports Server (NTRS)

    Cubicciotti, D.; Jones, R. L.

    1978-01-01

    Examinations of the inside surface of irradiated fuel cladding from two reactors show the Zircaloy cladding is exposed to a number of aggressive substances, among them iodine, cadmium, and iron-contaminated cesium. Iodine-induced stress corrosion cracking (SCC) of well characterized samples of Zircaloy sheet and tubing was studied. Results indicate that a threshold stress must be exceeded for iodine SCC to occur. The existence of a threshold stress indicates that crack formation probably is the key step in iodine SCC. Investigation of the crack formation process showed that the cracks responsible for SCC failure nucleated at locations in the metal surface that contained higher than average concentrations of alloying elements and impurities. A four-stage model of iodine SCC is proposed based on the experimental results and the relevance of the observations to pellet cladding interaction failures is discussed.

  11. A review and assessment of the stress-intensity factors for surface cracks

    NASA Technical Reports Server (NTRS)

    Newman, J. C., Jr.

    1979-01-01

    The stress-intensity factor solutions proposed for a surface crack in a finite plate subjected to uniform tension are reviewed. Fourteen different solutions obtained over the past 16 years using approximate analytical methods, experimental methods, and engineering estimates are compared. The accuracy of the various solutions is assessed by correlating fracture data on surface-cracked tension specimens made of a brittle epoxy material. Fracture of the epoxy material was characterized by a constant value of stress-intensity factor as failure. Thus, the correctness of various solutions is judged by the variations in the stress-intensity factors at failure. The solutions were ranked in order of minimum standard deviation. The highest ranking solutions correlated 95% of data analyzed within + or - 10% whereas the lowest ranking solutions correlated 95% of data analyzed within + or - 20%. Some solutions could be applied to all data considered, whereas others were limited with respect to crack shapes and crack sizes that could be analyzed.

  12. Extreme stress gradient effects on microstructural fatigue crack propagation rates in Ni microbeams

    SciTech Connect

    Sadeghi-Tohidi, F.; Pierron, O. N.

    2015-05-18

    The fatigue crack propagation behavior of microstructurally small cracks growing under extreme stress gradients was investigated in Ni microbeams under fully reversed cyclic loading. A technique to calculate the crack growth rates in microbeams with two different normalized stress gradients (17% and 50% μm{sup −1}) is developed and validated. Decreasing crack propagation rates are observed over the first 2 μm, and the rates are more than 1 order of magnitude slower for the devices with 50% μm{sup −1} stress gradients. This fundamental knowledge is critical to predict the fatigue reliability of advanced metallic microcomponents under bending such as in microelectromechanical systems or flexible/stretchable electronics.

  13. The Studies of Thiosulfate and Lead-induced Stress Corrosion Cracking of Alloy 800

    NASA Astrophysics Data System (ADS)

    Yu, Liang

    Scratch test and scanning electrochemical microscopy (SECM) were applied to study the effects of thiosulfate on stress corrosion cracking (SCC) of Alloy 800 in simulated crevice solutions. The results showed that thiosulfate cathodically shifted the pitting potential of Alloy 800 significantly and the pitting morphology on the electrode surface was also different from that formed in the absence of thiosulfate. The synergistic effect between thiosulfate and stress was also observed, which was mainly promoting enhanced anodic dissolution at active sites. In the lead-induced stress corrosion crackings (PbSCC) work, the crack propagation rate (CPR) of Alloy 800 double cantilever specimen were estimated in neutral crevice chemistries solutions at 300 degree Celsius. The PbSCC of alloy 800 at high temperature were investigated by comparing the CPR rate of Pb-contaminated and Pb-free conditions. A repetitive behavior of crack advance was observed from the measurement. This observation is consistent with the film rupture model.

  14. Three-dimensional analysis of surface crack-Hertzian stress field interaction

    NASA Technical Reports Server (NTRS)

    Ballarini, R.; Hsu, Y.

    1989-01-01

    The results are presented of a stress intensity factor analysis of semicircular surface cracks in the inner raceway of an engine bearing. The loading consists of a moving spherical Hertzian contact load and an axial stress due to rotation and shrink fit. A 3-D linear elastic Boundary Element Method code was developed to perform the stress analysis. The element library includes linear and quadratic isoparametric surface elements. Singular quarter point elements were employed to capture the square root displacement variation and the inverse square root stress singularity along the crack front. The program also possesses the capability to separate the whole domain into two subregions. This procedure enables one to solve nonsymmetric fracture mechanics problems without having to separate the crack surfaces a priori. A wide range of configuration parameters was investigated. The ratio of crack depth to bearing thickness was varied from one-sixtieth to one-fifth for several different locations of the Hertzian load. The stress intensity factors for several crack inclinations were also investigated. The results demonstrate the efficiency and accuracy of the Boundary Element Method. Moreover, the results can provide the basis for crack growth calculations and fatigue life prediction.

  15. Stress corrosion cracking resistance of weld metals 182, 72, and 308L

    SciTech Connect

    Sarver, J.M. . Research and Development Div.)

    1992-08-01

    A laboratory test program was conducted to compare the stress corrosion cracking (SCC) behavior of three weld metals in two boiling water reactor (BWR) environments. Tests were performed on compact tension specimens produced from Alloy 316L plates welded with weld metal 182, 308L, or 72. The specimens were notched, side-grooved, and precracked such that all crack growth would occur in weld metal. The specimens were notched to four different depths to allow several stress intensities to be studied at one time. Daisy-chained strings of specimens were loaded via the internal autoclave pressure. Tests were performed in a normal operating BWR environment and a BWR environment faulted with sulfate and oxygen. Test temperature was 550{degrees}F and test pressures ranged from 1200 to 2900 psi. Due to the specimen loading arrangement, varying the autoclave pressure changed the stress intensity on the specimens. Crack growth was monitored using a computer-automated potential drop (PD) system. A computer program was written which sequentially recorded PD and reference PD data, and calculated crack lengths and stress intensities for all the specimen. The crack growth rate was calculated for each specimen after every exposure. Plots of da/dt versusK were constructed for each weld metal in both environments. Following the test exposure, all the specimens were fractured and the fracture faces were examined. The visual examination results were then comparedto the PD-calculated crack lengths and stress intensities.

  16. Stress corrosion cracking resistance of weld metals 182, 72, and 308L. Final report

    SciTech Connect

    Sarver, J.M.

    1992-08-01

    A laboratory test program was conducted to compare the stress corrosion cracking (SCC) behavior of three weld metals in two boiling water reactor (BWR) environments. Tests were performed on compact tension specimens produced from Alloy 316L plates welded with weld metal 182, 308L, or 72. The specimens were notched, side-grooved, and precracked such that all crack growth would occur in weld metal. The specimens were notched to four different depths to allow several stress intensities to be studied at one time. Daisy-chained strings of specimens were loaded via the internal autoclave pressure. Tests were performed in a normal operating BWR environment and a BWR environment faulted with sulfate and oxygen. Test temperature was 550{degrees}F and test pressures ranged from 1200 to 2900 psi. Due to the specimen loading arrangement, varying the autoclave pressure changed the stress intensity on the specimens. Crack growth was monitored using a computer-automated potential drop (PD) system. A computer program was written which sequentially recorded PD and reference PD data, and calculated crack lengths and stress intensities for all the specimen. The crack growth rate was calculated for each specimen after every exposure. Plots of da/dt versusK were constructed for each weld metal in both environments. Following the test exposure, all the specimens were fractured and the fracture faces were examined. The visual examination results were then comparedto the PD-calculated crack lengths and stress intensities.

  17. Kinetic studies of the stress corrosion cracking of D6AC steel

    NASA Technical Reports Server (NTRS)

    Noronha, P. J.

    1975-01-01

    The effect of load interactions on the crack growth velocity of D6AC steel under stress corrosion cracking conditions was determined. The environment was a 3.5 percent salt solution. The modified-wedge opening load specimens were fatigue precracked and subjected to a deadweight loading in creep machines. The effects of load shedding on incubation times and crack growth rates were measured using high-sensitivity compliance measurement techniques. Load shedding results in an incubation time, the length of which depends on the amount of load shed and the baseline stress intensity. The sequence of unloading the specimen also controls the subsequent incubation period. The incubation period is shorter when load shedding passes through zero load than when it does not if the specimen initially had the same baseline stress intensity. The crack growth rates following the incubation period are also different from the steady-state crack growth rate at the operating stress intensity. These data show that the susceptibility of this alloy system to stress corrosion cracking depends on the plane-strain fracture toughness and on the yield strength of the material.

  18. Neutron diffraction determination of the residual stress redistribution in cracked autofrettaged tubing

    SciTech Connect

    Bourke, M.A. ); McGillivray, H.J.; Webster, G.A. . Dept. of Mechanical Engineering); Webster, P.J. . Dept. of Civil Engineering)

    1991-01-01

    Neutron diffraction has been used to measure the residual stress distributions in uncracked and fatigue cracked rings taken from a high strength, low alloy steel autofrettage tube with a bore diameter of 60mm and a wall thickness of 32mm. Stresses were determined to a precision of {plus minus} 10MPa. Three crack sixes were examines. No appreciable stress redistribution was observed until the crack was grown into a region which originally contained tensile residual hoop stress. When this occurred an increase in residual hoop tension was observed ahead of the crick tip. Qualitative agreement was achieved between the measured hoop stress distribution and values predicted using a boundary element method. 9 refs., 12 figs.

  19. On the measurement of the crack tip stress field as a means of determining Delta K(sub eff) under conditions of fatigue crack closure

    NASA Technical Reports Server (NTRS)

    Wallhead, Ian R.; Edwards, Lyndon; Poole, Peter

    1994-01-01

    The optical method of caustics has been successfully extended to enable stress intensity factors as low as 1MPa square root of m to be determined accurately for central fatigue cracks in 2024-T3 aluminium alloy test panels. The feasibility of using this technique to study crack closure, and to determine the effective stress intensity factor range, Delta K(sub eff), has been investigated. Comparisons have been made between the measured values of stress intensity factor, K(sub caus), and corresponding theoretical values, K(sub theo), for a range of fatigue cracks grown under different loading conditions. The values of K(sub caus) and K(sub theo) were in good agreement at maximum stress, where the cracks are fully open, while K(sub caus) exceeded K(sub theo) at minimum stress, due to crack closure. However, the levels of crack closure and values of Delta K(sub eff) obtained could not account for the variations of crack growth rate with loading conditions. It is concluded that the values of Delta K(sub eff), based on caustic measurements in a 1/square root of r stress field well outside the plastic zone, do not fully reflect local conditions which control crack tip behavior.

  20. Intergranular stress corrosion cracking: A rationalization of apparent differences among stress corrosion cracking tendencies for sensitized regions in the process water piping and in the tanks of SRS reactors

    SciTech Connect

    Louthan, M.R.

    1990-09-28

    The frequency of stress corrosion cracking in the near weld regions of the SRS reactor tank walls is apparently lower than the cracking frequency near the pipe-to-pipe welds in the primary cooling water system. The difference in cracking tendency can be attributed to differences in the welding processes, fabrication schedules, near weld residual stresses, exposure conditions and other system variables. This memorandum discusses the technical issues that may account the differences in cracking tendencies based on a review of the fabrication and operating histories of the reactor systems and the accepted understanding of factors that control stress corrosion cracking in austenitic stainless steels.

  1. Stress intensity factors for an underclad nozzle corner crack subjected to pressure and thermal loading

    SciTech Connect

    Wilkening, W.W.

    1991-06-01

    The opening mode linear elastic stress intensity factor, K{sub I}, was computed, via 3-D elastic finite element techniques, for an embedded elliptical crack located just beneath the cladding at the nozzle corner in a pressure vessel. Pressure loading and several thermal transient loading conditions were analyzed. The underclad crack was explicitly modeled and K{sub I} was computed explicitly, from the energy release rate, J. The variation of the maximum principal stress along the minor axis of the elliptical crack was determined for a companion set of thermal/structural analyses that were performed in the absence of the crack. These stress distributions were linearized into equivalent membrane and bending stress components that were used to compute K{sub I} from the Shah and Kobayashi solutions for near-surface embedded elliptical cracks. The explicitly computed K{sub I} values were found to be in very good agreement with the K{sub I} values computed from the flat plate'' solutions of Reference 1, for all the loading cases analyzed. An additional comparison was made between the energy release rate results and the results obtained by fitting the 1/{radical}r stress singularity to the crack tip stress field at the Gaussian integration points nearest to the crack front. The observed excellent agreement between the two independent explicit'' computational methods served to verify each of the methods and also demonstrated the adequacy of the refinement of the finite element mesh. These observations support the use of the Shah and Kobayashi flat plate K{sub I} solutions for analyzing underclad cracks at the nozzle corner. 7 refs., 11 figs.

  2. The influence of stress ratio and temperature on the fatigue crack growth rate behavior of ARALL

    SciTech Connect

    Salivar, G.C.; Gardini, C.A. Pratt Whitney Group, West Palm Beach, FL )

    1993-01-01

    The fatigue crack growth rate behavior of ARALL (aramid-reinforced aluminum laminate) was investigated as a function of stress ratio and temperature. The particular material was ARALL-3, a 7475-T76 aluminum alloy laminate. Tests were conducted for stress ratios of 0.1 and 0.5 at temperatures of 21, 82, and 93 C (70, 180, and 200 F) using a center-cracked panel geometry (measurements were made in English units and converted to SI units). The objective was to examine the contributions of the effects of crack closure and fiber bridging of the crack on the material behavior. Crack closure was monitored throughout the tests using compliance measurements. Fractography was used to investigate the influence of temperature on the integrity of the aluminum to epoxy/fiber bond to try to identify the effects of fiber bridging. Some crack closure, in the traditional metallic material sense, was evident through compliance measurements. However, the crack tip bridging by the fibers appears to be the dominant mechanism influencing the fatigue crack growth rate behavior in this material under these test conditions. Fractography indicates a considerable difference in fiber-bridging behavior between the room temperature and the elevated temperature tests. 19 refs.

  3. Analysis of stress corrosion cracking in alloy 718 following commercial reactor exposure

    NASA Astrophysics Data System (ADS)

    Leonard, Keith J.; Gussev, Maxim N.; Stevens, Jacqueline N.; Busby, Jeremy T.

    2015-11-01

    Alloy 718 is generally considered a highly corrosion-resistant material but can still be susceptible to stress corrosion cracking (SCC). The combination of factors leading to SCC susceptibility in the alloy is not always clear enough. In the present work, alloy 718 leaf spring (LS) materials that suffered stress corrosion damage during two 24-month cycles in pressurized water reactor service, operated to >45 MWd/mtU burn-up, was investigated. Compared to archival samples fabricated through the same processing conditions, little microstructural and property changes occurred in the material with in-service irradiation, contrary to high dose rate laboratory-based experiments reported in literature. Though the lack of delta phase formation along grain boundaries would suggest a more SCC resistant microstructure, grain boundary cracking in the material was extensive. Crack propagation routes were explored through focused ion beam milling of specimens near the crack tip for transmission electron microscopy as well as in polished plan view and cross-sectional samples for electron backscatter diffraction analysis. It has been shown in this study that cracks propagated mainly along random high-angle grain boundaries, with the material around cracks displaying a high local density of dislocations. The slip lines were produced through the local deformation of the leaf spring material above their yield strength. The cause for local SCC appears to be related to oxidation of both slip lines and grain boundaries, which under the high in-service stresses resulted in crack development in the material.

  4. Analysis of stress corrosion cracking in alloy 718 following commercial reactor exposure

    SciTech Connect

    Leonard, Keith J.; Gussev, Maxim N.; Stevens, Jacqueline N.; Busby, Jeremy T.

    2015-08-24

    Alloy 718 is generally considered a highly corrosion-resistant material but can still be susceptible to stress corrosion cracking (SCC). The combination of factors leading to SCC susceptibility in the alloy is not always clear enough. In this paper, alloy 718 leaf spring (LS) materials that suffered stress corrosion damage during two 24-month cycles in pressurized water reactor service, operated to >45 MWd/mtU burn-up, was investigated. Compared to archival samples fabricated through the same processing conditions, little microstructural and property changes occurred in the material with in-service irradiation, contrary to high dose rate laboratory-based experiments reported in literature. Though the lack of delta phase formation along grain boundaries would suggest a more SCC resistant microstructure, grain boundary cracking in the material was extensive. Crack propagation routes were explored through focused ion beam milling of specimens near the crack tip for transmission electron microscopy as well as in polished plan view and cross-sectional samples for electron backscatter diffraction analysis. It has been shown in this study that cracks propagated mainly along random high-angle grain boundaries, with the material around cracks displaying a high local density of dislocations. The slip lines were produced through the local deformation of the leaf spring material above their yield strength. Also, the cause for local SCC appears to be related to oxidation of both slip lines and grain boundaries, which under the high in-service stresses resulted in crack development in the material.

  5. Peak Stress Intensity Factor Governs Crack Propagation Velocity In Crosslinked UHMWPE

    PubMed Central

    Sirimamilla, P. Abhiram; Furmanski, Jevan; Rimnac, Clare

    2013-01-01

    Ultra high molecular weight polyethylene (UHMWPE) has been successfully used as a bearing material in total joint replacement components. However, these bearing materials can fail as a result of in vivo static and cyclic loads. Crack propagation behavior in this material has been considered using the Paris relationship which relates fatigue crack growth rate, da/dN (mm/cycle) versus the stress intensity factor range, ΔK (Kmax-Kmin, MPa√m). However, recent work suggests that the crack propagation velocity of conventional UHMWPE is driven by the peak stress intensity (Kmax), not ΔK. The hypothesis of this study is that the crack propagation velocity of highly crosslinked and remelted UHMWPE is also driven by the peak stress intensity, Kmax, during cyclic loading, rather than by ΔK. To test this hypothesis, two highly crosslinked (65 kGy and 100 kGy) and remelted UHMWPE materials were examined. Frequency, waveform and R-ratio were varied between test conditions to determine the governing factor for fatigue crack propagation. It was found that the crack propagation velocity in crosslinked UHMWPE is also driven by Kmax and not ΔK, and is dependent on loading waveform and frequency in a predictable quasi-static manner. The current study supports that crack growth in crosslinked UHMWPE materials, even under cyclic loading conditions, can be described by a relationship between the velocity of crack growth, da/dt and the peak stress intensity, Kmax. The findings suggest that stable crack propagation can occur as a result of static loading only and this should be taken into consideration in design of UHMWPE total joint replacement components. PMID:23165898

  6. Influence of texture on iodine-induced stress corrosion cracking of Zircaloy-4 cladding tubes

    NASA Astrophysics Data System (ADS)

    Schuster, I.; Lemaignan, C.

    1992-07-01

    A specific study was carried out to measure the influence of texture on the behaviour of Zircaloy-4 under iodine-induced stress corrosion cracking. The aim was to determine the relative effects of various metallurgical parameters involved in fuel rod fracture by pellet-clad interaction (PCI). Cladding tubes of different geometries were manufactured from a given Zircaloy-4 ingot. In this way tubes with different textures were obtained. Rings from these tubes were then subjected to slow tensile tests in an inert atmosphere and in an iodine vapour atmosphere. The sensitivity of the tubes to stress corrosion cracking is quantified by the loss of ductility on fracture between the tests in each atmosphere. Combined with the findings of other studies, the results showed that: (a) texture has a strong effect on the stress corrosion cracking behaviour of Zircaloy-4, (b) the mechanical properties do not have any bearing on the material behaviour under stress corrosion cracking, and that the better behaviour of a recrystallized material — compared to the same material in a stress-relieved state — can be explained solely by the texture effect, (c) texture is a more important parameter than chemical composition of Zircaloy-4, on condition that this composition remains within the ASTM specification. The conflict between the various mechanisms involved in stress corrosion crack propagation may explain these observations. Preliminary extrapolation of these conclusions to the irradiated material shows that a more specific study is needed using appropriate parameters.

  7. Mitigation of Stress Corrosion Cracking Susceptibility of Machined 304L Stainless Steel Through Laser Peening

    NASA Astrophysics Data System (ADS)

    Sundar, R.; Ganesh, P.; Kumar, B. Sunil; Gupta, R. K.; Nagpure, D. C.; Kaul, R.; Ranganathan, K.; Bindra, K. S.; Kain, V.; Oak, S. M.; Singh, Bijendra

    2016-07-01

    The paper describes an experimental study aimed at suppressing stress corrosion cracking susceptibility of machined 304L stainless steel specimens through laser shock peening. The study also evaluates a new approach of oblique laser shock peening to suppress stress corrosion cracking susceptibility of internal surface of type 304L stainless steel tube. The results of the study, performed with an indigenously developed 2.5 J/7 ns Nd:YAG laser, demonstrated that laser shock peening effectively suppresses chloride stress corrosion cracking susceptibility of machined surface of type 304L stainless steel. In the investigated range of incident laser power density (3.2-6.4 GW/cm2), machined specimens peened with power density of 4.5 and 6.4 GW/cm2 displayed lower stress corrosion cracking susceptibility considerably than those treated with 3.2 and 3.6 GW/cm2 in boiling magnesium chloride test. Oblique laser shock peening, performed on machined internal surface of a type 304L stainless steel tube (OD = 111 mm; ID = 101 mm), was successful in introducing residual compressive surface stresses which brought about significant suppression of its stress corrosion cracking susceptibility. The technique of oblique laser shock peening, in spite of its inherent limitations on the length of peened region being limited by tube internal diameter and the need for access from both the sides, presents a simplified approach for peening internal surface of small tubular components.

  8. Stress Corrosion Cracking Model for High Level Radioactive-Waste Packages

    SciTech Connect

    P. Andresen; G. Gordon; S. Lu

    2004-10-05

    A stress corrosion cracking (SCC) model has been adapted for performance prediction of high level radioactive-waste packages to be emplaced in the proposed Yucca Mountain repository. For waste packages of the proposed Yucca Mountain repository, the outer barrier material is the highly corrosion-resistant Alloy UNS-N06022 (Alloy 22), the environment is represented by aqueous brine films present on the surface of the waste package from dripping or deliquescence of soluble salts present in any surface deposits, and the tensile stress is principally from weld induced residual stress. SCC has historically been separated into ''initiation'' and ''propagation'' phases. Initiation of SCC will not occur on a smooth surface if the surface stress is below a threshold value defined as the threshold stress. Cracks can also initiate at and propagate from flaws (or defects) resulting from manufacturing processes (such as welding); or that develop from corrosion processes such as pitting or dissolution of inclusions. To account for crack propagation, the slip dissolution/film rupture (SDFR) model is adopted to provide mathematical formulae for prediction of the crack growth rate. Once the crack growth rate at an initiated SCC is determined, it can be used by the performance assessment to determine the time to through-wall penetration for the waste package. This paper presents the development of the SDFR crack growth rate model based on technical information in the literature as well as experimentally determined crack growth rates developed specifically for Alloy UNS-N06022 in environments relevant to high level radioactive-waste packages of the proposed Yucca Mountain radioactive-waste repository. In addition, a seismic damage related SCC crack opening area density model is briefly described.

  9. Real-time Observations of Rock Cracking and Weather Provide Insights into Thermal Stress-Related Processes of Mechanical Weathering.

    NASA Astrophysics Data System (ADS)

    Eppes, M. C.; Magi, B. I.; Keanini, R.

    2015-12-01

    The environmental conditions (weather and/or climate) that limit or drive mechanical weathering via thermal stress are poorly understood. Here we examine acoustic emission (AE) records of rock cracking in boulders sitting on the ground in humid-temperate (~1 year of data) and semi-arid (~3 years) locations. We compare on-site average ambient daily temperature for days in which cracking occurs to the average temperatures for those dates derived from local climate records. The temperatures characterizing days on which cracking occurs is similar for both stations (range = -10 C to +30 C); where 21% and 73% of cracking occurs on hot days (> 20C) in the humid and semi-arid climates respectively while 17% and 0.1% occurs on very cold days (-8C to -3C). When days during which cracking occurs are compared to climate averages, 81% (NC) and 51% (NM) of all cracking occurs on days with absolute temperature anomalies >1, regardless of the temperature. The proportion of cracking that occurs on anomalously hot or cold days rises to 92% and 77% when the data is normalized to account for uneven sampling of the days with extreme temperatures. In order to determine to what extent this trend holds true in a more complex setting, we examined an existing 100+ year record of rock falls from Yosemite Valley. Preliminary results, although more equivocal, are consistent with the boulder cracking AE data. We examine the AE datasets in the context of our previous numerical modeling of insolation-driven thermal stress in rock and hypothesize that there is an increased potential for fracture on days with extreme temperatures because 1) thermal-stress is dependent on temperature variance from far-field and/or average rock temperatures and 2) that days with climatologically extreme air temperatures result in maximums in such variance. An implication of our results is that environments with extreme weather variability may have higher thermal breakdown rates, including certain locations today and

  10. Hydrogen role in stress corrosion cracking process of iron aluminide Fe{sub 3}Al in NaCl solution

    SciTech Connect

    Chiu, H.; Qiao, L.; Mao, X.

    1995-09-01

    The stress corrosion cracking behavior of Fe3AI based intermetallic alloy in 3.5% NaCl solution was studied. The role of hydrogen in the cracking process was also defined. The susceptibility of the alloy to hydrogen embrittlement was first investigated by performing tensile tests in air environment and mineral oil. It was found that ductility increased with increasing strain rate when tested in air, but stayed at a high value when tested in mineral oil. This behavior indicates that the alloy is sensitive to hydrogen embrittlement in air. In 3.5% NaCl solution, the environmental effect was studied by slow strain rate tests that were done at electrochemical potentials ranging from {minus}1,000 mV to 0 mV vs SCE. When tested at anodic potentials, from {minus}500 mV to 0 mV vs SCE, ductility reduced from 8.7% to 3.9%. When tested in cathodic region, from {minus}500 mV to {minus}1,000 mV, the ductility was between 7.3% to 9.1%. Results of tests done on pre-immersed specimens and notched tensile specimens confirmed this material degradation to be caused by stress corrosion cracking (SCC). To identify the mechanism, an electrochemical permeation technique was employed. By measuring the diffusible hydrogen concentration, sensitivity to hydrogen embrittlement has been assessed at different potentials. Anodic dissolution is believed to be the controlling mechanism of the SCC as the alloy is less sensitive to hydrogen embrittlement at anodic potentials. Fracture surfaces were examined under the scanning electron microscope (SEM). Fracture mode was found to be mainly transgranular quasi-cleavage, except the ones tested at anodic potentials on which intergranular fracture area was found near the edge. This intergranular fracture, which increases with increasing anodic potential, is believed to be the stress corrosion cracking area. Pits which corroded intergranularly are the crack initiation sites.

  11. On the variation in crack-opening stresses at different locations in a three-dimensional body

    NASA Technical Reports Server (NTRS)

    Chermahini, R. G.; Blom, Anders F.

    1990-01-01

    Crack propagation and closure behavior of thin, and thick middle crack tension specimens under constant amplitude loading were investigated using a three dimensional elastic plastic finite element analysis of fatigue crack propagation and closure. In the thin specimens the crack front closed first on the exterior (free) surface and closed last in the interior during the unloading portion of cyclic loading; a load reduced displacement technique was used to determine crack opening stresses at specified locations in the plate from the displacements calculated after the seven cycle. All the locations were on the plate external surface and were located near the crack tip, behind the crack tip, at the centerline of the crack. With this technique, the opening stresses at the specified points were found to be 0.52, 0.42, and 0.39 times the maximum applied stress.

  12. Iron contamination causes stress corrosion cracking in stainless steels

    SciTech Connect

    Khatak, H.S.; Bharasi, N.S.; Gnanamoorthy, J.B. . Metallurgy Div.)

    1994-06-01

    Iron-contaminated U-bend samples of types 316 and 304 stainless steels (SS) were exposed to a sodium chloride solution in the laboratory at room temperature. Two of the four samples of 304 SS and one of the four samples of 316 SS showed cracking. The cracks initiated in the iron-contaminated regions. Based on the results of these tests, the failure of many components in industries can be explained and the importance of carrying out pickling and passivation immediately after fabrication to remove possible iron contamination is highlighted.

  13. Aqueous stress-corrosion cracking of high-toughness D6AC steel

    NASA Technical Reports Server (NTRS)

    Gilbreath, W. P.; Adamson, M. J.

    1976-01-01

    The crack growth behavior of D6AC steel as a function of stress intensity, stress and corrosion history, and test technique, under sustained load in filtered natural seawater, 3.3 per cent sodium chloride solution, and distilled water, was investigated. Reported investigations of D6AC were considered in terms of the present study with emphasis on thermal treatment, specimen configuration, fracture toughness, crack-growth rates, initiation period, and threshold. Both threshold and growth kinetics were found to be relatively insensitive to these test parameters. The apparent incubation period was dependent on technique, both detection sensitivity and precracking stress intensity level.

  14. Effects of texture and microstructure on the propagation of iodine stress corrosion cracks in Zircaloy

    SciTech Connect

    Knorr, D.B.; Pelloux, R.M.

    1982-01-01

    Failure of some fuel elements in light water nuclear reactors has been attributed to stress corrosion cracking of the fuel cladding. Mechanical interaction between the fuel pellets and cladding tube generates a tensile hoop stress. Release of volatile fission products, most likely iodine, provides a corrosive environment. An investigation of stress corrosion crack propagation is performed at 300/degree/C in four Pa flowing iodine environment. By varying the orientation of fracture mechanics specimens, the effect of crystallographic texture, heat treatment, and microstructure on K/sub I/(SCC) is studied. 27 refs.

  15. Effects of surface condition on the stress corrosion cracking of line pipe steel

    SciTech Connect

    Beavers, J.A.; Christman, T.K.; Parkins, R.N.

    1988-04-01

    The relationship between surface properties of line pipe steels and external stress corrosion cracking (SCC) is reviewed. Surface factors discussed include mill scale, surface pitting, decarburization, surface residual stresses, and near-surface stress state. Recent research results have demonstrated that the susceptibility of a line pipe steel to SCC initiation is dependent on complicated interaction among these properties. However, these studies also show that relatively simple surface preparation procedures such as grit blasting can be effective in reducing the susceptibility of pipelines to crack initiation.

  16. Proceedings: 1983 Workshop on Primary-Side Stress Corrosion Cracking of PWR Steam Generator Tubing

    SciTech Connect

    1987-11-01

    Utility and vendor representatives from around the world met to share information on stress corrosion cracking of steam generator tubing from the primary side. In 32 presentations, speakers discussed in-plant experience with the phenomenon and related laboratory data. The workshop was the first to present results of remedial stress relief programs.

  17. Some important considerations in the development of stress corrosion cracking test methods.

    NASA Technical Reports Server (NTRS)

    Wei, R. P.; Novak, S. R.; Williams, D. P.

    1972-01-01

    Discussion of some of the precaution needs the development of fracture-mechanics based test methods for studying stress corrosion cracking involves. Following a review of pertinent analytical fracture mechanics considerations and of basic test methods, the implications for test corrosion cracking studies of the time-to-failure determining kinetics of crack growth and life are examined. It is shown that the basic assumption of the linear-elastic fracture mechanics analyses must be clearly recognized and satisfied in experimentation and that the effects of incubation and nonsteady-state crack growth must also be properly taken into account in determining the crack growth kinetics, if valid data are to be obtained from fracture-mechanics based test methods.

  18. Evaluating Hydrogen Stress Cracking of Line Pipe Steels under Cathodic Protection Using Crack Tip Opening Displacement Tests

    NASA Astrophysics Data System (ADS)

    Hagiwara, Naoto; Meyer, Michel

    Crack tip opening displacement (CTOD, δ) tests were carried out for line pipe steels in buffer solutions, sand, and clay to evaluate initiation of hydrogen stress cracking (HSC) at surface defects in buried pipelines under cathodic protection. Four series of line pipe steels and two series of seam welds showed a similar tendency in cathodic current density (i) versus the critical CTOD (δc) curves, irrespective of types, pH and water content of the soils; δc showed a minimum (δHSC) when i>ith (ith=1mA/cm2) in all the testing conditions. δHSC increased with the increasing fracture toughness of the steel. Fluctuation of cathodic current density influenced δc when the maximum value of cathodic current density (imax) was larger than ith. HSC could be initiated at surface defects in pipelines only when imax>ith and δ≥δHSC.

  19. Stress crack resistance of some pigmented and unpigmented tablet film coating systems.

    PubMed

    Okhamafe, A O; York, P

    1985-07-01

    Stress crack resistance parameters--tensile strength: Young's modulus ratio, relative surface energy, and toughness index--have been examined for unpigmented free films of hydroxypropyl methylcellulose containing polyvinyl alcohol, and polyethylene glycols 400 and 1000, as well as similar film systems pigmented with either talc or titanium dioxide. Incorporation of either polyvinyl alcohol or polyethylene glycols 400 and 1000 in hydroxypropyl methylcellulose film coatings eliminated the incidence of edge splitting in the coated tablets. Increase in pigment concentration generally led to a decrease in the crack resistance of pigmented films. There was a relation between the stress crack resistance of pigmented free films and the incidence of edge splitting of corresponding film coatings applied to aspirin tablets--generally, the higher the crack resistance the lower the incidence of edge splitting. A similar relationship applied to the unpigmented films only when the tensile strength: Young's modulus ratio was considered. PMID:2863345

  20. Failure Pressure and Leak Rate of Steam Generator Tubes With Stress Corrosion Cracks

    SciTech Connect

    Majumdar, S.; Kasza, K.; Park, J.Y.; Bakhitiari, S.

    2002-07-01

    This paper illustrates the use of an 'equivalent rectangular crack' approach to predict leak rates through laboratory generated stress corrosion cracks. A comparison between predicted and observed test data on rupture and leak rate from laboratory generated stress corrosion cracks are provided. Specimen flaws were sized by post-test fractography in addition to pre-test advanced eddy current technique. The test failure pressures and leak rates are shown to be closer to those predicted on the basis of fractography than on NDE. However, the predictions based on NDE results are encouraging, particularly because they have the potential to determine a more detailed geometry of ligamentous cracks from which more accurate predictions of failure pressure and leak rate can be made in the future. (authors)

  1. Stress intensity magnification factors for fully circumferential cracks in valve bodies (thick cylinders)

    SciTech Connect

    Toor, P.M.

    1998-11-01

    The stress intensity solutions presented herein were obtained using an energy method in conjunction with a two-dimensional finite element program in order to explicitly account for curvature effect for fully circumferential cracks. The magnification factors for a specific crack depth were calculated by successively loading the crack surface by a uniform, linear, quadratic, and a cubic loading distribution. The magnification factors can be used to calculate the stress intensity factors by superposition method. The functions for each load condition in terms of radius to thickness ratio (R/t) and a fractional distance in terms of crack depth to thickness ratio (a/t) were developed. The validity of these functions is R/t = 1.5 to 10.0 and for 0.0125 {le} a/t {le} 0.8125. The functions agree to within 1% of the finite elements solutions for most magnification factors.

  2. Stress intensity and displacement coefficients for radially cracked ring segments subject to three-point bending

    NASA Technical Reports Server (NTRS)

    Gross, B.; Srawley, J. E.

    1983-01-01

    The boudary collocation method was used to generate Mode 1 stress intensity and crack mouth displacement coefficients for internally and externally radially cracked ring segments (arc bend specimens) subjected to three point radial loading. Numerical results were obtained for ring segment outer to inner radius ratios (R sub o/ R sub i) ranging from 1.10 to 2.50 and crack length to width ratios (a/W) ranging from 0.1 to 0.8. Stress intensity and crack mouth displacement coefficients were found to depend on the ratios R sub o/R sub i and a/W as well as the included angle between the directions of the reaction forces.

  3. Electrochemical aspects of stress-corrosion cracking in. cap alpha. -brass

    SciTech Connect

    Burstein, G T; Newman, R C

    1981-01-01

    This paper considers a number of aspects of the stress-corrosion cracking of brass from the point of view of the localized electrochemical processes occurring at the tip of a propagating crack. The principal system examined is the intergranular SCC of 70-30 brass in near-neutral ammoniacal solutions, for which a detailed mechanism is developed. In addition, the effects of nitrite ions in promoting SCC of both brass and copper are considered.

  4. Three-dimensional elastic stress and displacement analysis of finite circular geometry solids containing cracks

    NASA Technical Reports Server (NTRS)

    Gyekenyesi, J. P.; Mendelson, A.; Kring, J.

    1973-01-01

    A seminumerical method is presented for solving a set of coupled partial differential equations subject to mixed and coupled boundary conditions. The use of this method is illustrated by obtaining solutions for two circular geometry and mixed boundary value problems in three-dimensional elasticity. Stress and displacement distributions are calculated in an axisymmetric, circular bar of finite dimensions containing a penny-shaped crack. Approximate results for an annular plate containing internal surface cracks are also presented.

  5. A fractographic study of iodine-induced stress corrosion cracking in irradiated Zircaloy-2 cladding

    NASA Astrophysics Data System (ADS)

    Shimada, Sachio; Nagai, Masayuki

    1983-02-01

    A fractographic interpretation of stress corrosion cracking (SCC) of Zircaloy-2 was made through detailed scanning electron microscope (SEM) examination of cladding tubes irradiated and subjected to internal pressurization SCC tests in an iodine environment. The SEM examination of the fracture surface revealed that both intergranular and transgranular fracture appeared in the regions of crack initiation. The W-type voids were observed in the intergranular fracture. As the crack proceeded, transgranular fracture, or cleavage facet, became predominant. Cleavage facets were separated by tearing ridges as well as by fluting marks. The appearance of tearing ridges is consistent with the increase of slip systems in α-zirconium with increasing temperature.

  6. Stress corrosion cracking of Ti-8Al-1 Mo-1V in molten salts

    NASA Technical Reports Server (NTRS)

    Smyrl, W. H.; Blackburn, M. J.

    1975-01-01

    The stress corrosion cracking (SCC) behavior of Ti-8Al-1 Mo-1V has been studied in several molten salt environments. Extensive data are reported for the alloy in highly pure LiCl-KCl. The influence of the metallurgical heat treatment and texture, and the mechanical microstructure show similarities with aqueous solutions at lower temperature. The fracture path and cracking modes are also similar to that found in other environments. The influence of H2O and H(-) in molten LiCl-KCl lead to the conclusion that hydrogen does not play a major role in crack extension in this environment.

  7. Anodized aluminum coatings for thermal control. II - Environmental effects and cracking

    NASA Technical Reports Server (NTRS)

    Mcclung, R. C.; Alwitt, R. S.; Jacobs, S.

    1992-01-01

    The environmental effects of thermal cycling and humidity on coating cracking are examined. Experimental measurements of thermal deflection were used to calculate values for the thermal expansion coefficient and the in situ elastic modulus of an anodized aluminum. The thermal expansion coefficient is found to be approximately the same as for alumina in bulk form. The modulus in atmospheres with less than 100 ppm water is about 12,500 ksi. Two sets of experiments are used to study cracking directly during thermal excursions: one determines the minimum temperature (Tc) at which cracks first appear during a single heating cycle and the other involves rapid thermal cycling (RTC) between fixed T max and T min values. Fatigue models for describing initiation of the first crack and the development of multiple cracking are presented, which can be used as the basis for prediction of LEO cracking.

  8. Mechanical and metallurgical effects on low-pH stress corrosion cracking of natural gas pipelines

    SciTech Connect

    Harle, B.A.; Beavers, J.A.; Jaske, C.E.

    1995-12-01

    Stress corrosion cracking of natural gas pipelines in low-pH environments is a serious problem for the gas transmission industry. This paper describes results of an ongoing research program investigating crack growth of API X-65 and X-52 line pipe steels in a low-pH cracking environment using a J-integral technique. The overall objective of the work is to estimate crack growth rates on operating pipelines. In previous work, it was demonstrated that the technique could be utilized to reproduce the cracking observed in the field and that the J integral is a good parameter for characterizing crack growth behavior. Recent work has focused on the evaluation of the influence of loading parameters, such as displacement rate, and metallurgy, on crack growth. Testing has also been performed in which loading sequences involved: (a) a constant displacement rate, until cracking was detected, followed by maintaining a constant displacement; and, (b) slowly loading a specimen to fifty percent of its tensile strength in an inert, non-aqueous environment followed by loading in the low-pH environment.

  9. Stress-intensity factors for internal surface cracks in cylindrical pressure vessels

    NASA Technical Reports Server (NTRS)

    Newman, J. C., Jr.; Raju, I. S.

    1980-01-01

    The paper presents stress-intensity factors for a wide range of semi-elliptical surface cracks on the inside of pressurized cylinders. The ratio of crack depth to crack length ranged from 0.2 to 1; the ratio of crack depth to wall thickness ranged from 0.2 to 0.8; and the ratio of wall thickness to vessel radius was 0.1 to to 0.25. The stress-intensity factors were calculated by a three-dimensional finite-element method using singularity elements along the crack front and linear-strain elements elsewhere. An equation for the stress-intensity factors was obtained which applies over a wide range of configuration parameters and was within about 5 percent of the present results. A comparison was also made between the results and other analyses of internal surface cracks in cylinders. The results from a boundary-integral equation method were in agreement and those from another finite-element method were in fair agreement (+ or - 8 percent) with the results.

  10. A study on fatigue crack growth behavior subjected to a single tensile overload: Part II. Transfer of stress concentration and its role in overload-induced transient crack growth

    SciTech Connect

    Lee, S. Y.; Choo, Hahn; Liaw, Peter K; An, Ke; Hubbard, Camden R

    2011-01-01

    The combined effects of overload-induced enlarged compressive residual stresses and crack tip blunting with secondary cracks are suggested to be responsible for the observed changes in the crack opening load and resultant post-overload transient crack growth behavior [Lee SY, Liaw PK, Choo H, Rogge RB, Acta Mater 2010;59:485-94]. In this article, in situ neutron diffraction experiments were performed to quantify the influence of the combined effects by investigating the internal-stress evolution at various locations away from the crack tip. In the overload-retardation period, stress concentration occurs in the crack blunting region (an overload point) until a maximum crack arrest load is reached. The stress concentration is then transferred from the blunting region to the propagating crack tip (following the overload), requiring a higher applied load, as the closed crack is gradually opened. The transfer phenomena of the stress concentration associated with a crack opening process account for the nonlinearity of strain response in the vicinity of the crack tip. The delaying action of stress concentration at the crack tip is understood in conjunction with the concept of a critical stress (i.e. the stress required to open the closed crack behind the crack tip). A linear relationship between {Delta}{var_epsilon}{sub eff} and {Delta}K{sub eff} provides experimental support for the hypothesis that {Delta}K{sub eff} can be considered as the fatigue crack tip driving force.

  11. The contribution of activated processes to Q. [stress corrosion cracking in seismic wave attenuation

    NASA Technical Reports Server (NTRS)

    Spetzler, H. A.; Getting, I. C.; Swanson, P. L.

    1980-01-01

    The possible role of activated processes in seismic attenuation is investigated. In this study, a solid is modeled by a parallel and series configuration of dashpots and springs. The contribution of stress and temperature activated processes to the long term dissipative behavior of this system is analyzed. Data from brittle rock deformation experiments suggest that one such process, stress corrosion cracking, may make a significant contribution to the attenuation factor, Q, especially for long period oscillations under significant tectonic stress.

  12. In-situ stress analysis of multilayer environmental barrier coatings.

    SciTech Connect

    Harder, B. J.; Almer, J.; Lee, K. N.; Faber, K. T.; Northwestern Univ.; Rolls-Royce Corp.

    2009-06-01

    The biaxial stress and thermal expansion of multilayer doped-aluminosilicate environmental barrier coatings were measured in situ during cooling using microfocused high-energy X-rays in transmission. Coating stresses during cooling from 1000 C were measured for as-sprayed and thermally cycled samples. In the as-sprayed state, tensile stresses as high as 75 MPa were measured in the doped-aluminosilicate topcoat at 375 C, after which a drop in the stress occurred accompanied by through-thickness cracking of the two outermost layers. After thermally cycling the samples, the stress in the topcoat was reduced to approximately 50 MPa, and there was no drop in stress upon cooling. This stress reduction was attributed to a crystallographic phase transformation of the topcoat and the accompanying change in thermal expansion coefficient. The addition of a doped aluminosilicate to the mullite layer did not lower the stress in the topcoat, but may offer increased durability due to an increased compressive stress.

  13. Intergranular stress corrosion cracking susceptibility of neutron-irradiated, thermally sensitized type 304 stainless steel

    SciTech Connect

    Onchi, T.; Hide, K.; Mayuzumi, M.; Hoshiya, T.

    2000-05-01

    Austenitic stainless steels (SS) have been used as core component materials for light water reactors. As reactors age, however, the material tends to suffer from degradation primarily resulting from irradiation-assisted stress corrosion cracking (IASCC) as well as intergranular stress corrosion cracking (IGSCC). Neutron-irradiated, thermally sensitized Type 304 (UNS S30400) stainless steels (SS) were examined by slow strain rate (SSR) stress corrosion cracking (SCC) tests in 290 C water of 0.2 ppm dissolved oxygen concentration (DO) and by SSR tensile tests in 290 C inert gas environment. Neutron fluences ranged from 4 x 10{sup 22} n/m{sup 2} to 3 x 10{sup 25} n/m{sup 2} (energy [E] > 1 MeV). percent intergranular (%IG) cracking, which has been used as an intergranular (IG) cracking susceptibility indicator in the SSR SCC tests, changes anomalously with neutron fluence in spite of the strain-to-failure rate decreasing with an increase of neutron fluence. Apparently, %IG is a misleading indicator for the irradiated, thermally sensitized Type 304 SS and for the irradiated, nonsensitized SS when IG cracking susceptibility is compared at different neutron fluences, test temperatures, DO, and strain rates. These test parameters may affect deformation and fracture behaviors of the irradiated SS during the SSR SCC tests, resulting in changing %IG, which is given by the ratio of the total IG cracking area to the entire fracture surface area. It is suggested that strain-to-IG crack initiation for the irradiated, thermally sensitized SS and for the irradiated, nonsensitized SS is the alternative indicator in the SSR SCC tests. An engineering expedient to determine the IG crack initiation strain is given by a deviating point on superposed stress-strain curves in inert gas and in oxygenated water. The strain-to-IG crack initiation becomes smaller with an increase of neutron fluence and DO. The SSR tensile tests in inert gas are needed to obtain strain-to-IG crack initiation in

  14. Computer simulation of fast crack propagation and arrest in steel plate with temperature gradient based on local fracture stress criterion

    SciTech Connect

    Machida, Susumu; Yoshinari, Hitoshi; Aihara, Shuji

    1997-12-31

    A fracture mechanics model for fast crack propagation and arrest is proposed based on the local fracture stress criterion. Dynamic fracture toughness (K{sub D}) for a propagating crack is calculated as a function of crack velocity and temperature. The model is extended to incorporate the effect of unbroken ligament (UL) formed near the plate surfaces and crack-front-tunneling. The model simulates acceleration, deceleration and arrest of a crack in a ESSO or a double-tension test plate with temperature-gradient. Calculated arrested crack lengths compare well with experimental results. It is shown that the conventional crack arrest toughness calculated from applied stress and arrested crack length depends on temperature-gradient and the toughness is not a unique material property.

  15. SCCIG: a phenomenological model for iodine stress corrosion cracking of Zircaloy. Volume 1. Final report. [PWR; BWR

    SciTech Connect

    Miller, A.K.; Challenger, K.D.; Tasooji, A.; Ranjan, G.V.; Brooks, G.N.; Eisenberger, M.; Thomas, J.M.

    1981-04-01

    This report presents a new model for iodine stress corrosion cracking (SCC) of Zircaloy, developed as an ingredient of EPRI's SPEAR light-water reactor fuel performance code. The model is based on experimental data generated under related EPRI programs and elsewhere, as well as certain theoretical considerations. It is a unified treatment of SCC crack initiation, crack propagation, and non-SCC fracture, treating such sub-process as intergranular failure, transgranular (cleavage plus fluting) failure, ductile rupture, changes in the local stress and strain distribution due to crack formation and growth, iodine penetration along the SCC crack, and the mutual couplings among these processes.

  16. Stress-corrosion cracking in equiaxed 7075 aluminum under tension and torsion loading

    SciTech Connect

    Thompson, A.W. . Dept. of Materials Science and Engineering); Mueller, M.P. ); Bernstein, I.M. )

    1993-11-01

    The environmental response of commercially produced high-strength Al alloys, such as 7075, depends strongly on the anisotropy of the grain structure. Minimum resistance to both stress-corrosion cracking (SCC) and hydrogen embrittlement is observed in the short transverse direction of the pancake'' grain structure in commercially produced alloys. It has not been established, however, exactly how the morphology of the grain structure in commercially produced alloys. It has not been established, however, exactly how the morphology of the grain structure mediates the SCC response or the SCC mechanism. Therefore, stress-corrosion testing of a high-purity 7075 Al alloy (low in Fe, Si, and Cr), having equiaxed grains, under tension (mode I) and torsion (mode III) loading modes, including fractography, appeared to suggest that the predominant processes of SCC were hydrogen embrittlement in mode I and anodic dissolution in mode III, in agreement with prior work on a commercially produced 7075 alloy, but that severe corrosion during longer tests renders those results unsuitable for threshold determination in this very aggressive testing environment.

  17. Stress-corrosion cracking issues related to a water-cooled ITER

    NASA Astrophysics Data System (ADS)

    Jones, R. H.; Bruemmer, S. M.; Henager, C. H.

    1991-03-01

    A review of water impurity and temperature effects on stress-corrosion cracking of austenitic stainless steel is presented. These results demonstrate that stress-corrosion crack growth can occur at ITER relevant temperatures for certain water chemistries and material conditions. A model developed at PNL to calculate the degree of sensitization was used to estimate the potential for sensitization of Type 316 SS and US PCA. This analysis shows that both materials can be severely sensitized but, with proper processing and fabrication, sensitization should be avoidable.

  18. Determination of the residual stress-crack opening relationship of SFRC flexural members

    NASA Astrophysics Data System (ADS)

    Kaklauskas, Gintaris; Gribniak, Viktor; Meskenas, Adas; Rimkus, Arvydas; Kaklauskas, Arturas; Kupliauskas, Rimantas

    2013-10-01

    Steel fibre reinforced concrete (SFRC) has become widespread material in building areas such as underground shotcrete structures or industrial floors. However, due to the absence of universally accepted guidelines for SFRC, application fields of this material are still limited. This paper deals with assessment of the residual stresses of tensile SFRC. An adequate method for determination of residual stress-crack opening relation, based on test data of three-point bending beams is proposed. To verify the analysis results a numerical modelling is utilized employing a nonlinear finite element analysis program. Simulated load-crack width curves were compared with the experimental data validating adequacy of the proposed model.

  19. Effect of film thickness and particle size on cracking stresses in drying latex films.

    PubMed

    Yow, Huai Nyin; Goikoetxea, Monika; Goehring, Lucas; Routh, Alexander F

    2010-12-15

    The stress at which latex films crack during drying was investigated using beam bending. Two systems were investigated: (i) poly(methyl methacrylate/butyl acrylate) particles cast as thin films to examine the effect of film thickness on cracking film stress and (ii) polystyrene particles dried as drops to investigate the effect of particle size. Results indicated an inverse relationship between film thickness and film stress, whilst film stress was shown to be independent of the original particle size. These outcomes were in good agreement with Tirumkudulu and Russel's theoretical analysis [M.S. Tirumkudulu and W.B. Russel, Langmuir 21 (2005) 4938], albeit the measured stress values were almost twice the theoretical estimation. PMID:20851402

  20. The effect of focused ion beam machining on residual stress and crack morphologies in alumina

    NASA Astrophysics Data System (ADS)

    Inkson, B. J.; Leclere, D.; Elfallagh, F.; Derby, B.

    2006-02-01

    Focused ion beams (FIB) are widely used to locally sputter away material from surfaces at the nanoscale, but the effect of localised geometry changes and surface damage generated by FIB processing on material stress states are poorly understood. Evolution of stress states has been investigated in alumina samples with high local residual stress concentrations around nanoindents and scratches. Crack morphologies under the nanoindents and scratches have been investigated with respect to the location and geometry of the 'cross-sectional' surface trenches machined by FIB. It is found that the density of cracks observed around the nanoindentation sites depends on the location and milling sequence of the cross-sectional FIB trenches which alter local stress states. Cr3+ fluorescence spectroscopy has additionally been used to map stresses around alumina scratch and FIB-machined surface trenches.

  1. Stress Corrosion Cracking Study of Aluminum Alloys Using Electrochemical Noise Analysis

    NASA Astrophysics Data System (ADS)

    Rathod, R. C.; Sapate, S. G.; Raman, R.; Rathod, W. S.

    2013-12-01

    Stress corrosion cracking studies of aluminum alloys AA2219, AA8090, and AA5456 in heat-treated and non heat-treated condition were carried out using electrochemical noise technique with various applied stresses. Electrochemical noise time series data (corrosion potential vs. time) was obtained for the stressed tensile specimens in 3.5% NaCl aqueous solution at room temperature (27 °C). The values of drop in corrosion potential, total corrosion potential, mean corrosion potential, and hydrogen overpotential were evaluated from corrosion potential versus time series data. The electrochemical noise time series data was further analyzed with rescaled range ( R/ S) analysis proposed by Hurst to obtain the Hurst exponent. According to the results, higher values of the Hurst exponents with increased applied stresses showed more susceptibility to stress corrosion cracking as confirmed in case of alloy AA 2219 and AA8090.

  2. Remote field eddy current detection of stress-corrosion cracks. Final report

    SciTech Connect

    Nestleroth, J.B.

    1990-02-01

    The feasibility of detecting stress-corrosion cracks (SSC) using the Remote Field Eddy Current (RFEC) technique was demonstrated. The RFEC technique interrogates the entire thickness of the pipe and is applicable for in-line inspection. If it can be shown that the RFEC technique is effective in detecting SSC, then the technique is an ideal method for detecting the defects of interest. A defect detection model is proposed for explaining the mechanism for crack detection. For axially oriented, closed cracks, such as SCC, the conventional defect detection model proved to be too simplistic and not applicable. Therefore, a new detection mode that examines the flow of circumferential eddy currents was developed based on experimental results. This model, though not rigorous, provides a general understanding of the applicability of the RFEC technique for finding SSC. The data from the cracks and various artificial defects is presented in three formats: isometric projections, pseudocolor images and line-of-sight data. Though only two cracks were found, the experimental results correlate well with the circumferential eddy current theory. A theoretical analysis of the effects of motion on the output signal of the receiver is presented. This analysis indicates that inspection speed of simple implementations may be limited to a few miles per hour. Remote field eddy current inspection has excellent potential for inspection of gas transmission lines for detecting stress corrosion cracks that should be further developed.

  3. Cessation of environmentally-assisted cracking in a low-alloy steel: Experimental results

    SciTech Connect

    Li, Y.Y.

    1997-01-01

    The presence of dissolved metallurgical sulfides in pressure vessel and piping steels has been linked to Environmentally-Assisted Cracking (EAC), a phenomenon observed in laboratory tests that results in fatigue crack growth rates as high as 100 times that in air. Previous experimental and analytical work based on diffusion as the mass transport process has shown that surface cracks that are initially clean of sulfides will not initiate EAC in most applications. This is because the average crack tip velocity would not be sufficiently high to expose enough metallurgical sulfides per unit time and produce the sulfide concentration required for EAC. However, there is a potential concern for the case of a relatively large embedded crack breaking through to the wetted surface. Such a crack would not be initially clean of sulfides, and EAC could initiate. This paper presents the results of a series of experiments conducted on two heats of an EAC susceptible, high-sulfur, low-alloy steel in 243{degrees}C low-oxygen water to further study the phenomenon of EAC persistence at low crack tip velocities. A load cycle profile that incorporated a significant load dwell period at minimum load was used. In one experiment, the fatigue cycling history was such that relatively high crack tip velocities at the start of the experiment produced a persistent case of EAC even when crack tip velocities were later reduced to levels below the EAC initiation velocity. The other series of experiments used initial crack tip velocities that were much lower and probably more realistic. Air precracking of the compact tension specimens produced an initial inventory of undissolved sulfides on the crack flanks that directly simulates the array of sulfides expected from the breakthrough of an embedded crack. In all cases, results showed EAC ceased after several hundred hours of cycling.

  4. Refinery ring groove cracking experience

    SciTech Connect

    Ehmke, E.F.

    1982-05-01

    This paper presents the results of a questionnaire on the problem of ring groove cracking in reactors. The results were found to be inconclusive in providing any information on correcting the problem. One report pertaining to a ring groove crack on a 24-inch reactor nozzle served as a warning that cracks may progress beyond the overlay, through it is not known if the base metal can easily crack at low temperatures. The results did not indicate at what point the cracks occurred, but what was common to almost all cracks was that the flange had been in high-temperature, high-pressure hydrogen suggesting that dissolved hydrogen or environmental hydrogen assisted the cracking. The type of stress that contributes in the cracking has not been determined. It is indicated that many cracks were found after the questionnaire was done.

  5. Effect of stress and temperature on mode of fracture after reheat cracking

    SciTech Connect

    Ferraresi, V.A.; Exaltacao Trevisan, R. da

    1996-12-01

    The phenomenon of stress-relief cracking or reheat cracking can occur in the heat affected zones (HAZ) or weld fillet during Post Weld Heat Treatment (PWHT). The parts of the HAZ most susceptible to reheat cracking are the coarse-grained regions which result from heating at elevated temperatures in the austenitic region. The aim of the research is to study the effect of stress and temperature during PWHT for stress relief on modes of fractures in High Strength Low Alloy (HSLA) steel produced commercially. The Modified Implant Test was applied along with simulation of thermal cycles typically used for stress-relief treatment of welded components. Basically two different modes of fracture have been identified on basis of fracture appearance. For the temperature range of 500 to 600C, under conditions of high and low stresses, a low-ductility intergranular fracture mode (brittle decohesion) was observed and fracture surfaces were characterized by almost featureless facets. At higher temperatures (680 C) and lower stresses, the fractures were slightly more ductile and occurred by creep cavitation on the grain boundaries. Although intergranular, these fractures were basically dimpled due to coalescence of individual creep cavities. Surfaces of fractures were examined by scanning electron microscopy. Tests with varying initial loads and different heat-treatment temperatures were realized in order to render separation of stress and temperature effects. It was observed that fracture mode depends mainly on the temperature level rather than on stress range.

  6. Lead induced stress corrosion cracking of Alloy 690 in high temperature water

    SciTech Connect

    Chung, K.K.; Lim, J.K.; Moriya, Shinichi; Watanabe, Yutaka; Shoji, Tetsuo

    1995-12-31

    Recent investigations of cracked steam generator tubes at nuclear power plants concluded that lead significantly contributed to cracking the Alloy 600 materials. In order to investigate the stress corrosion cracking (SCC) behavior of Alloy 690, slow strain rate tests (SSRT) and anodic polarization measurements were performed. The SSRTs were conducted in a lead-chloride solution (PbCl{sub 2}) and in a chloride but lead free solution (NaCl) at pH of 3 and 4.5 at 288 C. The anodic polarization measurements were carried out at 30 C using the same solutions as in SSRT. The SSRT results showed that Alloy 690 was susceptible to SCC in both solutions. In the lead chloride solution, cracking had slight dependence on lead concentration and pH. Cracking tend to increase with a higher lead concentration and a lower pH and was mainly intergranular and was to be a few tens to hundreds micrometers in length. In the chloride only solution, cracking was similar to the lead induced SCC. The results of anodic polarization measurement and electron probe micro analysis (EPMA) helped to understand lead induced SCC. Lead was a stronger active corrosive element but had a minor affect on cracking susceptibility of the alloy. While, chloride was quite different from lead effect to SCC. A possible mechanism of lead induced SCC of Alloy 690 was also discussed based on the test results.

  7. Microstructural characterization on intergranular stress corrosion cracking of Alloy 600 in PWR primary water environment

    NASA Astrophysics Data System (ADS)

    Lim, Yun Soo; Kim, Hong Pyo; Hwang, Seong Sik

    2013-09-01

    Stress corrosion cracks in Alloy 600 compact tension specimens tested at 325 °C in a simulated primary water environment of a pressurized water reactor were analyzed using microscopic equipment. Oxygen diffused into the grain boundaries just ahead of the crack tips from the external primary water. As a result of oxygen penetration, Cr oxides were precipitated on the crack tips and the attacked grain boundaries. The oxide layer in the crack interior was revealed to consist of double (inner and outer) layers. Cr oxides were found in the inner layer, with NiO and (Ni,Cr) spinels in the outer layer. Cr depletion (or Ni enrichment) zones were created in the attacked grain boundary, the crack tip, and the interface between the crack and matrix, which means that the formation of Cr oxides was due to the Cr diffusion from the surrounding matrix. The oxygen penetration and resultant metallurgical changes around the crack tip are believed to be significant factors affecting the PWSCC initiation and growth behaviors of Alloy 600. For interpretation of color in Fig. 4, the reader is referred to the web version of this article.

  8. Residual stress and crack propagation in laminated composites

    SciTech Connect

    Yttergren, R.M.F.; Zeng, K.; Rowcliffe, D.J.

    1994-12-31

    Residual stress distributions in several laminated ceramic composites were measured by an indentation technique. The material included alumina-zirconia laminated composites, containing strong interfaces, and alumina-porcelain laminated composites with both weak and strong interfaces. The residual stress in these material originates from the mismatch of the thermal properties, differences in elastic properties, and different shrinkage of the laminates during sintering. An experimental technique is presented which gives a direct view of the residual stress state in the materials. Values of residual tensile stress are presented as a function of position relative to the interface in each material.

  9. Stress intensity factors in two bonded elastic layers containing cracks perpendicular to and on the interface. Part 1: Analysis

    NASA Technical Reports Server (NTRS)

    Lu, M. C.; Erdogan, F.

    1980-01-01

    The basic crack problem which is essential for the study of subcritical crack propagation and fracture of layered structural materials is considered. Because of the apparent analytical difficulties, the problem is idealized as one of plane strain or plane stress. An additional simplifying assumption is made by restricting the formulation of the problem to crack geometries and loading conditions which have a plane of symmetry perpendicular to the interface. The general problem is formulated in terms of a coupled system of four integral equations. For each relevant crack configuration of practical interest, the singular behavior of the solution near and at the ends and points of intersection of the cracks is investigated and the related characteristic equations are obtained. The edge crack terminating at and crossing the interface, the T-shaped crack consisting of a broken layer and a delamination crack, the cross-shaped crack which consists of a delamination crack intersecting a crack which is perpendicular to the interface, and a delamination crack initiating from a stress-free boundary of the bonded layers are some of the practical crack geometries considered.

  10. Stress-corrosion cracking of sensitized stainless steel by sulfur-containing compounds

    SciTech Connect

    Isaacs, H.S.; Vyas, B.; Kendig, M.W.

    1981-01-01

    The stress corrosion cracking (SCC) of sensitized Type 304 stainless steel in thiosulfate solutions has been studied using constant extension rate tests. Very low concentrations of about 6.10/sup -7/M Na/sub 2/S/sub 2/O/sub 3/ (0.1ppm) gave cracking. With boric acid added, higher concentrations (1ppm) were required. The SCC was shown to be electrochemically controlled. Below -0.5v/sub SCE/ (-0.75/sub SHE/) no SCC took place; above this potential the rate of SCC increased with potential. An induction period was required before SCC continued above -0.5v if the potential was held at or below this value for extended times. This period was associated with the build up of an aggressive solution of thiosulfate decomposition products within the crack. The cracking process has been considered to be controlled by rupture of a salt layer and not a passivating oxide.

  11. Improvement of the resistance to stress corrosion cracking in austenitic stainless steels by cyclic prestraining

    SciTech Connect

    Chambreuil-Paret, A.; Magnin, T.

    1999-05-01

    Austenitic stainless steels are known to be sensitive to stress corrosion cracking (SCC) in hot chloride solutions. The aim of the present study is to find improvements in the SCC behavior of 316L-type austenitic stainless steels in 117 C MgCl{sub 2} solutions. Previously, the authors have proposed the corrosion-enhanced plasticity model (CEPM) to describe the discontinuous cracking process which occurs in SCC. This model is based on localized corrosion (anodic dissolution, and hydrogen absorption)-deformation (dislocations) interactions (CDI). From the framework of this model, it is proposed that a prestraining in fatigue at saturation decreases the SCC sensitivity. This idea is experimentally confirmed for both crack initiation and crack propagation, through the analysis of the SCC behavior by slow-strain-rate tests of single and polycrystals after different prestraining conditions.

  12. Dynamic crack propagation in elastic-perfectly plastic solids under plane stress conditions

    NASA Astrophysics Data System (ADS)

    Deng, Xiaomin; Rosakis, Ares J.

    THE phenomenon of steady-state dynamic crack propagation in elastic-perfectly plastic solids under mode I plane stress, small-scale yielding conditions is investigated numerically. An Eulerian finite element scheme is employed. The materials are assumed to obey the von Mises yield criterion and the associated flow rule. The ratio of the crack tip plastic zone size to that of the element nearest to the crack tip is of the order of 1.6 × 10 4. Two subjects of general interest are discussed. These are the asymptotic structure of the crack tip stress and deformation fields, and the appropriateness of a crack growth fracture criterion based on the far-field dynamic stress intensity factor. The crack-line solution by ACHENBACH and LI (Report NU-SML-TR-No. 84-1, Dept. of Civil Engineering, Northwestern University, Evanston, IL 60201, 1984a; in Fundamentals of Deformation and Fracture (edited by B.A. Brilby et al.). Cambridge University Press, 1984b) is discussed and compared to the numerical solution. The results of this study strongly indicate that the crack tip strain and velocity fields possess logarithmic singularities, which is consistent with the assumptions in the asymptotic analysis by Gao ( Int. J. Fracture34, 111, 1987). However, it is revealed that the crack tip field variations in Gao's solution present features often contrary to the numerical findings. To this end, a preliminary asymptotic analysis is performed in an effort to resolve certain issues. Finally, the critical plastic strain criterion ( MCCLINTOCK and IRWIN, in Fracture Toughness Testing and Its Applications, ASTM STP 381, p. 84, 1964) is adopted to obtain theoretical relations between the critical dynamic stress intensity factor and the crack propagation speed. These relations are found to agree well with experimental measurements by Rosakis et al. ( J. Mech. Phys. Solids32, 443, 1984) and by ZEHNDER and ROSAKIS ( Int. J. Fracture, to appear 1990), performed on thin 4340 steel plates whose

  13. Three-dimensional stress intensity factor analysis of a surface crack in a high-speed bearing

    NASA Technical Reports Server (NTRS)

    Ballarini, Roberto; Hsu, Yingchun

    1990-01-01

    The boundary element method is applied to calculate the stress intensity factors of a surface crack in the rotating inner raceway of a high-speed roller bearing. The three-dimensional model consists of an axially stressed surface cracked plate subjected to a moving Hertzian contact loading. A multidomain formulation and singular crack-tip elements were employed to calculate the stress intensity factors accurately and efficiently for a wide range of configuration parameters. The results can provide the basis for crack growth calculations and fatigue life predictions of high-performance rolling element bearings that are used in aircraft engines.

  14. Mechanistic dissimilarities between environmentally-influenced fatigue-crack propagation at near-threshold and higher growth rates in lower-strength steels

    SciTech Connect

    Suresh, S.; Ritchie, R. O.

    1981-11-01

    The role of hydrogen gas in influencing fatigue crack propagation is examined for several classes of lower strength pressure vessel and piping steels. Based on measurements over a wide range of growth rates from 10/sup -8/ to 10/sup -2/ mm/cycle, crack propagation rates are found to be significantly higher in dehumidified gaseous hydrogen compared to moist air in two distinct regimes of crack growth, namely (i) at the intermediate range of growth typically above approx. 10/sup -5/ mm/cycle, and (ii) at the near-threshold region below approx. 10/sup -6/ mm/cycle approaching lattice dimensions per cycle. Both effects are seen at maximum stress intensities (K/sub max/) far below the sustained-load threshold stress intensity for hydrogen-assisted cracking (K/sub Iscc/). Characteristics of environmentally influenced fatigue crack growth in each regime are shown to be markedly different with regard to fractography and the effect of such variables as load ratio and frequency. It is concluded that the primary mechanisms responsible for the influence of the environment in each regime are distinctly different. Whereas corrosion fatigue behavior at intermediate growth rates can be attributed to hydrogen embrittlement processes, the primary role of moist environments at near-threshold levels is shown to involve a contribution from enhanced crack closure due to the formation of crack surface corrosion deposits at low load ratios.

  15. Characterization of damage due to stress corrosion cracking in carbon steel using nonlinear surface acoustic waves

    NASA Astrophysics Data System (ADS)

    Zeitvogel, D. T.; Matlack, K. H.; Kim, J.-Y.; Jacobs, L. J.; Singh, P. M.; Qu, J.

    2013-01-01

    Cold rolled carbon steel 1018C is widely used in pressurized fuel pipelines. In these structures, stress corrosion cracking (SCC) can pose a significant problem because cracks initiate late in the lifetime and often unexpectedly, but grow fast once they get started. To ensure a safe operation it is crucial that any damage can be detected before the structural stability is reduced by large cracks. In the early stages of SCC, microstructural changes occur which in many cases increase the acoustic nonlinearity of the material. Therefore, an initially monochromatic Rayleigh wave is distorted and measurable higher harmonics are generated. Different levels of stress corrosion cracking is induced in five specimens. For each specimen, nonlinear ultrasonic measurements are performed before and after inducing the damage. For the measurements, oil coupled wedge transducers are used to generate and detect tone burst Rayleigh wave signals. The amplitudes of the received fundamental and second harmonic waves are measured at varying propagation distances to obtain a measure for the acoustic nonlinearity of the specimens. The results show a damage-dependent increase in nonlinearity for early stages of damage, indicating the feasibility of this nonlinear ultrasonic method to detect the initiation of stress corrosion cracking.

  16. Corrosion fatigue crack propagation in metals

    SciTech Connect

    Gangloff, R.P.

    1990-06-01

    This review assesses fracture mechanics data and mechanistic models for corrosion fatigue crack propagation in structural alloys exposed to ambient temperature gases and electrolytes. Extensive stress intensity-crack growth rate data exist for ferrous, aluminum and nickel based alloys in a variety of environments. Interactive variables (viz., stress intensity range, mean stress, alloy composition and microstructure, loading frequency, temperature, gas pressure and electrode potential) strongly affect crack growth kinetics and complicate fatigue control. Mechanistic models to predict crack growth rates were formulated by coupling crack tip mechanics with occluded crack chemistry, and from both the hydrogen embrittlement and anodic dissolution/film rupture perspectives. Research is required to better define: (1) environmental effects near threshold and on crack closure; (2) damage tolerant life prediction codes and the validity of similitude; (3) the behavior of microcrack; (4) probes and improved models of crack tip damage; and (5) the cracking performance of advanced alloys and composites.

  17. Corrosion fatigue crack propagation in metals

    NASA Technical Reports Server (NTRS)

    Gangloff, Richard P.

    1990-01-01

    This review assesses fracture mechanics data and mechanistic models for corrosion fatigue crack propagation in structural alloys exposed to ambient temperature gases and electrolytes. Extensive stress intensity-crack growth rate data exist for ferrous, aluminum and nickel based alloys in a variety of environments. Interactive variables (viz., stress intensity range, mean stress, alloy composition and microstructure, loading frequency, temperature, gas pressure and electrode potential) strongly affect crack growth kinetics and complicate fatigue control. Mechanistic models to predict crack growth rates were formulated by coupling crack tip mechanics with occluded crack chemistry, and from both the hydrogen embrittlement and anodic dissolution/film rupture perspectives. Research is required to better define: (1) environmental effects near threshold and on crack closure; (2) damage tolerant life prediction codes and the validity of similitude; (3) the behavior of microcrack; (4) probes and improved models of crack tip damage; and (5) the cracking performance of advanced alloys and composites.

  18. Analysis of stress corrosion cracking in alloy 718 following commercial reactor exposure

    DOE PAGESBeta

    Leonard, Keith J.; Gussev, Maxim N.; Stevens, Jacqueline N.; Busby, Jeremy T.

    2015-08-24

    Alloy 718 is generally considered a highly corrosion-resistant material but can still be susceptible to stress corrosion cracking (SCC). The combination of factors leading to SCC susceptibility in the alloy is not always clear enough. In this paper, alloy 718 leaf spring (LS) materials that suffered stress corrosion damage during two 24-month cycles in pressurized water reactor service, operated to >45 MWd/mtU burn-up, was investigated. Compared to archival samples fabricated through the same processing conditions, little microstructural and property changes occurred in the material with in-service irradiation, contrary to high dose rate laboratory-based experiments reported in literature. Though the lackmore » of delta phase formation along grain boundaries would suggest a more SCC resistant microstructure, grain boundary cracking in the material was extensive. Crack propagation routes were explored through focused ion beam milling of specimens near the crack tip for transmission electron microscopy as well as in polished plan view and cross-sectional samples for electron backscatter diffraction analysis. It has been shown in this study that cracks propagated mainly along random high-angle grain boundaries, with the material around cracks displaying a high local density of dislocations. The slip lines were produced through the local deformation of the leaf spring material above their yield strength. Also, the cause for local SCC appears to be related to oxidation of both slip lines and grain boundaries, which under the high in-service stresses resulted in crack development in the material.« less

  19. Irradiation-Assisted Stress Corrosion Cracking of Austenitic Stainless Steels in BWR Environments

    SciTech Connect

    Chen, Y.; Chopra, O. K.; Gruber, Eugene E.; Shack, William J.

    2010-06-01

    The internal components of light water reactors are exposed to high-energy neutron irradiation and high-temperature reactor coolant. The exposure to neutron irradiation increases the susceptibility of austenitic stainless steels (SSs) to stress corrosion cracking (SCC) because of the elevated corrosion potential of the reactor coolant and the introduction of new embrittlement mechanisms through radiation damage. Various nonsensitized SSs and nickel alloys have been found to be prone to intergranular cracking after extended neutron exposure. Such cracks have been seen in a number of internal components in boiling water reactors (BWRs). The elevated susceptibility to SCC in irradiated materials, commonly referred to as irradiation-assisted stress corrosion cracking (IASCC), is a complex phenomenon that involves simultaneous actions of irradiation, stress, and corrosion. In recent years, as nuclear power plants have aged and irradiation dose increased, IASCC has become an increasingly important issue. Post-irradiation crack growth rate and fracture toughness tests have been performed to provide data and technical support for the NRC to address various issues related to aging degradation of reactor-core internal structures and components. This report summarizes the results of the last group of tests on compact tension specimens from the Halden-II irradiation. The IASCC susceptibility of austenitic SSs and heat-affected-zone (HAZ) materials sectioned from submerged arc and shielded metal arc welds was evaluated by conducting crack growth rate and fracture toughness tests in a simulated BWR environment. The fracture and cracking behavior of HAZ materials, thermally sensitized SSs and grain-boundary engineered SSs was investigated at several doses (≤3 dpa). These latest results were combined with previous results from Halden-I and II irradiations to analyze the effects of neutron dose, water chemistry, alloy compositions, and welding and processing conditions on IASCC

  20. Intergranular attack and stress corrosion cracking of Alloy 600 in high-temperature caustic solutions containing contaminants

    SciTech Connect

    Bandy, R.; Roberge, R.; van Rooyen, D.

    1985-06-01

    Concentrated caustic is a primary cause of stress corrosion cracking and intergranular attack of Alloy 600 tubing in PWRs. However, temperature, electrochemical potential, stress, and metallurgical state all play a role. This study provides the quantitative evidence needed to develop models of crack growth and to devise effective countermeasures.

  1. An experimental study on the effects of compressive stress on the fatigue crack growth of low-alloy steel

    SciTech Connect

    Jones, D.P.; Hoppe, R.G.; Hechmer, J.L.; James, B.A.

    1993-12-01

    A series of fatigue crack growth rate tests was conducted in order to study effects of negative stress ratio on fatigue crack growth rate of low-alloy steel in air. Four-point bend specimens were used to simulate linear stress distributions typical of pressure vessel applications. This type of testing adds to knowledge on negative stress ratio effects for low-alloy steels obtained in the past from uniform tension-compression tests. Applied bending stress range was varied over twice the yield strength. Load control was used for tests for which the stress range was less than twice the yield strength and deflection control was used for the higher stress range tests. Crack geometries were both short and long fatigue cracks started at notches and tight fatigue cracks for which crack closure could occur over the full crack face. Results are presented in terms of the stress intensity factor ratio R = K{sub MIN}/K{sub MAX}. The negative R-ratio test results were correlated to an equation of the form da/dN = C[{Delta}K/(A-R)]{sup n}, where A, C, and n are curve fitting parameters. It was found that effects of negative R-ratio on fatigue crack growth rates for even the high stress range tests could be bounded by correlating the above equation to only positive R-ratio test results and extending the resulting equation into the negative R-ratio regime.

  2. Ultrasonic Impact Treatment to Improve Stress Corrosion Cracking Resistance of Welded Joints of Aluminum Alloy

    NASA Astrophysics Data System (ADS)

    Yu, J.; Gou, G.; Zhang, L.; Zhang, W.; Chen, H.; Yang, Y. P.

    2016-07-01

    Stress corrosion cracking is one of the major issues for welded joints of 6005A-T6 aluminum alloy in high-speed trains. High residual stress in the welded joints under corrosion results in stress corrosion cracking. Ultrasonic impact treatment was used to control the residual stress of the welded joints of 6005A-T6 aluminum alloy. Experimental tests show that ultrasonic impact treatment can induce compressive longitudinal and transverse residual stress in the welded joint, harden the surface, and increase the tensile strength of welded joints. Salt-fog corrosion tests were conducted for both an as-welded sample and an ultrasonic impact-treated sample. The surface of the treated sample had far fewer corrosion pits than that of the untreated sample. The treated sample has higher strength and lower tensile residual stress than the untreated sample during corrosion. Therefore, ultrasonic impact treatment is an effective technique to improve the stress corrosion cracking resistance of the welded joints of 6005A-T6 aluminum alloy.

  3. Ultrasonic Impact Treatment to Improve Stress Corrosion Cracking Resistance of Welded Joints of Aluminum Alloy

    NASA Astrophysics Data System (ADS)

    Yu, J.; Gou, G.; Zhang, L.; Zhang, W.; Chen, H.; Yang, Y. P.

    2016-06-01

    Stress corrosion cracking is one of the major issues for welded joints of 6005A-T6 aluminum alloy in high-speed trains. High residual stress in the welded joints under corrosion results in stress corrosion cracking. Ultrasonic impact treatment was used to control the residual stress of the welded joints of 6005A-T6 aluminum alloy. Experimental tests show that ultrasonic impact treatment can induce compressive longitudinal and transverse residual stress in the welded joint, harden the surface, and increase the tensile strength of welded joints. Salt-fog corrosion tests were conducted for both an as-welded sample and an ultrasonic impact-treated sample. The surface of the treated sample had far fewer corrosion pits than that of the untreated sample. The treated sample has higher strength and lower tensile residual stress than the untreated sample during corrosion. Therefore, ultrasonic impact treatment is an effective technique to improve the stress corrosion cracking resistance of the welded joints of 6005A-T6 aluminum alloy.

  4. On the susceptibility to stress corrosion cracking of Zircaloy in an iodine containing environment

    NASA Astrophysics Data System (ADS)

    Tsing-Tyan, Yang; Chuen-Horng, Tsai

    1989-08-01

    The role of iodine and zirconium iodide in the process of stress corrosion cracking (SCC) of Zircaloy is studied by an internal pressurization SCC test and independent corrosion and creep tests, using iodine and zirconium tetraiodide crystals as the attacking species. Measurement of the critical values of iodine potential reveals that irradiated fuel rods should possess enough iodine potential to induce SCC failure of Zircaloy cladding. The difference between tests with I 2 and ZrI 4, and the morphology of microcraks at the site of corrosion pits suggest that the quantity of free iodine may play an important role in the crack initiation stage. Although the thick surface oxide can protect Zircaloy from iodine attack, it will rupture under sustaining a tensile stress, and then the iodine-bearing carrier will penetrate through the cracks to supply the necessary iodine potential and to proceed the propagation.

  5. Stress corrosion cracking of type 304L stainless steel core shroud welds.

    SciTech Connect

    Chung, H. M.; Park, J.-H.; Sanecki, J. E.; Zaluzec, N. J.; Yu, M. S.; Yang, T. T.

    1999-10-26

    Microstructural analyses by advanced metallographic techniques were conducted on mockup welds and a cracked BWR core shroud weld fabricated from Type 304L stainless steel. heat-affected zones of the shroud weld and mockup shielded-metal-arc welds were free of grain-boundary carbide, martensite, delta ferrite, or Cr depletion near grain boundaries. However, as a result of exposure to welding fumes, the heat-affected zones of the welds were significantly contaminated by fluorine and oxygen which migrate to grain boundaries. Significant oxygen contamination promotes fluorine contamination and suppresses classical thermal sensitization, even in Type 304 steels. Results of slow-strain-rate tensile tests indicate that fluorine exacerbates the susceptibility of irradiated steels to intergranular stress corrosion cracking. These observations, combined with previous reports on the strong influence of weld flux, indicate that oxygen and fluorine contamination and fluorine-catalyzed stress corrosion play a major role in cracking of Type 304L stainless steel core shroud welds.

  6. Internal stresses at the crystalline scale in textured ZrO2 films before lateral cracking

    NASA Astrophysics Data System (ADS)

    Berdin, Clotilde; Pascal, Serge; Tang, Yan

    2015-05-01

    Zirconium oxide layers are submitted to internal stresses that play a role in damage of the layer. Lateral cracking is often observed during Zr alloys oxidation. In this paper, we investigated the influence of the microstresses at the crystalline scale on the lateral cracking within a growing oxide on a plane substrate. A parametric study was carried out taking into account the crystallographic texture of the oxide and the presence of a tetragonal zirconia at the metal-oxide interface. Macroscopic computations and polycrystalline aggregate computations were performed. The result indicating the (1 0 6 bar) fiber texture as the most favorable was recovered. It was found that under macroscopic compressive stresses parallel to the plane metal-oxide interface, positive microstresses perpendicular to the interface develops. They can trigger the lateral cracking and the phenomenon is promoted by the presence of tetragonal zirconia at the metal-oxide interface.

  7. A STUDY OF CORROSION AND STRESS CORROSION CRACKING OF CARBON STEEL NUCLEAR WASTE STORAGE TANKS

    SciTech Connect

    BOOMER, K.D.

    2007-08-21

    The Hanford reservation Tank Farms in Washington State has 177 underground storage tanks that contain approximately 50 million gallons of liquid legacy radioactive waste from cold war plutonium production. These tanks will continue to store waste until it is treated and disposed. These nuclear wastes were converted to highly alkaline pH wastes to protect the carbon steel storage tanks from corrosion. However, the carbon steel is still susceptible to localized corrosion and stress corrosion cracking. The waste chemistry varies from tank to tank, and contains various combinations of hydroxide, nitrate, nitrite, chloride, carbonate, aluminate and other species. The effect of each of these species and any synergistic effects on localized corrosion and stress corrosion cracking of carbon steel have been investigated with electrochemical polarization, slow strain rate, and crack growth rate testing. The effect of solution chemistry, pH, temperature and applied potential are all considered and their role in the corrosion behavior will be discussed.

  8. Cracking and Stress-Strain Behavior of Rock-Like Material Containing Two Flaws Under Uniaxial Compression

    NASA Astrophysics Data System (ADS)

    Zhao, Yanlin; Zhang, Lianyang; Wang, Weijun; Pu, Chengzhi; Wan, Wen; Tang, Jingzhou

    2016-07-01

    This paper investigates the cracking and stress-strain behavior, especially the local strain concentration near the flaw tips, of rock-like material containing two flaws. A series of uniaxial compression tests were carried out on rock-like specimens containing two flaws, with strain gauges mounted near the flaw tips to measure the local strain concentration under the uniaxial compressive loading. Four different types of cracks (wing cracks, anti-wing cracks, coplanar shear cracks and oblique shear cracks) and seven patterns of crack coalescences (T1 and T2; S1 and S2; and TS1, TS2 and TS3) are observed in the experiments. The type of crack coalescence is related to the geometry of the flaws. In general, the crack coalescence varies from the S-mode to the TS-mode and then to the T-mode with the increase of the rock bridge ligament angle. The stress-strain curves of the specimens containing two flaws are closely related to the crack development and coalescence process. The strain measurements indicate that the local tensile strain concentration below or above the pre-existing flaw tip causes wing or anti-wing cracks, while the local compressive strain concentration near the flaw tip is related to the shear crack. The measured local tensile strain shows a jump at the initiation of wing- and anti-wing cracks, reflecting the instant opening of the wing- and anti-wing crack propagating through the strain gauge. During the propagation of wing- and anti-wing cracks, the measured local tensile strain gradually increases with few jumps, implying that the opening deformation of wing- and anti-wing cracks occurs in a stable manner. The shear cracks initiate followed by a large and abrupt compressive strain jump and then quickly propagate in an unstable manner resulting in the failure of specimens.

  9. Determination of Stress Intensity Factor Distributions for "Interface" Cracks in Incompressible, Dissimilar Materials

    NASA Technical Reports Server (NTRS)

    Smith, C. W.

    1997-01-01

    The present study was undertaken in order to develop test methods and procedures for measuring the variation of the stress intensity factor through the thickness in bimaterial specimens containing cracks within and parallel to the bond line using the frozen stress photoelastic method. Since stress freezing materials are incompressible above critical temperature, and since thick plates are to be employed which tend to produce a state of plane strain near the crack tip, the interface near tip fracture equations reduce to the classic form for homogeneous materials. Moreover, zero thickness interfaces do not exist when materials are bonded together. It was decided early on that it would be important to insure a uniform straight and accurate crack tip region through the thickness of the body to reduce scatter in the SIF distribution through the thickness. It was also observed that rubberlike materials which were desired to be modeled exhibited significant tip blunting prior to crack extension and that some blunting of the tip would provide a more realistic model. It should be noted that, in normal stress freezing photoelastic work, it is considered good practice to avoid utilizing data near bond lines in photoelastic models due to the bond line stresses which inevitably develop when two parts are bonded together. Thus, the present study involves certain exploratory aspects in deviating from standard practice in stress freezing work. With the above ideas in mind, several different test methods were investigated and are described in the following sections and appendices. The geometry selected for the program was a thick, edge cracked specimen containing a bond line.

  10. In-vitro characterization of stress corrosion cracking of aluminium-free magnesium alloys for temporary bio-implant applications.

    PubMed

    Choudhary, Lokesh; Singh Raman, R K; Hofstetter, Joelle; Uggowitzer, Peter J

    2014-09-01

    The complex interaction between physiological stresses and corrosive human body fluid may cause premature failure of metallic biomaterials due to the phenomenon of stress corrosion cracking. In this study, the susceptibility to stress corrosion cracking of biodegradable and aluminium-free magnesium alloys ZX50, WZ21 and WE43 was investigated by slow strain rate tensile testing in a simulated human body fluid. Slow strain rate tensile testing results indicated that each alloy was susceptible to stress corrosion cracking, and this was confirmed by fractographic features of transgranular and/or intergranular cracking. However, the variation in alloy susceptibility to stress corrosion cracking is explained on the basis of their electrochemical and microstructural characteristics. PMID:25063163

  11. Stress-corrosion crack growth of Si-Na-K-Mg-Ca-P-O bioactive glasses in simulated human physiological environment

    PubMed Central

    Bloyer, D. R.; McNaney, J. M.; Cannon, R. M.; Saiz, E.; Tomsia, A. P.; Ritchie, R. O.

    2007-01-01

    This paper describes research on the stress-corrosion crack growth (SCCG) behavior of a new series of bioactive glasses designed to fabricate coatings on Ti and Co-Cr-based implant alloys. These glasses should provide improved implant fixation between implant and exhibit good mechanical stability in vivo. It is then important to develop an understanding of the mechanisms that control environmentally-assisted crack growth in this new family of glasses and its effect on their reliability. Several compositions have been tested in both static and cyclic loading in simulated body fluid. These show only small dependences of stress-corrosion crack growth behavior on the composition. Traditional SCCG mechanisms for silicate glasses appear to be operative for the new bioactive glasses studied here. At higher velocities, hydrodynamic effects reduce growth rates under conditions that would rarely pertain for small natural flaws in devices. PMID:17714778

  12. Overview of corrosion, corrosion protection, and stress-corrosion cracking of uranium and uranium alloys

    SciTech Connect

    Koger, J.W.

    1981-12-14

    This paper covers some basic definitions and provides some data. The 51 slides illustrates these definitions, crack initiation and propagation, sources of stress, types of specimens used for SCC, potentiostatic polarization, data for Mulberry and U-Nb alloys, effects of environment, and data for U-0.75 Ti and U-Mo alloys. (DLC)

  13. Proceedings: 1985 Workshop on Primary-Side Stress Corrosion Cracking of PWR Steam Generator Tubing

    SciTech Connect

    1987-06-01

    To date, more than 30 PWRs have reported stress corrosion cracking of steam generator tubing from the primary water side. In 32 presentations, this report offers in-plant and laboratory data on the contributing factors, as well as discussing some promising remedial measures.

  14. A review and assessment of the stress-intensity factors for surface cracks

    NASA Technical Reports Server (NTRS)

    Newman, J. C., Jr.

    1978-01-01

    The stress-intensity factor solutions proposed for a surface crack in a finite plate subjected to uniform tension are reviewed. Fourteen different solutions for the stress-intensity factors are compared. These solutions were obtained over the past 16 years using approximate analytical methods, experimental methods, and engineering estimates. The accuracy is assessed of the various solutions by correlating fracture data on surface-cracked tension specimens made of a brittle epoxy material. Fracture of the epoxy material was characterized by a constant value of stress-intensity factor at failure. Thus, the correctness of the various solutions is judged by the variations in the stress-intensity factors at failure. The solutions were ranked in order of minimum standard deviation. The highest ranking solutions correlated 95 percent of data analyzed within + or - 10 percent, whereas the lowest ranking solutions correlated 95 percent of data analyzed within + or - 20 percent. However, some solutions could be applied to all data considered, whereas others are limited with respect to crack shapes and crack sizes that could be analyzed.

  15. Use of intelligent pigs to detect stress corrosion cracking in gas pipelines

    SciTech Connect

    Culbertson, D.L.

    1996-08-01

    To ensure the integrity and serviceability of gas pipelines, operators periodically utilize intelligent pigging. This inspection technique has proven to be a cost effective approach for determining the condition of operating pipelines. Recent advancements in intelligent pigging technology are now aiding the pipeline industry in the detection of stress corrosion cracking.

  16. Overlapping double etch technique for evaluation of metallic alloys to stress corrosion cracking

    DOEpatents

    Not Available

    1980-05-28

    A double overlapping etch zone technique for evaluation of the resistance of metallic alloys to stress corrosion cracking is described. The technique involves evaluating the metallic alloy along the line of demarcation between an overlapping double etch zone and single etch zone formed on the metallic alloy surface.

  17. Overlapping double etch technique for evaluation of metallic alloys to stress corrosion cracking

    DOEpatents

    Steeves, Arthur F.; Stewart, James C.

    1981-01-01

    A double overlapping etch zone technique for evaluation of the resistance of metallic alloys to stress corrosion cracking. The technique involves evaluating the metallic alloy along the line of demarcation between an overlapping double etch zone and single etch zone formed on the metallic alloy surface.

  18. Stress corrosion cracking in canistered waste package containers: Welds and base metals

    SciTech Connect

    Huang, J.S.

    1998-03-01

    The current design of waste package containers include outer barrier using corrosion allowable material (CAM) such as A516 carbon steel and inner barrier of corrosion resistant material (CRM) such as alloy 625 and C22. There is concern whether stress corrosion cracking would occur at welds or base metals. The current memo documents the results of our analysis on this topic.

  19. Dietary antioxidants and environmental stress.

    PubMed

    Kelly, Frank J

    2004-11-01

    Air is one of our most important natural resources; however, it is also in the front line for receiving environmental pollution. Air quality decreased markedly following the industrial revolution, but it was not until the great London Smog in 1952 that air quality made it onto the political agenda. The introduction of the Clean Air Act in 1956 led to dramatic decreases in black smoke and SO2 concentrations over the next two decades, as domestic and industrial coal-burning activities ceased. However, as these improvements progressed, a new threat to public health was being released into the air in ever-increasing quantities. Rapid motorisation of society from the 1960s onwards has led to the increased release of atmospheric pollutants such as tiny particles (particulate matter of <10 microm in aerodynamic diameter) and oxides of N, and the generation of the secondary pollutant O3. These primary and secondary traffic-related pollutants have all proved to be major risks factors to public health. Recently, oxidative stress has been identified as a unifying feature underlying the toxic actions of these pollutants. Fortunately, the surface of the lung is covered with a thin layer of fluid containing a range of antioxidants that appear to provide the first line of defence against oxidant pollutants. As diet is the only source of antioxidant micronutrients, a plausible link now exists between the sensitivity to air pollution and the quality of the food eaten. However, many questions remain unanswered in relation to inter-individual sensitivity to ambient air pollution, and extent to which this sensitivity is modified by airway antioxidant defences. PMID:15831130

  20. Free-edge stress analysis of glass-epoxy laminates with matrix cracks

    NASA Technical Reports Server (NTRS)

    Fish, John C.; O'Brien, T. K.

    1992-01-01

    The effect of matrix cracks on the composite delamination and interlaminar stresses is investigated in (+15/90n/-15)s glass-epoxy laminates (with values of n equal to 0, 1, 2, or 3) subjected to monotonically increasing tension loads. Three-dimensional (3D) and quasi-3D (Q3D) finite-element analyses are used to model the free-edge stress states in the laminates with and without a matrix crack, respectively. The Q3D results show that in-plane transverse tensile stresses exist in the +15 deg plies near the free edges of all of the laminates used and that only the interlaminar shear stress is high at the +15/theta interface. The results of 3D analysis indicate that large tensile interlaminar normal as well as shear stresses develop at the intersection of the matrix crack and the free edge. This suggests that the interlaminar normal stress plays a significant role in the failure of these laminates.

  1. Automated system for analyzing stress intensity factors of three-dimensional cracks: Its application to analyses of two dissimilar semi-elliptical surface cracks in plates

    SciTech Connect

    Yoshimura, S.; Lee, J.S.; Yagawa, G.

    1997-02-01

    This paper describes a new automated system for analyzing the stress intensity factors (SIFs) of three-dimensional cracks. A geometry model containing one or several three-dimensional cracks is defined using a commercial CAD system, DESIGNBASE. Several local distributions of node density are chosen from the database of the present system, and then automatically superposed on one another over the geometry model by using the fuzzy knowledge processing. Nodes are generated by the bucketing method, and ten-noded quadratic tetrahedral solid elements are generated by the Delaunay method. A user imposes material properties and boundary conditions onto parts of the geometry model such as loops and edges by clicking them with a mouse and by inputting values. For accurate analyses of the stress intensity factors, finer elements are generated in the vicinity of crack tips, thanks to the fuzzy knowledge processing. The singular elements such that the midpoint nodes near crack front are shifted at the quarter-points are automatically placed along the three-dimensional crack front. The complete finite element model generated is given to a commercial finite element code, MARC, and a stress analysis is performed. The stress intensity factors are calculated using the displacement extrapolation method. To demonstrate practical performances of the present system, two dissimilar semi-elliptical surface cracks in a plate subjected to uniform tension are solved, and their interaction effects are discussed in detail. It is shown from the results that ASME Boiler and Pressure Vessel Code, Section 11, Appendix A gives a conservative stress intensity factor for two identical adjacent surface cracks and for two dissimilar adjacent surface cracks.

  2. Development of Probabilistic Fracture Mechanics Analysis Code for Pipes with Stress Corrosion Cracks

    NASA Astrophysics Data System (ADS)

    Machida, Hideo; Arakawa, Manabu; Yamashita, Norimichi; Yoshimura, Shinobu

    Risk-Informed integrity management methodologies have been developed for Japanese nuclear power plants. One of the issues of concern is the reliability assessment of piping with flaws due to stress corrosion cracking (SCC). Therefore, the probabilistic fracture mechanics analysis code has been developed, which can perform the reliability assessment for austenitic stainless steel piping with flaws due to SCC. This paper describes technical basis of this code. This method is based on Monte-Carlo technique considering many sample cases in a piping section, where the initiation and growth of cracks are calculated and piping failures, including leaks and rapture, are evaluated. A notable feature is that multiple cracks can be treated, consequently, assessment of coalescence of cracks and intricate break evaluation of piping section have been included. Moreover, the in-service inspection (ISI) and integrity evaluation by Fitness-for-Service (FFS) code are integrated into the analysis, and the contribution to failure probability decrease can be assessed. Key parameters are determined on a probability basis with the designated probability type throughout the procedure. Size, location and time of crack initiation, coefficients of crack growth due to SCC and factors for piping failure are included in those parameters. With this method the reliability level of the piping through the operation periods can be estimated and the contribution of various parameters including ISI can be quantitatively evaluated.

  3. Thermal Stress Cracking of Slide-Gate Plates in Steel Continuous Casting

    NASA Astrophysics Data System (ADS)

    Lee, Hyoung-Jun; Thomas, Brian G.; Kim, Seon-Hyo

    2016-04-01

    The slide-gate plates in a cassette assembly control the steel flow through the tundish nozzle, and may experience through-thickness cracks, caused by thermal expansion and/or mechanical constraint, leading to air aspiration and safety concerns. Different mechanisms for common and rare crack formation are investigated with the aid of a three-dimensional finite-element model of thermal mechanical behavior of the slide-gate plate assembly during bolt pretensioning, preheating, tundish filling, casting, and cooling stages. The model was validated with previous plant temperature measurements of a ladle plate during preheating and casting, and then applied to a typical tundish-nozzle slide-gate assembly. The formation mechanisms of different types of cracks in the slide-gate plates are investigated using the model and evaluated with actual slide-gate plates at POSCO. Common through-thickness radial cracks, found in every plate, are caused during casting by high tensile stress on the outside surfaces of the plates, due to internal thermal expansion. In the upper plate, these cracks may also arise during preheating or tundish filling. Excessive bolt tightening, combined with thermal expansion during casting may cause rare radial cracks in the upper and lower plates. Rare radial and transverse cracks in middle plate appear to be caused during tundish filling by impingement of molten steel on the middle of the middle plate that generates tensile stress in the surrounding refractory. The mechanical properties of the refractory, the bolt tightening conditions, and the cassette/plate design are all important to service life.

  4. Stress intensity factors for large aspect ratio surface and corner cracks at a semi-circular notch in a tension specimen

    NASA Technical Reports Server (NTRS)

    Shivakumar, K. N.; Newman, J. C., Jr.

    1991-01-01

    Stress intensity factor solutions for semielliptic surface and quarter-elliptic corner cracks emanating from a semicircular notch in a tension specimen are presented. A three-dimensional finite-element analysis in conjunction with the equivalent domain integral was used to calculate stress intensity factors (SIF). SIF solutions for surface or corner crack (crack length to depth ratio of 2) at a notch are presented for a wide range of crack sizes and notch radii. Results showed that the SIF are larger for larger crack lengths and for larger notch radii. The SIF are nearly constant all along the crack front for deep surface cracks and for all corner cracks analysed.

  5. An Experimental Study of Fatigue Crack Growth in Aluminum Sheet Subjected to Combined Bending and Membrane Stresses

    NASA Technical Reports Server (NTRS)

    Phillips, Edward P.

    1997-01-01

    An experimental study was conducted to determine the effects of combined bending and membrane cyclic stresses on the fatigue crack growth behavior of aluminum sheet material. The materials used in the tests were 0.040-in.- thick 2024-T3 alclad and 0.090-in.-thick 2024-T3 bare sheet. In the tests, the membrane stresses were applied as a constant amplitude loading at a stress ratio (minimum to maximum stress) of 0.02, and the bending stresses were applied as a constant amplitude deflection in phase with the membrane stresses. Tests were conducted at ratios of bending to membrane stresses (B/M) of 0, 0.75, and 1.50. The general trends of the results were for larger effects of bending for the higher B/M ratios, the lower membrane stresses, and the thicker material. The addition of cyclic bending stresses to a test with cyclic membrane stresses had only a small effect on the growth rates of through-thickness cracks in the thin material, but had a significant effect on the crack growth rates of through-thickness cracks in the thick material. Adding bending stresses to a test had the most effect on the initiation and early growth of cracks and had less effect on the growth of long through-thickness cracks.

  6. Stress corrosion cracking of Zircaloys in unirradiated and irradiated CsI

    NASA Astrophysics Data System (ADS)

    Cox, B.; Surette, B. A.; Wood, J. C.

    1986-03-01

    Unirradiated split-ring specimens of Zircaloy fuel cladding, coated with CsI, cracked when stressed at elevated temperatures. The specimens have been reexamined fractographically and metallographically in order to confirm that the cause of cracking was stress corrosion (SCC) and not delayed hydride cracking (DHC). Further specimens have been cracked at 350°C by a solution of CsI in a fused mixture of nitrates of rubidium, cesium, strontium and barium, by a similar mechanism. CsI dissolved in a fused molybdate melt was not stable at 400°C, and rapidly evolved iodine, leaving a melt that was incapable of causing SCC. Irradiation of stressed split-ring specimens of Zircaloy fuel cladding in a γ-irradiator of 10 6 R/h and in the U-5 loop in the NRU reactor at an estimated 10 9 R/h caused SCC when the specimens were packed in dry CsI powder. Care had to be taken to dry the CsI, otherwise cracking occurred by a DHC mechanism from hydrogen absorbed from residual moisture in the CsI. Fractography showed that the crack surfaces obtained with dry CsI were typical of iodine-induced SCC rather than cesium-induced metal vapour embrittlement. Thus, if a transport process is provided for the iodide to obtain access to the zirconium surface, CsI is capable of causing SCC of Zircaloy. This transport process might be ionic diffusion in a fission product oxide melt in the fuel-clad gap, however, radiolysis of CsI to form a volatile iodine species in a radiation field is the more probable explanation of PCI failures.

  7. Microbe-enhanced environmental fatigue crack propagation in HY130 steel

    SciTech Connect

    Gangloff, R.P.; Kelly, R.G. . Dept. of Materials Science and Engineering)

    1994-05-01

    Research was undertaken to characterize the effect of sulfate-reducing bacteria (SRB) on aqueous environment-enhanced fatigue cracking in a high-strength alloy steel. Desulfovibrio vulgaris in Postgate C solution greatly increased rates of ambient-temperature fatigue crack propagation (FCP) in tempered martensitic HY130 steel (MIL-S-24371A) under cathodic polarization and low-frequency, constant stress intensity range ([Delta]K) loading. Crack growth rates (da/dN) in the SRB solution increased 50- to 1,000-fold relative to FCP in sterile sodium chloride (NaCl) solution at [minus]1,000 mV[sub SCE] and under vacuum, respectively. The presence of microbes shifted fatigue cracking from a transgranular path (typical in sterile NaCl) to an intergranular crack path consistent with the enhanced growth rates. The SRB reduced fatigue crack initiation resistance, countering the beneficial effect of cathodic polarization for sterile NaCl. Metal embrittlement and increased hydrogen uptake at the occluded crack tip caused by bacterially produced hydrosulfide (HS[sup [minus

  8. Stress-ratio effect on mode II propagation of interlaminar fatigue cracks in graphite/epoxy composites

    SciTech Connect

    Tanaka, Keisuke; Tanaka, Hiroshi

    1997-12-31

    The effect of the stress ratio on the propagation behavior of Mode II interlaminar fatigue cracks was studied with unidirectional graphite/epoxy laminates, Toray T800H/{number_sign}3631. End-notched flexure (ENF) specimens were used for fatigue tests under the stress ratios of R = 0.2, 0.5, and 0.6; and end-loaded split (ELS) specimens were used for tests under R = {minus}1.0, {minus}0.5, and 0.2. For each stress ratio, the crack propagation rate was given by a power function of the stress intensity range, {Delta}K{sub 11}, in the region of rates above 10{sup {minus}9} m/cycle. Below this region, there exists the threshold for fatigue crack propagation. The threshold condition is given by a constant value of the stress intensity range, {Delta}K{sub 11th} = 1.8 MPa{radical}m. The crack propagation rate is determined by {Delta}K{sub 11} near the threshold, while by the maximum stress identity factor, K{sub 11max}, at high rates. A fracture mechanics equation is proposed for predicting the propagation rate of Mode II fatigue cracks under various stress ratios. The effect of the stress ratio on the micromechanism of Mode II fatigue crack propagation was discussed on the basis of the microscopic observations of fracture surfaces and near-crack-tip regions.

  9. Microstructural effects on the stress corrosion cracking behavior of medium and high strength steels

    NASA Astrophysics Data System (ADS)

    Kerr, R.; Solana, F.; Bernstein, I. M.; Thompson, A. W.

    1987-01-01

    The effects of variations in microstructure and strength level on the stress corrosion cracking susceptibility of three medium to high strength steels, H13, 300M, and HY-130, in 3.5 pct NaCl have been systematically studied. Superimposed on the expected inverse dependence of KISCC on yield strength was more than an order of magnitude reduction in crack growth rate, with no strength penalty. These results have been analyzed in terms of the possible relative roles of different microstructural features, in particular retained austenite, whose detailed behavior is the subject of a companion paper.

  10. Microstructural effects on the stress corrosion cracking behavior of medium and high strength steels

    NASA Astrophysics Data System (ADS)

    Kerr, R.; Solana, F.; Bernstein, I. M.; Thompson, A. W.

    1991-01-01

    The effects of variations in microstructure and strength level on the stress corrosion cracking susceptibility of three medium to high strength steels, H13, 300M, and HY-130, in 3.5 pct NaCl have been systematically studied. Superimposed on the expected inverse dependence of KISCC on yield strength was more than an order of magnitude reduction in crack growth rate, with no strength penalty. These results have been analyzed in terms of the possible relative roles of different microstructural features, in particular retained austenite, whose detailed behavior is the subject of a companion paper.

  11. Macroscopic Segregation and Stress Corrosion Cracking in 7xxx Series Aluminum Alloy Arc Welds

    NASA Astrophysics Data System (ADS)

    Borchers, Tyler E.; McAllister, Donald P.; Zhang, Wei

    2015-05-01

    Arc welds of Al-Zn-Mg alloy with Al-Mg filler wire have shown a preferential macroscopic segregation of Mg and Zn to the weld toes. Islands of large precipitates, which are observed in those solute-enriched weld toes, are identified as T phase (Mg32(Al,Zn)49) using diffraction pattern analysis. The location of T precipitates consistently coincides with the initiation site for stress corrosion cracking. Therefore, it is hypothesized that they induce the crack initiation due to preferential dissolution.

  12. Stress Intensity Factors For Toe Cracks In Fillet Welded Joints - Finite Element Modelling And Thermoelastic Determination

    NASA Astrophysics Data System (ADS)

    Chan, S. W.; Oakley, Philip J.

    1989-07-01

    The application of fracture mechanics methods for assessing the significance of defects in welded structures or components may require accurate determination of stress intensity solution for typical joint configurations (1). At present, numerical methods such as finite element analysis are most widely used (2). Thermoelastic technique (SPATE) is a new experimental technique based on the measurement of infra-red radiant flux emitting from the surface of a body under cyclic stress. It has been shown from Refs. 3 and 4 that accurate stress intensity solutions can be derived from SPATE results obtained by scanning a cracked body with simple geometry under mode I and mode II loading. Hence the SPATE method offers an attractive alternative to numerical analysis, or a means of validating the numerical methods. In addition, it is anticipated that the new technique could be used for analysing a cracked body with complex geometries not easily analysed by numerical methods, for example semi-elliptical surface cracks in plates and cylinders, or tubular connections with weld toe cracks.

  13. Stress-intensity factors and crack-opening displacements for round compact specimens. [fracture toughness of metallic materials

    NASA Technical Reports Server (NTRS)

    Newman, J. C., Jr.

    1979-01-01

    A two dimensional, boundary collocation stress analysis was used to analyze various round compact specimens. The influence of the round external boundary and of pin-loaded holes on stress intensity factors and crack opening displacements was determined as a function of crack-length-to-specimen-width ratios. A wide-range equation for the stress intensity factors was developed. Equations for crack-surface displacements and load-point displacements were also developed. In addition, stress intensity factors were calculated from compliance methods to demonstrate that load-displacement records must be made at the loading points and not along the crack line for crack-length-to-specimen-width ratios less than about 0.4.

  14. Recent developments in analysis of crack propagation and fracture of practical materials. [stress analysis in aircraft structures

    NASA Technical Reports Server (NTRS)

    Hardrath, H. F.; Newman, J. C., Jr.; Elber, W.; Poe, C. C., Jr.

    1978-01-01

    The limitations of linear elastic fracture mechanics in aircraft design and in the study of fatigue crack propagation in aircraft structures are discussed. NASA-Langley research to extend the capabilities of fracture mechanics to predict the maximum load that can be carried by a cracked part and to deal with aircraft design problems are reported. Achievements include: (1) improved stress intensity solutions for laboratory specimens; (2) fracture criterion for practical materials; (3) crack propagation predictions that account for mean stress and high maximum stress effects; (4) crack propagation predictions for variable amplitude loading; and (5) the prediction of crack growth and residual stress in built-up structural assemblies. These capabilities are incorporated into a first generation computerized analysis that allows for damage tolerance and tradeoffs with other disciplines to produce efficient designs that meet current airworthiness requirements.

  15. Near-threshold fatigue crack growth behavior of 2195 aluminum-lithium-alloy—prediction of crack propagation direction and influence of stress ratio

    NASA Astrophysics Data System (ADS)

    Chen, D. L.; Chaturvedi, M. C.

    2000-06-01

    Tensile properties and fatigue crack propagation behavior of a 2195-T8 Al-Li alloy were investigated at different stress ratios, with particular emphasis on their dependence on specimen orientation. Specimens with orientations of 0, 15, 30, 45, and 90 deg to the rolling direction were tested. The alloy contained a strong brass-type texture and a profuse distribution of platelike precipitates of T 1 (Al2CuLi) phase on {111} matrix planes. Both tensile strength and fatigue thresholds were found to be strongly dependent on the specimen orientation, with the lowest values observed along the direction at 45 deg to the rolling direction. The effect of stress ratio on fatigue threshold could generally be explained by a modified crack closure concept. The growth of fatigue crack in this alloy was found to exhibit a significant crystallographic cracking and especially macroscopic crack deflection. The specimens oriented in the L-T + 45 deg had the smallest deflection angle, while the specimens in the L-T and T-L orientations exhibited a large deflection angle. The dependence of the fatigue threshold on the specimen orientation could be rationalized by considering an equivalent fatigue threshold calculated from both mode I and mode II values due to the crack deflection. A four-step approach on the basis of Schmid’s law combined with specific crystallographic textures is proposed to predict the fatigue crack deflection angle. Good agreement between the theoretical prediction and experimental results was observed.

  16. Evaluation of the stress corrosion cracking resistance of several high strength low alloy steels

    NASA Technical Reports Server (NTRS)

    Humphries, T. S.; Nelson, E. E.

    1980-01-01

    The stress corrosion cracking resistance was studied for high strength alloy steels 4130, 4340, for H-11 at selected strength levels, and for D6AC and HY140 at a single strength. Round tensile and C-ring type specimens were stressed up to 100 percent of their yield strengths and exposed to alternate immersion in salt water, salt spray, the atmosphere at Marshall Space Flight Center, and the seacoast at Kennedy Space Center. Under the test conditions, 4130 and 4340 steels heat treated to a tensile strength of 1240 MPa (180 ksi), H-11 and D6AC heat treated to a tensile strength of 1450 MPa (210 ksi), and HY140 (1020 MPa, 148 ksi) are resistant to stress corrosion cracking because failures were not encountered at stress levels up to 75 percent of their yield strengths. A maximum exposure period of one month for alternate immersion in salt water or salt spray and three months for seacoast is indicated for alloy steel to avoid false indications of stress corrosion cracking because of failure resulting from severe pitting.

  17. The relative stress-corrosion-cracking susceptibility of candidate aluminum-lithium alloys for aerospace applications

    NASA Technical Reports Server (NTRS)

    Pizzo, P. P.

    1982-01-01

    Stress corrosion tests of Al-Li-Cu powder metallurgy alloys are described. Alloys investigated were Al-2.6% Li-1.4% and Al-2.6% Li-1.4% Cu-1.6% Mg. The base properties of the alloys were characterized. Process, heat treatment, and size/orientational effects on the tensile and fracture behavior were investigated. Metallurgical and electrochemical conditions are identified which provide reproducible and controlled parameters for stress corrosion evaluation. Preliminary stress corrosion test results are reported. Both Al-Li-Cu alloys appear more susceptible to stress corrosion crack initiation than 7075-T6 aluminum, with the magnesium bearing alloy being the most susceptible. Tests to determine the threshold stress intensity for the base and magnesium bearing alloys are underway. Twelve each, bolt loaded DCB type specimens are under test (120 days) and limited crack growth in these precracked specimens has been observed. General corrosion in the aqueous sodium chloride environment is thought to be obscuring results through crack tip blunting.

  18. Determination of Stress-Corrosion Cracking in Aluminum-Lithium Alloy ML377

    NASA Technical Reports Server (NTRS)

    Valek, Bryan C.

    1995-01-01

    The use of aluminum-lithium alloys for aerospace applications is currently being studied at NASA Langley Research Center's Metallic Materials Branch. The alloys in question will operate under stress in a corrosive environment. These conditions are ideal for the phenomena of Stress-Corrosion Cracking (SCC) to occur. The test procedure for SCC calls for alternate immersion and breaking load tests. These tests were optimized for the lab equipment and materials available in the Light Alloy lab. Al-Li alloy ML377 specimens were then subjected to alternate immersion and breaking load tests to determine residual strength and resistance to SCC. Corrosion morphology and microstructure were examined under magnification. Data shows that ML377 is highly resistant to stress-corrosion cracking.

  19. Stress-intensity factors for internal surface cracks in cylindrical pressure vessels

    NASA Technical Reports Server (NTRS)

    Newman, J. C., Jr.; Raju, I. S.

    1979-01-01

    The stress intensity factors were calculated by a three dimensional finite element method. The finite element models employed singularity elements along the crack front and linear strain elements elsewhere. The models had about 6500 degrees of freedom. The stress intensity factors were evaluated from a nodal force method. An equation for the stress intensity factors was obtained form the results of the present analysis. The equation applies over a wide range of configuration parameters and was within about 5 percent of the present results. A comparison was made between the present results and other analyses of internal surface cracks in cylinders. The results from a boundary integral equation method were in agreement (+ or - 2 percent) and those from another finite element were in fair agreement (+ or - 8 percent) with the present results.

  20. Stress-intensity factors for circumferential surface cracks in pipes and rods under tension and bending loads

    NASA Technical Reports Server (NTRS)

    Raju, I. S.; Newman, J. C., Jr.

    1985-01-01

    The purpose of this paper is to present stress-intensity factors for a wide range of nearly semi-elliptical surface cracks in pipes and rods. The configurations were subjected to either remote tension or bending loads. For pipes, the ratio of crack depth to crack length (a/c) ranged from 0.6 to 1; the ratio of crack depth to wall thickness (a/t) ranged from 0.2 to 0.8; and the ratio of internal radius to wall thickness (R/t) ranged from 1 to 10. For rods, the ratio of crack depth to crack length also ranged from 0.6 to 1; and the ratio of crack depth to rod diameter (a/D) ranged from 0.05 to 0.35. These particular crack configurations were chosen to cover the range of crack shapes (a/c) that have been observed in experiments conducted on pipes and rods under tension and bending fatigue loads. The stress-intensity factors were calculated by a three-dimensional finite-element method. The finite-element models employed singularity elements along the crack front and linear-strain elements elsewhere. The models had about 6500 degrees of freedom. The stress-intensity factors were evaluated using a nodal-force method.

  1. Three-term Asymptotic Stress Field Expansion for Analysis of Surface Cracked Elbows in Nuclear Pressure Vessels

    NASA Astrophysics Data System (ADS)

    Labbe, Fernando

    2007-04-01

    Elbows with a shallow surface cracks in nuclear pressure pipes have been recognized as a major origin of potential catastrophic failures. Crack assessment is normally performed by using the J-integral approach. Although this one-parameter-based approach is useful to predict the ductile crack onset, it depends strongly on specimen geometry or constraint level. When a shallow crack exists (depth crack-to-thickness wall ratio less than 0.2) and/or a fully plastic condition develops around the crack, the J-integral alone does not describe completely the crack-tip stress field. In this paper, we report on the use of a three-term asymptotic expansion, referred to as the J- A 2 methodology, for modeling the elastic-plastic stress field around a three-dimensional shallow surface crack in an elbow subjected to internal pressure and out-of-plane bending. The material, an A 516 Gr. 70 steel, used in the nuclear industry, was modeled with a Ramberg-Osgood power law and flow theory of plasticity. A finite deformation theory was included to account for the highly nonlinear behavior around the crack tip. Numerical finite element results were used to calculate a second fracture parameter A 2 for the J- A 2 methodology. We found that the used three-term asymptotic expansion accurately describes the stress field around the considered three-dimensional shallow surface crack.

  2. An experimentally verified finite element study of the stress-strain response of crack geometries experiencing large-scale yielding

    SciTech Connect

    Panontin, T.L.; Sheppard, S.D.

    1997-12-01

    Large-strain, 3-D finite element analyses with incremental plasticity were performed for a variety of crack geometries to study local crack-tip stress-strain fields and associated global fracture parameters under conditions of large-scale yielding. The geometries analyzed include thin, single-edge crack tension, single-edge crack bending, and center-crack tension fracture specimens with varying crack depth (a/W) ratios. Two materials were investigated: a high-hardening, low-strength steel and a moderate-hardening, high-strength steel. Mesh refinement studies were performed to ensure convergence of the finite element predictions. The studies examine the effects of in-plane crack-tip element size, initial crack-tip radius size, and number of through-thickness layers on predicted distributions of crack-tip stress and plastic strain and predicted values of the J-integral and CTOD. In addition, the finite element predictions of specimen behavior were verified experimentally by direct measurements, namely load displacement, load longitudinal strain, and load CTOS, made during and following testing of the fracture specimens. Representative results of the finite element analyses are presented and compared to previously published data where pertinent. Results from the mesh refinement studies and the verification testing are shown. Predicted trends among the specimens and materials in local distributions of crack-tip plastic strain, triaxiality, and opening stress as well as in global parameters, J-integral and m-factor, are discussed.

  3. Stress Corrosion Crack Growth Rate Testing and Analytical Electron Microscopy of Alloy 600 as a Function of Pourbaix Space and Microstructure

    SciTech Connect

    N. Lewis; S.A. Attanasio; D.S. Morton; G.A. Young

    2000-10-04

    Stress corrosion crack (SCC) growth rate tests and analytical electron microscopy (AEM) studies were performed over a broad range of environments and heat treatments of Alloy 600. This effort was conducted to correlate bulk environmental conditions such as pH and electrochemical potential (EcP) with the morphology of the SCC crack. Development of a library of AEM morphologies formed by SCC in different environments is an important step in identifying the conditions that lead to SCC in components. Additionally, AEM examination of stress corrosion cracks formed in different environments and microstructures lends insight into the mechanism(s) of stress corrosion cracking. Testing was conducted on compact tension specimens in three environments: a mildly acidic oxidizing environment containing sulfate ions, a caustic environment containing 10% NaOH, and hydrogenated near-neutral buffered water. Additionally, stress corrosion cracking testing of a smooth specimen was conducted in hydrogenated steam. The following heat treatments of Alloy 600 were examined: mill annealed at 980 C (near-neutral water), mill annealed at 1010 C (steam), sensitized (acid and caustic), and mill annealed + healed to homogenize the grain boundary Cr concentration (caustic). Crack growth rate (CGR) testing showed that sensitized Alloy 600 tested in the mildly acidic, oxidizing environment containing sulfate ions produced the fastest cracking ({approx} 8.8 {micro}m/hr at 260 C), and AEM examination revealed evidence of sulfur segregation to the crack tip. The caustic environment produced slower cracking ({approx} 0.4 {micro}m/hr at 307 C) in the mill annealed + healed heat treatment but no observed cracking in the sensitized condition. In the caustic environment, fully oxidized carbides were present in the crack wake but not ahead of the crack tip. In near-neutral buffered water at 338 C, the CGR was a function of dissolved hydrogen in the water and exhibited a maximum (0.17 {micro}m/hr) near the

  4. Growth and stability of stress corrosion cracks in large-diameter BWR piping. Volume 1: summary. Final report

    SciTech Connect

    Hale, D A; Heald, J D; Horn, R M; Jewett, C W; Kass, J N; Mehta, H S; Ranganath, S; Sharma, S R

    1982-07-01

    This report presents the results of a research program conducted to evaluate the behavior of hypothetical stress corrosion cracks in large diameter austenitic piping. The program included major tasks, a design margin assessment, an evaluation of crack growth and crack arrest, and development of a predictive model. As part of the margin assessment, the program developed diagrams which predicted net section collapse as a function of crack size. In addition, plasticity and dynamic load effects were also considered in evaluating collapse. Analytical methods for evaluating these effects were developed and were benchmarked by dynamic tests of 4-in.-diameter piping. The task of evaluating the growth behavior of stress corrosion cracks focused on developing constant load and cyclic growth rate data that could be used with the predictive model. Secondly, laboratory tests were performed to evaluate the conditions under which growing stress corrosion cracks would arrest when they intersected stress corrosion resistant weld metal. The third task successfully developed a model to predict the behavior of cracks in austenitic piping. This model relies on crack growth data and the critical crack size predicted by the net section collapse approach.

  5. High-Performance Laser Peening for Effective Mitigation of Stress Corrosion Cracking

    SciTech Connect

    Hackel, L; Hao-Lin, C; Wong, F; Hill, M

    2002-10-02

    Stress corrosion cracking (SCC) in the Yucca Mountain waste package closure welds is believed to be the greatest threat to long-term containment. Use of stress mitigation to eliminate tensile stresses resulting from welding can prevent SCC. A laser technology with sufficient average power to achieve high throughput has been developed and commercially deployed with high peak power and sufficiently high average power to be an effective laser peening system. An appropriately applied version of this process could be applied to eliminate SCC in the waste package closure welds.

  6. Imaging in-plane and normal stresses near an interface crack using traction force microscopy

    PubMed Central

    Xu, Ye; Engl, Wilfried C.; Jerison, Elizabeth R.; Wallenstein, Kevin J.; Hyland, Callen; Wilen, Larry A.; Dufresne, Eric R.

    2010-01-01

    Colloidal coatings, such as paint, are all around us. However, we know little about the mechanics of the film-forming process because the composition and properties of drying coatings vary dramatically in space and time. To surmount this challenge, we extend traction force microscopy to quantify the spatial distribution of all three components of the stress at the interface of two materials. We apply this approach to image stress near the tip of a propagating interface crack in a drying colloidal coating and extract the stress intensity factor. PMID:20696929

  7. Ultrasonic inspection of austenitic stainless steel welds with artificially produced stress corrosion cracks

    SciTech Connect

    Dugan, Sandra; Wagner, Sabine

    2014-02-18

    Austenitic stainless steel welds and nickel alloy welds, which are widely used in nuclear power plants, present major challenges for ultrasonic inspection due to the grain structure in the weld. Large grains in combination with the elastic anisotropy of the material lead to increased scattering and affect sound wave propagation in the weld. This results in a reduced signal-to-noise ratio, and complicates the interpretation of signals and the localization of defects. Mechanized ultrasonic inspection was applied to study austenitic stainless steel test blocks with different types of flaws, including inter-granular stress corrosion cracks (IGSCC). The results show that cracks located in the heat affected zone of the weld are easily detected when inspection from both sides of the weld is possible. In cases of limited accessibility, when ultrasonic inspection can be carried out only from one side of a weld, it may be difficult to distinguish between signals from scattering in the weld and signals from cracks.

  8. Ultrasonic inspection of austenitic stainless steel welds with artificially produced stress corrosion cracks

    NASA Astrophysics Data System (ADS)

    Dugan, Sandra; Wagner, Sabine

    2014-02-01

    Austenitic stainless steel welds and nickel alloy welds, which are widely used in nuclear power plants, present major challenges for ultrasonic inspection due to the grain structure in the weld. Large grains in combination with the elastic anisotropy of the material lead to increased scattering and affect sound wave propagation in the weld. This results in a reduced signal-to-noise ratio, and complicates the interpretation of signals and the localization of defects. Mechanized ultrasonic inspection was applied to study austenitic stainless steel test blocks with different types of flaws, including inter-granular stress corrosion cracks (IGSCC). The results show that cracks located in the heat affected zone of the weld are easily detected when inspection from both sides of the weld is possible. In cases of limited accessibility, when ultrasonic inspection can be carried out only from one side of a weld, it may be difficult to distinguish between signals from scattering in the weld and signals from cracks.

  9. Influence of the slip conditions on the stress corrosion cracking microprocesses in fcc materials

    SciTech Connect

    Chambreuil-Paret, A.; Chateau, J.P.; Magnin, T.

    1997-11-01

    The aim of the present paper is to carefully analyze the stress corrosion cracking (SCC) microprocesses of f.c.c. single crystals, not only for the influence of the tensile axis orientation but also for the influence of the cracking direction (imposed or not). 316L (in MgCl{sub 2}) and copper (in nitrites) single crystals of well defined tensile axis will be strained using the slow strain rate technique. The authors focus on the influence of the relative orientations of the cracking direction and the slip planes on the crystallography of fracture. The effect of slip conditions on the corrosion-deformation interactions leading to fracture are then emphasized, which gives major information relevant to the micromodelling of SCC.

  10. Stress intensity factors for deep cracks emanating from the corner formed by a hole intersecting a plate surface

    NASA Technical Reports Server (NTRS)

    Mcgowan, J. J.; Smith, C. W.

    1974-01-01

    A technique consisting of freezing photo-elasticity and a numerical method was used to obtain stress intensity factors for natural cracks emanating from the corner at which a hole intersects a plate surface. Geometries studied were: (1) crack depth to thickness ratios of approximately 0.2, (2) 0.5 and 0.75; (3) crack depth to crack length ratios of approximately 1.0 to 2.0; and (4) crack length to hole radius ratios of about 0.5 to 2.0. All final crack geometries were grown under monotonic loading and growth was not self similar, with most of the growth occuring through the thickness under remote extension. Stress intensity factors were determined at the intersection of the flaw border.

  11. Environmental enhancement of creep crack growth in Inconel 718 by oxygen and water vapor

    SciTech Connect

    Valerio, P.; Gao, M.; Wei, R.P. . Dept. of Mechanical Engineering and Mechanics)

    1994-05-15

    Inconel 718 alloy is widely used in high temperature applications. Because of its sensitivity to environmentally enhanced crack growth at high temperatures, its use has been limited to modest temperatures (i.e., below 973 K). To improve its performance and to better predict its service life, it is important to develop a better understanding of the processes of crack growth at high temperatures in this alloy. It has been shown that the creep crack growth rates (CCGR) in air are at least two orders of magnitude faster than those in vacuum or inert environments. CCGR were also found to depend strongly on temperature. Fractographic studies showed that crack growth was intergranular in air and in vacuum with brittle appearing grain boundary separation in air and extensive cavity formation in vacuum. The increased CCGR in air has been attributed to the enhancement by oxygen; principally through enhanced cavity nucleation and growth by high-pressure carbon monoxide/dioxide formed by the reactions of oxygen that diffused into the material with the grain boundary carbides. The appropriateness of this mechanism, however, may be questioned by the absence of cavitation on the crack surfaces produced in air. As such the mechanism for crack growth needs to be re-examined. Because of the presence of moisture in air, the possible influence of hydrogen needs to be considered as well. In this study, preliminary experiments were conducted to examine the process of environmentally enhanced creep crack growth in Inconel 718 alloy in terms of possible mechanisms and rate controlling processes. Creep crack growth experiments were carried out in air, oxygen (from 2.67 to 100 kPa), moist argon (water vapor) and pure argon at temperatures from 873 to 973 K.

  12. Environmental fatigue of an Al-Li-Cu alloy; Part II: Microscopic hydrogen cracking processes

    SciTech Connect

    Piascik, R.S.; Gangloff, R.P.

    1993-12-01

    Microscopic fatigue crack propagation (FCP) paths in peak-aged unrecrystallized alloy 2090 are identified as functions of intrinsic da/dN-{Delta}K kinetics and environment. The FCP rates in longitudinal-transverse (LT)-oriented 2090 are accelerated by hydrogen-producing environments (pure water vapor, moist air, and aqueous NaCl), as defined in Part 1. Subgrain boundary cracking (SGC) dominates for {Delta}K values where the cyclic plastic zone is sufficient to envelop subgrains. At low {Delta}K, when this crack tip process zone is smaller than the subgrain size, environmental FCP progresses on or near [100] or [110] planes, based on etch-pit shape. For inert environments (vacuum and He) and pure O{sub 2} with crack surface oxidation, FCP produces large facets along [111] oriented slip bands. This mode does not change with {Delta}K, and T{sub 1} decorated subgrain boundaries do not effect an expected da/dN-{Delta}K transition for the inert environments. Rather, the complex dependence of da/dN on {Delta}K is controlled by the environmental contribution to process zone microstructure-plastic strain interactions. A hydrogen embrittlement mechanism for FCP in 2090 is supported by similar brittle crack paths for low pressure water vapor and the electrolyte, the SGC and [100]/[110] crystallographic cracking modes, the influence of cyclic plastic zone volume ({Delta}K), and the benignancy of O{sub 2}. The SGC may be due to hydrogen production and trapping at T{sub 1} bearing sub-boundaries after process zone dislocation transport, while crystallographic cracking may be due to lattice decohesion or hydride cracking.

  13. On stress analysis of a crack-layer

    NASA Technical Reports Server (NTRS)

    Chudnovsky, A.; Dolgopolsky, A.; Kachanov, M.

    1984-01-01

    This work considers the problem of elastic interaction of a macrocrack with an array of microcracks in the vicinity of the macrocrack tip. Using the double layer potential techniques, the solution to the problem within the framework of the plane problem of elastostatics has been obtained. Three particular problems of interest to fracture mechanics have been analyzed. It follows from analysis that microcrack array can either amplify or reduce the resulting stress field of the macrocrack-microcrack array system depending on the array's configuration. Using the obtained elastic solution the energy release rate associated with the translational motion of the macrocrack-microcrack array system has been evaluated.

  14. Initiation stress threshold irradiation assisted stress corrosion cracking criterion assessment for core internals in PWR environment

    SciTech Connect

    Tanguy, Benoit; Stern, Anthony; Bossis, Philippe; Pokor, Cedric

    2012-07-01

    Irradiation assisted stress corrosion cracking (IASCC) is a problem of growing importance in pressurized water reactors (PWR). An understanding of the mechanism(s) of IASCC is required in order to provide guidance for the development of mitigation strategies. One of the principal reasons why the IASCC mechanism(s) has been so difficult to understand is the inseparability of the different IASCC potential contributors evolutions due to neutron irradiation. The potential contributors to IASCC in PWR primary water are: (i) radiation induced segregation (RIS) at grain boundaries, (ii) radiation induced microstructure (formation and growth of dislocations loops, voids, bubbles, phases), (iii) localized deformation under loading, (iv) irradiation creep and transmutations. While the development of some of the contributors (RIS, microstructure) with increasing doses are at least qualitatively well understood, the role of these changes on IASCC remains unclear. Parallel to fundamental understanding developments relative to IASCC, well controlled laboratory tests on neutron irradiated stainless steels are needed to assess the main mechanisms and also to establish an engineering criterion relative to the initiation of fracture due to IASCC. First part of this study describes the methodology carried out at CEA in order to provide more experimental data from constant load tests dedicated to the study of initiation of SCC on neutron irradiated stainless steel. A description of the autoclave recirculation loop dedicated to SCC tests on neutron irradiated materials is then given. This autoclave recirculation loop has been started on July 2010 with the first SCC test on an irradiated stainless steel (grade 316) performed at CEA. The main steps of the interrupted SCC tests are then described. Second part of this paper reports the partial results of the first test performed on a highly neutron irradiated material. (authors)

  15. Effect of heat treatment on caustic stress corrosion cracking behavior of alloy 600

    SciTech Connect

    Sung, J.K.

    1999-12-01

    Constant elongation rate tests (CERT) were conducted to evaluate the effect of heat treatment on intergranular stress corrosion cracking (IGSCC) susceptibility of alloy 600 (UNS NO6600) in 140 C and 50% caustic solution at {minus}900 mV vs saturated calomel electrode (SCE). Results showed: (1) Heat treatment at low temperature for a long time (600 C for 260 h) led to a material that was not susceptible to caustic intergranular (IG) cracking. Increase in heat treatment temperature enhanced IG cracking susceptibility. Caustic IGSCC susceptibility was at maximum near the carbon solubility limit. However, when the heat treatment temperature was higher than the carbon solubility limit, a significant decrease in crack growth rate was observed. (2) Grain boundaries acted as a preferential crack path when grain boundary carbon segregation was likely. Thermodynamic considerations suggested that severe caustic IGSCC susceptibility near the carbon solubility limit could be explained in terms of carbon segregation at the grain boundaries. (3) IGSCC in caustic solution did not seem to be caused by chromium depletion. (4) Although formation of semi-continuous IG carbides and IGSCC resistance seemed to exhibit a similar chronological response with heat treatment, it was unlikely that grain boundary IG carbides played a role in caustic IGSCC susceptibility.

  16. Effects of surface preparation on pitting resistance, residual stress, and stress corrosion cracking in austenitic stainless steels

    NASA Astrophysics Data System (ADS)

    Rhouma, A. Ben; Sidhom, H.; Braham, C.; Lédion, J.; Fitzpatrick, M. E.

    2001-10-01

    Surface finishing treatments such as shot blasting and wire brushing can be beneficial in improving the integrity of machined surfaces of austenitic stainless steels. These operations optimize in-service properties such as resistance to pitting corrosion and stress corrosion cracking (SCC). In this study, ground steel surfaces were subjected to a series of sand blasting and wire brushing treatments. The surfaces were then characterized by their hardness, surface residual stress state, and resistance to stress corrosion and pitting corrosion. Some samples were selected for depth profiling of residual stress. It is found that surface hardening and the generation of near-surface compressive residual stress are the benefits that can be introduced by sand blasting and brushing operations.

  17. Analysis of corner cracks at hole by a 3-D weight function method with stresses from finite element method

    NASA Technical Reports Server (NTRS)

    Zhao, W.; Newman, J. C., Jr.; Sutton, M. A.; Wu, X. R.; Shivakumar, K. N.

    1995-01-01

    Stress intensity factors for quarter-elliptical corner cracks emanating from a circular hole are determined using a 3-D weight function method combined with a 3-D finite element method. The 3-D finite element method is used to analyze uncracked configuration and provide stress distribution in the region where crack is to occur. Using this stress distribution as input, the 3-D weight function method is used to determine stress intensity factors. Three different loading conditions, i.e. remote tension, remote bending and wedge loading, are considered for a wide range in geometrical parameters. The significance in using 3-D uncracked stress distribution and the difference between single and double corner cracks are studied. Typical crack opening displacements are also provided. Comparisons are made with solutions available in the literature.

  18. The effect of heat treatment and test parameters on the aqueous stress corrosion cracking of D6AC steel

    NASA Technical Reports Server (NTRS)

    Gilbreath, W. P.; Adamson, M. J.

    1974-01-01

    The crack growth behavior of D6AC steel as a function of stress intensity, stress and corrosion history and test technique, under sustained load in natural seawater, 3.3 percent NaCl solution, distilled water, and high humidity air was investigated. Reported investigations of D6AC were considered with emphasis on thermal treatment, specimen configuration, fracture toughness, crack-growth rates, initiation period, threshold, and the extension of corrosion fatigue data to sustained load conditions. Stress history effects were found to be most important in that they controlled incubation period, initial crack growth rates, and apparent threshold.

  19. Using transmission Kikuchi diffraction to study intergranular stress corrosion cracking in type 316 stainless steels.

    PubMed

    Meisnar, Martina; Vilalta-Clemente, Arantxa; Gholinia, Ali; Moody, Michael; Wilkinson, Angus J; Huin, Nicolas; Lozano-Perez, Sergio

    2015-08-01

    Transmission Kikuchi diffraction (TKD), also known as transmission-electron backscatter diffraction (t-EBSD) is a novel method for orientation mapping of electron transparent transmission electron microscopy specimen in the scanning electron microscope and has been utilized for stress corrosion cracking characterization of type 316 stainless steels. The main advantage of TKD is a significantly higher spatial resolution compared to the conventional EBSD due to the smaller interaction volume of the incident beam with the specimen. Two 316 stainless steel specimen, tested for stress corrosion cracking in hydrogenated and oxygenated pressurized water reactor chemistry, were characterized via TKD. The results include inverse pole figure (IPFZ) maps, image quality maps and misorientation maps, all acquired in very short time (<60 min) and with remarkable spatial resolution (up to 5 nm step size possible). They have been used in order to determine the location of the open crack with respect to the grain boundary, deformation bands, twinning and slip. Furthermore, TKD has been used to measure the grain boundary misorientation and establish a gauge for quantifying plastic deformation at the crack tip and other regions in the surrounding matrix. Both grain boundary migration and slip transfer have been detected as well. PMID:25974882

  20. Rupture of osteocyte processes across microcracks: the effect of crack length and stress.

    PubMed

    Dooley, Clodagh; Tisbo, Pietro; Lee, T Clive; Taylor, David

    2012-07-01

    Bone cells are connected to one another in a network, via their dendritic cellular processes. Previously, we hypothesized that these processes could be ruptured by microcracks. We proposed this as a mechanism by which osteoctyes could detect the presence of microcracks. In order for this mechanism to be effective, the number of ruptured processes would have to increase with microcrack length and also with the applied cyclic stress. This paper presents for the first time experimental data, which shows that this is indeed the case. We examined samples of bovine, ovine and murine bone ex vivo and observed processes passing across crack faces: some were still intact whilst others had ruptured. The number of intact processes per unit crack length decreased significantly with increasing crack length and also decreased in samples, which had been tested in vitro at higher stress levels. A theoretical model that we had developed previously was able to predict the overall magnitude and general trends in the experimental data. This work has provided further support for our "scissors" model, which proposes that microcracks can be detected because they disturb the osteocyte network, specifically by rupturing cellular processes where they pass across the crack faces. PMID:21927824

  1. Stress-intensity factors for a thick-walled cylinder containing an annular imbedded or external or internal surface crack

    NASA Technical Reports Server (NTRS)

    Erdol, R.; Erdogan, F.

    1976-01-01

    The elastostatic axisymmetric problem for a long thick-walled cylinder containing a ring-shaped internal or edge crack is considered. Using the standard transform technique the problem is formulated in terms of an integral equation which has a simple Cauchy kernel for the internal crack and a generalized Cauchy kernel for the edge crack as the dominant part. As examples the uniform axial load and the steady-state thermal stress problems have been solved and the related stress intensity factors have been calculated. Among other findings the results show that in the cylinder under uniform axial stress containing an internal crack the stress intensity factor at the inner tip is always greater than that at the outer tip for equal net ligament thicknesses and in the cylinder with an edge crack which is under a state of thermal stress the stress intensity factor is a decreasing function of the crack depth, tending to zero as the crack depth approaches the wall thickness.

  2. An experimental study on the effects of compressive stress on the fatigue crack growth of low-alloy steel

    SciTech Connect

    Jones, D.P.; Hoppe, R.G. . Bettis Atomic Power Lab.); Hechmer, J.L. ); James, B.A. . Metallurgy Dept.)

    1994-08-01

    A series of fatigue crack growth rate tests was conducted in order to study the effects of negative stress ratio upon the fatigue crack growth rate of low-alloy steel in air environment. The tests used four-point bend specimens in order to simulate linear stress distributions typical of many pressure vessel applications. This type of testing adds to the knowledge on negative stress ratio effects for low-alloy steels that in the past have been obtained from uniform tension-compression tests. Additionally, the applied bending stress range was varied from low values of applied stress to high values of applied stress over twice the yield strength. Load control was used for tests for which the stress range was less than twice the yield strength and deflection control was used for the higher stress range tests. The crack geometries involved were both short and long fatigue cracks started at notches and tight fatigue cracks for which crack closure could occur over the full crack face. The results are presented in terms of the stress intensity factor ratio R = K[sub MIN]/K[sub MAX]. The negative R-ratio test results were correlated to an equation of the form da/dN = C[[delta]K/(A-R)][sup n] where A, C and n are curve-fitting parameters. It was found that the effects of negative R-ratio on the fatigue crack growth rates for even the high stress range tests could be bounded by correlating the foregoing equation to only positive R-ratio test results and extending the resulting equation into the negative R-ratio regime.

  3. Environmentally enhanced crack growth in nickel-based alloys at elevated temperatures

    SciTech Connect

    Gao, M.; Chen, S.F.; Chen, G.S.; Wei, R.P.

    1997-12-31

    A recent understanding of environmentally enhanced sustained-load crack growth in nickel-based superalloys at elevated temperatures is presented. This understanding is based on the results of coordinated studies of crack growth kinetics, surface chemistry, and microstructure in a commercial Inconel 718. The results suggest that environmental enhancement of sustained-load crack growth in Inconel 718 is associated with the formation and rupture of niobium oxides at grain boundary surfaces and is controlled mainly by the rate of oxidation and decomposition of niobium carbides at the grain boundaries. Data on other nickel-based alloys in the literature appear to support this suggested role of niobium. Initial results from a study of a niobium-free Ni-18Cr-18Fe alloy (its base composition is identical to Inconel 718) confirm the possible influence of niobium and the proposed mechanism. Some open issues for further investigation are discussed.

  4. Caustic stress corrosion cracking susceptibility in continuous kraft digesters due to process loadings

    SciTech Connect

    Leinonen, H.

    1999-07-01

    Loads of the continuous kraft digester have been determined during the start-up of the digester house. Loading was caused by the pressure of the proof test, the start-up pressures of the digester and, finally, the normal working pressure. The apparent threshold stress level in the base metal was greater than that achieved during the normal continuous cooking process but the level in the weld of the impregnation zone were exceeded due to the superposition of the tensile residual stresses. This two-axial tension is considered as the precondition for stress corrosion cracking (SCC), which was confirmed by fractography studies. The results showed, that SCC in the impregnation zone is possible only in the welds during the normal continuous cooking process. During the refill and blow phase of the digester the measured loading stress changes corresponded to the stresses of the proof test and increased the risk for SCC. Some procedures to avoid or minimize SCC are discussed.

  5. Stress Corrosion Cracking Behavior of Peened Friction Stir Welded 2195 Aluminum Alloy Joints

    NASA Astrophysics Data System (ADS)

    Hatamleh, Omar; Singh, Preet M.; Garmestani, Hamid

    2009-06-01

    The surface treatment techniques of laser and shot peening were used to investigate their effect on stress corrosion cracking (SCC) in friction stir welded (FSW) 2195 aluminum alloy joints. The investigation consisted of two parts: the first part explored the peening effects on slow strain rate testing (SSRT) in a 3.5% NaCl solution, while the second part investigated the effects of peening on corrosion while submerged in a 3.5% NaCl solution with no external loads applied. For the SSRT, the laser-peened samples demonstrated superior properties to the other samples, but no signs of corrosion pitting or SCC were evident on any of the samples. For the second part of the study, the FSW plates were inspected periodically for signs of corrosion. After 60 days there were signs of corrosion pitting, but no stress corrosion cracking was noticed in any of the peened and unpeened samples.

  6. Normal and shear impact of layered composite with a crack - Dynamic stress intensification

    NASA Technical Reports Server (NTRS)

    Sih, G. C.; Chen, E. P.

    1980-01-01

    The dynamic response of a layered composite under normal and shear impact is analyzed by assuming that the composite contains an initial flaw in the matrix material. One of the objectives was to develop an analytical method for determining dynamic stress solutions which should lead to a numerical method which utilizes Fourier transform for the space variable and Laplace transform for the time variable. The time-dependent angle loading is separated into two parts: a symmetric and a skew-symmetric with reference to the crack plane. By superposition, the transient boundary conditions consist of applying normal and shear tractions to a crack embedded in a layered composite; one phase of the composite could represent the fiber while the other could be the matrix. Mathematically, these conditions reduce the problem to a system of dual integral equations solved in the transform plane for the transform of the dynamic stress-intensity factor.

  7. Stress corrosion cracking tests on high-level-waste container materials in simulated tuff repository environments

    SciTech Connect

    Abraham, T.; Jain, H.; Soo, P.

    1986-06-01

    Types 304L, 316L, and 321 austenitic stainless steel and Incoloy 825 are being considered as candidate container materials for emplacing high-level waste in a tuff repository. The stress corrosion cracking susceptibility of these materials under simulated tuff repository conditions was evaluated by using the notched C-ring method. The tests were conducted in boiling synthetic groundwater as well as in the steam/air phase above the boiling solutions. All specimens were in contact with crushed Topopah Spring tuff. The investigation showed that microcracks are frequently observed after testing as a result of stress corrosion cracking or intergranular attack. Results showing changes in water chemistry during test are also presented.

  8. The role of hydrogen in hot-salt stress corrosion cracking of titanium-aluminum alloys

    NASA Technical Reports Server (NTRS)

    Ondrejcin, R. S.

    1971-01-01

    Additional support is presented for the previously proposed role of hydrogen as an embrittling agent in hot-salt stress corrosion cracking of titanium-aluminum alloys. The main source of hydrogen formed during the reactions of titanium alloys with hot salt was identified as water associated with the salt. Hydrogen is produced by the reaction of an intermediate (hydrogen halide) with the alloy rather than from metal-water reactions. The fracture mode of precracked tensile specimens was ductile when the specimens were tested in air, and brittle when tests were made in high-pressure hydrogen. Stressed titanium-aluminum alloys also were cracked by bombardment with hydrogen ions produced in a proton accelerator. The approximate concentrations of the hydrogen ions in the alloys were calculated.

  9. Scanning electron acoustic microscopy of indentation-induced cracks and residual stresses in ceramics

    NASA Technical Reports Server (NTRS)

    Cantrell, John H.; Qian, Menglu; Ravichandran, M. V.; Knowles, K. M.

    1990-01-01

    The ability of scanning electron acoustic microscopy (SEAM) to characterize ceramic materials is assessed. SEAM images of Vickers indentations in SiC whisker-reinforced alumina clearly reveal not only the radial cracks, the length of which can be used to estimate the fracture toughness of the material, but also reveal strong contrast, interpreted as arising from the combined effects of lateral cracks and the residual stress field left in the SiC whisker-reinforced alumina by the indenter. The strong contrast is removed after the material is heat treated at 1000 C to relieve the residual stresses around the indentations. A comparison of these observations with SEAM and reflected polarized light observations of Vickers indentations in soda-lime glass both before and after heat treatment confirms the interpretation of the strong contrast.

  10. Internal Crack Propagation in a Continuously Cast Austenitic Stainless Steel Analyzed by Actual Residual Stress Tensor Distributions

    NASA Astrophysics Data System (ADS)

    Saito, Youichi; Tanaka, Shun-Ichiro

    2016-04-01

    Initiation, propagation, and termination of internal cracks in a continuously cast austenitic stainless steel has been investigated with emphasis on stress loading of the solidified shell during casting. Cracks were formed at the center of the slab, parallel to the width of the cast, and were observed near the narrow faces. Optimized two-dimensional X-ray diffraction method was employed to measure residual stress tensor distributions around the cracks in the as-cast slab with coarse and strongly preferentially oriented grains. The tensor distributions had a sharp peak, as high as 430 MPa, at the crack end neighboring the columnar grains. On the other hand, lower values were measured at the crack end neighboring the equiaxed grains, where the local temperatures were higher during solidification. The true residual stress distributions were determined by evaluating the longitudinal elastic constant for each measured position, resulting in more accurate stress values than before. Electron probe micro-analysis at the terminal crack position showed that Ni, Ti, and Si were concentrated at the boundaries of the equiaxed grains, where the tensile strength was estimated to be lower than at the primary grains. A model of the crack formation and engineering recommendations to reduce crack formation are proposed.

  11. STRESS CORROSION CRACK GROWTH RESPONSE FOR ALLOY 152/52 DISSIMILAR METAL WELDS IN PWR PRIMARY WATER

    SciTech Connect

    Toloczko, Mychailo B.; Olszta, Matthew J.; Overman, Nicole R.; Bruemmer, Stephen M.

    2015-08-15

    As part of ongoing research into primary water stress corrosion cracking (PWSCC) susceptibility of alloy 690 and its welds, SCC tests have been conducted on alloy 152/52 dissimilar metal (DM) welds with cracks positioned with the goal to assess weld dilution and fusion line effects on SCC susceptibility. No increased crack growth rate was found when evaluating a 20% Cr dilution zone in alloy 152M joined to carbon steel (CS) that had not undergone a post-weld heat treatment (PWHT). However, high SCC crack growth rates were observed when the crack reached the fusion line of that material where it propagated both on the fusion line and in the heat affected zone (HAZ) of the carbon steel. Crack surface and crack profile examinations of the specimen revealed that cracking in the weld region was transgranular (TG) with weld grain boundaries not aligned with the geometric crack growth plane of the specimen. The application of a typical pressure vessel PWHT on a second set of alloy 152/52 – carbon steel DM weld specimens was found to eliminate the high SCC susceptibility in the fusion line and carbon steel HAZ regions. PWSCC tests were also performed on alloy 152-304SS DM weld specimens. Constant K crack growth rates did not exceed 5x10-9 mm/s in this material with post-test examinations revealing cracking primarily on the fusion line and slightly into the 304SS HAZ.

  12. The role of local strains from prior cold work on stress corrosion cracking of α-brass in Mattsson's solution

    SciTech Connect

    Ulaganathan, Jaganathan Newman, Roger C.

    2014-06-01

    The dynamic strain rate ahead of a crack tip formed during stress corrosion cracking (SCC) under a static load is assumed to arise from the crack propagation. The strain surrounding the crack tip would be redistributed as the crack grows, thereby having the effect of dynamic strain. Recently, several studies have shown cold work to cause accelerated crack growth rates during SCC, and the slip-dissolution mechanism has been widely applied to account for this via a supposedly increased crack-tip strain rate in cold worked material. While these interpretations consider cold work as a homogeneous effect, dislocations are generated inhomogeneously within the microstructure during cold work. The presence of grain boundaries results in dislocation pile-ups that cause local strain concentrations. The local strains generated from cold working α-brass by tensile elongation were characterized using electron backscatter diffraction (EBSD). The role of these local strains in SCC was studied by measuring the strain distributions from the same regions of the sample before cold work, after cold work, and after SCC. Though, the cracks did not always initiate or propagate along boundaries with pre-existing local strains from the applied cold work, the local strains surrounding the cracked boundaries had contributions from both the crack propagation and the prior cold work. - Highlights: • Plastic strain localization has a complex relationship with SCC susceptibility. • Surface relief created by cold work creates its own granular strain localization. • Cold work promotes crack growth but several other factors are involved.

  13. Stress corrosion cracking of zirconium cladding tubes: IV. Effect of hydrogen saturation

    NASA Astrophysics Data System (ADS)

    Rozhnov, A. B.; Nikulin, S. A.; Khanzhin, V. G.; Belov, V. A.

    2011-04-01

    The effect of hydrogen saturation on the stress corrosion cracking (SCC) resistance of zirconium cladding tubes in an iodine-containing medium is studied. Comparative SCC tests are performed for tubes produced from E110 and E635 alloys with various hydrogen contents (up to 400 ppm). Hydrogen is shown to decrease the SCC resistance of the tubes predominantly because of the activation of pitting formation processes.

  14. Stress corrosion cracking of LWR fuel: Volume 2, The SCCIG-B model: Final report

    SciTech Connect

    Miller, A.K.; Tasooji, A.

    1988-03-01

    This report describes two major extensions of the SCCIG model for iodine stress corrosion cracking of Zircaloy. The first permits prediction of the effects of texture on SCC; the second (the SCCIG-B model) permits the prediction of the SCC behavior of zirconium-lined ''barrier'' cladding. A fast-running derivative model (CFMIII) has also been developed. A complete users manual for the SCCIG-B FORTRAN program is given. 42 refs.

  15. Experimental study on propagation of liquid-filled crack in gelatin: Shape and velocity in hydrostatic stress condition

    NASA Astrophysics Data System (ADS)

    Takada, Akira

    1990-06-01

    The three-dimensional shape and velocity of propagating cracks in the hydrostatic stress condition were studied by using gelatin, the physical properties of which were controlled to be constant. Various liquids (with various densities, viscosities, and volumes as the governed parameters) were injected in gelatin to form liquid-filled cracks. The directions of the crack growth and the propagation of an isolated crack are governed by the density difference between injected liquid and gelatin (Δρ), that is, a buoyancy. The propagation of a crack has two critical values: the first is the transition value to brittle fracture; the second is the value where segmentation begins to occur. The condition of a stable isolated crack formation is discussed. The crack shape of an isolated crack in the direction perpendicular to the crack plane is different from that of a growing crack with a fat tear drop form: the former has an elliptical top and a nearly flat bottom. The upper termination of an isolated crack in the vertical cross section has an elliptical shape, and the lower termination has a cusped shape. The lower part of the crack occupies the preexiting fracture which has formed by fracturing at the crack top. The crack thickness (w)/crack height (h) ratio is proportional to Δρ A, if the elastic moduli are constant. The crack length l/h ratio increase with h in the primary fracture, while the l/h ratio decreases with h in the preexisting fracture except for air-filled cracks. The ascending velocity of an isolated crack is proportional to Δρ3 h4, that is, Δρ w2, if the other physical properties are constant. The height and length of a growing penny-shaped crack are approximately proportional to A 3d1/3t4/9, so that the growth rate of height is in proportion to A3d3t-5/9 (A3d is constant injection rale). Some comparisons with the two-dimensional crack theory and applications for magma-filled cracks are discussed on the basis of these results.

  16. Hierarchical Petascale Simulation Framework For Stress Corrosion Cracking

    SciTech Connect

    Grama, Ananth

    2013-12-18

    A number of major accomplishments resulted from the project. These include: • Data Structures, Algorithms, and Numerical Methods for Reactive Molecular Dynamics. We have developed a range of novel data structures, algorithms, and solvers (amortized ILU, Spike) for use with ReaxFF and charge equilibration. • Parallel Formulations of ReactiveMD (Purdue ReactiveMolecular Dynamics Package, PuReMD, PuReMD-GPU, and PG-PuReMD) for Messaging, GPU, and GPU Cluster Platforms. We have developed efficient serial, parallel (MPI), GPU (Cuda), and GPU Cluster (MPI/Cuda) implementations. Our implementations have been demonstrated to be significantly better than the state of the art, both in terms of performance and scalability. • Comprehensive Validation in the Context of Diverse Applications. We have demonstrated the use of our software in diverse systems, including silica-water, silicon-germanium nanorods, and as part of other projects, extended it to applications ranging from explosives (RDX) to lipid bilayers (biomembranes under oxidative stress). • Open Source Software Packages for Reactive Molecular Dynamics. All versions of our soft- ware have been released over the public domain. There are over 100 major research groups worldwide using our software. • Implementation into the Department of Energy LAMMPS Software Package. We have also integrated our software into the Department of Energy LAMMPS software package.

  17. Combined effect of matrix cracking and stress-free edge on delamination

    NASA Technical Reports Server (NTRS)

    Salpekar, S. A.; Obrien, T. K.

    1990-01-01

    The effect of the stress-free edge on the growth of local delaminations initiating from a matrix crack in (0 sub 2/90 sub 4) sub s and (+ or - 45.90 sub 4) sub s glass epoxy laminates is investigated using 3-D finite element analysis. The presence of high interlaminar normal stresses at the intersection (corner) of the matrix crack with the stress-free edge, suggests that a mode I delamination may initiate at the corners. The strain energy release rates (G) were calculated by modeling a uniform through-width delamination and two inclined delaminations at 10.6 deg and 45 deg to the matrix crack. All components of G have high values near the free edges. The mode I component of G is high at small delamination length and becomes zero for a delamination length of one-ply thickness. The total G values near the free edge agreed well with previously derived closed form solution. The quasi-3D solutions agreed well with the 3-D interior solutions.

  18. Combined effect of matrix cracking and stress-free edge on delamination

    NASA Technical Reports Server (NTRS)

    Salpekar, Satish A.; O'Brien, T. K.

    1991-01-01

    The effect of the stress-free edge on the growth of local delaminations initiating from a matrix crack in (O sub 2/90 sub 4) sub s and (+/- 45.90 sub 4) sub s glass epoxy laminates is investigated using 3D finite element analysis. The presence of high interlaminar normal stresses at the intersection (corner) of the matrix crack with the stress-free edge, suggests that a mode I delamination may initiate at the corners. The strain energy release rates (G) were calculated by modeling a uniform through-width delamination and two inclined delaminations at 10.6 deg and 45 deg to the matrix crack. All components of G have high values near the free edges. The mode I component of G is high at small delamination length and becomes zero for a delamination length of one-ply thickness. The total G values near the free edge agreed well with previously derived closed form solution. The quasi-3D solutions agreed well with the 3D interior solutions.

  19. Environmentally assisted cracking in light-water reactors: Semi-annual report, January--June 1997. Volume 24

    SciTech Connect

    Chopra, O.K.; Chung, H.M.; Gruber, E.E.

    1998-04-01

    This report summarizes work performed by Argonne National Laboratory on fatigue and environmentally assisted cracking (EAC) in light water reactors from January 1997 to June 1997. Topics that have been investigated include (a) fatigue of carbon, low-alloy, and austenitic stainless steels (SSs) used in reactor piping and pressure vessels, (b) irradiation-assisted stress corrosion cracking of Types 304 and 304L SS, and (c) EAC of Alloys 600 and 690. Fatigue tests were conducted on ferritic and austenitic SSs in water that contained various concentrations of dissolved oxygen (DO) to determine whether a slow strain rate applied during various portions of a tensile-loading cycle is equally effective in decreasing fatigue life. Slow-strain-rate-tensile tests were conducted in simulated boiling water reactor (BWR) water at 288 C on SS specimens irradiated to a low fluence in the Halden reactor and the results were compared with similar data from a control-blade sheath and neutron-absorber tubes irradiated in BWRs to the same fluence level. Crack-growth-rate tests were conducted on compact-tension specimens from several heats of Alloys 600 and 690 in low-DO, simulated pressurized water reactor environments.

  20. Accurate Critical Stress Intensity Factor Griffith Crack Theory Measurements by Numerical Techniques

    PubMed Central

    Petersen, Richard C.

    2014-01-01

    Critical stress intensity factor (KIc) has been an approximation for fracture toughness using only load-cell measurements. However, artificial man-made cracks several orders of magnitude longer and wider than natural flaws have required a correction factor term (Y) that can be up to about 3 times the recorded experimental value [1-3]. In fact, over 30 years ago a National Academy of Sciences advisory board stated that empirical KIc testing was of serious concern and further requested that an accurate bulk fracture toughness method be found [4]. Now that fracture toughness can be calculated accurately by numerical integration from the load/deflection curve as resilience, work of fracture (WOF) and strain energy release (SIc) [5, 6], KIc appears to be unnecessary. However, the large body of previous KIc experimental test results found in the literature offer the opportunity for continued meta analysis with other more practical and accurate fracture toughness results using energy methods and numerical integration. Therefore, KIc is derived from the classical Griffith Crack Theory [6] to include SIc as a more accurate term for strain energy release rate (𝒢Ic), along with crack surface energy (γ), crack length (a), modulus (E), applied stress (σ), Y, crack-tip plastic zone defect region (rp) and yield strength (σys) that can all be determined from load and deflection data. Polymer matrix discontinuous quartz fiber-reinforced composites to accentuate toughness differences were prepared for flexural mechanical testing comprising of 3 mm fibers at different volume percentages from 0-54.0 vol% and at 28.2 vol% with different fiber lengths from 0.0-6.0 mm. Results provided a new correction factor and regression analyses between several numerical integration fracture toughness test methods to support KIc results. Further, bulk KIc accurate experimental values are compared with empirical test results found in literature. Also, several fracture toughness mechanisms

  1. Residual stress analysis of multilayer environmental barrier coatings.

    SciTech Connect

    Harder, B.; Almer, J.; Weyant, C.; Lee, K.; Faber, K.; Northwestern Univ.; Rolls-Royce Corp.

    2009-02-01

    Silicon-based ceramics (SiC, Si{sub 3}N{sub 4}) are promising materials systems for high-temperature structural applications in gas turbine engines. However, the silica layer that forms on these materials is susceptible to attack from water vapor present in combustion environments. To protect against this degradation, environmental barrier coatings (EBCs) have been developed to shield the underlying substrate and prevent degradation. Here we report on elastic and thermal properties, as well as internal stresses of candidate multilayer coatings, as measured in situ using microfocused high-energy X-rays in a transmission diffraction geometry. Doped aluminosilicate coatings were investigated for their stability on a SiC/SiC melt-infiltrated substrate. The coatings consisted of a Ba{sub 1-x}Sr{sub x}Al{sub 2}Si{sub 2}O{sub 8} topcoat with a mullite or mullite+SrAl{sub 2}Si{sub 2}O{sub 8} interlayer, and a silicon bond coat. A numerical model was used to compare the stress results with an ideal coating system. Experiments were carried out on as-sprayed and heat-treated samples in order to analyze the strain and phase evolution as a function of multilayer depth and temperature. The phase transformation of the topcoat promoted healing of cracks in the EBC and reduced stresses in the underlying layers and the addition of SAS to the interlayer reduced stresses in thermally cycled coatings, but did not stop cracks from forming.

  2. Transverse shear effects on the stress-intensity factor for a circumferentially cracked, specially orthotropic cylindrical shell

    NASA Technical Reports Server (NTRS)

    Delale, F.; Erdogan, F.

    1977-01-01

    The problem of a cylindrical shell containing a circumferential through crack is considered by taking into account the effect of transverse shear deformations. The formulation is given for a specially orthotropic material within the confines of a linearized shallow shell theory. The particular theory used permits the consideration of all five boundary conditions regarding moment and stress resultants on the crack surface. Consequently, aside from multiplicative constants representing the stress intensity factors, the membrane and bending components of the asymptotic stress fields near the crack tip are found to be identical. The stress intensity factors are calculated separately for a cylinder under a uniform membrane load, and that under a uniform bending moment. Sample results showing the nature of the out-of-plane crack surface displacement and the effect of the Poisson's ratio are presented.

  3. Slow Crack Growth Analysis of Brittle Materials with Finite Thickness Subjected to Constant Stress-Rate Flexural Loading

    NASA Technical Reports Server (NTRS)

    Chio, S. R.; Gyekenyesi, J. P.

    1999-01-01

    A two-dimensional, numerical analysis of slow crack growth (SCG) was performed for brittle materials with finite thickness subjected to constant stress-rate ("dynamic fatigue") loading in flexure. The numerical solution showed that the conventional, simple, one-dimensional analytical solution can be used with a maximum error of about 5% in determining the SCG parameters of a brittle material with the conditions of a normalized thickness (a ratio of specimen thickness to initial crack size) T > 3.3 and of a SCG parameter n > 10. The change in crack shape from semicircular to elliptical configurations was significant particularly at both low stress rate and low T, attributed to predominant difference in stress intensity factor along the crack front. The numerical solution of SCG parameters was supported within the experimental range by the data obtained from constant stress-rate flexural testing for soda-lime glass microslides at ambient temperature.

  4. Stress state of transversally isotropic body with elliptical crack in the presence of a uniform heat flux at its surface

    SciTech Connect

    Podil`chuk, Yu.N.

    1995-09-01

    An explicit solution of the state thermoelasticity problem is constructed for an infinite transversally isotropic body containing an internal elliptical crack in the isotropy plane. It is assumed that a uniform heat flux is specified at the crack surface and the body is free of external loads. Values of the stress-intensity coefficients depending on the heat flux, the crack dimensions, and the thermoelastic properties of the material are obtained. Note that the analogous problem was considered for an isotropic body. The static thermoelasticity problem for a transversally isotropic body with an internal elliptical crack at whose surface linear temperature variation is specified was solved.

  5. Inoculation Stress Hypothesis of Environmental Enrichment

    PubMed Central

    Crofton, Elizabeth J.; Zhang, Yafang; Green, Thomas A.

    2014-01-01

    One hallmark of psychiatric conditions is the vast continuum of individual differences in susceptibility vs. resilience resulting from the interaction of genetic and environmental factors. The environmental enrichment paradigm is an animal model that is useful for studying a range of psychiatric conditions, including protective phenotypes in addiction and depression models. The major question is how environmental enrichment, a non-drug and non-surgical manipulation, can produce such robust individual differences in such a wide range of behaviors. This paper draws from a variety of published sources to outline a coherent hypothesis of inoculation stress as a factor producing the protective enrichment phenotypes. The basic tenet suggests that chronic mild stress from living in a complex environment and interacting non-aggressively with conspecifics can inoculate enriched rats against subsequent stressors and/or drugs of abuse. This paper reviews the enrichment phenotypes, mulls the fundamental nature of environmental enrichment vs. isolation, discusses the most appropriate control for environmental enrichment, and challenges the idea that cortisol/corticosterone equals stress. The intent of the inoculation stress hypothesis of environmental enrichment is to provide a scaffold with which to build testable hypotheses for the elucidation of the molecular mechanisms underlying these protective phenotypes and thus provide new therapeutic targets to treat psychiatric/neurological conditions. PMID:25449533

  6. A re-evaluation of finite-element models and stress-intensity factors for surface cracks emanating from stress concentrations

    NASA Technical Reports Server (NTRS)

    Tan, P. W.; Raju, I. S.; Shivakumar, K. N.; Newman, J. C., Jr.

    1988-01-01

    A re-evaluation of the 3-D finite-element models and methods used to analyze surface crack at stress concentrations is presented. Previous finite-element models used by Raju and Newman for surface and corner cracks at holes were shown to have ill-shaped elements at the intersection of the hole and crack boundaries. These ill-shaped elements tended to make the model too stiff and, hence, gave lower stress-intensity factors near the hole-crack intersection than models without these elements. Improved models, without these ill-shaped elements, were developed for a surface crack at a circular hole and at a semi-circular edge notch. Stress-intensity factors were calculated by both the nodal-force and virtual-crack-closure methods. Both methods and different models gave essentially the same results. Comparisons made between the previously developed stress-intensity factor equations and the results from the improved models agreed well except for configurations with large notch-radii-to-plate-thickness ratios. Stress-intensity factors for a semi-elliptical surface crack located at the center of a semi-circular edge notch in a plate subjected to remote tensile loadings were calculated using the improved models. The ratio of crack depth to crack length ranged form 0.4 to 2; the ratio of crack depth to plate thickness ranged from 0.2 to 0.8; and the ratio of notch radius to the plate thickness ranged from 1 to 3. The models had about 15,000 degrees-of-freedom. Stress-intensity factors were calculated by using the nodal-force method.

  7. Strain energy density-distance criterion for the initiation of stress corrosion cracking of alloy X-750

    SciTech Connect

    Hall, M.M. Jr.; Symons, D.M.

    1996-05-01

    A strain energy density-distance criterion was previously developed and used to correlate rising-load K{sub c} initiation data for notched and fatigue precracked specimens of hydrogen precharged Alloy X-750. This criterion, which was developed for hydrogen embrittlement (HE) cracking, is used here to correlate static-load stress corrosion cracking (SCC) initiation times obtained for smooth geometry, notched and fatigue precracked specimens. The onset of SCC crack growth is hypothesized to occur when a critical strain, which is due to environment-enhanced creep, is attained within the specimen interior. For notched and precracked specimens, initiation is shown by analysis to occur at a variable distance from notch and crack tips. The initiation site varies from very near the crack tip, for highly loaded sharp cracks, to a site that is one grain diameter from the notch, for lower loaded, blunt notches. The existence of hydrogen gradients, which are due to strain-induced hydrogen trapping in the strain fields of notch and crack tips, is argued to be controlling the site for initiation of cracking. By considering the sources of the hydrogen, these observations are shown to be consistent with those from the previous HE study, in which the characteristic distance for crack initiation was found to be one grain diameter from the notch tip, independent of notch radius, applied stress intensity factor and hydrogen level.

  8. Environmental Change, the Stress Response, and Neurogenesis.

    PubMed

    LaDage, Lara D

    2015-09-01

    Previous to the 1980's, the prevailing neuroscience dogma held that no new neurons were produced in the brains of adult mammals. Now, we understand that the production of new neurons, or neurogenesis, is a common and plastic process in the adult brain. To date, however, researchers have not come to a unified understanding of the functional significance of neurogenesis. Several factors have been shown to modulate hippocampal neurogenesis including spatial learning, stress, and aspects of environmental change, but questions still remain. How do these modulating factors overlap? Which aspects of environmental change induce a stress response? Is there a relationship between hippocampal neurogenesis, the stress response, and environmental change? Can this relationship be altered when taking into consideration other factors such as perception and predictability of the environment? Finally, do results from neurobiological research on laboratory rodents translate to wild systems? This review attempts to address these questions and synthesize research from the fields of ecology, psychology, and behavioral neuroscience. PMID:25980567

  9. Effects of Changing Stress Amplitude on the Rate of Fatigue-Crack Propagation in Two Aluminum Alloys

    NASA Technical Reports Server (NTRS)

    Hudson, C. Michael; Hardrath, Herbert F.

    1961-01-01

    A series of fatigue tests with specimens subjected to constant amplitude and two-step axial loads were conducted on 12-inch-wide sheet specimens of 2024-T3 and 7075-T6 aluminum alloy to study the effects of a change in stress level on fatigue-crack propagation. Comparison of the results of the tests in which the specimens were tested at first a high and then a low stress level with those of the constant-stress- amplitude tests indicated that crack propagation was generally delayed after the transition to the lower stress level. In the tests in which the specimens were tested at first a low and then a high stress level, crack propagation continued at the expected rate after the change in stress levels.

  10. Residual stress and crack initiation in laser clad composite layer with Co-based alloy and WC + NiCr

    NASA Astrophysics Data System (ADS)

    Lee, Changmin; Park, Hyungkwon; Yoo, Jaehong; Lee, Changhee; Woo, WanChuck; Park, Sunhong

    2015-08-01

    Although laser cladding process has been widely used to improve the wear and corrosion resistance, there are unwanted cracking issues during and/or after laser cladding. This study investigates the tendency of Co-based WC + NiCr composite layers to cracking during the laser cladding process. Residual stress distributions of the specimen are measured using neutron diffraction and elucidate the correlation between the residual stress and the cracking in three types of cylindrical specimens; (i) no cladding substrate only, (ii) cladding with 100% stellite#6, and (iii) cladding with 55% stellite#6 and 45% technolase40s. The microstructure of the clad layer was composed of Co-based dendrite and brittle eutectic phases at the dendritic boundaries. And WC particles were distributed on the matrix forming intermediate composition region by partial melting of the surface of particles. The overlaid specimen exhibited tensile residual stress, which was accumulated through the beads due to contraction of the coating layer generated by rapid solidification, while the non-clad specimen showed compressive. Also, the specimen overlaid with 55 wt% stellite#6 and 45 wt% technolase40s showed a tensile stress higher than the specimen overlaid with 100% stellite#6 possibly, due to the difference between thermal expansion coefficients of the matrix and WC particles. Such tensile stresses can be potential driving force to provide an easy crack path ways for large brittle fractures combined with the crack initiation sites such as the fractured WC particles, pores and solidification cracks. WC particles directly caused clad cracks by particle fracture under the tensile stress. The pores and solidification cracks also affected as initiation sites and provided an easy crack path ways for large brittle fractures.

  11. Effect of dissolved oxygen content on stress corrosion cracking of a cold worked 316L stainless steel in simulated pressurized water reactor primary water environment

    NASA Astrophysics Data System (ADS)

    Zhang, Litao; Wang, Jianqiu

    2014-03-01

    Stress corrosion crack growth tests of a cold worked nuclear grade 316L stainless steel were conducted in simulated pressurized water reactor (PWR) primary water environment containing various dissolved oxygen (DO) contents but no dissolved hydrogen. The crack growth rate (CGR) increased with increasing DO content in the simulated PWR primary water. The fracture surface exhibited typical intergranular stress corrosion cracking (IGSCC) characteristics.

  12. Advanced TEM characterization of stress corrosion cracking of Alloy 600 in pressurized water reactor primary water environment

    NASA Astrophysics Data System (ADS)

    Sennour, M.; Laghoutaris, P.; Guerre, C.; Molins, R.

    2009-09-01

    Advanced transmission electron microscopy techniques were carried out in order to investigate stress corrosion cracking in Alloy 600 U-bend samples exposed in simulated PWR primary water at 330 °C. Using high-resolution imaging and fine-probe chemical analysis methods, ultrafine size oxides present inside cracks and intergranular attacks were nanoscale characterized. Results revealed predominance of Cr 2O 3 oxide and Ni-rich metal zones at the majority of encountered crack tip areas and at leading edge of intergranular attacks. However, NiO-structure oxide was predominant far from crack tip zones and within cracks propagating along twin boundaries and inside grains. These observations permit to suggest a mechanism for intergranular stress corrosion cracking of Alloy 600 in PWR primary water. Indeed, the results suggest that stress corrosion cracking is depending on chromium oxide growth in the grain boundary. Oxide growth seems to be dependent on oxygen diffusion in porous oxide and chromium diffusion in strained alloy and in grain boundary beyond crack tip. Strain could promote transport kinetic and oxide formation by increasing defaults rate like dislocations.

  13. Effect of layerwise structural inhomogeneity on stress- corrosion cracking of steel tubes

    NASA Astrophysics Data System (ADS)

    Perlovich, Yu A.; Krymskaya, O. A.; Isaenkova, M. G.; Morozov, N. S.; Fesenko, V. A.; Ryakhovskikh, I. V.; Esiev, T. S.

    2016-04-01

    Based on X-ray texture and structure analysis data of the material of main gas pipelines it was shown that the layerwise inhomogeneity of tubes is formed during their manufacturing. The degree of this inhomogeneity affects on the tendency of tubes to stress- corrosion cracking under exploitation. Samples of tubes were cut out from gas pipelines located under various operating conditions. Herewith the study was conducted both for sections with detected stress-corrosion defects and without them. Distributions along tube wall thickness for lattice parameters and half-width of X-ray lines were constructed. Crystallographic texture analysis of external and internal tube layers was also carried out. Obtained data testifies about considerable layerwise inhomogeneity of all samples. Despite the different nature of the texture inhomogeneity of gas pipeline tubes, the more inhomogeneous distribution of texture or structure features causes the increasing of resistance to stress- corrosion. The observed effect can be explained by saturation with interstitial impurities of the surface layer of the hot-rolled sheet and obtained therefrom tube. This results in rising of lattice parameters in the external layer of tube as compared to those in underlying metal. Thus, internal layers have a compressive effect on external layers in the rolling plane that prevents cracks opening at the tube surface. Moreover, the high mutual misorientation of grains within external and internal layers of tube results in the necessity to change the moving crack plane, so that the crack growth can be inhibited when reaching the layer with a modified texture.

  14. Assessing Primary Water Stress Corrosion Crack Morphology and Nondestructive Evaluation Reliability

    SciTech Connect

    Doctor, Steven R.; Schuster, George J.; Anderson, Michael T.

    2005-12-01

    A research program on primary water stress corrosion cracking (PWSCC) is being conducted by Pacific Northwest National Laboratory (PNNL). In this program, the material degradation problem in Alloys 600, 182 and 82 is being investigated, with objectives that include compiling a knowledge base on all cracking in nickel-base materials at all degradation sites in nuclear power plants, assessing nondestructive evaluation methods using mockups to quantify the detection, sizing, and characterization of tight cracks, determining the role of material parameters, such as welding processes, in the degradation. This work is being conducted as a part of an international cooperative research project that has been set up to leverage efforts in several countries to address a significant and common problem. The U.S. Nuclear Regulatory Commission is leading this cooperative project to address this generic problem in a systematic manner over the next four years. In this paper, published information on the failure history of Alloys 600, 182, and 82 is compiled and presented. The configurations of the welded assemblies that contain these alloys are shown to be important considerations for NDE reliability measurements. The product forms and the welding processes represented in the degraded components are described. The relevant data on crack morphology parameters such as shape and orientation are presented, and their impact on nondestructive evaluation (NDE) reliability is discussed.

  15. A linear least squares approach for evaluation of crack tip stress field parameters using DIC

    NASA Astrophysics Data System (ADS)

    Harilal, R.; Vyasarayani, C. P.; Ramji, M.

    2015-12-01

    In the present work, an experimental study is carried out to estimate the mixed-mode stress intensity factors (SIF) for different cracked specimen configurations using digital image correlation (DIC) technique. For the estimation of mixed-mode SIF's using DIC, a new algorithm is proposed for the extraction of crack tip location and coefficients in the multi-parameter displacement field equations. From those estimated coefficients, SIF could be extracted. The required displacement data surrounding the crack tip has been obtained using 2D-DIC technique. An open source 2D DIC software Ncorr is used for the displacement field extraction. The presented methodology has been used to extract mixed-mode SIF's for specimen configurations like single edge notch (SEN) specimen and centre slant crack (CSC) specimens made out of Al 2014-T6 alloy. The experimental results have been compared with the analytical values and they are found to be in good agreement, thereby confirming the accuracy of the algorithm being proposed.

  16. Stress corrosion cracking of type 304 stainless steel weldments in the active state

    SciTech Connect

    Fang, Z.; Wu, Y.; Zhu, R. . Dept. of Surface Science and Corrosion Engineering)

    1994-03-01

    Slow strain rate tests (SSRT) were conducted in solutions of hydrochloric acid (HCl) + sodium chloride (NaCl) at ambient temperature on type 304 (UNS S30400) stainless steel (SS) weldments that exhibited a duplex ferrite-austenite structure in the weld fusion zone. Results indicated the weld fusion zone corroded preferentially. Stress corrosion cracking (SCC) initiated and propagated along the ferrite-austenite interphase. Austenitic dendrite was observed by scanning electron microscopy (SEM) in the fracture surface morphology. This interfacial cracking was attributed to the formation of a complex cell structure consisting of weld fusion zone/parent metal with delta-ferrite/austenite in the weld zone. The delta-ferrite was microanodic phase. The proposed model of SCC for type 304 SS weldments in HCl + NaCl was film formation-slip (film rupture)-dissolution-crack propagation. Because of the presence of the complex cell structure, the surface film was nonuniform, which was favorable for crack initiation. SCC propagated faster through the active path of delta-ferrite than through the matrix.

  17. Estimation and Simulation of Slow Crack Growth Parameters from Constant Stress Rate Data

    NASA Technical Reports Server (NTRS)

    Salem, Jonathan A.; Weaver, Aaron S.

    2003-01-01

    Closed form, approximate functions for estimating the variances and degrees-of-freedom associated with the slow crack growth parameters n, D, B, and A(sup *) as measured using constant stress rate ('dynamic fatigue') testing were derived by using propagation of errors. Estimates made with the resulting functions and slow crack growth data for a sapphire window were compared to the results of Monte Carlo simulations. The functions for estimation of the variances of the parameters were derived both with and without logarithmic transformation of the initial slow crack growth equations. The transformation was performed to make the functions both more linear and more normal. Comparison of the Monte Carlo results and the closed form expressions derived with propagation of errors indicated that linearization is not required for good estimates of the variances of parameters n and D by the propagation of errors method. However, good estimates variances of the parameters B and A(sup *) could only be made when the starting slow crack growth equation was transformed and the coefficients of variation of the input parameters were not too large. This was partially a result of the skewered distributions of B and A(sup *). Parametric variation of the input parameters was used to determine an acceptable range for using closed form approximate equations derived from propagation of errors.

  18. Cracking Process and Stress Field Evolution in Specimen Containing Combined Flaw Under Uniaxial Compression

    NASA Astrophysics Data System (ADS)

    Liu, Ting; Lin, Baiquan; Yang, Wei; Zou, Quanle; Kong, Jia; Yan, Fazhi

    2016-08-01

    Hydraulic slotting, an efficient technique for underground enhanced coal bed methane (ECBM) recovery, has been widely used in China. However, its pressure relief mechanism is unclear. Thus far, only limited research has been conducted on the relationships among the mechanical properties, flaw parameters, and crack propagation patterns of coal after hydraulic slotting. In addition, because of the limitations of test methods, an in-depth information is not available for this purpose. In this work, numerical models of specimens containing combined flaws are established based on particle flow code method. Our results provide insights into the effects of flaw inclination angle on the mechanical properties, crack propagation patterns, and temporal and spatial evolution rules of stress field in specimens containing combined flaws during the loading process. Besides, based on the initiation position and underlying mechanism, three types of crack initiation modes are identified from the failure processes of specimens. Finally, the crack propagation pattern is quantitatively described by the fractal dimension, which is found to be inversely proportional to the uniaxial compressive strength and elastic modulus of the specimen. To verify the rationality of the numerical simulation results, laboratory tests were conducted and their results match well with those obtained from the numerical simulation.

  19. External stress-corrosion cracking of a 1.22-m-diameter type 316 stainless steel air valve

    NASA Technical Reports Server (NTRS)

    Moore, Thomas J.; Telesman, Jack; Moore, Allan S.; Johnson, Dereck F.; Kuivinen, David E.

    1993-01-01

    An investigation was conducted to determine the cause of the failure of a massive AISI Type 316 stainless steel valve which controlled combustion air to a jet engine test facility. Several through-the-wall cracks were present near welded joints in the valve skirt. The valve had been in outdoor service for 18 years. Samples were taken in the cracked regions for metallographic and chemical analyses. Insulating material and sources of water mist in the vicinity of the failed valve were analyzed for chlorides. A scanning electron microscope was used to determine whether foreign elements were present in a crack. On the basis of the information generated, the failure was characterized as external stress-corrosion cracking. The cracking resulted from a combination of residual tensile stress from welding and the presence of aqueous chlorides. Recommended countermeasures are included.

  20. Implementation of thermal residual stresses in the analysis of fiber bridged matrix crack growth in titanium matrix composites

    NASA Technical Reports Server (NTRS)

    Bakuckas, John G., Jr.; Johnson, W. Steven

    1994-01-01

    In this research, thermal residual stresses were incorporated in an analysis of fiber-bridged matrix cracks in unidirectional and cross-ply titanium matrix composites (TMC) containing center holes or center notches. Two TMC were investigated, namely, SCS-6/Timelal-21S laminates. Experimentally, matrix crack initiation and growth were monitored during tension-tension fatigue tests conducted at room temperature and at an elevated temperature of 200 C. Analytically, thermal residual stresses were included in a fiber bridging (FB) model. The local R-ratio and stress-intensity factor in the matrix due to thermal and mechanical loadings were calculated and used to evaluate the matrix crack growth behavior in the two materials studied. The frictional shear stress term, tau, assumed in this model was used as a curve-fitting parameter to matrix crack growth data. The scatter band in the values of tau used to fit the matrix crack growth data was significantly reduced when thermal residual stresses were included in the fiber bridging analysis. For a given material system, lay-up and temperature, a single value of tau was sufficient to analyze the crack growth data. It was revealed in this study that thermal residual stresses are an important factor overlooked in the original FB models.

  1. Aqueous environmental crack propagation in high-strength beta titanium alloys

    SciTech Connect

    Young, L.M.; Young, G.A. Jr.; Scully, J.R.; Gangloff, R.P.

    1995-05-01

    The aqueous environment-assisted cracking (EAC) behavior of two peak-aged beta-titanium was characterized with a fracture mechanics method. Beta-21S is susceptible to EAC under rising load in neutral 3.5 pct NaCi at 25 C and {minus}600 mV{sub SCE}, as indicated by a reduced threshold for subcritical crack growth (K{sub TH}), an average crack growth rate of up to 10 {mu}m s, and intergranular fracture compared to microvoid rupture in air. In contrast, the initiation fracture toughness (K{sub ICi}) of Ti-15-3 in moist air is lower than that of Beta-21S at similar high {sigma}{sub YS} (1,300 MPa) but is not degraded by chloride, and cracking is by transgranular microvoid formation. The intergranular EAC susceptibility of Beta-21S correlates with both {alpha}-colonies precipitated at {beta} grain boundaries and intense slip localization; however, the causal factor is not defined. Data suggest that both features, and EAC, are promoted by prolonged solution treatment at high temperature. In a hydrogen environment embrittlement (HEE) scenario, crack-tip H could be transported by planar slip bands to strongly binding trap sites and stress/strain concentrations at {alpha} colony or {beta} grain boundaries. The EAC in Beta-21S is eliminated by cathodic polarization (to {minus}1,000 mV{sub SCE}), as well as by static loading for times that otherwise produce rising-load EAC.

  2. Analysis of surface cracks at hole by a 3-D weight function method with stresses from finite element method

    NASA Technical Reports Server (NTRS)

    Zhao, W.; Newman, J. C., Jr.; Sutton, M. A.; Shivakumar, K. N.; Wu, X. R.

    1995-01-01

    Parallel with the work in Part-1, stress intensity factors for semi-elliptical surface cracks emanating from a circular hole are determined. The 3-D weight function method with the 3D finite element solutions for the uncracked stress distribution as in Part-1 is used for the analysis. Two different loading conditions, i.e. remote tension and wedge loading, are considered for a wide range in geometrical parameters. Both single and double surface cracks are studied and compared with other solutions available in the literature. Typical crack opening displacements are also provided.

  3. User's manual for FRAC3D: Supplement to report on stress analysis for structures with surface cracks

    NASA Technical Reports Server (NTRS)

    Bell, J. C.; Hopper, A. T.; Hayes, P. A.

    1978-01-01

    The FRAC3D computer program, designed for use in analyzing stresses in structures (including plates, bars, or blocks) which may contain part-circular surface cracks or embedded circular cracks is described. Instructions are provided for preparing input, including that for the supporting programs LATTICE and MATSOL as well as for FRAC3D. The course of a substantial illustrative calculation is shown with both input and output. The formulas underlying the calculations are summarized and related to the subroutines in which they are used. Many issues of strategy in using this program for analysing stresses around surface cracks are elucidated.

  4. Mechanics of fatigue crack closure

    NASA Technical Reports Server (NTRS)

    Newman, J. C., Jr. (Editor); Elber, Wolf (Editor)

    1988-01-01

    Papers are presented on plasticity induced crack closure, crack closure in fatigue crack growth, the dependence of crack closure on fatigue loading variables, and a procedure for standardizing crack closure levels. Also considered are a statistical approach to crack closure determination, the crack closure behavior of surface cracks under pure bending, closure measurements on short fatigue cracks, and crack closure under plane strain conditions. Other topics include fatigue crack closure behavior at high stress ratios, the use of acoustic waves for the characterization of closed fatigue cracks, and the influence of fatigue crack wake length and state of stress on crack closure.

  5. Growth and stability of stress corrosion cracks in large-diameter BWR piping. Volume 2: appendixes. Final report

    SciTech Connect

    Hale, D A; Heald, J D; Horn, R M; Jewett, C W; Kass, J N; Mehta, H S; Ranganath, S; Sharma, S R

    1982-07-01

    This report presents the results of a research program conducted to evaluate the behavior of hypothetical stress corrosion cracks in large diameter austenitic piping. The program included major tasks, a design margin assessment, an evaluation of crack growth and crack arrest, and development of a predictive model. As part of the margin assessment, the program developed diagrams which predicted net section collapse as a function of crack size. In addition, plasticity and dynamic load effects were also considered in evaluating collapse. Analytical methods for evaluating these effects were developed and were benchmarked by dynamic tests of 4-in.-diameter piping. The task of evaluating the growth behavior of stress corrosion cracks focused on developing constant load and cyclic growth rate data that could be used with the predictive model. Secondly, laboratory tests were performed to evaluate the conditions under which growing stress corrosion cracks would arrest when they intersected stress corrosion resistant weld metal. The third task successfully developed a model to predict the behavior of cracks in austenitic piping.

  6. Supersonic crack growth in a solid of upturn stress?strain relation under anti-plane shear

    NASA Astrophysics Data System (ADS)

    Guo, Gaofeng; Yang, Wei; Huang, Y.

    2003-11-01

    This paper examines, from the prospect of continuum analysis, the possibility for a supersonic crack growth in a solid with an upturn stress-strain relation. The stress has a linear-upturn power-law relation with the strain, resulting in an elastic modulus, and consequently a wave speed, that increase with the strain. Though appearing to be "supersonic", the local wave speed in the crack tip vicinity of the solid with a sufficient upturn stress-strain relation exceeds the crack extension speed. A pre-request for such a supersonic crack growth is the storage of sufficient deformation energy within the solid to nurse the energy flux drawn to the crack tip that extends at an "apparent supersonic" speed. The idea is demonstrated for the simplest case, the anti-plane shear. We examine the steady-state supersonic crack growth in a hyperelastic material. The governing equation is elliptical in the crack tip vicinity but hyperbolic elsewhere. The boundary between two regions is determined with a certain extent. An asymptotic solution is constructed within the super-hardening zone. The solution connects to the hyperbolic radiation strips by weak discontinuity boundaries and to the pre-stressed frontal field by a strong discontinuity boundary.

  7. Laplace-SGBEM analysis of the dynamic stress intensity factors and the dynamic T-stress for the interaction between a crack and auxetic inclusions

    NASA Astrophysics Data System (ADS)

    Kwon, Kibum

    A dynamic analysis of the interaction between a crack and an auxetic (negative Poisson ratio)/non-auxetic inclusion is presented. The two most important fracture parameters, namely the stress intensity factors and the T-stress are analyzed by using the symmetric Galerkin boundary element method in the Laplace domain for three different models of crack-inclusion interaction. To investigate the effects of auxetic inclusions on the fracture behavior of composites reinforced by this new type of material, comparisons of the dynamic stress intensity factors and the dynamic T-stress are made between the use of auxetic inclusions as opposed to the use of traditional inclusions. Furthermore, the technique presented in this research can be employed to analyze for the interaction between a crack and a cluster of auxetic/non-auxetic inclusions. Results from the latter models can be employed in crack growth analysis in auxetic-fiber-reinforced composites.

  8. Organelle redox autonomy during environmental stress.

    PubMed

    Bratt, Avishay; Rosenwasser, Shilo; Meyer, Andreas; Fluhr, Robert

    2016-09-01

    Oxidative stress is generated in plants because of inequalities in the rate of reactive oxygen species (ROS) generation and scavenging. The subcellular redox state under various stress conditions was assessed using the redox reporter roGFP2 targeted to chloroplastic, mitochondrial, peroxisomal and cytosolic compartments. In parallel, the vitality of the plant was measured by ion leakage. Our results revealed that during certain physiological stress conditions the changes in roGFP2 oxidation are comparable to application of high concentrations of exogenous H2 O2 . Under each stress, particular organelles were affected. Conditions of extended dark stress, or application of elicitor, impacted chiefly on the status of peroxisomal redox state. In contrast, conditions of drought or high light altered the status of mitochondrial or chloroplast redox state, respectively. Amalgamation of the results from diverse environmental stresses shows cases of organelle autonomy as well as multi-organelle oxidative change. Importantly, organelle-specific oxidation under several stresses proceeded cell death as measured by ion leakage, suggesting early roGFP oxidation as predictive of cell death. The measurement of redox state in multiple compartments enables one to look at redox state connectivity between organelles in relation to oxidative stress as well as assign a redox fingerprint to various types of stress conditions. PMID:27037976

  9. Matrix cracking initiation stress in fiber-reinforced ceramic-matrix composites

    SciTech Connect

    Kangutkar, P.B.

    1991-01-01

    One of the important design parameters in CMC's is the matrix cracking initiation stress (MCIS) which corresponds to the stress at which first matrix cracks are observed. Above the MCIS, the fibers will be exposed to the oxidizing environment which may degrade the mechanical property of the fibers and thus of the composite. In this thesis, a systematic study to explore the effects of matrix toughness and inherent strength, fiber diameter, stiffness and volume fraction, temperature and interfacial bonding on the MCIS was carried out. Composites were fabricated using three different matrices - borosilicate glass, aluminosilicate glass and polycrystalline zirconium silicate (or zircon), and two different reinforcing fibers - an SiC monofilament (140 {mu}m diameter) and an SiC yarn (16 {mu}m diameter). In-situ observations during 3-point bend test inside the SEM indicate that matrix cracking is a local phenomenon and occurs first in the matrix between widest spaced fibers. In all composites the MCIS was found to increase with fiber additions and scaled with the monolithic strength.

  10. Characterization of irradiated Zircaloys: susceptibility to stress corrosion cracking. Final report

    SciTech Connect

    Yaggee, F.L.; Mattas, R.F.; Neimark, L.A.

    1980-10-01

    Irradiated Zircaloy cladding specimens that reached burnups from 6 to 30 MWd/kg U were exposed to iodine to investigate their stress corrosion cracking (SCC) susceptibility. Constant-stress and stress-change tests were performed. Cladding from several sources (including BWRs and PWRs) was tested. Test temperatures ranged from 320 to 360/sup 0/C and applied hoop stresses ranged from 150 to 500 MPa )22 to 72 ksi). Two iodine concentrations, 6.0 and 0.6 mg/cm/sup 2/, were used. Failure times ranged from 360 s (0.1h) at high stresses to 5 x 10/sup 5/ s (142 h) at low stresses. The 24-h failure stress was 171 +- 18 MPa (24.8 +- 2.6 ksi) regardless of the preirradiation metallurgical condition for all specimens that reached a burnup > 10 MWd/kg U. This failure stress is lower than is typically measured on unirradiated Zircaloy. The effect on SCC behavior of an oxide that formed on the inner surface of one cladding type was evaluated. Uniaxial tensile tests were performed on some specimens. An analytical model for iodine-induced SCC of Zircaloy was developed that correlates reasonably well with the measurements.

  11. The susceptibility of low carbon steel welded joint to sulphide stress cracking (SSC)

    NASA Astrophysics Data System (ADS)

    Alshwigi, Mohamed A. M.; Musa, Salem. M.; Basir, Ali

    2013-12-01

    The resistance of low carbon steel pipes API 5L GR.B as welded joints to sulphide stress cracking SSC was tested using NACE Standard test method TM 0177_Method (C). Two stress levels of the material's yield strength were applied, 75 % σy and 100 % σy in three different conditions; as received, as welded, and stress relieved samples. Total of seventeen samples were tested; two as received samples without any welding process, six samples as heat treated, and nine samples as welded. The effect of hardness level on material's susceptibility to sulphide stress cracking was examined. Raw Natural Gas was used as a source of Hydrogen Sulphide (H2S) in the test, which represents the real environment that the material was exposed to. Results show that samples with high hardness (higher than 22 HRC) were failed the test which was expected as in the NACE Standard MR175. Samples with low hardness (lower than 22 HRC) were passed the test which was expected as in the NACE Standard MR175. The received samples of low hardness failed the test which was not expected.

  12. Development of a Fatigue Crack Growth Coupon for Highly Plastic Stress Conditions

    NASA Technical Reports Server (NTRS)

    Allen, Phillip A.; Aggarwal, Pravin K.; Swanson, Gregory R.

    2003-01-01

    This paper presents an analytical approach used to develop a novel fatigue crack growth coupon for a highly plastic 3-D stress field condition. The flight hardware investigated in this paper is a large separation bolt that fractures using pyrotechnics at the appointed time during the flight sequence. The separation bolt has a deep notch that produces a severe stress concentration and a large plastic zone when highly loaded. For this geometry, linear-elastic fracture mechanics (LEFM) techniques are not valid due to the large nonlinear stress field. Unfortunately, industry codes that are generally available for fracture mechanics analysis and fatigue crack growth (e.g. NASGRO (11) are limited to LEFM and are available for only a limited number of geometries. The results of LEFM based codes are questionable when used on geometries with significant plasticity. Therefore elastic-plastic fracture mechanics (EPFM) techniques using the finite element method (FEM) were used to analyze the bolt and test coupons. scale flight hardware is very costly in t e r n of assets, laboratory resources, and schedule. Therefore to alleviate some of these problems, a series of novel test coupons were developed to simulate the elastic-plastic stress field present in the bolt.

  13. Stress Corrosion Cracking Response of 304 Stainless Steel in ASerated and Dearated Water

    SciTech Connect

    Mills, W. J.

    2007-04-30

    Scoping stress corrosion cracking (SCC) tests of 304 stainless steel (SS) were performed in 75 C and 250 C aerated pressurized water (APW) and 250 C deaerated pressurized water (DPW). The 250 C APW environment was used to initiate intergranular stress corrosion cracking (IGSCC) and then the water was deaerated and hydrogenated to see if IGSCC continued in 250 C DPW. Tests were performed with and without 200 ppb SO{sub 4}{sup =}. The 304 SS test materials were evaluated in either the as-received, heavily sensitized (649 C for 1 h), fully sensitized (1099 C for 1 h/water quench/621 C for 17 h) or 20% cold rolled condition. At the beginning of each test sequence, specimens were subjected to continuous cycling with a 500s rise/500s fall or a 5000s rise/500s fall to promote the transition from a transgranular (TG) precrack to an IG crack. After generating a uniform crack under continuous cycling conditions, a trapezoidal waveform with 500s rise/9000s hold/500s fall was used to characterize the SCC behavior. Crack growth rates (CGRs) were monitored continuously with the electric potential drop (EPD) method and were corrected based on physical crack length measurements obtained when specimens were destructively evaluated. Continuous cycling with a 500s or 5000s rise time was found to produce both TG faceting and IGSCC in fully sensitized 304 SS tested in 75 C APW with 7 ppm O{sub 2} and 200 ppb SO{sub 4}{sup =}. However, no measurable crack extension occurred when a 9000 s hold time was introduced. Extensive IGSCC occurred in heavily sensitized and fully sensitized 304 SS in 250 C APW with 1 ppm O{sub 2} and 200 ppb SO{sub 4}{sup =}. IGSCC initiated under continuous cycling conditions with a 500 s rise time, and rapid IGSCC occurred when a 9000 s hold time was introduced. During the trapezoidal waveform test with a 9000 s hold, CGRs ranged from 1 to 3 mils/day for the heavily sensitized material and 5 to 10 mils/day for the fully sensitized material. When the test

  14. Stress Corrosion and Corrosion Fatigue Crack Growth of Zr-Based Bulk Metallic Glass in Aqueous Solutions

    NASA Astrophysics Data System (ADS)

    Nakai, Y.; Yoshioka, Y.

    2010-07-01

    Crack-propagation tests on a bulk metallic glass (BMG), Zr55Cu30Ni5Al10, were conducted either in aqueous sodium chloride (NaCl) solutions or in high-purity water under sinusoidal cyclic loading or sustained loading. Although the crack growth rate in high-purity water was almost identical to that in air, the rate in the NaCl solution was much higher than that in air, even in a very low concentration of NaCl such as 0.01 mass pct. In a 3.5 mass pct NaCl solution, the time-based crack growth rate during cyclic loading, da/ dt, was determined by the maximum stress-intensity factor, K max, but was almost independent of the loading frequency and the stress ratio, and the rate was close to that of stress corrosion cracking (SCC) under a sustained loading.

  15. Stress-corrosion cracking of low-strength carbon steels in candidate high-level waste repository environments

    SciTech Connect

    Beavers, J.A.; Thompson, N.G.; Parkins, R.N.

    1987-02-01

    A survey of the literature was performed to identify potential stress-corrosion cracking agents for low-strength carbon and low alloy steels in repository environments. It was found that a number of potent cracking agents are present, but stress-corrosion cracking is relatively unlikely in the bulk repository environments because of their low concentration. On the other hand, concentration of these species may occur by a number of mechanisms, and thus it is conceivable that the waste package could fail prematurely by stress corrosion. Accordingly, it is recommended that the lower concentration limits for potential cracking agents be identified under typical repository environments, in conjunction with modeling studies to assess the likelihood that the concentrating mechanisms will operate and to bound the upper limits of concentration for each mechanism. 82 refs.

  16. The elastostatic plane strain mode I crack tip stress and displacement fields in a generalized linear neo-Hookean elastomer

    NASA Astrophysics Data System (ADS)

    Begley, Matthew R.; Creton, Costantino; McMeeking, Robert M.

    2015-11-01

    A general asymptotic plane strain crack tip stress field is constructed for linear versions of neo-Hookean materials, which spans a wide variety of special cases including incompressible Mooney elastomers, the compressible Blatz-Ko elastomer, several cases of the Ogden constitutive law and a new result for a compressible linear neo-Hookean material. The nominal stress field has dominant terms that have a square root singularity with respect to the distance of material points from the crack tip in the undeformed reference configuration. At second order, there is a uniform tension parallel to the crack. The associated displacement field in plane strain at leading order has dependence proportional to the square root of the same coordinate. The relationship between the amplitude of the crack tip singularity (a stress intensity factor) and the plane strain energy release rate is outlined for the general linear material, with simplified relationships presented for notable special cases.

  17. The effect of broken stringers on the stress intensity factor for a uniformly stiffened sheet containing a crack

    NASA Technical Reports Server (NTRS)

    Poe, C. C., Jr.

    1973-01-01

    A linear elastic stress analysis was made of a centrally cracked sheet stiffened by riveted, uniformly spaced and sized stringers. The stress intensity factor for the sheet and the load concentration factor for the most highly loaded stringer were determined for various numbers of broken stringers. A broken stringer causes the stress intensity factor to be very high when the crack tip is near the broken stringer, but causes little effect when the crack tip extends beyond several intact stringers. A broken stringer also causes an increase in the load concentration factor of the adjacent stringers. The calculated residual strengths and fatigue-crack-growth lives of a stiffened aluminum sheet with a broken stringer were only slightly less than a sheet with all intact stringers, and were still much higher than those of an unstiffened sheet.

  18. Role of pH on the stress corrosion cracking of titanium alloys

    NASA Technical Reports Server (NTRS)

    Khokhar, M. I.; Beck, F. H.; Fontana, M. G.

    1973-01-01

    Stress corrosion cracking (SCC) experiments were conducted on Ti-8-1-1 wire specimens in hydrochloric and sulfuric acids of variable pH in order to determine the effect of pH on the susceptibility to cracking. The alloy exhibited increasing susceptibility with decreasing pH. By varying the applied potential, it was observed that susceptibility zones exist both in the cathodic and the anodic ranges. In the cathodic range, susceptibility also increased with decreasing applied potential. Corrosion potential-time data in hydrochloric acid (pH 1.7) and sulfuric acid (pH 1.7) indicate that chloride ions lower the corrosion potential of the specimen which, in turn, increases the susceptibility.

  19. Stress Corrosion Cracking of Ferritic Materials for Fossil Power Generation Applications

    SciTech Connect

    Pawel, Steven J; Siefert, John A.

    2014-01-01

    Creep strength enhanced ferritic (CSEF) steels Grades 23, 24, 91, and 92 have been widely implemented in the fossil fired industry for over two decades. The stress corrosion cracking (SCC) behavior of these materials with respect to mainstay Cr-Mo steels (such as Grades 11, 12 and 22) has not been properly assessed, particularly in consideration of recent reported issues of SCC in CSEF steels. This report details the results of Jones test exposures of a wide range of materials (Grades 11, 22, 23, 24, and 92), material conditions (as-received, improper heat treatments, normalized, weldments) and environments (salt fog; tube cleaning environments including decreasing, scale removal, and passivation; and high temperature water) to compare the susceptibility to cracking of these steels. In the as-received (normalized and tempered) condition, none of these materials are susceptible to SCC in the environments examined. However, in the hardened condition, certain combinations of environment and alloy reveal substantial SCC susceptibility.

  20. Off-axis impact of unidirectional composites with cracks: Dynamic stress intensification

    NASA Technical Reports Server (NTRS)

    Sih, G. C.; Chen, E. P.

    1979-01-01

    The dynamic response of unidirectional composites under off axis (angle loading) impact is analyzed by assuming that the composite contains an initial flaw in the matrix material. The analytical method utilizes Fourier transform for the space variable and Laplace transform for the time variable. The off axis impact is separated into two parts, one being symmetric and the other skew-symmetric with reference to the crack plane. Transient boundary conditions of normal and shear tractions are applied to a crack embedded in the matrix of the unidirectional composite. The two boundary conditions are solved independently and the results superimposed. Mathematically, these conditions reduce the problem to a system of dual integral equations which are solved in the Laplace transform plane for the transformation of the dynamic stress intensity factor. The time inversion is carried out numerically for various combinations of the material properties of the composite and the results are displayed graphically.

  1. Stability of cracked pipe under inertial stresses. Subtask 1.1 final report

    SciTech Connect

    Scott, P.; Wilson, M.; Olson, R.; Marschall, C.; Schmidt, R.; Wilkowski, G.

    1994-08-01

    This report presents the results of the pipe fracture experiments, analyses, and material characterization efforts performed within Subtask 1.1 of the IPIRG Program. The objective of Subtask 1.1 was to experimentally verify the analysis methodologies for circumferentially cracked pipe subjected primarily to inertial stresses. Eight cracked-pipe experiments were conducted on 6-inch nominal diameter TP304 and A106B pipe. The experimental procedure was developed using nonlinear time-history finite element analyses which included the nonlinear behavior due to the crack. The model did an excellent job of predicting the displacements, forces, and times to maximum moment. The comparison of the experimental loads to the predicted loads by the Net-Section-Collapse (NSC), Dimensionless Plastic-Zone Parameter, J-estimation schemes, R6, and ASME Section XI in-service flaw assessment criteria tended to underpredict the measured bending moments except for the NSC analysis of the A106B pipe. The effects of flaw geometry and loading history on toughness were evaluated by calculating the toughness from the pipe tests and comparing these results to C(l) values. These effects were found to be variable. The surface-crack geometry tended to increase the toughness (relative to CM results), whereas a negative load-ratio significantly decreased the TP304 stainless steel surface-cracked pipe apparent toughness. The inertial experiments tended to achieve complete failure within a few cycles after reaching maximum load in these relatively small diameter pipe experiments. Hence, a load-controlled fracture mechanics analysis may be more appropriate than a displacement-controlled analysis for these tests.

  2. A cylindrical shell with a stress-free end which contains an axial part-through or through crack

    NASA Technical Reports Server (NTRS)

    Erdogan, F.; Yahsi, O. S.

    1983-01-01

    The interaction problem of a through or a part through crack with a stress free boundary in a semi-infinite cylindrical shell is considered. It is assumed that the crack lies in a meridional plane which is a plane of symmetry with respect to the external loads as well as the geometry. The circular boundary of the semi-infinite cylinder is assumed to be stress free. By using a transverse shear theory the problem is formulated in terms of a system of singular integral equations. The line spring model is used to treat the part through crack problem. In the case of a through crack the interaction between the perturbed stress fields due to the crack and the free boundary is quite strong and there is a considerable increase in the stress intensity factors caused by the interaction. On the other hand in the problem of a surface crack the interaction appears to be much weaker and consequently the magnification in the stress intensity factors is much less significant.

  3. A cylindrical shell with a stress-free end which contains an axial part-through or through crack

    NASA Technical Reports Server (NTRS)

    Erdogan, F.; Yahsi, O. S.

    1985-01-01

    The interaction problem of a through or a part through crack with a stress free boundary in a semi-infinite cylindrical shell is considered. It is assumed that the crack lies in a meridional plane which is a plane of symmetry with respect to the external loads as well as the geometry. The circular boundary of the semi-infinite cylinder is assumed to be stress free. By using a transverse shear theory the problem is formulated in terms of a system of singular integral equations. The line spring model is used to treat the part through crack problem. In the case of a through crack the interaction between the perturbed stress fields due to the crack and the free boundary is quite strong and there is a considerable increase in the stress intensity factors caused by the interaction. On the other hand in the problem of a surface crack the interaction appears to be much weaker and consequently the magnification in the stress intensity factors is much less significant.

  4. Stress Corrosion Cracking of the Drip Shield, the Waste Package Outer Barrier, and the Stainless Steel Structural Material

    SciTech Connect

    G. Gordon

    2004-10-13

    Stress corrosion cracking is one of the most common corrosion-related causes for premature breach of metal structural components. Stress corrosion cracking is the initiation and propagation of cracks in structural components due to three factors that must be present simultaneously: metallurgical susceptibility, critical environment, and static (or sustained) tensile stresses. This report was prepared according to ''Technical Work Plan for: Regulatory Integration Modeling and Analysis of the Waste Form and Waste Package'' (BSC 2004 [DIRS 171583]). The purpose of this report is to provide an evaluation of the potential for stress corrosion cracking of the engineered barrier system components (i.e., the drip shield, waste package outer barrier, and waste package stainless steel inner structural cylinder) under exposure conditions consistent with the repository during the regulatory period of 10,000 years after permanent closure. For the drip shield and waste package outer barrier, the critical environment is conservatively taken as any aqueous environment contacting the metal surfaces. Appendix B of this report describes the development of the SCC-relevant seismic crack density model (SCDM). The consequence of a stress corrosion cracking breach of the drip shield, the waste package outer barrier, or the stainless steel inner structural cylinder material is the initiation and propagation of tight, sometimes branching, cracks that might be induced by the combination of an aggressive environment and various tensile stresses that can develop in the drip shields or the waste packages. The Stainless Steel Type 316 inner structural cylinder of the waste package is excluded from the stress corrosion cracking evaluation because the Total System Performance Assessment for License Application (TSPA-LA) does not take credit for the inner cylinder. This document provides a detailed description of the process-level models that can be applied to assess the performance of Alloy 22

  5. The effect of water flow rate upon the environmentally-assisted cracking response of a low-alloy steel

    SciTech Connect

    James, L.A.; Wire, G.L.; Cullen, W.H.

    1994-09-01

    Effect of water flow rate on the environmentally-assisted cracking (EAC) response of a high-sulfur ferritic steel was studied at 243C. In contrast to earlier studies with compact-type specimens, this study employed relatively large tight semi-elliptical surface cracks tested under generally linear-elastic conditions. Flow velocities parallel to the crack as low as 1.68 {minus} 1.84 m/s were effective in mitigating EAC.

  6. Environmentally Assisted Cracking of Alloy 7050-T7451 Exposed to Aqueous Chloride Solutions

    NASA Astrophysics Data System (ADS)

    Braun, Reinhold

    2016-03-01

    The stress corrosion cracking (SCC) behavior of 7050-T7451 plate material was investigated in short-transverse direction performing constant load and constant extension rate tests. Smooth and notched tensile specimens were permanently immersed in substitute ocean water and in an aqueous solution of 0.6 M NaCl + 0.06 M (NH4)2SO4. Alloy 7050-T7451 exhibited high SCC resistance in both synthetic environments. However, conducting cyclic loading tests, environment-induced cracking was observed. Applying a sawtooth waveform, notched tensile specimens were strained under constant load amplitude conditions at constant displacement rates ranging from 2 × 10-6 to 2 × 10-4 mms-1. The stress ratio R = σ min/ σ max was 0.1 with maximum stresses of 300 and 400 MPa. When cyclically loaded in substitute ocean water, notched specimens failed predominantly by transgranular environment-induced cracking. Striations were observed on the cleavage-like facets. The number of cycles-to-failure decreased with decreasing displacement rate. A slope of 0.5 was obtained by fitting the logarithmic plot of number of cycles-to-failure vs nominal loading frequency, indicating a hydrogen embrittlement mechanism controlled by diffusion.

  7. In situ investigation of high humidity stress corrosion cracking of 7075 aluminum alloy by three-dimensional (3D) X-ray synchrotron tomography

    SciTech Connect

    Singh, S. S.; Williams, J. J.; Lin, M. F.; Xiao, X.; De Carlo, F.; Chawla, N.

    2014-05-14

    In situ X-ray synchrotron tomography was used to investigate the stress corrosion cracking behavior of under-aged Al–Zn–Mg–Cu alloy in moisture. The discontinuous surface cracks (crack jumps) mentioned in the literature are actually a single continuous and tortuous crack when observed in three dimension (3D). Contrary to 2D measurements made at the surface which suggest non-uniform crack growth rates, 3D measurements of the crack length led to a much more accurate measurement of crack growth rates.

  8. In situ investigation of high humidity stress corrosion cracking of 7075 aluminum alloy by three-dimensional (3D) X-ray synchrotron tomography

    DOE PAGESBeta

    Singh, S. S.; Williams, J. J.; Lin, M. F.; Xiao, X.; De Carlo, F.; Chawla, N.

    2014-05-14

    In situ X-ray synchrotron tomography was used to investigate the stress corrosion cracking behavior of under-aged Al–Zn–Mg–Cu alloy in moisture. The discontinuous surface cracks (crack jumps) mentioned in the literature are actually a single continuous and tortuous crack when observed in three dimension (3D). Contrary to 2D measurements made at the surface which suggest non-uniform crack growth rates, 3D measurements of the crack length led to a much more accurate measurement of crack growth rates.

  9. Environmental stress, facilitation, competition, and coexistence.

    PubMed

    Hart, Simon P; Marshall, Dustin J

    2013-12-01

    The major theories regarding the combined influence of the environment and species interactions on population and community dynamics appear to conflict. Stress/ disturbance gradient models of community organization, such as the stress gradient hypothesis, emphasize a diminished role for competition in harsh environments whereas modern coexistence theory does not. Confusion about the role of species interactions in harsh environments is perpetuated by a disconnect between population dynamics theory and data. We linked theory and data using response surface experiments done in the field to parameterize mathematical, population-dynamic competition models. We replicated our experiment across two environments that spanned a common and important environmental stress gradient for determining community structure in benthic marine systems. We generated quantitative estimates of the effects of environmental stress on population growth rates and the direction and strength of intra- and interspecific interactions within each environment. Our approach directly addressed a perpetual blind spot in this field by showing how the effects of competition can be intensified in stressful environments even though the apparent strength of competition remains unchanged. Furthermore, we showed how simultaneous, reciprocal competitive and facilitative effects can stabilize population dynamics in multispecies communities in stressful environments. PMID:24597219

  10. Factors affecting the stress corrosion cracking susceptibility of zirconium in 90% nitric acid

    SciTech Connect

    Yau, T.L.

    1988-10-01

    U-band, C-ring, and slow strain rate tests were performed to evaluate the effects of texture, stress, surface condition, heat treatments electrochemical potential, and strain rate on stress corrosion cracking (SCC) of zirconium in 90% nitric acid at room temperature. Careful control of texture, surface condition (scratching, cleaning, and oxide coating), and/or applied stress was shown to effectively lead to the prevention of SCC of zirconium in 90% HNO/sub 3/. Heat treating at 760, 880, or 1000 C does not seem to improve the SCC resistance. However, if the potential of zirconium is maintained at 500 mV/sub SCE/ or lower, or 200 ppm of HF is added, zirconium's SCC susceptibility in 90% HNO/sub 3/ is eliminated. When adding HF, zirconium sponge must also be added to avoid corrosion rates.

  11. Stress Corrosion Cracking Behavior of Interstitial Free Steel Via Slow Strain Rate Technique

    NASA Astrophysics Data System (ADS)

    Murkute, Pratik; Ramkumar, J.; Mondal, K.

    2016-07-01

    An interstitial free steel is subjected to slow strain rate tests to investigate the stress corrosion cracking (SCC) behavior at strain rates ranging from 10-4 to 10-6s-1 in air and 3.5 wt.% NaCl solution. The ratios of time to failure, failure strain, and ultimate tensile stress at different strain rates in air to that in corrosive were considered as SCC susceptibility. Serrated stress-strain curve observed at lowest strain rate is explained by the Portevin-Le Chatelier effect. Maximum susceptibility to SCC at lowest strain rate is attributed to the soluble γ-FeOOH in the rust analyzed by Fourier Transformed Infrared spectroscopy. Mechanism for SCC relates to the anodic dissolution forming the groove, where hydrogen embrittlement can set in and finally fracture happens due to triaxiality.

  12. Growth of Matrix Cracks During Intermediate Temperature Stress Rupture of a SiC/SiC Composite in Air

    NASA Technical Reports Server (NTRS)

    Morscher, Gregory N.

    2000-01-01

    The crack density of woven Hi-Nicalon(sup TM) (Nippon Carbon, Japan) fiber, BN interphase, melt-infiltrated SiC matrix composites was determined for specimens subjected to tensile stress rupture at 815 C. A significant amount of matrix cracking occurs due to the growth of fiber-bridged microcracks even at stresses below the run-out condition. This increased cracking corresponded to time dependent strain accumulation and acoustic emission activity during the constant load test. However, the portion of the rupture specimens subjected to cooler temperatures (< 600 C than the hot section had significantly lower crack densities compared to the hotter regions. From the acoustic emission and time dependent strain data it can be inferred that most of the matrix crack growth occurred within the first few hours of the tensile rupture experiment. The crack growth was attributed to an interphase recession mechanism that is enhanced by the presence of a thin carbon layer between the fiber and the matrix as a result of the composite fabrication process. One important consequence of matrix crack growth at the lower stresses is poor retained strength at room temperature for specimens that did not fail.

  13. Mechanistic studies on stress corrosion cracking of pipeline steels in near-neutral pH environments

    NASA Astrophysics Data System (ADS)

    Gu, Biao

    2000-10-01

    Experimental and theoretical approaches towards the study on mechanism of stress corrosion cracking (SCC) of pipeline steels in near-neutral pH environment have been performed. The subject of the investigations included SCC susceptibility at various testing conditions, hydrogen distribution around SCC crack tip and the role of hydrogen in cracking process. SCC tests were mainly conducted using slow strain rate testing (SSRT). The hydrogen distribution around a stress corrosion crack tip was measured using secondary ion mass spectrometry (SIMS), and modelled using an elastic-plastic analysis. A thermodynamic model was proposed and used to calculate the effect that the presence of hydrogen and stress has on the SCC growth rate. SSRTs showed that transgranular stress corrosion cracking (TGSCC) of pipeline steels could occur in a dilute bicarbonate solution with a near-neutral pH value. SCC susceptibility increased as the applied electrochemical potential, the pH value of solution and applied strain rates during tension testing decreased. Hydrogen precharging or addition of carbon dioxide (CO2) facilitated the process of SCC, suggesting that dissolution and ingress of hydrogen are both involved in the cracking process. SIMS measurement indicated that low pH values and applying cathodic potential facilitate the generation, evolution and enrichment of hydrogen around the SCC crack tip. Hydrogen plays an important role in the SCC of pipeline steels by promoting anodic dissolution and SCC susceptibility. Thermodynamic analysis showed that hydrogen interacted with the stress field and changed the internal energy and entropy of the steel. These changes could result in an increase of the anodic dissolution rate of the steel and enhancing the SCC growth rate. The hydrogen-facilitated SCC growth rate obtained from the proposed model was in agreement with SSRT measurements. The mechanism of SCC for pipeline steels in near-neutral pH solutions may be that at near free corrosion

  14. Environmental stress, reactivity and ischaemic heart disease.

    PubMed

    Krantz, D S; Raisen, S E

    1988-03-01

    This article provides an overview of work in two areas of biobehavioural research: the effects of environmental stress and the role of psychophysiologic reactivity in the development of ischaemic heart disease. Attention is given first to evidence that low socio-economic status, low social support, and occupational settings characterized by high demands and low levels of control over the job are associated with increased coronary risk. Also discussed is a promising animal primate model of social stress and its role in development of coronary atherosclerosis. Next, we discuss physiological responsiveness (reactivity) to emotional stress, which is being studied as a marker of processes involved in the development of cardiovascular disease. Stress and psychophysiological reactivity constitute promising targets for research on biobehavioural antecedents of coronary disease and for clinical intervention studies. However, further evidence is needed before these variables can be regarded as proven coronary risk factors. PMID:3129010

  15. Phase transformations and residual stresses in environmental barrier coatings

    NASA Astrophysics Data System (ADS)

    Harder, Bryan J.

    Silicon-based ceramics (SiC, Si3N4) are promising materials for high-temperature structural applications in turbine engines. However, the silica layer that forms on these materials is susceptible to attack from water vapor present in combustion environments. To protect against this degradation, environmental barrier coatings (EBCs) were developed to protect the underlying substrate. In the case of silicon carbide (SiC), multilayer coating systems consist of a Ba1-xSrxAl2Si 2O8 (BSAS) topcoat, a mullite or mullite + SrAl2Si 2O8 (SAS) interlayer, and a silicon bond coat. In this work, biaxial strains were measured on as-sprayed and heat-treated samples to analyze the stress and phase evolution in the coating system as a function of depth and temperature. Models were used to compare the results with an ideal coating system. In the assprayed state, tensile stresses as high as 175 MPa were measured, and cracking was observed. After thermally cycling the samples, stresses were significantly reduced and cracks in the topcoat had closed. The addition of SAS to the interlayer increased the compressive stress in the BSAS topcoat in thermally-cycled samples, which was desirable for EBC applications. The BSAS topcoat transformed from the as-deposited hexacelsian state to the stable celsian above 1200°C. This phase transformation is accompanied by a CTE reduction. The kinetics of the hexacelsian-to-celsian transformation were quantified for freestanding plasma-sprayed BSAS. Activation energies for bulk bars and crushed powder were determined to be ˜340 kJ/mol and ˜500 kJ/mol, respectively. X-ray diffraction and electron backscatter diffraction were used to establish how microstructural constraints reduce the transformation energy. Barrier coating lifetime and stability are also influenced by exposure to reactive, low-melting point calcium-magnesium-aluminosilicate (CMAS) deposits formed from dust and sand. Multilayer doped aluminosilicate coatings and bulk BSAS material were

  16. Origins of Negative Strain Rate Dependence of Stress Corrosion Cracking Initiation in Alloy 690, and Intergranular Crack Formation in Thermally Treated Alloy 690

    NASA Astrophysics Data System (ADS)

    Kim, Young Suk; Kim, Sung Soo

    2016-07-01

    We show that enhanced stress corrosion cracking (SCC) initiation in cold-rolled Alloy 690 with decreasing strain rate is related to the rate of short-range ordering (SRO) but not to the time-dependent corrosion process. Evidence for SRO is provided by aging tests on cold-rolled Alloy 690 at 623 K and 693 K (350 °C and 420 °C), respectively, which demonstrate its enhanced lattice contraction and hardness increase with aging temperature and time, respectively. Secondary intergranular cracks formed only in thermally treated and cold-rolled Alloy 690 during SCC tests, which are not SCC cracks, are caused by its lattice contraction by SRO before SCC tests but not by the orientation effect.

  17. Origins of Negative Strain Rate Dependence of Stress Corrosion Cracking Initiation in Alloy 690, and Intergranular Crack Formation in Thermally Treated Alloy 690

    NASA Astrophysics Data System (ADS)

    Kim, Young Suk; Kim, Sung Soo

    2016-09-01

    We show that enhanced stress corrosion cracking (SCC) initiation in cold-rolled Alloy 690 with decreasing strain rate is related to the rate of short-range ordering (SRO) but not to the time-dependent corrosion process. Evidence for SRO is provided by aging tests on cold-rolled Alloy 690 at 623 K and 693 K (350 °C and 420 °C), respectively, which demonstrate its enhanced lattice contraction and hardness increase with aging temperature and time, respectively. Secondary intergranular cracks formed only in thermally treated and cold-rolled Alloy 690 during SCC tests, which are not SCC cracks, are caused by its lattice contraction by SRO before SCC tests but not by the orientation effect.

  18. Effects of alloy chemistry, cold work, and water chemistry on corrosion fatigue and stress corrosion cracking of nickel alloys and welds.

    SciTech Connect

    Chopra, O. K.; Soppet, W. K.; Shack, W. J.; Energy Technology

    2001-04-01

    Reactor vessel internal components made of nickel-base alloys are susceptible to environmentally assisted cracking (EAC). A better understanding of the causes and mechanisms of this cracking may permit less conservative estimates of damage accumulation and requirements on inspection intervals. The objective of this work is to evaluate and compare the resistance of Alloys 600 and 690 and their welds, such as Alloys 82, 182, 52, and 152, to EAC in simulated light water reactor environments. The existing crack growth rate (CGR) data for these alloys under cyclic and constant loads have been evaluated to establish the effects of alloy chemistry, cold work, and water chemistry. The experimental fatigue CGRs are compared with CGRs that would be expected in air under the same mechanical loading conditions to obtain a qualitative understanding of the degree and range of conditions for significant environmental enhancement in growth rates. The existing stress corrosion cracking (SCC) data on Alloys 600 and 690 and Alloy 82, 182, and 52 welds have been compiled and analyzed to determine the influence of key parameters on growth rates in simulated PWR and BWR environments. The SCC data for these alloys have been evaluated with correlations developed by Scott and by Ford and Andresen.

  19. Hot Salt Stress Corrosion Cracking Behavior of Ti-6242S Alloy

    NASA Astrophysics Data System (ADS)

    Pustode, Mangesh D.; Raja, V. S.

    2015-12-01

    The hot salt stress corrosion cracking behavior of Ti-6A1-2Sn-4Zr-2Mo-0.1Si (Ti-6242S) alloy was studied in the temperature range from 523.15 K to 673.15 K (250 °C to 400 °C). The alloy showed marginal susceptibility at 573.15 K (300 °C), and the extent susceptibility found to increase significantly at higher test temperatures. The specimens did not fail in long-term (1000 hours) hot salt constant load exposure tests carried out at 623.15 K and 673.15 K (350 °C and 400 °C), even at the stress levels more than the 80 pct of their ultimate tensile strength. However, the salt exposure in both stressed and unstressed conditions found to significantly impair the room-temperature ductility. The study shows that pitting and formation of slip step were the precursor events for SCC initiation; and the cracks were found to grow in transgranular manner in the primary- α phase and discontinuous-faceted manner in the transformed β colony. Furthermore, the XRD analysis of hot salt-exposed specimens revealed the presence of titanium hydride phase, which could be responsible for the embrittlement.

  20. The chloride stress-corrosion cracking behavior of stainless steels under different test methods

    NASA Astrophysics Data System (ADS)

    Jin, L. Z.

    1994-12-01

    Chloride-induced stress-corrosion cracking (SCC) is one of the failure modes of stainless steels. Highly alloyed austenitic stainless steels S32654, S31254, and N08028, and duplex grades S32750 and S31803 possess much improved resistance to SCC compared with S30400 and S31600 steels. With the development of a database, SSData, experimental data collected from calcium chloride tests, autoclave tests, and drop evaporation tests were evaluated. Stress-corrosion cracking data generated by autoclave tests agreed well with the practical service conditions and can be used to discriminate alloys for SCC resistance in sodium chloride solution. Drop evaporation test data can be used in situations where evaporation may occur and cyclic loading may be involved. The SCC resistance of alloys under each method increased with increasing molybdenum equivalent Mo + 0.25Cr + 0.1Ni. For a given alloy, the testing result depends on the stress state and environment; different test methods can give different ranking orders concerning SCC resistance. The performance of duplex stainless steels in a chloride-containing environment at higher temperatures was not as good as expected when dynamic loading was involved.

  1. Tensile stress corrosion cracking of type 304 stainless steel irradiated to very high dose

    SciTech Connect

    Chung, H. M.; Ruther, W. E.; Strain, R. V.; Shack, W. J.

    2001-09-01

    Certain safety-related core internal structural components of light water reactors, usually fabricated from Type 304 or 316 austenitic stainless steels (SSs), accumulate very high levels of irradiation damage (20--100 displacement per atom or dpa) by the end of life. The data bases and mechanistic understanding of, the degradation of such highly irradiated components, however, are not well established. A key question is the nature of irradiation-assisted intergranular cracking at very high dose, i.e., is it purely mechanical failure or is it stress-commotion cracking? In this work, hot-cell tests and microstructural characterization were performed on Type 304 SS from the hexagonal fuel can of the decommissioned EBR-11 reactor after irradiation to {approximately}50 dpa at {approximately}370 C. Slow-strain-rate tensile tests were conducted at 289 C in air and in water at several levels of electrochemical potential (ECP), and microstructural characteristics were analyzed by scanning and transmission electron microcopies. The material deformed significantly by twinning and exhibited surprisingly high ductility in air, but was susceptible to severe intergranular stress corrosion cracking (IGSCC) at high ECP. Low levels of dissolved O and ECP were effective in suppressing the susceptibility of the heavily irradiated material to IGSCC, indicating that the stress corrosion process associated with irradiation-induced grain-boundary Cr depletion, rather than purely mechanical separation of grain boundaries, plays the dominant role. However, although IGSCC was suppressed, the material was susceptible to dislocation channeling at low ECP, and this susceptibility led to poor work-hardening capability and low ductility.

  2. Modeling of stresses at grain boundaries with respect to occurrence of stress corrosion cracking

    SciTech Connect

    Kozaczek, K.J.; Sinharoy, A.; Ruud, C.O.; McIlree, A.R.

    1995-12-31

    The distributions of elastic stresses/strains in the grain boundary regions were studied by the analytical and the finite element models. The grain boundaries represent the sites where stress concentration occurs as a result of discontinuity of elastic properties across the grain boundary and the presence of second phase particles elastically different from the surrounding matrix grains. A quantitative analysis of those stresses for steels and nickel based alloys showed that the stress concentrations in the grain boundary regions are high enough to cause a local microplastic deformation even when the material is in the macroscopic elastic regime. The stress redistribution as a result of such a plastic deformation was discussed.

  3. Niobium enrichment and environmental enhancement of creep crack growth in nickel-base superalloys

    SciTech Connect

    Gao, M.; Wei, R.P.; Dwyer, D.J.

    1995-04-15

    In this paper, the possible role of niobium in the environmental enhancement of creep crack growth in nickel-base superalloys is further examined. The examination included (1) surface enrichment of Nb in a commercial Inconel 718; (2) a source of niobium and its interaction with oxygen; (3) preferential oxidation of Nb at the crack tip, and (4) correlations between environmental sensitivity and niobium concentration of nickel-base superalloys from the literature. The role of niobium was suggested by recent X-ray photoelectron spectroscopic (XPS) studies. The XPS studies show a significant increase in the concentration of niobium on the (001) surface of an Inconel 718 single crystal after heating at temperatures above 775 K. Considerable segregation of niobium was also found on the grain boundaries of a thermally aged commercial (polycrystalline) Inconel 718. The CCGR data showed significant enhancement by oxygen and water vapor at temperatures of 800--975 K where niobium enrichment occurred.

  4. Proceedings: Primary water stress corrosion cracking: 1989 EPRI remedial measures workshop

    SciTech Connect

    Gorman, J.A. )

    1990-04-01

    A meeting on PWSCC Remedial Measures'' was organized to give those working in this area an opportunity to share their results, ideas and plans with regard to development and application of remedial measures directed against the primary water stress corrosion cracking (PWSCC) phenomenon affecting alloy 600 steam generator tubes. Topics discussed included: utility experience and strategies; nondestructive examination (NDE) methods for PWSCC; technical topics ranging from predictive methods for occurrence of PWSCC to results of corrosion tests; and services provided by vendors that can help prevent the occurrence of PWSCC or can help address problems caused by PWSCC once it occurs.

  5. Stress corrosion cracking of zirconium cladding tubes: I. Proximate local SCC testing method

    NASA Astrophysics Data System (ADS)

    Rozhnov, A. B.; Belov, V. A.; Nikulin, S. A.; Khanzhin, V. G.

    2010-10-01

    The stress corrosion cracking (SCC) methods of testing zirconium cladding tubes are analyzed. A proximate method is proposed for estimating SCC of fuel claddings claddings in a iodine-containing environment with a limited contact zone between a metal and corrosive medium and simultaneous measurement of acoustic emission (AE) from forming corrosion defects. Criteria of estimating the SCC resistance of the tubes are proposed from measured AE and corrosion damage of the tube material. The results of local SCC tests of cladding tubes of E110 and E635 zirconium alloys are presented.

  6. EXPERT PANEL OVERSIGHT COMMITTEE ASSESSMENT OF FY2008 CORROSION AND STRESS CORROSION CRACKING SIMULANT TESTING PROGRAM

    SciTech Connect

    BOOMER KD

    2009-01-08

    The Expert Panel Oversight Committee (EPOC) has been overseeing the implementation of selected parts of Recommendation III of the final report, Expert Panel workshop for Hanford Site Double-Shell Tank Waste Chemistry Optimization, RPP-RPT-22126. Recommendation III provided four specific requirements necessary for Panel approval of a proposal to revise the chemistry control limits for the Double-Shell Tanks (DSTs). One of the more significant requirements was successful performance of an accelerated stress corrosion cracking (SCC) experimental program. This testing program has evaluated the optimization of the chemistry controls to prevent corrosion in the interstitial liquid and supernatant regions of the DSTs.

  7. INHIBITION OF STRESS CORROSION CRACKING OF CARBON STEEL STORAGE TANKS AT HANFORD

    SciTech Connect

    BOOMER, K.D.

    2007-01-31

    The stress corrosion cracking (SCC) behavior of A537 tank steel was investigated in a series of environments designed to simulate the chemistry of legacy nuclear weapons production waste. Tests consisted of both slow strain rate tests using tensile specimens and constant load tests using compact tension specimens. Based on the tests conducted, nitrite was found to be a strong SCC inhibitor. Based on the test performed and the tank waste chemistry changes that are predicted to occur over time, the risk for SCC appears to be decreasing since the concentration of nitrate will decrease and nitrite will increase.

  8. Time Variation of Seismic Anisotropy, Stress and Cracks on Active Volcanoes (Invited)

    NASA Astrophysics Data System (ADS)

    Savage, M. K.

    2013-12-01

    We summarize measurements of seismic anisotropy and its relation to other geophysical measurements of stress and cracks on eleven active volcanoes; Unzen (Unz), Sakurajima (Sak), Aso, Asama (Asm) and Kirishima (Kir) in Japan; Okmok (Okm) in Alaska, Ruapehu (Rua) and Tongariro (Ton) in New Zealand, Soufriere Hills (Sou) in Montserrat, Kilauea (Kil) in Hawaii and Piton de la Fournaise (PdF) in La Reunion. We used the MFAST shear wave splitting computer code, an objective code that is fully automatic except for the S arrival pick. Fast polarization directions (phi) should be parallel to cracks and hence the maximum horizontal stress direction. Time delays (dt) increase with path length and percent anisotropy, usually related to crack density. Where possible we used S waves from deep earthquakes to ensure that the movement of the earthquakes was not correlated with the volcanic activity. At some volcanoes we used families of repeating events with similar waveforms and at most volcanoes we also computed splitting at earthquakes local to the volcano. We compared the phi and dt variation in time to eruption occurrences and to other available parameters including seismicity rate, b-values, focal mechanisms, isotropic velocity changes from noise cross-correlation, Vp/Vs ratios, Geodetic measurements such as GPS and tilt, and gas flux. All volcanoes had some stations with excellent shear wave arrivals that yielded measureable splitting. Individual measurements showed scatter in most areas, but at most of the volcanoes, moving averages of phi or dt (or both) yielded time variations that correlated with other measurements related to volcanic activity or to stress changes or changes in crack-filling material such as gas flux. The multiplet studies did not yield slowly varying splitting but instead showed distinct jumps in splitting parameters at various times, which appears to be caused in part by cycle skipping. Time resolution of changes depends on the seismicity available

  9. Photoelastic stress analysis of internal fixation techniques for femur shaft crack

    NASA Astrophysics Data System (ADS)

    Liu, Tong; Chai, Gin B.; Asundi, Anand K.; Murugiah, Arumaaran

    2001-06-01

    In this paper, a photoelastic stress analysis is carried out for a cracked femur bone with compression plate fixation. A loading rig has been designed and manufactured to apply forces in the physical directions on the 2D modal of the femur bone based on a single-leg-stance. Three femur models made of photoelastic materials had been fabricated with three configurations and loaded. A recently developed three- load to phase shifting method is adopted to extract the full-field quantitative information from the fringe patterns of the loaded models. A comparison shows that the configuration where the screws point away from each other had the best effectiveness.

  10. Role of microstructures on stress corrosion cracking of pipeline steels in carbonate-bicarbonate solution

    SciTech Connect

    Asahi, H.; Kushida, T.; Kimura, M.; Fukai, H.; Okano, S.

    1999-07-01

    Stress corrosion cracking (SCC) on the external surface of pipelines contributes to the major failure of pipelines. The great majority of SCC is intergranular and occurs in a carbonate-bicarbonate environment. Metallurgical factors affecting SCC are still vague and therefore have been studied. Uniform microstructures, not mixed structures, are favorable for suppressing SCC. Low-C steels produced in a process such as thermomechanical-controlled processing are less susceptible to SCC. The presence of locally soft microstructures decreases resistance to SCC (mixed structure and decarburized structure). However, SCC resistance is high on hard layers, like grit-blasted surfaces.

  11. Photoelectrochemical protection of stainless alloys from the stress-corrosion cracking in BWR primary coolant environment

    SciTech Connect

    Akashi, Masatsune; Iso-o, Hiroyuki; Kubota, Nobuhiko; Fukuda, Takanori; Ayabe, Muneo; Hirano, Kenji

    1995-12-31

    The feasibility of counteracting or preventing the stress-corrosion cracking in the BWR core internals by the photoelectrochemical method has been examined. For the purpose TiO{sub 2} semiconductor is noted for its capability of photo electrochemically inducing the water-oxidizing anodic reaction in low enough potential domain if supplied with a light of a wavelength shorter than 410 nm. This paper offers an empirical proof by showing that Type 304 stainless steel and Alloy 600 stainless alloy that have been plasma-spray coated with TiO{sub 2} film will do quite well in environments of BWR primary coolant.

  12. Stress-intensity factors of r-cracks in fiber-reinforced composites under thermal and mechanical loading

    NASA Astrophysics Data System (ADS)

    Mueller, W. H.; Schmauder, S.

    1993-02-01

    The plane stress/plane strain problem of radial matrix cracking in fiber-reinforced composites, due to thermal mismatch and externally applied stress is solved numerically in the framework of linear elasticity, using Erdogan's integral equation technique. It is shown that, in order to obtain the results of the combined loading case, the solutions of purely thermal and purely mechanical loading can simply be superimposed. Stress-intensity factors are calculated for various lengths and distances of the crack from the interface for each of these loading conditions.

  13. The effect of alloy composition on the mechanism of stress corrosion cracking of titanium alloys in aqueous environments

    NASA Technical Reports Server (NTRS)

    Boyd, J. D.; Williams, D. N.; Wood, R. A.; Jaffee, R. I.

    1972-01-01

    The effects of alloy composition on the aqueous stress corrosion of titanium alloys were studied with emphasis on determining the interrelations among composition, phase structure, and deformation and fracture properties of the alpha phase in alpha-beta alloys. Accomplishments summarized include the effects of alloy composition on susceptibility, and metallurgical mechanisms of stress-corrosion cracking.

  14. Deformation-corrosion interactions for Zr alloys during I-SCC crack initiation. Part II: Localised stress and strain contributions

    NASA Astrophysics Data System (ADS)

    Jacques, Patrick; Lefebvre, Florence; Lemaignan, Clément

    1999-01-01

    For a better understanding of the initiation step of iodine induced stress corrosion cracking (SCC) in Zr alloys, responsible for pellet-cladding interaction (PCI) fuel rod failures, an analytical study has been undertaken, the aim of which being focused on the respective roles of local chemistry and stress/strain state on the crack nucleation. This second part is mostly related to the local stress induced by strain incompatibilities between grains. Using EBSP (electron back-scattering pattern) to analyze the crystallographic orientation of all the grains of the samples tested in SCC, it was possible to conclude that the major parameter controlling the nucleation of the intergranular cracks is not related to grain to grain strain incompatibilities, but to the orientation of the grain boundary planes with respect to the tensile stress.

  15. Stress corrosion cracking of austenitic weld deposits in a salt spray environment

    NASA Astrophysics Data System (ADS)

    Cai, J. B.; Yu, C.; Shiue, R. K.; Tsay, L. W.

    2015-10-01

    ER 308L and 309LMo were utilized as the filler metals for the groove and overlay welds of a 304L stainless steel substrate, which was prepared via a gas tungsten arc-welding process in multiple passes. U-bend and weight-loss tests were conducted by testing the welds in a salt spray containing 10 wt% NaCl at 120 °C. The dissolution of the skeletal structure in the fusion zone (FZ) caused the stress corrosion cracking (SCC) of the weld. The FZ in the cold-rolled condition showed the longest single crack length in the U-bend tests. Moreover, sensitization treatment at 650 °C for 10 h promoted the formation of numerous fine cracks, which resulted in a high SCC susceptibility. The weight loss of the deposits was consistent with the SCC susceptibility of the welds in a salt spray. The 309LMo deposit was superior to the 308L deposit in the salt spray.

  16. Stress corrosion cracking of austenitic weld deposits in a salt spray environment

    NASA Astrophysics Data System (ADS)

    Cai, J. B.; Yu, C.; Shiue, R. K.; Tsay, L. W.

    2015-10-01

    ER 308L and 309LMo were utilized as the filler metals for the groove and overlay welds of a 304L stainless steel substrate, which was prepared via a gas tungsten arc-welding process in multiple passes. U-bend and weight-loss tests were conducted by testing the welds in a salt spray containing 10 wt% NaCl at 120 °C. The dissolution of the skeletal structure in the fusion zone (FZ) caused the stress corrosion cracking (SCC) of the weld. The FZ in the cold-rolled condition showed the longest single crack length in the U-bend tests. Moreover, sensitization treatment at 650 °C for 10 h promoted the formation of numerous fine cracks, which resulted in a high SCC susceptibility. The weight loss of the deposits was consistent with the SCC susceptibility of the welds in a salt spray. The 309LMo deposit was superior to the 308L deposit in the salt spray.

  17. Assessment of Initial Test Conditions for Experiments to Assess Irradiation Assisted Stress Corrosion Cracking Mechanisms

    SciTech Connect

    Busby, Jeremy T; Gussev, Maxim N

    2011-04-01

    Irradiation-assisted stress corrosion cracking is a key materials degradation issue in today s nuclear power reactor fleet and affects critical structural components within the reactor core. The effects of increased exposure to irradiation, stress, and/or coolant can substantially increase susceptibility to stress-corrosion cracking of austenitic steels in high-temperature water environments. . Despite 30 years of experience, the underlying mechanisms of IASCC are unknown. Extended service conditions will increase the exposure to irradiation, stress, and corrosive environment for all core internal components. The objective of this effort within the Light Water Reactor Sustainability program is to evaluate the response and mechanisms of IASCC in austenitic stainless steels with single variable experiments. A series of high-value irradiated specimens has been acquired from the past international research programs, providing a valuable opportunity to examine the mechanisms of IASCC. This batch of irradiated specimens has been received and inventoried. In addition, visual examination and sample cleaning has been completed. Microhardness testing has been performed on these specimens. All samples show evidence of hardening, as expected, although the degree of hardening has saturated and no trend with dose is observed. Further, the change in hardening can be converted to changes in mechanical properties. The calculated yield stress is consistent with previous data from light water reactor conditions. In addition, some evidence of changes in deformation mode was identified via examination of the microhardness indents. This analysis may provide further insights into the deformation mode under larger scale tests. Finally, swelling analysis was performed using immersion density methods. Most alloys showed some evidence of swelling, consistent with the expected trends for this class of alloy. The Hf-doped alloy showed densification rather than swelling. This observation may be

  18. The effect of stress rate on crack damage evolution in polystyrene and PEEK. Ph.D. Thesis

    SciTech Connect

    Gregory, B.L.

    1993-01-01

    The effects of stress rate on fatigue crack propagation (FCP) in polystyrene (PS) and polyetheretherketone (PEEK) were examined emphasizing damage evolution during fatigue fracture. Extruded and compression molded PS were studied. Craze distributions along trailing edges of successive process zone configurations in each material were self-similar. A core of dense crazing was observed in the extruded PS; no core was observed in the compression molded material. These results have important implications for the kinematics of process zone evolution in compression molded PS. Crack growth kinetics were treated as dl/dn and dl/dt. Consideration of the loading waveform and the load-time-area (LTA) revealed that LTA and rate effects couldn`t be decoupled. However, by treating the data as dl/dt the contribution of LTA constant, and the effect of stress rate was determined. Attempts were made to quantify the contributions of fatigue and creep LTA on total FCP kinetics by linear summation. While these failed, it was subsequently determined that two linear regimes separated by a characteristic period could approximate the data. The contributions of both stress rate and LTA varied above and below this characteristic period. From this analysis, the contributions of time and cycle reversal could be evaluated. Crack growth due to creep exhibited strong correlation with an exponential function compatible with stress-temperature activated processes. The crack damage evolution of PEEK as a function of stress rate during fatigue was also investigated. A brittle-ductile transition was observed characterized by a transformation at the crack tip from a rounded to a triangular (90 deg angle) crack front. The results showed that the damaged material ahead of the crack tip behaved as an elastic perfectly plastic material (plane stress conditions). This damage zone was further characterized as a volume of transformed material.

  19. Investigation into the stress corrosion cracking properties of AA2099, an aluminum-lithium-copper alloy

    NASA Astrophysics Data System (ADS)

    Padgett, Barbara Nicole

    Recently developed Al-Li-Cu alloys show great potential for implementation in the aerospace industry because of the attractive mix of good mechanical properties and low density. AA2099 is an Al-Li-Cu alloy with the following composition Al-2.69wt%Cu-1.8wt%Li-0.6wt%Zn-0.3wt%Mg-0.3wt%Mn-0.08wt%Zr. The environmental assisted cracking and localized corrosion behavior of the AA2099 was investigated in this thesis. The consequences of uncontrolled grain boundary precipitation via friction stir welding on the stress corrosion cracking (SCC) behavior of AA2099 was investigated first. Using constant extension rate testing, intergranular corrosion immersion experiments, and potentiodynamic scans, the heat-affected zone on the trailing edge of the weld (HTS) was determined to be most susceptible of the weld zones. The observed SCC behavior for the HTS was linked to the dissolution of an active phase (Al2CuLi, T1) populating the grain boundary. It should be stated that the SCC properties of AA2099 in the as-received condition were determined to be good. Focus was then given to the electrochemical behavior of precipitate phases that may occupy grain and sub-grain boundaries in AA2099. The grain boundary micro-chemistry and micro-electrochemistry have been alluded to within the literature as having significant influence on the SCC behavior of Al-Li-Cu alloys. Major precipitates found in this alloy system are T1 (Al 2CuLi), T2 (Al7.5Cu4Li), T B (Al6CuLi3), and theta (Al2 Cu). These phases were produced in bulk form so that the electrochemical nature of each phase could be characterized. It was determined T1 was most active electrochemically and theta was least. When present on grain boundaries in the alloy, electrochemical behavior of the individual precipitates aligned with the observed corrosion behavior of the alloy (e.g. TB was accompanied by general pitting corrosion and T 1 was accompanied by intergranular corrosion attack). In addition to the electrochemical behavior of

  20. Stress Corrosion Cracking of Ni-Fe-Cr Alloys Relevant to Nuclear Power Plants

    NASA Astrophysics Data System (ADS)

    Persaud, Suraj

    Stress corrosion cracking (SCC) of Ni-Fe-Cr alloys and weld metals was investigated in simulated environments representative of high temperature water used in the primary and secondary circuits of nuclear power plants. The mechanism of primary water SCC (PWSCC) was studied in Alloys 600, 690, 800 and Alloy 82 dissimilar metal welds using the internal oxidation model as a guide. Initial experiments were carried out in a 480°C hydrogenated steam environment considered to simulate high temperature reducing primary water. Ni alloys underwent classical internal oxidation intragranularly resulting in the expulsion of the solvent metal, Ni, to the surface. Selective intergranular oxidation of Cr in Alloy 600 resulted in embrittlement, while other alloys were resistant owing to their increased Cr contents. Atom probe tomography was used to determine the short-circuit diffusion path used for Ni expulsion at a sub-nanometer scale, which was concluded to be oxide-metal interfaces. Further exposures of Alloys 600 and 800 were done in 315°C simulated primary water and intergranular oxidation tendency was comparable to 480°C hydrogenated steam. Secondary side work involved SCC experiments and electrochemical measurements, which were done at 315°C in acid sulfate solutions. Alloy 800 C-rings were found to undergo acid sulfate SCC (AcSCC) to a depth of up to 300 microm in 0.55 M sulfate solution at pH 4.3. A focused-ion beam was used to extract a crack tip from a C-ring and high resolution analytical electron microscopy revealed a duplex oxide structure and the presence of sulfur. Electrochemical measurements were taken on Ni alloys to complement crack tip analysis; sulfate was concluded to be the aggressive anion in mixed sulfate and chloride systems. Results from electrochemical measurements and crack tip analysis suggested a slip dissolution-type mechanism to explain AcSCC in Ni alloys.