Science.gov

Sample records for shroud crack probe

  1. Single-point representative sampling with shrouded probes

    SciTech Connect

    McFarland, A.R.; Rodgers, J.C.

    1993-08-01

    The Environmental Protection Agency (EPA) prescribed methodologies for sampling radionuclides in air effluents from stacks and ducts at US Department of Energy (DOE) facilities. Requirements include use of EPA Method 1 for the location of sampling sites and use of American National Standards Institute (ANSI) N13.1 for guidance in design of sampling probes and the number of probes at a given site. Application of ANSI N13.1 results in sampling being performed with multiprobe rakes that have as many as 20 probes. There can be substantial losses of aerosol particles in such sampling that will degrade the quality of emission estimates from a nuclear facility. Three alternate methods, technically justified herein, are proposed for effluent sampling. First, a shrouded aerosol sampling probe should replace the sharp-edged elbowed-nozzle recommended by ANSI. This would reduce the losses of aerosol particles in probes and result in the acquisition of more representative aerosol samples. Second, the rakes of multiple probes that are intended to acquire representative samples through spatial coverage should be replaced by a single probe located where contaminant mass and fluid momentum are both well mixed. A representative sample can be obtained from a well-mixed flow. Some effluent flows will need to be engineered to achieve acceptable mixing. Third, sample extraction should be performed at a constant flow rate through a suitable designed shrouded probe rather than at a variable flow rate through isokinetic probes. A shrouded probe is shown to have constant sampling characteristics over a broad range of stack velocities when operated at a fixed flow rate.

  2. TRAC-BF1 thermal-hydraulic, ANSYS stress analysis for core shroud cracking phenomena

    SciTech Connect

    Shoop, U.; Feltus, M.A.; Baratta, A.J.

    1996-12-31

    The U.S. Nuclear Regulatory Commission sent Generic Letter 94-03 informing all licensees about the intergranular stress corrosion cracking (IGSCC) of core shrouds found in both Dresden unit I and Quad Cities unit 1. The letter directed all licensees to perform safety analysis of their boiling water reactor (BWR) units. Two transients of special concern for the core shroud safety analysis include the main steam line break (MSLB) and recirculation line break transient.

  3. In situ repair welding of steam turbine shroud for replacing a cracked blade

    NASA Astrophysics Data System (ADS)

    Albert, S. K.; Das, C. R.; Ramasubbu, V.; Bhaduri, A. K.; Ray, S. K.; Raj, Baldev

    2002-06-01

    A root-cracked blade in a high-pressure steam turbine of a nuclear power plant had to be replaced with a new blade by cutting the shroud to remove the cracked blade. This necessitated in situ welding of a new shroud piece with the existing shroud after the blade replacement. The in situ welding of the shroud, a 12% Cr martensitic stainless steel with tempered martensite microstructure, was carried out using gastungsten arc welding and 316L austenitic stainless steel filler metal followed by localized postweld heat treatment at 873 K for 1 h using a specially designed electrical resistance-heating furnace. Mock-up trials were carried out to ensure that sound welds could be made under the constraints present during the in situ repair welding operation. In situ metallography of the repair weld after postweld heat treatment confirmed the adequate tempering of the martensitic structure in the heat-affected zone. Metallurgical investigations carried out in the laboratory on a shroud test-piece that had been welded using the same procedure as employed in the field confirmed the success of the in situ repair operation. The alternate option available was replacing the cracked blade and the shroud piece to which it is riveted with a new one, reducing the height of all the blades attached to the shroud by machining, riveting the blades with reduced height to the new shroud, and, finally, dynamic balancing of the entire turbine after completion of the repair. This option is both time-consuming and expensive. Hence, the successful completion of this repair welding resulted in enormous savings both in terms of reducing the downtime of the plant and the cost of the repair. The turbine has been put back into service and has been operating satisfactorily since December 2000.

  4. Crack growth rate in core shroud horizontal welds using two models for a BWR

    NASA Astrophysics Data System (ADS)

    Arganis Juárez, C. R.; Hernández Callejas, R.; Medina Almazán, A. L.

    2015-05-01

    An empirical crack growth rate correlation model and a predictive model based on the slip-oxidation mechanism for Stress Corrosion Cracking (SCC) were used to calculate the crack growth rate in a BWR core shroud. In this study, the crack growth rate was calculated by accounting for the environmental factors related to aqueous environment, neutron irradiation to high fluence and the complex residual stress conditions resulting from welding. In estimating the SCC behavior the crack growth measurements data from a Boiling Water Reactor (BWR) plant are referred to, and the stress intensity factor vs crack depth throughout thickness is calculated using a generic weld residual stress distribution for a core shroud, with a 30% stress relaxation induced by neutron irradiation. Quantitative agreement is shown between the measurements of SCC growth rate and the predictions of the slip-oxidation mechanism model for relatively low fluences (5 × 1024 n/m2), and the empirical model predicted better the SCC growth rate than the slip-oxidation model for high fluences (>1 × 1025 n/m2). The relevance of the models predictions for SCC growth rate behavior depends on knowing the model parameters.

  5. Effects of salt loading and flow blockage on the WIPP shrouded probe

    SciTech Connect

    Chandra, S.; Ortiz, C.A.; McFarland, A.R.

    1993-08-01

    The shrouded probes at the WIPP site operate in a salt aerosol environment that can cause a buildup of salt deposits on exposed surfaces of the probes that, in turn, could produce changes in the sampling performance of the probes. At Station A, three probes had been operated for a period of approximately 2 1/2 years when they were inspected with a remote television camera. There were visible deposits of unknown thickness on the probes, so WIPP removed the probes for inspection and cleanup. Measurements were made on the probes and they showed the buildups to be approximately 2.5 mm thick on the most critical dimension of a shrouded probe, which is the inside diameter of the inner probe. For reference, the diameter of a clean probe is 30 mm. The sampling performance of this particular shrouded probe had been previously evaluated in a wind tunnel at Aerosol Technology Laboratory (ATL) of Texas A&M University for two free stream velocities (14 and 21 m/s) and three particle sizes (5, 10 and 15 {mu}m AED).

  6. Reactor shroud joint

    DOEpatents

    Ballas, G.J.; Fife, A.B.; Ganz, I.

    1998-04-07

    A shroud for a nuclear reactor is described. In one embodiment, the shroud includes first and second shroud sections, and each shroud section includes a substantially cylindrical main body having a first end and a second end. With respect to each shroud section, a flange is located at the main body first end, and the flange has a plurality of bolt openings therein and a plurality of scalloped regions. The first shroud section is welded to the second shroud section, and at least some of the bolt openings in the first shroud section flange align with respective bolt openings in the second shroud section flange. In the event that the onset of inter-granular stress corrosion cracking is ever detected in the weld between the shroud section, bolts are inserted through bolt openings in the first shroud section flange and through aligned bolt openings the second shroud section flange. Each bolt, in one embodiment, has a shank section and first and second threaded end sections. Nuts are threadedly engaged to the threaded end sections and tightened against the respective flanges. 4 figs.

  7. Reactor shroud joint

    DOEpatents

    Ballas, Gary J.; Fife, Alex Blair; Ganz, Israel

    1998-01-01

    A shroud for a nuclear reactor is described. In one embodiment, the shroud includes first and second shroud sections, and each shroud section includes a substantially cylindrical main body having a first end and a second end. With respect to each shroud section, a flange is located at the main body first end, and the flange has a plurality of bolt openings therein and a plurality of scalloped regions. The first shroud section is welded to the second shroud section, and at least some of the bolt openings in the first shroud section flange align with respective bolt openings in the second shroud section flange. In the event that the onset of inter-granular stress corrosion cracking is ever detected in the weld between the shroud section, bolts are inserted through bolt openings in the first shroud section flange and through aligned bolt openings the second shroud section flange. Each bolt, in one embodiment, has a shank section and first and second threaded end sections. Nuts are threadedly engaged to the threaded end sections and tightened against the respective flanges.

  8. Revolving Eddy-Current Probe Detects Cracks Near Rivets

    NASA Technical Reports Server (NTRS)

    Namkung, Min; Wincheski, Buzz; Fulton, James P.; Nath, Shridhar; Simpson, John

    1995-01-01

    Scanning eddy-current probe in circular pattern increases sensitivity with which probe indicates fatigue cracks and other defects in metal surfaces in vicinity of rivets. Technique devised to facilitate inspection of riveted joints in aircraft. Eddy-current probe in question described in "Electro-magnetic Flaw Detector Is Easier To Use" (LAR-15046).

  9. Modeling of residual stresses in core shroud structures

    SciTech Connect

    Zhang, J.; Dong, P.; Brust, F.W.; Mayfield, M.; McNeil, M.; Shack, W.J.

    1997-10-01

    A BWR core shroud is a cylindrical shell that surrounds the reactor core. Feedwater for the reactor is introduced into the annulus between the reactor vessel wall and the shroud. The shroud separates the feedwater from the cooling water flowing up through the reactor core. The shroud also supports the top guide which provides lateral support to the fuel assemblies and maintains core geometry during operational transients and postulated accidents to permit control rod insertion and provides the refloodable volume needed to ensure safe shutdown and cooling of the core during postulated accident conditions. Core shrouds were fabricated from welded Type 304 or 304L stainless steel plates and are supported at the top and bottom by forged ring support structures. In 1990, cracking was reported in the core shroud of a non-U.S. BWR. The cracks were located in the heat-affected zone (HAZ) of a circumferential core shroud weld. Subsequent inspections in U.S. BWRs have revealed the presence of numerous flaw indications in some BWR core shrouds, primarily in weld HAZs. In several instances, this cracking was quite extensive, with the cracks extending 75% or more around the circumference of some welds. However, because the applied stresses on the shroud are low during operation and postulated accidents and because of the high fracture toughness of stainless steel, adequate structural margins can be preserved even in the presence of extensive cracking. Although assessments by the USNRC staff of the potential significance of this cracking have shown that core shroud cracking does not pose a high degree of risk in the short term, the staff concluded that the cracking was a safety concern for the long term because of the uncertainties associated with the behavior of core shrouds with complete 360{degrees} through-wall cracks under accident conditions and because it could eliminate a layer of defense-in-depth.

  10. Model-based probe state estimation and crack inverse methods addressing eddy current probe variability

    NASA Astrophysics Data System (ADS)

    Aldrin, John C.; Oneida, Erin K.; Shell, Eric B.; Sabbagh, Harold A.; Sabbagh, Elias; Murphy, R. Kim; Mazdiyasni, Siamack; Lindgren, Eric A.; Mooers, Ryan D.

    2017-02-01

    A model-based calibration process is introduced that estimates the state of the eddy current probe. First, a carefully designed surrogate model was built using VIC-3D® simulations covering the critical range of probe rotation angles, tilt in two directions, and probe offset (liftoff) for both transverse and longitudinal flaw orientations. Some approximations and numerical compromises in the model were made to represent tilt in two directions and reduce simulation time; however, this surrogate model was found to represent the key trends in the eddy current response for each of the four probe properties in experimental verification studies well. Next, this model was incorporated into an iterative inversion scheme during the calibration process, to estimate the probe state while also addressing the amplitude/phase fit and centering the calibration notch indication. Results are presented showing several examples of the blind estimation of tilt and rotation angle for known experimental cases with reasonable agreement. Once the probe state is estimated, the final step is to transform the base crack inversion surrogate model and apply it for crack characterization. Using this process, results are presented demonstrating improved crack inversion performance for extreme probe states.

  11. Large Deployable Shroud

    NASA Technical Reports Server (NTRS)

    Jacquemin, G. G.

    1987-01-01

    Preliminary design proposed for large, lightweight telescope shroud or light shield carried to orbit in single Space Shuttle cargo load. Shroud concept applied on Earth in portable, compactly storable displays or projection screens. Large telescope shroud includes four deployable masts erecting eight walls of hinged panels of polyimide film. Panels stored fanfolded before deployment and threaded on guide wires unwinding from spools and remain taut during deployment.

  12. Shroud leakage flow discouragers

    DOEpatents

    Bailey, Jeremy Clyde; Bunker, Ronald Scott

    2002-01-01

    A turbine assembly includes a plurality of rotor blades comprising a root portion, an airfoil having a pressure sidewall and a suction sidewall, and a top portion having a cap. An outer shroud is concentrically disposed about said rotor blades, said shroud in combination with said tip portions defining a clearance gap. At least one circumferential shroud leakage discourager is disposed within the shroud. The leakage discourager(s) increase the flow resistance and thus reduce the flow of hot gas flow leakage for a given pressure differential across the clearance gap to improve overall turbine efficiency.

  13. Core shroud corner joints

    DOEpatents

    Gilmore, Charles B.; Forsyth, David R.

    2013-09-10

    A core shroud is provided, which includes a number of planar members, a number of unitary corners, and a number of subassemblies each comprising a combination of the planar members and the unitary corners. Each unitary corner comprises a unitary extrusion including a first planar portion and a second planar portion disposed perpendicularly with respect to the first planar portion. At least one of the subassemblies comprises a plurality of the unitary corners disposed side-by-side in an alternating opposing relationship. A plurality of the subassemblies can be combined to form a quarter perimeter segment of the core shroud. Four quarter perimeter segments join together to form the core shroud.

  14. Localization and characterization of fatigue cracks around fastener holes using spherically focused ultrasonic probes

    NASA Astrophysics Data System (ADS)

    Hopkins, Deborah; Datuin, Marvin; Aldrin, John; Warchol, Mark; Warchol, Lyudmila; Forsyth, David

    2017-02-01

    Results are presented from laboratory experiments and simulations that demonstrate the ability to localize fatigue cracks around fastener holes using spherically focused ultrasonic probes for shear-wave inspections. For the experiments, fatigue cracks were created in aluminum plates in a testing frame under cyclic loading. With the exceptions of one specimen with a mid-bore crack and another with a "through" crack, the remaining specimens contain surface-breaking cracks. All of the specimens were inspected for the cracks intersecting the back wall, and some were flipped over and re-inspected with the crack intersecting the front surface. Parameter and variable sensitivity studies were performed using CIVA Simulation Software. In contrast to C-scans where detection and localization of small cracks can be very difficult, modeling and initial experimental results demonstrate that cracks can be accurately located in "True" B-scans (B-scans projected in the part along the beam path). Initial results show that small-amplitude diffracted/scattered signals from the crack tips and edges are essential in obtaining clear crack traces in the True B-scans. It is important therefore that experimental data be acquired with sufficient gain to capture the diffracted/scattered signals. In all of the cases studied here, saturating the high-amplitude specular reflections from the fastener hole and crack enhanced the crack trace in the True B-scans.

  15. NDE of a 3-D surface crack using closely coupled probes for DCPD technique

    SciTech Connect

    Saka, M.; Abe, H.; Hirota, D.; Komura, I.

    1998-11-01

    A procedure of applying the d-c potential drop technique using the closely coupled probes to NDE of a 3-D surface crack is newly developed. The calibration equation for three sensors which differ in the distance between the probes is derived. Experiments validated the use of the calibration equation for the NDE of cracks. The method to use the three sensors properly based on the measuring sensitivity is shown.

  16. Turbine inner shroud and turbine assembly containing such inner shroud

    DOEpatents

    Bagepalli, Bharat Sampathkumaran; Corman, Gregory Scot; Dean, Anthony John; DiMascio, Paul Stephen; Mirdamadi, Massoud

    2001-01-01

    A turbine inner shroud and a turbine assembly. The turbine assembly includes a turbine stator having a longitudinal axis and having an outer shroud block with opposing and longitudinally outward facing first and second sides having open slots. A ceramic inner shroud has longitudinally inward facing hook portions which can longitudinally and radially surround a portion of the sides of the outer shroud block. In one attachment, the hook portions are engageable with, and are positioned within, the open slots.

  17. Shrouded inducer pump

    DOEpatents

    Meng, S.Y.

    1989-08-08

    An improvement in a pump is described including a shrouded inducer, the improvement comprising first and second sealing means which cooperate with a first vortex cell and a series of secondary vortex cells to remove any tangential velocity components from the recirculation flow. 3 figs.

  18. Shrouded inducer pump

    SciTech Connect

    Meng, Sen Y.

    1989-01-01

    An improvement in a pump including a shrouded inducer, the improvement comprising first and second sealing means 32,36 which cooperate with a first vortex cell 38 and a series of secondary vortex cells 40 to remove any tangential velocity components from the recirculation flow.

  19. Skylab payload shroud jettison tests

    NASA Technical Reports Server (NTRS)

    Daye, C. J.

    1972-01-01

    The separation concept of the skylab payload shroud is presented, and its behavior in three full-scale jettison tests in vacuum is described. The shroud petal arresting mechanism is explained, as well as the primary and secondary data acquisition systems. The first two tests demonstrated the need for some structural design modifications although the separation process was satisfactory in each test. The third test, incorporating these design modifications, was satisfactory in all aspects of shroud performance.

  20. Improved high pressure turbine shroud

    NASA Technical Reports Server (NTRS)

    Bessen, I. I.; Rigney, D. V.; Schwab, R. C.

    1977-01-01

    A new high pressure turbine shroud material has been developed from the consolidation of prealloyed powders of Ni, Cr, Al and Y. The new material, a filler for cast turbine shroud body segments, is called Genaseal. The development followed the identification of oxidation resistance as the primary cause of prior shroud deterioration, since conversion to oxides reduces erosion resistance and increases spalling under thermal cycled engine conditions. The NICrAlY composition was selected in preference to NIAL and FeCRALY alloys, and was formulated to a prescribed density range that offers suitable erosion resistance, thermal conductivity and elastic modulus for improved behavior as a shroud.

  1. Detection of Fatigue Cracks at Rivets with Self-Nulling Probe

    NASA Technical Reports Server (NTRS)

    Wincheski, Buzz; Fulton, Jim; Nath, Shridhar; Namkung, Min

    1994-01-01

    A new eddy current probe developed at NASA Langley Research Center has been used to detect small cracks at rivets in aircraft lap splices [1]. The device has earlier been used to detect isolated fatigue cracks with a minimum detectable flaw size of roughly 1/2 to 1/3 the diameter of the probe [2]. The present work shows that the detectable flaw size for cracks originating at rivets can be greatly improved upon from that of isolated flaws. The use of a rotating probe method combined with spatial filtering has been used to detect 0.18 cm EDM notches, as measured from the rivet shank, with a 1.27 cm diameter probe and to detect flaws buried under the rivet head, down to a length of 0.076 cm, using a 0.32 cm diameter probe. The Self-Nulling Electromagnetic Flaw Detector induces a high density eddy current ring in the sample under test. A ferromagnetic flux focusing lens is incorporated such that in the absence of any inhomogeneities in the material under test only a minimal magnetic field will reach the interior of the probe. A magnetometer (pickup coil) located in the center of the probe therefore registers a null voltage in the absence of material defects. When a fatigue crack or other discontinuity is present in the test article the path of the eddy currents in the material is changed. The magnetic field associated with these eddy currents then enter into the interior of the probe, producing a large output voltage across the pickup coil leads. Further

  2. Ceramic gas turbine shroud

    SciTech Connect

    Shi, Jun; Green, Kevin E.

    2014-07-22

    An example gas turbine engine shroud includes a first annular ceramic wall having an inner side for resisting high temperature turbine engine gasses and an outer side with a plurality of radial slots. A second annular metallic wall is positioned radially outwardly of and enclosing the first annular ceramic wall and has a plurality of tabs in communication with the slot of the first annular ceramic wall. The tabs of the second annular metallic wall and slots of the first annular ceramic wall are in communication such that the first annular ceramic wall and second annular metallic wall are affixed.

  3. Crack

    MedlinePlus

    ... is cocaine that has been processed into rock crystal form. Like cocaine, crack is a powerful and ... with things that cause powdered cocaine to form crystals. Many of these are harmless, but sometimes producers ...

  4. Crack

    MedlinePlus

    ... are harmless, but sometimes producers add ingredients like amphetamines to make crack cheaper. These added ingredients raise ... For Kids For Parents MORE ON THIS TOPIC Amphetamines Drugs: What to Know Dealing With Addiction Cocaine ...

  5. Detection of Cracks at Welds in Steel Tubing Using Flux Focusing Electromagnetic Probe

    NASA Technical Reports Server (NTRS)

    Wincheski, Buzz; Fulton, Jim; Nath, Shridhar; Simpson, John; Namkung, Min

    1994-01-01

    The inspection of weldments in critical pressure vessel joints is a major concern in the nuclear power industry. Corrosive environments can speed the fatigue process and access to the critical area is often limited. Eddy current techniques have begun to be used to help overcome these obstacles [1]. As direct contact and couplants are not required, remote areas can be inspected by simply snaking an eddy current coil into the intake tube of the vessel. The drawback of the eddy current method has been the high sensitivity to small changes in the conductivity and permeability of the test piece which are known to vary at weldments [1]. The flaw detection mechanism of the flux focusing electromagnetic probe can help alleviate these difficulties and provide a unique capability for detecting longitudinal fatigue cracks in critical tube structures. The Flux Focusing Electromagnetic Flaw Detector, originally invented for the detection of fatigue and corrosion damage in aluminum plates [2-3], has been adapted for use in testing steel tubing for longitudinal fatigue cracks. The modified design allows for the probe to be placed axisymmetrically into the tubing, inducing eddy currents in the tube wall. The pickup coil of the probe is fixed slightly below the primary windings and is rotated 90 so that its axis is normal to the tube wall. The magnetic flux of the primary coil is focused through the use of ferromagnetic material so that in the absence of fatigue damage there will be no flux linkage with the pickup coil. The presence of a longitudinal fatigue crack will cause the eddy currents induced in the tube wall to flow around the flaw and directly under the pickup coil. The magnetic field associated with these currents will then link the pickup coil and an unambiguous increase in the output voltage of the probe will be measured. The use of the flux focusing electromagnetic probe is especially suited for the detection of flaws originating at or near tube welds. The probe is

  6. Main steam-line break core shroud loading calculations for BWRs

    SciTech Connect

    Shoop, U.; Feltus, M.A.; Baratta, A.J.

    1995-12-31

    In July 1994, the U.S. Nuclear regulatory Commission sent out Generic Letter 94-03 to all boiling water reactors in the United States, informing them of intergranular stress corrosion cracking of core shrouds found in 2 reactors. The letter directed all to perform safety analysis of the BWR units. Penn State performed scoping calculations to determine the forces experienced by the core shroud during a main-stream line break transient.

  7. Airfoil nozzle and shroud assembly

    DOEpatents

    Shaffer, J.E.; Norton, P.F.

    1997-06-03

    An airfoil and nozzle assembly are disclosed including an outer shroud having a plurality of vane members attached to an inner surface and having a cantilevered end. The assembly further includes a inner shroud being formed by a plurality of segments. Each of the segments having a first end and a second end and having a recess positioned in each of the ends. The cantilevered end of the vane member being positioned in the recess. The airfoil and nozzle assembly being made from a material having a lower rate of thermal expansion than that of the components to which the airfoil and nozzle assembly is attached. 5 figs.

  8. Airfoil nozzle and shroud assembly

    DOEpatents

    Shaffer, James E.; Norton, Paul F.

    1997-01-01

    An airfoil and nozzle assembly including an outer shroud having a plurality of vane members attached to an inner surface and having a cantilevered end. The assembly further includes a inner shroud being formed by a plurality of segments. Each of the segments having a first end and a second end and having a recess positioned in each of the ends. The cantilevered end of the vane member being positioned in the recess. The airfoil and nozzle assembly being made from a material having a lower rate of thermal expansion than that of the components to which the airfoil and nozzle assembly is attached.

  9. Application of Self Nulling Eddy Current Probe Technique to the Detection of Fatigue Crack Initiation and Control of Test Procedures

    NASA Technical Reports Server (NTRS)

    Namkung, M.; Nath, S.; Wincheski, B.; Fulton, J. P.

    1994-01-01

    A major part of fracture mechanics is concerned with studying the initiation and propagation of fatigue cracks. This typically requires constant monitoring of crack growth during fatigue cycles and the knowledge of the precise location of the crack tip at any given time. One technique currently available for measuring fatigue crack length is the Potential Drop method. The method, however, may be inaccurate if the direction of crack growth deviates considerably from what was assumed initially or the curvature of the crack becomes significant. Another popular approach is to optically view the crack using a high magnification microscope, but this entails a person constantly monitoring it. The present proposed technique uses an automated scheme, in order to eliminate the need for a person to constantly monitor the experiment. Another technique under development elsewhere is to digitize an optical image of the test specimen surface and then apply a pattern recognition algorithm to locate the crack tip. A previous publication showed that the self nulling eddy current probe successfully tracked a simulated crack in an aluminum sample. This was the impetus to develop an online real time crack monitoring system. An automated system has been developed which includes a two axis scanner mounted on the tensile testing machine, the probe and its instrumentation and a personal computer (PC) to communicate and control all the parameters. The system software controls the testing parameters as well as monitoring the fatigue crack as it propagates. This paper will discuss the experimental setup in detail and demonstrate its capabilities. A three dimensional finite element model is utilized to model the magnetic field distribution due to the probe and how the probe voltage changes as it scans the crack. Experimental data of the probe for different samples under zero load, static load and high cycle fatigue load will be discussed. The final section summarizes the major accomplishments

  10. Evaluation of eddy-current probe signals due to cracks in ferromagnetic parts of fast reactor

    NASA Astrophysics Data System (ADS)

    Wu, Tao; Bowler, John R.

    2017-02-01

    Eddy current testing to evaluate the condition of metallic parts in a sodium cooled fast reactor under standby conditions is challenging due to the presence of liquid sodium at 250 °C. The eddy current test system should be sensitive enough to capture small signal changes and hence an advanced inspection systems is needed. We have developed new hardware and improved numerical models to predict the eddy current probe signal due to cracks in metallic fast reactor parts by using volume integral equation method. The analytical expressions are derived for the quasi-static time-harmonic electromagnetic fields of a circular eddy current coil which interacts with conductive plate. Naturally, the method of moment is used to approximate the integral equation and obtain the discrete approximation of the field in the crack domain. A simple and accurate analytical method for dealing with the hyper-singularity element evaluation is also provided. An accurate controlled experiment is carried out on the ferromagnetic stainless steel plate with precision made notch to obtain reference impedance changes for comparison with the theoretical model predictions. Good agreement between predictions and experiment is obtained.

  11. Wind turbine ring/shroud drive system

    DOEpatents

    Blakemore, Ralph W.

    2005-10-04

    A wind turbine capable of driving multiple electric generators having a ring or shroud structure for reducing blade root bending moments, hub loads, blade fastener loads and pitch bearing loads. The shroud may further incorporate a ring gear for driving an electric generator. In one embodiment, the electric generator may be cantilevered from the nacelle such that the gear on the generator drive shaft is contacted by the ring gear of the shroud. The shroud also provides protection for the gearing and aids in preventing gear lubricant contamination.

  12. Radiocarbon dating of the Shroud of Turin

    NASA Astrophysics Data System (ADS)

    Damon, P. E.; Donahue, D. J.; Gore, B. H.; Hatheway, A. L.; Jull, A. J. T.; Linick, T. W.; Sercel, P. J.; Toolin, L. J.; Bronk, C. R.; Hall, E. T.; Hedges, R. E. M.; Housley, R.; Law, I. A.; Perry, C.; Bonani, G.; Trumbore, S.; Woelfli, W.; Ambers, J. C.; Bowman, S. G. E.; Leese, M. N.; Tite, M. S.

    1989-02-01

    Very small samples from the Shroud of Turin have been dated by accelerator mass spectrometry in laboratories at Arizona, Oxford and Zurich. As controls, three samples whose ages had been determined independently were also dated. The results provide conclusive evidence that the linen of the Shroud of Turin is mediaeval.

  13. Centaur Standard Shroud (CSS) cryogenic unlatch tests

    NASA Technical Reports Server (NTRS)

    1973-01-01

    Cryogenic tanking and partial jettison (unlatch) tests were performed on a full scale Centaur vehicle and Centaur Standard Shroud (CSS) to develop and qualify the CSS insulation system, the CSS and Centaur ground-hold purge systems, and the Centaur hydrogen tank flight vent system. Operation of the shroud/Centaur pyrotechnic systems, seals, and the shroud jettison springs, hinges, and other separation systems was demonstrated by a partial jettison of the shroud into catch nets. The Centaur tanks were filled with liquid hydrogen and liquid nitrogen. Prelaunch operations were performed, and data taken to establish system performances. Results from the initial tests showed a higher than expected heat transfer rate to the Centaur hydrogen tank. In addition, the release mechanism for the forward seal between the Centaur and the CSS did not function properly, and the seal was torn during jettison of the shroud.

  14. Turbine assembly containing an inner shroud

    DOEpatents

    Bagepalli, Bharat Sampathkumaran; Corman, Gregory Scot; Dean, Anthony John; DiMascio, Paul Stephen; Mirdamadi, Massoud

    2000-01-01

    A turbine assembly having a turbine stator, a ceramic inner shroud, and a first spring. The stator has a longitudinal axis and an outer shroud block with opposing and longitudinally outward facing first and second sides. The first side has a longitudinally outward projecting first ledge and has a first side portion located radially outward of the first ledge. The ceramic inner shroud has a first hook portion longitudinally and radially surrounding the first ledge. The first spring is attached to one of the first side portion and the first hook portion and unattachedly and resiliently contacts the other of the first side portion and the first hook portion.

  15. Nozzle and shroud assembly mounting structure

    DOEpatents

    Faulder, Leslie J.; Frey, deceased, Gary A.; Nielsen, Engward W.; Ridler, Kenneth J.

    1997-01-01

    The present nozzle and shroud assembly mounting structure configuration increases component life and reduces maintenance by reducing internal stress between the mounting structure having a preestablished rate of thermal expansion and the nozzle and shroud assembly having a preestablished rate of thermal expansion being less than that of the mounting structure. The mounting structure includes an outer sealing portion forming a cradling member in which an annular ring member is slidably positioned. The mounting structure further includes an inner mounting portion to which a hooked end of the nozzle and shroud assembly is attached. As the inner mounting portion expands and contracts, the nozzle and shroud assembly slidably moves within the outer sealing portion.

  16. Nozzle and shroud assembly mounting structure

    DOEpatents

    Faulder, L.J.; Frey, G.A.; Nielsen, E.W.; Ridler, K.J.

    1997-08-05

    The present nozzle and shroud assembly mounting structure configuration increases component life and reduces maintenance by reducing internal stress between the mounting structure having a preestablished rate of thermal expansion and the nozzle and shroud assembly having a preestablished rate of thermal expansion being less than that of the mounting structure. The mounting structure includes an outer sealing portion forming a cradling member in which an annular ring member is slidably positioned. The mounting structure further includes an inner mounting portion to which a hooked end of the nozzle and shroud assembly is attached. As the inner mounting portion expands and contracts, the nozzle and shroud assembly slidably moves within the outer sealing portion. 3 figs.

  17. Detection of Matrix Crack Density of CFRP using an Electrical Potential Change Method with Multiple Probes

    NASA Astrophysics Data System (ADS)

    Todoroki, Akira; Omagari, Kazuomi

    Carbon Fiber Reinforced Plastic (CFRP) laminates are adopted for fuel tank structures of next generation space rockets or automobiles. Matrix cracks may cause fuel leak or trigger fatigue damage. A monitoring system of the matrix crack density is required. The authors have developed an electrical resistance change method for the monitoring of delamination cracks in CFRP laminates. Reinforcement fibers are used as a self-sensing system. In the present study, the electric potential method is adopted for matrix crack density monitoring. Finite element analysis (FEA) was performed to investigate the possibility of monitoring matrix crack density using multiple electrodes mounted on a single surface of a specimen. The FEA reveals the matrix crack density increases electrical resistance for a target segment between electrodes. Experimental confirmation was also performed using cross-ply laminates. Eight electrodes were mounted on a single surface of a specimen using silver paste after polishing of the specimen surface with sandpaper. The two outermost electrodes applied electrical current, and the inner electrodes measured electric voltage changes. The slope of electrical resistance during reloading is revealed to be an appropriate index for the detection of matrix crack density.

  18. Compressor ported shroud for foil bearing cooling

    DOEpatents

    Elpern, David G.; McCabe, Niall; Gee, Mark

    2011-08-02

    A compressor ported shroud takes compressed air from the shroud of the compressor before it is completely compressed and delivers it to foil bearings. The compressed air has a lower pressure and temperature than compressed outlet air. The lower temperature of the air means that less air needs to be bled off from the compressor to cool the foil bearings. This increases the overall system efficiency due to the reduced mass flow requirements of the lower temperature air. By taking the air at a lower pressure, less work is lost compressing the bearing cooling air.

  19. The Shroud of Turin: Relic or icon?

    NASA Astrophysics Data System (ADS)

    Dale, W. S. A.

    1987-11-01

    The Shroud of Turin, a linen cloth on which appear the imprints of the front and back of a crucified man, can be historically traced to ca. 1354 a.d. Many believe it to be a true relic of the Passion of Christ. Many others regard it as a fake. This paper suggests a third alternative, that it is an icon dating from the 11th century. If future scientific tests, of which radiocarbon dating will be the most important, support this theory, the Shroud of Turin may well be recognized as one of the masterpieces of Christian art.

  20. Cooling circuit for a gas turbine bucket and tip shroud

    DOEpatents

    Willett, Fred Thomas; Itzel, Gary Michael; Stathopoulos, Dimitrios; Plemmons, Larry Wayne; Plemmons, Helen M.; Lewis, Doyle C.

    2002-01-01

    An open cooling circuit for a gas turbine bucket wherein the bucket has an airfoil portion, and a tip shroud, the cooling circuit including a plurality of radial cooling holes extending through the airfoil portion and communicating with an enlarged internal area within the tip shroud before exiting the tip shroud such that a cooling medium used to cool the airfoil portion is subsequently used to cool the tip shroud.

  1. Prediction of Microporosity in Shrouded Impeller Castings

    SciTech Connect

    Viswanathan, S. Nelson, C.D.

    1998-09-01

    The purpose of this Cooperative Research and Development Agreement (CRADA) between the Oak Ridge National Laboratory (ORNL) and Morris Bean and Company was to link computer models of heat and fluid flow with previously developed quality criteria for the prediction of microporosity in a Al-4.5% Cu alloy shrouded impeller casting. The results may be used to analyze the casting process design for the commercial production of 206 o alloy shrouded impeller castings. Test impeller castings were poured in the laboratory for the purpose of obtaining thermal data and porosity distributions. Also, a simulation of the test impeller casting was conducted and the results validated with porosity measurements on the test castings. A comparison of the predicted and measured microporosity distributions indicated an excellent correlation between experiments and prediction. The results of the experimental and modeling studies undertaken in this project indicate that the quality criteria developed for the prediction of microporosity in Al-4.5% Cu alloy castings can accurately predict regions of elevated microporosity even in complex castings such as the shrouded impeller casting. Accordingly, it should be possible to use quality criteria for porosity prediction in conjunction with computer models of heat and fluid flow to optimize the casting process for the production of shrouded impeller castings. Since high levels of microporosity may be expected to result in poor fatigue properties, casting designs that are optimized for low levels of microporosity should exhibit superior fatigue life.

  2. FIB-SEM Tomography Probes the Mesoscale Pore Space of an Individual Catalytic Cracking Particle

    PubMed Central

    2016-01-01

    The overall performance of a catalyst particle strongly depends on the ability of mass transport through its pore space. Characterizing the three-dimensional structure of the macro- and mesopore space of a catalyst particle and establishing a correlation with transport efficiency is an essential step toward designing highly effective catalyst particles. In this work, a generally applicable workflow is presented to characterize the transport efficiency of individual catalyst particles. The developed workflow involves a multiscale characterization approach making use of a focused ion beam-scanning electron microscope (FIB-SEM). SEM imaging is performed on cross sections of 10.000 μm2, visualizing a set of catalyst particles, while FIB-SEM tomography visualized the pore space of a large number of 8 μm3 cubes (subvolumes) of individual catalyst particles. Geometrical parameters (porosity, pore connectivity, and heterogeneity) of the material were used to generate large numbers of virtual 3D volumes resembling the sample’s pore space characteristics, while being suitable for computationally demanding transport simulations. The transport ability, defined as the ratio of unhindered flow over hindered flow, is then determined via transport simulations through the virtual volumes. The simulation results are used as input for an upscaling routine based on an analogy with electrical networks, taking into account the spatial heterogeneity of the pore space over greater length scales. This novel approach is demonstrated for two distinct types of industrially manufactured fluid catalytic cracking (FCC) particles with zeolite Y as the active cracking component. Differences in physicochemical and catalytic properties were found to relate to differences in heterogeneities in the spatial porosity distribution. In addition to the characterization of existing FCC particles, our method of correlating pore space with transport efficiency does also allow for an up-front evaluation of

  3. View-limiting shrouds for insolation radiometers

    NASA Technical Reports Server (NTRS)

    Dennison, E. W.; Trentelman, G. F.

    1985-01-01

    Insolation radiometers (normal incidence pyrheliometers) are used to measure the solar radiation incident on solar concentrators for calibrating thermal power generation measurements. The measured insolation value is dependent on the atmospheric transparency, solar elevation angle, circumsolar radiation, and radiometer field of view. The radiant energy entering the thermal receiver is dependent on the same factors. The insolation value and the receiver input will be proportional if the concentrator and the radiometer have similar fields of view. This report describes one practical method for matching the field of view of a radiometer to that of a solar concentrator. The concentrator field of view can be calculated by optical ray tracing methods and the field of view of a radiometer with a simple shroud can be calculated by using geometric equations. The parameters for the shroud can be adjusted to provide an acceptable match between the respective fields of view. Concentrator fields of view have been calculated for a family of paraboloidal concentrators and receiver apertures. The corresponding shroud parameters have also been determined.

  4. Experimental and analytical study of ceramic-coated turbine-tip shroud seals for small turbine engines

    NASA Technical Reports Server (NTRS)

    Biesiadny, T. J.; Mcdonald, G. E.; Hendricks, R. C.; Little, J. K.; Robinson, R. A.; Klann, G. A.; Lassow, E. S.

    1985-01-01

    The results of an experimental and analytical evaluation of ceramic turbine tip shrouds within a small turbine engine operating environment are presented. The ceramic shrouds were subjected to 1001 cycles between idle and high power and steady-state conditions for a total of 57.8 engine hr. Posttest engine inspection revealed mud-flat surface cracking, which was attributed to microcracking under tension with crack penetration to the ceramic and bond coat interface. Sections and micrographs tend to corroborate the thesis. The engine test data provided input to a thermomechanical analysis to predict temperature and stress profiles throughout the ceramic gas-path seal. The analysis predicts cyclic thermal stresses large enough to cause the seal to fail. These stresses are, however, mitigated by inelastic behavior of the shroud materials and by the microfracturing that tensile stresses produce. Microfracturing enhances shroud longevity during early life but provides the failure mechanism during life but provides the failure mechanism during extended life when coupled with the time dependent inelastic materials effects.

  5. Closed circuit steam cooled turbine shroud and method for steam cooling turbine shroud

    DOEpatents

    Burdgick, Steven Sebastian; Sexton, Brendan Francis; Kellock, Iain Robertson

    2002-01-01

    A turbine shroud cooling cavity is partitioned to define a plurality of cooling chambers for sequentially receiving cooling steam and impingement cooling of the radially inner wall of the shoud. An impingement baffle is provided in each cooling chamber for receiving the cooling media from a cooling media inlet in the case of the first chamber or from the immediately upstream chamber in the case of the second through fourth chambers and includes a plurality of impingement holes for effecting the impingement cooling of the shroud inner wall.

  6. Centaur Standard Shroud (CSS) static limit load structural tests

    NASA Technical Reports Server (NTRS)

    Eastwood, C.

    1975-01-01

    The structural capabilities of the jettisonable metal shroud were tested and the interaction of the shroud with the Centaur stage was evaluated. A flight-configured shroud and the assemblies of the associated Centaur stage were tested for applied axial and shear loads to flight limit values. The tests included various thermal, pressure, and load conditions to verify localized strength capabilities, to evaluate subsystem performance, and to determine the aging effect on insulation system properties. The tests series verified the strength capabilities of the shroud and of all associated flight assembles. Shroud deflections were shown to remain within allowable limits so long as load sharing members were connected between the shroud and the Centaur stage.

  7. Cleaning of a thermal vacuum chamber with shrouds in place

    NASA Technical Reports Server (NTRS)

    Bond, William R.

    1992-01-01

    In February, 1991, a failure of a rotary booster pump caused the diffusion pumps to backstream into a 10 ft x 15 ft thermal vacuum chamber. Concerns existed about the difficulty of removing and reinstalling the shrouds without causing leaks. The time required for the shroud removal was also of concern. These concerns prompted us to attempt to clean the chamber without removing the shrouds.

  8. Centaur Standard Shroud (CSS) full jettison test dynamic analysis

    NASA Technical Reports Server (NTRS)

    Kasper, H. J.; Donovan, R. M.

    1974-01-01

    During the space power facility jettison tests, the non-domed half of the Centaur standard shroud was allowed to completely separate from its hinge connection and was caught in a horizontal catch net. A rigid body dynamic analysis that was performed to predict the half shroud prior to and after net contact is presented. Analytical predictions of the longitudinal and circumferential bending moments imposed on the half shroud by the catch net and the net pressure on the half shroud corrugated skin are also presented.

  9. Ceramic turbine stator vane and shroud support

    DOEpatents

    Glenn, Robert G.

    1981-01-01

    A support system for supporting the stationary ceramic vanes and ceramic outer shrouds which define the motive fluid gas path in a gas turbine engine is shown. Each individual segment of the ceramic component whether a vane or shroud segment has an integral radially outwardly projecting stem portion. The stem is enclosed in a split collet member of a high-temperature alloy material having a cavity configured to interlock with the stem portion. The generally cylindrical external surface of the collet engages a mating internal cylindrical surface of an aperture through a supporting arcuate ring segment with mating camming surfaces on the two facing cylindrical surfaces such that radially outward movement of the collet relative to the ring causes the internal cavity of the collet to be reduced in diameter to tightly engage the ceramic stem disposed therein. A portion of the collet extends outwardly through the ring segment opposite the ceramic piece and is threaded for receiving a nut and a compression washer for retaining the collet in the ring segment under a continuous biasing force urging the collet radially outwardly.

  10. Vibration characteristics analysis of rotating shrouded blades with impacts

    NASA Astrophysics Data System (ADS)

    Ma, Hui; Xie, Fangtao; Nai, Haiqiang; Wen, Bangchun

    2016-09-01

    A dynamic model of rotating shrouded blades with impacts among adjacent shrouded blades is established considering the effects of the centrifugal stiffening, spin softening and Coriolis force, and the model is validated using finite element method. In the proposed model, the shrouded blade is simplified as a cantilever Euler-Bernoulli beam with a mass point at the free end, and the flexural dynamic stiffness of shrouded blade is selected as contact stiffness during collision. Based on the developed model, the effects of symmetric and asymmetric shroud gaps, rotational speeds, and aerodynamic force amplitudes on the dynamic characteristics of shrouded blades are analyzed through Newmark-β numerical method. The results indicate that (1) the vibro-impact responses of shrouded blades under some asymmetric gaps are more complicated than that under symmetric gap. (2) With the increase of rotational speed from 6000 to 10,000 rev/min, the system vibration experiences from period-three motion, through chaotic motion, finally to period-one motion during collision process because the increasing rotational speed changes the flexural dynamic stiffness of rotating blade. (3) The vibration displacements of shrouded blades increase linearly, and impact force increases linearly with the increase of aerodynamic force amplitude.

  11. Eddy current modeling by finite element method for evaluation of mechanical properties of the structure cracked in absolute probe

    NASA Astrophysics Data System (ADS)

    Harzallah, Salaheddine; Chabaat, Mohamed; Belgacem, Fethi Bin Muhammad

    2014-12-01

    In this paper, a nondestructive evaluation by sensor Eddy current is used as a tool to control cracks and micro-cracks in materials. A simulation by a numerical approach based on the finite element method is employed to detect cracks in materials and eventually to study their propagation using a crucial parameter such as a Stress Intensity Factor (SIF). This method has emerged as one of the most efficient techniques for prospecting cracks in materials, evaluating SIFs and analyzing crack's growth in the context of linear elastic fracture mechanics (LEFM). This technique uses extrapolation of displacements from results compared with those obtained by the integral interaction. On the other hand, crack's growth is analyzed as a model by combining the maximum circumferential stress criteria with the critical plane for predicting the direction of crack growth. Moreover, a constant crack growth increment is determined using the modified Paris's model. Furthermore, stress intensity factors needed for these models are calculated using the domain form of the J-integral interactions.

  12. Infrared fine-structure line diagnostics of shrouded active galactic nuclei

    NASA Technical Reports Server (NTRS)

    Voit, G. M.

    1993-01-01

    Far-infrared spectroscopy of celestial objects will improve dramatically in the coming decade, allowing astronomers to use fine-structure line emission to probe photoionized regions obscured in the optical band by thick clouds of dust. The ultraluminous far-IR galaxies revealed by IRAS, quasar-like in luminosity but smothered in molecular gas, probably conceal either immense starbursts or luminous active nuclei. In both scenarios, these objects ought to produce copious infrared fine-structure emission with several lines comparable to H(beta) in luminosity. This paper shows how these lines, if detected, can be used to determine the electron densities and far-IR obscurations of shrouded photoionized regions and to constrain the shape and ionization parameter of the ionizing spectra. The presence of (Ne V) emission in particular will distinguish shrouded AGN's from shrouded starbursts. Since all active galaxies photoionize at least some surrounding material, these diagnostics can also be applied to active galaxies in general and will aid in studying how an active nucleus interacts with the interstellar medium of its host galaxy.

  13. Influence of ventilated shrouds on the convective heat transfer to a circular cylinder

    NASA Technical Reports Server (NTRS)

    Daryabeigi, Kamran; Ash, Robert L.; Dillon-Townes, Lawrence A.

    1987-01-01

    Convective heat transfer to shrouded cylinders in transverse flow has been studied over the Reynolds number range 2000-20,000. The influence of shroud ventilation, relative shroud diameters, and orientation of the ventilation holes was studied. In some cases, average inner-cylinder Nusselt numbers were found to exceed the comparable bare-cylinder values by as much as 50 percent. Cylinder heat convection was influenced more by the degree of ventilation and shroud diameter than by hole orientation. An equivalent inner bare cylinder diameter, based on degree of shroud ventilation and shroud diameter, was developed which can be useful in shroud design studies.

  14. Centaur Standard Shroud (CSS) static ultimate load structural tests

    NASA Technical Reports Server (NTRS)

    1975-01-01

    A series of tests were conducted on the jettisonable metallic shroud used on the Titan/Centaur launch vehicle to verify its structural capabilities and to evaluate its structural interaction with the Centaur stage. A flight configured shroud and the interfacing Titan/Centaur structural assemblies were subjected to tests consisting of combinations of applied axial and shear loads to design ultimate values, including a set of tests on thermal conditions and two dynamic response tests to verify the analytical stiffness model. The strength capabilities were demonstrated at ultimate (125 percent of design limit) loads. It was also verified that the spring rate of the flight configured shroud-to-Centaur forward structural deflections of the specimen became nonlinear, as expected, above limit load values. This test series qualification program verified that the Titan/Centaur shroud and the Centaur and Titan interface components are qualified structurally at design ultimate loads.

  15. Fluidized-bed calciner with combustion nozzle and shroud

    DOEpatents

    Wielang, Joseph A.; Palmer, William B.; Kerr, William B.

    1977-01-01

    A nozzle employed as a burner within a fluidized bed is coaxially enclosed within a tubular shroud that extends beyond the nozzle length into the fluidized bed. The open-ended shroud portion beyond the nozzle end provides an antechamber for mixture and combustion of atomized fuel with an oxygen-containing gas. The arrangement provides improved combustion efficiency and excludes bed particles from the high-velocity, high-temperature portions of the flame to reduce particle attrition.

  16. Probing liquation cracking and solidification through modeling of momentum, heat, and solute transport during welding of aluminum alloys

    NASA Astrophysics Data System (ADS)

    Mishra, S.; Chakraborty, S.; DebRoy, T.

    2005-05-01

    A transport phenomena-based mathematical model is developed to understand liquation cracking in weldments during fusion welding. Equations of conservation of mass, momentum, heat, and solute transport are numerically solved considering nonequilibrium solidification and filler metal addition to determine the solid and liquid phase fractions in the solidifying region and the solute distribution in the weld pool. An effective partition coefficient that considers the local interface velocity and the undercooling is used to simulate solidification during welding. The calculations show that convection plays a dominant role in the solute transport inside the weld pool. The predicted weld-metal solute content agreed well with the independent experimental observations. The liquation cracking susceptibility in Al-Cu alloy weldments could be reliably predicted by the model based on the computed solidifying weld-metal composition and solid fraction considering nonequilibrium solidification.

  17. Cryogenic Shrouds for Testing Thermal-Insulation Panels

    NASA Technical Reports Server (NTRS)

    Norris, Jeffrey; Carroll, Robert; Kirch, Charles

    2007-01-01

    Cryogenic shrouds have been designed and built for use in thermomechanical testing of samples of thermalinsulation panels on cryogenic vessels. In the original application for which these shrouds were specifically designed, the samples are representative of the large-area thermal-insulation panels on the space-shuttle external tanks that hold liquid hydrogen and liquid oxygen, and the purpose of the testing is to demonstrate the ability of bonded layers in the panels to resist delamination under a combination of applied uniaxial mechanical loads and realistic operational temperatures. Presumably, the shrouds and the tests performed by use of them could be modified to enable similar evaluation of thermomechanical properties of thermal-insulation panels for cryogenic vessels other than the external tanks of the space shuttles. The shrouds are required to enable maintenance of required temperatures on the inner and outer surfaces of the thermal-insulation-panel samples, to enable visual observation of the outer surfaces of the samples, and not to introduce any measurable loads into the panels. For each panel sample, there are two shrouds: one to be mounted on the inner surface (the surface that would be in contact with a tank containing a cryogenic liquid during normal use) and one to be mounted on the outer surface (the surface that would be exposed to ambient air or other warmer environment during normal use). The shrouds for testing specimens of thermal-insulation- panels for the liquid-hydrogen tank are made largely of titanium; the shrouds for testing specimens of thermal- insulation-panels for the liquid-oxygen tank are made largely of an aluminum- lithium alloy. The specific temperature requirements are the following: The inner shroud must make it possible to maintain a temperature of 321 degrees F (196 degrees C) [the approximate temperature of liquid nitrogen] or 453 F (about 269 C) [the approximate temperature of liquid helium] on the inner face of the

  18. How was the Turin Shroud Man crucified?

    PubMed

    Bevilacqua, M; Fanti, G; D'Arienzo, M; Porzionato, A; Macchi, V; De Caro, R

    2014-12-01

    As the literature is not exhaustive with reference to the way the Turin Shroud (TS) Man was crucified, and it is not easy to draw significant information from only a "photograph" of a man on a linen sheet, this study tries to add some detail on this issue based on both image processing of high resolution photos of the TS and on experimental tests on arms and legs of human cadavers. With regard to the TS Man hands, a first hypothesis states that the left hand of the TS Man was nailed twice at two different anatomical sites: the midcarpal joint medially to the pisiform between the lunate/pyramidal and capitate/uncinate bones (Destot's space) and the radiocarpal joint between the radio, lunate and scaphoid; also the right hand would have been nailed twice. A second hypothesis, preferred by the authors, states that the hands were nailed only once in the Destot's space with partial lesion of the ulnar nerve and flexion of the metacarpophalangeal joint of the thumbs. With regard to the TS Man feet, the imprint of the sole of the right foot leads to the conclusion that TS Man suffered a dislocation at the ankle just before the nailing. The entrance hole of the nail on the right foot is a few inches from the ankle, and excludes a double nailing. The nail has been driven between the tarsal bones. The TS Man suffered the following tortures during crucifixion: a very serious and widespread causalgia due to total paralysis of the upper right limb (paradoxical causalgia); a nailing of the left wrist with damage to the ulnar nerve; a similar nailing of the right wrist; and a nailing to both feet using one only nail that injured the plantaris medialis nerves. The respiratory limitation was probably not sufficient to cause death by asphyxiation. Also considering the hypovolemia produced by scourging and the many other tortures detectable on the TS, the principal cause of death can be attributed to a myocardial infarction.

  19. Helium-Cooled Black Shroud for Subscale Cryogenic Testing

    NASA Technical Reports Server (NTRS)

    Tuttle, James; Jackson, Michael; DiPirro, Michael; Francis, John

    2011-01-01

    This shroud provides a deep-space simulating environment for testing scaled-down models of passively cooling systems for spaceflight optics and instruments. It is used inside a liquid-nitrogen- cooled vacuum chamber, and it is cooled by liquid helium to 5 K. It has an inside geometry of approximately 1.6 m diameter by 0.45 m tall. The inside surfaces of its top and sidewalls have a thermal absorptivity greater than 0.96. The bottom wall has a large central opening that is easily customized to allow a specific test item to extend through it. This enables testing of scale models of realistic passive cooling configurations that feature a very large temperature drop between the deepspace-facing cooled side and the Sun/Earth-facing warm side. This shroud has an innovative thermal closeout of the bottom wall, so that a test sample can have a hot (room temperature) side outside of the shroud, and a cold side inside the shroud. The combination of this closeout and the very black walls keeps radiated heat from the sample s warm end from entering the shroud, reflecting off the walls and heating the sample s cold end. The shroud includes 12 vertical rectangular sheet-copper side panels that are oriented in a circular pattern. Using tabs bent off from their edges, these side panels are bolted to each other and to a steel support ring on which they rest. The removable shroud top is a large copper sheet that rests on, and is bolted to, the support ring when the shroud is closed. The support ring stands on four fiberglass tube legs, which isolate it thermally from the vacuum chamber bottom. The insides of the cooper top and side panels are completely covered with 25- mm-thick aluminum honeycomb panels. This honeycomb is painted black before it is epoxied to the copper surfaces. A spiral-shaped copper tube, clamped at many different locations to the outside of the top copper plate, serves as part of the liquid helium cooling loop. Another copper tube, plumbed in a series to the

  20. Composite seal for turbomachinery. [backings for turbine engine shrouds

    NASA Technical Reports Server (NTRS)

    Bill, R. C.; Ludwig, L. P. (Inventor)

    1979-01-01

    A gas path seal suitable for use with a turbine engine or compressor is provided. A shroud wearable or abradable by the abrasion of the rotor blades of the turbine or compressor protects the rotor blades. A compliant backing surrounds the shroud. The backing may be made of corrugated sheets or the like with adjacent layers having off-set corrugations, with axes of the folds parallel to the rotor axis. The sheets may be bonded together at points of contact by brazing, welding or the like. In another embodiment a compliant material is covered with a thin ductile layer. A mounting fixture surrounds the backing.

  1. Measurements of the rotordynamic shroud forces for centrifugal pumps

    NASA Technical Reports Server (NTRS)

    Guinzburg, A.; Brennen, C. E.; Acosta, A. J.; Caughey, T. K.

    1990-01-01

    An experiment was designed to measure the rotordynamic shroud forces on a centrifugal pump impeller. The measurements were done for various whirl/impeller speed ratios and for different flow rates. A destabilizing tangential force was measured for small positive whirl ratios and this force decreased with increasing flow rate.

  2. 15. VIEW OF THE SPECIAL SHROUDING AND AIR HANDLING SYSTEM ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    15. VIEW OF THE SPECIAL SHROUDING AND AIR HANDLING SYSTEM USED IN BERYLLIUM PRODUCTION. (3/30/89) - Rocky Flats Plant, Non-Nuclear Production Facility, South of Cottonwood Avenue, west of Seventh Avenue & east of Building 460, Golden, Jefferson County, CO

  3. The Most Luminous Object in the Universe: Shrouded Quasar or Proto-Galaxy

    NASA Technical Reports Server (NTRS)

    Heckman, Timothy M.

    1999-01-01

    We have used ASCA to observe the IRAS source FSC 10214+4724, which is identified with a galaxy at a redshift of 2.286. When first discovered, it was believed to be the most luminous object in the universe. Subsequent HST images have established that it is gravitationally-lensed by a foreground cluster. It is still a very powerful object, but not extraordinarily so. Observations at other wavebands have not established whether it is a dust-shrouded quasar or a young, massive galaxy in the process of formation. Since quasars are strong emitters of hard X-rays, while proto-galaxies would not be, and since the opacity of gas and dust is relatively small in the energy regime probed by ASCA (3 to 30 keV in the galaxy rest frame), we undertook these observations to search for a heavily shrouded quasar that might be invisible at lower energies. However, the observations did not detect any emission from this object. This either means that the galaxy is in fact powered by a starburst or that the putative quasar is located behind a very high column density of absorbing gas (N_H > 10(exp 25)/sq cm), so that not even hard X-rays are transmitted. A hidden quasar should be visible in reflected light in X-ray data of higher sensitivity. Observations with NASA's Chandra X-ray Observatory or ESA's XMM are required to settle the matter. No publication resulted from our null result.

  4. BWR Vessel and Internals Project Removal and Analysis of Material Samples from Core Shroud and Top Guide at Susquehanna Unit 2

    SciTech Connect

    Howell, D; Haertel, T; Lindberg, J; Oliver, B; Greenwood, L

    2005-04-15

    Fast and thermal fluence were determined by a laboratory analysis of the samples. Fluence in the upper regions of the shroud (between the H1 and H2 welds) was substantially lower than that in the belt line region (near the H4 weld). Fluence in the top guide was significantly higher than fluence on the core shroud. As expected, helium concentrations were highest in regions where fluence was highest. Estimates of the initial boron concentration were similar to measurements made on materials removed from other reactors. A technical justification evaluated the acceptability of the sampling process with respect to structural consequences of material removal and to increased cracking susceptibility due to the as-left condition. It was determined that the sampling process was acceptable on both counts.

  5. Heat transfer and flow characteristics on a gas turbine shroud.

    PubMed

    Obata, M; Kumada, M; Ijichi, N

    2001-05-01

    The work described in this paper is an experimental investigation of the heat transfer from the main flow to a turbine shroud surface, which may be applicable to ceramic gas turbines. Three kinds of turbine shrouds are considered with a flat surface, a taper surface and a spiral groove surface opposite to the blades in an axial flow turbine of actual turbo-charger. Heat transfer measurements were performed for the experimental conditions of a uniform heat flux or a uniform wall temperature. The effects of the inlet flow angle, rotational speed, and tip clearance on the heat transfer coefficient were clarified under on- and off-design flow conditions. The mean heat transfer coefficient was correlated to the blade Reynolds number and tip clearance, and compared with an experimental correlation and measurements of a flat surface. A comparison was also made for the measurement of static pressure distributions.

  6. Vortex Rings Generated by a Shrouded Hartmann-Sprenger Tube

    NASA Technical Reports Server (NTRS)

    DeLoof, Richard L. (Technical Monitor); Wilson, Jack

    2005-01-01

    The pulsed flow emitted from a shrouded Hartmann-Sprenger tube was sampled with high-frequency pressure transducers and with laser particle imaging velocimetry, and found to consist of a train of vortices. Thrust and mass flow were also monitored using a thrust plate and orifice, respectively. The tube and shroud lengths were altered to give four different operating frequencies. From the data, the radius, velocity, and circulation of the vortex rings was obtained. Each frequency corresponded to a different length to diameter ratio of the pulse of air leaving the driver shroud. Two of the frequencies had length to diameter ratios below the formation number, and two above. The formation number is the value of length to diameter ratio below which the pulse converts to a vortex ring only, and above which the pulse becomes a vortex ring plus a trailing jet. A modified version of the slug model of vortex ring formation was used to compare the observations with calculated values. Because the flow exit area is an annulus, vorticity is shed at both the inner and outer edge of the jet. This results in a reduced circulation compared with the value calculated from slug theory accounting only for the outer edge. If the value of circulation obtained from laser particle imaging velocimetry is used in the slug model calculation of vortex ring velocity, the agreement is quite good. The vortex ring radius, which does not depend on the circulation, agrees well with predictions from the slug model.

  7. Dynamically tuned shroud for gun barrel vibration attenuation

    NASA Astrophysics Data System (ADS)

    Littlefield, Andrew G.; Kathe, Eric L.; Durocher, Robert

    2002-06-01

    Modern tank guns, such as the one on the Abrams, are stabilized to allow fire on the move while traversing uneven terrain. The current barrel is short enough that treating as a rigid beam allows engagement of another tank at ranges of over a kilometer. However, as the length of the tube is extended, to meet required muzzle exit velocities, the terrain induced vibrations lead to increased muzzle pointing errors. A method to reduce these vibrations is to use the forward thermal shroud as part of a mass tuned damper. In this case the system under study is an extended length version of the gun currently fielded. This extended length increases its susceptibility to terrain-induced vibrations. The forward thermal shroud has been shortened and additional mass has been added onto its forward collar. This collar is then supported by springs, which are preloaded so that they stay in contact through the full range of the shroud's movement. Varying the stiffness of these springs allows for tuning of the absorber. Different types of springs and attachments have been tried. The current version uses leaf springs and a wedge collar. This system has been modeled and experiments conducted to validate the model.

  8. Investigation of eddy current examination on OD fatigue crack for steam generator tubes

    NASA Astrophysics Data System (ADS)

    Kong, Yuying; Ding, Boyuan; Li, Ming; Liu, Jinhong; Chen, Huaidong; Meyendorf, Norbert G.

    2015-03-01

    The opening width of fatigue crack was very small, and conventional Bobbin probe was very difficult to detect it in steam generator tubes. Different sizes of 8 fatigue cracks were inspected using bobbin probe rotating probe. The analysis results showed that, bobbin probe was not sensitive for fatigue crack even for small through wall crack mixed with denting signal. On the other hand, the rotating probe was easily to detect all cracks. Finally, the OD phase to depth curve for fatigue crack using rotating probe was established and the results agreed very well with the true crack size.

  9. Energy efficient engine high pressure turbine ceramic shroud support technology report

    NASA Technical Reports Server (NTRS)

    Nelson, W. A.; Carlson, R. G.

    1982-01-01

    This work represents the development and fabrication of ceramic HPT (high pressure turbine) shrouds for the Energy Efficient Engine (E3). Details are presented covering the work performed on the ceramic shroud development task of the NASA/GE Energy Efficient Engine (E3) component development program. The task consists of four phases which led to the selection of a ZrO2-BY2O3 ceramic shroud material system, the development of an automated plasma spray process to produce acceptable shroud structures, the fabrication of select shroud systems for evaluation in laboratory, component, and CF6-50 engine testing, and finally, the successful fabrication of ZrO2-8Y2O3/superpeg, engine quality shrouds for the E3 engine.

  10. NK-1 Removable Cryogenic Shroud (A Study of the Bimba Pneumatic Cylinder)

    SciTech Connect

    Anderson, K; Stefanescu, D

    2003-02-07

    The Mark 1 Cryostat requires a cryogenic shroud that must be retracted immediately before firing the NIF laser. This paper evaluates a pneumatic cylinder that has been chosen to open and close the shroud. After a variety of motion control and vacuum compatibility experiments, we concluded that the Bimba feedback control cylinder may be used to retract the shroud with certain modifications to its control system and additional rod seals.

  11. Analysis, Verification, and Application of Equations and Procedures for Design of Exhaust-pipe Shrouds

    NASA Technical Reports Server (NTRS)

    Ellerbrock, Herman H.; Wcislo, Chester R.; Dexter, Howard E.

    1947-01-01

    Investigations were made to develop a simplified method for designing exhaust-pipe shrouds to provide desired or maximum cooling of exhaust installations. Analysis of heat exchange and pressure drop of an adequate exhaust-pipe shroud system requires equations for predicting design temperatures and pressure drop on cooling air side of system. Present experiments derive such equations for usual straight annular exhaust-pipe shroud systems for both parallel flow and counter flow. Equations and methods presented are believed to be applicable under certain conditions to the design of shrouds for tail pipes of jet engines.

  12. Analysis of Shroud Options in Support of the Human Exploration of Mars

    NASA Technical Reports Server (NTRS)

    Feldman, Stuart; Borowski, Stanley; Engelund, Walter; Hundley, Jason; Monk, Timothy; Munk, Michelle

    2010-01-01

    In support of the Mars Design Reference Architecture (DRA) 5.0, the NASA study team analyzed several shroud options for use on the Ares V launch vehicle.1,2 These shroud options included conventional "large encapsulation" shrouds with outer diameters ranging from 8.4 to 12.9 meters (m) and overall lengths of 22.0 to 54.3 meters, along with a "nosecone-only" shroud option used for Mars transfer vehicle component delivery. Also examined was a "multi-use" aerodynamic encapsulation shroud used for launch, Mars aerocapture, and entry, descent, and landing of the cargo and habitat landers. All conventional shroud options assessed for use on the Mars launch vehicles were the standard biconic design derived from the reference shroud utilized in the Constellation Program s lunar campaign. It is the purpose of this paper to discuss the technical details of each of these shroud options including material properties, structural mass, etc., while also discussing both the volume and mass of the various space transportation and surface system payload elements required to support a "minimum launch" Mars mission strategy, as well as the synergy, potential differences and upgrade paths that may be required between the Lunar and Mars mission shrouds.

  13. Leaf seal for gas turbine stator shrouds and a nozzle band

    DOEpatents

    Burdgick, Steven Sebastian; Sexton, Brendan Francis

    2002-01-01

    A leaf seal assembly is secured to the trailing edge of a shroud segment for sealing between the shroud segment and the leading edge side wall of a nozzle outer band. The leaf seal includes a circumferentially elongated seal plate biased by a pair of spring clips disposed in a groove along the trailing edge of the shroud segment to maintain the seal plate in engagement with the flange on the leading edge side wall of the nozzle outer band. The leaf seal plate and spring clips receive pins tack-welded to the shroud segment to secure the leaf seal assembly in place.

  14. Cylindrical and conical shrouds for the reduction of ground noise of paraboloidal antennas

    NASA Astrophysics Data System (ADS)

    Landecker, T. L.; Smegal, R. J.; McKinley, J. M.

    1997-11-01

    The spillover noise of a reflector antenna can be reduced by attaching a shroud extending forward from the edge of the reflector; the shroud prevents ground radiation from entering the feed. Symmetrical paraboloidal antennas of diameter 40 wavelengths, equipped with cylindrical and conical shrouds, are analyzed using the method of moments. A cylindrical shroud, parallel to the reflector axis, may reduce antenna noise, but it raises the sidelobe level in the front hemisphere substantially and can also reduce antenna gain. These drawbacks can be overcome by using a conical shroud, flared outward. Such a shroud reduces the spillover lobes in the back hemisphere, thus lowering the antenna noise temperature, but generates a conical sidelobe in the front hemisphere. The peak level of this sidelobe can be reduced by building the shroud using two cones of different flare angles or by curving its cross section. The decrease in noise temperature, as well as the location and level of the conical sidelobes in the front hemisphere, can be predicted to useful accuracy using geometrical optics. The addition of a shroud increases the level of cross polarization near the main beam. However, this effect is reduced if the sharp corner where the shroud joins the reflector rim is replaced by a smooth transition. The level of cross polarization is then at a level comparable to that produced by scattering from feed-support struts.

  15. Environmentally assisted cracking in LWR materials

    SciTech Connect

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

    1998-03-01

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

  16. 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.

  17. Thermal stress analysis of a new turbine shroud seal concept

    NASA Technical Reports Server (NTRS)

    Handschuh, R. F.

    1985-01-01

    The thermal stress field of a two piece turbine shroud seal concept was analyzed and results compared to one piece designs by finite element analysis. The two piece seal has independently formed structure (substrate) and ceramic components that are assembled at ambient conditions. The boundary conditions used for analysis were hot gas surface temperatures of 1370 and 1650 C (2500 and 3000 F) and cooled surface temperature of 700 C (1285 F). The resulting thermal stress field, of the two piece seal when compared to the one piece seals in the region of all ceramic material, was reduced substantially.

  18. The release of trapped gases from amorphous solid water films. I. "Top-down" crystallization-induced crack propagation probed using the molecular volcano.

    PubMed

    May, R Alan; Smith, R Scott; Kay, Bruce D

    2013-03-14

    In this (Paper I) and the companion paper (Paper II; R. May, R. Smith, and B. Kay, J. Chem. Phys. 138, 104502 (2013)), we investigate the mechanisms for the release of trapped gases from underneath amorphous solid water (ASW) films. In prior work, we reported the episodic release of trapped gases in concert with the crystallization of ASW, a phenomenon that we termed the "molecular volcano." The observed abrupt desorption is due to the formation of cracks that span the film to form a connected pathway for release. In this paper, we utilize the "molecular volcano" desorption peak to characterize the formation of crystallization-induced cracks. We find that the crack length distribution is independent of the trapped gas (Ar, Kr, Xe, CH4, N2, O2, or CO). Selective placement of the inert gas layer is used to show that cracks form near the top of the film and propagate downward into the film. Isothermal experiments reveal that, after some induction time, cracks propagate linearly in time with an Arrhenius dependent velocity corresponding to an activation energy of 54 kJ∕mol. This value is consistent with the crystallization growth rates reported by others and establishes a direct connection between crystallization growth rate and the crack propagation rate. A two-step model in which nucleation and crystallization occurs in an induction zone near the top of the film followed by the propagation of a crystallization∕crack front into the film is in good agreement with the temperature programmed desorption results.

  19. The Release of Trapped Gases from Amorphous Solid Water Films: I. “Top-Down” Crystallization-Induced Crack Propagation Probed using the Molecular Volcano

    SciTech Connect

    May, Robert A.; Smith, R. Scott; Kay, Bruce D.

    2013-03-14

    In this (Paper I) and the companion paper (Paper II) we investigate the mechanisms for the release of trapped gases from underneath of amorphous solid water (ASW) films. In prior work, we reported the episodic release of trapped gases in concert with the crystallization ASW, a phenomenon that we termed the "molecular volcano". The observed abrupt desorption is due to the formation of cracks that span the film to form a connected pathway for release. In this paper we utilize the "molecular volcano" desorption peak to characterize the formation of crystallization-induced cracks. We find that the crack length and distribution are independent of the trapped gas (Ar, Kr, Xe, CH4, N2, O2 or CO). Selective placement of the inert gas layer is used to show that cracks form near the top of the film and propagate downward into the film. Isothermal experiments reveal that, after some induction time, cracks propagate linearly in time with an Arrhenius dependent velocity corresponding to an activation energy of 54 kJ/mol. This value is consistent with the crystallization growth rate reported by others and establishes a direct connection between crystallization growth rate and the crack propagation rate. A two-step model in which nucleation and crystallization occurs in an induction zone near the top of the film followed by the propagation of a crystallization/crack front into the film is in good agreement with the temperature programmed desorption results.

  20. TOTAL SOLAR ECLIPSE OBSERVATIONS OF HOT PROMINENCE SHROUDS

    SciTech Connect

    Habbal, S. Rifai; Morgan, H.; Scholl, I.; Druckmueller, M.; Rusin, V.; Daw, A.; Johnson, J.; Arndt, M.

    2010-08-20

    Using observations of the corona taken during the total solar eclipses of 2006 March 29 and 2008 August 1 in broadband white light and in narrow bandpass filters centered at Fe X 637.4 nm, Fe XI 789.2 nm, Fe XIII 1074.7 nm, and Fe XIV 530.3 nm, we show that prominences observed off the solar limb are enshrouded in hot plasmas within twisted magnetic structures. These shrouds, which are commonly referred to as cavities in the literature, are clearly distinct from the overlying arch-like structures that form the base of streamers. The existence of these hot shrouds had been predicted by model studies dating back to the early 1970s, with more recent studies implying their association with twisted magnetic flux ropes. The eclipse observations presented here, which cover a temperature range of 0.9 to 2 x10{sup 6} K, are the first to resolve the long-standing ambiguity associated with the temperature and magnetic structure of prominence cavities.

  1. Uncovering the sources of DNA found on the Turin Shroud

    PubMed Central

    Barcaccia, Gianni; Galla, Giulio; Achilli, Alessandro; Olivieri, Anna; Torroni, Antonio

    2015-01-01

    The Turin Shroud is traditionally considered to be the burial cloth in which the body of Jesus Christ was wrapped after his death approximately 2000 years ago. Here, we report the main findings from the analysis of genomic DNA extracted from dust particles vacuumed from parts of the body image and the lateral edge used for radiocarbon dating. Several plant taxa native to the Mediterranean area were identified as well as species with a primary center of origin in Asia, the Middle East or the Americas but introduced in a historical interval later than the Medieval period. Regarding human mitogenome lineages, our analyses detected sequences from multiple subjects of different ethnic origins, which clustered into a number of Western Eurasian haplogroups, including some known to be typical of Western Europe, the Near East, the Arabian Peninsula and the Indian sub-continent. Such diversity does not exclude a Medieval origin in Europe but it would be also compatible with the historic path followed by the Turin Shroud during its presumed journey from the Near East. Furthermore, the results raise the possibility of an Indian manufacture of the linen cloth. PMID:26434580

  2. Design of Shrouded Airborne Wind Turbine & CFD Analysis

    NASA Astrophysics Data System (ADS)

    Anbreen, Faiqa; Faiqa Anbreen Collaboration

    2015-11-01

    The focus is to design a shrouded airborne wind turbine, capable to generate 70 kW to propel a leisure boat. The idea of designing an airborne turbine is to take the advantage of different velocity layers in the atmosphere. The blades have been designed using NREL S826 airfoil, which has coefficient of lift CL of 1.4 at angle of attack, 6°. The value selected for CP is 0.8. The rotor diameter is 7.4 m. The balloon (shroud) has converging-diverging nozzle design, to increase the mass flow rate through the rotor. The ratio of inlet area to throat area, Ai/At is 1.31 and exit area to throat area, Ae/At is1.15. The Solidworks model has been analyzed numerically using CFD. The software used is StarCCM +. The Unsteady Reynolds Averaged Navier Stokes Simulation (URANS) K- ɛ model has been selected, to study the physical properties of the flow, with emphasis on the performance of the turbine. Stress analysis has been done using Nastran. From the simulations, the torque generated by the turbine is approximately 800N-m and angular velocity is 21 rad/s.

  3. Prediction of leakage flow in a shrouded centrifugal blood pump.

    PubMed

    Teo, Ji-Bin; Chan, Weng-Kong; Wong, Yew-Wah

    2010-09-01

    This article proposes a phenomenological model to predict the leakage flow in the clearance gap of shrouded centrifugal blood pumps. A good washout in the gap clearance between the rotating impeller surfaces and volute casing is essential to avoid thrombosis. However, excessive leakage flow will result in higher fluid shear stress that may lead to hemolysis. Computational fluid dynamics (CFD) analysis was performed to investigate the leakage flow in a miniaturized shrouded centrifugal blood pump operating at a speed of 2000 rpm. Based on an analytical model derived earlier, a phenomenological model is proposed to predict the leakage flow. The leakage flow rate is found to be proportional to h(α) , where h is the gap size and the exponent α ranges from 2.955 to 3.15 for corresponding gap sizes of 0.2-0.5 mm. In addition, it is observed that α is a linear function of the gap size h. The exponent α compensates for the variation of pressure difference along the circumferential direction as well as inertia effects that are dominant for larger gap clearances. The proposed model displays good agreement with computational results. The CFD analysis also showed that for larger gap sizes, the total leakage flow rate is of the same order of magnitude as the operating flow rate, thus suggesting low volumetric efficiency.

  4. Uncovering the sources of DNA found on the Turin Shroud.

    PubMed

    Barcaccia, Gianni; Galla, Giulio; Achilli, Alessandro; Olivieri, Anna; Torroni, Antonio

    2015-10-05

    The Turin Shroud is traditionally considered to be the burial cloth in which the body of Jesus Christ was wrapped after his death approximately 2000 years ago. Here, we report the main findings from the analysis of genomic DNA extracted from dust particles vacuumed from parts of the body image and the lateral edge used for radiocarbon dating. Several plant taxa native to the Mediterranean area were identified as well as species with a primary center of origin in Asia, the Middle East or the Americas but introduced in a historical interval later than the Medieval period. Regarding human mitogenome lineages, our analyses detected sequences from multiple subjects of different ethnic origins, which clustered into a number of Western Eurasian haplogroups, including some known to be typical of Western Europe, the Near East, the Arabian Peninsula and the Indian sub-continent. Such diversity does not exclude a Medieval origin in Europe but it would be also compatible with the historic path followed by the Turin Shroud during its presumed journey from the Near East. Furthermore, the results raise the possibility of an Indian manufacture of the linen cloth.

  5. User manual for SPLASH (Single Panel Lamp and Shroud Helper).

    SciTech Connect

    Larsen, Marvin Elwood

    2006-02-01

    The radiant heat test facility develops test sets providing well-characterized thermal environments, often representing fires. Many of the components and procedures have become standardized to such an extent that the development of a specialized design tool to determine optimal configurations for radiant heat experiments was appropriate. SPLASH (Single Panel Lamp and Shroud Helper) is that tool. SPLASH is implemented as a user-friendly, Windows-based program that allows a designer to describe a test setup in terms of parameters such as number of lamps, power, position, and separation distance. This document is a user manual for that software. Any incidental descriptions of theory are only for the purpose of defining the model inputs. The theory for the underlying model is described in SAND2005-2947 (Ref. [1]). SPLASH provides a graphical user interface to define lamp panel and shroud designs parametrically, solves the resulting radiation enclosure problem for up to 2500 surfaces, and provides post-processing to facilitate understanding and documentation of analyzed designs.

  6. On Wind Tunnel Tests and Computations Concerning the Problem of Shrouded Propellers

    NASA Technical Reports Server (NTRS)

    Kruger, W.

    1949-01-01

    Results of measurements on a shrouded propeller are given. The propeller is designed for the high ratio of advance and high thrust loading. The effect of the shape of propeller and shroud upon the aerodynamic coefficients of the propulsion unit can be seen from the results. The highest efficiency measured is 0.71. The measurements permit the conclusion that the maximum efficiency can be essentially improved by shroud profiles of small chord and thickness. The largest static thrust factor of merit measured reaches according to Bendemann, a value of about zeta = 1.1. By the use of a nose split flap the static thrust for thin shroud profiles with small nose radius can be about doubled. In a separate section numerical investigations of the behavior of shrouded propellers for the ideal case and for the case with energy losses are carried out. The calculations are based on the assumption that the slipstream cross section depends solely on the shape of the shroud and not on the propeller loading. The reliability of this hypothesis is confirmed experimentally and by flow photographs for a shroud with small circulation. Calculation and test are also in good agreement concerning efficiency and static thrust factor of merit. The prospects of applicability for shrouded propellers and their essential advantages are discussed.

  7. Teeming stream protection using an argon shroud during casting of steel ingots

    NASA Astrophysics Data System (ADS)

    Zhang, Chao-jie; Bao, Yan-ping; Wang, Min; Zhang, Le-chen

    2017-01-01

    Two kinds of argon shroud protection devices with two different basic structures were designed and investigated. Industrial experiments and numerical simulations were used to examine the protection effect, and the mechanism of air entrapment during the casting of steel ingots was analyzed. The influence of the structure of the argon shroud protection device on the protection effect was investigated. An argon shroud protection device mounted to the nozzle holder on the bottom of the ladle does not provide a good protection effect because air can easily flow into the teeming system and cause reoxidation of molten steel during teeming. By contrast, an argon shroud protection device seated on the top of the central trumpet provides an excellent protection effect, where air has little chance of flowing into the teeming system during casting. The feasibilities of the argon shroud protection devices are discussed.

  8. 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.

  9. Seal with Integrated Shroud for Androgynous Docking and Berthing

    NASA Technical Reports Server (NTRS)

    Daniels, Christopher C.

    2010-01-01

    A specially configured seal system (see figure) has been developed and produced that provides a barrier to gas leakage between a pressurized module and its external environment. The seal system includes a shroud covering that both protects the sealing surface from its environment when not in use and retracts to expose the sealing surface when engaged. The seal system is constructed and arranged to mate with a replicate seal system or with a flat surface. When mated with a replicate seal system, the seal system functions when the two sealing surfaces are aligned or misaligned. The seal system can operate over a wide range of temperatures, limited only by the glass transition and melt temperatures of the material from which the sealing surface is manufactured.

  10. Apparatus for the ultrasonic examination of shroud hold down bolts

    SciTech Connect

    Richardson, D.L.; Clark, J.P.; Smith, T.; Perry, R.W.

    1989-04-04

    A process of testing hold down bolts depending from the sides of a steam separator within a nuclear reactor is described the process comprising the steps of: maintaining the steam separator under water; moving the bolts to unlatch the bolts from brackets on the shroud adjacent the steam separator; providing a shoe having a piezoelectric device mounted to the bottom of the shoe and exposed upwardly; providing a remotely actuated clamp attached to the shoe overlying the piezoelectric device; providing a mount to the shoe for manipulating the shoe underwater in a depending relationship at the bottom end of a pole; providing a pole and attaching the pole to the shoe; manipulating the shoe to the bottom of the bolt; and clamping the shoe to the bolt; and testing the bolt with the piezoelectric device.

  11. Convective heat transfer from circular cylinders located within perforated cylindrical shrouds

    NASA Technical Reports Server (NTRS)

    Daryabeigi, K.; Ash, R. L.

    1986-01-01

    The influence of perforated cylindrical shrouds on the convective heat transfer to circular cylinders in transverse flow has been studied experimentally. Geometries studied were similar to those used in industrial platinum resistance thermometers. The influence of Reynolds number, ventilation factor (ratio of the open area to the total surface area of shroud), radius ratio (ratio of shroud's inside radius to bare cylinder's radius), and shroud orientation with respect to flow were studied. The experiments showed that perforated shrouds with ventilation factors in the range 0.1 to 0.4 and radius ratios in the range 1.1 to 2.1 could enhance the convective heat transfer to bare cylinders up to 50%. The maximum enhancement occurred for a radius ratio of 1.4 and ventilation factors between 0.2 and 0.3. It was found that shroud orientation influenced the heat transfer, with maximum heat transfer generally occurring when the shroud's holes were centered on either side of the stagnation line. However, the hole orientation effect is of second order compared to the influence of ventilation factor and radius ratio.

  12. Experimental investigation of the hydrodynamic forces on the shroud of a centrifugal pump impeller. Thesis

    NASA Technical Reports Server (NTRS)

    Zhuang, Fei

    1989-01-01

    Fluid-induced forces acting on a rotating impeller are known to cause rotor-dynamic problems in turbomachines. The forces generated by leakage flow along the front shroud surface of a centrifugal turbomachine impeller play an important role among these fluid-induced forces. The present research was aimed to gain a better understanding of these shroud forces. An experimental apparatus was designed and constructed to simulate the impeller shroud leakage flow. Hydrodynamic forces and steady and unsteady pressure distributions on the rotating shroud were measured as functions of eccentricity, width of shroud clearance, face seal clearance and shaft rotating speed. The forces measured from the dynamometer and manometers agreed well. The hydrodynamic force matrices were found skew-symmetric and statically unstable. This is qualitatively similar to the result of previous hydrodynamic volute force measurements. Nondimensionalized normal and tangential forces decrease slightly as Reynolds number increases. As the width of the shroud clearance decreases and/or the eccentricity increases, the hydrodynamic forces increase nonlinearly. There was some evidence found that increased front seal clearance could reduce the radial shroud forces and the relative magnitude of the destabilizing tangential force. Subharmonic pressure fluctuations were also observed which may adversely affect the behavior of the rotor system.

  13. Investigation of flow in axial turbine stage without shroud-seal

    NASA Astrophysics Data System (ADS)

    Straka, Petr; Němec, Martin; Jelínek, Thomáš

    2015-05-01

    This article deals with investigation of the influence of the radial gaps on the efficiency of the axial turbine stage. The investigation was carried out for the axial stage of the low-power turbine with the drum-type rotor without the shroud. In this configuration the flow through the radial gap under the hub-end of the stator blades and above the tip-end of the rotor blades leads to generation of the strong secondary flows, which decrease the efficiency of the stage. This problem was studied by experiment as well as by numerical modelling. The experiment was performed on the test rig equipped with the water brake dynamometer, torque meter and rotatable stator together with the linear probe manipulator. Numerical modelling was carried out for both the steady flow using the "mixing plane" interface and the unsteady flow using the "sliding mesh" interface between the stator and rotor wheels. The influence of the radial gap was studied in two configuration a) positive and b) negative overlapping of the tip-ends of the rotor blades. The efficiency of the axial stage in dependence on the expansion ratio, velocity ratio and the configuration as well as the details of the flow fields are presented in this paper.

  14. Analysis of Gas Turbine Rotor Blade Tip and Shroud Heat Transfer

    NASA Technical Reports Server (NTRS)

    Ameri, A. A.; Steinthorsson, E.

    1996-01-01

    Predictions of the rate of heat transfer to the tip and shroud of a gas turbine rotor blade are presented. The simulations are performed with a multiblock computer code which solves the Reynolds Averaged Navier-Stokes equations. The effect of inlet boundary layer thickness as well as rotation rate on the tip and shroud heat transfer is examined. The predictions of the blade tip and shroud heat transfer are in reasonable agreement with the experimental measurements. Areas of large heat transfer rates are identified and physical reasoning for the phenomena presented.

  15. Experience with technical diagnostics of generator shroud rings at thermal plants

    NASA Astrophysics Data System (ADS)

    Dubov, A. A.

    2009-02-01

    Experience with the application of the method of magnetic memory of metal while controlling the state of the generator shroud rings for in-time recognition of damage that develops in the zones of stress concentration is considered.

  16. Measurement of convective heat transfer to solid cylinders inside ventilated shrouds

    NASA Technical Reports Server (NTRS)

    Daryabeigi, K.; Germain, E. F.; Ash, R. L.

    1984-01-01

    The influence of ventilated cylindrical shrouds on the convective heat transfer to circular cylinders has been studied experimentally. Geometries studied were similar to those used in commercially available platinum resistance thermometers. Experiments showed that thermal response (convection) was enhanced when the shroud ventilation factor was approximately 20 percent (80 percent solid), and that maximum enhancement occurred when the ventilation holes were located symmetrically on either side of the stagnation lines.

  17. Influence of impeller shroud forces on turbopump rotor dynamics

    NASA Technical Reports Server (NTRS)

    Williams, J. P.; Childs, Dara W.

    1993-01-01

    The shrouded-impeller leakage path forces calculated by Childs have been analyzed to answer two questions. First, because of certain characteristics or the results of Childs, the forces could not be modeled with traditional approaches. Therefore, an approach has been devised to include the forces in conventional rotordynamic analyses. The forces were found to be well-modeled with this approach. Finally, the effect these forces had on a simple rotor-bearing system was analyzed, and, therefore, they, in addition to seal forces, were applied to a Jeffcott rotor. The traditional methods of dynamic system analysis were modified to incorporate the impeller forces and yielded results for the eigenproblem, frequency response, critical speed, transient response, and an iterative technique for finding the frequency of free vibration as well as system stability. All results lead to the conclusion that the forces have little influence on natural frequency but can have appreciable effects on system stability. Specifically, at higher values of fluid swirl at the leakage path entrance, relative stability is reduced. The only unexpected response characteristics that occurred are attributed to the nonlinearity of the model.

  18. Influence of impeller shroud forces on turbopump rotor dynamics

    NASA Technical Reports Server (NTRS)

    Williams, Jim P.; Childs, Dara W.

    1989-01-01

    The shrouded-impeller leakage path forces calculated by Childs (1987) have been analyzed to answer two questions. First, because of certain characteristics of the results of Childs, the forces could not be modeled with traditional approaches. Therefore, an approach has been devised to include the forces in conventional rotordynamic analyses. The forces were approximated by traditional stiffness, damping and inertia coefficients with the addition of whirl-frequency-dependent direct and cross-coupled stiffness terms. The forces were found to be well-modeled with this approach. Finally, the effect these forces had on a simple rotor-bearing system was analyzed, and, therefore, they, in addition to seal forces, were applied to a Jeffcott rotor. The traditional methods of dynamic system analysis were modified to incorporate the impeller forces and yielded results for the eigenproblem, frequency response, critical speed, transient response and an iterative technique for finding the frequency of free vibration as well as system stability. All results lead to the conclusion that the forces have little influence on natural frequency but can have appreciable effects on system stability. Specifically, at higher values of fluid swirl at the leakage path entrance, relative stability is reduced. The only unexpected response characteristics that occurred are attributed to the nonlinearity of the model.

  19. Centaur Standard Shroud (CSS) Heated Altitude Jettison Tests

    NASA Technical Reports Server (NTRS)

    1975-01-01

    Altitude jettison tests, at a pressure of 20 torr (0.39 psia), were performed on the Centaur Standard Shroud (CSS) in a 100-foot diameter vacuum chamber. These jettison tests were part of a series of flight qualification tests which were performed on the new CSS system in preparation for the Helios and Viking missions. The first two tests subjected the CSS to a thermal cycle which simulated aerodynamic heating during ascent flight and the third test was performed at altitude pressure and in ambient temperature conditions. The purpose of the ambient temperature test was to provide base line data by which the separate machanical and thermal factors that influence jettison performance could be evaluated individually. The CSS was successfully jettisoned in each of the three tests. Also, thermal, stress, and structural deflection data were obtained which verified the analytical predictions of CSS response to flight environmental conditions and performance during jettison. In addition, much important information was obtained on critical CSS-to-payload clearance losses due to shell motions prior to and during jettison. The effectiveness of the separation system was successfully demonstrated at maximum flight temperatures.

  20. Structure interaction due to thermal bowing of shrouds in steam generator of gas-cooled reactor

    SciTech Connect

    Woo, H.H.

    1981-01-01

    The design of the gas-cooled reactor steam generators includes a tube bundle support plate system which restrains and supports the helical tubes in the steam generator. The support system consists of an array of radially oriented, perforated plates through which the helical tube coils are wound. These support plates have tabs on their edges which fit into vertical slots in the inner and outer shrouds. When the helical tube bundle and support plates are installed in the steam generator, they most likely cannot fit evenly between the inner and outer shrouds. This imperfection leads to different gaps between two extreme sides of the tube bundle and the shrouds. With different gaps through the tube bundle height, the helium flow experiences different cooling effects from the tube bundle. Hence, the temperature distribution in the shrouds will be non-uniform circumferentially since their surrounding helium flow temperatures are varied. These non-uniform temperatures in the shrouds result in the phenomenon of thermal bowing of shrouds.

  1. Comparative evaluation of test methods to simulate acoustic response of shroud-enclosed spacecraft structures

    NASA Technical Reports Server (NTRS)

    On, F. J.

    1975-01-01

    Test methods were evaluated to ascertain whether a spacecraft, properly tested within its shroud, could be vibroacoustic tested without the shroud, with adjustments made in the acoustic input spectra to simulate the acoustic response of the missing shroud. The evaluation was based on vibroacoustic test results obtained from a baseline model composed (1) of a spacecraft with adapter, lower support structure, and shroud; (2) of the spacecraft, adapter, and lower structure, but without the shroud; and (3) of the spacecraft and adapter only. Emphasis was placed on the magnitude of the acoustic input changes required to substitute for the shroud and the difficulty of making such input changes, and the degree of missimulation which can result from the performance of a particular, less-than optimum test. Conclusions are drawn on the advantages and disadvantages derived from the use of input spectra adjustment methods and lower support structure simulations. Test guidelines were also developed for planning and performing a launch acoustic-environmental test.

  2. Experimental Investigation of a Shrouded Rotor Micro Air Vehicle in Hover and in Edgewise Gusts

    NASA Astrophysics Data System (ADS)

    Hrishikeshavan, Vikram

    Due to the hover capability of rotary wing Micro Air Vehicles (MAVs), it is of interest to improve their aerodynamic performance, and hence hover endurance (or payload capability). In this research, a shrouded rotor configuration is studied and implemented, that has the potential to offer two key operational benefits: enhanced system thrust for a given input power, and improved structural rigidity and crashworthiness of an MAV platform. The main challenges involved in realising such a system for a lightweight craft are: design of a lightweight and stiff shroud, and increased sensitivity to external flow disturbances that can affect flight stability. These key aspects are addressed and studied in order to assess the capability of the shrouded rotor as a platform of choice for MAV applications. A fully functional shrouded rotor vehicle (disk loading 60 N/ m2) was designed and constructed with key shroud design variables derived from previous studies on micro shrouded rotors. The vehicle weighed about 280 g (244 mm rotor diameter). The shrouded rotor had a 30% increase in power loading in hover compared to an unshrouded rotor. Due to the stiff, lightweight shroud construction, a net payload benefit of 20-30 g was achieved. The different components such as the rotor, stabilizer bar, yaw control vanes and the shroud were systematically studied for system efficiency and overall aerodynamic improvements. Analysis of the data showed that the chosen shroud dimensions was close to optimum for a design payload of 250 g. Risk reduction prototypes were built to sequentially arrive at the final configuration. In order to prevent periodic oscillations in ight, a hingeless rotor was incorporated in the shroud. The vehicle was successfully ight tested in hover with a proportional-integralderivative feedback controller. A flybarless rotor was incorporated for efficiency and control moment improvements. Time domain system identification of the attitude dynamics of the flybar and

  3. Cracking catalyst

    SciTech Connect

    Otterstedt, J. E. A.; Jaras, S. G.; Pudas, R.; Upson, L. L.

    1985-05-07

    A cracking catalyst having good resistance to metal poisoning has at least two particle fractions of different particle sizes, the cracking catalyzing zeolite material being concentrated to the coarser particle size fractions, and the finer particle size fractions being formed from material having relatively lower or no or insignificant cracking catalyzing activity. The particles of the finer particle size fractions have a matrix of kaolin and amorphous alumina--silica and may contain for example, an SO /SUB x/ eliminating additive such as Al/sub 2/O/sub 3/, CaO and/or MgO. The coarser particle size fractions having cracking catalyzing effect have a mean particle size of from 80 to 125 ..mu..m and the finer particle size fractions a mean particle size of from 30 to 75 ..mu..m. The coarser particle size fractions have a zeolite content of at least 20 weight % and may have a zeolite content of up to 100 weight %, the remainder consisting essentially of material which has relatively lower or no or insignificant cracking-catalyzing activity and which consists of kaolin and amorphous alumina-silica. The catalyst mass as a whole may have a zeolite content of up to 50 weight %.

  4. ACT Payload Shroud Structural Concept Analysis and Optimization

    NASA Technical Reports Server (NTRS)

    Zalewski, Bart B.; Bednarcyk, Brett A.

    2010-01-01

    Aerospace structural applications demand a weight efficient design to perform in a cost effective manner. This is particularly true for launch vehicle structures, where weight is the dominant design driver. The design process typically requires many iterations to ensure that a satisfactory minimum weight has been obtained. Although metallic structures can be weight efficient, composite structures can provide additional weight savings due to their lower density and additional design flexibility. This work presents structural analysis and weight optimization of a composite payload shroud for NASA s Ares V heavy lift vehicle. Two concepts, which were previously determined to be efficient for such a structure are evaluated: a hat stiffened/corrugated panel and a fiber reinforced foam sandwich panel. A composite structural optimization code, HyperSizer, is used to optimize the panel geometry, composite material ply orientations, and sandwich core material. HyperSizer enables an efficient evaluation of thousands of potential designs versus multiple strength and stability-based failure criteria across multiple load cases. HyperSizer sizing process uses a global finite element model to obtain element forces, which are statistically processed to arrive at panel-level design-to loads. These loads are then used to analyze each candidate panel design. A near optimum design is selected as the one with the lowest weight that also provides all positive margins of safety. The stiffness of each newly sized panel or beam component is taken into account in the subsequent finite element analysis. Iteration of analysis/optimization is performed to ensure a converged design. Sizing results for the hat stiffened panel concept and the fiber reinforced foam sandwich concept are presented.

  5. Melt Infiltrated Ceramic Matrix Composites for Shrouds and Combustor Liners of Advanced Industrial Gas Turbines

    SciTech Connect

    Gregory Corman; Krishan Luthra; Jill Jonkowski; Joseph Mavec; Paul Bakke; Debbie Haught; Merrill Smith

    2011-01-07

    This report covers work performed under the Advanced Materials for Advanced Industrial Gas Turbines (AMAIGT) program by GE Global Research and its collaborators from 2000 through 2010. A first stage shroud for a 7FA-class gas turbine engine utilizing HiPerComp{reg_sign}* ceramic matrix composite (CMC) material was developed. The design, fabrication, rig testing and engine testing of this shroud system are described. Through two field engine tests, the latter of which is still in progress at a Jacksonville Electric Authority generating station, the robustness of the CMC material and the shroud system in general were demonstrated, with shrouds having accumulated nearly 7,000 hours of field engine testing at the conclusion of the program. During the latter test the engine performance benefits from utilizing CMC shrouds were verified. Similar development of a CMC combustor liner design for a 7FA-class engine is also described. The feasibility of using the HiPerComp{reg_sign} CMC material for combustor liner applications was demonstrated in a Solar Turbines Ceramic Stationary Gas Turbine (CSGT) engine test where the liner performed without incident for 12,822 hours. The deposition processes for applying environmental barrier coatings to the CMC components were also developed, and the performance of the coatings in the rig and engine tests is described.

  6. Electrochemical machining process for forming surface roughness elements on a gas turbine shroud

    DOEpatents

    Lee, Ching-Pang; Johnson, Robert Alan; Wei, Bin; Wang, Hsin-Pang

    2002-01-01

    The back side recessed cooling surface of a shroud defining in part the hot gas path of a turbine is electrochemically machined to provide surface roughness elements and spaces therebetween to increase the heat transfer coefficient. To accomplish this, an electrode with insulating dielectric portions and non-insulating portions is disposed in opposition to the cooling surface. By passing an electrolyte between the cooling surface and electrode and applying an electrical current between the electrode and a shroud, roughness elements and spaces therebetween are formed in the cooling surface in opposition to the insulating and non-insulating portions of the electrode, hence increasing the surface area and heat transfer coefficient of the shroud.

  7. Anode shroud for off-gas capture and removal from electrolytic oxide reduction system

    DOEpatents

    Bailey, James L.; Barnes, Laurel A.; Wiedmeyer, Stanley G.; Williamson, Mark A.; Willit, James L.

    2014-07-08

    An electrolytic oxide reduction system according to a non-limiting embodiment of the present invention may include a plurality of anode assemblies and an anode shroud for each of the anode assemblies. The anode shroud may be used to dilute, cool, and/or remove off-gas from the electrolytic oxide reduction system. The anode shroud may include a body portion having a tapered upper section that includes an apex. The body portion may have an inner wall that defines an off-gas collection cavity. A chimney structure may extend from the apex of the upper section and be connected to the off-gas collection cavity of the body portion. The chimney structure may include an inner tube within an outer tube. Accordingly, a sweep gas/cooling gas may be supplied down the annular space between the inner and outer tubes, while the off-gas may be removed through an exit path defined by the inner tube.

  8. Colouring fabrics with excimer lasers to simulate encoded images: the case of the Shroud of Turin

    NASA Astrophysics Data System (ADS)

    Di Lazzaro, P.; Baldacchini, G.; Fanti, G.; Murra, D.; Santoni, A.

    2008-10-01

    The faint body image embedded into the Turin Shroud has not yet explained by traditional science. We present experimental results of excimer laser irradiation (wavelengths 308 nm and 193 nm) of a raw linen fabric and of a linen cloth, seeking for a possible mechanism of image formation. The permanent coloration of both linens is a threshold effect on the laser beam intensity and it can be achieved only in a surprisingly narrow range of irradiation parameters: the shorter the wavelength, the narrower the range. We also obtained the first direct evidence of latent images impressed on linen that appear in a relatively long period (one year) after a laser irradiation that at first did not generate a clear image. The results are compared to the characteristics of the Turin Shroud, commenting the possibility that a burst of directional ultraviolet radiation may have played a role in the formation of the Shroud image.

  9. Coloring linens with excimer lasers to simulate the body image of the Turin Shroud

    NASA Astrophysics Data System (ADS)

    Baldacchini, Giuseppe; di Lazzaro, Paolo; Murra, Daniele; Fanti, Giulio

    2008-03-01

    The body image of the Turin Shroud has not yet been explained by traditional science; so a great interest in a possible mechanism of image formation still exists. We present preliminary results of excimer laser irradiation (wavelength of 308 nm) of a raw linen fabric and of a linen cloth. The permanent coloration of both linens is a threshold effect of the laser beam intensity, and it can be achieved only in a narrow range of irradiation parameters, which are strongly dependent on the pulse width and time sequence of laser shots. We also obtained the first direct evidence of latent images impressed on linen that appear in a relatively long period (one year) after laser irradiation that at first did not generate a clear image. The results are compared with the characteristics of the Turin Shroud, reflecting the possibility that a burst of directional ultraviolet radiation may have played a role in the formation of the Shroud image.

  10. Infrared fine-structure line diagnostics of shrouded active galactic nuclei

    NASA Technical Reports Server (NTRS)

    Voit, G. M.

    1992-01-01

    The ultraluminous far-IR galaxies revealed by IRAS, quasar-like in luminosity but smothered in molecular gas, probably conceal either immense starbursts or luminous active nuclei. In both scenarios, these objects ought to produce copious infrared fine-structure emission with several lines comparable to H-beta in luminosity. We show how these lines, if detected, can be used to determine the electron densities and far-IR obscurations of shrouded photoionized regions and to constrain the shape and ionization parameter of the ionizing spectra. The presence of Ne v emission in particular will distinguish shrouded AGNs from shrouded starbursts. Since all active galaxies photoionize at least some surrounding material, these diagnostics can also be applied to active galaxies in general and will aid in studying how an active nucleus interacts with the interstellar medium of its host galaxy.

  11. Simpson Probe Lab Test

    NASA Technical Reports Server (NTRS)

    1994-01-01

    In order to study the fatigue processes of aerospace materials it is necessary to perform controlled experiments on the crack growth rates and number of fatigue cycles to failure under specific loading conditions. The photo shows an aluminum compact tension specimen installed in a hydraulic load frame. The load frame is used to apply well defined cyclic stresses to the sample under test. Also mounted on the load frame is the Langley developed automated fatigue crack tip tracing system. The system incorporates the Self-Nulling Eddy Current Probe and a two-axis scanner in order to locate the position of the fatigue crack tip in the sample. The position of the crack tip is continuously updated as the fatigue process continues. The system is fully automated, with the ability to update loading parameters based on crack tip position while compiling a complete history of crack tip position versus fatigue cycles.

  12. Mcnp-Based Methodology to Calculate Helium Production in Bwr Shrouds

    NASA Astrophysics Data System (ADS)

    Sitaraman, S.; Chiang, R.-T.; Oliver, B. M.

    2003-06-01

    A three-dimensional computational method based on Monte Carlo radiation transport techniques was developed to calculate thermal and fast neutron fields in the downcomer region of a Boiling Water Reactor (BWR). This methodology was validated using measured data obtained from an operating BWR. The helium production was measured in stainless steel at locations near the shroud and compared with values from the Monte Carlo calculations. The methodology produced results that were in agreement with measurements, thereby providing a useful tool for the determination of helium levels in shroud components.

  13. Stochastic distribution of the fibrils that yielded the Shroud of Turin body image

    NASA Astrophysics Data System (ADS)

    Fazio, G.; Mandaglio, G.

    2011-07-01

    The fibrils that yielded the Shroud body image show a stochastic distribution on the Linen of Turin. In fact, the probability of a fibril yellowing is a function of the energy, while this is not the case for the optical density value. This means that the above image is a latent image. We suggest thermal radiation or low-temperature chemical processes as possible natural energy sources to explain, by stochastic effects, the Shroud body image formation. Unfortunately, due to the nature of the phenomenon, we are not able to extract the energy source.

  14. Concepts for a Shroud or Propellant Tank Derived Deep Space Habitat

    NASA Technical Reports Server (NTRS)

    Howard, Robert L.

    2012-01-01

    Long duration human spaceflight missions beyond Low Earth Orbit will require much larger spacecraft than capsules such as the Russian Soyuz or American Orion Multi-Purpose Crew Vehicle. A concept spacecraft under development is the Deep Space Habitat, with volumes approaching that of space stations such as Skylab, Mir, and the International Space Station. This paper explores several concepts for Deep Space Habitats constructed from a launch vehicle shroud or propellant tank. It also recommends future research using mockups and prototypes to validate the size and crew station capabilities of such a habitat. Keywords: Exploration, space station, lunar outpost, NEA, habitat, long duration, deep space habitat, shroud, propellant tank.

  15. 124. Pre1911. View forward from mizzen shrouds, starboard side; Chinese ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    124. Pre-1911. View forward from mizzen shrouds, starboard side; Chinese cannery workers boarding ship from barge, S/V BENJAMIN F. PACKARD in background. Note main fife rail with fresh water pump. Fred Heick Collection. (G12.799) - Ship BALCLUTHA, 2905 Hyde Street Pier, San Francisco, San Francisco County, CA

  16. Computational fluid dynamic modeling of a medium-sized surface mine blasthole drill shroud

    PubMed Central

    Zheng, Y.; Reed, W.R.; Zhou, L.; Rider, J.P.

    2016-01-01

    The Pittsburgh Mining Research Division of the U.S. National Institute for Occupational Safety and Health (NIOSH) recently developed a series of models using computational fluid dynamics (CFD) to study airflows and respirable dust distribution associated with a medium-sized surface blasthole drill shroud with a dry dust collector system. Previously run experiments conducted in NIOSH’s full-scale drill shroud laboratory were used to validate the models. The setup values in the CFD models were calculated from experimental data obtained from the drill shroud laboratory and measurements of test material particle size. Subsequent simulation results were compared with the experimental data for several test scenarios, including 0.14 m3/s (300 cfm) and 0.24 m3/s (500 cfm) bailing airflow with 2:1, 3:1 and 4:1 dust collector-to-bailing airflow ratios. For the 2:1 and 3:1 ratios, the calculated dust concentrations from the CFD models were within the 95 percent confidence intervals of the experimental data. This paper describes the methodology used to develop the CFD models, to calculate the model input and to validate the models based on the experimental data. Problem regions were identified and revealed by the study. The simulation results could be used for future development of dust control methods for a surface mine blasthole drill shroud. PMID:27932851

  17. Aerodynamic effect of a honeycomb rotor tip shroud on a 50.8-centimeter-tip-diameter core turbine

    NASA Technical Reports Server (NTRS)

    Moffitt, T. P.; Whitney, W. J.

    1983-01-01

    A 50.8-cm-tip-diameter turbine equipped with a rotor tip shroud of hexagonal cell (or honeycomb) cross section has been tested in warm air (416 K) for a range of shroud coolant to primary flow rates. Test results were also obtained for the same turbine operated with a solid shroud for comparison. The results showed that the combined effect of the honeycomb shroud and the coolant flow was to cause a reduction of 2.8 points in efficiency at design speed, pressure ratio, and coolant flow rate. With the coolant system inactivated, the honeycomb shroud caused a decrease in efficiency of 2.3 points. These results and those obtained from a small reference turbine indicate that the dominant factor governing honeycomb tip shroud loss is the ratio of honeycomb depth to blade span. The loss results of the two shrouds could be correlated on this basis. The same honeycomb and coolant effects are expected to occur for the hot (2200 K) version of this turbine.

  18. Numerical Investigation of the Interaction between Mainstream and Tip Shroud Leakage Flow in a 2-Stage Low Pressure Turbine

    NASA Astrophysics Data System (ADS)

    Jia, Wei; Liu, Huoxing

    2014-06-01

    The pressing demand for future advanced gas turbine requires to identify the losses in a turbine and to understand the physical mechanisms producing them. In low pressure turbines with shrouded blades, a large portion of these losses is generated by tip shroud leakage flow and associated interaction. For this reason, shroud leakage losses are generally grouped into the losses of leakage flow itself and the losses caused by the interaction between leakage flow and mainstream. In order to evaluate the influence of shroud leakage flow and related losses on turbine performance, computational investigations for a 2-stage low pressure turbine is presented and discussed in this paper. Three dimensional steady multistage calculations using mixing plane approach were performed including detailed tip shroud geometry. Results showed that turbines with shrouded blades have an obvious advantage over unshrouded ones in terms of aerodynamic performance. A loss mechanism breakdown analysis demonstrated that the leakage loss is the main contributor in the first stage while mixing loss dominates in the second stage. Due to the blade-to-blade pressure gradient, both inlet and exit cavity present non-uniform leakage injection and extraction. The flow in the exit cavity is filled with cavity vortex, leakage jet attached to the cavity wall and recirculation zone induced by main flow ingestion. Furthermore, radial gap and exit cavity size of tip shroud have a major effect on the yaw angle near the tip region in the main flow. Therefore, a full calculation of shroud leakage flow is necessary in turbine performance analysis and the shroud geometric features need to be considered during turbine design process.

  19. The electrical conductivities of the DSS-13 beam-waveguide antenna shroud material and other antenna reflector surface materials

    NASA Technical Reports Server (NTRS)

    Otoshi, T. Y.; Franco, M. M.; Reilly, H. F., Jr.

    1992-01-01

    A significant amount of noise temperature can potentially be generated by currently unknown dissipative losses in the beam waveguide (BWG) shroud. The amount of noise temperature contribution from this source is currently being studied. In conjunction with this study, electrical conductivity measurements were made on samples of the DSS-13 BWG shroud material at 8.420 GHz. The effective conductivities of unpainted and painted samples of the BWG shroud were measured to be 0.01 x 10(exp 7) and 0.0036 x 10(exp 7) mhos/m, respectively. This value may be compared with 5.66 x 10(exp 7) mhos/m for high conductivity copper.

  20. Crack, crack house sex, and HIV risk.

    PubMed

    Inciardi, J A

    1995-06-01

    Limited attention has been focused on HIV risk behaviors of crack smokers and their sex partners, yet there is evidence that the crack house and the crack-using life-style may be playing significant roles in the transmission of HIV and other sexually transmitted diseases. The purposes of this research were to study the attributes and patterns of "sex for crack" exchanges, particularly those that occurred in crack houses, and to assess their potential impact on the spread of HIV. Structured interviews were conducted with 17 men and 35 women in Miami, Florida, who were regular users of crack and who had exchanged sex for crack (or for money to buy crack) during the past 30 days. In addition, participant observation was conducted in 8 Miami crack houses. Interview and observational data suggest that individuals who exchange sex for crack do so with considerable frequency, and through a variety of sexual activities. Systematic data indicated that almost a third of the men and 89% of the women had had 100 or more sex partners during the 30-day period prior to study recruitment. Not only were sexual activities anonymous, extremely frequent, varied, uninhibited (often undertaken in public areas of crack houses), and with multiple partners but, in addition, condoms were not used during the majority of contacts. Of the 37 subjects who were tested for HIV and received their test results 31% of the men and 21% of the women were HIV seropositive.

  1. Analysis of Fretting Fatigue Strength of Integral Shroud Blade for Steam Turbine

    NASA Astrophysics Data System (ADS)

    Kaneko, Yasutomo; Tomii, Masayuki; Ohyama, Hiroharu; Kurimura, Takayuki

    To improve the reliability and the thermal efficiency of LP (Low Pressure) end blades of steam turbine, new standard series of LP end blades have been developed. The new LP end blades are characterized by the ISB (Integral Shroud Blade) structure. In the ISB structure, blades are continuously coupled by blade untwist due to centrifugal force when the blades rotate at high speed. One of the probable failure modes of the ISB structure seems to be fretting fatigue, because the ISB utilizes friction damping between adjacent shrouds and stubs. Therefore, in order to design a blade with high reliability, the design procedure for evaluating the fretting fatigue strength was established by the model test and the nonlinear contact analysis. This paper presents the practical design method for predicting the fretting fatigue strength of the ISB structure, and the some applications are explained.

  2. Saturn I S-IB Stage, Lower Shroud, at Michoud Assembly Facility (MAF)

    NASA Technical Reports Server (NTRS)

    1969-01-01

    In one of the initial assembly steps for the Saturn IB launch vehicle's S-IB (first) stage, workers at the Michoud Assembly Facility (MAF) near New Orleans, Louisiana, complete the lower shroud assembly. Developed by the Marshall Space Flight Center and built by the Chrysler Corporation at Michoud Assembly Facility (MAF), the S-IB utilized the eight H-1 engines and each produced 200,000 pounds of thrust, a combined thrust of 1,600,000 pounds.

  3. Seal with integrated shroud for androgenous docking and berthing in contaminated environments

    NASA Technical Reports Server (NTRS)

    Daniels, Christopher C. (Inventor)

    2012-01-01

    The present invention is directed to a specially configured seal system which provides a barrier to gas leakage flow between a pressurized module and its external environment. The seal includes a shroud covering which protects the sealing interface from its environment when not in use, and retracts to expose the sealing interface when mated. The seal system is constructed and arranged to mate with a seal of identical construction and arrangement or to mate with a flat surface.

  4. Bladed-shrouded-disc aeroelastic analyses: Computer program updates in NASTRAN level 17.7

    NASA Technical Reports Server (NTRS)

    Gallo, A. M.; Elchuri, V.; Skalski, S. C.

    1981-01-01

    In October 1979, a computer program based on the state-of-the-art compressor and structural technologies applied to bladed-shrouded-disc was developed. The program was more operational in NASTRAN Level 16. The bladed disc computer program was updated for operation in NASTRAN Level 17.7. The supersonic cascade unsteady aerodynamics routine UCAS, delivered as part of the NASTRAN Level 16 program was recorded to improve its execution time. These improvements are presented.

  5. Instrumentation package for a shrouded SWERVE/EPW rocket sled test

    SciTech Connect

    Garavaglia, E.G.

    1987-08-01

    A shrouded SWERVE test vehicle was instrumented and tested at MACH 3. The instrumentation consisted of accelerometers, pressure transducers, and event markers arranged in a nine-channel configuration. Data from the instrumentation were transmitted from the vehicle through an FM/FM telemetry system. Two fire sets and their associated command and controls were also included in this package. The event was recorded on high-speed color film, and the trajectory data were recorded by a laser tracker.

  6. Application of the aeroacoustic analogy to a shrouded, subsonic, radial fan

    NASA Astrophysics Data System (ADS)

    Buccieri, Bryan M.; Richards, Christopher M.

    2016-12-01

    A study was conducted to investigate the predictive capability of computational aeroacoustics with respect to a shrouded, subsonic, radial fan. A three dimensional unsteady fluid dynamics simulation was conducted to produce aerodynamic data used as the acoustic source for an aeroacoustics simulation. Two acoustic models were developed: one modeling the forces on the rotating fan blades as a set of rotating dipoles located at the center of mass of each fan blade and one modeling the forces on the stationary fan shroud as a field of distributed stationary dipoles. Predicted acoustic response was compared to experimental data measured at two operating speeds using three different outlet restrictions. The blade source model predicted overall far field sound power levels within 5 dB averaged over the six different operating conditions while the shroud model predicted overall far field sound power levels within 7 dB averaged over the same conditions. Doubling the density of the computational fluids mesh and using a scale adaptive simulation turbulence model increased broadband noise accuracy. However, computation time doubled and the accuracy of the overall sound power level prediction improved by only 1 dB.

  7. Steady computational analysis of shrouded plug nozzle flows using unequal stream pressures

    NASA Astrophysics Data System (ADS)

    Ruhs, Kevin Paul

    This study focuses on the effects of unequal core and bypass stream feed pressures in a high pressure ratio, two-stream nozzle notionally designed for supersonic business jet applications. Whereas previous analysis used a measured mass average pressure of the core and bypass streams, equal pressures were not exactly maintained in the experimental work and the effect of the imbalance is the primary motivation for the present study. The plug nozzle geometry used is a sub-scale model of a Gulfstream Aerospace Corporation concept that features an extended shroud. It uses two inlet streams, representing core and bypass streams from a turbofan engine. Nozzle pressure ratios range from unity to 6.23. Experimental measurements included pressure taps on the plug and shroud, schlieren and shadowgraph figures, mass flows for both streams, and thrust values. The computational analysis employed the General Equation and Mesh Solver, or GEMS code. Previous computational analysis was performed by Kapilavai, giving a basis analysis involving grid generation and refinement, error convergence studies, axisymmetric analysis, and unsteady computations. Unequal core and bypass stream pressure or swirl in the core stream is used to replicate experimental data and assess performance. The results of using these conditions were explored, including pressure on the plug and shroud, shock characteristics, separation and recirculation zones, mass flows and discharge coefficients, and thrust efficiencies.

  8. Theory and experimental validation of SPLASH (Single Panel Lamp and Shroud Helper).

    SciTech Connect

    Larsen, Marvin Elwood; Porter, Jason M.

    2005-06-01

    The radiant heat test facility develops test sets providing well-characterized thermal environments, often representing fires. Many of the components and procedures have become standardized to such an extent that the development of a specialized design tool was appropriate. SPLASH (Single Panel Lamp and Shroud Helper) is that tool. SPLASH is implemented as a user-friendly program that allows a designer to describe a test setup in terms of parameters such as lamp number, power, position, and separation distance. Thermal radiation is the dominant mechanism of heat transfer and the SPLASH model solves a radiation enclosure problem to estimate temperature distributions in a shroud providing the boundary condition of interest. Irradiance distribution on a specified viewing plane is also estimated. This document provides the theoretical development for the underlying model. A series of tests were conducted to characterize SPLASH's ability to analyze lamp and shroud systems. The comparison suggests that SPLASH succeeds as a design tool. Simplifications made to keep the model tractable are demonstrated to result in estimates that are only approximately as uncertain as many of the properties and characteristics of the operating environment.

  9. Gear Crack Propagation Investigation

    NASA Technical Reports Server (NTRS)

    1995-01-01

    Reduced weight is a major design goal in aircraft power transmissions. Some gear designs incorporate thin rims to help meet this goal. Thin rims, however, may lead to bending fatigue cracks. These cracks may propagate through a gear tooth or into the gear rim. A crack that propagates through a tooth would probably not be catastrophic, and ample warning of a failure could be possible. On the other hand, a crack that propagates through the rim would be catastrophic. Such cracks could lead to disengagement of a rotor or propeller from an engine, loss of an aircraft, and fatalities. To help create and validate tools for the gear designer, the NASA Lewis Research Center performed in-house analytical and experimental studies to investigate the effect of rim thickness on gear-tooth crack propagation. Our goal was to determine whether cracks grew through gear teeth (benign failure mode) or through gear rims (catastrophic failure mode) for various rim thicknesses. In addition, we investigated the effect of rim thickness on crack propagation life. A finite-element-based computer program simulated gear-tooth crack propagation. The analysis used principles of linear elastic fracture mechanics, and quarter-point, triangular elements were used at the crack tip to represent the stress singularity. The program had an automated crack propagation option in which cracks were grown numerically via an automated remeshing scheme. Crack-tip stress-intensity factors were estimated to determine crack-propagation direction. Also, various fatigue crack growth models were used to estimate crack-propagation life. Experiments were performed in Lewis' Spur Gear Fatigue Rig to validate predicted crack propagation results. Gears with various backup ratios were tested to validate crack-path predictions. Also, test gears were installed with special crack-propagation gages in the tooth fillet region to measure bending-fatigue crack growth. From both predictions and tests, gears with backup ratios

  10. 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.

  11. Surface-crack detection by microwave methods

    NASA Technical Reports Server (NTRS)

    Feinstein, L.; Hruby, R.

    1967-01-01

    Microwave surface-crack detection system examines metallic surfaces with a noncontacting probe. The change in the microwave signal reflected from the surface under investigation is an indication of the existence of surface flaws. This technique can detect flaws and scratches as small as 100 microinches.

  12. 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.

  13. Seeing Inscriptions on the Shroud of Turin: The Role of Psychological Influences in the Perception of Writing.

    PubMed

    Jordan, Timothy R; Sheen, Mercedes; Abedipour, Lily; Paterson, Kevin B

    2015-01-01

    The Shroud of Turin (hereafter the Shroud) is one of the most widely known and widely studied artifacts in existence, with enormous historical and religious significance. For years, the Shroud has inspired worldwide interest in images on its fabric which appear to be of the body and face of a man executed in a manner consistent with crucifixion, and many believe that these images were formed in the Shroud's fibers during the Resurrection of Jesus of Nazareth. But, more recently, other reports have suggested that the Shroud also contains evidence of inscriptions, and these reports have been used to add crucial support to the view that the Shroud is the burial cloth of Jesus. Unfortunately, these reports of inscriptions are based on marks that are barely visible on the Shroud, even when images are enhanced, and the actual existence of writing on the Shroud is still a matter of considerable debate. Here we discuss previous evidence concerning the psychological processes involved generally in the perception of writing, and especially when letters and words are indistinct. We then report two experiments in which the influence of religious context on perception of inscriptions was addressed specifically, using an image of woven fabric (modern linen) containing no writing and with no religious provenance. This image was viewed in two different contexts: in the Religious Context, participants were informed that the image was of a linen artifact that was important to the Christian faith whereas, in the non-religious Neutral Context, participants were informed that the image was of a simple piece of linen. Both groups were told that the image may contain faint words and were asked to report any words they could see. All participants detected words on the image, and indicated that these words were visible and were able to trace on the image the words they detected. In each experiment, more religious words were detected in the Religious Context condition than in the Neutral

  14. Effects of Hydrocarbon-Based Grease on Rapid Prototype Material Used for Grease Retention Shrouds

    NASA Technical Reports Server (NTRS)

    Zakrajsek, Andrew J.; Valco, Daniel J.; Street, Kenneth W., Jr.

    2010-01-01

    Effects of hydrocarbon-based greases on specific rapid prototype (RP) materials used to fabricate grease retention shrouds (GRS) were explored in this study. Grease retention shrouds are being considered as a way to maintain adequate grease lubrication at the gear mesh in a prototype research transmission system. Due to their design and manufacturing flexibility, rapid prototype materials were chosen for the grease retention shrouds. In order to gain a better understanding of the short and long term effects grease pose on RP materials, research was conducted on the interaction of hydrocarbon-based grease with RP materials. The materials used in this study were durable polyamide (nylon), acrylonitrile butadiene styrene (ABS), and WaterClear 10120. Testing was conducted using Mobilgrease 28 and Syn-Tech 3913G grease (gear coupling grease). These greases were selected due to their regular use with mechanical components. To investigate the effect that grease has on RP materials, the following methods were used to obtain qualitative and quantitative data: Fourier transform infrared spectroscopy (FT-IR), interference profilometer measurements, digital camera imaging, physical shape measurement, and visual observations. To record the changes in the RP materials due to contact with the grease, data was taken before and after the grease application. Results showed that the WaterClear 10120 RP material provided the best resistance to grease penetration as compared to nylon and ABS RP materials. The manufacturing process, and thus resulting surface conditions of the RP material, played a key role in the grease penetration properties and resilience of these materials.

  15. Effects of Shrouded Stator Cavity Flows on Multistage Axial Compressor Aerodynamic Performance

    NASA Technical Reports Server (NTRS)

    Wellborn, Steven R.; Okiishi, Theodore H.

    1996-01-01

    Experiments were performed on a low-speed multistage axial-flow compressor to assess the effects of shrouded stator cavity flows on aerodynamic performance. Five configurations, which involved changes in seal-tooth leakage rates and/or elimination of the shrouded stator cavities, were tested. Data collected enabled differences in overall individual stage and the third stage blade element performance parameters to be compared. The results show conclusively that seal-tooth leakage ran have a large impact on compressor aerodynamic performance while the presence of the shrouded stator cavities alone seemed to have little influence. Overall performance data revealed that for every 1% increase in the seal-tooth clearance to blade-height ratio the pressure rise dropped up to 3% while efficiency was reduced by 1 to 1.5 points. These observed efficiency penalty slopes are comparable to those commonly reported for rotor and cantilevered stator tip clearance variations. Therefore, it appears that in order to correctly predict overall performance it is equally important to account for the effects of seal-tooth leakage as it is to include the influence of tip clearance flows. Third stage blade element performance data suggested that the performance degradation observed when leakage was increased was brought about in two distinct ways. First, increasing seal-tooth leakage directly spoiled the near hub performance of the stator row in which leakage occurred. Second, the altered stator exit now conditions caused by increased leakage impaired the performance of the next downstream stage by decreasing the work input of the downstream rotor and increasing total pressure loss of the downstream stator. These trends caused downstream stages to progressively perform worse. Other measurements were acquired to determine spatial and temporal flow field variations within the up-and-downstream shrouded stator cavities. Flow within the cavities involved low momentum fluid traveling primarily

  16. Accelerated aging of cellulose by laser irradiation. [Development for Shroud of Turin

    SciTech Connect

    Jackson, J.P.; Arthurs, E.; Schwalbe, L.A.; Sega, R.M.; Windish, D.; Long, W.H.; Stappaerts, E.A.

    1988-01-01

    We describe a new technique for studying thermally-induced chemical transformations in cellulose developed for the Shroud of Turin. The apparatus consists of a carbon dioxide laser for heating, an infrared thermometer, and an optical reflectance spectrometer for tracking the progressive discoloration of the sample. To illustrate the technique, we present measurements from a single piece of sample linen along five isotherms in the range 200-290/degree/C. The results are explained in terms of first-order chemical rate theory and a four-step model. From the measurements we derive the activation energies, Arrhenius constants, and reflectivities of the chromophoric states. 4 refs., 2 figs., 1 tab.

  17. Hover and Wind-Tunnel Testing of Shrouded Rotors for Improved Micro Air Vehicle Design

    DTIC Science & Technology

    2008-01-01

    and Loy, who took me into their family and gave me a home away from home; and my other aunts and uncles — Lisa -Ann, TJ, Bryan, Madeline, Neal and...University XV-11A Marvel. (i) Piasecki 16H-1 Pathfinder . (j) Piasecki 16H-1A Pathfinder II. Figure 1.6: Applications of shrouded rotors: STOL aircraft and...like the Mississippi State University’s XAZ-1 Marvelette and XV-11A Marvel STOL aircraft [77] and the Piasecki 16H-1 Pathfinder and 16H-1A Pathfinder II

  18. 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.

  19. Design and performance of a centimetre-scale shrouded wind turbine for energy harvesting

    NASA Astrophysics Data System (ADS)

    Howey, D. A.; Bansal, A.; Holmes, A. S.

    2011-08-01

    A miniature shrouded wind turbine aimed at energy harvesting for power delivery to wireless sensors in pipes and ducts is presented. The device has a rotor diameter of 2 cm, with an outer diameter of 3.2 cm, and generates electrical power by means of an axial-flux permanent magnet machine built into the shroud. Fabrication was accomplished using a combination of traditional machining, rapid prototyping, and flexible printed circuit board technology for the generator stator, with jewel bearings providing low friction and start up speed. Prototype devices can operate at air speeds down to 3 m s-1, and deliver between 80 µW and 2.5 mW of electrical power at air speeds in the range 3-7 m s-1. Experimental turbine performance curves, obtained by wind tunnel testing and corrected for bearing losses using data obtained in separate vacuum run-down tests, are compared with the predictions of an elementary blade element momentum (BEM) model. The two show reasonable agreement at low tip speed ratios. However, in experiments where a maximum could be observed, the maximum power coefficient (~9%) is marginally lower than predicted from the BEM model and occurs at a lower than predicted tip speed ratio of around 0.6.

  20. Force and moment rotordynamic coefficients for pump-impeller shroud surfaces

    NASA Technical Reports Server (NTRS)

    Childs, Dara W.

    1987-01-01

    Governing equations of motion are derived for a bulk-flow model of the leakage path between an impeller shroud and a pump housing. The governing equations consist of a path-momentum, a circumferential - momentum, and a continuity equation. The fluid annulus between the impeller shroud and pump housing is assumed to be circumferentially symmetric when the impeller is centered; i.e., the clearance can vary along the pump axis but does not vary in the circumferential direction. A perturbation expansion of the governing equations in the eccentricity ratio yields a set of zeroth and first-order governing equations. The zeroth-order equations define the leaking rate and the circumferential and path velocity distributions and pressure distributions for a centered impeller position. The first-order equations define the perturbations in the velocity and pressure distributions due to either a radial-displacement perturbation or a tilt perturbation of the impeller. Integration of the perturbed pressure and shear-stress distribution acting on the rotor yields the reaction forces and moments acting on the impeller face.

  1. Seeing Inscriptions on the Shroud of Turin: The Role of Psychological Influences in the Perception of Writing

    PubMed Central

    Jordan, Timothy R.; Sheen, Mercedes; Abedipour, Lily; Paterson, Kevin B.

    2015-01-01

    The Shroud of Turin (hereafter the Shroud) is one of the most widely known and widely studied artifacts in existence, with enormous historical and religious significance. For years, the Shroud has inspired worldwide interest in images on its fabric which appear to be of the body and face of a man executed in a manner consistent with crucifixion, and many believe that these images were formed in the Shroud’s fibers during the Resurrection of Jesus of Nazareth. But, more recently, other reports have suggested that the Shroud also contains evidence of inscriptions, and these reports have been used to add crucial support to the view that the Shroud is the burial cloth of Jesus. Unfortunately, these reports of inscriptions are based on marks that are barely visible on the Shroud, even when images are enhanced, and the actual existence of writing on the Shroud is still a matter of considerable debate. Here we discuss previous evidence concerning the psychological processes involved generally in the perception of writing, and especially when letters and words are indistinct. We then report two experiments in which the influence of religious context on perception of inscriptions was addressed specifically, using an image of woven fabric (modern linen) containing no writing and with no religious provenance. This image was viewed in two different contexts: in the Religious Context, participants were informed that the image was of a linen artifact that was important to the Christian faith whereas, in the non-religious Neutral Context, participants were informed that the image was of a simple piece of linen. Both groups were told that the image may contain faint words and were asked to report any words they could see. All participants detected words on the image, and indicated that these words were visible and were able to trace on the image the words they detected. In each experiment, more religious words were detected in the Religious Context condition than in the Neutral

  2. 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.

  3. GPR abilities in investigation of the pavement transversal cracks

    NASA Astrophysics Data System (ADS)

    Krysiński, Lech; Sudyka, Jacek

    2013-10-01

    This paper describes the results of an investigation into the capabilities of the GPR technique within the field of pavement crack diagnostics. Initially, laboratory tests were performed on prototypes simulating idealized cracks. Next, long-term visual observation and repeated GPR scanning were performed, on three roads of semi-rigid construction, several hundreds of meters long and subjected to heavy traffic. Furthermore, a road of rigid construction was tested, having a more than 70-year history of use. In several cases the cracks were probed by drillings, in order to recognize structures responsible for signal generation, or to explain reasons of signal lacking. The main result of this work is a list of GPR indications of cracks, which can be noticed on echograms. It was created through a correlation of the visually-observed cracks with the corresponding echograms, with decimeter accuracy. Several types of GPR responses were classified and linked to possible categories of crack structures, or to processes associated with the presence of cracks (as crumbling, erosion, and lithological alterations). The poor visibility of cracks was also studied, due to small crack size, or to the blurred character of the damaged area, or else to masking effects related to coarse grains in the asphalt mixture. The efficiency of the proposed method for the identification and localization of cracks is higher when a long-term GPR observation is performed.

  4. Catalytic cracking of hydrocarbons

    SciTech Connect

    Absil, R.P.L.; Bowes, E.; Green, G.J.; Marler, D.O.; Shihabi, D.S.; Socha, R.F.

    1992-02-04

    This patent describes an improvement in a catalytic cracking process in which a hydrocarbon feed is cracked in a cracking zone in the absence of added hydrogen and in the presence of a circulating inventory of solid acidic cracking a catalyst which acquires a deposit of coke that contains chemically bound nitrogen while the cracking catalyst is in the cracking zone, the coke catalyst being circulated to t regeneration zone to convert the coke catalyst to a regenerated catalyst with the formation of a flue gas comprising nitrogen oxides: the improvement comprises incorporating into the circulating catalyst inventory an amount of additive particles comprising a synthetic porous crystalline material containing copper metal or cations, to reduce the content of nitrogen oxides in the flue gas.

  5. Elevated temperature crack growth

    NASA Technical Reports Server (NTRS)

    Kim, K. S.; Vanstone, R. H.

    1992-01-01

    The purpose of this program was to extend the work performed in the base program (CR 182247) into the regime of time-dependent crack growth under isothermal and thermal mechanical fatigue (TMF) loading, where creep deformation also influences the crack growth behavior. The investigation was performed in a two-year, six-task, combined experimental and analytical program. The path-independent integrals for application to time-dependent crack growth were critically reviewed. The crack growth was simulated using a finite element method. The path-independent integrals were computed from the results of finite-element analyses. The ability of these integrals to correlate experimental crack growth data were evaluated under various loading and temperature conditions. The results indicate that some of these integrals are viable parameters for crack growth prediction at elevated temperatures.

  6. The cracked tooth.

    PubMed

    Zuckerman, G R

    1998-01-01

    Fractured molars and premolars are very common. Fractures usually result from cracks that develop and slowly extend until the tooth separates into buccal and lingual fragments. Sometimes, as these cracks expand, the patient exhibits symptoms of what is commonly referred to as "cracked tooth syndrome" (CTS). When CTS occurs, an opportunity exists to diagnose and treat these patients, to relieve their discomfort and prevent sequelae that would require more extensive treatment.

  7. Quenched catalytic cracking process

    SciTech Connect

    Krambeck, F.J.; Penick, J.E.; Schipper, P.H.

    1990-12-18

    This paper describes improvement in a fluidized catalytic cracking process wherein a fluidizable catalyst cracking catalyst and a hydrocarbon feed are charged to a reactor riser at catalytic riser cracking conditions to form catalytically cracked vapor product and spent catalyst which are discharged into a reactor vessel having a volume via a riser reactor outlet equipped with a separation means to produce a catalyst lean phase. It comprises: a majority of the cracked product, and a catalyst rich phase comprising a majority of the spend catalyst. The the catalyst rich phase is discharged into a dense bed of catalyst maintained below the riser outlet and the catalyst lean phase is discharged into the vessel for a time, and at a temperature, which cause unselective thermal cracking of the cracked product in the reactor volume before product is withdrawn from the vessel via a vessel outlet. The improvement comprises: addition, after riser cracking is completed, and after separation of cracked products from catalyst, of a quenching stream into the vessel above the dense bed of catalyst, via a quench stream addition point which allows the quench stream to contact at least a majority of the volume of the vessel above the dense bed.

  8. Elevated temperature crack growth

    NASA Technical Reports Server (NTRS)

    Kim, K. S.; Vanstone, R. H.

    1989-01-01

    Alloy 718 crack growth experiments were conducted to assess the ability of the selected path-independent (P-I) integrals to describe the elevated temperature crack growth behavior. These tests were performed on single edge notch (SEN) specimens under displacement control with multiple extensometers to monitor the specimen and crack mouth opening displacement (CMOD). The displacements in these tests were sufficiently high to induce bulk cyclic inelastic deformation of the specimen. Under these conditions, the linear elastic fracture mechanics (LEFM) parameter K does not correlate the crack growth data. The experimentally measured displacement gradients at the end of specimen gage length were used as the boundary conditions in elastic-plastic finite element method (FEM) analyses. These analyses were performed with a node release approach using CYANIDE, a GEAE FEM code, which included a gap element which is capable of efficiently simulating crack closure. Excellent correlation was obtained between the experimentally measured and predicted variation of stress and CMOD with crack length and the stress-CMOD loops for Alloy 718 tests conducted at 538 C. This confirmed the accuracy of the FEM crack growth simulation approach. The experimentally measured crack growth rate data correlated well the selected P-I integrals. These investigations have produced significant progress in developing P-I integrals as non-linear fracture mechanics parameters. The results suggest that this methodology has the potential of accurately describing elevated temperature crack growth behavior under the combined influence of thermal cycling and bulk elastic-inelastic deformation states.

  9. The effect of inlet swirl on the rotordynamic shroud forces in a centrifugal pump

    NASA Technical Reports Server (NTRS)

    Ginzburg, A.; Brennen, C. E.; Acosta, A. J.; Caughey, T. K.

    1992-01-01

    The role played by fluid forces in determining the rotordynamic stability of a centrifugal pump is gaining increasing attention. The present research investigates the contributions to the rotordynamic forces from the discharge-to-suction leakage flows between the front shroud of the rotating impeller and the stationary pump casing. In particular, the dependency of the rotordynamic characteristics of leakage flows on the swirl at the inlet to the leakage path was examined. An inlet guide vane was designed for the experiment so that swirl could be introduced at the leakage flow inlet. The data demonstrates substantial rotordynamic effects and a destabilizing tangential force for small positive whirl ratios; this force decreased with increasing flow rate. The effect of swirl on the rotordynamic forces was found to be destabilizing.

  10. Diagnostic methods of a bladed disc mode shape evaluation used for shrouded blades in steam turbines

    NASA Astrophysics Data System (ADS)

    Strnad, Jaromir; Liska, Jindrich

    2015-11-01

    This paper deals with advanced methods for the evaluation of a bladed disc behavior in terms of the wheel vibration and blade service time consumption. These methods are developed as parts of the noncontact vibration monitoring system of the steam turbine shrouded blades. The proposed methods utilize the time-frequency processing (cross spectra) and the method using least squares to analyse the data from the optical and magnetoresistive sensors, which are mounted in the stator radially above the rotor blades. Fundamentally, the blade vibrations are detected during the blade passages under the sensors and the following signal processing, which covers also the proposed methods, leads to the estimation of the blade residual service life. The prototype system implementing above mentioned techniques was installed into the last stage of the new steam turbine (LP part). The methods for bladed disc mode shape evaluation were successfully verified on the signals, which were obtained during the commission operation of the turbine.

  11. Computer simulation of temperatures on the Centaur standard shroud during heated jettison tests

    NASA Technical Reports Server (NTRS)

    Hemminger, J. A.

    1973-01-01

    A heating fixture for simulating the heating and environment encountered by the Centaur standard shroud (CSS) during its ascent through the earth's atmosphere is discussed. A computer program was developed to provide a means of determining the overall temperature profile of a free-skin model of the CSS during the heating portion of the heated jettison tests. The program treats the energy contribution of each lamp on the heater to various points on the CSS surface. The analytic model was verified by adapting the computer program to the configuration of the hardware used in a series of Intermediate Scale Tests performed on a 2.4 meters by 2.4 meters section of the CSS corrugated structure. A comparison of some predicted versus experimental results from these tests is presented.

  12. The Turin Shroud face: the evidence of maxillo-facial trauma.

    PubMed

    Majorana, A; Bardellini, E; Gulino, G; Conti, G; Farronato, G; Rodella, L

    2015-01-01

    The Turin Shroud (TS) is a linen cloth commonly associated with Jesus Christ, his crucifixion and burial. Several medical specialists have debated the injuries of the TS Man, nevertheless there are no detailed and quantitative data about the anatomy of the TS face. The purpose of this study was to analyse the cephalometric measurements of the face image of the TS. The TS face image was acquired by a picture and processed using a cephalometric software, Oris Ceph® (Up to date 2012). The image of the soft tissues was processed in order to obtain skeletal points and a cephalometric analysis of the soft and skeletal tissues was performed. Image processing of the TS face shows that the Man represented in it has undergone a maxillo-facial trauma, especially a left displacement of the mandible, probably due to temporo-mandibular joint lesions. This condition has not been described before, despite several studies on the subject.

  13. Temperature dependence of the intrinsic small fatigue crack growth behavior in ni-base superalloys based on measurement of crack closure

    NASA Astrophysics Data System (ADS)

    Okazaki, M.; Yamada, H.; Nohmi, S.

    1996-04-01

    The effect of temperature on the small fatigue crack growth behavior of a single crystal and directionally solidified Ni-base superalloys was investigated at temperatures between 873 to 1123 K by measuring the crack closure. The results were also compared with those of the physically long crack. It was found that the propagation resistance and the fatigue threshold of the long cracks increased with temperature in all the materials. The long crack growth rates at three temperatures were approximately represented by an unique curve, after taking account of crack closure level and elastic modulus. In contrast, the small crack growth resistance decreased with temperature even when the crack closure phenomenon was taken into consideration. Furthermore, the small fatigue cracks exhibited considerably higher growth rates than the long cracks at a given effective stress intensity factor range and also grew under effective stress intensity factor ranges below the long crack threshold. The factors responsible for the lack of similitude in propagation rates between small and long cracks were also discussed, based on these observations and the chemical analysis near the crack tip using the electron probe microanalyzer.

  14. Pyrolytic carbon indentation crack morphology.

    PubMed

    Ely, J L; Stupka, J; Haubold, A D

    1996-06-01

    In studying fatigue and fracture behavior of brittle materials, Vickers diamond indentation cracks are often used. Many of the studies of indentation cracks use crack system models such as the radial-median crack or Palmqvist crack. These systems are also used to study small crack growth in brittle materials, and have been studied for pyrolytic carbon. However, the true morphology of these cracks in pyrolytic carbon coatings on graphite substrates have not been described. This study examined Vickers diamond and spherical ball indentation cracks in pyrolytic carbon coatings using several techniques, including serial metallographic cross sections, indentation fracture in bending, acoustic emission, and residual surface indentation scanning. The crack systems developed using these techniques were not typical of either radial median or Palmqvist systems. The morphology is unique to this material, possibly because of the coating thickness limitations. Given the difference in crack system, the application of standard indentation crack equations in studying fracture mechanics, especially for small cracks, must be questioned.

  15. Electromagnetic Detection of Fatigue Cracks under Protruding Head Ferromagnetic Fasteners

    NASA Technical Reports Server (NTRS)

    Wincheski, Buzz; Namkung, Min

    2004-01-01

    The detection of fatigue cracks under installed fasteners has been a major goal of the aging aircraft NDE community. The Sliding Probe, Magneto-Optic Imager, Rotating Self-Nulling Probe, Low Frequency Eddy Current Array, and Eddyscan systems are among the instruments developed for this inspection. It has been verified that the detection of fatigue cracks under flush head aluminum and titanium fasteners can be accomplished with a high resolution by the above techniques. The detection of fatigue cracks under ferromagnetic and protruding head fasteners, however, has been found to be much more difficult. For the present work, the inspection for fatigue cracks under SAE 4340 Steel Hi-Lok fasteners is explored. Modifications to the Rotating Self-Nulling Eddy Current Probe System are presented which enable the detection of fatigue cracks hidden under the protruding head of the ferromagnetic fastener. Inspection results for samples with varying length EDM notches are shown, as well as a comparison between the signature from an EDM notch and an actual fatigue crack. Finite Element Modeling is used to investigate the effect of the ferromagnetic fastener on the induced eddy current distribution in order to help explain the detection characteristics of the system. This paper will also introduce a modification to the Rotating Probe System designed specifically for the detection of deeply buried flaws in multilayer conductors. The design change incorporates a giant magnetoresistive (GMR) sensor as the pickup device to improve the low frequency performance of the probe. The flaw detection capabilities of the GMR based Self- Nulling Probe are presented along with the status of the GMR based Rotating Probe System for detection of deeply buried flaws under installed fasteners.

  16. 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.

  17. Electrical Impedance Spectroscopy-Based Defect Sensing Technique in Estimating Cracks

    PubMed Central

    Zhang, Tingting; Zhou, Liangdong; Ammari, Habib; Seo, Jin Keun

    2015-01-01

    A defect sensing method based on electrical impedance spectroscopy is proposed to image cracks and reinforcing bars in concrete structures. The method utilizes the frequency-dependent behavior of thin insulating cracks: low-frequency electrical currents are blocked by insulating cracks, whereas high-frequency currents can pass through thin cracks to probe the conducting bars. From various frequency-dependent electrical impedance tomography (EIT) images, we can show its advantage in terms of detecting both thin cracks with their thickness and bars. We perform numerical simulations and phantom experiments to support the feasibility of the proposed method. PMID:26007713

  18. Quantity effect of radial cracks on the cracking propagation behavior and the crack morphology.

    PubMed

    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.

  19. 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.

  20. Elevated Temperature Crack Propagation

    NASA Technical Reports Server (NTRS)

    Orange, Thomas W.

    1994-01-01

    This paper is a summary of two NASA contracts on high temperature fatigue crack propagation in metals. The first evaluated the ability of fairly simple nonlinear fracture parameters to correlate crack propagation. Hastelloy-X specimens were tested under isothermal and thermomechanical cycling at temperatures up to 980 degrees C (1800 degrees F). The most successful correlating parameter was the crack tip opening displacement derived from the J-integral. The second evaluated the ability of several path-independent integrals to correlate crack propagation behavior. Inconel 718 specimens were tested under isothermal, thermomechanical, temperature gradient, and creep conditions at temperatures up to 650 degrees C (1200 degrees F). The integrals formulated by Blackburn and by Kishimoto correlated the data reasonably well under all test conditions.

  1. Elevated temperature crack propagation

    SciTech Connect

    Orange, T.W.

    1994-02-01

    This paper is a summary of two NASA contracts on high temperature fatigue crack propagation in metals. The first evaluated the ability of fairly simple nonlinear fracture parameters to correlate crack propagation. Hastelloy-X specimens were tested under isothermal and thermomechanical cycling at temperatures up to 980 degrees C (1800 degrees F). The most successful correlating parameter was the crack tip opening displacement derived from the J-integral. The second evaluated the ability of several path-independent integrals to correlate crack propagation behavior. Inconel 718 specimens were tested under isothermal, thermomechanical, temperature gradient, and creep conditions at temperatures up to 650 degrees C (1200 degrees F). The integrals formulated by Blackburn and by Kishimoto correlated the data reasonably well under all test conditions.

  2. 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)

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

    PubMed

    Withers, P J

    2015-03-06

    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.

  4. 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

  5. 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.

  6. 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.

  7. Centrifugal acceleration modes for incompressible fluid in the leakage annulus between a shrouded pump impeller and its housing

    NASA Technical Reports Server (NTRS)

    Childs, D. W.

    1991-01-01

    An algorithm is developed for calculating complex eigenvalues and eigenvectors associated with the fluid resonances and is used to analyze the perturbed flow in the leakage path between a shrouded-pump impeller and its housing. The eigenvalues obtained are consistent with the forced-response curves. First- and second-natural-frequency eigensolutions are presented for mode shapes corresponding to lateral excitations, and first-natural-frequency eigensolutions are presented for mode shapes corresponding to axial excitation.

  8. Evaluation of the impeller shroud performance of an axial flow ventricular assist device using computational fluid dynamics.

    PubMed

    Su, Boyang; Chua, Leok P; Lim, Tau M; Zhou, Tongming

    2010-09-01

    Generally, there are two types of impeller design used in the axial flow blood pumps. For the first type, which can be found in most of the axial flow blood pumps, the magnet is embedded inside the impeller hub or blades. For the second type, the magnet is embedded inside the cylindrical impeller shroud, and this design has not only increased the rotating stability of the impeller but has also avoided the flow interaction between the impeller blade tip and the pump casing. Although the axial flow blood pumps with either impeller design have been studied individually, the comparisons between these two designs have not been conducted in the literature. Therefore, in this study, two axial flow blood pumps with and without impeller shrouds were numerically simulated with computational fluid dynamics and compared with each other in terms of hydraulic and hematologic performances. For the ease of comparison, these two models have the same inner components, which include a three-blade straightener, a two-blade impeller, and a three-blade diffuser. The simulation results showed that the model with impeller shroud had a lower static pressure head with a lower hydraulic efficiency than its counterpart. It was also found that the blood had a high possibility to deposit on the impeller shroud inner surface, which greatly enhanced the possibility of thrombus formation. The blood damage indices in both models were around 1%, which was much lower than the 13.1% of the axial flow blood pump of Yano et al. with the corresponding experimental hemolysis of 0.033 g/100 L.

  9. Acoustic far-field of shroud-lip-scattered instability modes of supersonic co-flowing jets

    NASA Astrophysics Data System (ADS)

    Samanta, Arnab; Freund, Jonathan B.

    2013-11-01

    We consider the acoustic radiation of instability modes in dual-stream jets, with the inner nozzle buried within the outer shroud, particularly the upstream scattering into acoustic modes that occurs at the shroud lip. For supersonic core jets, several families of instability waves are possible, beyond the regular Kelvin-Helmholtz (K-H) mode, with very different modal shapes and propagation characteristics, which are candidates for changing the sound character of very high-speed jets. The co-axial shear layers are modeled as vortex sheets, with the Wiener-Hopf method used to compute these modes coupled with an asymptotic solution for the far-field radiation. A broadband mode spectra as well as single propagating modes are considered as incident and scattered waves. The resulting far-field directivity patterns are quantified, to show the efficiency of some of these radiation mechanisms, particularly in the upstream direction, which is not directly affected by the Mach-wave-like sound that is radiated from these modes irrespective of any scattering surface. A full Kutta condition, which provides the usual boundary condition at the shroud lip, is altered to examine how vortex shedding, perhaps controllable at the lip, affects the radiated sound.

  10. Do we really need new medical information about the Turin Shroud?

    PubMed

    Bevilacqua, M; Fanti, G; D'Arienzo, M; De Caro, R

    2014-02-01

    Image processing of the Turin Shroud (TS) shows that the Man represented in it has undergone an under glenoidal dislocation of the humerus on the right side and lowering of the shoulder, and has a flattened hand and enophthalmos; conditions that have not been described before, despite several studies on the subject. These injuries indicate that the Man suffered a violent blunt trauma to the neck, chest and shoulder from behind, causing neuromuscular damage and lesions of the entire brachial plexus. The posture of the left claw-hand is indicative of an injury of the lower brachial plexus, as is the crossing of the hands on the pubis, not above the pubis as it would normally be, and are related to traction of the limbs as a result of the nailing to the patibulum. The disappearance of the thumbprints is because of entrainment of the flexor pollicis longus tendons while the nails were driven through the wrists. The blunt chest trauma, which resulted in the body falling forwards, was the direct cause of a lung contusion and haemothorax, confirmed by the post-mortem leakage of clots and serum from the chest caused by the stabbing with the spear, and was a likely cause of cardiac contusion. All the evidence is in favour of the hypothesis that the TS Man is Jesus of Nazareth.

  11. An experimental investigation on the tip leakage noise in axial-flow fans with rotating shroud

    NASA Astrophysics Data System (ADS)

    Canepa, Edward; Cattanei, Andrea; Mazzocut Zecchin, Fabio; Milanese, Gabriele; Parodi, Davide

    2016-08-01

    The tip leakage noise generated by a shrouded rotor of an axial-flow fan has been experimentally studied. The measurements have been taken at high flow rate and at the design point in a hemi-anechoic chamber, at constant rotational speed and during speed ramps. A test plenum designed according to ISO 10302 has been employed to modify the operating conditions and different inlet configurations, ducted and unducted with standard and reduced tip gap, have been considered. The basic features of the inflow have been studied by means of aerodynamic measurements taken upstream of the rotor. To separate the noise generating mechanisms from the acoustic propagation effects, the acoustic response function of the test configuration has been computed employing the spectral decomposition method, and then it has been compared with the velocity-scaled, constant-Strouhal number SPL. In this way, the noise components related to the tip leakage flow have been identified and their connection with geometry have been highlighted. The broadband part of the spectra and the peaks related to the tip leakage flow are affected by the same propagation effects, but show a different dependence on the rotational speed and on the operating point. The upstream geometry affects the radiated noise much more than the performance and even a strong reduction in the tip-gap cannot completely eliminate the related noise.

  12. Evaluation of the effect of crack closure on fatigue crack growth of simulated short cracks

    NASA Technical Reports Server (NTRS)

    Telesman, J.; Fisher, D. M.

    1984-01-01

    A test program was performed to determine the influence of crack closure on fatigue crack growth (FCG) rates of short cracks. By use of the standard compact tension specimen, test procedures were devised to evaluate closure loads in the wake of the crack behind its tip. The first procedure determined the magnitude of crack closure as a function of the fatigued crack wave by incrementally removing the contacting wake surfaces and measuring closure load at each increment. The second procedure used a low-high loading sequence to simulate short crack behavior. Based on the results, it was concluded that crack closure is not the major reason for the more rapid growth of short cracks as compared to long crack growth.

  13. Single point aerosol sampling: Evaluation of mixing and probe performance in a nuclear stack

    SciTech Connect

    Rodgers, J.C.; Fairchild, C.I.; Wood, G.O.

    1995-02-01

    Alternative Reference Methodologies (ARMs) have been developed for sampling of radionuclides from stacks and ducts that differ from the methods required by the U.S. EPA. The EPA methods are prescriptive in selection of sampling locations and in design of sampling probes whereas the alternative methods are performance driven. Tests were conducted in a stack at Los Alamos National Laboratory to demonstrate the efficacy of the ARMs. Coefficients of variation of the velocity tracer gas, and aerosol particle profiles were determined at three sampling locations. Results showed numerical criteria placed upon the coefficients of variation by the ARMs were met at sampling stations located 9 and 14 stack diameters from flow entrance, but not at a location that is 1.5 diameters downstream from the inlet. Experiments were conducted to characterize the transmission of 10 {mu}m aerodynamic equivalent diameter liquid aerosol particles through three types of sampling probes. The transmission ratio (ratio of aerosol concentration at the probe exit plane to the concentration in the free stream) was 107% for a 113 L/min (4-cfm) anisokinetic shrouded probe, but only 20% for an isokinetic probe that follows the EPA requirements. A specially designed isokinetic probe showed a transmission ratio of 63%. The shrouded probe performance would conform to the ARM criteria; however, the isokinetic probes would not.

  14. Crack propagation in Hastelloy X

    SciTech Connect

    Weerasooriya, T.; Strizak, J.P.

    1980-05-01

    The fatigue and creep crack growth rates of Hastelloy X were examined both in air and impure helium. Creep crack growth rate is higher in air and impure helium at 650/sup 0/C. Initial creep crack growth from the original sharp fatigue crack is by an intergranular mode of fracture. As the cracking accelerates at higher stress intensities, growth is by a mixed mode of both intergranular and transgranular fracture. Fatigue crack growth rate increases with increasing temperature and decreasing frequency for the range of stress intensities reported in the literature and is lower in impure helium than in air.

  15. Double shroud delivery of silica precursor for reducing hexavalent chromium in welding fume.

    PubMed

    Wang, Jun; Kalivoda, Mark; Guan, Jianying; Theodore, Alexandros; Sharby, Jessica; Wu, Chang-Yu; Paulson, Kathleen; Es-Said, Omar

    2012-01-01

    The welding process yields a high concentration of nanoparticles loaded with hexavalent chromium (Cr(6+)), a known human carcinogen. Previous studies have demonstrated that using tetramethylsilane (TMS) as a shielding gas additive can significantly reduce the Cr(6+) concentration in welding fume particles. In this study, a novel insulated double shroud torch (IDST) was developed to further improve the reduction of airborne Cr(6+) concentration by separating the flows of the primary shielding gas and the TMS carrier gas. Welding fumes were collected from a welding chamber in the laboratory and from a fixed location near the welding arc in a welding facility. The Cr(6+) content was analyzed with ion chromatography and X-ray photoelectron spectroscopy (XPS). Results from the chamber sampling demonstrated that the addition of 3.2 ≈ 5.1% of TMS carrier gas to the primary shielding gas resulted in more than a 90% reduction of airborne Cr(6+) under all shielding gas flow rates. The XPS result confirmed complete elimination of Cr(6+) inside the amorphous silica shell. Adding 100 ≈ 1000 ppm of nitric oxide or carbon monoxide to the shielding gas could also reduce Cr(6+) concentrations up to 57% and 35%, respectively; however, these reducing agents created potential hazards from the release of unreacted agents. Results of the field test showed that the addition of 1.6% of TMS carrier gas to the primary shielding gas reduced Cr(6+) concentration to the limitation of detection (1.1 μg/m(3)). In a worst-case scenario, if TMS vapor leaked into the environment without decomposition and ventilation, the estimated TMS concentration in the condition of field sampling would be a maximum 5.7 ppm, still well below its flammability limit (1%). Based on a previously developed cost model, the use of TMS increases the general cost by 3.8%. No visual deterioration of weld quality caused by TMS was found, although further mechanical testing is necessary.

  16. Rotating concave eddy current probe

    DOEpatents

    Roach, Dennis P.; Walkington, Phil; Rackow, Kirk A.; Hohman, Ed

    2008-04-01

    A rotating concave eddy current probe for detecting fatigue cracks hidden from view underneath the head of a raised head fastener, such as a buttonhead-type rivet, used to join together structural skins, such as aluminum aircraft skins. The probe has a recessed concave dimple in its bottom surface that closely conforms to the shape of the raised head. The concave dimple holds the probe in good alignment on top of the rivet while the probe is rotated around the rivet's centerline. One or more magnetic coils are rigidly embedded within the probe's cylindrical body, which is made of a non-conducting material. This design overcomes the inspection impediment associated with widely varying conductivity in fastened joints.

  17. 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…

  18. Thermal cracking of retort oil

    SciTech Connect

    Dearth, J.D.; Smith, R.H.

    1980-10-14

    The thermal cracking of retort oil vapors in an elongated reactor is improved by passing the effluent oil vapors and gases from a retort to a thermal cracking unit before the temperature of the retort effluent falls below 680* F. This encourages the more desirable cracking reactions, increases the thermal efficiency of the process, and avoids preheater coking.

  19. A Review of Crack Closure

    DTIC Science & Technology

    1984-04-01

    OVERLOAD EFFECTS [27,32,36,55,65,80-94] 104 4.3 SHORT CRACK BEHAVIOUR 113 4.4 SURFACE CRACK BEHAVIOUR 116 4.5 EFFECT OF RESIDUAL STRESS 117 4.6...Compressive Stresses Developed 16 on a Growing Fatigue Crack During a Constant Amplitude Cyclic Load Control Test. 4 Plastic Zone and Residual Compressive... Stresses Developed 18 on a Saw Cut Sharp Crack During a Constant Amplitude Cyclic Load Control Test. Residual Stresses Developed in the Plane of Crack

  20. Cascaded image analysis for dynamic crack detection in material testing

    NASA Astrophysics Data System (ADS)

    Hampel, U.; Maas, H.-G.

    Concrete probes in civil engineering material testing often show fissures or hairline-cracks. These cracks develop dynamically. Starting at a width of a few microns, they usually cannot be detected visually or in an image of a camera imaging the whole probe. Conventional image analysis techniques will detect fissures only if they show a width in the order of one pixel. To be able to detect and measure fissures with a width of a fraction of a pixel at an early stage of their development, a cascaded image analysis approach has been developed, implemented and tested. The basic idea of the approach is to detect discontinuities in dense surface deformation vector fields. These deformation vector fields between consecutive stereo image pairs, which are generated by cross correlation or least squares matching, show a precision in the order of 1/50 pixel. Hairline-cracks can be detected and measured by applying edge detection techniques such as a Sobel operator to the results of the image matching process. Cracks will show up as linear discontinuities in the deformation vector field and can be vectorized by edge chaining. In practical tests of the method, cracks with a width of 1/20 pixel could be detected, and their width could be determined at a precision of 1/50 pixel.

  1. 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.

  2. Elevated temperature crack growth

    NASA Technical Reports Server (NTRS)

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

    1985-01-01

    The purpose is to determine the ability of currently available P-I integrals to correlate fatigue crack propagation under conditions that simulate the turbojet engine combustor liner environment. The utility of advanced fracture mechanics measurements will also be evaluated during the course of the program. To date, an appropriate specimen design, a crack displacement measurement method, and boundary condition simulation in the computational model of the specimen were achieved. Alloy 718 was selected as an analog material based on its ability to simulate high temperature behavior at lower temperatures. Tensile and cyclic tests were run at several strain rates so that an appropriate constitutive model could be developed. Suitable P-I integrals were programmed into a finite element post-processor for eventual comparison with experimental data.

  3. 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.

  4. 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).

  5. 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.

  6. 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

  7. 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.

  8. Distributed Password Cracking

    DTIC Science & Technology

    2009-12-01

    conduit to this significant source of processing power and John the Ripper is the key. BOINC is a distributed data processing system that...processed without changing significant portions of the structure. John the Ripper is a password cracking program that takes a password file and...strength of their password security policy. This thesis goes into detail on the inner workings of BOINC, John the Ripper , and the merger of the two

  9. 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.

  10. 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.

  11. Combination of thermal cracking with vacuum distillation of cracked tar

    SciTech Connect

    Telyashev, G.G.; Gimaev, R.N.; Makhov, A.F.; Usmanov, R.M.; Baimbetov, A.M.; Vafin, I.A.

    1987-11-01

    A method of obtaining greater amounts of distillate feedstocks from the heavy gasoil recovered by vacuum distillation of the products of thermal cracking of petroleum resids was examined. At the Novo-Ufa Petroleum Refinery, a two-furnace thermal cracking unit was reconstructed, adding a vacuum section for distillation of the cracked tar. A simplified flow plan of this unit is shown. Vacuum resid from atmospheric-vacuum tubestill units is heated in double-pipe heat exchangers, using heat from the gasoil and cracked tar. The new method makes it possible to curtail production of boiler fuel, expand the resources of feed, and improve the quality of petroleum coke.

  12. 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.

  13. Spectrophotometric probe

    DOEpatents

    Prather, W.S.; O'Rourke, P.E.

    1994-08-02

    A support structure is described bearing at least one probe for making spectrophotometric measurements of a fluid using a source of light and a spectrophotometer. The probe includes a housing with two optical fibers and a planoconvex lens. A sleeve bearing a mirror surrounds the housing. The lens is separated from the mirror by a fixed distance, defining an interior space for receiving a volume of the fluid sample. A plurality of throughholes extending through the sleeve communicate between the sample volume and the exterior of the probe, all but one hole bearing a screen. A protective jacket surrounds the probe. A hollow conduit bearing a tube is formed in the wall of the probe for venting any air in the interior space when fluid enters. The probe is held at an acute angle so the optic fibers carrying the light to and from the probe are not bent severely on emergence from the probe. 3 figs.

  14. Spectrophotometric probe

    DOEpatents

    Prather, William S.; O'Rourke, Patrick E.

    1994-01-01

    A support structure bearing at least one probe for making spectrophotometric measurements of a fluid using a source of light and a spectrophotometer. The probe includes a housing with two optical fibers and a planoconvex lens. A sleeve bearing a mirror surrounds the housing. The lens is separated from the mirror by a fixed distance, defining an interior space for receiving a volume of the fluid sample. A plurality of throughholes extending through the sleeve communicate between the sample volume and the exterior of the probe, all but one hole bearing a screen. A protective jacket surrounds the probe. A hollow conduit bearing a tube is formed in the wall of the probe for venting any air in the interior space when fluid enters. The probe is held at an acute angle so the optic fibers carrying the light to and from the probe are not bent severely on emergence from the probe.

  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. Aeroacoustic wind-tunnel tests of a light twin-boom general-aviation airplane with free or shrouded-pusher propellers. [in the Langley full-scale tunnel

    NASA Technical Reports Server (NTRS)

    Mclemore, H. C.; Pegg, R. J.

    1980-01-01

    Tests were conducted in the Langley full-scale tunnel to determine the aerodynamic performance and acoustic characteristics of four different pusher-propeller configurations on a twin boom, general aviation airplane. The propellers included a 2-blade free propeller, two 3-blade shrouded propellers, and a 5-blade shrouded propeller. The tests were conducted for a range of airplane angles of attack from about 0 deg to 16 deg for test speeds from 0 to about 36 m/sec and for a range of propeller blade angles and rotation speeds. The free propeller provided the best aerodynamic propulsive performance. For forward flight conditions, the free propeller noise levels were lower than those of the shrouded propellers. In the static conditions the free propeller noise levels were as low as those for the shrouded propellers, except for the propeller in-plane noise where the shrouded propeller noise levels were lower.

  17. 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.

  18. Fatigue Crack Topography.

    DTIC Science & Technology

    1984-01-01

    continents, rihst-i- " the battlement line Nile - Lake Albert - Lake Tanganyika - Lake Malawi in Attica. Iscr~l example are all ocean ridges, for...marker band application. MARKER MARKER MARKER BANDS BANDS BANDS 6". Ist5 4..% 2M.d - W.S. 0,0 CRACK K*MAX SPECI CORD 64 8 5 q. 14 969 kg9133 0cu LR) G...AFTER HIGHEST 1-7 LOW LEVEL PEAK MARKER BLOCK BEFORE ADDED TO SEQUENCE SEVERE 1-8 FLIGHT SNO BIRD 1-9 2-40 2-5KB 2-111 2-120 LOW LEVEL 427 CYCLES

  19. Retrofitting olefin cracking plants

    SciTech Connect

    Sumner, C.; Fernandez-Baujin, J.M.

    1983-12-01

    This article discusses the retrofitting of liquid crackers which produce olefins so that gaseous feedstocks can be used. Naphtha and gas oil are the predominant design feedstocks for producing olefins. The price of gaseous feedstocks such as ethane, propane and butane have become economically more attractive than liquid feedstocks. Existing liquid crackers will be able to produce ethylene at 85% or higher capacity when cracking propane and butane feedstock with only minor changes. Topics considered include revamping for vacuum gas oil (VGO) feedstocks and revamping for liquefied petroleum gas (LPG) feedstocks.

  20. Mode II fatigue crack propagation.

    NASA Technical Reports Server (NTRS)

    Roberts, R.; Kibler, J. J.

    1971-01-01

    Fatigue crack propagation rates were obtained for 2024-T3 bare aluminum plates subjected to in-plane, mode I, extensional loads and transverse, mode II, bending loads. These results were compared to the results of Iida and Kobayashi for in-plane mode I-mode II extensional loads. The engineering significance of mode I-mode II fatigue crack growth is considered in view of the present results. A fatigue crack growth equation for handling mode I-mode II fatigue crack growth rates from existing mode I data is also discussed.

  1. Three-Dimensional Gear Crack Propagation Studies

    NASA Technical Reports Server (NTRS)

    Lewicki, David G.; Sane, Ashok D.; Drago, Raymond J.; Wawrzynek, Paul A.

    1998-01-01

    Three-dimensional crack growth simulation was performed on a split-tooth gear design using boundary element modeling and linear elastic fracture mechanics. Initial cracks in the fillet of the teeth produced stress intensity factors of greater magnitude (and thus, greater crack growth rates) than those in the root or groove areas of the teeth. Crack growth simulation was performed on a case study to evaluate crack propagation paths. Tooth fracture was predicted from the crack growth simulation for an initial crack in the tooth fillet region. Tooth loads on the uncracked mesh of the split-tooth design were up to five times greater than those on the cracked mesh if equal deflections of the cracked and uncracked teeth were considered. Predicted crack shapes as well as crack propagation life are presented based on calculated stress intensity factors, mixed-mode crack propagation trajectory theories, and fatigue crack growth theories.

  2. 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.

  3. 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... such wheat, other than moisture, remain unaltered. Cracked wheat contains not more than 15 percent...

  4. 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... such wheat, other than moisture, remain unaltered. Cracked wheat contains not more than 15 percent...

  5. Effect of Crack Opening on Penetrant Crack Detectability

    NASA Technical Reports Server (NTRS)

    Weaver, Devin

    2009-01-01

    Results: From the testing we were able to determine all the cracks within the test range were detectable or better with developer. Many of the indications after development lost their linearity and gave circular indications. Our tests were performed in a laboratory and our procedure would be difficult in an industrial setting. Conclusions: The "V" did not significantly affect our ability to detect the POD cracks with fluorescent penetrant. Conduct same experiment with more cracks. The 0.025 and 0.050 POD specimens are clean and documented with the SEM. Conduct water-wash fluorescent penetrant test at EAFB. The poppet cracks are tighter than the POD specimen cracks. Flight FCV poppets: 0.01 mils (0.3 microns) Langley fatigue cracked poppets: 0.02 mils (0.5 microns) POD specimen (post 5 mils): 0.05 mils (1.4 microns) We could not detect cracks in Langley fatigue-cracked poppets with fluorescent penetrant. Investigate inability of penetrant to wet the poppet surface.

  6. A finite-element-based perturbation model for the rotordynamic analysis of shrouded pump impellers: Part 1: Model development and applications

    NASA Technical Reports Server (NTRS)

    Baskharone, Erian A.

    1993-01-01

    This study concerns the rotor dynamic characteristics of fluid-encompassed rotors, with special emphasis on shrouded pump impellers. The core of the study is a versatile and categorically new finite-element-based perturbation model, which is based on a rigorous flow analysis and what we have generically termed the 'virtually' deformable finite-element approach. The model is first applied to the case of a smooth annular seal for verification purposes. The rotor excitation components, in this sample problem, give rise to a purely cylindrical, purely conical, and a simultaneous cylindrical/conical rotor whirl around the housing centerline. In all cases, the computed results are compared to existing experimental and analytical data involving the same seal geometry and operating conditions. Next, two labyrinth-seal configurations, which share the same tooth-to-tooth chamber geometry but differ in the total number of chambers, were investigated. The results, in this case, are compared to experimental measurements for both seal configurations. The focus is finally shifted to the shrouded-impeller problem, where the stability effects of the leakage flow in the shroud-to-housing secondary passage are investigated. To this end, the computational model is applied to a typical shrouded-impeller pump stage, fabricated and rotor dynamically tested by Sulzer Bros., and the results compared to those of a simplified 'bulk-flow' analysis and Sulzer Bros.' test data. In addition to assessing the computed rotor dynamic coefficients, the shrouded-impeller study also covers a controversial topic, namely that of the leakage-passage inlet swirl, which was previously cited as the origin of highly unconventional (resonance-like) trends of the fluid-exerted forces. In order to validate this claim, a 'microscopic' study of the fluid/shroud interaction mechanism is conducted, with the focus being on the structure of the perturbed flow field associated with the impeller whirl. The conclusions

  7. Pressure oscillation in the leakage annulus between a shrouded impeller and its housing due to impeller-discharge-pressure disturbances

    NASA Technical Reports Server (NTRS)

    Childs, D. W.

    1992-01-01

    The perturbed flow in the leakage path between a shrouded-pump impeller and its housing is analyzed using experiences with the Space Shuttle Main Engine (SSME), high pressure fuel turbopump (HPFTP) wearing-ring seals. Analysis is based on a bulk-flow model which consists of the path-momentum, circumferential momentum, and continuity equations. The pressure oscillations in the leakage annulus are driven by a circumferential variation of the impeller discharge pressure. It is shown that the occurrence and nature of the pressure oscillations depend on the tangential-velocity ratio of the fluid entering the seal, the order of the Fourier coefficient, the closeness of the precessional frequency of the rotating pressure field to the first natural frequency of the fluid annulus, and the clearance of the wearing-ring seal. The results obtained may explain the internal melting observed on SSME HPFTP seal parts.

  8. Evaluation of the behavior of shrouded plasma spray coatings in the platen superheater of coal-fired boilers

    NASA Astrophysics Data System (ADS)

    Sidhu, Buta Singh; Prakash, S.

    2006-06-01

    Nickel- and cobalt-based coatings were formulated by a shrouded plasma spray process on boiler tube steels, namely, ASTM-SA210-grade A1 (GrA1), ASTM-SA213-T-11 (T11), and ASTM-SA213-T-22 (T22). The Ni-22Cr-10Al-1Y alloy powder was sprayed as a bond in each case before the final coating. The degradation behavior of the bared and coated steels was studied in the platen superheater of the coal-fired boiler. The samples were inserted through the soot blower dummy points with the help of stainless steel wires. The coatings were found to be effective in increasing resistance to degradation in the given boiler environment. The maximum protection was observed in the case of Stellite-6 (St-6) coating.

  9. Preliminary study of cyclic thermal shock resistance of plasma-sprayed zirconium oxide turbine outer air seal shrouds

    NASA Technical Reports Server (NTRS)

    Bill, R. C.; Wisander, D. W.

    1977-01-01

    Several experimental concepts representing potential high pressure turbine seal material systems were subjected to cyclic thermal shock exposures similar to those that might be encountered under severe engine start-up and shut-down sequences. All of the experimental concepts consisted of plasma-sprayed yttria stabilized ZrO2 on the high temperature side of the blade tip seal shroud. Between the ZrO2 and a cooled, dense metal backing, various intermediate layer concepts intended to mitigate thermal stresses were incorporated. Performance was judged on the basis of the number of thermal shock cycles required to cause loss of seal material through spallation. The most effective approach was to include a low modulus, sintered metal pad between the ZrO2 and the metallic backing. It was also found that reducing the density of the ZrO2 layer significantly improved the performance of specimens with plasma-sprayed metal/ceramic composite intermediate layers.

  10. NO{sub x} emissions of a jet diffusion flame which is surrounded by a shroud of combustion air

    SciTech Connect

    Tran, P.X.; White, F.P.; Mathur, M.P.; Ekmann, J.M.

    1996-08-01

    The present work reports an experimental study on the behavior of a jet flame surrounded by a shroud of combustion air. Measurements focussed on the flame length and the emissions of NO{sub x}, total unburned hydrocarbons, CO{sub 2}, and O{sub 2}. Four different fuel flow rates (40.0, 78.33, 138.33, and 166.6 cm/s), air flow rates up to 2500 cm{sup 3}/s and four different air injector diameters (0.079 cm, 0. 158 cm, 0.237 cm, and 0.316 cm) were used. The shroud of combustion air causes the flame length to decrease by a factor proportional to 1/[p{sub a}/p{sub f} + C{sub 2}({mu}{sub a}Re,a/{mu}{sub f}Re,f){sup 2}]{sup {1/2}}. A substantial shortening of the flame length occurred by increasing the air injection velocity keeping fuel rate fixed or conversely by lowering the fuel flow rate keeping air flow rate constant. NO{sub x} emissions ranging from 5 ppm to 64 ppm were observed and the emission of NO{sub x} decreased strongly with the increased air velocity. The decrease of NO{sub x} emissions was found to follow a similar scaling law as does the flame length. However, the emission of the total hydrocarbons increased with the increased air velocity or the decreased fuel flow rate. A crossover condition where both NO{sub x} and unburned- hydrocarbon emissions are low, was identified. At an air-to-fuel velocity ratio of about 1, the emissions of NO{sub x} and the total hydrocarbons were found to be under 20 ppm.

  11. 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.

  12. 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).

  13. Hydrocarbon cracking and reforming process

    SciTech Connect

    Le, Q.N.; Schipper, P.H.; Owen, H.

    1992-03-31

    This patent describes a process for upgrading paraffinic naphtha to high octane fuel. It comprises: contacting a fresh naphtha feedstock stream containing a major amount of C{sub 7+} alkanes and naphthenes with medium pore acid cracking catalyst under low pressure selective cracking conditions effective to produce 4-C5 isoalkene and C4-C5 isoalkane, the cracking catalyst being substantially free of hydrogenation-dehydrogenation metal components and having an acid cracking activity less than 15; separating cracking effluent to obtain an olefinic fraction rich in C4-C5 isoalkene and a C6+ fraction; etherifying the C4-C5 isoalkene fraction by catalytic reaction with lower alkanol to produce tertiary-alkyl ether product; and reforming the C6+ fraction to provide high octane gasoline components.

  14. 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.

  15. [A microstructural approach to fatigue crack processes in poly crystalline BCC materials]. Progress report

    SciTech Connect

    Gerberich, W.W.

    1992-12-31

    Objective was to study fatigue where a combination of low temperature and cyclic loading produced cyclic cleavage in bcc Fe-base systems. Both dislocation dynamics and quasi-statics of crack growth were probed. This document reviews progress over the past 6 years: hydrogen embrittlement and cleavage, computations (stress near crack tip), dislocation emission from grain boundaries, fracture process zones, and understanding brittle fracture at the atomistic/dislocation scales and at the microscopic/macroscopic scale.

  16. [A microstructural approach to fatigue crack processes in poly crystalline BCC materials

    SciTech Connect

    Gerberich, W.W.

    1992-01-01

    Objective was to study fatigue where a combination of low temperature and cyclic loading produced cyclic cleavage in bcc Fe-base systems. Both dislocation dynamics and quasi-statics of crack growth were probed. This document reviews progress over the past 6 years: hydrogen embrittlement and cleavage, computations (stress near crack tip), dislocation emission from grain boundaries, fracture process zones, and understanding brittle fracture at the atomistic/dislocation scales and at the microscopic/macroscopic scale.

  17. Self-healing of cracks in Ag joining layer for die-attachment in power devices

    NASA Astrophysics Data System (ADS)

    Chen, Chuantong; Nagao, Shijo; Suganuma, Katsuaki; Jiu, Jinting; Zhang, Hao; Sugahara, Tohru; Iwashige, Tomohito; Sugiura, Kazuhiko; Tsuruta, Kazuhiro

    2016-08-01

    Sintered silver (Ag) joining has attracted significant interest in power devices modules for its ability to form stable joints with a porous interconnection layer. A function for the self-healing of cracks in sintered porous Ag interlayers at high temperatures is discovered and reported here. A crack which was prepared on a Ag joining layer was closed after heating at 200 °C in air. The tensile strength of pre-cracked Ag joining layer specimens recovers to the value of non-cracked specimens after heating treatment. Transmission electron microscopy (TEM) was used to probe the self-healing mechanism. TEM images and electron diffraction patterns show that a large quantity of Ag nanoparticles formed at the gap with the size less than 10 nm, which bridges the crack in the self-healing process. This discovery provides additional motivation for the application of Ag as an interconnection material for power devices at high temperature.

  18. Crack detection and analyses using resonance ultrasonic vibrations in full-size crystalline silicon wafers

    SciTech Connect

    Belyaev, A.; Polupan, O.; Dallas, W.; Ostapenko, S.; Hess, D.; Wohlgemuth, J.

    2006-03-13

    An experimental approach for fast crack detection and length determination in full-size solar-grade crystalline silicon wafers using a resonance ultrasonic vibrations (RUV) technique is presented. The RUV method is based on excitation of the longitudinal ultrasonic vibrations in full-size wafers. Using an external piezoelectric transducer combined with a high sensitivity ultrasonic probe and computer controlled data acquisition system, real-time frequency response analysis can be accomplished. On a set of identical crystalline Si wafers with artificially introduced periphery cracks, it was demonstrated that the crack results in a frequency shift in a selected RUV peak to a lower frequency and increases the resonance peak bandwidth. Both characteristics were found to increase with the length of the crack. The frequency shift and bandwidth increase serve as reliable indicators of the crack appearance in silicon wafers and are suitable for mechanical quality control and fast wafer inspection.

  19. Flux focusing eddy current probe

    NASA Technical Reports Server (NTRS)

    Simpson, John W. (Inventor); Clendenin, C. Gerald (Inventor); Fulton, James P. (Inventor); Wincheski, Russell A. (Inventor); Todhunter, Ronald G. (Inventor); Namkung, Min (Inventor); Nath, Shridhar C. (Inventor)

    1997-01-01

    A flux-focusing electromagnetic sensor which uses a ferromagnetic flux-focusing lens simplifies inspections and increases detectability of fatigue cracks and material loss in high conductivity material. The unique feature of the device is the ferrous shield isolating a high-turn pick-up coil from an excitation coil. The use of the magnetic shield is shown to produce a null voltage output across the receiving coil in the presence of an unflawed sample. A redistribution of the current flow in the sample caused by the presence of flaws, however, eliminates the shielding condition and a large output voltage is produced, yielding a clear unambiguous flaw signal. The maximum sensor output is obtained when positioned symmetrically above the crack. Hence, by obtaining the position of the maximum sensor output, it is possible to track the fault and locate the area surrounding its tip. The accuracy of tip location is enhanced by two unique features of the sensor; a very high signal-to-noise ratio of the probe's output which results in an extremely smooth signal peak across the fault, and a rapidly decaying sensor output outside a small area surrounding the crack tip which enables the region for searching to be clearly defined. Under low frequency operation, material thinning due to corrosion damage causes an incomplete shielding of the pick-up coil. The low frequency output voltage of the probe is therefore a direct indicator of the thickness of the test sample.

  20. Eddy-Current Inspection of Cracking in Land-Based Gas Turbine Blades

    NASA Astrophysics Data System (ADS)

    Fukutomi, H.; Ogata, T.

    2004-02-01

    There has been a growing need in the electric utility industry to assess the remaining life of blades in gas turbines. It is quite important to nondestructively comprehend the depths of surface-breaking cracks in blades. Flexible eddy current array probes have been developed to overcome the major limitations of existing eddy current inspection systems. The use of an array of sensors allows cracks of all lengths to be detected and will ultimately allow real time data imaging to provide rapid inspection and easy interpretation. For this study using eddy current techniques, crack detection equipment has been developed and applied to gas turbine Stage 1 blades for field use.

  1. Analysis of Crack Arrest Toughness.

    DTIC Science & Technology

    1988-01-15

    vload(m) vp tn(m) Vertical Source Load (kN) on wedge HY80 Finite Element 0.0122 0.0099 3.81x10 -4 144 Steel Calculations Experiment 0.0122 --- 3.74x10-4...curve, are bona fide measures of the fracture arrest capability of tough ductile steels . The second is that the J-values represent the crack driving...fibrous mode of crack extension. (b) A new test method for studying fast fracture and arrest in tough steels . (c) Measurements of fast fracture and crack

  2. 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.

  3. 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.

  4. Simulation of Fluid Flow and Collection Efficiency for an SEA Multi-element Probe

    NASA Technical Reports Server (NTRS)

    Rigby, David L.; Struk, Peter M.; Bidwell, Colin

    2014-01-01

    Numerical simulations of fluid flow and collection efficiency for a Science Engineering Associates (SEA) multi-element probe are presented. Simulation of the flow field was produced using the Glenn-HT Navier-Stokes solver. Three-dimensional unsteady results were produced and then time averaged for the heat transfer and collection efficiency results. Three grid densities were investigated to enable an assessment of grid dependence. Simulations were completed for free stream velocities ranging from 85-135 meters per second, and free stream total pressure of 44.8 and 93.1 kilopascals (6.5 and 13.5 pounds per square inch absolute). In addition, the effect of angle of attack and yaw were investigated by including 5 degree deviations from straight for one of the flow conditions. All but one of the cases simulated a probe in isolation (i.e. in a very large domain without any support strut). One case is included which represents a probe mounted on a support strut within a finite sized wind tunnel. Collection efficiencies were generated, using the LEWICE3D code, for four spherical particle sizes, 100, 50, 20, and 5 micron in diameter. It was observed that a reduction in velocity of about 20% occurred, for all cases, as the flow entered the shroud of the probe. The reduction in velocity within the shroud is not indicative of any error in the probe measurement accuracy. Heat transfer results are presented which agree quite well with a correlation for the circular cross section heated elements. Collection efficiency results indicate a reduction in collection efficiency as particle size is reduced. The reduction with particle size is expected, however, the results tended to be lower than the previous results generated for isolated two-dimensional elements. The deviation from the two-dimensional results is more pronounced for the smaller particles and is likely due to the reduced flow within the protective shroud. As particle size increases differences between the two

  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. 46 CFR 59.10-5 - Cracks.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 2 2011-10-01 2011-10-01 false Cracks. 59.10-5 Section 59.10-5 Shipping COAST GUARD... APPURTENANCES Welding Repairs to Boilers and Pressure Vessels in -Service § 59.10-5 Cracks. (a) Cracks extending... cracks are veed out so that complete penetration of the weld metal is secured. (b) Circumferential...

  7. 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…

  8. Shaft vibrations in turbomachinery excited by cracks

    NASA Technical Reports Server (NTRS)

    Grabowski, B.

    1982-01-01

    During the past years the dynamic behavior of rotors with cracks has been investigated mainly theoretically. This paper deals with the comparison of analytical and experimental results of the dynamics of a rotor with an artificial crack. The experimental results verify the crack model used in the analysis. They show the general possibility to determine a crack by extended vibration control.

  9. 46 CFR 59.10-5 - Cracks.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 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. (e... any direction, nor more than a total of four cracks in a drum, and further provided the welding...

  10. Microscopic origins of stochastic crack growth

    NASA Astrophysics Data System (ADS)

    Pardee, W. J.; Morris, W. L.; Cox, B. N.

    Physical arguments are made to obtain a mathematical model of the stochastic growth of surface fatigue cracks in a ductile metal alloy. The model is a set of coupled partial differential equations for the expected statistical density of cracks per unit area. The differential equations describe the smooth, deterministic local evolution of crack states, with the stochastic effects of abrupt local changes of material in the crack path appearing as transitions between distinct subspaces of single crack state space. Results are related to observables such as statistical distributions of crack growth rate and of time for at least one crack to reach macroscopic length.

  11. The kinetics of hydrocarbon cracking

    SciTech Connect

    Groten, W.A.; Wojciechowski, B.W. )

    1993-03-01

    A general kinetic model which describes the catalytic cracking of pure hydrocarbons is presented. The model includes a monomolecular cracking path based on the Langmuir adsorption isotherm as well as a bimolecular path, following Rideal kinetics, which accounts for the possibility of a chain cracking mechanism being involved. Catalyst decay is accounted for using the time-on-stream-decay function. Fitting of experimental data from n-nonane cracking on USHY at 673 K, combined with Monte Carlo simulations indicates that, in that case, the total catalytic activity could include between 0 and 90% of activity due to chain processes. This large margin of error stems from the combined effects of a large decay rate, forcing the experimenter to use average conversion data, and of experimental error. Fitting of the model to previously published cracking data for 2-methylpentane on USHY showed that the model lacks a suitable parameter to account for thermal reactions which were not accounted for in the original data set. This observation supports the impression that the model is sensitive to departures from the postulated mechanism. The above kinetic model has also been fitted to the results of n-nonane cracking at three temperatures as well as to previously published data for various other linear paraffins. 32 refs., 17 figs., 6 tabs.

  12. 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.

  13. Fatigue Growth and Closure of Short Cracks

    DTIC Science & Technology

    1989-06-03

    stLdy has been carried out to investigate the growth and closure behavior of shortýýcracks in 2024-T351 aluminum alloy and four different conditions of...that short cracks show lessclosure behavior than longcracks. The estimates of initlal.crack lengths based on linearelastic data were made. tThese...anomalous behavior of short cracks. Advances in small crack growth have enabled increasingly quantitative studies that affect initi- ation and growth at

  14. Optical probe

    DOEpatents

    Hencken, Kenneth; Flower, William L.

    1999-01-01

    A compact optical probe is disclosed particularly useful for analysis of emissions in industrial environments. The instant invention provides a geometry for optically-based measurements that allows all optical components (source, detector, rely optics, etc.) to be located in proximity to one another. The geometry of the probe disclosed herein provides a means for making optical measurements in environments where it is difficult and/or expensive to gain access to the vicinity of a flow stream to be measured. Significantly, the lens geometry of the optical probe allows the analysis location within a flow stream being monitored to be moved while maintaining optical alignment of all components even when the optical probe is focused on a plurality of different analysis points within the flow stream.

  15. 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.

  16. 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

  17. The Role of Spraying Parameters and Inert Gas Shrouding in Hybrid Water-Argon Plasma Spraying of Tungsten and Copper for Nuclear Fusion Applications

    NASA Astrophysics Data System (ADS)

    Matějíček, J.; Kavka, T.; Bertolissi, G.; Ctibor, P.; Vilémová, M.; Mušálek, R.; Nevrlá, B.

    2013-06-01

    Tungsten-based coatings have potential application in the plasma-facing components in future nuclear fusion reactors. By the combination of refractory tungsten with highly thermal conducting copper, or steel as a construction material, functionally graded coatings can be easily obtained by plasma spraying, and may result in the development of a material with favorable properties. During plasma spraying of these materials in the open atmosphere, oxidation is an important issue, which could have adverse effects on their properties. Among the means to control it is the application of inert gas shrouding, which forms the subject of this study and represents a lower-cost alternative to vacuum or low-pressure plasma spraying, potentially applicable also for spraying of large surfaces or spacious components. It is a continuation of recent studies focused on the effects of various parameters of the hybrid water-argon torch on the in-flight behavior of copper and tungsten powders and the resultant coatings. In the current study, argon shrouding with various configurations of the shroud was applied. The effects of torch parameters, such as power and argon flow rate, and powder morphology were also investigated. Their influence on the particle in-flight behavior as well as the structure, composition and properties of the coatings were quantified. With the help of auxiliary calculations, the mass changes of the powder particles, associated with oxidation and evaporation, were assessed.

  18. Inhomogeneity of microstructure, mechanical properties, magnetism, and corrosion observed in a 12Cr18Ni10Ti fuel assembly shroud irradiated in BN-350 to 59 dpa

    NASA Astrophysics Data System (ADS)

    Maksimkin, O. P.; Tsay, K. V.; Garner, F. A.

    2015-12-01

    A hexagonal shroud containing a standard in-core fueled subassembly from the BN-350 reactor was examined after reaching 59 dpa maximum, followed by long-term storage underwater. Specimens were derived from both mid-face and rib-corner positions. It was shown that there were complex spatial variations in void swelling, mechanical properties, microhardness, radiation-induced magnetism as well as corrosion while underwater. The spatial variations arose from two major sources. The first source was variations in height associated with variations in dpa rate and irradiation temperature. The second source was shown to be spatial variations in starting microstructure arising primarily from a higher level of initial deformation and hardness in the rib-corners of the hexagonal shroud. With irradiation the differences in microhardness between the two regions disappeared, but void swelling in the rib areas was larger than at mid-face positions. The swelling enhancement at the corners is thought to arise primarily from the combined effect of temper annealing at a temperature known to remove carbon from the matrix before irradiation, and the influence of higher deformed microstructures to accelerate recrystallization, possibly with assistance from localized residual stresses. Swelling was relatively low at the bottom low-temperature end of the shroud, but increased on the upper end of the assembly, reflecting primarily a transition between a precipitation regime involving titanium carbide to one involving nickel-rich and silicon-rich G-phase.

  19. 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.

  20. Crack propagation driven by crystal growth

    SciTech Connect

    A. Royne; Paul Meaking; A. Malthe-Sorenssen; B. Jamtveit; D. K. Dysthe

    2011-10-01

    Crystals that grow in confinement may exert a force on their surroundings and thereby drive crack propagation in rocks and other materials. We describe a model of crystal growth in an idealized crack geometry in which the crystal growth and crack propagation are coupled through the stress in the surrounding bulk solid. Subcritical crack propagation takes place during a transient period, which may be very long, during which the crack velocity is limited by the kinetics of crack propagation. When the crack is sufficiently large, the crack velocity becomes limited by the kinetics of crystal growth. The duration of the subcritical regime is determined by two non-dimensional parameters, which relate the kinetics of crack propagation and crystal growth to the supersaturation of the fluid and the elastic properties of the surrounding material.

  1. 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.

  2. Review of Environmentally Assisted Cracking

    NASA Astrophysics Data System (ADS)

    Sadananda, K.; Vasudevan, A. K.

    2011-02-01

    Many efforts have been made in the past by several researchers to arrive at some unifying principles governing the embrittlement phenomena. An inescapable conclusion reached by all these efforts was that the behavior is very complex. Hence, recognizing the complexity of material/environment behavior, we focus our attention here only in extracting some similarities in the experimental trends to arrive at some generic principles of behavior. Crack nucleation and growth are examined under static load in the presence of internal and external environments. Stress concentration, either pre-existing or in-situ generated, appears to be a requirement for embrittlement. A chemical stress concentration factor is defined for a given material/environment system as the ratio of failure stress with and without the damaging chemical environment. All factors that affect the buildup of the required stress concentration, such as planarity of slip, stacking fault energy, etc., also affect the stress-corrosion behavior. The chemical stress concentration factor is coupled with the mechanical stress concentration factor. In addition, generic features for all systems appear to be (a) an existence of a threshold stress as a function of concentration of the damaging environment and flow properties of the material, and (b) an existence of a limiting threshold as a function of concentration, indicative of a damage saturation for that environment. Kinetics of crack growth also depends on concentration and the mode of crack growth. In general, environment appears to enhance crack tip ductility on one side by the reduction of energy for dislocation nucleation and glide, and to reduce cohesive energy for cleavage, on the other. These two opposing factors are coupled to provide environmentally induced crack nucleation and growth. The relative ratio of these two opposing factors depends on concentration and flow properties, thereby affecting limiting thresholds. The limiting concentration or

  3. 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.

  4. 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.

  5. 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.

  6. A finite-element-based perturbation model for the rotordynamic analysis of shrouded pump impellers: Part 2: User's guide

    NASA Technical Reports Server (NTRS)

    Baskharone, Erian A.

    1993-01-01

    This report describes the computational steps involved in executing a finite-element-based perturbation model for computing the rotor dynamic coefficients of a shrouded pump impeller or a simple seal. These arise from the fluid/rotor interaction in the clearance gap. In addition to the sample cases, the computational procedure also applies to a separate category of problems referred to as the 'seal-like' category. The problem, in this case, concerns a shrouded impeller, with the exception that the secondary, or leakage, passage is totally isolated from the primary-flow passage. The difference between this and the pump problem is that the former is analytically of the simple 'seal-like' configuration, with two (inlet and exit) flow-permeable stations, while the latter constitutes a double-entry / double-discharge flow problem. In all cases, the problem is that of a rotor clearance gap. The problem here is that of a rotor excitation in the form of a cylindrical whirl around the housing centerline for a smooth annular seal. In its centered operation mode, the rotor is assumed to give rise to an axisymmetric flow field in the clearance gap. As a result, problems involving longitudinal or helical grooves, in the rotor or housing surfaces, go beyond the code capabilities. Discarding, for the moment, the pre- and post-processing phases, the bulk of the computational procedure consists of two main steps. The first is aimed at producing the axisymmetric 'zeroth-order' flow solution in the given flow domain. Detailed description of this problem, including the flow-governing equations, turbulence closure, boundary conditions, and the finite-element formulation, was covered by Baskharone and Hensel. The second main step is where the perturbation model is implemented, with the input being the centered-rotor 'zeroth-order' flow solution and a prescribed whirl frequency ratio (whirl frequency divided by the impeller speed). The computational domain, in the latter case, is treated

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

    SciTech Connect

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

    1995-12-31

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

  8. Pollution Probe.

    ERIC Educational Resources Information Center

    Chant, Donald A.

    This book is written as a statement of concern about pollution by members of Pollution Probe, a citizens' anti-pollution group in Canada. Its purpose is to create public awareness and pressure for the eventual solution to pollution problems. The need for effective government policies to control the population explosion, conserve natural resources,…

  9. 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.

  10. 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.

  11. Interacting Cracks in an Environmentally Assisted Fracture

    NASA Astrophysics Data System (ADS)

    Levandovsky, Artem; Balazs, Anna

    2006-03-01

    We perform the study of environmentally assisted fracture within the framework of a lattice model. Formation of an ensemble of environmentally assisted microcracks, their coalescence and formation of crack ``avalanches'' lead to a very rich dynamical picture. Under specific condition crack healing can occur due to cohesive forces, which hold material together and tend to pull atoms together even if they are separated by a crack over several lattice units. We investigate the dynamical interplay between crack formation, arrest, healing and re-cracking. The goal here is to provide an understanding of the conditions leading to the phenomena of crack healing that happens along with the crack formation. We study the morphology of crack patterns with the intentions to establish a way to enhance the healing property of a material sample.

  12. Fracture mechanics parameters for small fatigue cracks

    NASA Technical Reports Server (NTRS)

    Newman, J. C., Jr.

    1992-01-01

    This paper presents a review of some common small-crack test specimens, the underlying causes of the small-crack effect, and the fracture-mechanics parameters that have been used to correlate or predict their growth behavior. This review concentrates on continuum mechanics concepts and on the nonlinear behavior of small cracks. The paper reviews some stress-intensity factor solutions for small-crack test specimens and develops some simple elastic-plastic J integral and cyclic J integral expressions that include the influence of crack-closure. These parameters were applied to small-crack growth data on two aluminum alloys, and a fatigue life prediction methodology is demonstrated. For these materials, the crack-closure transient from the plastic wake was found to be the major factor in causing the small-crack effect.

  13. 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.

  14. Methylecgonidine coats the crack particle.

    PubMed

    Wood, R W; Shojaie, J; Fang, C P; Graefe, J F

    1996-01-01

    Crack is a form of cocaine base self-administered by smoking. When heated, it volatilizes and may partially pyrolyze to methylecgonidine (MEG). Upon cooling, a condensation aerosol forms. Heating cocaine base in model crack pipes produced particles of about 1 micron in diameter, regardless of the amount heated; however, MEG concentration increased from < or = 2% at 10 mg per heating to as much as 5% at 30 mg per heating. Methylecgonidine was < or = 1% of the recovered material when cocaine was vaporized off a heated wire coil, but the particles were larger (2-5 microns), and the distribution disperse. The vapor pressure of MEG was higher [log P(mm Hg) = 9.994 - 3530/T] than cocaine base, consistent with MEG coating the droplet during condensation, and with evaporation during aging or dilution. Disappearance of MEG from a chamber filled with crack smoke was a two-component process, one proceeding at the rate of cocaine particle removal, and the other at the desorption rate from other surfaces. Particle diameter influences the deposition site in the respiratory tract; thus, the likely different patterns of deposition in the respiratory tract of humans and animals of crack aerosols produced by different techniques warrant consideration, as they may influence our understanding of immediate and delayed sequelae of the inhalation of cocaine and its pyrolysis product, MEG.

  15. 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…

  16. Confining crack propagation in defective graphene.

    PubMed

    López-Polín, Guillermo; Gómez-Herrero, Julio; Gómez-Navarro, Cristina

    2015-03-11

    Crack propagation in graphene is essential to understand mechanical failure in 2D materials. We report a systematic study of crack propagation in graphene as a function of defect content. Nanoindentations and subsequent images of graphene membranes with controlled induced defects show that while tears in pristine graphene span microns length, crack propagation is strongly reduced in the presence of defects. Accordingly, graphene oxide exhibits minor crack propagation. Our work suggests controlled defect creation as an approach to avoid catastrophic failure in graphene.

  17. A study of crack closure in fatigue

    NASA Technical Reports Server (NTRS)

    Shih, T. T.; Wei, R. P.

    1973-01-01

    Crack closure phenomenon in fatigue was studied by using a Ti-6Al-4V titanium alloy. The occurrence of crack closure was directly measured by an electrical-potential method, and indirectly by load-strain measurement. The experimental results showed that the onset of crack closure depends on both the stress ratio, and the maximum stress intensity factor. No crack closure was observed for stress ratio, greater than 0.3 in this alloy. A two-dimensional elastic model was used to explain the behavior of the recorded load-strain curves. Closure force was estimated by using this model. Yield level stress was found near the crack tip. Based on this estimated closure force, the crack opening displacement was calculated. This result showed that onset of crack closure detected by electrical-potential measurement and crack-opening-displacement measurement is the same. The implications of crack closure on fatigue crack are considered. The experimental results show that crack closure cannot fully account for the effect of stress ratio, on crack growth, and that it cannot be regarded as the sole cause for delay.

  18. 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

  19. Jumplike fatigue crack growth in compressor blades

    NASA Astrophysics Data System (ADS)

    Limar', L. V.; Demina, Yu. A.; Botvina, L. R.

    2014-04-01

    It is shown that power relations between the two main fractographic characteristics of fracture surfaces forming during jumplike fatigue crack growth, namely, the crack depth and the corresponding crack front length, can be used to estimate the fracture stress during vibration tests of the compressor blades of an aviation gas turbine engine, which are made of VT3-1 titanium alloy.

  20. Crack-opening displacements in center-crack, compact, and crack-line wedge-loaded specimens. [of flat plates

    NASA Technical Reports Server (NTRS)

    Newman, J. C., Jr.

    1976-01-01

    The theoretical crack-opening displacements for center-crack, compact, and crack-line wedge-loaded specimens (reported in the ASTM Proposed Recommended Practice for R-Curve Determination (1974)) disagree with experimental measurements in the literature. The disagreement is a result of using approximate specimen configurations and load representation to obtain the theoretical displacements. An improved method of boundary collocation is presented which was used to obtain the theoretical displacements in these three specimen types; the actual specimen configurations and more accurate load representation were used. In the analysis of crack-opening displacements in the compact and crack-line wedge-loaded specimens, the effects of the pin-loaded holes were also included. The theoretical calculations agree with the experimental measurements reported in the literature. Also examined are accurate polynomial expressions for crack-opening displacements in both compact and crack-line wedge-loaded specimens.

  1. 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.

  2. An Experimental Study of Penny-shaped Fluid-driven Cracks in an Elastic Matrix

    NASA Astrophysics Data System (ADS)

    Stone, Howard

    2015-11-01

    When a pressurized fluid is injected into an elastic matrix, the fluid generates a fracture that grows along a plane and forms a fluid-filled disc-like shape. For example, such problems occur in various natural and industrial applications involving the subsurface of Earth, such as hydraulic fracturing operations. We report a laboratory study of such a fluid-driven crack in a gelatin matrix, study the crack shape as a function of time, and investigate the influence of different experimental parameters such as the injection flow rate, Young's modulus of the matrix, and fluid viscosity. We find that the crack radius increases with time as a power law, which has been predicted both for the limit where viscous effects in the flow along the crack opening control the rate of crack propagation, as well as the limit where fracture toughness controls crack propagation. We vary experimental parameters to probe the physical limits and highlight that for our typical parameters both effects can be significant. Also, we measure the time evolution of crack shape, which has not been studied before. The rescaled crack shapes collapse at longer times, based on an appropriate scaling argument, and again we compare the scaling arguments in different physical limits. The gelatin system provides a useful laboratory model for further studies of fluid-driven cracks, some of which we will mention as they are inspired by the physics of hydraulic fracturing. This work is part of the PhD thesis of Ching-Yao Lai and is a collaboration with Drs. Zhong Zheng and Jason Wexler (Princeton University) and Professor Emilie Dressaire (NYU). Department of Mechanical and Aerospace Engineering.

  3. Response of a structural health monitoring fastener to fatigue crack growth and loads in metallic joints

    NASA Astrophysics Data System (ADS)

    Rakow, Alexi S.; Chang, Fu-Kuo

    2009-03-01

    Fatigue cracks initiating at fastener hole locations in metallic structure are among the most common form of airframe damage. Current methods for inspecting airframes for these cracks are manual, whereby inspectors rely on nondestructive inspection equipment or hand-held probes to scan over areas to be monitored. Use of this equipment often demands disassembly of the airframe to search appropriate hole locations for cracks, which elevates the complexity and cost of maintenance inspections. In this study an Additive, Interleaved, Multi-layer Electromagnetic (AIME) sensor was developed and integrated with the shank of a fastener to form a Structural Health Monitoring Fastener, a new technology targeted at insitu detection of fastener hole cracks. The major advantages of the Structural Health Monitoring (SHM) Fastener over other SHM technologies are its installation, which does not require joint layer disassembly, its capability to detect inner layer cracks in a multi-layer joint, and its capability to operate in a continuous monitoring mode. The AIME sensor design, SHM Fastener, and complete SHM system are presented along with experimental results from a series of single-layer and bolted double lap-joint aluminum specimens to validate the capability of these sensors to monitor metallic joints for fastener hole cracks and loads. Fatigue cracks were successfully tracked to over 0.7 inches from the fastener hole in these tests. Sensor output obtained from single-layer fatigue specimens was compared with analytical predictions for fatigue crack growth versus cycle number showing a good correlation in trend between sensor output and predicted crack size.

  4. Crack modeling of rotating blades with cracked hexahedral finite element method

    NASA Astrophysics Data System (ADS)

    Liu, Chao; Jiang, Dongxiang

    2014-06-01

    Dynamic analysis is the basis in investigating vibration features of cracked blades, where the features can be applied to monitor health state of blades, detect cracks in an early stage and prevent failures. This work presents a cracked hexahedral finite element method for dynamic analysis of cracked blades, with the purpose of addressing the contradiction between accuracy and efficiency in crack modeling of blades in rotor system. The cracked hexahedral element is first derived with strain energy release rate method, where correction of stress intensity factors of crack front and formulation of load distribution of crack surface are carried out to improve the modeling accuracy. To consider nonlinear characteristics of time-varying opening and closure effects caused by alternating loads, breathing function is proposed for the cracked hexahedral element. Second, finite element method with contact element is analyzed and used for comparison. Finally, validation of the cracked hexahedral element is carried out in terms of breathing effects of cracked blades and natural frequency in different crack depths. Good consistency is acquired between the results with developed cracked hexahedral element and contact element, while the computation time is significantly reduced in the previous one. Therefore, the developed cracked hexahedral element achieves good accuracy and high efficiency in crack modeling of rotating blades.

  5. Crack branching in carbon steel. Fracture mechanisms

    NASA Astrophysics Data System (ADS)

    Syromyatnikova, A. S.; Alekseev, A. A.; Levin, A. I.; Lyglaev, A. V.

    2010-04-01

    The fracture surfaces of pressure vessels made of carbon steel that form during crack branching propagation are examined by fractography. Crack branching is found to occur at a crack velocity higher than a certain critical value V > V c . In this case, the material volume that is involved in fracture and depends on the elastoplastic properties of the material and the sample width has no time to dissipate the energy released upon crack motion via the damage mechanisms intrinsic in the material under given deformation conditions (in our case, via cracking according to intragranular cleavage).

  6. Crack use in São Paulo.

    PubMed

    Nappo, S A; Galduróz, J C; Noto, A R

    1996-04-01

    Documented crack use emerged in São Paulo, Brazil, from 1991 onward. Therefore, it is a recent behavior among drug users. The present work draws a profile of São Paulo crack users, employing an ethnographic approach. Twenty-five crack users were interviewed on selected social and demographic characteristics, on the drug itself and its consumption, and on the consequences of this use. Crack cocaine is harmful for the user, leading within a short period to a condition of dependence. The crack users reported ultimately lapsing into "marginality" due to social isolation, neglect of bodily needs, and breakdown of family ties and other relationships.

  7. Compressibility effects on rotor forces in the leakage path between a shrouded pump impeller and its housing

    NASA Technical Reports Server (NTRS)

    Cao, Nhai The

    1993-01-01

    A modified approach to Childs' previous work on fluid-structure interaction forces in the leakage path between an impeller shroud and its housing is presented in this paper. Three governing equations consisting of continuity, path-momentum, and circumferential-momentum equations were developed to describe the leakage path inside a pump impeller. Radial displacement perturbations were used to solve for radial and circumferential force coefficients. In addition, impeller-discharge pressure disturbances were used to obtain pressure oscillation responses due to precessing impeller pressure wave pattern. Childs' model was modified from an incompressible model to a compressible barotropic-fluid model (the density of the working fluid is a function of the pressure and a constant temperature only). Results obtained from this model yielded interaction forces for radial and circumferential force coefficients. Radial and circumferential forces define reaction forces within the impeller leakage path. An acoustic model for the same leakage path was also developed. The convective, Coriolis, and centrifugal acceleration terms are removed from the compressible model to obtain the acoustics model. A solution due to impeller discharge pressure disturbances model was also developed for the compressible and acoustics models. The results from these modifications are used to determine what effects additional perturbation terms in the compressible model have on the acoustic model. The results show that the additional fluid mechanics terms in the compressible model cause resonances (peaks) in the force coefficient response curves. However, these peaks only occurred at high values of inlet circumferential velocity ratios greater than 0.7. The peak pressure oscillation was shown to occur at the wearing ring seal. Introduction of impeller discharge disturbances with n = 11 diametral nodes showed that maximum peak pressure oscillations occurred at nondimensional precession frequencies of f

  8. Compressibility effects on rotor forces in the leakage path between a shrouded pump impeller and its housing

    NASA Astrophysics Data System (ADS)

    Cao, Nhai The

    1993-12-01

    A modified approach to Childs' previous work on fluid-structure interaction forces in the leakage path between an impeller shroud and its housing is presented in this paper. Three governing equations consisting of continuity, path-momentum, and circumferential-momentum equations were developed to describe the leakage path inside a pump impeller. Radial displacement perturbations were used to solve for radial and circumferential force coefficients. In addition, impeller-discharge pressure disturbances were used to obtain pressure oscillation responses due to precessing impeller pressure wave pattern. Childs' model was modified from an incompressible model to a compressible barotropic-fluid model (the density of the working fluid is a function of the pressure and a constant temperature only). Results obtained from this model yielded interaction forces for radial and circumferential force coefficients. Radial and circumferential forces define reaction forces within the impeller leakage path. An acoustic model for the same leakage path was also developed. The convective, Coriolis, and centrifugal acceleration terms are removed from the compressible model to obtain the acoustics model. A solution due to impeller discharge pressure disturbances model was also developed for the compressible and acoustics models. The results from these modifications are used to determine what effects additional perturbation terms in the compressible model have on the acoustic model. The results show that the additional fluid mechanics terms in the compressible model cause resonances (peaks) in the force coefficient response curves. However, these peaks only occurred at high values of inlet circumferential velocity ratios greater than 0.7. The peak pressure oscillation was shown to occur at the wearing ring seal. Introduction of impeller discharge disturbances with n = 11 diametral nodes showed that maximum peak pressure oscillations occurred at nondimensional precession frequencies of f

  9. Simulation of Fluid Flow and Collection Efficiency for an SEA Multi-element Probe

    NASA Technical Reports Server (NTRS)

    Rigby, David L.; Struk, Peter M.; Bidwell, Colin

    2014-01-01

    Numerical simulations of fluid flow and collection efficiency for a Science Engineering Associates (SEA) multi-element probe are presented. Simulation of the flow field was produced using the Glenn-HT Navier-Stokes solver. Three dimensional unsteady results were produced and then time averaged for the collection efficiency results. Three grid densities were investigated to enable an assessment of grid dependence. Collection efficiencies were generated for three spherical particle sizes, 100, 20, and 5 micron in diameter, using the codes LEWICE3D and LEWICE2D. The free stream Mach number was 0.27, representing a velocity of approximately 86 ms. It was observed that a reduction in velocity of about 15-20 occurred as the flow entered the shroud of the probe.Collection efficiency results indicate a reduction in collection efficiency as particle size is reduced. The reduction with particle size is expected, however, the results tended to be lower than previous results generated for isolated two-dimensional elements. The deviation from the two-dimensional results is more pronounced for the smaller particles and is likely due to the effect of the protective shroud.

  10. Improved imaging algorithm for bridge crack detection

    NASA Astrophysics Data System (ADS)

    Lu, Jingxiao; Song, Pingli; Han, Kaihong

    2012-04-01

    This paper present an improved imaging algorithm for bridge crack detection, through optimizing the eight-direction Sobel edge detection operator, making the positioning of edge points more accurate than without the optimization, and effectively reducing the false edges information, so as to facilitate follow-up treatment. In calculating the crack geometry characteristics, we use the method of extracting skeleton on single crack length. In order to calculate crack area, we construct the template of area by making logical bitwise AND operation of the crack image. After experiment, the results show errors of the crack detection method and actual manual measurement are within an acceptable range, meet the needs of engineering applications. This algorithm is high-speed and effective for automated crack measurement, it can provide more valid data for proper planning and appropriate performance of the maintenance and rehabilitation processes of bridge.

  11. Rub tolerant shroud

    NASA Technical Reports Server (NTRS)

    Gay, Jr., Charles H. (Inventor); Lenahan, Dean T. (Inventor)

    1985-01-01

    A seal structure between first and second relatively moveable members for preventing gas flow in the space between the members and transverse to their general direction of motion is disclosed. The seal structure includes a plurality of substantially parallel strips within 30.degree. of normal to the radial plane generally containing these first and second relatively moveable members. The strips are thin and closely spaced and arranged so that one strip edge is attached to the first member and another edge is free to resiliently deflect when in rubbing contact with the second member.

  12. Energy Absorbing Protective Shroud

    NASA Technical Reports Server (NTRS)

    Schneider, William C. (Inventor)

    2001-01-01

    The present invention is a dissipating protection energy system designed to receive and safely dissipate the kinetic energy from high energy fragments. The energy dissipation system dissipates energy transferred to it by the incremental and progressive rupturing at an approximately constant force of strategically placed sacrificial stitching applied to a number of high strength straps, such as an aromatic polyimide fiber of extremely high tensile strength. Thus, the energy dissipation system provides a lightweight device for controlling and dissipating the dangerous and destructive energy stored in high strength fragments released by catastrophic failures of machinery minimizing damage to other critical components.

  13. Polygon/Cracked Sedimentary Rock

    NASA Technical Reports Server (NTRS)

    2004-01-01

    4 December 2004 Exposures of sedimentary rock are quite common on the surface of Mars. Less common, but found in many craters in the regions north and northwest of the giant basin, Hellas, are sedimentary rocks with distinct polygonal cracks in them. This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows an example from the floor of an unnamed crater near 21.0oS, 311.9oW. Such cracks might have formed by desiccation as an ancient lake dried up, or they might be related to ground ice freeze/thaw cycles or some other stresses placed on the original sediment or the rock after it became lithified. The 300 meter scale bar is about 328 yards long. The scene is illuminated by sunlight from the upper left.

  14. Biaxial Fatigue Cracking from Notch

    DTIC Science & Technology

    2013-03-04

    Leevers (reference 11) noticed that the variation in  from 0 to 2 has little effect on the da/dN in PVC ( polyvinyl - chloride ), but reduces the da/dN...under biaxial rotating and bending. Ahmad (reference 2) formulated a model for the biaxial fatigue crack growth in aggressive environment, outlined by...1962, Vol. 90, pp. 238-239. 20. ASM Handbook , Vol. 12 Fractography: 1992, p. 430, 438. 21. Metals Handbook , Vol. 9 Fractography and Atlas of

  15. Crack, sex work, and HIV.

    PubMed

    Leggett, T

    1999-01-01

    South Africa's long isolation, and perhaps deliberate efforts by the apartheid government, have led to an unusual pattern of drug abuse in the country. Drugs not commonly used in other countries, such as Mandrax and Welconol, are widespread in South Africa, while the street drugs commonly found in other countries, such as cocaine and heroin, have been relatively rare. However, this is changing, as international drug traffickers now import a broad range of drugs, including heroin and cocaine. Demand for these drugs has been established in South Africa, including among the urban lower classes. Immigration, especially of other Africans and particularly Nigerians, has accelerated the trend. While both mandrax and crack cocaine are smoked, the former is a sedative and the latter is a stimulant with pro-sexual effects. These sexual effects, together with very strong addictive potential, have led to very high HIV seroprevalence in user populations. Addiction often leads female users into prostitution, with prostitutes being a prime conduit for the spread of both the drug and HIV infection. Desperate to earn funds to meet their crack consumption needs, drug-addicted female prostitutes in South Africa service many clients and engage in practices shunned by their nonaddicted peers, such as unprotected and anal sex. There will be serious long-term effects of crack cocaine consumption, together with prostitution, upon all of South African society.

  16. The Origin of Griffith Cracks

    NASA Astrophysics Data System (ADS)

    Campbell, John

    2011-12-01

    As a result of the extremely strong interatomic bonds, pores and cracks are difficult to form in metals. They seem unlikely to be created intrinsically by the normal mechanisms involved in the formation of a solid by solidification from liquid, or condensation from vapor phases, or probably, by lattice mechanisms in the solid state. It is proposed here that initiation sites for pores and cracks for most failures of metals can only be initiated from unbonded interfaces. Such unbonded defects are introduced into metals only via extrinsic ( entrainment) mechanisms resulting from production processes, particularly melting and casting. Only entrained inclusions, particularly bifilms, have unbonded interfaces that can be opened to constitute Griffith cracks and can explain the initiation of macroscopic fracture and related microscopic processes, such as a decohesion between the second phases and a matrix. In the absence of entrained defects, metals would be predicted to fail in tension only either (1) at high stresses probably in excess of 20 GPa or (2) by ductile flow to the point of 100 pct reduction in area. Improved melting and casting processes giving freedom from entrained defects promise unprecedented performance and reliability of engineering metals.

  17. 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.

  18. 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.

  19. Predicting failure of specimens with either surface cracks or corner cracks at holes

    NASA Technical Reports Server (NTRS)

    Newman, J. C., Jr.

    1976-01-01

    A previously developed fracture criterion was applied to fracture data for surface-cracked specimens subjected to remote tensile loading and for specimens with a corner crack (or cracks) emanating from a circular hole subjected to either remote tensile loading or pin loading in the hole. The failure stresses calculated from this criterion were consistent with experimental failure stresses for both surface and corner cracks for a wide range of crack shapes and crack sizes in specimens of aluminum alloy, titanium alloy, and steel. Empirical equations for the elastic stress-intensity factors for a surface crack and for a corner crack (or cracks) emanating from a circular hole in a finite-thickness and finite-width specimen were also developed.

  20. Fatigue cracks in Eurofer 97 steel: Part II. Comparison of small and long fatigue crack growth

    NASA Astrophysics Data System (ADS)

    Kruml, T.; Hutař, P.; Náhlík, L.; Seitl, S.; Polák, J.

    2011-05-01

    The fatigue crack growth rate in the Eurofer 97 steel at room temperature was measured by two different methodologies. Small crack growth data were obtained using cylindrical specimens with a shallow notch and no artificial crack starters. The growth of semicircular cracks of length between 10-2000 μm was followed in symmetrical cycling with constant strain amplitude ( R ɛ = -1). Long crack data were measured using standard CT specimen and ASTM methodology, i.e. R = 0.1. The growth of cracks having the length in the range of 10-30 mm was measured. It is shown that the crack growth rates of both types of cracks are in a very good agreement if J-integral representation is used and usual assumptions of the crack closure effects are taken into account.

  1. Transmit-receive eddy current probes for defect detection and sizing in steam generator tubes

    SciTech Connect

    Obrutsky, L.S.; Cecco, V.S.; Sullivan, S.P.

    1997-02-01

    Inspection of steam generator tubes in aging Nuclear Generating Stations is increasingly important. Defect detection and sizing, especially in defect prone areas such as the tubesheet, support plates and U-bend regions, are required to assess the fitness-for-service of the steam generators. Information about defect morphology is required to address operational integrity issues, i.e., risk of tube rupture, number of tubes at risk, consequential leakage. A major challenge continues to be the detection and sizing of circumferential cracks. Utilities around the world have experienced this type of tube failure. Conventional in-service inspection, performed with eddy current bobbin probes, is ineffectual in detecting circumferential cracks in tubing. It has been demonstrated in CANDU steam generators, with deformation, magnetite and copper deposits that multi-channel probes with transmit-receive eddy current coils are superior to those using surface impedance coils. Transmit-receive probes have strong directional properties, permitting probe optimization according to crack orientation. They are less sensitive to lift-off noise and magnetite deposits and possess good discrimination to internal defects. A single pass C3 array transmit-receive probe developed by AECL can detect and size circumferential stress corrosion cracks as shallow as 40% through-wall. Since its first trial in 1992, it has been used routinely for steam generator in-service inspection of four CANDU plants, preventing unscheduled shutdowns due to leaking steam generator tubes. More recently, a need has surfaced for simultaneous detection of both circumferential and axial cracks. The C5 probe was designed to address this concern. It combines transmit-receive array probe technology for equal sensitivity to axial and circumferential cracks with a bobbin probe for historical reference. This paper will discuss the operating principles of transmit-receive probes, along with inspection results.

  2. Thermal Wave Imaging for Non-Destructive Evaluation of Subsurface Cracks in Opaque Materials

    NASA Astrophysics Data System (ADS)

    Grice, Kenneth Russell

    The technique of thermal wave imaging has been applied using two approaches to detect subsurface cracks in opaque materials. These two approaches are (1) the scanning photoacoustic microscopy (SPAM) and (2) the optical deflection of laser probes (MIRAGE). These two approaches have been examined and compared in terms of signal magnitude and phase both theoretically and experimentally. The effects of sample crack size, orientation and closure on the thermal wave signal has been considered and discussed. Cracks as small as 40 (mu)m in length have been detected. Also nearly vertical closed cracks have been detected using the MIRAGE technique. As a more difficult test of the thermal wave technique, we examined the feasibility of detecting a fatigue crack on the inner surface of a bolt hole. This experiment represents the first time that a crack on the interior wall of a bolt hole has been detected using thermal wave imaging. These results emphatically demonstrate the versatility of the SPAM approach when applied to complex geometries. Thermal wave imaging has been shown to have considerable potential for non-destructive evaluation (NDE) of solids for science and industry.

  3. Assessment of an Impulse GPR Antenna Abilities in Investigation of Transversal Cracks of the Bituminous Pavement

    NASA Astrophysics Data System (ADS)

    Krysiński, L.; Sudyka, J.

    2012-04-01

    Ground Penetrating Radar (GPR) technique is commonly used for detection of internal singularities of construction structure. The method is particularly efficient in the case of linear horizontal objects when profile scanning is being performed in the direction perpendicular to object elongation and polarization of the electric field is parallel to the elongation. Then the singular object manifests itself in the echogram as a scattering hyperbola. Similar response is generated by an object having shape close to a vertical half plane with horizontal edge, when the edge acts like the scattering linear object. The use of GPR technique for investigation of transversal cracks in the bituminous pavement would seem to be promising, but numerous paradoxes occur just at the beginning tests. Even well visible cracks of more than ten millimeters thickness doesn't generate noticeable GPR response, while thinner ones sometimes can produce strong response but in the deeper interior of the pavement. Thus arise a more general question: what the GPR technique can tell us about the cracks? Trying to study this problem some laboratory tests were performed to estimate efficiency of signal generation by structures simulating idealized cracks' shapes. Next long-term (several years) visual observation and repeated GPR scanning was performed on the three road sections (each one of several hundred meters length) with heavy traffic, where ongoing cracking process occurs. The preliminary measurements were directed to obtain the proper way of scanning. The main aim of the analysis was to find GPR characteristics of cracks that can be noticed on echograms. It was performed by detailed correlation of the visually observed cracks position with echograms using decimeter precision. These efforts provided a list of diagnostic GPR characteristics of cracks and some provisional scale of their intensity. In several cases the cracks were probed by drillings to recognize structures responsible for signal

  4. Failure Diagram for Chemically Assisted Crack Growth

    NASA Astrophysics Data System (ADS)

    Sadananda, K.; Vasudevan, A. K.

    2011-02-01

    A failure diagram that combines the thresholds for failure of a smooth specimen to that of a fracture mechanics specimen, similar to the modified Kitagawa diagram in fatigue, is presented. For a given material/environment system, the diagram defines conditions under which a crack initiated at the threshold stress in a smooth specimen becomes a propagating crack, by satisfying the threshold stress intensity of a long crack. In analogy with fatigue, it is shown that internal stresses or local stress concentrations are required to provide the necessary mechanical crack tip driving forces, on one hand, and reaction/transportation kinetics to provide the chemical potential gradients, on the other. Together, they help in the initiation and propagation of the cracks. The chemical driving forces can be expressed as equivalent mechanical stresses using the failure diagram. Both internal stresses and their gradients, in conjunction with the chemical driving forces, have to meet the minimum magnitude and the minimum gradients to sustain the growth of a microcrack formed. Otherwise, nonpropagating conditions will prevail or a crack formed will remain dormant. It is shown that the processes underlying the crack nucleation in a smooth specimen and the crack growth of a fracture mechanics specimen are essentially the same. Both require building up of internal stresses by local plasticity. The process involves intermittent crack tip blunting and microcrack nucleation until the crack becomes unstable under the applied stress.

  5. An Assessment of Remote Visual Methods to Detect Cracking in Reactor Components

    SciTech Connect

    Cumblidge, Stephen E.; Anderson, Michael T.; Doctor, Steven R.; Simonen, Fredric A.; Elliot, Anthony J.

    2008-01-01

    Recently, the U.S. nuclear industry has proposed replacing current volumetric and/or surface examinations of certain components in commercial nuclear power plants, as required by the American Society of Mechanical Engineers Boiler and Pressure Vessel Code Section XI, “Inservice Inspection of Nuclear Power Plant Components,” with a simpler visual testing (VT) method. The advantages of VT are that these tests generally involve much less radiation exposure and time to perform the examination than do volumetric examinations such as ultrasonic testing. The issues relative to the reliability of VT in determining the structural integrity of reactor components were examined. Some piping and pressure vessel components in a nuclear power station are examined using VT as they are either in high radiation fields or component geometry precludes the use of ultrasonic testing (UT) methodology. Remote VT with radiation-hardened video systems has been used by nuclear utilities to find cracks in pressure vessel cladding in pressurized water reactors, core shrouds in boiling water reactors, and to investigate leaks in piping and reactor components. These visual tests are performed using a wide variety of procedures and equipment. The techniques for remote VT use submersible closed-circuit video cameras to examine reactor components and welds. PNNL conducted a parametric study that examined the important variables influencing the effectiveness of a remote visual test. Tested variables included lighting techniques, camera resolution, camera movement, and magnification. PNNL also conducted a limited laboratory test using a commercial visual testing camera system to experimentally determine the ability of the camera system to detect cracks of various widths under ideal conditions. The results of these studies and their implications are presented in this paper.

  6. Modelling and measurement of crack closure and crack growth following overloads and underloads

    NASA Technical Reports Server (NTRS)

    Dexter, R. J.; Hudak, S. J.; Davidson, D. L.

    1989-01-01

    Ignoring crack growth retardation following overloads can result in overly conservative life predictions in structures subjected to variable amplitude fatigue loading. Crack closure is believed to contribute to the crack growth retardation, although the specific closure mechanism is dabatable. The delay period and corresponding crack growth rate transients following overload and overload/underload cycles were systematically measured as a function of load ratio and overload magnitude. These responses are correlated in terms of the local 'driving force' for crack growth, i.e. the effective stress intensity factor range. Experimental results are compared with the predictions of a Dugdale-type (1960) crack closure model, and improvements in the model are suggested.

  7. Crack Turning in Integrally Stiffened Aircraft Structures

    NASA Technical Reports Server (NTRS)

    Pettit, Richard Glen

    2000-01-01

    Current emphasis in the aircraft industry toward reducing manufacturing cost has created a renewed interest in integrally stiffened structures. Crack turning has been identified as an approach to improve the damage tolerance and fail-safety of this class of structures. A desired behavior is for skin cracks to turn before reaching a stiffener, instead of growing straight through. A crack in a pressurized fuselage encounters high T-stress as it nears the stiffener--a condition favorable to crack turning. Also, the tear resistance of aluminum alloys typically varies with crack orientation, a form of anisotropy that can influence the crack path. The present work addresses these issues with a study of crack turning in two-dimensions, including the effects of both T-stress and fracture anisotropy. Both effects are shown to have relation to the process zone size, an interaction that is central to this study. Following an introduction to the problem, the T-stress effect is studied for a slightly curved semi-infinite crack with a cohesive process zone, yielding a closed form expression for the future crack path in an infinite medium. For a given initial crack tip curvature and tensile T-stress, the crack path instability is found to increase with process zone size. Fracture orthotropy is treated using a simple function to interpolate between the two principal fracture resistance values in two-dimensions. An extension to three-dimensions interpolates between the six principal values of fracture resistance. Also discussed is the transition between mode I and mode II fracture in metals. For isotropic materials, there is evidence that the crack seeks out a direction of either local symmetry (pure mode I) or local asymmetry (pure mode II) growth. For orthotropic materials the favored states are not pure modal, and have mode mixity that is a function of crack orientation.

  8. Revised FORTRAN program for calculating velocities and streamlines on the hub-shroud midchannel stream surface of an axial-, radial-, or mixed-flow turbomachine or annular duct. 2: Programmer's manual

    NASA Technical Reports Server (NTRS)

    Katsanis, T.; Mcnally, W. D.

    1977-01-01

    A FORTRAN IV computer program has been developed that obtains a detailed subsonic or shock free transonic flow solution on the hub-shroud midchannel stream surface of a turbomachine. The blade row may be fixed or rotating, and the blades may be twisted and leaned. Flow may be axial, mixed, or radial. Upstream and downstream flow variables may vary from hub to shroud, and provisions are made to correct for loss of stagnation pressure. The results include velocities, streamlines, and flow angles on the stream surface and approximate blade surface velocities.

  9. Crack Closure Characteristics Considering Center Cracked and Compact Tension Specimens.

    DTIC Science & Technology

    1984-12-01

    adjacent elements differed in size by no more than a factor of 2. The fine mesh elements near the crack tip were much smaller than the -7 2CTS with an area...N .1- £KO.~.-N 0 0 td t + U.Us* 0 C.+ *4 w O mcow K O4 ’ 4u 0. X Ulf! W I 2 0 Z K0 NO- N Cos.@-0S W.N a-1 WW m .M0 000004.*0 00 4-W-M. R800*x -3-o" 0

  10. Detection of Real Flaw using Uniform Eddy Current Multi-probe

    NASA Astrophysics Data System (ADS)

    Fukuoka, Katsuhiro; Hashimoto, Mitsuo

    The establishment of the nondestructive inspection technology with plant structures has been stimulated by the recent occurrence of cracks in the nuclear power plant structures. In this research, a uniform eddy current multi-probe to apply to the complex structure and inspect the cracks at high-speed data acquisition was developed. Pick-up coils of the developed probe were arranged on a flexible printed circuit board. This probe was able to obtain clear signal for an EDM (electro-discharge machining) slit with 0.5 mm depth and distinguish EDM slits arranged at 2 mm intervals. It was confirmed that the SCC (stress corrosion cracking) of real flaw was able to be detected with developed uniform eddy current multi-probe by using the ferrite core for the exciting coil and considering the impedance matching of the exciting coil and the flaw detection device.

  11. Characterization of the roles of electrochemistry, convection and crack chemistry in stress corrosion cracking

    SciTech Connect

    Andresen, P.L.; Young, L.M.

    1995-12-31

    Understanding the role of ionic current flow within a crack and near the crack tip is fundamental to modeling of environmentally assisted crack advance. Critical conceptual issues and models related to ionic current flow within cracks, and the associated ``crevice`` chemistry and metal oxidation that results, are presented and examined in the light of experimental evidence. Various advanced techniques have been developed to evaluate the roles of electrochemistry, transport, and crack chemistry in stress corrosion cracking, with emphasis on high temperature ``pure`` water. These include high resolution crack length measurement by dc potential drop performed simultaneously with microsampling, electrochemical microprobe mapping, microinjection of species, and micropolarization of the crack. Conceptual issues addressed include the importance of the corrosion potential vs. oxidant concentration, the absence of oxidants and associated low corrosion potential within cracks, the location and role of macrocell currents associated with potential gradients from differential aeration cells, the localized nature of the microcell currents associated with dissolution at the crack tip, the importance of pH and adsorbed species on repassivation and crack advance, and the role of convection in crack chemistry and crack advance. Correct concepts are shown to be an essential pre-cursor to quantitative modeling.

  12. A probabilistic model of brittle crack formation

    NASA Technical Reports Server (NTRS)

    Chudnovsky, A.; Kunin, B.

    1987-01-01

    Probability of a brittle crack formation in an elastic solid with fluctuating strength is considered. A set Omega of all possible crack trajectories reflecting the fluctuation of the strength field is introduced. The probability P(X) that crack penetration depth exceeds X is expressed as a functional integral over Omega of a conditional probability of the same event taking place along a particular path. Various techniques are considered to evaluate the integral. Under rather nonrestrictive assumptions, the integral is reduced to solving a diffusion-type equation. A new characteristic of fracture process, 'crack diffusion coefficient', is introduced. An illustrative example is then considered where the integration is reduced to solving an ordinary differential equation. The effect of the crack diffusion coefficient and of the magnitude of strength fluctuations on probability density of crack penetration depth is presented. Practical implications of the proposed model are discussed.

  13. Crack Propagation in Bamboo's Hierarchical Cellular Structure

    PubMed Central

    Habibi, Meisam K.; Lu, Yang

    2014-01-01

    Bamboo, as a natural hierarchical cellular material, exhibits remarkable mechanical properties including excellent flexibility and fracture toughness. As far as bamboo as a functionally graded bio-composite is concerned, the interactions of different constituents (bamboo fibers; parenchyma cells; and vessels.) alongside their corresponding interfacial areas with a developed crack should be of high significance. Here, by using multi-scale mechanical characterizations coupled with advanced environmental electron microscopy (ESEM), we unambiguously show that fibers' interfacial areas along with parenchyma cells' boundaries were preferred routes for crack growth in both radial and longitudinal directions. Irrespective of the honeycomb structure of fibers along with cellular configuration of parenchyma ground, the hollow vessels within bamboo culm affected the crack propagation too, by crack deflection or crack-tip energy dissipation. It is expected that the tortuous crack propagation mode exhibited in the present study could be applicable to other cellular natural materials as well. PMID:24998298

  14. Crack propagation in bamboo's hierarchical cellular structure.

    PubMed

    Habibi, Meisam K; Lu, Yang

    2014-07-07

    Bamboo, as a natural hierarchical cellular material, exhibits remarkable mechanical properties including excellent flexibility and fracture toughness. As far as bamboo as a functionally graded bio-composite is concerned, the interactions of different constituents (bamboo fibers; parenchyma cells; and vessels.) alongside their corresponding interfacial areas with a developed crack should be of high significance. Here, by using multi-scale mechanical characterizations coupled with advanced environmental electron microscopy (ESEM), we unambiguously show that fibers' interfacial areas along with parenchyma cells' boundaries were preferred routes for crack growth in both radial and longitudinal directions. Irrespective of the honeycomb structure of fibers along with cellular configuration of parenchyma ground, the hollow vessels within bamboo culm affected the crack propagation too, by crack deflection or crack-tip energy dissipation. It is expected that the tortuous crack propagation mode exhibited in the present study could be applicable to other cellular natural materials as well.

  15. Drug user settings: a crack house typology.

    PubMed

    Geter, R S

    1994-06-01

    Both lay persons and members of the scientific community have come to view the inner-city crack house as a facility where drug dealers and crack addicts sell, buy, and use crack cocaine. It is suggested in this article that the term "crack house" be unbundled into four more meaningful terms based on the physical conditions of the house, its functionality, and the social relationships that it supports. Two typologies are proposed. The first separates drug houses into four general categories: (1) Crack House, (2) Cop House, (3) Drug House III, and (4) Drug House IV. The second typology categorizes the Crack House into four types: (A) the Party House, (B) the Hit House, (C) the Smoke House, and (D) the Bandominium. Each of these types is explored in detail.

  16. Prediction of thermal cycling induced matrix cracking

    NASA Technical Reports Server (NTRS)

    Mcmanus, Hugh L.

    1992-01-01

    Thermal fatigue has been observed to cause matrix cracking in laminated composite materials. A method is presented to predict transverse matrix cracks in composite laminates subjected to cyclic thermal load. Shear lag stress approximations and a simple energy-based fracture criteria are used to predict crack densities as a function of temperature. Prediction of crack densities as a function of thermal cycling is accomplished by assuming that fatigue degrades the material's inherent resistance to cracking. The method is implemented as a computer program. A simple experiment provides data on progressive cracking of a laminate with decreasing temperature. Existing data on thermal fatigue is also used. Correlations of the analytical predictions to the data are very good. A parametric study using the analytical method is presented which provides insight into material behavior under cyclical thermal loads.

  17. Online bridge crack monitoring with smart film.

    PubMed

    Zhang, Benniu; Wang, Shuliang; Li, Xingxing; Zhou, Zhixiang; Zhang, Xu; Yang, Guang; Qiu, Minfeng

    2013-01-01

    Smart film crack monitoring method, which can be used for detecting initiation, length, width, shape, location, and propagation of cracks on real bridges, is proposed. Firstly, the fabrication of the smart film is developed. Then the feasibility of the method is analyzed and verified by the mechanical sensing character of the smart film under the two conditions of normal strain and crack initiation. Meanwhile, the coupling interference between parallel enameled wires of the smart film is discussed, and then low-frequency detecting signal and the custom communication protocol are used to decrease interference. On this basis, crack monitoring system with smart film is designed, where the collected crack data is sent to the remote monitoring center and the cracks are simulated and recurred. Finally, the monitoring system is applied to six bridges, and the effects are discussed.

  18. Online Bridge Crack Monitoring with Smart Film

    PubMed Central

    Wang, Shuliang; Li, Xingxing; Zhou, Zhixiang; Zhang, Xu; Yang, Guang; Qiu, Minfeng

    2013-01-01

    Smart film crack monitoring method, which can be used for detecting initiation, length, width, shape, location, and propagation of cracks on real bridges, is proposed. Firstly, the fabrication of the smart film is developed. Then the feasibility of the method is analyzed and verified by the mechanical sensing character of the smart film under the two conditions of normal strain and crack initiation. Meanwhile, the coupling interference between parallel enameled wires of the smart film is discussed, and then low-frequency detecting signal and the custom communication protocol are used to decrease interference. On this basis, crack monitoring system with smart film is designed, where the collected crack data is sent to the remote monitoring center and the cracks are simulated and recurred. Finally, the monitoring system is applied to six bridges, and the effects are discussed. PMID:24489496

  19. Measuring Crack Length in Coarse Grain Ceramics

    NASA Technical Reports Server (NTRS)

    Salem, Jonathan A.; Ghosn, Louis J.

    2010-01-01

    Due to a coarse grain structure, crack lengths in precracked spinel specimens could not be measured optically, so the crack lengths and fracture toughness were estimated by strain gage measurements. An expression was developed via finite element analysis to correlate the measured strain with crack length in four-point flexure. The fracture toughness estimated by the strain gaged samples and another standardized method were in agreement.

  20. Crack Path Prediction Near an Elliptical Inhomogeneity

    DTIC Science & Technology

    1991-09-01

    Prediction Near an Elliptical Inhomogeneity 1L162618AH80 6. AUTHOR(S) Edward M. Patton 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8 . PERFORMING...oriented crack. Erdogan and Gupta [ 8 ] later solved the problem in which the crack crosses the interface. These solutions are based on the Green’s...the crack propagation direction 8 is greatest. This criterion implies that the stress parallel to that direction would be a minimum, or that the

  1. Application of Piezocomposite Twin, Side by Side, Phased Array UT Probes for the Inspection of Stainless Steel

    SciTech Connect

    Delaide, M.; Dumas, Ph

    2005-04-09

    UT probes to be used for the examination of coarse-grain structure must allow to detect and size cracks, with a high reliability level. The combination of TRL probes, with phased array and piezocomposite technologies allows to improve probes performances and inspection speed. Single element crystals are replaced by matrix arrays, allowing to deflect and skew the beams, to change the inspection depth. This paper describes the designing, the manufacturing and the characterisation of several probes.

  2. Thermomechanical Manipulation of Crack-Tip Stress Field for Resistance to Stress Corrosion Crack Propagation

    NASA Astrophysics Data System (ADS)

    Singh Raman, R. K.; Ibrahim, R. N.; Wu, F.; Rihan, R.

    2008-12-01

    Corrosion-assisted propagation of an existing crack is profoundly influenced by the stress intensity at the crack tip. This article presents the first results of thermomechanical conditioning (TMC) for local manipulation of material at and ahead of the crack tip, in an attempt to retard/stop crack propagation. Prenotched round tensile specimens of mild steel were subjected to rotating bending to generate a fatigue precrack, and then to apply localized thermomechanical conditioning. The threshold stress intensity factor ( K ISCC ) for stress corrosion cracking (SCC) of precracked specimens with and without TMC was determined in a caustic environment. Results suggest that TMC can increase K ISCC . Finite element analysis of the specimens suggests development of compressive stresses at and around the crack tip, which is expected to improve the resistance to stress corrosion crack propagation (since stress corrosion cracks can propagate only under tensile loading).

  3. Catalytic cracking of heavy oils

    SciTech Connect

    Otterstedt, J.E.; Gevert, B.; Sterte, J. )

    1987-08-01

    Of the many factors which influence product yields in a fluid catalytic cracker, the feed stock quality and the catalyst composition are of particular interest as they can be controlled only to a limited extent by the refiner. In the past decade there has been a trend towards using heavier feedstocks in the FCC-unit, which is expected to continue in the foreseeable future. It is therefore important to study how molecular types, characteristic not only of heavy petroleum oil but also of e.g. coal liquid, shale oil and biomass oil, respond to cracking over catalysts of different compositions.

  4. Fatigue Crack Closure - A Review

    DTIC Science & Technology

    1990-09-01

    gauge along the crack line. They used CCT speci- mens of high tensile strength steel ( HY80 ). The measured value of U was found to be a minimum at the...ultrasonic surface wave technique on 12.5mm thick specimens of 2024-T851, 2024-T351, Al 2219, Ti-6AI-4V and 17-4 PH steel . Most of the results were...medium and high strength steels . Exami- nation of the fracture surfaces suggested that raising the mean stress in low fracture toughness steels could

  5. Crack Healing in Quartz: Influence of Crack Morphology and pOH-

    NASA Astrophysics Data System (ADS)

    Fallon, J. A.; Kronenberg, A. K.; Popp, R. K.; Lamb, W. M.

    2004-12-01

    Crack healing in quartz has been investigated by optical microscopy and interferometry of rhombohedral r-cleavage cracks in polished Brazilian quartz prisms that were hydrothermally annealed. Quartz prisms were pre-cracked at room temperature and then annealed at temperatures T of 250° and 400° C for 2.4 to 240 hours, fluid pressure Pf = 41 MPa (equal to confining pressure Pc), and varying pOH- (from 5.4 to 1.2 at 250° C for fluids consisting of distilled water and NaOH solutions). Crack morphologies before and after annealing were recorded for each sample in plane light digital images and apertures were determined from interference fringes recorded using transmitted monochromatic light (λ = 598 nm). As documented in previous studies (Smith and Evans, 1984; Brantley et al., 1990; Beeler and Hickman, 1996), crack healing of quartz is driven by reductions in surface energy and healing rates appear to be limited by diffusional solute transport; sharply defined crack tips become blunted and break up into fluid-filled tubes and inclusions. However, fluid inclusion geometries are also observed with nonequilibrium shapes that depend on initial surface roughness. Crack healing is significant at 400° C after short run durations (24 hr) with healing rates reaching 10-5 mm/s. Crack healing is also observed at T=250° C, but only for smooth cracks with apertures < 0.6 μ m or for cracks subject to low pOH-. The extent of crack healing is sensitive to crack aperture and to hackles formed by fine-scale crack branching during crack growth. Initial crack apertures appear to be governed by the presence of fine particles, often found in the vicinity of hackles, which maintain the separation of crack surfaces. Where rough cracks exhibit healing, hackles are sites of either enhanced or reduced loss of fluid-solid interface depending on slight mismatches and sense of twist of opposing crack surfaces. Hackles of open r-cleavage cracks are replaced either by (1) healed curvilinear

  6. Competition between fatigue crack propagation and wear

    SciTech Connect

    Fan, H.; Keer, L.M.; Cheng, W.; Cheng, H.S. )

    1993-01-01

    Based on a semi-empirical derivation of the Paris fatigue law, the fatigue crack length a is related to the yield limit or flow stress, which ultimately is related to the hardness of the material. The analysis considers together the cyclic loading, which tends to increase the surface crack length, and the wear, which tends to decrease the crack length at the surface, and shows that under certain conditions a stable crack length may be developed. Experiments conducted on two test groups (Rc = 58.5 and Rc = 62.7) tend to support the present analysis. 10 refs.

  7. Combustion in cracks of PBX 9501

    SciTech Connect

    Berghout, H. L.; Son, S. F.; Bolme, C. A.; Hill, L. G.; Asay, B. W.; Dickson, P. M.; Henson, B. F.; Smilowitz, L. B.

    2002-01-01

    Recent experiments involving the combustion of PBX 9501 explosive under confined conditions reveal the importance of crack and flaws in reaction violence. Experiments on room temperature confined disks of pristine and thermally damaged PBX 9501 reveal that crack ignition depends on hot gases entering existing or pressure induced cracks rather than on energy release at the crack tip. PBX 9501 slot combustion experiments show that the reaction propagation rate in the slot does not depend on the external pressure. We have observed 1500 d s in long slots of highly-confined PBX 9501. We present experiments that examine the combustion of mechanically and thermally damaged samples of PBX 9501.

  8. Investigations of Low Temperature Time Dependent Cracking

    SciTech Connect

    Van der Sluys, W A; Robitz, E S; Young, B A; Bloom, J

    2002-09-30

    The objective of this project was to investigate metallurgical and mechanical phenomena associated with time dependent cracking of cold bent carbon steel piping at temperatures between 327 C and 360 C. Boiler piping failures have demonstrated that understanding the fundamental metallurgical and mechanical parameters controlling these failures is insufficient to eliminate it from the field. The results of the project consisted of the development of a testing methodology to reproduce low temperature time dependent cracking in laboratory specimens. This methodology was used to evaluate the cracking resistance of candidate heats in order to identify the factors that enhance cracking sensitivity. The resultant data was integrated into current available life prediction tools.

  9. [Desiccation cracking of soil body: a review].

    PubMed

    Pei, Yin-Ge; Xu, Ze-Min; Zhang, Jia-Ming

    2012-04-01

    Desiccation cracking of soil body is a complex physical process, which can affect the strength, stability, and permeability of soil body, and involve in several disciplines such as soil science, agricultural science, engineering geology, and environmental science. This paper introduced the significances of the study on the desiccation cracking of soil body, reviewed the related theoretical and applied researches and the quantitative analysis of crack morphology, and discussed the deficiencies in the research fields, research contents, and research methods. The future research directions about the desiccation cracking of soil body were pointed out.

  10. 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.

  11. On cracking of charged anisotropic polytropes

    NASA Astrophysics Data System (ADS)

    Azam, M.; Mardan, S. A.

    2017-01-01

    Recently in [1], the role of electromagnetic field on the cracking of spherical polytropes has been investigated without perturbing charge parameter explicitly. In this study, we have examined the occurrence of cracking of anisotropic spherical polytropes through perturbing parameters like anisotropic pressure, energy density and charge. We consider two different types of polytropes in this study. We discuss the occurrence of cracking in two different ways (i) by perturbing polytropic constant, anisotropy and charge parameter (ii) by perturbing polytropic index, anisotropy and charge parameter for each case. We conclude that cracking appears for a wide range of parameters in both cases. Also, our results are reduced to [2] in the absence of charge.

  12. Controlled crack growth specimen for brittle systems

    NASA Technical Reports Server (NTRS)

    Calomino, Anthony M.; Brewer, David N.

    1992-01-01

    A pure Mode 1 fracture specimen and test procedure has been developed which provides extended, stable, through-thickness crack growth in ceramics and other brittle, nonmetallic materials. Fixed displacement loading, applied at the crack mouth, promotes stable crack extension by reducing the stored elastic strain energy. Extremely fine control of applied displacements is achieved by utilizing the Poisson's expansion of a compressively loaded cylindrical pin. Stable cracks were successfully grown in soda-lime glass and monolithic Al2O3 for lengths in excess of 2O mm without uncontrollable catastrophic failure.

  13. Cracks in Sheets Draped on Curved Surfaces

    NASA Astrophysics Data System (ADS)

    Mitchell, Noah P.; Koning, Vinzenz; Vitelli, Vincenzo; Irvine, William T. M.

    Conforming materials to surfaces with Gaussian curvature has proven a versatile tool to guide the behavior of mechanical defects such as folds, blisters, scars, and pleats. In this talk, we show how curvature can likewise be used to control material failure. In our experiments, thin elastic sheets are confined on curved geometries that stimulate or suppress the growth of cracks, and steer or arrest their propagation. By redistributing stresses in a sheet, curvature provides a geometric tool for protecting certain regions and guiding crack patterns. A simple model captures crack behavior at the onset of propagation, while a 2D phase-field model successfully captures the crack's full phenomenology.

  14. Controlled crack growth specimen for brittle systems

    NASA Technical Reports Server (NTRS)

    Calomino, Anthony M.; Brewer, David N.

    1990-01-01

    A pure Mode 1 fracture specimen and test procedure has been developed which provides extended, stable, through-thickness crack growth in ceramics and other brittle, nonmetallic materials. Fixed displacement loading, applied at the crack mouth, promotes stable crack extension by reducing the stored elastic strain energy. Extremely fine control of applied displacements is achieved by utilizing the Poisson's expansion of a compressively loaded cylindrical pin. Stable cracks were successfully grown in soda-lime glass and monolithic Al2O3 for lengths in excess of 20 mm without uncontrollable catastrophic failure.

  15. Fracture Mechanics of Crack Growth During Sonic-IR Inspection

    NASA Astrophysics Data System (ADS)

    Chen, J. C.; Riddell, W. T.; Lick, Kyle; Wong, Chang-Hwa

    2007-03-01

    In past studies, we showed that cracks synthesized under carefully controlled conditions will propagate when subjected to sonic IR testing. The extent or severity of the propagation observed depended on several parameters including the stress intensity factor (which corresponds to crack growth rate) under which the crack was synthesized, the tightness of the crack closure, and the initial crack length. Furthermore, we showed that crack propagation during sonic IR testing occurs for 2024 aluminum, titanium and 304 stainless steel specimens. In this study, we extend the range of experimental conditions for synthesizing cracks to further elucidate their effect on the crack propagation, and we focus more specifically on the stress intensity factor. The stress intensity factor not only determines the rate of crack growth, but it has two profound effects on crack characteristics: the establishment of plastic zones around the crack tip and the variation of the topography of the mating crack surfaces. These two factors strongly affect crack propagation.

  16. Fatigue Crack Closure Analysis Using Digital Image Correlation

    NASA Technical Reports Server (NTRS)

    Leser, William P.; Newman, John A.; Johnston, William M.

    2010-01-01

    Fatigue crack closure during crack growth testing is analyzed in order to evaluate the critieria of ASTM Standard E647 for measurement of fatigue crack growth rates. Of specific concern is remote closure, which occurs away from the crack tip and is a product of the load history during crack-driving-force-reduction fatigue crack growth testing. Crack closure behavior is characterized using relative displacements determined from a series of high-magnification digital images acquired as the crack is loaded. Changes in the relative displacements of features on opposite sides of the crack are used to generate crack closure data as a function of crack wake position. For the results presented in this paper, remote closure did not affect fatigue crack growth rate measurements when ASTM Standard E647 was strictly followed and only became a problem when testing parameters (e.g., load shed rate, initial crack driving force, etc.) greatly exceeded the guidelines of the accepted standard.

  17. Liquid metal embrittlement. [crack propagation in metals with liquid metal in crack space

    NASA Technical Reports Server (NTRS)

    Tiller, W. A.

    1973-01-01

    Crack propagation is discussed for metals with liquid metal in the crack space. The change in electrochemical potential of an electron in a metal due to changes in stress level along the crack surface was investigated along with the change in local chemistry, and interfacial energy due to atomic redistribution in the liquid. Coupled elastic-elastrostatic equations, stress effects on electron energy states, and crack propagation via surface roughening are discussed.

  18. Determining fatigue crack opening loads from near-crack-tip displacement measurements

    SciTech Connect

    Riddell, W.T.; Piascik, R.S.; Sutton, M.A.; Zhao, W.; McNeill, S.R.; Helm, J.D.

    1999-07-01

    The aim of this research was to develop a near-crack-tip measurement method that quantifies crack closure levels in the near-threshold fatigue crack growth regime--a regime where crack closure is not well characterized by remote compliance methods. Further understanding of crack closure mechanics was gained by performing novel crack growth experiments in conjunction with numerical simulations of three-dimensional crack-front propagation. Steady-state (i.e., constant growth rate) fatigue crack growth rates were characterized by performing constant cyclic stress intensity range ({Delta}K) experiments over a wide range of stress ratios (R). Near-crack-tip (less than 0.3 mm behind) load-versus-displacement measurements were conducted on the specimen surface using a novel noncontact experimental technique (Digital Imaging Displacement System--DIDS). The experiments and simulations revealed that the three-dimensional aspects of fatigue crack closure must be considered to determine correct opening load levels from near-crack-tip load-versus-displacement data. It was shown that near-crack-front, but increase near the free surface. The interior opening load was found to collapse closure-affected data to intrinsic rates, and thus shown to relate to the true crack-front driving force parameter. Surface opening load DIDS measurements made at an optimal distance behind the crack tip were used to correlate da/dN with {Delta}K{sub eff}. Opening load determinations made less than the optimal distance behind the crack tip were shown to be too high to correlate fatigue crack growth rates.

  19. Effect of Crack Closure on Ultrasonic Detection of Fatigue Cracks at Fastener Holes

    NASA Astrophysics Data System (ADS)

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

    2009-03-01

    The ultrasonic response from closed fatigue cracks grown in aluminium alloy specimens using a representative aircraft spectrum loading has been characterised as a function of tensile applied load using pulse-echo 45° shear-wave ultrasonic C-scans with focused immersion transducers. Observed trends with crack size and applied load are described and compared to results for artificial machined defects. The results demonstrate that crack closure significantly reduces the ultrasonic response compared to open cracks or machined defects.

  20. Analysis of the interaction of two parallel surface cracks

    NASA Astrophysics Data System (ADS)

    Hahn, Jeeyeon

    The objective of this research is to analyze and predict the interaction of surface cracks that occur in parallel planes. Multiple cracks may form in aging aircraft that forms at stress concentrations such as fastener holes and notched components by stress corrosion and fatigue cracking. The lifetime of the structures are significantly affected by the interaction between these cracks. Depending on relative positions and orientations of neighboring cracks, local stress fields and crack driving forces can be affected by the presence of adjacent cracks. Even small subcritical cracks may rapidly grow to a size that will cause failure in service due to interaction and coalescence with other cracks. The interaction behavior and crack propagation direction of two parallel surface cracks is studied using three-dimensional finite element analysis (FEA). FEA models with wide range of crack configurations in a finite plate under tension are evaluated to investigate the correlation between the crack shapes and the separation distance between two cracks. The relative distance (vertical and horizontal) between two cracks and size and shape of these cracks are varied to create different stress interaction fields. Stress intensity factors (SIF) along the crack fronts are obtained from FEA, and then, cracking behaviors of the cracks are predicted by considering the influence of the interaction on the SIF and the coalescence of two cracks. The results obtained are then compared with existing experimental and analytical data for validation. All of the data analyses are presented in tabular forms and figures.

  1. Failure processes in polymers: Environmental stress crack growth and adhesion of elastomeric copolymers to polypropylene

    NASA Astrophysics Data System (ADS)

    Ayyer, Ravishankar

    time (ITT)'. It depended on concentration and molecular weight of Igepal. Both fatigue and creep crack growth rate in Igepal showed significantly higher crack growth rate after 'ITT' relative to air. To probe the Igepal effect on kinetics, fracture processes involved in first craze failure were compared to that in air.

  2. A Creaking and Cracking Comet

    NASA Astrophysics Data System (ADS)

    Faurschou Hviid, Stubbe; Hüttig, Christian; Groussin, Olivier; Mottola, Stefano; Keller, Horst Uwe; OSIRIS Team

    2016-10-01

    Since the middle of 2014 the OSIRIS cameras on the ESA Rosetta mission have been monitoring the evolution of the comet 67P/Churyumov-Gerasimenko as it passed through perihelion. During the perihelion passage several change events have been observed on the nucleus surface. For example existing large scale cracks have expanded and new large scale cracks have been created. Also several large scale "wave pattern" like change events have been observed in the Imhotep and Hapi regions. These are events not directly correlated with any normal visible cometary activity. One interpretation is that these are events likely caused by "seismic" activity. The seismic activity is created by the self-gravity stress of the non-spherical comet nucleus and stress created by the non-gravitational forces acting on the comet. The non-gravitational forces are changing the rotation period of the comet (~20min/perihelion passage) which induces a changing mechanical stress pattern through the perihelion passage. Also the diurnal cycle with its changing activity pattern is causing a periodic wobble in the stress pattern that can act as a trigger for a comet quake. The stress pattern has been modeled using a finite element model that includes self-gravity, the comet spin and the non-gravitational forces based on a cometary activity model. This paper will discuss what can be learned about the comet nucleus structure and about the cometary material properties from these events and from the FEM model.

  3. 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.

  4. Laboratory Study of Crack Development and Crack Interaction in Concrete Blocks due to Swelling of Cracking Agent

    NASA Astrophysics Data System (ADS)

    Frühwirt, Thomas; Plößer, Arne; Konietzky, Heinz

    2015-04-01

    The main focus of this work was to investigate temporary and spatial features of crack development in concrete blocks due to the action of a swelling agent. A commercial available cement-based mortar which shows heavily swelling behaviour when hydrating is used to provide inside pressure in boreholes in conrete blocks and hence serves as cracking agent. As no data for the swelling behaviour of the cracking agent were available the maximum axial swelling stress and axial free swelling strain were determined experimentally. In a first series of tests on concrete blocks the influence of an external mechanical, unidirectional stress on the development-time and orientation of cracks has been investigated for a range of loading levels. The stress state in the blocks prepared with a single borehole was determined by a superposition of internal stresses caused by swelling pressure and external mechanical loading. For a second series of tests prismatic blocks with two boreholes where prepared. This test setup allowed to realize different orientation of boreholes with respect to the uniaxial loading direction. Complementary tests were done using the cracking agent in both, only one or none of the boreholes. Different modes of crack interaction and influence of filled or unfilled boreholes have been observed. Features of crack development showed significant sensitivity to external loading. Starting even at very low load levels crack orientation was primarely determined by the direction of the external load. Temporal change in crack development due to the different load levels was insignificant and no consistent conclusion could be drawn. Crack interaction phenomena only were observed with two boreholes orientated primarely in direction of the external loading. Even in these cases crack orientation was mainly determined by the external stress field and only locally influenced by other cracks or the unfilled borehole. The work provides us with an extensive catalogue of

  5. Effects of crack aspect ratio on the behavior of small surface cracks in fatigue: Part I. Simulation

    NASA Astrophysics Data System (ADS)

    Ravichandran, K. S.

    1997-01-01

    A simple simulation of alternate growth of a small surface crack in the surface and depth directions was performed to illustrate the changes in crack aspect ratio, induced by grain boundaries, as a function of crack size. It is shown that at small crack sizes, large variations in aspect ratio, a/c ( a is the crack depth and c is the half-surface length), occur, due to local crack front perturbations induced by grains that are oriented for crack growth. At these crack sizes, the assumption of a semicircular crack shape ( a/c=1.0) was found to cause errors in stress intensity range (Δ K) calculations. This, in turn, led to significant scatter or “anomaly” in small crack growth rates relative to large cracks. At large crack sizes, the effects of local crack front perturbations on crack aspect ratio and Δ K were found to be insignificant. As a result, the scatter in crack growth data was found to decrease to a negligible level at large crack sizes. It is suggested that the limiting crack size above which the small crack behaves as a large crack, l 2=10 d ( d = grain size), proposed by Taylor and Knott, is related to the crack size above which the effects due to aspect ratio variations are small.

  6. Microwave detection of hairline surface-breaking cracks in metals using open-ended coaxial sensors: preliminary results

    NASA Astrophysics Data System (ADS)

    Zoughi, Reza; Hayes, Kent; Ganchev, Stoyan I.

    1996-11-01

    Recent microwave methods have shown to be capable of detecting and sizing surface slots and cracks in metals. These methods have incorporated the use of an open-ended rectangular waveguide probe for such measurements. A new microwave method utilizing an open-ended coaxial line sensor has been under investigation for some time now. Coaxial line sensors have certain features that make them quite attractive for surface crack detection. These features include their high level of sensitivity to the presence of very narrow cracks as will as the fact that their geometry may include complicated bends allowing access to hard to reach places. This paper presents and comments on some preliminary experimental results of using this sensor for hairline surface crack detection.

  7. Development of crack shape: LBB methodology for cracked pipes

    SciTech Connect

    Moulin, D.; Chapuliot, S.; Drubay, B.

    1997-04-01

    For structures like vessels or pipes containing a fluid, the Leak-Before-Break (LBB) assessment requires to demonstrate that it is possible, during the lifetime of the component, to detect a rate of leakage due to a possible defect, the growth of which would result in a leak before-break of the component. This LBB assessment could be an important contribution to the overall structural integrity argument for many components. The aim of this paper is to review some practices used for LBB assessment and to describe how some new R & D results have been used to provide a simplified approach of fracture mechanics analysis and especially the evaluation of crack shape and size during the lifetime of the component.

  8. The growth of small corrosion fatigue cracks in alloy 2024

    NASA Technical Reports Server (NTRS)

    Piascik, Robert S.; Willard, Scott A.

    1993-01-01

    The corrosion fatigue crack growth characteristics of small surface and corner cracks in aluminum alloy 2024 is established. The damaging effect of salt water on the early stages of small crack growth is characterized by crack initiation at constituent particle pits, intergranular microcracking for a less than 100 micrometers, and transgranular small crack growth for a micrometer. In aqueous 1 percent NaCl and at a constant anodic potential of -700 mV(sub SCE), small cracks exhibit a factor of three increase in fatigue crack growth rates compared to laboratory air. Small cracks exhibit accelerated corrosion fatigue crack growth rates at low levels of delta-K (less than 1 MPa square root of m) below long crack delta-K (sub th). When exposed to Paris regime levels of crack tip stress intensity, small corrosion fatigue cracks exhibit growth rates similar to that observed for long cracks. Results suggest that crack closure effects influence the corrosion fatigue crack growth rates of small cracks (a less than or equal to 100 micrometers). This is evidenced by similar small and long crack growth behavior at various levels of R. Contrary to the corrosion fatigue characteristics of small cracks in high strength steels, no pronounced chemical crack length effect is observed for Al by 2024 exposed to salt water.

  9. Wind tunnel investigation of a Centaur standard shroud compartment vent from Mach number of 0.70 to 1.96

    NASA Technical Reports Server (NTRS)

    Johns, A. L.; Jones, M. L.

    1975-01-01

    An experimental investigation was conducted in the Lewis Research Center 8- by 6-foot supersonic wind tunnel to determine the vent discharge coefficient for the Centaur standard shroud/liquid hydrogen tank compartment vent. The test was conducted from Mach 0.70 to 1.96 with the vent mounted in a flat plate. Full scale simulated flight hardware, such as the vent, corrugations, aft field joint ring and ice bag clip was used. Air was discharged from a plenum chamber, located on the tunnel sidewall behind the plate, through five 6.35 cm diameter vent orifices into the free stream. Boundary layer thickeners, analytically predicted displacement thickness for the vehicle nominal flight trajectory could be simulated over the Mach number range. The highest vent discharge coefficient for any given Mach number and vent pressure ratio generally occurred at the maximum displacement thickness.

  10. Fatigue life and crack growth prediction methodology

    NASA Technical Reports Server (NTRS)

    Newman, J. C., Jr.; Phillips, E. P.; Everett, R. A., Jr.

    1993-01-01

    The capabilities of a plasticity-induced crack-closure model and life-prediction code to predict fatigue crack growth and fatigue lives of metallic materials are reviewed. Crack-tip constraint factors, to account for three-dimensional effects, were selected to correlate large-crack growth rate data as a function of the effective-stress-intensity factor range (delta(K(sub eff))) under constant-amplitude loading. Some modifications to the delta(K(sub eff))-rate relations were needed in the near threshold regime to fit small-crack growth rate behavior and endurance limits. The model was then used to calculate small- and large-crack growth rates, and in some cases total fatigue lives, for several aluminum and titanium alloys under constant-amplitude, variable-amplitude, and spectrum loading. Fatigue lives were calculated using the crack growth relations and microstructural features like those that initiated cracks. Results from the tests and analyses agreed well.

  11. Grain boundary resistance to fatigue crack growth

    NASA Technical Reports Server (NTRS)

    Chen, QI; Liu, H. W.

    1993-01-01

    Results of an experimental study tracing the grain boundary effect on the fatigue crack growth rate are reported. Direct experimental evidence for the grain boundary blockage mechanism is presented. The orientation difference between two neighboring grains directly contributed to the extent of crack growth retardation.

  12. Use of vacuum residue in thermal cracking

    SciTech Connect

    Mikulla, K.D.; Wernicke, H.J.

    1981-03-24

    Vacuum residue is used for production of olefins by first separating, preferably by solvent extraction, the asphalt therein , blending resultant asphalt depleted fraction with a lighter fraction, E.G., a vacuum gas oil, and then subjecting the blend to a conventional catalytic hydrogenation step prior to thermal cracking. The hydrogenate may be separated into fractions with the heavy fraction only being thermally cracked.

  13. Characterization of crack growth under combined loading

    NASA Technical Reports Server (NTRS)

    Feldman, A.; Smith, F. W.; Holston, A., Jr.

    1977-01-01

    Room-temperature static and cyclic tests were made on 21 aluminum plates in the shape of a 91.4x91.4-cm Maltese cross with 45 deg flaws to develop crack growth and fracture toughness data under mixed-mode conditions. During cyclic testing, it was impossible to maintain a high proportion of shear-mode deformation on the crack tips. Cracks either branched or turned. Under static loading, cracks remained straight if shear stress intensity exceeded normal stress intensity. Mixed-mode crack growth rate data compared reasonably well with published single-mode data, and measured crack displacements agreed with the straight and branched crack analyses. Values of critical strain energy release rate at fracture for pure shear were approximately 50% higher than for pure normal opening, and there was a large reduction in normal stress intensity at fracture in the presence of high shear stress intensity. Net section stresses were well into the inelastic range when fracture occurred under high shear on the cracks.

  14. The crack-inclusion interaction problem

    NASA Technical Reports Server (NTRS)

    Xue-Hui, L.; Erdogan, F.

    1984-01-01

    The general plane elastostatic problem of interaction between a crack and an inclusion is considered. The Green's functions for a pair of dislocations and a pair of concentrated body forces are used to generate the crack and the inclusion. Integral equations are obtained for a line crack and an elastic line inclusion having an arbitrary relative orientation and size. The nature of stress singularity around the end points of rigid and elastic inclusions is described and three special cases of this intersection problem are studied. The problem is solved for an arbitrary uniform stress state away from the crack-inclusion region. The nonintersecting crack-inclusion problem is considered for various relative size, orientation, and stiffness parameters, and the stress intensity factors at the ends of the inclusion and the crack are calculated. For the crack-inclusion intersection case, special stress intensity factors are defined and are calculated for various values of the parameters defining the relative size and orientation of the crack and the inclusion and the stiffness of the inclusion.

  15. Positioning Community Art Practices in Urban Cracks

    ERIC Educational Resources Information Center

    Verschelden, Griet; Van Eeghem, Elly; Steel, Riet; De Visscher, Sven; Dekeyrel, Carlos

    2012-01-01

    This article addresses the position of community art practices and the role of practitioners in urban cracks. Community art practices raise possibilities for a reconceptualisation of the concept of community and an extension of the concept of art in public space. Urban cracks are conceptualised as spatial, temporal and relational manifestations of…

  16. Entering a Crack: An Encounter with Gossip

    ERIC Educational Resources Information Center

    Henderson, Linda

    2014-01-01

    In this paper, I enter a crack to think otherwise about the concept "gossip". Drawing on previous scholarship engaging with Deleuzian concepts to inform research methodologies, this paper builds on this body of work. Following Deleuze and Guattari, the paper undertakes a mapping of gossip, subsequent to an encounter with a crack.…

  17. Seismic wave propagation in cracked porous media

    NASA Astrophysics Data System (ADS)

    Pointer, Tim; Liu, Enru; Hudson, John A.

    2000-07-01

    The movement of interstitial fluids within a cracked solid can have a significant effect on the properties of seismic waves of long wavelength propagating through the solid. We consider three distinct mechanisms of wave-induced fluid flow: flow through connections between cracks in an otherwise non-porous material, fluid movement within partially saturated cracks, and diffusion from the cracks into a porous matrix material. In each case the cracks may be aligned or randomly oriented, leading, respectively, to anisotropic or isotropic wave speeds and attenuation factors. In general, seismic velocities exhibit behaviour that is intermediate between that of empty cracks and that of isolated liquid-filled cracks if fluid flow is significant. In the range of frequencies for which considerable fluid flow occurs there is high attenuation and dispersion of seismic waves. Fluid flow may be on either a wavelength scale or a local scale depending on the model and whether the cracks are aligned or randomly oriented, resulting in completely different effects on seismic wave propagation. A numerical analysis shows that all models can have an effect over the exploration seismic frequency range.

  18. Effect of size on cracking of materials

    NASA Technical Reports Server (NTRS)

    Glucklick, J.

    1971-01-01

    Brittle behavior of large mild steel elements, glass plasticity, and fatigue specimen size sensitivity are manifestations of strain-energy size effect. Specimens physical size effect on material cracking initiation occurs according to flaw distribution statistics. Fracture size effect depends on stability or instability of crack propagation.

  19. Probing and repairing damaged surfaces with nanoparticle-containing microcapsules

    NASA Astrophysics Data System (ADS)

    Kratz, Katrina; Narasimhan, Amrit; Tangirala, Ravisubhash; Moon, Sungcheal; Revanur, Ravindra; Kundu, Santanu; Kim, Hyun Suk; Crosby, Alfred J.; Russell, Thomas P.; Emrick, Todd; Kolmakov, German; Balazs, Anna C.

    2012-02-01

    Nanoparticles have useful properties, but it is often important that they only start working after they are placed in a desired location. The encapsulation of nanoparticles allows their function to be preserved until they are released at a specific time or location, and this has been exploited in the development of self-healing materials and in applications such as drug delivery. Encapsulation has also been used to stabilize and control the release of substances, including flavours, fragrances and pesticides. We recently proposed a new technique for the repair of surfaces called `repair-and-go'. In this approach, a flexible microcapsule filled with a solution of nanoparticles rolls across a surface that has been damaged, stopping to repair any defects it encounters by releasing nanoparticles into them, then moving on to the next defect. Here, we experimentally demonstrate the repair-and-go approach using droplets of oil that are stabilized with a polymer surfactant and contain CdSe nanoparticles. We show that these microcapsules can find the cracks on a surface and selectively deliver the nanoparticle contents into the crack, before moving on to find the next crack. Although the microcapsules are too large to enter the cracks, their flexible walls allow them to probe and adhere temporarily to the interior of the cracks. The release of nanoparticles is made possible by the thin microcapsule wall (comparable to the diameter of the nanoparticles) and by the favourable (hydrophobic-hydrophobic) interactions between the nanoparticle and the cracked surface.

  20. Crack tip field and fatigue crack growth in general yielding and low cycle fatigue

    NASA Technical Reports Server (NTRS)

    Minzhong, Z.; Liu, H. W.

    1984-01-01

    Fatigue life consists of crack nucleation and crack propagation periods. Fatigue crack nucleation period is shorter relative to the propagation period at higher stresses. Crack nucleation period of low cycle fatigue might even be shortened by material and fabrication defects and by environmental attack. In these cases, fatigue life is largely crack propagation period. The characteristic crack tip field was studied by the finite element method, and the crack tip field is related to the far field parameters: the deformation work density, and the product of applied stress and applied strain. The cyclic carck growth rates in specimens in general yielding as measured by Solomon are analyzed in terms of J-integral. A generalized crack behavior in terms of delta is developed. The relations between J and the far field parameters and the relation for the general cyclic crack growth behavior are used to analyze fatigue lives of specimens under general-yielding cyclic-load. Fatigue life is related to the applied stress and strain ranges, the deformation work density, crack nucleus size, fracture toughness, fatigue crack growth threshold, Young's modulus, and the cyclic yield stress and strain. The fatigue lives of two aluminum alloys correlate well with the deformation work density as depicted by the derived theory. The general relation is reduced to Coffin-Manson low cycle fatigue law in the high strain region.

  1. Method of continuously determining crack length

    NASA Technical Reports Server (NTRS)

    Prabhakaran, Ramamurthy (Inventor); Lopez, Osvaldo F. (Inventor)

    1993-01-01

    The determination of crack lengths in an accurate and straight forward manner is very useful in studying and preventing load created flaws and cracks. A crack length sensor according to the present invention is fabricated in a rectangular or other geometrical form from a conductive powder impregnated polymer material. The long edges of the sensor are silver painted on both sides and the sensor is then bonded to a test specimen via an adhesive having sufficient thickness to also serve as an insulator. A lead wire is connected to each of the two outwardly facing silver painted edges. The resistance across the sensor changes as a function of the crack length in the specimen and sensor. The novel aspect of the present invention includes the use of relatively uncomplicated sensors and instrumentation to effectively measure the length of generated cracks.

  2. The crack problem for a nonhomogeneous plane

    NASA Technical Reports Server (NTRS)

    Delale, F.; Erdogan, F.

    1982-01-01

    The plane elasticity problem for a nonhomogeneous medium containing a crack is considered. It is assumed that the Poisson's ratio of the medium is constant and the Young's modulus E varies exponentially with the coordinate parallel to the crack. First the half plane problem is formulated and the solution is given for arbitrary tractions along the boundary. Then the integral equation for the crack problem is derived. It is shown that the integral equation having the derivative of the crack surface displacement as the density function has a simple Cauchy type kernel. Hence, its solution and the stresses around the crack tips have the conventional square root singularity. The solution is given for various loading conditions. The results show that the effect of the Poisson's ratio and consequently that of the thickness constraint on the stress intensity factors are rather negligible.

  3. Stress analysis for structures with surface cracks

    NASA Technical Reports Server (NTRS)

    Bell, J. C.

    1978-01-01

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

  4. 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.

  5. Small crack test program for helicopter materials

    NASA Technical Reports Server (NTRS)

    Annigeri, Bal; Schneider, George

    1994-01-01

    Crack propagation tests were conducted to determine crack growth behavior in five helicopter materials for surface cracks between 0.005 to 0.020 inches in depth. Constant amplitude tests were conducted at stress ratios R equals 0.1 and 0.5, and emphasis was placed on near threshold data (i.e., 10-8 to 10-6 inches/cycle). Spectrum tests were conducted using a helicopter spectrum. The test specimen was an unnotched tension specimen, and cracks were initiated from a small EDM notch. An optical/video system was used to monitor crack growth. The material for the test specimens was obtained from helicopter part forgings. Testing was conducted at stresses below yield to reflect actual stresses in helicopter parts.

  6. 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.

  7. Fatigue Crack Detection Using Digital Image Correlation

    NASA Astrophysics Data System (ADS)

    Cawley, P.; Hutt, T. D.

    2009-03-01

    At present, detecting structural defects such as cracking and corrosion before they become critical is largely achieved by time consuming techniques such as eddy current and ultrasonic testing. These techniques require point-by-point scanning over the area to be tested. Digital Image Correlation could provide a cheaper and quicker testing technique. It works by correlating images of the structure surface in unloaded and loaded states taken with a standard digital camera, giving the displacement and strain fields. The specific case of a crack at a hole in an aluminium plate was investigated. It was found that the strain concentration around the crack tip is too localised to detect; however the displacement jump across the crack could be seen. This technique allows the cracks to be detected and would allow rapid testing of a structure if it can easily be loaded.

  8. Measurement and analysis of critical crack tip processes during fatigue crack growth

    NASA Technical Reports Server (NTRS)

    Davidson, D. L.; Hudak, S. J.; Dexter, R. J.

    1985-01-01

    The mechanics of fatigue crack growth under constant-amplitudes and variable-amplitude loading were examined. Critical loading histories involving relatively simple overload and overload/underload cycles were studied to provide a basic understanding of the underlying physical processes controlling crack growth. The material used for this study was 7091-T7E69, a powder metallurgy aluminum alloy. Local crack-tip parameters were measured at various times before, during, and after the overloads, these include crack-tip opening loads and displacements, and crack-tip strain fields. The latter were useed, in combination with the materials cyclic and monotonic stress-strain properties, to compute crack-tip residual stresses. The experimental results are also compared with analytical predictions obtained using the FAST-2 computer code. The sensitivity of the analytical model to constant-amplitude fatigue crack growth rate properties and to through-thickness constrain are studied.

  9. Crack shape developments and leak rates for circumferential complex-cracked pipes

    SciTech Connect

    Brickstad, B.; Bergman, M.

    1997-04-01

    A computerized procedure has been developed that predicts the growth of an initial circumferential surface crack through a pipe and further on to failure. The crack growth mechanism can either be fatigue or stress corrosion. Consideration is taken to complex crack shapes and for the through-wall cracks, crack opening areas and leak rates are also calculated. The procedure is based on a large number of three-dimensional finite element calculations of cracked pipes. The results from these calculations are stored in a database from which the PC-program, denoted LBBPIPE, reads all necessary information. In this paper, a sensitivity analysis is presented for cracked pipes subjected to both stress corrosion and vibration fatigue.

  10. Micromechanical predictions of crack initiation, propagation and crack growth resistance in boron/aluminum composites

    NASA Technical Reports Server (NTRS)

    Mahishi, J. M.; Adams, D. F.

    1982-01-01

    An elastoplastic, axisymmetric finite element model has been used to predict the initiation and propagation of a crack in a composite model consisting of a single broken boron fiber embedded in an annular sheath of aluminum matrix. The accuracy of the axisymmetric finite element model for crack problems has been established by solving the classical problem of a penny-shaped crack in a thick cylindrical rod under axial tension. Also, the stress intensity factors predicted by the present numerical model are compared with continuum results. A constant displacement boundary condition applied during an increment of crack growth permits a substantial amount of stable crack growth in the matrix material. The concept of Crack Growth Resistance Curves (KR-curves) has been used to determine the point of crack instability

  11. Fatigue Crack Length Sizing Using a Novel Flexible Eddy Current Sensor Array.

    PubMed

    Xie, Ruifang; Chen, Dixiang; Pan, Mengchun; Tian, Wugang; Wu, Xuezhong; Zhou, Weihong; Tang, Ying

    2015-12-21

    The eddy current probe, which is flexible, array typed, highly sensitive and capable of quantitative inspection is one practical requirement in nondestructive testing and also a research hotspot. A novel flexible planar eddy current sensor array for the inspection of microcrack presentation in critical parts of airplanes is developed in this paper. Both exciting and sensing coils are etched on polyimide films using a flexible printed circuit board technique, thus conforming the sensor to complex geometric structures. In order to serve the needs of condition-based maintenance (CBM), the proposed sensor array is comprised of 64 elements. Its spatial resolution is only 0.8 mm, and it is not only sensitive to shallow microcracks, but also capable of sizing the length of fatigue cracks. The details and advantages of our sensor design are introduced. The working principal and the crack responses are analyzed by finite element simulation, with which a crack length sizing algorithm is proposed. Experiments based on standard specimens are implemented to verify the validity of our simulation and the efficiency of the crack length sizing algorithm. Experimental results show that the sensor array is sensitive to microcracks, and is capable of crack length sizing with an accuracy within ±0.2 mm.

  12. Fatigue Crack Length Sizing Using a Novel Flexible Eddy Current Sensor Array

    PubMed Central

    Xie, Ruifang; Chen, Dixiang; Pan, Mengchun; Tian, Wugang; Wu, Xuezhong; Zhou, Weihong; Tang, Ying

    2015-01-01

    The eddy current probe, which is flexible, array typed, highly sensitive and capable of quantitative inspection is one practical requirement in nondestructive testing and also a research hotspot. A novel flexible planar eddy current sensor array for the inspection of microcrack presentation in critical parts of airplanes is developed in this paper. Both exciting and sensing coils are etched on polyimide films using a flexible printed circuit board technique, thus conforming the sensor to complex geometric structures. In order to serve the needs of condition-based maintenance (CBM), the proposed sensor array is comprised of 64 elements. Its spatial resolution is only 0.8 mm, and it is not only sensitive to shallow microcracks, but also capable of sizing the length of fatigue cracks. The details and advantages of our sensor design are introduced. The working principal and the crack responses are analyzed by finite element simulation, with which a crack length sizing algorithm is proposed. Experiments based on standard specimens are implemented to verify the validity of our simulation and the efficiency of the crack length sizing algorithm. Experimental results show that the sensor array is sensitive to microcracks, and is capable of crack length sizing with an accuracy within ±0.2 mm. PMID:26703608

  13. Life prediction for bridged fatigue cracks

    SciTech Connect

    Cox, B.N.

    1994-08-01

    One of the more promising classes of composites touted for high temperature applications, and certainly the most available, is that of relatively brittle matrices, either ceramic or intermetallic, reinforced by strong, aligned, continuous fibers. Under cyclic loading in the fiber direction, these materials develop matrix cracks that often run perpendicular to the fibers, while the fibers remain intact in the crack wake, supplying bridging tractions across the fracture surfaces. The bridging tractions shield the crack tip from the applied load, dramatically reducing the crack velocity from that expected in an unreinforced material subjected to the same value, {Delta}K{sub a}, of the cyclic applied stress intensity factor. An important issue in reliability is the prediction of the growth rates of the bridged cracks. The growth rates of matrix fatigue cracks bridged by sliding fibers are now commonly predicted by models based on the micromechanics of frictional interfaces. However, there exist many reasons, both theoretical and experimental, for suspecting that the most popular micromechanical models are probably wrong in detail in the context of fatigue cracks. Furthermore, a review of crack growth data reveals that the validity of the micromechanics-based predictive model has never been tested and may never be tested. In this paper, two alternative approaches are suggested to the engineering problem of predicting the growth rates of bridged cracks without explicit recourse to micromechanics. Instead, it is shown that the material properties required to analyze bridging effects can be deduced directly from crack growth data. Some experiments are proposed to test the validity of the proposals.

  14. Investigating Reaction-Driven Cracking

    NASA Astrophysics Data System (ADS)

    Kelemen, P. B.; Hirth, G.; Savage, H. M.

    2013-12-01

    Many metamorphic reactions lead to large volume changes, and potentially to reaction-driven cracking [1,2]. Large-scale hydration of mantle peridotite to produce serpentine or talc is invoked to explain the rheology of plate boundaries, the nature of earthquakes, and the seismic properties of slow-spread ocean crust and the 'mantle wedge' above subduction zones. Carbonation of peridotite may be an important sink in the global carbon cycle. Zones of 100% magnesite + quartz replacing peridotite, up to 200 m thick, formed where oceanic mantle was thrust over carbonate-bearing metasediments in Oman. Talc + carbonate is an important component of the matrix in subduction mélanges at Santa Catalina Island , California, and the Sanbagawa metamorphic belt, Japan. Engineered systems to emulate natural mineral carbonation could provide relatively inexpensive CO2 capture and storage [3]. More generally, engineered reaction-driven cracking could supplement or replace hydraulic fracture in geothermal systems, solution mining, and extraction of tight oil and gas. The controls on reaction-driven cracking are poorly understood. Hydration and carbonation reactions can be self-limiting, since they potentially reduce permeability and armor reactive surfaces [4]. Also, in some cases, hydration or carbonation may take place at constant volume. Small changes in volume due to precipitation of solid products increases stress, destabilizing solid reactants, until precipitation and dissolution rates become equal at a steady state stress [5]. In a third case, volume change due to precipitation of solid products causes brittle failure. This has been invoked on qualitative grounds to explain, e.g., complete serpentinization of mantle peridotite [6]. Below ~ 300°C, the available potential energy for hydration and carbonation of olivine could produce stresses of 100's of MPa [2], sufficient to fracture rocks to 10 km depth or more, causing brittle failure below the steady state stress required

  15. Environmental stress cracking of polymers

    NASA Technical Reports Server (NTRS)

    Mahan, K. I.

    1980-01-01

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

  16. Plane strain crack growth models for fatigue crack growth life predictions

    SciTech Connect

    Bloom, J.M.; Daniewicz, S.R.; Hechmer, J.L.

    1996-02-01

    Experimental data and analytical models have shown that a growing fatigue crack produces a plastic wake. This, in turn, leads to residual compressive stresses acting over the crack faces during the unloading portion of the fatigue cycle. This crack closure effect results in an applied stress intensity factor during unloading which is greater than that associated with the K{sub min}, thus producing a crack-driving force which is less than {Delta}K = K{sub max} {minus} K{sub min}. Life predictions which do not account for this crack closure effect give inaccurate life estimates, especially for fully reversed loadings. This paper discusses the development of a crack closure expression for the 4-point bend specimen using numerical results obtained from a modified strip-yield model. Data from tests of eight 4-point bend specimens were used to estimate the specimen constraint factor (stress triaxiality effect). The constraint factor was then used in the estimation of the crack opening stresses for each of the bend tests. The numerically estimated crack opening stresses were used to develop an effective stress intensity factor range, {Delta}K{sub eff}. The resulting crack growth rate data when plotted versus {Delta}K{sub eff} resulted in a material fatigue crack growth rate property curve independent of test specimen type, stress level, and R-ratio. Fatigue crack growth rate data from center-cracked panels using Newman`s crack closure model, from compact specimens using Eason`s R-ratio expression, and from bend specimens using the model discussed in this paper are all shown to fall along the same straight line (on log-log paper) when plotted versus {Delta}K{sub eff}, even though crack closure differs for each specimen type.

  17. Three-Dimensional Gear Crack Propagation Studied

    NASA Technical Reports Server (NTRS)

    Lewicki, David G.

    1999-01-01

    Gears used in current helicopters and turboprops are designed for light weight, high margins of safety, and high reliability. However, unexpected gear failures may occur even with adequate tooth design. To design an extremely safe system, the designer must ask and address the question, "What happens when a failure occurs?" With gear-tooth bending fatigue, tooth or rim fractures may occur. A crack that propagates through a rim will be catastrophic, leading to disengagement of the rotor or propeller, loss of an aircraft, and possible fatalities. This failure mode should be avoided. A crack that propagates through a tooth may or may not be catastrophic, depending on the design and operating conditions. Also, early warning of this failure mode may be possible because of advances in modern diagnostic systems. One concept proposed to address bending fatigue fracture from a safety aspect is a splittooth gear design. The prime objective of this design would be to control crack propagation in a desired direction such that at least half of the tooth would remain operational should a bending failure occur. A study at the NASA Lewis Research Center analytically validated the crack-propagation failsafe characteristics of a split-tooth gear. It used a specially developed three-dimensional crack analysis program that was based on boundary element modeling and principles of linear elastic fracture mechanics. Crack shapes as well as the crack-propagation life were predicted on the basis of the calculated stress intensity factors, mixed-mode crack-propagation trajectory theories, and fatigue crack-growth theories. The preceding figures show the effect of the location of initial cracks on crack propagation. Initial cracks in the fillet of the teeth produced stress intensity factors of greater magnitude (and thus, greater crack growth rates) than those in the root or groove areas of the teeth. Crack growth was simulated in a case study to evaluate crack-propagation paths. Tooth

  18. A structural health monitoring fastener for tracking fatigue crack growth in bolted metallic joints

    NASA Astrophysics Data System (ADS)

    Rakow, Alexi Schroder

    Fatigue cracks initiating at fastener hole locations in metallic components are among the most common form of airframe damage. The fastener hole site has been surveyed as the second leading initiation site for fatigue related accidents of fixed wing aircraft. Current methods for inspecting airframes for these cracks are manual, whereby inspectors rely on non-destructive inspection equipment or hand-held probes to scan over areas of a structure. Use of this equipment often demands disassembly of the vehicle to search appropriate hole locations for cracks, which elevates the complexity and cost of these maintenance inspections. Improved reliability, safety, and reduced cost of such maintenance can be realized by the permanent integration of sensors with a structure to detect this damage. Such an integrated system of sensors would form a structural health monitoring (SHM) system. In this study, an Additive, Interleaved, Multi-layer Electromagnetic (AIME) sensor was developed and integrated with the shank of a fastener to form a SHM Fastener, a new SHM technology targeted at detection of fastener hole cracks. The major advantages of the SHM Fastener are its installation, which does not require joint layer disassembly, its capability to detect inner layer cracks, and its capability to operate in a continuous autonomous mode. Two methods for fabricating the proposed SHM Fastener were studied. The first option consisted of a thin flexible printed circuit film that was bonded around a thin metallic sleeve placed around the fastener shank. The second option consisted of coating sensor materials directly to the shank of a part in an effort to increase the durability of the sensor under severe loading conditions. Both analytical and numerical models were developed to characterize the capability of the sensors and provide a design tool for the sensor layout. A diagnostic technique for crack growth monitoring was developed to complete the SHM system, which consists of the

  19. Hierarchically-Driven Approach for Quantifying Fatigue Crack Initiation and Short Crack Growth Behavior in Aerospace Materials

    DTIC Science & Technology

    2016-08-31

    AFRL-AFOSR-VA-TR-2016-0308 Hierarchically-Driven Approach for Quantifying Fatigue Crack Initiation and Short Crack Growth Behavior inAerospace...Quantifying Fatigue Crack Initiation and Short Crack Growth Behavior inAerospace Materials 5a. CONTRACT NUMBER FA9550-13-1-0144 5b. GRANT NUMBER 5c...Approach for Quantifying Fatigue Crack Initiation and Short Crack Growth Behavior inAerospace Materials Principal Investigator K.N. Solanki

  20. Fatigue Crack Measurement in Composite Materials by Ultrasonic Methods

    NASA Technical Reports Server (NTRS)

    Walker, James L.; Russell, Samuel S.; Suits, Michael W.; Workman, Gary L.; Watson, Jason M.; Thom, Robert (Technical Monitor)

    2002-01-01

    The nondestructive detection of intra-ply microcracking in unlined pressure vessels fabricated from composite materials is critical to ensuring mission success. Microcracking in composite structures due to combined fatigue and cryogenic thermal loading can be very troublesome to detect in-service and when it begins to link through the thickness can cause leakage and failure of the structure. These leaks may lead to loss of pressure/propellant, increased risk of explosion and possible cryo-pumping. The work presented herein develops a method and an instrument to locate and measure intraply fatigue cracking through the thickness of laminated composite material by means of correlation with ultrasonic resonance. Resonant ultrasound spectroscopy provides measurements which are, sensitive to both the microscopic and macroscopic properties of an object. Elastic moduli, acoustic attenuation, and geometry can all be probed. The approach is based on the premise of half-wavelength resonance. The method injects a broadband ultrasonic wave into the test structure using a swept frequency technique. This method provides dramatically increased energy input into the test article, as compared to conventional spike pulsed ultrasonics. This relative energy increase improves the ability to measure finer details in the materials character, such as micro-cracking and porosity. As the micro-crack density increases, more interactions occur with the higher frequency (small wavelength) components of the signal train causing the spectrum to shift toward lower frequencies. Preliminary experiments have verified a measurable effect on the resonance spectrum of the ultrasonic data to detect microcracking. Methods involving self organizing neural networks and other clustering algorithms show that the resonance ultrasound signatures from composites vary with the degree of microcracking and can be separated and identified.

  1. Lattice theory of three-dimensional cracks

    NASA Technical Reports Server (NTRS)

    Esterling, D. M.

    1976-01-01

    The problem of the stability of a three-dimensional crack is analyzed within a lattice-statics approximation. The consequence of introducing a jog into the crack face as well as the effects of various nonlinear-force laws are studied. The phenomenon of lattice trapping (upper and lower bounds on the applied stress for an equilibrium crack of given length) is again obtained. It is possible to obtain some physical insight into which aspects of the force law are critical for crack stability. In particular, the inadequacy of a thermodynamic approach - which relates the critical stress to a surface energy corresponding to the area under the cohesive-force-vs-displacement curve - is demonstrated. Surface energy is a global property of the cohesive-force law. Crack stability is sensitive to much more refined aspects of the cohesive-force law. Crack healing is sensitive to the long-range portion of the cohesive force. Crack expansion is sensitive to the position of the maximum in the cohesive-force relation.

  2. Closure of fatigue cracks at high strains

    NASA Technical Reports Server (NTRS)

    Iyyer, N. S.; Dowling, N. E.

    1985-01-01

    Experiments were conducted on smooth specimens to study the closure behavior of short cracks at high cyclic strains under completely reversed cycling. Testing procedures and methodology, and closure measurement techniques, are described in detail. The strain levels chosen for the study cover from predominantly elastic to grossly plastic strains. Crack closure measurements are made at different crack lengths. The study reveals that, at high strains, cracks close only as the lowest stress level in the cycle is approached. The crack opening is observed to occur in the compressive part of the loading cycle. The applied stress needed to open a short crack under high strain is found to be less than for cracks under small scale yielding. For increased plastic deformations, the value of sigma sub op/sigma sub max is observed to decrease and approaches the value of R. Comparison of the experimental results with existing analysis is made and indicates the limitations of the small scale yielding approach where gross plastic deformation behavior occurs.

  3. Ultrasonic characterization of fatigue crack closure

    SciTech Connect

    Thompson, R.B.; Buck, O.; Rehbein, D.K.

    1991-01-01

    The characterization of fatigue crack closure is an important objective because of its influence on fatigue crack propagation, particularly under conditions of variable amplitude loading. This paper describes a nontraditional technique for characterizing closure, in which ultrasonic scattering measurements are used to obtain estimates of the number density and size of asperities bridging the crack faces, with subsequent estimates of the crack tip shielding being based on those geometrical parameters. The paper first reviews the experimental configuration and the basic elasto-dynamic theory underlying the technique. It then presents recent results obtained in studies of the influence of block overloads and load shedding on the growth of fatigue cracks in aluminum alloys. In both cases, the change in the closure state after the overload can be unambiguously seen even in the raw data. Moreover, data analysis suggests that it may be possible to predict when the crack will reinitiate based on more subtle changes in the ultrasonically inferred closure state. In the case of load shedding, a massive closure region is observed, whose characteristics appear consistent with the notion that threshold phenomena can be explained in terms of crack closure. 20 refs., 10 figs.

  4. Identification of cracks in thick beams with a cracked beam element model

    NASA Astrophysics Data System (ADS)

    Hou, Chuanchuan; Lu, Yong

    2016-12-01

    The effect of a crack on the vibration of a beam is a classical problem, and various models have been proposed, ranging from the basic stiffness reduction method to the more sophisticated model involving formulation based on the additional flexibility due to a crack. However, in the damage identification or finite element model updating applications, it is still common practice to employ a simple stiffness reduction factor to represent a crack in the identification process, whereas the use of a more realistic crack model is rather limited. In this paper, the issues with the simple stiffness reduction method, particularly concerning thick beams, are highlighted along with a review of several other crack models. A robust finite element model updating procedure is then presented for the detection of cracks in beams. The description of the crack parameters is based on the cracked beam flexibility formulated by means of the fracture mechanics, and it takes into consideration of shear deformation and coupling between translational and longitudinal vibrations, and thus is particularly suitable for thick beams. The identification procedure employs a global searching technique using Genetic Algorithms, and there is no restriction on the location, severity and the number of cracks to be identified. The procedure is verified to yield satisfactory identification for practically any configurations of cracks in a beam.

  5. Spiral Bevel Pinion Crack Detection in a Helicopter Gearbox

    NASA Technical Reports Server (NTRS)

    Decker, Harry J.; Lewicki, David G.

    2003-01-01

    The vibration resulting from a cracked spiral bevel pinion was recorded and analyzed using existing Health and Usage Monitoring System (HUMS) techniques. A tooth on the input pinion to a Bell OH-58 main rotor gearbox was notched and run for an extended period at severe over-torque condition to facilitate a tooth fracture. Thirteen vibration-based diagnostic metrics were calculated throughout the run. After 101.41 hours of run time, some of the metrics indicated damage. At that point a visual inspection did not reveal any damage. The pinion was then run for another 12 minutes until a proximity probe indicated that a tooth had fractured. This paper discusses the damage detection effectiveness of the different metrics and a comparison of effects of the different accelerometer locations.

  6. Elastic, Plastic, Cracking Aspects of the Hardness of Materials

    NASA Astrophysics Data System (ADS)

    Armstrong, R. W.; Elban, W. L.; Walley, S. M.

    2013-03-01

    The hardness properties of materials are tracked from early history until the present time. Emphasis is placed on the hardness test being a useful probe for determining the local elastic, plastic and cracking properties of single crystal, polycrystalline, polyphase or amorphous materials. Beginning from connection made between individual hardness pressure measurements and the conventional stress-strain properties of polycrystalline materials, the newer consideration is described of directly specifying a hardness-type stress-strain relationship based on a continuous loading curve, particularly, as obtained with a spherical indenter. Such effort has received impetus from order-of-magnitude improvements in load and displacement measuring capabilities that are demonstrated for nanoindentation testing. Details of metrology assessments involved in various types of hardness tests are reviewed. A compilation of measurements is presented for the separate aspects of Hertzian elastic, dislocation-mechanics-based plasticity and indentation-fracture-mechanics-based cracking behaviors of materials, including elastic and plastic deformation rate effects. A number of test applications are reviewed, most notably involving the hardness of thin film materials and coatings.

  7. An unsupervised learning algorithm for fatigue crack detection in waveguides

    NASA Astrophysics Data System (ADS)

    Rizzo, Piervincenzo; Cammarata, Marcello; Dutta, Debaditya; Sohn, Hoon; Harries, Kent

    2009-02-01

    Ultrasonic guided waves (UGWs) are a useful tool in structural health monitoring (SHM) applications that can benefit from built-in transduction, moderately large inspection ranges, and high sensitivity to small flaws. This paper describes an SHM method based on UGWs and outlier analysis devoted to the detection and quantification of fatigue cracks in structural waveguides. The method combines the advantages of UGWs with the outcomes of the discrete wavelet transform (DWT) to extract defect-sensitive features aimed at performing a multivariate diagnosis of damage. In particular, the DWT is exploited to generate a set of relevant wavelet coefficients to construct a uni-dimensional or multi-dimensional damage index vector. The vector is fed to an outlier analysis to detect anomalous structural states. The general framework presented in this paper is applied to the detection of fatigue cracks in a steel beam. The probing hardware consists of a National Instruments PXI platform that controls the generation and detection of the ultrasonic signals by means of piezoelectric transducers made of lead zirconate titanate. The effectiveness of the proposed approach to diagnose the presence of defects as small as a few per cent of the waveguide cross-sectional area is demonstrated.

  8. Crack growth monitoring at CFRP bond lines

    NASA Astrophysics Data System (ADS)

    Rahammer, M.; Adebahr, W.; Sachse, R.; Gröninger, S.; Kreutzbruck, M.

    2016-02-01

    With the growing need for lightweight technologies in aerospace and automotive industries, fibre-reinforced plastics, especially carbon-fibre (CFRP), are used with a continuously increasing annual growth rate. A promising joining technique for composites is adhesive bonding. While rivet holes destroy the fibres and cause stress concentration, adhesive bond lines distribute the load evenly. Today bonding is only used in secondary structures due to a lack of knowledge with regard to long-term predictability. In all industries, numerical simulation plays a critical part in the development process of new materials and structures, while it plays a vital role when it comes to CFRP adhesive bondings conducing the predictability of life time and damage tolerance. The critical issue with adhesive bondings is crack growth. In a dynamic tensile stress testing machine we dynamically load bonded CFRP coupon specimen and measure the growth rate of an artificially started crack in order to feed the models with the results. We also investigate the effect of mechanical crack stopping features. For observation of the bond line, we apply two non-contact NDT techniques: Air-coupled ultrasound in slanted transmission mode and active lockin-thermography evaluated at load frequencies. Both methods give promising results for detecting the current crack front location. While the ultrasonic technique provides a slightly higher accuracy, thermography has the advantage of true online monitoring, because the measurements are made while the cyclic load is being applied. The NDT methods are compared to visual inspection of the crack front at the specimen flanks and show high congruence. Furthermore, the effect of crack stopping features within the specimen on the crack growth is investigated. The results show, that not all crack fronts are perfectly horizontal, but all of them eventually come to a halt in the crack stopping feature vicinity.

  9. Slow crack propagation in composite restorative materials.

    PubMed

    Montes-G, G M; Draughn, R A

    1987-05-01

    The double-torsion test technique was used to study slow crack propagation in a set of dental composite resins including two glass-filled and two microfilled materials. The microstructure within each pair was the same but one of the resins was selfcured and the other photocured. The fracture behavior was dependent on the filler concentration and the presence of absorbed water. Wet materials fractured by slow crack growth in the range of crack velocity studied (10(-7) to 10(-3) m/s), and the microfilled composites, which contain a lower concentration of inorganic filler, had lower stress intensity factors (K1c) than the glass-filled composites tested. Dry specimens of the microfilled materials and the selfcured, glass-filled composite also showed unstable, stick-slip fracture behavior indicative of a crack blunting mechanism which leads to an elevation of the stress intensity factor for crack initiation over K1c for stable crack growth. The plasticizing effect of water increased the viscoelastic response of the materials measured by the slope of curves of slow crack growth. Analysis of fracture surfaces showed that cracks propagated at low velocities (10(-7) to 10(-5) m/s) by the apparent failure of the filler/matrix interfacial bond, and absorbed water affected the strength or fracture resistance of the interface. At high crack velocities the properties of the composite depend on the properties of the polymeric matrix, the filler, and the filler volume fraction, but at low velocities the interface is the controlling factor in the durability of these composites exposed to an aqueous environment.

  10. Hydrodynamic ultrasonic probe

    DOEpatents

    Day, Robert A.; Conti, Armond E.

    1980-01-01

    An improved probe for in-service ultrasonic inspection of long lengths of a workpiece, such as small diameter tubing from the interior. The improved probe utilizes a conventional transducer or transducers configured to inspect the tubing for flaws and/or wall thickness variations. The probe utilizes a hydraulic technique, in place of the conventional mechanical guides or bushings, which allows the probe to move rectilinearly or rotationally while preventing cocking thereof in the tube and provides damping vibration of the probe. The probe thus has lower friction and higher inspection speed than presently known probes.

  11. Probe tip heating assembly

    SciTech Connect

    Schmitz, Roger William; Oh, Yunje

    2016-10-25

    A heating assembly configured for use in mechanical testing at a scale of microns or less. The heating assembly includes a probe tip assembly configured for coupling with a transducer of the mechanical testing system. The probe tip assembly includes a probe tip heater system having a heating element, a probe tip coupled with the probe tip heater system, and a heater socket assembly. The heater socket assembly, in one example, includes a yoke and a heater interface that form a socket within the heater socket assembly. The probe tip heater system, coupled with the probe tip, is slidably received and clamped within the socket.

  12. 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.

  13. MECHANICS OF CRACK BRIDGING UNDER DYNAMIC LOADS

    SciTech Connect

    N. SRIDHAR; ET AL

    2001-02-01

    A bridging law for fiber reinforced composites under dynamic crack propagation conditions has been derived. Inertial effects in the mechanism of fiber pullout during dynamic propagation of a bridged crack are critically examined for the first time. By reposing simple shear lag models of pullout as problems of dynamic wave propagation, the effect of the frictional coupling between the fibers and the matrix is accounted for in a fairly straightforward way. The solutions yield the time-dependent relationship between the crack opening displacement and the bridging traction. Engineering criteria and the role of material and geometrical parameters for significant inertial effects are identified.

  14. Fatigue-Crack-Growth Computer Program

    NASA Technical Reports Server (NTRS)

    Forman, Royce G.; Shivakumar, V.; Newman, James C., Jr.

    1991-01-01

    Fatigue Crack Growth (NASA/FLAGRO) computer program developed as aid in predicting growth of preexisting flaws and cracks in structural components of space systems. Is enhanced version of FLAGRO4 and incorporates state-of-the-art improvements in both fracture mechanics and computer technology. Provides fracture-mechanics analyst with computerized method of evaluating "safe-crack-growth-life" capabilities of structural components. Also used to evaluate tolerance to damage of structure of given design. Designed modular to facilitate revisions and operation on minicomputers. Written in FORTRAN 77.

  15. Characterization of Surface Cracks Using Rayleigh Waves

    SciTech Connect

    Masserey, B.; Mazza, E.

    2005-04-09

    The characterization of surface cracks in steel plates using surface acoustic waves is investigated. In the experiments Rayleigh wave is generated by a standard wedge technique and the surface displacement is measured pointwise by means of a heterodyne laser interferometer. The presence of a crack in the acoustic field leads to an amplitude increase due to the scattering of the surface wave at the defect. The time-of-flight method is extended to crack depth smaller than the wavelength by correlating the time delay of the transmitted wave with the defect depth. The method is shown to provide good results for defect depths down to 0.2 mm.

  16. 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.

  17. Crack initiation around prestressed rock bolts

    NASA Astrophysics Data System (ADS)

    Wijk, G.

    1982-07-01

    The stress fields in the rock in the immediate vicinities of the ends of prestressed rock bolts are considered. In particular, the tensile stresses that are likely to initiate cracks are studies. A fracture mechanics analysis shows that if cracks are initiated they will normally not be extended more than a few bore hole diameters and cause negligable reduction of the tensile force in the rock bolts. It is suggested that the initiated cracks can be considerably extended by blasting activities in the neighborhood and accordingly cause loss of bolt tension. If so retensioning of the rock bolts is quite meaningless.

  18. Prediction of Crack Growth in Aqueous Environments.

    DTIC Science & Technology

    1986-07-01

    Impedance for the Propagation of a Crack Through HY80 Steel in 3.5Z NaCl Solution at 25*C Under Sinusoidal Loading Condi t ions...THE PROPAGATION OF A CRACK THROUGH HY80 STEEL IN 3.5% NaCI SOLUTION AT 25°C UNDER SINUSOIDAL LOADING CONDITIONS 49 and the properties of greatest...VELOCITY AS A FUNCTION OF TIME FOR A CRACK GROWN AT CONSTANT CURRENT IN HY80 STEEL Initial conditions CI in Table 5. 66 400 UJ x v> l/> L. 0

  19. Closing of cracks under impact loading

    SciTech Connect

    Finkel', V.M.; Fomin, I.M.; Shegai, V.V.

    1985-12-01

    The healing of cracks has been studied in crystalline materials such as diamond, sodium chloride, tungsten, molybdenum and quartz, and the possibility has also been studied of restoring material continuity to sodium chloride and lithium fluoride single crystals under conditions of relatively prolonged compression over a time range of from one to tens of seconds. Potential restoration of interatomic bonds between surfaces of failed material (reanimation) precedes collapse of a crack as a process of approach of its edges before mechanical contact. The goal of this work is to study crack closing with short-term impact.

  20. Crack tip mechanics in periodically layered composites

    NASA Astrophysics Data System (ADS)

    Jha, Mahendra

    In this work, the plane strain problems of periodically layered composites consisting of alternate matrix and fiber layers weakened by a crack perpendicular or parallel to the interfaces are considered. Elasto-static analytical solutions for the crack-tip micromechanical fields under mode-I, mode-II and mixed-mode loading are developed using principles of asymptotic homogenization and the method of complex elastic potentials. In a separate formulation, the mode-I crack-tip fields for a crack normal to the interfaces are also obtained using the method of non-standard analysis. The analytical model predictions are compared with the numerical solutions obtained through refined near-tip micro-macro hybrid finite element analyses. Extensive numerical studies addressing the crack-tip location effects on the near-tip fields are presented. In all cases considered, the zero-order micro-stresses obtained from the analytical solutions are found to exhibit an overall rsp{{-}{1/2}} singularity. The numerical studies have revealed that the near-tip micro-stress field in cracked layered systems is structured in three distinct zones. In systems with isotropic layers, the stress field in the matrix phase surrounding the immediate vicinity of crack-tip is found to exhibit a universal isotropic field behavior dominated by a matrix material dependent stress intensity factor. In the far-field region, the admissible discontinuous micro-stress field is observed to depend on the microstructural heterogeneity and the global anisotropy of the system. The transition from the universal isotropic to the far field behavior takes place within a relatively small region. Crack tip amplification or shielding are shown to take place for a crack approaching a bimaterial interface. The mode-I near-tip fields for a crack normal to the interface in a laminate consisting of alternate brittle and ductile layers are also studied numerically. The Gurson constitutive model that accounts for the ductile

  1. Analysis of Eddy Current Capabilities for the Detection of Outer Diameter Stress Corrosion Cracking in Small Bore Metallic Structures

    NASA Technical Reports Server (NTRS)

    Wincheski, Buzz; Williams, Phillip; Simpson, John

    2007-01-01

    The use of eddy current techniques for the detection of outer diameter damage in tubing and many complex aerospace structures often requires the use of an inner diameter probe due to a lack of access to the outside of the part. In small bore structures the probe size and orientation are constrained by the inner diameter of the part, complicating the optimization of the inspection technique. Detection of flaws through a significant remaining wall thickness becomes limited not only by the standard depth of penetration, but also geometrical aspects of the probe. Recently, an orthogonal eddy current probe was developed for detection of such flaws in Space Shuttle Primary Reaction Control System (PRCS) Thrusters. In this case, the detection of deeply buried stress corrosion cracking by an inner diameter eddy current probe was sought. Probe optimization was performed based upon the limiting spatial dimensions, flaw orientation, and required detection sensitivity. Analysis of the probe/flaw interaction was performed through the use of finite and boundary element modeling techniques. Experimental data for the flaw detection capabilities, including a probability of detection study, will be presented along with the simulation data. The results of this work have led to the successful deployment of an inspection system for the detection of stress corrosion cracking in Space Shuttle Primary Reaction Control System (PRCS) Thrusters.

  2. Interfacial Crack Arrest in Sandwich Panels with Embedded Crack Stoppers Subjected to Fatigue Loading

    NASA Astrophysics Data System (ADS)

    Martakos, G.; Andreasen, J. H.; Berggreen, C.; Thomsen, O. T.

    2017-02-01

    A novel crack arresting device has been implemented in sandwich panels and tested using a special rig to apply out-of-plane loading on the sandwich panel face-sheets. Fatigue crack propagation was induced in the face-core interface of the sandwich panels which met the crack arrester. The effect of the embedded crack arresters was evaluated in terms of the achieved enhancement of the damage tolerance of the tested sandwich panels. A finite element (FE) model of the experimental setup was used for predicting propagation rates and direction of the crack growth. The FE simulation was based on the adoption of linear fracture mechanics and a fatigue propagation law (i.e. Paris law) to predict the residual fatigue life-time and behaviour of the test specimens. Finally, a comparison between the experimental results and the numerical simulations was made to validate the numerical predictions as well as the overall performance of the crack arresters.

  3. Crack-face displacements for embedded elliptic and semi-elliptical surface cracks

    NASA Technical Reports Server (NTRS)

    Raju, I. S.

    1989-01-01

    Analytical expressions for the crack-face displacements of an embedded elliptic crack in infinite solid subjected to arbitrary tractions are obtained. The tractions on the crack faces are assumed to be expressed in a polynomial form. These displacements expressions complete the exact solution of Vijayakumar and Atluri, and Nishioki and Atluri. For the special case of an embedded crack in an infinite solid subjected to uniform pressure loading, the present displacements agree with those by Green and Sneddon. The displacement equations derived were used with the finite-element alternating method (FEAM) for the analysis of a semi-elliptic surface crack in a finite solid subjected to remote tensile loading. The maximum opening displacements obtained with FEAM are compared to those with the finite-element method with singularity elements. The maximum crack opening displacements by the two methods showed good agreement.

  4. The crack problem in bonded nonhomogeneous materials

    NASA Technical Reports Server (NTRS)

    Erdogan, F.; Joseph, P. F.; Kaya, A. C.

    1991-01-01

    The plane elasticity problem for two bonded half planes containing a crack perpendicular to the interface was considered. The effect of very steep variations in the material properties near the diffusion plane on the singular behavior of the stresses and stress intensity factors were studied. The two materials were thus, assumed to have the shear moduli mu(o) and mu(o) exp (Beta x), x=0 being the diffusion plane. Of particular interest was the examination of the nature of stress singularity near a crack tip termination at the interface where the shear modulus has a discontinuous derivative. The results show that, unlike the crack problem in piecewise homogeneous materials for which the singularity is of the form r/alpha, 0 less than alpha less than 1, in this problem the stresses have a standard square-root singularity regardless of the location of the crack tip. The nonhomogeneity constant Beta has, however, considerable influence on the stress intensity factors.

  5. The Effect of Water on Crack Interaction

    NASA Astrophysics Data System (ADS)

    Gaede, O.; Regenauer-Lieb, K.

    2009-04-01

    While the mechanical coupling between pore fluid and solid phase is relatively well understood, quantitative studies dealing with chemical-mechanical weakening in geological materials are rare. Many classical poroelastic problems can be addressed with the simple law of effective stress. Experimental studies show that the presence of a chemically active fluid can have effects that exceed the predictions of the law of effective stress. These chemical fluid-rock interactions alter the mechanical properties of the solid phase. Especially chemical-mechanical weakening has important ramifications for many areas of applied geosciences ranging from nuclear waste disposal over reservoir enhancement to fault stability. In this study, we model chemically induced changes of the size of the process zone around a crack tip. The knowledge of the process zone size is used to extend existing effective medium approximations of cracked solids. The stress distribution around a crack leads to a chemical potential gradient. This gradient will be a driver for mass diffusion through the solid phase. As an example, mass diffusion is towards the crack tip for a mode I crack. In this case a chemical reaction, that weakens the solid phase, will increase the size of the process zone around the crack tip. We apply our model to the prominent hydrolytic weakening effect observed in the quartz-water system (Griggs and Blacic, 1965). Hydrolytic weakening is generally attributed to water hydrolyzing the strong Si-O bonds of the quartz crystal. The hydrolysis replaces a Si-O-Si bridge with a relatively weak hydrogen bridge between two silanol groups. This enhances dislocation mobility and hence the yield stress is reduced. The plastic process zone around a crack tip is therefore larger in a wet crystal than in a dry crystal. We calculate the size of the process zone by solving this coupled mechanical-chemical problem with the Finite Element code ABAQUS. We consider single crack, collinear crack and

  6. Cracked shells under skew-symmetric loading

    NASA Technical Reports Server (NTRS)

    Lelale, F.

    1982-01-01

    A shell containing a through crack in one of the principal planes of curvature and under general skew-symmetric loading is considered. By employing a Reissner type shell theory which takes into account the effect of transverse shear strains, all boundary conditions on the crack surfaces are satisfied separately. Consequently, unlike those obtained from the classical shell theory, the angular distributions of the stress components around the crack tips are shown to be identical to the distributions obtained from the plane and antiplane elasticity solutions. Extensive results are given for axially and circumferentially cracked cylindrical shells, spherical shells, and toroidal shells under uniform inplane shearing, out of plane shearing, and torsion. The effect of orthotropy on the results is also studied.

  7. The interaction between inclusions and cracks

    NASA Technical Reports Server (NTRS)

    Erdogan, F.

    1973-01-01

    Some current fracture theories are reviewed and a group of mechanics problems of practical interest relating to the elastic interaction between cracks and inclusions are identified and results summarized.

  8. Struggling with Fitzgerald's "Crack-Up" Essays.

    ERIC Educational Resources Information Center

    Fulcher, James

    1998-01-01

    Ponders F. Scott Fitzgerald's essays about his "crack-up" and relates them to the many complex aspects of the struggles of a teacher using post-structural literary theory and teaching two-year college students. (SR)

  9. Crack arrest in thick section steel plate

    NASA Astrophysics Data System (ADS)

    Smith, E.

    1983-03-01

    Crack arrest in thick section steel plate is considered in relation to the conditions for crack arrest in a nuclear reactor pressure vessel, when this is subjected to thermal stresses resulting from a hypothetical loss of coolant accident. The results of a theoretical analysis, based primarily on recent developments in quasi-static crack propagation theory, provide further support for the view that the arrest toughness KIa is essentially a material property. However, since the theoretical results also suggest that KIa is reduced by neutron irradiation, and because there is, as yet, no conclusive experimental data on the effect of neutron irradiation on KIa, it is proposed that with highly irradiated steel, instead of using a KIa crack arrest criterion, it is better to use a more conservative criterion, based on the concept that arrest occurs within the vessel at a position where the temperature exceeds that temperature above which the cleavage fracture mode is unable to operate.

  10. Crack instabilities of a heated glass strip

    NASA Astrophysics Data System (ADS)

    Adda-Bedia, Mokhtar; Pomeau, Yves

    1995-10-01

    Recently, Yuse and Sano [Nature (London) 362, 329 (1993)] have observed that a crack traveling in a glass strip submitted to a nonuniform thermal diffusion field undergoes numerous instabilities. We study two cases of quasistatic crack propagation. The crack extension condition in straight propagation is determined. An asymptotic analysis of the elastic free energy is introduced and scaling laws are derived. A linear stability analysis of the straight propagation is performed, based on the assumption that the crack tip propagation deviates from the centered straight one as soon as it is submitted to a ``physical'' singular shear stress. It is shown that a straight propagation can become unstable after which a wavy instability appears. The condition for instability as well as the selected wavelength is calculated quantitatively. The results are compared with experiments and the agreement is favorable.

  11. Survey updates amine stress corrosion cracking data

    SciTech Connect

    Not Available

    1992-01-13

    The final report by National Association of Corrosion Engineers (NACE) task group T-8-14 has been published, revising and expanding the information on stress information on stress corrosion cracking of carbon steel in diethanolamine and diisopropanolamine service. A major conclusion of the survey was that cracking frequency was more prevalent in monoethanolamine (MEA) than in other amines. This paper reports that further examination of the DEA data indicated that some units were previously in MEA service and the reported cracks were actually associated with that period. A detailed follow-up review of the DEA data also revealed that some cases were caused by processes other than amine cracking. In many cases, further inspection or testing had been done after the original survey was submitted.

  12. Three-dimensional measurements of fatigue crack closure

    NASA Technical Reports Server (NTRS)

    Ray, S. K.; Grandt, A. F., Jr.

    1984-01-01

    Fatigue crack growth and retardation experiments conducted in polycarbonate test specimen are described. The transparent test material allows optical interferometry measurements of the fatigue crack opening (and closing) profiles. Crack surface displacements are obtained through the specimen thickness and three dimensional aspects of fatigue crack closure are discussed.

  13. 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.

  14. Crack-mouth displacements for semielliptical surface cracks subjected to remote tension and bending loads

    NASA Technical Reports Server (NTRS)

    Raju, Ivatury S.; Newman, James C., Jr.; Atluri, Satya N.

    1992-01-01

    The exact analytical solution for an embedded elliptical crack in an infinite body subjected to arbitrary loading was used in conjunction with the finite element alternating method to obtain crack-mouth-opening displacements (CMOD) for surface cracks in finite plates subjected to remote tension. Identical surface-crack configurations were also analyzed with the finite element method using 20-noded element for plates subjected to both remote tension and bending. The CMODs from these two methods generally agreed within a few percent of each other. Comparisons made with experimental results obtained from surface cracks in welded aluminum alloy specimens subjected to tension also showed good agreement. Empirical equations were developed for CMOD for a wide range of surface-crack shapes and sizes subjected to tension and bending loads. These equations were obtained by modifying the Green-Sneddon exact solution for an elliptical crack in an infinite body to account for finite boundary effects. These equations should be useful in monitoring surface-crack growth in tests and in developing complete crack-face-displacement equations for use in three-dimensional weight-function methods.

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

    NASA Technical Reports Server (NTRS)

    Ballarini, Roberto; Plesha, Michael E.

    1987-01-01

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

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

    NASA Technical Reports Server (NTRS)

    Ballarini, Roberto; Plesha, Michael E.

    1987-01-01

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

  17. Measurement and analysis of critical crack tip processes associated with variable amplitude fatigue crack growth

    NASA Technical Reports Server (NTRS)

    Hudak, S. J., Jr.; Davidson, D. L.; Chan, K. S.

    1983-01-01

    Crack growth retardation following overloads can result in overly conservative life predictions in structures subjected to variable amplitude fatigue loading when linear damage accumulation procedures are employed. Crack closure is believed to control the crack growth retardation, although the specific closure mechanism is debatable. Information on the relative contributions to crack closure from: (1) plasticity left in the wake of the advancing crack and (2) crack tip residual stresses is provided. The delay period and corresponding crack growth rate transients following overloads are systematically measured as a function of load ratio (R) and overload magnitude. These responses are correlated in terms of the local 'driving force' for crack growth as measured by crack tip opening loads and delta K sub eff. The latter measurements are obtained using a scanning electron microscope equipped with a cyclic loading stage; measurements are quantified using a relatively new stereoimaging technique. Combining experimental results with analytical predictions suggests that both plastic wake and residual stress mechanism are operative, the latter becoming predominate as R increases.

  18. The algorithm of crack and crack tip coordinates detection in optical images during fatigue test

    NASA Astrophysics Data System (ADS)

    Panin, S. V.; Chemezov, V. O.; Lyubutin, P. S.; Titkov, V. V.

    2017-02-01

    An algorithm of crack detection during fatigue testing of materials, designed to automate the process of cyclic loading and tracking the crack tip, is proposed and tested. The ultimate goal of the study is aimed at controlling the displacements of the optical system with regard to the specimen under fatigue loading to ensure observation of the ‘area of interest’. It is shown that the image region that contains the crack may be detected and positioned with an average error of 1.93%. In terms of determining the crack tip position, the algorithm provides the accuracy of its localization with the average error value of 56 pixels.

  19. Composite Pressure Vessel Including Crack Arresting Barrier

    NASA Technical Reports Server (NTRS)

    DeLay, Thomas K. (Inventor)

    2013-01-01

    A pressure vessel includes a ported fitting having an annular flange formed on an end thereof and a tank that envelopes the annular flange. A crack arresting barrier is bonded to and forming a lining of the tank within the outer surface thereof. The crack arresting barrier includes a cured resin having a post-curing ductility rating of at least approximately 60% through the cured resin, and further includes randomly-oriented fibers positioned in and throughout the cured resin.

  20. Fatigue crack growth in aluminum laminate composites

    SciTech Connect

    Hoffman, P.B.; Carpenter, R.D.; Gibeling, J.C.

    1996-12-31

    Fatigue crack growth has been measured in a laminated metal composite (LMC) consisting of alternating layers of AA6090/SiC/25p metal matrix composite (MMC) and AA5182 alloy. This material was tested in both as-pressed (F temper) and aged (T6 temper) conditions. Corresponding crack growth measurements were made in self-laminates of both the MMC and AA5182 materials to examine the role of the interfaces.

  1. Molecular dynamics simulation of propagating cracks

    NASA Technical Reports Server (NTRS)

    Mullins, M.

    1982-01-01

    Steady state crack propagation is investigated numerically using a model consisting of 236 free atoms in two (010) planes of bcc alpha iron. The continuum region is modeled using the finite element method with 175 nodes and 288 elements. The model shows clear (010) plane fracture to the edge of the discrete region at moderate loads. Analysis of the results obtained indicates that models of this type can provide realistic simulation of steady state crack propagation.

  2. Atomistic observation of a crack tip approaching coherent twin boundaries.

    PubMed

    Liu, L; Wang, J; Gong, S K; Mao, S X

    2014-03-18

    Coherent twin boundaries (CTBs) in nano-twinned materials could improve crack resistance. However, the role of the CTBs during crack penetration has never been explored at atomic scale. Our in situ observation on nano-twinned Ag under a high resolution transmission electron microscope (HRTEM) reveals the dynamic processes of a crack penetration across the CTBs, which involve alternated crack tip blunting, crack deflection, twinning/detwinning and slip transmission across the CTBs. The alternated blunting processes are related to the emission of different types of dislocations at the crack tip and vary with the distance of the crack tip from the CTBs.

  3. Crack growth direction in unidirectional off-axis graphite epoxy

    NASA Technical Reports Server (NTRS)

    Herakovich, C. T.; Gregory, M. A.; Beuth, J. L., Jr.

    1984-01-01

    An anisotropic elasticity crack tip stress analysis is implemented using three crack extension direction criteria (the normal stress ratio, the tensor polynominal and the strain energy density) to predict the direction of crack extension in unidirectional off axis graphite-epoxy. The theoretical predictions of crack extension direction are then compared with experimental results for 15 deg off axis tensile coupons with center cracks. Specimens of various aspect ratios and crack orientations are analyzed. It is shown that only the normal stress ratio criterion predicts the correct direction of crack growth.

  4. Low-energy EDX--a novel approach to study stress corrosion cracking in SUS304 stainless steel via scanning electron microscopy.

    PubMed

    Meisnar, Martina; Lozano-Perez, Sergio; Moody, Michael; Holland, James

    2014-11-01

    Intergranular stress corrosion cracking (IGSCC) in type SUS304 stainless steels, tested under pressurized water reactor (PWR) primary water conditions, has been characterized with unprecedented spatial resolution using scanning electron microscopy (SEM) and novel low-energy (∼3 kV) energy dispersive X-ray spectroscopy (EDX). An advancement of the large area silicon drift detector (SDD) has enhanced its sensitivity for X-rays in the low-energy part of the atomic spectrum. Therefore, it was possible to operate the SEM at lower accelerating voltages in order to reduce the interaction volume of the beam with the material and achieve higher spatial resolution and better signal-to-noise ratio. In addition to studying the oxide chemistry at the surface of intergranular stress corrosion cracks, the technique has proven capable of resolving Ni enrichment ahead of some crack tips. Active cracks could be distinguished from inactive ones due to the presence of oxides in the open crack and Ni-rich regions ahead of the crack tip. Furthermore, it has been established that SCC features can be better resolved with low-energy (3 kV) than high-energy (12 kV) EDX. The low effort in sample preparation, execution and data analysis makes SEM the ideal tool for initial characterization and selection of the most important SCC features such as dominant cracks and interesting crack tips, later to be studied by transmission electron microscopy (TEM) and atom probe tomography (APT).

  5. Electromagnetic pulsed thermography for natural cracks inspection.

    PubMed

    Gao, Yunlai; Tian, Gui Yun; Wang, Ping; Wang, Haitao; Gao, Bin; Woo, Wai Lok; Li, Kongjing

    2017-02-07

    Emerging integrated sensing and monitoring of material degradation and cracks are increasingly required for characterizing the structural integrity and safety of infrastructure. However, most conventional nondestructive evaluation (NDE) methods are based on single modality sensing which is not adequate to evaluate structural integrity and natural cracks. This paper proposed electromagnetic pulsed thermography for fast and comprehensive defect characterization. It hybrids multiple physical phenomena i.e. magnetic flux leakage, induced eddy current and induction heating linking to physics as well as signal processing algorithms to provide abundant information of material properties and defects. New features are proposed using 1st derivation that reflects multiphysics spatial and temporal behaviors to enhance the detection of cracks with different orientations. Promising results that robust to lift-off changes and invariant features for artificial and natural cracks detection have been demonstrated that the proposed method significantly improves defect detectability. It opens up multiphysics sensing and integrated NDE with potential impact for natural understanding and better quantitative evaluation of natural cracks including stress corrosion crack (SCC) and rolling contact fatigue (RCF).

  6. Electromagnetic pulsed thermography for natural cracks inspection

    PubMed Central

    Gao, Yunlai; Tian, Gui Yun; Wang, Ping; Wang, Haitao; Gao, Bin; Woo, Wai Lok; Li, Kongjing

    2017-01-01

    Emerging integrated sensing and monitoring of material degradation and cracks are increasingly required for characterizing the structural integrity and safety of infrastructure. However, most conventional nondestructive evaluation (NDE) methods are based on single modality sensing which is not adequate to evaluate structural integrity and natural cracks. This paper proposed electromagnetic pulsed thermography for fast and comprehensive defect characterization. It hybrids multiple physical phenomena i.e. magnetic flux leakage, induced eddy current and induction heating linking to physics as well as signal processing algorithms to provide abundant information of material properties and defects. New features are proposed using 1st derivation that reflects multiphysics spatial and temporal behaviors to enhance the detection of cracks with different orientations. Promising results that robust to lift-off changes and invariant features for artificial and natural cracks detection have been demonstrated that the proposed method significantly improves defect detectability. It opens up multiphysics sensing and integrated NDE with potential impact for natural understanding and better quantitative evaluation of natural cracks including stress corrosion crack (SCC) and rolling contact fatigue (RCF). PMID:28169361

  7. 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.

  8. Creep Behavior and Durability of Cracked CMC

    NASA Technical Reports Server (NTRS)

    Bhatt, R. T.; Fox, Dennis; Smith, Craig

    2015-01-01

    To understand failure mechanisms and durability of cracked Ceramic matrix composites (CMCs), Melt Infiltration (MI) SiCSiC composites with Sylramic-iBN fibers and full Chemical vapour infiltration SiCSiC composites with Sylramic-ion bombarded BN (iBN) and Hi-Nicalon -S fibers were pre-cracked between 150 to 200 megapascal and then creep and Sustained Peak Low Cycle Fatigue (SPLCF) tested at 13150 C at stress levels from 35 to 103 megapascal for up to 200 hours under furnace and burner rig conditions. In addition creep testing was also conducted on pre-cracked full Chemical vapour infiltration SiCSiC composites at 14500 C between 35 and 103 megapascal for up to 200 hours under furnace conditions. If the specimens survived the 200 hour durability tests, then they were tensile tested at room temperature to determine their residual tensile properties. The failed specimens were examined by Scanning electron microscope (SEM) to determine the failure modes and mechanisms. The influence of crack healing matrix, fiber types, crack density, testing modes and interface oxidation on durability of cracked Ceramic matrix composites (CMCs) will be discussed.

  9. Electromagnetic pulsed thermography for natural cracks inspection

    NASA Astrophysics Data System (ADS)

    Gao, Yunlai; Tian, Gui Yun; Wang, Ping; Wang, Haitao; Gao, Bin; Woo, Wai Lok; Li, Kongjing

    2017-02-01

    Emerging integrated sensing and monitoring of material degradation and cracks are increasingly required for characterizing the structural integrity and safety of infrastructure. However, most conventional nondestructive evaluation (NDE) methods are based on single modality sensing which is not adequate to evaluate structural integrity and natural cracks. This paper proposed electromagnetic pulsed thermography for fast and comprehensive defect characterization. It hybrids multiple physical phenomena i.e. magnetic flux leakage, induced eddy current and induction heating linking to physics as well as signal processing algorithms to provide abundant information of material properties and defects. New features are proposed using 1st derivation that reflects multiphysics spatial and temporal behaviors to enhance the detection of cracks with different orientations. Promising results that robust to lift-off changes and invariant features for artificial and natural cracks detection have been demonstrated that the proposed method significantly improves defect detectability. It opens up multiphysics sensing and integrated NDE with potential impact for natural understanding and better quantitative evaluation of natural cracks including stress corrosion crack (SCC) and rolling contact fatigue (RCF).

  10. Ultrasonic testing of plates containing edge cracks

    NASA Technical Reports Server (NTRS)

    Williams, J. H., Jr.; Karagulle, H.; Lee, S. S.

    1985-01-01

    The stress wave factor (SWF) signal is utilized for the nondestructive evaluation of plates containing perpendicular edge cracks. The effects of the existence lateral location and depth of the crack on the magnitude spectra of individual reflections in the SWF signal are studied. If the reflections in the SWF signal are not overlapped the short time Fourier analysis is applied. If the reflections are overlapped the short time homomorphic analysis (cepstrum analysis) is applied. Several reflections which have average resonant frequencies approximately at 0.9, 1.3, and 1.7 MHz are analyzed. It is observed that the magnitude ratios evaluated at average resonant frequencies decrease more with increasing d/h if the crack is located between the transducers, where h is plate thickness and d is crack depth. Moreover, for the plates, crack geometries, reflections, and frequencies considered, the average decibel drop depends mainly on the dimensionless parameter d/h and it is approximately -1 dB per 0.07 d/h. Changes in the average resonant frequencies of the magnitude spectra are also observed due to changes in the location of the crack.

  11. Micro-Cracking Detection in Laminated Composites

    NASA Technical Reports Server (NTRS)

    Chu, Tsuchin; Leyte, Alma; DiGregorio, Anthony; Russell, Samuel S.; Walker, James L.; Thom, Robert (Technical Monitor)

    2002-01-01

    Porosity and fatigue cracking are two critical factors that affect the performance and safety of cryogenic fuel tanks and feedlines made from unlined laminated or weaved carbon/epoxy materials. This paper presents the experiments to induce fatigue cracking of laminated composites through thermal cycling as well as the feasibility of using Thermography and Ultrasound Spectroscopy technology (UT) to detect and measure such micro-cracking. Carbon/epoxy laminated composite panels were built and cut into strips. These specimens were partially submerged in liquid nitrogen while subjected to various loads on a test machine. Edges of some specimens were polished and etched to determine the degree of micro-cracking. The rest of specimens were then examined with Thermography and Ultrasound Spectroscopy NDE systems to investigate the feasibility of finding such micro-cracking in the laminated composites. Thermography is utilized to determine changes in thermal diffusivity. The degree of cracking may reduce the apparent thermal diffusivity and therefore change the thermal response on the surface. Thermography testing was conducted on a group of specimens where it is desired to have some correlation between the predetermined stress and the thermography data. Ultrasound Spectroscopy was used to determine peak changes between the pre-stressed and stressed samples. Data from the inspections were analyzed and the results are presented in this paper.

  12. Slow crack growth behaviour of hydroxyapatite ceramics.

    PubMed

    Benaqqa, Chahid; Chevalier, Jerome; Saädaoui, Malika; Fantozzi, Gilbert

    2005-11-01

    Among materials for medical applications, hydroxyapatite is one of the best candidates in orthopedics, since it exhibits a composition similar to the mineral part of bone. Double torsion technique was here performed to investigate slow crack growth behaviour of dense hydroxyapatite materials. Crack rate, V, versus stress intensity factor, K(I), laws were obtained for different environments and processing conditions. Stress assisted corrosion by water molecules in oxide ceramics is generally responsible for slow crack growth. The different propagation stages obtained here could be analyzed in relation to this process. The presence of a threshold defining a safety range of use was also observed. Hydroxyapatite ceramics appear to be very sensitive to slow crack growth, crack propagation occurring even at very low K(I). This can be explained by the fact that they contain hydroxyl groups (HAP: Ca(10)(PO(4))(6)(OH)(2)), favouring water adsorption on the crack surface and thus a strong decrease of surface energy in the presence of water. This study demonstrates that processing conditions must be carefully controlled, specially sintering temperature, which plays a key role on V-K(I) laws. Sintering at 50 degrees C above or below the optimal temperature, for example, may shift the V-K(I) law towards very low stress intensity factors. The influence of ageing is finally discussed.

  13. Dynamic behaviour of a rotating cracked beam

    NASA Astrophysics Data System (ADS)

    Yashar, Ahmed; Ghandchi-Tehrani, Maryam; Ferguson, Neil

    2016-09-01

    This paper presents a new approach to investigate and analyse the vibrational behaviour of cracked rotating cantilever beams, which can for example represent helicopter or wind turbine blades. The analytical Hamiltonian method is used in modelling the rotating beam and two numerical methods, the Rayleigh-Ritz and FEM, are used to study the natural frequencies and the mode shapes of the intact rotating beams. Subsequently, a crack is introduced into the FE model and simulations are performed to identify the modal characteristics for an open cracked rotating beam. The effect of various parameters such as non-dimensional rotating speed, hub ratio and slenderness ratio are investigated for both the intact and the cracked rotating beam, and in both directions of chordwise and flapwise motion. The veering phenomena in the natural frequencies as a function of the rotational speed and the buckling speed are considered with respect to the slenderness ratio. In addition, the mode shapes obtained for the flapwise vibration are compared using the modal assurance criterion (MAC). Finally, a new three dimensional design chart is produced, showing the effect of crack location and depth on the natural frequencies of the rotating beam. This chart will be subsequently important in identifying crack defects in rotating blades.

  14. 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.

  15. Hierarchical Formation of Intrasplat Cracks in Thermal Spray Ceramic Coatings

    NASA Astrophysics Data System (ADS)

    Chen, Lin; Yang, Guan-Jun; Li, Cheng-Xin; Li, Chang-Jiu

    2016-06-01

    Intrasplat cracks, an essential feature of thermally sprayed ceramic coatings, play important roles in determining coating properties. However, final intrasplat crack patterns are always considered to be disordered and irregular, resulting from random cracking during splat cooling, since the detailed formation process of intrasplat cracks has scarcely been considered. In the present study, the primary formation mechanism for intrasplat cracking was explored based on both experimental observations and mechanical analysis. The results show that the intrasplat crack pattern in thermally sprayed ceramic splats presents a hierarchical structure with four sides and six neighbors, indicating that intrasplat crack patterns arise from successive domain divisions due to sequential cracking during splat cooling. The driving forces for intrasplat cracking are discussed, and the experimental data quantitatively agree well with theoretical results. This will provide insight for further coating structure designs and tailoring by tuning of intrasplat cracks.

  16. Fatigue crack layer propagation in silicon-iron

    NASA Technical Reports Server (NTRS)

    Birol, Y.; Welsch, G.; Chudnovsky, A.

    1986-01-01

    Fatigue crack propagation in metal is almost always accompanied by plastic deformation unless conditions strongly favor brittle fracture. The analysis of the plastic zone is crucial to the understanding of crack propagation behavior as it governs the crack growth kinetics. This research was undertaken to study the fatigue crack propagation in a silicon iron alloy. Kinetic and plasticity aspects of fatigue crack propagation in the alloy were obtained, including the characterization of damage evolution.

  17. The Capabilities and Limitation of Remote Visual Methods to Detect Service-Induced Cracks in Reactor Components

    SciTech Connect

    Cumblidge, Stephen E.; Doctor, Steven R.; Anderson, Michael T.

    2006-11-01

    Since 1977, the U.S. Nuclear Regulatory Commission (NRC) Office of Nuclear Regulatory Research has funded a multiyear program at the Pacific Northwest National Laboratory (PNNL) to evaluate the reliability and accuracy of nondestructive evaluation (NDE) techniques employed for inservice inspection (ISI). Recently, the U.S. nuclear industry proposed replacing current volumetric and/or surface examinations of certain components in commercial nuclear power plants, as required by ASME Boiler and Pressure Vessel Code Section XI, with a simpler visual testing (VT) method. The advantages of VT are that these tests generally involve much less radiation exposure and examination times than do volumetric examinations such as ultrasonic testing (UT). However, for industry to justify supplamenting volumetric metods with VT, and analysis of pertinent issues is needed to support the reliability of VT in determining the structural intefrity of reactor components. As piping and pressure vessel compoents in a nuclear power station are generally underwater and in high radiation field, they need to be examined by VT from a distance with radiation-hardened video systems. Remote visual testing has been used by nuclear utilities to find cracks in pressure vessel cladding in pressurized water reactors, for shrouds in boiling water reactors, and to investigate leaks in piping and reactor components. These visual tests are performed using a wide variety of procedures and equipment. The techniques for remote visual testing use submersible closed-circuit video cameras to examine reactor components and welds. PNNL has conducted a parametric study that examines the important variables that affect the effectiveness of a remote visual test. Tested variables include lighting techniques, camera resolution, camera movement, and magnification. PNNL has also conductrd a laboratory test using a commercial visual testing camera system to experimentally determine the ability of the camera system to

  18. FORTRAN program for calculating velocities and streamlines on the hub-shroud mid-channel flow surface of an axial-or mixed-flow turbomachine. 2: Programmer's manual

    NASA Technical Reports Server (NTRS)

    Katsanis, T.; Mcnally, W. D.

    1974-01-01

    A FORTRAN-IV computer program, MERIDL, has been developed that obtains a subsonic or shock-free transonic flow solution on the hub-shroud mid-channel flow surface of a turbomachine. The blade row may be fixed or rotating and may be twisted and leaned. Flow may be axial or mixed, up to 45 deg from axial. Upstream and downstream flow variables can vary from hub to shroud, and provision is made to correct for loss of stagnation pressure. The results include velocities, streamlines, and flow angles on the flow surface and approximate blade surface velocities. Subsonic solutions are obtained by a finite-difference stream-function solution. Transonic solutions are obtained by a velocity-gradient method, using information from a finite-difference stream-function solution at a reduced mass flow.

  19. Revised FORTRAN program for calculating velocities and streamlines on the hub-shroud midchannel stream surface of an axial-, radial-, or mixed-flow turbomachine or annular duct. 1: User's manual

    NASA Technical Reports Server (NTRS)

    Katsanis, T.; Mcnally, W. D.

    1977-01-01

    A FORTRAN 4 computer program was developed that obtains a detailed subsonic or shock-free transonic flow solution on the hub-shroud midchannel stream surface of a turbomachine. The blade row may be fixed or rotating, and the blades may be twisted and leaned. Flow may be axial, mixed, or radial. Upstream and downstream flow variables may vary from hub to shroud, and provision is made to correct for loss of stagnation pressure. The results include velocities, streamlines, and flow angles on the stream surface as well as approximate blade surface velocities. Subsonic solutions are obtained by a finite-difference, stream-function solution. Transonic solutions are obtained by a velocity-gradient method that uses information from a finite-difference, stream-function solution at a reduced mass flow.

  20. Biogenic Cracks in Porous Rock

    NASA Astrophysics Data System (ADS)

    Hemmerle, A.; Hartung, J.; Hallatschek, O.; Goehring, L.; Herminghaus, S.

    2014-12-01

    Microorganisms growing on and inside porous rock may fracture it by various processes. Some of the mechanisms of biofouling and bioweathering are today identified and partially understood but most emphasis is on chemical weathering, while mechanical contributions have been neglected. However, as demonstrated by the perseverance of a seed germinating and cracking up a concrete block, the turgor pressure of living organisms can be very significant. Here, we present results of a systematic study of the effects of the mechanical forces of growing microbial populations on the weathering of porous media. We designed a model porous medium made of glass beads held together by polydimethylsiloxane (PDMS), a curable polymer. The rheological properties of the porous medium, whose shape and size are tunable, can be controlled by the ratio of crosslinker to base used in the PDMS (see Fig. 1). Glass and PDMS being inert to most chemicals, we are able to focus on the mechanical processes of biodeterioration, excluding any chemical weathering. Inspired by recent measurements of the high pressure (~0.5 Mpa) exerted by a growing population of yeasts trapped in a microfluidic device, we show that yeast cells can be cultured homogeneously within porous medium until saturation of the porous space. We investigate then the effects of such an inner pressure on the mechanical properties of the sample. Using the same model system, we study also the complex interplay between biofilms and porous media. We focus in particular on the effects of pore size on the penetration of the biofilm within the porous sample, and on the resulting deformations of the matrix, opening new perspectives into the understanding of life in complex geometry. Figure 1. Left : cell culture growing in a model porous medium. The white spheres represent the grains, bonds are displayed in grey, and microbes in green. Right: microscopy picture of glass beads linked by PDMS bridges, scale bar: 100 μm.

  1. 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

  2. Stochastic modeling of crack initiation and short-crack growth under creep and creep-fatigue conditions

    NASA Technical Reports Server (NTRS)

    Kitamura, Takayuki; Ghosn, Louis J.; Ohtani, Ryuichi

    1989-01-01

    A simplified stochastic model is proposed for crack initiation and short-crack growth under creep and creep-fatigue conditions. Material inhomogeneity provides the random nature of crack initiation and early growth. In the model, the influence of microstructure is introduced by the variability of: (1) damage accumulation along grain boundaries, (2) critical damage required for crack initiation or growth, and (3) the grain-boundary length. The probabilities of crack initiation and growth are derived by using convolution integrals. The model is calibrated and used to predict the crack density and crack-growth rate of short cracks of 304 stainless steel under creep and creep-fatigue conditions. The mean-crack initiation lives are predicted to be within an average deviation of about 10 percent from the experimental results. The predicted cumulative distributions of crack-growth rate follow the experimental data closely. The applicability of the simplified stochastic model is discussed and the future research direction is outlined.

  3. Hot-wire probe

    NASA Technical Reports Server (NTRS)

    Mikulla, V.

    1976-01-01

    High-temperature platinum probe measures turbulence and Reynolds shear stresses in high-temperature compressible flows. Probe does not vibrate at high velocities and does not react like strain gage on warmup.

  4. Crack-tip-opening angle measurements and crack tunneling under stable tearing in thin sheet 2024-T3 aluminum alloy

    NASA Technical Reports Server (NTRS)

    Dawicke, D. S.; Sutton, M. A.

    1993-01-01

    The stable tearing behavior of thin sheets 2024-T3 aluminum alloy was studied for middle crack tension specimens having initial cracks that were: flat cracks (low fatigue stress) and 45 degrees through-thickness slant cracks (high fatigue stress). The critical crack-tip-opening angle (CTOA) values during stable tearing were measured by two independent methods, optical microscopy and digital image correlation. Results from the two methods agreed well. The CTOA measurements and observations of the fracture surfaces showed that the initial stable tearing behavior of low and high fatigue stress tests is significantly different. The cracks in the low fatigue stress tests underwent a transition from flat-to-slant crack growth, during which the CTOA values were high and significant crack tunneling occurred. After crack growth equal to about the thickness, CTOA reached a constant value of 6 deg and after crack growth equal to about twice the thickness, crack tunneling stabilized. The initial high CTOA values, in the low fatigue crack tests, coincided with large three-dimensional crack front shape changes due to a variation in the through-thickness crack tip constraint. The cracks in the high fatigue stress tests reach the same constant CTOA value after crack growth equal to about the thickness, but produced only a slightly higher CTOA value during initial crack growth. For crack growth on the 45 degree slant, the crack front and local field variables are still highly three-dimensional. However, the constant CTOA values and stable crack front shape may allow the process to be approximated with two-dimensional models.

  5. Treatment of singularities in cracked bodies

    NASA Technical Reports Server (NTRS)

    Shivakumar, K. N.; Raju, I. S.

    1990-01-01

    Three-dimensional finite-element analyses of middle-crack tension (M-T) and bend specimens subjected to mode I loadings were performed to study the stress singularity along the crack front. The specimen was modeled using 20-node isoparametric elements. The displacements and stresses from the analysis were used to estimate the power of singularities using a log-log regression analysis along the crack front. The analyses showed that finite-sized cracked bodies have two singular stress fields of the form rho = C sub o (theta, z) r to the -1/2 power + D sub o (theta, phi) R to the lambda rho power. The first term is the cylindrical singularity with the power -1/2 and is dominant over the middle 96 pct (for Poisson's ratio = 0.3) of the crack front and becomes nearly zero at the free surface. The second singularity is a vertex singularity with the vertex point located at the intersection of the crack front and the free surface. The second term is dominant at the free surface and becomes nearly zero away from the boundary layer. The thickness of the boundary layer depends on Poisson's ratio of the material and is independent of the specimen type. The thickness of the boundary layer varied from 0 pct to about 5 pct of the total specimen thickness as Poisson's ratio varied from 0.0 to 0.45. Because there are two singular stress fields near the free surface, the strain energy release rate (G) is an appropriate parameter to measure the severity of the crack.

  6. TRANSPORT THROUGH CRACKED CONCRETE: LITERATURE REVIEW

    SciTech Connect

    Langton, C.

    2012-05-11

    Concrete containment structures and cement-based fills and waste forms are used at the Savannah River Site to enhance the performance of shallow land disposal systems designed for containment of low-level radioactive waste. Understanding and measuring transport through cracked concrete is important for describing the initial condition of radioactive waste containment structures at the Savannah River Site (SRS) and for predicting performance of these structures over time. This report transmits the results of a literature review on transport through cracked concrete which was performed by Professor Jason Weiss, Purdue University per SRR0000678 (RFP-RQ00001029-WY). This review complements the NRC-sponsored literature review and assessment of factors relevant to performance of grouted systems for radioactive waste disposal. This review was performed by The Center for Nuclear Waste Regulatory Analyses, San Antonio, TX, and The University of Aberdeen, Aberdeen Scotland and was focused on tank closure. The objective of the literature review on transport through cracked concrete was to identify information in the open literature which can be applied to SRS transport models for cementitious containment structures, fills, and waste forms. In addition, the literature review was intended to: (1) Provide a framework for describing and classifying cracks in containment structures and cementitious materials used in radioactive waste disposal, (2) Document the state of knowledge and research related to transport through cracks in concrete for various exposure conditions, (3) Provide information or methodology for answering several specific questions related to cracking and transport in concrete, and (4) Provide information that can be used to design experiments on transport through cracked samples and actual structures.

  7. Treatment of singularities in cracked bodies

    NASA Technical Reports Server (NTRS)

    Shivakumar, K. N.; Raju, I. S.

    1989-01-01

    Three-dimensional finite-element analyses of middle-crack tension (M-T) and bend specimens subjected to mode I loadings were performed to study the stress singularity along the crack front. The specimen was modeled using 20-node isoparametric elements. The displacements and stresses from the analysis were used to estimate the power of singularities using a log-log regression analysis along the crack front. The analyses showed that finite-sized cracked bodies have two singular stress fields of the form rho = C sub o (theta, z) r to the -1/2 power + D sub o (theta, phi) R to the lambda rho power. The first term is the cylindrical singularity with the power -1/2 and is dominant over the middle 96 pct (for Poisson's ratio = 0.3) of the crack front and becomes nearly zero at the free surface. The second singularity is a vertex singularity with the vertex point located at the intersection of the crack front and the free surface. The second term is dominant at the free surface and becomes nearly zero away from the the boundary layer. The thickness of the boundary layer depends on Poisson's ratio of the material and is independent of the specimen type. The thickness of the boundary layer varied from 0 pct to about 5 pct of the total specimen thickness as Poisson's ratio varied from 0.0 to 0.45. Because there are two singular stress fields near the free surface, the strain energy release rate (G) is an appropriate parameter to measure the severity of the crack.

  8. Crack propagation modeling using Peridynamic theory

    NASA Astrophysics Data System (ADS)

    Hafezi, M. H.; Alebrahim, R.; Kundu, T.

    2016-04-01

    Crack propagation and branching are modeled using nonlocal peridynamic theory. One major advantage of this nonlocal theory based analysis tool is the unifying approach towards material behavior modeling - irrespective of whether the crack is formed in the material or not. No separate damage law is needed for crack initiation and propagation. This theory overcomes the weaknesses of existing continuum mechanics based numerical tools (e.g. FEM, XFEM etc.) for identifying fracture modes and does not require any simplifying assumptions. Cracks grow autonomously and not necessarily along a prescribed path. However, in some special situations such as in case of ductile fracture, the damage evolution and failure depend on parameters characterizing the local stress state instead of peridynamic damage modeling technique developed for brittle fracture. For brittle fracture modeling the bond is simply broken when the failure criterion is satisfied. This simulation helps us to design more reliable modeling tool for crack propagation and branching in both brittle and ductile materials. Peridynamic analysis has been found to be very demanding computationally, particularly for real-world structures (e.g. vehicles, aircrafts, etc.). It also requires a very expensive visualization process. The goal of this paper is to bring awareness to researchers the impact of this cutting-edge simulation tool for a better understanding of the cracked material response. A computer code has been developed to implement the peridynamic theory based modeling tool for two-dimensional analysis. A good agreement between our predictions and previously published results is observed. Some interesting new results that have not been reported earlier by others are also obtained and presented in this paper. The final objective of this investigation is to increase the mechanics knowledge of self-similar and self-affine cracks.

  9. The effect of a capillary bridge on the crack opening of a penny crack.

    PubMed

    Yang, Fuqian; Zhao, Ya-Pu

    2016-02-07

    Young's relation is based on the equilibrium of horizontal components of surface tensions for a liquid droplet on a "rigid" substrate without addressing the substrate deformation induced by the net vertical component of surface tensions. Upon realizing the importance of wetting in controlling the integrity of flexible structures and electronics, the effect of a capillary bridge or a liquid droplet on the crack opening of a penny crack under the action of a far-field tensile stress is analyzed. Closed-form solutions are derived for both the crack opening and the stress intensity factor, which are functions of the size of the capillary bridge or the droplet, surface tension, and the contact angle. Both the capillary bridge and the droplet can introduce the crack closure. The minimum far-field tensile stresses needed for complete crack opening, i.e. no crack closure, are obtained analytically. The net vertical component of the surface tensions introduces the formation of a surface ridge on the crack face at the edge of the droplet for an open crack. The amplitude of the surface ridge increases with the increase of the net vertical component of the surface tensions and the decrease of the breadth width.

  10. Recent evaluations of crack-opening-area in circumferentially cracked pipes

    SciTech Connect

    Rahman, S.; Brust, F.; Ghadiali, N.; Wilkowski, G.; Miura, N.

    1997-04-01

    Leak-before-break (LBB) analyses for circumferentially cracked pipes are currently being conducted in the nuclear industry to justify elimination of pipe whip restraints and jet shields which are present because of the expected dynamic effects from pipe rupture. The application of the LBB methodology frequently requires calculation of leak rates. The leak rates depend on the crack-opening area of the through-wall crack in the pipe. In addition to LBB analyses which assume a hypothetical flaw size, there is also interest in the integrity of actual leaking cracks corresponding to current leakage detection requirements in NRC Regulatory Guide 1.45, or for assessing temporary repair of Class 2 and 3 pipes that have leaks as are being evaluated in ASME Section XI. The objectives of this study were to review, evaluate, and refine current predictive models for performing crack-opening-area analyses of circumferentially cracked pipes. The results from twenty-five full-scale pipe fracture experiments, conducted in the Degraded Piping Program, the International Piping Integrity Research Group Program, and the Short Cracks in Piping and Piping Welds Program, were used to verify the analytical models. Standard statistical analyses were performed to assess used to verify the analytical models. Standard statistical analyses were performed to assess quantitatively the accuracy of the predictive models. The evaluation also involved finite element analyses for determining the crack-opening profile often needed to perform leak-rate calculations.

  11. Characterization of Fatigue Crack Growth in Bonded Structures. Volume 2. Analysis of Cracked Bonded Structures

    DTIC Science & Technology

    1977-06-01

    in the initially cracked layer, andc a crack in the initially sound layer. 102 REFERENCES 1. Ratwani, M.M. and Wilhem , D.P., "Development and...1953. 10. Higdon, A., Ohlsen, E.H., and Stiles, W.B., "Mechanics of Materials," John Wiley & Sons Inc., New York, 1967. 11. Sih, G.C., "Handbook of

  12. Evolving fracture patterns: columnar joints, mud cracks, and polygonal terrain

    NASA Astrophysics Data System (ADS)

    Goehring, L.

    2012-12-01

    Contraction cracks can form captivating patterns, such as the artistic craquelure sometimes found in pottery glazes, to the cracks in dried mud, or the polygonal networks covering the polar regions of Earth and Mars. Two types are frequently encountered: those with irregular rectilinear patterns, such as that formed by an homogeneous slurry when dried (or cooled) uniformly, and more regular hexagonal patterns, such as those typified by columnar joints. Once cracks start to form in a thin contracting layer, they will sequentially break the layer into smaller and smaller pieces. A rectilinear crack pattern encodes information about the order of cracks, as later cracks tend to intersect with earlier cracks at right angles. In this manner they relieve the stresses perpendicular to the pre-existing crack. In a hexagonal pattern, in contrast, the angles between all cracks at a vertex are near 120°. In this presentation it will be shown how both types of pattern can arise from identical forces, and that a rectilinear, T-junction dominated pattern will develop into to a hexagonal pattern, with Y-junctions, if allowed to. Such an evolution can be explained as the result of three conditions: (1) if cracks advance through space, or heal and recur, that the previous positions of a crack tip acts as a line of weakness, guiding the next iteration of cracking; (2) that the order of opening of cracks can change in each iteration; and (3) that crack tips curve to maximise the local strain energy release rate. The ordering of crack patterns are seen in a number of systems: columnar joints in starch and lava; desiccation cracks in clays that are repeatedly wetted and dried; cracks in eroding gypsum-cemented sand layers; and the cracks in permafrost known as polygonal terrain. These patterns will each be briefly explored, in turn, and shown to obey the above principles of crack pattern evolution.

  13. Eddy current monitoring of fatigue crack growth in Zr-2.5% Nb pressure tube

    NASA Astrophysics Data System (ADS)

    Krause, T. W.; Martin, A. E.; Sheppard, R. R.; Schankula, J. J.

    2000-05-01

    Zr-2.5% wt. Nb pressure tubes (PTs) form the core of the heat transport system in CANDU nuclear reactors. These 6 m long, 100 mm diameter tubes are operated at elevated temperatures (nominally 300 °C) and at pressures that produce hoop stresses that are 25% of the ultimate tensile strength of the PT (120 Mpa). Therefore, detection and characterization of flaws in these components becomes crucial for their continued pressure retaining integrity. If a flaw is detected, however, the cost of PT replacement is expensive. Periodic in-service inspection of a flaw that demonstrates no change in flaw characteristics can be used to allow a pressure tube to remain in-service. This requires confidence in the accuracy and reliability of methods used to inter flaw characteristics. Such confidence can only be developed by comparing nondestructive predictions with results from destructive examinations. In this work, eddy current testing was used to monitor the progressive stages of a fatigue crack, grown through pressure cycling from a notch on the inner surface of a PT. Results from a differential lift-off compensated eddy current probe were used to produce sizing estimates of the crack grown between 35% (base of notch) and 74% of the PT wall. A comparison with a destructive examination of the crack demonstrated sensitivity too changes in crack depth accurate to 5% of the tube wall thickness. Such results, combined with similar information obtained from ultrasonics will increase confidence in interpretation of PT inspection data.

  14. Galileo Probe Battery System

    NASA Technical Reports Server (NTRS)

    Dagarin, B. P.; Taenaka, R. K.; Stofel, E. J.

    1997-01-01

    The conclusions of the Galileo probe battery system are: the battery performance met mission requirements with margin; extensive ground-based and flight tests of batteries prior to probe separation from orbiter provided good prediction of actual entry performance at Jupiter; and the Li-SO2 battery was an important choice for the probe's main power.

  15. A Magnetoresistance Measuring Probe.

    DTIC Science & Technology

    The in line four point probe, commonly used for measuring the sheet resistance in a conductor, cannot measure the anisotropic ferromagnetic magnetoresistance. However, the addition of two contact points that are not collinear with the current contacts give the probe the ability to non-destructively measure the anistropic magnetoresistance. Keywords: Magnetoresistance; Anisotropic; Thin-Film; Permalloy; Four Point Probe; Anisotropic Resistance.

  16. Crack detection for a Jeffcott rotor with a transverse crack: An experimental investigation

    NASA Astrophysics Data System (ADS)

    Guo, Chaozhong; Yan, Jihong; Yang, Weicheng

    2017-01-01

    In this paper, an experimental investigation is carried out to verify the theoretical results of the dynamic behavior and the EMD based crack detection method for the cracked rotor proposed in our former research. The breathing crack in the rotor is simulated by a real fatigue crack. The whirl orbits during passage through the 1/2, 1/3 and 1/4 subcritical speeds are investigated. The dynamic responses in these subcritical speed zones are decomposed into several subcomponents by the EMD method, and the variation of the high-frequency component are studied. As a comparison, the fast Fourier transform method is used to derive the amplitude variation of the high order frequencies from the frequency spectra of the experimental vibration signal. The experimental results are well concordant with the theoretical analysis, which indicates that the EMD based crack detection method is practicable.

  17. Carbon Nanotube Based Sensor to Monitor Crack Growth in Cracked Aluminum Structures Underneath Composite Patching

    NASA Astrophysics Data System (ADS)

    Olson, T. M.; Kwon, Y. W.; Hart, D. C.; Loup, D. C.; Rasmussen, E. A.

    2015-10-01

    The paper investigates a carbon nanotube-based sensor to detect crack propagation in aluminum structures underneath composite patching. Initial tests are conducted to determine the correct procedure and materials to properly fabricate a carbon nanotube (CNT) based sensor, which is then placed in between a composite patch and the aluminum structure. The CNTs have been utilized as sensors in previous studies but only for sensing crack propagation within the composite itself. This study focuses on crack propagation in the base material and is not concerned with the composite. In this application, the composite is only a patch and can be replaced if damaged. The study conducts both tension and fatigue testing to determine the usefulness of the CNT sensor. The CNT sensor is shown to be effective in giving an indication of the crack propagation in the aluminum. Correlation is done between the crack propagation length and the increase in electrical resistance in the CNT sensor under tensile and cyclic loading, respectively.

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

    NASA Technical Reports Server (NTRS)

    Riddell, William T.; Piascik, Robert S.

    1998-01-01

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

  19. CRACK TIP OPENING DISPLACEMENT AND ANGLE FOR A GROWING CRACK IN CARBON STEEL

    SciTech Connect

    LAM, POH-SANG

    2005-01-18

    The crack tip opening displacements and angles (CTOD/CTOA) are calculated with finite element method based on the test data of a set of constraint-dependent J-R curves for A285 carbon steel. The values of the CTOD/CTOA are initially high at initiation, but rapidly decrease to a nearly constant value. When the common practice is adopted by using only the constant part of CTOD/CTOA as the fracture criterion, the crack growth behavior is shown to be severely underestimated. However, with a bilinear form of CTOD/CTOA fracture criterion which approximates the initial non-constant portion, the experimental load vs. crack extension curves can be closely predicted. Furthermore, it is demonstrated that the CTOD/CTOA is crack tip constraint dependent. The values of CTOD/CTOA for specimens with various ratios of crack length to specimen width (a/W) are reflected by the J-R curves and their slopes.

  20. 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

  1. Burst Pressure Prediction of Multiple Cracks in Pipelines

    NASA Astrophysics Data System (ADS)

    Razak, N. A.; Alang, N. A.; Murad, M. A.

    2013-12-01

    Available industrial code such as ASME B1G, modified ASME B1G and DNV RP-F101 to assess pipeline defects appear more conservative for multiple crack like- defects than single crack-like defects. Thus, this paper presents burst pressure prediction of pipe with multiple cracks like defects. A finite element model was developed and the burst pressure prediction was compared with the available code. The model was used to investigate the effect of the distance between the cracks and the crack length. The coalescence diagram was also developed to evaluate the burst pressure of the multiple cracks. It was found as the distance between crack increases, the interaction effect comes to fade away and multiple cracks behave like two independent single cracks.

  2. Modeling the Interactions Between Multiple Crack Closure Mechanisms at Threshold

    NASA Technical Reports Server (NTRS)

    Newman, John A.; Riddell, William T.; Piascik, Robert S.

    2003-01-01

    A fatigue crack closure model is developed that includes interactions between the three closure mechanisms most likely to occur at threshold; plasticity, roughness, and oxide. This model, herein referred to as the CROP model (for Closure, Roughness, Oxide, and Plasticity), also includes the effects of out-of plane cracking and multi-axial loading. These features make the CROP closure model uniquely suited for, but not limited to, threshold applications. Rough cracks are idealized here as two-dimensional sawtooths, whose geometry induces mixed-mode crack- tip stresses. Continuum mechanics and crack-tip dislocation concepts are combined to relate crack face displacements to crack-tip loads. Geometric criteria are used to determine closure loads from crack-face displacements. Finite element results, used to verify model predictions, provide critical information about the locations where crack closure occurs.

  3. 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.

  4. 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.

  5. Surface crack growth in fiber composites

    NASA Technical Reports Server (NTRS)

    Im, J.; Mandell, J. F.; Wang, S. S.; Mcgarry, F. J.

    1976-01-01

    The results of an experimental study of damage extension and failure in glass and graphite/epoxy laminates containing partially through-thickness surface cracks are presented. The laminates studied are divided between those containing four plies, 90/0/0/90, 15/-15/-15/15, and 45/-45/-45/45, and those containing 12-16 plies of the general configurations 0/90, + or - 45, and 0/+ or - 60. Most of the results are for surface cracks of various lengths and several depths. Stable damage extension in laminates containing surface cracks is predominantly delamination between plies, and tends to be much more extensive prior to failure than is the case with through-thickness cracks, resulting in approximately notch-insensitive behavior in most cases. A greater tendency for notch-sensitive behavior is found for 0/90 graphite/epoxy laminates for which stable damage extension is more limited. The rate of damage extension with increasing applied stress depends upon the composite system and ply configuration as well as the crack length and depth. An approximate semiempirical method is presented for estimating the growth rate of large damage-regions.

  6. Applied Stress Affecting the Environmentally Assisted Cracking

    NASA Astrophysics Data System (ADS)

    Vasudevan, A. K.

    2013-03-01

    Stress corrosion cracking (SCC) is affected by the mode of applied stress, i.e., tension, compression, or torsion. The cracking is measured in terms of initiation time to nucleate a crack or time to failure. In a simple uniaxial loading under tension or compression, it is observed that the initiation time can vary in orders of magnitude depending on the alloy and the environment. Fracture can be intergranular or transgranular or mixed mode. Factors that affect SCC are solubility of the metal into surrounding chemical solution, and diffusion rate (like hydrogen into a tensile region) of an aggressive element into the metal and liquid metallic elements in the grain boundaries. Strain hardening exponent that affects the local internal stresses and their gradients can affect the diffusion kinetics. We examine two environments (Ga and 3.5 pct NaCl) for the same alloy 7075-T651, under constant uniaxial tension and compression load. These two cases provide us application to two different governing mechanisms namely liquid metal embrittlement (7075-Ga) and hydrogen-assisted cracking (7075-NaCl). We note that, in spite of the differences in their mechanisms, both systems show similar behavior in the applied K vs crack initiation time plots. One common theme among them is the transport mechanism of a solute element to a tensile-stress region to initiate fracture.

  7. Crack Detection with Lamb Wave Wavenumber Analysis

    NASA Technical Reports Server (NTRS)

    Tian, Zhenhua; Leckey, Cara; Rogge, Matt; Yu, Lingyu

    2013-01-01

    In this work, we present our study of Lamb wave crack detection using wavenumber analysis. The aim is to demonstrate the application of wavenumber analysis to 3D Lamb wave data to enable damage detection. The 3D wavefields (including vx, vy and vz components) in time-space domain contain a wealth of information regarding the propagating waves in a damaged plate. For crack detection, three wavenumber analysis techniques are used: (i) two dimensional Fourier transform (2D-FT) which can transform the time-space wavefield into frequency-wavenumber representation while losing the spatial information; (ii) short space 2D-FT which can obtain the frequency-wavenumber spectra at various spatial locations, resulting in a space-frequency-wavenumber representation; (iii) local wavenumber analysis which can provide the distribution of the effective wavenumbers at different locations. All of these concepts are demonstrated through a numerical simulation example of an aluminum plate with a crack. The 3D elastodynamic finite integration technique (EFIT) was used to obtain the 3D wavefields, of which the vz (out-of-plane) wave component is compared with the experimental measurement obtained from a scanning laser Doppler vibrometer (SLDV) for verification purposes. The experimental and simulated results are found to be in close agreement. The application of wavenumber analysis on 3D EFIT simulation data shows the effectiveness of the analysis for crack detection. Keywords: : Lamb wave, crack detection, wavenumber analysis, EFIT modeling

  8. STRESS CORROSION CRACKING IN TEAR DROP SPECIMENS

    SciTech Connect

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

    2009-05-01

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

  9. The Effect of Crack Orientation on the Nonlinear Interaction of a P-wave with an S-wave

    SciTech Connect

    TenCate, J. A.; Malcolm, A. E.; Feng, X.; Fehler, M. C.

    2016-06-06

    Cracks, joints, fluids, and other pore-scale structures have long been hypothesized to be the cause of the large elastic nonlinearity observed in rocks. It is difficult to definitively say which pore-scale features are most important, however, because of the difficulty in isolating the source of the nonlinear interaction. In this work, we focus on the influence of cracks on the recorded nonlinear signal and in particular on how the orientation of microcracks changes the strength of the nonlinear interaction. We do this by studying the effect of orientation on the measurements in a rock with anisotropy correlated with the presence and alignment of microcracks. We measure the nonlinear response via the traveltime delay induced in a low-amplitude P wave probe by a high-amplitude S wave pump. We find evidence that crack orientation has a significant effect on the nonlinear signal.

  10. The Effect of Crack Orientation on the Nonlinear Interaction of a P-wave with an S-wave

    DOE PAGES

    TenCate, J. A.; Malcolm, A. E.; Feng, X.; ...

    2016-06-06

    Cracks, joints, fluids, and other pore-scale structures have long been hypothesized to be the cause of the large elastic nonlinearity observed in rocks. It is difficult to definitively say which pore-scale features are most important, however, because of the difficulty in isolating the source of the nonlinear interaction. In this work, we focus on the influence of cracks on the recorded nonlinear signal and in particular on how the orientation of microcracks changes the strength of the nonlinear interaction. We do this by studying the effect of orientation on the measurements in a rock with anisotropy correlated with the presencemore » and alignment of microcracks. We measure the nonlinear response via the traveltime delay induced in a low-amplitude P wave probe by a high-amplitude S wave pump. We find evidence that crack orientation has a significant effect on the nonlinear signal.« less

  11. Propagation of stress corrosion cracks in alpha-brasses

    SciTech Connect

    Beggs, Dennis Vinton

    1981-01-01

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

  12. Ultrafast scanning probe microscopy

    DOEpatents

    Weiss, Shimon; Chemla, Daniel S.; Ogletree, D. Frank; Botkin, David

    1995-01-01

    An ultrafast scanning probe microscopy method for achieving subpicosecond-temporal resolution and submicron-spatial resolution of an observation sample. In one embodiment of the present claimed invention, a single short optical pulse is generated and is split into first and second pulses. One of the pulses is delayed using variable time delay means. The first pulse is then directed at an observation sample located proximate to the probe of a scanning probe microscope. The scanning probe microscope produces probe-sample signals indicative of the response of the probe to characteristics of the sample. The second pulse is used to modulate the probe of the scanning probe microscope. The time delay between the first and second pulses is then varied. The probe-sample response signal is recorded at each of the various time delays created between the first and second pulses. The probe-sample response signal is then plotted as a function of time delay to produce a cross-correlation of the probe sample response. In so doing, the present invention provides simultaneous subpicosecond-temporal resolution and submicron-spatial resolution of the sample.

  13. Traversing probe system

    DOEpatents

    Mashburn, Douglas N.; Stevens, Richard H.; Woodall, Harold C.

    1977-01-01

    This invention comprises a rotatable annular probe-positioner which carries at least one radially disposed sensing probe, such as a Pitot tube having a right-angled tip. The positioner can be coaxially and rotatably mounted within a compressor casing or the like and then actuated to orient the sensing probe as required to make measurements at selected stations in the annulus between the positioner and compressor casing. The positioner can be actuated to (a) selectively move the probe along its own axis, (b) adjust the yaw angle of the right-angled probe tip, and (c) revolve the probe about the axis common to the positioner and casing. A cam plate engages a cam-follower portion of the probe and normally rotates with the positioner. The positioner includes a first-motor-driven ring gear which effects slidable movement of the probe by rotating the positioner at a time when an external pneumatic cylinder is actuated to engage the cam plate and hold it stationary. When the pneumatic cylinder is not actuated, this ring gear can be driven to revolve the positioner and thus the probe to a desired circumferential location about the above-mentioned common axis. A second motor-driven ring gear included in the positioner can be driven to rotate the probe about its axis, thus adjusting the yaw angle of the probe tip. The positioner can be used in highly corrosive atmosphere, such as gaseous uranium hexafluoride.

  14. Ultrafast scanning probe microscopy

    DOEpatents

    Weiss, S.; Chemla, D.S.; Ogletree, D.F.; Botkin, D.

    1995-05-16

    An ultrafast scanning probe microscopy method is described for achieving subpicosecond-temporal resolution and submicron-spatial resolution of an observation sample. In one embodiment of the present claimed invention, a single short optical pulse is generated and is split into first and second pulses. One of the pulses is delayed using variable time delay means. The first pulse is then directed at an observation sample located proximate to the probe of a scanning probe microscope. The scanning probe microscope produces probe-sample signals indicative of the response of the probe to characteristics of the sample. The second pulse is used to modulate the probe of the scanning probe microscope. The time delay between the first and second pulses is then varied. The probe-sample response signal is recorded at each of the various time delays created between the first and second pulses. The probe-sample response signal is then plotted as a function of time delay to produce a cross-correlation of the probe sample response. In so doing, the present invention provides simultaneous subpicosecond-temporal resolution and submicron-spatial resolution of the sample. 6 Figs.

  15. Electrical resistivity probes

    DOEpatents

    Lee, Ki Ha; Becker, Alex; Faybishenko, Boris A.; Solbau, Ray D.

    2003-10-21

    A miniaturized electrical resistivity (ER) probe based on a known current-voltage (I-V) electrode structure, the Wenner array, is designed for local (point) measurement. A pair of voltage measuring electrodes are positioned between a pair of current carrying electrodes. The electrodes are typically about 1 cm long, separated by 1 cm, so the probe is only about 1 inch long. The electrodes are mounted to a rigid tube with electrical wires in the tube and a sand bag may be placed around the electrodes to protect the electrodes. The probes can be positioned in a borehole or on the surface. The electrodes make contact with the surrounding medium. In a dual mode system, individual probes of a plurality of spaced probes can be used to measure local resistance, i.e. point measurements, but the system can select different probes to make interval measurements between probes and between boreholes.

  16. Crack velocity jumps engendered by a transformational process zone.

    PubMed

    Boulbitch, A; Korzhenevskii, A L

    2016-06-01

    We study a concerted propagation of a fast crack with the process zone where a rearrangement of the solid structure takes place. The latter is treated as a second-order local phase transformation. We demonstrate that the propagation of such a zone gives rise to a nonlinear frictionlike force exerted on the crack tip, resisting its propagation. Depending on the temperature, it produces three regimes of crack motion, which differ in the behavior of the crack tip process zone: (i) always existing, (ii) only emerging at a high crack speed, and (iii) flickering. We show that the latter regime exhibits crack velocity jumps.

  17. Crack detection using pulsed eddy current stimulated thermography

    SciTech Connect

    Kostson, E.; Weekes, B.; Almond, D. P.; Wilson, J.; Tian, G. Y.

    2011-06-23

    This contribution presents results from studies investigating factors that influence the detection of surface breaking cracks using pulsed eddy current thermography. The influences of the current strength and crack orientation in both ferromagnetic and non-ferromagnetic metals have been investigated. It has been found that crack detection is far more sensitive to crack orientation in non-ferromagnetic metals than in ferromagnetic metals. The effects of crack size on detectability are presented for a large number of steel, nickel alloy and titanium samples. Results of studies comparing crack images obtained prior and after coating a nickel alloy sample with a thermal barrier coating are presented.

  18. Crack-shape effects for indentation fracture toughness measurements

    SciTech Connect

    Smith, S.M.; Scattergood, R.O. . Dept. of Materials Science and Engineering)

    1992-02-01

    Various methods to measure fracture toughness using indentation precracks were compared using soda-lime glass as a test material. In situ measurements of crack size as a function of applied stress allow both the toughness K[sub c] and the residual-stress factor [chi] to be independently determined. Analysis of the data showed that stress intensity factors based on classical half-penny crack shapes overestimate toughness values and produce an apparent R-curve effect. This is due to a constraint on crack shape imposed by primary lateral cracks in soda-lime glass. Models based on elliptical cracks were developed to account for the crack-shape effects.

  19. Evaluation of a Small-Crack Monitoring System

    NASA Technical Reports Server (NTRS)

    Newman, John A.; Johnston, William M.

    2010-01-01

    A new system has been developed to obtain fatigue crack growth rate data from a series of images acquired during fatigue testing of specimens containing small surface cracks that initiate at highly-polished notches. The primary benefit associated with replica-based crack growth rate data methods is preserving a record of the crack configuration during the life of the specimen. Additionally, this system has the benefits of both reducing time and labor, and not requiring introduction of surface replica media into the crack. Fatigue crack growth rate data obtained using this new system are found to be in good agreement with similar results obtained from surface replicas.

  20. Interaction of Cracks Between Two Adjacent Indents in Glass

    NASA Technical Reports Server (NTRS)

    Choi, S. R.; Salem, J. A.

    1993-01-01

    Experimental observations of the interaction behavior of cracks between two adjacent indents were made using an indentation technique in soda-lime glass. It was specifically demonstrated how one indent crack initiates and propagates in the vicinity of another indent crack. Several types of crack interactions were examined by changing the orientation and distance of one indent relative to the other. It was found that the residual stress field produced by elastic/plastic indentation has a significant influence on controlling the mode of crack interaction. The interaction of an indent crack with a free surface was also investigated for glass and ceramic specimens.

  1. COD measurements at various positions along a crack

    NASA Technical Reports Server (NTRS)

    Sharpe, W. N., Jr.; Su, X.

    1988-01-01

    Load versus crack-opening-displacement (COD) was measured at various positions along the border of a fatigue crack as it grew from a small surface crack on the edge of an aluminum specimen into a through-the-thickness crack. Displacements were measured with a laser-based interferometric system with a gage length of 70 microns and a resolution of 0.01 micron. These load-COD curves can be used to determine opening loads and thereby investigate the effect of closure on the growth of small cracks. In general, the opening loads decrease as the crack grows.

  2. FInal Report - Investment Casting Shell Cracking

    SciTech Connect

    Von Richards

    2003-12-01

    This project made a significant contribution to the understanding of the investment casting shell cracking problem. The effects of wax properties on the occurrence of shell cracking were demonstrated and can be measured. The properties measured include coefficient of thermal expansion, heating rate and crystallinity of the structure. The important features of production molds and materials properties have been indicated by case study analysis and fractography of low strength test bars. It was found that stress risers in shell cavity design were important and that typical critical flaws were either oversize particles or large pores just behind the prime coat. It was also found that the true effect of fugitive polymer fibers was not permeability increase, but rather a toughening mechanism due to crack deflection.

  3. Barnacles resist removal by crack trapping.

    PubMed

    Hui, Chung-Yuen; Long, Rong; Wahl, Kathryn J; Everett, Richard K

    2011-06-06

    We study the mechanics of pull-off of a barnacle adhering to a thin elastic layer which is bonded to a rigid substrate. We address the case of barnacles having acorn shell geometry and hard, calcarious base plates. Pull-off is initiated by the propagation of an interface edge crack between the base plate and the layer. We compute the energy release rate of this crack as it grows along the interface using a finite element method. We also develop an approximate analytical model to interpret our numerical results and to give a closed-form expression for the energy release rate. Our result shows that the resistance of barnacles to interfacial failure arises from a crack-trapping mechanism.

  4. Barnacles resist removal by crack trapping

    PubMed Central

    Hui, Chung-Yuen; Long, Rong; Wahl, Kathryn J.; Everett, Richard K.

    2011-01-01

    We study the mechanics of pull-off of a barnacle adhering to a thin elastic layer which is bonded to a rigid substrate. We address the case of barnacles having acorn shell geometry and hard, calcarious base plates. Pull-off is initiated by the propagation of an interface edge crack between the base plate and the layer. We compute the energy release rate of this crack as it grows along the interface using a finite element method. We also develop an approximate analytical model to interpret our numerical results and to give a closed-form expression for the energy release rate. Our result shows that the resistance of barnacles to interfacial failure arises from a crack-trapping mechanism. PMID:21208968

  5. Seacoast stress corrosion cracking of aluminum alloys

    NASA Technical Reports Server (NTRS)

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

    1981-01-01

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

  6. Cracks at disclinated grain boundaries in graphene

    NASA Astrophysics Data System (ADS)

    Ovid'ko, I. A.; Sheinerman, A. G.

    2013-08-01

    A theoretical model is suggested which describes the formation of cracks at grain boundaries (GBs) containing partial (non-topological) disclinations and their dipoles in graphene. Such partial disclinations and their dipoles at GBs are associated with experimentally observed structural irregularities of real GBs in graphene. Within the suggested model, the dependences of the critical stress for crack formation on the parameters of sole disclinations and their dipole configurations at GBs are calculated. The results of the model effectively explain the experimental data (Huang et al 2011 Nature 469 389, Ruiz-Vargas et al 2011 Nano Lett. 11 2259) on crack formation in polycrystalline graphene at comparatively low levels of the applied stress and their discrepancy with the results of computer simulations (presented in the scientific literature) of strength exhibited by graphene bi-crystals with structurally perfect, periodic GBs.

  7. Crack Tip Dislocation Nucleation in FCC Solids

    NASA Astrophysics Data System (ADS)

    Knap, J.; Sieradzki, K.

    1999-02-01

    We present results of molecular dynamic simulations aimed at examining crack tip dislocation emission in fcc solids. The results are analyzed in terms of recent continuum formulations of this problem. In mode II, Au, Pd, and Pt displayed a new unanticipated mechanism of crack tip dislocation emission involving the creation of a pair of Shockley partials on a slip plane one plane below the crack plane. In mode I, for all the materials examined, Rice's continuum formulation [J. Mech. Phys. Solids 40, 239 (1992)] underestimated the stress intensity for dislocation emission by almost a factor of 2. Surface stress corrections to the emission criterion brought the agreement between continuum predictions and simulations to within 20%.

  8. Crack propagation and arrest in pressurized containers

    NASA Technical Reports Server (NTRS)

    Erdogan, F.; Delale, F.; Owczarek, J. A.

    1976-01-01

    The problem of crack propagation and arrest in a finite volume cylindrical container filled with pressurized gas is considered. It is assumed that the cylinder contains a symmetrically located longitudinal part-through crack with a relatively small net ligament. The net ligament suddenly ruptures initiating the process of fracture propagation and depressurization in the cylinder. Thus the problem is a coupled gas dynamics and solid mechanics problem the exact formulation of which does not seem to be possible. The problem is reduced to a proper initial value problem by introducing a dynamic fracture criterion which relates the crack acceleration to the difference between a load factor and the corresponding strength parameter. The results indicate that generally in gas filled cylinders fracture arrest is not possible unless the material behaves in a ductile manner and the container is relatively long.

  9. Stress crack testing of polyethylene geomembranes

    NASA Astrophysics Data System (ADS)

    Halse, Y. H.; Koerner, R. M.; Lord, A. E., Jr.

    The sensitivity of high density polyethylene (HDPE) geomembranes to stress cracking is evaluated under accelerated conditions at a constant stress. The test specimens are in accordance with ASTM D-1822, and are of the dumbbell shape with a constant length in the central section. The accelerated testing conditions consist of a 10 percent Igepal wetting solution in tap water, at a constant temperature of 50 C. The applied stresses are from 30 to 50 percent of the yield stress. It was found that most commercially available HDPE sheet material performs quite well in this type of test. Only one specimen in 80 showed any evidence of cracking and this may have been caused by other reasons. Testing of field fabricated seams, however, resulted in relatively large numbers of cracked specimens. Many of these test specimens showed signs of overgrinding and/or overheating. The results indicate that great care and excellent workmanship are required in the field fabrication of HDPE seams.

  10. Crack detection using resonant ultrasound spectroscopy

    DOEpatents

    Migliori, A.; Bell, T.M.; Rhodes, G.W.

    1994-10-04

    Method and apparatus are provided for detecting crack-like flaws in components. A plurality of exciting frequencies are generated and applied to a component in a dry condition to obtain a first ultrasonic spectrum of the component. The component is then wet with a selected liquid to penetrate any crack-like flaws in the component. The plurality of exciting frequencies are again applied to the component and a second ultrasonic spectrum of the component is obtained. The wet and dry ultrasonic spectra are then analyzed to determine the second harmonic components in each of the ultrasonic resonance spectra and the second harmonic components are compared to ascertain the presence of crack-like flaws in the component. 5 figs.

  11. Crack detection using resonant ultrasound spectroscopy

    DOEpatents

    Migliori, Albert; Bell, Thomas M.; Rhodes, George W.

    1994-01-01

    Method and apparatus are provided for detecting crack-like flaws in components. A plurality of exciting frequencies are generated and applied to a component in a dry condition to obtain a first ultrasonic spectrum of the component. The component is then wet with a selected liquid to penetrate any crack-like flaws in the component. The plurality of exciting frequencies are again applied to the component and a second ultrasonic spectrum of the component is obtained. The wet and dry ultrasonic spectra are then analyzed to determine the second harmonic components in each of the ultrasonic resonance spectra and the second harmonic components are compared to ascertain the presence of crack-like flaws in the component.

  12. Modeling radon transport in dry, cracked soil

    SciTech Connect

    Holford, D.J. ); Schery, S.D.; Wilson, J.L.; Phillips, F.M. )

    1993-01-10

    A two-dimensional finite element code was used to investigate the effect of changes in surface air pressure on radon flux from soil with parallel, partially penetrating cracks. A sensitivity analysis investigates the effects of various crack dimensions, soil characteristics, and surface air pressure on radon flux from the soil surface to the atmosphere. Simulation results indicate that radon flux is most sensitive to soil properties; the diffusion coefficient is most important, followed by permeability and porosity. Radon flux is also sensitive to changes in barometric pressure, which cause variations in radon flux above and below the average diffusive flux. Sinusoidal variations in barometric pressure cause a net increase in the average radon flux from the soil, because increases in flux during periods of decreasing pressure are greater than the decreases in flux during periods of decreasing pressure of equal magnitude. Cracks were found to significantly increase radon flux from soils of low permeability. 33 refs. 19 figs., 1 tab.

  13. STS-82 Crack on Mobile Launch Platform

    NASA Technical Reports Server (NTRS)

    1997-01-01

    Robert T. Nelson of KSC Security points to an approximately 24- foot-long crack on the Mobile Launch Platform (MLP) which is holding the Space Shuttle Discovery en route to Launch Pad 39A for the STS-82 mission. Nelson was riding on the MLP when he heard a loud noise and noticed the crack. Rollout had begun shortly after 7 a.m. EST and was stopped at about 8:25 a.m. This Y-shaped crack is on the MLP surface and runs from near the left- hand solid rocket booster flame hole toward the near corner of the MLP. Rollout of Discovery resumed just past 12 noon after structural engineers determined that the integrity of the MLP had not been compromised. Discovery is scheduled to lift off on the second Hubble Space Telescope servicing mission on Feb. 11.

  14. Residual strength of thin panels with cracks

    NASA Technical Reports Server (NTRS)

    Madenci, Erdogan

    1994-01-01

    The previous design philosophies involving safe life, fail-safe and damage tolerance concepts become inadequate for assuring the safety of aging aircraft structures. For example, the failure mechanism for the Aloha Airline accident involved the coalescence of undetected small cracks at the rivet holes causing a section of the fuselage to peel open during flight. Therefore, the fuselage structure should be designed to have sufficient residual strength under worst case crack configurations and in-flight load conditions. Residual strength is interpreted as the maximum load carrying capacity prior to unstable crack growth. Internal pressure and bending moment constitute the two major components of the external loads on the fuselage section during flight. Although the stiffeners in the form of stringers, frames and tear straps sustain part of the external loads, the significant portion of the load is taken up by the skin. In the presence of a large crack in the skin, the crack lips bulge out with considerable yielding; thus, the geometric and material nonlinearities must be included in the analysis for predicting residual strength. Also, these nonlinearities do not permit the decoupling of in-plane and out-of-plane bending deformations. The failure criterion combining the concepts of absorbed specific energy and strain energy density addresses the aforementioned concerns. The critical absorbed specific energy (local toughness) for the material is determined from the global specimen response and deformation geometry based on the uniaxial tensile test data and detailed finite element modeling of the specimen response. The use of the local toughness and stress-strain response at the continuum level eliminates the size effect. With this critical parameter and stress-strain response, the finite element analysis of the component by using STAGS along with the application of this failure criterion provides the stable crack growth calculations for residual strength predictions.

  15. Residual strength of thin panels with cracks

    NASA Astrophysics Data System (ADS)

    Madenci, Erdogan

    1994-12-01

    The previous design philosophies involving safe life, fail-safe and damage tolerance concepts become inadequate for assuring the safety of aging aircraft structures. For example, the failure mechanism for the Aloha Airline accident involved the coalescence of undetected small cracks at the rivet holes causing a section of the fuselage to peel open during flight. Therefore, the fuselage structure should be designed to have sufficient residual strength under worst case crack configurations and in-flight load conditions. Residual strength is interpreted as the maximum load carrying capacity prior to unstable crack growth. Internal pressure and bending moment constitute the two major components of the external loads on the fuselage section during flight. Although the stiffeners in the form of stringers, frames and tear straps sustain part of the external loads, the significant portion of the load is taken up by the skin. In the presence of a large crack in the skin, the crack lips bulge out with considerable yielding; thus, the geometric and material nonlinearities must be included in the analysis for predicting residual strength. Also, these nonlinearities do not permit the decoupling of in-plane and out-of-plane bending deformations. The failure criterion combining the concepts of absorbed specific energy and strain energy density addresses the aforementioned concerns. The critical absorbed specific energy (local toughness) for the material is determined from the global specimen response and deformation geometry based on the uniaxial tensile test data and detailed finite element modeling of the specimen response. The use of the local toughness and stress-strain response at the continuum level eliminates the size effect. With this critical parameter and stress-strain response, the finite element analysis of the component by using STAGS along with the application of this failure criterion provides the stable crack growth calculations for residual strength predictions.

  16. Realistic and efficient 2D crack simulation

    NASA Astrophysics Data System (ADS)

    Yadegar, Jacob; Liu, Xiaoqing; Singh, Abhishek

    2010-04-01

    Although numerical algorithms for 2D crack simulation have been studied in Modeling and Simulation (M&S) and computer graphics for decades, realism and computational efficiency are still major challenges. In this paper, we introduce a high-fidelity, scalable, adaptive and efficient/runtime 2D crack/fracture simulation system by applying the mathematically elegant Peano-Cesaro triangular meshing/remeshing technique to model the generation of shards/fragments. The recursive fractal sweep associated with the Peano-Cesaro triangulation provides efficient local multi-resolution refinement to any level-of-detail. The generated binary decomposition tree also provides efficient neighbor retrieval mechanism used for mesh element splitting and merging with minimal memory requirements essential for realistic 2D fragment formation. Upon load impact/contact/penetration, a number of factors including impact angle, impact energy, and material properties are all taken into account to produce the criteria of crack initialization, propagation, and termination leading to realistic fractal-like rubble/fragments formation. The aforementioned parameters are used as variables of probabilistic models of cracks/shards formation, making the proposed solution highly adaptive by allowing machine learning mechanisms learn the optimal values for the variables/parameters based on prior benchmark data generated by off-line physics based simulation solutions that produce accurate fractures/shards though at highly non-real time paste. Crack/fracture simulation has been conducted on various load impacts with different initial locations at various impulse scales. The simulation results demonstrate that the proposed system has the capability to realistically and efficiently simulate 2D crack phenomena (such as window shattering and shards generation) with diverse potentials in military and civil M&S applications such as training and mission planning.

  17. Analyses of Fatigue Crack Growth and Closure Near Threshold Conditions for Large-Crack Behavior

    NASA Technical Reports Server (NTRS)

    Newman, J. C., Jr.

    1999-01-01

    A plasticity-induced crack-closure model was used to study fatigue crack growth and closure in thin 2024-T3 aluminum alloy under constant-R and constant-K(sub max) threshold testing procedures. Two methods of calculating crack-opening stresses were compared. One method was based on a contact-K analyses and the other on crack-opening-displacement (COD) analyses. These methods gave nearly identical results under constant-amplitude loading, but under threshold simulations the contact-K analyses gave lower opening stresses than the contact COD method. Crack-growth predictions tend to support the use of contact-K analyses. Crack-growth simulations showed that remote closure can cause a rapid rise in opening stresses in the near threshold regime for low-constraint and high applied stress levels. Under low applied stress levels and high constraint, a rise in opening stresses was not observed near threshold conditions. But crack-tip-opening displacement (CTOD) were of the order of measured oxide thicknesses in the 2024 alloy under constant-R simulations. In contrast, under constant-K(sub max) testing the CTOD near threshold conditions were an order-of-magnitude larger than measured oxide thicknesses. Residual-plastic deformations under both constant-R and constant-K(sub max) threshold simulations were several times larger than the expected oxide thicknesses. Thus, residual-plastic deformations, in addition to oxide and roughness, play an integral part in threshold development.

  18. Nucleation of squat cracks in rail, calculation of crack initiation angles in three dimensions

    NASA Astrophysics Data System (ADS)

    Naeimi, Meysam; Li, Zili; Dollevoet, Rolf

    2015-07-01

    A numerical model of wheel-track system is developed for nucleation of squat-type fatigue cracks in rail material. The model is used for estimating the angles of squat cracks in three dimensions. Contact mechanics and multi-axial fatigue analysis are combined to study the crack initiation mechanism in rails. Nonlinear material properties, actual wheel-rail geometries and realistic loading conditions are considered in the modelling process. Using a 3D explicit finite element analysis the transient rolling contact behaviour of wheel on rail is simulated. Employing the critical plane concept, the material points with the largest possibility of crack initiation are determined; based on which, the 3D orientations/angles of the possible squat cracks are estimated. Numerical estimations are compared with sample results of experimental observations on a rail specimen with squat from the site. The findings suggest a proper agreement between results of modelling and experiment. It is observed that squat cracks initiate at an in-plane angle around 13°-22° relative to the rail surface. The initiation angle seen on surface plane is calculated around 29°-48°, while the crack tend to initiate in angles around 25°-31° in the rail cross-section.

  19. Dynamic crack propagation in a viscoelastic strip

    NASA Astrophysics Data System (ADS)

    Popelar, C. H.; Atkinson, C.

    1980-04-01

    THE DYNAMIC PROPAGATION of a semi-infinite crack in a finite linear viscoelastic strip subjected to Mode I loading is investigated. Through the use of integral transforms the problem is reduced to solving a Wiener-Hopf equation. The asymptotic properties of the transforms are exploited to establish the stress intensity factor. Plane-stress and plane-strain stress intensity factors as a function of crack speed for both fully-clamped and shear-free lateral boundaries are presented for the standard linear viscoelastic solid. Comparisons are made with previously obtained asymptotic stress intensity factors and with stress intensity factors for the equivalent elastic strips.

  20. Thermographic characterization of stress during crack growth

    NASA Technical Reports Server (NTRS)

    Cramer, K. E.; Dawicke, David S.; Welch, Christopher S.

    1992-01-01

    A full-field-thermographic technique for imaging stress patterns in dynamically loaded structures using general purpose IR imaging and image processing hardware is described. The inspection technique is based on the thermoelastic effect. A simple geometry is examined, and the experimentally determined values for the stress invariant are shown to be consistent with theoretical and numerical calculations. The application of full-field-thermographic measurement would ensure that the observed stress field has a common sampling period, thus allowing the observation of rapidly occurring stress anomalies such as the propagation of a fatigue crack. Fatigue crack propagation in two consecutive thermoelastic stress images from an aluminum sample is shown.

  1. Hot cracking during welding and casting

    NASA Astrophysics Data System (ADS)

    Cao, Guoping

    Aluminum welds are susceptible to liquation cracking in the partially melted zone (PMZ). Using the multicomponent Scheil model, curves of temperature vs. fraction solid (T-fS) during solidification were calculated for the PMZ and weld metals (WMs). These curves were used to predict the crack susceptibility by checking if the harmful condition of WM fS > PMZ fS exists during PMZ solidification and reduce the susceptibility by minimizing this condition. This approach was tested against full-penetration welds of alloys 7075 and 2024 and it can be used to guide the selection or development of filler metals. Liquation cracking in the PMZ in welds of Al-Si cast alloys was also investigated. The crack susceptibility was evaluated by circular-patch test, and full-penetration welds made with filler metals 1100, 4043, 4047 and 5356. Liquation cracking was significant with filler metals 1100 and 5356 but slight with filler metals 4043 and 4047. In all welds, liquation cracks were completely backfilled, instead of open as in full-penetration welds of wrought alloys 2219 and 6061. The T-fS curves showed that alloy A357 has a much higher fraction liquid for backfilling before PMZ solidification was essentially over. Hot tearing in Mg-xAl-yCa alloys was studied by constrained rod casting (CRC) in a steel mold. The hot tearing susceptibility decreased significantly with increasing Ca content (y) but did not change much with the Al content (x). An instrumented CRC with a steel mold was developed to detect the onset of hot tearing. The secondary phases, eutectic content, solidification path, and freezing range were examined. Hot tearing in Mg-Al-Sr alloys was also studied by CRC in a steel mold. With Mg-(4,6,8)Al-1.5Sr alloys, the hot tearing susceptibility decreased significantly with increasing Al content. With Mg-(4,6,8)Al-3Sr alloys, the trend was similar but not as significant. At the same Al content, the hot tearing susceptibility decreased significantly with increasing Sr

  2. Crack detection on HU-25 Guardian aircraft

    SciTech Connect

    Moore, D.G.; Jones, C.R.; Mihelic, J.E.; Dassler, E.; Walizer, J.

    1996-10-01

    An ultrasonic inspection method was developed at FAA`s Airworthiness Assurance NDI Validation Center (AANC) to easily and rapidly detect hidden fatigue cracks in the copilot vertical windshield post on USCG (Coast Guard) HU-25 `Guardian` aircraft. The inspection procedure locates hidden cracks as small as 3.2 mm emanating from internal fastener holes and determines their length. A test procedure was developed and a baseline assessment of the USCG fleet conducted. Inspection results on 41 aircraft revealed good correlation with results made during subsequent structural disassembly and visual inspection of selected aircraft.

  3. Fatigue crack growth under variable amplitude loading

    NASA Technical Reports Server (NTRS)

    Sidawi, Jihad A.

    1994-01-01

    Fatigue crack growth tests were conducted on an Fe 510 E C-Mn steel and a submerged arc welded joint from the same material under constant, variable, and random loading amplitudes. Paris-Erdogan's crack growth rate law was tested for the evaluation of m and C using the stress intensity factor K, the J-integral, the effective stress intensity factor K(sub eff), and the root mean square stress intensity factor K(sub rms) fracture mechanics concepts. The effect of retardation and residual stresses resulting from welding was also considered. It was found that all concepts gave good life predictions in all cases.

  4. Fast electromigration crack in nanoscale aluminum film

    NASA Astrophysics Data System (ADS)

    Emelyanov, O. A.; Ivanov, I. O.

    2014-08-01

    The current-induced breakage of 20 nm thin aluminum layers deposited onto capacitor grade polypropylene (PP) films is experimentally studied. Biexponential current pulses of different amplitude (10-15 A) and duration (0.1-1 μs) were applied to the samples. Breakage occurred after fast development of electromigrating ˜200 nm-wide cracks with initial propagation velocity of ˜1 m/s under a high current density of ˜1012 A/m2. The cracks stopped when their lengths reached 250-450 μm. This behavior is explained by the balance of electromigration and stress-induced atomic fluxes.

  5. Matrix cracking of fiber-reinforced ceramic composites in shear

    NASA Astrophysics Data System (ADS)

    Rajan, Varun P.; Zok, Frank W.

    2014-12-01

    The mechanics of cracking in fiber-reinforced ceramic matrix composites (CMCs) under general loadings remains incomplete. The present paper addresses one outstanding aspect of this problem: the development of matrix cracks in unidirectional plies under shear loading. To this end, we develop a model based on potential energy differences upstream and downstream of a fully bridged steady-state matrix crack. Through a combination of analytical solutions and finite element simulations of the constituent stresses before and after cracking, we identify the dominant stress components that drive crack growth. We show that, when the axial slip lengths are much larger than the fiber diameter and when interfacial slip precedes cracking, the shear stresses in the constituents are largely unaffected by the presence of the crack; the changes that do occur are confined to a 'core' region within a distance of about one fiber diameter from the crack plane. Instead, the driving force for crack growth derives mainly from the axial stresses-tensile in the fibers and compressive in the matrix-that arise upon cracking. These stresses are well-approximated by solutions based on shear-lag analysis. Combining these solutions with the governing equation for crack growth yields an analytical estimate of the critical shear stress for matrix cracking. An analogous approach is used in deriving the critical stresses needed for matrix cracking under arbitrary in-plane loadings. The applicability of these results to cross-ply CMC laminates is briefly discussed.

  6. Development of Eddy Current Technique for the Detection of Stress Corrosion Cracking in Space Shuttle Primary Reaction Control Thrusters

    NASA Technical Reports Server (NTRS)

    Wincheski, Buzz; Simpson, John; Koshti, Ajay

    2006-01-01

    A recent identification of stress corrosion cracking in the Space Shuttle Primary Reaction Control System (PRCS) thrusters triggered an extensive nondestructive evaluation effort to develop techniques capable of identifying such damage on installed shuttle hardware. As a part of this effort, specially designed eddy current probes inserted into the acoustic cavity were explored for the detection of such flaws and for evaluation of the remaining material between the crack tip and acoustic cavity. The technique utilizes two orthogonal eddy current probes which are scanned under stepper motor control in the acoustic cavity to identify cracks hidden with as much as 0.060 remaining wall thickness to the cavity. As crack growth rates in this area have been determined to be very slow, such an inspection provides a large safety margin for continued operation of the critical shuttle hardware. Testing has been performed on thruster components with both actual and fabricated defects. This paper will review the design and performance of the developed eddy current inspection system. Detection of flaws as a function of remaining wall thickness will be presented along with the proposed system configuration for depot level or on-vehicle inspection capabilities.

  7. Development of Eddy Current Techniques for the Detection of Cracking in Space Shuttle Primary Reaction Control Thrusters

    NASA Technical Reports Server (NTRS)

    Wincheski, Buzz A.; Simpson, John W.; Koshti, Ajay

    2007-01-01

    A recent identification of cracking in the Space Shuttle Primary Reaction Control System (PRCS) thrusters triggered an extensive nondestructive evaluation effort to develop techniques capable of identifying such damage on installed shuttle hardware. As a part of this effort, specially designed eddy current probes inserted into the acoustic cavity were explored for the detection of such flaws and for evaluation of the remaining material between the crack tip and acoustic cavity. The technique utilizes two orthogonal eddy current probes which are scanned under stepper motor control in the acoustic cavity to identify cracks hidden with as much as 0.060 remaining wall thickness to the cavity. As crack growth rates in this area have been determined to be very slow, such an inspection provides a large safety margin for continued operation of the critical shuttle hardware. Testing has been performed on thruster components with both actual and fabricated defects. This paper will review the design and performance of the developed eddy current inspection system. Detection of flaws as a function of remaining wall thickness will be presented along with the proposed system configuration for depot level or on-vehicle inspection capabilities.

  8. The Effects of Slip Character and Crack Closure on the Growth of Small Fatigue Cracks in Titanium-Aluminium Alloys

    DTIC Science & Technology

    1990-02-01

    Measurement of Small Cracks 128 4.2.5.4 Propagation of Small Cracks 134 4.2.5.4.1 Effect of Stress Level 135 4.2.5.4.2 Effect of Stress Ratio 139...Initiation from Persistent Slip Bands 197 5.1.3.3 Crack -Shape Effects on the Stress Intensity Factor 198 5.2 Primary Experimental Variables 201 5.2.1 Effects...demonstrating the "anomalous" behavior of 6 small fatigue cracks [20,211. Fig. 2.2 Fatigue-limit stress predicted by combining crack initiation and 8 crack

  9. Flux-focusing eddy current probe and rotating probe method for flaw detection

    NASA Astrophysics Data System (ADS)

    Wincheski, Buzz A.; Fulton, James P.; Nath, Shridhar C.; Simpson, John W.; Namkung, Min

    1994-11-01

    A flux-focusing electromagnetic sensor which uses a ferromagnetic flux-focusing lens simplifies inspections and increases detectability of fatigue cracks about circular fasteners and other circular inhomogeneities in high conductivity material. The unique feature of the device is the ferrous shield isolating a high-turn pick-up coil from an excitation coil. The use of the magnetic shield is shown to produce a null voltage output across the receiving coil in the presence of an unflawed sample. A redistribution of the current flow in the sample caused by the presence of flaws, however, eliminates the shielding condition and a large output voltage is produced, yielding a clear unambiguous flaw signal. By rotating the probe in a path around a circular fastener such as a rivet while maintaining a constant distance between the probe and the center of a rivet, the signal due to current flow about the rivet can be held constant. Any further changes in the current distribution, such as due to a fatigue crack at the rivet joint, can be detected as an increase in the output voltage above that due to the flow about the rivet head.

  10. Models in the Design and Validation of Eddy Current Inspection for Cracking in the Shuttle Reaction Control System Thruster

    NASA Technical Reports Server (NTRS)

    Aldrin, John C.; Williams, Phillip A.; Wincheski, Russell (Buzz) A.

    2008-01-01

    A case study is presented for using models in eddy current NDE design for crack detection in Shuttle Reaction Control System thruster components. Numerical methods were used to address the complex geometry of the part and perform parametric studies of potential transducer designs. Simulations were found to show agreement with experimental results. Accurate representation of the coherent noise associated with the measurement and part geometry was found to be critical to properly evaluate the best probe designs.

  11. Acoustic emission assessment of interface cracking in thermal barrier coatings

    NASA Astrophysics Data System (ADS)

    Yang, Li; Zhong, Zhi-Chun; Zhou, Yi-Chun; Zhu, Wang; Zhang, Zhi-Biao; Cai, Can-Ying; Lu, Chun-Sheng

    2016-04-01

    In this paper, acoustic emission (AE) and digital image correlation methods were applied to monitor interface cracking in thermal barrier coatings under compression. The interface failure process can be identified via its AE features, including buckling, delamination incubation and spallation. According to the Fourier transformation of AE signals, there are four different failure modes: surface vertical cracks, opening and sliding interface cracks, and substrate deformation. The characteristic frequency of AE signals from surface vertical cracks is 0.21 MHz, whilst that of the two types of interface cracks are 0.43 and 0.29 MHz, respectively. The energy released of the two types of interface cracks are 0.43 and 0.29 MHz, respectively. Based on the energy released from cracking and the AE signals, a relationship is established between the interface crack length and AE parameters, which is in good agreement with experimental results.

  12. A Parametric Study of Crack Propagation During Sonic IR Inspection

    NASA Astrophysics Data System (ADS)

    Chen, J. C.; Kephart, J.; Riddell, W. T.

    2006-03-01

    We have developed an experiment to study the propagation of synthetic cracks under various controlled conditions during sonic IR inspection. The experiment provides for good repeatability in testing. The parameters of interest include the initial crack length, load history (stress intensity and load ratio) during crack generation, geometry of the crack, material, and also the various conditions involving the ultrasonic source. In general, we find that under typical sonic IR inspection conditions, the initial crack will propagate when subjected to sonic IR testing. The crack growth after each inspection event varies and exhibits a distribution in length of propagation. The results show that the average crack propagation decreases with increasing initial crack length and increasing stress intensity.

  13. Measurement of fatigue crack closure for negative stress ratio

    SciTech Connect

    Romeiro, F.F.J.; Domingos, C.A.; Freitas, M.J.M. de

    1999-07-01

    The concept of fatigue crack closure, introduced in the 60's by Elber, has been used to explain a wide range of positive stress ratio crack propagation results (R {ge} 0). Less attention has been given to fatigue loading for negative stress ratios (R {lt} 0). In this work the results of crack propagation tests of middle-crack tension M(T) specimens of a normalized medium carbon steel DIN Ck 45 for a wide range of stress ratios from 0.7 {ge} R {ge} {minus}3 are presented. Crack closure loads were measured with the compliance technique at test frequency, using a data acquisition system. Negative crack closure loads were found for negative stress ratios R {le} {minus}1, which can explain higher crack propagation rates and accelerations in crack growth during variable-amplitude tests where compressive loads of different stress ratios are present.

  14. Subharmonic phased array for crack evaluation using surface acoustic wave

    NASA Astrophysics Data System (ADS)

    Ouchi, Akihiro; Sugawara, Azusa; Ohara, Yoshikazu; Yamanaka, Kazushi

    2015-07-01

    To accurately measure closed crack length, we proposed an imaging method using a subharmonic phased array for crack evaluation using surface acoustic waves (SAW SPACE) with water immersion. We applied SAW SPACE to the hole specimen in a fundamental array (FA) image. The hole was imaged with high resolution. Subsequently, SAW SPACE was applied to fatigue crack and stress corrosion crack (SCC) specimens. A fatigue crack was imaged in FA and subharmonic array (SA) images, and the length of this particular fatigue crack measured in the images was almost the same as that measured by optical observation. The SCC was imaged and its length was accurately measured in the SA image, whereas it was underestimated in the FA image and by optical observation. Thus, we demonstrated that SAW SPACE with water immersion is useful for the accurate measurement of closed crack length and for imaging the distribution of open and closed parts of cracks with high resolution.

  15. Influence of Subsurface Cracks on Laser Induced Surface Damage

    SciTech Connect

    Feit, M D; Rubenchik, A M

    2003-11-07

    Cracks can affect laser damage susceptibility in three ways. These are field intensification due to interference, enhanced absorption due to trapped material in the cracks, and increased mechanical weakness. Enhanced absorption is the most important effect.

  16. Cracking the Genetic Code | NIH MedlinePlus the Magazine

    MedlinePlus

    ... this page please turn Javascript on. Cracking the Genetic Code, From NIH Director Dr. Francis S. Collins Past ... moment in science in 2000: Cracking of the genetic code raised the prospect of pinpointing the root ...

  17. Joints That Make Those Popping or Cracking Sounds

    MedlinePlus

    ... html Joints That Make Those Popping or Cracking Sounds The noises may be irritating, but they're ... joints to make popping and cracking noises. These sounds can be caused by a number of things, ...

  18. Subharmonic wave analysis in crack using the developed FEM

    NASA Astrophysics Data System (ADS)

    Mihara, Tsuyoshi; Shimaya, Koji; Ikegami, Yasushi; Furukawa, Takashi; Komura, Ichiro

    2012-09-01

    As the first step of the improvement of developed FEM code to extend the subharmonic wave generation at nano scale gap crack, we investigated the basic crack model for accurate simulator of subharmonic behavior using the voxel mesh FEM code.

  19. Control and Manipulation of Nano Cracks Mimicking Optical Wave

    NASA Astrophysics Data System (ADS)

    Suh, Young D.; Yeo, Junyeob; Lee, Habeom; Hong, Sukjoon; Kwon, Jinhyeong; Kim, Kyunkyu; Ko, Seung Hwan

    2015-11-01

    Generally, a fracture is considered as an uncontrollable thus useless phenomenon due to its highly random nature. The aim of this study is to investigate highly ordered cracks such as oscillatory cracks and to manipulate via elaborate control of mechanical properties of the cracking medium including thickness, geometry, and elastic mismatch. Specific thin film with micro-sized notches was fabricated on a silicon based substrate in order to controllably generate self-propagating cracks in large area. Interestingly, various nano-cracks behaved similar to optical wave including refraction, total internal reflection and evanescent wave. This novel phenomena of controlled cracking was used to fabricate sophisticated nano/micro patterns in large area which cannot be obtained even with conventional nanofabrication methods. We also have showed that the cracks are directly implementable into a nano/micro-channel application since the cracks naturally have a form of channel-like shape.

  20. Control and Manipulation of Nano Cracks Mimicking Optical Wave

    PubMed Central

    Suh, Young D.; Yeo, Junyeob; Lee, Habeom; Hong, Sukjoon; Kwon, Jinhyeong; Kim, Kyunkyu; Ko, Seung Hwan

    2015-01-01

    Generally, a fracture is considered as an uncontrollable thus useless phenomenon due to its highly random nature. The aim of this study is to investigate highly ordered cracks such as oscillatory cracks and to manipulate via elaborate control of mechanical properties of the cracking medium including thickness, geometry, and elastic mismatch. Specific thin film with micro-sized notches was fabricated on a silicon based substrate in order to controllably generate self-propagating cracks in large area. Interestingly, various nano-cracks behaved similar to optical wave including refraction, total internal reflection and evanescent wave. This novel phenomena of controlled cracking was used to fabricate sophisticated nano/micro patterns in large area which cannot be obtained even with conventional nanofabrication methods. We also have showed that the cracks are directly implementable into a nano/micro-channel application since the cracks naturally have a form of channel-like shape. PMID:26612107