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Sample records for environment assisted cracking

  1. Fracture mechanics and surface chemistry investigations of environment-assisted crack growth

    NASA Technical Reports Server (NTRS)

    Wei, R. P.; Klier, K.; Simmons, G. W.; Chou, Y. T.

    1984-01-01

    It is pointed out that environment-assisted subcritical crack growth in high-strength steels and other high-strength alloys (particularly in hydrogen and in hydrogenous environments) is an important technological problem of long standing. This problem is directly related to issues of structural integrity, durability, and reliability. The terms 'hydrogen embrittlement' and 'stress corrosion cracking' have been employed to describe the considered phenomenon. This paper provides a summary of contributions made during the past ten years toward the understanding of environmentally assisted crack growth. The processes involved in crack growth are examined, and details regarding crack growth and chemical reactions are discussed, taking into account crack growth in steels exposed to water/water vapor, the effect of hydrogen, reactions involving hydrogen sulfide, and aspects of fracture surface morphology and composition. Attention is also given to the modeling of crack growth response, crack growth in gas mixtures, and the interaction of solute atoms with the crack-tip stress field.

  2. Measurement and Modeling of Hydrogen Environment-Assisted Cracking in Monel K-500

    NASA Astrophysics Data System (ADS)

    Gangloff, Richard P.; Ha, Hung M.; Burns, James T.; Scully, John R.

    2014-08-01

    Hydrogen environment-assisted cracking (HEAC) of Monel K-500 is quantified using slow-rising stress intensity loading with electrical potential monitoring of small crack propagation and elastoplastic J-integral analysis. For this loading, with concurrent crack tip plastic strain and H accumulation, aged Monel K-500 is susceptible to intergranular HEAC in NaCl solution when cathodically polarized at -800 mVSCE ( E A, vs saturated calomel) and lower. Intergranular cracking is eliminated by reduced cathodic polarization more positive than -750 mVSCE. Crack tip diffusible H concentration rises, from near 0 wppm at E A of -765 mVSCE, with increasing cathodic polarization. This behavior is quantified by thermal desorption spectroscopy and barnacle cell measurements of hydrogen solubility vs overpotential for planar electrodes, plus measured-local crevice potential, and pH scaled to the crack tip. Using crack tip H concentration, excellent agreement is demonstrated between measurements and decohesion-based model predictions of the E A dependencies of threshold stress intensity and Stage II growth rate. A critical level of cathodic polarization must be exceeded for HEAC to occur in aged Monel K-500. The damaging-cathodic potential regime likely shifts more negative for quasi-static loading or increasing metallurgical resistance to HEAC.

  3. Chemistry and electrochemistry of environment-assisted cracking of an aluminum-zinc-magnesium-copper alloy

    NASA Astrophysics Data System (ADS)

    Cooper, Kevin Richard

    2001-11-01

    The mechanism of environment-assisted cracking (EAC) of 7xxx-series alloys is unclear, involving uncertain contributions of hydrogen embrittlement (HE) and anodic dissolution (AD). Fundamental understanding of the EAC mechanism is lacking in part because the role of the crack environment is not well understood. The objective of this research was to characterize and understand the role of the crack chemistry and electrochemistry during aqueous EAC of AA 7050. The crack environment can differ significantly from bulk conditions. Cations, produced by AD, hydrolyze causing local acidification; anions from the bulk electrolyte concentrate within the crack to maintain charge neutrality; ohmic potential drop results from ion migration and diffusion. A positive correlation exists between da/dt and [Al3+]Tip in chromate-chloride electrolyte wherein tip dissolution dominates flank corrosion in establishing the crack chemistry. Tip pH was 2 to 4 and determined by the reaction Al3+ + H 2O = AlOH2+ + H+. The tip potential (ETip) was approximately -0.90 VSCE and independent of EApp . The low ETip and pH promote H+ reduction, generating atomic and molecular H. Hydrogen bubbles restrict ion movement, substantially increasing the effective crack resistance over bulk conditions. Absorbed atomic hydrogen facilitates HE. The spontaneous transition from slow, incubation to high-rate da/dt coincides with the establishment of a critical aggressive tip chemistry and tip depolarization. Development of the critical occluded chemistry necessary for accelerated da/dt is a competitive process between opposing forces: AD, hydrolysis and migration promote an aggressive environment whereas diffusion reduces concentration gradients, thereby retarding the formation of an aggressive chemistry. Quantitative assessment of the contribution of tip dissolution to crack advance is hindered by a lack of knowledge of two key parameters: the tip corrosion front height and the effective crack conductivity

  4. 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

  5. Factors Affecting the Hydrogen Environment Assisted Cracking Resistance of an AL-Zn-Mg-(Cu) Alloy

    SciTech Connect

    Young, G A; Scully, J R

    2002-04-09

    Precipitation hardenable Al-Zn-Mg alloys are susceptible to hydrogen environment assisted cracking (HEAC) when exposed to aqueous environments. In Al-Zn-Mg-Cu alloys, overaged tempers are used to increase HEAC resistance at the expense of strength but overaging has little benefit in low copper alloys. However, the mechanism or mechanisms by which overaging imparts HEAC resistance is poorly understood. The present research investigated hydrogen uptake, diffusion, and crack growth rate in 90% relative humidity (RH) air for both a commercial copper bearing Al-Zn-Mg-Cu alloy (AA 7050) and a low copper variant of this alloy in order to better understand the factors which affect HEAC resistance. Experimental methods used to evaluate hydrogen concentrations local to a surface and near a crack tip include nuclear reaction analysis (NRA), focused ion beam, secondary ion mass spectroscopy (FIB/SIMS) and thermal desorption spectroscopy (TDS). Results show that overaging the copper bearing alloys both inhibits hydrogen ingress from oxide covered surfaces and decreases the apparent hydrogen diffusion rates in the metal.

  6. The use of potential drop techniques for the evaluation of environment assisted cracking of austenitic alloys

    SciTech Connect

    Lidar, P.; Hwang, I.S.; Ballinger, R.G.

    1992-12-31

    The DC potential drop technique has been adapted for strain measurements. An AC potential drop technique has been developed for crack detection. It has been demonstrated that a DC with switched polarity can have a strain accuracy of {+-}0.12% after yielding and a multi-frequency AC system with up to 200 kHz frequency can have a sensitivity of 50 {mu}m for crack detection. The techniques have been applied to environment assisted cracking tests of Ni-Cr-Fe alloys in 350{degrees}C water and austenitic stainless steel in 288{degrees}C water using both static and dynamic loading. Long term signal stability is maintained given: (1) rigid probe attachments; (2) local preamplification; and (3) adequate lead grounding and shielding. The AC potential drop technique is found to be more suitable for constant load than for dynamic loading and is also compatible with aggressive environments. During dynamic loading, sensitivity can be significantly reduced due to serrated yielding. An analytical model has been developed to predict the DC and AC potential drops in a round bar geometry. A sensitivity analysis has been made to determine test to test variation associated with variations in supplied current, specimen dimensions, and probe spacing. Multifrequency analysis shows that the measured data agrees with the prediction at frequencies up to about 100 kHz. Above 100 kHz induced signal in the probes results in increases in potential drop and phase angle. The induced signal is reproducible and therefore may be related to the crack mouth opening displacement.

  7. Factors Affecting the Hydrogen Environment Assisted Cracking Resistance of an Al-Zn-Mg-(Cu) Alloy

    SciTech Connect

    G.A. Young; J.R. Scully

    2001-09-12

    It is well established that Al-Zn-Mg-(Cu) aluminum alloys are susceptible to hydrogen environment assisted cracking (HEAC) when exposed to aqueous environments. In Al-Zn-Mg-Cu alloys, overaged tempers are commonly used to increase HEAC resistance at the expense of strength. Overaging has little benefit in low copper alloys. However, the mechanism or mechanisms by which overaging imparts HEAC resistance is poorly understood. The present research investigated hydrogen uptake, diffusion, and crack growth rate in 90% relative humidity (RH) air for both a commercial copper bearing Al-Zn-Mg-Cu alloy (AA 7050) and a low copper variant of this alloy in order to better understand the factors which affect HEAC resistance. Experimental methods used to evaluate hydrogen concentrations local to a surface and near a crack tip include nuclear reaction analysis (NRA), focused ion beam, secondary ion mass spectroscopy (FIB/SIMS) and thermal desorption spectroscopy (TDS). When freshly bared coupons of AA 7050 are exposed to 90 C, 90% RH air, hydrogen ingress follows inverse-logarithmic-type kinetics and is equivalent for underaged (HEAC susceptible) and overaged (HEAC resistant) tempers. However, when the native oxide is allowed to form (24 hrs in 25 C, 40% RH lab air) prior to exposure to 90 C, 90% RH air, underaged alloy shows significantly greater hydrogen ingress than the overaged alloy. Humid air is a very aggressive environment producing local ({approx}1{micro}m) hydrogen concentrations in excess of 10,000 wt. ppm at 90 C. In the copper bearing alloy, overaging also effects the apparent diffusivity of hydrogen. As AA 7050 is aged from underaged {yields} peak aged {yields} overaged, the activation energy for hydrogen diffusion increases and the apparent diffusivity for hydrogen decreases, In the low copper alloy, overaging has little effect on hydrogen diffusion. Comparison of the apparent activation energies for hydrogen diffusion and for K independent (stage II) crack growth

  8. The Effect of Microstructural Variation on the Hydrogen Environment-Assisted Cracking of Monel K-500

    NASA Astrophysics Data System (ADS)

    Harris, Zachary D.; Dolph, Justin D.; Pioszak, Greger L.; Rincon Troconis, Brendy C.; Scully, John R.; Burns, James T.

    2016-07-01

    The influence of microstructural variation on hydrogen environment-assisted cracking (HEAC) of Monel K-500 was evaluated using five nominally peak-aged lots of material tested under slow-rising stress intensity loading while immersed in NaCl solution under cathodic polarizations. Minimal variation in HEAC resistance among material lots was observed for an applied potential of -950 mVSCE ( E app, vs saturated calomel), whereas lot-to-lot variability in the fracture morphology demonstrates a significant difference in the HEAC resistance at the less negative potential of -850 mVSCE, suggesting that relatively severe H environments produce sufficient crack-tip H to minimize the impact of metallurgical differences. Sensitivity analyses accomplished by varying the inputs used in decohesion-based, micromechanical models imply significant variations in HEAC resistance are possible for realistic changes in grain boundary toughness, hydrogen uptake behavior, and yield strength. Grain size, impurity segregation (including the effects of gettering elements), grain boundary character/connectivity, and crack path tortuosity are also considered in the context of HEAC susceptibility. Yield strength, global hydrogen content, as well as impurity segregation to grain boundaries, especially boron and sulfur, are speculatively considered to be the dominant contributions in determining HEAC resistance. Modifications that would incorporate the effects of grain boundary segregation are proposed for the K TH model; detailed validation of such changes require high-fidelity and quantitative inputs for the degree of grain boundary segregation. Regardless, fracture mechanics-based HEAC results, detailed microstructural characterization, and micromechanical modeling were successfully coupled to gain insights into the influences governing the microstructure-dependent HEAC susceptibility of Monel K-500.

  9. Slow Strain Rate Tensile Testing to Assess the Ability of Superalloys to Resist Environment-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, ATI 718Plus alloy, Haynes 282, and Inconel 740. 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.

  10. Modeling and experiments to explain the potential dependency of an UHSS to hydrogen environment assisted cracking

    NASA Astrophysics Data System (ADS)

    Kehler, Beth A.

    Modern ultra high strength steels have been developed with outstanding combinations of strength and fracture toughness but lack intrinsic corrosion resistance. Such steels are used by the military for aircraft components such as landing gears but require coatings and cathodic protection which can lead to various rates of hydrogen production depending on material, geometry, and electro(chemistry). The susceptibility of such steels to internal hydrogen embrittlement (IHE) and hydrogen environment embrittlement (HEE) limits their use in marine environments. The objective of this research is to develop the understanding necessary to design coated ultra high strength steels that resist HEE when stressed in marine environments. The cause of HEE is the establishment of high diffusible hydrogen concentrations (CH,diff) at the crack tip. There is a window of applied potentials (Eapplied) where susceptibility to HEE is reduced because CH,diff is reduced. However, Eapplied itself does not yield insight as to the exact conditions at the crack tip. Ohmic potential drop and electrochemical/chemical reactions in the crack can lead to a significantly different environment at the crack tip than on the surface. The issues that hinder understanding of HEE center on the capability to quantify and ultimately predict crack tip hydrogen concentrations (C H,Tip) relative to critical concentrations that trigger fracture as a function of Eapplied. CH,tip was characterized using a multi-pronged approach. Scaling laws were developed to enable measurements of E and pH in a scaled-up crack as a function of the scaling parameter, x2/G and Eapplied . Such measurements were correlated with CH,diff using an experimentally determined hydrogen uptake law based on first order absorption laws and trapping theory. CH,diff values were then used as inputs into existing micromechanical models for KTH and da/dtII to predict cracking susceptibility. The scientific contributions of this work include the

  11. Environmentally assisted cracking behavior of dissimilar metal weldments in simulated BWR coolant environments

    NASA Astrophysics Data System (ADS)

    Huang, J. Y.; Chiang, M. F.; Jeng, S. L.; Huang, J. S.; Kuo, R. C.

    2013-01-01

    The environmentally assisted cracking behavior of dissimilar metal (DM) welds, including Alloy 52-A 508 and Alloy 82-A508, under simulated BWR coolant conditions was studied. Effects of postweld heat treatment and sulfur content of the base metal on the corrosion fatigue and SCC growth rates of DM welds were evaluated. The crack growth rates for the DM weld heat-treated at 621 °C for 24 h were observed to be faster than those for the as-welded. But the DM weld heat-treated at 621 °C for 8 h + 400 °C for 200 h showed better SCC resistance than the as-welded. The longer the heat treatment at 621 °C, the higher the chromium carbides density along the grain boundary was observed. Sulfur could diffuse out of the base metal and segregate along the grain boundaries of the dilution zone, leading to weakening the grain boundary strength and the SCC resistance of the Alloy 52-A508 weld.

  12. Environment-assisted-cracking under measured and/or controlled ectrochemical potential

    SciTech Connect

    Roy, A

    1997-11-07

    Longer-term stress corrosion cracking (SCC) experiments, described in the activity plan E-20-56, are well underway at LLNL to evaluate the SCC susceptibility of candidate corrosion-resistant inner container materials in a 90°ºC acidic brine containing 5 weight percent (wt%) NaCl using fatigue-precracked wedge-loaded double-cantilever-beam (DCB) specimens. The results of a recent localized corrosion study have revealed that the propensity to pitting and crevice corrosion in susceptible alloys is characterized by "critical potentials" obtained from the cyclic potentiodynamic polarization (CPP) experiments described in the activity plan E-20-43/44. It is also well known that the tendency to SCC can be influenced by the electrochemical potential. But the role of electrochemistry in SCC has not been explored to a large extent. Therefore, the proposed activity is aimed at evaluating the SCC behavior of susceptible container materials under measured and/or controlled electrochemical potential in repository-relevant environments using DCB and slow-strain-rate (SSR) test specimens. The magnitude of the controlled potential will be selected based on the measured "critical potentials" obtained from the CPP experiment performed earlier in a similar environment. The resultant data will enable the mechanistic understanding of the cracking process in materials of interest under the synergistic influence of applied stress and corrosive medium, which will be utilized in developing and validating the SCC models for long-term performance assessment.

  13. Microstructural and strain rate effects on the environment-assisted cracking of alpha/beta-titanium alloys in aqueous chloride

    NASA Astrophysics Data System (ADS)

    Richey, Edward, III

    2000-10-01

    The objectives of this research are to determine the effect of microstructure and crack tip strain rate on environment assisted cracking (EAC) of Ti-6Al-2Sn-2Zr-2Mo-2Cr-Si, and to understand crack tip damage in terms of hydrogen/microstructure/plasticity interaction. Beta-extrusion of Ti-6-22-22, in the alpha/beta solution treated and aged (STA) condition, is susceptible to EAC under active loading in NaCl. KJTH is as low as 33% of KJIC and a fracture mode transition to transgranular (alpha-cleavage is affected by chloride exposure. Ti-6-4 (ELI) in chloride solution exhibits a minimum KJTH of 65 MPa√m, corresponding to a mill-annealed microstructure with alpha2 (K JIC = 79 MPa√m), and higher EAC resistance for a Widmanstatten microstructure. EAC growth rates in Ti-6-4 (ELI) average 3mum/s and are 10-fold slower than those for Ti-6-22-22. Ti-6-22-22 was susceptible to EAC for active loading rates ranging between 10--4 MPa√m/s and 5 Mpa√m/s. alpha2, formed during slow cooling or isothermal aging, dominates the EAC susceptibility of Ti-6-22-22. alpha/beta microstructures without intermetallics or alphas exhibit the highest EAC resistance (KJTH = 50 MPa√m, KJIC = 74 MPa√m). alpha 2 promotes a large reduction in the EAC threshold; KJTH = 34 MPa√m when alpha2 and alphas are present (KJIC = 69 MPa√m). For all microstructures, the fracture path is transgranular through alpha plates. Based on hydrogen environment embrittlement, the increased EAC in STA Ti-6-22-22 vs STA Ti-6-4 is due to increased strain localization occurring in the Ti-6-22-22 which results in larger slip offsets at the surface and increased hydrogen uptake. alphas precipitates in Ti-6--22--22 may exacerbate strain localization; alphas precipitates were not observed in Ti-6-4. A change in the operative dislocation mechanism to dislocation looping would have homogenized deformation and reduced EAC susceptibility; rather, severe EAC was observed in all aged Ti-6-22-22 microstructures

  14. 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

  15. Technical basis for the initiation and cessation of environmentally-assisted cracking of low-alloy steels in elevated temperature PWR environments

    SciTech Connect

    James, L.A.

    1997-10-01

    The Section 11 Working Group on Flaw Evaluation of the ASME B and PV Code Committee is considering a Code Case to allow the determination of the conditions under which environmentally-assisted cracking of low-alloy steels could occur in PWR primary environments. This paper provides the technical support basis for such an EAC Initiation and Cessation Criterion by reviewing the theoretical and experimental information in support of the proposed Code Case.

  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. 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.

  18. Measurement and Modeling of Hydrogen Environment-Assisted Cracking in a Ni-Cu-Al-Ti Superalloy

    NASA Astrophysics Data System (ADS)

    Burns, James T.; Harris, Zachary D.; Dolph, Justin D.; Gangloff, Richard P.

    2016-03-01

    This research improves H decohesion mechanism-based modeling of intergranular stress corrosion cracking in a Ni-Cu superalloy, Monel K-500. New cracking data plus improved model parameters lead to accurate predictions of the cathodic potential dependencies of K TH and H diffusion-limited d a/d t II for Monel K-500 under slow-rising K in 0.6 M NaCl solution. Experiments and modeling demonstrate that IGSCC is eliminated for applied potentials more positive than a critical level between -900 and -840 mVSCE, but slow-subcritical cracking persists by a microvoid-based mechanism.

  19. 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.

  20. 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.

  1. 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.

  2. Path planning for machine vision assisted, teleoperated pavement crack sealer

    SciTech Connect

    Kim, Y.S.; Haas, C.T.; Greer, R.

    1998-03-01

    During the last few years, several teleoperated and machine-vision-assisted systems have been developed in construction and maintenance areas such as pavement crack sealing, sewer pipe rehabilitation, excavation, surface finishing, and materials handling. This paper presents a path-planning algorithm used for a machine-vision-assisted automatic pavement crack sealing system. In general, path planning is an important task for optimal motion of a robot whether its environment is structured or unstructured. Manual path planning is not always possible or desirable. A simple greedy path algorithm is utilized for optimal motion of the automated pavement crack sealer. Some unique and broadly applicable computational tools and data structures are required to implement the algorithm in a digital image domain. These components are described, then the performance of the algorithm is compared with the implicit manual path plans of system operators. The comparison is based on computational cost versus overall gains in crack-sealing-process efficiency. Applications of this work in teleoperation, graphical control, and other infrastructure maintenance areas are also suggested.

  3. 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.

  4. Initiation of environmentally-assisted cracking in low-alloy steels

    SciTech Connect

    Wire, G.L.; Li, Y.Y.

    1996-06-01

    Environmentally-Assisted Cracking (EAC) in low alloy steels is activated by a critical level of sulfide ions at the crack tip, which is produced from dissolution of sulfide inclusions (MnS, FeS, etc.) in the steel following exposure by a growing crack. EAC of concern herein is the increase of fatigue crack growth rate of up to 40 to 100 times the rate in air that occurs at 240--300 C in high temperature LWR or boiler water environments. The initiation of EAC is the onset of the higher fatigue crack growth rates in fully developed cracks already presumed to be present due to fatigue, stress corrosion cracking, or induced by fabrication. Initiation of EAC is induced by a change in loading parameters causing the fatigue crack growth rate to increase from a small multiple (2--4) to 40--100 times the air rate. A steady state theory developed by Combrade, suggests that EAC will initiate only above a critical crack velocity and cease below this same velocity. However, more recent tests show that EAC can persist down to much lower velocities (100 times lower) in low oxygen water at slightly lower temperatures. A special set of experiments on high sulfur plate material demonstrate that EAC will not initiate from surface cracks with low sulfide inventories at low crack tip velocities. Transient diffusion calculations show that a finite crack extension at a high crack tip velocity is necessary to initiate EAC, providing a possible explanation for the lack of high crack growth observations reported in low alloy steels in structural applications involving low oxygen environments.

  5. 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.

  6. 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.

  7. Cracking-assisted photolithography for mixed-scale patterning and nanofluidic applications.

    PubMed

    Kim, Minseok; Ha, Dogyeong; Kim, Taesung

    2015-01-01

    Cracks are observed in many environments, including walls, dried wood and even the Earth's crust, and are often thought of as an unavoidable, unwanted phenomenon. Recent research advances have demonstrated the the ability to use cracks to produce various micro and nanoscale patterns. However, patterns are usually limited by the chosen substrate material and the applied tensile stresses. Here we describe an innovative cracking-assisted nanofabrication technique that relies only on a standard photolithography process. This novel technique produces well-controlled nanopatterns in any desired shape and in a variety of geometric dimensions, over large areas and with a high throughput. In addition, we show that mixed-scale patterns fabricated using the 'crack-photolithography' technique can be used as master moulds for replicating numerous nanofluidic devices via soft lithography, which to the best of our knowledge is a technique that has not been reported in previous studies on materials' mechanical failure, including cracking.

  8. Cracking-assisted photolithography for mixed-scale patterning and nanofluidic applications

    NASA Astrophysics Data System (ADS)

    Kim, Minseok; Ha, Dogyeong; Kim, Taesung

    2015-02-01

    Cracks are observed in many environments, including walls, dried wood and even the Earth’s crust, and are often thought of as an unavoidable, unwanted phenomenon. Recent research advances have demonstrated the the ability to use cracks to produce various micro and nanoscale patterns. However, patterns are usually limited by the chosen substrate material and the applied tensile stresses. Here we describe an innovative cracking-assisted nanofabrication technique that relies only on a standard photolithography process. This novel technique produces well-controlled nanopatterns in any desired shape and in a variety of geometric dimensions, over large areas and with a high throughput. In addition, we show that mixed-scale patterns fabricated using the ‘crack-photolithography’ technique can be used as master moulds for replicating numerous nanofluidic devices via soft lithography, which to the best of our knowledge is a technique that has not been reported in previous studies on materials’ mechanical failure, including cracking.

  9. Research progress on expansive soil cracks under changing environment.

    PubMed

    Shi, Bei-xiao; Zheng, Cheng-feng; Wu, Jin-kun

    2014-01-01

    Engineering problems shunned previously rise to the surface gradually with the activities of reforming the natural world in depth, the problem of expansive soil crack under the changing environment becoming a control factor of expansive soil slope stability. The problem of expansive soil crack has gradually become a research hotspot, elaborates the occurrence and development of cracks from the basic properties of expansive soil, and points out the role of controlling the crack of expansive soil strength. We summarize the existing research methods and results of expansive soil crack characteristics. Improving crack measurement and calculation method and researching the crack depth measurement, statistical analysis method, crack depth and surface feature relationship will be the future direction. PMID:25013869

  10. 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.

  11. Threshold velocity for environmentally-assisted cracking in low alloy steels

    SciTech Connect

    Wire, G.L.; Kandra, J.T.

    1997-04-01

    Environmentally Assisted Cracking (EAC) in low alloy steels is generally believed to be activated by dissolution of MnS inclusions at the crack tip in high temperature LWR environments. EAC is the increase of fatigue crack growth rate of up to 40 to 100 times the rate in air that occurs in high temperature LWR environments. A steady state theory developed by Combrade, suggested that EAC will initiate only above a critical crack velocity and cease below this same velocity. A range of about twenty in critical crack tip velocities was invoked by Combrade, et al., to describe data available at that time. This range was attributed to exposure of additional sulfides above and below the crack plane. However, direct measurements of exposed sulfide densities on cracked specimens were performed herein and the results rule out significant additional sulfide exposure as a plausible explanation. Alternatively, it is proposed herein that localized EAC starting at large sulfide clusters reduces the calculated threshold velocity from the value predicted for a uniform distribution of sulfides. Calculations are compared with experimental results where the threshold velocity has been measured, and the predicted wide range of threshold values for steels of similar sulfur content but varying sulfide morphology is observed. The threshold velocity decreases with the increasing maximum sulfide particle size, qualitatively consistent with the theory. The calculation provides a basis for a conservative minimum velocity threshold tied directly to the steel sulfur level, in cases where no details of sulfide distribution are known.

  12. Crack growth rates of nickel alloy welds in a PWR environment.

    SciTech Connect

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

    2006-05-31

    In light water reactors (LWRs), vessel internal components made of nickel-base alloys are susceptible to environmentally assisted cracking. A better understanding of the causes and mechanisms of this cracking may permit less conservative estimates of damage accumulation and requirements on inspection intervals. A program is being conducted at Argonne National Laboratory to evaluate the resistance of Ni alloys and their welds to environmentally assisted cracking in simulated LWR coolant environments. This report presents crack growth rate (CGR) results for Alloy 182 shielded-metal-arc weld metal in a simulated pressurized water reactor (PWR) environment at 320 C. Crack growth tests were conducted on 1-T compact tension specimens with different weld orientations from both double-J and deep-groove welds. The results indicate little or no environmental enhancement of fatigue CGRs of Alloy 182 weld metal in the PWR environment. The CGRs of Alloy 182 in the PWR environment are a factor of {approx}5 higher than those of Alloy 600 in air under the same loading conditions. The stress corrosion cracking for the Alloy 182 weld is close to the average behavior of Alloy 600 in the PWR environment. The weld orientation was found to have a profound effect on the magnitude of crack growth: cracking was found to propagate faster along the dendrites than across them. The existing CGR data for Ni-alloy weld metals have been compiled and evaluated to establish the effects of key material, loading, and environmental parameters on CGRs in PWR environments. The results from the present study are compared with the existing CGR data for Ni-alloy welds to determine the relative susceptibility of the specific Ni-alloy weld to environmentally enhanced cracking.

  13. 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.

  14. A ``Hydrogen partitioning'' model for hydrogen assisted crack growth

    NASA Astrophysics Data System (ADS)

    Gao, M.; Wei, R. P.

    1985-11-01

    A “hydrogen partitioning” model has been developed to account for the pressure and temperature dependence for hydrogen-assisted crack growth. The model gives explicit recognition to the role of hydr en-microstructure interactions in determining the distribution (or partitioning) of hydrogen among the various microstructural elements (principally between the prior-austenite grain boundaries and the matrix) and the rate of crack growth along the elements. It also takes into account the role of various rate controlling processes in determining the rate that hydrogen is being supplied to the fracture process (or embrittlement) zone. Quantitative assessment of the model indicates very good agreements between the model predictions and the observed crack growth responses for AISI 4340 and 4130 steels tested in hydrogen and for AISI 4340 steel tested in hydrogen sulfide. This model accurately characterizes the reduction in crack growth rate and the concomitant change in fracture mode at “high” temperatures. Through its integration with the earlier models, based on rate controlling processes, the model predicts the pressure and temperature dependence for K-independent crack growth over the entire range of environmental conditions.

  15. Effects of microstructure banding on hydrogen assisted fatigue crack growth in X65 pipeline steels

    SciTech Connect

    Ronevich, Joseph A.; Somerday, Brian P.; San Marchi, Chris W.

    2015-09-10

    Banded ferrite-pearlite X65 pipeline steel was tested in high pressure hydrogen gas to evaluate the effects of oriented pearlite on hydrogen assisted fatigue crack growth. Test specimens were oriented in the steel pipe such that cracks propagated either parallel or perpendicular to the banded pearlite. The ferrite-pearlite microstructure exhibited orientation dependent behavior in which fatigue crack growth rates were significantly lower for cracks oriented perpendicular to the banded pearlite compared to cracks oriented parallel to the bands. Thus the reduction of hydrogen assisted fatigue crack growth across the banded pearlite is attributed to a combination of crack-tip branching and impeded hydrogen diffusion across the banded pearlite.

  16. Environmentally Assisted Cracking of Commercial Ni-Cr-Mo Alloys - A Review

    SciTech Connect

    Rebak, R B

    2004-11-09

    Nickel-Chromium-Molybdenum alloys (Ni-Cr-Mo) are highly resistant to general corrosion, localized corrosion and environmentally assisted cracking (EAC). Cr acts as a beneficial element under oxidizing acidic conditions and Mo under reducing conditions. All three elements (Ni, Cr and Mo) act synergistically to provide resistance to EAC in environments such as hot concentrated chloride solutions. Ni-Cr-Mo alloys may suffer EAC in environments such as hot caustic solutions, hot wet hydrofluoric acid (HF) solutions and in super critical water oxidation (SCWO) applications. Not all the Ni-Cr-Mo alloys have the same susceptibility to cracking in the mentioned environments. Most of the available data regarding EAC is for the oldest Ni-Cr-Mo alloys such as N10276 and N06625.

  17. Environment Assisted Precision Magnetometry

    NASA Astrophysics Data System (ADS)

    Cappellaro, P.; Goldstein, G.; Maze, J. R.; Jiang, L.; Hodges, J. S.; Sorensen, A. S.; Lukin, M. D.

    2010-03-01

    We describe a method to enhance the sensitivity of magnetometry and achieve nearly Heisenberg-limited precision measurement using a novel class of entangled states. An individual qubit is used to sense the dynamics of surrounding ancillary qubits, which are in turn affected by the external field to be measured. The resulting sensitivity enhancement is determined by the number of ancillas strongly coupled to the sensor qubit, it does not depend on the exact values of the couplings (allowing to use disordered systems), and is resilient to decoherence. As a specific example we consider electronic spins in the solid-state, where the ancillary system is associated with the surrounding spin bath. The conventional approach has been to consider these spins only as a source of decoherence and to adopt decoupling scheme to mitigate their effects. Here we describe novel control techniques that transform the environment spins into a resource used to amplify the sensor spin response to weak external perturbations, while maintaining the beneficial effects of dynamical decoupling sequences. We discuss specific applications to improve magnetic sensing with diamond nano-crystals, using one Nitrogen-Vacancy center spin coupled to Nitrogen electronic spins.

  18. Environmentally assisted cracking in light water reactors. Semiannual report, April 1994--September 1994, Volume 19

    SciTech Connect

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

    1995-09-01

    This report summarizes work performed by Argonne National Laboratory (ANL) on fatigue and environmentally assisted cracking (EAC) in light water reactors from April to September 1994. Topics that have been investigated include (a) fatigue of carbon and low-alloy steel used in piping and reactor pressure vessels, (b) EAC of austenitic stainless steels (SSs) and Alloy 600, and (c) irradiation-assisted stress corrosion cracking (IASCC) of Type 304 SS. Fatigue tests have been conducted on A106-Gr B and A533-Gr B steels in oxygenated water 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 data were obtained on fracture-mechanics specimens of SSs and Alloy 600 to investigate EAC in simulated boiling water reactor (BWR) and pressurized water reactor environments at 289{degrees}C. The data were compared with predictions from crack growth correlations developed at ANL for SSs in water and from rates in air from Section XI of the ASME Code. Microchemical 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 to determine whether trace impurity elements may contribute to IASCC of these materials.

  19. The effect of aqueous environments upon the initiation and propagation of fatigue cracks in low-alloy steels

    SciTech Connect

    James, L.A.; Van Der Sluys, W.A.

    1996-01-01

    The effect of elevated temperature aqueous environments upon the initiation and propagation of fatigue cracks in low-alloy steels is discussed in terms of the several parameters which influence such behavior. These parameters include water chemistry, impurities within the steels themselves, as well as factors such as the water flow rate, loading waveform and loading rates. Some of these parameters have similar effects upon both crack initiation and propagation, while others exhibit different effects in the two stages of cracking. In the case of environmentally-assisted crack (EAC) growth, the most important impurities within the steel are metallurgical sulfide inclusions which dissolve upon contact with the water. A ``critical`` concentration of sulfide ions at the crack tip can then induce environmentally-assisted cracking which proceeds at significantly increased crack growth rates over those observed in air. The occurrence, or non-occurrence, of EAC is governed by the mass-transport of sulfide ions to and from the crack-tip region, and the mass-transport is discussed in terms of diffusion, ion migration, and convection induced within the crack enclave. Examples are given of convective mass-transport within the crack enclave resulting from external free stream flow. The initiation of fatigue cracks in elevated temperature aqueous environments, as measured by the S-N fatigue lifetimes, is also strongly influenced by the parameters identified above. The influence of sulfide inclusions does not appear to be as strong on the crack initiation process as it is on crack propagation. The oxygen content of the environment appears to be the dominant factor, although loading frequency (strain rate) and temperature are also important factors.

  20. Computer Assisted Virtual Environment - CAVE

    SciTech Connect

    Erickson, Phillip; Podgorney, Robert; Weingartner, Shawn; Whiting, Eric

    2014-01-14

    Research at the Center for Advanced Energy Studies is taking on another dimension with a 3-D device known as a Computer Assisted Virtual Environment. The CAVE uses projection to display high-end computer graphics on three walls and the floor. By wearing 3-D glasses to create depth perception and holding a wand to move and rotate images, users can delve into data.

  1. Computer Assisted Virtual Environment - CAVE

    ScienceCinema

    Erickson, Phillip; Podgorney, Robert; Weingartner, Shawn; Whiting, Eric

    2016-07-12

    Research at the Center for Advanced Energy Studies is taking on another dimension with a 3-D device known as a Computer Assisted Virtual Environment. The CAVE uses projection to display high-end computer graphics on three walls and the floor. By wearing 3-D glasses to create depth perception and holding a wand to move and rotate images, users can delve into data.

  2. Temperature and environmentally assisted cracking in low alloy steel

    SciTech Connect

    Auten, T.A.; Monter, J.V.

    1995-04-01

    Environmental assisted cracking (EAC) can be defined as the propagation of fatigue cracks in water at rates from 3 to over 40 times the growth rates in air. For low alloy steels with sulfur contents > 0.0125% by weight, EAC is normal behavior in the 240 to 290C range. However, literature yields mixed results for low alloy steels with compositions just below this sulfur level; some reports indicate EAC while others do not. Also, several authors have reported an increased tendency toward EAC when the water temperatures were lowered. In the present work, five ASTM A 508 Class 2 forgings with ladle and check analyses that ranged from 0.010 to 0.019 wt% S were tested in high purity deaerated water in the temperature range of 93 to 260C. At 260C these forgings did not exhibit EAC, reinforcing earlier results for two similar forgings. This broad sampling indicates strong resistance to EAC for this class of forging at 260C. On the other hand, EAC occurred consistently in the three of these forgings that were tested below 204C, provided the test conditions (loading frequency, {Delta}K, and R) were high enough to produce a high baseline fatigue crack growth rate (FCGR), where the baseline FCGR is that expected in air. At 149C, EAC occurred at test conditions that combined to yield a baseline FCGR greater than {approx}2E-6 mm/s. At 204, 121, and 93C, this critical crack growth rate appeared to shift to lower baseline values. The EAC that occurred at lower temperatures was a factor of 3 to 12 times higher than baseline air rates, which was not as strong as the effect for higher sulfur steels at 240 to 290C. Also, no plateau in the growth rates occurred as it does with the higher sulfur steels. In another approach, EAC was induced at 93 and at 260C by raising the dissolved oxygen content of the water from <10 to >15 ppb.

  3. 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

  4. Environmentally assisted cracking in Light Water Reactors: Semiannual report, October 1994--March 1995. Volume 20

    SciTech Connect

    Chung, H.M.; Chopra, O.K.; Gavenda, D.J.; Hins, A.G.; Kassner, T.F.; Ruther, W.E.; Shack, W.J.; Soppet, W.K.

    1996-01-01

    This report summarizes work performed by Argonne National Laboratory on fatigue and environmentally assisted cracking (EAC) in light water reactors (LWRS) from October 1994 to March 1995. Topics that have been investigated include (a) fatigue of carbon and low-alloy steel used in reactor piping and pressure vessels, (b) EAC of Alloy 600 and 690, and (c) irradiation-assisted stress corrosion cracking (IASCC) of Type 304 SS. Fatigue tests were conducted on ferritic steels in water with several dissolvedoxygen (DO) concentrations to determine whether a slow strain rate applied during different portions of a tensile-loading cycle are equally effective in decreasing fatigue life. Tensile properties and microstructures of several heats of Alloy 600 and 690 were characterized for correlation with EAC of the alloys in simulated LWR environments. Effects of DO and electrochemical potential on susceptibility to intergranular cracking of high- and commercial-purity Type 304 SS specimens from control-blade absorber tubes and a control-blade sheath irradiated in boiling water reactors were determined in slow-strain-rate-tensile tests at 289{degrees}C. 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.

  5. Effects of microstructure banding on hydrogen assisted fatigue crack growth in X65 pipeline steels

    DOE PAGESBeta

    Ronevich, Joseph A.; Somerday, Brian P.; San Marchi, Chris W.

    2015-09-10

    Banded ferrite-pearlite X65 pipeline steel was tested in high pressure hydrogen gas to evaluate the effects of oriented pearlite on hydrogen assisted fatigue crack growth. Test specimens were oriented in the steel pipe such that cracks propagated either parallel or perpendicular to the banded pearlite. The ferrite-pearlite microstructure exhibited orientation dependent behavior in which fatigue crack growth rates were significantly lower for cracks oriented perpendicular to the banded pearlite compared to cracks oriented parallel to the bands. Thus the reduction of hydrogen assisted fatigue crack growth across the banded pearlite is attributed to a combination of crack-tip branching and impededmore » hydrogen diffusion across the banded pearlite.« less

  6. Effects of crack tip plastic zone on corrosion fatigue cracking of alloy 690(TT) in pressurized water reactor environments

    NASA Astrophysics Data System (ADS)

    Xiao, J.; Qiu, S. Y.; Chen, Y.; Fu, Z. H.; Lin, Z. X.; Xu, Q.

    2015-01-01

    Alloy 690(TT) is widely used for steam generator tubes in pressurized water reactor (PWR), where it is susceptible to corrosion fatigue. In this study, the corrosion fatigue behavior of Alloy 690(TT) in simulated PWR environments was investigated. The microstructure of the plastic zone near the crack tip was investigated and labyrinth structures were observed. The relationship between the crack tip plastic zone and fatigue crack growth rates and the environment factor Fen was illuminated.

  7. 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.

  8. 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

  9. 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

  10. 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

  11. 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

  12. The initiation of environmentally-assisted cracking in semi-elliptical surface cracks

    SciTech Connect

    James, L.A.

    1997-02-01

    A criterion to predict under what conditions EAC would Initiate In cracks In a high-sulfur steel in contact with low-oxygen water was recently proposed by Wire and U. This EAC Initiation Criterion was developed using transient analyses for the diffusion of sulfides plus experimental test results. The experiments were conducted mainly on compact tension-type specimens with initial crack depths of about 2.54 mm. The present paper expands upon the work of Wire and U by presenting results for significantly deeper initial semi-elliptical surface cracks. In addition, in one specimen, the surface crack penetrated weld-deposited cladding into the high-sulfur steel. The results for the semi-elliptical surface cracks agreed quite well with the EAC Initiation Criterion, and provide confirmation of the applicability of the criterion to crack configurations with more restricted access to water.

  13. Clay with Desiccation Cracks is an Advection Dominated Environment

    NASA Astrophysics Data System (ADS)

    Baram, S.; Kurtzman, D.; Sher, Y.; Ronen, Z.; Dahan, O.

    2012-04-01

    , indicating deep soil evaporation. Daily fluctuation of the air temperature in the desiccation cracks supported thermally induced air convection within the cracks void and could explain the deep soil salinization process. Combination of all the abovementioned observations demonstrated that the formation of desiccation cracks network in dispersive clay sediments generates a bulk advection dominated environment for both air and water flow, and that the reference to clay sediments as "hydrologically safe" should to be reconsidered.

  14. Cracking-assisted fabrication of nanoscale patterns for micro/nanotechnological applications

    NASA Astrophysics Data System (ADS)

    Kim, Minseok; Kim, Dong-Joo; Ha, Dogyeong; Kim, Taesung

    2016-05-01

    Cracks are frequently observed in daily life, but they are rarely welcome and are considered as a material failure mode. Interestingly, cracks cause critical problems in various micro/nanofabrication processes such as colloidal assembly, thin film deposition, and even standard photolithography because they are hard to avoid or control. However, increasing attention has been given recently to control and use cracks as a facile, low-cost strategy for producing highly ordered nanopatterns. Specifically, cracking is the breakage of molecular bonds and occurs simultaneously over a large area, enabling fabrication of nanoscale patterns at both high resolution and high throughput, which are difficult to obtain simultaneously using conventional nanofabrication techniques. In this review, we discuss various cracking-assisted nanofabrication techniques, referred to as crack lithography, and summarize the fabrication principles, procedures, and characteristics of the crack patterns such as their position, direction, and dimensions. First, we categorize crack lithography techniques into three technical development levels according to the directional freedom of the crack patterns: randomly oriented, unidirectional, or multidirectional. Then, we describe a wide range of novel practical devices fabricated by crack lithography, including bioassay platforms, nanofluidic devices, nanowire sensors, and even biomimetic mechanosensors.

  15. Hydrogen assisted cracking and inhibition of spring alloys in acidizing solutions

    SciTech Connect

    Coyle, W.R.; Chitwood, G.B.; Rice, P.W.; Walker, M.L.

    1994-12-31

    Several experiments were conducted to investigate and compare the hydrogen assisted cracking resistance of high strength, corrosion resistant spring alloys to acidizing fluids. Two cobalt-based alloys, UNS R30035 and UNS R30003, and one nickel-based alloy, UNS N07750, were evaluated. The tests involved exposing stressed spring segments of all alloys and C-rings of R30035 to uninhibited 28% HCl, 28% HCl with two different inhibitors, and the NACE TM0177 solution. Failures of N07750 spring segments in the uninhibited acid parallel field performance of this alloy. There were no failures of the R30035 or R30003 spring segments in the environments tested. Springs made from N07750 are more susceptible to hydrogen embrittlement than either R30035 or R30003. The C-ring tests of R30035 revealed the benefit of corrosion inhibition as a means of elevating the threshold cracking stress and increasing the time to failure in corrosive media. A strong beneficial effect of elevated-temperature thermal processing was observed for UNS R30035. High performance acidizing inhibitors are required in order to provide effective protection to high alloy spring materials.

  16. 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.

  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. 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 , ...

  19. Subcritical crack growth in glasses under cyclic loads: Effect of hydrodynamic pressure in aqueous environments

    SciTech Connect

    Yi, K.S.; Dill, S.J.; Dauskardt, R.H.

    1997-07-01

    The effect of hydrodynamic pressure developed in the wake of a crack growing in a brittle material under cyclic loads in an aqueous environment is considered. The pressure acts in opposition to the movement of the crack faces, thus shielding the crack up from the applied loads. A general hydrodynamic fluid pressure relation based on a one-dimensional Reynolds equation, which applicable to a crack with an arbitrary crack opening profile, is developed. The model is modified to account for side flow through the thickness of the sample and cavitation near the crack tip. Both effects significantly modify the hydrodynamic pressure distribution. Finally, the resulting hydrodynamic pressure relations are combined with a fracture mechanics model to account for the change in the near-tip stress intensity. Resulting predictions of the cyclic crack-growth rate are found to be in good agreement with measured values for a borosilicate glass tested at various frequencies in a water environment.

  20. Modelling of hydrogen assisted cracking of nickel-base Alloy X-750 in water

    SciTech Connect

    Oka, T.; Ballinger, R.G.; Hwang, I.S.

    1992-12-31

    A closed-form, semi-empirical, electrochemical model has been developed to rationalize the intergranular corrosion fatigue behavior of alloy X-750 in aqueous electrolytes. The model is based on the assumption that, in the electrolytes investigated and for the microstructures studied, that hydrogen assisted crack growth is the dominant mechanism. Further, it is assumed that the rate of hydrogen reduction is a controlling factor in the magnitude of the environmental component of crack growth. Electrolyte conductivity, dissolution and passivation kinetics of precipitates, grain boundary coverage of precipitates are identified as important environmental and microstructural variables governing the hydrogen reduction rate at the crack tip. The model is compared with experimental data for fatigue crack growth where hydrogen is supplied by external charging and with data where galvanically-generated local hydrogen is responsible for enhanced crack growth. It is shown that predicted results characterize the observed effects of frequency, microstructure, electrolyte conductivity, and stress intensity factor. The agreement between the hydrogen reduction model and measured crack growth rate is believed to support the proposed galvanic corrosion mechanism for the intergranular cracking of alloy X-750 in low temperature water.

  1. Adaptive Dialogue Systems for Assistive Living Environments

    ERIC Educational Resources Information Center

    Papangelis, Alexandros

    2013-01-01

    Adaptive Dialogue Systems (ADS) are intelligent systems, able to interact with users via multiple modalities, such as speech, gestures, facial expressions and others. Such systems are able to make conversation with their users, usually on a specific, narrow topic. Assistive Living Environments are environments where the users are by definition not…

  2. 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.

  3. 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.

  4. 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.

  5. Grain boundary chemistry effects on environment-induced crack growth of iron-based alloys

    SciTech Connect

    Jones, R.H.

    1992-11-01

    Relation between grain boundary chemistry and environment-induced crack growth of Fe-based alloys is reviewed. The importance of the cleanliness of steels is clearly demonstrated by direct relations between grain boundary chemistry and crack growth behavior for both H and anodic dissolution-induced crack growth. Relationships between strain to failure, work of fracture, K{sub ISCC}, crack velocity and fracture mode and grain boundary chemistry are presented. Only results in which the grain boundary chemistry has been measured directly by Auger electron spectroscopy (AES) on intergranular surfaces exposed by in situ fracture have been considered in this review.

  6. Grain boundary chemistry effects on environment-induced crack growth of iron-based alloys

    SciTech Connect

    Jones, R.H.

    1992-11-01

    Relation between grain boundary chemistry and environment-induced crack growth of Fe-based alloys is reviewed. The importance of the cleanliness of steels is clearly demonstrated by direct relations between grain boundary chemistry and crack growth behavior for both H and anodic dissolution-induced crack growth. Relationships between strain to failure, work of fracture, K[sub ISCC], crack velocity and fracture mode and grain boundary chemistry are presented. Only results in which the grain boundary chemistry has been measured directly by Auger electron spectroscopy (AES) on intergranular surfaces exposed by in situ fracture have been considered in this review.

  7. Effects of chemical environments on slow crack growth in glasses and ceramics

    NASA Astrophysics Data System (ADS)

    Freiman, S. W.

    1984-06-01

    This paper presents a review of our current understanding of environmentally induced slow crack growth in glasses, single crystals, and polycrystalline ceramics. It is shown that the rate of crack growth is controlled by the chemical activity of the active species in the environment as well as by the stress intensity at the crack tip. A recently developed molecular model of stress-induced chemical reaction between vitreous silica and water is described. The implications of this model for the effects of other chemical species on crack growth are discussed. Finally, the complications introduced by the presence of grain boundaries in polycrystalline ceramics are pointed out.

  8. 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.

  9. Hydrogen-assisted stable crack growth in iron-3 wt% silicon steel

    SciTech Connect

    Marrow, T.J.; Prangnell, P.; Aindow, M.; Strangwood, M.; Knott, J.F.

    1996-08-01

    Observations of internal hydrogen cleavage in Fe-3Si are reported. Hydrogen-assisted stable crack growth (H-SCG) is associated with cleavage striations of a 300 nm spacing, observed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). High resolution SEM revealed finer striations, previously undetected, with a spacing of approximately 30 nm. These were parallel to the coarser striations. Scanning tunneling microscopy (STM) also showed the fine striation spacing, and gave a striation height of approximately 15 nm. The crack front was not parallel to the striations. Transmission electron microscopy (TEM) of crack tip plastic zones showed {l_brace}112{r_brace} and {l_brace}110{r_brace} slip, with a high dislocation density (around 10{sup 14}m{sup {minus}2}). The slip plane spacing was approximately 15--30 nm. Parallel arrays of high dislocation density were observed in the wake of the hydrogen cleavage crack. It is concluded that H-ScG in Fe-3Si occurs by periodic brittle cleavage on the {l_brace}001{r_brace} planes. This is preceded by dislocation emission. The coarse striations are produced by crack tip blunting and the fine striations by dislocations attracted by image forces to the fracture surface after cleavage. The effects of temperature, pressure and yield strength on the kinetics of H-SCG can be predicted using a model for diffusion of hydrogen through the plastic zone.

  10. 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.

  11. Innovative Approach to Establish Root Causes for Cracking in Aggressive Reactor Environments

    SciTech Connect

    Bruemmer, Stephen M.; Thomas, Larry E.; Vetrano, John S.; Simonen, Edward P.

    2003-10-31

    The research focuses on the high-resolution characterization of degradation microstructures and microchemistries in specimens tested under controlled conditions for the environment and for the material where in-service complexities can be minimized. Thermodynamic and kinetic modeling of crack-tip processes is employed to analyze corrosion-induced structures and gain insights into degradation mechanisms. Novel mechanistic ''fingerprinting'' of crack-tip structures is used to isolate causes of environmental cracking in tandem with quantitative measurements of crack growth. Sample preparation methods and advanced analytical techniques are used to characterize corrosion/oxidation reactions and crack-tip structures at near atomic dimensions in order to gain insight into fundamental environmental cracking mechanisms. Reactions at buried interfaces, not accessible by conventional approaches, are being systematically interrogated. Crack-growth experiments in high-temperature water environments are evaluating and isolating the effects of material condition (matrix strength, grain boundary composition and precipitation) on stress corrosion cracking (SCC). The fundamental understanding of crack advance mechanisms will establish the basis to design new corrosion-resistant alloys for current light-water reactors and advanced reactor systems.

  12. Hydrogen assisted cracking of 2205 duplex stainless steel in synthetic sea water

    NASA Astrophysics Data System (ADS)

    Michalska, J.; Łabanowski, J.; Ćwiek, J.

    2012-05-01

    The cracking behavior of 2205 duplex stainless steels (DSSs) in synthetic sea water under cathodic polarization condition was investigated. (SSRT) method was employed in aim to evaluate the susceptibility to hydrogen assisted cracking. The results showed that the reduction in the uniform elongation (UEL) and the reduction of area (RA) varied with the applied cathodic current density. Significant reductions in ductility were found, indicating its susceptibility to hydrogen-assisted fracture at current density of 10 mA cm-2. Fractographical examinations showed that increase in hydrogenation current density cause an increase in brittle character on the fracture surface. Complete brittle fractures were observed after SSRT at10 and 20 mA cm-2.

  13. 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.

  14. Fatigue Crack Propagation from Notched Specimens of 304 SS in elevated Temperature Aqueous Environment

    SciTech Connect

    Wire, G. L.; Mills, W. J.

    2002-08-01

    Fatigue crack propagation (FCP) rates for 304 stainless steel (304SS) were determined in 24 degree C and 288 degree C air and 288 degree C water using double-edged notch (DEN) specimens of 304 stainless steel (304 SS). Test performed at matched loading conditions in air and water at 288 degree C with 20-6- cc h[sub]2/kg h[sub]2O provided a direct comparison of the relative crack growth rates in air and water over a wide range of crack growth rates. The DEN crack extension ranged from short cracks (0.03-0.25 mm) to long cracks up to 4.06 mm, which are consistent with conventional deep crack tests. Crack growth rates of 304 SS in water were about 12 times the air rate. This 12X environmental enhancement persisted to crack extensions up to 4.06 mm, far outside the range associated with short crack effects. The large environmental degradation for 304 SS crack growth is consistent with the strong reduction of fatigue life in high hydrogen water. Further, very similar environmental effects w ere reported in fatigue crack growth tests in hydrogen water chemistry (HWC). Most literature data in high hydrogen water show only a mild environmental effect for 304 SS, of order 2.5 times air or less, but the tests were predominantly performed at high cyclic stress intensity or equivalently, high air rates. The environmental effect in low oxygen environments at low stress intensity depends strongly on both the stress ratio, R, and the load rise time, T[sub]r, as recently reported for austenitic stainless steel in BWR water. Fractography was performed for both tests in air and water. At 288 degree C in water, the fracture surfaces were crisply faceted with a crystallographic appearance, and showed striations under high magnification. The cleavage-like facets on the fracture surfaces suggest that hydrogen embrittlement is the primary cause of accelerated cracking.

  15. Influence of environment on the fatigue crack growth behaviour of 12% Cr steel.

    PubMed

    Schönbauer, Bernd M; Stanzl-Tschegg, Stefanie E

    2013-12-01

    In the present work, the influence of different environments on the fatigue crack growth behaviour of 12% Cr steam turbine blade steel is investigated. Fatigue crack growth rates (FCGRs) in the near threshold regime are measured with ultrasonic fatigue testing technique. Fatigue tests are performed in vacuum, air and different aqueous environments with defined chloride and oxygen content. Furthermore, the influence of different stress ratios is investigated. It is found that crack propagation is not necessarily enhanced with increasing corrosiveness. In the aqueous environments, the FCGRs below 10⁻⁸ m/cycle are lower than in air. The threshold stress intensity factor ranges are higher or equal. Observation of the fracture surfaces shows oxide formation and partly intergranular fracture for specimens tested in aqueous environments. Crack closure effects seem to be responsible for this unexpected behaviour. PMID:23490013

  16. Influence of environment on the fatigue crack growth behaviour of 12% Cr steel.

    PubMed

    Schönbauer, Bernd M; Stanzl-Tschegg, Stefanie E

    2013-12-01

    In the present work, the influence of different environments on the fatigue crack growth behaviour of 12% Cr steam turbine blade steel is investigated. Fatigue crack growth rates (FCGRs) in the near threshold regime are measured with ultrasonic fatigue testing technique. Fatigue tests are performed in vacuum, air and different aqueous environments with defined chloride and oxygen content. Furthermore, the influence of different stress ratios is investigated. It is found that crack propagation is not necessarily enhanced with increasing corrosiveness. In the aqueous environments, the FCGRs below 10⁻⁸ m/cycle are lower than in air. The threshold stress intensity factor ranges are higher or equal. Observation of the fracture surfaces shows oxide formation and partly intergranular fracture for specimens tested in aqueous environments. Crack closure effects seem to be responsible for this unexpected behaviour.

  17. Environmentally assisted cracking in light water reactors. Semiannual report, October 1993--March 1994. Volume 18

    SciTech Connect

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

    1995-03-01

    This report summarizes work performed by Argonne National Laboratory (ANL) on fatigue and environmentally assisted cracking (EAC) in light water reactors (LWRs) during the six months from October 1993 to March 1994. EAC and fatigue of piping, pressure vessels, and core components in LWRs are important concerns in operating plants and 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 wrought and cast austenitic stainless steels (SSs), and (c) radiation-induced segregation and irradiation-assisted stress corrosion cracking (IASCC) of Type 304 SS after accumulation of relatively high fluence. Fatigue tests have been conducted on A302-Gr B low-alloy steel to verify whether the current predictions of modest decreases of fatigue life in simulated pressurized water reactor water are valid for high-sulfur heats that show environmentally enhanced fatigue crack growth rates. Additional crack growth data were obtained on fracture-mechanics specimens of austenitic SSs to investigate threshold stress intensity factors for EAC in high-purity oxygenated water at 289{degrees}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 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 boiling water reactors were studied by Auger electron spectroscopy and scanning electron microscopy to determine whether trace impurity elements, which are not specified in the ASTM specifications, may contribute to IASCC of solution-annealed materials.

  18. Identifying and Understanding Environment-Induced Crack propagation Behavior in Ni-based Superalloy INCONEL 617

    SciTech Connect

    Ma, Longzhou

    2012-11-30

    The nickel-based superalloy INCONEL 617 is a candidate material for heat exchanger applications in the next-generation nuclear plant (NGNP) system. This project will study the crack propagation process of alloy 617 at temperatures of 650°C-950°C in air under static/cyclic loading conditions. The goal is to identify the environmental and mechanical damage components and to understand in-depth the failure mechanism. Researchers will measure the fatigue crack propagation (FCP) rate (da/dn) under cyclic and hold-time fatigue conditions, and sustained crack growth rates (da/dt) at elevated temperatures. The independent FCP process will be identified and the rate-controlled sustained loading crack process will be correlated with the thermal activation equation to estimate the oxygen thermal activation energy. The FCP-dependent model indicates that if the sustained loading crack growth rate, da/dt, can be correlated with the FCP rate, da/dn, at the full time dependent stage, researchers can confirm stress-accelerated grain-boundary oxygen embrittlement (SAGBOE) as a predominate effect. Following the crack propagation tests, the research team will examine the fracture surface of materials in various cracking stages using a scanning electron microscope (SEM) and an optical microscope. In particular, the microstructure of the crack tip region will be analyzed in depth using high resolution transmission electron microscopy (TEM) and electron energy loss spectrum (EELS) mapping techniques to identify oxygen penetration along the grain boundary and to examine the diffused oxygen distribution profile around the crack tip. The cracked sample will be prepared by focused ion beam nanofabrication technology, allowing researchers to accurately fabricate the TEM samples from the crack tip while minimizing artifacts. Researchers will use these microscopic and spectroscopic results to interpret the crack propagation process, as well as distinguish and understand the environment or

  19. Environment enhanced fatigue crack propagation in metals: Inputs to fracture mechanics life prediction models

    NASA Technical Reports Server (NTRS)

    Gangloff, Richard P.; Kim, Sang-Shik

    1993-01-01

    This report is a critical review of both environment-enhanced fatigue crack propagation data and the predictive capabilities of crack growth rate models. This information provides the necessary foundation for incorporating environmental effects in NASA FLAGRO and will better enable predictions of aerospace component fatigue lives. The review presents extensive literature data on 'stress corrosion cracking and corrosion fatigue.' The linear elastic fracture mechanics approach, based on stress intensity range (Delta(K)) similitude with microscopic crack propagation threshold and growth rates, provides a basis for these data. Results are presented showing enhanced growth rates for gases (viz., H2 and H2O) and electrolytes (e.g. NaCl and H2O) in aerospace alloys including: C-Mn and heat treated alloy steels, aluminum alloys, nickel-based superalloys, and titanium alloys. Environment causes purely time-dependent accelerated fatigue crack growth above the monotonic load cracking threshold (KIEAC) and promotes cycle-time dependent cracking below (KIEAC). These phenomenon are discussed in terms of hydrogen embrittlement, dissolution, and film rupture crack tip damage mechanisms.

  20. Hydrogen Assisted Crack in Dissimilar Metal Welds for Subsea Service under Cathodic Protection

    NASA Astrophysics Data System (ADS)

    Bourgeois, Desmond

    Dissimilar metal welds (DMWs) are routinely used in the oil and gas industries for structural joining of high strength steels in order to eliminate the need for post weld heat treatment (PWHT) after field welding. There have been reported catastrophic failures in these DMWs, particularly the AISI 8630 steel - Alloy 625 DMW combination, during subsea service while under cathodic protection (CP). This is due to local embrittlement that occurs in susceptible microstructures that are present at the weld fusion boundary region. This type of cracking is known as hydrogen assisted cracking (HAC) and it is influenced by base/filler metal combination, and welding and PWHT procedures. DMWs of two material combinations (8630 steel -- Alloy 625 and F22 steel -- Alloy 625), produced with two welding procedures (BS1 and BS3) in as welded and PWHT conditions were investigated in this study. The main objectives included: 1) evaluation of the effect of materials composition, welding and PWHT procedures on the gradients of composition, microstructure, and properties in the dissimilar transition region and on the susceptibility to HAC; 2) investigation of the influence of microstructure on the HAC failure mechanism and identification of microstructural constituents acting as crack nucleation and propagation sites; 3) assessment of the applicability of two-step PWHT to improve the resistance to HAC in DMWs; 4) establishment of non-failure criterion for the delayed hydrogen cracking test (DHCT) that is applicable for qualification of DMWs for subsea service under cathodic protection (CP).

  1. Mechanical behaviour of metallic thin films on polymeric substrates and the effect of ion beam assistance on crack propagation

    SciTech Connect

    George, M. , E-Mail: matthieu.george@bnfl.com; Coupeau, C.; Colin, J.; Grilhe, J.

    2005-01-10

    The mechanisms of crack propagation in metallic films on polymeric substrates have been studied through in situ atomic force microscopy observations of thin films under tensile stresses and finite element stress calculations. Two series of films - ones deposited with ion beam assistance, the others without - have been investigated. The observations and stress calculations show that ion beam assistance can change drastically the propagation of cracks in coated materials: by improving the adhesion film/substrate, it slows down the delamination process, but in the same time enhances the cracks growth in the thickness of the material.

  2. 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.

  3. 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.

  4. A new criterion for failure of materials by environment-induced cracking

    NASA Technical Reports Server (NTRS)

    Williams, D. P.

    1973-01-01

    A new criterion has been developed for predicting failure of materials by environment-induced cracking. The criterion has been developed by the use of fracture mechanics concepts and assumes that the relationship between crack-growth rate and stress intensity can be described by three separable regions of behavior as first suggested by Wiederhorn. The analytical form of the criterion relates failure time to the initial crack length and the critical crack length or alternatively, to the initial stress intensity and the fracture toughness for various conditions of stress and the environmental variables. The analytical expression is examined by the use of some experimental data on the hydrogen-induced cracking of Ti-5Al-2.5 Sn, and it is demonstrated that the expression predicts the general expected form of the relationship between the normalized stress intensity parameter and the failure time.

  5. 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.

  6. 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

  7. 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.

  8. 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.

  9. Creep-assisted slow crack growth in bio-inspired dental multilayers.

    PubMed

    Du, Jing; Niu, Xinrui; Soboyejo, Wole

    2015-06-01

    Ceramic crown structures under occlusal contact are often idealized as flat multilayered structures that are deformed under Hertzian contact loading. Previous models treated each layer as linear elastic materials and resulted in differences between the measured and predicted critical loads. This paper examines the combined effects of creep (in the adhesive and substrate layers) and creep-assisted slow crack growth (in the ceramic layer) on the contact-induced deformation of bio-inspired, functionally graded multilayer (FGM) structures and the conventional tri-layers. The time-dependent moduli of each of the layers were determined from constant load creep tests. The resulting modulus-time characteristics were modeled using Prony series. These were then incorporated into a finite element model for the computation of stress distributions in the sub-surface regions of the top ceramic layer, in which sub-surface radial cracks, are observed as the clinical failure mode. The time-dependent stresses are incorporated into a slow crack growth (SCG) model that is used to predict the critical loads of the dental multilayers under Hertzian contact loading. The predicted loading rate dependence of the critical loads is shown to be consistent with experimental results. The implications of the results are then discussed for the design of robust dental multilayers.

  10. Environmentally assisted cracking in light water reactors. Semiannual report, April--September 1991: Volume 13

    SciTech Connect

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

    1992-03-01

    This report summarizes work performed by Argonne National Laboratory on fatigue and environmentally assisted cracking in high water reactors during the six months from April 1991 through September 1991. Topics that have been investigated during this period include (1) fatigue and stress corrosion cracking (SCC) of low-alloy steel used in piping and in steam generator and reactor pressure vessels; (2) role of chromate and sulfate in simulated boiling water reactor (BWR) water on SCC of sensitized Type 304 SS; and (3) radiation-induced segregation (RIS) and irradiation-assisted SCC of Type 304 SS after accumulation of relatively high fluence. Fatigue data were obtained on medium-S-content A533-Gr B and A106-Gr B steels in high-purity (HP) deoxygenated water, in simulated pressurized water reactor (PWR) water, and in air. Crack-growth-rates (CGRs) of composite specimens of A533-Gr B/Inconel-182/Inconel-600 (plated with nickel) and homogeneous specimens of A533-Gr B were determined under small- amplitude cyclic loading in HP water with {approx} 300 ppb dissolved oxygen. CGR tests on sensitized Type 304 SS indicate that low chromate concentrations in BWR water (25--35 ppb) may actually have a beneficial effect on SCC if the sulfate concentration is below a critical level. Microchemical and microstructural changes in HP and commercial-purity Type 304 SS specimens from control-blade absorber tubes used in two operating BWRs were studied by Auger electron spectroscopy and scanning electron microscopy, and slow-strain,rate- tensile tests were conducts on tubular specimens in air and in simulated BWR water at 289{degrees}C.

  11. Irradiation Programs and Test Plans to Assess High-Fluence Irradiation Assisted Stress Corrosion Cracking Susceptibility.

    SciTech Connect

    Teysseyre, Sebastien

    2015-03-01

    . Irradiation assisted stress corrosion cracking (IASCC) is a known issue in current reactors. In a 60 year lifetime, reactor core internals may experience fluence levels up to 15 dpa for boiling water reactors (BWR) and 100+ dpa for pressurized water reactors (PWR). To support a safe operation of our fleet of reactors and maintain their economic viability it is important to be able to predict any evolution of material behaviors as reactors age and therefore fluence accumulated by reactor core component increases. For PWR reactors, the difficulty to predict high fluence behavior comes from the fact that there is not a consensus of the mechanism of IASCC and that little data is available. It is however possible to use the current state of knowledge on the evolution of irradiated microstructure and on the processes that influences IASCC to emit hypotheses. This report identifies several potential changes in microstructure and proposes to identify their potential impact of IASCC. The susceptibility of a component to high fluence IASCC is considered to not only depends on the intrinsic IASCC susceptibility of the component due to radiation effects on the material but to also be related to the evolution of the loading history of the material and interaction with the environment as total fluence increases. Single variation type experiments are proposed to be performed with materials that are representative of PWR condition and with materials irradiated in other conditions. To address the lack of IASCC propagation and initiation data generated with material irradiated in PWR condition, it is proposed to investigate the effect of spectrum and flux rate on the evolution of microstructure. A long term irradiation, aimed to generate a well-controlled irradiation history on a set on selected materials is also proposed for consideration. For BWR, the study of available data permitted to identify an area of concern for long term performance of component. The efficiency of

  12. Influences of gaseous environment on low growth-rate fatigue crack propagation in steels. Annual report No. 1, January 1980. Report No. FPL/R/80/1030

    SciTech Connect

    Ritchie, R.O.; Suresh, S.; Toplosky, J.

    1980-01-01

    The influence of gaseous environment is examined on fatigue crack propagation behavior in steels. Specifically, a fully martensitic 300-M ultrahigh strength steel and a fully bainitic 2-1/4Cr-1Mo lower strength steel are investigated in environments of ambient temperature moist air and low pressure dehumidified hydrogen and argon gases over a wide range of growth rates from 10/sup -8/ to 10/sup -2/ mm/cycle, with particular emphasis given to behavior near the crack propagation threshold ..delta..K/sub 0/. It is found that two distinct growth rate regimes exist where hydrogen can markedly accelerate crack propagation rates compared to air, (1) at near-threshold levels below (5 x 10/sup -6/ mm/cycle) and (2) at higher growth rates, typically around 10/sup -5/ mm/cycle above a critical maximum stress intensity K/sub max//sup T/. Hydrogen-assisted crack propagation at higher growth rates is attributed to a hydrogen embrittlement mechanism, with K/sub max//sup T/ nominally equal to K/sub Iscc/ (the sustained load stress corrosion threshold) in high strength steels, and far below K/sub Iscc/ in the strain-rate sensitive lower strength steels. Hydrogen-assisted crack propagation at near-threshold levels is attributed to a new mechanism involving fretting-oxide-induced crack closure generated in moist (or oxygenated) environments. The absence of hydrogen embrittlement mechanisms at near-threshold levels is supported by tests showing that ..delta..K/sub 0/ values in dry gaseous argon are similar to ..delta..K/sub 0/ values in hydrogen. The potential ramifications of these results are examined in detail.

  13. Effect of Microstructure and Environment on Static Crack Growth Resistance in Alloy 706

    NASA Astrophysics Data System (ADS)

    Yang, Ling; Hawk, Jeffrey A.; Duquette, David J.; Schwant, Robin C.

    2009-06-01

    The relationship between thermo-mechanical processing, resultant microstructure, and mechanical properties has been of interest in the field of metallurgy for centuries. In this work, the effect of heat treatment on microstructure and key mechanical properties important for turbine rotor design has been investigated. Specifically, the tensile yield strength and crack growth resistance for a nickel-iron based superalloy 706 has been examined. Through a systematic study, a correlation was found between the processing parameters and the microstructure. Specifically, differences in grain boundary and grain interior precipitates were identified and correlated with processing conditions. Further, a strong relationship between microstructure and mechanical properties was identified. The type and orientation of grain boundary precipitates affect time-dependent crack propagation resistance, and the size and volume fraction of grain interior precipitates were correlated with tensile yield strength. It was also found that there is a strong environmental effect on time-dependent crack propagation resistance, and the sensitivity to environmental damage is microstructure dependent. Microstructures with η decorated grain boundaries were more resistant to environmental damage through oxygen embrittlement than microstructures with no η phase on the grain boundaries. An effort was made to explore the mechanisms of improving the time-dependent crack propagation resistance through thermo-mechanical processing, and several mechanisms were identified in both the environment-dependent and the environment-independent category. These mechanisms were ranked based on their contributions to crack propagation resistance.

  14. Mechanism of Irradiation Assisted Cracking of Core Components in Light Water Reactors

    SciTech Connect

    Was, Gary S; Atzmon, Michael; Wang, Lumin

    2003-04-28

    The overall goal of the project is to determine the mechanism of irradiation assisted stress corrosion cracking (IASCC). IASCC has been linked to hardening, microstructural and microchemical changes during irradiation. Unfortunately, all of these changes occur simultaneously and at similar rates during irradiation, making attribution of IASCC to any one of these features nearly impossible to determine. The strategy set forth in this project is to develop means to separate microstructural from microchemical changes to evaluate each separately for their effect on IASCC. In the first part, post irradiation annealing (PIA) treatments are used to anneal the irradiated microstructure, leaving only radiation induced segregation (RIS) for evaluation for its contribution to IASCC. The second part of the strategy is to use low temperature irradiation to produce a radiation damage dislocation loop microstructure without radiation induced segregation in order to evaluate the effect of the dislocation microstructure alone.

  15. Localized Deformation as a Primary Cause of Irradiation Assisted Stress Corrosion Cracking

    SciTech Connect

    Gary S. Was

    2009-03-31

    The objective of this project is to determine whether deformation mode is a primary factor in the mechanism of irradiation assisted intergranular stress corrosion cracking of austenitic alloys in light watert reactor core components. Deformation mode will be controlled by both the stacking fault energy of the alloy and the degree of irradiation. In order to establish that localized deformation is a major factor in IASCC, the stacking fault energies of the alloys selected for study must be measured. Second, it is completely unknown how dose and SFE trade-off in terms of promoting localized deformation. Finally, it must be established that it is the localized deformation, and not some other factor that drives IASCC.

  16. Irradiation-assisted stress corrosion cracking of HTH Alloy X-750 and Alloy 625

    SciTech Connect

    Bajaj, R.; Mills, W.J.; Lebo, M.R.; Hyatt, B.Z.; Burke, M.G.

    1995-07-01

    In-reactor testing of bolt-loaded compact tension specimens was performed in 360 C water. New data confirms previous results that high irradiation levels reduce SCC resistance in Alloy X-750. Low boron heats show improved IASCC (irradiation-assisted stress corrosion cracking). Alloy 625 is resistant to IASCC. Microstructural, microchemical, and deformation studies were carried out. Irradiation of X-750 caused significant strengthening and ductility loss associated with formation of cavities and dislocation loops. High irradiation did not cause segregation in X-750. Irradiation of 625 resulted in formation of small dislocation loops and a fine body-centered-orthorhombic phase. The strengthening due to loops and precipitates was apparently offset in 625 by partial dissolution of {gamma} precipitates. Transmutation of boron to helium at grain boundaries, coupled with matrix strengthening, is believed to be responsible for IASCC in X-750, and the absence of these two effects results in superior IASCC resistance in 625.

  17. Study of Near-Threshold Fatigue Crack Propagation in Pipeline Steels in High Pressure Environments

    NASA Technical Reports Server (NTRS)

    Mitchell, M.

    1981-01-01

    Near threshold fatigue crack propagation in pipeline steels in high pressure environments was studied. The objective was to determine the level of threshold stress intensity for fatigue crack growth rate behavior in a high strength low alloy X60 pipeline-type steel. Complete results have been generated for gaseous hydrogen at ambient pressure, laboratory air at ambient pressure and approximately 60% relative humidity as well as vacuum of 0.000067 Pa ( 0.0000005 torr) at R-ratios = K(min)/K(max) of 0.1, 0.5, and 0.8. Fatigue crack growth rate behavior in gaseous hydrogen, methane, and methane plus 10 percent hydrogen at 6.89 MPa (100 psi) was determined.

  18. A fracture mechanics approach for estimating fatigue crack initiation in carbon and low-alloy steels in LWR coolant environments

    SciTech Connect

    Park, H. B.; Chopra, O. K.

    2000-04-10

    A fracture mechanics approach for elastic-plastic materials has been used to evaluate the effects of light water reactor (LWR) coolant environments on the fatigue lives of carbon and low-alloy steels. The fatigue life of such steel, defined as the number of cycles required to form an engineering-size crack, i.e., 3-mm deep, is considered to be composed of the growth of (a) microstructurally small cracks and (b) mechanically small cracks. The growth of the latter was characterized in terms of {Delta}J and crack growth rate (da/dN) data in air and LWR environments; in water, the growth rates from long crack tests had to be decreased to match the rates from fatigue S-N data. The growth of microstructurally small cracks was expressed by a modified Hobson relationship in air and by a slip dissolution/oxidation model in water. The crack length for transition from a microstructurally small crack to a mechanically small crack was based on studies on small crack growth. The estimated fatigue S-N curves show good agreement with the experimental data for these steels in air and water environments. At low strain amplitudes, the predicted lives in water can be significantly lower than the experimental values.

  19. Creep-Environment Interactions in Dwell-Fatigue Crack Growth of Nickel Based Superalloys

    NASA Astrophysics Data System (ADS)

    Maciejewski, Kimberly; Dahal, Jinesh; Sun, Yaofeng; Ghonem, Hamouda

    2014-05-01

    A multi-scale, mechanistic model is developed to describe and predict the dwell-fatigue crack growth rate in the P/M disk superalloy, ME3, as a function of creep-environment interactions. In this model, the time-dependent cracking mechanisms involve grain boundary sliding and dynamic embrittlement, which are identified by the grain boundary activation energy, as well as, the slip/grain boundary interactions in both air and vacuum. Modeling of the damage events is achieved by adapting a cohesive zone (CZ) approach which considers the deformation behavior of the grain boundary element at the crack tip. The deformation response of this element is controlled by the surrounding continuum in both far field (internal state variable model) and near field (crystal plasticity model) regions and the intrinsic grain boundary viscosity which defines the mobility of the element by scaling up the motion of dislocations into a mesoscopic scale. This intergranular cracking process is characterized by the rate at which the grain boundary sliding reaches a critical displacement. A damage criterion is introduced by considering the grain boundary mobility limit in the tangential direction leading to strain incompatibility and failure. Results of simulated intergranular crack growth rate using the CZ model are generated for temperatures ranging from 923 K to 1073 K (650 °C to 800 °C), in both air and vacuum. These results are compared with those experimentally obtained and analysis of the model sensitivity to loading conditions, particularly temperature and oxygen partial pressure, are presented.

  20. Susceptibility of Welded and Non-Welded Titanium Alloys to Environmentally Assisted Cracking in Simulated Concentrated Ground Waters

    SciTech Connect

    Fix, D V; Estill, J C; Wong, L L; Rebak, R B

    2003-10-14

    The engineering barriers for the nuclear waste repository at Yucca Mountain include a double walled container and a detached drip shield. The material selected to construct the drip shield will be Titanium Grade 7 (Ti Gr 7 or R52400). Ti Gr 7 is highly resistant to corrosion and consequently it is widely used to handle aggressive industrial environments. The model for the degradation of the engineering barriers includes three modes of corrosion, namely general corrosion, localized corrosion and environmentally assisted cracking (EAC). The objective of the current research was to characterize the susceptibility of three titanium alloys to EAC in several environmental conditions with varying solution composition, pH and temperature. The susceptibility to EAC was evaluated using constant deformation (deflection) U-bend specimens in both the non-welded and welded conditions. Results show that after more than five years exposure in the vapor and liquid phases of alkaline (pH {approx} 10) and acidic (pH {approx} 3) multi-ionic environments at 60 C and 90 C, most of the specimens were free from EAC. The only specimens that suffered EAC were welded Ti Gr 12 (R53400) exposed to liquid simulated concentrated water (SCW) at 90 C.

  1. UNDERSTANDING THE MECHANISMS CONTROLLING ENVIRONMENTALLY-ASSISTED INTERGRANULAR CRACKING OF NICKEL-BASE ALLOYS

    SciTech Connect

    Gary S. Was

    2004-02-13

    Creep and IG cracking of nickel-base alloys depend principally on two factors--the deformation behavior and the effect of the environment. We have shown that both contribute to the observed degradation in primary water. The understanding of cracking does not lie wholly within the environmental effects arena, nor can it be explained only by intrinsic mechanical behavior. Rather, both processes contribute to the observed behavior in primary water. In this project, we had three objectives: (1) to verify that grain boundaries control deformation in Ni-16Cr-9Fe at 360 C, (2) to identify the environmental effect on IGSCC, and (3) to combine CSLBs and GBCs to maximize IGSCC resistance in Ni-Cr-Fe in 360 C primary water. Experiments performed in hydrogen gas at 360 C confirm an increase in the primary creep rate in Ni-16Cr-9Fe at 360 C due to hydrogen. The creep strain transients caused by hydrogen are proposed to be due to the collapse of dislocation pile-ups, as confirmed by observations in HVEM. The observations only partially support the hydrogen-enhanced plasticity model, but also suggest a potential role of vacancies in the accelerate creep behavior in primary water. In high temperature oxidation experiments designed to examine the potential for selective internal oxidation in the IGSCC process, cracking is greatest in the more oxidizing environments compared to the low oxygen potential environments where nickel metal is stable. In Ni-Cr-Fe alloys, chromium oxides form preferentially along the grain boundaries, even at low oxygen potential, supporting a potential role in grain boundary embrittlement due to preferential oxidation. Experiments designed to determine the role of grain boundary deformation on intergranular cracking have established, for the first time, a cause-and-effect relationship between grain boundary deformation and IGSCC. That is, grain boundary deformation in Ni-16Cr-9Fe in 360 C primary water leads to IGSCC of the deformed boundaries. As well

  2. Microstructural and Microchemical Characterization of Dual Step Aged Alloy X-750 and its Relationship to Environmentally Assisted Cracking

    SciTech Connect

    G.A. Young; N. Lewis; M. Hanson; W. Matuszyk; B. Wiersma; S. Gonzalez

    2001-05-08

    When exposed to deaerated high purity water, Alloy X-750 is susceptible to both high temperature (> 249 C) intergranular stress corrosion cracking (IGSCC) and intergranular low temperature (< 149 C) fracture (LTF). However, the microstructural and microchemical factors that govern environmentally assisted cracking (EAC) susceptibility are poorly understood. The present study seeks to characterize the grain boundary microstructure and microchemistry in order to gain a better mechanistic understanding of stress corrosion crack initiation, crack growth rate, and low temperature fracture. Light microscopy, scanning electron microscopy, transmission electron microscopy, orientation imaging microscopy, scanning Auger microscopy, and thermal desorption spectroscopy were performed on selected heats of Alloy X-750 AH. These data were correlated to EAC tests performed in 338 C deaerated water. Results show that grain boundary MC-type [(Ti,Nb)C] carbides and increased levels of grain boundary phosphorus correlate with an increase in LTF susceptibility but have little effect on the number of initiation sites or the SCC crack growth rate. Thermal desorption data show that multiple hydrogen trapping states exist in Alloy X-750 condition AH. Moreover, it appears that exposure to high temperature (> 249 C), hydrogen deaerated water increases the hydrogen concentration in strong hydrogen trap states and degrades the resistance of the material to low temperature fracture. These findings are consistent with a hydrogen embrittlement based mechanism of LTF where intergranular fracture occurs ahead of a crack tip and is exacerbated by phosphorus segregation to grain boundaries and grain boundary hydrogen trap states.

  3. Irradiation-assisted stress corrosion cracking behavior of austenitic stainless steels applicable to LWR core internals.

    SciTech Connect

    Chung, H. M.; Shack, W. J.; Energy Technology

    2006-01-31

    This report summarizes work performed at Argonne National Laboratory on irradiation-assisted stress corrosion cracking (IASCC) of austenitic stainless steels that were irradiated in the Halden reactor in simulation of irradiation-induced degradation of boiling water reactor (BWR) core internal components. Slow-strain-rate tensile tests in BWR-like oxidizing water were conducted on 27 austenitic stainless steel alloys that were irradiated at 288 C in helium to 0.4, 1.3, and 3.0 dpa. Fractographic analysis was conducted to determine the fracture surface morphology. Microchemical analysis by Auger electron spectroscopy was performed on BWR neutron absorber tubes to characterize grain-boundary segregation of important elements under BWR conditions. At 0.4 and 1.4 dpa, transgranular fracture was mixed with intergranular fracture. At 3 dpa, transgranular cracking was negligible, and fracture surface was either dominantly intergranular, as in field-cracked core internals, or dominantly ductile or mixed. This behavior indicates that percent intergranular stress corrosion cracking determined at {approx}3 dpa is a good measure of IASCC susceptibility. At {approx}1.4 dpa, a beneficial effect of a high concentration of Si (0.8-1.5 wt.%) was observed. At {approx}3 dpa, however, such effect was obscured by a deleterious effect of S. Excellent resistance to IASCC was observed up to {approx}3 dpa for eight heats of Types 304, 316, and 348 steel that contain very low concentrations of S. Susceptibility of Types 304 and 316 steels that contain >0.003 wt.% S increased drastically. This indicates that a sulfur related critical phenomenon plays an important role in IASCC. A sulfur content of <0.002 wt.% is the primary material factor necessary to ensure good resistance to IASCC. However, for Types 304L and 316L steel and their high-purity counterparts, a sulfur content of <0.002 wt.% alone is not a sufficient condition to ensure good resistance to IASCC. This is in distinct contrast to

  4. Irradiation-assisted stress corrosion cracking of model austenitic stainless steel.

    SciTech Connect

    Chung, H. M.; Ruther, W. E.; Strain, R. V.; Shack, W. J.; Karlsen, T. M.

    1999-10-26

    Slow-strain-rate tensile (SSRT) tests were conducted on model austenitic stainless steel (SS) alloys that were irradiated at 289 C in He. After irradiation to {approx}0.3 x 10{sup 21} n {center_dot} cm{sup 2} and {approx} 0.9 x 10{sup 21} n {center_dot} cm{sup -2} (E > 1 MeV), significant heat-to-heat variations in the degree of intergranular and transgranular stress corrosion cracking (IGSCC and TGSCC) were observed. At {approx}0.3 x 10{sup 21} n {center_dot} cm{sup -2}, a high-purity heat of Type 316L SS that contains a very low concentration of Si exhibited the highest susceptibility to IGSCC. In unirradiated state, Types 304 and 304L SS did not exhibit a systematic effect of Si content on alloy strength. However, at {approx}0.3 x 10{sup 21} n {center_dot} cm{sup -2}, yield and maximum strengths decreased significantly as Si content was increased to >0.9 wt.%. Among alloys that contain low concentrations of C and N, ductility and resistance to TGSCC and IGSCC were significantly greater for alloys with >0.9 wt.% Si than for alloys with <0.47 wt.% Si. Initial data at {approx}0.9 x 10{sup 21} n {center_dot} cm{sup -2} were also consistent with the beneficial effect of high Si content. This indicates that to delay onset of and reduce susceptibility to irradiation-assisted stress corrosion cracking (IASCC), at least at low fluence levels, it is helpful to ensure a certain minimum concentration of Si. High concentrations of Cr were also beneficial; alloys that contain <15.5 wt.% Cr exhibited greater susceptibility to IASCC than alloys with {approx}18 wt.% Cr, whereas an alloy that contains >21 wt.% Cr exhibited less susceptibility than the lower-Cr alloys under similar conditions.

  5. Irradiation-assisted stress corrosion cracking in HTH Alloy X-750 and Alloy 625

    SciTech Connect

    Bajaj, R.; Mills, W.J.; Lebo, M.R.; Hyatt, B.Z.; Burke, M.G.

    1995-12-31

    In-reactor testing of bolt-loaded compact tension specimens was performed in 360 C water to determine the irradiation-assisted stress corrosion cracking (IASCC) behavior of HTH Alloy X-750 and direct-aged Alloy 625. New data confirm previous results showing that high irradiation levels reduce SCC resistance in Alloy X-750. Heat-to-heat variability correlates with boron content, with low boron heats showing improved IASCC properties. Alloy 625 is resistant to IASCC, as no cracking was observed in any Alloy 625 specimens. Microstructural, microchemical and deformation studies were performed to characterize the mechanisms responsible for IASCC in Alloy X-750 and the lack of an effect in Alloy 625. The mechanisms under investigation are: boron transmutation effects, radiation-induced changes in microstructure and deformation characteristics, and radiation-induced segregation. Irradiation of Alloy X-750 caused significant strengthening and ductility loss that was associated with the formation of cavities and dislocation loops. High irradiation levels did not cause significant segregation of alloying or trace elements in Alloy X-750. Irradiation of Alloy 625 resulted in the formation of small dislocation loops and a fine body-centered-orthorhombic phase. The strengthening due to the loops and precipitates was apparently offset by a partial dissolution of {gamma}{double_prime} precipitates, as Alloy 625 showed no irradiation-induced strengthening or ductility loss. In the nonirradiated condition, an IASCC susceptible HTH heat containing 28 ppm B showed grain boundary segregation of boron, whereas a nonsusceptible HTH heat containing 2 ppm B and Alloy 625 with 20 ppm B did not show significant boron segregation. Transmutation of boron to helium at grain boundaries, coupled with matrix strengthening, is believed to be responsible for IASCC in Alloy X-750, and the absence of these two effects results in the superior IASCC resistance displayed by Alloy 625.

  6. Model-Assisted POD for Ultrasonic Detection of Cracks at Fastener Holes

    NASA Astrophysics Data System (ADS)

    Harding, C. A.; Hugo, G. R.; Bowles, S. J.

    2006-03-01

    To reduce the cost of conducting experimental probability of detection (POD) trials, methods which utilize models to account for factors that influence the inspection reliability are being developed. This paper reports the application of POD modeling to ultrasonic detection of cracks emanating from fastener holes. The differences between ultrasonic responses from EDM notches compared to fatigue cracks are examined, including the effects of natural variation in fatigue cracks and crack closure due to residual stresses.

  7. Kohonen mapping of the crack growth under fatigue loading conditions of stainless steels in BWR environments and of nickel alloys in PWR environments

    NASA Astrophysics Data System (ADS)

    Urquidi-Macdonald, Mirna

    2008-09-01

    In this study, crack growth rate data under fatigue loading conditions generated by Argonne National Laboratories and published in 2006 were analyzed [O.K. Chopra, B. Alexandreanu, E.E. Gruber, R.S. Daum, W.J. Shack, Argonne National Laboratory, NUREG CR 6891-series ANL 04/20, Crack Growth Rates of Austenitic Stainless Steel Weld Heat Affected Zone in BWR Environments, January, 2006; B. Alexandreanu, O.K. Chopra, H.M. Chung, E.E. Gruber, W.K. Soppet, R.W. Strain, W.J. Shack, Environmentally Assisted Cracking in Light Water Reactors, vol. 34 in the NUREG/CR-4667 series annual report of Argonne National Laboratory program studies for Calendar (Annual Report 2003). Manuscript Completed: May 2005, Date Published: May 2006], and reported by DoE [B. Alexandreanu, O.K. Chopra, W.J. Shack, S. Crane, H.J. Gonzalez, NRC, Crack Growth Rates and Metallographic Examinations of Alloy 600 and Alloy 82/182 from Field Components and Laboratory Materials Tested in PWR Environments, NUREG/CR-6964, May 2008]. The data collected were measured on austenitic stainless steels in BWR (boiling water reactor) environments and on nickel alloys in PWR (pressurized water reactor) environments. The data collected contained information on material composition, temperature, conductivity of the environment, oxygen concentration, irradiated sample information, weld information, electrochemical potential, load ratio, rise time, hydrogen concentration, hold time, down time, maximum stress intensity factor ( Kmax), stress intensity range (Δ Kmax), crack length, and crack growth rates (CGR). Each position on that Kohonen map is called a cell. A Kohonen map clusters vectors of information by 'similarities.' Vectors of information were formed using the metal composition, followed by the environmental conditions used in each experiments, and finally followed by the crack growth rate (CGR) measured when a sample of pre-cracked metal is set in an environment and the sample is cyclically loaded. Accordingly

  8. Template-assisted growth of nominally cubic (100)-oriented three-dimensional crack-free photonic crystals.

    PubMed

    Jin, Chongjun; McLachlan, Martyn A; McComb, David W; De La Rue, Richard M; Johnson, Nigel P

    2005-12-01

    Three-dimensional (3D) photonic crystals (PhCs) are now beginning to acquire functionality via the use of dopants and heterostructures. However, the self-organized fabrication of large-area single crystals that are free of cracks and stacking faults has remained a challenge. We demonstrate a technology for the fabrication of (100)-oriented thin film 3D opal PhCs that exhibit no cracks over areas having no intrinsic size limit via a modified template-assisted colloidal self-assembly approach onto a patterned substrate. This technology potentially makes available large area regions of single photonic crystal, which can be used for optoelectronic devices.

  9. Effects of aqueous chemical environments on crack and hydraulic fracture propagation and morphologies

    SciTech Connect

    Dunning, J.D.; Huf, W.L.

    1983-08-10

    The role of surface active aqueous environments in chemomechanical weakening of geologic materials is examined using the results of hydraulic fracture tests in sandstone, calorimetric studies, and crack propagation tests in synthetic quartz. In hydraulic fracture tests it was found that the effective hydraulic fracture pressure was reduced, over that attained with distilled water, when 5 X 10/sup -4/ M aqueous solutions of dodecyl trimethyl ammonium bromide (DTAB) were used as the hydraulic fracture medium. The degree of branching of the fractures also was increased in the presence of the DTAB solution. Previously reported crack propagation stress values in quartz exposed to distilled water and various DTAB solutions displayed the same trend. These results and results from calorimetric measurements of the heats of adsorption and desorption from quartz of distilled water and DTAB are synthesized in a model relating effects to a reduction in the surface free energy due to adsorption from the chemical environment. 24 references.

  10. Computer modeling the fatigue crack growth rate behavior of metals in corrosive environments

    NASA Technical Reports Server (NTRS)

    Richey, Edward, III; Wilson, Allen W.; Pope, Jonathan M.; Gangloff, Richard P.

    1994-01-01

    The objective of this task was to develop a method to digitize FCP (fatigue crack propagation) kinetics data, generally presented in terms of extensive da/dN-Delta K pairs, to produce a file for subsequent linear superposition or curve-fitting analysis. The method that was developed is specific to the Numonics 2400 Digitablet and is comparable to commercially available software products as Digimatic(sup TM 4). Experiments demonstrated that the errors introduced by the photocopying of literature data, and digitization, are small compared to those inherent in laboratory methods to characterize FCP in benign and aggressive environments. The digitizing procedure was employed to obtain fifteen crack growth rate data sets for several aerospace alloys in aggressive environments.

  11. Irradiation-Assisted Stress-Corrosion Cracking of Nitinol During eBeam Sterilization

    NASA Astrophysics Data System (ADS)

    Smith, Stuart A.; Gause, Brock; Plumley, David; Drexel, Masao J.

    2012-12-01

    Medical device fractures during gamma and electron beam (eBeam) sterilization have been reported. Two common factors in these device fractures were a constraining force and the presence of fluorinated ethylene propylene (FEP). This study investigated the effects of eBeam sterilization on constrained light-oxide nitinol wires in FEP. The goal was to recreate these fractures and determine their root cause. Superelastic nitinol wires were placed inside FEP tubes and constrained with nominal outer fiber strains of 10, 15, and 20%. These samples were then subjected to a range of eBeam sterilization doses up to 400 kGy and compared with unconstrained wires also subjected to sterilization. Fractures were observed at doses of >100 kGy. Analysis of the fracture surfaces indicated that the samples failed due to irradiation-assisted stress-corrosion cracking (IASCC). This same effect was also observed to occur with PTFE at 400 kGy. These results suggest that nitinol is susceptible to IASCC when in the presence of a constraining stress, fluorinated polymers, and irradiation.

  12. Effects of a Hydrogen Gas Environment on Fatigue Crack Growth of a Stable Austenitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Kawamoto, Kyohei; Oda, Yasuji; Noguchi, Hiroshi; Higashida, Kenji

    In order to clarify the effects of a hydrogen gas environment on the fatigue crack growth characteristics of stable austenitic stainless steels, bending fatigue tests were carried out in a hydrogen gas, in a nitrogen gas at 1.0 MPa and in air on a SUS316L using the Japanese Industrial Standards (type 316L). Also, in order to discuss the difference in the hydrogen sensitivity between austenitic stainless steels, the fatigue tests were also carried out on a SUS304 using the Japanese Industrial Standards (type 304) metastable austenitic stainless steel as a material for comparison. The main results obtained are as follows. Hydrogen gas accelerates the fatigue crack growth rate of type 316L. The degree of the fatigue crack growth acceleration is low compared to that in type 304. The fracture surfaces of both the materials practically consist of two parts; the faceted area seemed to be brittle and the remaining area occupying a greater part of the fracture surface and seemed to be ductile. The faceted area does not significantly contribute to the fatigue crack growth rate in both austenitic stainless steels. The slip-off mechanism seems to be valid not only in air and in nitrogen, but also in hydrogen. Also, the main cause of the fatigue crack growth acceleration of both materials occurs by variation of the slip behaviour. The difference in the degree of the acceleration, which in type 316L is lower than in type 304, seems to be caused by the difference in the stability of the γ phase.

  13. Irradiation-assisted stress corrosion cracking of materials from commercial BWRs: Role of grain-boundary microchemistry

    SciTech Connect

    Chung, H.M.; Ruther, W.E.; Sanecki, J.E.; Hins, A.G.; Kassner, T.F.

    1993-12-01

    Constant-extension-rate tensile tests and grain-boundary analysis by Auger electron spectroscopy which were conducted on high- and commercial-purity (HP and CP) Type 304 stainless steel (SS) specimens from irradiated boiling-water reactor (BWR) components to determine susceptibility to irradiation-assisted stress corrosion cracking (IASCC) and to identify the mechanisms of intergranular failure. The susceptibility of HP neutron absorber tubes to intergranular stress corrosion cracking (IGSCC) was higher than that of CP absorber tubes or CP control blade sheath. Contrary to previous beliefs, susceptibility to intergranular fracture could not be correlated with radiation-induced segregation of impurities such as Si, P, C, N, or S, but a correlation was obtained with grain-boundary Cr concentration, indicating a role for Cr depletion that promotes IASCC. Detailed analysis of grain-boundary chemistry was conducted on neutron absorber tubes that were fabricated from two similar heats of HP Type 304 SS of virtually identical bulk chemical composition but exhibiting a significant difference in susceptibility to IGSCC for similar fluence. Grain-boundary concentrations of Cr, Ni, Si, P, S, and C in the crack-resistant and susceptible HP heats were virtually identical. However, grain boundaries of the cracking-resistant material contained less N and more B and Li (transmutation product from B) than those of the crack-susceptible material, indicating beneficial effects of low N and high B contents.

  14. The effects of aqueous chemical environments on crack and hydraulic fracture propagation and morphologies

    NASA Astrophysics Data System (ADS)

    Dunning, J. D.; Huf, W. L.

    1983-08-01

    The role of surface active aqueous environments in chemomechanical weakening of geologic materials is examined in light of the results of hydraulic fracture tests in sandstone, calorimetric studies, and crack propagation tests in synthetic quartz. In hydraulic fracture tests mploying Crab Orchard Sandstone it was found that the effective hydraulic fracture pressure was reduced, over that attained with distilled water, when 5×10-4 M aqueous solutions of dodecyl trimethyl ammonium bromide (DTAB) were used as the hydraulic fracture medium. The degree of branching of the fractures was also increased in the presence of the DTAB solution. Previously reported crack propagation stress values in quartz exposed to distilled water and various DTAB solutions displayed the same trend. When examined in this study, the cracks propagated in the presence of DTAB solutions also displayed a greater degree of branching than those propagated in the presence of distilled water or the ambient atmosphere. These results and results from calorimetric measurements of the heats of adsorption and desorption from quartz of distilled water and DTAB are synthesized in a model relating the weakening and morphological effects to a reduction in the surface free energy of quartz due to adsorption of species from the chemical environment onto the surfaces of the quartz and sandstone.

  15. Model Predictions of Chemically Controlled Slow Crack Growth with Application to Mechanical Effects in Geothermal Environments

    SciTech Connect

    Viani, B E

    2001-04-11

    Representative, simplified geothermal rock-fluid systems are investigated with a modeling approach to estimate how rock water interactions affect coupled properties related to mechanical stability and permeability improvement through fracturing. First, geochemical modeling is used to determine the evolution of fluid chemistry at temperatures up to 300 C when fluids are in contact with representative rocks of continental origin. Then, a kinetic crack growth model for quartz is used to predict growth rate for subcritical cracks in acidic and basic environments. The predicted growth rate is highly sensitive to temperature and pH in the ranges tested. At present, the model is limited to situations in which quartz controls the mechanical process of interest, such as well bore stability in silica cemented rocks and the opening of quartz filled veins to enhance permeability.

  16. Mechanism and estimation of fatigue crack initiation in austenitic stainless steels in LWR environments.

    SciTech Connect

    Chopra, O. K.; Energy Technology

    2002-08-01

    The ASME Boiler and Pressure Vessel Code provides rules for the construction of nuclear power plant components. Figures I-9.1 through I-9.6 of Appendix I to Section III of the Code specify fatigue design curves for structural materials. However, the effects of light water reactor (LWR) coolant environments are not explicitly addressed by the Code design curves. Existing fatigue strain-vs.-life ({var_epsilon}-N) data illustrate potentially significant effects of LWR coolant environments on the fatigue resistance of pressure vessel and piping steels. This report provides an overview of fatigue crack initiation in austenitic stainless steels in LWR coolant environments. The existing fatigue {var_epsilon}-N data have been evaluated to establish the effects of key material, loading, and environmental parameters (such as steel type, strain range, strain rate, temperature, dissolved-oxygen level in water, and flow rate) on the fatigue lives of these steels. Statistical models are presented for estimating the fatigue {var_epsilon}-N curves for austenitic stainless steels as a function of the material, loading, and environmental parameters. Two methods for incorporating environmental effects into the ASME Code fatigue evaluations are presented. The influence of reactor environments on the mechanism of fatigue crack initiation in these steels is also discussed.

  17. Effect of material heat treatment on fatigue crack initiation in austenitic stainless steels in LWR environments.

    SciTech Connect

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

    2005-07-31

    The ASME Boiler and Pressure Vessel Code provides rules for the design of Class 1 components of nuclear power plants. Figures I-9.1 through I-9.6 of Appendix I to Section III of the Code specify design curves for applicable structural materials. However, the effects of light water reactor (LWR) coolant environments are not explicitly addressed by the Code design curves. The existing fatigue strain-vs.-life ({var_epsilon}-N) data illustrate potentially significant effects of LWR coolant environments on the fatigue resistance of pressure vessel and piping steels. Under certain environmental and loading conditions, fatigue lives of austenitic stainless steels (SSs) can be a factor of 20 lower in water than in air. This report presents experimental data on the effect of heat treatment on fatigue crack initiation in austenitic Type 304 SS in LWR coolant environments. A detailed metallographic examination of fatigue test specimens was performed to characterize the crack morphology and fracture morphology. The key material, loading, and environmental parameters and their effect on the fatigue life of these steels are also described. Statistical models are presented for estimating the fatigue {var_epsilon}-N curves for austenitic SSs as a function of material, loading, and environmental parameters. Two methods for incorporating the effects of LWR coolant environments into the ASME Code fatigue evaluations are presented.

  18. 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.

  19. Crack growth rates of irradiated austenitic stainless steel weld heat affected zone in BWR environments.

    SciTech Connect

    Chopra, O. K.; Alexandreanu, B.; Gruber, E. E.; Daum, R. S.; Shack, W. J.; Energy Technology

    2006-01-31

    Austenitic stainless steels (SSs) are used extensively as structural alloys in the internal components of reactor pressure vessels because of their superior fracture toughness. However, exposure to high levels of neutron irradiation for extended periods can exacerbate the corrosion fatigue and stress corrosion cracking (SCC) behavior of these steels by affecting the material microchemistry, material microstructure, and water chemistry. Experimental data are presented on crack growth rates of the heat affected zone (HAZ) in Types 304L and 304 SS weld specimens before and after they were irradiated to a fluence of 5.0 x 10{sup 20} n/cm{sup 2} (E > 1 MeV) ({approx} 0.75 dpa) at {approx}288 C. Crack growth tests were conducted under cycling loading and long hold time trapezoidal loading in simulated boiling water reactor environments on Type 304L SS HAZ of the H5 weld from the Grand Gulf reactor core shroud and on Type 304 SS HAZ of a laboratory-prepared weld. The effects of material composition, irradiation, and water chemistry on growth rates are discussed.

  20. Biaxial Fatigue Crack Growth Behavior in Aluminum Alloy 5083-H116 Under Ambient Laboratory and Saltwater Environments

    NASA Astrophysics Data System (ADS)

    Perel, V. Y.; Misak, H. E.; Mall, S.; Jain, V. K.

    2015-04-01

    Crack growth of aluminum alloy 5083 was investigated when subjected to the in-plane biaxial tension-tension fatigue with stress ratio of 0.5 under ambient laboratory and saltwater environments. Cruciform specimens with a center hole, containing a notch and precrack at 45° to the specimen's arms, were tested in a biaxial fatigue test machine. Two biaxiality ratios, λ = 1 and λ = 1.5, were studied. For λ = 1, crack propagated along a straight line collinearly with the precrack, while for λ = 1.5 case, the crack path was curved and non-collinear with the precrack. Uniaxial fatigue tests were also conducted. Crack growth rates were faster under the biaxiality fatigue in comparison to uniaxial fatigue at a given crack driving force (Δ K I or Δ G) in both environments. Further, an increase in biaxiality ratio increased the crack growth rate, i.e., faster for λ = 1.5 case than λ = 1 case. Both biaxial fatigue and saltwater environment showed detrimental effects on the fatigue crack growth resistance of 5083, and its combination is highly detrimental when compared to uniaxial fatigue.

  1. Irradiation-assisted stress corrosion cracking of austenitic stainless steels: Recent progress and new approaches

    SciTech Connect

    Chung, H.M.; Ruther, W.E.; Sanecki, J.E.; Hins, A.; Zaluzec, N.J.; Kassner, T.F.

    1996-09-01

    Irradiation-assisted stress corrosion cracking (IASCC) of several types of BWR field components fabricated from solution-annealed austenitic stainless steels (SSs), including a core internal weld, were investigated by means of slow-strain-rate test (SSRT), scanning electron microscopy (SEM), Auger electron spectroscopy (AES), and field-emission-gun advanced analytical electron microscopy (FEG-AAEM). Based on the results of the tests and analyses, separate effects of neutron fluence, tensile properties, alloying elements and major impurities identified in the American Society for Testing and Materials (ASTM) specifications, minor impurities, water chemistry, and fabrication-related variables were determined. The results indicate strongly that minor impurities not specified by the ASTM-specifications play important roles, probably through a complex synergism with grain-boundary Cr depletion. These impurities, typically associated with steelmaking and component fabrication processes, are very low or negligible in solubility in steels and are the same impurities that have been known to promote intergranular SCC significantly when they are present in water as ions or soluble compounds. It seems obvious that IASCC is a complex integral problem which involves many variables that are influenced strongly by not only irradiation conditions, water chemistry, and stress but also iron and steelmaking processes, fabrication of the component, and joining and welding. Therefore, for high-stress components in particular, it would be difficult to mitigate IASCC problems at high fluence based on the consideration of water chemistry alone, and other considerations based on material composition and fabrication procedure would be necessary as well.

  2. The effect of fretting and environment on fatigue crack initiation and early propagation in a quenched and tempered 4130 Steel

    NASA Astrophysics Data System (ADS)

    Gaul, D. J.; Duquette, D. J.

    1980-09-01

    Fretting fatigue studies were performed on quenched and tempered 4130 steel in laboratory air and in argon as functions of relative slip displacement, normal pressure and applied cyclic stress. Significant reductions in fatigue resistance were observed at all stress levels and increased with increasing normal pressures. However, a minimum in resistance was observed for relative slip magnitudes of 20 to 30 μm. Inert environments improve fatigue resistance under fretting conditions. Metallographic observations indicated that subsurface cracking was generally observed and that stress concentrations associated with this cracking resulted in deviations to and away from the faying surfaces. Fretting cracks which deviated into the alloy become initiated fatigue cracks. A mechanical model is proposed for fretting induced fatigue crack initiation which suggests that this phenomenon is a simple extension of the basic fretting process.

  3. 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.

  4. Physical Environments of Assisted Living: Research Needs and Challenges

    ERIC Educational Resources Information Center

    Cutler, Lois J.

    2007-01-01

    Purpose: This article aims to review research measures and findings related to physical environments of assisted living (AL) according to multiple conceptual perspectives--ecological, cultural, and Maslovian hierarchy. Design and Methods: A literature and research review was undertaken with two foci: performance measures for physical environments,…

  5. Oxidation products of Inconel alloys 600 and 690 in hydrogenated steam environments and their role in stress corrosion cracking

    NASA Astrophysics Data System (ADS)

    Ferguson, J. Bryce

    Inconel Alloys 600 and 690 are used extensively in components of Nuclear Pressurized Water Reactors (PWR) in the primary water loop which consists of H2 supersaturated steam. Alloy 600 has been found to crack intergranularly when exposed to primary water conditions. Alloy 690 was designed as a replacement and is generally regarded as immune to cracking. There is no consensus as to the mechanism which is responsible for cracking or the lack thereof in these alloys. In this work thermodynamic arguments for the stability of Ni and Cr compounds developed under pressurized water reactor environments ( PH2O and PH2 ) were experimentally tested. A mechanism is proposed to explain crack initiation and propagation alloy 600 along the grain boundaries where Cr2O3 has formed from the leaching of Cr from the matrix leaving behind a porous Ni-rich region. The mechanism is based on the thermodynamic potential for the transformation of a protective NiO surface layer into an amorphous non-protective Ni(OH)2 gel. This gel would also form along the grain boundaries and when hydrogenated steam reaches the porous Ni-rich regions. Crack initiation is then favored by tensile stressing of the grain boundary regions which can easily rupture the gelatinous film. The leaching of matrix Cr to form non-protective CrOOH gel at the crack tip followed by the exposure of fresh porous Ni to the environment also explains crack propagation in inconel alloy 600. The proposed crack initiation mechanism is not expected to occur in alloy 690 where a protective Cr2O 3 film covers the entire metal surface. However, crack propagation along the grain boundaries in alloy 600 and pre-cracked alloy 690 is expected to be active as hydroxide-forming reactions weaken the material at the grain boundaries.

  6. Effects of Low Temperature on Hydrogen-Assisted Crack Growth in Forged 304L Austenitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Jackson, Heather; San Marchi, Chris; Balch, Dorian; Somerday, Brian; Michael, Joseph

    2016-08-01

    The objective of this study was to evaluate effects of low temperature on hydrogen-assisted crack propagation in forged 304L austenitic stainless steel. Fracture initiation toughness and crack-growth resistance curves were measured using fracture mechanics specimens that were thermally precharged with 140 wppm hydrogen and tested at 293 K or 223 K (20 °C or -50 °C). Fracture initiation toughness for hydrogen-precharged forgings decreased by at least 50 to 80 pct relative to non-charged forgings. With hydrogen, low-temperature fracture initiation toughness decreased by 35 to 50 pct relative to room-temperature toughness. Crack growth without hydrogen at both temperatures was microstructure-independent and indistinguishable from blunting, while with hydrogen microcracks formed by growth and coalescence of microvoids. Initiation of microvoids in the presence of hydrogen occurred where localized deformation bands intersected grain boundaries and other deformation bands. Low temperature additionally promoted fracture initiation at annealing twin boundaries in the presence of hydrogen, which competed with deformation band intersections and grain boundaries as sites of microvoid formation and fracture initiation. A common ingredient for fracture initiation was stress concentration that arose from the intersection of deformation bands with these microstructural obstacles. The localized deformation responsible for producing stress concentrations at obstacles was intensified by low temperature and hydrogen. Crack orientation and forging strength were found to have a minor effect on fracture initiation toughness of hydrogen-supersaturated 304L forgings.

  7. Stress corrosion cracking of candidate structural materials under simulated first-wall/aqueous coolant environments

    SciTech Connect

    Fox, M.R.; Hull, A.B.; Kassner, T.F.

    1990-10-01

    Stress corrosion cracking (SCC) susceptibility of Types 316NG, 316, and 304 stainless steels (SS) was investigated in slow-strain-rate tests (SSRTs) in oxygenated water that simulates important parameters anticipated in first-wall/blanket systems. The water chemistry was based on a computer code which yielded the nominal concentrations of radiolytic species produced in an aqueous environment under ITER-type conditions. Actual SSRTs were performed in a less benign, more oxidizing reference environment at temperatures from 52 to 150{degree}C. Predominantly ductile fracture was observed in Type 316NG and nonsensitized Types 316 SS and 304 SS SSRT specimens strained to failure in a reference ITER water chemistry. The failure behavior of Type 304 SS specimens heat-treated to yield sensitization values of 2, 3, or 20 Coulomb (C)/cm{sup 2} by the electrochemical potentiokinetic reactivation (EPR) technique, demonstrated that the degree of sensitization had a dramatic effect on intergranular stress corrosion cracking (IGSCC) susceptibility. Ranking for resistance to SCC in simulated ITER water by electron microscopy and SSRT parameters, i.e., failure time, ultimate strength, total elongation and stress ratio is 304 SS (EPR = 20 <2 C/cm{sup 2}) < 316NG SS. 11 refs., 6 figs., 7 tabs.

  8. A novel acoustic emission monitoring and signal processing to elucidate the fracture dynamics of hydrogen assisted cracking

    SciTech Connect

    Hayashi, Yasuhisa; Takemoto, Makoto; Takemoto, Mikio

    1994-12-31

    An advanced Acoustic Emission (AE) monitoring and signal processing system was developed and applied to elucidate the fracture dynamics of hydrogen assisted cracking (HAC) of quenched-tempered low alloy steel. The developed system enables one to monitor an initiation of microcrack correctly and also to elucidate the dynamics of microcracks when multi-channel moment tensor analysis is jointly used. The system consists of 8-channel monitoring. One channel monitors the surface displacement in loading direction excited by the propagation of elastic wave, and gives the source wave by the deconvolution integral of it with the Green`s function of the second kind. Another 7 channels were designed to measure arrival time and relative amplitude of the P-waves, and to determine both the source location and the crack kinematics by tensor analysis. This paper introduces the developed monitoring system and signal processing method, and fracture dynamics of microcracks in HAC.

  9. Centrifugation-assisted Assembly of Colloidal Silica into Crack-Free and Transferrable Films with Tunable Crystalline Structures

    PubMed Central

    Fan, Wen; Chen, Min; Yang, Shu; Wu, Limin

    2015-01-01

    Self-assembly of colloidal particles into colloidal films has many actual and potential applications. While various strategies have been developed to direct the assembly of colloidal particles, fabrication of crack-free and transferrable colloidal film with controllable crystal structures still remains a major challenge. Here we show a centrifugation-assisted assembly of colloidal silica spheres into free-standing colloidal film by using the liquid/liquid interfaces of three immiscible phases. Through independent control of centrifugal force and interparticle electrostatic repulsion, polycrystalline, single-crystalline and quasi-amorphous structures can be readily obtained. More importantly, by dehydration of silica particles during centrifugation, the spontaneous formation of capillary water bridges between particles enables the binding and pre-shrinkage of the assembled array at the fluid interface. Thus the assembled colloidal films are not only crack-free, but also robust and flexible enough to be easily transferred on various planar and curved substrates. PMID:26159121

  10. Centrifugation-assisted Assembly of Colloidal Silica into Crack-Free and Transferrable Films with Tunable Crystalline Structures

    NASA Astrophysics Data System (ADS)

    Fan, Wen; Chen, Min; Yang, Shu; Wu, Limin

    2015-07-01

    Self-assembly of colloidal particles into colloidal films has many actual and potential applications. While various strategies have been developed to direct the assembly of colloidal particles, fabrication of crack-free and transferrable colloidal film with controllable crystal structures still remains a major challenge. Here we show a centrifugation-assisted assembly of colloidal silica spheres into free-standing colloidal film by using the liquid/liquid interfaces of three immiscible phases. Through independent control of centrifugal force and interparticle electrostatic repulsion, polycrystalline, single-crystalline and quasi-amorphous structures can be readily obtained. More importantly, by dehydration of silica particles during centrifugation, the spontaneous formation of capillary water bridges between particles enables the binding and pre-shrinkage of the assembled array at the fluid interface. Thus the assembled colloidal films are not only crack-free, but also robust and flexible enough to be easily transferred on various planar and curved substrates.

  11. Subcritical crack growth and other time- and environment-dependent behavior in crustal rocks

    NASA Technical Reports Server (NTRS)

    Swanson, P. L.

    1984-01-01

    Stable crack growth strongly influences both the fracture strength of brittle rocks and some of the phenomena precursory to catastrophic failure. Quantification of the time and environment dependence of fracture propagation is attempted with the use of a fracture mechanics technique. Some of the difficulties encountered when applying techniques originally developed for simple synthetic materials to complex materials like rocks are examined. A picture of subcritical fracture propagation is developed that embraces the essential ingredients of the microstructure, a microcrack process zone, and the different roles that the environment plays. To do this, the results of (1) fracture mechanics experiments on five rock types, (2) optical and scanning electron microscopy, (3) studies of microstructural aspects of fracture in ceramics, and (4) exploratory tests examining the time-dependent response of rock to the application of water are examined.

  12. The effect of initiation feature and environment on fatigue crack formation and early propagation in aluminum zinc magnesium copper

    NASA Astrophysics Data System (ADS)

    Burns, James T.

    The current research provides insight into fatigue crack formation and progression in the poorly understood size regime that bridges safe-life and damage tolerance approaches; particular attention is given to the influences of corrosion-induced degradation and time-cycle dependent loading environment effects. Quantitative analysis of crack formation life (Ni), microstructurally small crack (<500 microm) propagation kinetics (da/dN), and the effect of cold loading environment provide the means to validate mechanism-based modeling. Both pristine and corroded (L-S surface) 7075-T651 specimens were fatigued at 23°C, -50°C and -90°C under various applied stresses. Microscopy of programmed loading-induced crack surface marks produced an unparalleled Ni and small crack da/dN database. Results show that fatigue crack formation involves a complex interaction of elastic stress concentration, due to a 3-dimensional macro-pit, coupled with local micro-feature (and constituent) induced plastic strain concentration. Such interactions cause high Ni variability, but, from an engineering perspective, a broadly corroded surface should contain an extreme group of features driving Ni to ˜0. At low-applied stresses, Ni consumes a significant portion of total life, which is well predicted by coupling elastic-plastic FEA with empirical low-cycle fatigue life models. All pristine and corroded da/dN were uniquely correlated using complex continuum stress intensity (K) and crack opening solutions which account for the stress concentrating formation feature. Multiple crack growth regimes were observed, typical of environment enhanced fatigue in Al alloys. Such behavior is not captured by prominent mechanics-based small crack models. Furthermore, neither local closure nor slip-based models captured the order of magnitude variability in da/dN attributed to microstructure. Low temperature loading produces an order of magnitude increase in Ni, and even larger reduction in da/dN, due to

  13. 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.

  14. Modeling Hydrogen-Induced Cracking of Titanium Alloys in Nuclear Waste Repository Environments

    SciTech Connect

    F. Hua; K. Mon; P. Pasupathi; G. Gordon

    2004-09-08

    This paper reviews the current understanding of hydrogen-induced cracking (HIC) of Ti Grade 7 and other relevant titanium alloys within the context of the current waste package design for the repository environmental conditions anticipated within the Yucca Mountain repository. The review concentrates on corrosion processes possible in the aqueous environments expected within this site. A brief background discussion of the relevant properties of titanium alloys, the hydrogen absorption process, and the properties of passive film on titanium alloys is presented as the basis for the subsequent discussion of model developments. The key corrosion processes that could occur are addressed individually. Subsequently, the expected corrosion performance of these alloys under the specific environmental conditions anticipated at Yucca Mountain is considered. It can be concluded that, based on the conservative modeling approaches adopted, hydrogen-induced cracking of titanium alloys will not occur under nuclear waste repository conditions since there will not be sufficient hydrogen in the alloy after 10,000 years of emplacement.

  15. Assistive Technology for Young Children: Creating Inclusive Learning Environments

    ERIC Educational Resources Information Center

    Sadao, Kathleen C.; Robinson, Nancy B.

    2010-01-01

    Assistive technology (AT) can help young children with disabilities fully participate in natural, inclusive learning environments--but many early childhood professionals don't get the training they need to harness the power of AT. Fill that gap with this unintimidating, reader-friendly resource, the go-to guide to recommended AT practice for…

  16. Crack growth rates and metallographic examinations of Alloy 600 and Alloy 82/182 from field components and laboratory materials tested in PWR environments.

    SciTech Connect

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

    2008-05-05

    In light water reactors, components made of nickel-base alloys are susceptible to environmentally assisted cracking. This report summarizes the crack growth rate results and related metallography for field and laboratory-procured Alloy 600 and its weld alloys tested in pressurized water reactor (PWR) environments. The report also presents crack growth rate (CGR) results for a shielded-metal-arc weld of Alloy 182 in a simulated PWR environment as a function of temperature between 290 C and 350 C. These data were used to determine the activation energy for crack growth in Alloy 182 welds. The tests were performed by measuring the changes in the stress corrosion CGR as the temperatures were varied during the test. The difference in electrochemical potential between the specimen and the Ni/NiO line was maintained constant at each temperature by adjusting the hydrogen overpressure on the water supply tank. The CGR data as a function of temperature yielded activation energies of 252 kJ/mol for a double-J weld and 189 kJ/mol for a deep-groove weld. These values are in good agreement with the data reported in the literature. The data reported here and those in the literature suggest that the average activation energy for Alloy 182 welds is on the order of 220-230 kJ/mol, higher than the 130 kJ/mol commonly used for Alloy 600. The consequences of using a larger value of activation energy for SCC CGR data analysis are discussed.

  17. Application requirements for Robotic Nursing Assistants in hospital environments

    NASA Astrophysics Data System (ADS)

    Cremer, Sven; Doelling, Kris; Lundberg, Cody L.; McNair, Mike; Shin, Jeongsik; Popa, Dan

    2016-05-01

    In this paper we report on analysis toward identifying design requirements for an Adaptive Robotic Nursing Assistant (ARNA). Specifically, the paper focuses on application requirements for ARNA, envisioned as a mobile assistive robot that can navigate hospital environments to perform chores in roles such as patient sitter and patient walker. The role of a sitter is primarily related to patient observation from a distance, and fetching objects at the patient's request, while a walker provides physical assistance for ambulation and rehabilitation. The robot will be expected to not only understand nurse and patient intent but also close the decision loop by automating several routine tasks. As a result, the robot will be equipped with sensors such as distributed pressure sensitive skins, 3D range sensors, and so on. Modular sensor and actuator hardware configured in the form of several multi-degree-of-freedom manipulators, and a mobile base are expected to be deployed in reconfigurable platforms for physical assistance tasks. Furthermore, adaptive human-machine interfaces are expected to play a key role, as they directly impact the ability of robots to assist nurses in a dynamic and unstructured environment. This paper discusses required tasks for the ARNA robot, as well as sensors and software infrastructure to carry out those tasks in the aspects of technical resource availability, gaps, and needed experimental studies.

  18. Biologically inspired crack delocalization in a high strain-rate environment.

    PubMed

    Knipprath, Christian; Bond, Ian P; Trask, Richard S

    2012-04-01

    Biological materials possess unique and desirable energy-absorbing mechanisms and structural characteristics worthy of consideration by engineers. For example, high levels of energy dissipation at low strain rates via triggering of crack delocalization combined with interfacial hardening by platelet interlocking are observed in brittle materials such as nacre, the iridescent material in seashells. Such behaviours find no analogy in current engineering materials. The potential to mimic such toughening mechanisms on different length scales now exists, but the question concerning their suitability under dynamic loading conditions and whether these mechanisms retain their energy-absorbing potential is unclear. This paper investigates the kinematic behaviour of an 'engineered' nacre-like structure within a high strain-rate environment. A finite-element (FE) model was developed which incorporates the pertinent biological design features. A parametric study was carried out focusing on (i) the use of an overlapping discontinuous tile arrangement for crack delocalization and (ii) application of tile waviness (interfacial hardening) for improved post-damage behaviour. With respect to the material properties, the model allows the permutation and combination of a variety of different material datasets. The advantage of such a discontinuous material shows notable improvements in sustaining high strain-rate deformation relative to an equivalent continuous morphology. In the case of the continuous material, the shockwaves propagating through the material lead to localized failure while complex shockwave patterns are observed in the discontinuous flat tile arrangement, arising from platelet interlocking. The influence of the matrix properties on impact performance is investigated by varying the dominant material parameters. The results indicate a deceleration of the impactor velocity, thus delaying back face nodal displacement. A final series of FE models considered the

  19. Biologically inspired crack delocalization in a high strain-rate environment

    PubMed Central

    Knipprath, Christian; Bond, Ian P.; Trask, Richard S.

    2012-01-01

    Biological materials possess unique and desirable energy-absorbing mechanisms and structural characteristics worthy of consideration by engineers. For example, high levels of energy dissipation at low strain rates via triggering of crack delocalization combined with interfacial hardening by platelet interlocking are observed in brittle materials such as nacre, the iridescent material in seashells. Such behaviours find no analogy in current engineering materials. The potential to mimic such toughening mechanisms on different length scales now exists, but the question concerning their suitability under dynamic loading conditions and whether these mechanisms retain their energy-absorbing potential is unclear. This paper investigates the kinematic behaviour of an ‘engineered’ nacre-like structure within a high strain-rate environment. A finite-element (FE) model was developed which incorporates the pertinent biological design features. A parametric study was carried out focusing on (i) the use of an overlapping discontinuous tile arrangement for crack delocalization and (ii) application of tile waviness (interfacial hardening) for improved post-damage behaviour. With respect to the material properties, the model allows the permutation and combination of a variety of different material datasets. The advantage of such a discontinuous material shows notable improvements in sustaining high strain-rate deformation relative to an equivalent continuous morphology. In the case of the continuous material, the shockwaves propagating through the material lead to localized failure while complex shockwave patterns are observed in the discontinuous flat tile arrangement, arising from platelet interlocking. The influence of the matrix properties on impact performance is investigated by varying the dominant material parameters. The results indicate a deceleration of the impactor velocity, thus delaying back face nodal displacement. A final series of FE models considered the

  20. Biologically inspired crack delocalization in a high strain-rate environment.

    PubMed

    Knipprath, Christian; Bond, Ian P; Trask, Richard S

    2012-04-01

    Biological materials possess unique and desirable energy-absorbing mechanisms and structural characteristics worthy of consideration by engineers. For example, high levels of energy dissipation at low strain rates via triggering of crack delocalization combined with interfacial hardening by platelet interlocking are observed in brittle materials such as nacre, the iridescent material in seashells. Such behaviours find no analogy in current engineering materials. The potential to mimic such toughening mechanisms on different length scales now exists, but the question concerning their suitability under dynamic loading conditions and whether these mechanisms retain their energy-absorbing potential is unclear. This paper investigates the kinematic behaviour of an 'engineered' nacre-like structure within a high strain-rate environment. A finite-element (FE) model was developed which incorporates the pertinent biological design features. A parametric study was carried out focusing on (i) the use of an overlapping discontinuous tile arrangement for crack delocalization and (ii) application of tile waviness (interfacial hardening) for improved post-damage behaviour. With respect to the material properties, the model allows the permutation and combination of a variety of different material datasets. The advantage of such a discontinuous material shows notable improvements in sustaining high strain-rate deformation relative to an equivalent continuous morphology. In the case of the continuous material, the shockwaves propagating through the material lead to localized failure while complex shockwave patterns are observed in the discontinuous flat tile arrangement, arising from platelet interlocking. The influence of the matrix properties on impact performance is investigated by varying the dominant material parameters. The results indicate a deceleration of the impactor velocity, thus delaying back face nodal displacement. A final series of FE models considered the

  1. Human-inspired sound environment recognition system for assistive vehicles

    NASA Astrophysics Data System (ADS)

    González Vidal, Eduardo; Fredes Zarricueta, Ernesto; Auat Cheein, Fernando

    2015-02-01

    Objective. The human auditory system acquires environmental information under sound stimuli faster than visual or touch systems, which in turn, allows for faster human responses to such stimuli. It also complements senses such as sight, where direct line-of-view is necessary to identify objects, in the environment recognition process. This work focuses on implementing human reaction to sound stimuli and environment recognition on assistive robotic devices, such as robotic wheelchairs or robotized cars. These vehicles need environment information to ensure safe navigation. Approach. In the field of environment recognition, range sensors (such as LiDAR and ultrasonic systems) and artificial vision devices are widely used; however, these sensors depend on environment constraints (such as lighting variability or color of objects), and sound can provide important information for the characterization of an environment. In this work, we propose a sound-based approach to enhance the environment recognition process, mainly for cases that compromise human integrity, according to the International Classification of Functioning (ICF). Our proposal is based on a neural network implementation that is able to classify up to 15 different environments, each selected according to the ICF considerations on environment factors in the community-based physical activities of people with disabilities. Main results. The accuracy rates in environment classification ranges from 84% to 93%. This classification is later used to constrain assistive vehicle navigation in order to protect the user during daily activities. This work also includes real-time outdoor experimentation (performed on an assistive vehicle) by seven volunteers with different disabilities (but without cognitive impairment and experienced in the use of wheelchairs), statistical validation, comparison with previously published work, and a discussion section where the pros and cons of our system are evaluated. Significance

  2. Biomolecule-assisted synthesis of single-crystalline selenium nanowires and nanoribbons via a novel flake-cracking mechanism

    NASA Astrophysics Data System (ADS)

    Zhang, Bin; Ye, Xingchen; Dai, Wei; Hou, Weiyi; Zuo, Fan; Xie, Yi

    2006-01-01

    Recently, the biomolecule-assisted synthesis method has been a new and promising focus in the preparation of various nanomaterials. But current works mainly focus on the synthesis of metal nanoparticles and nanowires using macro-biomolecules (e.g. virus, protein and DNA) as templates in the presence of a reducing agent. Beta-carotene, one of the most common bio-antioxidants, can be oxidized to form species with both hydrophilic and hydrophobic ends, which can provide an in situ soft template for the synthesis of nanomaterials. Herein, a simple beta-carotene-assisted method was developed for the first time to synthesize t-Se nanowires and nanoribbons with high crystallinity. We demonstrate that beta-carotene serves as not only the reducing agent, but also an in situ template in the preparation of Se one-dimensional nanostructures. It is found that the growth mechanism of Se nanomaterials is different from the familiar sphere-wire process. A novel flake-cracking mechanism is proposed. By this biomolecule-assisted route, Te one-dimensional nanostructures and Pd nanowires were also fabricated. The assisted-biomolecule in our method may be spread to carotenoids and other antioxidants, and thus broaden the application fields of biomolecules. Our preliminary investigations have shown that the facile, solution-phase biomolecule-assisted method can be potentially extended to the preparation of other low-dimensional nanostructures. The synthesized t-Se nanowires and nanoribbons may serve as templates to generate other tubular functional nanomaterials and find applications in the studies of structure-property relationships as well as in the fabrication of nanoscale optoelectronic devices.

  3. Evaluation of stress corrosion cracking of irradiated 304L stainless steel in PWR environment using heavy ion irradiation

    NASA Astrophysics Data System (ADS)

    Gupta, J.; Hure, J.; Tanguy, B.; Laffont, L.; Lafont, M.-C.; Andrieu, E.

    2016-08-01

    IASCC has been a major concern regarding the structural and functional integrity of core internals of PWR's, especially baffle-to-former bolts. Despite numerous studies over the past few decades, additional evaluation of the parameters influencing IASCC is still needed for an accurate understanding and modeling of this phenomenon. In this study, Fe irradiation at 450 °C was used to study the cracking susceptibility of 304 L austenitic stainless steel. After 10 MeV Fe irradiation to 5 dpa, irradiation-induced damage in the microstructure was characterized and quantified along with nano-hardness measurements. After 4% plastic strain in a PWR environment, quantitative information on the degree of strain localization, as determined by slip-line spacing, was obtained using SEM. Fe-irradiated material strained to 4% in a PWR environment exhibited crack initiation sites that were similar to those that occur in neutron- and proton-irradiated materials, which suggests that Fe irradiation may be a representative means for studying IASCC susceptibility. Fe-irradiated material subjected to 4% plastic strain in an inert argon environment did not exhibit any cracking, which suggests that localized deformation is not in itself sufficient for initiating cracking for the irradiation conditions used in this study.

  4. Ultrasensitive Cracking-Assisted Strain Sensors Based on Silver Nanowires/Graphene Hybrid Particles.

    PubMed

    Chen, Song; Wei, Yong; Wei, Siman; Lin, Yong; Liu, Lan

    2016-09-28

    Strain sensors with ultrahigh sensitivity under microstrain have numerous potential applications in heartbeat monitoring, pulsebeat detection, sound signal acquisition, and recognition. In this work, a two-part strain sensor (i.e., polyurethane part and brittle conductive hybrid particles layer on top) based on silver nanowires/graphene hybrid particles is developed via a simple coprecipitation, reduction, vacuum filtration, and casting process. Because of the nonuniform interface, weak interfacial bonding, and the hybrid particles' point-to-point conductive networks, the crack and overlap morphologies are successfully formed on the strain sensor after a prestretching; the crack-based stain sensor exhibits gauge factors as high as 20 (Δε < 0.3%), 1000 (0.3% < Δε < 0.5%), and 4000 (0.8% < Δε < 1%). In addition, we demonstrate the sensing mechanism under strain results in the high gauge factor of the strain sensor. Combined with its good response to bending, high strain resolution, and high working stability, the developed strain sensor is promising in the applications of electronic skins, motion sensors, and health monitoring sensors.

  5. Ultrasensitive Cracking-Assisted Strain Sensors Based on Silver Nanowires/Graphene Hybrid Particles.

    PubMed

    Chen, Song; Wei, Yong; Wei, Siman; Lin, Yong; Liu, Lan

    2016-09-28

    Strain sensors with ultrahigh sensitivity under microstrain have numerous potential applications in heartbeat monitoring, pulsebeat detection, sound signal acquisition, and recognition. In this work, a two-part strain sensor (i.e., polyurethane part and brittle conductive hybrid particles layer on top) based on silver nanowires/graphene hybrid particles is developed via a simple coprecipitation, reduction, vacuum filtration, and casting process. Because of the nonuniform interface, weak interfacial bonding, and the hybrid particles' point-to-point conductive networks, the crack and overlap morphologies are successfully formed on the strain sensor after a prestretching; the crack-based stain sensor exhibits gauge factors as high as 20 (Δε < 0.3%), 1000 (0.3% < Δε < 0.5%), and 4000 (0.8% < Δε < 1%). In addition, we demonstrate the sensing mechanism under strain results in the high gauge factor of the strain sensor. Combined with its good response to bending, high strain resolution, and high working stability, the developed strain sensor is promising in the applications of electronic skins, motion sensors, and health monitoring sensors. PMID:27599264

  6. Irradiation assisted stress corrosion cracking of HTH Alloy X-750 and Alloy 625

    SciTech Connect

    Mills, W.J.; Lebo, M.R.; Bajaj, R.; Kearns, J.J.; Hoffman, R.C.; Korinko, J.J.

    1994-06-01

    In-reactor testing of bolt-loaded precracked compact tension specimens was performed in 360{degree}C water to determine effect of irradiation on the SCC behavior of HTH Alloy X-750 and direct aged Alloy 625. Out-of-flux and autoclave control specimens provided baseline data. Primary test variables were stress intensity factor, fluence, chemistry, processing history, prestrain. Results for the first series of experiments were presented at a previous conference. Data from two more recent experiments are compared with previous results; they confirm that high irradiation levels significantly reduce SCC resistance in HTH Alloy X-750. Heat-to-heat differences in IASCC were related to differences in boron content, with low boron heats showing improved SCC resistance. The in-reactor SCC performance of Alloy 625 was superior to that for Alloy X-750, as no cracking was observed in any Alloy 625 specimens even though they were tested at very high K{sub 1} and fluence levels. A preliminary SCC usage model developed for Alloy X-750 indicates that in-reactor creep processes, which relax stresses but also increase crack tip strain rates, and radiolysis effects accelerate SCC. Hence, in-reactor SCC damage under high flux conditions may be more severe than that associated with postirradiation tests. In addition, preliminary mechanism studies were performed to determine the cause of IASCC In Alloy X-750.

  7. Simulation of RCC Crack Growth Due to Carbon Oxidation in High-Temperature Gas Environments

    NASA Technical Reports Server (NTRS)

    Titov, E. V.; Levin, D. A.; Picetti, Donald J.; Anderson, Brian P.

    2009-01-01

    The carbon wall oxidation technique coupled with a CFD technique was employed to study the flow in the expanding crack channel caused by the oxidation of the channel carbon walls. The recessing 3D surface morphing procedure was developed and tested in comparison with the arcjet experimental results. The multi-block structured adaptive meshing was used to model the computational domain changes due to the wall recession. Wall regression rates for a reinforced carbon-carbon (RCC) samples, that were tested in a high enthalpy arcjet environment, were computationally obtained and used to assess the channel expansion. The test geometry and flow conditions render the flow regime as the transitional to continuum, therefore Navier-Stokes gas dynamic approach with the temperature jump and velocity slip correction to the boundary conditions was used. The modeled mechanism for wall material loss was atomic oxygen reaction with bare carbon. The predicted channel growth was found to agree with arcjet observations. Local gas flow field results were found to affect the oxidation rate in a manner that cannot be predicted by previous mass loss correlations. The method holds promise for future modeling of materials gas-dynamic interactions for hypersonic flight.

  8. Development of an assistive patient mobile system for hospital environments.

    PubMed

    Nguyen, Huy Hoang; Nguyen, Tuan Nghia; Clout, Raymont; Gibson, Alexander; Nguyen, Hung T

    2013-01-01

    This paper presents an assistive patient mobile system for hospital environments, which focuses on transferring the patient without nursing help. The system is a combination of an advanced hospital bed and an autonomous navigating robot. This intelligent bed can track the robot and routinely navigates and communicates with the bed. The work centralizes in building a structure, hardware design and robot detection and tracking algorithms by using laser range finder. The assistive patient mobile system has been tested and the real experiments are shown with a high performance of reliability and practicality. The accuracy of the method proposed in this paper is 91% for the targeted testing object with the error rate of classification by 6%. Additionally, a comparison between our method and a related one is also described including the comparison of results. PMID:24110232

  9. Non-destructive in situ mapping of macroholes, cracks and inhomogeneities of stalagmites in cave environments

    NASA Astrophysics Data System (ADS)

    Hegymegi, Erika; Gyöngy, Miklós; Bodolai, Tamás; Divós, Ferenc; Barta, Edit; Gribovszki, Katalin; Bokelmann, Götz; Hegymegi, Csaba; Lednická, Markéta; Kovács, Károly

    2016-04-01

    Intact and vulnerable, candle-stick type stalagmites can be used as prehistoric-earthquake indicators during seismic-hazard analysis of a given region, because they are old enough to survive several earthquakes. The continued intactness of the stalagmites indicates a lack of earthquakes that had the strength to destroy them. To make sure that the stalagmites are intact, we have to image their internal structure in order to estimate the steadiness more accurate and potential failure in the last few thousand years, during their evolution. These stalagmites play an important indicator role and carry fundamental information; however, legally they are strictly protected natural objects in Europe. Therefore it is impossible to examine them in the laboratory by conventional equipment such as computer tomography (CT) or X-ray, because this would require taking samples. With the presented non-destructive methods (ultrasound and acoustic tomography) we tried to detect macroholes, cracks and velocity anomalies inside the stalagmites on the mm scale in situ, in the cave. The acoustic tomography applied in the current work is an existing method in forest research. Forest researchers use it to non-destructively detect the size and location of decayed or hollow parts in the trunk and this technique is able to detect the velocity changing of wave propagation and anomalies in the stalagmites as well. The other method that we use is ultrasound imaging, which uses (and is able to calculate) the velocity of sound propagation. Here, the frequency used is much higher (typically 250 kHz to 5 MHz), which increases resolution but at the same time decreases penetration depth compared to acoustic tomography. In this latter work, through transmission and TOFD (time-of-flight-diffraction) ultrasound methods are using thickness-mode ultrasound transducers (Panametrics, Olympus). Such equipment is well-adapted to the cave environment and this is the first time that it has been used for these

  10. SCC crack growth rate of cold worked 316L stainless steel in PWR environment

    NASA Astrophysics Data System (ADS)

    Du, Donghai; Chen, Kai; Yu, Lun; lu, Hui; Zhang, Lefu; Shi, Xiuqiang; Xu, Xuelian

    2015-01-01

    Many component failures in nuclear power plants were found to be caused by stress corrosion cracking (SCC) of cold worked austenitic steels. Some of the pressure boundary component materials are even cold worked up to 35% plastic deformation, leaving high residual stress and inducing high growth rate of corrosion crack. Controlling water chemistry is one of the best counter measure to mitigate this problem. In this work, the effects of temperature (200 up to 325 °C) and dissolved oxygen (0 up to 2000 μg/L) on SCC crack growth rates of cold worked austenitic stainless steel type 316L have been tested by using direct current potential drop (DCPD) method. The results showed that temperature affected SCC crack growth rates more significantly in oxygenated water than in deaerated water. In argon deaerated water, the crack growth rate exhibited a peak at about 250 °C, which needs further verification. At 325 °C, the SCC crack growth rate increased rapidly with the increase of dissolved oxygen concentration within the range from 0 up to 200 μg/L, while when dissolved oxygen was above 200 μg/L, the crack growth rate followed a shallower dependence on dissolved oxygen concentration.

  11. Getting up at the Crack of Noon: Children on Public Assistance.

    ERIC Educational Resources Information Center

    Bruckerhoff, Charles E.

    This study presents findings from an ongoing study of urban childhood on public assistance. The study used interviews with aldermen, social workers, police, public housing and ghetto neighborhood residents, and medical personnel as well as the collection of field study data from local institutions and their representatives. The results appear in…

  12. 32 CFR 700.325 - The Assistant Secretary of the Navy (Installations and Environment).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... (Installations and Environment). 700.325 Section 700.325 National Defense Department of Defense (Continued... Assistants § 700.325 The Assistant Secretary of the Navy (Installations and Environment). The Assistant Secretary of the Navy (Installations and Environment) is responsible for: (a) Policy relating to...

  13. 32 CFR 700.325 - The Assistant Secretary of the Navy (Installations and Environment).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... (Installations and Environment). 700.325 Section 700.325 National Defense Department of Defense (Continued... Assistants § 700.325 The Assistant Secretary of the Navy (Installations and Environment). The Assistant Secretary of the Navy (Installations and Environment) is responsible for: (a) Policy relating to...

  14. 32 CFR 700.325 - The Assistant Secretary of the Navy (Installations and Environment).

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... (Installations and Environment). 700.325 Section 700.325 National Defense Department of Defense (Continued... Assistants § 700.325 The Assistant Secretary of the Navy (Installations and Environment). The Assistant Secretary of the Navy (Installations and Environment) is responsible for: (a) Policy relating to...

  15. 32 CFR 700.325 - The Assistant Secretary of the Navy (Installations and Environment).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... (Installations and Environment). 700.325 Section 700.325 National Defense Department of Defense (Continued... Assistants § 700.325 The Assistant Secretary of the Navy (Installations and Environment). The Assistant Secretary of the Navy (Installations and Environment) is responsible for: (a) Policy relating to...

  16. The Cooperate Assistive Teamwork Environment for Software Description Languages.

    PubMed

    Groenda, Henning; Seifermann, Stephan; Müller, Karin; Jaworek, Gerhard

    2015-01-01

    Versatile description languages such as the Unified Modeling Language (UML) are commonly used in software engineering across different application domains in theory and practice. They often use graphical notations and leverage visual memory for expressing complex relations. Those notations are hard to access for people with visual impairment and impede their smooth inclusion in an engineering team. Existing approaches provide textual notations but require manual synchronization between the notations. This paper presents requirements for an accessible and language-aware team work environment as well as our plan for the assistive implementation of Cooperate. An industrial software engineering team consisting of people with and without visual impairment will evaluate the implementation. PMID:26294461

  17. Influence of hydrogen environment on fatigue crack growth in forged Ti-6Al-4V: fractographic analysis

    NASA Astrophysics Data System (ADS)

    Gaddam, R.; Pederson, R.; Hörnqvist, M.; Antti, M.-L.

    2013-12-01

    The influence of high-pressure gaseous hydrogen environment (15 MPa) on the fatigue crack growth in forged Ti-6A1-4V at room temperature is investigated. It is observed that the fatigue crack growth (FCG) rate is fluctuating at 20 <= ΔK <= 26 MPa√m, and increase drastically at ΔK > 26 MPa√m in hydrogen environment. The effect of hydrogen on the FCG rate is dependent on the stress intensity level (ΔK). Detailed fractographic analysis of the fracture surfaces is performed at different ΔK using field emission scanning electron microscope (FE-SEM). The differences in appearance of fracture surfaces in air and hydrogen are discussed.

  18. Modeling Users, Context and Devices for Ambient Assisted Living Environments

    PubMed Central

    Castillejo, Eduardo; Almeida, Aitor; López-de-Ipiña, Diego; Chen, Liming

    2014-01-01

    The participation of users within AAL environments is increasing thanks to the capabilities of the current wearable devices. Furthermore, the significance of considering user's preferences, context conditions and device's capabilities help smart environments to personalize services and resources for them. Being aware of different characteristics of the entities participating in these situations is vital for reaching the main goals of the corresponding systems efficiently. To collect different information from these entities, it is necessary to design several formal models which help designers to organize and give some meaning to the gathered data. In this paper, we analyze several literature solutions for modeling users, context and devices considering different approaches in the Ambient Assisted Living domain. Besides, we remark different ongoing standardization works in this area. We also discuss the used techniques, modeled characteristics and the advantages and drawbacks of each approach to finally draw several conclusions about the reviewed works. PMID:24643006

  19. The effects of cold rolling orientation and water chemistry on stress corrosion cracking behavior of 316L stainless steel in simulated PWR water environments

    NASA Astrophysics Data System (ADS)

    Chen, Junjie; Lu, Zhanpeng; Xiao, Qian; Ru, Xiangkun; Han, Guangdong; Chen, Zhen; Zhou, Bangxin; Shoji, Tetsuo

    2016-04-01

    Stress corrosion cracking behaviors of one-directionally cold rolled 316L stainless steel specimens in T-L and L-T orientations were investigated in hydrogenated and deaerated PWR primary water environments at 310 °C. Transgranular cracking was observed during the in situ pre-cracking procedure and the crack growth rate was almost not affected by the specimen orientation. Locally intergranular stress corrosion cracks were found on the fracture surfaces of specimens in the hydrogenated PWR water. Extensive intergranular stress corrosion cracks were found on the fracture surfaces of specimens in deaerated PWR water. More extensive cracks were found in specimen T-L orientation with a higher crack growth rate than that in the specimen L-T orientation with a lower crack growth rate. Crack branching phenomenon found in specimen L-T orientation in deaerated PWR water was synergistically affected by the applied stress direction as well as the preferential oxidation path along the elongated grain boundaries, and the latter was dominant.

  20. Stress corrosion cracking of a titanium alloy in chloride-containing liquid environments

    NASA Technical Reports Server (NTRS)

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

    1974-01-01

    Ti-8 Al-1 Mo-1 V was tested in solvents containing chloride, bromide or iodide ions. It was found that the region II plateau velocity could be correlated with the inverse of the viscosity for several solvents. It seems most likely that this reflects the influence of the viscosity on the diffusion coefficient of some species involved in a mass transfer process which limits the crack growth. Associated tests were performed in which the potential, pH and concentration of Cl- were varied, in some of the same solutions as used for the viscosity tests. It is concluded from these tests that the absence of cathodic protection against cracking in solutions of low pH arises from an ohmic effect which isolates the crack tip from external potential control.

  1. Microbe-assisted phytoremediation of hydrocarbons in estuarine environments.

    PubMed

    Oliveira, Vanessa; Gomes, Newton C M; Almeida, Adelaide; Silva, Artur M S; Silva, Helena; Cunha, Ângela

    2015-01-01

    Estuaries are sinks for various anthropogenic contaminants, such as petroleum hydrocarbons, giving rise to significant environmental concern. The demand for organisms and processes capable of degrading pollutants in a clean, effective, and less expensive process is of great importance. Phytoremedition approaches involving plant/bacteria interactions have been explored as an alternative, and halophyte vegetation has potential for use in phytoremedition of hydrocarbon contamination. Studies with plant species potentially suitable for microbe-assisted phytoremediation are widely represented in scientific literature. However, the in-depth understanding of the biological processes associated with the re-introduction of indigenous bacteria and plants and their performance in the degradation of hydrocarbons is still the limiting step for the application of these bioremediation solutions in a field context. The intent of the present review is to summarize the sources and effects of hydrocarbon contamination in estuarine environments, the strategies currently available for bioremediation (potential and limitations), and the perspectives of the use of halophyte plants in microbe-assisted phytoremediation approaches.

  2. Challenges and Limitations of Intelligent Ambient Assisted Living Environments

    NASA Astrophysics Data System (ADS)

    Wichert, Reiner

    As a result of changing demographics, residing and being cared for in one's own familiar environment versus in an institutionalised inpatient setting is becoming the more attractive alternative for an ever increasing portion of the population. Despite its tremendous market potential, the AAL (Ambient Assisted Living) branch is still on the cusp of a mainstream breakthrough. A lack of viable business models is considered almost unanimously to be the greatest market obstacle to a broad implementation of innovative AAL systems. This paper highlights possible explanations for this deficit and shows why the AAL community has yet to arrive at joint solutions based on a unified AAL reference platform. Furthermore, this paper describes the enormous potential of AmI and AAL, as the first real opportunity for their success is provided through universAAL and AALOA.

  3. Effect of Gas Tungsten Arc Welding Parameters on Hydrogen-Assisted Cracking of Type 321 Stainless Steel

    NASA Astrophysics Data System (ADS)

    Rozenak, Paul; Unigovski, Yaakov; Shneck, Roni

    2016-05-01

    The susceptibility of AISI type 321 stainless steel welded by the gas tungsten arc welding (GTAW) process to hydrogen-assisted cracking (HAC) was studied in a tensile test combined with in situ cathodic charging. Specimen charging causes a decrease in ductility of both the as-received and welded specimens. The mechanical properties of welds depend on welding parameters. For example, the ultimate tensile strength and ductility increase with growing shielding gas (argon) rate. More severe decrease in the ductility was obtained after post-weld heat treatment (PWHT). In welded steels, in addition to discontinuous grain boundary carbides (M23C6) and dense distribution of metal carbides MC ((Ti, Nb)C) precipitated in the matrix, the appearance of delta-ferrite phase was observed. The fracture of sensitized specimens was predominantly intergranular, whereas the as-welded specimens exhibited mainly transgranular regions. High-dislocation density regions and stacking faults were found in delta-ferrite formed after welding. Besides, thin stacking fault plates and epsilon-martensite were found in the austenitic matrix after the cathodic charging.

  4. 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.

  5. 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.

  6. Surface Crack Growth Behavior of Pipeline Steel Under Disbonded Coating at Free Corrosion Potential in Near-Neutral pH Soil Environments

    NASA Astrophysics Data System (ADS)

    Egbewande, Afolabi; Chen, Weixing; Eadie, Reg; Kania, Richard; Van Boven, Greg; Worthingham, Robert; Been, Jenny

    2014-10-01

    Crack growth behavior of X65 pipeline steel at free corrosion potential in near-neutral pH soil environment under a CO2 concentration gradient inside a disbonded coating was studied. Growth rates were found to be highest at the open mouth of the simulated disbondment where CO2 concentrations, hence local hydrogen concentration in the local environment, was highest. Careful analysis of growth rate data using a corrosion-fatigue model of the form Δ K α / K {max/ β }/ f γ , where (1/ f γ ) models environmental contribution to growth, revealed that environmental contribution could vary by up to a factor of three. Such intense environmental contribution at the open mouth kept the crack tip atomically sharp despite the simultaneous occurrence of low-temperature creep and crack tip dissolution, which are the factors that blunt the crack tip. At other locations where environmental enhancement was lower, significant crack tip blunting attributed to both low-temperature creep and crack tip dissolution was observed. These factors both led to lower crack growth rates away from the open mouth.

  7. Facilitating Inter-Domain Synergies in Ambient Assisted Living Environments.

    PubMed

    Schwartze, Jonas; Schrom, Harald; Wolf, Klaus-Hendrik; Marschollek, Michael

    2016-01-01

    Current Ambient Assisted Living (AAL) environments lack integration of sensors and actuators of other sub-domains. Creating technical and organizational integration is addressed by the BASIS project (Build Automation by a Scalable and Intelligent System), which aims to build a cross-domain home bus system. The main objective of this paper is to present an overview of design, architecture and state of realization of BASIS by describing the requirements development process, underlying hardware design and software architecture. We built a distributed system of one independent building manager with several redundantly meshed segment controllers, each controlling a bus segment with any number of bus nodes. The software system layer is divided into logical partitions representing each sub-domain. Structured data storage is possible with a special FHIR based home centered data warehouse. The system has been implemented in six apartments running under daily living conditions. BASIS integrates a broad range of sub-domains, which poses challenges to all project partners in terms of a common terminology, and project management methods, but enables development of inter-domain synergies like using the same sensor and actuator hardware for a broad range of services and use cases. PMID:27577428

  8. Facilitating Inter-Domain Synergies in Ambient Assisted Living Environments.

    PubMed

    Schwartze, Jonas; Schrom, Harald; Wolf, Klaus-Hendrik; Marschollek, Michael

    2016-01-01

    Current Ambient Assisted Living (AAL) environments lack integration of sensors and actuators of other sub-domains. Creating technical and organizational integration is addressed by the BASIS project (Build Automation by a Scalable and Intelligent System), which aims to build a cross-domain home bus system. The main objective of this paper is to present an overview of design, architecture and state of realization of BASIS by describing the requirements development process, underlying hardware design and software architecture. We built a distributed system of one independent building manager with several redundantly meshed segment controllers, each controlling a bus segment with any number of bus nodes. The software system layer is divided into logical partitions representing each sub-domain. Structured data storage is possible with a special FHIR based home centered data warehouse. The system has been implemented in six apartments running under daily living conditions. BASIS integrates a broad range of sub-domains, which poses challenges to all project partners in terms of a common terminology, and project management methods, but enables development of inter-domain synergies like using the same sensor and actuator hardware for a broad range of services and use cases.

  9. Environment assisted degradation mechanisms in aluminum-lithium alloys

    NASA Technical Reports Server (NTRS)

    Gangloff, Richard P.; Stoner, Glenn E.; Swanson, Robert E.

    1988-01-01

    Section 1 of this report records the progress achieved on NASA-LaRC Grant NAG-1-745 (Environment Assisted Degradation Mechanisms in Al-Li Alloys), and is based on research conducted during the period April 1 to November 30, 1987. A discussion of work proposed for the project's second year is included. Section 2 provides an overview of the need for research on the mechanisms of environmental-mechanical degradation of advanced aerospace alloys based on aluminum and lithium. This research is to provide NASA with the basis necessary to permit metallurgical optimization of alloy performance and engineering design with respect to damage tolerance, long term durability and reliability. Section 3 reports on damage localization mechanisms in aqueous chloride corrosion fatigue of aluminum-lithium alloys. Section 4 reports on progress made on measurements and mechanisms of localized aqueous corrosion in aluminum-lithium alloys. Section 5 provides a detailed technical proposal for research on environmental degradation of Al-Li alloys, and the effect of hydrogen in this.

  10. Simulation of Mechanical Behaviors of Ceramic Composites Under Stress-Oxidation Environment While Considering the Effect of Matrix Cracks

    NASA Astrophysics Data System (ADS)

    Sun, Zhigang; Shao, Hongyan; Niu, Xuming; Song, Yingdong

    2016-06-01

    This article proposes a model which takes the effect of matrix cracking into consideration and analyzes the mechanical behaviors of unidirectional ceramic matrix composites under stress-oxidation environment. The change in the rules of mass loss ratio, residual modulus and residual strength of unidirectional C/SiC composite under different stress, oxidation time, temperature and fiber volume fraction with the temperature varying from 400 to 900 °C have been discussed in this paper. The comparison between the predicted residual mechanics properties and the experiment results demonstrates that the predicted results have a good agreement with the experiment results, which means that the model is feasible to simulate mechanical behaviors of unidirectional C/SiC composite under stress oxidation environment.

  11. Crack growth rates and fracture toughness of irradiated austenitic stainless steels in BWR environments.

    SciTech Connect

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

    2008-01-21

    In light water reactors, austenitic stainless steels (SSs) are used extensively as structural alloys in reactor core internal components because of their high strength, ductility, and fracture toughness. However, exposure to high levels of neutron irradiation for extended periods degrades the fracture properties of these steels by changing the material microstructure (e.g., radiation hardening) and microchemistry (e.g., radiation-induced segregation). Experimental data are presented on the fracture toughness and crack growth rates (CGRs) of wrought and cast austenitic SSs, including weld heat-affected-zone materials, that were irradiated to fluence levels as high as {approx} 2x 10{sup 21} n/cm{sup 2} (E > 1 MeV) ({approx} 3 dpa) in a light water reactor at 288-300 C. The results are compared with the data available in the literature. The effects of material composition, irradiation dose, and water chemistry on CGRs under cyclic and stress corrosion cracking conditions were determined. A superposition model was used to represent the cyclic CGRs of austenitic SSs. The effects of neutron irradiation on the fracture toughness of these steels, as well as the effects of material and irradiation conditions and test temperature, have been evaluated. A fracture toughness trend curve that bounds the existing data has been defined. The synergistic effects of thermal and radiation embrittlement of cast austenitic SS internal components have also been evaluated.

  12. Empirical modeling of environment-enhanced fatigue crack propagation in structural alloys for component life prediction

    NASA Technical Reports Server (NTRS)

    Richey, Edward, III

    1995-01-01

    This research aims to develop the methods and understanding needed to incorporate time and loading variable dependent environmental effects on fatigue crack propagation (FCP) into computerized fatigue life prediction codes such as NASA FLAGRO (NASGRO). In particular, the effect of loading frequency on FCP rates in alpha + beta titanium alloys exposed to an aqueous chloride solution is investigated. The approach couples empirical modeling of environmental FCP with corrosion fatigue experiments. Three different computer models have been developed and incorporated in the DOS executable program. UVAFAS. A multiple power law model is available, and can fit a set of fatigue data to a multiple power law equation. A model has also been developed which implements the Wei and Landes linear superposition model, as well as an interpolative model which can be utilized to interpolate trends in fatigue behavior based on changes in loading characteristics (stress ratio, frequency, and hold times).

  13. Relative Humidity and the Susceptibility of Austenitic Stainless Steel to Stress Corrosion Cracking in an impure Plutonium Oxide Environment

    SciTech Connect

    Zapp, P.; Duffey, J.; Lam, P.; Dunn, K.

    2010-05-05

    Laboratory tests to investigate the corrosivity of moist plutonium oxide/chloride salt mixtures on 304L and 316L stainless steel coupons showed that corrosion occurred in selected samples. The tests exposed flat coupons for pitting evaluation and 'teardrop' stressed coupons for stress corrosion cracking (SCC) evaluation at room temperature to various mixtures of PuO{sub 2} and chloride-bearing salts for periods up to 500 days. The exposures were conducted in sealed containers in which the oxide-salt mixtures were loaded with about 0.6 wt % water from a humidified helium atmosphere. Observations of corrosion ranged from superficial staining to pitting and SCC. The extent of corrosion depended on the total salt concentration, the composition of the salt and the moisture present in the test environment. The most significant corrosion was found in coupons that were exposed to 98 wt % PuO{sub 2}, 2 wt % chloride salt mixtures that contained calcium chloride and 0.6 wt% water. SCC was observed in two 304L stainless steel teardrop coupons exposed in solid contact to a mixture of 98 wt % PuO{sub 2}, 0.9 wt % NaCl, 0.9 wt % KCl, and 0.2 wt % CaCl{sub 2}. The cracking was associated with the heat-affected zone of an autogenous weld that ran across the center of the coupon. Cracking was not observed in coupons exposed to the headspace gas above the solid mixture, or in coupons exposed to other mixtures with either no CaCl{sub 2} or 0.92 wt% CaCl{sub 2}. SCC was present where the 0.6 wt % water content exceeded the value needed to fully hydrate the available CaCl{sub 2}, but was absent where the water content was insufficient. These results reveal the significance of the relative humidity in the austenitic stainless steels environment to their susceptibility to corrosion. The relative humidity in the test environment was controlled by the water loading and the concentration of the hydrating salts such as CaCl{sub 2}. For each salt or salt mixture there is a threshold relative

  14. Assessment of susceptibility of Type 304 stainless steel to intergranular stress corrosion cracking in simulated Savannah River Reactor environments

    SciTech Connect

    Ondrejcin, R.S.; Caskey, C.R. Jr.

    1989-12-01

    Intergranular stress corrosion cracking (IGSCC) of Type 304 stainless steel rate tests (CERT) of specimens machined was evaluated by constant extension from Savannah River Plant (SRP) decontaminated process water piping. Results from 12 preliminary CERT tests verified that IGSCC occurred over a wide range of simulated SRP envirorments. 73 specimens were tested in two statistical experimental designs of the central composite class. In one design, testing was done in environments containing hydrogen peroxide; in the other design, hydrogen peroxide was omitted but oxygen was added to the environment. Prediction equations relating IGSCC to temperature and environmental variables were formulated. Temperature was the most important independent variable. IGSCC was severe at 100 to 120C and a threshold temperature between 40C and 55C was identified below which IGSCC did not occur. In environments containing hydrogen peroxide, as in SRP operation, a reduction in chloride concentration from 30 to 2 ppB also significantly reduced IGSCC. Reduction in sulfate concentration from 50 to 7 ppB was effective in reducing IGSCC provided the chloride concentration was 30 ppB or less and temperature was 95C or higher. Presence of hydrogen peroxide in the environment increased IGSCC except when chloride concentration was 11 ppB or less. Actual concentrations of hydrogen peroxide, oxygen and carbon dioxide did not affect IGSCC. Large positive ECP values (+450 to +750 mV Standard Hydrogen Electrode (SHE)) in simulated SRP environments containing hydrogen peroxide and were good agreement with ECP measurements made in SRP reactors, indicating that the simulated environments are representative of SRP reactor environments. Overall CERT results suggest that the most effective method to reduce IGSCC is to reduce chloride and sulfate concentrations.

  15. 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

  16. AN EVALUATION OF HYDROGEN INDUCED CRACKING SUSCEPTIBILITY OF TITANIUM ALLOYS IN US HIGH-LEVEL NUCLEAR WASTE REPOSITORY ENVIRONMENTS

    SciTech Connect

    G. De; K. Mon; G. Gordon; D. Shoesmith; F. Hua

    2006-02-21

    This paper evaluates hydrogen-induced cracking (HIC) susceptibility of titanium alloys in environments anticipated in the Yucca Mountain nuclear waste repository with particular emphasis on the. effect of the oxide passive film on the hydrogen absorption process of titanium alloys being evaluated. The titanium alloys considered in this review include Ti 2, 5 , 7, 9, 11, 12, 16, 17, 18, 24 and 29. In general, the concentration of hydrogen in a titanium alloy can increase due to absorption of atomic hydrogen produced from passive general corrosion of that alloy or galvanic coupling of it to a less noble metal. It is concluded that under the exposure conditions anticipated in the Yucca Mountain repository, the HIC of titanium drip shield will not occur because there will not be sufficient hydrogen in the metal even after 10,000 years of emplacement. Due to the conservatisms adopted in the current evaluation, this assessment is considered very conservative.

  17. Corrosion, stress corrosion cracking, and electrochemistry of the iron and nickel base alloys in caustic environments

    SciTech Connect

    Koehler, R.; Beck, F. H.; Agrawal, A. K.; Soendjasmono, B.; Staehle, R. W.

    1980-02-01

    The electrochemical behavior of high purity (99.95% to 99.99%) iron in 0.6M NaCl and 1.0M Na/sub 2/SO/sub 4/ containing H/sub 2/S (50 ppM to 34,000 ppM) was studied using cyclic voltammetry, chronoamperometry, and slow scan rate polarization. Results have indicated that iron does undergo passivation in sulfate solutions containing H/sub 2/S. Iron dissolution depends on the presence of Cl/sup -/, the concentration of H/sub 2/S and solution pH. An equation is given that describes the anodic Tafel current densities. The slow strain rate test was used to evaluate the effect of electrode potential on the susceptibility of 2-1/4Cr, Mo steel to stress corrosion cracking in boiling 50% NaOH solution. Susceptibility decreased and general corrosion increased with increasing potentials. Failures contained a combination of ductile and brittle fracture. Time-to-failure was longest for controlled potentials of -700 and -600mV (Hg/HgO reference) in the -1100 to -400mV range used in this study.

  18. Electrochemical and Sulfide Stress Corrosion Cracking Behaviors of Tubing Steels in a H2S/CO2 Annular Environment

    NASA Astrophysics Data System (ADS)

    Liu, Z. Y.; Wang, X. Z.; Liu, R. K.; Du, C. W.; Li, X. G.

    2014-04-01

    The electrochemical and sulfide stress corrosion cracking (SSCC) behaviors of 13Cr stainless steel and P110 steel were investigated in a simulated acidic annular environment with low-temperature and high-pressure H2S/CO2 using electrochemical methods, U-bend immersion tests, and scanning electron microscopy. In the solution containing high pressure CO2, 13Cr, and P110 steels exhibited general corrosion and severe pitting, respectively. Compared with sweet corrosion, additional H2S in the solution enhanced the corrosion of 13Cr steel but inhibited the corrosion of P110 steel. By contrast, in a solution containing 4 MPa CO2 and different (0-0.3 MPa), the susceptibility of both 13Cr stainless steel and P110 steel toward SSCC was significantly promoted by increases in H2S partial pressure. The 13Cr stainless steel exhibited higher susceptibility toward SSCC than P110 steel under a H2S/CO2 environment but lower susceptibility under a pure CO2 environment.

  19. Education Assistance Program, Racine Environment Committee, Inc., Racine, Wisconsin. Program Case Study, No. 4.

    ERIC Educational Resources Information Center

    Kepler, Edwin C.

    The education assistance program is a task force of the Racine Environment Committee (REC), which is a non-profit organization formed in the fall of 1967 for the purpose of studying and seeing that action is taken on community problems which affect the Racine metropolitan area. The education assistance committee reviews applications for assistance…

  20. Identification of the Competencies, Knowledge, and Skills Needed by School Nutrition Assistants in the Current Environment

    ERIC Educational Resources Information Center

    Nettles, Mary Frances; Carr, Deborah H.; Cater, Jerry B.; Federico, Holly A.

    2009-01-01

    Purpose/Objectives: Study objectives were to identify the functional areas, competencies, knowledge, and skills needed by effective school nutrition (SN) assistants in the current SN environment, and determine at what point the SN assistant should be able to know/perform the knowledge/skill statement, at time of hire or after training. Methods: In…

  1. Effect of Loading History on Stress Corrosion Cracking of 7075-T651 Aluminum Alloy in Saline Aqueous Environment

    NASA Astrophysics Data System (ADS)

    Zhang, Jixi; Kalnaus, Sergiy; Behrooz, Majid; Jiang, Yanyao

    2011-02-01

    An experimental study of stress corrosion cracking (SCC) was conducted on 7075-T651 aluminum alloy in a chromate-inhibited, acidic 3.5 pct sodium chloride aqueous solution using compact tension specimens with a thickness of 3.8 mm under permanent immersion conditions. The effects of loading magnitude, overload, underload, and two-step high-low sequence loading on incubation time and crack growth behavior were investigated. The results show that the SCC process consists of three stages: incubation, transient crack growth, and stable crack growth. The incubation time is highly dependent on the load level. Tensile overload or compressive underload applied prior to SCC significantly altered the initiation time of corrosion cracking. Transition from a high to a low loading magnitude resulted in a second incubation but much shorter or disappearing transient stage. The stable crack growth rate is independent of stress intensity factor in the range of 10 to 22 MPa sqrt {{m}}.

  2. Implementing Learning Assistants and Tutorials in the Laboratory Environment

    NASA Astrophysics Data System (ADS)

    Stewart, John; Henderson, Rachel; Miller, Paul

    2016-03-01

    This talk describes the results of a novel implementation of a Learning Assistant (LA) program where the LAs facilitated the presentation of the Tutorials in Introductory Physics as part of an otherwise traditional laboratory. LAs received both general training in the teaching of science and specific training in the presentation of the Tutorials. The LAs acted as the lead laboratory instructor for one hour each lab. The program required very little interaction from the lecturer. The program showed a substantial increase in learning gains on the Force and Motion Conceptual Inventory in the first semester course, but weaker improvement of learning gains on the Conceptual Survey of Electricity and Magnetism in the second semester course. Multiple linear regression showed that gender, student ability, and whether the student was on-sequence were significant regressors. The instructor was a substantial random effect (SD = 0 . 10), but the teaching assistant (SD = 0 . 00) and learning assistant (SD = 0 . 01) were much weaker random effects on the normalized gain. The instructor standing (tenure-track, teaching faculty, or adjunct) was a weakly significant regressor (p < 0 . 05).

  3. Environment assisted degradation mechanisms in advanced light metals

    NASA Technical Reports Server (NTRS)

    Gangloff, R. P.; Stoner, G. E.; Swanson, R. E.

    1989-01-01

    A multifaceted research program on the performance of advanced light metallic alloys in aggressive aerospace environments, and associated environmental failure mechanisms was initiated. The general goal is to characterize alloy behavior quantitatively and to develop predictive mechanisms for environmental failure modes. Successes in this regard will provide the basis for metallurgical optimization of alloy performance, for chemical control of aggressive environments, and for engineering life prediction with damage tolerance and long term reliability.

  4. Investigating the mechanism of transgranular stress corrosion cracking in near-neutral pH environments on buried fuel transmission pipelines

    NASA Astrophysics Data System (ADS)

    Asher, Stefanie Lynn

    This research investigates the mechanism of transgranular stress corrosion cracking on fuel transmission pipelines. This research proposes that in near-neutral pH environments, hydrogen can be generated by the dissociation of carbonic acid and the reaction of metal ions with bicarbonate solutions, significantly increasing the available hydrogen for diffusion into the pipeline steel. This research has shown that TGSCC of pipeline steels is possible in simple groundwater solutions containing bicarbonate ions and carbon dioxide. Microstructural characterization coupled with hydrogen permeation indicates that the level of strain in the microstructure has the most influence on hydrogen diffusivity. Hydrogen accumulation occurs preferentially in at high energy discontinuous interfaces such as inclusion interfaces. It was determined that a stress concentration is required to facilitate sufficient hydrogen accumulation in the pipeline steel in order to initiate TGSCC. It was discovered that these stress concentrations develop from inclusions falling out of the pipeline surface. Slow strain rate tests found that TGSCC occurred in a wide range of compositions and temperatures as long as near-neutral conditions were maintained. Microcracks ahead of the crack tip provide evidence of hydrogen in these cracking processes. Morphology of these microcracks indicates that cracks propagate by the coalescence of microcracks with the main crack tip. Further research findings, scientific impact, and potential future work are also discussed.

  5. Computing environment for the ASSIST data warehouse at Lawrence Livermore National Laboratory

    SciTech Connect

    Shuk, K.

    1995-11-01

    The current computing environment for the ASSIST data warehouse at Lawrence Livermore National Laboratory is that of a central server that is accessed by a terminal or terminal emulator. The initiative to move to a client/server environment is strong, backed by desktop machines becoming more and more powerful. The desktop machines can now take on parts of tasks once run entirely on the central server, making the whole environment computationally more efficient as a result. Services are tasks that are repeated throughout the environment such that it makes sense to share them; tasks such as email, user authentication and file transfer are services. The new client/;server environment needs to determine which services must be included in the environment for basic functionality. These services then unify the computing environment, not only for the forthcoming ASSIST+, but for Administrative Information Systems as a whole, joining various server platforms with heterogeneous desktop computing platforms.

  6. Environment assisted degradation mechanisms in advanced light metals

    NASA Technical Reports Server (NTRS)

    Gangloff, Richard P.; Stoner, Glenn E.; Swanson, Robert E.

    1988-01-01

    The general goals of the research program are to characterize alloy behavior quantitatively and to develop predictive mechanisms for environmental failure modes. Successes in this regard will provide the basis for metallurgical optimization of alloy performance, for chemical control of aggressive environments, and for engineering life prediction with damage tolerance and long term reliability.

  7. Intelligent Assistance for Teachers in Collaborative E-Learning Environments

    ERIC Educational Resources Information Center

    Casamayor, Agustin; Amandi, Analia; Campo, Marcelo

    2009-01-01

    Collaborative learning environments provide a set of tools for students acting in groups to interact and accomplish an assigned task. In this kind of systems, students are free to express and communicate with each other, which usually lead to collaboration and communication problems that may require the intervention of a teacher. In this article,…

  8. Research Issues in Computer-Assisted Learning Environments.

    ERIC Educational Resources Information Center

    MacGregor, S. Kim

    This review of the research on concerns associated with the use of computers in school learning environments focuses primarily on issues related to the impact of computer technology on equity, especially the reasons for differential use of computers by boys and girls and the effects of economic disparities among schools and students; differences…

  9. Development of an Assistance Environment for Tutors Based on a Co-Adaptive Design Approach

    ERIC Educational Resources Information Center

    Lavoue, Elise; George, Sebastien; Prevot, Patrick

    2012-01-01

    In this article, we present a co-adaptive design approach named TE-Cap (Tutoring Experience Capitalisation) that we applied for the development of an assistance environment for tutors. Since tasks assigned to tutors in educational contexts are not well defined, we are developing an environment which responds to needs which are not precisely…

  10. On the stress corrosion cracking of lean duplex steel in chloride environment

    NASA Astrophysics Data System (ADS)

    Tayyaba, Qanita; Farooq, Hina; Shahid, Muhammad; Jadoon, Ammer Khan; Shahzad, M.; Qureshi, A. H.

    2014-06-01

    Duplex stainless steel having attractive combination of austenitic and ferritic properties is being used in industry such as petrochemical, pulp and paper mills. In this study, the corrosion and stress corrosion behavior of duplex stainless steel in 3.5% sodium chloride environment was investigated by weight loss measurements, electrochemical DC testing and slow strain rate test (SSRT). Weight loss data showed no significant corrosion after 1700 hours. Electrochemical polarization test in 3.5% NaCl solution exhibited a uniform corrosion rate of 0.008 mpy (calculated using Tafel analysis) showing passivity in the range of 735-950 mV. A comparison of the slow strain rate test in 3.5% NaCl solution with air shows almost a similar stress strain curve for duplex stainless steel. In comparison, the stress strain curves for 0.15% carbon steel show a loss of about 25% tensile elongation for the same comparison. The excellent corrosion and especially resistance to localized corrosion (pitting) is responsible for no loss of ductility in duplex stainless steel.

  11. Environmental Crack Driving Force

    NASA Astrophysics Data System (ADS)

    Hall, M. M.

    2013-03-01

    The effect of environment on the crack driving force is considered, first by assuming quasistatic extension of a stationary crack and second, by use of stress corrosion cracking (SCC) crack growth rate models developed previously by this author and developed further here. A quasistatic thermodynamic energy balance approach, of the Griffith-Irwin type, is used to develop stationary crack threshold expressions, tilde{J}_c , which represent the conjoint mechanical and electrochemical conditions, below which stationary cracks are stable. Expressions for the electrochemical crack driving force (CDF) were derived using an analysis that is analogous to that used by Irwin to derive his "strain energy release rate," G, which Rice showed as being equivalent to his mechanical CDF, J. The derivations show that electrochemical CDFs both for active path dissolution (APD) and hydrogen embrittlement (HE) mechanisms of SCC are simply proportional to Tafel's electrochemical anodic and cathodic overpotentials, η a and η c, respectively. Phenomenological SCC models based on the kinetics of APD and HE crack growth are used to derive expressions for the kinetic threshold, J scc, below which crack growth cannot be sustained. These models show how independent mechanical and environmental CDFs may act together to drive SCC crack advance. Development of a user-friendly computational tool for calculating Tafel's overpotentials is advocated.

  12. Investigation of hydrogen induced cracking in 2205 duplex stainless steel in wet H{sub 2}S environments after isothermal treatment at 675, 750 and 900 deg. C

    SciTech Connect

    Sozanska, Maria . E-mail: maria.sozanska@polsl.pl; Klyk-Spyra, Katarzyna

    2006-06-15

    The effect of isothermal treatment (at 675, 750 and 900 deg. C) on HIC (hydrogen induced cracking) in sour environments containing hydrogen sulphide of a 2205 duplex stainless steel has been investigated. The performance and microstructure of failed material were characterized by optical microscopy, scanning electron microscopy and also X-ray diffraction. Two kinds of Cr-, Mo-enriched intermetallic phases, {sigma} and {chi}, were found to precipitate preferentially at {alpha}/{gamma} interfaces and within {alpha} grains after different times of aging in the temperature range of 650-900 deg. C. After performing tests according to the NACE Standard TM 0284 (1987) the specimens were investigated by using quantitative metallography methods. The volume fraction of {sigma} phase was changed with the time of aging and {sigma} phase developed into coarse particles due to the high diffusibility of solute atoms at high temperatures. The variation of size and shape of {sigma} phase particles was obtained by applying different heat treatment conditions to 2205 steel specimens. The results showed that 2205 duplex stainless steel containing nearly 12 vol.% of {sigma} phase in dispersed conditions was resistant to step cracking in wet environments containing hydrogen sulphide. It was highly possible that a crack would propagate faster along the embrittled {sigma} phase. However, very small cracks were found at austenite-ferrite boundaries where o phase particles were also present.

  13. Environment-assisted quantum-information correction for continuous variables

    SciTech Connect

    Sabuncu, Metin; Filip, Radim; Leuchs, Gerd

    2010-01-15

    Quantum-information protocols are inevitably affected by decoherence which is associated with the leakage of quantum information into an environment. In this article we address the possibility of recovering the quantum information from an environmental measurement. We investigate continuous-variable quantum information, and we propose a simple environmental measurement that under certain circumstances fully restores the quantum information of the signal state although the state is not reconstructed with unit fidelity. We implement the protocol for which information is encoded into conjugate quadratures of coherent states of light and the noise added under the decoherence process is of Gaussian nature. The correction protocol is tested using both a deterministic as well as a probabilistic strategy. The potential use of the protocol in a continuous-variable quantum-key distribution scheme as a means to combat excess noise is also investigated.

  14. Moles: Tool-Assisted Environment Isolation with Closures

    NASA Astrophysics Data System (ADS)

    de Halleux, Jonathan; Tillmann, Nikolai

    Isolating test cases from environment dependencies is often desirable, as it increases test reliability and reduces test execution time. However, code that calls non-virtual methods or consumes sealed classes is often impossible to test in isolation. Moles is a new lightweight framework which addresses this problem. For any .NET method, Moles allows test-code to provide alternative implementations, given as .NET delegates, for which C# provides very concise syntax while capturing local variables in a closure object. Using code instrumentation, the Moles framework will redirect calls to provided delegates instead of the original methods. The Moles framework is designed to work together with the dynamic symbolic execution tool Pex to enable automated test generation. In a case study, testing code programmed against the Microsoft SharePoint Foundation API, we achieved full code coverage while running tests in isolation without an actual SharePoint server. The Moles framework integrates with .NET and Visual Studio.

  15. Environmental fatigue of an Al-Li-Cu alloy. Part 1: Intrinsic crack propagation kinetics in hydrogenous environments

    NASA Technical Reports Server (NTRS)

    Piascik, Robert S.; Gangloff, Richard P.

    1991-01-01

    Deleterious environmental effects on steady-state, intrinsic fatigue crack propagation (FCP) rates (da/dN) in peak aged Al-Li-Cu alloy 2090 are established by electrical potential monitoring of short cracks with programmed constant delta K and K(sub max) loading. The da/dN are equally unaffected by vacuum, purified helium, and oxygen but are accelerated in order of decreasing effectiveness by aqueous 1 percent NaCl with anodic polarization, pure water vapor, moist air, and NaCl with cathodic polarization. While da/dN depends on delta K(sup 4.0) for the inert gases, water vapor and chloride induced multiple power-laws, and a transition growth rate 'plateau'. Environmental effects are strongest at low delta K. Crack tip damage is ascribed to hydrogen embrittlement because of the following: (1) accelerated da/dN due to part-per-million levels of H2O without condensation; (2) impeded molecular flow model predictions of the measured water vapor pressure dependence of da/dN as affected by mean crack opening; (3) the lack of an effect of film-forming O2; (4) the likelihood for crack tip hydrogen production in NaCl, and (5) the environmental and delta K-process zone volume dependencies of the microscopic cracking modes. For NaCl, growth rates decrease with decreasing loading frequency, with the addition of passivating Li2CO3, and upon cathodic polarization. These variables increase crack surface film stability to reduce hydrogen entry efficiency. The hydrogen environmental FCP resistance of 2090 is similar to other 2000 series alloys and is better than 7075.

  16. Environmental fatigue of an Al-Li-Cu alloy. I - Intrinsic crack propagation kinetics in hydrogenous environments

    NASA Technical Reports Server (NTRS)

    Piascik, Robert S.; Gangloff, Richard P.

    1991-01-01

    Deleterious environmental effects on steady-state, intrinsic fatigue crack propagation (FCP) rates (da/dN) in peak aged Al-Li-Cu alloy 2090 are established by electrical potential monitoring of short cracks with programmed constant delta K and K(sub max) loading. The da/dN are equally unaffected by vacuum, purified helium, and oxygen but are accelerated in order of decreasing effectiveness of aqueous 1 percent NaCl with anodic polarization, pure water vapor, moist air, and NaCl with cathodic polarization. While da/dN depends on delta K(sup 4.0) for the inert gases, water vapor and chloride induced multiple power-laws, and a transition growth rate 'plateau'. Environmental effects are strongest at low delta K. Crack tip damage is ascribed to hydrogen embrittlement because of the following: (1) accelerated da/dN due to part-per-million levels of H2O without condensation; (2) impeded molecular flow model predictions of the measured water vapor pressure dependence of da/dN as affected by mean crack opening; (3) the lack of an effect of film-forming O2; (4) the likelihood for crack tip hydrogen production in NaCl; and (5) the environmental and delta K-process zone volume dependencies of the microscopic cracking modes. For NaCl, growth rates decrease with decreasing loading frequency, with the addition of passivating Li2CO3, and upon cathodic polarization. These variables increase crack surface film stability to reduce hydrogen entry efficiency. The hydrogen environmental FCP resistance of 2090 is similar to other 2000 series alloys and is better than 7075.

  17. Environment-Assisted Speed-up of the Field Evolution in Cavity Quantum Electrodynamics.

    PubMed

    Cimmarusti, A D; Yan, Z; Patterson, B D; Corcos, L P; Orozco, L A; Deffner, S

    2015-06-12

    We measure the quantum speed of the state evolution of the field in a weakly driven optical cavity QED system. To this end, the mode of the electromagnetic field is considered as a quantum system of interest with a preferential coupling to a tunable environment: the atoms. By controlling the environment, i.e., changing the number of atoms coupled to the optical cavity mode, an environment-assisted speed-up is realized: the quantum speed of the state repopulation in the optical cavity increases with the coupling strength between the optical cavity mode and this non-Markovian environment (the number of atoms). PMID:26196802

  18. Environment-Assisted Speed-up of the Field Evolution in Cavity Quantum Electrodynamics.

    PubMed

    Cimmarusti, A D; Yan, Z; Patterson, B D; Corcos, L P; Orozco, L A; Deffner, S

    2015-06-12

    We measure the quantum speed of the state evolution of the field in a weakly driven optical cavity QED system. To this end, the mode of the electromagnetic field is considered as a quantum system of interest with a preferential coupling to a tunable environment: the atoms. By controlling the environment, i.e., changing the number of atoms coupled to the optical cavity mode, an environment-assisted speed-up is realized: the quantum speed of the state repopulation in the optical cavity increases with the coupling strength between the optical cavity mode and this non-Markovian environment (the number of atoms).

  19. Environment-Assisted Speed-up of the Field Evolution in Cavity Quantum Electrodynamics

    SciTech Connect

    Cimmarusti, A. D.; Yan, Z.; Patterson, B. D.; Corcos, L. P.; Orozco, L. A.; Deffner, S.

    2015-06-11

    We measure the quantum speed of the state evolution of the field in a weakly-driven optical cavity QED system. To this end, the mode of the electromagnetic field is considered as a quantum system of interest with a preferential coupling to a tunable environment: the atoms. By controlling the environment, i.e., changing the number of atoms coupled to the optical cavity mode, an environment assisted speed-up is realized: the quantum speed of the state re-population in the optical cavity increases with the coupling strength between the optical cavity mode and this non-Markovian environment (the number of atoms).

  20. The role of Hydrogen and Creep in Intergranular Stress Corrosion Cracking of Alloy 600 and Alloy 690 in PWR Primary Water Environments ? a Review

    SciTech Connect

    Rebak, R B; Hua, F H

    2004-07-12

    Intergranular attack (IGA) and intergranular stress corrosion cracking (IGSCC) of Alloy 600 in PWR steam generator environment has been extensively studied for over 30 years without rendering a clear understanding of the essential mechanisms. The lack of understanding of the IGSCC mechanism is due to a complex interaction of numerous variables such as microstructure, thermomechanical processing, strain rate, water chemistry and electrochemical potential. Hydrogen plays an important role in all these variables. The complexity, however, significantly hinders a clearer and more fundamental understanding of the mechanism of hydrogen in enhancing intergranular cracking via whatever mechanism. In this work, an attempt is made to review the role of hydrogen based on the current understanding of grain boundary structure and chemistry and intergranular fracture of nickel alloys, effect of hydrogen on electrochemical behavior of Alloy 600 and Alloy 690 (e.g. the passive film stability, polarization behavior and open-circuit potential) and effect of hydrogen on PWSCC behavior of Alloy 600 and Alloy 690. Mechanistic studies on the PWSCC are briefly reviewed. It is concluded that further studies on the role of hydrogen on intergranular cracking in both inert and primary side environments are needed. These studies should focus on the correlation of the results obtained at different laboratories by different methods on materials with different metallurgical and chemical parameters.

  1. Design of Teacher Assistance Tools in an Exploratory Learning Environment for Algebraic Generalization

    ERIC Educational Resources Information Center

    Gutierrez-Santos, S.; Geraniou, E.; Pearce-Lazard, D.; Poulovassilis, A.

    2012-01-01

    The MiGen project is designing and developing an intelligent exploratory environment to support 11-14-year-old students in their learning of algebraic generalization. Deployed within the classroom, the system also provides tools to assist teachers in monitoring students' activities and progress. This paper describes the design of these Teacher…

  2. Secondary School Students' Attitudes towards Mathematics Computer--Assisted Instruction Environment in Kenya

    ERIC Educational Resources Information Center

    Mwei, Philip K.; Wando, Dave; Too, Jackson K.

    2012-01-01

    This paper reports the results of research conducted in six classes (Form IV) with 205 students with a sample of 94 respondents. Data represent students' statements that describe (a) the role of Mathematics teachers in a computer-assisted instruction (CAI) environment and (b) effectiveness of CAI in Mathematics instruction. The results indicated…

  3. Learning Tools for Knowledge Nomads: Using Personal Digital Assistants (PDAs) in Web-based Learning Environments.

    ERIC Educational Resources Information Center

    Loh, Christian Sebastian

    2001-01-01

    Examines how mobile computers, or personal digital assistants (PDAs), can be used in a Web-based learning environment. Topics include wireless networks on college campuses; online learning; Web-based learning technologies; synchronous and asynchronous communication via the Web; content resources; Web connections; and collaborative learning. (LRW)

  4. Workplace Environments That Assist and Hinder the Career Progression of Women in Information Technology

    ERIC Educational Resources Information Center

    Wentling, Rose Mary; Thomas, Steven P.

    2007-01-01

    The purpose of this study was to develop an understanding of the workplace environment characteristics that hinder and assist the career progression of women in information technology (IT). The study examined the satisfaction with the career progression of the women in IT as well as why the women in IT like and dislike their careers. The major…

  5. The Growth of Small Corrosion Fatigue Cracks in Alloy 7075

    NASA Technical Reports Server (NTRS)

    Piascik, R. S.

    2001-01-01

    The corrosion fatigue crack growth characteristics of small (less than 35 microns) surface and corner cracks in aluminum alloy 7075 is established. The early stage of crack growth is studied by performing in situ long focal length microscope (500X) crack length measurements in laboratory air and 1% NaCl environments. To quantify the "small crack effect" in the corrosive environment, the corrosion fatigue crack propagation behavior of small cracks is compared to long through-the-thickness cracks grown under identical experimental conditions. In salt water, long crack constant K(sub max) growth rates are similar to small crack da/dN.

  6. The Growth of Small Corrosion Fatigue Cracks in Alloy 7075

    NASA Technical Reports Server (NTRS)

    Piascik, Robert S.

    2015-01-01

    The corrosion fatigue crack growth characteristics of small (greater than 35 micrometers) surface and corner cracks in aluminum alloy 7075 is established. The early stage of crack growth is studied by performing in situ long focal length microscope (500×) crack length measurements in laboratory air and 1% sodium chloride (NaCl) environments. To quantify the "small crack effect" in the corrosive environment, the corrosion fatigue crack propagation behavior of small cracks is compared to long through-the-thickness cracks grown under identical experimental conditions. In salt water, long crack constant K(sub max) growth rates are similar to small crack da/dN.

  7. US NRC-Sponsored Research on Stress Corrosion Cracking Susceptibility of Dry Storage Canister Materials in Marine Environments - 13344

    SciTech Connect

    Oberson, Greg; Dunn, Darrell; Mintz, Todd; He, Xihua; Pabalan, Roberto; Miller, Larry

    2013-07-01

    At a number of locations in the U.S., spent nuclear fuel (SNF) is maintained at independent spent fuel storage installations (ISFSIs). These ISFSIs, which include operating and decommissioned reactor sites, Department of Energy facilities in Idaho, and others, are licensed by the U.S. Nuclear Regulatory Commission (NRC) under Title 10 of the Code of Federal Regulations, Part 72. The SNF is stored in dry cask storage systems, which most commonly consist of a welded austenitic stainless steel canister within a larger concrete vault or overpack vented to the external atmosphere to allow airflow for cooling. Some ISFSIs are located in marine environments where there may be high concentrations of airborne chloride salts. If salts were to deposit on the canisters via the external vents, a chloride-rich brine could form by deliquescence. Austenitic stainless steels are susceptible to chloride-induced stress corrosion cracking (SCC), particularly in the presence of residual tensile stresses from welding or other fabrication processes. SCC could allow helium to leak out of a canister if the wall is breached or otherwise compromise its structural integrity. There is currently limited understanding of the conditions that will affect the SCC susceptibility of austenitic stainless steel exposed to marine salts. NRC previously conducted a scoping study of this phenomenon, reported in NUREG/CR-7030 in 2010. Given apparent conservatisms and limitations in this study, NRC has sponsored a follow-on research program to more systematically investigate various factors that may affect SCC including temperature, humidity, salt concentration, and stress level. The activities within this research program include: (1) measurement of relative humidity (RH) for deliquescence of sea salt, (2) SCC testing within the range of natural absolute humidity, (3) SCC testing at elevated temperatures, (4) SCC testing at high humidity conditions, and (5) SCC testing with various applied stresses. Results

  8. 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.

  9. A novel "wastes-treat-wastes" technology: role and potential of spent fluid catalytic cracking catalyst assisted ozonation of petrochemical wastewater.

    PubMed

    Chen, Chunmao; Yu, Ji; Yoza, Brandon A; Li, Qing X; Wang, Gang

    2015-04-01

    Catalytic ozonation is a promising wastewater treatment technology. However, the high cost of the catalyst hinders its application. A novel "wastes-treat-wastes" technology was developed to reuse spent fluid catalytic cracking catalysts (sFCCc) for the ozonation of petrochemical wastewater in this study. Multivalent vanadium (V(4+) and V(5+)), iron (Fe(2+) and Fe(3+)) and nickel (Ni(2+)) oxides that are distributed on the surface of sFCCc and poisoned FCC catalysts are the catalytic components for ozonation. The sFCCc assisted catalytic ozonation (sFCCc-O) of nitrobenzene indicated that the sFCCc significantly promoted hydroxyl radical mediated oxidation. The degradation rate constant of nitrobenzene in sFCCc-O (0.0794 min(-1) at 298 K) was approximately doubled in comparison with that in single ozonation (0.0362 min(-1) at 298 K). The sFCCc-O of petrochemical wastewater increased chemical oxygen demand removal efficiency by three-fold relative to single ozonation. The number of oxygen-containing (Ox) polar contaminants in the effluent (253) from sFCCc-O treatment decreased to about 70% of the initial wastewater (353). The increased oxygen/carbon atomic ratio and decreased number of Ox polar contaminants indicated a high degree of degradation. The present study showed the role and potential of sFCCc for catalytic ozonation of petrochemical wastewater, particularly in an advantage of the cost-effectiveness through "wastes-treat-wastes".

  10. A Comparative Study of Two ESL Writing Environments: A Computer-Assisted Classroom and a Traditional Oral Classroom.

    ERIC Educational Resources Information Center

    Sullivan, Nancy; Pratt, Ellen

    1996-01-01

    Compares students in two English-as-a-Second-Language writing environments: a networked computer-assisted classroom and a traditional oral classroom. Results indicate that while the writing environment has no effect on attitudes toward writing with computers or writing apprehension, writing quality improves in the computer-assisted classroom and…

  11. The effect of alloy composition on the mechanism of stress corrosion cracking of titanium alloys in aqueous environments

    NASA Technical Reports Server (NTRS)

    Williams, D. N.

    1971-01-01

    Emphasis has been placed on determining the interrelations among the composition, phase structure, deformation, and fracture properties of the alpha phase in susceptible alpha-beta alloys. The program is divided into two parts: (1) evaluation of the aqueous stress corrosion susceptibility of a series of alloys that contain various alpha-soluble elements; and (2) investigations of the metallurgical aspects of the mechanism of aqueous stress corrosion cracking.

  12. Environment-assisted error correction of single-qubit phase damping

    NASA Astrophysics Data System (ADS)

    Trendelkamp-Schroer, Benjamin; Helm, Julius; Strunz, Walter T.

    2011-12-01

    Open quantum system dynamics of random unitary type may in principle be fully undone. Closely following the scheme of environment-assisted error correction proposed by Gregoratti and Werner [J. Mod. Opt.10.1080/09500340308234541 50, 915 (2003)], we explicitly carry out all steps needed to invert a phase-damping error on a single qubit. Furthermore, we extend the scheme to a mixed-state environment. Surprisingly, we find cases for which the uncorrected state is closer to the desired state than any of the corrected ones.

  13. Environment-assisted error correction of single-qubit phase damping

    SciTech Connect

    Trendelkamp-Schroer, Benjamin; Helm, Julius; Strunz, Walter T.

    2011-12-15

    Open quantum system dynamics of random unitary type may in principle be fully undone. Closely following the scheme of environment-assisted error correction proposed by Gregoratti and Werner [J. Mod. Opt. 50, 915 (2003)], we explicitly carry out all steps needed to invert a phase-damping error on a single qubit. Furthermore, we extend the scheme to a mixed-state environment. Surprisingly, we find cases for which the uncorrected state is closer to the desired state than any of the corrected ones.

  14. Subcritical crack growth in marble

    NASA Astrophysics Data System (ADS)

    Nara, Yoshitaka; Nishida, Yuki; Toshinori, Ii; Harui, Tomoki; Tanaka, Mayu; Kashiwaya, Koki

    2016-04-01

    It is essential to study time-dependent deformation and fracturing in various rock materials to prevent natural hazards related to the failure of a rock mass. In addition, information of time-dependent fracturing is essential to ensure the long-term stability of a rock mass surrounding various structures. Subcritical crack growth is one of the main causes of time-dependent fracturing in rock. It is known that subcritical crack growth is influenced by not only stress but also surrounding environment. Studies of subcritical crack growth have been widely conducted for silicate rocks such as igneous rocks and sandstones. By contrast, information of subcritical crack growth in carbonate rocks is not enough. Specifically, influence of surrounding environment on subcritical crack growth in carbonate rock should be clarified to ensure the long-term stability of a rock mass. In this study, subcritical crack growth in marble was investigated. Especially, the influence of the temperature, relative humidity and water on subcritical crack growth in marble is investigated. As rock samples, marbles obtained in Skopje-City in Macedonia and Carrara-City in Italy were used. To measure subcritical crack growth, we used the load relaxation method of the double-torsion (DT) test. All measurements by DT test were conducted under controlled temperature and relative humidity. For both marbles, it was shown that the crack velocity in marble in air increased with increasing relative humidity at a constant temperature. Additionally, the crack velocity in water was much higher than that in air. It was also found that the crack velocity increased with increasing temperature. It is considered that temperature and water have significant influences on subcritical crack growth in marble. For Carrara marble in air, it was recognized that the value of subcritical crack growth index became low when the crack velocity was higher than 10-4 m/s. This is similar to Region II of subcritical crack growth

  15. Effects of Hydrogen on the Fatigue Crack Growth Rate of Low Alloy Steels

    SciTech Connect

    Sang Gyu, Lee; Changheui, Jang; In Sup, Kim

    2006-07-01

    Fatigue crack growth rate of low alloy steels in air and oxygen-controlled water, from room temperature to 288 deg C, were measured and the results were analyzed. In high dissolved oxygen water, the loading frequency effect was observed; on the other hand, the effect of loading frequency was not clearly seen in low dissolved oxygen water. Moreover, crystallographic features, especially the formation of highly localized strained zone, that is related to the hydrogen assisted cracking was observed on the fracture surface of the sample tested in the water environments. To confirm this mechanism, some samples were hydrogen charged and fatigue tested in air and in argon gas, at RT and at 288 deg. C, respectively. The fatigue crack growth rate increased in the hydrogen charged samples. The fracture surface of the hydrogen charged samples showed brittle cracking at 288 deg C as well as at room temperature, which resulted in the fast crack growth rate. (authors)

  16. A novel "wastes-treat-wastes" technology: role and potential of spent fluid catalytic cracking catalyst assisted ozonation of petrochemical wastewater.

    PubMed

    Chen, Chunmao; Yu, Ji; Yoza, Brandon A; Li, Qing X; Wang, Gang

    2015-04-01

    Catalytic ozonation is a promising wastewater treatment technology. However, the high cost of the catalyst hinders its application. A novel "wastes-treat-wastes" technology was developed to reuse spent fluid catalytic cracking catalysts (sFCCc) for the ozonation of petrochemical wastewater in this study. Multivalent vanadium (V(4+) and V(5+)), iron (Fe(2+) and Fe(3+)) and nickel (Ni(2+)) oxides that are distributed on the surface of sFCCc and poisoned FCC catalysts are the catalytic components for ozonation. The sFCCc assisted catalytic ozonation (sFCCc-O) of nitrobenzene indicated that the sFCCc significantly promoted hydroxyl radical mediated oxidation. The degradation rate constant of nitrobenzene in sFCCc-O (0.0794 min(-1) at 298 K) was approximately doubled in comparison with that in single ozonation (0.0362 min(-1) at 298 K). The sFCCc-O of petrochemical wastewater increased chemical oxygen demand removal efficiency by three-fold relative to single ozonation. The number of oxygen-containing (Ox) polar contaminants in the effluent (253) from sFCCc-O treatment decreased to about 70% of the initial wastewater (353). The increased oxygen/carbon atomic ratio and decreased number of Ox polar contaminants indicated a high degree of degradation. The present study showed the role and potential of sFCCc for catalytic ozonation of petrochemical wastewater, particularly in an advantage of the cost-effectiveness through "wastes-treat-wastes". PMID:25617869

  17. Pressure vessel and piping codes. Technical basis for revised reference crack growth rate curves for pressure boundary steels in LWR environment

    SciTech Connect

    Bamford, W.H.

    1980-11-01

    Since the inception of the pressure vessel and piping codes the reference fatigue crack growth rate curves have been contained in Appendix A of Sect. XI. The curves have been designed to be applicable to carbon and low alloy pressure vessel steels exposed to either air or light water reactor coolant environments. Data obtained over the past several years have shown a different behavior of these steels in the light water reactor environment than that predicted by the present reference curve. A revised set of reference curves has been formulated, incorporating a new curve shape as well as a dependency of growth rate on R ratio (minimum load/maximum load). This work provides the background and justification for such a revision, details the methodology used to develop the revised curves, and includes an evalution of the adequacy and impact of the revised curves as compared with the single curve which they replace. 24 references.

  18. Identifying the Potential for Robotics to Assist Older Adults in Different Living Environments.

    PubMed

    Mitzner, Tracy L; Chen, Tiffany L; Kemp, Charles C; Rogers, Wendy A

    2014-04-01

    As the older adult population grows and becomes more diverse, so will their needs and preferences for living environments. Many adults over 65 years of age require some assistance [1, 2]; yet it is important for their feelings of well-being that the assistance not restrict their autonomy [3]. Not only is autonomy correlated with quality of life [4], autonomy enhancement may improve functionality [2, 5]. The goal of this paper is to provide guidance for the development of technology to enhance autonomy and quality of life for older adults. We explore the potential for robotics to meet these needs. We evaluated older adults' diverse living situations and the predictors of residential moves to higher levels of care in the United States. We also examined older adults' needs for assistance with activities of daily living (ADLs), instrumental activities of daily living (IADLs), and medical conditions when living independently or in a long-term care residence. By providing support for older adults, mobile manipulator robots may reduce need-driven, undesired moves from residences with lower levels of care (i.e., private homes, assisted living) to those with higher levels of care (i.e., skilled nursing). PMID:24729800

  19. Identifying the Potential for Robotics to Assist Older Adults in Different Living Environments

    PubMed Central

    Mitzner, Tracy L.; Chen, Tiffany L.; Kemp, Charles C.; Rogers, Wendy A.

    2014-01-01

    As the older adult population grows and becomes more diverse, so will their needs and preferences for living environments. Many adults over 65 years of age require some assistance [1, 2]; yet it is important for their feelings of well-being that the assistance not restrict their autonomy [3]. Not only is autonomy correlated with quality of life [4], autonomy enhancement may improve functionality [2, 5]. The goal of this paper is to provide guidance for the development of technology to enhance autonomy and quality of life for older adults. We explore the potential for robotics to meet these needs. We evaluated older adults' diverse living situations and the predictors of residential moves to higher levels of care in the United States. We also examined older adults' needs for assistance with activities of daily living (ADLs), instrumental activities of daily living (IADLs), and medical conditions when living independently or in a long-term care residence. By providing support for older adults, mobile manipulator robots may reduce need-driven, undesired moves from residences with lower levels of care (i.e., private homes, assisted living) to those with higher levels of care (i.e., skilled nursing). PMID:24729800

  20. Pacific Northwest Laboratory annual report for 1990 to the Assistant Secretary for Environment, Safety, and Health

    SciTech Connect

    Faust, L.G.; Moraski, R.V.; Selby, J.M.

    1991-05-01

    Part 5 of the 1990 Annual Report to the US Department of Energy's Assistant Secretary for Environment, Safety, and Health presents Pacific Northwest Laboratory's progress on work performed for the Office of Environmental Guidance, the Office of Environmental Compliance, the Office of Environmental Audit, the Office of National Environmental Policy Act Project Assistance, the Office of Nuclear Safety, the Office of Safety Compliance, and the Office of Policy and Standards. For each project, as identified by the Field Work Proposal, there is an article describing progress made during fiscal year 1990. Authors of these articles represent a broad spectrum of capabilities derived from five of the seven technical centers of the Laboratory, reflecting the interdisciplinary nature of the work.

  1. Effects of fatigue and environment on residual strengths of center-cracked graphite/epoxy buffer strip panels

    SciTech Connect

    Bigelow, C.A. )

    1989-03-01

    The effects of fatigue, moisture conditioning, and heating on the residual tension strengths of center-cracked graphite/epoxy buffer strip panels were evaluated using specimens made with T300/5208 graphite epoxy in a 16-ply quasi-isotropic layup, with two different buffer strip materials, Kevlar-49 or S-glass. It was found that, for panels subjected to fatigue loading, the residual strengths were not significantly affected by the fatigue loading, the number of repetitions of the loading spectrum, or the maximum strain level. The moisture conditioning reduced the residual strengths of the S-glass buffer strip panels by 10 to 15 percent below the ambient results, but increased the residual strengths of the Kevlar-49 buffer strip panels slightly. For both buffer strip materials, the heat increased the residual strengths of the buffer strip panels slightly over the ambient results. 6 refs.

  2. Empirical modeling of environment-enhanced fatigue crack propagation in structural alloys for component life prediction. Final report

    SciTech Connect

    Richey, E. III

    1995-10-01

    This research aims to develop the methods and understanding needed to incorporate time and loading variable dependent environmental effects on fatigue crack propagation (FCP) into computerized fatigue life prediction codes such as NASA FLAGRO (NASGRO). In particular, the effect of loading frequency on FCP rates in alpha + beta titanium alloys exposed to an aqueous chloride solution is investigated. The approach couples empirical modeling of environmental FCP with corrosion fatigue experiments. Three different computer models have been developed and incorporated in the DOS executable program. UVAFAS. A multiple power law model is available, and can fit a set of fatigue data to a multiple power law equation. A model has also been developed which implements the Wei and Landes linear superposition model, as well as an interpolative model which can be utilized to interpolate trends in fatigue behavior based on changes in loading characteristics (stress ratio, frequency, and hold times).

  3. Effects of fatigue and environment on residual strengths of center-cracked graphite/epoxy buffer strip panels

    NASA Technical Reports Server (NTRS)

    Bigelow, Catherine A.

    1989-01-01

    The effects of fatigue, moisture conditioning, and heating on the residual tension strengths of center-cracked graphite/epoxy buffer strip panels were evaluated using specimens made with T300/5208 graphite epoxy in a 16-ply quasi-isotropic layup, with two different buffer strip materials, Kevlar-49 or S-glass. It was found that, for panels subjected to fatigue loading, the residual strengths were not significantly affected by the fatigue loading, the number of repetitions of the loading spectrum, or the maximum strain level. The moisture conditioning reduced the residual strengths of the S-glass buffer strip panels by 10 to 15 percent below the ambient results, but increased the residual strengths of the Kevlar-49 buffer strip panels slightly. For both buffer strip materials, the heat increased the residual strengths of the buffer strip panels slightly over the ambient results.

  4. Experiences on IGSCC crack manufacturing

    SciTech Connect

    Veron, P.

    1997-02-01

    The author presents his experience in manufacturing IGSCC realistic defects, mainly in INCONEL 600 MA Steam Generator Tubes. From that experience he extracts some knowledge about this cracking (influence of chemistry in the environment, stress state, crack growth rate, and occurrence in laboratory condition of break before leak).

  5. Stress corrosion cracking of Al-Li-Cu-Zr alloy 2090 in aqueous Cl sup minus and mixed CO sub 3 sup 2 minus /Cl sup minus environments

    SciTech Connect

    Buchheit, R.G. ); Wall, F.D.; Stoner, G.E. . Dept. of Materials Science); Moran, J.P. )

    1991-01-01

    A comparison of the short-transverse SCC behavior of 2090 in pH 5.5 Cl{sup {minus}} and alkaline CO{sub 3}{sup 2 {minus}}/Cl{sup {minus}} solutions using a static load smooth bar SCC technique was made. In the alkaline CO{sub 3}{sup 2 {minus}}/Cl{sup {minus}} solutions, E{sub br} for the {alpha}-Al matrix phase was 0.130 V more positive than the E{sub br} of the subgrain boundary T{sub 1} phase. In this environment, stress corrosion cracking test specimens subjected to potentials in the window defined by the two breakaway potentials failed along an intersubgranular path in less than an hour. In the Cl{sup {minus}} environment, the E{sub br} values for the two phases were nearly equal and this rapid SCC condition could not be satisfied; accordingly SCC failures were not observed. Rapid SCC failure of 2090 in CO{sub 3}{sup 2 {minus}}/Cl{sup {minus}} in our static load, constant immersion experiments appear to be related to recently reported pre-exposure embrittlement'' failures induced by immersing stressed specimens removed into ambient laboratory air after immersion in aerated NaCl solution for 7 days. In those experiments, specimens failed in less than 24 hours after removal from solution. Our polarization experiments have shown that the corrosion behavior of T{sub 1}, CO{sub 3}{sup 2 {minus}}/Cl{sup {minus}} environments, but the {alpha}-Al phase crack walls, is rapidly passivated. X-ray diffraction of the films which formed in simulated crevices suggests that this passivating film belongs to a class of compounds known as hydrotalcites.

  6. Knuckle Cracking

    MedlinePlus

    ... older obese people. Question: Can cracking knuckles / joints lead to arthritis? Answer: There is no evidence of ... or damaged joints due to arthritis could potentially lead more easily to ligament injury or acute trauma ...

  7. Quantitative image analysis of WE43-T6 cracking behavior

    NASA Astrophysics Data System (ADS)

    Ahmad, A.; Yahya, Z.

    2013-06-01

    Environment-assisted cracking of WE43 cast magnesium (4.2 wt.% Yt, 2.3 wt.% Nd, 0.7% Zr, 0.8% HRE) in the T6 peak-aged condition was induced in ambient air in notched specimens. The mechanism of fracture was studied using electron backscatter diffraction, serial sectioning and in situ observations of crack propagation. The intermetallic (rare earthed-enriched divorced intermetallic retained at grain boundaries and predominantly at triple points) material was found to play a significant role in initiating cracks which leads to failure of this material. Quantitative measurements were required for this project. The populations of the intermetallic and clusters of intermetallic particles were analyzed using image analysis of metallographic images. This is part of the work to generate a theoretical model of the effect of notch geometry on the static fatigue strength of this material.

  8. Endovascular navigation based on real/virtual environments cooperation for computer-assisted TEAM procedures

    NASA Astrophysics Data System (ADS)

    Goksu, Cemil; Haigron, Pascal; Acosta, Oscar; Lucas, Antoine

    2004-05-01

    Transfemoral Endovascular Aneurysm Management, the less invasive treatment of Aortic Abdominal Aneurysms (AAA), is a highly specialized procedure, using advanced devices and requiring a high degree of clinical expertise. There is a great need for a navigation guidance system able to make this procedure safer and more precise. In this context of computer-assisted minimally invasive interventional procedures, we propose a new framework based on the cooperation between the real environment where the intervention takes place and a patient-specific virtual environment, which contains a virtual operating room including a C-arm model as well as the 3D preoperative patient data. This approach aims to deal with the problem of lack of knowledge about soft tissue behavior by better exploiting available information before and during the intervention through a cooperative approach. In order to assist the TEAM procedure in standard interventional conditions, we applied this framework to design a 3D navigation guidance system, which has been successfully used during three TEAM interventions in the operating room. Intra-operatively, anatomical feature-based 2D/3D registration between a single 2D fluoroscopic view, reproduced from the pose planned in the virtual environment, and the preoperative CT volume, is performed by means of a chamfer distance map. The 3D localization of the endovascular devices (sheath, guide wire, prosthesis) tracked either interactively or automatically on 2D sequences, is constrained to either the 3D vascular tree or a 3D device model. Moreover, we propose a first solution to take into account the tissue deformations during this particular intervention and to update the virtual environment with the intraoperative data.

  9. The effect of alloy composition on the mechanism of stress-corrosion cracking of titanium alloys in aqueous environments

    NASA Technical Reports Server (NTRS)

    Wood, R. A.; Boyd, J. D.; Williams, D. N.; Jaffee, R. I.

    1972-01-01

    A detailed study was made of the relation between the size distribution of Ti3Al particles in a Ti-8Al alloy and the tensile properties measured in air and in saltwater. The size distribution of Ti3Al was varied by isothermal aging for various times at temperatures in the range 770 to 970 K (930 to 1290 F). The aging kinetics were found to be relatively slow. Quantitative measurements of the particle coarsening rate at 920 K (1200 F) showed good agreement with the predicted behavior for coarsening controlled by matrix diffusion, and suggested that the specific free energy of the Ti3Al alpha interface in negligible small. In all cases, the Ti3Al particles were sheared by the glide dislocations. It was concluded that there is a definite correlation between the presence of deformable Ti3Al particles and an alloy's susceptibility to aqueous stress corrosion cracking. Furthermore, the appearance of the surface slip lines and the dislocation substructure in deformed specimens suggest that the specific effect of the Ti3Al particles is to cause a nonhomogeneous planar slip character and an enhanced chemical potential of the slip bands.

  10. 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.

  11. Initiation of Stress Corrosion Cracks in X80 and X100 Pipe Steels in Near-Neutral pH Environment

    NASA Astrophysics Data System (ADS)

    Kang, Jidong; Zheng, Wenyue; Bibby, Darren; Amirkhiz, Babak Shalchi; Li, Jian

    2016-01-01

    Tests were conducted on X80 and X100 pipe steels at 95% specified minimum yield stress in NS4 solution mixed with soil using specimens machined along the transverse direction of the pipes. Crack initiation in X100 is much easier than in X80. With test time increasing from 110 to 220 days, less numerous but deeper cracks were found in both pipe steels. Cracks showed higher growth rates in the transverse specimens than those in longitudinal ones. TEM results revealed concentration of Ni or Cr elements, formation of oxide layer at crack walls, and TiN-related dissolution at the crack tip.

  12. A Movement-Assisted Deployment of Collaborating Autonomous Sensors for Indoor and Outdoor Environment Monitoring

    PubMed Central

    Niewiadomska-Szynkiewicz, Ewa; Sikora, Andrzej; Marks, Michał

    2016-01-01

    Using mobile robots or unmanned vehicles to assist optimal wireless sensors deployment in a working space can significantly enhance the capability to investigate unknown environments. This paper addresses the issues of the application of numerical optimization and computer simulation techniques to on-line calculation of a wireless sensor network topology for monitoring and tracking purposes. We focus on the design of a self-organizing and collaborative mobile network that enables a continuous data transmission to the data sink (base station) and automatically adapts its behavior to changes in the environment to achieve a common goal. The pre-defined and self-configuring approaches to the mobile-based deployment of sensors are compared and discussed. A family of novel algorithms for the optimal placement of mobile wireless devices for permanent monitoring of indoor and outdoor dynamic environments is described. They employ a network connectivity-maintaining mobility model utilizing the concept of the virtual potential function for calculating the motion trajectories of platforms carrying sensors. Their quality and utility have been justified through simulation experiments and are discussed in the final part of the paper. PMID:27649186

  13. A Movement-Assisted Deployment of Collaborating Autonomous Sensors for Indoor and Outdoor Environment Monitoring.

    PubMed

    Niewiadomska-Szynkiewicz, Ewa; Sikora, Andrzej; Marks, Michał

    2016-09-14

    Using mobile robots or unmanned vehicles to assist optimal wireless sensors deployment in a working space can significantly enhance the capability to investigate unknown environments. This paper addresses the issues of the application of numerical optimization and computer simulation techniques to on-line calculation of a wireless sensor network topology for monitoring and tracking purposes. We focus on the design of a self-organizing and collaborative mobile network that enables a continuous data transmission to the data sink (base station) and automatically adapts its behavior to changes in the environment to achieve a common goal. The pre-defined and self-configuring approaches to the mobile-based deployment of sensors are compared and discussed. A family of novel algorithms for the optimal placement of mobile wireless devices for permanent monitoring of indoor and outdoor dynamic environments is described. They employ a network connectivity-maintaining mobility model utilizing the concept of the virtual potential function for calculating the motion trajectories of platforms carrying sensors. Their quality and utility have been justified through simulation experiments and are discussed in the final part of the paper.

  14. A Movement-Assisted Deployment of Collaborating Autonomous Sensors for Indoor and Outdoor Environment Monitoring.

    PubMed

    Niewiadomska-Szynkiewicz, Ewa; Sikora, Andrzej; Marks, Michał

    2016-01-01

    Using mobile robots or unmanned vehicles to assist optimal wireless sensors deployment in a working space can significantly enhance the capability to investigate unknown environments. This paper addresses the issues of the application of numerical optimization and computer simulation techniques to on-line calculation of a wireless sensor network topology for monitoring and tracking purposes. We focus on the design of a self-organizing and collaborative mobile network that enables a continuous data transmission to the data sink (base station) and automatically adapts its behavior to changes in the environment to achieve a common goal. The pre-defined and self-configuring approaches to the mobile-based deployment of sensors are compared and discussed. A family of novel algorithms for the optimal placement of mobile wireless devices for permanent monitoring of indoor and outdoor dynamic environments is described. They employ a network connectivity-maintaining mobility model utilizing the concept of the virtual potential function for calculating the motion trajectories of platforms carrying sensors. Their quality and utility have been justified through simulation experiments and are discussed in the final part of the paper. PMID:27649186

  15. Subcritical crack-growth behavior of borosilicate glass under cyclic loads: Evidence of a mechanical fatigue effect

    SciTech Connect

    Dill, S.J.; Dauskardt, R.H.; Bennison, S.J.

    1997-03-01

    Amorphous glasses are generally considered immune to mechanical fatigue effects associated with cyclic loading. In this study surprising new evidence is presented for a mechanical fatigue effect in borosilicate glass, in both moist air and dry nitrogen environments. The fatigue effect occurs at near threshold subcritical crack-growth rates (da/dt < 3 {times} 10{sup {minus}8} m/s) as the crack extension per cycle approaches the dimensions of the borosilicate glass network. While subcritical crack growth under cyclic loads at higher load levels is entirely consistent with environmentally assisted crack growth, lower growth rates actually exceed those measured under monotonic loads. This suggests a mechanical fatigue effect which accelerates subcritical crack-growth rates. Likely mechanisms for the mechanical fatigue effect are presented.

  16. Corrosion fatigue crack growth in clad low-alloy steels: Part 1, medium-sulfur forging steel

    SciTech Connect

    James, L.A.; Poskie, T.J.; Auten, T.A; Cullen, W.H.

    1996-04-01

    Corrosion fatigue crack propagation tests were conducted on a medium- sulfur ASTM A508-2 forging steel overlaid with weld-deposited Alloy EN82H cladding. The specimens featured semi-elliptical surface cracks penetrating approximately 6.3 mm of cladding into the underlying steel. The initial crack sizes were relatively large with surface lengths of 30.3--38.3 mm, and depths of 13.1--16.8 mm. The experiments were conducted in a quasi-stagnant low-oxygen (O{sub 2} < 10 ppb) aqueous environment at 243{degrees}C, under loading conditions ({Delta}K, R, and cyclic frequency) conductive to environmentally-assisted cracking (EAC) in higher-sulfur steels under quasi-stagnant conditions. Earlier experiments on unclad compact tension specimens of this heat of steel did not exhibit EAC, and the present experiments on semi-elliptical surface cracks penetrating cladding also did not exhibit EAC.

  17. SLAM algorithm applied to robotics assistance for navigation in unknown environments

    PubMed Central

    2010-01-01

    Background The combination of robotic tools with assistance technology determines a slightly explored area of applications and advantages for disability or elder people in their daily tasks. Autonomous motorized wheelchair navigation inside an environment, behaviour based control of orthopaedic arms or user's preference learning from a friendly interface are some examples of this new field. In this paper, a Simultaneous Localization and Mapping (SLAM) algorithm is implemented to allow the environmental learning by a mobile robot while its navigation is governed by electromyographic signals. The entire system is part autonomous and part user-decision dependent (semi-autonomous). The environmental learning executed by the SLAM algorithm and the low level behaviour-based reactions of the mobile robot are robotic autonomous tasks, whereas the mobile robot navigation inside an environment is commanded by a Muscle-Computer Interface (MCI). Methods In this paper, a sequential Extended Kalman Filter (EKF) feature-based SLAM algorithm is implemented. The features correspond to lines and corners -concave and convex- of the environment. From the SLAM architecture, a global metric map of the environment is derived. The electromyographic signals that command the robot's movements can be adapted to the patient's disabilities. For mobile robot navigation purposes, five commands were obtained from the MCI: turn to the left, turn to the right, stop, start and exit. A kinematic controller to control the mobile robot was implemented. A low level behavior strategy was also implemented to avoid robot's collisions with the environment and moving agents. Results The entire system was tested in a population of seven volunteers: three elder, two below-elbow amputees and two young normally limbed patients. The experiments were performed within a closed low dynamic environment. Subjects took an average time of 35 minutes to navigate the environment and to learn how to use the MCI. The SLAM

  18. 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

  19. Importance of excitation and trapping conditions in photosynthetic environment-assisted energy transport.

    PubMed

    León-Montiel, Roberto de J; Kassal, Ivan; Torres, Juan P

    2014-09-11

    It has been argued that excitonic energy transport in photosynthetic complexes is efficient because of a balance between coherent evolution and decoherence, a phenomenon called environment-assisted quantum transport (ENAQT). Studies of ENAQT have usually assumed that the excitation is initially localized on a particular chromophore, and that it is transferred to a reaction center through a similarly localized trap. However, these assumptions are not physically accurate. We show that more realistic models of excitation and trapping can lead to very different predictions about the importance of ENAQT. In particular, although ENAQT is a robust effect if one assumes a localized trap, its effect can be negligible if the trapping is more accurately modeled as Förster transfer to a reaction center. Our results call into question the suggested role of ENAQT in the photosynthetic process of green sulfur bacteria and highlight the subtleties associated with drawing lessons for designing biomimetic light-harvesting complexes.

  20. A Beowulf Class parallel remote-sensed image database retrieval system developed in ASSIST environment

    NASA Astrophysics Data System (ADS)

    Di Lecce, Vincenzo; Guerriero, Andrea; Guarino, I.

    2005-01-01

    Image databases are now currently utilized in a wide range of different areas, in particular, the development and application of remote sensing platforms result in the production of huge amounts of image data. One of the major problem in the practical implementation of a Content-based Image Retrieval (CBIR) for remotely sensed images is that the content-based indexing and searching process always requires extremely high computational power. On the other hand, the content-based image retrieval algorithms are very suitable for parallel computation as the algorithms can be broken into several data independent processes for running on a parallel computer. In this paper, we discuss the porting problem of a sequential application of remote sensed image retrieval in a parallel environment using the new paradigm of programming introduced by the birth of a new structured program languages (Assist 1.2) and compared performances to sequential and to commercial multiprocessors solutions.

  1. A Beowulf Class parallel remote-sensed image database retrieval system developed in ASSIST environment

    NASA Astrophysics Data System (ADS)

    Di Lecce, Vincenzo; Guerriero, Andrea; Guarino, I.

    2004-12-01

    Image databases are now currently utilized in a wide range of different areas, in particular, the development and application of remote sensing platforms result in the production of huge amounts of image data. One of the major problem in the practical implementation of a Content-based Image Retrieval (CBIR) for remotely sensed images is that the content-based indexing and searching process always requires extremely high computational power. On the other hand, the content-based image retrieval algorithms are very suitable for parallel computation as the algorithms can be broken into several data independent processes for running on a parallel computer. In this paper, we discuss the porting problem of a sequential application of remote sensed image retrieval in a parallel environment using the new paradigm of programming introduced by the birth of a new structured program languages (Assist 1.2) and compared performances to sequential and to commercial multiprocessors solutions.

  2. Investigation of environmentally assisted fracture of metallic nuclear waste package barrier materials in simulated basalt repository environments

    SciTech Connect

    Pitman, S.G.

    1982-11-01

    Statically loaded corrosion tests, slow strain rate (SSR) tests, and fatigue crack growth rate (FCGR) tests were conducted to evaluate the relative susceptibility of two titanium-base nuclear waste package candidate structural barrier materials Ti-grade 2 and Ti-grade 12-to environmentally enhanced cracking in a simulated repository environment. Statically loaded corrosion tests were done in oxic basalt ground water at 250/sup 0/C; SSR tests were done in oxic basalt ground water at 150, 250, and 300/sup 0/C and in air at 20 and 250/sup 0/C; and FCGR tests were done in basalt ground water, fluoride-ion-enhanced basalt ground water, high-purity water, and air at 90/sup 0/C. The following conclusions can be drawn: the general corrosion rate of statically loaded corrosion coupons was very low in a 3-mo test, and no pitting or cracking of the specimens was observed. Ti-grade 2 and Ti-grade 12 exhibited strain rate dependent ductility diminution in SSR tests. The ductility diminution was most severe in Ti-grade 2 at 300/sup 0/C and in Ti-grade 12 at 250/sup 0/C. For of Ti-grade 12 it was found to be highly orientation dependent. The ductility diminution was also found in tests conducted in air as well as in those conducted in the basalt ground water environment; however, the extent of the degradation was less in air. The ductility diminution cannot be attributed to stress corrosion cracking because the fracture mode was microvoid coalescence in all tests. Evidence obtained in the current study and correlation of the present results with results obtained by other researchers indicate that dynamic strain aging is responsible for the loss of ductility. The FCGR of Ti-grade 2 and Ti-grade 12 was not affected by any of the environmental conditions used in this study, which indicates that no environmental cracking mechanism is operative under the conditions tested (90/sup 0/C, oxic ground water, and frequencies from 0.01 to 5 Hz).

  3. Epigenetic effects on the embryo as a result of periconceptional environment and assisted reproduction technology.

    PubMed

    Lucas, Emma

    2013-11-01

    The early embryonic environment has been shown to be remarkably influential on the developing organism, despite the relative brevity of this developmental stage. The cells of the zygote and cleavage-stage embryo hold the potential to form all cell lineages of the embryonic and extra-embryonic tissues, with gradual fate restriction occurring from the time of compaction and blastocyst formation. As such, these cells carry with them the potential to influence the phenotype of all successive cell types as the organism grows, differentiates and ages. The implication is, therefore, that sublethal adverse conditions which alter the developmental trajectory of these cells may have long-term implications for the health and development of the resulting offspring. One confirmed mechanism for the translation of environmental cues to phenotypic outcome is epigenetic modification of the genome to modulate chromatin packaging and gene expression in a cell- and lineage-specific manner. The influence of the periconceptional milieu on the epigenetic profile of the developing embryo has become a popular research focus in the quest to understand the effects of environment, nutrition and assisted reproduction technology on human development and health.

  4. Fatigue crack propagation at polymer adhesive interfaces

    SciTech Connect

    Ritter, J.E.

    1996-12-31

    Delamination of polymer adhesive interfaces often occurs due to slow crack growth under either monotonic or cyclic loading. The author`s previous research showed that moisture-assisted crack growth at epoxy/glass and epoxy acrylate/glass interfaces under monotonic loading was directly related to the applied energy release rate and relative humidity and that cyclic loading could enhance crack growth. The purpose of the present research is to compare crack growth along epoxy acrylate/glass and epoxy/PMMA interfaces under monotonic and cyclic loading.

  5. Pacific Northwest Laboratory annual report for 1987 to the Assistant Secretary for Environment, Safety, and Health: Part 5: Environment, safety, health, and quality assurance

    SciTech Connect

    Faust, L.G.; Steelman, B.L.; Selby, J.M.

    1988-02-01

    Part 5 of the 1987 Annual Report to the US Department of Energy's Assistant Secretary for Environment, Safety, and Health presents Pacific Northwest Laboratory's progress on work performed for the Office of Nuclear Safety, the Office of Environmental Guidance and Compliance, the Office of Environmental Audit, and the Office of National Environmental Policy Act Project Assistance. For each project, as identified by the Field Work Proposal, articles describe progress made during fiscal year 1987. Authors of these articles represent a broad spectrum of capabilities derived from five of the seven technical centers of the Laboratory, reflecting the interdisciplinary nature of the work.

  6. The Effect of a Graph-Oriented Computer-Assisted Project-Based Learning Environment on Argumentation Skills

    ERIC Educational Resources Information Center

    Hsu, P. -S.; Van Dyke, M.; Chen, Y.; Smith, T. J.

    2015-01-01

    The purpose of this quasi-experimental study was to explore how seventh graders in a suburban school in the United States developed argumentation skills and science knowledge in a project-based learning environment that incorporated a graph-oriented, computer-assisted application. A total of 54 students (three classes) comprised this treatment…

  7. Pacific Northwest Laboratory annual report for 1980 to the DOE Assistant Secretary for Environment. Part 2 supplement, ecological sciences

    SciTech Connect

    Vaughan, B.E.

    1981-06-01

    This supplement replaces the list of Publications and Presentations in the Pacific Northwest Laboratory Annual Report for 1980 to the Assistant Secretary for Environment, PNL-3700 PT2, Ecological Sciences. The listings in the report as previously distributed were incomplete owing to changeovers in the bibliographic-tracking system.

  8. A user profile ontology based approach for assisting people with dementia in mobile environments.

    PubMed

    Skillen, Kerry-Louise; Chen, Liming; Nugent, Chris D; Donnelly, Mark P; Solheim, Ivar

    2012-01-01

    Personalization and context-aware applications have attracted increasing amounts of attention over recent years due to the emergence of pervasive computing applications. Nevertheless, it still remains a challenge to meet the needs of users while they are on the move. This paper introduces a novel approach for providing personalized, context-aware assistance services for users in mobile environments. Central to the approach is the use of ontological user profile modeling which captures various characteristics of a user in order to create a unique set of profile information. In addition, user profiles can adapt to changing user behavior, thus enabling services to respond to evolving user needs and preferences. We describe the overall system architecture of the proposed approach with special emphasis being placed on the user profile modelling and its expected utility based on a typical use case scenario, i.e., using a smart-phone to address the problem of the outdoor mobility of a person with Dementia. A prototype based on the Android OS is used to illustrate the application. The use of everyday technology for a real world problem highlights the potential and utility of our approach. PMID:23367391

  9. 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.

  10. 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.

  11. BWR pipe crack remedies evaluation

    SciTech Connect

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

    1986-10-01

    This paper presents results on: (a) the influence of simulated BWR environments on the stress-corrosion-craking (SCC) susceptibility of Types 304, 316NG, and 347 stainless (SS); (b) fracture-mechanics crack-growth-rate measurements on these materials and weld overlay specimens in different environments; and (c) residual stress measurements and metallographic evaluations of conventional pipe weldments treated by a mechanical-stress-improvement process (MSIP) as well as those produced by a narrow-gap welding procedure. Crack initiation studies on Types 304 and 316NG SS under crevice and non-crevice conditions in 289/sup 0/C water containing 0.25 ppM dissolved oxygen with low sulfate concentrations indicate that SCC initiates at very low strains (<3%) in the nuclear grade material. Crack growth measurements on fracture-mechanics-type specimens, under low-frequency cyclic loading, show that the Type 316NG steel cracks at a somewhat lower rate (approx.40%) than sensitized Type 304 SS in an impurity environment with 0.25 ppM dissolved-oxygen; however, the latter material stops cracking when sulfate is removed from the water. Crack growth in both materials ceases under simulated hydrogen-water chemistry conditions (<5 ppB oxygen) even with 100 ppB sulfate present in the water. An unexpected result was obtained in the test on a weld overlay specimen in the impurity environment, viz., the crack grew to the overlay interface at a nominal rate, branched at 90/sup 0/ in both directions, and then grew at high rate (parallel to the nominal applied load). Residual stress measurements on MSIP-treated weldments and those produced by a narrow-gap welding procedure indicate that these techniques produce compressive stresses over most of the inner surface near the weld and heat-affected zones.

  12. The Effects of Test Temperature, Temper, and Alloyed Copper on the Hydrogen-Controlled Crack Growth Rate of an Al-Zn-Mg-(Cu) Alloy

    SciTech Connect

    G.A. Young, Jr.; J.R. Scully

    2000-09-17

    The hydrogen embrittlement controlled stage II crack growth rate of AA 7050 (6.09 wt.% Zn, 2.14 wt% Mg, 2.19 wt.% Cu) was investigated as a function of temper and alloyed copper level in a humid air environment at various temperatures. Three tempers representing the underaged, peak aged, and overaged conditions were tested in 90% relative humidity (RH) air at temperatures between 25 and 90 C. At all test temperatures, an increased degree of aging (from underaged to overaged) produced slower stage II crack growth rates. The stage II crack growth rate of each alloy and temper displayed Arrhenius-type temperature dependence with activation energies between 58 and 99 kJ/mol. For both the normal copper and low copper alloys, the fracture path was predominantly intergranular at all test temperatures (25-90 C) in each temper investigated. Comparison of the stage II crack growth rates for normal (2.19 wt.%) and low (0.06 wt.%) copper alloys in the peak aged and overaged tempers showed the beneficial effect of copper additions on stage II crack growth rate in humid air. In the 2.19 wt.% copper alloy, the significant decrease ({approx} 10 times at 25 C) in stage II crack growth rate upon overaging is attributed to an increase in the apparent activation energy for crack growth. IN the 0.06 wt.% copper alloy, overaging did not increase the activation energy for crack growth but did lower the pre-exponential factor, {nu}{sub 0}, resulting in a modest ({approx} 2.5 times at 25 C) decrease in crack growth rate. These results indicate that alloyed copper and thermal aging affect the kinetic factors that govern stage II crack growth rate. Overaged, copper bearing alloys are not intrinsically immune to hydrogen environment assisted cracking but are more resistant due to an increased apparent activation energy for stage II crack growth.

  13. Strain oxidation cracking of austenitic stainless steels at 610 C

    SciTech Connect

    Calvar, M. Le; Scott, P.M.; Magnin, T.; Rieux, P.

    1998-02-01

    Strain oxidation cracking of both forged and welded austenitic stainless steels (SS) was studied. Creep and slow strain rate tests (SSRT) were performed in vacuum, air, and a gas furnace environment (air + carbon dioxide [CO{sub 2}] + water [H{sub 2}O]). Results showed cracking was environmentally dependent. Almost no cracking was observed in vacuum, whereas intergranular cracking was observed with increasing severity in passing from an air to a gas furnace environment. The most severe cracking was associated with formation of a less protective film formed in the gas furnace environment (air: haematite-like M{sub 2}O{sub 3} oxide; gas furnace environment: spinel M{sub 3}O{sub 4} oxide). Cracking depended strongly on the carbon content and the sensitization susceptibility of the material: the higher the carbon content, the more susceptible the alloy. This cracking was believed to be similar to other oxidation-induced cracking phenomena.

  14. Special studies and analyses for the Assistant Secretary for Policy, Safety, and Environment. Final report

    SciTech Connect

    Not Available

    1984-11-01

    The report identifies major tasks accomplished, details plans for the orderly completion of all work in process, and provides a complete listing of deliverables (reports, briefings, letters, etc.) provided under the contract. Purpose of this contract was to provide environmental studies, analytical planning, evaluation, and other technical assistance and support to the DOE Office of the Assistant Secretary for Environmental Protection, Safety and Emergency Preparedness (EP) and designated EP offices and divisions.

  15. 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.

  16. 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.

  17. Pacific Northwest Laboratory annual report for 1989 to the Assistant Secretary for Environment, Safety, and Health - Part 5: Environment, Safety, Health, and Quality Assurance

    SciTech Connect

    Faust, L.G.; Doctor, P.G.; Selby, J.M.

    1990-04-01

    Part 5 of the 1989 Annual Report to the US Department of Energy's Assistant Secretary for Environment, Safety, and Health presents Pacific Northwest Laboratory's progress on work performed for the Office of Environmental Guidance and Compliance, the Office of Environmental Audit, the Office of National Environmental Policy Act Project Assistance, the Office of Nuclear Safety, the Office of Safety Compliance, and the Office of Policy and Standards. For each project, as identified by the Field Work Proposal, there is an article describing progress made during fiscal year 1989. Authors of these articles represent a broad spectrum of capabilities derived from five of the seven technical centers of the Laboratory, reflecting the interdisciplinary nature of the work. 35 refs., 1 fig.

  18. 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.

  19. Building the Scientific Modeling Assistant: An interactive environment for specialized software design

    NASA Technical Reports Server (NTRS)

    Keller, Richard M.

    1991-01-01

    The construction of scientific software models is an integral part of doing science, both within NASA and within the scientific community at large. Typically, model-building is a time-intensive and painstaking process, involving the design of very large, complex computer programs. Despite the considerable expenditure of resources involved, completed scientific models cannot easily be distributed and shared with the larger scientific community due to the low-level, idiosyncratic nature of the implemented code. To address this problem, we have initiated a research project aimed at constructing a software tool called the Scientific Modeling Assistant. This tool provides automated assistance to the scientist in developing, using, and sharing software models. We describe the Scientific Modeling Assistant, and also touch on some human-machine interaction issues relevant to building a successful tool of this type.

  20. 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.

  1. Description of crack growth using the strip-yield model for computation of crack opening loads, crack tip stretch, and strain rates

    SciTech Connect

    Koning, A.U. de; Hoeve, H.J. ten; Henriksen, T.K.

    1999-07-01

    Nowadays, application of the strip-yield model for computation of crack opening load levels is well known. In this paper the incremental formulation of a fatigue crack growth law is used to demonstrate the role of the crack opening load level in time-independent fatigue crack growth. Less known is the ability of the strip-yield model to define the strain rate at the crack tip. A threshold level {dot {var{underscore}epsilon}}{sub th} of this strain rate is introduced and used to formulate a criterion for initiation of time-dependent accelerated fatigue crack growth. This process is called corrosion fatigue. To account for effects of environment and frequency on the crack growth rate a time-dependent part is added to the incremental fatigue crack growth law. The resulting incremental crack growth equation is integrated to obtain the crack growth rate for a load cycle. The model discussed in this paper is a mechanical model. Physical aspects other than strain rate, loading frequency and load wave shape are not modeled in an explicit way. Hence, the model is valid for specific environment/base metal combinations. However, in consideration of the effects of small variations of environment, temperature, and other variables on the crack growth rates, it can be used as a reference solution. The fatigue crack growth model has been implemented in the NASGRO (ESACRACK) software. The time-dependent part is still subject to further evaluation.

  2. Implementing Glossing in Mobile-Assisted Language Learning Environments: Directions and Outlook

    ERIC Educational Resources Information Center

    Lee, Hansol; Lee, Jang Ho

    2013-01-01

    While mobile technology, such as the touch-based smart-phone, has become part of our daily lives, research into and classroom practices surrounding mobile-assisted language learning (MALL) have generally not kept up with the pace of technological development. This situation may be caused in part by the fact that a considerable proportion of…

  3. Animal-Assisted Literacy: A Supportive Environment for Constrained and Unconstrained Learning

    ERIC Educational Resources Information Center

    Friesen, Lori; Delisle, Esther

    2012-01-01

    Over the last 20 years or so, the popularity of animal-assisted literacy learning programs has gained momentum in schools and libraries around the world (Intermountain Therapy Animals, 2011). To date, such programs are currently running in four Canadian provinces and 43 U.S. states, as well as in Australia, the United Kingdom, Italy, and India…

  4. 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.

  5. Fracture toughness and crack growth of Zerodur

    NASA Technical Reports Server (NTRS)

    Viens, Michael J.

    1990-01-01

    The fracture toughness and crack growth parameters of Zerodur, a low expansion glass ceramic material, were determined. The fracture toughness was determined using indentation techniques and was found to be 0.9 MPa x m(sup 1/2). The crack growth parameters were determined using indented biaxial specimens subjected to static and dynamic loading in an aqueous environment. The crack growth parameters n and 1n(B) were found to be 30.7 and -6.837, respectively. The crack growth parameters were also determined using indented biaxial specimens subjected to dynamic loading in an ambient 50 percent relative humidity environment. The crack growth parameters n and 1n(B) at 50 percent relative humidity were found to be 59.3 and -17.51, respectively.

  6. Effect of halide ions on electrochemical behavior and stress corrosion cracking of 67/33 {alpha}-brass in aqueous environments

    SciTech Connect

    Lee, C.K.; Shih, H.C.

    1996-09-01

    The slow strain rate tension technique was used to study the effect of strain rate on susceptibility to stress corrosion cracking (SCC) and crack velocity of 67/33 {alpha}-brass (UNS C26800) in 0.1 M sodium halide solutions (pH = 6.8) at 25 C. The effect of halide ions on electrochemical behavior of {alpha}-brass also was investigated using cyclic polarization techniques. Results indicated fluoride ions induced a significant susceptibility to intergranular stress corrosion cracking. Susceptibility increased with decreasing strain rate. Crack velocity also increased with strain rate in a double logarithmic relationship. The entire fracture surface was characteristic of IGSCC at a critical strain rate of 2 {times} 10{sup {minus}6}/s. The open-circuit potential (OCP) was within the potential range where cuprous oxide is stable. Electrochemical polarization analysis confirmed that 67/33 {alpha}-brass can form a passive Cu{sub 2}O film in 0.1 M sodium fluoride solution and that this passive film can break down. Results suggested film rupture and slip-dealloying dissolution may be involved in IGSCC of 67/33 {alpha}-brass in F{sup {minus}} solution. In 0.1 M chloride, bromide, or iodide solutions, no SCC susceptibility was observed regardless of strain rate. OCP moved to more active potentials in the presence of Cl{sup {minus}}, Br{sup {minus}}, and I{sup {minus}}. This result was attributed to formation of soluble cuprous complexes controlling the dealloying process through precipitation of metal ion salts on the surface of {alpha}-brass.

  7. Crack Growth Properties of Sealing Glasses

    NASA Technical Reports Server (NTRS)

    Salem, Jonathan A.; Tandon, R.

    2008-01-01

    The crack growth properties of several sealing glasses were measured using constant stress rate testing in 2% and 95% RH (relative humidity). Crack growth parameters measured in high humidity are systematically smaller (n and B) than those measured in low humidity, and velocities for dry environments are approx. 100x lower than for wet environments. The crack velocity is very sensitivity to small changes in RH at low RH. Confidence intervals on parameters that were estimated from propagation of errors were comparable to those from Monte Carlo simulation.

  8. Surface modification of polymer by ion assisted reaction in reactive gases environment

    SciTech Connect

    Koh, S.K.; Choi, S.C.; Choi, W.K.; Jung, H.J.; Hur, H.H.

    1997-12-01

    Wettable surface of polymers (advanced wetting angle {approximately}10{degree} and surface energy {approximately}60--70 erg/cm{sup 2}) have been accomplished by the ion assisted reaction, in which energetic ions are irradiated on polymer with blowing oxygen gas. The energies of ions are varied from 0.5 to 1.5 keV, doses 10{sup 14} to 10{sup 17} ions/cm{sup 2}, and blowing rate of oxygen 0--8 ml/min. The wetting angles are increased when the wettable polymers were exposed in air, but are remained in pure water. Improvement of surface energy is mainly due to the polar force. Surface analysis shows hydrophilic functional groups such as C{double_bond}O, (C{double_bond}O){single_bond}O, C{single_bond}O, etc., are formed without surface damage after the ion assisted reaction treatment. Comparisons between the conventional surface treatments and the ion assisted reaction are described in term of physical bombardment, surface damage, functional group, and chain mobility in polymer.

  9. Crack spectra analysis

    SciTech Connect

    Tiernan, M.

    1980-09-01

    Crack spectra derived from velocity data have been shown to exhibit systematics which reflect microstructural and textural differences between samples (Warren and Tiernan, 1980). Further research into both properties and information content of crack spectra have yielded the following: Spectral features are reproducible even at low pressures; certain observed spectral features may correspond to non-in-situ crack populations created during sample retrieval; the functional form of a crack spectra may be diagnostic of the sample's grain texture; hysteresis is observed in crack spectra between up and down pressure runs - it may be due to friction between the faces of closed crack populations.

  10. Deployment of assistive living technology in a nursing home environment: methods and lessons learned

    PubMed Central

    2013-01-01

    Background With an ever-growing ageing population, dementia is fast becoming the chronic disease of the 21st century. Elderly people affected with dementia progressively lose their autonomy as they encounter problems in their Activities of Daily Living (ADLs). Hence, they need supervision and assistance from their family members or professional caregivers, which can often lead to underestimated psychological and financial stress for all parties. The use of Ambient Assistive Living (AAL) technologies aims to empower people with dementia and relieve the burden of their caregivers. The aim of this paper is to present the approach we have adopted to develop and deploy a system for ambient assistive living in an operating nursing home, and evaluate its performance and usability in real conditions. Based on this approach, we emphasise on the importance of deployments in real world settings as opposed to prototype testing in laboratories. Methods We chose to conduct this work in close partnership with end-users (dementia patients) and specialists in dementia care (professional caregivers). Our trial was conducted during a period of 14 months within three rooms in a nursing home in Singapore, and with the participation of eight dementia patients and two caregivers. A technical ambient assistive living solution, consisting of a set of sensors and devices controlled by a software platform, was deployed in the collaborating nursing home. The trial was preceded by a pre-deployment period to organise several observation sessions with dementia patients and focus group discussions with professional caregivers. A process of ground truth and system’s log data gathering was also planned prior to the trial and a system performance evaluation was realised during the deployment period with the help of caregivers. An ethical approval was obtained prior to real life deployment of our solution. Results Patients’ observations and discussions allowed us to gather a set of requirements

  11. Gear crack propagation investigations

    NASA Technical Reports Server (NTRS)

    Lewicki, David G.; Ballarini, Roberto

    1996-01-01

    Analytical and experimental studies were performed to investigate the effect of gear rim thickness on crack propagation life. The FRANC (FRacture ANalysis Code) computer program was used to simulate crack propagation. The FRANC program used principles of linear elastic fracture mechanics, finite element modeling, and a unique re-meshing scheme to determine crack tip stress distributions, estimate stress intensity factors, and model crack propagation. Various fatigue crack growth models were used to estimate crack propagation life based on the calculated stress intensity factors. Experimental tests were performed in a gear fatigue rig to validate predicted crack propagation results. Test gears were installed with special crack propagation gages in the tooth fillet region to measure bending fatigue crack growth. Good correlation between predicted and measured crack growth was achieved when the fatigue crack closure concept was introduced into the analysis. As the gear rim thickness decreased, the compressive cyclic stress in the gear tooth fillet region increased. This retarded crack growth and increased the number of crack propagation cycles to failure.

  12. Corrosion fatigue crack growth in clad low-alloy steel. Part 2, Water flow rate effects in high sulfur plate steel

    SciTech Connect

    James, L.A; Lee, H.B.; Wire, G.L.; Novak, S.R.; Cullen, W.H.

    1996-04-01

    Corrosion fatigue crack propagation tests were conducted on a high- sulfur ASTM A302-B plate steel overlaid with weld-deposited Alloy EN82H cladding. The specimens featured semi-elliptical surface cracks penetrating approximately 6.3 mm of cladding into the underlying steel. The initial crack sizes were relatively large with surface lengths of 22.8--27.3 mm, and depths of 10.5--14.1 mm. The experiments were initiated in a quasi-stagnant low-oxygen (O{sub 2} < 10 ppb) aqueous environment at 243{degrees}C, under loading conditions ({Delta}K, R, cyclic frequency) conducive to environmentally-assisted cracking (EAC) under quasi-stagnant conditions. Following fatigue testing under quasi-stagnant conditions where EAC was observed, the specimens were then fatigue tested under conditions where active water flow of either 1.7 m/sec. or 4.7 m/sec. was applied parallel to the crack. Earlier experiments on unclad surface-cracked specimens of the same steel exhibited EAC under quasi- stagnant conditions, but water flow rates at 1.7 m/sec. and 5.0 m/sec. parallel to the crack mitigated EAC. In the present experiments on clad specimens, water flow at approximately the same as the lower of these velocities did not mitigate EAC, and a free stream velocity approximately the same as the higher of these velocities resulted in sluggish mitigation of EAC. The lack of robust EAC mitigation was attributed to the greater crack surface roughness in the cladding interfering with flow induced within the crack cavity. An analysis employing the computational fluid dynamics code, FIDAP, confirmed that frictional forces associated with the cladding crack surface roughness reduced the interaction between the free stream and the crack cavity.

  13. An HL7-FHIR-based Object Model for a Home-Centered Data Warehouse for Ambient Assisted Living Environments.

    PubMed

    Schwartze, Jonas; Jansen, Lars; Schrom, Harald; Wolf, Klaus-Hendrik; Haux, Reinhold; Marschollek, Michael

    2015-01-01

    Current AAL environments focus on assisting a single person with seperated technologies. There is no interoperability between sub-domains in home environments, like building energy management or housing industry services. BASIS (Building Automation by a Scalable and Intelligent System) aims to integrate all sensors and actuators into a single, efficient home bus. First step is to create a semtically enriched data warehouse object model. We choose FHIR and built an object model mainly based on the Observation, Device and Location resources with minor extensions needed by AAL-foreign sub domains. FHIR turned out to be very flexible and complete for other home related sub-domains. The object model is implemented in a separated software-partition storing all structural and procedural data of BASIS.

  14. An HL7-FHIR-based Object Model for a Home-Centered Data Warehouse for Ambient Assisted Living Environments.

    PubMed

    Schwartze, Jonas; Jansen, Lars; Schrom, Harald; Wolf, Klaus-Hendrik; Haux, Reinhold; Marschollek, Michael

    2015-01-01

    Current AAL environments focus on assisting a single person with seperated technologies. There is no interoperability between sub-domains in home environments, like building energy management or housing industry services. BASIS (Building Automation by a Scalable and Intelligent System) aims to integrate all sensors and actuators into a single, efficient home bus. First step is to create a semtically enriched data warehouse object model. We choose FHIR and built an object model mainly based on the Observation, Device and Location resources with minor extensions needed by AAL-foreign sub domains. FHIR turned out to be very flexible and complete for other home related sub-domains. The object model is implemented in a separated software-partition storing all structural and procedural data of BASIS. PMID:26262359

  15. Status of activities on the inactive uranium mill tailings sites remedial action program. Office of the Assistant Secretary for Environment

    SciTech Connect

    Not Available

    1981-04-01

    This report on the status of the Office of Environment's program for inactive uranium mill tailings sites is an analysis of the current status and a forecast of future activities of the Office of Environment. The termination date for receipt of information was September 30, 1980. Aerial radiological surveys and detailed ground radiological assessments of properties within the communities in the vicinity of the designated processing sites in Canonsburg, Pennsylvania, Salt Lake City, Utah, and Boise, Idaho led to the designation of an initial group of vicinity properties for remedial action. The potential health effects of the residual radioactive materials on or near these properties were estimated, and the Assistant Secretary for Environment recommended priorities for performing remedial action to the Department's Assistant Secretary for Nuclear Energy. In designating these properties and establishing recommended priorities for performing remedial action, the Office of Environment consulted with the Environmental Protection Agency, the Nuclear Regulatory Commission, representatives from the affected State and local governments, and individual property owners. After notifying the Governors of each of the affected States and the Navajo Nation of the Secretary of Energy's designation of processing sites within their areas of jurisdiction and establishment of remedial action priorities, a Sample Cooperative Agreement was developed by the Department in consultation with the Nuclear Regulatory Commission and provided to the affected States and the Navajo Nation for comments. During September 1980, a Cooperative Agreement with the Commonwealth of Pennsylvania for the designated Canonsburg processing site was executed by the Department. It is anticipated that a Cooperative Agreement between the State of Utah and the Department to perform remedial actions at the designated Salt Lake City site will be executed in the near future.

  16. Anomalous mechanical behavior and crack growth of oxide glasses

    NASA Astrophysics Data System (ADS)

    Seaman, Jared Hilliard

    This thesis is concerned with analytically describing anomalous mechanical behaviors of glass. A new slow crack growth model is presented that considers a semi-elliptical crack in a cylindrical glass rod subjected to 4-point bending that is both loaded statically and under a time-dependent load. This model is used to explain a suppression of the loading-rate dependency of ion-exchanged strengthened glass. The stress relaxation behavior of an ion-exchanged strengthened glass is then analyzed in view of a newly observed water-assisted surface stress relaxation mechanism. By making refinements to a time-dependent Maxwell material model for stress buildup and relaxation, the anomalous subsurface compressive stress peak in ion-exchanged strengthened glass is explained. The notion of water-assisted stress relaxation is extended to the crack tip, where high tensile stresses exist. A toughening effect has historically been observed for cracks aged at subcritical stress intensity factors, where crack tip stress relaxation is hypothesized. A simple fracture mechanics model is developed that estimates a shielding stress intensity factor that is then superimposed with the far-field stress intensity factor. The model is used to estimate anomalous "restart" times for aged cracks. The same model predicts a non-linear crack growth rate for cracks loaded near the static fatigue limit. Double cantilever beam slow crack growth experiments were performed and new slow crack growth data for soda-lime silicate glass was collected. Interpretation of this new experimental slow crack growth data suggests that the origin of the static fatigue limit in glass is due to water-assisted stress relaxation. This thesis combines a number of studies that offer a new unified understanding of historical anomalous mechanical behaviors of glass. These anomalies are interpreted as simply the consequence of slow crack growth and water-assisted surface stress relaxation.

  17. Cocaine (Coke, Crack) Facts

    MedlinePlus

    ... That People Abuse » Cocaine (Coke, Crack) Facts Cocaine (Coke, Crack) Facts Listen Cocaine is a white ... Version Download "My life was built around getting cocaine and getting high." Stacey is recovering from her ...

  18. Effects of crack geometry and material behavior on scattering by cracks for QNDE applications

    SciTech Connect

    Achenbach, J.D.

    1989-09-15

    In work carried out on this project, the usual mathematical modeling of ultrasonic wave scattering by flaws is being extended to account for several typical characteristics of fatigue and stress-corrosion cracks, and the environment of such cracks. Work has been completed on scattering by macrocrack-microcrack configurations. We have also investigated reflection and transmission by a flaw plane consisting of an infinite array of randomly oriented cracks. In another investigation the propagation of mechanical disturbances in solids with periodically distributed cracks has been studied.

  19. 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

  20. Co-Designing Ambient Assisted Living (AAL) Environments: Unravelling the Situated Context of Informal Dementia Care

    PubMed Central

    Hwang, Amy S.; Truong, Khai N.; Cameron, Jill I.; Lindqvist, Eva; Nygård, Louise; Mihailidis, Alex

    2015-01-01

    Ambient assisted living (AAL) aims to help older persons “age-in-place” and manage everyday activities using intelligent and pervasive computing technology. AAL research, however, has yet to explore how AAL might support or collaborate with informal care partners (ICPs), such as relatives and friends, who play important roles in the lives and care of persons with dementia (PwDs). In a multiphase codesign process with six (6) ICPs, we envisioned how AAL could be situated to complement their care. We used our codesigned “caregiver interface” artefacts as triggers to facilitate envisioning of AAL support and unpack the situated, idiosyncratic context within which AAL aims to assist. Our findings suggest that AAL should be designed to support ICPs in fashioning “do-it-yourself” solutions that complement tacitly improvised care strategies and enable them to try, observe, and adapt to solutions over time. In this way, an ICP could decide which activities to entrust to AAL support, when (i.e., scheduled or spontaneous) and how a system should provide support (i.e., using personalized prompts based on care experience), and when adaptations to system support are needed (i.e., based alerting patterns and queried reports). Future longitudinal work employing participatory, design-oriented methods with care dyads is encouraged. PMID:26161410

  1. Co-Designing Ambient Assisted Living (AAL) Environments: Unravelling the Situated Context of Informal Dementia Care.

    PubMed

    Hwang, Amy S; Truong, Khai N; Cameron, Jill I; Lindqvist, Eva; Nygård, Louise; Mihailidis, Alex

    2015-01-01

    Ambient assisted living (AAL) aims to help older persons "age-in-place" and manage everyday activities using intelligent and pervasive computing technology. AAL research, however, has yet to explore how AAL might support or collaborate with informal care partners (ICPs), such as relatives and friends, who play important roles in the lives and care of persons with dementia (PwDs). In a multiphase codesign process with six (6) ICPs, we envisioned how AAL could be situated to complement their care. We used our codesigned "caregiver interface" artefacts as triggers to facilitate envisioning of AAL support and unpack the situated, idiosyncratic context within which AAL aims to assist. Our findings suggest that AAL should be designed to support ICPs in fashioning "do-it-yourself" solutions that complement tacitly improvised care strategies and enable them to try, observe, and adapt to solutions over time. In this way, an ICP could decide which activities to entrust to AAL support, when (i.e., scheduled or spontaneous) and how a system should provide support (i.e., using personalized prompts based on care experience), and when adaptations to system support are needed (i.e., based alerting patterns and queried reports). Future longitudinal work employing participatory, design-oriented methods with care dyads is encouraged. PMID:26161410

  2. Seismological investigation of crack formation in hydraulic rock fracturing experiments and in natural geothermal environments. Progress report, September 1, 1979-August 31, 1980

    SciTech Connect

    Aki, K.

    1980-09-01

    Progress is reported in the following research areas: a synthesis of seismic experiments at the Fenton Hill Hot-Dry-Rock System; attenuation of high-frequency shear waves in the lithosphere; a new kinematic source model for deep volcanic tremors; ground motion in the near-field of a fluid-driven crack and its interpretation in the study of shallow volcanic tremor; low-velocity bodies under geothermal areas; and operation of event recorders in Mt. St. Helens and Newberry Peak with preliminary results from them. (MHR)

  3. Space shuttle main engine high pressure fuel turbopump turbine blade cracking

    SciTech Connect

    Lee, H.

    1988-05-01

    The analytical results from two-dimensional (2D) and three-dimensional (3D) finite element model investigations into the cracking of Space Shuttle Main Engine (SSME) High Pressure Fuel Turbopump (HPFTP) first- and second-stage turbine blades are presented. Specifically, the initiation causes for transverse cracks on the pressure side of the firststage blade fir tree lobes and face/corner cracks on the downstream fir tree face of the second-state blade are evaluated. Because the blade material, MAR-M-246 Hf (DS), is highly susceptible to hydrogen embrittlement in the -100 F to 400 F thermal environment, a steady-state condition (full power level = 109 percent) rather than a start-up or shut-down transient was considered to be the most likely candidate for generating a high-strain state in the fir tree areas. Results of the analyses yielded strain levels on both first- and second-stage blade fir tree regions that are of a magnitude to cause hydrogen assisted low cycle fatigue cracking. Also evident from the analysis is that a positive margin against fir tree cracking exists for the planned design modifications, which include shot peening for both first- and second-stage blade fir tree areas.

  4. Space Shuttle Main Engine High Pressure Fuel Turbopump Turbine Blade Cracking

    NASA Technical Reports Server (NTRS)

    Lee, Henry

    1988-01-01

    The analytical results from two-dimensional (2D) and three-dimensional (3D) finite element model investigations into the cracking of Space Shuttle Main Engine (SSME) High Pressure Fuel Turbopump (HPFTP) first- and second-stage turbine blades are presented. Specifically, the initiation causes for transverse cracks on the pressure side of the firststage blade fir tree lobes and face/corner cracks on the downstream fir tree face of the second-state blade are evaluated. Because the blade material, MAR-M-246 Hf (DS), is highly susceptible to hydrogen embrittlement in the -100 F to 400 F thermal environment, a steady-state condition (full power level = 109 percent) rather than a start-up or shut-down transient was considered to be the most likely candidate for generating a high-strain state in the fir tree areas. Results of the analyses yielded strain levels on both first- and second-stage blade fir tree regions that are of a magnitude to cause hydrogen assisted low cycle fatigue cracking. Also evident from the analysis is that a positive margin against fir tree cracking exists for the planned design modifications, which include shot peening for both first- and second-stage blade fir tree areas.

  5. Strain rate effects in stress corrosion cracking

    SciTech Connect

    Parkins, R.N. . Dept. of Metallurgy and Engineering Materials)

    1990-03-01

    Slow strain rate testing (SSRT) was initially developed as a rapid, ad hoc laboratory method for assessing the propensity for metals an environments to promote stress corrosion cracking. It is now clear, however, that there are good theoretical reasons why strain rate, as opposed to stress per se, will often be the controlling parameter in determining whether or not cracks are nucleated and, if so, are propagated. The synergistic effects of the time dependence of corrosion-related reactions and microplastic strain provide the basis for mechanistic understanding of stress corrosion cracking in high-pressure pipelines and other structures. However, while this may be readily comprehended in the context of laboratory slow strain tests, its extension to service situations may be less apparent. Laboratory work involving realistic stressing conditions, including low-frequency cyclic loading, shows that strain or creep rates give good correlation with thresholds for cracking and with crack growth kinetics.

  6. An Evaluation of an Inquiry-Based Computer-Assisted Learning Environment.

    ERIC Educational Resources Information Center

    Maor, Dorit; Fraser, Barry

    1994-01-01

    This study focused on students' development of inquiry skills in a computerized learning environment. Seven Year-11 classes (n=120) interacted with a computerized database, "Birds of Antarctica," and curriculum materials while the teacher used an inquiry approach to learning. Students perceived their classes as more investigative and open-ended…

  7. Fluid catalytic cracking

    SciTech Connect

    Petty, R.H.; Bartley, B.H.

    1984-05-01

    A fluid catalytic cracking process is disclosed for sulfur-containing petroleum charge stocks. Sulfur contained in coke deposited on the fluidized cracking catalyst in the reactor is converted to sulfur oxides in the regenerator and removed from regenerator off-gases by incorporating a composite of alumina and bismuth oxides in a particulate cracking catalyst. Sulfur oxides produced during regeneration of the catalyst by burning the coke with air in the regenerator are captured by the alumina-bismuth oxides composite and converted to hydrogen sulfide in the cracking reactor. The hydrogen sulfide so produced is readily separated from petroleum products of the catalytic cracking reaction process.

  8. Ambient and smartphone sensor assisted ADL recognition in multi-inhabitant smart environments

    PubMed Central

    Misra, Archan; Cook, Diane

    2016-01-01

    Activity recognition in smart environments is an evolving research problem due to the advancement and proliferation of sensing, monitoring and actuation technologies to make it possible for large scale and real deployment. While activities in smart home are interleaved, complex and volatile; the number of inhabitants in the environment is also dynamic. A key challenge in designing robust smart home activity recognition approaches is to exploit the users' spatiotemporal behavior and location, focus on the availability of multitude of devices capable of providing different dimensions of information and fulfill the underpinning needs for scaling the system beyond a single user or a home environment. In this paper, we propose a hybrid approach for recognizing complex activities of daily living (ADL), that lie in between the two extremes of intensive use of body-worn sensors and the use of ambient sensors. Our approach harnesses the power of simple ambient sensors (e.g., motion sensors) to provide additional ‘hidden’ context (e.g., room-level location) of an individual, and then combines this context with smartphone-based sensing of micro-level postural/locomotive states. The major novelty is our focus on multi-inhabitant environments, where we show how the use of spatiotemporal constraints along with multitude of data sources can be used to significantly improve the accuracy and computational overhead of traditional activity recognition based approaches such as coupled-hidden Markov models. Experimental results on two separate smart home datasets demonstrate that this approach improves the accuracy of complex ADL classification by over 30 %, compared to pure smartphone-based solutions. PMID:27042240

  9. Fuel-Optimal Trajectories in a Planet-Moon Environment Using Multiple Gravity Assists

    NASA Technical Reports Server (NTRS)

    Ross, Shane D.; Grover, Piyush

    2007-01-01

    For low energy spacecraft trajectories such as multi-moon orbiters for the Jupiter system, multiple gravity assists by moons could be used in conjunction with ballistic capture to drastically decrease fuel usage. In this paper, we outline a procedure to obtain a family of zero-fuel multi-moon orbiter trajectories, using a family of Keplerian maps derived by the first author previously. The maps capture well the dynamics of the full equations of motion; the phase space contains a connected chaotic zone where intersections between unstable resonant orbit manifolds provide the template for lanes of fast migration between orbits of different semimajor axes. Patched three body approach is used and the four body problem is broken down into two three-body problems, and the search space is considerably reduced by the use of properties of the Keplerian maps. We also introduce the notion of Switching Region where the perturbations due to the two perturbing moons are of comparable strength, and which separates the domains of applicability of the corresponding two Keplerian maps.

  10. Slow crack growth in spinel in water

    NASA Technical Reports Server (NTRS)

    Schwantes, S.; Elber, W.

    1983-01-01

    Magnesium aluminate spinel was tested in a water environment at room temperature to establish its slow crack-growth behavior. Ring specimens with artificial flaws on the outside surface were loaded hydraulically on the inside surface. The time to failure was measured. Various precracking techniques were evaluated and multiple precracks were used to minimize the scatter in the static fatigue tests. Statistical analysis techniques were developed to determine the strength and crack velocities for a single flaw. Slow crack-growth rupture was observed at stress intensities as low as 70 percent of K sub c. A strengthening effect was observed in specimens that had survived long-time static fatigue tests.

  11. Thermally activated dislocation creep model for primary water stress corrosion cracking of NiCrFe alloys

    SciTech Connect

    Hall, M.M., Jr

    1995-12-31

    There is a growing awareness that awareness that environmentally assisted creep plays an important role in integranular stress corrosion cracking (IGSCC) of NiCrFe alloys in the primary coolant water environment of a pressurized water reactor (PWR). The expected creep mechanism is the thermally activated glide of dislocations. This mode of deformation is favored by the relatively low temperature of PWR operation combined with the large residual stresses that are most often identified as responsible for the SCC failure of plant components. Stress corrosion crack growth rate (CGR) equations that properly reflect the influence of this mechanism of crack tip deformation are required for accurate component life predictions. A phenomenological IGSCC-CGR model, which is based on an apriori assumption that the IGSCC-CGR is controlled by a low temperature dislocation creep mechanism, is developed in this report. Obstacles to dislocation creep include solute atoms such as carbon, which increase the lattice friction force, and forest dislocations, which can be introduced by cold prestrain. Dislocation creep also may be environmentally assisted due to hydrogen absorption at the crack tip. The IGSCC-CGR model developed here is based on an assumption that crack growth occurs by repeated fracture events occurring within an advancing crack-tip creep-fracture zone. Thermal activation parameters for stress corrosion cracking are obtained by fitting the CGR model to IGSCC-CGR data obtained on NiCrFe alloys, Alloy X-750 and Alloy 600. These IGSCC-CGR activation parameters are compared to activation parameters obtained from creep and stress relaxation tests. Recently reported CGR data, which exhibit an activation energy that depends on yield stress and the applied stress intensity factor, are used to benchmark the model. Finally, the effects of matrix carbon concentration, grain boundary carbides and absorbed hydrogen concentration are discussed within context of the model.

  12. Fatigue crack propagation of nickel-base superalloys at 650 deg C

    NASA Technical Reports Server (NTRS)

    Gayda, J.; Gabb, T. P.; Miner, R. V.

    1988-01-01

    The 650 C fatigue crack propagation behavior of two nickel-base superalloys, Rene 95 and Waspaloy, is studied with particular emphasis placed on understanding the roles of creep, environment, and two key grain boundary alloying additions, boron and zirconium. Comparison of air and vacuum data shows the air environment to be detrimental over a wide range of frequencies for both alloys. More in-depth analysis on Rene 95 shows at lower frequencies, such as 0.02 Hz, failure in air occurs by intergranular, environmentally-assisted creep crack growth, while at higher frequencies, up to 5.0 Hz, environmental interaction are still evident but creep effects are minimized. The effect of B and Zr in Waspaloy is found to be important where environmental and/or creep interactions are presented. In those instances, removal of B and Zr dramatically increases crack growth and it is therefore plausible that effective dilution of these elements may explain a previously observed trend in which crack growth rates increase with decreasing grain size.

  13. Fatigue crack propagation of nickel-base superalloys at 650 deg C

    NASA Technical Reports Server (NTRS)

    Gayda, J.; Gabb, T. P.; Miner, R. V.

    1985-01-01

    The 650 C fatigue crack propagation behavior of two nickel-base superalloys, Rene 95 and Waspaloy, is studied with particular emphasis placed on understanding the roles of creep, environment, and two key grain boundary alloying additions, boron and zirconium. Comparison of air and vacuum data shows the air environment to be detrimental over a wide range of frequencies for both alloys. More in-depth analysis on Rene 95 shows at lower frequencies, such as 0.02 Hz, failure in air occurs by intergranular, environmentally-assisted creep crack growth, while at higher frequencies, up to 5.0 Hz, environmental interactions are still evident but creep effects are minimized. The effect of B and Zr in Waspaloy is found to be important where environmental and/or creep interactions are presented. In those instances, removal of B and Zr dramatically increases crack growth and it is therefore plausible that effective dilution of these elements may explain a previously observed trend in which crack growth rates increase with decreasing grain size.

  14. A Review Corrosion of TI Grade 7 and Other TI Alloys in Nuclear Waste Repository Environments

    SciTech Connect

    F. Hua; K. Mon; P. Pasupathi; G. Gordon

    2004-05-11

    Titanium alloy degradation modes are reviewed in relation to their performance in repository environments. General corrosion, localized corrosion, stress corrosion cracking, hydrogen induced cracking, microbially influenced corrosion, and radiation-assisted corrosion of Ti alloys are considered. With respect to the Ti Grade 7 drip shields selected for emplacement in the repository at Yucca Mountain, general corrosion, hydrogen induced cracking, and radiation-assisted corrosion will not lead to failure within the 10,000 year regulatory period; stress corrosion cracking (in the absence of disruptive events) is of no consequence to barrier performance; and localized corrosion and microbially influenced corrosion are not expected to occur. To facilitate the discussion, Ti Grades 2, 5, 7, 9, 11, 12, 16, 17, 18, and 24 are included in this review.

  15. Investigation of Helicopter Longeron Cracks

    NASA Technical Reports Server (NTRS)

    Newman, John A.; Baughman, James; Wallace, Terryl A.

    2009-01-01

    Four cracked longerons, containing a total of eight cracks, were provided for study. Cracked regions were cut from the longerons. Load was applied to open the cracks, enabling crack surface examination. Examination revealed that crack propagation was driven by fatigue loading in all eight cases. Fatigue crack initiation appears to have occurred on the top edge of the longerons near geometric changes that affect component bending stiffness. Additionally, metallurgical analysis has revealed a local depletion in alloying elements in the crack initiation regions that may be a contributing factor. Fatigue crack propagation appeared to be initially driven by opening-mode loading, but at a crack length of approximately 0.5 inches (12.7 mm), there is evidence of mixed-mode crack loading. For the longest cracks studied, shear-mode displacements destroyed crack-surface features of interest over significant portions of the crack surfaces.

  16. Small fatigue cracks; Proceedings of the Second International Conference/Workshop, Santa Barbara, CA, Jan. 5-10, 1986

    SciTech Connect

    Ritchie, R.O.; Lankford, J.

    1986-01-01

    Topics discussed in this volume include crack initiation and stage I growth, microstructure effects, crack closure, environment effects, the role of notches, analytical modeling, fracture mechanics characterization, experimental techniques, and engineering applications. Papers are presented on fatigue crack initiation along slip bands, the effect of microplastic surface deformation on the growth of small cracks, short fatigue crack behavior in relation to three-dimensional aspects and the crack closure effect, the influence of crack depth on crack electrochemistry and fatigue crack growth, and nondamaging notches in fatigue. Consideration is also given to models of small fatigue cracks, short crack theory, assessment of the growth of small flaws from residual strength data, the relevance of short crack behavior to the integrity of major rotating aero engine components, and the relevance of short fatigue crack growth data to the durability and damage tolerance analyses of aircraft.

  17. Fluid catalytic cracking

    SciTech Connect

    Bartley, B.H.; Petty, R.H.

    1982-08-17

    Gaseous sulfur compounds are removed from a sulfur-containing gas mixture by reacting sulfur oxides in the gas mixture with alumina in association with bismuth. The process is particularly useful in fluid catalytic cracking of sulfur-containing petroleum charge stocks wherein sulfur is contained in coke deposited on the fluidized cracking catalyst. By the process of this invention, sulfur oxides may be removed from regenerator off-gases from a fluidized catalytic cracking unit by incorporating particulate alumina impregnated with bismuth in particulate cracking catalyst whereby sulfur oxides generated in the regeneration of the catalyst are reacted with bismuth-impregnated alumina. Sulfur oxides produced during regeneration of the catalyst by burning the coke with air are captured and converted to hydrogen sulfide in the cracking reactor. The hydrogen sulfide so produced is readily separated from petroleum products of the catalytic cracking reaction process.

  18. Recent trends in robot-assisted therapy environments to improve real-life functional performance after stroke

    PubMed Central

    Johnson, Michelle J

    2006-01-01

    Upper and lower limb robotic tools for neuro-rehabilitation are effective in reducing motor impairment but they are limited in their ability to improve real world function. There is a need to improve functional outcomes after robot-assisted therapy. Improvements in the effectiveness of these environments may be achieved by incorporating into their design and control strategies important elements key to inducing motor learning and cerebral plasticity such as mass-practice, feedback, task-engagement, and complex problem solving. This special issue presents nine articles. Novel strategies covered in this issue encourage more natural movements through the use of virtual reality and real objects and faster motor learning through the use of error feedback to guide acquisition of natural movements that are salient to real activities. In addition, several articles describe novel systems and techniques that use of custom and commercial games combined with new low-cost robot systems and a humanoid robot to embody the " supervisory presence" of the therapy as possible solutions to exercise compliance in under-supervised environments such as the home. PMID:17176474

  19. A strategy to assist management in workforce engagement and employee retention in the high tech engineering environment.

    PubMed

    Kennedy, Elizabeth; Daim, Tugrul U

    2010-11-01

    Many companies use survey methods in an attempt to gauge employees' attitudes and opinions toward the company. These attitudes and opinions are directly related to an employee's engagement within the company. In many instances, employees wait in vain for the survey response and the subsequent employer actions, but the truth is sometimes management does not know what to do with the results. For this reason, we theorize that this type of survey, typically utilizing the Likert-scale, is not adequately assisting management in addressing employee engagement and retention issues. For instance, in many occasions, once the survey results are tabulated, companies are doing little or nothing to address the issues. In fact, far too many companies make the mistake of conducting employee engagement surveys, and then ignore the answers. Thus, we propose that a company should take advantage of the survey results, and utilize them to provide data to bridge employees' needs and goals with stakeholders' responsibilities and goals by refining and incorporating them into a hierarchical decision model (HDM). Thus, this would essentially be utilizing the quantitative data to determine what to measure qualitatively. We use a case from the high tech industry, specifically focusing on the engineering environment. Engineering environments are known to be more creative and such approaches would be more beneficial. PMID:20116102

  20. Analyzing Leakage Through Cracks

    NASA Technical Reports Server (NTRS)

    Romine, William D.

    1993-01-01

    Two related computer programs written for use in analyzing leakage through cracks. Leakage flow laminar or turbulent. One program used to determine dimensions of crack under given flow conditions and given measured rate of leakage. Other used to determine rate of leakage of gas through crack of given dimensions under given flow conditions. Programs, written in BASIC language, accelerate and facilitate iterative calculations and parametric analyses. Solve equations of Fanno flow. Enables rapid solution of leakage problem.

  1. Crack Modelling for Radiography

    NASA Astrophysics Data System (ADS)

    Chady, T.; Napierała, L.

    2010-02-01

    In this paper, possibility of creation of three-dimensional crack models, both random type and based on real-life radiographic images is discussed. Method for storing cracks in a number of two-dimensional matrices, as well algorithm for their reconstruction into three-dimensional objects is presented. Also the possibility of using iterative algorithm for matching simulated images of cracks to real-life radiographic images is discussed.

  2. 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.

  3. Automatic crack propagation tracking

    NASA Technical Reports Server (NTRS)

    Shephard, M. S.; Weidner, T. J.; Yehia, N. A. B.; Burd, G. S.

    1985-01-01

    A finite element based approach to fully automatic crack propagation tracking is presented. The procedure presented combines fully automatic mesh generation with linear fracture mechanics techniques in a geometrically based finite element code capable of automatically tracking cracks in two-dimensional domains. The automatic mesh generator employs the modified-quadtree technique. Crack propagation increment and direction are predicted using a modified maximum dilatational strain energy density criterion employing the numerical results obtained by meshes of quadratic displacement and singular crack tip finite elements. Example problems are included to demonstrate the procedure.

  4. Effects of Chromate and Non-Chromate Coating Systems on Environmentally Assisted Fatigue of an Aluminum Alloy

    NASA Astrophysics Data System (ADS)

    Schubbe, Joel J.; Westmoreland, Sophoria N.

    2014-10-01

    Fatigue crack growth testing of 2024-T3 Aluminum plate was performed using compact tension (CT) specimens with chromate and non-chromate primer paint systems to evaluate the effects of the coatings on fatigue crack growth rates. The tests were conducted in lab air and sea water environments for each of the coating systems. Standard E399 CT specimens were tested to determine the influence level of environmentally assisted cracking (corrosion fatigue) on crack growth rates and cyclic count to prescribed pre-crack and final crack lengths. Increasing stress range (Δ K) tests were conducted at 10 Hz in the range of 6.5 to 26.5 MPa. It was determined that the coated specimens exhibited a 12% shorter total life, on average, than the bare specimens for the lab air cases. In the case of salt water exposure, the coated specimens exhibited approximately 10% life increase over the bare specimens. The number of cycles to the 2.54 mm pre-crack length for the coated specimens was all less than the cycle count for the bare tests. In each case (coated or bare), there was an increased growth rate at the lower stress ranges in the salt water environment, with the chromate system case displaying the smallest change (increase). It can be concluded that the coated specimens initiate cracks and propagate faster than the bare specimens for short cracks at low stress range, but the environmental influence on the specimens is quickly overshadowed as the cracks elongate and the rate of growth increases. The coated specimens exhibited a higher total life cycle count to final crack length for this testing.

  5. Aircraft fatigue and crack growth considering loads by structural component

    NASA Technical Reports Server (NTRS)

    Yost, J. D.

    1994-01-01

    The indisputable 1968 C-130 fatigue/crack growth data is reviewed to obtain additional useful information on fatigue and crack growth. The proven Load Environment Model concept derived empirically from F-105D multichannel recorder data is refined to a simpler method by going from 8 to 5 variables in the spectra without a decrease in accuracy. This approach provides the true fatigue/crack growth and load environment by structural component for both fatigue and strength design. Methods are presented for defining fatigue scatter and damage at crack initiation. These design tools and criteria may be used for both metal and composite aircraft structure.

  6. Subcritical crack growth in two titanium alloys.

    NASA Technical Reports Server (NTRS)

    Williams, D. N.

    1973-01-01

    Measurement of subcritical crack growth during static loading of precracked titanium alloys in salt water using samples too thin for plane strain loading to predominate was examined as a method for determining the critical stress intensity for crack propagation in salt water. Significant internal crack growth followed by arrest was found at quite low stress intensities, but crack growth rates were relatively low. Assuming these techniques provided a reliable measurement of the critical stress intensity, the value for annealed Ti-4Al-1.5Mo-0.5V alloy was apparently about 35 ksi-in. to the 1/2 power, while that for annealed Ti-4Al-3Mo-1V was below 45 ksi-in. to the 1/2 power. Crack growth was also observed in tests conducted in both alloys in an air environment. At 65 ksi-in. to the 1/2 power, the extent of crack growth was greater in air than in salt water. Ti-4Al-3Mo-1V showed arrested crack growth in air at a stress intensity of 45 ksi-in. to the 1/2 power.

  7. Characterization of Cracking and Crack Growth Properties of the C5A Aircraft Tie-Box Forging

    NASA Technical Reports Server (NTRS)

    Piascik, Robert S.; Smith, Stephen W.; Newman, John A.; Willard, Scott A.

    2003-01-01

    Detailed destructive examinations were conducted to characterize the integrity and material properties of two aluminum alloy (7075-T6) horizontal stabilizer tie box forgings removed.from US. Air Force C5A and C5B transport aircraft. The C5B tie box forging was,found to contain no evidence of cracking. Thirteen cracks were found in the CSA,forging. All but one of the cracks observed in the C5A component were located along the top cap region (one crack was located in the bottom cap region). The cracks in the C5A component initiated at fastener holes and propagated along a highly tunneled intergranular crack path. The tunneled crack growth configuration is a likelv result of surface compressive stress produced during peening of the .forging suijace. The tie box forging ,fatigue crack growth, fracture and stress corrosion cracking (SCC) properties were characterized. Reported herein are the results of laboratory air ,fatigue crack growth tests and 95% relative humidity SCC tests conducted using specimens machined from the C5A ,forging. SCC test results revealed that the C5A ,forging material was susceptible to intergranular environmental assisted cracking: the C5A forging material exhibited a SCC crack-tip stress-intensity factor threshold of less than 6 MPadn. Fracture toughness tests revealed that the C5A forging material exhibited a fracture toughness that was 25% less than the C5B forging. The C5A forging exhibited rapid laboratory air fatigue crack growth rates having a threshold crack-tip stress-intensity factor range of less than 0.8 MPa sup m. Detailed fractographic examinations revealed that the ,fatigue crack intergranular growth crack path was similar to the cracking observed in the C5A tie box forging. Because both fatigue crack propagation and SCC exhibit similar intergranular crack path behavior, the damage mechanism resulting in multi-site cracking of tie box forgings cannot be determined unless local cyclic stresses can be quantified.

  8. Environmentally Asisted Cracking Behavior of Nickel Alloys in Simulated Acidic and Alkaline Ground Waters Using U-bend Specimens

    SciTech Connect

    Fix, D V; Estill, J C; Hust, G A; Wong, L L; Rebak, R B

    2003-10-17

    The model for the degradation of the containers for nuclear waste includes three modes of corrosion, namely general corrosion, localized corrosion and environmentally assisted cracking (EAC). The objective of the current research was to quantify the susceptibility of five nickel alloys to EAC in several environmental conditions with varying solution composition, temperature and electrochemical potential. These alloys included: Alloy 22 (N06022), Alloy C-4 (N06455), Alloy 625 (N06625), Alloy G-3 (N06985) and Alloy 825 (N08825). The susceptibility to EAC was evaluated using constant deformation (deflection) U-bend specimens in both the non-welded (wrought) and welded conditions. Results show that after more than five years exposure in the vapor and liquid phases of alkaline (pH {approx} 10) and acidic (pH {approx} 3) multi-ionic environments at 60 C and 90 C, none of the tested alloys suffered environmentally assisted cracking.

  9. 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.

  10. Associations between maternal older age, family environment and parent and child wellbeing in families using assisted reproductive techniques to conceive.

    PubMed

    Boivin, J; Rice, Frances; Hay, Dale; Harold, Gordon; Lewis, Allyson; van den Bree, Marianne M B; Thapar, Anita

    2009-06-01

    Maternal age effects on parenting and family outcomes are of increasing interest because of the demographic shift toward older maternal age at first birth. Maternal age is also of interest because of the greater use of assisted reproductive techniques (ART) to bypass age-related infertility in couples trying to conceive late in the reproductive life cycle of the woman. The aim of the present study was to investigate maternal age effects associated with delayed parenting by comparing families of mothers who gave birth at a younger (<31 years) or older (>38 years) age and to ascertain whether associations were linear associations by comparing these groups to women who had conceived in between these ages (i.e., >31 and <38 years). All children (4-11 year olds) were first-born and conceived using ART. Participants were recruited from one of 20 fertility clinics and mothers (n=642) and fathers (n=439) completed a postal questionnaire about demographic and reproductive characteristics, family environment as well as parent and child wellbeing. Our results demonstrate that parenthood via assisted conception later in the reproductive life cycle is not associated with a negative impact on child wellbeing. Despite maternal age-group differences on demographic (education, income) and reproductive characteristics (bleeding during pregnancy, caesarean rate, breast feeding), and parental warmth and depressive symptoms, child wellbeing was similar across mother age groups. We conclude that the parenting context is different for older mother families (more depressive symptoms in mothers and fathers, less expressed warmth in the couple) but that this difference is not associated with child wellbeing in early and middle childhood. PMID:19346045

  11. Fatigue crack propagation analysis of plaque rupture.

    PubMed

    Pei, Xuan; Wu, Baijian; Li, Zhi-Yong

    2013-10-01

    Rupture of atheromatous plaque is the major cause of stroke or heart attack. Considering that the cardiovascular system is a classic fatigue environment, plaque rupture was treated as a chronic fatigue crack growth process in this study. Fracture mechanics theory was introduced to describe the stress status at the crack tip and Paris' law was used to calculate the crack growth rate. The effect of anatomical variation of an idealized plaque cross-section model was investigated. The crack initiation was considered to be either at the maximum circumferential stress location or at any other possible locations around the lumen. Although the crack automatically initialized at the maximum circumferential stress location usually propagated faster than others, it was not necessarily the most critical location where the fatigue life reached its minimum. We found that the fatigue life was minimum for cracks initialized in the following three regions: the midcap zone, the shoulder zone, and the backside zone. The anatomical variation has a significant influence on the fatigue life. Either a decrease in cap thickness or an increase in lipid pool size resulted in a significant decrease in fatigue life. Comparing to the previously used stress analysis, this fatigue model provides some possible explanations of plaque rupture at a low stress level in a pulsatile cardiovascular environment, and the method proposed here may be useful for further investigation of the mechanism of plaque rupture based on in vivo patient data.

  12. Environmental Crack Growth Behavior Affected by Thickness/Geometry Constraint

    NASA Astrophysics Data System (ADS)

    Kujawski, Daniel

    2013-03-01

    This article gives a short review on the effects of thickness/constraint and environment on crack growth behavior under cyclic and static loadings. Fatigue crack growth data taken from the literature, corresponding to different environments, ranging from vacuum to air and NaCl solution for a number of alloys and different specimens geometries are presented and analyzed. Reported results indicate that for relatively inert material/environment systems, there is a weak thickness/constraint effect on fatigue crack growth behavior. On the other hand, for corrosive material/environment systems, there is a significant thickness/constraint effect on crack growth rate behavior under both cyclic and static loadings. Some implications related to crack growth modeling are suggested.

  13. Crack healing in silicon nitride due to oxidation

    SciTech Connect

    Choi, S.R.; Tikare, V.; Pawlik, R.

    1991-10-01

    The crack healing behavior of a commercial, MgO-containing, hot pressed Si3N4 was studied as a function of temperature in oxidizing and inert annealing environments. Crack healing occurred at a temperature 800 C or higher due to oxidation regardless of crack size, which ranged from 100 microns (indentation crack) to 1.7 mm (SEPB precrack). The resulting strength and apparent fracture toughness increased at crack healing temperature by 100 percent and 300 percent, respectively. The oxide layer present in the crack plane was found to be highly fatigue resistant, indicating that the oxide is not solely silicate glass, but a mixture of glass, enstatite, and/or cristobalite that was insensitive to fatigue in a room temperature water environment. 20 refs.

  14. Crack healing in silicon nitride due to oxidation

    NASA Technical Reports Server (NTRS)

    Choi, Sung R.; Tikare, Veena; Pawlik, Ralph

    1991-01-01

    The crack healing behavior of a commercial, MgO-containing, hot pressed Si3N4 was studied as a function of temperature in oxidizing and inert annealing environments. Crack healing occurred at a temperature 800 C or higher due to oxidation regardless of crack size, which ranged from 100 microns (indentation crack) to 1.7 mm (SEPB precrack). The resulting strength and apparent fracture toughness increased at crack healing temperature by 100 percent and 300 percent, respectively. The oxide layer present in the crack plane was found to be highly fatigue resistant, indicating that the oxide is not solely silicate glass, but a mixture of glass, enstatite, and/or cristobalite that was insensitive to fatigue in a room temperature water environment.

  15. BWR internal cracking issues

    SciTech Connect

    Carpenter, C.E. Jr.; Lund, A.L.

    1999-07-01

    The regulatory issues associated with cracking of boiling water reactor (BWR) internals is being addressed by the Nuclear Regulatory Commission (NRC) staff and is the subject of a voluntary industry initiative. The lessons learned from this effort will be applied to pressurized water reactor (PWR) internals cracking issues.

  16. Contributing influences of work environment on sleep quantity and quality of nursing assistants in long-term care facilities: A cross-sectional study.

    PubMed

    Zhang, Yuan; Punnett, Laura; McEnany, Geoffry Phillips; Gore, Rebecca

    2016-01-01

    The effect of shift work on nurses' sleep is well-studied, but there are other challenging aspects of health care work that might also affect the sleep of direct caregivers. This study examined the influence of the long-term care work environment on sleep quantity and quality of nursing assistants. A cross-sectional survey collected data from 650 nursing assistants in 15 long-term care facilities; 46% reported short sleep duration and 23% reported poor sleep quality. A simple additive index of the number of beneficial work features (up to 7) was constructed for analysis with Poisson regression. With each unit increase of beneficial work features, nursing assistants were 7% less likely to report short sleep duration and 17% less likely to report poor sleep quality. These results suggest that effective workplace interventions should address a variety of work stressors, not only work schedule arrangements, in order to improve nursing assistants' sleep health. PMID:26384714

  17. Contributing influences of work environment on sleep quantity and quality of nursing assistants in long-term care facilities: A cross-sectional study.

    PubMed

    Zhang, Yuan; Punnett, Laura; McEnany, Geoffry Phillips; Gore, Rebecca

    2016-01-01

    The effect of shift work on nurses' sleep is well-studied, but there are other challenging aspects of health care work that might also affect the sleep of direct caregivers. This study examined the influence of the long-term care work environment on sleep quantity and quality of nursing assistants. A cross-sectional survey collected data from 650 nursing assistants in 15 long-term care facilities; 46% reported short sleep duration and 23% reported poor sleep quality. A simple additive index of the number of beneficial work features (up to 7) was constructed for analysis with Poisson regression. With each unit increase of beneficial work features, nursing assistants were 7% less likely to report short sleep duration and 17% less likely to report poor sleep quality. These results suggest that effective workplace interventions should address a variety of work stressors, not only work schedule arrangements, in order to improve nursing assistants' sleep health.

  18. Crack layer theory

    NASA Technical Reports Server (NTRS)

    Chudnovsky, A.

    1984-01-01

    A damage parameter is introduced in addition to conventional parameters of continuum mechanics and consider a crack surrounded by an array of microdefects within the continuum mechanics framework. A system consisting of the main crack and surrounding damage is called crack layer (CL). Crack layer propagation is an irreversible process. The general framework of the thermodynamics of irreversible processes are employed to identify the driving forces (causes) and to derive the constitutive equation of CL propagation, that is, the relationship between the rates of the crack growth and damage dissemination from one side and the conjugated thermodynamic forces from another. The proposed law of CL propagation is in good agreement with the experimental data on fatigue CL propagation in various materials. The theory also elaborates material toughness characterization.

  19. A Review of Fatigue Crack Growth for Pipeline Steels Exposed to Hydrogen

    PubMed Central

    Nanninga, N.; Slifka, A.; Levy, Y.; White, C.

    2010-01-01

    Hydrogen pipeline systems offer an economical means of storing and transporting energy in the form of hydrogen gas. Pipelines can be used to transport hydrogen that has been generated at solar and wind farms to and from salt cavern storage locations. In addition, pipeline transportation systems will be essential before widespread hydrogen fuel cell vehicle technology becomes a reality. Since hydrogen pipeline use is expected to grow, the mechanical integrity of these pipelines will need to be validated under the presence of pressurized hydrogen. This paper focuses on a review of the fatigue crack growth response of pipeline steels when exposed to gaseous hydrogen environments. Because of defect-tolerant design principles in pipeline structures, it is essential that designers consider hydrogen-assisted fatigue crack growth behavior in these applications. PMID:27134796

  20. A simulation environment for assisting system design of coherent laser doppler wind sensor for active wind turbine pitch control

    NASA Astrophysics Data System (ADS)

    Shinohara, Leilei; Pham Tran, Tuan Anh; Beuth, Thorsten; Umesh Babu, Harsha; Heussner, Nico; Bogatscher, Siegwart; Danilova, Svetlana; Stork, Wilhelm

    2013-05-01

    In order to assist a system design of laser coherent Doppler wind sensor for active pitch control of wind turbine systems (WTS), we developed a numerical simulation environment for modeling and simulation of the sensor system. In this paper we present this simulation concept. In previous works, we have shown the general idea and the possibility of using a low cost coherent laser Doppler wind sensing system for an active pitch control of WTS in order to achieve a reduced mechanical stress, increase the WTS lifetime and therefore reduce the electricity price from wind energy. Such a system is based on a 1.55μm Continuous-Wave (CW) laser plus an erbium-doped fiber amplifier (EDFA) with an output power of 1W. Within this system, an optical coherent detection method is chosen for the Doppler frequency measurement in megahertz range. A comparatively low cost short coherent length laser with a fiber delay line is used for achieving a multiple range measurement. In this paper, we show the current results on the improvement of our simulation by applying a Monte Carlo random generation method for positioning the random particles in atmosphere and extend the simulation to the entire beam penetrated space by introducing a cylindrical co-ordinate concept and meshing the entire volume into small elements in order to achieve a faster calculation and gain more realistic simulation result. In addition, by applying different atmospheric parameters, such as particle sizes and distributions, we can simulate different weather and wind situations.

  1. Assessing Older Adults’ Perceptions of Sensor Data and Designing Visual Displays for Ambient Assisted Living Environments: An Exploratory Study

    PubMed Central

    Reeder, B.; Chung, J.; Le, T.; Thompson, H.J.; Demiris, G.

    2014-01-01

    Summary Objectives Our objectives were to: 1) characterize older adult participants’ perceived usefulness of in-home sensor data and 2) develop novel visual displays for sensor data from Ambient Assisted Living environments that can become part of electronic health records. Methods Semi-structured interviews were conducted with community-dwelling older adult participants during three and six-month visits. We engaged participants in two design iterations by soliciting feedback about display types and visual displays of simulated data related to a fall scenario. Interview transcripts were analyzed to identify themes related to perceived usefulness of sensor data. Results Thematic analysis identified three themes: perceived usefulness of sensor data for managing health; factors that affect perceived usefulness of sensor data and; perceived usefulness of visual displays. Visual displays were cited as potentially useful for family members and health care providers. Three novel visual displays were created based on interview results, design guidelines derived from prior AAL research, and principles of graphic design theory. Conclusions Participants identified potential uses of personal activity data for monitoring health status and capturing early signs of illness. One area for future research is to determine how visual displays of AAL data might be utilized to connect family members and health care providers through shared understanding of activity levels versus a more simplified view of self-management. Connecting informal and formal caregiving networks may facilitate better communication between older adults, family members and health care providers for shared decision-making. PMID:24728081

  2. Energy systems programs funded by the Assistant Secretary for Environment, Safety and Health: FY 1993--FY 1994

    SciTech Connect

    Buttram, A.W.

    1994-12-31

    This document presents an overview of work at Martin Marietta Energy Systems, Inc., (Energy Systems) during FY 1993--FY 1994 that was funded by the Department of Energy`s (DOE`s) Assistant Secretary for Environment, Safety and Health (ASEH). To illustrate the programmatic breadth of Energy Systems and to establish the context within which this work was accomplished, this document also includes representative descriptions of ASEH-related work at Energy Systems done for other sponsors. Activities for ASEH cover a wide variety of subjects that are geared towards the environmental, safety, and health aspects of DOE operations. Subjects include the following: environmental compliance, environmental guidance, environmental audits, NEPA oversight, epidemiology and health surveillance, transportation and packaging safety, safety and quality assurance; technical standards, performance indicators, occurrence reporting, health physics instrumentation, risk management, security evaluations, and medical programs. The technical support section describes work in progress for ASEH, including specific program accomplishments. The work for others section describes work for non-ASEH sponsors that reinforces and supplements the ASEH work. Appendix A includes a list of FY 1993--FY 1994 publications related to the ASEH work.

  3. 40 CFR 63.1564 - What are my requirements for metal HAP emissions from catalytic cracking units?

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... emissions from catalytic cracking units? 63.1564 Section 63.1564 Protection of Environment ENVIRONMENTAL... Refineries: Catalytic Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Catalytic Cracking... requirements for metal HAP emissions from catalytic cracking units? (a) What emission limitations and...

  4. Fatigue crack growth in lithium hydride

    SciTech Connect

    Healy, T.E.

    1993-09-01

    Subcritical fatigue crack growth, from cyclic tensile loading, was demonstrated in warm pressed Polycrystalline lithium hydride. Experiments were performed with cyclic tension-tension crack opening (mode I) loads applied to a pre-cracked compact type specimen in an argon environment at a temperature of 21C (70F). The fatigue crack growth was found to occur between 7.56 {times} 10{sup {minus}ll} M/cycle (2.98 {times} l0{sup {minus}9} in/cycle) and 2.35 {times} l0{sup {minus}8} m/cycle (9.24{times}10{sup {minus}7} in/cycle) for a range of stress intensity factors between 1.04 MPa{center_dot}{radical}m (0.95 ksi{center_dot}{radical}in) and 1.49 MPa{center_dot}{radical}m (1.36 ksi{center_dot}{radical}in). The rate of fatigue crack growth from cyclic tensile loading was found to be in excess of crack growth from sustained loading at an equivalent stress intensity factor. Furthermore, a fatigue threshold was not evident from the acquired data.

  5. Near-neutral pH SCC in pipelines: Effects of pressure fluctuations on crack propagation

    SciTech Connect

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

    1998-12-31

    Currently, there is a poor understanding of the effects of pressure related parameters (operating pressure, pressure fluctuations, and hydrostatic testings) on external stress corrosion crack propagation in pipelines in near-neutral-pH environments. A better definition of the role of these parameters on crack propagation is needed to aid in the prediction of crack growth rates on operating pipelines and to develop strategies to mitigate this form of cracking. The objective of the research described in this paper was to determine the roles and synergistic effects of operating pressure, pressure fluctuations, and hydrostatic testing on crack growth in line pipe steels in a near-neutral-pH SCC environment. All testing was performed on one X-65 line pipe steel in a near-neutral-pH cracking environment, designated NS4. Fatigue precracked compact-type specimens of the line pipe steel were cyclically loaded while immersed in the cracking environment. The desired loading regime was applied using a servo-hydraulic tensile testing machine. Crack growth was monitored using the electric potential drop technique. The loading conditions applied to the specimen were related to field conditions using the J-integral parameter. It was found that the prior load history applied to the specimens had a significant effect on crack growth behavior. Overloading inhibited crack growth while unloading stimulated crack growth. Hydrostatic testing, which combines overloading and unloading, caused some crack extension but reduced the crack velocity.

  6. Quantity Effect of Radial Cracks on the Cracking Propagation Behavior and the Crack Morphology

    PubMed Central

    Chen, Jingjing; Xu, Jun; Liu, Bohan; Yao, Xuefeng; Li, Yibing

    2014-01-01

    In this letter, the quantity effect of radial cracks on the cracking propagation behavior as well as the circular crack generation on the impacted glass plate within the sandwiched glass sheets are experimentally investigated via high-speed photography system. Results show that the radial crack velocity on the backing glass layer decreases with the crack number under the same impact conditions during large quantities of repeated experiments. Thus, the “energy conversion factor” is suggested to elucidate the physical relation between the cracking number and the crack propagation speed. Besides, the number of radial crack also takes the determinative effect in the crack morphology of the impacted glass plate. This study may shed lights on understanding the cracking and propagation mechanism in laminated glass structures and provide useful tool to explore the impact information on the cracking debris. PMID:25048684

  7. Elevated temperature crack growth

    NASA Technical Reports Server (NTRS)

    Kim, K. S.; Vanstone, R. H.; Malik, S. N.; Laflen, J. H.

    1988-01-01

    A study was performed to examine the applicability of path-independent (P-I) integrals to crack growth problems in hot section components of gas turbine aircraft engines. Alloy 718 was used and the experimental parameters included combined temperature and strain cycling, thermal gradients, elastic-plastic strain levels, and mean strains. A literature review was conducted of proposed P-I integrals, and those capable of analyzing hot section component problems were selected and programmed into the postprocessor of a finite element code. Detailed elastic-plastic finite element analyses were conducted to simulate crack growth and crack closure of the test specimen, and to evaluate the P-I integrals. It was shown that the selected P-I integrals are very effective for predicting crack growth for isothermal conditions.

  8. Ethylene by Naphta Cracking

    ERIC Educational Resources Information Center

    Wiseman, Peter

    1977-01-01

    Presents a discussion of the manufacture of ethylene by thermal cracking of hydrocarbon feedstocks that is useful for introducing the subject of industrial chemistry into a chemistry curriculum. (MLH)

  9. Inspecting cracks in foam insulation

    NASA Technical Reports Server (NTRS)

    Cambell, L. W.; Jung, G. K.

    1979-01-01

    Dye solution indicates extent of cracking by penetrating crack and showing original crack depth clearly. Solution comprised of methylene blue in denatured ethyl alcohol penetrates cracks completely and evaporates quickly and is suitable technique for usage in environmental or structural tests.

  10. Cracked Plain, Buried Craters

    NASA Technical Reports Server (NTRS)

    2004-01-01

    4 September 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a cracked plain in western Utopia Planitia. The three circular crack patterns indicate the location of three buried meteor impact craters. These landforms are located near 41.9oN, 275.9oW. The image covers an area approximately 3 km (1.9 mi) across. Sunlight illuminates this scene from the lower left.

  11. Inhibition of environmental fatigue crack propagation in age-hardenable aluminum alloys

    NASA Astrophysics Data System (ADS)

    Warner, Jenifer S.

    Age-hardenable aluminum alloys, such as C47A-T86 (Al-Cu-Li) and 7075-T651 (Al-Zn-Mg-Cu), used in aerospace structures are susceptible to environment assisted fatigue crack propagation (EFCP) by hydrogen environment embrittlement. This research demonstrates effective inhibition of EFCP in C47A-T86 and 7075-T651 under both full immersion in aqueous chloride solution and atmospheric exposure which more accurately describes aircraft service conditions. Inhibition is attributed to the presence of a crack tip passive film reducing H production and uptake, as explained by the film rupture-hydrogen embrittlement mechanism, and can be accomplished through both addition of a passivating ion (ion-assisted inhibition) and localized-alloy corrosion creating passivating conditions (self inhibition). Addition of molybdate to both bulk chloride solution and surface chloride droplets eliminates the effect of environment on fatigue crack propagation in C47A-T86 and 7075-1651 at sufficiently low loading frequencies and high stress ratio by yielding crack growth rates equivalent to those for fatigue in ultra high vacuum. The preeminent corrosion inhibitor, chromate, has not been reported to produce such complete inhibition. Inhibition is promoted by reduced loading frequency, increased crack tip molybdate concentration, and potential at or anodic to free corrosion; each of which favors passivity. The inhibiting effect of molybdate parallels chromate, establishing molybdate as a viable chromate replacement inhibitor. The ability of molybdate to inhibit EFCP is enhanced by atmospheric exposures producing surface electrolyte droplets; crack growth rates are reduced by an order of magnitude under loading frequencies as high as 30 Hz, a frequency at which inhibition was not possible under full immersion. Al-Cu-Mg/Li alloys, including 2024-T351, are capable of self inhibition of EFCP. This behavior is attributed to localized corrosion through dealloying of anodic Al2CuMg or Al2Cu

  12. A Crack Growth Evaluation Method for Interacting Multiple Cracks

    NASA Astrophysics Data System (ADS)

    Kamaya, Masayuki

    When stress corrosion cracking or corrosion fatigue occurs, multiple cracks are frequently initiated in the same area. According to section XI of the ASME Boiler and Pressure Vessel Code, multiple cracks are considered as a single combined crack in crack growth analysis, if the specified conditions are satisfied. In crack growth processes, however, no prescription for the interference between multiple cracks is given in this code. The JSME Post-Construction Code, issued in May 2000, prescribes the conditions of crack coalescence in the crack growth process. This study aimed to extend this prescription to more general cases. A simulation model was applied, to simulate the crack growth process, taking into account the interference between two cracks. This model made it possible to analyze multiple crack growth behaviors for many cases (e. g. different relative position and length) that could not be studied by experiment only. Based on these analyses, a new crack growth analysis method was suggested for taking into account the interference between multiple cracks.

  13. Pacific Northwest Laboratory annual report for 1979 to the DOE Assistant Secretary for Environment. Part 5. Environmental assessment, control, health, and safety

    SciTech Connect

    Baalman, R.W.; Dotson, C.W.

    1980-02-01

    Part 5 of the 1979 Annual Report to the Department of Energy Assistant Secretary for the Environment presents Pacific Northwest Laboratory's progress on work performed for the Office of Technology Impacts, the Office of Environmental Compliance and Overview, and the Office of Health and Environmental Research. The report is in four sections, corresponding to the program elements: technology impacts, environmental control engineering, operational and environmental compliance, and human health studies. In each section, articles describe progress made during FY 1979 on individual projects.

  14. 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.

  15. Cracked cue ball

    NASA Astrophysics Data System (ADS)

    Carlowicz, Michael

    The latest images sent by the Galileo spacecraft reveal that the surface of Jupiter's moon Europa may have contained a layer of “warm ice” or even liquid water. In fact, planetologists are wondering if perhaps it still does.Photos taken earlier this summer show Europa to have a crust of smooth white and brown-tinted ice scarred by long, jagged cracks; some scientists have said the moon looks like a cracked cue ball. “The scale of fracture patterns—extending a distance equivalent to the width of the western United States—dwarf the San Andreas fault in length and width,” said Ronald Greeley, a geologist from Arizona State University and a member of the Galileo imaging team. The cracks are believed to have been caused by the stress of tidal forces created by Jupiter's gravity. Warmth generated by tidal heating also may have been sufficient to soften or liquefy some of the ice.

  16. Effect of CTE on Fatigue Cracking of Stainless Steel Vessels

    SciTech Connect

    Bird, E. L.; Mustaleski, T. M.

    2002-01-31

    Visual examination of lithium hydride reactor vessels revealed cracks that were adjacent to welds. Most cracks were parallel to the weld in the bottom portion of the vessel. Sections were cut out of the vessel containing these cracks and examined using the metallograph, scanning electron microscope, and microprobe to determine the cause of cracking. most of the cracks originated on the outer surface just outside the weld fusion line in the heat affected zone and propagated along grain boundaries. Crack depth of those sections examined ranged from about 300 to 500 {micro}m. Other cracks were reported to have reached a maximum depth of 0.32-cm (0.125-inch). The primary cause of cracking was the creation of high tensile stresses associated with the CTE differences between the filler metal and the base metal during operation of the vessel in a thermally cyclic environment. This failure mechanism could be described as creep-type fatigue whereby crack propagation might have been aided by the presence of brittle chromium carbides along the grain boundaries, which is indicative of a slightly sensitized microstructure.

  17. Fatigue crack tip deformation and fatigue crack propagation

    NASA Technical Reports Server (NTRS)

    Kang, T. S.; Liu, H. W.

    1972-01-01

    The effects of stress ratio, prestress cycling and plate thickness on the fatigue crack propagation rate are studied on 2024-T351 aluminum alloy. Fatigue crack propagation rate increases with the plate thickness and the stress ratio. Prestress cycling below the static yield strength has no noticeable effect on the fatigue crack propagation rate. However, prestress cycling above the static yield strength causes the material to strain harden and increases the fatigue crack propagation rate. Crack tip deformation is used to study the fatigue crack propagation. The crack tip strains and the crack opening displacements were measured from moire fringe patterns. The moire fringe patterns were obtained by a double exposure technique, using a very high density master grille (13,400 lines per inch).

  18. Towards Context-Aware and User-Centered Analysis in Assistive Environments: A Methodology and a Software Tool.

    PubMed

    Fontecha, Jesús; Hervás, Ramón; Mondéjar, Tania; González, Iván; Bravo, José

    2015-10-01

    One of the main challenges on Ambient Assisted Living (AAL) is to reach an appropriate acceptance level of the assistive systems, as well as to analyze and monitor end user tasks in a feasible and efficient way. The development and evaluation of AAL solutions based on user-centered perspective help to achive these goals. In this work, we have designed a methodology to integrate and develop analytics user-centered tools into assistive systems. An analysis software tool gathers information of end users from adapted psychological questionnaires and naturalistic observation of their own context. The aim is to enable an in-deep analysis focused on improving the life quality of elderly people and their caregivers.

  19. An Experimental Investigation of the Effects of Vacuum Environment on the Fatigue Life, Fatigue-Crack-Growth Behavior, and Fracture Toughness of 7075-T6 Aluminum Alloy. Ph.D. Thesis - North Carolina State Univ.

    NASA Technical Reports Server (NTRS)

    Hudson, C. M.

    1972-01-01

    Axial load fatigue life, fatigue-crack propagation, and fracture toughness tests were conducted on 0.090-inch thick specimens made of 7075-T6 aluminum alloy. The fatigue life and fatigue-crack propagation experiments were conducted at a stress ratio of 0.02. Maximum stresses ranged from 33 to 60 ksi in the fatigue life experiments, and from 10 to 40 ksi in the fatigue-crack propagation experiments, and fatigue life experiments were conducted at gas pressures of 760, 0.5, 0.05, and 0.00000005 torr. Fatigue-crack-growth and fracture toughness experiments were conducted at gas pressures of 760 and 5 x 10 to the minus 8th power torr. Residual stress measurements were made on selected fatigue life specimens to determine the effect of such stresses on fatigue life. Analysis of the results from the fatigue life experiments indicated that fatigue life progressively increased as the gas pressure decreased. Analysis of the results from the fatigue-crack-growth experiments indicates that at low values of stress-intensity range, the fatigue crack growth rates were approximately twice as high in air as in vacuum. Fracture toughness data showed there was essentially no difference in the fracture toughness of 7075-T6 in vacuum and in air.

  20. Assessment of Embrittlement of VHTR Structural Alloys in Impure Helium Environments

    SciTech Connect

    Crone, Wendy; Cao, Guoping; Sridhara, Kumar

    2013-05-31

    The helium coolant in high-temperature reactors inevitably contains low levels of impurities during steady-state operation, primarily consisting of small amounts of H{sub 2}, H{sub 2}O, CH{sub 4}, CO, CO{sub 2}, and N{sub 2} from a variety of sources in the reactor circuit. These impurities are problematic because they can cause significant long-term corrosion in the structural alloys used in the heat exchangers at elevated temperatures. Currently, the primary candidate materials for intermediate heat exchangers are Alloy 617, Haynes 230, Alloy 800H, and Hastelloy X. This project will evaluate the role of impurities in helium coolant on the stress-assisted grain boundary oxidation and creep crack growth in candidate alloys at elevated temperatures. The project team will: • Evaluate stress-assisted grain boundary oxidation and creep crack initiation and crack growth in the temperature range of 500-850°C in a prototypical helium environment. • Evaluate the effects of oxygen partial pressure on stress-assisted grain boundary oxidation and creep crack growth in impure helium at 500°C, 700°C, and 850°C respectively. • Characterize the microstructure of candidate alloys after long-term exposure to an impure helium environment in order to understand the correlation between stress-assisted grain boundary oxidation, creep crack growth, material composition, and impurities in the helium coolant. • Evaluate grain boundary engineering as a method to mitigate stress-assisted grain boundary oxidation and creep crack growth of candidate alloys in impure helium. The maximum primary helium coolant temperature in the high-temperature reactor is expected to be 850-1,000°C.Corrosion may involve oxidation, carburization, or decarburization mechanisms depending on the temperature, oxygen partial pressure, carbon activity, and alloy composition. These corrosion reactions can substantially affect long-term mechanical properties such as crack- growth rate and fracture

  1. Surface Enhancement Improves Crack Resistance

    NASA Technical Reports Server (NTRS)

    2002-01-01

    The low plasticity burnishing (LPB) process produces a deep layer of surface compression in a quick and affordable manner to produce metal surfaces free of scratches, nicks, and gouges. The process, designed for easy inclusion in the manufacturing environment, can be performed with conventional Computer Numerical Control machine tools. This allows parts to be processed during manufacturing, rather than as a post process in a separate facility. A smooth, free-rolling spherical ball suspended in a fluid allows for single-point contact. The ball comes into mechanical contact only with the surface to be burnished, and can be moved in any direction. LPB can be applied to all types of carbon and alloy steel, stainless steel, cast iron, aluminum, titanium, and nickel- based super alloys. In addition to improving a surface's resistance to fatigue and damage, treatment stops the growth of shallow cracks. The LPB process is used on the leading edges of turbine blades to improve resistance to foreign object damage and crack growth. This means significant savings for aircraft owners, since maintenance requirements to inspect for fatigue damage, replace parts, and remove corrosion damage increase the cost of operation.

  2. Time-dependent corrosion fatique crack propagation in 7000 series aluminum alloys. M.S. Thesis

    NASA Technical Reports Server (NTRS)

    Mason, Mark E.

    1995-01-01

    The goal of this research is to characterize environmentally assisted subcritical crack growth for the susceptible short-longitudinal orientation of aluminum alloy 7075-T651, immersed in acidified and inhibited NaCl solution. This work is necessary in order to provide a basis for incorporating environmental effects into fatigue crack propagation life prediction codes such as NASA-FLAGRO (NASGRO). This effort concentrates on determining relevant inputs to a superposition model in order to more accurately model environmental fatigue crack propagation.

  3. Early establishment response of different Pinus nigra ssp. salzmanii seed sources on contrasting environments: Implications for future reforestation programs and assisted population migration.

    PubMed

    Taïbi, K; del Campo, A D; Aguado, A; Mulet, J M

    2016-04-15

    Forest restoration constitutes an important issue within adaptive environmental management for climate change at global scale. However, effective implementation of these programs can only be achieved by revising current seed transfer guidelines, as they lack inherent spatial and temporal dynamics associated with climate change. In this sense, provenance trials may provide key information on the relative performance of different populations and/or genotypes under changing ecological conditions. This study addresses a methodological approach to evaluate early plantation performance and the consequent phenotypic plasticity and the pattern of the adaptation of different seed sources in contrasting environments. To this end, six seed sources of Salzmann pine were tested at three contrasting trial sites testing a hypothetical assisted population migration. Adaptation at each site was assessed through Joint Regression and Additive Main effect and Multiplication Interaction (AMMI) models. Most of the observed variation was attributed to the environment (above 90% for all traits), even so genotype and genotype by environment interaction (GxE) were significant. Seedlings out-planted under better site conditions did not differ in survival but in height growth. However, on sites with higher constraints, survival differed among seed sources and diameter growth was high. The adaptation analyses (AMMI) indicated that the cold-continental seed source 'Soria' performed as a generalist seed source, whereas 'Cordilleras Béticas', the southernmost seed source, was more adapted to harsh environments (frost and drought) in terms of survival. The results supported partially the hypothesis that assisted migration of seed sources makes sense within limited transfer distances, and this was reinforced by the GxE results. The present study could be valuable to address adaptive transfer of seedings in ecological restoration and to determine the suitable seed sources for reforestation programs

  4. Environment.

    ERIC Educational Resources Information Center

    White, Gilbert F.

    1980-01-01

    Presented are perspectives on the emergence of environmental problems. Six major trends in scientific thinking are identified including: holistic approaches to examining environments, life support systems, resource management, risk assessment, streamlined methods for monitoring environmental change, and emphasis on the global framework. (Author/SA)

  5. Passivating metals on cracking catalysts

    SciTech Connect

    Mckay, D.L.

    1980-01-15

    Metals such as nickel, vanadium and iron contaminating a cracking catalyst are passivated by contacting the cracking catalyst under elevated temperature conditions with antimony selenide, antimony sulfide, antimony sulfate, bismuth selenide, bismuth sulfide, or bismuth phosphate.

  6. Crack injection in silver gold alloys

    NASA Astrophysics Data System (ADS)

    Chen, Xiying

    Stress corrosion cracking (SCC) is a materials degradation phenomena resulting from a combination of stress and a corrosive environment. Among the alphabet soup of proposed mechanism of SCC the most important are film-rupture, film-induced cleavage and hydrogen embrittlement. This work examines various aspects of film-induced cleavage in gold alloys for which the operation of hydrogen embrittlement processes can be strictly ruled out on thermodynamic grounds. This is so because in such alloys SCC occurs under electrochemical conditions within which water is stable to hydrogen gas evolution. The alloy system examined in this work is AgAu since the corrosion processes in this system occur by a dealloying mechanism that results in the formation of nanoporous gold. The physics behind the dealloying process as well as the resulting formation of nanoporous gold is today well understood. Two important aspects of the film-induced cleavage mechanism are examined in this work: dynamic fracture in monolithic nanoporous gold and crack injection. In crack injection there is a finite thickness dealloyed layer formed on a AgAu alloy sample and the question of whether or not a crack that nucleates within this layer can travel for some finite distance into the un-corroded parent phase alloy is addressed. Dynamic fracture tests were performed on single edge-notched monolithic nanoporous gold samples as well as "infinite strip" sample configurations for which the stress intensity remains constant over a significant portion of the crack length. High-speed photography was used to measure the crack velocity. In the dynamic fracture experiments cracks were observed to travel at speeds as large as 270 m/s corresponding to about 68% of the Raleigh wave velocity. Crack injection experiments were performed on single crystal Ag77Au23, polycrystalline Ag72Au28 and pure gold, all of which had thin nanoporous gold layers on the surface of samples. Through-thickness fracture was seen in both the

  7. Analysis of Students' After-School Mobile-Assisted Artifact Creation Processes in a Seamless Language Learning Environment

    ERIC Educational Resources Information Center

    Wong, Lung-Hsiang

    2013-01-01

    As part of a learner's learning ecology, the informal, out-of-school settings offer virtually boundless opportunities to advance one's learning. This paper reports on "Move, Idioms!", a design for Mobile-Assisted Language Learning experience that accentuates learners' habit of mind and skills in making meaning with their…

  8. Development of a Peer-Assisted Learning Strategy in Computer-Supported Collaborative Learning Environments for Elementary School Students

    ERIC Educational Resources Information Center

    Tsuei, Mengping

    2011-01-01

    This study explores the effects of Electronic Peer-Assisted Learning for Kids (EPK), on the quality and development of reading skills, peer interaction and self-concept in elementary students. The EPK methodology uses a well-developed, synchronous computer-supported, collaborative learning system to facilitate students' learning in Chinese. We…

  9. How Artefacts Mediate Small-Group Co-Creation Activities in a Mobile-Assisted Seamless Language Learning Environment?

    ERIC Educational Resources Information Center

    Wong, L. -H.; Chen, W.; Jan, M.

    2012-01-01

    The rich learning resources and contexts learners experience in their everyday life could play important roles in complementing formal learning, but are often neglected by learners and teachers. In this paper, we present an intervention study in "Move, Idioms!", a mobile-assisted Chinese language learning approach that emphasizes contextualized…

  10. Cracking the Credit Hour

    ERIC Educational Resources Information Center

    Laitinen, Amy

    2012-01-01

    The basic currency of higher education--the credit hour--represents the root of many problems plaguing America's higher education system: the practice of measuring time rather than learning. "Cracking the Credit Hour" traces the history of this time-based unit, from the days of Andrew Carnegie to recent federal efforts to define a credit hour. If…

  11. Adaptation of Crack Growth Detection Techniques to US Material Test Reactors

    SciTech Connect

    A. Joseph Palmer; Sebastien P. Teysseyre; Kurt L. Davis; Joy L. Rempe; Gordon Kohse; Yakov Ostrovsky; David M. Carpenter

    2014-04-01

    A key component in evaluating the ability of Light Water Reactors to operate beyond 60 years is characterizing the degradation of materials exposed to radiation and various water chemistries. Of particular concern is the response of reactor materials to Irradiation Assisted Stress Corrosion Cracking (IASCC). Some materials testing reactors (MTRs) outside the U.S., such as the Halden Boiling Water Reactor (HBWR), have deployed a technique to measure crack growth propagation during irradiation. This technique incorporates a compact loading mechanism to stress the specimen during irradiation. A crack in the specimen is monitored using the Direct Current Potential Drop (DCPD) method. A project is underway to develop and demonstrate the performance of a similar type of test rig for use in U.S. MTRs. The first year of this three year project was devoted to designing, analyzing, fabricating, and bench top testing a mechanism capable of applying a controlled stress to specimens while they are irradiated in a pressurized water loop (simulating PWR reactor conditions). During the second year, the mechanism will be tested in autoclaves containing high pressure, high temperature water with representative water chemistries. In addition, necessary documentation and safety reviews for testing in a reactor environment will be completed. In the third year, the assembly will be tested in the Massachusetts Institute of Technology Reactor (MITR) and Post Irradiation Examinations (PIE) will be performed.

  12. Crack patterns over uneven substrates.

    PubMed

    Nandakishore, Pawan; Goehring, Lucas

    2016-02-28

    Cracks in thin layers are influenced by what lies beneath them. From buried craters to crocodile skin, crack patterns are found over an enormous range of length scales. Regardless of absolute size, their substrates can dramatically influence how cracks form, guiding them in some cases, or shielding regions from them in others. Here we investigate how a substrate's shape affects the appearance of cracks above it, by preparing mud cracks over sinusoidally varying surfaces. We find that as the thickness of the cracking layer increases, the observed crack patterns change from wavy to ladder-like to isotropic. Two order parameters are introduced to measure the relative alignment of these crack networks, and, along with Fourier methods, are used to characterise the transitions between crack pattern types. Finally, we explain these results with a model, based on the Griffith criteria of fracture, that identifies the conditions for which straight or wavy cracks will be seen, and predicts how well-ordered the cracks will be. Our metrics and results can be applied to any situation where connected networks of cracks are expected, or found. PMID:26762761

  13. ADAPTATION OF CRACK GROWTH DETECTION TECHNIQUES TO US MATERIAL TEST REACTORS

    SciTech Connect

    A. Joseph Palmer; Sebastien P. Teysseyre; Kurt L. Davis; Gordon Kohse; Yakov Ostrovsky; David M. Carpenter; Joy L. Rempe

    2015-04-01

    A key component in evaluating the ability of Light Water Reactors to operate beyond 60 years is characterizing the degradation of materials exposed to radiation and various water chemistries. Of particular concern is the response of reactor materials to Irradiation Assisted Stress Corrosion Cracking (IASCC). Some test reactors outside the United States, such as the Halden Boiling Water Reactor (HBWR), have developed techniques to measure crack growth propagation during irradiation. The basic approach is to use a custom-designed compact loading mechanism to stress the specimen during irradiation, while the crack in the specimen is monitored in-situ using the Direct Current Potential Drop (DCPD) method. In 2012 the US Department of Energy commissioned the Idaho National Laboratory and the MIT Nuclear Reactor Laboratory (MIT NRL) to take the basic concepts developed at the HBWR and adapt them to a test rig capable of conducting in-pile IASCC tests in US Material Test Reactors. The first two and half years of the project consisted of designing and testing the loader mechanism, testing individual components of the in-pile rig and electronic support equipment, and autoclave testing of the rig design prior to insertion in the MIT Reactor. The load was applied to the specimen by means of a scissor like mechanism, actuated by a miniature metal bellows driven by pneumatic pressure and sized to fit within the small in-core irradiation volume. In addition to the loader design, technical challenges included developing robust connections to the specimen for the applied current and voltage measurements, appropriate ceramic insulating materials that can endure the LWR environment, dealing with the high electromagnetic noise environment of a reactor core at full power, and accommodating material property changes in the specimen, due primarily to fast neutron damage, which change the specimen resistance without additional crack growth. The project culminated with an in

  14. Fracture mechanics by three-dimensional crack-tip synchrotron X-ray microscopy

    PubMed Central

    Withers, P. J.

    2015-01-01

    To better understand the relationship between the nucleation and growth of defects and the local stresses and phase changes that cause them, we need both imaging and stress mapping. Here, we explore how this can be achieved by bringing together synchrotron X-ray diffraction and tomographic imaging. Conventionally, these are undertaken on separate synchrotron beamlines; however, instruments capable of both imaging and diffraction are beginning to emerge, such as ID15 at the European Synchrotron Radiation Facility and JEEP at the Diamond Light Source. This review explores the concept of three-dimensional crack-tip X-ray microscopy, bringing them together to probe the crack-tip behaviour under realistic environmental and loading conditions and to extract quantitative fracture mechanics information about the local crack-tip environment. X-ray diffraction provides information about the crack-tip stress field, phase transformations, plastic zone and crack-face tractions and forces. Time-lapse CT, besides providing information about the three-dimensional nature of the crack and its local growth rate, can also provide information as to the activation of extrinsic toughening mechanisms such as crack deflection, crack-tip zone shielding, crack bridging and crack closure. It is shown how crack-tip microscopy allows a quantitative measure of the crack-tip driving force via the stress intensity factor or the crack-tip opening displacement. Finally, further opportunities for synchrotron X-ray microscopy are explored. PMID:25624521

  15. Pacific Northwest Laboratory: Annual report for 1986 to the Assistant Secretary for Environment, Safety and Health: Part 5, Nuclear and operational safety

    SciTech Connect

    Faust, L.G.; Kennedy, W.E.; Steelman, B.L.; Selby, J.M.

    1987-02-01

    Part 5 of the 1986 Annual Report to the Department of Energy's Assistant Secretary for Environment, Safety and Health presents Pacific Northwest Laboratory's progress on work performed for the Office of Nuclear Safety, the Office of Operational Safety, and for the Office of Environmental Analysis. For each project, as identified by the Field Task Proposal/Agreement, articles describe progress made during fiscal year 1986. Authors of these articles represent a broad spectrum of capabilities derived from three of the seven research departments of the Laboratory, reflecting the interdisciplinary nature of the work.

  16. On Modeling Hydrogen-Induced Crack Propagation Under Sustained Load

    NASA Astrophysics Data System (ADS)

    Dadfarnia, Mohsen; Somerday, Brian p.; Schembri, Philip E.; Sofronis, Petros; Foulk, James W.; Nibur, Kevin A.; Balch, Dorian K.

    2014-08-01

    The failure of hydrogen containment components is generally associated with subcritical cracking. Understanding subcritical crack growth behavior and its dependence on material and environmental variables can lead to methods for designing structural components in a hydrogen environment and will be beneficial in developing materials resistant to hydrogen embrittlement. In order to identify the issues underlying crack propagation and arrest, we present a model for hydrogen-induced stress-controlled crack propagation under sustained loading. The model is based on the assumptions that (I) hydrogen reduces the material fracture strength and (II) crack propagation takes place when the opening stress over the characteristic distance ahead of a crack tip is greater than the local fracture strength. The model is used in a finite-element simulation of crack propagation coupled with simultaneous hydrogen diffusion in a model material through nodal release. The numerical simulations show that the same physics, i.e., diffusion-controlled crack propagation, can explain the existence of both stages I and II in the velocity versus stress intensity factor ( V- K) curve.

  17. 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.

  18. Prediction of pure water stress corrosion cracking (PWSCC) in nickel base alloys using crack growth rate models

    SciTech Connect

    Thompson, C.D.; Krasodomski, H.T.; Lewis, N.; Makar, G.L.

    1995-02-22

    The Ford/Andresen slip dissolution SCC model, originally developed for stainless steel components in BWR environments, has been applied to Alloy 600 and Alloy X-750 tested in deaerated pure water chemistry. A method is described whereby the crack growth rates measured in compact tension specimens can be used to estimate crack growth in a component. Good agreement was found between model prediction and measured SCC in X-750 threaded fasteners over a wide range of temperatures, stresses, and material condition. Most data support the basic assumption of this model that cracks initiate early in life. The evidence supporting a particular SCC mechanism is mixed. Electrochemical repassivation data and estimates of oxide fracture strain indicate that the slip dissolution model can account for the observed crack growth rates, provided primary rather than secondary creep rates are used. However, approximately 100 cross-sectional TEM foils of SCC cracks including crack tips reveal no evidence of enhanced plasticity or unique dislocation patterns at the crack tip or along the crack to support a classic slip dissolution mechanism. No voids, hydrides, or microcracks are found in the vicinity of the crack tips creating doubt about classic hydrogen related mechanisms. The bulk oxide films exhibit a surface oxide which is often different than the oxides found within a crack. Although bulk chromium concentration affects the rate of SCC, analytical data indicates the mechanism does not result from chromium depletion at the grain boundaries. The overall findings support a corrosion/dissolution mechanism but not one necessarily related to slip at the crack tip.

  19. Sudden bending of cracked laminates

    NASA Technical Reports Server (NTRS)

    Sih, G. C.; Chen, E. P.

    1980-01-01

    A dynamic approximate laminated plate theory is developed with emphasis placed on obtaining effective solution for the crack configuration where the 1/square root of r stress singularity and the condition of plane strain are preserved. The radial distance r is measured from the crack edge. The results obtained show that the crack moment intensity tends to decrease as the crack length to laminate plate thickness is increased. Hence, a laminated plate has the desirable feature of stabilizing a through crack as it increases its length at constant load. Also, the level of the average load intensity transmitted to a through crack can be reduced by making the inner layers to be stiffer than the outer layers. The present theory, although approximate, is useful for analyzing laminate failure to crack propagation under dynamic load conditions.

  20. Crack growth in high temperature materials

    SciTech Connect

    Stoloff, N.S.

    1998-12-31

    Many intermetallic compounds are brittle at low temperatures. Some compounds, including NiAl and MoSi, seem to be intrinsically brittle. Other compounds, including Ni{sub 3}Al, FeAl and Fe{sub 3}Al, are reasonably ductile when tested in inert environments. Water and water vapor can severely embrittle these and other compounds because they contain an active element such as aluminum or silicon. The release of atomic hydrogen from water leads, at room temperature, to hydrogen embrittlement. Another source of embrittlement, at elevated temperatures, is oxygen from the atmosphere. The effects of aggressive environments on the crack growth behavior of several intermetallics under monotonic or cyclic loading are described. Alleviation of embrittlement by means of alloying, the use of coatings or by prestrain are described, although no single method is effective for all intermetallics. A brief survey of environmentally induced crack growth in superalloys is included.

  1. Elevated temperature crack growth

    NASA Technical Reports Server (NTRS)

    Yau, J. F.; Malik, S. N.; Kim, K. S.; Vanstone, R. H.; Laflen, J. H.

    1985-01-01

    The objective of the Elevated Temperature Crack Growth Project is to evaluate proposed nonlinear fracture mechanics methods for application to combustor liners of aircraft gas turbine engines. During the first year of this program, proposed path-independent (P-I) integrals were reviewed for such applications. Several P-I integrals were implemented into a finite-element postprocessor which was developed and verified as part of the work. Alloy 718 was selected as the analog material for use in the forthcoming experimental work. A buttonhead, single-edge notch specimen was designed and verified for use in elevated-temperature strain control testing with significant inelastic strains. A crack mouth opening displacement measurement device was developed for further use.

  2. Statistical crack mechanics

    SciTech Connect

    Dienes, J.K.

    1983-01-01

    An alternative to the use of plasticity theory to characterize the inelastic behavior of solids is to represent the flaws by statistical methods. We have taken such an approach to study fragmentation because it offers a number of advantages. Foremost among these is that, by considering the effects of flaws, it becomes possible to address the underlying physics directly. For example, we have been able to explain why rocks exhibit large strain-rate effects (a consequence of the finite growth rate of cracks), why a spherical explosive imbedded in oil shale produces a cavity with a nearly square section (opening of bedding cracks) and why propellants may detonate following low-speed impact (a consequence of frictional hot spots).

  3. Cracked and Pitted Plain

    NASA Technical Reports Server (NTRS)

    2003-01-01

    MGS MOC Release No. MOC2-536, 6 November 2003

    This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a typical view--at 1.5 meters (5 feet) per pixel--of surfaces in far western Utopia Planitia. In this region, the plains have developed cracks and pit chains arranged in a polygonal pattern. The pits form by collapse along the trend of a previously-formed crack. This picture is located near 45.0oN, 275.4oW. This April 2003 image covers an area 3 km (1.9 mi) wide and is illuminated by sunlight from the lower left.

  4. Upgrading of cracking gasoline

    SciTech Connect

    Harandi, M.N.; Owen, H.; Ragonese, F.P.; Yurchak, S.

    1990-08-21

    This patent describes an integrated catalytic cracking and gasoline upgrading process. It comprises: withdrawing a product stream from the riser reactor of a catalytic cracking process unit; charging the product stream to a primary fractionation zone; withdrawing an intermediate gasoline stream from the primary fractionation zone, the intermediate gasoline stream comprising olefinic gasoline having an ASTM D86 boiling range from about 90{degrees} to about 170{degrees} C.; contacting a first portion of the intermediate gasoline stream and a C{sub 2}{minus}C{sub 5} olefinic stream with a catalyst under conversion conditions to form an upgraded gasoline stream; and charging a second portion of the intermediate gasoline stream together with the upgraded gasoline stream to a gasoline product storage facility.

  5. Replica-based Crack Inspection

    NASA Technical Reports Server (NTRS)

    Newman, John A.; Smith, Stephen W.; Piascik, R. S.; Willard, Scott A.; Dawicke, David S.

    2007-01-01

    A surface replica-based crack inspection method has recently been developed for use in Space Shuttle main engine (SSME) hydrogen feedline flowliners. These flowliners exist to ensure favorable flow of liquid hydrogen over gimble joint bellows, and consist of two rings each containing 38 elongated slots. In the summer of 2002, multiple cracks ranging from 0.1 inches to 0.6 inches long were discovered; each orbiter contained at least one cracked flowliner. These long cracks were repaired and eddy current inspections ensured that no cracks longer than 0.075 inches were present. However, subsequent fracture-mechanics review of flight rationale required detection of smaller cracks, and was the driving force for development of higher-resolution inspection method. Acetate tape surface replicas have been used for decades to detect and monitor small cracks. However, acetate tape replicas have primarily been limited to laboratory specimens because complexities involved in making these replicas - requiring acetate tape to be dissolved with acetone - are not well suited for a crack inspection tool. More recently developed silicon-based replicas are better suited for use as a crack detection tool. A commercially available silicon-based replica product has been determined to be acceptable for use in SSME hydrogen feedlines. A method has been developed using this product and a scanning electron microscope for analysis, which can find cracks as small as 0.005 inches and other features (e.g., pits, scratches, tool marks, etc.) as small as 0.001 inches. The resolution of this method has been validated with dozens of cracks generated in a laboratory setting and this method has been used to locate 55 cracks (ranging in size from 0.040 inches to 0.004 inches) on space flight hardware. These cracks were removed by polishing away the cracked material and a second round of replicas confirmed the repair.

  6. Utopia Cracks and Polygons

    NASA Technical Reports Server (NTRS)

    2003-01-01

    MGS MOC Release No. MOC2-339, 23 April 2003

    This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a pattern of polygonal cracks and aligned, elliptical pits in western Utopia Planitia. The picture covers an area about 3 km (about 1.9 mi) wide near 44.9oN, 274.7oW. Sunlight illuminates the scene from the left.

  7. Pacific Northwest Laboratory annual report for 1980 to the DOE Assistant Secretary for Environment. Part 5. Environmental assessment, control, health and safety

    SciTech Connect

    Baalman, R.W.; Hays, I.D.

    1981-02-01

    Pacific Northwest Laboratory's (PNL) 1980 annual report to the DOE Assistant Secretary for Environment describes research in environment, health, and safety conducted during fiscal year 1980. Part 5 includes technology assessments for natural gas, enhanced oil recovery, oil shale, uranium mining, magnetic fusion energy, solar energy, uranium enrichment and industrial energy utilization; regional analysis studies of environmental transport and community impacts; environmental and safety engineering for LNG, oil spills, LPG, shale oil waste waters, geothermal liquid waste disposal, compressed air energy storage, and nuclear/fusion fuel cycles; operational and environmental safety studies of decommissioning, environmental monitoring, personnel dosimetry, and analysis of criticality safety; health physics studies; and epidemiological studies. Also included are an author index, organization of PNL charts and distribution lists of the annual report, along with lists of presentations and publications. (DLS)

  8. 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.

  9. Simulation of the ultrasonic array response from real branched cracks using an efficient finite element method

    SciTech Connect

    Felice, Maria V.; Velichko, Alexander; Wilcox, Paul D.; Barden, Tim J.; Dunhill, Tony K.

    2014-02-18

    A hybrid model to simulate the ultrasonic array response from stress corrosion cracks is presented. These cracks are branched and difficult to detect so the model is required to enable optimization of an array design. An efficient frequency-domain finite element method is described and selected to simulate the ultrasonic scattering. Experimental validation results are presented, followed by an example of the simulated ultrasonic array response from a real stress corrosion crack whose geometry is obtained from an X-ray Computed Tomography image. A simulation-assisted array design methodology, which includes the model and use of real crack geometries, is proposed.

  10. Investigation of Cracks Found in Helicopter Longerons

    NASA Technical Reports Server (NTRS)

    Newman, John A.; Baughman, James M.; Wallace, Terryl A.

    2009-01-01

    Four cracked longerons, containing a total of eight cracks, were provided for study. Cracked regions were cut from the longerons. Load was applied to open the cracks, enabling crack surface examination. Examination revealed that crack propagation was driven by fatigue loading in all eight cases. Fatigue crack initiation appears to have occurred on the top edge of the longerons near geometric changes that affect component bending stiffness. Additionally, metallurigical analysis has revealed a local depletion in alloying elements in the crack initiation regions that may be a contributing factor. Fatigue crack propagation appeared to be initially driven by opening-mode loading, but at a crack length of approximately 0.5 inches (12.7 mm), there is evidence of mixed-mode crack loading. For the longest cracks studied, shear-mode displacements destroyed crack-surface features of interest over significant portions of the crack surfaces.

  11. On the Crack Bifurcation and Fanning of Crack Growth Data

    NASA Technical Reports Server (NTRS)

    Forman, Royce G.; Zanganeh, Mohammad

    2015-01-01

    Crack growth data obtained from ASTM load shedding method for different R values show some fanning especially for aluminum alloys. It is believed by the authors and it has been shown before that the observed fanning is due to the crack bifurcation occurs in the near threshold region which is a function of intrinsic properties of the alloy. Therefore, validity of the ASTM load shedding test procedure and results is confirmed. However, this position has been argued by some experimentalists who believe the fanning is an artifact of the test procedure and thus the obtained results are invalid. It has been shown that using a special test procedure such as using compressively pre-cracked specimens will eliminate the fanning effect. Since not using the fanned data fit can result in a significantly lower calculated cyclic life, design of a component, particularly for rotorcraft and propeller systems will considerably be impacted and therefore this study is of paramount importance. In this effort both test procedures i.e. ASTM load shedding and the proposed compressive pre-cracking have been used to study the fatigue crack growth behavior of compact tension specimens made of aluminum alloy 2524-T3. Fatigue crack growth paths have been closely observed using SEM machines to investigate the effects of compression pre-cracking on the crack bifurcation behavior. The results of this study will shed a light on resolving the existing argument by better understanding of near threshold fatigue crack growth behavior.

  12. The prevalence of malnutrition in elderly residents in a warden-assisted setting compared with a home-living environment.

    PubMed

    Riches, Kerry; Jeanes, Yvonne

    2014-07-01

    Malnutrition in elderly people is associated with many adverse clinical outcomes. However, few studies exist investigating malnutrition in the community setting. This study aimed to report the prevalence of malnutrition in elderly people living in warden-assisted (WA) accommodation compared with those living at home. A total of 20 WA and 20 home-living (HL) participants were assessed using hand-grip strength and the Mini Nutritional Assessment (MNA). Some 30% of the WA group were malnourished, compared with 10% of the HL group. This study demonstrates an alarmingly large proportion of individuals in WA accommodation to be either malnourished or at risk of malnutrition. This is a relatively small study, and further research into the key factors influencing malnutrition and interventions to minimise malnutrition with WA accommodation are clearly warranted.

  13. Fostering Self-Regulated Learning in a Blended Environment Using Group Awareness and Peer Assistance as External Scaffolds

    ERIC Educational Resources Information Center

    Lin, J-W.; Lai, Y-C.; Lai, Y-C.; Chang, L-C.

    2016-01-01

    Most systems for training self-regulated learning (SRL) behaviour focus on the provision of a learner-centred environment. Such systems repeat the training process and place learners alone to experience that process iteratively. According to the relevant literature, external scaffolds are more promising for effective SRL training. In this work,…

  14. Cracking the perfusion code?: Laser-assisted Indocyanine Green angiography and combined laser Doppler spectrophotometry for intraoperative evaluation of tissue perfusion in autologous breast reconstruction with DIEP or ms-TRAM flaps.

    PubMed

    Ludolph, Ingo; Arkudas, Andreas; Schmitz, Marweh; Boos, Anja M; Taeger, Christian D; Rother, Ulrich; Horch, Raymund E; Beier, Justus P

    2016-10-01

    The aim of this prospective study was to assess the correlation of flap perfusion analysis based on laser-assisted Indocyanine Green (ICG) angiography with combined laser Doppler spectrophotometry in autologous breast reconstruction using free DIEP/ms-TRAM flaps. Between February 2014 and July 2015, 35 free DIEP/ms-TRAM flaps were included in this study. Besides the clinical evaluation of flaps, intraoperative perfusion dynamics were assessed by means of laser-assisted ICG angiography and post-capillary oxygen saturation and relative haemoglobin content (rHb) using combined laser Doppler spectrophotometry. Correlation of the aforementioned parameters was analysed, as well as the impact on flap design and postoperative complications. Flap survival rate was 100%. There were no partial flap losses. In three cases, flap design was based on the angiography, contrary to clinical evaluation and spectrophotometry. The final decision on the inclusion of flap areas was based on the angiographic perfusion pattern. Angiography and spectrophotometry showed a correlation in most of the cases regarding tissue perfusion, post-capillary oxygen saturation and relative haemoglobin content. Laser-assisted ICG angiography is a useful tool for intraoperative evaluation of flap perfusion in autologous breast reconstruction with DIEP/ms-TRAM flaps, especially in decision making in cases where flap perfusion is not clearly assessable by clinical signs and exact determination of well-perfused flap margins is difficult to obtain. It provides an objective real-time analysis of flap perfusion, with high sensitivity for the detection of poorly perfused flap areas. Concerning the topographical mapping of well-perfused flap areas, laser-assisted angiography is superior to combined laser Doppler spectrophotometry.

  15. Preventing Cracking of Anodized Coatings

    NASA Technical Reports Server (NTRS)

    He, Charles C.; Heslin, Thomas M.

    1995-01-01

    Anodized coatings have been used as optical and thermal surfaces in spacecraft. Particulate contamination from cracked coatings is a concern for many applications. The major cause for the cracking is the difference in the coefficient of thermal expansion between the oxide coatings and the aluminum substrate. The loss of water when the coating is exposed to a vacuum also could induce cracking of the coating. Hot-water sealing was identified as the major cause for the cracking of the coatings because of the large temperature change when the parts were immersed in boiling water and the water was absorbed in the coating. when the hot-water sealing process was eliminated, the cracking resistance of the anodized coatings was greatly improved. Also, it was found that dyed black coatings were more susceptible than clear coatings to cracking during thermo-vacuum cyclings.

  16. 40 CFR Table 2 to Subpart Uuu of... - Operating Limits for Metal HAP Emissions From Catalytic Cracking Units

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... Emissions From Catalytic Cracking Units 2 Table 2 to Subpart UUU of Part 63 Protection of Environment... Petroleum Refineries: Catalytic Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63... Catalytic Cracking Units As stated in § 63.1564(a)(2), you shall meet each operating limit in the...

  17. 40 CFR 63.1565 - What are my requirements for organic HAP emissions from catalytic cracking units?

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... HAP emissions from catalytic cracking units? 63.1565 Section 63.1565 Protection of Environment... Petroleum Refineries: Catalytic Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Catalytic Cracking Units, Catalytic Reforming Units, Sulfur Recovery Units, and Bypass Lines § 63.1565...

  18. 40 CFR Table 2 to Subpart Uuu of... - Operating Limits for Metal HAP Emissions From Catalytic Cracking Units

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... Emissions From Catalytic Cracking Units 2 Table 2 to Subpart UUU of Part 63 Protection of Environment... Petroleum Refineries: Catalytic Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63... Catalytic Cracking Units As stated in § 63.1564(a)(2), you shall meet each operating limit in the...

  19. Shuttle Fuel Feedliner Cracking Investigation

    NASA Technical Reports Server (NTRS)

    Nesman, Tomas E.; Turner, Jim (Technical Monitor)

    2002-01-01

    This presentation provides an overview of material covered during 'Space Shuttle Fuel Feedliner Cracking Investigation MSFC Fluids Workshop' held November 19-21, 2002. Topics covered include: cracks on fuel feed lines of Orbiter space shuttles, fluid driven cracking analysis, liner structural modes, structural motion in a fluid, fluid borne drivers, three dimensional computational fluid dynamics models, fluid borne drivers from pumps, amplification mechanisms, flow parameter mapping, and flight engine flow map.

  20. 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.

  1. Catalyst for cracking kerosene

    SciTech Connect

    Hsie, C. H.

    1985-06-04

    A catalyst capable of cracking kerosene under lower pressure and temperature comprising kerosene; metal powder mixture of chromium powder, copper powder, lead powder, zinc powder, nickel powder, manganese powder in an amount of 12 to 13 parts by weight per 100 parts by weight of said kerosene; sulfuric acid in an amount of 15 to 30 parts by weight per 100 parts by weight of said kerosene; inorganic powder mixture of aluminum oxide powder, serpentine powder, alum powder, magnesium oxide powder, limestone powder, slake lime powder, silica powder, and granite powder in an amount of 150 to 170 parts by weight per 100 parts by weight of said kerosene.

  2. Threshold intensity factors as lower boundaries for crack propagation in ceramics

    PubMed Central

    Marx, Rudolf; Jungwirth, Franz; Walter, Per-Ole

    2004-01-01

    Background Slow crack growth can be described in a v (crack velocity) versus KI (stress intensity factor) diagram. Slow crack growth in ceramics is attributed to corrosion assisted stress at the crack tip or at any pre-existing defect in the ceramic. The combined effect of high stresses at the crack tip and the presence of water or body fluid molecules (reducing surface energy at the crack tip) induces crack propagation, which eventually may result in fatigue. The presence of a threshold in the stress intensity factor, below which no crack propagation occurs, has been the subject of important research in the last years. The higher this threshold, the higher the reliability of the ceramic, and consequently the longer its lifetime. Methods We utilize the Irwin K-field displacement relation to deduce crack tip stress intensity factors from the near crack tip profile. Cracks are initiated by indentation impressions. The threshold stress intensity factor is determined as the time limit of the tip stress intensity when the residual stresses have (nearly) disappeared. Results We determined the threshold stress intensity factors for most of the all ceramic materials presently important for dental restorations in Europe. Of special significance is the finding that alumina ceramic has a threshold limit nearly identical with that of zirconia. Conclusion The intention of the present paper is to stress the point that the threshold stress intensity factor represents a more intrinsic property for a given ceramic material than the widely used toughness (bend strength or fracture toughness), which refers only to fast crack growth. Considering two ceramics with identical threshold limits, although with different critical stress intensity limits, means that both ceramics have identical starting points for slow crack growth. Fast catastrophic crack growth leading to spontaneous fatigue, however, is different. This growth starts later in those ceramic materials that have larger

  3. Characterization and Prediction of Cracks in Coated Materials: Direction and Length of Crack Propagation in Bimaterials

    PubMed Central

    Azari, Z.; Pappalettere, C.

    2015-01-01

    The behaviour of materials is governed by the surrounding environment. The contact area between the material and the surrounding environment is the likely spot where different forms of degradation, particularly rust, may be generated. A rust prevention treatment, like bluing, inhibitors, humidity control, coatings, and galvanization, will be necessary. The galvanization process aims to protect the surface of the material by depositing a layer of metallic zinc by either hot-dip galvanizing or electroplating. In the hot-dip galvanizing process, a metallic bond between steel and metallic zinc is obtained by immersing the steel in a zinc bath at a temperature of around 460°C. Although the hot-dip galvanizing procedure is recognized to be one of the most effective techniques to combat corrosion, cracks can arise in the intermetallic δ layer. These cracks can affect the life of the coated material and decrease the lifetime service of the entire structure. In the present paper the mechanical response of hot-dip galvanized steel submitted to mechanical loading condition is investigated. Experimental tests were performed and corroborative numerical and analytical methods were then applied in order to describe both the mechanical behaviour and the processes of crack/cracks propagation in a bimaterial as zinc-coated material. PMID:27347531

  4. Distributed Denial of Service Attack Source Detection Using Efficient Traceback Technique (ETT) in Cloud-Assisted Healthcare Environment.

    PubMed

    Latif, Rabia; Abbas, Haider; Latif, Seemab; Masood, Ashraf

    2016-07-01

    Security and privacy are the first and foremost concerns that should be given special attention when dealing with Wireless Body Area Networks (WBANs). As WBAN sensors operate in an unattended environment and carry critical patient health information, Distributed Denial of Service (DDoS) attack is one of the major attacks in WBAN environment that not only exhausts the available resources but also influence the reliability of information being transmitted. This research work is an extension of our previous work in which a machine learning based attack detection algorithm is proposed to detect DDoS attack in WBAN environment. However, in order to avoid complexity, no consideration was given to the traceback mechanism. During traceback, the challenge lies in reconstructing the attack path leading to identify the attack source. Among existing traceback techniques, Probabilistic Packet Marking (PPM) approach is the most commonly used technique in conventional IP- based networks. However, since marking probability assignment has significant effect on both the convergence time and performance of a scheme, it is not directly applicable in WBAN environment due to high convergence time and overhead on intermediate nodes. Therefore, in this paper we have proposed a new scheme called Efficient Traceback Technique (ETT) based on Dynamic Probability Packet Marking (DPPM) approach and uses MAC header in place of IP header. Instead of using fixed marking probability, the proposed scheme uses variable marking probability based on the number of hops travelled by a packet to reach the target node. Finally, path reconstruction algorithms are proposed to traceback an attacker. Evaluation and simulation results indicate that the proposed solution outperforms fixed PPM in terms of convergence time and computational overhead on nodes. PMID:27189623

  5. A Hybrid Laser Surface Treatment for Refurbishment of Stress Corrosion Cracking Damaged 304L Stainless Steel

    NASA Astrophysics Data System (ADS)

    Gupta, R. K.; Sundar, R.; Kumar, B. Sunil; Ganesh, P.; Kaul, R.; Ranganathan, K.; Bindra, K. S.; Kain, V.; Oak, S. M.; Kukreja, L. M.

    2015-06-01

    The paper describes a new hybrid laser surface treatment approach, combining laser surface melting and laser shock peening treatments, for refurbishment stress corrosion cracking damaged type 304L stainless steel specimens. Hybrid laser surface treatment produced crack-free compressively stressed surface. With respect to as-machined specimens, laser-rejuvenated specimens demonstrated significantly reduced susceptibility to stress corrosion cracking in chloride environment with minor increase in mean surface roughness. The results of the study, although particularly applicable to shallow stress corrosion cracking damage, are important for life extension of in-service stainless steel components operating in corrosive chloride environment.

  6. Shear fatigue crack growth - A literature survey

    NASA Technical Reports Server (NTRS)

    Liu, H. W.

    1985-01-01

    Recent studies of shear crack growth are reviewed, emphasizing test methods and data analyses. The combined mode I and mode II elastic crack tip stress fields are considered. The development and design of the compact shear specimen are described, and the results of fatigue crack growth tests using compact shear specimens are reviewed. The fatigue crack growth tests are discussed and the results of inclined cracks in tensile panels, center cracks in plates under biaxial loading, cracked beam specimens with combined bending and shear loading, center-cracked panels and double edge-cracked plates under cyclic shear loading are examined and analyzed in detail.

  7. Socioeconomic Status and Depressive Syndrome: The Role of Inter- and Intra-generational Mobility, Government Assistance, and Work Environment*

    PubMed Central

    EATON, WILLIAM W.; MUNTANER, CARLES; BOVASSO, GREGORY; SMITH, COREY

    2009-01-01

    This paper assesses the hypothesis that depressive syndrome is associated with socioeconomic status, using longitudinal data from the Baltimore Epidemiologic Catchment Area Followup. Socioeconomic measures include those used in most studies of status attainment, as well as measures of financial dependence, non-job income, and work environment. Analyses include inter-and intra- generational mobility, and replicate the basic aspects of the status attainment process, as well as psychiatric epidemiologic findings regarding gender, family history of depression, life events, and depressive syndrome. But the involvement of depressive syndrome in the process of status attainment, either as cause or consequence, is small and not statistically significant. There are strong effects of financial dependence and work environment on depressive syndrome. The findings shed doubt on the utility of the causation/selection/drift model for depression, to the extent it is based on linear relationships and socioeconomic rank at the macro level, while lending credibility to social-psychologically oriented theories of work environment, poverty, and depression. PMID:11668774

  8. Development of an audio-based virtual gaming environment to assist with navigation skills in the blind.

    PubMed

    Connors, Erin C; Yazzolino, Lindsay A; Sánchez, Jaime; Merabet, Lotfi B

    2013-01-01

    Audio-based Environment Simulator (AbES) is virtual environment software designed to improve real world navigation skills in the blind. Using only audio based cues and set within the context of a video game metaphor, users gather relevant spatial information regarding a building's layout. This allows the user to develop an accurate spatial cognitive map of a large-scale three-dimensional space that can be manipulated for the purposes of a real indoor navigation task. After game play, participants are then assessed on their ability to navigate within the target physical building represented in the game. Preliminary results suggest that early blind users were able to acquire relevant information regarding the spatial layout of a previously unfamiliar building as indexed by their performance on a series of navigation tasks. These tasks included path finding through the virtual and physical building, as well as a series of drop off tasks. We find that the immersive and highly interactive nature of the AbES software appears to greatly engage the blind user to actively explore the virtual environment. Applications of this approach may extend to larger populations of visually impaired individuals. PMID:23568182

  9. Effects of crack geometry and material behavior on scattering by cracks for QNDE applications. Technical progress report, March 1, 1988--August 30, 1989

    SciTech Connect

    Achenbach, J.D.

    1989-09-15

    In work carried out on this project, the usual mathematical modeling of ultrasonic wave scattering by flaws is being extended to account for several typical characteristics of fatigue and stress-corrosion cracks, and the environment of such cracks. Work has been completed on scattering by macrocrack-microcrack configurations. We have also investigated reflection and transmission by a flaw plane consisting of an infinite array of randomly oriented cracks. In another investigation the propagation of mechanical disturbances in solids with periodically distributed cracks has been studied.

  10. Pacific Northwest Laboratory annual report for 1979 to the DOE Assistant Secretary for Environment. Part 2. Ecological sciences

    SciTech Connect

    Vaughan, B.E.

    1980-02-01

    Research in Environment, Health, and Safety conducted during fiscal year 1979 is reported. This volume consists of project reports from the Ecological Sciences research department. The reports are grouped under the following subject areas: National Environmental Research Park and land use; Alaskan resource research; shale oil; synfuels; nuclear waste; fission; marine research programs; statistical development of field research; nuclear fusion; pumped storage and hydroelectric development; pathways modelling, assessment and Hanford project support; electric field and microwave research; and energy research for other agencies. (ACR)

  11. Cardiovascular health outcomes of Latinos in the Affordable Housing as an Obesity Mediating Environment (AHOME) study: a study of rental assistance use.

    PubMed

    Chambers, Earle C; Rosenbaum, Emily

    2014-06-01

    Studies have shown that households subsidized with vouchers live in higher quality units and exhibit fewer physical, mental, and social problems than do their peers living in public housing. However, none of these studies have included cardiovascular outcomes. The objective of this study was to assess if use/type of rental assistance is independently associated with poor cardiovascular health among Latino adults (ages ≥ 18) who are eligible for federal low-income rental assistance and living in the Bronx, NY. Data from the cross-sectional, Affordable Housing as an Obesity Mediating Environment study, collected over 18 months (January 2011 to August 2012) were used. The prevalence of cardiovascular disease (CVD) outcomes was determined by measured high blood pressure and self-reported heart attack and/or stroke. Type of housing status was defined as: public housing units, units subsidized by section 8 vouchers, and units unassisted by either federal program. Statistical techniques used were analysis of variance and multivariate logistic regression. The prevalence of CVD was significantly higher among public housing residents than unassisted participants even in the presence of all individual level covariates. Public housing residents also have higher levels of CVD than do section 8 participants. The prevalence of CVD was similar for unassisted and section 8 participants. These findings point to the potential for health benefits arising from housing voucher use even within a fairly delimited geographic area. PMID:24190105

  12. More Than Just a Break from Treatment: How Substance Use Disorder Patients Experience the Stable Environment in Horse-Assisted Therapy

    PubMed Central

    Kern-Godal, Ann; Brenna, Ida Halvorsen; Arnevik, Espen Ajo; Ravndal, Edle

    2016-01-01

    Inclusion of horse-assisted therapy (HAT) in substance use disorder (SUD) treatment is rarely reported. Our previous studies show improved treatment retention and the importance of the patient–horse relationship. This qualitative study used thematic analysis, within a social constructionist framework, to explore how eight patients experienced contextual aspects of HAT’s contribution to their SUD treatment. Participants described HAT as a “break from usual treatment”. However, four interrelated aspects of this experience, namely “change of focus”, “activity”, “identity”, and “motivation,” suggest HAT is more than just a break from usual SUD treatment. The stable environment is portrayed as a context where participants could construct a positive self: one which is useful, responsible, and accepted; more fundamentally, a different self from the “patient/self” receiving treatment for a problem. The implications extend well beyond animal-assisted or other adjunct therapies. Their relevance to broader SUD policy and treatment practices warrants further study. PMID:27746677

  13. Cardiovascular health outcomes of Latinos in the Affordable Housing as an Obesity Mediating Environment (AHOME) study: a study of rental assistance use.

    PubMed

    Chambers, Earle C; Rosenbaum, Emily

    2014-06-01

    Studies have shown that households subsidized with vouchers live in higher quality units and exhibit fewer physical, mental, and social problems than do their peers living in public housing. However, none of these studies have included cardiovascular outcomes. The objective of this study was to assess if use/type of rental assistance is independently associated with poor cardiovascular health among Latino adults (ages ≥ 18) who are eligible for federal low-income rental assistance and living in the Bronx, NY. Data from the cross-sectional, Affordable Housing as an Obesity Mediating Environment study, collected over 18 months (January 2011 to August 2012) were used. The prevalence of cardiovascular disease (CVD) outcomes was determined by measured high blood pressure and self-reported heart attack and/or stroke. Type of housing status was defined as: public housing units, units subsidized by section 8 vouchers, and units unassisted by either federal program. Statistical techniques used were analysis of variance and multivariate logistic regression. The prevalence of CVD was significantly higher among public housing residents than unassisted participants even in the presence of all individual level covariates. Public housing residents also have higher levels of CVD than do section 8 participants. The prevalence of CVD was similar for unassisted and section 8 participants. These findings point to the potential for health benefits arising from housing voucher use even within a fairly delimited geographic area.

  14. Near threshold fatigue crack growth in ultrafinegrained copper

    NASA Astrophysics Data System (ADS)

    Arzaghi, M.; Fintová, S.; Sarrazin-Baudoux, C.; Kunz, L.; Petit, J.

    2014-08-01

    The near threshold fatigue crack growth in ultrafine-grained (UFG) copper at room temperature was studied in comparison to conventional coarse-grained (CG) copper. The fatigue crack growth rates da/dN in UFG copper were enhanced at ΔK <= 7 MPa√m compared to the CG material. The crack closure shielding, as evaluated using the compliance variation technique, was shown to explain these differences. The effective stress intensity factor amplitude AKeff appears to be the same driving force in both materials. Tests performed in high vacuum on UFG copper demonstrate the existence of a huge effect of environment with growth rates higher of about two orders of magnitude in air compared to high vacuum. This environmental effect on the crack path and the related microstructure is discussed on the basis of fractography observations performed using scanning electron microscope and completed with field emission scanning electron microscope combined with the focused ion beam technique.

  15. 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.

  16. Nanochemistry in confined environments: polyelectrolyte brush-assisted synthesis of gold nanoparticles inside ordered mesoporous thin films.

    PubMed

    Calvo, Alejandra; Fuertes, M Cecilia; Yameen, Basit; Williams, Federico J; Azzaroni, Omar; Soler-Illia, Galo J A A

    2010-04-20

    A robust and straightforward strategy allowing the controlled confinement of metal nanoparticles within the 3D framework of mesoporous films is presented. The chemical methodology is based on the inner surface modification of mesoporous silica films with polyelectrolyte brushes. We demonstrate that the macromolecular building blocks significantly enhance the site-selective preconcentration of nanoparticle precursors in the inner environment of the mesoporous film. Then, chemical reduction of the preconcentrated precursors led to the formation of metal nanoparticles locally addressed in the mesoporous structure. We show that the synergy taking place between two versatile functional nanobuilding blocks (ordered mesocavities and polymer brushes) can produce stable embedded nanoparticles with tuned optical properties in a very simple manner. As a general framework, the strategy can be easily adapted to different sets of polymer brushes and mesoporous films in order to regulate the monomer-precursor interactions and, consequently, manipulate the site-selective character of the different chemistries taking place in the film. We consider that the "integrative chemistry" approach described in this work provides new pathways to manipulate the physicochemical characteristics of hybrid organic-inorganic advanced functional assemblies based on the rational design of chemistry and topology in confined environments.

  17. Test Method Variability in Slow Crack Growth Properties of Sealing Glasses

    NASA Technical Reports Server (NTRS)

    Salem, J. A.; Tandon, R.

    2010-01-01

    The crack growth properties of several sealing glasses were measured by using constant stress rate testing in 2 and 95 percent RH (relative humidity). Crack growth parameters measured in high humidity are systematically smaller (n and B) than those measured in low humidity, and crack velocities for dry environments are 100x lower than for wet environments. The crack velocity is very sensitive to small changes in RH at low RH. Biaxial and uniaxial stress states produced similar parameters. Confidence intervals on crack growth parameters that were estimated from propagation of errors solutions were comparable to those from Monte Carlo simulation. Use of scratch-like and indentation flaws produced similar crack growth parameters when residual stresses were considered.

  18. 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

  19. Interface cracks in piezoelectric materials

    NASA Astrophysics Data System (ADS)

    Govorukha, V.; Kamlah, M.; Loboda, V.; Lapusta, Y.

    2016-02-01

    Due to their intrinsic electromechanical coupling behavior, piezoelectric materials are widely used in sensors, actuators and other modern technologies. It is well known that piezoelectric ceramics are very brittle and susceptible to fracture. In many cases, fracture occurs at interfaces as debonding and cracks. This leads to an undesired degradation of electrical and mechanical performance. Because of the practical and fundamental importance of the problem, interface cracks in piezoelectric materials have been actively studied in the last few decades. This review provides a comprehensive survey of recent works on cracks situated at the interface of two materials, at least one of which has piezoelectric or piezoelectromagnetic properties. Different electric boundary conditions along the crack faces are discussed. The oscillating and contact zone models for in-plane straight interface cracks between two dissimilar piezoelectric materials or between piezoelectric and non-piezoelectric ones are reviewed. Different peculiarities related to the investigation of interface cracks in piezoelectric materials for the anti-plane case, for functionally graded and thermopiezoelectric materials are presented. Papers related to magnetoelectroelastic bimaterials, to steady state motion of interface cracks in piezoelectric bimaterials and to circular arc-cracks at the interface of piezoelectric materials are reviewed, and various methods used to address these problems are discussed. The review concludes with an outlook on future research directions.

  20. Bonded orthotropic strips with cracks

    NASA Technical Reports Server (NTRS)

    Delale, F.; Erdogan, F.

    1979-01-01

    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. The problem of cracks fully imbedded into the homogeneous strips is considered. The singular behavior of the stresses for two special crack geometries is studied. The first is the case of a broken laminate in which the crack tips touch the interfaces. The second is the case of cracks crossing the interfaces. An interesting result found from the analysis of the latter is that for certain orthotropic material combinations the stress state at the point of intersection of a crack and an interface may be bounded whereas in isotropic materials at this point stresses are always singular. A number of numerical examples are worked out 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. Some numerical results are given for the stress intensity factors in certain basic crack geometries and for typical material combinations.

  1. Replica-Based Crack Inspection

    NASA Technical Reports Server (NTRS)

    Newman, John A.; Willard, Scott A.; Smith, Stephen W.; Piascik, Robert S.

    2008-01-01

    Surface replication has been proposed as a method for crack detection in space shuttle main engine flowliner slots. The results of a feasibility study show that examination of surface replicas with a scanning electron microscope can result in the detection of cracks as small as 0.005 inch, and surface flaws as small as 0.001 inch, for the flowliner material.

  2. 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.

  3. High speed thin plate fatigue crack monitor

    NASA Technical Reports Server (NTRS)

    Wincheski, Buzz A. (Inventor); Heyman, Joseph S. (Inventor); Namkung, Min (Inventor); Fulton, James P. (Inventor)

    1996-01-01

    A device and method are provided which non-destructively detect crack length and crack geometry in thin metallic plates. A non-contacting vibration apparatus produces resonant vibrations without introducing extraneous noise. Resulting resonant vibration shifts in cracked plates are correlated to known crack length in plates with similar resonant vibration shifts. In addition, acoustic emissions of cracks at resonance frequencies are correlated to acoustic emissions from known crack geometries.

  4. Characterization of the Resistance of Alloy 22 to Stress Corrosion Cracking

    SciTech Connect

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

    2002-05-30

    In its current design, the high-level nuclear waste containers include an external layer of 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). The objective of the current research was to characterize the effect of applied potential and temperature on the susceptibility of Alloy 22 to EAC in simulated concentrated water (SCW) using the slow strain rate test (SSRT). Results show that Alloy 22 may suffer EAC at applied potentials approximately 400 mV more anodic than the corrosion potential (E{sub corr}).

  5. 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

    model. The method can be also used to predict fatigue crack growth under constant amplitude and spectrum loading in various environmental conditions such as vacuum, air, and corrosive environment providing that appropriate limited constant amplitude fatigue crack growth data obtained in the same environment are available. The proposed methodology is equally suitable for fatigue analysis of smooth, notched, and cracked components.

  6. Including parameterization of the discrete ablation process into a planning and simulation environment for robot-assisted laser osteotomy.

    PubMed

    Burgner, Jessica; Kahrs, Lüder Alexander; Raczkowsky, Jörg; Wörn, Heinz

    2009-01-01

    Material processing using laser became a widely used method especially in the scope of industrial automation. The systems are mostly based on a precise model of the laser process and the according parameterization. Beside the industrial use the laser as an instrument to treat human tissue has become an integral part in medicine as well. Human tissue as an inhomogeneous material to process, poses the question of how to determine a model, which reflects the interaction processes with a specific laser.Recently it could be shown that the pulsed CO2 laser is suitable to ablate bony and cartilage tissue. Until now this thermo-mechanical bone ablation is not characterized as a discrete process. In order to plan and simulate the ablation process in the correct level of detail, the parameterization is indispensable. We developed a planning and simulation environment, determined parameters by confocal measurements of bony specimen and use these results to transfer planned cutting trajectories into a pulse sequence and corresponding robot locations.

  7. 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.

  8. Fabrication of reconfigurable protein matrices by cracking

    NASA Astrophysics Data System (ADS)

    Zhu, Xiaoyue; Mills, Kristen L.; Peters, Portia R.; Bahng, Joong Hwan; Liu, Elizabeth Ho; Shim, Jeongsup; Naruse, Keiji; Csete, Marie E.; Thouless, M. D.; Takayama, Shuichi

    2005-05-01

    The interface between extracellular matrices and cells is a dynamic environment that is crucial for regulating important cellular processes such as signal transduction, growth, differentiation, motility and apoptosis. In vitro cellular studies and the development of new biomaterials would benefit from matrices that allow reversible modulation of the cell adhesive signals at a scale that is commensurate with individual adhesion complexes. Here, we describe the fabrication of substrates containing arrays of cracks in which cell-adhesive proteins are selectively adsorbed. The widths of the cracks (120-3,200 nm) are similar in size to individual adhesion complexes (typically 500-3,000 nm) and can be modulated by adjusting the mechanical strain applied to the substrate. Morphology of cells can be reversibly manipulated multiple times through in situ adjustment of crack widths and hence the amount of the cell-adhesive proteins accessible to the cell. These substrates provide a new tool for assessing cellular responses associated with exposure to matrix proteins.

  9. A methodological framework to assist decision-making on prioritising conflicting uses ion multi-functional environments

    NASA Astrophysics Data System (ADS)

    Esteves, L. S.; Foord, J.; Draux, H.

    2012-04-01

    A strong and evidence-based environmental legislation contributes to reduce the generalised degradation of natural and semi-natural environments. However, the wide range of coastal settings and the complexity of interactions between physical, biological and socio-economic factors prevent the development of very specific guidelines at national and regional levels. Often coastal management decisions are taken locally as local governments are better placed to engage with local community. However, they can also be more influenced by stronger local sectors and suffer from lack of expertise, experience and funding. Significant conflicts might arise between sectoral interests, especially in multi-functional coastal areas. Reaching a consensus on which function is more important is a difficult task. Here a methodological framework is suggested to support decision-making in (1) the identification of priority objectives (e.g. which function should be preserved; how much loss is acceptable etc.); (2) the selection of measurable indicators to assess environmental damage (e.g. loss of habitats, services etc.) and (3) assessment of habitat/service compensation. Amongst the initial decisions, it is necessary to (a) determine at which scales (temporal and spatial) the objectives will be defined and (b) the sensitivity of each step to conflicts between experts' opinion (what is scientifically more adequate) and local needs (what the local community expects). The framework is applied to address conflicts identified in the management of Farlington Marshes (Langstone Harbour, Portsmouth, southern England) between habitat conservation, management of flood risk and provision of recreational grounds/green areas. Langstone Harbour is a designated conservation area of national, European and international importance. The North Solent Shoreline Management Plan (2011) indicates that 'hold-the-line' is the most adequate approach to be implemented along most of Langstone Harbour's shoreline in

  10. Fatigue and Creep Crack Propagation behaviour of Alloy 617 in the Annealed and Aged Conditions

    SciTech Connect

    Julian K. Benz; Richard N. Wright

    2013-10-01

    The crack propagation behaviour of Alloy 617 was studied under various conditions. Elevated temperature fatigue and creep-fatigue crack growth experiments were conducted at 650 and 800 degrees C under constant stress intensity (triangle K) conditions and triangular or trapezoidal waveforms at various frequencies on as-received, aged, and carburized material. Environmental conditions included both laboratory air and characteristic VHTR impure helium. As-received Alloy 617 displayed an increase in the crack growth rate (da/dN) as the frequency was decreased in air which indicated a time-dependent contribution component in fatigue crack propagation. Material aged at 650°C did not display any influence on the fatigue crack growth rates nor the increasing trend of crack growth rate with decreasing frequency even though significant microstructural evolution, including y’ (Ni3Al) after short times, occurred during aging. In contrast, carburized Alloy 617 showed an increase in crack growth rates at all frequencies tested compared to the material in the standard annealed condition. Crack growth studies under quasi-constant K (i.e. creep) conditions were also completed at 650 degrees C and a stress intensity of K = 40 MPa9 (square root)m. The results indicate that crack growth is primarily intergranular and increased creep crack growth rates exist in the impure helium environment when compared to the results in laboratory air. Furthermore, the propagation rates (da/dt) continually increased for the duration of the creep crack growth either due to material aging or evolution of a crack tip creep zone. Finally, fatigue crack propagation tests at 800 degrees C on annealed Alloy 617 indicated that crack propagation rates were higher in air than impure helium at the largest frequencies and lowest stress intensities. The rates in helium, however, eventually surpass the rates in air as the frequency is reduced and the stress intensity is decreased which was not observed at 650

  11. Password Cracking Using Sony Playstations

    NASA Astrophysics Data System (ADS)

    Kleinhans, Hugo; Butts, Jonathan; Shenoi, Sujeet

    Law enforcement agencies frequently encounter encrypted digital evidence for which the cryptographic keys are unknown or unavailable. Password cracking - whether it employs brute force or sophisticated cryptanalytic techniques - requires massive computational resources. This paper evaluates the benefits of using the Sony PlayStation 3 (PS3) to crack passwords. The PS3 offers massive computational power at relatively low cost. Moreover, multiple PS3 systems can be introduced easily to expand parallel processing when additional power is needed. This paper also describes a distributed framework designed to enable law enforcement agents to crack encrypted archives and applications in an efficient and cost-effective manner.

  12. A Monitoring Method Based on FBG for Concrete Corrosion Cracking.

    PubMed

    Mao, Jianghong; Xu, Fangyuan; Gao, Qian; Liu, Shenglin; Jin, Weiliang; Xu, Yidong

    2016-07-14

    Corrosion cracking of reinforced concrete caused by chloride salt is one of the main determinants of structure durability. Monitoring the entire process of concrete corrosion cracking is critical for assessing the remaining life of the structure and determining if maintenance is needed. Fiber Bragg Grating (FBG) sensing technology is extensively developed in photoelectric monitoring technology and has been used on many projects. FBG can detect the quasi-distribution of strain and temperature under corrosive environments, and thus it is suitable for monitoring reinforced concrete cracking. According to the mechanical principle that corrosion expansion is responsible for the reinforced concrete cracking, a package design of reinforced concrete cracking sensors based on FBG was proposed and investigated in this study. The corresponding relationship between the grating wavelength and strain was calibrated by an equal strength beam test. The effectiveness of the proposed method was verified by an electrically accelerated corrosion experiment. The fiber grating sensing technology was able to track the corrosion expansion and corrosion cracking in real time and provided data to inform decision-making for the maintenance and management of the engineering structure.

  13. A Monitoring Method Based on FBG for Concrete Corrosion Cracking

    PubMed Central

    Mao, Jianghong; Xu, Fangyuan; Gao, Qian; Liu, Shenglin; Jin, Weiliang; Xu, Yidong

    2016-01-01

    Corrosion cracking of reinforced concrete caused by chloride salt is one of the main determinants of structure durability. Monitoring the entire process of concrete corrosion cracking is critical for assessing the remaining life of the structure and determining if maintenance is needed. Fiber Bragg Grating (FBG) sensing technology is extensively developed in photoelectric monitoring technology and has been used on many projects. FBG can detect the quasi-distribution of strain and temperature under corrosive environments, and thus it is suitable for monitoring reinforced concrete cracking. According to the mechanical principle that corrosion expansion is responsible for the reinforced concrete cracking, a package design of reinforced concrete cracking sensors based on FBG was proposed and investigated in this study. The corresponding relationship between the grating wavelength and strain was calibrated by an equal strength beam test. The effectiveness of the proposed method was verified by an electrically accelerated corrosion experiment. The fiber grating sensing technology was able to track the corrosion expansion and corrosion cracking in real time and provided data to inform decision-making for the maintenance and management of the engineering structure. PMID:27428972

  14. Anomolous Fatigue Crack Growth Phenomena in High-Strength Steel

    NASA Technical Reports Server (NTRS)

    Forth, Scott C.; James, Mark A.; Johnston, William M., Jr.; Newman, James C., Jr.

    2004-01-01

    The growth of a fatigue crack through a material is the result of a complex interaction between the applied loading, component geometry, three-dimensional constraint, load history, environment, material microstructure and several other factors. Previous studies have developed experimental and computational methods to relate the fatigue crack growth rate to many of the above conditions, with the intent of discovering some fundamental material response, i.e. crack growth rate as a function of something. Currently, the technical community uses the stress intensity factor solution as a simplistic means to relate fatigue crack growth rate to loading, geometry and all other variables. The stress intensity factor solution is a very simple linear-elastic representation of the continuum mechanics portion of crack growth. In this paper, the authors present fatigue crack growth rate data for two different high strength steel alloys generated using standard methods. The steels exhibit behaviour that appears unexplainable, compared to an aluminium alloy presented as a baseline for comparison, using the stress intensity factor solution.

  15. A Monitoring Method Based on FBG for Concrete Corrosion Cracking.

    PubMed

    Mao, Jianghong; Xu, Fangyuan; Gao, Qian; Liu, Shenglin; Jin, Weiliang; Xu, Yidong

    2016-01-01

    Corrosion cracking of reinforced concrete caused by chloride salt is one of the main determinants of structure durability. Monitoring the entire process of concrete corrosion cracking is critical for assessing the remaining life of the structure and determining if maintenance is needed. Fiber Bragg Grating (FBG) sensing technology is extensively developed in photoelectric monitoring technology and has been used on many projects. FBG can detect the quasi-distribution of strain and temperature under corrosive environments, and thus it is suitable for monitoring reinforced concrete cracking. According to the mechanical principle that corrosion expansion is responsible for the reinforced concrete cracking, a package design of reinforced concrete cracking sensors based on FBG was proposed and investigated in this study. The corresponding relationship between the grating wavelength and strain was calibrated by an equal strength beam test. The effectiveness of the proposed method was verified by an electrically accelerated corrosion experiment. The fiber grating sensing technology was able to track the corrosion expansion and corrosion cracking in real time and provided data to inform decision-making for the maintenance and management of the engineering structure. PMID:27428972

  16. 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.

  17. A computational algorithm for crack determination: The multiple crack case

    NASA Technical Reports Server (NTRS)

    Bryan, Kurt; Vogelius, Michael

    1992-01-01

    An algorithm for recovering a collection of linear cracks in a homogeneous electrical conductor from boundary measurements of voltages induced by specified current fluxes is developed. The technique is a variation of Newton's method and is based on taking weighted averages of the boundary data. The method also adaptively changes the applied current flux at each iteration to maintain maximum sensitivity to the estimated locations of the cracks.

  18. 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.

  19. 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.

  20. Stress intensity estimates by a computer assisted photoelastic method

    NASA Technical Reports Server (NTRS)

    Smith, C. W.

    1977-01-01

    Following an introductory history, the frozen stress photoelastic method is reviewed together with analytical and experimental aspects of cracks in photoelastic models. Analytical foundations are then presented upon which a computer assisted frozen stress photoelastic technique is based for extracting estimates of stress intensity factors from three-dimensional cracked body problems. The use of the method is demonstrated for two currently important three-dimensional crack problems.

  1. Matrix Fatigue Cracking Mechanisms of Alpha(2) TMC for Hypersonic Applications

    NASA Technical Reports Server (NTRS)

    Gabb, Timothy P.; Gayda, John

    1994-01-01

    The objective of this work was to understand matrix cracking mechanisms in a unidirectional alpha(sub 2) TMC in possible hypersonic applications. A (0)(sub 8) SCS-6/Ti-24Al-11Nb (at. percent) TMC was first subjected to a variety of simple isothermal and nonisothermal fatigue cycles to evaluate the damage mechanisms in simple conditions. A modified ascent mission cycle test was then performed to evaluate the combined effects of loading modes. This cycle mixes mechanical cycling at 150 and 483 C, sustained loads, and a slow thermal cycle to 815 C. At low cyclic stresses and strains more common in hypersonic applications, environment-assisted surface cracking limited fatigue resistance. This damage mechanism was most acute for out-of-phase nonisothermal cycles having extended cycle periods and the ascent mission cycle. A simple linear fraction damage model was employed to help understand this damage mechanism. Time-dependent environmental damage was found to strongly influence out-of-phase and mission life, with mechanical cycling damage due to the combination of external loading and CTE mismatch stresses playing a smaller role. The mechanical cycling and sustained loads in the mission cycle also had a smaller role.

  2. The effect of low energy protons on silicon solar cells with simulated coverglass cracks

    NASA Technical Reports Server (NTRS)

    Gasner, S.; Anspaugh, B.; Francis, R.; Marvin, D.

    1991-01-01

    Results of a series of low-energy proton (LEP) tests are presented. The purpose of the tests was to investigate the effect of low-energy protons on the electrical performance of solar cells with simulated cracked covers. The results of the tests were then related to the space environment. A matrix of LEP tests was set up using solar cells with simulated cracks to determine the effect on electrical performance as a function of fluence, energy, crack width, coverglass adhesive shielding, crack location, and solar cell size. The results of the test were, for the most part, logical, and consistent.

  3. 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.

  4. The Use of Atomic Force Microscopy to Study Crack Tips in Glass

    NASA Astrophysics Data System (ADS)

    Wiederhorn, Sheldon M.; Guin, Jean-Pierre; Fett, Theo

    2011-02-01

    This article presents a review of the application of atomic force microscopy (AFM) to crack-tip corrosion during subcritical crack growth in glass. The two principal experimental techniques used in this type of study are (1) the direct observation of crack motion by scanning the tip of a crack during crack growth and (2) the examination of fracture surfaces once the specimen has been fractured in two. The first technique has been used to demonstrate and quantify water condensation at crack tips during subcritical crack growth and is particularly useful at low crack velocities. The second technique has been used to quantify the crack-tip corrosion process and the shape of the crack tip during crack growth. In this article, we discuss experimental results showing that the environment that develops at the tips of freshly fractured glass surfaces in soda lime glass can corrode the glass surfaces near the crack tip. Soda lime silicate glass contains mobile alkali ions that will exchange with hydronium ions in solution at the crack tip, forming a highly basic solution that is corrosive to glass. Experimental evidence for such corrosion has been obtained by the atomic force microscope, which demonstrates a displacement of the two fracture surfaces near the crack tip that can be as much as 20 nm, depending on how long the crack is held open at the fatigue limit. Despite the corrosion and displacement of the crack surfaces, the crack tip itself appears to remain sharp, suggesting that the fatigue limit in soda lime silicate glass is not due to crack-tip blunting. Most likely, the fatigue limit is a consequence of ion exchange at the crack tip, in which hydronium ions in the crack-tip solution exchange with sodium ions in the glass. As hydronium ions are larger than sodium ions, this exchange process leaves a compressive stress within the fresh fracture surface of the glass that resists crack motion and results in a stress-corrosion fatigue limit, as first proposed by Bunker

  5. Peridynamic model for fatigue cracking.

    SciTech Connect

    Silling, Stewart Andrew; Abe Askari

    2014-10-01

    The peridynamic theory is an extension of traditional solid mechanics in which the field equations can be applied on discontinuities, such as growing cracks. This paper proposes a bond damage model within peridynamics to treat the nucleation and growth of cracks due to cyclic loading. Bond damage occurs according to the evolution of a variable called the "remaining life" of each bond that changes over time according to the cyclic strain in the bond. It is shown that the model reproduces the main features of S-N data for typical materials and also reproduces the Paris law for fatigue crack growth. Extensions of the model account for the effects of loading spectrum, fatigue limit, and variable load ratio. A three-dimensional example illustrates the nucleation and growth of a helical fatigue crack in the torsion of an aluminum alloy rod.

  6. 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.

  7. 21 CFR 137.190 - Cracked wheat.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 2 2012-04-01 2012-04-01 false Cracked wheat. 137.190 Section 137.190 Food and... Related Products § 137.190 Cracked wheat. Cracked wheat is the food prepared by so cracking or cutting into angular fragments cleaned wheat other than durum wheat and red durum wheat that, when tested...

  8. 21 CFR 137.190 - Cracked wheat.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 2 2014-04-01 2014-04-01 false Cracked wheat. 137.190 Section 137.190 Food and... Related Products § 137.190 Cracked wheat. Cracked wheat is the food prepared by so cracking or cutting into angular fragments cleaned wheat other than durum wheat and red durum wheat that, when tested...

  9. 21 CFR 137.190 - Cracked wheat.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 2 2011-04-01 2011-04-01 false Cracked wheat. 137.190 Section 137.190 Food and... Related Products § 137.190 Cracked wheat. Cracked wheat is the food prepared by so cracking or cutting into angular fragments cleaned wheat other than durum wheat and red durum wheat that, when tested...

  10. 21 CFR 137.190 - Cracked wheat.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 2 2013-04-01 2013-04-01 false Cracked wheat. 137.190 Section 137.190 Food and... Related Products § 137.190 Cracked wheat. Cracked wheat is the food prepared by so cracking or cutting into angular fragments cleaned wheat other than durum wheat and red durum wheat that, when tested...

  11. 21 CFR 137.190 - Cracked wheat.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 2 2010-04-01 2010-04-01 false Cracked wheat. 137.190 Section 137.190 Food and... Related Products § 137.190 Cracked wheat. Cracked wheat is the food prepared by so cracking or cutting into angular fragments cleaned wheat other than durum wheat and red durum wheat that, when tested...

  12. Cocaine/Crack: The Big Lie.

    ERIC Educational Resources Information Center

    National Inst. on Drug Abuse (DHHS/PHS), Rockville, MD.

    This pamphlet focuses on cocaine and crack use and the addictive nature of cocaine/crack. It contains a set of 21 questions about crack and cocaine, each accompanied by a clear and complete response. Interspersed throughout the booklet are photographs and quotes from former cocaine or crack users/addicts. Questions and answers focus on what…

  13. Causes and solutions for cracking of coextruded and weld overlay floor tubes in black liquor recovery boilers

    SciTech Connect

    Keiser, J.R.; Taljat, B.; Wang, X.L.

    1998-09-01

    Cracking of coextruded, black liquor recovery boiler floor tubes is both a safety and an economic issue to mill operators. In an effort to determine the cause of the cracking and to identify a solution, extensive studies, described in this and three accompanying papers, are being conducted. In this paper, results of studies to characterize both the cracking and the chemical and thermal environment are reported. Based on the results described in this series of papers, a possible mechanism is presented and means to lessen the likelihood of cracking or to totally avoid cracking of floor tubes are offered.

  14. Cracking behavior of cored structures

    SciTech Connect

    Wahid, A.; Olson, D.L.; Matlock, D.K. . Center for Welding and Joining Research); Kelly, T.J. )

    1991-01-01

    The effects of compositional gradients, are considered based on a thermodynamic analysis, referred to as the Cahn-Hillard analysis, which describes the degree to which a local surface energy is modified by the presence of a composition gradient. The analysis predicts that both ductile and brittle fracture mechanisms are enhanced by the presence of a composition gradient. Data on stress corrosion cracking and fatigue crack growth in selected FCC alloys are used to illustrate the significance of microsegregation on mechanical properties.

  15. Cracking behavior of cored structures

    SciTech Connect

    Wahid, A.; Olson, D.L.; Matlock, D.K.; Kelly, T.J.

    1991-12-31

    The effects of compositional gradients, are considered based on a thermodynamic analysis, referred to as the Cahn-Hillard analysis, which describes the degree to which a local surface energy is modified by the presence of a composition gradient. The analysis predicts that both ductile and brittle fracture mechanisms are enhanced by the presence of a composition gradient. Data on stress corrosion cracking and fatigue crack growth in selected FCC alloys are used to illustrate the significance of microsegregation on mechanical properties.

  16. Slow crack growth in glass in combined mode I and mode II loading

    NASA Technical Reports Server (NTRS)

    Shetty, D. K.; Rosenfield, A. R.

    1991-01-01

    Slow crack growth in soda-lime glass under combined mode I and mode II loading was investigated in precracked disk specimens in which pure mode I, pure mode II, and various combinations of mode I and mode II were achieved by loading in diametral compression at selected angles with respect to symmetric radial cracks. It is shown that slow crack growth under these conditions can be described by a simple exponential relationship with elastic strain energy release rate as the effective crack-driving force parameter. It is possible to interpret this equation in terms of theoretical models that treat subcritical crack growth as a thermally activated bond-rupture process with an activation energy dependent on the environment, and the elastic energy release rate as the crack-driving force parameter.

  17. Status Report on Studies of Recovery Boiler Composite Floor Tube Cracking

    SciTech Connect

    Eng, P.; Frederick, L.A.; Hoffmann, C.M.; Keiser, J.R.; Mahmood, J.; Maziasz, P.J.; Prescott, R.; Sarma, G.B.; Singbeil, D.L.; Singh, P.M.; Swindeman, R.W.; Wang, X.-L.

    1999-09-12

    Cracking of the stainless steel layer of co-extruded 304L stainless steel/SA210 Gd A 1 carbon steel black liquor recovery boiler floor tubes has been identified as one of the most serious material problems in the pulp and paper industry. A DOE-funded study was initiated in 1995 with the goal of determining the cause of and possible solutions to this cracking problem. These studies have characterized tube cracking as well as the chemical and thermal environment and stress state of floor tubes. Investigations of possible cracking mechanisms indicate that stress corrosion cracking rather than thermal fatigue is a more likely cause of crack initiation. The cracking mechanism appears to require the presence of hydrated sodium sulfide and is most likely active during shut-downs and/or start-ups. Based on these results and operating experience, certain alloys appear to be more resistant than others to cracking in the floor environment, and certain operating practices appear to significantly lessen the likelihood of cracking. This report is the latest in a series of progress reports presented on this project.

  18. A Cross-Cultural Study of the Effect of a Graph-Oriented Computer-Assisted Project-Based Learning Environment on Middle School Students' Science Knowledge and Argumentation Skills

    ERIC Educational Resources Information Center

    Hsu, P.-S.; Van Dyke, M.; Chen, Y.; Smith, T. J.

    2016-01-01

    The purpose of this mixed-methods study was to explore how seventh graders in a suburban school in the United States and sixth graders in an urban school in Taiwan developed argumentation skills and science knowledge in a project-based learning environment that incorporated a graph-oriented, computer-assisted application (GOCAA). A total of 42…

  19. Initiation and propagation of small corner cracks

    NASA Technical Reports Server (NTRS)

    Ellyin, Ferdnand; Kujawski, Daniel; Craig, David F.

    1994-01-01

    The behaviour of small corner cracks, inclined or perpendicular to loading direction, is presented. There are two aspects to this investigation: initiation of small cracks and monitoring their subsequent growth. An initial pre-cracking procedure under cyclic compression is adopted to minimize the residual damage at the tip of the growing and self-arresting crack under cyclic compression. A final fatigue specimen, cut from the larger pre-cracked specimen, has two corner flaws. The opening load of corner flaw is monitored using a novel strain gauge approach. The behaviour of small corner cracks is described in terms of growth rate relative to the size of the crack and its shape.

  20. Mitigation of Crack Damage in Metallic Materials

    NASA Technical Reports Server (NTRS)

    Leser, Patrick E.; Newman, John A.; Smith, Stephen W.; Leser, William P.; Wincheski, Russell A.; Wallace, Terryl A.; Glaessgen, Edward H.; Piascik, Robert S.

    2014-01-01

    A system designed to mitigate or heal crack damage in metallic materials has been developed where the protected material or component is coated with a low-melting temperature film. After a crack is formed, the material is heated, melting the film which then infiltrates the crack opening through capillary action. Upon solidification, the healing material inhibits further crack damage in two ways. While the crack healing material is intact, it acts like an adhesive that bonds or bridges the crack faces together. After fatigue loading damages, the healing material in the crack mouth inhibits further crack growth by creating artificially-high crack closure levels. Mechanical test data show that this method sucessfully arrests or retards crack growth in laboratory specimens.

  1. Cracks in Utopia

    NASA Technical Reports Server (NTRS)

    1999-01-01

    Many of the craters found on the northern plains of Mars have been partly filled or buried by some material (possibly sediment). The Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image presented here (MOC2-136b, above left) shows a high-resolution view of a tiny portion of the floor of one of these northern plains craters. The crater, located in Utopia Planitia at 44oN, 258oW, is shown on the right (MOC2-136a)with a small white box to indicate the location of the MOC image. The MOC image reveals that the material covering the floor of this crater is cracked and pitted. The origin and source of material that has been deposited in this crater is unknown.

    The MOC image was acquired in June 1999 and covers an area only 1.1 kilometers (0.7 miles) wide at a resolution of 1.8 meters (6 feet) per pixel. The context picture is a mosaic of Viking 2 orbiter images 010B53 and 010B55, taken in 1976. Both images are illuminated from the left. Malin Space Science Systems and the California Institute of Technology built the MOC using spare hardware from the Mars Observer mission. MSSS operates the camera from its facilities in San Diego, CA. The Jet Propulsion Laboratory's Mars Surveyor Operations Project operates the Mars Global Surveyor spacecraft with its industrial partner, Lockheed Martin Astronautics, from facilities in Pasadena, CA and Denver, CO.

  2. A physiological, rather than a superovulated, post-implantation environment can attenuate the compromising effect of assisted reproductive techniques on gene expression in developing mice embryos.

    PubMed

    Bonakdar, E; Edriss, M A; Bakhtari, A; Jafarpour, F; Asgari, V; Hosseini, S M; Boroujeni, N Sadeghi; Hajian, M; Rahmani, H R; Nasr-Esfahani, M H

    2015-03-01

    Assisted reproductive techniques (ARTs) may perturb the pre-/peri-conception microenvironments, which subsequently threaten the health of offspring. This study aimed to investigate the effects of superovulation, vitrification, in vitro culture, and embryo transfer on the expression of epigenetic modulators, imprinted genes, and pluripotency markers in expanded blastocysts and Day-9.5 (D9.5) concepti. Results revealed that 53.4% (8/15) and 86.7% (13/15) of genes in the fetus and placenta, respectively, have similar patterns of transcription in all D9.5 concepti, despite the perturbed mRNA expression observed at the blastocyst stage for each embryo-production technique. These observations indicate a counterbalancing of the abnormal expression pattern analyzed at the blastocyst stage during post-implantation development, particularly when the uterus of a naturally synchronized foster mother is employed. Superovulation resulted in the most abnormal expression patterns compared to other treatment groups, although these same blastocysts were able to develop in a synchronized uterus. Thus, superovulation creates a hormonal environment that negatively affected gene expression and impairs fetal growth more adversely during post-implantation development than other ART protocols, such as in vitro culture, vitrification, or embryo transfer-although each did contribute negatively to the implantation and development process. Together, these results may have implications for treating infertility in humans. PMID:25728573

  3. Formation and interpretation of dilatant echelon cracks.

    USGS Publications Warehouse

    Pollard, D.D.; Segall, P.; Delaney, P.T.

    1982-01-01

    The relative displacements of the walls of many veins, joints, and dikes demonstrate that these structures are dilatant cracks. We infer that dilatant cracks propagate in a principal stress plane, normal to the maximum tensile or least compressive stress. Arrays of echelon crack segments appear to emerge from the peripheries of some dilatant cracks. Breakdown of a parent crack into an echelon array may be initiated by a spatial or temporal rotation of the remote principal stresses about an axis parallel to the crack propagation direction. Near the parent-crack tip, a rotation of the local principal stresses is induced in the same sense, but not necessarily through the same angle. Incipient echelon cracks form at the parent-crack tip normal to the local maximum tensile stress. Further longitudinal growth along surfaces that twist about axes parallel to the propagation direction realigns each echelon crack into a remote principal stress plane. The walls of these twisted cracks may be idealized as helicoidal surfaces. An array of helicoidal cracks sweeps out less surface area than one parent crack twisting through the same angle. Thus, many echelon cracks grow from a single parent because the work done in creating the array, as measured by its surface area decreases as the number of cracks increases. -from Authors

  4. Coalescence, Cracking, and Crack Healing in Drying Dispersion Droplets.

    PubMed

    van der Kooij, Hanne M; de Kool, Marleen; van der Gucht, Jasper; Sprakel, Joris

    2015-04-21

    The formation of a uniform film from a polymer dispersion is a complex phenomenon involving the interplay of many processes: evaporation and resulting fluid flows through confined geometries, particle packing and deformation, coalescence, and cracking. Understanding this multidimensional problem has proven challenging, precluding a clear understanding of film formation to date. This is especially true for drying dispersion droplets, where the particular geometry introduces additional complexity such as lateral flow toward the droplet periphery. We study the drying of these droplets using a simplified approach in which we systematically vary a single parameter: the glass transition temperature (Tg) of the polymer. We combine optical with scanning electron microscopy to elucidate these processes from the macroscopic down to the single-particle level, both qualitatively and quantitatively, over times ranging from seconds to days. Our results indicate that the polymer Tg has a marked influence on the time evolution of particle deformation and coalescence, giving rise to a distinct and sudden cracking transition. Moreover, in cracked droplets it affects the frequently overlooked time scale of crack healing, giving rise to a second transition from self-healing to permanently cracked droplets. These findings are in line with the classical Routh-Russel model for film formation yet extend its scope from particle-level dynamics to long-range polymer flow.

  5. Observation of Intralaminar Cracking in the Edge Crack Torsion Specimen

    NASA Technical Reports Server (NTRS)

    Czabaj, Michael W.; Ratcliffe, James G.; Davidson, Barry D.

    2013-01-01

    The edge crack torsion (ECT) test is evaluated to determine its suitability for measuring fracture toughness associated with mode III delamination growth onset. A series of ECT specimens with preimplanted inserts with different lengths is tested and examined using nondestructive and destructive techniques. Ultrasonic inspection of all tested specimens reveals that delamination growth occurs at one interface ply beneath the intended midplane interface. Sectioning and optical microscopy suggest that the observed delamination growth results from coalescence of angled intralaminar matrix cracks that form and extend across the midplane plies. The relative orientation of these cracks is approximately 45 deg with respect to the midplane, suggesting their formation is caused by resolved principal tensile stresses arising due to the global mode-III shear loading. Examination of ECT specimens tested to loads below the level corresponding to delamination growth onset reveals that initiation of intralaminar cracking approximately coincides with the onset of nonlinearity in the specimen's force-displacement response. The existence of intralaminar cracking prior to delamination growth onset and the resulting delamination extension at an unintended interface render the ECT test, in its current form, unsuitable for characterization of mode III delamination growth onset. The broader implications of the mechanisms observed in this study are also discussed with respect to the current understanding of shear-driven delamination in tape-laminate composites.

  6. Fatigue reliability of cracked engineering structures

    NASA Astrophysics Data System (ADS)

    Lanning, David Bruce, Jr.

    1997-12-01

    This study investigates the reliability of engineering structures containing fatigue cracks. Stress concentrations and welded joints are probable locations for the initiation and propagation of fatigue cracks. Due to the many unknowns of loading, materials properties, crack sizes and crack shapes present at these locations, a statistics-based reliability analysis is valuable in the careful consideration of these many different random factors involved in a fatigue life analysis, several of which are expanded upon in this study. The basic problem of a crack near a stress concentration is first considered. A formulation for the aspect ratio (a/c) of a propagating semi-elliptical fatigue crack located at the toe of a welded T-joint is developed using Newman and Raju's stress intensity factor for a cracked flat plate with a weld magnification factor and compared to that of a cracked flat plate, and the reliability in terms of fatigue lifetime is calculated with the aid of Paris' crack propagation equation for membrane and bending loadings. Crack closure effects are then introduced in the consideration of short crack effects, where crack growth rates typically may exceed those found using traditional linear elastic fracture mechanics solutions for long cracks. The probability of a very small, microstructurally influenced crack growing to a size influenced by local plastic conditions is calculated utilizing the probability of a crack continuing to grow past an obstacle, such as a grain boundary. The result is then combined with the probability for failure defined using the crack closure-modified Paris equation to find an overall reliability for the structure. Last, the probability of fracture is determined when a crack front encounters regions of non-uniform toughness, such as typical in the heat affected zone of a welded joint. An expression for the effective crack lengths of the dissimilar regions is derived, and used in a weakest-link fracture model in the evaluation

  7. Distributed coaxial cable crack sensors for crack mapping in RC

    NASA Astrophysics Data System (ADS)

    Greene, Gary G.; Belarbi, Abdeldjelil; Chen, Genda; McDaniel, Ryan

    2005-05-01

    New type of distributed coaxial cable sensors for health monitoring of large-scale civil infrastructure was recently proposed and developed by the authors. This paper shows the results and performance of such sensors mounted on near surface of two flexural beams and a large scale reinforced concrete box girder that was subjected to twenty cycles of combined shear and torsion. The main objectives of this health monitoring study was to correlate the sensor's response to strain in the member, and show that magnitude of the signal's reflection coefficient is related to increases in applied load, repeated cycles, cracking, crack mapping, and yielding. The effect of multiple adjacent cracks, and signal loss was also investigated.

  8. 40 CFR 35.9050 - Assistance amount.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 1 2010-07-01 2010-07-01 false Assistance amount. 35.9050 Section 35.9050 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY GRANTS AND OTHER FEDERAL ASSISTANCE STATE AND LOCAL ASSISTANCE Financial Assistance for the National Estuary Program § 35.9050...

  9. 40 CFR 35.9050 - Assistance amount.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 1 2011-07-01 2011-07-01 false Assistance amount. 35.9050 Section 35.9050 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY GRANTS AND OTHER FEDERAL ASSISTANCE STATE AND LOCAL ASSISTANCE Financial Assistance for the National Estuary Program § 35.9050...

  10. 40 CFR 35.9050 - Assistance amount.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 1 2013-07-01 2013-07-01 false Assistance amount. 35.9050 Section 35.9050 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY GRANTS AND OTHER FEDERAL ASSISTANCE STATE AND LOCAL ASSISTANCE Financial Assistance for the National Estuary Program § 35.9050...

  11. 40 CFR 35.9050 - Assistance amount.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 1 2014-07-01 2014-07-01 false Assistance amount. 35.9050 Section 35.9050 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY GRANTS AND OTHER FEDERAL ASSISTANCE STATE AND LOCAL ASSISTANCE Financial Assistance for the National Estuary Program § 35.9050...

  12. 40 CFR 35.9050 - Assistance amount.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 1 2012-07-01 2012-07-01 false Assistance amount. 35.9050 Section 35.9050 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY GRANTS AND OTHER FEDERAL ASSISTANCE STATE AND LOCAL ASSISTANCE Financial Assistance for the National Estuary Program § 35.9050...

  13. Repeated crack healing in MAX-phase ceramics revealed by 4D in situ synchrotron X-ray tomographic microscopy

    PubMed Central

    Sloof, Willem G.; Pei, Ruizhi; McDonald, Samuel A.; Fife, Julie L.; Shen, Lu; Boatemaa, Linda; Farle, Ann-Sophie; Yan, Kun; Zhang, Xun; van der Zwaag, Sybrand; Lee, Peter D.; Withers, Philip J.

    2016-01-01

    MAX phase materials are emerging as attractive engineering materials in applications where the material is exposed to severe thermal and mechanical conditions in an oxidative environment. The Ti2AlC MAX phase possesses attractive thermomechanical properties even beyond a temperature of 1000 K. An attractive feature of this material is its capacity for the autonomous healing of cracks when operating at high temperatures. Coupling a specialized thermomechanical setup to a synchrotron X-ray tomographic microscopy endstation at the TOMCAT beamline, we captured the temporal evolution of local crack opening and healing during multiple cracking and autonomous repair cycles at a temperature of 1500 K. For the first time, the rate and position dependence of crack repair in pristine Ti2AlC material and in previously healed cracks has been quantified. Our results demonstrate that healed cracks can have sufficient mechanical integrity to make subsequent cracks form elsewhere upon reloading after healing. PMID:26972608

  14. Repeated crack healing in MAX-phase ceramics revealed by 4D in situ synchrotron X-ray tomographic microscopy.

    PubMed

    Sloof, Willem G; Pei, Ruizhi; McDonald, Samuel A; Fife, Julie L; Shen, Lu; Boatemaa, Linda; Farle, Ann-Sophie; Yan, Kun; Zhang, Xun; van der Zwaag, Sybrand; Lee, Peter D; Withers, Philip J

    2016-01-01

    MAX phase materials are emerging as attractive engineering materials in applications where the material is exposed to severe thermal and mechanical conditions in an oxidative environment. The Ti2AlC MAX phase possesses attractive thermomechanical properties even beyond a temperature of 1000 K. An attractive feature of this material is its capacity for the autonomous healing of cracks when operating at high temperatures. Coupling a specialized thermomechanical setup to a synchrotron X-ray tomographic microscopy endstation at the TOMCAT beamline, we captured the temporal evolution of local crack opening and healing during multiple cracking and autonomous repair cycles at a temperature of 1500 K. For the first time, the rate and position dependence of crack repair in pristine Ti2AlC material and in previously healed cracks has been quantified. Our results demonstrate that healed cracks can have sufficient mechanical integrity to make subsequent cracks form elsewhere upon reloading after healing. PMID:26972608

  15. Humidity Testing of PME and BME Ceramic Capacitors with Cracks

    NASA Technical Reports Server (NTRS)

    Teverovsky, Alexander A.; Herzberger, Jaemi

    2014-01-01

    Cracks in ceramic capacitors are one of the major causes of failures during operation of electronic systems. Humidity testing has been successfully used for many years to verify the absence of cracks and assure quality of military grade capacitors. Traditionally, only precious metal electrode (PME) capacitors were used in high reliability applications and the existing requirements for humidity testing were developed for this type of parts. With the advance of base metal electrode (BME) capacitors, there is a need for assessment of the applicability of the existing techniques for the new technology capacitors. In this work, variety of different PME and BME capacitors with introduced cracks were tested in humid environments at different voltages and temperatures. Analysis of the test results indicates differences in the behavior and failure mechanisms for BME and PME capacitors and the need for different testing conditions.

  16. Rotor acoustic monitoring system (RAMS): a fatigue crack detection system

    NASA Astrophysics Data System (ADS)

    Schoess, Jeffrey N.

    1996-05-01

    The Rotor Acoustic Monitoring System (RAMS) is an embedded structural health monitoring system to demonstrate the ability to detect rotor head fatigue cracks and provide early warning of propagating fatigue cracks in rotor components of Navy helicopters. The concept definition effort was performed to assess the feasibility of detecting rotor head fatigue cracks using bulk- wave wide-bandwidth acoustic emission technology. A wireless piezo-based transducer system is being designed to capture rotor fatigue data in real time and perform acoustic emission (AE) event detection, feature extraction, and classification. A flight test effort will be performed to characterize rotor acoustic background noise and flight environment characteristics. The long- term payoff of the RAMS technology includes structural integrity verification and leak detection for large industrial tanks, and nuclear plant cooling towers could be performed using the RAMS AE technology. A summary of the RAMS concept, bench-level AE fatigue testing, and results are presented.

  17. 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.

  18. Star-Shaped Crack Pattern of Broken Windows

    NASA Astrophysics Data System (ADS)

    Vandenberghe, Nicolas; Vermorel, Romain; Villermaux, Emmanuel

    2013-04-01

    Broken thin brittle plates like windows and windshields are ubiquitous in our environment. When impacted locally, they typically present a pattern of cracks extending radially outward from the impact point. We study the variation of the pattern of cracks by performing controlled transverse impacts on brittle plates over a broad range of impact speed, plate thickness, and material properties, and we establish from experiments a global scaling law for the number of radial cracks incorporating all these parameters. A model based on Griffith’s theory of fracture combining bending elastic energy and fracture energy accounts for our observations. These findings indicate how the postmortem shape of broken samples are related to material properties and impact parameters, a procedure relevant to forensic science, archaeology, or astrophysics.

  19. 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.

  20. High-Resolution Analytical Electron Microscopy Characterization of Corrosion and Cracking at Buried Interfaces

    SciTech Connect

    Bruemmer, Stephen M.; Thomas, Larry E.

    2001-07-01

    Recent results are presented demonstrating the application of cross-sectional analytical transmission electron microscopy (ATEM) to corrosion and cracking in high-temperature water environments. Microstructural, chemical and crystallographic characterization of buried interfaces at near-atomic resolutions is shown to reveal evidence for unexpected local environments, corrosion reactions and material transformations. Information obtained by a wide variety of high-resolution imaging and analysis methods indicates the processes occurring during crack advance and provides insights into the mechanisms controlling environmental degradation.

  1. Fatigue Crack Growth Rate of Inconel 718 Sheet at Cryogenic Temperatures

    NASA Technical Reports Server (NTRS)

    Wells, Douglas; Wright, Jonathan; Hastings, Keith

    2005-01-01

    Inconel 718 sheet material was tested to determine fatigue crack growth rate (FCGR) at cryogenic conditions representative of a liquid hydrogen (LH2) environment at -423 degree F. Tests utilized M(T) and ESE(T) specimen geometries and environments were either cold gaseous helium or submersion in LH2. The test results support a significant improvement in the fatigue crack growth threshold at -423 degree F compared to -320 degree F or 70 degree F.

  2. Getter materials for cracking ammonia

    DOEpatents

    Boffito, Claudio; Baker, John D.

    1999-11-02

    A method is provided for cracking ammonia to produce hydrogen. The method includes the steps of passing ammonia over an ammonia-cracking catalyst which is an alloy including (1) alloys having the general formula Zr.sub.1-x Ti.sub.x M.sub.1 M.sub.2, wherein M.sub.1 and M.sub.2 are selected independently from the group consisting of Cr, Mn, Fe, Co, and Ni, and x is between about 0.0 and about 1.0 inclusive; and between about 20% and about 50% Al by weight. In another aspect, the method of the invention is used to provide methods for operating hydrogen-fueled internal combustion engines and hydrogen fuel cells. In still another aspect, the present invention provides a hydrogen-fueled internal combustion engine and a hydrogen fuel cell including the above-described ammonia-cracking catalyst.

  3. In situ measurements of stress-corrosion crack growth using laser ultrasonics

    NASA Astrophysics Data System (ADS)

    Kacmar, Chris; Blackshire, James L.

    2003-07-01

    A detailed microscopic characterization of stress-corrosion cracking (SCC) processes has been conducted for electro-chemically pitted AA 2024-T3 aluminum dogbone specimens in a high-cycle fatigue environment. The measurements were done in-situ using scanning laser ultrasonic detection of Rayleigh waves propagating along the material surface. Detailed microscopic NDE evaluations of crack extent and position, crack growth rates, and local crack depth were made based on near-field ultrasonic scattering signatures. A variety of electro-chemically generated corrosion pits were studied, where variations of pit depth, pitting surface area, and pit volume loss were correlated to fatigue life, crack initiation, and crack growth rates. The measurement technique provided an advanced crack 'imaging' capability that proved to be a very useful NDE tool for the micro-characterization of crack growth processes, and provided a wealth of information regarding the micro-features of the cracks whcih are currently not available with any other advanced NDE technique.

  4. Gaseous hydrogen-induced cracking of Ti-5Al-2.5Sn.

    NASA Technical Reports Server (NTRS)

    Williams, D. P.; Nelson, H. G.

    1972-01-01

    Study of the kinetics of hydrogen-induced cracking in the Ti-5Al-2.5Sn titanium alloy, which has a structure of acicular alpha platelets in a beta matrix. The crack-growth rate at low stress-intensity levels was found to be exponentially dependent on stress intensity but essentially independent of temperature. The crack-growth rate at intermediate stress-intensity levels was found to be independent of stress intensity but dependent on temperature in such a way that crack-growth rate was controlled by a thermally activated mechanism having an activation energy of 5500 cal/mole and varied as the square root of the hydrogen pressure. The crack-growth rate at stress-intensity levels very near the fracture toughness is presumed to be independent of environment. The results are interpreted to suggest that crack growth at high stress intensities is controlled by normal, bulk failure mechanisms such as void coalescence and the like. At intermediate stress-intensity levels the transport of hydrogen to some interaction site along the alpha-beta boundary is the rate-controlling mechanism. The crack-growth behavior at low stress intensities suggests that the hydrogen interacts at this site to produce a strain-induced hydride which, in turn, induces crack growth by restricting plastic flow at the crack tip.

  5. Controlling Chaos: The Perceptions of Long-Term Crack Cocaine Users in Vancouver, British Columbia, Canada

    PubMed Central

    Kuo, Margot; Bungay, Vicky; Buxton, Jane A.

    2013-01-01

    People who smoke crack cocaine are described as chaotic and more likely to engage in risky sex, polysubstance use and contract infectious diseases. However, little is known about how individuals perceive smoking crack as compared to other forms of cocaine use, especially injection. We explored the lived experience of people who smoke crack cocaine. Six gender-specific focus groups (n = 31) of individuals who currently smoke crack in Vancouver, Canada, were conducted using a semi-structured interview guide. Focus groups were transcribed and analyzed by constant comparative methodology. We applied Rhodes' risk environment to the phenomenological understanding that individuals have regarding how crack has affected their lives. Subjects reported that smoking rather than injecting cocaine allows them to begin “controlling chaos” in their lives. Controlling chaos was self-defined using nontraditional measures such as the ability to maintain day-to-day commitments and housing stability. The phenomenological lens of smoking crack instead of injecting cocaine “to control chaos” contributes a novel perspective to our understanding of the crack-smoking population. This study examines narratives which add to prior reports of the association of crack smoking and increased chaos and suggests that, for some, inhaled crack may represent efforts towards self-directed harm reduction. PMID:24826370

  6. Crack Development in Cross-Ply Laminates Under Uniaxial Tension

    NASA Technical Reports Server (NTRS)

    Gyekenyesi, Andrew L.

    1996-01-01

    This study addresses matrix-dominated failures in carbon fiber/polymer matrix composite laminates in a cross-ply lay-up. The events of interest are interlaminar fracture in the form of transverse cracks in the 90' plies and longitudinal splitting in the 0 deg plies and interlaminar fracture in the form of 0/90 delamination. These events were observed using various nondestructive evaluation (NDE) techniques during static tensile tests. Acoustic emission (AE) x radiography, and edge view microscopy were the principal ones utilized in a real-time environment. A comparison of the NDE results with an analytical model based on the classical linear fracture mechanics concept of strain energy release rate as a criterion for crack growth was performed. The virtual crack closure theory was incorporated with a finite element model to generate strain energy release rate curves for the analytical case. Celion carbon fiber/polyimide matrix (G30-500/PMR-15) was the material tested with cross-ply lay-ups of (0(2)/90(6))s and (0(4)/90(4))s. The test specimens contained thermally induced cracks caused by the high-temperature processing. The analytical model was updated to compensate for the initial damage and to study further accumulation by taking into account the crack interactions. By correlating the experimental and analytical data, the critical energy release rates were found for the observable events of interest.

  7. Near-Neutral pH SCC Crack Initiation Studies

    NASA Astrophysics Data System (ADS)

    Hiebert, John

    4-Point bend studies on X-52 linepipe steel with ''natural'' surfaces (sigmamax = 95% SMYS, f = 0.001 Hz, R = 0.6) in synthetic soil solutions indicate that crack initiation and transgranular crack formation occurs more readily in C2 solutions than in C4 solutions. This increase is associated with solution compositions that increase general corrosion rates and that reduce the precipitation of carbonates. When it is assumed that relative differences in bulk solution properties are manifested at the crack tip, then these differences may promote a more favourable environment for crack tip dissolution, ion transport, and microplastic deformation. Although the results are not definitive, in these studies the development of longer and transgranular cracks appear to be associated more with differences in solution composition than with differences in surface finish. Increased corrosion and hydrogen permeation rates are associated with increased proton, carbonic acid, and bicarbonate ion concentrations and not explicitly with lower pH. Calculations show, at open circuit corrosion conditions, that FeCO3 precipitation can limit pH increases.

  8. Nondestructive Crack Detection in a Fuel System Component

    NASA Technical Reports Server (NTRS)

    Koshti, Ajay; Wincheski, Russell; Prosser, William; Russell, Richard; Devries, Robert; Engel, James; Ruffino, Norman

    2010-01-01

    The paper discusses development of various NDE techniques to detect cracks in A40 steel poppets used in a valve of the fuel system of the Space Shuttle Orbiter. The valve assembly experiences a severe high cycle fatigue environment during its operation. Cracks were discovered at the radius of the poppet flange. Experience shows that very small cracks or material anomalies do not cause failure in a single operation event. While the design is being modified to eliminate the issue, NDE has been used to screen the poppets for cracks before every use. Several surface flaw detection techniques were considered and a few NDE techniques were developed to provide NDE screening for the flaw detection. The primary method used was the eddy current testing. In the eddy current technique, the X-Y channel test data from the eddy current instrument was recorded as computer files. A Matlab data review and plotting application was developed to analyze the data files. The Matlab application provides much higher resolution than the eddy current instrument that was used to acquire the data. Other techniques that were used included ultrasonic surface wave and magnetic particle testing. A probability of detection (POD) study was undertaken to determine the 90/95 size for the eddy current technique. This study used specimens with same geometry and material as the poppet. Fatigue cracks were grown in these specimens. Information on results of the NDE techniques and results of the POD study are provided.

  9. Three dimensional observations and modelling of intergranular stress corrosion cracking in austenitic stainless steel

    NASA Astrophysics Data System (ADS)

    Marrow, T. J.; Babout, L.; Jivkov, A. P.; Wood, P.; Engelberg, D.; Stevens, N.; Withers, P. J.; Newman, R. C.

    2006-06-01

    Stress corrosion cracking is a life-limiting factor in many components of nuclear power plant in which failure of structural components presents a substantial hazard to both safety and economic performance. Uncertainties in the kinetics of short crack behaviour can have a strong influence on lifetime prediction, and arise due both to the complexity of the underlying mechanisms and to the difficulties of making experimental observations. This paper reports on an on-going research programme into the dynamics and morphology of intergranular stress corrosion cracking in austenitic stainless steels in simulated light water environments, which makes use of recent advances in high resolution X-ray microtomography. In particular in situ, three dimensional X-ray tomographic images of intergranular stress corrosion crack nucleation and growth in sensitised austenitic stainless steel provide evidence for the development of crack bridging ligaments, caused by the resistance of non-sensitised special grain boundaries. In parallel a simple grain bridging model, introduced to quantify the effect of crack bridging on crack development, has been assessed for thermo-mechanically processed microstructures via statically loaded room temperature simulant solution tests and as well as high temperature/pressure autoclave studies. Thermo-mechanical treatments have been used to modify the grain size, grain boundary character and triple junction distributions, with a consequent effect on crack behaviour. Preliminary three-dimensional finite element models of intergranular crack propagation have been developed, with the aim of investigating the development of crack bridging and its effects on crack propagation and crack coalescence.

  10. Modified Mode-I Cracked Sandwich Beam (CSB) Fracture Test

    NASA Technical Reports Server (NTRS)

    Smith, S. A.; Shivakumar, K. N.

    2001-01-01

    Five composite sandwich panels were fabricated using vacuum assisted resin transfer molding (VARTM). Four of these panels had E-glass/vinylester facesheets and one had carbon/epoxy facesheets. The sandwich panels had different density PVC foam cores. The four E-glass panels had core densities of 80, 100, 130, 200 kg/cu m. The sandwich with carbon/epoxy 3 facesheets had a core with density of 100 kg/cu m. Fracture tests were conducted using a modified Cracked Sandwich Beam (CSB) test configuration. Load displacement curves were obtained for loading and unloading of the specimens during crack growth. Various increments of crack growth were monitored. Critical Strain Energy Release Rates (SERR) were determined from the tests using the area method. The critical values of SERR can be considered the fracture toughness of the sandwich material. The fracture toughness ranged 367 J/sq m to 1350 J/sq m over the range of core densities. These results are compared to the Mode-I fracture toughness of the PVC foam core materials and values obtained for foam-cored sandwiches using the TSD specimen. Finite-element analyses (FEA) were performed for the test configuration and Strain Energy Release Rates were calculated using the Virtual Crack Closure Technique (VCCT). The SERR values determined from the FEA were scaled to the fracture loads, or critical loads, obtained from the modified CSB tests. These critical loads were in close agreement with the test values.

  11. Subcritical crack growth under mode I, II, and III loading for Coconino sandstone

    NASA Astrophysics Data System (ADS)

    Ko, Tae Young

    In systems subjected to long-term loading, subcritical crack growth is the principal mechanism causing the time-dependent deformation and failure of rocks. Subcritical crack growth is environmentally-assisted crack growth, which can allow cracks to grow over a long period of time at stresses far smaller than their failure strength and at tectonic strain rates. The characteristics of subcritical crack growth can be described by a relationship between the stress intensity factor and the crack velocity. This study presents the results of studies conducted to validate the constant stress-rate test for determining subcritical crack growth parameters in Coconino sandstone, compared with the conventional testing method, the double torsion test. The results of the constant stress-rate test are in good agreement with the results of double torsion test. More importantly, the stress-rate tests can determine the parameter A with a much smaller standard deviation than the double torsion test. Thus the constant stress-rate test seems to be both a valid and preferred test method for determining the subcritical crack growth parameters in rocks. We investigated statistical aspects of the constant stress-rate test. The effects of the number of tests conducted on the subcritical crack growth parameters were examined and minimum specimen numbers were determined. The mean and standard deviation of the subcritical crack growth parameters were obtained by randomly selecting subsets from the original strength data. In addition, the distribution form of the subcritical crack growth parameters and the relation between the parameter n and A were determined. We extended the constant stress-rate test technique to modes II and III subcritical crack growth in rocks. The experimental results of the modes I, II and III tests show that the values of the subcritical crack growth parameters are similar to each other. The subcritical crack growth parameter n value for Coconino sandstone has the range

  12. Slow Crack Growth of Germanium

    NASA Technical Reports Server (NTRS)

    Salem, Jon

    2016-01-01

    The fracture toughness and slow crack growth parameters of germanium supplied as single crystal beams and coarse grain disks were measured. Although germanium is anisotropic (A=1.7), it is not as anisotropic as SiC, NiAl, or Cu, as evidence by consistent fracture toughness on the 100, 110, and 111 planes. Germanium does not exhibit significant slow crack growth in distilled water. (n=100). Practical values for engineering design are a fracture toughness of 0.7 MPam and a Weibull modulus of m=6+/-2. For well ground and reasonable handled coupons, fracture strength should be greater than 30 MPa.

  13. Nonlinear structural crack growth monitoring

    DOEpatents

    Welch, Donald E.; Hively, Lee M.; Holdaway, Ray F.

    2002-01-01

    A method and apparatus are provided for the detection, through nonlinear manipulation of data, of an indicator of imminent failure due to crack growth in structural elements. The method is a process of determining energy consumption due to crack growth and correlating the energy consumption with physical phenomena indicative of a failure event. The apparatus includes sensors for sensing physical data factors, processors or the like for computing a relationship between the physical data factors and phenomena indicative of the failure event, and apparatus for providing notification of the characteristics and extent of such phenomena.

  14. Crack growth resistance in nuclear graphites

    NASA Astrophysics Data System (ADS)

    Ouagne, Pierre; Neighbour, Gareth B.; McEnaney, Brian

    2002-05-01

    Crack growth resistance curves for the non-linear fracture parameters KR, JR and R were measured for unirradiated PGA and IM1-24 graphites that are used as moderators in British Magnox and AGR nuclear reactors respectively. All the curves show an initial rising part, followed by a plateau region where the measured parameter is independent of crack length. JR and R decreased at large crack lengths. The initial rising curves were attributed to development of crack bridges in the wake of the crack front, while, in the plateau region, the crack bridging zone and the frontal process zone, ahead of the crack tip, reached steady state values. The decreases at large crack lengths were attributed to interaction of the frontal zone with the specimen end face. Microscopical evidence for graphite fragments acting as crack bridges showed that they were much smaller than filler particles, indicating that the graphite fragments are broken down during crack propagation. There was also evidence for friction points in the crack wake zone and shear cracking of some larger fragments. Inspection of KR curves showed that crack bridging contributed ~0.4 MPa m0.5 to the fracture toughness of the graphites. An analysis of JR and R curves showed that the development of the crack bridging zone in the rising part of the curves contributed ~20% to the total work of fracture. Energies absorbed during development of crack bridges and steady state crack propagation were greater for PGA than for IM1-24 graphite. These differences reflect the greater extent of irreversible processes occurring during cracking in the coarser microtexture of PGA graphite.

  15. Stress-Assisted Corrosion in Boiler Tubes

    SciTech Connect

    Preet M Singh; Steven J Pawel

    2006-05-27

    A number of industrial boilers, including in the pulp and paper industry, needed to replace their lower furnace tubes or decommission many recovery boilers due to stress-assisted corrosion (SAC) on the waterside of boiler tubes. More than half of the power and recovery boilers that have been inspected reveal SAC damage, which portends significant energy and economic impacts. The goal of this project was to clarify the mechanism of stress-assisted corrosion (SAC) of boiler tubes for the purpose of determining key parameters in its mitigation and control. To accomplish this in-situ strain measurements on boiler tubes were made. Boiler water environment was simulated in the laboratory and effects of water chemistry on SAC initiation and growth were evaluated in terms of industrial operations. Results from this project have shown that the dissolved oxygen is single most important factor in SAC initiation on carbon steel samples. Control of dissolved oxygen can be used to mitigate SAC in industrial boilers. Results have also shown that sharp corrosion fatigue and bulbous SAC cracks have similar mechanism but the morphology is different due to availability of oxygen during boiler shutdown conditions. Results are described in the final technical report.

  16. Crack problems in cylindrical and spherical shells

    NASA Technical Reports Server (NTRS)

    Erdogan, F.

    1976-01-01

    Standard plate or shell theories were used as a starting point to study the fracture problems in thin-walled cylindrical and spherical shells, assuming that the plane of the crack is perpendicular to the surface of the sheet. Since recent studies have shown that local shell curvatures may have a rather considerable effect on the stress intensity factor, the crack problem was considered in conjunction with a shell rather than a plate theory. The material was assumed to be isotropic and homogeneous, so that approximate solutions may be obtained by approximating the local shell crack geometry with an ideal shell which has a solution, namely a spherical shell with a meridional crack, a cylindrical shell with a circumferential crack, or a cylindrical shell with an axial crack. A method of solution for the specially orthotropic shells containing a crack was described; symmetric and skew-symmetric problems are considered in cylindrical shells with an axial crack.

  17. Crack Formation in Cement-Based Composites

    NASA Astrophysics Data System (ADS)

    Sprince, A.; Pakrastinsh, L.; Vatin, N.

    2016-04-01

    The cracking properties in cement-based composites widely influences mechanical behavior of construction structures. The challenge of present investigation is to evaluate the crack propagation near the crack tip. During experiments the tension strength and crack mouth opening displacement of several types of concrete compositions was determined. For each composition the Compact Tension (CT) specimens were prepared with dimensions 150×150×12 mm. Specimens were subjected to a tensile load. Deformations and crack mouth opening displacement were measured with extensometers. Cracks initiation and propagation were analyzed using a digital image analysis technique. The formation and propagation of the tensile cracks was traced on the surface of the specimens using a high resolution digital camera with 60 mm focal length. Images were captured during testing with a time interval of one second. The obtained experimental curve shows the stages of crack development.

  18. Electrochemical situation in corrosion-mechanical cracks

    SciTech Connect

    Petrov, L.N.; Kalinkov, A.Yu.

    1995-01-01

    It is shown that the electrochemical situation in corrosion cracks is determined by the electromotive force of local galvanic cells at the crack tip and the polarization resistance of anodic processes.

  19. Steam Hydrocarbon Cracking and Reforming

    ERIC Educational Resources Information Center

    Golombok, Michael

    2004-01-01

    The interactive methods of steam hydrocarbon reforming and cracking of the oil and chemical industries are scrutinized, with special focus on their resemblance and variations. The two methods are illustrations of equilibrium-controlled and kinetically-controlled processes, the analysis of which involves theories, which overlap and balance each…

  20. Junction formation during desiccation cracking.

    PubMed

    Toga, K B; Alaca, B Erdem

    2006-08-01

    In order to provide a sound physical basis for the understanding of the formation of desiccation crack networks, an experimental study is presented addressing junction formation. Focusing on junctions, basic features of the network determining the final pattern, provides an elemental approach and imparts conceptual clarity to the rather complicated problem of the evolution of crack patterns. Using coffee-water mixtures a clear distinction between junction formation during nucleation and propagation is achieved. It is shown that for the same drying suspension, one can switch from the well-known symmetric triple junctions that are unique to the nucleation phase to propagation junctions that are purely dictated by the variations of the stress state. In the latter case, one can even manipulate the path of a propagating crack in a deterministic fashion by changing the stress state within the suspension. Clear microscopic evidence is provided for the formation of propagation junctions, and material inhomogeneity is observed to be reflected by a broad distribution of angles, in stark contrast to shrinkage cracks in homogeneous solid films.

  1. TV fatigue crack monitoring system

    NASA Technical Reports Server (NTRS)

    Exton, R. J. (Inventor)

    1977-01-01

    An apparatus is disclosed for monitoring the development and growth of fatigue cracks in a test specimen subjected to a pulsating tensile load. A plurality of television cameras photograph a test specimen which is illuminated at the point of maximum tensile stress. The television cameras have a modified vidicon tube which has an increased persistence time thereby eliminating flicker in the displayed images.

  2. Desiccation-crack-induced salinization in deep clay sediment

    NASA Astrophysics Data System (ADS)

    Baram, S.; Ronen, Z.; Kurtzman, D.; Külls, C.; Dahan, O.

    2013-04-01

    A study on water infiltration and solute transport in a clayey vadose zone underlying a dairy farm waste source was conducted to assess the impact of desiccation cracks on subsurface evaporation and salinization. The study is based on five years of continuous measurements of the temporal variation in the vadose zone water content and on the chemical and isotopic composition of the sediment and pore water in it. The isotopic composition of water stable isotopes (δ18O and δ2H) in water and sediment samples, from the area where desiccation crack networks prevail, indicated subsurface evaporation down to ~ 3.5 m below land surface, and vertical and lateral preferential transport of water, following erratic preferential infiltration events. Chloride (Cl-) concentrations in the vadose zone pore water substantially increased with depth, evidence of deep subsurface evaporation and down flushing of concentrated solutions from the evaporation zones during preferential infiltration events. These observations led to development of a desiccation-crack-induced salinization (DCIS) conceptual model. DCIS suggests that thermally driven convective air flow in the desiccation cracks induces evaporation and salinization in relatively deep sections of the subsurface. This conceptual model supports previous conceptual models on vadose zone and groundwater salinization in fractured rock in arid environments and extends its validity to clayey soils in semi-arid environments.

  3. Desiccation-crack-induced salinization in deep clay sediment

    NASA Astrophysics Data System (ADS)

    Baram, S.; Ronen, Z.; Kurtzman, D.; Küells, C.; Dahan, O.

    2012-11-01

    A study on water infiltration and solute transport in a clayey vadose zone underlying a dairy farm waste source was conducted to assess the impact of desiccation cracks on subsurface evaporation and salinization. The study is based on five years of continuous measurements of the temporal variation in the vadose zone water-content and on the chemical and isotopic composition of the sediment and pore-water in it. The isotopic composition of water stable isotopes (δ18O and δ2H) in water and sediment samples, from the area where desiccation crack networks prevail, indicated subsurface evaporation down to ∼3.5 m below land surface, and vertical and lateral preferential transport of water, following erratic preferential infiltration events. Chloride (Cl-) concentrations in the vadose zone pore water substantially increased with depth, evidence of deep subsurface evaporation and down flushing of concentrated solutions from the evaporation zones during preferential infiltration events. These observations led to development of a Desiccation-Crack-Induced Salinization (DCIS) conceptual model. DCIS suggests that thermally driven convective air flow in the desiccation cracks induces evaporation and salinization in relatively deep sections of the subsurface. This conceptual model supports previous conceptual models on vadose zone and groundwater salinization in fractured rock in arid environments and extends its validity to clayey soils in semi-arid environments.

  4. Cracks preserve kimberlite melt composition

    NASA Astrophysics Data System (ADS)

    Brett, R. C.; Vigouroux-Caillibot, N.; Donovan, J. J.; Russell, K.

    2009-12-01

    The chemical composition of kimberlite melts has previously been estimated by measuring aphanitic intrusive rocks (deposit composition) or by partial melting experiments on carbonated lherzolites (source composition). Pervasively altered, degassed and contaminated material preclude the determination of the primitive melt composition. Here we present data on melt compositions trapped in unaltered olivine cracks that have been healed and overgrown prior to shallow level emplacement. During the ascent of kimberlite magma the prograding crack tip samples mantle peridotite xenoliths. Xenoliths rapidly disaggregate over the first few kilometers of transport producing a population of olivine xenocrysts that are released to the fluid-rich melt. Rapid ascent of the kimberlite magma causes depressurization and creates internal elastic stresses in the olivine crystals that can only be alleviated by volumetric expansion or brittle failure. On the time scales operative during kimberlite ascent volume expansion is negligible and brittle failure occurs. Small wetting angles between the fluid-rich melt and olivine allow infiltration of the melt into the crack. These very thin cracks (<5 µm) heal rapidly and preserve primary kimberlitic material en route to the surface. We use the electron microprobe with a focused beam (interaction volume less than 2 µm) to analyze the small volumes of material found in the healed cracks of the olivine. We analyzed for 18 elements including oxygen, which we obtained by utilizing a non-linear time dependent intensity acquisition and empirically determined mass absorption coefficients. By accurately knowing the amount of oxygen in a sample, we assign oxygen molecules to all other analyzed elements (e.g. MgO, Al2O3) and the remaining oxygen is assigned to hydrogen and carbon. The analysis total is used as a constraint on the proportion of each species. Mg/Ca ratios of the cracks vary from 0.6-5 indicating a compositional continuum between alkali

  5. Pacific Northwest Laboratory annual report for 1984 to the DOE Office of the Assistant Secretary for Policy, Safety, and Environment. Part 5. Overview and assessment

    SciTech Connect

    Bair, W.J.

    1985-02-01

    Research conducted in 1984 is briefly described. Research areas include: (1) uncertainties in modeling source/receptor relations for acidic deposition; (2) health physics support and assistance to the DOE; (3) technical guidelines for radiological calibrations; (4) personnel neutron dosemeter evaluation and upgrade program; (5) beta measurement evaluation and upgrade; (6) accreditation program for occupational exposure measurements; (7) assurance program for Remedial Action; (8) environmental protection support and assistance; (9) hazardus waste risk assessment; and (10) radiation policy studies. (ACR)

  6. Crack/Cocaine: An Overview and Directory.

    ERIC Educational Resources Information Center

    Minisman-Chin, Linda; And Others

    This compilation presents background information and a resource directory concerning the growing dilemma of crack-exposed infants. Information on the incidence of crack use among women of child-bearing age is reviewed. The effects of crack on young children are outlined, and ways in which parents, educators, and other professionals can help these…

  7. The transition from subsonic to supersonic cracks

    PubMed Central

    Behn, Chris; Marder, M.

    2015-01-01

    We present the full analytical solution for steady-state in-plane crack motion in a brittle triangular lattice. This allows quick numerical evaluation of solutions for very large systems, facilitating comparisons with continuum fracture theory. Cracks that propagate faster than the Rayleigh wave speed have been thought to be forbidden in the continuum theory, but clearly exist in lattice systems. Using our analytical methods, we examine in detail the motion of atoms around a crack tip as crack speed changes from subsonic to supersonic. Subsonic cracks feature displacement fields consistent with a stress intensity factor. For supersonic cracks, the stress intensity factor disappears. Subsonic cracks are characterized by small-amplitude, high-frequency oscillations in the vertical displacement of an atom along the crack line, while supersonic cracks have large-amplitude, low-frequency oscillations. Thus, while supersonic cracks are no less physical than subsonic cracks, the connection between microscopic and macroscopic behaviour must be made in a different way. This is one reason supersonic cracks in tension had been thought not to exist. PMID:25713443

  8. Cracked Teeth: A Review of the Literature

    PubMed Central

    Lubisich, Erinne B.; Hilton, Thomas J.; FERRACANE, JACK

    2013-01-01

    Although cracked teeth are a common problem for patients and dentists, there is a dearth of evidence-based guidelines on how to prevent, diagnose, and treat cracks in teeth. The purpose of this article is to review the literature to establish what evidence exists regarding the risk factors for cracked teeth and their prevention, diagnosis, and treatment. PMID:20590967

  9. Evolution of Rock Cracks Under Unloading Condition

    NASA Astrophysics Data System (ADS)

    Huang, R. Q.; Huang, D.

    2014-03-01

    Underground excavation normally causes instability of the mother rock due to the release and redistribution of stress within the affected zone. For gaining deep insight into the characteristics and mechanism of rock crack evolution during underground excavation, laboratory tests are carried out on 36 man-made rock specimens with single or double cracks under two different unloading conditions. The results show that the strength of rock and the evolution of cracks are clearly influenced by both the inclination angle of individual cracks with reference to the unloading direction and the combination geometry of cracks. The peak strength of rock with a single crack becomes smaller with the inclination angle. Crack propagation progresses intermittently, as evidenced by a sudden increase in deformation and repeated fluctuation of measured stress. The rock with a single crack is found to fail in three modes, i.e., shear, tension-shear, and splitting, while the rock bridge between two cracks is normally failed in shear, tension-shear, and tension. The failure mode in which a crack rock or rock bridge behaves is found to be determined by the inclination angle of the original crack, initial stress state, and unloading condition. Another observation is that the secondary cracks are relatively easily created under high initial stress and quick unloading.

  10. 46 CFR 59.10-5 - Cracks.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... CFR 59.01-2). For thicknesses exceeding three-fourths inch, suitable U grooves should be employed. A... APPURTENANCES Welding Repairs to Boilers and Pressure Vessels in -Service § 59.10-5 Cracks. (a) Cracks extending... corrugated furnaces may be repaired by welding provided any one crack does not exceed 20 inches in length....

  11. 46 CFR 59.10-5 - Cracks.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... CFR 59.01-2). For thicknesses exceeding three-fourths inch, suitable U grooves should be employed. A... APPURTENANCES Welding Repairs to Boilers and Pressure Vessels in -Service § 59.10-5 Cracks. (a) Cracks extending... corrugated furnaces may be repaired by welding provided any one crack does not exceed 20 inches in length....

  12. 46 CFR 59.10-5 - Cracks.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... CFR 59.01-2). For thicknesses exceeding three-fourths inch, suitable U grooves should be employed. A... APPURTENANCES Welding Repairs to Boilers and Pressure Vessels in -Service § 59.10-5 Cracks. (a) Cracks extending... corrugated furnaces may be repaired by welding provided any one crack does not exceed 20 inches in length....

  13. 46 CFR 59.10-5 - Cracks.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... CFR 59.01-2). For thicknesses exceeding three-fourths inch, suitable U grooves should be employed. A... APPURTENANCES Welding Repairs to Boilers and Pressure Vessels in -Service § 59.10-5 Cracks. (a) Cracks extending... corrugated furnaces may be repaired by welding provided any one crack does not exceed 20 inches in length....

  14. 46 CFR 59.10-5 - Cracks.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... CFR 59.01-2). For thicknesses exceeding three-fourths inch, suitable U grooves should be employed. A... APPURTENANCES Welding Repairs to Boilers and Pressure Vessels in -Service § 59.10-5 Cracks. (a) Cracks extending... corrugated furnaces may be repaired by welding provided any one crack does not exceed 20 inches in length....

  15. 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.

  16. Crack healing behavior of hot pressed silicon nitride due to oxidation

    NASA Technical Reports Server (NTRS)

    Choi, S. R.; Tikare, V.

    1992-01-01

    It is shown that limited oxidation of an MgO-containing, hot-pressed silicon nitride ceramic at 800 deg C and above results in increased strength due to crack healing. Slight oxidation of the surface produces enstatite and cristobalite which fills in cracks. More extensive oxidation leads to strength degradation due to the formation of new flaws by the evolution of N2 gas at the surface. The apparent fracture toughness also increased at 800 deg C and above due to oxidation. Bonds formed between the two surfaces of the crack during oxidation leads to a reduction in stress intensity at the crack tip, suggesting that valid high-temperature toughness values cannot be obtained in an air environment. The increase in strength due to crack healing by oxidation can be achieved without compromising the fatigue properties of the silicon nitride ceramic.

  17. Fatigue cracking of a bare steel first wall in an inertial confinement fusion chamber

    SciTech Connect

    Hunt, R. M.; Abbott, R. P.; Havstad, M. A.; Dunne, A. M.

    2013-06-01

    Inertial confinement fusion power plants will deposit high energy X-rays onto the outer surfaces of the first wall many times a second for the lifetime of the plant. These X-rays create brief temperature spikes in the first few microns of the wall, which cause an associated highly compressive stress response on the surface of the material. The periodicity of this stress pulse is a concern due to the possibility of fatigue cracking of the wall. We have used finite element analyses to simulate the conditions present on the first wall in order to evaluate the driving force of crack propagation on fusion-facing surface cracks. Analysis results indicate that the X-ray induced plastic compressive stress creates a region of residual tension on the surface between pulses. This tension film will likely result in surface cracking upon repeated cycling. Additionally, the compressive pulse may induce plasticity ahead of the crack tip, leaving residual tension in its wake. However, the stress amplitude decreases dramatically for depths greater than 80–100 μm into the fusion-facing surface. Crack propagation models as well as stress-life estimates agree that even though small cracks may form on the surface of the wall, they are unlikely to propagate further than 100 μm without assistance from creep or grain erosion phenomena.

  18. Stress corrosion cracking of candidate materials for nuclear waste containers

    SciTech Connect

    Maiya, P.S.; Shack, W.J.; Kassner, T.F.

    1989-09-01

    Types 304L and 316L stainless steel (SS), Incoloy 825, Cu, Cu-30%Ni, and Cu-7%Al have been selected as candidate materials for the containment of high-level nuclear waste at the proposed Yucca Mountain Site in Nevada. The susceptibility of these materials to stress corrosion cracking has been investigated by slow-strain-rate tests (SSRTs) in water which simulates that from well J-13 (J-13 water) and is representative of the groundwater present at the Yucca Mountain site. The SSRTs were performed on specimens exposed to simulated J-13 water at 93{degree}C and at a strain rate 10{sup {minus}7} s{sup {minus}1} under crevice conditions and at a strain rate of 10{sup {minus}8} s{sup {minus}1} under both crevice and noncrevice conditions. All the tests were interrupted after nominal elongation strains of 1--4%. Examination by scanning electron microscopy showed some crack initiation in virtually all specimens. Optical microscopy of metallographically prepared transverse sections of Type 304L SS suggests that the crack depths are small (<10 {mu}m). Preliminary results suggest that a lower strain rate increases the severity of cracking of Types 304L and 316L SS, Incoloy 825, and Cu but has virtually no effect on Cu-30%Ni and Cu-7%Al. Differences in susceptibility to cracking were evaluated in terms of a stress ratio, which is defined as the ratio of the increase in stress after local yielding in the environment to the corresponding stress increase in an identical test in air, both computed at the same strain. On the basis of this stress ratio, the ranking of materials in order of increasing resistance to cracking is: Types 304L SS < 316L SS < Incoloy 825 {congruent} Cu-30%Ni < Cu {congruent} Cu-7%Al. 9 refs., 12 figs., 7 tabs.

  19. Prediction of PWSCC in nickel base alloys using crack growth rate models

    SciTech Connect

    Thompson, C.D.; Krasodomski, H.T.; Lewis, N.; Makar, G.L.

    1995-12-31

    The Ford/Andresen slip-dissolution SCC model, originally developed for stainless steel components in BWR environments, has been applied to Alloy 600 and Alloy X-750 tested in deaerated pure water chemistry. A method is described whereby the crack growth rates measured in compact tension specimens can be used to estimate crack growth in a component. Good agreement was found between model prediction and measured SCC in X-750 threaded fasteners over a wide range of temperatures, stresses, and material conditions. Most data support the basic assumption of this model that cracks initiate early in life. The evidence supporting a particular SCC mechanism is mixed. Electrochemical repassivation data and estimates of oxide fracture strain indicate that the slip-dissolution model can account for the observed crack growth rates, provided primary rather than secondary creep rates are used. However, approximately 100 cross-sectional TEM foils of SCC cracks including crack tips reveal no evidence of enhanced plasticity or unique dislocation patterns at the crack tip or along the crack to support a classic slip-dissolution mechanism. No voids, hydrides, or microcracks are found in the vicinity of the crack tips creating doubt about classic hydrogen related mechanisms. The bulk oxide films exhibit a surface oxide which is often different than the oxides found within a crack. Although bulk chromium concentration affects the rate of SCC, analytical data indicates the mechanism does not result from chromium depletion at the grain boundaries. The overall findings support a corrosion/dissolution mechanism but not one necessarily related to slip at the crack tip.

  20. Cracking behavior of structural slab bridge decks

    NASA Astrophysics Data System (ADS)

    Baah, Prince

    Bridge deck cracking is a common problem throughout the United States, and it affects the durability and service life of concrete bridges. Several departments of transportation (DOTs) in the United States prefer using continuous three-span solid structural slab bridges without stringers over typical four-lane highways. Recent inspections of such bridges in Ohio revealed cracks as wide as 0.125 in. These measured crack widths are more than ten times the maximum limit recommended in ACI 224R-01 for bridge decks exposed to de-icing salts. Measurements using digital image correlation revealed that the cracks widened under truck loading, and in some cases, the cracks did not fully close after unloading. This dissertation includes details of an experimental investigation of the cracking behavior of structural concrete. Prism tests revealed that the concrete with epoxy-coated bars (ECB) develops the first crack at smaller loads, and develops larger crack widths compared to the corresponding specimens with uncoated (black) bars. Slab tests revealed that the slabs with longitudinal ECB developed first crack at smaller loads, exhibited wider cracks and a larger number of cracks, and failed at smaller ultimate loads compared to the corresponding test slabs with black bars. To develop a preventive measure, slabs with basalt and polypropylene fiber reinforced concrete were also included in the test program. These test slabs exhibited higher cracking loads, smaller crack widths, and higher ultimate loads at failure compared to the corresponding slab specimens without fibers. Merely satisfying the reinforcement spacing requirements given in AASHTO or ACI 318-11 is not adequate to limit cracking below the ACI 224R-01 recommended maximum limit, even though all the relevant design requirements are otherwise met. Addition of fiber to concrete without changing any steel reinforcing details is expected to reduce the severity and extent of cracking in reinforced concrete bridge decks.