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1

Weld pool phenomena  

SciTech Connect

During welding, the composition, structure and properties of the welded structure are affected by the interaction of the heat source with the metal. The interaction affects the fluid flow, heat transfer and mass transfer in the weld pool, and the solidification behavior of the weld metal. In recent years, there has been a growing recognition of the importance of the weld pool transport processes and the solid state transformation reactions in determining the composition, structure and properties of the welded structure. The relation between the weld pool transport processes and the composition and structure is reviewed. Recent applications of various solidification theories to welding are examined to understand the special problems of weld metal solidification. The discussion is focussed on the important problems and issues related to weld pool transport phenomena and solidification. Resolution of these problems would be an important step towards a science based control of composition, structure and properties of the weld metal.

David, S.A.; Vitek, J.M.; Zacharia, T. [Oak Ridge National Lab., TN (United States); DebRoy, T. [Pennsylvania State Univ., University Park, PA (United States)

1994-09-01

2

INFLUENCE OF SURFACE DEPRESSION AND CONVECTION ON ARC WELD POOL GEOMETRY  

E-print Network

) ) INFLUENCE OF SURFACE DEPRESSION AND CONVECTION ON ARC WELD POOL GEOMETRY M. L. Lin and T. W into account because all a r e found to have more or less influence on the weld pool geometry. If the welding process i s to be automated with cl osed l oop control of the weld zone size, it is desirable to more

Eagar, Thomas W.

3

Ultrasonic detection of molten\\/solid interfaces of weld pools  

Microsoft Academic Search

Results of the study indicate that it is possible to detect molten weld-pool interfaces and obtain information about their size and location using ultrasonic techniques. The study has also identified problems which must be solved before the technique can be used for weld process control: (1) making a positive identification of reflected ultrasonic signals, i.e., distinguishing between signals reflected from

Lott

1982-01-01

4

Numerical Study for Gta Weld Shape Variation by Coupling Welding Arc and Weld Pool  

NASA Astrophysics Data System (ADS)

A numerical modeling of the welding arc and weld pool is studied for moving GTA welding to investigate the effect of the surface active element oxygen and the plasma drag force on the weld shape. Based on the 2D axisymmetric numerical modeling of the argon arc, the heat flux, current density and plasma drag force are obtained under different welding currents. Numerical calculations to the weld pool development are carried out for moving GTA welding on SUS304 stainless steel with different oxygen contents 30 ppm and 220 ppm, respectively. The results show that the plasma drag force is another dominating driving force affecting the liquid pool flow pattern, except for the Marangoni force. The different welding currents will change the temperature distribution and plasma drag force on the pool surface, and affect the strength of Marangoni convection and the weld shape. The weld D/W ratio initially increases, followed by a constant value around 0.5 with the increasing welding current under high oxygen content. The weld D/W ratio under the low oxygen content slightly decreases with the increasing welding current. The predicted weld shape by simulation agrees well with experimental results.

Dong, Wenchao; Lu, Shanping; Li, Dianzhong; Li, Yiyi

5

Heat and fluid flow in pulsed current GTA weld pool  

Microsoft Academic Search

In this study the heat transfer, fluid flow and phase change of the weld pool in pulsed current gas tungsten arc (GTA) welding were investigated. Transporting phenomena from the welding arc to the base material surface, such as current density, heat flux, arc pressure and shear stress acting on the weld pool surface, were taken from the simulation results of

W.-H. Kim; S.-J. Na

1998-01-01

6

Weld pool flow visualization studies during gas tungsten arc welding of steel and aluminum. Master's thesis  

Microsoft Academic Search

A flow visualization study of current distribution effects on weld pool stirring in GTA steel welds is presented using a pulsed ultraviolet laser vision system. Weld pool stirring is almost eliminated in HY-80 steel by the use of symmetric current flow path within the weld samples. Periodic radial surface pulses are observed at low currents in stationary welds while flows

Schupp

1992-01-01

7

Weld pool flow visualization studies during gas tungsten arc welding of steel and aluminum  

Microsoft Academic Search

A flow visualization study of current distribution effects on weld pool stirring in GTA steel welds is presented using a pulsed ultraviolet laser vision system. Weld pool stirring is almost eliminated in HY-80 steel by the use of symmetric current flow path within the weld samples. Periodic radial surface pulses are observed at low currents in stationary welds while flows

Peter E. Schupp

1992-01-01

8

Thermocapillary flow in a pulsed-laser weld pool  

Microsoft Academic Search

Pulsed-laser welding produces short-lived weld pools which have strong radial temperature gradients at the pool surface. These gradients produce surface tension variations which usually reinforce the weak natural convective flows caused by radial temperature gradients. The flow in the molten pool is of interest because it can change the temperature distribution in and around the molten zone which can alter

A. J. Russo; R. L. Akau; J. L. Jellison

1986-01-01

9

A shape optimization formulation of weld pool determination. , A. Ellabibb  

E-print Network

, 25 (2011) 374-379" DOI : 10.1016/j.aml.2011.09.017 #12;Figure 1: The solid part of the weldedA shape optimization formulation of weld pool determination. A. Chakiba , A. Ellabibb , A modeling a process of welding. We show the existence of an optimal solution. The finite element method

Paris-Sud XI, Université de

10

Ultrasonic detection of molten\\/solid interfaces of weld pools  

Microsoft Academic Search

Ultrasonic techniques are being studied for the detection and location of the liquid\\/solid interfaces of molten weld pools in metals during the welding process. The objective of the study is to develop a technique for sensing the depth or lateral position of a weld pool and providing a real-time control signal to the welder to achieve a completely automated, process-controlled

Lott

1984-01-01

11

Influence of the arc plasma parameters on the weld pool profile in TIG welding  

NASA Astrophysics Data System (ADS)

Magneto-hydrodynamic simulations of the arc and fluid simulations of the weld pool can be beneficial in the analysis and further development of arc welding processes and welding machines. However, the appropriate coupling of arc and weld pool simulations needs further improvement. The tungsten inert gas (TIG) welding process is investigated by simulations including the weld pool. Experiments with optical diagnostics are used for the validation. A coupled computational model of the arc and the weld pool is developed using the software ANSYS CFX. The weld pool model considers the forces acting on the motion of the melt inside and on the surface of the pool, such as Marangoni, drag, electromagnetic forces and buoyancy. The experimental work includes analysis of cross-sections of the workpieces, highspeed video images and spectroscopic measurements. Experiments and calculations have been performed for various currents, distances between electrode and workpiece and nozzle diameters. The studies show the significant impact of material properties like surface tension dependence on temperature as well as of the arc structure on the weld pool behaviour and finally the weld seam depth. The experimental weld pool profiles and plasma temperatures are in good agreement with computational results.

Toropchin, A.; Frolov, V.; Pipa, A. V.; Kozakov, R.; Uhrlandt, D.

2014-11-01

12

TOPICAL REVIEW: Predictions of weld pool profiles using plasma physics  

NASA Astrophysics Data System (ADS)

This paper gives a review of recent papers which have led to the capability of the prediction of weld depths for gas tungsten arc welding, for any given arc current, electrode shape or separation and welding gas. The methodology is given for deriving plasma composition as a function of temperature and pressure from basic atomic and molecular properties. Transport coefficients of density, specific heat, enthalpy, electrical conductivity, thermal conductivity, viscosity and radiation emission coefficients can then be derived as a function of temperature. The conservation equations of fluid dynamics are then used to derive weld profiles for stainless steel for welding gases such as argon, helium, carbon dioxide and a 10% mixture of hydrogen in argon. The markedly different weld depths which are obtained are related to basic material functions such as specific heat, electrical and thermal conductivity. The temperature dependence of the surface tension coefficient has a marked effect on weld depth and profiles because it can influence the direction of circulatory flow in the weld pool. Electric arcs in helium and carbon dioxide are more constricted than arcs in argon and as a consequence the magnetic pinch pressure of the arc, transmitted to the weld pool, can force strong downward flows in the weld pool and thus lead to a deep weld. It is found that because of the interactions of the arc and the weld pool through effects such as viscous drag forces of the plasma on the weld pool, it is necessary to treat the arc, the electrode and the weld pool in a unified system.

Tanaka, M.; Lowke, J. J.

2007-01-01

13

Modeling of the Weld Shape Development During the Autogenous Welding Process by Coupling Welding Arc with Weld Pool  

NASA Astrophysics Data System (ADS)

A numerical model of the welding arc is coupled to a model for the heat transfer and fluid flow in the weld pool of a SUS304 stainless steel during a moving GTA welding process. The described model avoids the use of the assumption of the empirical Gaussian boundary conditions, and at the same time, provides reliable boundary conditions to analyze the weld pool. Based on the two-dimensional axisymmetric numerical modeling of the argon arc, the heat flux to workpiece, the input current density, and the plasma drag stress are obtained. The arc temperature contours, the distributions of heat flux, and current density at the anode are in fair agreement with the reported experimental results. Numerical simulation and experimental studies to the weld pool development are carried out for a moving GTA welding on SUS304 stainless steel with different oxygen content from 30 to 220 ppm. The calculated result show that the oxygen can change the Marangoni convection from outward to inward direction on the liquid pool surface and make the wide shallow weld shape become narrow deep one. The calculated result for the weld shape and weld D/W ratio agrees well with the experimental one.

Dong, Wenchao; Lu, Shanping; Li, Dianzhong; Li, Yiyi

2010-10-01

14

Vision-based weld pool boundary extraction and width measurement during keyhole fiber laser welding  

NASA Astrophysics Data System (ADS)

In keyhole fiber laser welding processes, the weld pool behavior is essential to determining welding quality. To better observe and control the welding process, the accurate extraction of the weld pool boundary as well as the width is required. This work presents a weld pool edge detection technique based on an off axial green illumination laser and a coaxial image capturing system that consists of a CMOS camera and optic filters. According to the difference of image quality, a complete developed edge detection algorithm is proposed based on the local maximum gradient of greyness searching approach and linear interpolation. The extracted weld pool geometry and the width are validated by the actual welding width measurement and predictions by a numerical multi-phase model.

Luo, Masiyang; Shin, Yung C.

2015-01-01

15

Process parameter selection for optimizing the weld pool geometry in the tungsten inert gas welding of stainless steel  

Microsoft Academic Search

In this paper, the selection of process parameters for obtaining an optimal weld pool geometry in the tungsten inert gas (TIG) welding of stainless steel is presented. Basically, the geometry of the weld pool has several quality characteristics, for example, the front height, front width, back height and back width of the weld pool. To consider these quality characteristics together

S. C Juang; Y. S Tarng

2002-01-01

16

Bubble flow and the formation of cavity defect in weld pool of vacuum electron beam welding  

Microsoft Academic Search

Seen from gas-liquid two-phase-flow system, the gas phase and liquid phase of bubble flow in weld pool are studied by means of isolated phase based on the conservation of mass and momentum. The two-dimensional fractional flow model of bubble flow in weld pool of vacuum electron beam welding is developed. And the gas distribution and the phenomenon of bubble flow

Yi Luo; Jinhe Liu; Hong Ye

2011-01-01

17

Molten pool characterization of laser lap welded copper and aluminum  

NASA Astrophysics Data System (ADS)

A 3D finite volume simulation model for laser welding of a Cu-Al lap joint was developed using ANSYS FLUENT to predict the weld pool temperature distribution, velocity field, geometry, alloying element distribution and transition layer thickness—all key attributes and performance characteristics for a laser-welded joint. Melting and solidification of the weld pool was simulated with an enthalpy-porosity formulation. Laser welding experiments and metallographic examination by SEM and EDX were performed to investigate the weld pool features and validate the simulated results. A bowl-shaped temperature field and molten pool, and a unique maximum fusion zone width were observed near the Cu-Al interface. Both the numerical simulation and experimental results indicate an arch-shaped intermediate layer of Cu and Al, and a gradual transition of Cu concentration from the aluminum plate to the copper plate with high composition gradient. For the conditions used, welding with Cu on top was found to result in a better weld joint.

Xue, Zhiqing; Hu, Shengsun; Zuo, Di; Cai, Wayne; Lee, Dongkyun; Elijah, Kannatey-Asibu, Jr.

2013-12-01

18

A study of arc force, pool depression and weld penetration during gas tungsten arc welding  

SciTech Connect

Weld pool depression, arc force, weld penetration, and their interrelations have been studied as a function of welding current. Pool depression and welding arc force have been measured simultaneously using a recently developed technique. The authors found quadratic dependence of arc force on current, confirming similar findings in previous studies. Pool depression is essentially zero below a threshold level of current (200 A in this experiment) and then increases quadratically with current. A perfectly linear relation between arc force and pool depression was found in the current range from 200 to 350 A, with pool depression onset at about 0.35 g force (0.34 [center dot] 10[sup [minus]2]N). The total surface tension and gravitational forces were calculated, from the measured surface topography, and found to be about five times that required to balance the arc force at 300 A. Thus electromagnetic and hydrodynamic forces must be taken into account to explain the measured levels of pool depression. The relation between weld penetration and pool depression for different welding currents has been established. Three distinct regimes of weld penetration on weld current were found.

Rokhlin, S.I.; Guu, A.C. (Ohio State Univ., Columbus, OH (United States). Dept. of Welding Engineering)

1993-08-01

19

On the calculation of the free surface temperature of gas-tungsten-arc weld pools from first principles: Part II. modeling the weld pool and comparison with experiments  

Microsoft Academic Search

By combining a mathematical model of the welding arc and of the weld pool, calculations are presented to describe the free\\u000a surface temperature of weld pools for spot welding operations. The novel aspects of the treatment include the calculation\\u000a of the heat and current fluxes falling on the free weld pool surface from first principles, a realistic allowance for heat

R. T. C. Choo; J. Szekely; S. A. David

1992-01-01

20

Experimental and Numerical Investigation of an Electromagnetic Weld Pool Control for Laser Beam Welding  

NASA Astrophysics Data System (ADS)

The objective of this study was to investigate the influence of externally applied magnetic fields on the weld quality in laser beam welding. The optimization of the process parameters was performed using the results of computer simulations. Welding tests were performed with up to 20 kW laser beam power. It was shown that the AC magnet with 3 kW power supply allows for a prevention of the gravity drop-out for full penetration welding of 20 mm thick stainless steel plates. For partial penetration welding it was shown that an0.5 T DC magnetic field is enough for a suppression of convective flows in the weld pool. Partial penetration welding tests with 4 kW beam power showed that the application of AC magnetic fields can reduce weld porosity by a factor of 10 compared to the reference joints. The weld surface roughness was improved by 50%.

Bachmann, M.; Avilov, V.; Gumenyuk, A.; Rethmeier, M.

21

Process stability and weld pool oscillation during short circuiting GMA welding  

SciTech Connect

In this paper the results are presented of an investigation dealing with short circuiting GMA welding. Experiments were carried out under different conditions and during these experiments various process parameters were continuously monitored. It was found that the maximum in process stability coincides with the maximum in the short circuit frequency. Outside this maximum either irregular material transfer takes place with a tendency for open arc droplet transfer, or stubbing of the welding wire in the weld pool starts to occur, accompanied by highly irregular melt-off behavior. The results show that process stability is directly related to weld pool oscillation. More specifically, it appears that process stability is maximum (optimum welding conditions) when the short circuit frequency equals the oscillation frequency of the weld pool. Under these conditions the weld pool touches the droplet at every oscillation, which results in regular droplet transfer and high stability of the overall welding process. This was confirmed by high-speed films. In order to determine the influence of the chemical composition of the liquid metal and the shielding gas on the short circuiting behavior, welding experiments were carried out with different base metals and shielding gas mixtures. The results of these experiments show that the chemical composition of the shielding gas and the weld metal has a pronounced effect on the optimal welding conditions. For instance, when austenitic stainless steel AISI 316 is used, the maximum short circuit frequency (being equal to the oscillation frequency) is approximately 6% higher than in the case of unalloyed steel. The results obtained can be explained in terms of the physical properties of the liquid metal, in particular the surface tension.

Hermans, M.J.M.; Ouden, G. den [Delft Univ. of Technology (Netherlands)

1996-12-31

22

Stability of Full Penetration, Flat Position Weld Pools  

NASA Technical Reports Server (NTRS)

The dynamics of the dropthrough distance of a full penetration, flat position weld pool is described. Close to incipient root side penetration the dropthrough is metastable, so that a small drop in power can cause a loss of penetration if not followed soon enough by a compensating rise in power. The SPA (Soft Plasma Arc) process with higher pressure on top of the weld pool loses penetration more quickly than the GTA (Gas Tungsten Arc) process. 2195 aluminum-lithium alloy with a lower surface tension loses penetration more quickly than 2219 aluminum alloy. An instance of loss of penetration of a SPA weld in 2195 aluminum-lithium alloy is discussed in the light of the model.

Nunes, Arthur C., Jr.; Coan, Al. B.

1999-01-01

23

Effect of Welding Parameters on the Size of Heat Affected Zone of Submerged Arc Welding  

Microsoft Academic Search

This paper discusses the effect of welding parameters on the size of the heat affected zone (HAZ) and its relative size as compared to the weld bead of submerged arc welding. It is discovered that the welding parameters influences the size of weld bead and HAZ differently which can be relate to the effect of welding parameters on the various

C. S. Lee; R. S. Chandel; H. P. Seow

2000-01-01

24

On the calculation of the free surface temperature of gas-tungsten-arc weld pools from first principles: Part II. modeling the weld pool and comparison with experiments  

NASA Astrophysics Data System (ADS)

By combining a mathematical model of the welding arc and of the weld pool, calculations are presented to describe the free surface temperature of weld pools for spot welding operations. The novel aspects of the treatment include the calculation of the heat and current fluxes falling on the free weld pool surface from first principles, a realistic allowance for heat losses due to vaporization, and a realistic allowance for the temperature dependence of the surface tension. The most important finding reported in this article is that the free surface temperature of weld pools appears to be limited by Marangoni convection, rather than heat losses due to vaporiza-tion. Furthermore, it was found that once thermocapillary flow can produce high enough surface velocities (>25 cm/s), the precise nature of the relationship between temperature and surface tension will become less important.

Choo, R. T. C.; Szekely, J.; David, S. A.

1992-06-01

25

Simultaneous vision image sensing of weld pool of pulsed GTAW in multi-orientation in a frame  

NASA Astrophysics Data System (ADS)

Welding arc light spectrum in the range of 600nm~700nm basically composes of continuous spectrum without metal spectrum and argon spectrum. The radiation strength of this continuous spectrum is low and smooth, which is benefit for reducing process, and the response sensitivity of CCD camera is high at this wavelength range. So, choose a suitable imaging spectrum window, use the continuous spectrum of this window to illuminate the welding pool and use CCD camera to sample the pool image. The reflection of arc light from liquid metal pool surface is specular reflection, the reflection of arc light from the workpiece surface is diffuse reflection, which improves the contrast of the welding pool image. This kind of vision image sensing method takes full advantage of the arc light as a benefit factor, and realizes to acquire the comprehensive information of the pool only from a single sensing source. Based on the above principle, this paper develops a visual image sensing system for weld zone of pulsed GTAW. The system as a part of the control system for weld shape can realize simultaneous image sensing of front topside, back topside and bottom side weld pool in a frame. Both the topside and bottom images concentrate on the same target of the CCD camera through the visual sensing light path system. The composite filter technology with low sampling image current is used to overcome the influence of arc light. The high quality and clear images of weld zones are acquired, which supply plenty information to study the dynamic process of pulsed GTAW. In addition, in order to extract the actual size parameters of weld pool, the image sensing system is calibrated.

Zhang, Guangjun; Chen, Shanben; Liu, Xiaodong; Wu, Lin

2001-09-01

26

Heat transfer and fluid flow in a partially or fully penetrated weld pool in gas tungsten arc welding  

Microsoft Academic Search

In this study, fluid flow driven by a combination of electromagnetic force, buoyancy force, arc drag force, and surface tension gradient is numerically analyzed for a partially or fully penetrated weld pool in stationary gas tungsten arc welding (GTAW). Irregular shape of the weld pool and the moving liquid–solid interface is handled by a boundary-fitted-coordinates technique. Surface tension on the

H. G. Fan; H. L. Tsai; S. J. Na

2000-01-01

27

Automatic Welding System of Aluminum Pipe by Monitoring Backside Image of Molten Pool Using Vision Sensor  

NASA Astrophysics Data System (ADS)

An automatic welding system using Tungsten Inert Gas (TIG) welding with vision sensor for welding of aluminum pipe was constructed. This research studies the intelligent welding process of aluminum alloy pipe 6063S-T5 in fixed position and moving welding torch with the AC welding machine. The monitoring system consists of a vision sensor using a charge-coupled device (CCD) camera to monitor backside image of molten pool. The captured image was processed to recognize the edge of molten pool by image processing algorithm. Neural network model for welding speed control were constructed to perform the process automatically. From the experimental results it shows the effectiveness of the control system confirmed by good detection of molten pool and sound weld of experimental result.

Baskoro, Ario Sunar; Kabutomori, Masashi; Suga, Yasuo

28

Convection in Arc Weld Pools Electromagnetic and surface tension forces are shown to  

E-print Network

Convection in Arc Weld Pools Electromagnetic and surface tension forces are shown to dominate flow and heat flow in weld pools is of considerable practical interest because convective heat flow will affect majority of heat flow analyses, no allowance has been made for convective heat flow in the melt

Eagar, Thomas W.

29

Metal Vaporization from Weld Pools A. BLOCK-BOLTEN and T. W. EAGAR  

E-print Network

TRANSAcnONS B Water- cooled turntable and gas-coaled electrode-holder Fig. I-Water-cooled turntable and gas-cooled) ) Metal Vaporization from Weld Pools A. BLOCK-BOLTEN and T. W. EAGAR Experimental studies of alloy vaporization from aluminum and stainless steel weld pools have been made in order to test

Eagar, Thomas W.

30

Measurement of laser welding pool geometry using a closed convex active contour model  

NASA Astrophysics Data System (ADS)

The purpose of this study was to develop a computer vision method to measure geometric parameters of the weld pool in a deep penetration CO2 laser welding system. Accurate measurement was achieved by removing a huge amount of interference caused by spatter, arc light and plasma to extract the true weld pool contour. This paper introduces a closed convex active contour (CCAC) model derived from the active contour model (snake model), which is a more robust high-level vision method than the traditional low-level vision methods. We made an improvement by integrating an active contour with the information that the weld pool contour is almost a closed convex curve. An effective thresholding method and an improved greedy algorithm are also given to complement the CCAC model. These influences can be effectively removed by using the CCAC model to acquire and measure the weld pool contour accurately and relatively fast.

Zheng, Rui; Zhang, Pu; Duan, Aiqing; Xiao, Peng

2014-03-01

31

Experimental characterization of the weld pool flow in a TIG configuration  

NASA Astrophysics Data System (ADS)

Tungsten Inert Gas (TIG) welding process relies on heat transfer between plasma and work piece leading to a metallic weld pool. Combination of different forces produces movements on the molten pool surface. One of our aims is to determine the velocity on the weld pool surface. This provides a set of data that leads to a deeper comprehension of the flow behavior and allows us to validate numerical models used to study TIG parameters. In this paper, two diagnostic methods developed with high speed imaging for the determination of velocity of an AISI 304L stainless steel molten pool are presented. Application of the two methods to a metallic weld pool under helium with a current intensity of 100 A provides velocity values around 0.70 m/s which are in good agreement with literature works.

Stadler, M.; Masquère, M.; Freton, P.; Franceries, X.; Gonzalez, J. J.

2014-11-01

32

Use of Aria to simulate laser weld pool dynamics for neutron generator production.  

SciTech Connect

This report documents the results for the FY07 ASC Integrated Codes Level 2 Milestone number 2354. The description for this milestone is, 'Demonstrate level set free surface tracking capabilities in ARIA to simulate the dynamics of the formation and time evolution of a weld pool in laser welding applications for neutron generator production'. The specialized boundary conditions and material properties for the laser welding application were implemented and verified by comparison with existing, two-dimensional applications. Analyses of stationary spot welds and traveling line welds were performed and the accuracy of the three-dimensional (3D) level set algorithm is assessed by comparison with 3D moving mesh calculations.

Noble, David R.; Notz, Patrick K.; Martinez, Mario J.; Kraynik, Andrew Michael

2007-09-01

33

Weld pool penetration measurement using ultrasound with thermal gradient correction factors  

NASA Astrophysics Data System (ADS)

Weld penetration is critical to final weld performance. There are many techniques for determining surface parameters of weld pools but the transient nature of the pools, high temperatures and intense electromagnetic energy make direct measurement of the penetration of weld pools difficult. In order to determine weld pool penetration ultrasonically from below the weld pool it is necessary to compensate for the variation in the time of flight of the ultrasound wave due to temperature gradients. This requires both a precise understanding of the location and magnitude of the temperature gradients and the time of flight of ultrasound at the range of temperatures seen in the gradients. Given this information it is possible to develop a correction factor to an ultrasonic time of flight reading that accurately represents the actual penetration of a weld pool. This research examines the electroslag surfacing (ESS) processing of AISI 1005 low carbon steel clad onto a ductile iron substrate. The high temperature cladding on low temperature substrate provides a deep weld penetration. Ultrasonic time of flight measurements were made from a piezoelectric transducer on the backside of the substrate to the solid/liquid interface of the weld pool during welding. The speed of ultrasound over a range of temperatures was determined from furnace heated ductile iron substrates. The sample was stepped and contact piezoelectric methods used to determine time of flight. A finite element model was developed and analyzed to predict thermal gradients in the substrate around the weld pool. The model was correlated to thermocouple data of substrate heating during welding. The predicted thermal gradients and speed/temperature curves are combined with the time of flight measurement to determine the location of the solid/liquid weld interface. An automated seam tracking system for ESS was also developed. This system utilizes a line laser at right angles to the view of a CCD camera which illuminates the relief of the existing bead for the camera. Optimas software was used to locate the edge of the bead and determine the correct location for the weld head to overlap the existing bead.

Anderton, John Martin

34

TOWARDS AN FVEFAC METHOD FOR DETERMINING THERMOCAPILLARY EFFECTS ON WELD POOL SHAPE  

E-print Network

TOWARDS AN FVE­FAC METHOD FOR DETERMINING THERMOCAPILLARY EFFECTS ON WELD POOL SHAPE David Canright Several practical materials processes, e.g., welding, float­zone purification, and Czochralski crystal this mechanism and its effect on the solid­liquid interface through a model problem: a half space of pure

35

Residual Stresses and Critical Initial Flaw Size Analyses of Welds  

NASA Technical Reports Server (NTRS)

An independent assessment was conducted to determine the critical initial flaw size (CIFS) for the flange-to-skin weld in the Ares I-X Upper Stage Simulator (USS). A series of weld analyses are performed to determine the residual stresses in a critical region of the USS. Weld residual stresses both increase constraint and mean stress thereby having an important effect on the fatigue life. The purpose of the weld analyses was to model the weld process using a variety of sequences to determine the 'best' sequence in terms of weld residual stresses and distortions. The many factors examined in this study include weld design (single-V, double-V groove), weld sequence, boundary conditions, and material properties, among others. The results of this weld analysis are included with service loads to perform a fatigue and critical initial flaw size evaluation.

Brust, Frederick W.; Raju, Ivatury, S.; Dawocke, David S.; Cheston, Derrick

2009-01-01

36

TOPICAL REVIEW: Predictions of weld pool profiles using plasma physics  

Microsoft Academic Search

This paper gives a review of recent papers which have led to the capability of the prediction of weld depths for gas tungsten arc welding, for any given arc current, electrode shape or separation and welding gas. The methodology is given for deriving plasma composition as a function of temperature and pressure from basic atomic and molecular properties. Transport coefficients

M. Tanaka; J. J. Lowke

2007-01-01

37

Gravitational effects on the weld pool shape and microstructural evolution during gas tungsten arc and laser beam welding of 304 stainless steel and Al-4 wt% Cu alloy.  

PubMed

Effects of gravitational acceleration were investigated on the weld pool shape and microstructural evolution for 304 stainless steel and Al-4wt% Cu alloy. Effects of welding heat source were investigated by using laser beam welding (LBW) and gas tungsten arc welding (GTAW). As the gravitational level was increased from low gravity (LG approximately 1.2 g) to high gravity (HG approximately 1.8 g) using a NASA KC-135 aircraft, the weld pool shape for 304 stainless steel was influenced considerably during GTAW. However, insignificant change in the microstructure and solute distribution was observed at gravitational levels between LG and HG. The GTAW on Al-4 wt% Cu alloy was used to investigate the effect of gravitational orientation on the weld solidification behavior. Gravitational orientation was manipulated by varying the welding direction with respect to gravity vector; that is, by welding upward opposing gravity ( ||-U) and downward with gravity ( ||-D) on a vertical weld piece and welding perpendicular to gravity (perpendicular) on a horizontal weld piece. Under the same welding conditions, a larger primary dendrite spacing in the ||-U weld was observed near the weld pool surface and the fusion boundary than in the case of perpendicular or ||-D welds. The ||-D weld exhibited different solidification morphology and abnormal S shape of solidification rate curve during its growth. For 304 stainless steel GTAW, significant effects of gravitational orientation were observed on the weld pool shape that was associated with weld surface morphology and convection flow. However, the weld pool shape for LBW was mostly constant with respect to the gravitational orientation. PMID:15644379

Kang, Namhyun; Singh, Jogender; Kulkarni, Anil K

2004-11-01

38

Predicting the backside width of weld pool during pulsed GTAW process based on a neural network model  

Microsoft Academic Search

Modeling of welding process is the base of process control. Because welding process is a multivariable, strong coupling, time-varying and nonlinear system, traditional modeling methods are not suitable. In this paper, the dynamic neural network model for predicting backside width of pulsed GTAW weld pool by welding parameters and topside shape parameters was constructed. Orthogonal method was applied to design

Guangjun Zhang; Shanben Chen; Xiaodong Liu; Lin Wu

2001-01-01

39

Effect of Shoulder Size on Weld Properties of Dissimilar Metal Friction Stir Welds  

Microsoft Academic Search

This article reports a research study that shows the effect of shoulder diameter size on the resulting weld properties of dissimilar friction stir welds between 5754 aluminum alloy (AA) and C11000 copper (Cu). Welds were produced using three different shoulder diameter tools: 15, 18, and 25 mm by varying the rotational speed between 600 and 1200 rpm and the traverse

E. T. Akinlabi

2011-01-01

40

Weld pool temperatures of steel S235 while applying a controlled short-circuit gas metal arc welding process and various shielding gases  

NASA Astrophysics Data System (ADS)

The temperature determination of liquid metals is difficult and depends strongly on the emissivity. However, the surface temperature distribution of the weld pool is an important characteristic of an arc weld process. As an example, short-arc welding of steel with a cold metal transfer (CMT) process is considered. With optical emission spectroscopy in the spectral region between 660 and 840 nm and absolute calibrated high-speed camera images the relation between temperature and emissivity of the weld pool is determined. This method is used to obtain two-dimensional temperature profiles in the pictures. Results are presented for welding materials (wire G3Si1 on base material S235) using different welding CMT processes with CO2 (100%), Corgon 18 (18% CO2 + 82% Ar), VarigonH6 (93.5% Ar + 6.5% H2) and He (100%) as shielding gases. The different gases are used to study their influence on the weld pool temperature.

Kozakov, R.; Schöpp, H.; Gött, G.; Sperl, A.; Wilhelm, G.; Uhrlandt, D.

2013-11-01

41

Monitoring of high-power fiber laser welding based on principal component analysis of a molten pool configuration  

NASA Astrophysics Data System (ADS)

There exists plenty of welding quality information on a molten pool during high-power fiber laser welding. An approach for monitoring the high-power fiber laser welding status based on the principal component analysis (PCA) of a molten pool configuration is investigated. An infrared-sensitive high-speed camera was used to capture the molten pool images during laser butt-joint welding of Type 304 austenitic stainless steel plates with a high-power (10 kW) continuous wave fiber laser. In order to study the relationship between the molten pool configuration and the welding status, a new method based on PCA is proposed to analyze the welding stability by comparing the situation when the laser beam spot moves along, and when it deviates from the weld seam. Image processing techniques were applied to process the molten pool images and extract five characteristic parameters. Moreover, the PCA method was used to extract a composite indicator which is the linear combination of the five original characteristics to analyze the different status during welding. Experimental results showed that the extracted composite indicator had a close relationship with the actual welding results and it could be used to evaluate the status of the high-power fiber laser welding, providing a theoretical basis for the monitoring of laser welding quality.

Xiangdong, Gao; Qian, Wen

2013-12-01

42

Onset of the initial instability during the solidification of welding pool of aluminum alloy under transient conditions  

NASA Astrophysics Data System (ADS)

Onset of initial morphological instability is predicted by using a new analytic model and quantitative phase field model during the solidification of the welding pool of Al-Cu alloy under transient conditions. In the linear growth stage of the welding pool, the dynamic evolution of the interface instability is analyzed, and the interface behaviors under infinitesimal fluctuations are also investigated. The results show that the mean wavelength at the crossover time evaluated from this analytic model is in good agreement with those obtained by the quantitative phase field simulations and the experiments. The linear growth stage takes up quite a long time of the whole solidification of welding pool and thus it should be primarily considered in investigating the transient growth of welding pool. This study establishes a valid numerical framework for studying the dendrite growth under transient solidification conditions and provides a new approach for studying the transient solidification of welding pool.

Zheng, Wenjian; Dong, Zhibo; Wei, Yanhong; Song, Kuijing

2014-09-01

43

[Impact of introduction of O2 on the welding arc of gas pool coupled activating TIG].  

PubMed

In the present paper, Boltzmann plot method was applied to analyze the temperature distributions of the are plasma when the gas pool coupled activating TIG welding was at different coupling degrees with the outer gas being O2. Based on this study of temperature distributions, the changing regularities of are voltage and are appearance were studied. The result shows that compared with traditional TIG welding, the introduction of O2 makes the welding arc constricted slightly, the temperature of the are center build up, and the are voltage increase. When argon being the inner gas, oxygen serving as the outer gas instead of argon makes the are constricted more obviously. When the coupling degree increases from 0 to 2, the temperature of the are center and the are voltage both increase slightly. In the gas pool coupled activating TIG welding the are is constricted not obviously, and the reason why the weld penetration is improved dramatically in the welding of stainless steel is not are constriction. PMID:25095400

Huang, Yong; Wang, Yan-Lei; Zhang, Zhi-Guo

2014-05-01

44

Effect of Shoulder Size on Weld Properties of Dissimilar Metal Friction Stir Welds  

NASA Astrophysics Data System (ADS)

This article reports a research study that shows the effect of shoulder diameter size on the resulting weld properties of dissimilar friction stir welds between 5754 aluminum alloy (AA) and C11000 copper (Cu). Welds were produced using three different shoulder diameter tools: 15, 18, and 25 mm by varying the rotational speed between 600 and 1200 rpm and the traverse speed between 50 and 300 mm/min to achieve the best result. Each parameter combination was chosen to represent different heat input conditions (low, intermediates and high). The welds were characterized through microstructural evaluation, tensile testing, microhardness measurements, x-ray diffraction analysis, and electrical resistivity. Microstructural evaluation of the welds revealed that the welds produced consisted of all the friction stir welding (FSW) microstructure zones with organized flow lines comprising mixture layers of aluminum (Al) and copper (Cu) at the Stir Zones. The average Ultimate Tensile Strength (UTS) of the welds considered ranged from 178 to 208 MPa. Higher Vickers microhardness values were measured at the joint interfaces of all the welds because of the presence of intermetallic compounds in these regions. The x-ray diffraction analysis revealed the presence of Al4Cu9 and Al2Cu intermetallics at the interfacial regions, and low electrical resistivities were obtained at the joint interfaces. An optimized parameter setting for FSW of Al and Cu was obtained at the weld produced at 950 rpm and 50 mm/min with the 18-mm shoulder diameter tool.

Akinlabi, E. T.

2012-07-01

45

On the calculation of the free surface temperature of gas-tungsten-arc weld pools from first principles: Part I. modeling the welding arc  

Microsoft Academic Search

A mathematical formulation has been developed and computed results are presented describing the temperature profiles in gas\\u000a tungsten arc welding (GTAW) arcs and, hence, the net heat flux from the welding arc to the weld pool. The formulation consists\\u000a of the statement of Maxwell's equations, coupled to the Navier-Stokes equations and the differential thermal energy balance\\u000a equation. The theoretical predictions

R. T. C. Choo; J. Szekely; R. C. Westhoff

1992-01-01

46

Invertebrate community structure along a habitat-patch size gradient within a bog pool complex   

E-print Network

This thesis characterises species richness and community structure over a habitat-patch size gradient of a typical bog-pool complex, investigating the effect of pool size on aquatic invertebrate communities. In this study, twenty-two pools were...

Towers, Naomi M.

47

Modelling the transient behaviours of a fully penetrated gas-tungsten arc weld pool with surface deformation  

Microsoft Academic Search

Numerical analysis of the dynamic behaviours of a gas-tungsten arc (GTA) weld pool with full penetration is of great significance to designing the process control algorithm. In this paper, a three-dimensional transient numerical model is developed to investigate the dynamic behaviours of a fully penetrated GTA weld pool with surface deformation. A body-fitted coordinate system is used to transform the

P C Zhao; Y M Zhang

2005-01-01

48

Plasma effect on weld pool surface reconstruction by shape-from-polarization analysis  

SciTech Connect

The polarimetric state of the thermal radiations emitted by the weld metal contains geometric information about the emitting surface. Even though the analysed thermal radiation has a wavelength corresponding to a blind spectral window of the arc plasma, the physical presence of the arc plasma itself interferes with the rays radiated by the weld pool surface before attaining the polarimeter, thus modifying the geometric information transported by the ray. In the present work, the effect of the arc plasma-surrounding zone on the polarimetric state and propagation direction of the radiated ray is analyzed. The interaction with the arc plasma zone induces a drop in ray intensity and a refraction of ray optical path.

Coniglio, N.; Mathieu, A., E-mail: alexandre.mathieu@u-bourgogne.fr [Laboratoire Interdisciplinaire Carnot de Bourgogne (ICB), UMR 6303 CNRS/Université de Bourgogne, 12 rue de la Fonderie, 71200 Le Creusot (France); Aubreton, O.; Stolz, C. [Université de Bourgogne Laboratoire Le2i UMR CNRS 6306, allée Alain Savary, 21000 Dijon (France)

2014-03-31

49

Relationship between spatter formation and dynamic molten pool during high-power deep-penetration laser welding  

NASA Astrophysics Data System (ADS)

The spatter and the molten pool behavior, which were the important phenomena concerned with the welding quality, were observed and studied by using the high-speed camera and the X-ray transmission imaging system during laser welding under different welding parameters. The formation mechanism of spatter and the corresponding relationships between the spatter and molten pool behavior were investigated. The increase of laser power could cause more intense evaporation and lead to more spatter. When the focal position of laser beam was changed, different forms of spatter were generated, as well as the flow trends of molten metal on the front keyhole wall and at the rear molten pool were changed. The results revealed that the behavior of molten pool, which could be affected by the absorbed energy distribution in the keyhole, was the key factor to determine the spatter formation during laser welding. The relatively sound weld seam could be obtained during laser welding with the focal position located inside the metal.

Li, Shichun; Chen, Genyu; Katayama, Seiji; Zhang, Yi

2014-06-01

50

Effects of shielding gas composition on arc profile and molten pool dynamics in gas metal arc welding of steels  

NASA Astrophysics Data System (ADS)

In gas metal arc welding, gases of different compositions are used to produce an arc plasma, which heats and melts the workpiece. They also protect the workpiece from the influence of the air during the welding process. This paper models gas metal arc welding (GMAW) processes using an in-house simulation code. It investigates the effects of the gas composition on the temperature distribution in the arc and on the molten pool dynamics in gas metal arc welding of steels. Pure argon, pure CO2 and different mixtures of argon and CO2 are considered in the study. The model is validated by comparing the calculated weld profiles with physical weld measurements. The numerical calculations reveal that gas composition greatly affects the arc temperature profile, heat transfer to the workpiece, and consequently the weld dimension. As the CO2 content in the shielding gas increases, a more constricted arc plasma with higher energy density is generated as a result of the increased current density in the arc centre and increased Lorentz force. The calculation also shows that the heat transferred from the arc to the workpiece increases with increasing CO2 content, resulting in a wider and deeper weld pool and decreased reinforcement height.

Wang, L. L.; Lu, F. G.; Wang, H. P.; Murphy, A. B.; Tang, X. H.

2014-11-01

51

10 CFR 905.32 - Resource extensions and resource pool size.  

Code of Federal Regulations, 2010 CFR

...Resource extensions and resource pool size. 905.32 Section 905.32 Energy DEPARTMENT OF ENERGY ENERGY PLANNING AND MANAGEMENT PROGRAM Power Marketing Initiative § 905.32 Resource extensions and resource pool size....

2010-01-01

52

Computational modeling of stationary gastungsten-arc weld pools and comparison to stainless steel 304 experimental results  

Microsoft Academic Search

A systematic study was carried out to verify the predictions of a transient multidimensional computational model by comparing\\u000a the numerical results with the results of an experimental study. The welding parameters were chosen such that the predictions\\u000a of the model could be correlated with the results of an earlier experimental investigation of the weld pool surface temperatures\\u000a during spot gas-tungsten-arc

T. Zacharia; S. A. David; J. M. Vitek; H. G. Kraus

1991-01-01

53

Plasma-weld pool interaction in tungsten inert-gas configuration  

NASA Astrophysics Data System (ADS)

A three-dimensional (3D) transient model of a transferred argon arc in interaction with an anode material is presented and the results discussed. The model based on a finite volume method is developed using the open software @Saturne distributed by Electricité de France. The 3D model includes the characterization of the plasma gas and of the work piece with a current continuity resolution in the whole domain. Transport and thermodynamic properties are dependent on the local temperature and on the vapours emitted by the eroded material due to the heat flux transferred by the plasma. Drag force, Marangoni force, Laplace and gravity forces are taken into account on the weld pool description. The plasma and the weld pool characteristics are presented and compared with experimental and theoretical results from the literature. For a distance between the two electrodes of d = 5 mm and an applied current intensity of I = 200 A, the vapour concentration is weak. The influence of the parameters used in the Marangoni formulation is highlighted. Finally, in agreement with some authors, we show with this global transient 3D model that it is not necessary to include the voltage drop in the energy balance.

Mougenot, J.; Gonzalez, J.-J.; Freton, P.; Masquère, M.

2013-04-01

54

Physical-chemical reactions at welding arc/molten pool interfaces: FY-1986 annual report  

SciTech Connect

The arc heat source has been shown to have a strong influence on the characteristics of the molten weld pool and resulting weld bead morphology. The existence of nonequilibrium temperature distribution between arc species and the presence of metallic vapor in the arc plasma above the anode have been suggested to have an influence on the current distribution. These two influences have been investigated. A multi-fluid treatment of the arc to discern the impact on the anode current distribution and transport properties by nonequilibrium temperature distribution between electrons and heavy species in the welding arc suggests that nonequilibrium has a pronounced influence on the transport properties. However, the resulting anode current distribution is only slightly perturbed. Results suggest that nonequilibrium between species in the interfacial region of the arc above the anode produces only a second-order influence on the anode current distribution. The presence of small amounts (5-10%) of manganese can significantly enhance the low temperature conductivity of the plasma. This results in broadening of the anode current distribution relative to that found when only argon is present in the arc. Attemps to develop optical and laser diagnostics for the interfacial region above the anode are reported. Results suggest that laser induced fluorescence has considerable merit for determining species distributions in the arc and possibly in the interfacial region. 29 refs., 23 figs., 1 tab.

Key, J.F.; McIlwain, M.E.

1987-09-01

55

Number size distribution of fine and ultrafine fume particles from various welding processes.  

PubMed

Studies in the field of environmental epidemiology indicate that for the adverse effect of inhaled particles not only particle mass is crucial but also particle size is. Ultrafine particles with diameters below 100 nm are of special interest since these particles have high surface area to mass ratio and have properties which differ from those of larger particles. In this paper, particle size distributions of various welding and joining techniques were measured close to the welding process using a fast mobility particle sizer (FMPS). It turned out that welding processes with high mass emission rates (manual metal arc welding, metal active gas welding, metal inert gas welding, metal inert gas soldering, and laser welding) show mainly agglomerated particles with diameters above 100 nm and only few particles in the size range below 50 nm (10 to 15%). Welding processes with low mass emission rates (tungsten inert gas welding and resistance spot welding) emit predominantly ultrafine particles with diameters well below 100 nm. This finding can be explained by considerably faster agglomeration processes in welding processes with high mass emission rates. Although mass emission is low for tungsten inert gas welding and resistance spot welding, due to the low particle size of the fume, these processes cannot be labeled as toxicologically irrelevant and should be further investigated. PMID:23028013

Brand, Peter; Lenz, Klaus; Reisgen, Uwe; Kraus, Thomas

2013-04-01

56

Electromagnetically and Thermally Driven Flow Phenomena in Electroslag Welding  

E-print Network

. Electroslag welding has been shown to produce rela- tively defect-free joints at fast deposition rates, with, that the size and shape of the weld pool are the controlling factors in the production of sound welds. While) Electromagnetically and Thermally Driven Flow Phenomena in Electroslag Welding A. H. DILAWARI, J

Eagar, Thomas W.

57

Towards and FVE-FAC Method for Determining Thermocapillary Effects on Weld Pool Shape  

NASA Technical Reports Server (NTRS)

Several practical materials processes, e.g., welding, float-zone purification, and Czochralski crystal growth, involve a pool of molten metal with a free surface, with strong temperature gradients along the surface. In some cases, the resulting thermocapillary flow is vigorous enough to convect heat toward the edges of the pool, increasing the driving force in a sort of positive feedback. In this work we examine this mechanism and its effect on the solid-liquid interface through a model problem: a half space of pure substance with concentrated axisymmetric surface heating, where surface tension is strong enough to keep the liquid free surface flat. The numerical method proposed for this problem utilizes a finite volume element (FVE) discretization in cylindrical coordinates. Because of the axisymmetric nature of the model problem, the control volumes used are torroidal prisms, formed by taking a polygonal cross-section in the (r, z) plane and sweeping it completely around the z-axis. Conservation of energy (in the solid), and conservation of energy, momentum, and mass (in the liquid) are enforced globally by integrating these quantities and enforcing conservation over each control volume. Judicious application of the Divergence Theorem and Stokes' Theorem, combined with a Crank-Nicolson time-stepping scheme leads to an implicit algebraic system to be solved at each time step. It is known that near the boundary of the pool, that is, near the solid-liquid interface, the full conduction-convection solution will require extremely fine length scales to resolve the physical behavior of the system. Furthermore, this boundary moves as a function of time. Accordingly, we develop the foundation of an adaptive refinement scheme based on the principles of Fast Adaptive Composite Grid methods (FAC). Implementation of the method and numerical results will appear in a later report.

Canright, David; Henson, Van Emden

1996-01-01

58

Inertia Radial Friction Welding Joint of Large Size H90 Brass\\/D60 Steel Dissimilar Metals  

Microsoft Academic Search

CT-130 Special Inertia Friction Welding Machine is used to weld a large size (156 mm diameter) of brass\\/steel by radial friction welding. Optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and Vickers microhardness measurements are used to analyze the welding joint. The results show a refined grain zone near the welding interface at the brass side, which is

Jian Luo; Xiaoming Wang; Dejia Liu; Fei Li; Junfeng Xiang

2012-01-01

59

Inertia Radial Friction Welding Joint of Large Size H90 Brass\\/D60 Steel Dissimilar Metals  

Microsoft Academic Search

CT-130 Special Inertia Friction Welding Machine is used to weld a large size (156 mm diameter) of brass\\/steel by radial friction welding. OM, SEM, EDS and Vickers microhardness measurements are used to analyze the welding joint. The results show a refined grain zone near the welding interface at the brass side, which is closely related to the smaller stacking fault energy

Dejia Liu; Jian Luo; Xiaoming Wang; Fei Li; Junfeng Xiang

2011-01-01

60

Estimating the number and sizes of undiscovered oil and gas pools  

SciTech Connect

This study introduces a new specification of oil and gas exploration as a sampling process, in order to estimate the number and sizes of undiscovered oil and gas pools by statistical inference from discovered pools as a sample. Oil and gas exploration is quite unlike drawing samples at random in that actual sampling is sized-biased, subject to truncation of uneconomic pools, and to censorship of discovered pool sizes. The method of estimating the number and sizes of undiscovered pools proposed in this study specifically accounts for these non-random components of exploration as a sampling process, and can be easily implemented using the Expectation-Maximization algorithm. The method allows for choices between single and multiple point truncation of uneconomic pool sizes, and generalizes quite easily to the bivariate case necessary to analyze plays with pools that contain oil with associated gas. Its usefulness is enhanced by the introduction of powerful tests of fit of the lognormal distribution to the distribution of discovered pool sizes, and of meaningful measures of the uncertainty of estimates of the number and sizes of undiscovered pools. Application of the method to oil and gas plays in the San Juan basin of northwest New Mexico show that it yields quite reasonable and useful results. The method, when applied to data analyzed using other methods of estimating the number and sizes of undiscovered pools, confirms that failure to account for truncation of uneconomic pools will result in an overestimate of the average size of pools in a play. By avoiding this, and other, problems, the proposed estimation procedure should lead to better assessments of a play's potential for future discoveries of economically recoverable oil and gas.

Long, K.R.

1988-01-01

61

Adaptive Neuro-Fuzzy Inference System (ANFIS)-Based Models for Predicting the Weld Bead Width and Depth of Penetration from the Infrared Thermal Image of the Weld Pool  

NASA Astrophysics Data System (ADS)

Type 316 LN stainless steel is the major structural material used in the construction of nuclear reactors. Activated flux tungsten inert gas (A-TIG) welding has been developed to increase the depth of penetration because the depth of penetration achievable in single-pass TIG welding is limited. Real-time monitoring and control of weld processes is gaining importance because of the requirement of remoter welding process technologies. Hence, it is essential to develop computational methodologies based on an adaptive neuro fuzzy inference system (ANFIS) or artificial neural network (ANN) for predicting and controlling the depth of penetration and weld bead width during A-TIG welding of type 316 LN stainless steel. In the current work, A-TIG welding experiments have been carried out on 6-mm-thick plates of 316 LN stainless steel by varying the welding current. During welding, infrared (IR) thermal images of the weld pool have been acquired in real time, and the features have been extracted from the IR thermal images of the weld pool. The welding current values, along with the extracted features such as length, width of the hot spot, thermal area determined from the Gaussian fit, and thermal bead width computed from the first derivative curve were used as inputs, whereas the measured depth of penetration and weld bead width were used as output of the respective models. Accurate ANFIS models have been developed for predicting the depth of penetration and the weld bead width during TIG welding of 6-mm-thick 316 LN stainless steel plates. A good correlation between the measured and predicted values of weld bead width and depth of penetration were observed in the developed models. The performance of the ANFIS models are compared with that of the ANN models.

Subashini, L.; Vasudevan, M.

2012-02-01

62

Regulation of trachebronchial tissue-specific stem cell pool size.  

PubMed

Tissue-specific stem cell (TSC) number is tightly regulated in normal individuals but can change following severe injury. We previously showed that tracheobronchial epithelial TSC number increased after severe naphthalene (NA) injury and then returned to normal. This study focused on the fate of the supernumerary TSC and the signals that regulate TSC pool size. We used the Keratin 5-rTA/Histone 2B:green fluorescent protein (GFP) model to purify basal cells that proliferated infrequently (GFP(bright) ) or frequently (GFP(dim) ) after NA injury. Both populations contained TSC but TSCs were 8.5-fold more abundant in the GFP(bright) population. Interestingly, both populations also contained a unipotential basal progenitor (UPB), a mitotic basal cell subtype whose daughters were terminally differentiated basal cells. The ratio of TSC to UPB was 5:1 in the GFP(bright) population and 1:5 in the GFP(dim) population. These data suggested that TSC proliferation in vivo promoted TSC-to-UPB differentiation. To evaluate this question, we cloned TSC from the GFP(bright) and GFP(dim) populations and passaged the clones seven times. We found that TSC number decreased and UPB number increased at each passage. Reciprocal changes in TSC and UPB frequency were more dramatic in the GFP(dim) lineage. Gene expression analysis showed that ?-catenin and Notch pathway genes were differentially expressed in freshly isolated TSC derived from GFP(bright) and GFP(dim) populations. We conclude that (a) TSC and UPB are members of a single lineage; (b) TSC proliferation in vivo or in vitro promotes TSC-to-UPB differentiation; and (c) an interaction between the ?-catenin and Notch pathways regulates the TSC-to-UPB differentiation process. PMID:23712882

Ghosh, Moumita; Smith, Russell W; Runkle, Christine M; Hicks, Douglas A; Helm, Karen M; Reynolds, Susan D

2013-12-01

63

Welding.  

ERIC Educational Resources Information Center

This curriculum guide is designed for use by South Carolina vocational education teachers as a continuing set of lesson plans for a two-year course on welding. Covered in the individual sections of the guide are the following topics: an orientation to welding, oxyacetylene welding, advanced oxyacetylene welding, shielded metal arc welding, TIG…

South Carolina State Dept. of Education, Columbia. Office of Vocational Education.

64

Instantaneous liquid release from a rail tanker: the influence of noise shields on pool shape and pool size.  

PubMed

In the Netherlands, the Betuweline is a dedicated freight railway. It will, among other things, be used for transportation of all kinds of hazardous materials from the Port of Rotterdam to the German Hinterland and vice versa. The line is approximately 150 km long. Alongside the line, more than 100 km noise shields have been constructed. The question is how, and to what extent, this noise shield will affect the pool shape and size of an instantaneous release of a flammable liquid, such as liquefied petroleum gas (LPG). In case of an instantaneous release of liquid from a rail tanker (50 m(3)), both risk analysts and emergency responders use a circular pool shape of about 600 m(2) would result. To assess the influence of a noise shield, a full scale test was conducted on an already constructed part of the Betuweline. A rail tanker was filled with 50 m(3) red-colored environmentally safe liquid. The liquid was instantaneously released. A very peculiar pool shape actually results due to the presence of a noise shield. A zone between the rails and the noise shield (2m wide and 90 m long) is within 2-3 min filled with 15 cm of liquid. The total pool size area was about 750 m(2). Both shape and size deviate substantially from the traditional figures. These insights are both relevant to emergency responders for disaster abatement purposes and to risk analysts for effective modeling purposes. The Dutch Ministry of Transport is examining possible strategies to deal with these results. The results of this study are based upon one single instantaneous release test. In addition, it is valuable to find out what the pool shape and size would be in case of a continuous release from the rail tanker near a noise shield. PMID:18849112

Rosmuller, Nils

2009-05-30

65

Smoothed particle hydrodynamics modelling of the fluid flow and heat transfer in the weld pool during laser spot welding  

NASA Astrophysics Data System (ADS)

Smoothed particle hydrodynamics is employed, for the first time, to develop a numerical model for the melting and fluid flow during laser welding process. In this meshlessLagrangian method the gas-melt two phase flow, heat transfer, surface tension, and melting of solid parent material are considered. This model was used to study the evolution of temperature field and fluid flow in the case study of laser spot welding in 2D. The simulation results show a strong influence of the melting process on the flow of liquid metal and a clear influence of the Marangoni flow on the heat transfer is also found.

Tong, Mingming; Browne, David J.

2012-01-01

66

Operating Systems Review 34(2), 42-55, 2000 Analysis of Optimal Thread Pool Size  

E-print Network

Operating Systems Review 34(2), 42-55, 2000 Analysis of Optimal Thread Pool Size 1 Yibei Ling, 1. However, creating and destroying a thread is far from free, requiring run-time memory allocation behind system slowdowns. A thread-pool architecture addresses this problem by prespawning

Mullen, Tracy

67

Sensing of weld pool surface using non-transferred plasma charge sensor  

Microsoft Academic Search

Gas tungsten arc welding (GTAW) is the primary process for precision joining of metals due to its capability for accurate control of heat input. As a close relative and modification of GTAW, plasma arc welding (PAW) has higher energy density and can penetrate thicker workpieces while maintaining the desired capability for accurate control of heat input. In order to produce

W. Lu; Y. M. Zhang; John Emmerson

2004-01-01

68

Effects of temperature-dependent material properties and shielding gas on molten pool formation during continuous laser welding of AZ91 magnesium alloy  

NASA Astrophysics Data System (ADS)

Laser welding processes are widely used for fabrications in many engineering applications such as aerospace and automotives. In this paper, a moving distributed heat source model based on Goldak's method [1] has been implemented into finite volume thermal simulations in order to predict temperature distributions during the welding process of a magnesium alloy and to study the effects of variations in thermal properties, absorption coefficient and gas shielding on the computed temperature distributions and weld pool dimensions. The main conclusion is the significant effects of varying the thermal conductivity and absorption coefficient of magnesium. Also, it has been seen that the shielding gas, besides its main role of protection against oxidation, has a significant effect on the width of the weld pool. Finally, the obtained results have been compared to the experimental ones and a satisfactory correlation has been observed, indicating the reliability of the model developed in this study.

Bannour, Sana; Abderrazak, Kamel; Mhiri, Hatem; Le Palec, Georges

2012-11-01

69

Controls on the Size and Occurrence of Pools in Coarse-Grained Forest Rivers  

NASA Astrophysics Data System (ADS)

Controls on pool formation are examined in gravel- and cobble-bed rivers in forest mountain drainage basins of northern California, southern Oregon, and southeastern Alaska. We demonstrate that the majority of pools at our study sites are formed by flow obstructions and that pool geometry and frequency largely depend on obstruction characteristics (size, type, and frequency). However, the effectiveness of obstructions to induce scour also depends on channel characteristics, such as channel gradient, width-depth ratio, relative submergence (ratio of flow depth to grain size), and the caliber and rate of bed material supply. Moreover, different reach-scale channel types impose different characteristic physical processes and boundary conditions that further control the occurrence of pools within a watershed. Our findings indicate that effective management of pools and associated aquatic habitat requires consideration of a variety of factors, each of which may be more or less important depending on channel type and location within a watershed. Consequently, strategies for managing pools that are based solely on single-factor, regional target values (e.g. a certain number of wood pieces or pools per stream length) are likely to be ineffective because they do not account for the variety of local and watershed controls on pool scour and, therefore, may be of limited value for proactive management of complex ecosystems.

Buffington, J. M.; Lisle, T. E.; Woodsmith, R. D.; Hilton, S.

2001-12-01

70

Possibility of Underwater Explosive Welding for Making Large-Sized Thin Metal Plate Clad by Overlapping Plates  

NASA Astrophysics Data System (ADS)

The authors have developed a new method of explosive welding using underwater shock wave for the welding of thin plate on a substrate. Considering the size limitation of the welding area in using the technique, the possibility of overlapping thin plates to make large-sized welding area is investigated. In general, the results for the welding of Inconel 600 on 304 stainless steel show a macroscopically successful weld, but the microstructure shows some melting spots caused due to the trapping of metal jet during the welding process when the welding condition is changed. The welding process is discussed based on the experimental results in comparison with some numerically simulated results obtained by AUTODYN-2D code.

Hokamoto, Kazuyuki; Mori, Akihisa; Fujita, Masahiro

71

Welding.  

ERIC Educational Resources Information Center

This curriculum guide provides materials for a 12-unit secondary course in welding. Purpose stated for the flexible entry and exit course is to help students master manipulative skills to develop successful welding techniques and to gain an understanding of the specialized tools and equipment used in the welding field. Units cover oxyacetylene…

Lehigh County Area Vocational-Technical School, Schnecksville, PA.

72

Application of eddy current inversion technique to the sizing of defects in Inconel welds with rough surfaces  

Microsoft Academic Search

This paper evaluates the applicability of eddy current inversion techniques to the sizing of defects in Inconel welds with rough surfaces. For this purpose, a plate Inconel weld specimen, which models the welding of a stub tube in a boiling water nuclear reactor is fabricated, and artificial notches machined into the specimen. Eddy current inspections using six different eddy current

Noritaka Yusa; Eiji Machida; Ladislav Janousek; Mihai Rebican; Zhenmao Chen; Kenzo Miya

2005-01-01

73

Laser assisted non-consumable arc welding process development  

SciTech Connect

The employment of Laser Beam Welding (LBW) for many traditional arc welding applications is often limited by the inability of LBW to compensate for variations in the weld joint gap. This limitation is associated with fluctuations in the energy transfer efficiency along the weld joint. Since coupling of the laser beam to the workpiece is dependent on the maintenance of a stable absorption keyhole, perturbations to the weld pool can lead to decreased energy transfer and resultant weld defects. Because energy transfer in arc welding does not similarly depend on weld pool geometry, it is expected that combining these two processes together will lead to an enhanced fusion welding process that exhibits the advantages of both arc welding and LBW. Laser assisted non-consumable arc welds have been made on thin section aluminum. The welds combine the advantages of arc welding and laser welding, with enhanced penetration and fusion zone size. The use of a pulsed Nd:YAG laser with the combined process appears to be advantageous since this laser is effective in removing the aluminum oxide and thereby allowing operation with the tungsten electrode negative. The arc appears to increase the size of the weld and also to mitigate hot cracking tendencies that are common with the pulsed Nd:YAG laser.

Fuerschach, P.W.; Hooper, F.M.

1997-09-01

74

The Size of the Sensitization Zone in 304 Stainless Steel Welds  

E-print Network

) ) viS i tf. f. t ~ I~ i \\ ! l The Size of the Sensitization Zone in 304 Stainless Steel Welds N. S. TSAI and T. W. EAGAR Factors influencing the size wrcl slrcrpe oftire sensitization zone in 304 is eliminated. INTRODUCTION Sensitization-induced intergranular corrosion in 304 stain- less steel weldments has

Eagar, Thomas W.

75

Effects of electrode bevel angle on argon arc properties and weld shape  

NASA Astrophysics Data System (ADS)

A numerical modeling of coupled welding arc with weld pool is established using FLUENT software for moving shielded GTA welding to systematically investigate the effects of electrode bevel angle on the argon arc properties as well as the weld shape on SUS304 stainless steel. The calculated results show that the argon arc is constricted and the peak values of heat flux and shear stress on the weld pool decrease with increasing electrode bevel angle, while the radial distribution of heat flux and shear stress varying slightly. The weld shape is controlled by the pool flow patterns driving by the surface tension, gas shear stress, electromagnetic force and buoyancy. The Marangoni convection induced by surface tension plays an important role on weld shapes. All the weld shapes are wide and shallow with low weld metal oxygen content, while the narrow and deep weld shapes form under high weld metal oxygen content, which is related with the oxygen concentration in the shielding gas. The weld depth/width (D/W) ratio increases with increasing electrode bevel angle for high weld metal oxygen content and is not sensitive to the electrode bevel angle under low weld metal oxygen content. The calculated results for the weld shape, weld size and weld D/W ratio agree well with the experimental ones.

Dong, W. C.; Lu, S. P.; Li, D. Z.; Y Li, Y.

2012-07-01

76

ASSOCIATION BETWEEN ZINC POOL SIZES AND IRON STORES IN PREMENOPAUSAL WOMEN  

Technology Transfer Automated Retrieval System (TEKTRAN)

Background: Zinc (Zn) nutriture is assumed to be associated with iron (Fe) nutriture based on common food factors in humans. Objective: The objective was to evaluate relationships between Zn pool sizes and Fe stores assessed by serum ferritin, and to find common food factors that affect both Zn an...

77

Swimming Pools.  

ERIC Educational Resources Information Center

Technical and engineering data are set forth on the design and construction of swimming pools. Consideration is given to site selection, pool construction, the comparative merits of combining open air and enclosed pools, and alternative uses of the pool. Guidelines are presented regarding--(1) pool size and use, (2) locker and changing rooms, (3)…

Ministry of Housing and Local Government, London (England).

78

A study of the effects of heater size, subcooling, and gravity level on pool boiling heat transfer  

E-print Network

A study of the effects of heater size, subcooling, and gravity level on pool boiling heat transfer Martin Hill, College Park, MD 20742, USA Abstract Pool boiling heat transfer measurements from different. Boiling on three heaters of different size (0.65, 2.62, 7.29 mm2 ) was studied. Control circuitry was used

Kim, Jungho

79

A Complete Solution for Weld Inspections - Phased Arrays and Diffraction Sizing  

Microsoft Academic Search

Welds have been inspected by radiography for years, but this technology has major drawbacks: low detection rates for critical planar defects (i.e. cracks and lack of fusion), subjective interpretation, no vertical sizing capab ility, significant safety hazards, licensing issues, plant closures, and generally slo w inspection rates. For decades, the main alternative was manual ultrasonics, which is a lso slow,

Michael MOLES; Simon LABBÉ

80

Constitutive Cylindrospermopsin Pool Size in Cylindrospermopsis raciborskii under Different Light and CO2 Partial Pressure Conditions.  

PubMed

Cylindrospermopsin (CYN) and 7-deoxy-cylindrospermopsin (dCYN) are potent hepatotoxic alkaloids produced by numerous species of cyanobacteria, including the freshwater Cylindrospermopsis raciborskii. C. raciborskii is an invasive cyanobacterium, and the study of how environmental parameters drive CYN production has received significant interest from water managers and health authorities. Light and CO2 affect cell growth and physiology in photoautotrophs, and these are potential regulators of cyanotoxin biosynthesis. In this study, we investigated how light and CO2 affect CYN and dCYN pool size as well as the expression of the key genes, cyrA and cyrK, involved in CYN biosynthesis in a toxic C. raciborskii strain. For cells growing at different light intensities (10 and 100 ?mol photons m(-2) s(-1)), we observed that the rate of CYN pool size production (?CYN) was coupled to the cell division rate (?c) during batch culture. This indicated that CYN pool size under our experimental conditions is constant and cell quotas of CYN (QCYN) and dCYN (QdCYN) are fixed. Moreover, a lack of correlation between expression of cyrA and total CYN cell quotas (QCYNs) suggests that the CYN biosynthesis is regulated posttranscriptionally. Under elevated CO2 (1,300 ppm), we observed minor effects on QCYN and no effects on expression of cyrA and cyrK. We conclude that the CYN pool size is constitutive and not affected by light and CO2 conditions. Thus, C. raciborskii bloom toxicity is determined by the absolute abundance of C. raciborskii cells within the water column and the relative abundance of toxic and nontoxic strains. PMID:25724956

Pierangelini, Mattia; Sinha, Rati; Willis, Anusuya; Burford, Michele A; Orr, Philip T; Beardall, John; Neilan, Brett A

2015-05-01

81

Estimation and control of droplet size and frequency in projected spray mode of a gas metal arc welding (GMAW) process.  

PubMed

New estimators are designed based on the modified force balance model to estimate the detaching droplet size, detached droplet size, and mean value of droplet detachment frequency in a gas metal arc welding process. The proper droplet size for the process to be in the projected spray transfer mode is determined based on the modified force balance model and the designed estimators. Finally, the droplet size and the melting rate are controlled using two proportional-integral (PI) controllers to achieve high weld quality by retaining the transfer mode and generating appropriate signals as inputs of the weld geometry control loop. PMID:21444083

Anzehaee, Mohammad Mousavi; Haeri, Mohammad

2011-07-01

82

Increases in plasma pool size of lipoprotein components in copper-deficient hamsters  

SciTech Connect

Twenty-four male Golden Syrian hamsters, were randomly assigned to 2 dietary copper (Cu) treatments; deficient and adequate. Reductions in weight gain, hematocrit and liver Cu as well as increases in heart weight and plasma volume were observed in CD hamsters after 7 weeks of treatment. Plasma very low (VLDL), low (LDL) and high (HDL) density lipoproteins were isolated by ultracentrifugation and Sepharose column chromatography. The percentage of total plasma cholesterol carried by LDL was increased from 20 to 24% but was reduced from 71 to 68% for HDL as a result of Cu deficiency. In LDL the % composition of triglycerides (TG) and phospholipids (PL) was increased by 25% but that of cholesterol was reduced by 13%. The % composition of protein was reduced 24% but that of TG was increased 18% in VLDL by Cu deficiency. Since plasma volume was increased 50% in CD hamsters, the data were expressed as the amount present in the plasma pool corrected for body weight. With the exceptions of smaller increased in VLDL protein and PL as well as the more than threefold increases in LDL TG and PL plasma pool size, the pool size for the rest of the lipoprotein components were increased about twofold in CD hamsters. The lipoprotein data further indicate that Cu deficiency increased the particle number of VLDL, LDL and HDL but enlarged the size of only VLDL and LDL.

Al-Othman, A.A.; Rosenstein, F.; Lei, K.Y. (Univ. of Arizona, Tucson (United States))

1991-03-15

83

Egfr signaling controls the size of the stem cell precursor pool in the Drosophila ovary.  

PubMed

In many animals, germline progenitors are kept undifferentiated to give rise to germline stem cells (GSCs), enabling continuous production of gametes throughout animal life. In the Drosophila ovary, GSCs arise from a subset of primordial germ cells (PGCs) that stay undifferentiated even after gametogenesis has started. How a certain population of PGCs is protected against differentiation, and the significance of its regulatory mechanisms on GSC establishment remain elusive. Here we show that epidermal growth factor receptor (Egfr) signaling in somatic stromal intermingled cells (ICs), activated by its ligand produced in germ cells, controls the size of the PGC pool at the onset of gametogenesis. Egfr signaling in ICs limits the number of cells that express the heparan sulfate proteoglycan Dally, which is required for the movement and stability of the locally-produced stromal morphogen, Decapentaplegic (Dpp, a BMP2/4 homologue). Dpp is received by PGCs and maintains them in an undifferentiated state. Altering Egfr signaling levels changes the size of the PGC pool and affects the number of GSCs established during development. While excess GSC formation is compensated by the adult stage, insufficient GSC formation can lead to adult ovarioles that completely lack GSCs, suggesting that ensuring an absolute size of the PGC pool is crucial for the GSC system. PMID:23376160

Matsuoka, Shinya; Hiromi, Yasushi; Asaoka, Miho

2013-01-01

84

Computational modeling of GTA (gas tungsten arc) welding with emphasis on surface tension effects  

SciTech Connect

A computational study of the convective heat transfer in the weld pool during gas tungsten arch (GTA) welding of Type 304 stainless steel is presented. The solution of the transport equations is based on a control volume approach which utilized directly, the integral form of the governing equations. The computational model considers buoyancy and electromagnetic and surface tension forces in the solution of convective heat transfer in the weld pool. In addition, the model treats the weld pool surface as a deformable free surface. The computational model includes weld metal vaporization and temperature dependent thermophysical properties. The results indicate that consideration of weld pool vaporization effects and temperature dependent thermophysical properties significantly influence the weld model predictions. Theoretical predictions of the weld pool surface temperature distributions and the cross-sectional weld pool size and shape wee compared with corresponding experimental measurements. Comparison of the theoretically predicted and the experimentally obtained surface temperature profiles indicated agreement with {plus minus} 8%. The predicted weld cross-section profiles were found to agree very well with actual weld cross-sections for the best theoretical models. 26 refs., 8 figs.

Zacharia, T.; David, S.A.

1990-01-01

85

Modeling of Heat and Mass Transfer in Fusion Welding  

SciTech Connect

In fusion welding, parts are joined together by melting and subsequent solidification. Although this principle is simple, complex transport phenomena take place during fusion welding, and they determine the final weld quality and performance. The heat and mass transfer in the weld pool directly affect the size and shape of the pool, the solidification microstructure, the formation of weld defects such as porosity and humping, and the temperature distribution in the fusion zone and heat-affected zone (HAZ). Furthermore, the temperature evolution affects the kinetics and extent of various solid-state phase transformations, which in turn determine the final weld microstructure and mechanical properties. The formation of residual stresses and distortion originates from the thermal expansion and contraction during welding heating and cooling, respectively.

Zhang, Wei [ORNL

2011-01-01

86

Welding.  

ERIC Educational Resources Information Center

The curriculum guide for welding instruction contains 16 units presented in six sections. Each unit is divided into the following areas, each of which is color coded: terminal objectives, specific objectives, suggested activities, and instructional materials; information sheet; transparency masters; assignment sheet; test; and test answers. The…

Cowan, Earl; And Others

87

Welding.  

ERIC Educational Resources Information Center

This curriculum guide is intended to assist vocational instructors in preparing students for entry-level employment as welders and preparing them for advanced training in the workplace. The package contains an overview of new and emerging welding technologies, a competency/skill and task list, an instructor's guide, and an annotated bibliography.…

Baldwin, Harold; Whitney, Gregory

88

Ultrasonic Phased Array Technique for Accurate Flaw Sizing in Dissimilar Metal Welds  

SciTech Connect

Described is a manual,portable non-destructive technique to determine the through wall height of cracks present in dissimilar metal welds used in the primary coolling systems of pressure water and boiler light water reactors. Current manual methods found in industry have proven not to exhibit the sizing accuracy required by ASME inspection requirement. The technique described demonstrated an accuracy approximately three times that required to ASME Section XI, Appendix 8 qualification.

Jonathan D Buttram

2005-03-11

89

Influence of the Diadinoxanthin Pool Size on Photoprotection in the Marine Planktonic Diatom Phaeodactylum tricornutum1  

PubMed Central

The pool size of the xanthophyll cycle pigment diadinoxanthin (DD) in the diatom Phaeodactylum tricornutum depends on illumination conditions during culture. Intermittent light caused a doubling of the DD pool without significant change in other pigment contents and photosynthetic parameters, including the photosystem II (PSII) antenna size. On exposure to high-light intensity, extensive de-epoxidation of DD to diatoxanthin (DT) rapidly caused a very strong quenching of the maximum chlorophyll fluorescence yield (Fm, PSII reaction centers closed), which was fully reversed in the dark. The non-photochemical quenching of the minimum fluorescence yield (Fo, PSII centers open) decreased the quantum efficiency of PSII proportionally. For both Fm and Fo, the non-photochemical quenching expressed as F/F? ? 1 (with F? the quenched level) was proportional to the DT concentration. However, the quenching of Fo relative to that of Fm was much stronger than random quenching in a homogeneous antenna could explain, showing that the rate of photochemical excitation trapping was limited by energy transfer to the reaction center rather than by charge separation. The cells can increase not only the amount of DT they can produce, but also its efficiency in competing with the PSII reaction center for excitation. The combined effect allowed intermittent light grown cells to down-regulate PSII by 90% and virtually eliminated photoinhibition by saturating light. The unusually rapid and effective photoprotection by the xanthophyll cycle in diatoms may help to explain their dominance in turbulent waters. PMID:12114593

Lavaud, Johann; Rousseau, Bernard; van Gorkom, Hans J.; Etienne, Anne-Lise

2002-01-01

90

A subunit-sized butyrylcholinesterase present in high concentrations in pooled rabbit serum  

PubMed Central

A butyrylcholinesterase of mol.wt. approx. 83000 was observed in pooled rabbit serum. The enzyme was named monomeric butyrylcholinesterase to distinguish it from the larger oligomeric butyrylcholinesterase of horse and human serum whose subunits are the same size as the monomeric enzyme. The active-site concentration of monomeric butyrylcholinesterase in the pooled serum was 0.18?m, which is five times the concentration of butyrylcholinesterase in pooled horse serum. This was surprising, since the horse serum is regarded as a rich source of butyrylcholinesterase, whereas rabbit serum is not generally thought to contain significant amounts of any butyrylcholinesterase. The explanation, in large part, was the relatively low kcat. of the monomeric enzyme, which was approx. 57s?1 with butyrylthiocholine as substrate and is one-thirtieth of the comparable kcat. of horse butyrylcholinesterase. The substrate specificity of monomeric butyrylcholinesterase also differed significantly from that of horse and human butyrylcholinesterase. For example, with the monomeric enzyme, the hydrolysis of 1mm-acetylthiocholine was only 4% the rate for 1mm-butyrylthiocholine, whereas human and horse butyrylcholinesterases hydrolysed 1mm-acetylthiocholine at 50% of the rate for 1mm-butyrylthiocholine. Moreover, monomeric butyrylcholinesterase generally hydrolysed aromatic esters more rapidly than choline esters, whereas the reverse is true of the butyrylcholinesterases. To facilitate the study of monomeric butyrylcholinesterase, it was separated from the larger butyrylcholinesterase and acetylcholinesterase, also present in rabbit serum, and purified 89-fold by fractionation with (NH4)2SO4 and ion-exchange chromatography. ImagesFig. 1. PMID:597249

Main, A. Russell; McKnelly, Susan C.; Burgess-Miller, Sybil K.

1977-01-01

91

Use of a multivariate optimization algorithm to develop a self-consistent numerical heat transfer model for laser spot welding  

Microsoft Academic Search

Laser spot welding as a joining method offers many outstanding advantages, such as localized heating and melting, high weld-strength-to-weld-size\\u000a ratio, and minimal heat affected zone. These provide the benefits of low heat distortion, repeatability, ability to automate\\u000a and high throughout that are always in demand in industry. An accurate knowledge of the temperature-time history of the weld\\u000a pool is a

S. Bag; A. Trivedi; A. De

2008-01-01

92

Effects of Fusion Zone Size and Failure Mode on Peak Load and Energy Absorption of Advanced High Strength Steel Spot Welds under Lap Shear Loading Conditions  

SciTech Connect

This paper examines the effects of fusion zone size on failure modes, static strength and energy absorption of resistance spot welds (RSW) of advanced high strength steels (AHSS) under lap shear loading condition. DP800 and TRIP800 spot welds are considered. The main failure modes for spot welds are nugget pullout and interfacial fracture. Partial interfacial fracture is also observed. Static weld strength tests using lap shear samples were performed on the joint populations with various fusion zone sizes. The resulted peak load and energy absorption levels associated with each failure mode were studied for all the weld populations using statistical data analysis tools. The results in this study show that AHSS spot welds with conventionally required fusion zone size of can not produce nugget pullout mode for both the DP800 and TRIP800 welds under lap shear loading. Moreover, failure mode has strong influence on weld peak load and energy absorption for all the DP800 welds and the TRIP800 small welds: welds failed in pullout mode have statistically higher strength and energy absorption than those failed in interfacial fracture mode. For TRIP800 welds above the critical fusion zone level, the influence of weld failure modes on peak load and energy absorption diminishes. Scatter plots of peak load and energy absorption versus weld fusion zone size were then constructed, and the results indicate that fusion zone size is the most critical factor in weld quality in terms of peak load and energy absorption for both DP800 and TRIP800 spot welds.

Sun, Xin; Stephens, Elizabeth V.; Khaleel, Mohammad A.

2008-06-01

93

Computer modeling of arc welds to predict effects of critical variables on weld penetration  

SciTech Connect

In recent years, there have been several attempts to study the effect of critical variables on welding by computational modeling. It is widely recognized that temperature distributions and weld pool shapes are keys to quality weldments. It would be very useful to obtain relevant information about the thermal cycle experienced by the weld metal, the size and shape of the weld pool, and the local solidification rates, temperature distributions in the heat-affected zone (HAZ), and associated phase transformations. The solution of moving boundary problems, such as weld pool fluid flow and heat transfer, that involve melting and/or solidification is inherently difficult because the location of the solid-liquid interface is not known a priori and must be obtained as a part of the solution. Because of non-linearity of the governing equations, exact analytical solutions can be obtained only for a limited number of idealized cases. Therefore, considerable interest has been directed toward the use of numerical methods to obtain time-dependant solutions for theoretical models that describe the welding process. Numerical methods can be employed to predict the transient development of the weld pool as an integral part of the overall heat transfer conditions. The structure of the model allows each phenomenon to be addressed individually, thereby gaining more insight into their competing interactions. 19 refs., 6 figs., 1 tab.

Zacharia, T.; David, S.A.

1991-01-01

94

Probabilistic Estimation of Critical Flaw Sizes in the Primary Structure Welds of the Ares I-X Launch Vehicle  

NASA Technical Reports Server (NTRS)

The primary structure of the Ares I-X Upper Stage Simulator (USS) launch vehicle is constructed of welded mild steel plates. There is some concern over the possibility of structural failure due to welding flaws. It was considered critical to quantify the impact of uncertainties in residual stress, material porosity, applied loads, and material and crack growth properties on the reliability of the welds during its pre-flight and flight. A criterion--an existing maximum size crack at the weld toe must be smaller than the maximum allowable flaw size--was established to estimate the reliability of the welds. A spectrum of maximum allowable flaw sizes was developed for different possible combinations of all of the above listed variables by performing probabilistic crack growth analyses using the ANSYS finite element analysis code in conjunction with the NASGRO crack growth code. Two alternative methods were used to account for residual stresses: (1) The mean residual stress was assumed to be 41 ksi and a limit was set on the net section flow stress during crack propagation. The critical flaw size was determined by parametrically increasing the initial flaw size and detecting if this limit was exceeded during four complete flight cycles, and (2) The mean residual stress was assumed to be 49.6 ksi (the parent material s yield strength) and the net section flow stress limit was ignored. The critical flaw size was determined by parametrically increasing the initial flaw size and detecting if catastrophic crack growth occurred during four complete flight cycles. Both surface-crack models and through-crack models were utilized to characterize cracks in the weld toe.

Pai, Shantaram S.; Hoge, Peter A.; Patel, B. M.; Nagpal, Vinod K.

2009-01-01

95

Development of a comprehensive weld process model  

SciTech Connect

This cooperative research and development agreement (CRADA) between Concurrent Technologies Corporation (CTC) and Lockheed Martin Energy Systems (LMES) combines CTC`s expertise in the welding area and that of LMES to develop computer models and simulation software for welding processes. This development is of significant impact to the industry, including materials producers and fabricators. The main thrust of the research effort was to develop a comprehensive welding simulation methodology. A substantial amount of work has been done by several researchers to numerically model several welding processes. The primary drawback of most of the existing models is the lack of sound linkages between the mechanistic aspects (e.g., heat transfer, fluid flow, and residual stress) and the metallurgical aspects (e.g., microstructure development and control). A comprehensive numerical model which can be used to elucidate the effect of welding parameters/conditions on the temperature distribution, weld pool shape and size, solidification behavior, and microstructure development, as well as stresses and distortion, does not exist. It was therefore imperative to develop a comprehensive model which would predict all of the above phenomena during welding. The CRADA built upon an already existing three-dimensional (3-D) welding simulation model which was developed by LMES which is capable of predicting weld pool shape and the temperature history in 3-d single-pass welds. However, the model does not account for multipass welds, microstructural evolution, distortion and residual stresses. Additionally, the model requires large resources of computing time, which limits its use for practical applications. To overcome this, CTC and LMES have developed through this CRADA the comprehensive welding simulation model described above.

Radhakrishnan, B.; Zacharia, T.; Paul, A.

1997-05-01

96

Chemical stabilization of organic carbon pools in particle size fractions in no-till and meadow soils  

Technology Transfer Automated Retrieval System (TEKTRAN)

Land use and soil management affects soil organic carbon (SOC) pools associated with particle size fractions and their chemical stabilization. No-till (NT) production of corn (Zea mays L.) is a recommended management practice that reduces erosion and increases SOC concentration, but the knowledge a...

97

Regulation of the Pool Size of Valine in Escherichia coli K-12  

PubMed Central

Three mutations (ilvH611, ilvH612, and ilvH613) are described which make Escherichia coli K-12 resistant to valine inhibition and are located near leu. The expression of the ilv genes appears to be normal in these mutants since the isoleucine-valine biosynthetic enzymes are not derepressed relative to the wild type. The intracellular concentration of valine is, however, higher in the mutants than in the isogenic ilvH+ strain. These mutants also excrete valine, probably because of the high intracellular concentration of this amino acid. The pool size of valine is regulated independently from that of isoleucine and leucine. The increased intracellular concentration of valine is due to a decreased feedback inhibition that valine exerts on its own biosynthetic pathway. In fact, acetolactate synthase activity assayed in extracts of ilvH612 and ilvH613 mutants is more resistant to valine inhibition than the activity assayed in the ilvH+ isogenic strain. Two forms of acetolactate synthase activity can be separated from these extracts by adsorption and elution on hydroxylapatite. One of them is as sensitive to valine inhibition as that of the wild type, the other is more resistant to valine inhibition. PMID:4612002

Felice, Maurilio De; Guardiola, John; Malorni, Maria C.; Klopotowski, Tadeusz; Iaccarino, Maurizio

1974-01-01

98

Orphan G Protein–Coupled Receptor GPR116 Regulates Pulmonary Surfactant Pool Size  

PubMed Central

Pulmonary surfactant levels within the alveoli are tightly regulated to maintain lung volumes and promote efficient gas exchange across the air/blood barrier. Quantitative and qualitative abnormalities in surfactant are associated with severe lung diseases in children and adults. Although the cellular and molecular mechanisms that control surfactant metabolism have been studied intensively, the critical molecular pathways that sense and regulate endogenous surfactant levels within the alveolus have not been identified and constitute a fundamental knowledge gap in the field. In this study, we demonstrate that expression of an orphan G protein–coupled receptor, GPR116, in the murine lung is developmentally regulated, reaching maximal levels 1 day after birth, and is highly expressed on the apical surface of alveolar type I and type II epithelial cells. To define the physiological role of GPR116 in vivo, mice with a targeted mutation of the Gpr116 locus, Gpr116?exon17, were generated. Gpr116?exon17 mice developed a profound accumulation of alveolar surfactant phospholipids at 4 weeks of age (12-fold) that was further increased at 20 weeks of age (30-fold). Surfactant accumulation in Gpr116?exon17 mice was associated with increased saturated phosphatidylcholine synthesis at 4 weeks and the presence of enlarged, lipid-laden macrophages, neutrophilia, and alveolar destruction at 20 weeks. mRNA microarray analyses indicated that P2RY2, a purinergic receptor known to mediate surfactant secretion, was induced in Gpr116?exon17 type II cells. Collectively, these data support the concept that GPR116 functions as a molecular sensor of alveolar surfactant lipid pool sizes by regulating surfactant secretion. PMID:23590306

Ludwig, Marie-Gabrielle; Mueller, Matthias; Kinzel, Bernd; Sato, Atsuyasu; Xu, Yan; Whitsett, Jeffrey A.; Ikegami, Machiko

2013-01-01

99

Candidate Pooling Regions (PRs) are generated by dense sampling of their location and size  

E-print Network

. REGULARISED DUAL AVERAGING (RDA) · Stochastic proximal gradient method well suited for non-smooth objectives, leading to state-of-the-art performance · Pooling region selection using Rank-SVM with L1 regularisation

Kim, Tae-Kyun

100

Time-dependent calculations of molten pool formation and thermal plasma with metal vapour in gas tungsten arc welding  

NASA Astrophysics Data System (ADS)

A gas tungsten arc (GTA) was modelled taking into account the contamination of the plasma by metal vapour from the molten anode. The whole region of GTA atmosphere including the tungsten cathode, the arc plasma and the anode was treated using a unified numerical model. A viscosity approximation was used to express the diffusion coefficient in terms of viscosity of the shielding gas and metal vapour. The transient two-dimensional distributions of temperature, velocity of plasma flow and iron vapour concentration were predicted, together with the molten pool as a function of time for a 150 A arc current at atmospheric pressure, both for helium and argon gases. It was shown that the thermal plasma in the GTA was influenced by iron vapour from the molten pool surface and that the concentration of iron vapour in the plasma was dependent on the temperature of the molten pool. GTA on high sulfur stainless steel was calculated to discuss the differences between a low sulfur and a high sulfur stainless steel anode. Helium was selected as the shielding gas because a helium GTA produces more metal vapour than an argon GTA. In the GTA on a high sulfur stainless steel anode, iron vapour and current path were constricted. Radiative emission density in the GTA on high sulfur stainless steel was also concentrated in the centre area of the arc plasma together with the iron vapour although the temperature distributions were almost the same as that in the case of a low sulfur stainless steel anode.

Tanaka, M.; Yamamoto, K.; Tashiro, S.; Nakata, K.; Yamamoto, E.; Yamazaki, K.; Suzuki, K.; Murphy, A. B.; Lowke, J. J.

2010-11-01

101

Establishing Mathematical Models to Predict Grain Size and Hardness of the Friction Stir-Welded AA 7020 Aluminum Alloy Joints  

NASA Astrophysics Data System (ADS)

In this study, response surface methodology in conjunction with a central composite design was applied to predict the grain size and hardness of friction stir-welded AA 7020 aluminum alloy joints. For this purpose, three welding parameters, including tool rotational speed, traverse speed, and tool axial force, at five levels and 20 runs were considered. In order to validate the predicted models, the analysis of variance was performed. Hardness and microstructural features of the joints were investigated using microhardness test and optical microscopy, respectively. In addition, the influences of friction stir welding parameters on grain size and hardness of the joints were examined thoroughly. The analysis of variance results revealed that the developed models were significant and accurate to predict the responses. Furthermore, with increasing the heat input, the hardness of the joints decreased, where the grain size increased continuously. In addition, the optimized condition for achieving the lowest grain size and highest hardness of the joints was reached as 800 rpm, 125 mm/min and 8 kN.

Rahimzadeh Ilkhichi, A.; Soufi, R.; Hussain, G.; Vatankhah Barenji, R.; Heidarzadeh, A.

2015-02-01

102

A Scanning Transmission Electron Microscopy Method for Determining Manganese Composition in Welding Fume as a Function of Primary Particle Size  

PubMed Central

Increasing evidence suggests that the physicochemical properties of inhaled nanoparticles influence the resulting toxicokinetics and toxicodynamics. This report presents a method using scanning transmission electron microscopy (STEM) to measure the Mn content throughout the primary particle size distribution of welding fume particle samples collected on filters for application in exposure and health research. Dark field images were collected to assess the primary particle size distribution and energy-dispersive X-ray and electron energy loss spectroscopy were performed for measurement of Mn composition as a function of primary particle size. A manual method incorporating imaging software was used to measure the primary particle diameter and to select an integration region for compositional analysis within primary particles throughout the size range. To explore the variation in the developed metric, the method was applied to 10 gas metal arc welding (GMAW) fume particle samples of mild steel that were collected under a variety of conditions. The range of Mn composition by particle size was ?0.10 to 0.19 %/nm, where a positive estimate indicates greater relative abundance of Mn increasing with primary particle size and a negative estimate conversely indicates decreasing Mn content with size. However, the estimate was only statistically significant (p<0.05) in half of the samples (n=5), which all had a positive estimate. In the remaining samples, no significant trend was measured. Our findings indicate that the method is reproducible and that differences in the abundance of Mn by primary particle size among welding fume samples can be detected. PMID:21625364

Richman, Julie D.; Livi, Kenneth J.T.; Geyh, Alison S.

2011-01-01

103

A Scanning Transmission Electron Microscopy Method for Determining Manganese Composition in Welding Fume as a Function of Primary Particle Size.  

PubMed

Increasing evidence suggests that the physicochemical properties of inhaled nanoparticles influence the resulting toxicokinetics and toxicodynamics. This report presents a method using scanning transmission electron microscopy (STEM) to measure the Mn content throughout the primary particle size distribution of welding fume particle samples collected on filters for application in exposure and health research. Dark field images were collected to assess the primary particle size distribution and energy-dispersive X-ray and electron energy loss spectroscopy were performed for measurement of Mn composition as a function of primary particle size. A manual method incorporating imaging software was used to measure the primary particle diameter and to select an integration region for compositional analysis within primary particles throughout the size range. To explore the variation in the developed metric, the method was applied to 10 gas metal arc welding (GMAW) fume particle samples of mild steel that were collected under a variety of conditions. The range of Mn composition by particle size was -0.10 to 0.19 %/nm, where a positive estimate indicates greater relative abundance of Mn increasing with primary particle size and a negative estimate conversely indicates decreasing Mn content with size. However, the estimate was only statistically significant (p<0.05) in half of the samples (n=5), which all had a positive estimate. In the remaining samples, no significant trend was measured. Our findings indicate that the method is reproducible and that differences in the abundance of Mn by primary particle size among welding fume samples can be detected. PMID:21625364

Richman, Julie D; Livi, Kenneth J T; Geyh, Alison S

2011-06-01

104

Welding system  

SciTech Connect

An electric arc welding gas system utilizing a welding gas comprising a mixture of argon, helium, carbon dioxide and oxygen; electrode currents in the range of 100 to 1100 amperes so as to form electrode metal globules of at least the size of the electrode diameter at the rate of 400 to 1200 globules per second.

Church, J.G.

1984-07-31

105

Laser Beam Welding of Nitride Steel Components  

NASA Astrophysics Data System (ADS)

Laser beam welding is a joining technique that has many advantages over conventional GMAW welding, such as low heat input, short cycle time as well as good cosmetic welds. Laser beam welding has been widely used for welding powertrain components in automotive industry. When welding nitride steel components, however, laser beam welding faces a great challenge. The difficulty lies in the fact that the nitride layer in the joint releases the nitrogen into the weld pool, resulting in a porous weld. This research presents an industrial ready solution to prevent the nitrogen from forming gas bubbles in the weld.

Gu, Hongping; Yin, Guobin; Shulkin, Boris

106

X-ray and neutron diffraction measurements of dislocation density and subgrain size in a friction stir welded aluminum alloy  

SciTech Connect

The dislocation density and subgrain size were determined in the base material and friction-stir welds of 6061-T6 aluminum alloy. High-resolution X-ray diffraction measurement was performed in the base material. The result of the line profile analysis of the X-ray diffraction peak shows that the dislocation density is about 4.5 x 10{sup 14} m{sup 02} and the subgrain size is about 200 nm. Meanwhile, neutron diffraction measurements have been performed to observe the diffraction peaks during friction-stir welding (FSW). The deep penetration capability of the neutron enables us to measure the peaks from the midplane of the Al plate underneath the tool shoulder of the friction-stir welds. The peak broadening analysis result using the Williamson-Hall method shows the dislocation density of about 3.2 x 10{sup 15} m{sup -2} and subgrain size of about 160 nm. The significant increase of the dislocation density is likely due to the severe plastic deformation during FSW. This study provides an insight into understanding the transient behavior of the microstructure under severe thermomechanical deformation.

Claussen, Bjorn [Los Alamos National Laboratory; Woo, Wanchuck [ORNL; Zhili, Feng [ORNL; Edward, Kenik [ORNL; Ungar, Tamas [EOTVOS UNIV.

2009-01-01

107

ECOLOGICAL STUDIES AND MATHEMATICAL MODELING OF 'CLADOPHORA' IN LAKE HURON: 3. THE DEPENDENCE OF GROWTH RATES ON INTERNAL PHOSPHOROUS POOL SIZE (JOURNAL VERSION)  

EPA Science Inventory

The relationship between growth rate and internal phosphorus pool size was examined using field populations of Cladophora golmerata from Lake Huron. Algal samples, representing a range of internal phosphorus concentrations, were harvested from the lake and used for laboratory mea...

108

Forage intake, N and NDF flow to the abomasum and rumen pool sizes of NDF in Bos indicus (Boran) steers fed oat,  

E-print Network

detergent fibre) and N flow to the abomasum and rumen pool sizes of NDF in Boran steers fed oat ((0) Avena sativa) hay, lablab ((L) Lablab purpureus) hay, or grass ((G) Andropogon sp, Danthonia subulata) hay

Boyer, Edmond

109

Laser beam welding of any metal.  

SciTech Connect

The effect of a metal's thermophysical properties on its weldability are examined. The thermal conductivity, melting point, absorptivity and thermal diffusivity of the metal and the laser beam focused diameter and welding speed influence the minimum beam irradiance required for melting and welding. Beam diameter, surface tension and viscosity of the molten metal affect weld pool stability and weld quality. Lower surface tension and viscosity increases weld pool instability. With larger beam diameters causing wider welds, dropout also increases. Effects of focused beam diameter and joint fitup on weldability are also examined. Small beam diameters are sensitive to beam coupling problems in relation to fitup precision in addition to beam alignment to the seam. Welding parameters for mitigating weld pool instability and increasing weld quality are derived from the above considerations. Guidelines are presented for the tailoring of welding parameters to achieve good welds. Weldability problems can also be anticipated from the properties of a metal.

Leong, K. H.

1998-10-01

110

Why and when channelling can decrease pool size at constant net flux in a simple dynamic channel.  

PubMed

Cornish-Bowden and Cárdenas (Cornish-Bowden, A. and Cárdenas M.L. (1993) Eur. J. Biochem. 213, 87-92) have suggested that simulation results peviously published by us (Mendes, P., Kell, D.B. and Westerhoff, H.V. (1992) Eur. J. Biochem. 204, 255-266) which had demonstrated that large reductions of intermediate pool sizes could be accompanied by increasing channel flux in a model metabolic pathway, were an artefact of changes in the pathway's overall flux of the order of 0.0075%, or of inappropriate alterations of enzyme activities. They also asserted to prove that the "channelling of an intermediate cannot affect its free concentration at constant net flux". We consider the co-response of the intermediate metabolite concentration ('pool') and the channel flux to changes in kinetic (or thermodynamic) parameters. Both by analytical proofs and by numerical examples we show that this co-response can be positive, negative or null, depending on the parameter change. In particular, we prove that there is always a number of ways of changing parameters such that the intermediate metabolite concentration decreases with increasing channel flux, whether the total flux varies or is constant. We also show that increased stability of the (dynamic) enzyme-intermediate-enzyme complex, as well as a single parameter change that similarly displays no cross-over effects, can lead to decreased intermediate metabolite concentration and increased channel flux at constant total flux. In general, a non-zero co-response of the intermediate metabolite concentration ('pool') and the channel flux to changes in kinetic (or other) parameters is the rule rather than the exception. More specifically: (i) The algebraic analysis ('general proof') given in Cornish-Bowden and Cárdenas (1993) contains the constraint that the elasticities of various steps to the modulation parameters which were used to vary the channel flux at constant net flux were unity. This is an unfortunate and unnecessary constraint which, when lifted, means that the concentration of the pool in the general case can indeed change at constant net flux. A 'simplified proof' given in Cornish-Bowden and Cárdenas (1993) also fails, due in addition to the consequent failure to include mass conservation relations for some of the enzymes. (ii) In the systems studied by Cornish-Bowden and Cárdenas (1993), flux is properly to be considered as a variable (since it varies during the transition to the steady state), and not a parameter, and as such cannot per se affect the magnitude of other variables in the steady state. (iii) By relaxing the constraint referred to in (i), above, and by making dual modulations (i.e., of more than one parameter at once) which are different from those carried out in Cornish-Bowden and Cárdenas (1993) we find many instances in which channelling (described by a parameter p) does significantly affect the concentration of the pool intermediate C at constant total flux. (iv) In the same pathways, but in which the flux is held constant by setting it via a zero-order flux-generating reaction, the addition of a channel is also able to significantly to modulate the size of the pool at constant total flux. Our results show that the effectiveness of channelling in decreasing a pool, even at constant flux, is very much a reality. PMID:8600971

Mendes, P; Kell, D B; Westerhoff, H V

1996-03-15

111

Platelet size and function in septic rats: changes in the adenylate pool.  

PubMed

Cecal ligation and puncture (CLP) were performed in rats. After 4 hr (early sepsis) and 16 hr (late sepsis), platelet morphology and function were studied. At 16 hr, platelet counts for the CLP group were significantly lower than for the sham-operated control group. Low maximum aggregation rates (MAR) and decreased platelet counts were elicited in platelet-rich plasma with 4 M ADP and 2 micrograms/ml collagen. However, with platelet counts equalized, MAR for the CLP group increased significantly, especially after 16 hr. The platelet-large cell rate and platelet distribution width decreased temporarily at 4 hr, then rose significantly at 16 hr. No significant changes were observed in the mean platelet volume after 4 hr, but there were significant increases after 16 hr. Total adenine nucleotide (TAN) levels within the platelets rose significantly in the CLP group, suggesting the appearance during the late sepsis of large, heavy platelets or adenine nucleotide-rich platelets. The platelet adenylate pool was divided into granular and cytoplasmic fractions, respectively characterized by ADP and ATP increases. However, no septicemia-related differences were noted in the degree of binding between goat antirat fibrinogen and platelet surface glycoprotein IIb/IIIa complex. Internal environment changes in the platelets indicated that during septicemia hyperfunctional or hypersensitive platelets with a latent capacity for active aggregation and release appeared in the circulation. Hypercoagulability in septicemia involves activation of coagulation factors, stimulation of the coagulation cascade, volume changes accompanying increased platelet TAN content, and changes in AN distribution in the two pools. These findings significantly increase our understanding of the transition from the prethrombotic state to thrombosis in septicemia. PMID:2174092

Taniguchi, T; Takagi, D; Takeyama, N; Kitazawa, Y; Tanaka, T

1990-11-01

112

WELDING RESEARCH -s57WELDING JOURNAL  

E-print Network

the HAZ size, microstructure, and the hard- ness of high-strength steel ASTM A514 welded by DEWELDING RESEARCH -s57WELDING JOURNAL ABSTRACT. Low heat input is typically desired for welding high-strength steels to ensure that the mechanical behavior of material in the HAZ would not change significantly after

Zhang, YuMing

113

Presynaptic calcium influx controls neurotransmitter release in part by regulating the effective size of the readily releasable pool.  

PubMed

The steep calcium dependence of synaptic strength that has been observed at many synapses is thought to reflect a calcium dependence of the probability of vesicular exocytosis (p), with the cooperativity of three to six corresponding to the multiple calcium ion binding sites on the calcium sensor responsible for exocytosis. Here we test the hypothesis that the calcium dependence of the effective size of the readily releasable pool (RRP) also contributes to the calcium dependence of release at the calyx of Held synapse in mice. Using two established methods of quantifying neurotransmitter release evoked by action potentials (effective RRP), we find that when calcium influx is changed by altering the external calcium concentration, the calcium cooperativity of p is insufficient to account for the full calcium dependence of EPSC size; the calcium dependence of the RRP size also contributes. Reducing calcium influx by blocking R-type voltage-gated calcium channels (VGCCs) with Ni(2+), or by blocking P/Q-type VGCCs with ?-agatoxin IVA also changes EPSC amplitude by reducing both p and the effective RRP size. This suggests that the effective RRP size is dependent on calcium influx through VGCCs. Furthermore, activation of GABAB receptors, which reduces presynaptic calcium through VGCCs without other significant effects on release, also reduces the effective RRP size in addition to reducing p. These findings indicate that calcium influx regulates the RRP size along with p, which contributes to the calcium dependence of synaptic strength, and it influences the manner in which presynaptic modulation of presynaptic calcium channels affects neurotransmitter release. PMID:23486937

Thanawala, Monica S; Regehr, Wade G

2013-03-13

114

gone early, a Novel Germline Factor, Ensures the Proper Size of the Stem Cell Precursor Pool in the Drosophila Ovary  

PubMed Central

In order to sustain lifelong production of gametes, many animals have evolved a stem cell–based gametogenic program. In the Drosophila ovary, germline stem cells (GSCs) arise from a pool of primordial germ cells (PGCs) that remain undifferentiated even after gametogenesis has initiated. The decision of PGCs to differentiate or remain undifferentiated is regulated by somatic stromal cells: specifically, epidermal growth factor receptor (EGFR) signaling activated in the stromal cells determines the fraction of germ cells that remain undifferentiated by shaping a Decapentaplegic (Dpp) gradient that represses PGC differentiation. However, little is known about the contribution of germ cells to this process. Here we show that a novel germline factor, Gone early (Goe), limits the fraction of PGCs that initiate gametogenesis. goe encodes a non-peptidase homologue of the Neprilysin family metalloendopeptidases. At the onset of gametogenesis, Goe was localized on the germ cell membrane in the ovary, suggesting that it functions in a peptidase-independent manner in cell–cell communication at the cell surface. Overexpression of Goe in the germline decreased the number of PGCs that enter the gametogenic pathway, thereby increasing the proportion of undifferentiated PGCs. Inversely, depletion of Goe increased the number of PGCs initiating differentiation. Excess PGC differentiation in the goe mutant was augmented by halving the dose of argos, a somatically expressed inhibitor of EGFR signaling. This increase in PGC differentiation resulted in a massive decrease in the number of undifferentiated PGCs, and ultimately led to insufficient formation of GSCs. Thus, acting cooperatively with a somatic regulator of EGFR signaling, the germline factor goe plays a critical role in securing the proper size of the GSC precursor pool. Because goe can suppress EGFR signaling activity and is expressed in EGF-producing cells in various tissues, goe may function by attenuating EGFR signaling, and thereby affecting the stromal environment. PMID:25420147

Matsuoka, Shinya; Gupta, Swati; Suzuki, Emiko; Hiromi, Yasushi; Asaoka, Miho

2014-01-01

115

Origin of wavy weld boundary  

NASA Astrophysics Data System (ADS)

In conduction mode laser welding, the shape of the fusion boundary affects the solidification process, microstructure, and properties of the weld. Although significant progress has been made in the calculations of the shape and size of the fusion zone in recent decades, the conditions for the formation of the wavy fusion boundary are still not well understood. Here we examine the conditions for its formation in terms of important dimensionless numbers. In particular, the computed flow patterns, temperature fields, and molten pool shapes under the flat free surface are examined for various values of Marangoni, Prandtl, Peclet, and dimensionless heat input values. In the absence of electromagnetic force, it is shown that the wavy fusion boundary forms for specific ranges of Marangoni and Prandtl numbers.

Wei, P. S.; Ting, C. N.; Yeh, J. S.; DebRoy, T.; Chung, F. K.; Yan, G. H.

2009-03-01

116

In-process monitoring and feedback control for stable production of full-penetration weld in continuous wave fibre laser welding  

NASA Astrophysics Data System (ADS)

Laser micro-welding has been applied for device sealing in electronics and automobile industries. Welding of corners in goods and products is a problem owing to easier formation of a weld with burn-through, shallow penetration or a non-bonded part when a drastic change in the welding speed or laser power occurs. This research was therefore undertaken with the objective of obtaining a fundamental knowledge of in-process monitoring and feedback control for the stable production of a full-penetration weld with a constant bead width on the bottom surface irrespective of the changes in the laser power and the welding speed. Variation in weld penetration geometry was investigated by rapid deceleration and acceleration in the welding speed during lap welding of pure titanium thin sheets with a continuous wave (CW) single-mode fibre laser beam. The rapid deceleration in the welding speed led to a considerable change in the full-penetration weld geometry or a partially penetrated weld (if the power was accordingly reduced), resulting in the difficulty in the stable production of a full-penetration weld bead. The heat radiation intensity measured from the laser-irradiated area was useful as an in-process monitoring signal for detecting the molten pool size on the laser-irradiated surface. However, the utilization of monitoring of heat radiation was difficult for predicting the weld bead width on the bottom surface due to the formation of partial penetration or the change in the penetration shape. The laser power was controlled at a 4 ms interval according to the heat radiation signal in order to adjust the weld bead width on the laser-irradiated surface to the target weld penetration geometry affected by thermal storage. Consequently, the feedback-controlled laser power produced a stable full-penetration weld with the designed bead width on the bottom surface irrespective of the rapid deceleration of the welding speed and the corresponding decrease in laser power. Furthermore, the developed feedback control algorithm was effective in rapid acceleration of the welding speed. From these results, it was confirmed that the consideration of the feedback control algorithm including a thermophysical property such as thermal storage was essential for the suppression of the effect due to rapid deceleration and acceleration of the welding speed and the laser power in lap seam micro-welding with a CW fibre laser.

Kawahito, Yousuke; Ohnishi, Terumasa; Katayama, Seiji

2009-04-01

117

Flow Dynamics in Arc Welding  

SciTech Connect

The state of the art for numerical computations has now advanced so that the capability is within sight of calculating weld shapes for any arc current, welding gas, welding material or configuration. Inherent in these calculations is 'flow dynamics' applied to plasma flow in the arc and liquid metal flow in the weld pool. Examples of predictions which are consistent with experiment, are discussed for (1) conventional tungsten inert gas welding, (2) the effect of a fraction of a percent of sulfur in steel, which can increase weld depth by more than a factor of two through changes in the surface tension, (3) the effect of a flux, which can produce increased weld depth due to arc constriction, (4) use of aluminium instead of steel, when the much larger thermal conductivity of aluminium greatly reduces the weld depth and (5) addition of a few percent of hydrogen to argon, which markedly increases weld depth.

Lowke, John J. [CSIRO Materials Science and Engineering, PO Box 218, Lindfield, Sydney NSW 2070 (Australia); Tanaka, Manabu [Joining and Welding Research Institute, Osaka University, 11-1 Mihogaoka, Ibaraki (Japan)

2008-02-21

118

Flow Dynamics in Arc Welding  

NASA Astrophysics Data System (ADS)

The state of the art for numerical computations has now advanced so that the capability is within sight of calculating weld shapes for any arc current, welding gas, welding material or configuration. Inherent in these calculations is "flow dynamics" applied to plasma flow in the arc and liquid metal flow in the weld pool. Examples of predictions which are consistent with experiment, are discussed for (1) conventional tungsten inert gas welding (2) the effect of a fraction of a percent of sulfur in steel, which can increase weld depth by more than a factor of two through changes in the surface tension (3) the effect of a flux, which can produce increased weld depth due to arc constriction (4) use of aluminium instead of steel, when the much larger thermal conductivity of aluminium greatly reduces the weld depth and (5) addition of a few percent of hydrogen to argon, which markedly increases weld depth.

Lowke, John J.; Tanaka, Manabu

2008-02-01

119

Method for enhanced control of welding processes  

DOEpatents

Method and system for producing high quality welds in welding processes, in general, and gas tungsten arc (GTA) welding, in particular by controlling weld penetration. Light emitted from a weld pool is collected from the backside of a workpiece by optical means during welding and transmitted to a digital video camera for further processing, after the emitted light is first passed through a short wavelength pass filter to remove infrared radiation. By filtering out the infrared component of the light emitted from the backside weld pool image, the present invention provides for the accurate determination of the weld pool boundary. Data from the digital camera is fed to an imaging board which focuses on a 100.times.100 pixel portion of the image. The board performs a thresholding operation and provides this information to a digital signal processor to compute the backside weld pool dimensions and area. This information is used by a control system, in a dynamic feedback mode, to automatically adjust appropriate parameters of a welding system, such as the welding current, to control weld penetration and thus, create a uniform weld bead and high quality weld.

Sheaffer, Donald A. (Livermore, CA); Renzi, Ronald F. (Tracy, CA); Tung, David M. (Livermore, CA); Schroder, Kevin (Pleasanton, CA)

2000-01-01

120

The activity of nitrate reductase and the pool sizes of some amino acids and some sugars in water-stressed maize leaves  

Microsoft Academic Search

The activity of nitrate reductase and the pool sizes of some amino acids and some sugars were measured in relation to the leaf water potential (?) of maize leaves. The activity of nitrate reductase was severely inhibited in water-stressed maize leaves. This was not due to substrate shortage or the presence of an inhibitor at reduced leaf water potential. While

T. W. Becker; H. P. Fock

1986-01-01

121

Cholesterol kinetics in subjects with bile fistula. Positive relationship between size of the bile acid precursor pool and bile acid synthetic rate.  

PubMed Central

Our aim was to identify and quantitate cholesterol pools and transport pathways in blood and liver. By studying bile fistula subjects, using several types of isotopic preparations, simultaneous labeling of separate cholesterol pools and sampling all components of blood and bile at frequent intervals, we developed a comprehensive multicompartmental model for cholesterol within the rapidly miscible pool. Data in six components (bile acids, esterified cholesterol in whole plasma, and free cholesterol in blood cells, bile, alpha lipoproteins, and beta lipoproteins) were modeled simultaneously with the SAAM program. The analysis revealed extensive exchange of free cholesterol between HDL and liver, blood cells, and other tissues. There was net free cholesterol transport from HDL to the liver in most subjects. The major organ that removed esterified cholesterol from blood was the liver. A large portion (4,211 mumol) of total hepatic cholesterol comprised a pool that turned over rapidly (t1/2 of 72 min) by exchanging mainly with plasma HDL and was the major source of bile acids and biliary cholesterol. Only 6% of hepatic newly synthesized cholesterol was used directly for bile acid synthesis: the analysis showed that 94% of newly synthesized cholesterol was partitioned into the large hepatic pool (putative plasma membrane free cholesterol) which exchanged rapidly with plasma lipoproteins. Bile acid synthetic rate correlated directly with the size of the large hepatic pool. In conclusion, hepatic and blood cholesterol pools and transports have been quantitated. HDL plays a central role in free cholesterol exchange/transport between all tissues and plasma. In humans, the metabolically active pool comprises a large portion of total hepatic cholesterol that, in part, regulates bile acid synthesis. PMID:8450070

Schwartz, C C; Zech, L A; VandenBroek, J M; Cooper, P S

1993-01-01

122

Welding Penetration Control of Fixed Pipe in TIG Welding Using Fuzzy Inference System  

NASA Astrophysics Data System (ADS)

This paper presents a study on welding penetration control of fixed pipe in Tungsten Inert Gas (TIG) welding using fuzzy inference system. The welding penetration control is essential to the production quality welds with a specified geometry. For pipe welding using constant arc current and welding speed, the bead width becomes wider as the circumferential welding of small diameter pipes progresses. Having welded pipe in fixed position, obviously, the excessive arc current yields burn through of metals; in contrary, insufficient arc current produces imperfect welding. In order to avoid these errors and to obtain the uniform weld bead over the entire circumference of the pipe, the welding conditions should be controlled as the welding proceeds. This research studies the intelligent welding process of aluminum alloy pipe 6063S-T5 in fixed position using the AC welding machine. The monitoring system used a charge-coupled device (CCD) camera to monitor backside image of molten pool. The captured image was processed to recognize the edge of molten pool by image processing algorithm. Simulation of welding control using fuzzy inference system was constructed to simulate the welding control process. The simulation result shows that fuzzy controller was suitable for controlling the welding speed and appropriate to be implemented into the welding system. A series of experiments was conducted to evaluate the performance of the fuzzy controller. The experimental results show the effectiveness of the control system that is confirmed by sound welds.

Baskoro, Ario Sunar; Kabutomori, Masashi; Suga, Yasuo

123

Experimental Investigation into the Effects of Weld Sequence and Fixture on Residual Stresses in Arc Welding Process  

NASA Astrophysics Data System (ADS)

This study concentrates on the effects of weld sequence and welding fixtures on distribution and magnitude of induced arc welding residual stresses built up in butt-joint of Gas Tungsten Arc Welding (GTAW) AA5251 plates. Aluminum plates have been welded under different welding conditions and then, longitudinal and transverse residual stresses were measured in different points of the welded plates employing hole-drilling technique. The results indicate that welding sequence significantly alters the distributions of both longitudinal and transverse residual stresses while the changing in the weld sequence leads to 44% decrease in longitudinal residual stress. Besides, both the geometry of weld pool and distribution of residual stresses are affected by the welding fixtures while implementation of fixture causes about 21 and 76% reductions in the depth of weld pool and transverse residual stress, respectively, for the material and welding conditions used in this research.

Kohandehghan, A. R.; Serajzadeh, S.

2012-06-01

124

Lowering bile acid pool size with a synthetic farnesoid X receptor (FXR) agonist induces obesity and diabetes through reduced energy expenditure.  

PubMed

We evaluated the metabolic impact of farnesoid X receptor (FXR) activation by administering a synthetic FXR agonist (GW4064) to mice in which obesity was induced by a high fat diet. Administration of GW4064 accentuated body weight gain and glucose intolerance induced by the high fat diet and led to a pronounced worsening of the changes in liver and adipose tissue. Mechanistically, treatment with GW4064 decreased bile acid (BA) biosynthesis, BA pool size, and energy expenditure, whereas reconstitution of the BA pool in these GW4064-treated animals by BA administration dose-dependently reverted the metabolic abnormalities. Our data therefore suggest that activation of FXR with synthetic agonists is not useful for long term management of the metabolic syndrome, as it reduces the BA pool size and subsequently decreases energy expenditure, translating as weight gain and insulin resistance. In contrast, expansion of the BA pool size, which can be achieved by BA administration, could be an interesting strategy to manage the metabolic syndrome. PMID:21632533

Watanabe, Mitsuhiro; Horai, Yasushi; Houten, Sander M; Morimoto, Kohkichi; Sugizaki, Taichi; Arita, Eri; Mataki, Chikage; Sato, Hiroyuki; Tanigawara, Yusuke; Schoonjans, Kristina; Itoh, Hiroshi; Auwerx, Johan

2011-07-29

125

Nutrient demand interacts with legume particle length to affect digestion responses and rumen pool sizes in dairy cows.  

PubMed

Effects of legume particle length on dry matter intake (DMI), milk production, ruminal fermentation and pool sizes, and digestion and passage kinetics, and the relationship of these effects with preliminary DMI (pDMI) were evaluated using 13 ruminally and duodenally cannulated Holstein cows in a crossover design with a 14-d preliminary period and two 19-d treatment periods. During the preliminary period, pDMI of individual cows ranged from 22.8 to 32.4 kg/d (mean=26.5 kg/d) and 3.5% fat-corrected milk yield ranged from 22.9 to 62.4 kg/d (mean=35.1 kg/d). Experimental treatments were diets containing alfalfa silage chopped to (1) 19 mm (long cut, LC) or (2) 10 mm (short cut, SC) theoretical length of cut as the sole forage. Alfalfa silages contained approximately 43% neutral detergent fiber (NDF); diets contained approximately 47% forage and 20% forage NDF. Preliminary DMI, an index of nutrient demand, was determined during the last 4 d of the preliminary period, when cows were fed a common diet, and used as a covariate. Main effects of legume particle length and their interaction with pDMI were tested by ANOVA. Alfalfa particle length and its interaction with pDMI did not affect milk yield or rumen pH. The LC diet decreased milk fat concentration more per kilogram of pDMI increase than the SC diet and increased yields of milk fat and fat-corrected milk less per kilogram of pDMI increase than the SC diet, resulting in a greater benefit for LC at low pDMI and for SC at high pDMI. The LC diet tended to decrease DMI compared with the SC diet. Ruminal digestion and passage rates of feed fractions did not differ between LC and SC and were not related to level of intake. The LC diet tended to decrease the rate of ruminal turnover for NDF but increased NDF rumen pools at a slower rate than the SC diet as pDMI increased. This indicated that the faster NDF turnover rate did not counterbalance the higher DMI for SC, resulting in larger NDF rumen pools for SC than LC. As pDMI increased, LC increased ruminal digestibility of potentially digestible NDF and total NDF, and SC decreased them, but total-tract digestibilities of potentially digestible NDF, total NDF, organic matter, and dry matter were lower for LC than for SC. Ruminal digestibilities of starch and organic matter interacted quadratically with level of intake. When legume silage was the only source of forage in the diet, increasing chop length from 10 to 19 mm tended to decrease DMI but did not negatively affect productivity of cows. PMID:22541490

Kammes, K L; Ying, Y; Allen, M S

2012-05-01

126

Improvement of reliability of welding by in-process sensing and control (development of smart welding machines for girth welding of pipes). Final report  

SciTech Connect

Closed-loop control of the welding variables represents a promising, cost-effective approach to improving weld quality and therefore reducing the total cost of producing welded structures. The ultimate goal is to place all significant weld variables under direct closed-loop control; this contrasts with preprogrammed machines which place the welding equipment under control. As the first step, an overall strategy has been formulated and an investigation of weld pool geometry control for gas tungsten arc process has been completed. The research activities were divided into the areas of arc phenomena, weld pool phenomena, sensing techniques and control activities.

Hardt, D.E.; Masubuchi, K.; Paynter, H.M.; Unkel, W.C.

1983-04-01

127

Nitrogen Stress Affects the Turnover and Size of Nitrogen Pools Supplying Leaf Growth in a Grass1[C][W][OPEN  

PubMed Central

The effect of nitrogen (N) stress on the pool system supplying currently assimilated and (re)mobilized N for leaf growth of a grass was explored by dynamic 15N labeling, assessment of total and labeled N import into leaf growth zones, and compartmental analysis of the label import data. Perennial ryegrass (Lolium perenne) plants, grown with low or high levels of N fertilization, were labeled with 15NO3?/14NO3? from 2 h to more than 20 d. In both treatments, the tracer time course in N imported into the growth zones fitted a two-pool model (r2 > 0.99). This consisted of a “substrate pool,” which received N from current uptake and supplied the growth zone, and a recycling/mobilizing “store,” which exchanged with the substrate pool. N deficiency halved the leaf elongation rate, decreased N import into the growth zone, lengthened the delay between tracer uptake and its arrival in the growth zone (2.2 h versus 0.9 h), slowed the turnover of the substrate pool (half-life of 3.2 h versus 0.6 h), and increased its size (12.4 ?g versus 5.9 ?g). The store contained the equivalent of approximately 10 times (low N) and approximately five times (high N) the total daily N import into the growth zone. Its turnover agreed with that of protein turnover. Remarkably, the relative contribution of mobilization to leaf growth was large and similar (approximately 45%) in both treatments. We conclude that turnover and size of the substrate pool are related to the sink strength of the growth zone, whereas the contribution of the store is influenced by partitioning between sinks. PMID:23757403

Lehmeier, Christoph Andreas; Wild, Melanie; Schnyder, Hans

2013-01-01

128

Developing mathematical models to predict grain size and hardness of argon tungsten pulse current arc welded titanium alloy  

Microsoft Academic Search

Titanium (Ti–6Al–4V) alloy has gathered wide acceptance in the fabrication of light weight structures requiring a high strength-to-weight ratio, such as transportable bridge girders, military vehicles, road tankers and railway transport systems. The frequently preferred welding process of titanium alloy is argon tungsten arc welding due to its comparatively easier applicability and better economy. In case of single pass welding

M. Balasubramanian; V. Jayabalan; V. Balasubramanian

2008-01-01

129

Autogeneous Friction Stir Weld Lack-of-Penetration Defect Detection and Sizing Using Directional Conductivity Measurements with MWM Eddy Current Sensor  

NASA Technical Reports Server (NTRS)

Al 2195-T8 plate specimens containing Friction Stir Welds (FSW), provided by Lockheed Martin, were inspected using directional conductivity measurements with the MWM sensor. Sensitivity to lack-of-penetration (LOP) defect size has been demonstrated. The feature used to determine defect size was the normalized longitudinal component of the MWM conductivity measurements. This directional conductivity component was insensitive to the presence of a discrete crack. This permitted correlation of MWM conductivity measurements with the LOP defect size as changes in conductivity were apparently associated with metallurgical features within the first 0.020 in. of the LOP defect zone. Transverse directional conductivity measurements also provided an indication of the presence of discrete cracks. Continued efforts are focussed on inspection of a larger set of welded panels and further refinement of LOP characterization tools.

Goldfine, Neil; Zilberstei, Vladimir; Lawson, Ablode; Kinchen, David; Arbegast, William

2000-01-01

130

Melting Efficiency During Plasma Arc Welding  

NASA Technical Reports Server (NTRS)

A series of partial penetration Variable Polarity Plasma Arc welds were made at equal power but various combinations of current and voltage on 2219 aluminum. Arc Efficiency was measured calorimetrically and ranged between 48% and 66%. Melting efficiency depends on the weld pool shape. Increased current increases the melting efficiency as it increases the depth to width ratio of the weld pool. Higher currents are thought to raise arc pressure and depress the liquid at the bottom of the weld pool causing a more nearly two dimensional heat flow condition.

McClure, J.C.; Evans, D. M.; Tang, W.; Nunes, A. C.

1999-01-01

131

Heat transfer and fluid flow during laser spot welding of 304 stainless steel  

Microsoft Academic Search

The evolution of temperature and velocity fields during laser spot welding of 304 stainless steel was studied using a transient, heat transfer and fluid flow model based on the solution of the equations of conservation of mass, momentum and energy in the weld pool. The weld pool geometry, weld thermal cycles and various solidification parameters were calculated. The fusion zone

X He; P W Fuerschbach; T DebRoy

2003-01-01

132

Variation in species richness and species pool size across a pH gradient in forests of the southern Blue Ridge Mountains  

Microsoft Academic Search

Pärtel (Ecology 83: 2361–2366, 2002) andEwald (Folia Geobot. 38: 357–366, 2003) suggest that the relationship between local species density and soil pH is determined by regional species\\u000a pool size, which in turn reflects the relative abundance of soil types during the evolutionary history of the flora. Ewald\\u000a observed that calcareous sites in Central Europe have higher species density and larger

Robert K. Peet; Jason D. Fridley; Joel M. Gramling

2003-01-01

133

A Study on the Welding Characteristics of Tailor Welded Blank Metal Sheets Using GTAW and Laser Welding  

NASA Astrophysics Data System (ADS)

In this study, a computational and experimental effort was carried out to qualitatively understand the weld pool shape, distortion and residual stress for continuous laser welding and manual pulsed gas metal arc welding. For all the welding simulations given in this dissertation, a welding specific finite element package, SYSWELD, is used. This research focuses on the welding behavior observed in light-weight metal structures known as the tailor-welded blanks, TWBs. They are a combination of two or more metal sheets with different thickness and/or different materials that are welded together in a single plane prior to forming, e.g., stamping. They made from the low carbon steel. As laser welding experiment results show, the weld pool shape at the top and bottom surface, is strongly influenced by surface tension, giving it a characteristic hourglass shape. In order to simulate the hourglass shape, a new volumetric heat source model was developed to predict the transient temperature profile and weld pool shape, including the effect of surface tension. Tailor welded blanks with different thicknesses were examined in the laser welding process. All major physical phenomena such as thermal conduction, heat radiation and convection heat losses are taken into account in the model development as well as temperature-dependant thermal and mechanical material properties. The model is validated for the case of butt joint welding of cold rolled steel sheets. The results of the numerical simulations provide temperature distributions representing the shape of the molten pool, distortion and residual stress with varying laser beam power and welding speed. It is demonstrated that the finite element simulation results are in good agreement with the experiment results. This includes the weld pool shape and sheet metal distortion. While there is no experimental data to compare directly with residual stress results, the distorted shape provides an indirect measure of the welding residual stresses. The welding details such as clamping, butt joint configuration, material, sample thickness are similar for both the laser welding process and the manual pulsed GTAW process. Also as same metallurgical investigation, the weld pool shape displays wider full penetration without the effect of surface tension. The double ellipsoid volumetric heat source is applied in the finite element simulation to determine the temperature distribution, distortion and residual stress. The simulation results are compared with the experimental results and show good agreement. In addition, the results from the laser welding process are compared to the equivalent results from the GTAW process in the order to better understand the fundamental differences between these two welding processes.

Thasanaraphan, Pornsak

134

Nd:YAG laser welding of coated sheet steel  

SciTech Connect

Coated sheet steels are used extensively in the automotive industry for the fabrication of automobile body components; however, their reduced weldability by the traditional welding processes has led to numerous studies into the use of alternate process such as laser welding. In this paper, we present a modified joint geometry which allows high quality lap welds of coated sheet steels to be made by laser welding processes. Hot-dipped galvanized sheet (16 gauge), with a 60 g/m zinc coating was used in this study. A groove was created in the top sheet of a specimen pair by pressing piano wires of various diameters into the sheet. The specimens were clamped together in a lag-joint configuration such that they were in contacted only along the grove projection. A parametric study was conducted using the variables of welding speed, laser mean power (685 W, 1000 W and 1350 W), and grove size. Weld quality and weld pool dimensions were assessed using metallurgical cross-sections and image analysis techniques. Acceptable quality seam welds were produced in the galvanized sheet steel with both grove sizes when using 1000 W and 1350 W laser mean powers and a range of welding speeds. Results of the shear-tensile tests showed that high loads to failure, with failure occurring in the parent material, were predominately found in welds produced at speeds over 1.2 m/min and when using the high mean laser powers: 1000 W and 1350 W. A modified lap joint geometry, in which a groove is pre-placed in the top sheet of the lap-joint configuration, has been developed which permits laser welding of coated sheet steels. Good quality seam welds have been produced in 16 gauge galvanized sheet steels at speeds up to 2.7 m/min using a 2 kW CW Nd:YAG laser operating at 1350 W laser mean power. Weld quality was not affected by changes in groove size.

Graham, M.P.; Kerr, H.W.; Weckman, D.C.

1994-12-31

135

The influence of operating parameters on number-weighted aerosol size distribution generated from a gas metal arc welding process  

Microsoft Academic Search

In light of recent research on the potential health problems associated with sub-micrometer aerosols, a study was conducted to determine the effect that droplet mass transfer mode, shield gas composition, and welding spatter had upon the aerosols generated from a Gas Metal Arc Welding (GMAW) Operation. The results revealed that the sub-micrometer aerosols produced during spray transfer resulted in markedly

Anthony T Zimmer; Paul A Baron; Pratim Biswas

2002-01-01

136

X-Ray and Neutron Diffraction Measurements of Dislocation Density and Subgrain Size in a Friction-Stir-Welded Aluminum Alloy  

SciTech Connect

The dislocation density and subgrain size were determined in the base material and friction-stir welds of 6061-T6 aluminum alloy. High-resolution X-ray diffraction measurement was performed in the base material. The result of the line profile analysis of the X-ray diffraction peak shows that the dislocation density is about 4.5 x 10{sup 14} m{sup -2} and the subgrain size is about 200 nm. Meanwhile, neutron diffraction measurements have been performed to observe the diffraction peaks during friction-stir welding (FSW). The deep penetration capability of the neutron enables us to measure the peaks from the midplane of the Al plate underneath the tool shoulder of the friction-stir welds. The peak broadening analysis result using the Williamson-Hall method shows the dislocation density of about 3.2 x 10{sup 15} m{sup -2} and subgrain size of about 160 nm. The significant increase of the dislocation density is likely due to the severe plastic deformation during FSW. This study provides an insight into understanding the transient behavior of the microstructure under severe thermomechanical deformation.

Woo, Wan Chuck [ORNL; Ungar, Prof Tomas [Eotvos University, Budapest, Hungary; Feng, Zhili [ORNL; Kenik, Edward A [ORNL; Clausen, B [Los Alamos National Laboratory (LANL)

2009-01-01

137

Real-time ultrasonic sensing of arc welding processes  

Microsoft Academic Search

NDE techniques are being investigated for fusion zone sensing of arc welding processes for closed-loop process control. An experimental study of pulse-echo ultrasonics for sensing the depth of penetration of molten weld pools in structural metals during welding indicates that real-time ultrasonic sensing is feasible. Results on the detection of liquid\\/solid weld pool interfaces, the determination of interface location, and

L. A. Lott; J. A. Johnson; H. B. Smartt

1983-01-01

138

A theoretical model for gas metal arc welding and gas tungsten arc welding. I  

Microsoft Academic Search

A recently developed theory for predicting arc and electrode properties in gas metal arc welding (GMAW) has been generalized to include arc-electrode interfaces, variation of surface tension pressure with temperature, Marangoni forces and handling of weld pool development in stationary gas tungsten arc welding (GTAW). The new theory is a unified treatment of the arc, the anode, and the cathode,

J. Haidar

1998-01-01

139

Numerical Analysis for Weld Formation Using a Free-Burning Helium Arc at Atmospheric Pressure  

Microsoft Academic Search

In order to clarify the formative mechanism of weld penetration in an arc welding process, a numerical model is useful to understand quantitative values of the balances of mass, energy and force in the welding phenomena. In the present paper, the whole region of welding process using a free-burning arc, namely, tungsten cathode, arc plasma and weld pool is treated

Manabu Tanaka; Masao Ushio; John James Lowke

2005-01-01

140

BDNF increases release probability and the size of a rapidly recycling vesicle pool within rat hippocampal excitatory synapses  

Microsoft Academic Search

Exerting its actions pre-, post- and peri-synaptically, brain-derived neurotrophic factor (BDNF) is one of the most potent modulators of hippocampal synaptic function. Here, we examined the effects of BDNF on a rapidly recycling pool (RRP) of vesicles within excitatory synapses. First, we estimated vesicular release in hippocampal cultures by performing FM4-64 imaging in terminals impinging on enhanced green fluorescent protein

William J. Tyler; Xiao-lei Zhang; Kenichi Hartman; Jochen Winterer; Wolfgang Muller; Patric K. Stanton; Lucas Pozzo-Miller

2006-01-01

141

Diets high in resistant starch and arabinoxylan modulate digestion processes and SCFA pool size in the large intestine and faecal microbial composition in pigs.  

PubMed

The effects of a high level of dietary fibre (DF) either as arabinoxylan (AX) or resistant starch (RS) on digestion processes, SCFA concentration and pool size in various intestinal segments and on the microbial composition in the faeces were studied in a model experiment with pigs. A total of thirty female pigs (body weight 63.1 (sem 4.4) kg) were fed a low-DF, high-fat Western-style control diet (WSD), an AX-rich diet (AXD) or a RS-rich diet (RSD) for 3 weeks. Diet significantly affected the digestibility of DM, protein, fat, NSP and NSP components, and the arabinose:xylose ratio, as well as the disappearance of NSP and AX in the large intestine. RS was mainly digested in the caecum. AX was digested at a slower rate than RS. The digesta from AXD-fed pigs passed from the ileum to the distal colon more than twice as fast as those from WSD-fed pigs, with those from RSD-fed pigs being intermediate (P< 0.001). AXD feeding resulted in a higher number of Faecalibacterium prausnitzii, Roseburia intestinalis, Blautia coccoides-Eubacterium rectale, Bifidobacterium spp. and Lactobacillus spp. in the faeces sampled at week 3 of the experimental period (P< 0.05). In the caecum, proximal and mid colon, AXD feeding resulted in a 3- to 5-fold higher pool size of butyrate compared with WSD feeding, with the RSD being intermediate (P <0.001). In conclusion, the RSD and AXD differently affected digestion processes compared with the WSD, and the AXD most efficiently shifted the microbial composition towards butyrogenic species in the faeces and increased the large-intestinal butyrate pool size. PMID:25327182

Nielsen, Tina S; Lærke, Helle N; Theil, Peter K; Sørensen, Jens F; Saarinen, Markku; Forssten, Sofia; Knudsen, Knud E Bach

2014-12-14

142

AMINO ACID SYNTHESIS IN PHOTO-SYNTHESIZING SPINACH CELLS. EFFECTS OF AMMONIA ON POOL SIZES AND RATES OF LABELING FROM {sup 14}CO{sub 2}  

SciTech Connect

Isolated cells from leaves of Spinacea oleracea have been maintained in a state capable of high rates of photosynthetic CO{sub 2} fixation for more than 60 h. The incorporation of {sup 14}CO{sub 2} under saturating CO{sub 2} conditions into carbohydrates, carboxylic acids, and amino acids, and the effect of ammonia on this incorporation have been studied. Total incorporation, specific radioactivity and pool size have been determined as a function of time for most of the protein amino acids and for {gamma}-aminobutyric acid. the measurements of specific activities and of the approaches to {sup 14}C "saturation" of some amino acids indicate the presence and relative sizes of metabolically active and passive pools of these amino acids. Added ammonia decreased carbon fixation into carbohydrates and increased fixation into carboxylic acids and amino acids. Different amino acids were, however, affected in different and highly specific ways. Ammonia caused large stimulatory effects in incorporation of {sup 14}C into glutamine (a factor of 16), No effect or slight decreases were seen in glycine, serine, phenylalanine, and tyrosine labeling, In.the case of glutamate, {sup 14}C-labeling decreased, but specific activity increased. The production of labeled {gamma}-aminobutyric acid was virtually stopped by ammonia. The results indicate that added ammonia stimulates the reactions mediated by pyruvate kinase and phosphoenolpyruvate carboxylase, as seen with other plant systems. The data on the effects of added ammonia on total labeling, pool sizes, and specific activities of several amino acids provides a number of indications about the intracellular sites of principal synthesis from carbon skeletons of these amino acids and the selective nature of effects of increased intracellular ammonia concentration on such synthesis.

Larsen, Peder Olesen; Cornwell, Karen L.; Gee, Sherry L.; Bassham, James A.

1980-10-01

143

Size and dynamics of mucosal and peripheral IL-17A+ T-cell pools in pediatric age, and their disturbance in celiac disease.  

PubMed

Mucosal interleukin (IL)-17A-producing T cells contribute to protective antimicrobial responses and to epithelial barrier integrity; their role in celiac disease (CD) is debated. We analyzed the frequency and developmental dynamics of mucosal (intraepithelial lymphocytes (IEL)) and circulating (peripheral blood (PB)) IL-17A (T17) and/or interferon (IFN)-?-producing (T1, T1/T17) T-cell populations in 86 pediatric controls and 116 age-matched CD patients upon phorbol myristate acetate/ionomycin or CD3/CD28 stimulation. T17 and T1/17 are physiologically present among IEL and PB populations, and their frequency is selectively and significantly reduced in CD IEL. The physiological age-dependent increase of Th17 IEL is also absent in CD, while IFN-?-producing PB-T cells significantly accumulate with patient's age. Finally, the amplitude of IL-17A+ and IFN-?+ T-cell pools are significantly correlated in different individuals; this relationship only applies to CD4+ T cells in controls, while it involves also the CD4- counterpart in CD patients. In conclusion, both size and dynamics of mucosa-associated and circulating IL-17A+ T-cell pools are finely regulated in human pediatric subjects, and severely disturbed in CD. The impaired IL-17A+ IEL-T pool may negatively impact on epithelial barrier efficiency, and contribute to CD mucosa damage; the disturbed dynamics of circulating IL-17A+ and IFN-?+ T-cell pools may be involved in the extraintestinal autoimmune manifestations associated with CD. PMID:22569303

La Scaleia, R; Barba, M; Di Nardo, G; Bonamico, M; Oliva, S; Nenna, R; Valitutti, F; Mennini, M; Barbato, M; Montuori, M; Porzia, A; Petrarca, L; Battella, S; Cucchiara, S; Piccoli, M; Santoni, A; Mainiero, F; Palmieri, G

2012-09-01

144

REST regulates the pool size of the different neural lineages by restricting the generation of neurons and oligodendrocytes from neural stem/progenitor cells  

PubMed Central

REST is a master repressor of neuronal genes; however, whether it has any role during nervous system development remains largely unknown. Here, we analyzed systematically the role of REST in embryonic stem cells and multipotent neural stem/progenitor (NS/P) cells, including neurogenic and gliogenic NS/P cells derived from embryonic stem (ES) cells or developing mouse embryos. We showed that REST-null ES cells remained pluripotent and generated teratomas consisting of the three germ layers. By contrast, multipotent NS/P cells lacking REST displayed significantly reduced self-renewal capacity owing to reduced cell cycle kinetics and precocious neuronal differentiation. Importantly, although early-born neurogenic NS/P cells that lack REST were capable of differentiating to neurons and glia, the neuronal and oligodendrocytic pools were significantly enlarged and the astrocytic pool was shrunken. However, gliogenic NS/P cells lacking REST were able to generate a normal astrocytic pool size, suggesting that the shrinkage of the astrocytic pool generated from neurogenic NS/P cells lacking REST probably occurs by default. Microarray profiling of early-born NS/P cells lacking REST showed upregulation of neuronal as well as oligodendrocytic genes, specifically those involved in myelination. Furthermore, chromatin immunoprecipitation analyses showed that some of the upregulated oligodendrocytic genes contain an RE1 motif and are direct REST targets. Together, our data support a central role for REST during neural development in promoting NS/P cell self-renewal while restricting the generation and maturation of neurons and oligodendrocytes. PMID:22791895

Covey, Matthew V.; Streb, Jeffrey W.; Spektor, Roman; Ballas, Nurit

2012-01-01

145

REST regulates the pool size of the different neural lineages by restricting the generation of neurons and oligodendrocytes from neural stem/progenitor cells.  

PubMed

REST is a master repressor of neuronal genes; however, whether it has any role during nervous system development remains largely unknown. Here, we analyzed systematically the role of REST in embryonic stem cells and multipotent neural stem/progenitor (NS/P) cells, including neurogenic and gliogenic NS/P cells derived from embryonic stem (ES) cells or developing mouse embryos. We showed that REST-null ES cells remained pluripotent and generated teratomas consisting of the three germ layers. By contrast, multipotent NS/P cells lacking REST displayed significantly reduced self-renewal capacity owing to reduced cell cycle kinetics and precocious neuronal differentiation. Importantly, although early-born neurogenic NS/P cells that lack REST were capable of differentiating to neurons and glia, the neuronal and oligodendrocytic pools were significantly enlarged and the astrocytic pool was shrunken. However, gliogenic NS/P cells lacking REST were able to generate a normal astrocytic pool size, suggesting that the shrinkage of the astrocytic pool generated from neurogenic NS/P cells lacking REST probably occurs by default. Microarray profiling of early-born NS/P cells lacking REST showed upregulation of neuronal as well as oligodendrocytic genes, specifically those involved in myelination. Furthermore, chromatin immunoprecipitation analyses showed that some of the upregulated oligodendrocytic genes contain an RE1 motif and are direct REST targets. Together, our data support a central role for REST during neural development in promoting NS/P cell self-renewal while restricting the generation and maturation of neurons and oligodendrocytes. PMID:22791895

Covey, Matthew V; Streb, Jeffrey W; Spektor, Roman; Ballas, Nurit

2012-08-01

146

Investigation of molten pool oscillation during GMAW-P process based on a 3D model  

NASA Astrophysics Data System (ADS)

In order to better reveal the oscillation mechanism of the pulsed gas metal arc welding (GMAW-P) process due to an alternately varied welding current, arc plasma and molten pool oscillation were simulated through a self-consistent three-dimensional model. Based on an experimental analysis of the dynamic variation of the arc plasma and molten pool captured by a high-speed camera, the model was validated by comparison of the measured and predicted results. The calculated results showed that arc pressure was the key factor causing the molten pool to oscillate. The variation in arc size and temperature from peak time to base time resulted in a great difference in the heat input and arc pressure acting on the molten pool. The surface deformation of the molten pool due to the varying degrees of arc pressure induced alternate displacement and backflow in the molten metal. The periodic iteration of deeper and shallower surface deformation, drain and backflow of molten metal caused the molten pool to oscillate at a certain frequency. In this condition, the arc pressure at the peak time is more than six times higher than that at the base time, and the maximum surface depression is 1.4?mm and 0.6?mm, respectively, for peak time and base time.

Wang, L. L.; Lu, F. G.; Cui, H. C.; Tang, X. H.

2014-11-01

147

Application of welding science to welding engineering: A lumped parameter gas metal arc welding dynamic process model  

SciTech Connect

We develop a model of the depth of penetration of the weld pool in gas metal arc welding (GMAW) which demonstrates interaction between the arc, filler wire and weld pool. This model is motivated by the observations of Essers and Walter which suggest a relationship between droplet momentum and penetration depth. A model of gas metal arc welding was augmented to include an improved model of mass transfer and a simple model of accelerating droplets in a plasma jet to obtain the mass and momentum of impinging droplets. The force of the droplets and depth of penetration is correlated by a dimensionless linear relation used to predict weld pool depth for a range of values of arc power and contact tip to workpiece distance. Model accuracy is examined by comparing theoretical predictions and experimental measurements of the pool depth obtained from bead on plate welds of carbon steel in an argon rich shielding gas. Moreover, theoretical predictions of pool depth are compared to the results obtained from the heat conduction model due to Christensen et al. which suggest that in some cases the momentum of impinging droplets is a better indicator of the depth of the weld pool and the presence of a deep, narrow penetration.

Murray, P.E.; Smartt, H.B.; Johnson, J.A. [Lockheed Martin Idaho Technologies, Idaho Falls, ID (United States)

1997-12-31

148

Evaluation of weld porosity in laser beam seam welds: optimizing continuous wave and square wave modulated processes.  

SciTech Connect

Nd:YAG laser joining is a high energy density (HED) process that can produce high-speed, low-heat input welds with a high depth-to-width aspect ratio. This is optimized by formation of a ''keyhole'' in the weld pool resulting from high vapor pressures associated with laser interaction with the metallic substrate. It is generally accepted that pores form in HED welds due to the instability and frequent collapse of the keyhole. In order to maintain an open keyhole, weld pool forces must be balanced such that vapor pressure and weld pool inertia forces are in equilibrium. Travel speed and laser beam power largely control the way these forces are balanced, as well as welding mode (Continuous Wave or Square Wave) and shielding gas type. A study into the phenomenon of weld pool porosity in 304L stainless steel was conducted to better understand and predict how welding parameters impact the weld pool dynamics that lead to pore formation. This work is intended to aid in development and verification of a finite element computer model of weld pool fluid flow dynamics being developed in parallel efforts and assist in weld development activities for the W76 and future RRW programs.

Ellison, Chad M. (Honeywell FM& T, Kansas City, MO); Perricone, Matthew; Faraone, Kevin M. (Honeywell FM& T, Kansas City, MO); Roach, Robert Allen; Norris, Jerome T.

2007-02-01

149

Pooled ANOVA  

Microsoft Academic Search

We introduce Pooled ANOVA, a greedy algorithm to sequentially select the rare important factors from a large set of factors. Problems such as computer simulations and software performance tuning involve a large number of factors, few of which have an important effect on the outcome or performance measure. We pool multiple factors together, and test the pool for significance. If

Michael Last; Gheorghe Luta; Alexandro Orso; Adam A. Porter; Stan Young

2008-01-01

150

Numerical analysis of fume formation mechanism in arc welding  

NASA Astrophysics Data System (ADS)

In order to clarify the fume formation mechanism in arc welding, a quantitative investigation based on the knowledge of interaction among the electrode, arc and weld pool is indispensable. A fume formation model consisting of a heterogeneous condensation model, a homogeneous nucleation model and a coagulation model has been developed and coupled with the GTA or GMA welding model. A series of processes from evaporation of metal vapour to fume formation from the metal vapour was totally investigated by employing this simulation model. The aim of this paper is to visualize the fume formation process and clarify the fume formation mechanism theoretically through a numerical analysis. Furthermore, the reliability of the simulation model was also evaluated through a comparison of the simulation result with the experimental result. As a result, it was found that the size of the secondary particles consisting of small particles with a size of several tens of nanometres reached 300 nm at maximum and the secondary particle was in a U-shaped chain form in helium GTA welding. Furthermore, it was also clarified that most part of the fume was produced in the downstream region of the arc originating from the metal vapour evaporated mainly from the droplet in argon GMA welding. The fume was constituted by particles with a size of several tens of nanometres and had similar characteristics to that of GTA welding. On the other hand, if the metal transfer becomes unstable and the metal vapour near the droplet diffuses directly towards the surroundings of the arc not getting into the plasma flow, the size of the particles reaches several hundred nanometres.

Tashiro, Shinichi; Zeniya, Tasuku; Yamamoto, Kentaro; Tanaka, Manabu; Nakata, Kazuhiro; Murphy, Anthony B.; Yamamoto, Eri; Yamazaki, Kei; Suzuki, Keiichi

2010-11-01

151

Mathematical Model Of Variable-Polarity Plasma Arc Welding  

NASA Technical Reports Server (NTRS)

Mathematical model of variable-polarity plasma arc (VPPA) welding process developed for use in predicting characteristics of welds and thus serves as guide for selection of process parameters. Parameters include welding electric currents in, and durations of, straight and reverse polarities; rates of flow of plasma and shielding gases; and sizes and relative positions of welding electrode, welding orifice, and workpiece.

Hung, R. J.

1996-01-01

152

The keyhole region in VPPA welds  

NASA Technical Reports Server (NTRS)

The morphology and properties of the Variable Polarity Plasma Arc (VPPA) weld composite zone are intimately related to the physical processes associated with the keyhole. The effects of microsegregation and transient weld stress on macrosegregation in the weld tool are examined. In addition the electrical character of straight and reverse polarity portions of the arc cycle were characterized. The results of the former study indicate that alloy 2219 is weldable because large liquid volumes are available during latter stages of weld solidification. Strains in the pool region, acting in conjunction with weld microsegregation can produce macrosegregation great enough to produce radiographic contrast effects in welds. Mechanisms of surface copper enrichment were identified. The latter study has demonstrated that increased heat is delivered to workpieces if the reverse polarity proportion of the weld cycle is increased. Current in the straight polarity portion of the welding cycle increased as the reverse cycle proportion increased. Voltage during reverse polarity segments is large.

Walsh, Daniel W.

1988-01-01

153

Three-dimensional modeling of arc plasma and metal transfer in gas metal arc welding  

Microsoft Academic Search

An integrated comprehensive 3D model has been developed to study the transport phenomena in gas metal arc welding (GMAW). This includes the arc plasma, droplet generation, transfer and impingement onto the weld pool, and weld pool dynamics. The continuum formulation is used for the conservation equations of mass, momentum, and energy in the metal zone. The free surface is tracked

G. Xu; J. Hu; H. L. Tsai

2009-01-01

154

EFFECT OF VARIOUS DRIVING FORCES ON HEAT AND MASS TRANSFER IN ARC WELDING  

Microsoft Academic Search

In this study the heat transfer and fluid flow of the molten pool in stationary gas tungsten arc welding using argon shielding gas were investigated. Transporting phenomena from the welding arc to the base material surface, such as current density, heat flux, arc pressure, and shear stress acting on the weld pool surface, were taken from the simulation results of

W.-H. Kim; H. G. Fan; S.-J. Na

1997-01-01

155

Thermochemical Analysis of Hydrogen Absorption in Welding  

E-print Network

the amount of hy- drogen initially absorbed by the weld pool. Diffusible hydrogen measurements can be converted to initially absorbed hy· drogen values by using Terasaki's theo· retical analysis {Ref. 3

Eagar, Thomas W.

156

Determination of welding fume size with time using E7018 electrodes and A131B base metal  

E-print Network

LITERATURE REVIEW TABLE OF CONTENTS Page vii Health Hazards Respiratory System Particle Deposition Parti cle Agglomeration The . Problem METHODOLOGY Equi pnmnt Test Procedures TEST RESULT Verification Tests Results Experimental Tests Results... constitutents of welding fumes The human respiratory system 3 Particle fate in the lung 4 Approximation of selected parameters influencing deposition of particles in the respiratory tract 5 Fume agglomerate exampl e 6 Particle concentration with time . 7...

Owen, Richard James

1976-01-01

157

Variable-Polarity Plasma Arc Welding Of Alloy 2219  

NASA Technical Reports Server (NTRS)

Report presents results of study of variable-polarity plasma arc (VPPA) welding of aluminum alloy 2219. Consists of two parts: Examination of effects of microsegregation and transient weld stress on macrosegregation in weld pool and, electrical characterization of straight- and reverse-polarity portions of arc cycle.

Walsh, Daniel W.; Nunes, Arthur C., Jr.

1989-01-01

158

Numerical analysis of fume formation mechanism in arc welding  

Microsoft Academic Search

In order to clarify the fume formation mechanism in arc welding, a quantitative investigation based on the knowledge of interaction among the electrode, arc and weld pool is indispensable. A fume formation model consisting of a heterogeneous condensation model, a homogeneous nucleation model and a coagulation model has been developed and coupled with the GTA or GMA welding model. A

Shinichi Tashiro; Tasuku Zeniya; Kentaro Yamamoto; Manabu Tanaka; Kazuhiro Nakata; Anthony B. Murphy; Eri Yamamoto; Kei Yamazaki; Keiichi Suzuki

2010-01-01

159

Neurofuzzy Model-Based Weld Fusion State Estimation  

E-print Network

.found that the slope of the infrared intensity be- comes zero when the liquid- solid interface of the weld poolNeurofuzzy Model-Based Weld Fusion State Estimation Radovan Kovacevic and Yu M. Zhang roper fusion is crucial in Pgenerating a sound weld. Successful control of the fu- sion state requires accurate

Zhang, YuMing

160

Welding I.  

ERIC Educational Resources Information Center

Instructional objectives and performance requirements are outlined in this course guide for Welding I, a performance-based course offered at the Community College of Allegheny County to introduce students to shielded arc welding procedures involving stringer beads, butt welds, and lap welds. After introductory material outlining course objectives,…

Allegheny County Community Coll., Pittsburgh, PA.

161

Welding Curriculum.  

ERIC Educational Resources Information Center

This competency-based curriculum guide is a handbook for the development of welding trade programs. Based on a survey of Alaskan welding employers, it includes all competencies a student should acquire in such a welding program. The handbook stresses the importance of understanding the principles associated with the various elements of welding.…

Alaska State Dept. of Education, Juneau. Div. of Adult and Vocational Education.

162

Welding IV.  

ERIC Educational Resources Information Center

Instructional objectives and performance requirements are outlined in this course guide for Welding IV, a competency-based course in advanced arc welding offered at the Community College of Allegheny County to provide students with proficiency in: (1) single vee groove welding using code specifications established by the American Welding Society…

Allegheny County Community Coll., Pittsburgh, PA.

163

Nicotine enhancement of dopamine release by a calcium-dependent increase in the size of the readily releasable pool of synaptic vesicles.  

PubMed

A major factor underlying compulsive tobacco use is nicotine-induced modulation of dopamine release in the mesolimbic reward pathway (Wise and Rompre, 1989). An established biochemical mechanism for nicotine-enhanced dopamine release is by activating presynaptic nicotinic acetylcholine receptors (nAChRs) (Wonnacott, 1997). Prolonged application of 10(-7) to 10(-5) m nicotine to striatal synaptosomes promoted a sustained efflux of [3H]dopamine. This nicotine effect was mediated by non-alpha7 nAChRs, because it was blocked by 5 mum mecamylamine but was resistant to 100 nm alpha-bungarotoxin (alphaBgTx). Dopamine release was diminished by omitting Na+ or by applying peptide calcium channel blockers, indicating that nAChRs trigger release by depolarizing the nerve terminals. However, because alpha7 receptors rapidly desensitize in the continuous presence of agonists, a repetitive stimulation protocol was used to evaluate the possible significance of desensitization. This protocol produced a transient increase in [3H]dopamine released by depolarization and a significant increase in the response to hypertonic solutions that measure the size of the readily releasable pool (RRP) of synaptic vesicles. The nicotine-induced increase in the size of the readily releasable pool was blocked by alphaBgTx and by the calmodulin antagonist calmidazolium, suggesting that Ca2+ entry through alpha7 nAChRs specifically enhances synaptic vesicle mobilization at dopamine terminals. Thus, nicotine enhances dopamine release by two complementary actions mediated by discrete nAChR subtypes and suggest that the alpha7 nAChR-mediated pathway is tightly and specifically coupled to refilling of the RRP of vesicles in dopamine terminals. PMID:15601939

Turner, Timothy J

2004-12-15

164

Pool Purification  

NASA Technical Reports Server (NTRS)

Caribbean Clear, Inc. used NASA's silver ion technology as a basis for its automatic pool purifier. System offers alternative approach to conventional purification chemicals. Caribbean Clear's principal markets are swimming pool owners who want to eliminate chlorine and bromine. Purifiers in Caribbean Clear System are same silver ions used in Apollo System to kill bacteria, plus copper ions to kill algae. They produce spa or pool water that exceeds EPA Standards for drinking water.

1988-01-01

165

Primary Water Stress Corrosion Cracks in Nickel Alloy Dissimilar Metal Welds: Detection and Sizing Using Established and Emerging Nondestructive Examination Techniques  

SciTech Connect

The U.S. Nuclear Regulatory Commission has established the Program to Assess the Reliability of Emerging Nondestructive Techniques (PARENT) as a follow-on to the international cooperative Program for the Inspection of Nickel Alloy Components (PINC). The goal of PINC was to evaluate the capabilities of various nondestructive evaluation (NDE) techniques to detect and characterize surface-breaking primary water stress corrosion cracks in dissimilar-metal welds (DMW) in bottom-mounted instrumentation (BMI) penetrations and small-bore (?400-mm diameter) piping components. A series of international blind round-robin tests were conducted by commercial and university inspection teams. Results from these tests showed that a combination of conventional and phased-array ultrasound techniques provided the highest performance for flaw detection and depth sizing in dissimilar metal piping welds. The effective detection of flaws in BMIs by eddy current and ultrasound shows that it may be possible to reliably inspect these components in the field. The goal of PARENT is to continue the work begun in PINC and apply the lessons learned to a series of open and blind international round-robin tests that will be conducted on a new set of piping components including large-bore (?900-mm diameter) DMWs, small-bore DMWs, and BMIs. Open round-robin testing will engage universities and industry worldwide to investigate the reliability of emerging NDE techniques to detect and accurately size flaws having a wide range of lengths, depths, orientations, and locations. Blind round-robin testing will invite testing organizations worldwide, whose inspectors and procedures are certified by the standards for the nuclear industry in their respective countries, to investigate the ability of established NDE techniques to detect and size flaws whose characteristics range from easy to very difficult to detect and size. This paper presents highlights of PINC and reports on the plans and progress for PARENT round-robin tests.

Braatz, Brett G.; Cumblidge, Stephen E.; Doctor, Steven R.; Prokofiev, Iouri

2012-12-31

166

Friction Stir Welding Development  

NASA Technical Reports Server (NTRS)

The research of this summer was a continuation of work started during the previous summer faculty fellowship period. The Friction Stir Welding process (FSW) patented by The Welding Institute (TWI), in Great Britain, has become a popular topic at the Marshall Space Flight Center over the past year. Last year it was considered a novel approach to welding but few people took it very seriously as a near term solution. However, due to continued problems with cracks in the new aluminum-lithium space shuttle external tank (ET), the friction stir process is being mobilized at full speed in an effort to mature this process for the potential manufacture of flight hardware. It is now the goal of NASA and Lockheed-Martin Corporation (LMC) to demonstrate a full-scale friction stir welding system capable of welding ET size barrel sections. The objectives this summer were: (1) Implementation and validation of the rotating dynamometer on the MSFC FSW system; (2) Collection of data for FSW process modeling efforts; (3) Specification development for FSW implementation on the vertical weld tool; (4) Controls and user interface development for the adjustable pin tool; and (5) Development of an instrumentation system for the planishing process. The projects started this summer will lead to a full scale friction stir welding system that is expected to produce a friction stir welded shuttle external tank type barrel section. The success of this could lead to the implementation of the friction stir process for manufacturing future shuttle external tanks.

Romine, Peter L.

1998-01-01

167

Effects of electrode bevel angle on argon arc properties and weld shape  

Microsoft Academic Search

A numerical modeling of coupled welding arc with weld pool is established using FLUENT software for moving shielded GTA welding to systematically investigate the effects of electrode bevel angle on the argon arc properties as well as the weld shape on SUS304 stainless steel. The calculated results show that the argon arc is constricted and the peak values of heat

W C Dong; S P Lu; D Z Li; Y Y Li

2012-01-01

168

Thermal and Fluid Flow Characteristics and their Relationships with Porosity in Laser Welding of AA5083  

NASA Astrophysics Data System (ADS)

A computational fluid dynamics (CFD) model was developed to numerically analyse the temperature and fluid flow during laser butt welding, and a heat source model was proposed, which, with adjustment, was suitable for both partial and full penetration welds over a wide range of conditions. The models were then used to study the laser welding of a 4 mm thickness aluminum alloy (AA5083), and the results predicted were analysed to better understand the formation of porosity in aluminium laser welds. The flow patterns predicted in the melt pool are essentially the same for various welding parameters: vortices can be found close to the surfaces of the weld pool (top surface only for partial penetration; both top and bottom surfaces for full penetration). The dimensions of the weld pool are predicted to increase with increasing laser power and decreasing welding speed, and the maximum velocity to increase with increasing laser power and welding speed. In partial penetration cases, there are no simple relations between porosity levels and laser power and welding speed. A sharp decrease in porosity content, when changing from partial to full penetration, was thought to be a result of an extra driving force from the outwards fluid flow at the weld pool bottom for the pores to escape out of the melt pool. In full penetration cases, the lower porosity content when using higher laser power and/or lower welding speed was attributed to the longer time for pores to escape before the weld pool solidifies.

Chang, B.; Allen, C.; Blackburn, J.; Hilton, P.

169

Palmitate increases L-type Ca2+ currents and the size of the readily releasable granule pool in mouse pancreatic ?-cells  

PubMed Central

We have investigated the in vitro effects of the saturated free fatty acid palmitate on mouse pancreatic ?-cells by a combination of electrophysiological recordings, intracellular Ca2+ ([Ca2+]i) microfluorimetry and insulin release measurements. Addition of palmitate (1 mm, bound to fatty acid-free albumin) to intact islets exposed to 15 mm glucose increased the [Ca2+]i by ?30% and insulin secretion 2-fold. Palmitate remained capable of increasing [Ca2+]i and insulin release in the presence of tolbutamide and in islets depolarized by high K+ in combination with diazoxide, indicating that the stimulation occurs independently of closure of ATP-regulated K+ channels (KATP channels). Palmitate (0.5 mm) augmented exocytosis (measured as an increase in cell capacitance) in single ?-cells and increased the size of the readily releasable pool (RRP) of granules 2-fold. Whole-cell peak Ca2+ currents rose by ?25% following addition of 0.5 mm palmitate, an effect that was abolished in the presence of 10 ?m isradipine indicating that the free fatty acid specifically acts on L-type Ca2+ channels. The actions of palmitate on exocytosis and Ca2+ currents were not mimicked by intracellular application of palmitoyl-CoA. We conclude that palmitate increases insulin secretion by a KATP channel-independent mechanism exerted at the level of exocytosis and that involves both augmentation of L-type Ca2+ currents and an increased size of the RRP. PMID:15090611

Olofsson, Charlotta S; Salehi, Albert; Holm, Cecilia; Rorsman, Patrik

2004-01-01

170

Biosynthesis of bile acids in cerebrotendinous xanthomatosis. Relationship of bile acid pool sizes and synthesis rates to hydroxylations at C-12, C-25, and C-26.  

PubMed Central

To examine the defect in side-chain oxidation during the formation of bile acids in cerebrotendinous xanthomatosis, we measured in vitro hepatic microsomal hydroxylations at C-12 and C-25 and mitochondrial hydroxylation at C-26 and related them to the pool size and synthesis rates of cholic acid and chenodeoxycholic acid as determined by the isotope dilution technique. Hepatic microsomes and mitochondria were prepared from seven subjects with cerebrotendinous xanthomatosis and five controls. Primary bile acid synthesis was markedly reduced in cerebrotendinous xanthomatosis as follows: cholic acid, 133 +/- 30 vs. 260 +/- 60 mg/d in controls; and chenodeoxycholic acid, 22 +/- 10 vs. 150 +/- 30 mg/d in controls. As postulated for chenodeoxycholic acid synthesis, mitochondrial 26-hydroxylation of 5 beta-cholestane-3 alpha, 7 alpha-diol was present in all specimens and was 30-fold more active than the corresponding microsomal 25-hydroxylation. However, mean mitochondrial 26-hydroxylation of 5 beta-cholestane-3 alpha,7 alpha-diol was less active in cerebrotendinous xanthomatosis than in controls: 59 +/- 17 compared with 126 +/- 21 pmol/mg protein per min. As for cholic acid synthesis, microsomal 25-hydroxylation of 5 beta-cholestane-3 alpha,7 alpha,12 alpha-triol was substantially higher in cerebrotendinous xanthomatosis and control preparations (620 +/- 103 and 515 +/- 64 pmol/mg protein per min, respectively) than the corresponding control mitochondrial 26-hydroxylation of the same substrate (165 +/- 25 pmol/mg protein per min). Moreover in cerebrotendinous xanthomatosis, mitochondrial 5 beta-cholestane-3 alpha,7 alpha,12 alpha-triol-26-hydroxylase activity was one-seventh as great as in controls. Hepatic microsomal 12 alpha-hydroxylation, which may be rate-controlling for the cholic acid pathway, was three times more active in cerebrotendinous xanthomatosis than in controls: 1,600 vs. 500 pmol/mg protein per min. These results demonstrate severely depressed primary bile acid synthesis in cerebrotendinous xanthomatosis with a reduction in chenodeoxycholic acid formation and pool size disproportionately greater than that for cholic acid. The deficiency of chenodeoxycholic acid can be accounted for by hyperactive microsomal 12 alpha-hydroxylation that diverts precursors into the cholic acid pathway combined with decreased side-chain oxidation (mitochondrial 26-hydroxylation). However, side-chain oxidation in cholic acid biosynthesis may be initiated via microsomal 25-hydroxylation of 5beta-cholestane-3alpha,7alpha,12alpha-triol was substantially lower in control and cerebrotendinous xanthomatosis liver. Thus, separate mechanisms may exist for the cleavage of the cholesterol side chain in cholic acid and chenodeoxycholic acid biosynthesis. PMID:4031069

Salen, G; Shefer, S; Tint, G S; Nicolau, G; Dayal, B; Batta, A K

1985-01-01

171

Marangoni convection and weld shape variations in He–CO 2 shielded gas tungsten arc welding on SUS304 stainless steel  

Microsoft Academic Search

Bead-on-plate GTA welding (gas tungsten arc welding) on a SUS304 substrate is carried out to investigate the effect of carbon\\u000a dioxide gas in the helium base shielding on the oxygen content in the weld pool and the weld shape variations. Experimental\\u000a results show that small addition of carbon dioxide to the shielding gas can precisely adjust the weld metal oxygen

Shanping Lu; Hidetoshi Fujii; Kiyoshi Nogi

2008-01-01

172

Examination of the physical processes associated with the keyhole region of variable polarity plasma arc welds in aluminum alloy 2219  

NASA Technical Reports Server (NTRS)

The morphology and properties of the Variable Polarity Plasma Arc (VPPA) weld composite zone are intimately related to the physical processes associated with the keyhole. This study examined the effects of oxide, halide, and sulfate additions to the weld plate on the keyhole and the weld pool. Changes in both the arc plasma character and the bead morphology were correlated to the chemical environment of the weld. Pool behavior was observed by adding flow markers to actual VPPA welds. A low temperature analog to the welding process was developed. The results of the study indicate that oxygen, even at low partial pressures, can disrupt the stable keyhole and weld pool. The results also indicate that the Marangoni surface tension driven flows dominate the weld pool over the range of welding currents studied.

Walsh, Daniel W.

1987-01-01

173

WELDING RESEARCH -s87WELDING JOURNAL  

E-print Network

range. For the purpose of comparison and illustration, this paper uses several characterization, particularly with regard to stud- ies involving energy dispersive spec- troscopy with scanning electron micro in size from 0.005 to 20 µm, although less than 10­30% (depending on the welding process) of the fume mass

Eagar, Thomas W.

174

Effects of shielding gas compositions on arc plasma and metal transfer in gas metal arc welding  

SciTech Connect

This article presents the effects of shielding gas compositions on the transient transport phenomena, including the distributions of temperature, flow velocity, current density, and electromagnetic force in the arc and the metal, and arc pressure in gas metal arc welding of mild steel at a constant current input. The shielding gas considered includes pure argon, 75% Ar, 50% Ar, and 25% Ar with the balance of helium. It is found that the shielding gas composition has significant influences on the arc characteristics; droplet formation, detachment, transfer, and impingement onto the workpiece; and weld pool dynamics and weld bead profile. As helium increases in the shielding gas, the droplet size increases but the droplet detachment frequency decreases. For helium-rich gases, the current converges at the workpiece with a 'ring' shape which produces non-Gaussian-like distributions of arc pressure and temperature along the workpiece surface. Detailed explanations to the physics of the very complex but interesting transport phenomena are given.

Rao, Z. H. [School of Energy Science and Engineering, Central South University, Changsha 410083 (China); Department of Mechanical and Aerospace Engineering, Missouri University of Science and Technology, Rolla, Missouri 65409 (United States); Liao, S. M. [School of Energy Science and Engineering, Central South University, Changsha 410083 (China); Tsai, H. L. [Department of Mechanical and Aerospace Engineering, Missouri University of Science and Technology, Rolla, Missouri 65409 (United States)

2010-02-15

175

Effects of shielding gas compositions on arc plasma and metal transfer in gas metal arc welding  

NASA Astrophysics Data System (ADS)

This article presents the effects of shielding gas compositions on the transient transport phenomena, including the distributions of temperature, flow velocity, current density, and electromagnetic force in the arc and the metal, and arc pressure in gas metal arc welding of mild steel at a constant current input. The shielding gas considered includes pure argon, 75% Ar, 50% Ar, and 25% Ar with the balance of helium. It is found that the shielding gas composition has significant influences on the arc characteristics; droplet formation, detachment, transfer, and impingement onto the workpiece; and weld pool dynamics and weld bead profile. As helium increases in the shielding gas, the droplet size increases but the droplet detachment frequency decreases. For helium-rich gases, the current converges at the workpiece with a "ring" shape which produces non-Gaussian-like distributions of arc pressure and temperature along the workpiece surface. Detailed explanations to the physics of the very complex but interesting transport phenomena are given.

Rao, Z. H.; Liao, S. M.; Tsai, H. L.

2010-02-01

176

Welding Technician  

ERIC Educational Resources Information Center

About 95% of all manufactured goods in this country are welded or joined in some way. These welded products range in nature from bicycle handlebars and skyscrapers to bridges and race cars. The author discusses what students need to know about careers for welding technicians--wages, responsibilities, skills needed, career advancement…

Smith, Ken

2009-01-01

177

Virtual welding equipment for simulation of GMAW processes with integration of power source regulation  

NASA Astrophysics Data System (ADS)

A two dimensional transient numerical analysis and computational module for simulation of electrical and thermal characteristics during electrode melting and metal transfer involved in Gas-Metal-Arc-Welding (GMAW) processes is presented. Solution of non-linear transient heat transfer equation is carried out using a control volume finite difference technique. The computational module also includes controlling and regulation algorithms of industrial welding power sources. The simulation results are the current and voltage waveforms, mean voltage drops at different parts of circuit, total electric power, cathode, anode and arc powers and arc length. We describe application of the model for normal process (constant voltage) and for pulsed processes with U/I and I/I-modulation modes. The comparisons with experimental waveforms of current and voltage show that the model predicts current, voltage and electric power with a high accuracy. The model is used in simulation package SimWeld for calculation of heat flux into the work-piece and the weld seam formation. From the calculated heat flux and weld pool sizes, an equivalent volumetric heat source according to Goldak model, can be generated. The method was implemented and investigated with the simulation software SimWeld developed by the ISF at RWTH Aachen University.

Reisgen, Uwe; Schleser, Markus; Mokrov, Oleg; Zabirov, Alexander

2011-06-01

178

The Effects of Droplet Size and Injection Orientation on Water Mist Suppression of Low and High Boiling Point Liquid Pool Fires  

Microsoft Academic Search

This paper presents the results of an experimental parametric study of water mist suppression of large-scale liquid pool fires. The experiments were conducted with 50cm diameter pan heptane and JP8 pool fires. Mist was injected into the fire from the base at 90 and 45 and from the top at 90. The results show that base injection of droplets enhanced

CHUKA C. NDUBIZU; RAMAGOPAL ANANTH; PATRICIA A. TATEM

2000-01-01

179

GLD-4-Mediated Translational Activation Regulates the Size of the Proliferative Germ Cell Pool in the Adult C. elegans Germ Line  

PubMed Central

To avoid organ dysfunction as a consequence of tissue diminution or tumorous growth, a tight balance between cell proliferation and differentiation is maintained in metazoans. However, cell-intrinsic gene expression mechanisms controlling adult tissue homeostasis remain poorly understood. By focusing on the adult Caenorhabditis elegans reproductive tissue, we show that translational activation of mRNAs is a fundamental mechanism to maintain tissue homeostasis. Our genetic experiments identified the Trf4/5-type cytoplasmic poly(A) polymerase (cytoPAP) GLD-4 and its enzymatic activator GLS-1 to perform a dual role in regulating the size of the proliferative zone. Consistent with a ubiquitous expression of GLD-4 cytoPAP in proliferative germ cells, its genetic activity is required to maintain a robust proliferative adult germ cell pool, presumably by regulating many mRNA targets encoding proliferation-promoting factors. Based on translational reporters and endogenous protein expression analyses, we found that gld-4 activity promotes GLP-1/Notch receptor expression, an essential factor of continued germ cell proliferation. RNA-protein interaction assays documented also a physical association of the GLD-4/GLS-1 cytoPAP complex with glp-1 mRNA, and ribosomal fractionation studies established that GLD-4 cytoPAP activity facilitates translational efficiency of glp-1 mRNA. Moreover, we found that in proliferative cells the differentiation-promoting factor, GLD-2 cytoPAP, is translationally repressed by the stem cell factor and PUF-type RNA-binding protein, FBF. This suggests that cytoPAP-mediated translational activation of proliferation-promoting factors, paired with PUF-mediated translational repression of differentiation factors, forms a translational control circuit that expands the proliferative germ cell pool. Our additional genetic experiments uncovered that the GLD-4/GLS-1 cytoPAP complex promotes also differentiation, forming a redundant translational circuit with GLD-2 cytoPAP and the translational repressor GLD-1 to restrict proliferation. Together with previous findings, our combined data reveals two interconnected translational activation/repression circuitries of broadly conserved RNA regulators that maintain the balance between adult germ cell proliferation and differentiation. PMID:25254367

Millonigg, Sophia; Eckmann, Christian R.

2014-01-01

180

GLD-4-mediated translational activation regulates the size of the proliferative germ cell pool in the adult C. elegans germ line.  

PubMed

To avoid organ dysfunction as a consequence of tissue diminution or tumorous growth, a tight balance between cell proliferation and differentiation is maintained in metazoans. However, cell-intrinsic gene expression mechanisms controlling adult tissue homeostasis remain poorly understood. By focusing on the adult Caenorhabditis elegans reproductive tissue, we show that translational activation of mRNAs is a fundamental mechanism to maintain tissue homeostasis. Our genetic experiments identified the Trf4/5-type cytoplasmic poly(A) polymerase (cytoPAP) GLD-4 and its enzymatic activator GLS-1 to perform a dual role in regulating the size of the proliferative zone. Consistent with a ubiquitous expression of GLD-4 cytoPAP in proliferative germ cells, its genetic activity is required to maintain a robust proliferative adult germ cell pool, presumably by regulating many mRNA targets encoding proliferation-promoting factors. Based on translational reporters and endogenous protein expression analyses, we found that gld-4 activity promotes GLP-1/Notch receptor expression, an essential factor of continued germ cell proliferation. RNA-protein interaction assays documented also a physical association of the GLD-4/GLS-1 cytoPAP complex with glp-1 mRNA, and ribosomal fractionation studies established that GLD-4 cytoPAP activity facilitates translational efficiency of glp-1 mRNA. Moreover, we found that in proliferative cells the differentiation-promoting factor, GLD-2 cytoPAP, is translationally repressed by the stem cell factor and PUF-type RNA-binding protein, FBF. This suggests that cytoPAP-mediated translational activation of proliferation-promoting factors, paired with PUF-mediated translational repression of differentiation factors, forms a translational control circuit that expands the proliferative germ cell pool. Our additional genetic experiments uncovered that the GLD-4/GLS-1 cytoPAP complex promotes also differentiation, forming a redundant translational circuit with GLD-2 cytoPAP and the translational repressor GLD-1 to restrict proliferation. Together with previous findings, our combined data reveals two interconnected translational activation/repression circuitries of broadly conserved RNA regulators that maintain the balance between adult germ cell proliferation and differentiation. PMID:25254367

Millonigg, Sophia; Minasaki, Ryuji; Nousch, Marco; Eckmann, Christian R

2014-09-01

181

Deconvoluting the Friction Stir Weld Process for Optimizing Welds  

NASA Technical Reports Server (NTRS)

In the friction stir welding process, the rotating surfaces of the pin and shoulder contact the weld metal and force a rotational flow within the weld metal. Heat, generated by the metal deformation as well as frictional slippage with the contact surface, softens the metal and makes it easier to deform. As in any thermo-mechanical processing of metal, the flow conditions are critical to the quality of the weld. For example, extrusion of metal from under the shoulder of an excessively hot weld may relax local pressure and result in wormhole defects. The trace of the weld joint in the wake of the weld may vary geometrically depending upon the flow streamlines around the tool with some geometry more vulnerable to loss of strength from joint contamination than others. The material flow path around the tool cannot be seen in real time during the weld. By using analytical "tools" based upon the principles of mathematics and physics, a weld model can be created to compute features that can be observed. By comparing the computed observations with actual data, the weld model can be validated or adjusted to get better agreement. Inputs to the model to predict weld structures and properties include: hot working properties ofthe metal, pin tool geometry, travel rate, rotation and plunge force. Since metals record their prior hot working history, the hot working conditions imparted during FSW can be quantified by interpreting the final microstructure. Variations in texture and grain size result from variations in the strain accommodated at a given strain rate and temperature. Microstructural data from a variety of FSWs has been correlated with prior marker studies to contribute to our understanding of the FSW process. Once this stage is reached, the weld modeling process can save significant development costs by reducing costly trial-and-error approaches to obtaining quality welds.

Schneider, Judy; Nunes, Arthur C.

2008-01-01

182

Friction welding.  

NASA Technical Reports Server (NTRS)

Results of an exploratory study of the structure and properties of friction welds in Udimet 700 (U-700) and TD-nickel (TD-Ni) bar materials, as well as dissimilar U-700/TD-Ni friction welds. Butt welds were prepared by friction welding 12.7-mm-diam U-700 bars and TD-Ni bars. Specimens for elevated temperature tensile and stress rupture testing were machined after a postweld heat treatment. Friction welding of U-700 shows great potential because the welds were found to be as strong as the parent metal in stress rupture and tensile tests at 760 and 980 C. In addition, the weld line was not detectable by metallographic examination after postheating. Friction welds in TD-Ni or between U-700 and TD-Ni were extremely weak at elevated temperatures. The TD-Ni friction welds could support only 9% as much stress as the base metal for 10-hour stress rupture life at 1090 C. The U-700/TD-Ni weld could sustain only 15% as much stress as the TD-Ni parent metal for a 10-hour stress rupture life at 930 C. Thus friction welding is not a suitable joining method for obtaining high-strength TD-Ni or U-700/TD-Ni weldments.

Moore, T. J.

1972-01-01

183

A CO2 Laser Weld Shape-Predicting Neural Network  

Microsoft Academic Search

We describe two artificial neural networks (ANN) which predict CO2<\\/sub> partial penetration laser welds on grade 304 stainless steel. Given the laser irradiance and travel speed, one ANN (direct) predicts the resulting weld's depth, width, overall shape, energy transfer efficiency, melting efficiency and porosity likelihood in the weld fusion zone. Given the weld size and shape, the second ANN (inverse)

P. W. Fuerschbach; G. A. Knorovsky

1998-01-01

184

Measurements of fillet weld by 3D laser scanning system  

Microsoft Academic Search

The external geometry of a fillet weld affects not only the quality but also the safety of a structure. Two parameters that influence the geometric quality of a fillet weld are the weld size and the weld surface profile. A 3D laser scanning measurement system integrating the techniques of reverse engineering is adopted in this study to provide a more

Chia-Lung Chang; Yen-Hung Chen

2005-01-01

185

Effects of Friction Stir Processing on the Microstructure and Mechanical Properties of Fusion Welded 304L Stainless Steel  

Microsoft Academic Search

A variation of FSW, friction stir processing (FSP), has been used to modify selected regions of materials to enhance specific properties while eliminating fusion welding defects such as porosity, cracking, and the cast microstructure. The combination of fusion welding defects and high tensile residual stresses caused by the solidification of the molten weld pool adversely affect the post weld service

C. J. Sterling; T. W. Nelson; C. D. Sorensen; M. Posada

186

Effect of rapid solidification on stainless steel weld metal microstructures and its implications on the Schaeffler diagram  

Microsoft Academic Search

An investigation was carried out to determine the effect of rapid solidification on the weld metal microstructure of austenitic stainless steels and its implication on the ferrite constitution diagram. A wide variety of stainless steels were laser welded at different welding speeds and laser power levels. Results indicate that both weld pool cooling rate and the postsolidification solid state cooling

S. A. David; J. M. Vitek; R. W. Reed; T. L. Hebble

1987-01-01

187

Effect of rapid solidification on stainless steel weld metal microstructures and its implications on the Schaeffler diagram  

Microsoft Academic Search

An investigation was carried out to determine the effect of rapid solidification on the weld metal microstructure of austenitic stainless steels and its implication on the ferrite constitution diagram. A wide variety of stainless steels were laser beam welded at different welding speeds and laser power levels. The results indicate that both weld pool cooling rate and the postsolidification solid-state

S. A. David; J. M. Vitek; T. L. Hebble

1987-01-01

188

Tailoring weld geometry during keyhole mode laser welding using a genetic algorithm and a heat transfer model  

NASA Astrophysics Data System (ADS)

Tailoring of weld attributes based on scientific principles remains an important goal in welding research. The current generation of unidirectional laser keyhole models cannot determine sets of welding variables that can lead to a particular weld attribute such as specific weld geometry. Here we show how a computational heat transfer model of keyhole mode laser welding can be restructured for systematic tailoring of weld attributes based on scientific principles. Furthermore, the model presented here can calculate multiple sets of laser welding variables, i.e. laser power, welding speed and beam defocus, with each set leading to the same weld pool geometry. Many sets of welding variables were obtained via a global search using a real number-based genetic algorithm, which was combined with a numerical heat transfer model of keyhole laser welding. The reliability of the numerical heat transfer calculations was significantly improved by optimizing values of the uncertain input parameters from a limited volume of experimental data. The computational procedure was applied to the keyhole mode laser welding of the 5182 Al-Mg alloy to calculate various sets of welding variables to achieve a specified weld geometry. The calculated welding parameter sets showed wide variations of the values of welding parameters, but each set resulted in a similar fusion zone geometry. The effectiveness of the computational procedure was examined by comparing the computed weld geometry for each set of welding parameters with the corresponding experimental geometry. The results provide hope that systematic tailoring of weld attributes via multiple pathways, each representing alternative welding parameter sets, is attainable based on scientific principles.

Rai, R.; Roy, T. Deb

2006-03-01

189

Infrared sensing techniques for adaptive robotic welding  

SciTech Connect

The objective of this research is to investigate the feasibility of using infrared sensors to monitor the welding process. Data were gathered using an infrared camera which was trained on the molten metal pool during the welding operation. Several types of process perturbations which result in weld defects were then intentionally induced and the resulting thermal images monitored. Gas tungsten arc using ac and dc currents and gas metal arc welding processes were investigated using steel, aluminum and stainless steel plate materials. The thermal images obtained in the three materials and different welding processes revealed nearly identical patterns for the same induced process perturbation. Based upon these results, infrared thermography is a method which may be very applicable to automation of the welding process.

Lin, T.T.; Groom, K.; Madsen, N.H.; Chin, B.A.

1986-01-01

190

Huntingtin-associated protein 1 regulates exocytosis, vesicle docking, readily releasable pool size and fusion pore stability in mouse chromaffin cells  

PubMed Central

Huntingtin-associated protein 1 (HAP1) was initially established as a neuronal binding partner of huntingtin, mutations in which underlie Huntington's disease. Subcellular localization and protein interaction data indicate that HAP1 may be important in vesicle trafficking and cell signalling. In this study, we establish that HAP1 is important in several steps of exocytosis in adrenal chromaffin cells. Using carbon-fibre amperometry, we measured single vesicle exocytosis in chromaffin cells obtained from HAP1?/? and HAP1+/+ littermate mice. Numbers of Ca2+-dependent and Ca2+-independent full fusion events in HAP1?/? cells are significantly decreased compared with those in HAP1+/+ cells. We observed no change in the frequency of ‘kiss-and-run’ fusion events or in Ca2+ entry. Whereas release per full fusion event is unchanged in HAP1?/? cells, early fusion pore duration is prolonged, as indicated by the increased duration of pre-spike foot signals. Kiss-and-run events have a shorter duration, indicating opposing roles for HAP1 in the stabilization of the fusion pore during full fusion and transient fusion, respectively. We use electron microscopy to demonstrate a reduction in the number of vesicles docked at the plasma membrane of HAP1?/? cells, where membrane capacitance measurements reveal the readily releasable pool of vesicles to be reduced in size. Our study therefore illustrates that HAP1 regulates exocytosis by influencing the morphological docking of vesicles at the plasma membrane, the ability of vesicles to be released rapidly upon stimulation, and the early stages of fusion pore formation. PMID:24366265

Mackenzie, Kimberly D; Duffield, Michael D; Peiris, Heshan; Phillips, Lucy; Zanin, Mark P; Teo, Ee Hiok; Zhou, Xin-Fu; Keating, Damien J

2014-01-01

191

Huntingtin-associated protein 1 regulates exocytosis, vesicle docking, readily releasable pool size and fusion pore stability in mouse chromaffin cells.  

PubMed

Huntingtin-associated protein 1 (HAP1) was initially established as a neuronal binding partner of huntingtin, mutations in which underlie Huntington's disease. Subcellular localization and protein interaction data indicate that HAP1 may be important in vesicle trafficking and cell signalling. In this study, we establish that HAP1 is important in several steps of exocytosis in adrenal chromaffin cells. Using carbon-fibre amperometry, we measured single vesicle exocytosis in chromaffin cells obtained from HAP1(-/-) and HAP1(+/+) littermate mice. Numbers of Ca(2+)-dependent and Ca(2+)-independent full fusion events in HAP1(-/-) cells are significantly decreased compared with those in HAP1(+/+) cells. We observed no change in the frequency of 'kiss-and-run' fusion events or in Ca(2+) entry. Whereas release per full fusion event is unchanged in HAP1(-/-) cells, early fusion pore duration is prolonged, as indicated by the increased duration of pre-spike foot signals. Kiss-and-run events have a shorter duration, indicating opposing roles for HAP1 in the stabilization of the fusion pore during full fusion and transient fusion, respectively. We use electron microscopy to demonstrate a reduction in the number of vesicles docked at the plasma membrane of HAP1(-/-) cells, where membrane capacitance measurements reveal the readily releasable pool of vesicles to be reduced in size. Our study therefore illustrates that HAP1 regulates exocytosis by influencing the morphological docking of vesicles at the plasma membrane, the ability of vesicles to be released rapidly upon stimulation, and the early stages of fusion pore formation. PMID:24366265

Mackenzie, Kimberly D; Duffield, Michael D; Peiris, Heshan; Phillips, Lucy; Zanin, Mark P; Teo, Ee Hiok; Zhou, Xin-Fu; Keating, Damien J

2014-04-01

192

Cave Pool  

USGS Multimedia Gallery

A pool in the Caverns of Sonora. This cave, like many others, was formed by water combining with carbon dioxide to create a weak carbonic acid. This acid then dissolved the limestone to carve out chambers. The dissolved calcium from the limestone then combined with the carbon dioxide to create calci...

193

Influence of thermal deformation and shielding gas on topography of weld in deep penetration laser welding  

SciTech Connect

The thermal deformation in penetration welding with a laser has been investigated as a factor which results in the elevation on the surface of the weld. Qualitative analysis of the course of thermal deformation during which elevation is made has been presented in detail. A series of comparison laser welding experiments was done with a 5kW CO{sub 2} laser. The experimental results showed that there were always a slight warp and a lateral shrinking of the workpiece together with the elevation on the surface, which had been predicted by the analysis. The influence exerted by shielding gas on the topography of the weld has also been discussed. The shielding gas is supposed to affect the pressure above the surface of the welding pool. The shape of the surface of the welding pool is determined by the difference between pressures on both sides of the surface in term of Laplace equation. When the distribution of the gas pressure was homogeneous within the range of the welding pool, a fairly smooth topography was experimentally obtained. Otherwise, obvious ripples were observed along the weld.

Qiang Hongliang; Cheng Zhaogu; Luo Jiangtao; Chen Gang; Wang Runwen [Academia Sinica, Shanghai (China). Shanghai Inst. of Optics and Fine Mechanics

1996-12-31

194

Analysis of the free-burning high-intensity argon arc for gas tungsten arc welding and gas metal arc welding  

Microsoft Academic Search

P CTAS - Air Liquide Welding, Saint Ouen l'Aumone, 95315 Cergy-Pontoise cedex - France For arc welding process analysis, detailed information on both the distribution of energy flow and excess pressure at the weld pool surface is needed. Numerical arc modelling can deliver such information. Through simultaneous solutions of the set of conservation equations for mass, momentum, energy and current,

A. Boutaghane; F. Valensi; S. Pellerin; K. Bouhadef; F. Briand

195

46 CFR 52.05-30 - Minimum requirements for attachment welds (modifies PW-16).  

Code of Federal Regulations, 2010 CFR

... Minimum requirements for attachment welds (modifies PW-16). 52.05-30... Minimum requirements for attachment welds (modifies PW-16). (a) The location and minimum size of attachment welds for nozzles and other...

2010-10-01

196

Structure and mechanical properties of 1570C alloy welds produced by friction stir welding  

NASA Astrophysics Data System (ADS)

The effect of the conditions of friction stir welding (FSW) of 1570C aluminum alloy sheets on the structure and mechanical properties of the welded joints is studied. A recrystallized fine-grained structure with a grain size changing with the rate of welding tool rotation forms in a weld during FSW. As compared to the base metal, the yield strength of the weld metal decreases by 9-22% depending on the rate of welding tool rotation, and the ultimate tensile strength is almost independent of the FSW conditions and accounts for ˜90% of the ultimate tensile strength of the base metal. The plasticity of the weld metal is >13% for all rates of welding tool rotation. The microstructure and mechanical properties of the weld zone are discussed.

Malopheyev, S. S.; Kulitskiy, V. A.

2012-09-01

197

Soldadura (Welding). Spanish Translations for Welding.  

ERIC Educational Resources Information Center

Thirty transparency masters with Spanish subtitles for key words are provided for a welding/general mechanical repair course. The transparency masters are on such topics as oxyacetylene welding; oxyacetylene welding equipment; welding safety; different types of welds; braze welding; cutting torches; cutting with a torch; protective equipment; arc…

Hohhertz, Durwin

198

Ultrasound in arc welding: a review.  

PubMed

During the last decade, the introduction of ultrasound techniques in arc welding with the intention of improving the operational performance and technical characteristics of the welding processes have been studied intensively. In this work is presented a broad review of the literature surrounding the utilization of this technique. Firstly, we discuss the use of traditional mechanical transducers to generate ultrasound in arc welding. Furthermore, we describe the various methods and their application in arc-welding processes. After, is presented a recent method of introducing ultrasonic energy in arc welding, which forms a potential alternative to the use of traditional mechanical type transducers. This method was originally developed in the late 1990s and is called arc with ultrasonic excitation of current. Here, the arc acts not only as a thermal source but also as an emission mechanism for ultrasound, acting directly on the weld pool. We presented and discussed various innovative concepts based on this method, which allows the introduction of ultrasonic energy in the arc welding without the need of any auxiliary device of welding. In addition, we also presented the variations of this method reported in the literature. Finally, we have described the respective effects attributed to the use of this method in the welding of different materials using various welding processes. PMID:25455190

da Cunha, Tiago Vieira; Bohórquez, Carlos Enrique Niño

2015-02-01

199

Plasma arc welding weld imaging  

NASA Technical Reports Server (NTRS)

A welding torch for plasma arc welding apparatus has a transparent shield cup disposed about the constricting nozzle, the cup including a small outwardly extending polished lip. A guide tube extends externally of the torch and has a free end adjacent to the lip. First and second optical fiber bundle assemblies are supported within the guide tube. Light from a strobe light is transmitted along one of the assemblies to the free end and through the lip onto the weld site. A lens is positioned in the guide tube adjacent to the second assembly and focuses images of the weld site onto the end of the fiber bundle of the second assembly and these images are transmitted along the second assembly to a video camera so that the weld site may be viewed continuously for monitoring the welding process.

Rybicki, Daniel J. (inventor); Mcgee, William F. (inventor)

1994-01-01

200

An Assessment of Molten Metal Detachment Hazards During Electron Beam Welding in Space  

NASA Technical Reports Server (NTRS)

The safety issue has been raised with regards to potential molten metal detachments from the weld pool and cold filler wire during electron beam welding in space. This investigation was undertaken to evaluate if molten metal could detach and come in contact with astronauts and burn through the fabric of the astronauts' Extravehicular Mobility Unit (EMU) during electron beam welding in space. Molten metal detachments from either the weld/cut substrate or weld wire could present harm to a astronaut if the detachment was to burn through the fabric of the EMU. Theoretical models were developed to predict the possibility and size of the molten metal detachment hazards during the electron beam welding exercises at Low Earth Orbit (LEO). The primary molten metal detachment concerns were those cases of molten metal separation from the metal surface due to metal cutting, weld pool splashing, entrainment and release of molten metal due to filler wire snap-out from the weld puddle, and molten metal accumulation and release from the end of the weld wire. Some possible ways of obtaining molten metal drop detachments would include an impulse force, or bump, to the weld sample, cut surface, or filler wire. Theoretical models were developed for these detachment concerns from principles of impact and kinetic energies, surface tension, drop geometry, surface energies, and particle dynamics. The surface tension represents the force opposing the liquid metal drop from detaching whereas the weight of the liquid metal droplet represents a force that is tending to detach the molten metal drop. Theoretical calculations have indicated that only a small amount of energy is required to detach a liquid metal drop; however, much of the energy of an impact is absorbed in the sample or weld plate before it reaches the metal drop on the cut edge or surface. The tendency for detachment is directly proportional to the weld pool radius and metal density and inversely proportional to the surface tension of the liquid metal. For a detachment the initial kinetic energy of the weld pool with respect to the plate has to exceed the energy to form the extra surface required for the detachment of the pool. The difficulty is in transferring the energy from the point of impact through the plate and sample to the cut edge. It is likely that not all of the kinetic energy is available for detaching the pool; some may be sequestered in weld pool oscillations. The coefficient of restitution for the collision will be lower than one if irreversible deformation, for example plastic flow deformation, takes place during the collision. Thus determining the amount of energy from an impact that actually reaches the molten metal droplet is critical. Various molten metal detachment scenarios were tested experimentally in an enclosed vacuum chamber using the Ukrainian Universal Hand Tool, an electron beam welder designed for space welding. The experimental testing was performed in a 4 ft. X 4 ft. vacuum chamber at Marshall Space Flight Center, evacuated to vacuum levels of at least 50 microTorr, and also some welding garment material was utilized to observe the effect of the molten metal detachments on the material. A "carillon" apparatus consisting of four pendulum hammer strikers, each weighing approximately 3.65 lbs, raised to predetermined specific heights was used to apply an impact force to the weld sample/plate during electron beam welding and cutting exercises. The strikers were released by switching on an electric motor to rotate a pin holding wires retaining the strikers at desired heights. The specimens were suspended so as to be free to respond to the blows with a sudden velocity increment. The specimens were mounted on a hinged plate for minimizing effective mass with the option to fasten it down so as to raise its effective mass closer to that anticipated for an actual space welding scenario. Measurements were made of the impact energy and the horizontal fling distances of the detached metal drops. It was not particularly easy to generate the detachments fo

Fragomeni, James M.; Nunes, Arthur C., Jr.

1998-01-01

201

Damage Tolerance Assessment of Friction Pull Plug Welds  

NASA Technical Reports Server (NTRS)

Friction stir welding is a solid state welding process developed and patented by The Welding Institute in Cambridge, England. Friction stir welding has been implemented in the aerospace industry in the fabrication of longitudinal welds in pressurized cryogenic propellant tanks. As the industry looks to implement friction stir welding in circumferential welds in pressurized cryogenic propellant tanks, techniques to close out the termination hole associated with retracting the pin tool are being evaluated. Friction pull plug welding is under development as a one means of closing out the termination hole. A friction pull plug weld placed in a friction stir weld results in a non-homogenous weld joint where the initial weld, plug weld, their respective heat affected zones and the base metal all interact. The welded joint is a composite, plastically deformed material system with a complex residual stress field. In order to address damage tolerance concerns associated with friction plug welds in safety critical structures, such as propellant tanks, nondestructive inspection and proof testing may be required to screen hardware for mission critical defects. The efficacy of the nondestructive evaluation or the proof test is based on an assessment of the critical flaw size in the test or service environments. Test data relating residual strength capability to flaw size in two aluminum alloy friction plug weld configurations is presented.

McGill, Preston; Burkholder, Jonathan

2012-01-01

202

Welding II.  

ERIC Educational Resources Information Center

Instructional objectives and performance requirements are outlined in this course guide for Welding II, a performance-based course offered at the Community College of Allegheny County to introduce students to out-of-position shielded arc welding with emphasis on proper heats, electrode selection, and alternating/direct currents. After introductory…

Allegheny County Community Coll., Pittsburgh, PA.

203

Welding Curriculum.  

ERIC Educational Resources Information Center

The purpose of this welding program is to provide students with skills and techniques to become employed as advanced apprentice welders. The welding program manual includes the following sections: (1) course description; (2) general objectives; (3) competencies; (4) curriculum outline for 13 areas; (5) 13 references; and (6) student progress…

EASTCONN Regional Educational Services Center, North Windham, CT.

204

Welding III.  

ERIC Educational Resources Information Center

Instructional objectives and performance requirements are outlined in this course guide for Welding III, an advanced course in arc welding offered at the Community College of Allegheny County to provide students with the proficiency necessary for industrial certification. The course objectives, which are outlined first, specify that students will…

Allegheny County Community Coll., Pittsburgh, PA.

205

Virginia Tech - Buffer Pool  

NSDL National Science Digital Library

Allows user to select from FIFO, LRU, and LFU page replacement strategies. User then gives a series of page requests and the AV shows the decisions made regarding page replacement. Simple to use, clearly shows the process. It would be nice if the user could pick the size of the backing memory and the buffer pool. Recommended as lecture aide, standalone, self-study suppliment to tutorial or lecture.

Cliff Shaffer

206

Increasing Productivity of Welding  

E-print Network

-20, 1983 Welding Process Filler Metal Utilization (% deposited) 100% 908070 Figure No. )4. Pipe We/ding Glv\\AW 40 Plasma Arc (c:old wire) Flux Cored Arc Electroslag Gas Tungsten Arc (cold wire) Submerged Arc ~~Im... processes. These are shown by Figure 2 and included shielded metal-arc welding (stick welding), gas tungsten arc welding (TIG), gas metal arc welding (MIG), flux cored arc welding, submerged arc welding, plasma arc welding, stud arc welding and carbon...

Uhrig, J. J.

1983-01-01

207

On-line weld penetration detection and control in automated gas tungsten arc welding. Ph.D. Thesis  

SciTech Connect

The present work was undertaken to study the feasibility of monitoring and controlling weld penetration variations in real-time using an infrared detector. Weld penetration variations induced on mild steel plates were examined with an infrared detector and the acquired data analyzed to detect weld penetration variations using a mathematical analysis. Selected weld penetration indicators were developed and used to demonstrate on-line weld penetration control. A three-dimensional solid-state, transient heat transfer model was also developed to help identify key changes in thermal distributions which could be used as weld penetration indicators. A transient three-dimensional heat transfer model was used to solve the differential energy balance for the GTA welding process. The computed temperatures obtained from the model were used to determine the variation of the isothermal map, surface temperature profile and temperature gradient with weld penetration. Good agreement between experimental and computed indicators was obtained. Gas tungsten arc welds were performed on steel plates with intentionally introduced defects such as sudden thickness changes and minor element content changes. Extensive mathematical analysis helped correlate weld penetration variations to parameters such as the peak infrared intensity, intensity gradient over a fixed distance, intensity gradient at the inflection points in the first differential of the intensity profile (linescan), computed width of the weld pool, intensity gradient at a point in the weld pool, area enclosed by the linescan and area enclosed by the linescan after compensating for background illumination. The shape of the weld pool front was also determined from a differential analysis of the infrared data. Inconsistent behavior of some weld penetration indicators led to their elimination from the selection process for the best error signal.

Banerjee, P.

1994-01-01

208

FINITE VOLUME METHODS APPLIED TO THE COMPUTATIONAL MODELLING OF WELDING PHENOMENA  

E-print Network

) and Computational Solid Mechanics (CSM). With regard to the CFD modelling of the weld pool fluid dynamics, heat of reference solutions. KEYWORDS: Welding Phenomena, Fluid Dynamics, Solid Mechanics, Finite Volume Methods #121 FINITE VOLUME METHODS APPLIED TO THE COMPUTATIONAL MODELLING OF WELDING PHENOMENA Gareth A

Taylor, Gary

209

Internal Wire Guide For Gas/Tungsten-Arc Welding  

NASA Technical Reports Server (NTRS)

Wire kept in shielding gas, preventing oxidation. Guide inside gas cup of gas/tungsten-arc welding torch feeds filler wire to weld pool along line parallel to axis of torch. Eliminates problem of how to place and orient torch to provide clearance for external wire guide.

Morgan, Gene E.; Dyer, Gerald E.

1990-01-01

210

Effect of the Pool Size of Stromal Reductants on the Alternative Pathway of Electron Transfer to Photosystem I in Chloroplasts of Intact Leaves  

Microsoft Academic Search

The effect of elevated temperature on electron flow to plastoquinone pool and to PSI from sources alternative to PSII was studied in barley (Hordeum vulgare L.) and maize (Zea mays L.) leaves. Alternative electron flow was characterized by measuring variable fluorescence of chlorophyll and absorption changes at 830 nm that reflect redox changes of P700, the primary electron donor of

E. A. Egorova; N. G. Bukhov; U. Heber; G. Samson; R. Carpentier

2003-01-01

211

Welding superalloy sheet for superconducting cable jackets  

SciTech Connect

Autogenous gas tungsten arc welds produced in A-286 exhibit significantly lower yield and ultimate tensile strengths than comparably heat-treated base metal. Deformation in the aged weld metal is highly localized and delineates the dendritic microstructure. The observed mechanical properties are caused by the formation of precipitate-free regions located at the dendrite cores. These regions form as the result of titanium segregation during weld pool solidification which yields dendrite cores sufficiently lean in titanium as to prevent nucleation of the hardening phase.

Summers, L.T.; Strum, M.J.; Morris, J.W. Jr.

1983-08-01

212

Cellular automata modeling of weld solidification structure  

SciTech Connect

The authors explore the use of cellular automata in modeling arc-welding processes. A brief discussion of cellular automata and their previous use in micro-scale solidification simulations is presented. Macro-scale thermal calculations for arc-welding at a thin plate are shown to give good quantitative and qualitative results. Combining the two calculations in a single cellular array provides a realistic simulation of grain growth in a welding process. Results of simulating solidification in a moving melt pool in a poly-crystalline alloy sheet are presented.

Dress, W.B.; Zacharia, T.; Radhakrishnan, B.

1993-12-31

213

Vaccum Gas Tungsten Arc Welding, phase 1  

NASA Technical Reports Server (NTRS)

This two year program will investigate Vacuum Gas Tungsten Arc Welding (VGTAW) as a method to modify or improve the weldability of normally difficult-to-weld materials. VGTAW appears to offer a significant improvement in weldability because of the clean environment and lower heat input needed. The overall objective of the program is to develop the VGTAW technology and implement it into a manufacturing environment that will result in lower cost, better quality and higher reliability aerospace components for the space shuttle and other NASA space systems. Phase 1 of this program was aimed at demonstrating the process's ability to weld normally difficult-to-weld materials. Phase 2 will focus on further evaluation, a hardware demonstration and a plan to implement VGTAW technology into a manufacturing environment. During Phase 1, the following tasks were performed: (1) Task 11000 Facility Modification - an existing vacuum chamber was modified and adapted to a GTAW power supply; (2) Task 12000 Materials Selection - four difficult-to-weld materials typically used in the construction of aerospace hardware were chosen for study; (3) Task 13000 VGTAW Experiments - welding experiments were conducted under vacuum using the hollow tungsten electrode and evaluation. As a result of this effort, two materials, NARloy Z and Incoloy 903, were downselected for further characterization in Phase 2; and (4) Task 13100 Aluminum-Lithium Weld Studies - this task was added to the original work statement to investigate the effects of vacuum welding and weld pool vibration on aluminum-lithium alloys.

Weeks, J. L.; Krotz, P. D.; Todd, D. T.; Liaw, Y. K.

1995-01-01

214

WELDING RESEARCH -s77WELDING JOURNAL  

E-print Network

) in 1991 (Ref. 1), is a solid-state welding process that offers an attractive alternative to fusion weldingWELDING RESEARCH -s77WELDING JOURNAL ABSTRACT. The microstructure of AL- 6XN plates joined via a double-sided fric- tion stir weld has been investigated. The microstructural zones that develop during

DuPont, John N.

215

NIR-camera-based online diagnostics of laser beam welding processes  

NASA Astrophysics Data System (ADS)

We have developed an on-axis camera-based online sensor system for laser beam welding diagnostics that detects the thermal radiation in the near-infrared (NIR) spectral range between 1200 and 1700 nm. In addition to a sensor in the visible (VIS) range, our camera detects the thermal radiation of the weld pool more clearly, and it is also sensible to the radiation of the solidified weld seam. The NIR images are analyzed by real-time image processing. Features are extracted from the images and evaluated to characterize the welding process. Keyhole and weld pool analysis complement VIS diagnostics, whereas the observation of the weld seam and heat affected zone with an NIR camera allows online heat flux thermography. By this means we are able to detect bad joints in overlap weldings ("false friends") online during the welding process.

Dorsch, Friedhelm; Braun, Holger; Keßler, Steffen; Pfitzner, Dieter; Rominger, Volker

2012-03-01

216

Hatching phenology, life history and egg bank size of fairy shrimp Branchipodopsis spp. (Branchiopoda, Crustacea) in relation to the ephemerality of their rock pool habitat  

Microsoft Academic Search

In temporary aquatic habitats, permanence and the severe disturbance associated with desiccation are strong selective agents\\u000a expected to lead to differentiation in life history strategies in populations experiencing different disturbance regimes.\\u000a Besides optimal timing of hatching of dormant life stages, maturation and reproduction, pool inhabitants also benefit from\\u000a the acquisition of reliable cues for the quality of the ambient environment.

Bram Vanschoenwinkel; Maitland Seaman; Luc Brendonck

2010-01-01

217

The size of the intracellular beta 1-integrin precursor pool regulates maturation of beta 1-integrin subunit and associated alpha-subunits.  

PubMed Central

A large pool of precursor beta 1-integrin subunits is frequently found intracellularly. During malignant transformation this pool often disappears. Concomitantly, integrin-mediated cell-adhesion functions are disturbed, even though no change in the number of beta 1-integrin receptors on the cell surface can be observed. Here, we have studied the role of an intracellular pre-beta 1-integrin pool by transfecting human MG-63 osteosarcoma cells with plasmid construction producing an antisense RNA for the beta 1-integrin subunit. Stable cell clones expressing beta 1-integrin antisense RNA were shown to have a reduced intracellular pool of pre-beta 1-integrin subunits. In the antisense-transfected cells, the synthesis of the beta 1-integrin chain was reduced by 65% compared with non-transfected or vector-transfected MG-63 cells. The decreased synthesis of the beta 1-integrin chain was associated with accelerated maturation of the beta 1-integrin chain (half-maturation time about 5 h in antisense-transfected cells compared with about 10.5 h in control cells), whereas maturation of the alpha-integrin chain slowed down. The amount of beta 1-integrins on the cell surface, however, remained unaltered. Cell clones with the largest decrease in the relative amount of the pre-beta 1-integrin subunit also showed altered integrin function. They were found to synthesize fibronectin, but were unable to assemble it into a fibronectin matrix on the cell surface. Thus we conclude that the repression of biosynthesis of the beta 1-integrin chain leads to alterations in receptor maturation and may be connected with altered receptor function. Images Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 PMID:8010959

Koivisto, L; Heino, J; Häkkinen, L; Larjava, H

1994-01-01

218

Keyhole and weld shapes for plasma arc welding under normal and zero gravity  

NASA Technical Reports Server (NTRS)

A first order study of the interfacial (keyhole) shape between a penetrating argon plasma arc jet and a stationary liquid metal weld pool is presented. The interface is determined using the Young-Laplace equation by assuming that the plasma jet behaves as a one-dimensional ideal gas flow and by neglecting flow within the weld pool. The solution for the keyhole shape allows an approximate determination of the liquid-solid metal phase boundary location based on the assumption that the liquid melt is a stagnant thermal boundary layer. Parametric studies examine the effect of plasma mass flow rate, initial plasma enthalpy, liquid metal surface tension, and jet shear on weldment shape under both normal and zero gravity. Among the more important findings of this study is that keyhole and weld geometries are minimally affected by gravity, suggesting that data gathered under gravity can be used in planning in-space welding.

Keanini, R. G.; Rubinsky, B.

1990-01-01

219

Wonder Weld  

SciTech Connect

Engineers at the U.S. Department of Energy's Princeton Plasma Physics Laboratory are using the process shown here to create a super-strong weld for the upgrade of a key component of the Lab's experimental nuclear fusion reactor.

None

2012-01-01

220

Welding Supervisor  

NSDL National Science Digital Library

In this video segment adapted from Pennsylvania College of Technology and WVIA, get a behind-the-scenes look at a Toyota manufacturing plant with a manufacturing specialist who oversees robotic welding cells.

WGBH Educational Foundation

2009-12-24

221

Welding and Weldability of Thorium-Doped Iridium Alloys  

SciTech Connect

Ir-0.3%W alloys doped with thorium are currently used as post-impact containment material for radioactive fuel in thermoelectric generators that provide stable electrical power for a variety of outer planetary space exploration missions. Welding and weldability of a series of alloys was investigated using arc and laser welding processes. Some of these alloys are prone to severe hot-cracking during welding. Weldability of these alloys was characterized using Sigmajig weldability test. Hot-cracking is influenced to a great extent by the fusion zone microstructure and composition. Thorium content and welding atmosphere were found to be very critical. The weld cracking behavior in these alloys can be controlled by modifying the fusion zone microstructure. Fusion zone microstructure was found to be controlled by welding process, process parameters, and the weld pool shape.

David, S.A.; Ohriner, E.K.; King, J.F.

2000-03-12

222

Microstructures and mechanical properties of Inconel 718 welds by CO 2 laser welding  

Microsoft Academic Search

CO2 laser welding characteristics of Inconel 718, heat treatment effects on microstructures, and tensile\\/fatigue properties were researched. CO2 laser welding was carried out on 5mm thick plates having two different grain sizes, ASTM #4 and #10. For the fine-grain sized specimens (ASTM #10), the optimum laser welding conditions without defects were 6kW with 2.5m\\/min and 8kW with 4.0m\\/min. However, on

J. K. Hong; J. H. Park; N. K. Park; I. S. Eom; M. B. Kim; C. Y. Kang

2008-01-01

223

Syllabus in Trade Welding.  

ERIC Educational Resources Information Center

The syllabus outlines material for a course two academic years in length (minimum two and one-half hours daily experience) leading to entry-level occupational ability in several welding trade areas. Fourteen units covering are welding, gas welding, oxyacetylene welding, cutting, nonfusion processes, inert gas shielded-arc welding, welding cast…

New York State Education Dept., Albany. Bureau of Secondary Curriculum Development.

224

Electrode carrying wire for GTAW welding  

NASA Technical Reports Server (NTRS)

A welding torch for gas tungsten arc welding apparatus has a hollow tungsten electrode including a ceramic liner and forms the filler metal wire guide. The wire is fed through the tungsten electrode thereby reducing the size of the torch to eliminate clearance problems which exist with external wire guides. Since the wire is preheated from the tungsten more wire may be fed into the weld puddle, and the wire will not oxidize because it is always within the shielding gas.

Morgan, Gene E. (inventor); Dyer, Gerald E. (inventor)

1990-01-01

225

Shielding gas selection for increased weld penetration and productivity in GTA welding  

SciTech Connect

The effects of hydrogen and helium additions to the argon shielding gas on GTA weld pool profiles in the case of two austenitic stainless steel sheets 3 mm thick are investigated here in detail. One of the test steels shows good weldability, with a relatively deep, narrow weld pool profile, but the other is poorly weldable, with a shallow, wide weld pool when argon shielding gas is used. Bead-on-plate test welds were produced with arc shields of argon, argon with hydrogen additions of 2 to 18.2% and argon with helium additions of 20 to 80%. The hydrogen additions increases the depth of weld penetration in both test steels, but productivity with respect to maximum welding speed can be improved to an accepted level only with steel sheets of good weldability in terms of a relatively high depth/width (D/W) ratio. The depth of penetration in the test steel of good weldability increased somewhat with helium additions and the D/W ratio remained unchanged, while these parameters increased markedly in the poorly weldable steel when a He-20% Ar shielding gas was used and resembled those of the more weldable steel.

Leinonen, J.I. [Univ. of Oulu (Finland)

1996-12-31

226

Depth of penetration in gas metal arc welding  

SciTech Connect

The authors present a model of the depth of penetration in gas metal arc welding. This model is based on the assumption that the heat and mass transfer to the weld pool and the depth of penetration may be correlated by a dimensionless relation. This correlation leads to an analytical expression for depth of penetration, which involves empirical constants that are related to the efficiency of heat and mass transfer to the pool. They examine the accuracy of the model by comparing the theoretical depth of penetration and the measured depth of the weld pool for a range of processing variables encompassing short arc and free flight mass transfer. Measurements are obtained from bead on plate welds of stainless steel using a stainless steel electrode and a shielding gas that is rich in argon. The results confirm that the depth of penetration is affected by variations in the rate of mass transfer.

Murray, P.E. [Lockheed Martin Idaho Technologies Co., Idaho Falls, ID (United States). Idaho National Engineering and Environmental Lab.; Scotti, A. [Univ. Federal de Uberlandi (Brazil)

1998-07-01

227

Detection of embedded fatigue cracks in Inconel weld overlay and the evaluation of the minimum thickness of the weld overlay using eddy current testing  

Microsoft Academic Search

This study evaluates the applicability of eddy current testing to the detection and sizing of fatigue cracks embedded in Inconel weld overlays. Welded plate specimens, which model head penetration welds and their weld overlays, are fabricated, and fatigue cracks are artificially introduced into the specimens. Eddy current inspections are performed using a uniform eddy current probe driven with 10?kHz, and

Noritaka Yusa; Ladislav Janousek; Mihai Rebican; Zhenmao Chen; Kenzo Miya; Naoki Chigusa; Hajime Ito

2006-01-01

228

Bone Magnesium Pools in Uremia  

PubMed Central

Bone magnesium pools were studied in vitro in bone specimens obtained from control subjects, from patients with chronic renal failure before and after renal transplantation, and in a patient with chronic hypomagnesemia. 30% of bone magnesium is in a surface limited pool present either within the hydration shell or else on the crystal surface. The larger fraction of bone magnesium was shown not to be associated with bone matrix but rather to be an integral part of the bone crystal. With incineration this pool was mobilized at the same temperature that sudden enlargement of bone crystal size occurred. It is suggested that heating causes surface calcium to displace magnesium from the apatite crystal. Both magnesium pools are increased in patients with chronic renal failure. The major factor determining magnesium concentration in bone would appear to be the serum magnesium level. Following renal transplantation, in association with the fall in serum magnesium, surface magnesium was within the normal range; whereas, residual magnesium was not different from the other urenic bones. Both magnesium pools were significantly reduced in a patient with chronic hypomagnesemia. The in vitro studies would suggest that surface magnesium should rapidly reflect changes in serum magnesium levels, whereas, the deeper magnesium pool is probably deposited at time of bone formation with mobilization being dependent upon the resorptive processes. Since magnesium can influence crystal size and stability it seems possible that excess bone magnesium may play a role in renal osteodystrophy. PMID:4584344

Alfrey, Allen C.; Miller, Nancy L.

1973-01-01

229

Tool For Friction Stir Tack Welding of Aluminum Alloys  

NASA Technical Reports Server (NTRS)

A small friction-stir-welding tool has been developed for use in tack welding of aluminum-alloy workpieces. It is necessary to tack-weld the workpieces in order to hold them together during friction stir welding because (1) in operation, a full-size friction-stir-welding tool exerts a large force that tends to separate the workpieces and (2) clamping the workpieces is not sufficient to resist this force. It is possible to tack the pieces together by gas tungsten arc welding, but the process can be awkward and time-consuming and can cause sufficient damage to necessitate rework. Friction stir tack welding does not entail these disadvantages. In addition, friction stir tack welding can be accomplished by use of the same automated equipment (except for the welding tool) used in subsequent full friction stir welding. The tool for friction stir tack welding resembles the tool for full friction stir welding, but has a narrower shoulder and a shorter pin. The shorter pin generates a smaller workpiece-separating force so that clamping suffices to keep the workpieces together. This tool produces a continuous or intermittent partial-penetration tack weld. The tack weld is subsequently consumed by action of the larger tool used in full friction stir welding tool.

Bjorkman, Gerald W.; Dingler, Johnny W.; Loftus, Zachary

2003-01-01

230

Laser welding of fused quartz  

DOEpatents

Refractory materials, such as fused quartz plates and rods are welded using a heat source, such as a high power continuous wave carbon dioxide laser. The radiation is optimized through a process of varying the power, the focus, and the feed rates of the laser such that full penetration welds may be accomplished. The process of optimization varies the characteristic wavelengths of the laser until the radiation is almost completely absorbed by the refractory material, thereby leading to a very rapid heating of the material to the melting point. This optimization naturally occurs when a carbon dioxide laser is used to weld quartz. As such this method of quartz welding creates a minimum sized heat-affected zone. Furthermore, the welding apparatus and process requires a ventilation system to carry away the silicon oxides that are produced during the welding process to avoid the deposition of the silicon oxides on the surface of the quartz plates or the contamination of the welds with the silicon oxides.

Piltch, Martin S.; Carpenter, Robert W.; Archer III, McIlwaine

2003-06-10

231

Contrasting styles of welding observed in the proximal Askja 1875 eruption deposits II: Local welding  

NASA Astrophysics Data System (ADS)

As an alternative to classical welding models of fall deposits due to the progressive accumulation of hot tephra which then weld, we describe here welded deposits on the northern 1875 caldera rim of Askja volcano that have welded due to the influence of hot, discrete spatter bombs impacting into and supplying heat to a halo of surrounding tephra. This style of welding we term 'local welding' in contrast to 'regional welding' which is described elsewhere [Carey, R.J., Houghton, B.F., Thordarson, T., 2008. Contrasting styles of welding observed in the proximal Askja 1875 eruption deposits I: Regional welding. J. Volcanol. Geotherm. Res. 171, 1-19. doi:10.1016/j.jvolgeores.2007.11.020]. Locally welded deposits are associated with the rhyolitic Plinian phase of the 1875 eruption of Askja volcano. Two distinct welding units (W1 and W2) are interbedded with Plinian fall on the northern caldera rim, and grade outwards to weakly dispersed non-welded fall. Spatter bombs are found in both welding units but vary in their characteristic sizes and internal features. In the W1 unit simple bombs with homogeneous internal characteristics up to ˜ 60 cm in diameter are found. In the W2 unit, large discrete spatter bombs with complex internal features range up to 9 m in diameter. We describe here two case studies showing the effects of a) single small spatter bombs; b) multiple small spatter bombs and c) large discrete spatter bombs varying in size. Vertical and lateral profiles through welding zones reveal that the primary controls on local welding are the availability of supplied or added heat and the loading capacity of the spatter bomb. Local welding grades are much higher than that of regional welding, as the combined effects of heat, compaction and insulation can provide suitable conditions which lead to dense welding and, proximal to the spatter bomb, rheomorphic flowage. If heating and loading exceed the critical requirement for welding, porosity loss via matrix welding and vesicle collapse occurs to a point where further strain must be accommodated as shearing and ductile flowage. The spatter bombs are found only within the weakly dispersed welding units and are the final erupted products of each fountaining phase. Their low viscosities are evident by their deformation on impact and fluidal forms, and hold some important clues to eruption dynamics in the shallow conduit and vent regions.

Carey, R. J.; Houghton, B. F.; Thordarson, T.

2008-03-01

232

Phase transformations and microstructure development in low alloy steel welds  

SciTech Connect

Microstructure development in low alloy steel welds depends on various phase transformations that are a function of weld heating and cooling. The phase changes include non-metallic oxide inclusion formation in the liquid state, weld pool solidification, and solid state transformations. In this paper the mechanism of inclusion formation during low alloy steel welding is considered and the model predictions are compared with published results. The effect of inclusions on the austenite to ferrite transformation kinetics is measured and the mechanisms of transformation are discussed. The austenite gain development is related to the driving force for transformation of {delta} ferrite to austenite.

Babu, S.S.; David, S.A.; Vitek, J.M. [and others

1995-07-01

233

A Laser-Based Vision System for Weld Quality Inspection  

PubMed Central

Welding is a very complex process in which the final weld quality can be affected by many process parameters. In order to inspect the weld quality and detect the presence of various weld defects, different methods and systems are studied and developed. In this paper, a laser-based vision system is developed for non-destructive weld quality inspection. The vision sensor is designed based on the principle of laser triangulation. By processing the images acquired from the vision sensor, the geometrical features of the weld can be obtained. Through the visual analysis of the acquired 3D profiles of the weld, the presences as well as the positions and sizes of the weld defects can be accurately identified and therefore, the non-destructive weld quality inspection can be achieved. PMID:22344308

Huang, Wei; Kovacevic, Radovan

2011-01-01

234

Pool & Spa Safety Act  

MedlinePLUS

... Stories Pool Safely Home Consumer Product Safety Commission, CPSC CPSC Home The Pool & Spa Safety Act Contact Information About PoolSafely.gov and CPSC The U.S. Consumer Product Safety Commission (CPSC) is ...

235

Effect of carbon black on temperature field and weld profile during laser transmission welding of polymers: A FEM study  

NASA Astrophysics Data System (ADS)

The influence of the carbon black on temperature distribution and weld profile, during laser transmission welding of polymers, is investigated in the present research work. A transient numerical model, based on conduction mode heat transfer, is developed to analyze the process. The heat input to the model is considered to be the volumetric Gaussian heat source. The computation of temperature field during welding is carried out for polycarbonates having different proportion of carbon black in polymer matrix. The temperature dependent material properties of polycarbonate are taken into account for modeling. The finite element code ANSYS ® is employed to obtain the numerical results. The numerically computed results of weld pool dimensions are compared with the experimental results. The comparison shows a fair agreement between them, which gives confidence to use the developed model for intended investigation with acceptable accuracy. The results obtained have revealed that the carbon black has considerable influence on the temperature field distribution and the formation of the weld pool geometry.

Acherjee, Bappa; Kuar, Arunanshu S.; Mitra, Souren; Misra, Dipten

2012-04-01

236

Evaluation of electrode shape and nondestructive evaluation method for welded solar cell interconnects  

NASA Technical Reports Server (NTRS)

Resistance welds of solar cell interconnect tabs were evaluated. Both copper-silver and silver-silver welds were made with various heat inputs and weld durations. Parallel gap and annular gap weld electrode designs were used. The welds were analyzed by light microscope, electron microprobe and scanning laser acoustic microscope. These analyses showed the size and shape of the weld, the relationship between the acoustic micrographs, the visible electrode footprint, and the effect of electrode misalignment. The effect of weld heat input on weld microstructure was also shown.

Baraona, C. R.; Klima, S. J.; Moore, T. J.; Frey, W. E.; Forestieri, A. F.

1982-01-01

237

Pulsed magnetic welding  

SciTech Connect

Solid state welding techniques are an alternative to fusion welding. Two solid state welding techniques are pulsed magnetic welding and explosive bonding. Both achieve bonds by impacting the metals to be joined at high velocity. Development of the pulsed magnetic welding process by Hanford Engineers for fuel fabrication may make this process useful for a variety of other applications. Hanford engineers have developed advanced equipment for pulsed magnetic welding and have defined conditions for reliably welding stainless steel fuel pins using this equipment.

Sheely, W.F.

1986-11-20

238

Weld repair method for aluminum lithium seam  

NASA Technical Reports Server (NTRS)

Aluminum-lithium plates are butt-welded by juxtaposing the plates and making a preliminary weld from the rear or root side of the seam. An initial weld is then made from the face side of the seam, which may cause a defect in the root portion. A full-size X-ray is made and overlain over the seam to identify the defects. The defect is removed from the root side, and rewelded. Material is then removed from the face side, and the cavity is rewelded. The procedure repeats, alternating from the root side to the face side, until the weld is sound.

McGee, William Floyd (Inventor); Rybicki, Daniel John (Inventor)

1998-01-01

239

Effect of welding variables and solidification substructure on weld metal porosity  

SciTech Connect

Porosity is defined as cavity-type discontinuities formed by gas entrapment during solidification. Causes of porosity in fusion welds are the dissolved gases in weld metal and welding process variables that control the solidification rate. To study the mechanisms of porosity formation in weld metal, single-pass gas tungsten-arc weld metal was produced using the bead-on-plate technique on three nickel-copper alloys (80 wt pct Ni-20 wt pct Cu, 65 wt pct Ni-35 wt pct Cu, 35 wt pct Ni-65 wt pct Cu). Four different welding speeds were used under various amounts of nitrogen content in argon-shielding atmosphere. A qualitative model was proposed to characterize the effect of welding variables and solidification substructure on bulk and interdendritic porosity formation. Increasing amounts of nitrogen gas (from 0.2 pct to 6.0 pct in volume) introduced in argon-shielding atmosphere increased the amount of porosity in weld metal. The amount of bulk and total porosity increased as the solubility of nitrogen in the weld metal alloy decreased. The solidification rate of the weld pool is the most important factor controlling the mechanism of porosity formation. The observed amount of bulk pores in this study increased with the increase of welding speed; that is, if the time is insufficient for dissolved and evolved gases to escape during solidification, porosity will result. However, a decrease in the amount of interdendritic pores was observed with increasing welding speed in the 80Ni-20Cu and 35Ni-65Cu alloys. This decrease can be related to the effect of solidification rate on the balance between the disjoining pressure, resistance of the liquid film to be disrupted, repulsion of the bubble from the solidification front, and the hydrodynamic force resisting the movement of the bubble.

Ramirez, J.E.; Liu, S. (Colorado School of Mines, Golden, CO (United States). Dept. of Metallurgical and Materials Engineering); Han, B. (Samsung Heavy Industries, Daeduk (Korea, Republic of))

1994-10-01

240

WELDING RESEARCH -s281WELDING JOURNAL  

E-print Network

WELDING RESEARCH -s281WELDING JOURNAL ABSTRACT. Superaustenitic stainless steel alloys can often beam welds were also deposited on the surfaces of the button melts in order to observe the influ- ence. There- fore, the processing parameters used dur- ing welding must be carefully controlled in order

DuPont, John N.

241

WELDING RESEARCH -S237WELDING JOURNAL  

E-print Network

the tallest building in the world -- Fig. 1. These are all made from steel and rely on welding there is little that can be done once the weld is completed (Refs. 1­3). This contrasts with wrought steel, which of welding consum- ables involves all weld-metal tests in which a joint is deposited such that sam- ples can

Cambridge, University of

242

WELDING RESEARCH -S125WELDING JOURNAL  

E-print Network

- rosion resistance. However, during solid- ification of the weld, Mo segregates pref- erentiallyWELDING RESEARCH -S125WELDING JOURNAL ABSTRACT. Microstructural evolution and solidification cracking susceptibility of dissimilar metal welds between AL- 6XN super austenitic stainless steel and two

DuPont, John N.

243

Study of the hovering period and bubble size in fully developed pool nucleate boiling of saturated liquid with a time-dependent heat source  

SciTech Connect

In this paper, the bubble behavior in saturated pool boiling with a time-dependent heat source is analyzed. The study is restricted to the period from fully developed nucleate boiling until critical heat flux occurs. The hovering period and the departure volume of the bubble are selected as the characteristic parameters for bubble behavior. These parameters are quantified by solving the equation of motion for an idealized bubble. This equation is solved for cases in which the surface heat flux changes linearly and exponentially as a function of time. After nondimensionalization, the results are compared directly with the results of the steady-state problem. The comparison shows that the transient heat input has practically no effect on the hovering period. However, the transient heat flux causes a decreased volume at bubble departure. The volume decrease is dependent on the severity of the transient. These results are in qualitative agreement with the experimental observation quoted in the literature.

Pasamehmetoglu, K.O.; Nelson, R.A.

1987-01-01

244

Effect of Welding Current on the Structure and Properties of Resistance Spot Welded Dissimilar (Austenitic Stainless Steel and Low Carbon Steel) Metal Joints  

NASA Astrophysics Data System (ADS)

1.5 mm thick sheet metal coupons of austenitic stainless steel and plain low carbon steel were welded by resistance spot welding technique. The effects of welding current in the range 3-9 kA on the structure and mechanical properties of welded joint were investigated. The structure was studied by macroscopic, microscopic and scanning electron microscopy techniques. Mechanical properties were determined by tensile testing and microhardness measurements. Asymmetrical shape weld nugget was found to have formed in the welded joint which increased in size with an increase in welding current. The fusion zone showed cast structure with coarse columnar grain and dendritic with excess delta ferrite in austenitic matrix. Microhardness of the weld nugget was maximum because of martensite formation. An increase in welding current also increased tensile strength of the weld coupon. An attempt has also been made to relate the mode of fracture with the welding current.

Shawon, M. R. A.; Gulshan, F.; Kurny, A. S. W.

2015-04-01

245

Multi-physical Simulation of Laser Welding  

NASA Astrophysics Data System (ADS)

Laser welding is a highly demanded technology for manufacturing of body parts in the automotive industry. Application of powerful multi-physical simulation models permits detailed investigation of the laser process avoiding intricate experimental setups and procedures. Features like the degree of power coupling, keyhole evolution or currents inside the melt pool can be analyzed easily. The implementation of complex physical phenomena, like multi-reflection absorption provides insight into process characteristics under selectable conditions and yields essential information concerning the driving mechanisms. The implementation of additional physical models e. g. for diffusion discloses new potential for investigating welding of dissimilar materials. In this paper we present a computational study of laser welding for different conditions. Applied to a real case model predictions show good agreement with experimental results. Initial tests including species diffusion during welding of dissimilar materials are also presented.

Vázquez, Rodrigo Gómez; Koch, Holger M.; Otto, Andreas

246

Preliminary Study on the Formability of a Laser-Welded Superplastic Aluminum Alloy  

NASA Astrophysics Data System (ADS)

In this work, the effect of the laser-material interaction on the formability of a superplastic aluminum alloy was investigated. In applications such as Tailor-Welded Blanks and in the manufacturing of very large components with a complex shape, laser welding combined with superplastic forming may be a very fitting industrial tool. Bead on plate tests were carried out in order to simulate the laser-welding process and then, free inflation tests were performed to evaluate the compatibility of these two processing techniques. The Al-Mg alloy used in this work has a very small grain size which ensures the superplastic behavior. With the aim of preserving this peculiarity, the following aspects on the formability were investigated: (i) the surface condition of the bead before the forming test (with and without the removal of the excess of metal); (ii) the effect of the travel speed of the laser source on the mean grain size; (iii) the introduction of a refiner, commonly used in aluminum casts, in the molten pool in order to further reduce the mean grain size.

Sorgente, D.; Corizzo, O.; Brandizzi, M.; Tricarico, L.

2014-11-01

247

Influence of Aluminum Content on Grain Refinement and Strength of AZ31 Magnesium GTA Weld Metal  

SciTech Connect

The goal is to characterize the effect of Al content on AZ31 weld metal, the grain size and strength, and examine role of Al on grain refinement. The approach is to systematically vary the aluminum content of AZ31 weld metal, Measure average grain size in weld metal, and Measure cross-weld tensile properties and hardness. Conclusions are that: (1) increased Al content in AZ31 weld metal results in grain refinement Reason: higher undercooling during solidification; (2) weld metal grain refinement resulted in increased strength & hardness Reason: grain boundary strengthening; and (3) weld metal strength can be raised to wrought base metal levels.

Babu, N. Kishore [Singapore Institute of Manufacturing Technology; Cross, Carl E. [Los Alamos National Laboratory

2012-06-28

248

An Assessment of Molten Metal Detachment Hazards for Electron Beam Welding in the Space Environment: Analysis and Test Results  

NASA Technical Reports Server (NTRS)

Conditions under which molten metal detachments might occur in a space welding environment are analyzed. A weld pool detachment parameter specifying conditions for pool detachment by impact is derived and corroborated by experimental evidence. Impact detachment for the pool is unlikely. Impact detachment for a drop of metal on the end of the weld wire may be possible under extreme conditions. Other potential causes of molten metal detachment considered, vaporization pressure forces and wire flickout from the pool, did not appear to present significant detachment threats.

Nunes, A. C., Jr.; Russell, C.; Bhat, B.; Fragomeni, J. M.

1998-01-01

249

Narrow gap laser welding  

DOEpatents

A laser welding process including: (a) using optical ray tracing to make a model of a laser beam and the geometry of a joint to be welded; (b) adjusting variables in the model to choose variables for use in making a laser weld; and (c) laser welding the joint to be welded using the chosen variables. 34 figs.

Milewski, J.O.; Sklar, E.

1998-06-02

250

Pulsed magnetic welding  

Microsoft Academic Search

Solid state welding techniques are an alternative to fusion welding. Two solid state welding techniques are pulsed magnetic welding and explosive bonding. Both achieve bonds by impacting the metals to be joined at high velocity. Development of the pulsed magnetic welding process by Hanford Engineers for fuel fabrication may make this process useful for a variety of other applications. Hanford

Sheely

1986-01-01

251

Narrow gap laser welding  

DOEpatents

A laser welding process including: (a) using optical ray tracing to make a model of a laser beam and the geometry of a joint to be welded; (b) adjusting variables in the model to choose variables for use in making a laser weld; and (c) laser welding the joint to be welded using the chosen variables.

Milewski, John O. (Santa Fe, NM); Sklar, Edward (Santa Fe, NM)

1998-01-01

252

Welded Scoria  

USGS Multimedia Gallery

Samples of welded scoria. Scoria is another word for the ‘cinders’ that make up volcanic cinder cones. Roza Member, Columbia River Basalt Group. Southeast of Winona, WA. Cinder cones (otherwise known as scoria cones) are the most common type of volcano on Earth. They’re also one o...

253

Effects of laser-weld joint opening size on fatigue strength of Ti-6Al-4V structures with several diameters.  

PubMed

This study was conducted to evaluate the fatigue strength of Ti-6Al-4V laser-welded joints with several diameters and joint openings. Sixty dumbbell rods were machined in Ti-6Al-4V alloy with central diameters of 1·5, 2·0 and 3·5 mm. The specimens were sectioned and then welded using two joint openings (0·0 and 0·6 mm). The combination of variables created six groups, which when added to the intact groups made a total of nine groups (n = 10). Laser welding was executed as follows: 360 V per 8 ms (1·5 and 2·0 mm) and 380 V per 9 ms (3·5 mm) with focus and frequency regulated to zero. The joints were finished, polished and submitted to radiographic examination to be analysed visually for the presence of porosity. The specimens were then subjected to a mechanical cyclic test, and the number of cycles until failure was recorded. The fracture surface was examined with a scanning electron microscope (SEM). The Kruskal-Wallis test and Dunn test (? = 0·05) indicated that the number of cycles required for fracture was lower for all specimens with joint openings of 0·6 mm, and for 3·5-mm-diameter specimens with joint openings of 0·0 mm. The Spearman correlation coefficient (? = 0·05) indicated that there was a negative correlation between the number of cycles and the presence of porosity. So, laser welding of Ti-6Al-4V structures with a thin diameter provides the best conditions for the juxtaposition of parts. Radiographic examination allows for the detection of internal voids in titanium joints. PMID:20678101

Nuñez-Pantoja, J M C; Vaz, L G; Nóbilo, M A A; Henriques, G E P; Mesquita, M F

2011-03-01

254

Laser Beam Welding of Brass  

NASA Astrophysics Data System (ADS)

Up to date the evaporation process in laser beam welding of alloys with volatile elements is not completely understood. This paper discusses the phenomena occurring at the welding process of brass with 37m% zinc. Since copper has a solidification temperature of 1,087 °C and zinc vaporizes at a temperature of 907 °C, a strong evaporation takes place and anelongation of the keyhole can be observed. Depending upon welding velocity, the ratio of keyhole length to width is between one and six. Furthermore it is observed that a defect free weld seam is formed. Since the melt pool does not leak also for high ratios of keyhole length to width, the conventional keyhole model with a dynamic flow around the laser beam has to be adapted to a model in which the melt flow at the side of the capillary is stabilized also outside of the interaction zone of the laser beam with the melt due to strong evaporation at the flank of the keyhole.

Hugger, Florian; Hofmann, Konstantin; Stein, Stefan; Schmidt, Michael

255

Careers in Welding  

NSDL National Science Digital Library

Careers in Welding is a portal jointly produced by the American Welding Society and Weld-Ed, the Nation Center for Welding Education and Training. Here, visitors will find information for educators, students, and welding professionals, in addition to general information about exploring a career in welding. Educators can find teaching tips, curriculum, professional development information, resources and products, events, and networking opportunities. Students can find information about schools with welding programs, scholarships, jobs, and much more. For the welding professional, the site has tips for building a resume, finding a job, and AWS certification information. The site also features videos of technicians and general articles, such as "Why Welding?" and "Welding Fast Facts," that offer information on why to choose a career in welding.

256

Welding deep water pipelines  

SciTech Connect

The objective of this research program was to investigate the girth welding of pipe in the vertical or near vertical position (2G) for J-welding construction in deep-water applications. The tasks investigated included two approaches (depositing the root pass on the pipe I.D. with the balance of welding on the O.D. and all welding on the O.D.), arc-welding processes, shielding gases, arc welding parameters, weld joint design, mechanical properties of deposited welds, and determination of the extent of heat buildup in the pipe during welding. Welding procedures were developed for both the internal root/balance O.D. welding and for the all external welding approaches.

Teale, R.A.; Laing, B.S. [CRC-Evans Automatic Welding, Houston, TX (United States)

1994-12-31

257

Field comparison of three inhalable samplers (IOM, PGP-GSP 3.5 and Button) for welding fumes.  

PubMed

Inhalable sampler efficiency depends on the aerodynamic size of the airborne particles to be sampled and the wind speed. The aim of this study was to compare the behaviour of three personal inhalable samplers for welding fumes generated by Manual Metal Arc (MMA) and Metal Active Gas (MAG) processes. The selected samplers were the ones available in Spain when the study began: IOM, PGP-GSP 3.5 (GSP) and Button. Sampling was carried out in a welding training center that provided a homogeneous workplace environment. The static sampling assembly used allowed the placement of 12 samplers and 2 cascade impactors simultaneously. 183 samples were collected throughout 2009 and 2010. The range of welding fumes' mass concentrations was from 2 mg m(-3) to 5 mg m(-3). The pooled variation coefficients for the three inhalable samplers were less than or equal to 3.0%. Welding particle size distribution was characterized by a bimodal log-normal distribution, with MMADs of 0.7 ?m and 8.2 ?m. For these welding aerosols, the Button and the GSP samplers showed a similar performance (P = 0.598). The mean mass concentration ratio was 1.00 ± 0.01. The IOM sampler showed a different performance (P < 0.001). The mean mass concentration ratios were 0.90 ± 0.01 for Button/IOM and 0.92 ± 0.02 for GSP/IOM. This information is useful to consider the measurements accomplished by the IOM, GSP or Button samplers together, in order to assess the exposure at workplaces over time or to study exposure levels in a specific industrial activity, as welding operations. PMID:22037834

Zugasti, Agurtzane; Montes, Natividad; Rojo, José M; Quintana, M José

2012-02-01

258

Fiber laser welding of nickel-based superalloy inconel 718  

NASA Astrophysics Data System (ADS)

Inconel 718 (IN 718) is widely used in applications, such as aircraft and power turbine components. Recently, fiber laser welding has become an attractive joining technique in industry for fabrication and repair of service-damaged components. However, a major limitation in the laser welding of IN 718 is that liquation cracking occurs. In the present work, autogenous fiber laser welding of IN 718 was used to study the effects of welding parameters and different pre-weld heat treatments on liquation cracking. Contrary to previous studies, a dual effect of heat input on cracking is observed. A rarely reported effect of heat input is attributed to process instability. Liquation cracking increases with pre-weld heat treatment temperatures that increase grain size and/or, possibly, intregranular boron segregation. The study shows that pre-weld heat treatment at 950oC can be used for repair welding of IN 718 without significant loss in cracking resistance.

Oshobe, Omudhohwo Emaruke

259

Emissions of chromium (VI) from arc welding.  

PubMed

The presence of Cr in the +6 oxidation state (Cr[VI]) is still observed in ambient air samples in California despite steps taken to reduce emissions from plating operations. One known source of emission of Cr(VI) is welding, especially with high Cr-content materials, such as stainless steels. An experimental effort was undertaken to expand and update Cr(VI) emission factors by conducting tests on four types of arc-welding operations: gas-metal arc welding (GMAW), shielded metal arc welding (SMAW), fluxcore arc welding, and pulsed GMAW. Standard American Welding Society hood results were compared with a total enclosure method that permitted isokinetic sampling for particle size-cut measurement, as well as total collection of the aerosol. The fraction of Cr(VI) emitted per unit mass of Cr electrode consumed was determined. Consistent with AP-42 data, initial results indicate that a significant fraction of the total Cr in the aerosol is in the +6 oxidation state. The fraction of Cr(VI) and total aerosol mass produced by the different arc welding methods varies with the type of welding process used. Self-shielded electrodes that do not use a shield gas, for example, SMAW, produce greater amounts of Cr(VI) per unit mass of electrode consumed. The formation of Cr(VI) from standard electrode wires used for welding mild steel was below the method detection limit after eliminating an artifact in the analytical method used. PMID:17355086

Heung, William; Yun, Myoung-Jin; Chang, Daniel P Y; Green, Peter G; Halm, Chris

2007-02-01

260

Contrasting styles of welding observed in the proximal Askja 1875 eruption deposits I: Regional welding  

NASA Astrophysics Data System (ADS)

Welded fall deposits on the northern caldera rim at Askja volcano are associated with the Plinian phase of the 1875 eruption. Two welding units occur within the proximal Plinian fall centered on stratigraphic sub-units which, where non-welded, are poorly sorted and ash-rich with high abundances of fluidal and needle-like ash particles. Welding has formed due to two discrete processes; a) the sintering of hot ash and lapilli which forms the two distinct units that are laterally continuous on distance scales of tens of meters (termed 'regional welding'), and b) creation of welding halos enclosing large, dense, discrete, non- to poorly vesicular spatter bombs that are up to 9 m in diameter (termed 'local welding'). This paper is concerned with the nature of regional welding and the companion paper (this issue) focuses on the phenomenon of local welding. Three case studies documenting the range of welding patterns observed in regional welding are presented here. Vertical and lateral profiles of welding intensity, together with the deposit characteristics reveal that welding could only occur when the accumulation rates were sufficient and that grain size and thickness are second order factors facilitating welding. Rapid and reversible shifts in both thickness and welding grade are observed on a ~ 10 m scale laterally along the caldera rim suggesting considerable unsteadiness of the transport regime, which promoted localized fluctuations of the accumulation rate. The welded deposits prompt re-examination of both the dynamics of the Plinian phase of the 1875 eruption and the distribution of source vents. The dispersal of the welding units is not compatible with deposition from the full height of the Plinian plume. Similarly to the ultra-proximal deposits of Novarupta or Tarawera, these clasts probably fell from heights of hundreds of meters to < 4 km, retaining sufficient heat to weld after deposition. The E-W elongated distribution of the welded units is also not compatible with a single source vent, and favors several vents that were in a fountaining phase, and located adjacent to the northern rim.

Carey, R. J.; Houghton, B. F.; Thordarson, T.

2008-03-01

261

Friction Stir Weld System for Welding and Weld Repair  

NASA Technical Reports Server (NTRS)

A friction stir weld system for welding and weld repair has a base foundation unit connected to a hydraulically controlled elevation platform and a hydraulically adjustable pin tool. The base foundation unit may be fixably connected to a horizontal surface or may be connected to a mobile support in order to provide mobility to the friction stir welding system. The elevation platform may be utilized to raise and lower the adjustable pin tool about a particular axis. Additional components which may be necessary for the friction stir welding process include back plate tooling, fixturing and/or a roller mechanism.

Ding, R. Jeffrey (Inventor); Romine, Peter L. (Inventor); Oelgoetz, Peter A. (Inventor)

2001-01-01

262

Structural evolution and superplastic formability of friction stir welded AA 2095 sheets  

Microsoft Academic Search

Friction stir welding was used to join superplastic AA 2095 sheets. The effect of welding rate on the grain size distribution\\u000a and grain boundary misorientations in the stir zone was investigated. The superplastic behavior of the weld nugget parallel\\u000a to the welding direction was also characterized at 495 °C and strain rates from 10?4s?1 to 10?2s?1. Increasing the welding rate

H. G. Salem; A. P. Reynolds; J. S. Lyons

2004-01-01

263

Friction plug welding  

NASA Technical Reports Server (NTRS)

Friction plug welding (FPW) usage is advantageous for friction stir welding (FSW) hole close-outs and weld repairs in 2195 Al--Cu--Li fusion or friction stir welds. Current fusion welding methods of Al--Cu--Li have produced welds containing varied defects. These areas are found by non-destructive examination both after welding and after proof testing. Current techniques for repairing typically small (<0.25) defects weaken the weldment, rely heavily on welders' skill, and are costly. Friction plug welding repairs increase strength, ductility and resistance to cracking over initial weld quality, without requiring much time or operator skill. Friction plug welding while pulling the plug is advantageous because all hardware for performing the weld can be placed on one side of the workpiece.

Takeshita, Riki (Inventor); Hibbard, Terry L. (Inventor)

2001-01-01

264

Friction Stir Welding  

NASA Technical Reports Server (NTRS)

Friction stir welding (FSW) is a solid state welding process invented in 1991 at The Welding Institute in the United Kingdom. A weld is made in the FSW process by translating a rotating pin along a weld seam so as to stir the sides of the seam together. FSW avoids deleterious effects inherent in melting and promises to be an important welding process for any industries where welds of optimal quality are demanded. This article provides an introduction to the FSW process. The chief concern is the physical effect of the tool on the weld metal: how weld seam bonding takes place, what kind of weld structure is generated, potential problems, possible defects for example, and implications for process parameters and tool design. Weld properties are determined by structure, and the structure of friction stir welds is determined by the weld metal flow field in the vicinity of the weld tool. Metal flow in the vicinity of the weld tool is explained through a simple kinematic flow model that decomposes the flow field into three basic component flows: a uniform translation, a rotating solid cylinder, and a ring vortex encircling the tool. The flow components, superposed to construct the flow model, can be related to particular aspects of weld process parameters and tool design; they provide a bridge to an understanding of a complex-at-first-glance weld structure. Torques and forces are also discussed. Some simple mathematical models of structural aspects, torques, and forces are included.

Nunes, Arthur C., Jr.

2008-01-01

265

Manganese in occupational arc welding fumes--aspects on physiochemical properties, with focus on solubility.  

PubMed

Physicochemical properties, such as particle sizes, composition, and solubility of welding fumes are decisive for the bioaccessibility of manganese and thereby for the manganese cytotoxic and neurotoxic effects arising from various welding fumes. Because of the diverse results within the research on welding fume solubility, this article aims to review and discuss recent literature on physicochemical properties of gas metal arc welding, shielded metal arc welding, and flux-cored arc welding fumes, with focus on solubility properties. This article also presents a short introduction to the literature on arc welding techniques, health effects from manganese, and occupational exposure to manganese among welders. PMID:22997412

Taube, Fabian

2013-01-01

266

March madness? Strategic behavior in NCAA basketball tournament betting pools  

Microsoft Academic Search

This paper uses data from the natural experiment of NCAA Basketball Tournament “betting pools” in a descriptive study of strategic behavior. The observed behavior in these pools differs from equilibrium behavior in a robust manner; bettors overback the heaviest favorites. The size of this bias falls slightly in larger pools, where the induced profit opportunities are higher than in smaller

Andrew Metrick

1996-01-01

267

WELDING RESEARCH -s229WELDING JOURNAL  

E-print Network

- minum alloy welded structures have been widely applied. The use of aluminum as an alternative material in more applications has brought a higher requirement and challenge to aluminum welding (Ref. 1). As one of the widely used aluminum weld- ing methods, the GMAW process needs improvements in order to achieve higher

Zhang, YuMing

268

WELDING RESEARCH -s51WELDING JOURNAL  

E-print Network

where the composition varies continuously from that of the fer- ritic steel to that of the weld metal625 and 309L stainless steel were de- posited onto A285 carbon steel using the electroslag welding- served in the welds deposited using 309L (Fig. 1A) and 625 (Fig. 1B) filler metals. The black vertical

DuPont, John N.

269

WELDING RESEARCH -S289WELDING JOURNAL  

E-print Network

WELDING RESEARCH -S289WELDING JOURNAL ABSTRACT. The development of Gd- enriched austenitic alloys. In this research, the physical and welding metallurgy of Gd-enriched austenitic alloys has been investigated by a solid-state transformation, producing a final microstructure that has an austenitic matrix with remnant

DuPont, John N.

270

Automated Spot Weld Inspection using Infrared Thermography  

SciTech Connect

An automated non-contact and non-destructive resistance spot weld inspection system based on infrared (IR) thermography was developed for post-weld applications. During inspection, a weld coupon was heated up by an auxiliary induction heating device from one side of the weld, while the resulting thermal waves on the other side were observed by an IR camera. The IR images were analyzed to extract a thermal signature based on normalized heating time, which was then quantitatively correlated to the spot weld nugget size. The use of normalized instead of absolute IR intensity was found to be useful in minimizing the sensitivity to the unknown surface conditions and environment interference. Application of the IR-based inspection system to different advanced high strength steels, thickness gauges and coatings were discussed.

Chen, Jian [ORNL] [ORNL; Zhang, Wei [ORNL] [ORNL; Yu, Zhenzhen [ORNL] [ORNL; Feng, Zhili [ORNL] [ORNL

2012-01-01

271

Performance Study and Dynamic Optimization Design for Thread Pool Systems  

SciTech Connect

Thread pools have been widely used by many multithreaded applications. However, the determination of the pool size according to the application behavior still remains problematic. To automate this process, in this thesis we have developed a set of performance metrics for quantitatively analyzing thread pool performance. For our experiments, we built a thread pool system which provides a general framework for thread pool research. Based on this simulation environment, we studied the performance impact brought by the thread pool on different multithreaded applications. Additionally, the correlations between internal characterizations of thread pools and their throughput were also examined. We then proposed and evaluated a heuristic algorithm to dynamically determine the optimal thread pool size. The simulation results show that this approach is effective in improving overall application performance.

Dongping Xu

2004-12-19

272

Virtual Tide Pool  

NSDL National Science Digital Library

Virtual Tide Pool features a three dimensional view of a tide pool during both low and high tides. Students can see animals that live under, above, and at the waters surface. This site offers the ability to pan the tide pool for a 360 degree view, with zoom options, and gives descriptions of the animals found during both low and high tides.

Science NetLinks (PBS; )

2003-04-29

273

Verification of temperature distribution in the system for pad welding by means of infrared thermography  

Microsoft Academic Search

The heat transfer in the system for pad welding of plates is considered. Particularly, the presence of air gap between the padded material and technological stand is investigated. The air gap appears due to the extremely high temperatures in the vicinity of the welding pool, which involve a deformation of the padded plate. The heat resistance of the air gap

I. Szczygie?; A. Fic; T. Kruczek; A. Sachajdak

274

Numerical Analysis of Heat Transfer and Fluid Flow in Keyhole Plasma Arc Welding  

Microsoft Academic Search

Modeling and simulation of fluid flow and heat transfer in keyhole plasma arc welding is of great significance for optimizing the process parameters, and obtaining deep insight of the process mechanisms. In this study, a three-dimensional transient model is established to analyze numerically the evolution of the weld pool, the keyhole shape and dimensions, and the fluid convection and temperature

Tao Zhang; Chuan Song Wu; Yanhui Feng

2011-01-01

275

Influence of different configurations of assisting gas in high-power cw-CO2-laser welding  

Microsoft Academic Search

In high power cw-CO2-laser welding, assisting gas is necessary. It has a great effect on the welding results, such as penetration depth, cross section, size of the heat affected zone and welds surface. Much has been done on discussing the influence of its kind and flow rate on the welding results, but little attention was given to its configurations. In

Jiangtao Luo; Zhaogu Cheng; Hongliang Qiang; Gang Chen; Runwen Wang

1996-01-01

276

Physicochemical characterisation of different welding aerosols.  

PubMed

Physicochemical properties important in exposure characterisation of four different welding aerosols were investigated. Particle number size distributions were determined by scanning mobility particle sizer (SMPS), mass size distributions by separation and weighing the individual size fractions of an 11-stage cascade impactor. The size distribution of the primary particles of agglomerates, chemical composition and morphology of the particles were examined by TEM. There were significant differences in the particle number size distributions of the different welding aerosols according to the SMPS determinations. The particle mass size distributions determined gravimetrically were, however, not really different. The dominant range with respect to mass was between 0.1 and 1 ?m, regardless of the welding technique. Most of the primary particles in all different welding aerosols had diameters between 5 and 40 nm. All types of primary particles had a tendency to form chainlike agglomerates. A clear size dependence of the particle chemical composition was encountered in the case of manual metal arc welding aerosol. Small particles with diameters below 50 nm were mostly metal oxides in contrast to larger particles which also contained more volatile elements (e.g. potassium, fluorine, sodium, sulphur). PMID:20845032

Berlinger, B; Benker, N; Weinbruch, S; L'Vov, B; Ebert, M; Koch, W; Ellingsen, D G; Thomassen, Y

2011-02-01

277

A theoretical model for gas metal arc welding and gas tungsten arc welding. I.  

NASA Astrophysics Data System (ADS)

A recently developed theory for predicting arc and electrode properties in gas metal arc welding (GMAW) has been generalized to include arc-electrode interfaces, variation of surface tension pressure with temperature, Marangoni forces and handling of weld pool development in stationary gas tungsten arc welding (GTAW). The new theory is a unified treatment of the arc, the anode, and the cathode, and includes a detailed account of sheath effects near the electrodes. The electrodes are included as dynamic entities and the volume of fluid method is used to handle the movement of the free surface of the molten metal at one electrode. Predictions can be made of the formation and shape of the welding droplets as a function of time in GMAW and also of weld pool development in GTAW, accounting for effects of surface tension, inertia, gravity, arc pressure, viscous drag force of the plasma, Marangoni effect and magnetic forces, and also for wire feed rate in GMAW. Calculations are made of current densities, electric potential, temperatures, pressures and velocities in two dimensions, both in the arc and also within the molten metal and solid electrodes. Calculations are presented for GMAW and GTAW for an arc in argon and the results are compared with experimental temperature measurements for the plasma and the electrodes.

Haidar, J.

1998-10-01

278

Welding Phenomenon and Removal Mechanism of Aluminum-Oxide Films by Space GHTA Welding Process in Vacuum  

NASA Astrophysics Data System (ADS)

Aluminum alloys have been widely used in constructing various space structures including the ISS (International Space Station) and launch vehicles. In order to apply the welding technology in space, welding experiments on aluminum alloy were performed using by the GHTA (Gas Hollow Tungsten Arc) welding processes using an inverter controlled DC/AC GTA welding machine in vacuum. We observed the removal mechanism of aluminum-oxide films on molten metal in detail during the welding using a high-speed video camera. As a result, it is clarified that the impact arc pressure produced by pulsed current mechanically crushes and removes aluminum-oxide films on the molten pool. This removal mechanism of aluminum-oxide films is completely different from a removal mechanism by cleaning action.

Suita, Yoshikazu; Ekuni, Tomohide; Kamei, Misa; Tsukuda, Yoshiyuki; Terajima, Noboru; Yamashita, Masahiro; Imagawa, Kichiro; Masubuchi, Koichi

279

Inactive and Protein Precursor Pools of Amino Acids in the Soybean Hypocotyl 1  

PubMed Central

There are at least 2 amino pools for leucine and for valine in the soybean hypocotyl, a small protein precursor pool and a large inactive pool. The precursor pool decreased in size during incubation of excised hypocotyls presumably because the cotyledonary sources of amino acids had been removed. The precursor pool was subject to expansion by supplying the amino acid externally at high concentrations. After the transfer of tissue to unsupplemented media, the expanded pool was rapidly depleted. PMID:16656482

Holleman, James M.; Key, Joe L.

1967-01-01

280

Simulation of deep penetration welding of stainless steel using geometric constraints based on experimental information  

NASA Astrophysics Data System (ADS)

Results of a numerical simulation of deep penetration welding of 304 stainless steel are presented. This numerical model calculates the temperature and fluid velocity fields in a three-dimensional workpiece undergoing deep-penetration electron beam welding. The deposition of power from the beam and energy outflow at the model-system boundaries is effected by means of time-dependent boundary conditions on the equations of energy and momentum transfer. The vapor-liquid interface defining the keyhole is represented by a surface whose temperature is that of vaporization for the steel. On this surface, are specified boundary conditions for the momentum transfer equations such that the component of the velocity normal to the keyhole vapor-liquid interface is zero. In addition, this study introduces two new numerical procedures. These procedures are based on the inclusion of experimental information concerning beam spot size and weld pool geometry into the model system via constraints and the deduction of effective keyhole shape via an inverse mapping scheme.

Lambrakos, S. G.; Metzbower, E. A.; Milewski, J.; Lewis, G.; Dixon, R.; Korzekwa, D.

1994-10-01

281

Laser weld jig  

DOEpatents

A system is provided for welding a workpiece (10, FIG. 1) along a predetermined weld line (12) that may be of irregular shape, which includes the step of forming a lip (32) on the workpiece to extend parallel to the weld line, and moving the workpiece by engaging the lip between a pair of rotatable members (34, 36). Rotation of one of the members at a constant speed, causes the workpiece to move so that all points on the weld line sequentially pass a fixed point in space (17) at a constant speed, so that a laser welding beam can be directed at that fixed point to form a weld along the weld line. The workpiece can include a reuseable jig (24) forming the lip, and with the jig constructed to detachably hold parts (22, 20) to be welded at a position wherein the weld line of the parts extends parallel to the lip on the jig.

Van Blarigan, Peter (Livermore, CA); Haupt, David L. (Livermore, CA)

1982-01-01

282

Laser weld jig  

SciTech Connect

A system is provided for welding a workpiece along a predetermined weld line that may be of irregular shape, which includes the step of forming a lip on the workpiece to extend parallel to the weld line, and moving the workpiece by engaging the lip between a pair of rotatable members. Rotation of one of the members at a constant speed, causes the workpiece to move so that all points on the weld line sequentially pass a fixed point in space at a constant speed, so that a laser welding beam can be directed at that fixed point to form a weld along the weld line. The workpiece can include a reuseable jig forming the lip, and with the jig constructed to detachably hold parts to be welded at a position wherein the weld line of the parts extends parallel to the lip on the jig.

Haupt, D.L.; Van Blarigan, P.

1982-11-09

283

Variations in welding characteristics within the Plinian air-fall deposit of the Middle Pumice eruption, Santorini, Greece  

NASA Astrophysics Data System (ADS)

The welded Plinian air-fall deposit of the Middle Pumice A (MP-A) eruption, Santorini, Greece (144.6 ka), was analysed in order to document welding characteristics and determine the factors that control welding due to the sintering of hot ash- to block-sized pyroclasts. There are vertical and lateral variations in welding intensity, with welding increasing upwards within deposit sections and decreasing laterally away from the source. Four welding grades are distinguished: a = densely-welded, b = slightly-welded, c = tack-welded, and d = non-welded. Lateral welding zones are defined by the highest welding grade observed: zone A = densely-welded (< 0.25 km from the source); zone B = slightly-welded (0.25-1.26 km); zone C = tack-welded (1.26-3.7 km), and zone D = non-welded (> 3.7 km). Pumice density increases (and porosity decreases) with welding, with the most densely-welded part having a density of 2290 kg m- 3 and a porosity of 5%. Distal, non-welded pumices have a density of 370 kg m- 3 and porosities of > 75%. Clast oblateness varies from 0.79 in the densely-welded proximal deposit sections to 0.54 in the distal, non-welded deposits in southern Thera. Strain, determined using the Rf/? method, indicates that the deposit is moderately flattened but relatively undeformed. The MP-A deposit is dacitic to andesitic in composition, becoming more mafic with stratigraphic height, where the degree of welding is highest. Welding is controlled by geochemical variations, compactional load and local variations in accumulation rate and clast sizes.

Boyce, Julie Ann; Gertisser, Ralf

2012-04-01

284

Coarsening Behavior of the (Ti, Nb)(C, N) Complex Particle in a Microalloyed Steel Weld Heat-Affected Zone Considering the Critical Particle Size  

NASA Astrophysics Data System (ADS)

Our recent report revealed the effect of critical particle size on the particle coarsening behavior of the TiN particle. In the present work, the equation for critical particle size is extended by considering the change of particle volume fraction during the continuous thermal cycle. By considering the concept of modified critical particle size, coarsening of the (Ti, Nb)(C, N) complex particle is calculated, and the calculated results are in good agreement with experimental data.

Moon, Joonoh; Kim, Sanghoon; Lee, Jongbong; Lee, Changhee

2007-11-01

285

Internal wire guide for GTAW welding  

NASA Technical Reports Server (NTRS)

A welding torch for gas tungsten arc welding apparatus has a filler metal wire guide positioned within the torch, and within the shielding gas nozzle. The wire guide is adjacent to the tungsten electrode and has a ceramic liner through which the wire is fed. This reduces the size of the torch and eliminates the outside clearance problems that exit with external wire guides. Additionally, since the wire is always within the shielding gas, oxidizing of the wire is eliminated.

Morgan, Gene E. (inventor); Dyer, Gerald E. (inventor)

1989-01-01

286

Numerical simulation of transient temperature field during laser keyhole welding of 304 stainless steel sheet  

NASA Astrophysics Data System (ADS)

A three-dimensional transient numerical model was developed to study the temperature field and molten pool shape during continuous laser keyhole welding. The volume-of-fluid (VOF) method was employed to track free surfaces. Melting and evaporation enthalpy, recoil pressure, surface tension, and energy loss due to evaporating materials were considered in this model. The enthalpy-porosity technique was employed to account for the latent heat during melting and solidification. Temperature fields and weld pool shape were calculated using FLUENT software. The calculated weld dimensions agreed reasonable well with the experimental results. The effectiveness of the developed computational procedure had been confirmed.

Wang, Renping; Lei, Yongping; Shi, Yaowu

2011-06-01

287

Low-temperature friction-stir welding of 2024 aluminum  

SciTech Connect

Solid-state, friction-stir welding (FSW) has been demonstrated to involve dynamic recrystallization producing ultra-fine, equiaxed grain structures to facilitate superplastic deformation as the welding or joining mechanism. Since the recrystallization temperature also decreases with increasing strain rate, the FSW process is somewhat complicated because the ambient temperature, the frictional heating fraction, and the adiabatic heating fraction (proportional to the product of strain and strain-rate) will all influence both the recrystallization and grain growth within the FSW zone. Significantly reducing the ambient temperature of the base metal or work pieces to be welded would be expected to reduce the residual weld-zone grain size. The practical consequences of this temperature reduction would be the achievement of low-temperature welding. This study compares the residual grain sizes and microstructures in 2024 Al friction-stir welded at room temperature ({approximately} 30 C) and low temperature ({minus} 30 C).

Benavides, S.; Li, Y.; Murr, L.E.; Brown, D.; McClure, J.C. [Univ. of Texas, El Paso, TX (United States). Dept. of Metallurgical and Materials Engineering] [Univ. of Texas, El Paso, TX (United States). Dept. of Metallurgical and Materials Engineering

1999-09-10

288

Damage Tolerance Behavior of Friction Stir Welds in Aluminum Alloys  

NASA Technical Reports Server (NTRS)

Friction stir welding is a solid state welding process used in the fabrication of various aerospace structures. Self-reacting and conventional friction stir welding are variations of the friction stir weld process employed in the fabrication of cryogenic propellant tanks which are classified as pressurized structure in many spaceflight vehicle architectures. In order to address damage tolerance behavior associated with friction stir welds in these safety critical structures, nondestructive inspection and proof testing may be required to screen hardware for mission critical defects. The efficacy of the nondestructive evaluation or the proof test is based on an assessment of the critical flaw size. Test data describing fracture behavior, residual strength capability, and cyclic mission life capability of friction stir welds at ambient and cryogenic temperatures have been generated and will be presented in this paper. Fracture behavior will include fracture toughness and tearing (R-curve) response of the friction stir welds. Residual strength behavior will include an evaluation of the effects of lack of penetration on conventional friction stir welds, the effects of internal defects (wormholes) on self-reacting friction stir welds, and an evaluation of the effects of fatigue cycled surface cracks on both conventional and selfreacting welds. Cyclic mission life capability will demonstrate the effects of surface crack defects on service load cycle capability. The fracture data will be used to evaluate nondestructive inspection and proof test requirements for the welds.

McGill, Preston; Burkholder, Jonathan

2012-01-01

289

Characterization of 2024-T351 friction stir welding joints  

Microsoft Academic Search

Characterization of macrostructure, microstructure, hardness, precipitate distribution, residual stress, and cyclic deformation\\u000a behavior of 2024-T351 friction stir welded joints has been conducted. Inhomogeneous microparameters governing the nonuniform\\u000a residual stresses and cyclic strength are discussed. The cyclic strength of the weld microregimes is controlled by grain size\\u000a and distribution of precipitates achieved during the weld process. The comprehensive information of micro-and

A. Ali; M. W. Brown; C. A. Rodopoulos; S. Gardiner

2006-01-01

290

Determination of momentum as a mean of quantifying the mechanical energy delivered by droplets during MIG/MAG welding  

NASA Astrophysics Data System (ADS)

The objective of this work was to propose and assess, under the light of modern techniques for arc visualization and welding parameter monitoring, a parameter that would quantify properly the effect of the droplets reaching the pool over the bead penetration during MIG/MAG welding (GMAW). High-speed filming shadowgraphy, synchronized with the electrical signals, was used. Dedicated computational programs were employed to measure arc lengths and size, frequency, acceleration and speed of the droplets. Calibration of the system by employing metallic spheres was used to guaranty the performance of the image recording and measurement programs. Statistics were employed for sampling size determination. A non-common approach to correlate Momentum to bead geometry is propose and discussed. The methodology was assessed through MIG/MAG bead-on-plate welds shielded with an Ar+5%O{2} blend, at three levels of currents and arc lengths. It was concluded that the proposed parameter denominated in this paper as “Effective Momentum” is the one which better represents the action of the droplets over bead formation.

Scotti, A.; Rodrigues, C. E. A. L.

2009-01-01

291

Damage Tolerance Assessment of Friction Pull Plug Welds in an Aluminum Alloy  

NASA Technical Reports Server (NTRS)

Friction stir welding is a solid state welding process used in the fabrication of cryogenic propellant tanks. Self-reacting friction stir welding is one variation of the friction stir weld process being developed for manufacturing tanks. Friction pull plug welding is used to seal the exit hole that remains in a circumferential self-reacting friction stir weld. A friction plug weld placed in a self-reacting friction stir weld results in a non-homogenous weld joint where the initial weld, plug weld, their respective heat affected zones and the base metal all interact. The welded joint is a composite plastically deformed material system with a complex residual stress field. In order to address damage tolerance concerns associated with friction plug welds in safety critical structures, such as propellant tanks, nondestructive inspection and proof testing may be required to screen hardware for mission critical defects. The efficacy of the nondestructive evaluation or the proof test is based on an assessment of the critical flaw size. Test data relating residual strength capability to flaw size in an aluminum alloy friction plug weld will be presented.

McGill, Preston; Burkholder, Jonathan

2012-01-01

292

An engineering model to simulate the thermal response of electronic devices during pulsed Nd:YAG laser welding  

SciTech Connect

A model is developed to predict the thermal response of real electronic devices during pulsed Nd:YAG laser welding. Modeling laser-part interaction requires incorporation of weld pool hydrodynamics, and laser-metal vapor and laser-surface interactions. Although important information can be obtained from these models, they are not appropriate for use in design of actual components due to computational limitations. In lieu of solving for these detailed physics, a simple model is constructed. In this model, laser-part interactions are accounted for through an empirically determined energy transfer efficiency which is developed through the use of modeling and experiments. This engineering model is appropriate since part thermal response near the weld pool and weld pool shape is not of interest here. Reasonable agreement between predictions and experimental measurements for welding of real components are indicated.

Gianoulakis, S.E.; Voth, T.E.; Fuerschbach, P.W. [Sandia National Labs., Albuquerque, NM (United States). Engineering Sciences Center; Prinzbach, J.H. [Wilson Greatbatch Ltd., Clarence, NY (United States). Technology Dept.

1996-12-31

293

C. D. Sorensen Department of Mechanical Engineering  

E-print Network

Several investigators have proposed controlling the size and shape of the weld pool based on the weld pool and controlled in the arc welding process is the size and shape of the weld pool. Several researchers have, 1983). These studies have proven the ability to control the weld pool size and shape in many cases

Eagar, Thomas W.

294

WELDING RESEARCH JANUARY 2004-S6  

E-print Network

WELDING RESEARCH JANUARY 2004-S6 ABSTRACT. The influence of microstruc- ture on the fatigue crack with improved fatigue resistance relative to the base metal. The influence of grain size on fatigue resistance fatigue re- sistance occurred predominately at low stress intensity ranges where the plastic zone size

DuPont, John N.

295

Hardness, Microstructure, and Residual Stresses in Low Carbon Steel Welding with Post-weld Heat Treatment and Temper Bead Welding  

NASA Astrophysics Data System (ADS)

This paper investigates the effects of post-weld heat treatment (PWHT) and temper bead welding (TBW) on hardness, microstructure and residual stresses in multi-layer welding on low carbon steel specimens made with two different weld geometries, viz. (1) smooth-contoured and (2) U-shaped. It was found that the PWHT technique gave overall lower hardness than the TBW technique, but the hardness values in both techniques were acceptable. Microscopy analysis showed that the TBW technique was more effective in tempering the heat affected zone as the grain size decreased slightly at the fusion line in spite of the higher temperature at the fusion line. Residual stresses measured using the hole-drilling method showed that the residual stress is not reduced below yield stress near the last bead solidified in TBW. Only PWHT gives low residual stress results in this area. High tensile residual stresses may result in sensitivity to fatigue loading.

Aloraier, Abdulkareem S.; Joshi, Suraj; Price, John W. H.; Alawadhi, Khaled

2014-04-01

296

Thermocapillary and arc phenomena in stainless steel welding  

SciTech Connect

This investigation characterized the effects of power level and Gaussian heat source size on thermocapillary-induced weld shape and estimated the relative influence of various possible arc phenomena in determining weld shape. Welds made with the CTAW process were compared with similar ones made with a conduction-mode EBW process and the differences were related to arc effects. Evidence of thermocapillary flow was readily apparent in both the GTA welds and the conduction-mode EB welds and was qualitatively similar in both. The similarity between the results obtained with the two processes serves to demonstrate that thermocapillary convection is the dominant factor in heat-to-heat weld shape variability. However, a similar one-to-one correspondence between welds produced with the two processes does not exist. Especially at high power, the EB welds showed stronger thermocapillary convection than the GTA welds. One important arc factor that limits thermocapillary flow in ar welds appears to be an increase in arc size with arc length and arc current. A non-Gaussian arc power distribution in GTAW seems to be most important in limiting the fluid flow. Apparently, the arc power distribution is more nearly rectangular in shape for an argon gas arc. At higher currents, above 200 A, plasma shear force may also be an important contributor to weld shape development. The conduction-mode EB welds demonstrate that thermocapillary flow reversal probably does not occur in welds made with a simple Gaussian heat source. The complex shape behavior is likely a result of an arc effect such as plasma shear.

Pierce, S.W.; Olson, D.L. [Colorado School of Mines, Golden, CO (United States); Burgardt, P. [Los Alamos National Lab., NM (United States)

1999-02-01

297

Fanfares & Fireworks Pool Party  

E-print Network

Highlights Fanfares & Fireworks Pool Party Notes from the Office Class Photo TheELIWeekly Fireworks & Pool Party This is a very exciting week! We have two activities for you to participate in. As always, feel free to bring your family and conversation partners. Fanfares & Fireworks On Tuesday, we

Pilyugin, Sergei S.

298

Fanfares & Fireworks Pool Party  

E-print Network

Highlights Fanfares & Fireworks Pool Party Ramadan Reminder ELI Places of Origin Notes from the Office Birthdays TheELIWeekly Fireworks & Pool Party This is a very exciting week! We have two. Fanfares & Fireworks On Wednesday, we will be going to Fanfares and Fireworks. Come listen

Pilyugin, Sergei S.

299

Effect of Pre- and Post-weld Heat Treatments on Linear Friction Welded Ti-5553  

NASA Astrophysics Data System (ADS)

Linear friction welding allows solid-state joining of near-beta ( ?) titanium alloy Ti-5553 (Ti-5Al-5V-5Mo-3Cr). In the as-welded condition, the weld zone (WZ) exhibits ? grain refinement and marked softening as compared with Ti-5553 in the solution heat treated and aged condition. The softening of the weldment is attributed to the depletion of the strengthening alpha ( ?) phase in the WZ and the adjacent thermo-mechanically affected zone (TMAZ). Specifically, in near- ? titanium alloys, the strength of the material mainly depends on the shape, size, distribution, and fraction of the primary ? and other decomposition products of the ? phase. Hence, a combination of pre- and post-weld heat treatments were applied to determine the conditions that allow mitigating the ? phase depletion in the WZ and TMAZ of the welds. The mechanical response of the welded samples to the heat treatments was determined by performing microhardness measurements and tensile testing at room temperature with an automated 3D deformation measurement system. It was found that though the joint efficiency in the as-welded condition was high (96 pct), strain localization and failure occurred in the TMAZ. The application of post-weld solution heat treatment with aging was effective in restoring ?, increasing the joint efficiency (97 to 99 pct) and inducing strain localization and failure in the parent material region.

Wanjara, Priti; Dalgaard, Elvi; Gholipour, Javad; Cao, Xinjin; Cuddy, Jonathan; Jonas, John J.

2014-10-01

300

Microhardness Testing of Aluminum Alloy Welds  

NASA Technical Reports Server (NTRS)

A weld is made when two pieces of metal are united or fused together using heat or pressure, and sometimes both. There are several different types of welds, each having their own unique properties and microstructure. Strength is a property normally used in deciding which kind of weld is suitable for a certain metal or joint. Depending on the weld process used and the heat required for that process, the weld and the heat-affected zone undergo microstructural changes resulting in stronger or weaker areas. The heat-affected zone (HAZ) is the region that has experienced enough heat to cause solid-state microstructural changes, but not enough to melt the material. This area is located between the parent material and the weld, with the grain structure growing as it progresses respectively. The optimal weld would have a short HAZ and a small fluctuation in strength from parent metal to weld. To determine the strength of the weld and decide whether it is suitable for the specific joint certain properties are looked at, among these are ultimate tensile strength, 0.2% offset yield strength and hardness. Ultimate tensile strength gives the maximum load the metal can stand while the offset yield strength gives the amount of stress the metal can take before it is 0.2% longer than it was originally. Both of these are good tests, but they both require breaking or deforming the sample in some way. Hardness testing, however, provides an objective evaluation of weld strengths, and also the difference or variation in strength across the weld and HAZ which is difficult to do with tensile testing. Hardness is the resistance to permanent or plastic deformation and can be taken at any desired point on the specimen. With hardness testing, it is possible to test from parent metal to weld and see the difference in strength as you progress from parent material to weld. Hardness around grain boundaries and flaws in the material will show how these affect the strength of the metal while still retaining the sample. This makes hardness testing a good test for identifying grain size and microstructure.

Bohanon, Catherine

2009-01-01

301

Variable polarity arc welding  

NASA Technical Reports Server (NTRS)

Technological advances generate within themselves dissatisfactions that lead to further advances in a process. A series of advances in welding technology which culminated in the Variable Polarity Plasma Arc (VPPA) Welding Process and an advance instituted to overcome the latest dissatisfactions with the process: automated VPPA welding are described briefly.

Bayless, E. O., Jr.

1991-01-01

302

Portable Weld Tester.  

ERIC Educational Resources Information Center

This training manual, which was developed for employees of an automotive plant, is designed to teach trainees to operate a portable weld tester (Miyachi MM-315). In chapter 1, the weld tester's components are illustrated and described, and the procedure for charging its batteries is explained. Chapter 2 illustrates the weld tester's parts,…

Eckert, Douglas

303

Welding Course Curriculum.  

ERIC Educational Resources Information Center

This guide is intended for use in helping students gain a fundamental background on the major aspects of the welding trade. The course emphasis is on mastery of the manipulative skills necessary to develop successful welding techniques and on acquisition of an understanding of the specialized tools and equipment used in welding. The first part…

Genits, Joseph C.

304

Instructional Guidelines. Welding.  

ERIC Educational Resources Information Center

Using the standards of the American Welding Society and the American Society of Mechanical Engineers, this welding instructional guidelines manual presents a course of study in accordance with the current practices in industry. Intended for use in welding programs now practiced within the Federal Prison System, the phases of the program are…

Fordyce, H. L.; Doshier, Dale

305

Solid state weld evaluation  

Microsoft Academic Search

Theoretical and experimental investigations currently being conducted for diffusion, inertia, and pinch welds are discussed, in conjunction with two physical model types for weld bonds. A model must encompass the causes of defective solid-state welds, the acoustic interaction, and the influence of substrate microstructure. Attention is given to the applicability of acoustic microscopy, in which certain specimen configurations can image

Graham H. Thomas

1993-01-01

306

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

SciTech Connect

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.

Mishra, S.; Chakraborty, S.; DebRoy, T. [Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802-5005 (United States)

2005-05-01

307

INSTALLATION CERTIFICATE CF-6R-MECH-03 Pool And Spa Heating Systems (Page 1 of 2)  

E-print Network

in the CEC database of certified pool pumps. 2. The pump flow rate shall be calculated based on pool sizing for outdoor pools or spas that have a heat pump or gas heater. 3. Pool system has directional inlets off-peak periods only §150(p) Pump Sizing and flow rate specification 1. The pump specified is listed

308

Gas tungsten arc welding of vanadium alloys with impurity control  

NASA Astrophysics Data System (ADS)

Gas tungsten arc welding in vanadium alloys is controlled by interstitial impurities. Techniques have been developed to weld V-4Cr-4Ti in a high-purity argon atmosphere resulting in a DBTT of -20 °C. The atmosphere was controlled by a Zr-Al getter which is activated at high temperature to obtain a clean surface then cooled and allowed to absorb hydrogen and oxygen impurities. Through the use of low-oxygen base metal and high-purity weld filler wire, a DBTT of -145 °C was obtained. Experiments using electron beam welding have shown that grain size also has an important effect on weld ductility. Introduction of nitrogen and yttrium has been used to study their effect on grain size. Using a combination of atmosphere control, alloy purity control, and grain size control, it is anticipated that V-Cr-Ti alloys will be weldable in field conditions.

Grossbeck, M. L.; King, J. F.; Nagasaka, T.; David, S. A.

2002-12-01

309

Welding High Strength Modern Line Pipe Steel  

NASA Astrophysics Data System (ADS)

The effect of modern mechanized girth welding on high strength line pipe has been investigated. The single cycle grain coarsened heat affected zone in three grade 690 line pipe steels and a grade 550 steel has been simulated using a Gleeble thermo-mechanical simulator. The continuous cooling transformation diagrams applicable to the grain coarsened heat affected zone resulting from a range of heat inputs applicable to modern mechanized welding have been established by dilatometry and metallography. The coarse grained heat affected zone was found to transform to lath martensite, bainite, and granular bainite depending on the cooling rate. The impact toughness of the steels was measured using Charpy impact toughness and compared to the toughness of the grain coarsened heat affected zone corresponding to a welding thermal cycle. The ductile to brittle transition temperature was found to be lowest for the steel with the highest hardenability. The toughness resulting from three different thermal cycles including a novel interrupted intercritically reheated grain coarsened (NTR ICR GC HAZ) that can result from dual torch welding at fast travel speed and close torch spacing have been investigated. All of the thermally HAZ regions showed reduced toughness that was attributed to bainitic microstructure and large effective grain sizes. Continuous cooling transformation diagrams for five weld metal chemistries applicable to mechanized pulsed gas metal arc welding of modern high strength pipe steel (SMYS>550 MPa) have been constructed. Welds at heat inputs of 1.5 kJmm-1 and 0.5 kJmm-1 have been created for simulation and analysis. Dilatometric analysis was performed on weld metal specimens cut from single pass 1.5 kJmm-1 as deposited beads. The resulting microstructures were found to range from martensite to polygonal ferrite. There is excellent agreement between the simulated and as deposited weld metal regions. Toughness testing indicates improved energy absorption at -20 °C with increased cooling time.

Goodall, Graeme Robertson

310

What is a Welding Engineer?  

NSDL National Science Digital Library

This document from Weld-Ed, the National Center for Welding Education and Training, presents the fundamentals of the career path of welding engineer. It lists the typical job responsibilities, educational requirements, recommended areas of knowledge and/or skill, and salary/wage data for welding engineers. It would be an excellent addition to any welding or materials joining classroom, or to recruitment resources for welding two-year or certification programs.

311

What is a Welding Technician?  

NSDL National Science Digital Library

This document from Weld-Ed, the National Center for Welding Education and Training, presents the fundamentals of the career path of welding technician. It lists the typical job responsibilities, educational requirements, recommended areas of knowledge and/or skill, and salary/wage data for welding technicians. It would be an excellent addition to any welding or materials joining classroom, or to recruitment resources for welding two-year or certification programs.

312

Microstructure and failure behavior of dissimilar resistance spot welds between low carbon galvanized and austenitic stainless steels  

Microsoft Academic Search

Resistance spot welding was used to join austenitic stainless steel and galvanized low carbon steel. The relationship between failure mode and weld fusion zone characteristics (size and microstructure) was studied. It was found that spot weld strength in the pullout failure mode is controlled by the strength and fusion zone size of the galvanized steel side. The hardness of the

P. Marashi; M. Pouranvari; S. Amirabdollahian; A. Abedi; M. Goodarzi

2008-01-01

313

WELD—an environment for Web-based electronic design  

Microsoft Academic Search

Increasing size and geographical separation of design data and teams has created a need for a network-based electronic design environment that is scaleable, adaptable, secure, highly available, and cost effective. In the WELD project we are evaluating aspects of the network integration and communication infrastructure needed to enable such a distributed design environment. The architecture of WELD and the components

Francis L. Chan; Mark D. Spiller; A. Richard Newton

1998-01-01

314

In-service Inspection Ultrasonic Testing of Reactor Pressure Vessel Welds for Assessing Flaw Density and Size Distribution per 10 CFR 50.61a, Alternate Fracture Toughness Requirements  

SciTech Connect

Pressurized thermal shock (PTS) events are system transients in a pressurized water reactor (PWR) in which there is a rapid operating temperature cool-down that results in cold vessel temperatures with or without repressurization of the vessel. The rapid cooling of the inside surface of the reactor pressure vessel (RPV) causes thermal stresses that can combine with stresses caused by high pressure. The aggregate effect of these stresses is an increase in the potential for fracture if a pre-existing flaw is present in a material susceptible to brittle failure. The ferritic, low alloy steel of the reactor vessel beltline adjacent to the core, where neutron radiation gradually embrittles the material over the lifetime of the plant, can be susceptible to brittle fracture. The PTS rule, described in the Code of Federal Regulations, Title 10, Section 50.61 (§50.61), “Fracture Toughness Requirements for Protection against Pressurized Thermal Shock Events,” adopted on July 23, 1985, establishes screening criteria to ensure that the potential for a reactor vessel to fail due to a PTS event is deemed to be acceptably low. The U.S. Nuclear Regulatory Commission (NRC) completed a research program that concluded that the risk of through-wall cracking due to a PTS event is much lower than previously estimated. The NRC subsequently developed a rule, §50.61a, published on January 4, 2010, entitled “Alternate Fracture Toughness Requirements for Protection Against Pressurized Thermal Shock Events” (75 FR 13). Use of the new rule by licensees is optional. The §50.61a rule differs from §50.61 in that it requires licensees who choose to follow this alternate method to analyze the results from periodic volumetric examinations required by the ASME Code, Section XI, Rules for Inservice Inspection (ISI) of Nuclear Power Plants. These analyses are intended to determine if the actual flaw density and size distribution in the licensee’s reactor vessel beltline welds are bounded by the flaw density and size distribution values used in the PTS technical basis. Under a contract with the NRC, Pacific Northwest National Laboratory (PNNL) has been working on a program to assess the ability of current inservice inspection (ISI)-ultrasonic testing (UT) techniques, as qualified through ASME Code, Appendix VIII, Supplements 4 and 6, to detect small fabrication or inservice-induced flaws located in RPV welds and adjacent base materials. As part of this effort, the investigators have pursued an evaluation, based on the available information, of the capability of UT to provide flaw density/distribution inputs for making RPV weld assessments in accordance with §50.61a. This paper presents the results of an evaluation of data from the 1993 Browns Ferry Nuclear Plant, Unit 3, Spirit of Appendix VIII reactor vessel examination, a comparison of the flaw density/distribution from this data with the distribution in §50.61a, possible reasons for differences, and plans and recommendations for further work in this area.

Sullivan, Edmund J.; Anderson, Michael T.; Norris, Wallace

2012-09-17

315

Surface preparation effects on GTA weld shape in JBK-75 stainless steel  

SciTech Connect

The results of a study are reported here on the effects of surface preparation on the shape of autogenous gas tungsten arc (GTA) welds in JBK-75, an austenitic precipitation hardenable stainless steel similar to A286. Minor changes in surface preparation produced substantial changes in the fusion zone shape and welding behavior of this alloy. Increased and more consistent depth of fusion (higher d/w ratios) along with improved arc stability and less arc wander resulted from wire brushing and other abrasive surface preparations, although chemical and machining methods did not produce any increase in depth of fusion. Abrasive treatments roughen the surface, increase the surface area, increase the surface oxide thickness, and entrap oxide. The increased weld d/w ratio is attributed to oxygen added to the weld pool from the surface oxide on the base metal. The added oxygen alters the surface-tension-driven fluid flow pattern in the weld pool. Increased depth of fusion in wire-fed U-groove weld joints also resulted when welding wire with a greater surface oxide thickness was used. Increasing the amount of wire brushing produced even deeper welds. However, a maximum in depth of fusion was observed with further wire brushing, beyond which weld fusion depth decreased.

Campbell, R.D.; Robertson, A.M. (AWS Precision Joining Center, Wheat Ridge, CO (United States)); Heiple, C.R. (EG and G Rocky Flats Plant, Golden (Colombia)); Sturgill, P.L.; Jamsay, R.

1993-02-01

316

Some studies on temperature profiles in AISI 304 stainless steel sheet during laser beam welding using FE simulation  

Microsoft Academic Search

The investigation of transient temperature profiles of a weld joint produced by the laser welding process is presented. A\\u000a three-dimensional finite element model is developed using a commercial finite element code ANSYS in order to obtain the behavior\\u000a of temperature field and molten pool shape during the welding process. A three-dimensional conical Gaussian heat source is\\u000a employed as a heat

N. Siva Shanmugam; G. Buvanashekaran; K. Sankaranarayanasamy; K. Manonmani

2009-01-01

317

Welding, terms and definitions  

SciTech Connect

This book provides a dictionary of the technical language used in the welding industry. Its purpose is to establish standard terms to aid in the communication of welding information. Since it is intended to be a comprehensive compilation of welding terminology, nonstandard terms used in the welding industry are also included. All terms are either standard or non-standard. They are arranged in the conventional dictionary letter-by-letter alphabetical sequence. A total of 946 terms are defined and the definitions are illustrated by 41 Figures. Also included is the Master Chart of Welding and Allied Processes and the Joining Method Diagram with corollary classification diagrams.

Not Available

1985-01-01

318

Method for welding beryllium  

DOEpatents

A method is provided for joining beryllium pieces which comprises: depositing aluminum alloy on at least one beryllium surface; contacting that beryllium surface with at least one other beryllium surface; and welding the aluminum alloy coated beryllium surfaces together. The aluminum alloy may be deposited on the beryllium using gas metal arc welding. The aluminum alloy coated beryllium surfaces may be subjected to elevated temperatures and pressures to reduce porosity before welding the pieces together. The aluminum alloy coated beryllium surfaces may be machined into a desired welding joint configuration before welding. The beryllium may be an alloy of beryllium or a beryllium compound. The aluminum alloy may comprise aluminum and silicon.

Dixon, Raymond D. (Los Alamos, NM); Smith, Frank M. (Espanola, NM); O'Leary, Richard F. (Los Alamos, NM)

1997-01-01

319

Shielding gas oxygen equivalent in weld metal microstructure optimization  

SciTech Connect

One of the compositional variables that strongly influence low-carbon structural steel weld metal microstructure and mechanical properties is the weld metal oxygen content. As the weld metal oxygen content varies, a change in microstructure occurs. At low concentrations of oxygen, ferrite with aligned or nonaligned second phases may become predominant, slightly higher oxygen levels may result in the formation of the desired acicular ferrite, and further increases in the oxygen content to promote the formation of grain boundary ferrite. The start of austenite decomposition and ferrite nucleation are very sensitive to variations in the amount of oxygen present in the weld metal. Thus, in gas metal arc welding, adjusting the shielding gas oxygen potential provides a means of controlling the weld metal oxygen content. Bead-in-groove gas metal arc welding experiments were performed on HSLA steel coupons using three different welding wires and two heat inputs. A total of 17 different argon-based oxygen and carbon dioxide shielding gas mixtures was used. Complete metallographic and chemical analyses were carried out to evaluate the weld specimens. Sub-size Charpy V-notch toughness testing was performed on selected welds.

Onsoeien, M.I. [SINTEF Materials Technology, Trondheim (Norway); Liu, S.; Olson, D.L. [Colorado School of Mines, Golden, CO (United States). Center for Welding and Joining Research

1996-07-01

320

Welding of 316L Austenitic Stainless Steel with Activated Tungsten Inert Gas Process  

NASA Astrophysics Data System (ADS)

The use of activating flux in TIG welding process is one of the most notable techniques which are developed recently. This technique, known as A-TIG welding, increases the penetration depth and improves the productivity of the TIG welding. In the present study, four oxide fluxes (SiO2, TiO2, Cr2O3, and CaO) were used to investigate the effect of activating flux on the depth/width ratio and mechanical property of 316L austenitic stainless steel. The effect of coating density of activating flux on the weld pool shape and oxygen content in the weld after the welding process was studied systematically. Experimental results indicated that the maximum depth/width ratio of stainless steel activated TIG weld was obtained when the coating density was 2.6, 1.3, 2, and 7.8 mg/cm2 for SiO2, TiO2, Cr2O3, and CaO, respectively. The certain range of oxygen content dissolved in the weld, led to a significant increase in the penetration capability of TIG welds. TIG welding with active fluxes can increase the delta-ferrite content and improves the mechanical strength of the welded joint.

Ahmadi, E.; Ebrahimi, A. R.

2015-02-01

321

Swimming Pools and Molluscum Contagiosum  

MedlinePLUS

Molluscum Home > Swimming Pools > Swimming Pools and Molluscum Contagiosum Parents and others often ask if molluscum virus can be spread in swimming pools. There is also concern that it can be spread ...

322

How to map your industry's profit pool.  

PubMed

Many managers chart strategy without a full understanding of the sources and distribution of profits in their industry. Sometimes they focus their sights on revenues instead of profits, mistakenly assuming that revenue growth will eventually translate into profit growth. In other cases, they simply lack the data or the analytical tools required to isolate and measure variations in profitability. In this Manager's Tool Kit, the authors present a way to think clearly about where the money's being made in any industry. They describe a framework for analyzing how profits are distributed among the activities that form an industry's value chain. Such an analysis can provide a company's managers with a rich understanding of their industry's profit structure--what the authors call its profit pool--enabling them to identify which activities are generating disproportionately large or small shares of profits. Even more important, a profit-pool map opens a window onto the underlying structure of the industry, helping managers see the various forces that are determining the distribution of profits. As such, a profit-pool map provides a solid basis for strategic thinking. Mapping a profit pool involves four steps: defining the boundaries of the pool, estimating the pool's overall size, estimating the size of each value-chain activity in the pool, and checking and reconciling the calculations. The authors briefly describe each step and then apply the process by providing a detailed example of a hypothetical retail bank. They conclude by looking at ways of organizing the data in chart form as a first step toward plotting a profit-pool strategy. PMID:10179650

Gadiesh, O; Gilbert, J L

1998-01-01

323

Explosive welding of pipes  

NASA Astrophysics Data System (ADS)

For connection by welding it is suggested to use the explosive welding method. This method is rather new. Nevertheless, it has become commonly used among the technological developments. This method can be advantageous (saving material and physical resources) comparing to its statical analogs (electron-beam welding, argon-arc welding, plasma welding, gas welding, etc.), in particular, in hard-to-reach areas due to their geographic and climatic conditions. The suggestion is to use water as filler. The principle of non-compressibility of liquid under quasi-dynamic loading is used. In one-dimensional gasdynamic and elastic-plastic calculations we determined non-deformed mass of water. Model experiments with pipes having radii R = 57 mm confirmed results of the calculations and the possibility in principle to weld pipes by explosion with use of water as filler.

Drennov, O.; Burtseva, O.; Kitin, A.

2006-08-01

324

Robotic Welding Of Injector Manifold  

NASA Technical Reports Server (NTRS)

Brief report presents history, up through October 1990, of continuing efforts to convert from manual to robotic gas/tungsten arc welding in fabrication of main injector inlet manifold of main engine of Space Shuttle. Includes photographs of welding machinery, welds, and weld preparations. Of interest to engineers considering establishment of robotic-welding facilities.

Gilbert, Jeffrey L.; Shelley, D. Mark

1992-01-01

325

Characterization of tool wear and weld optimization in the friction-stir welding of cast aluminum 359+20% SiC metal-matrix composite  

SciTech Connect

Tool wear for threaded steel pin tools declines with decreasing rotation speed and increasing traverse or weld speeds for the friction-stir welding (FSW) of Al 359+20% SiC metal-matrix composite (MMC). Less than 10% tool wear occurs when the threaded tool erodes to a self-optimized shape resembling a pseudo-hour glass at weld traverse distances in excess of 3 m. There is only a 7% reduction in the SiC mean particle size in the weld zone for self-optimized pin tools with no threads as compared with a 25% variation for threaded tools wearing significantly at the start of welding. The weld zone becomes more homogeneous for efficient welding with self-optimized tools, and there is a reduction in the weld zone grain size due to dynamic recrystallization, which facilitates the solid-state flow. Transmission electron microscopy shows little difference in the dislocation density from the base material to the weld zone, but there is a propensity of dislocation loops in the weld zone. The weld zone is observed to harden by as much as 30%, in contrast to the base material, as a consequence of the recrystallized grain size reduction and the SiC particles distributed therein.

Fernandez, G.J.; Murr, L.E

2004-03-15

326

Microstructural Characteristics of a Stainless Steel/Copper Dissimilar Joint Made by Laser Welding  

NASA Astrophysics Data System (ADS)

The microstructures and its formation mechanism of a stainless steel/copper dissimilar joint by laser welding were investigated. It was found that the two modes of joining, i.e., welding-brazing and fusion welding, depend on different processing parameters. In the welding-brazing mode, the interface between copper and the fusion zone has scraggy morphology because the molten pool is frozen by solid copper with high thermal conductivity. The interdiffusion of elements occurs in the neighborhood of the interface, which leads to the metallurgy bond of the mode. In the fusion welding mode, the liquid phase in the fusion zone undergoes not only primary but also secondary liquid separation due to the high cooling rate and high supercooling level of laser welding. Some microcracks generated in the fusion zone by thermal stress mismatch are healed by liquid copper filling.

Chen, Shuhai; Huang, Jihua; Xia, Jun; Zhang, Hua; Zhao, Xingke

2013-08-01

327

CW/PW dual-beam YAG laser welding of steel/aluminum alloy sheets  

NASA Astrophysics Data System (ADS)

The lap welding of JSC270CC steel and A6111-T4 aluminum alloys were carried out by a dual-beam YAG laser with the continuous wave (CW) and pulse wave (PW) modes. The microstructure of the welded joints were examined with SEM, EPMA while the properties were checked with microhardness tester and tensile testing machine. It was shown that the dual-beam laser welding can effectively reduce or avoid the formation of the blowholes in the welded joints. The PW laser beam penetrated the welding pool, leading to the root-shape structures with enhanced bonding strength at the weld interface. A 10 ?m intermetallic compound (IMC) layer was generated at the interface. The shearing strength of lap joint was measured to be 128 MPa.

Yan, Shi; Hong, Zhang; Watanabe, Takehiro; Jingguo, Tang

2010-07-01

328

Processing-Microstructure Relationships in Friction Stir Welding of MA956 Oxide Dispersion Strengthened Steel  

NASA Astrophysics Data System (ADS)

A comprehensive set of processing-microstructure relationships is presented for friction stir welded oxide dispersion strengthened MA956 steel. Eight rotational speed/traverse speed combinations were used to produce friction stir welds on MA956 plates using a polycrystalline cubic boron nitride tool. Weld conditions with high thermal input produced defect-free, full-penetration welds. Electron backscatter diffraction results showed a significant increase in grain size, a persistent body centered cubic torsional texture in the stir zone, and a sharp transition in grain size across the thermo-mechanically affected zone sensitive to weld parameters. Micro-indentation showed an asymmetric reduction in hardness across a transverse section of the weld. This gradient in hardness was greatly increased with higher heat inputs. The decrease in hardness after welding correlates directly with the increase in grain size and may be explained with a Hall-Petch type relationship.

Baker, Bradford W.; Menon, E. Sarath K.; McNelley, Terry R.; Brewer, Luke N.; El-Dasher, Bassem; Farmer, Joseph C.; Torres, Sharon G.; Mahoney, Murray W.; Sanderson, Samuel

2014-12-01

329

The Vernal Pool Association  

NSDL National Science Digital Library

This site is based at Reading Memorial High School in Reading, MA. It features general information defining and describing vernal pools as a habitat type, including an illustrated cartoon series. Resources for educators and students include suggestions for classroom and field trip activities, examples of school projects, field guides, and teacher resources such as workshops. While this site contains several references to state-specific resources and regulations, it is relevant and useful outside of Massachusetts wherever vernal pools are found. The teacher responsible for the text on this site spent a sabbatical developing a resource kit for educators, which is available for purchase. Links are provided to scientific researchers conducting vernal pool studies, including their methods and results. There is an extensive page of resources, both digital in print. Educators and students are encouraged to download and use the collection of 78 slides of vernal pools and associated species on this site.

Leo Kenney

330

Swimming Pool Safety  

MedlinePLUS

... ladders to prevent access by children. Other protection products, when used with an “isolation” fence, may be ... Never dive through inner tubes or other pool toys. Learn how to dive properly by taking classes. ...

331

An integrated meso-scale numerical model of melting and solidification in laser welding  

NASA Astrophysics Data System (ADS)

The authors present an integrated numerical model for the simulation of laser spot welding of an aluminium alloy at meso-scale in 2D. This model deals with the melting of the parent materials which form the weld pool and the subsequent solidification of the liquid metal in the pool, during the welding process. The melting of the parent materials due to the applied heating power is an important phenomenon, which determines the conditions at the onset of solidification, such as the geometry of the weld pool and the distribution of the temperature field. An enthalpy method is employed to predict the melting during the heating phase of welding. A Gaussian distribution is used to model the heat input from the laser. Once the laser beam is switched off and the melting halts, solidification commences. The UCD front tracking model [1,2] for alloy solidification is applied to predict the advancement of the columnar dendritic front, and a volume-averaging formulation is used to simulate nucleation and growth of equiaxed dendrites. A mechanical blocking criterion is used to define dendrite coherency, and the columnar-to-equiaxed transition within the weld pool is predicted.

Duggan, G.; Tong, M.; Browne, D. J.

2012-01-01

332

Critical Initial Flaw Size Analysis  

NASA Technical Reports Server (NTRS)

An independent assessment was conducted to determine the critical initial flaw size (CIFS) for the flange-to-skin weld in the Ares I-X Upper Stage Simulator (USS). The USS consists of several "tuna can" segments that are approximately 216 inches in diameter, 115 inches tall, and 0.5 inches thick. A 6 inch wide by 1 inch thick flange is welded to the skin and is used to fasten adjacent tuna cans. A schematic of a "tuna can" and the location of the flange-to-skin weld are shown in Figure 1. Gussets (shown in yellow in Figure 1) are welded to the skin and flange every 10 degrees around the circumference of the "tuna can". The flange-to-skin weld is a flux core butt weld with a fillet weld on the inside surface, as illustrated in Figure 2. The welding process may create loss of fusion defects in the weld that could develop into fatigue cracks and jeopardize the structural integrity of the Ares I-X vehicle. The CIFS analysis was conducted to determine the largest crack in the weld region that will not grow to failure within 4 lifetimes, as specified by NASA standard 5001 & 5019 [1].

Dawicke, David S.; Raju, Ivatury S.; Cheston, Derrick J.

2008-01-01

333

Bobbin-Tool Friction-Stir Welding of Thick-Walled Aluminum Alloy Pressure Vessels  

SciTech Connect

It was desired to assemble thick-walled Al alloy 2219 pressure vessels by bobbin-tool friction-stir welding. To develop the welding-process, mechanical-property, and fitness-for-service information to support this effort, extensive friction-stir welding-parameter studies were conducted on 2.5 cm. and 3.8 cm. thick 2219 Al alloy plate. Starting conditions of the plate were the fully-heat-treated (-T62) and in the annealed (-O) conditions. The former condition was chosen with the intent of using the welds in either the 'as welded' condition or after a simple low-temperature aging treatment. Since preliminary stress-analyses showed that stresses in and near the welds would probably exceed the yield-strength of both 'as welded' and welded and aged weld-joints, a post-weld solution-treatment, quenching, and aging treatment was also examined. Once a suitable set of welding and post-weld heat-treatment parameters was established, the project divided into two parts. The first part concentrated on developing the necessary process information to be able to make defect-free friction-stir welds in 3.8 cm. thick Al alloy 2219 in the form of circumferential welds that would join two hemispherical forgings with a 102 cm. inside diameter. This necessitated going to a bobbin-tool welding-technique to simplify the tooling needed to react the large forces generated in friction-stir welding. The bobbin-tool technique was demonstrated on both flat-plates and plates that were bent to the curvature of the actual vessel. An additional issue was termination of the weld, i.e. closing out the hole left at the end of the weld by withdrawal of the friction-stir welding tool. This was accomplished by friction-plug welding a slightly-oversized Al alloy 2219 plug into the termination-hole, followed by machining the plug flush with both the inside and outside surfaces of the vessel. The second part of the project involved demonstrating that the welds were fit for the intended service. This involved determining the room-temperature tensile and elastic-plastic fracture-toughness properties of the bobbin-tool friction-stir welds after a post-weld solution-treatment, quenching, and aging heat-treatment. These mechanical properties were used to conduct fracture-mechanics analyses to determine critical flaw sizes. Phased-array and conventional ultrasonic non-destructive examination was used to demonstrate that no flaws that match or exceed the calculated critical flaw-sizes exist in or near the friction-stir welds.

Dalder, E C; Pastrnak, J W; Engel, J; Forrest, R S; Kokko, E; Ternan, K M; Waldron, D

2007-06-06

334

Influence on the dilution by laser welding of aluminum with magnetic stirring  

NASA Astrophysics Data System (ADS)

The Aluminum 6xxx alloys are well-known for their high susceptibility to hot cracking. It has been reported that this problem can be effectively resolved by introducing silicon into the molten pool. However, the high welding speed by laser welding process results in an inhomogeneous dilution of the silicon, which may lead to hot cracks in the Sipoor area. The idea of applying a low frequency magnetic field during laser welding process has been already carried out recently in order to make a stir effect inside the molten pool and therefore to improve the element dilution in the weld joint. In this paper, the effects of the magnetic field on the melt flow as well as the element dilution are shown by applying copper as 'tracer' inside the molten pool. Several methods were designed with different forms of copper at different positions in the workpieces to visualize the melt flow and the corresponding element dilution in different areas of the molten pool. In addition, laser welding with AlSi18 filler wire was also conducted to realize a real welding process comparing to that with 'tracer'. WDX analysis was then carried out to investigate how silicon distributed inside the welds with the help of magnetic stirring. The results demonstrate that a DC magnetic field, with its direction coaxial to the laser, tends to modify the melt flow dynamics at flux density up to 100 mT. The results of laser welding with filler wire showed that by the help of an AC magnetic field with a frequency up to 10 Hz and flux density above 100 mT, the element dilution could be improved in the weld joint. The WDX analysis showed that under the influence of an alternating magnetic field a periodicity of the silicon distribution can be achieved, which depends greatly on the magnetic frequency.

Tang, Z.; Gatzen, M.

335

VPPA weld model evaluation  

NASA Technical Reports Server (NTRS)

NASA uses the Variable Polarity Plasma Arc Welding (VPPAW) process extensively for fabrication of Space Shuttle External Tanks. This welding process has been in use at NASA since the late 1970's but the physics of the process have never been satisfactorily modeled and understood. In an attempt to advance the level of understanding of VPPAW, Dr. Arthur C. Nunes, Jr., (NASA) has developed a mathematical model of the process. The work described in this report evaluated and used two versions (level-0 and level-1) of Dr. Nunes' model, and a model derived by the University of Alabama at Huntsville (UAH) from Dr. Nunes' level-1 model. Two series of VPPAW experiments were done, using over 400 different combinations of welding parameters. Observations were made of VPPAW process behavior as a function of specific welding parameter changes. Data from these weld experiments was used to evaluate and suggest improvements to Dr. Nunes' model. Experimental data and correlations with the model were used to develop a multi-variable control algorithm for use with a future VPPAW controller. This algorithm is designed to control weld widths (both on the crown and root of the weld) based upon the weld parameters, base metal properties, and real-time observation of the crown width. The algorithm exhibited accuracy comparable to that of the weld width measurements for both aluminum and mild steel welds.

Mccutcheon, Kimble D.; Gordon, Stephen S.; Thompson, Paul A.

1992-01-01

336

Welding arc plasma physics  

NASA Technical Reports Server (NTRS)

The problems of weld quality control and weld process dependability continue to be relevant issues in modern metal welding technology. These become especially important for NASA missions which may require the assembly or repair of larger orbiting platforms using automatic welding techniques. To extend present welding technologies for such applications, NASA/MSFC's Materials and Processes Lab is developing physical models of the arc welding process with the goal of providing both a basis for improved design of weld control systems, and a better understanding of how arc welding variables influence final weld properties. The physics of the plasma arc discharge is reasonably well established in terms of transport processes occurring in the arc column itself, although recourse to sophisticated numerical treatments is normally required to obtain quantitative results. Unfortunately the rigor of these numerical computations often obscures the physics of the underlying model due to its inherent complexity. In contrast, this work has focused on a relatively simple physical model of the arc discharge to describe the gross features observed in welding arcs. Emphasis was placed of deriving analytic expressions for the voltage along the arc axis as a function of known or measurable arc parameters. The model retains the essential physics for a straight polarity, diffusion dominated free burning arc in argon, with major simplifications of collisionless sheaths and simple energy balances at the electrodes.

Cain, Bruce L.

1990-01-01

337

Welding of Metallic Foil with Electron Beam  

NASA Astrophysics Data System (ADS)

In this study, microelectron beam welding was applied to the joining of two thin metal foils. An electron beam is adaptable to microwelding due to its deep penetration and thin width. The foil materials used were SUS and Ti with a thickness of 20 µm. The relationship between the input energy of electron beam irradiation and the size of the heat affected zone was investigated. Furthermore, spot welding and overlap welding were carried out for foils of either the same or dissimilar materials. The surface and cross section of the welded zone were observed by a scanning electron microscope (SEM) or confocal laser scanning microscope (CLSM). In the case of the same material, it was possible to weld two overlapped Ti foils (marked as Ti/Ti) with thickness of 20 µm. In the case of dissimilar materials, it was possible to weld SUS304 was top and Ti was bottom (marked as SUS304/Ti) with thickness of 20 µm. The results show that microwelding can be considered a new technology for microelectrical mechanical systems (MEMS) in addition to microfabrication.

Ogawa, Hiroki; Yang, Ming; Matsumoto, Yukiko; Guo, Wei

338

Analysis of effect of temperature gradients on surface-tension phenomena in gas-tungsten-arc welds  

SciTech Connect

Fluid motion directed by surface tension is considered as a contributor to heat penetration in a weld pool. The potential phenomena at the gas-liquid interface were analyzed, and the dependence of surface motion on temperature in the gas-tungsten-arc (GTA) welding process was examined. An existing heat-transfer model was used and was able to predict weld size to +- 50% of the actual value. A momentum-transfer equation was derived by considering the contribution of Lorentz force. The momentum boundary condition was developed and was able to predict the Marangoni effect. The magnitude of surface-tension-driven force is comparable to the gravitational force on one gram. An empirical approach was proposed to couple heat-transfer and momentum-transfer phenomena. A dimensional analysis identified the pertinent dimensionless groups as Reynolds, Weber, Froude, Peclet, and Power numbers and a dimensionless velocity. A simplified form of the correction was developed by combining dimensionless groups to yield a correlation with the Bond, Prandtl, and modified power numbers. Future experimental work was proposed to test the functionality of the dimensionless groups.

Lee, H.A.; Chien, P.S.J.

1982-10-01

339

Low-Temperature Friction-Stir Welding of 2024 Aluminum  

NASA Technical Reports Server (NTRS)

Solid state friction-stir welding (FSW) has been demonstrated to involve dynamic recrystallization producing ultra-fine, equiaxed grain structures to facilitate superplastic deformation as the welding or joining mechanism. However, the average residual, equiaxed, grain size in the weld zone has ranged from roughly 0.5 micron to slightly more than 10 micron, and the larger weld zone grain sizes have been characterized as residual or static grain growth as a consequence of the temperatures in the weld zone (where center-line temperatures in the FSW of 6061 Al have been shown to be as high as 480C or -0.8 T(sub M) where T(sub M) is the absolute melting temperature)). In addition, the average residual weld zone grain size has been observed to increase near the top of the weld, and to decrease with distance on either side of the weld-zone centerline, an d this corresponds roughly to temperature variations within the weld zone. The residual grain size also generally decreases with decreasing FSW tool rotation speed. These observations are consistent with the general rules for recrystallization where the recrystallized grain size decreases with increasing strain (or deformation) at constant strain rate, or with increasing strain-rate, or with increasing strain rate at constant strain; especially at lower ambient temperatures, (or annealing temperatures). Since the recrystallization temperature also decreases with increasing strain rate, the FSW process is somewhat complicated because the ambient temperature, the frictional heating fraction, and the adiabatic heating fraction )proportional to the product of strain and strain-rate) will all influence both the recrystallization and growth within the FSW zone. Significantly reducing the ambient temperature of the base metal or work pieces to be welded would be expected to reduce the residual weld-zone grain size. The practical consequences of this temperature reduction would be the achievement of low temperature welding. This study compares the residual grain sizes and microstructures in 2024 Al friction-stir welded at room temperature (about 30C and low temperature (-30C).

Benavides, S.; Li, Y.; Murr, L. E.; Brown, D.; McClure, J. C.

1998-01-01

340

A heat-transfer and fluid-flow-based model to obtain a specific weld geometry using various combinations of welding variables  

NASA Astrophysics Data System (ADS)

Numerical heat transfer and fluid flow models have provided significant insight into welding processes and welded materials that could not have been achieved otherwise. However, the use of these models has been limited by two major problems. First, the model predictions do not always agree with the experimental results because some input parameters such as the arc efficiency cannot be accurately prescribed. Second, and more important, these models cannot determine multiple pathways or sets of welding variables that can lead to a particular weld attribute such as the weld pool geometry, which is defined by an equilibrium temperature surface. Here we show that the computational heat transfer and fluid flow models of fusion welding can overcome the aforementioned difficulties by combining with a genetic algorithm. The reliability of the convective heat transfer model can be significantly improved by optimizing the values of the uncertain input parameters from a limited volume of the experimental data. Furthermore, the procedure can calculate multiple sets of welding variables, each leading to the same weld geometry. These multiple paths were obtained via a global search using a genetic algorithm within the phenomenological framework of the equations of conservation of mass, momentum, and energy. This computational procedure was applied to the gas tungsten arc welding of Ti-6Al-4V alloy to calculate various sets of welding variables to achieve a specified weld geometry. The calculated sets of welding parameters showed wide variations of values. However, each set of welding parameters resulted in a specified geometry showing the effectiveness of the computational procedure.

Mishra, S.; DebRoy, T.

2005-08-01

341

GMA-laser Hybrid Welding of High-strength Fine-grain Structural Steel with an Inductive Preheating  

NASA Astrophysics Data System (ADS)

The industrial useof GMA-laser hybrid welding has increased in the last 10 years, due to the brilliant quality of the laser beam radiation, and higher laser output powers. GMA-laser hybrid welding processes operate in a common molten pool. The combination of the laser beam and the arc results in improved welding speed, penetration depth, heat affected zone and gap bridgeability. Single-layer, GMA-laser hybrid welding processes have been developed for high-strength fine-grain structural steels with a grade of S690QL and a thickness of 15 mm and 20 mm. In addition, the welding process is assisted by an integrated, inductive preheating process to improve the mechanical properties of the welding seam. By using the determined parameters regarding the energy per unit length, and the preheating temperature, welding seams with high quality can be achieved.

Lahdo, Rabi; Seffer, Oliver; Springer, André; Kaierle, Stefan; Overmeyer, Ludger

342

Welding and joining: A compilation  

NASA Technical Reports Server (NTRS)

A compilation is presented of NASA-developed technology in welding and joining. Topics discussed include welding equipment, techniques in welding, general bonding, joining techniques, and clamps and holding fixtures.

1975-01-01

343

Computerized adaptive control weld skate with CCTV weld guidance project  

NASA Technical Reports Server (NTRS)

This report summarizes progress of the automatic computerized weld skate development portion of the Computerized Weld Skate with Closed Circuit Television (CCTV) Arc Guidance Project. The main goal of the project is to develop an automatic welding skate demonstration model equipped with CCTV weld guidance. The three main goals of the overall project are to: (1) develop a demonstration model computerized weld skate system, (2) develop a demonstration model automatic CCTV guidance system, and (3) integrate the two systems into a demonstration model of computerized weld skate with CCTV weld guidance for welding contoured parts.

Wall, W. A.

1976-01-01

344

EVALUATION OF CONSTANT CURRENT WELD CONTROL FOR PINCH WELDING  

SciTech Connect

Modern weld controllers typically use current to control the weld process. SRS uses a legacy voltage control method. This task was undertaken to determine if the improvements in the weld control equipment could be implemented to provide improvements to the process control. The constant current mode of operation will reduce weld variability by about a factor of 4. The constant voltage welds were slightly hotter than the constant current welds of the same nominal current. The control mode did not appear to adversely affect the weld quality, but appropriate current ranges need to be established and a qualification methodology for both welding and shunt calibrations needs to be developed and documented.

Korinko, P; STANLEY, S; HOWARD, H

2005-10-11

345

LECHUGUILLA CAVE POOL CHEMISTRY, 1986-1999  

Microsoft Academic Search

In May 1986, cavers dug into Lechuguilla Cave, in southeastern New Mexico, USA. Subsequent explo- ration and research have demonstrated that Lechuguilla is a world-class cave, both in size and in spele- ological importance. Of particular interest to hydrologists and geochemists are the numerous isolated pools throughout much of the cave. Since 1986, close to 200 water samples have been

H. J. TURIN; M. A. PLUMMER

346

A Compact Gas/Tungsten-Arc Welding Torch  

NASA Technical Reports Server (NTRS)

Compact gas/tungsten-arc welding torch delivers 100-A current, yet used in confined spaces inaccessible to even smallest commercially available torch. Despite its extremely small size, torch contains all usual components and delivers high current.

Morgen, Gene E.

1991-01-01

347

Fluid Flow Characteristics and Porosity Behavior in Full Penetration Laser Welding of a Titanium Alloy  

NASA Astrophysics Data System (ADS)

In this paper, a computational fluid mechanics model is developed for full penetration laser welding of titanium alloy Ti6Al4V. This has been used to analyze possible porosity formation mechanisms, based on predictions of keyhole behavior and fluid flow characteristics in the weld pool. Numerical results show that when laser welding 3 mm thickness titanium alloy sheets with given laser beam focusing optics, keyhole depth oscillates before a full penetration keyhole is formed, but thereafter keyhole collapses are not predicted numerically. For lower power, lower speed welding, the fluid flow behind the keyhole is turbulent and unstable, and vortices are formed. Molten metal is predicted to flow away from the center plane of the weld pool, and leave a gap or void within the weld pool behind the keyhole. For higher power, higher speed welding, fluid flow is less turbulent, and such vortices are not formed. Corresponding experimental results show that porosity was absent in the melt runs made at higher power and higher welding speed. In contrast, large pores were present in melt runs made at lower power and lower welding speed. Based on the combination of experimental results and numerical predictions, it is proposed that porosity formation when keyhole laser welding may result from turbulent fluid flow behind the keyhole, with the larger the value of associated Reynolds number, the higher the possibility of porosity formation. For such fluid flow controlled porosities, measures to decrease Reynolds number of the fluid flow close to the keyhole could prove effective in reducing or avoiding porosity.

Chang, Baohua; Allen, Chris; Blackburn, Jon; Hilton, Paul; Du, Dong

2014-11-01

348

Welding in Space Workshop  

NASA Technical Reports Server (NTRS)

The potential was discussed for welding in space, its advantages and disadvantages, and what type of programs can benefit from the capability. Review of the various presentations and comments made in the course of the workshop suggests several routes to obtaining a better understanding of how welding processes can be used in NASA's initiatives in space. They are as follows: (1) development of a document identifying well processes and equipment requirements applicable to space and lunar environments; (2) more demonstrations of welding particular hardware which are to be used in the above environments, especially for space repair operations; (3) increased awareness among contractors responsible for building space equipment as to the potential for welding operations in space and on other planetary bodies; and (4) continuation of space welding research projects is important to maintain awareness within NASA that welding in space is viable and beneficial.

Workman, Gary L.

1990-01-01

349

Tidal Pool on Folly Island  

USGS Multimedia Gallery

A tidal pool on Folly Island. Tidal pools are small pools of water that are left when the tide recedes. Because these pools have water more or less permanently, distinct ecosystems can develop separate from the surrounding beach. Folly Island, a preserve owned by the Maine Coast Heritage Trust, is a...

350

DROWNING IN DISINFECTION BY-PRODUCTS? ASSESSING SWIMMING POOL WATER  

EPA Science Inventory

The development of treated water for swimming pools has made swimming a year round activity, widely enjoyed for leisure as well as exercise. Swimming pools can be found in different kinds and sizes in public areas, hotels and spas, or at private homes. In Germany ~250-300 million...

351

Arc Welding Fundamentals  

NSDL National Science Digital Library

This page from SnoCAMP provides an in-depth, technical introduction to the topic of arc welding. Sections covered are basic welding circuit, arc shielding and nature of the arc. The page also provides a number of downloadable resources on the topic, most of which are available as Microsoft Word documents. This page is an excellent reference for students learning the basics of this type of welding technology.

352

Enhanced diffusion welding  

NASA Technical Reports Server (NTRS)

Surfaces of unrecrystallized alloys are sanded and polished. This is followed by a two-step welding process by which the strength of the parent metal is retained at the weld joint. The first step forces the surfaces into intimate contact at a temperature where the metal still has good ductility. The second step causes diffusion, recrystallization, and grain growth across the original weld interface.

Holko, K. H.; Moore, T. J. (inventors)

1973-01-01

353

A simulation model for estimating probabilities of defects in welds  

SciTech Connect

In recent work for the US Nuclear Regulatory Commission in collaboration with Battelle Pacific Northwest National Laboratory, Rolls-Royce and Associates, Ltd., has adapted an existing model for piping welds to address welds in reactor pressure vessels. This paper describes the flaw estimation methodology as it applies to flaws in reactor pressure vessel welds (but not flaws in base metal or flaws associated with the cladding process). Details of the associated computer software (RR-PRODIGAL) are provided. The approach uses expert elicitation and mathematical modeling to simulate the steps in manufacturing a weld and the errors that lead to different types of weld defects. The defects that may initiate in weld beads include center cracks, lack of fusion, slag, pores with tails, and cracks in heat affected zones. Various welding processes are addressed including submerged metal arc welding. The model simulates the effects of both radiographic and dye penetrant surface inspections. Output from the simulation gives occurrence frequencies for defects as a function of both flaw size and flaw location (surface connected and buried flaws). Numerical results are presented to show the effects of submerged metal arc versus manual metal arc weld processes.

Chapman, O.J.V. [Rolls-Royce and Associates, Ltd., Derby (United Kingdom); Khaleel, M.A.; Simonen, F.A. [Battelle Memorial Inst., Richland, WA (United States). Pacific Northwest National Lab.

1996-12-01

354

Friction Stir Weld Restart+Reweld Repair Allowables  

NASA Technical Reports Server (NTRS)

A friction stir weld (FSW) repair method has been developed and successfully implemented on Al 2195 plate material for the Space Shuttle External Fuel Tank (ET). The method includes restarting the friction stir weld in the termination hole of the original weld followed by two reweld passes. Room temperature and cryogenic temperature mechanical properties exceeded minimum FSW design strength and compared well with the development data. Simulated service test results also compared closely to historical data for initial FSW, confirming no change to the critical flaw size or inspection requirements for the repaired weld. Testing of VPPA fusion/FSW intersection weld specimens exhibited acceptable strength and exceeded the minimum design value. Porosity, when present at the intersection was on the root side toe of the fusion weld, the "worst case" being 0.7 inch long. While such porosity may be removed by sanding, this "worst case" porosity condition was tested "as is" and demonstrated that porosity did not negatively affect the strength of the intersection weld. Large, 15-inch "wide panels" FSW repair welds were tested to demonstrate strength and evaluate residual stresses using photo stress analysis. All results exceeded design minimums, and photo stress analysis showed no significant stress gradients due to the presence of the restart and multi-pass FSW repair weld.

Clifton, Andrew

2008-01-01

355

Dual wire welding torch and method  

DOEpatents

A welding torch includes a nozzle with a first welding wire guide configured to orient a first welding wire in a first welding wire orientation, and a second welding wire guide configured to orient a second welding wire in a second welding wire orientation that is non-coplanar and divergent with respect to the first welding wire orientation. A method of welding includes moving a welding torch with respect to a workpiece joint to be welded. During moving the welding torch, a first welding wire is fed through a first welding wire guide defining a first welding wire orientation and a second welding wire is fed through a second welding wire guide defining a second welding wire orientation that is divergent and non-coplanar with respect to the first welding wire orientation.

Diez, Fernando Martinez (Peoria, IL); Stump, Kevin S. (Sherman, IL); Ludewig, Howard W. (Groveland, IL); Kilty, Alan L. (Peoria, IL); Robinson, Matthew M. (Peoria, IL); Egland, Keith M. (Peoria, IL)

2009-04-28

356

REVIEW ARTICLE: Modelling of thermal plasmas for arc welding: the role of the shielding gas properties and of metal vapour  

NASA Astrophysics Data System (ADS)

The methods used to model thermal plasmas, including treatments of diffusion in arcs in gas mixtures, are reviewed. The influence of thermophysical properties on the parameters of tungsten-inert-gas (TIG) welding arcs, particularly those that affect the weld pool, is investigated using a two-dimensional model in which the arc, anode and cathode are included self-consistently. The effect of changing each of six thermophysical properties on the characteristics of an argon TIG arc is assessed. The influence of the product of specific heat and mass density is found to be particularly important in determining the arc constriction. By examining the influence of the different properties on the heat flux density, current density and shear stress at the anode, it is concluded that the weld pool depth can be increased by using shielding gases with high specific heat, thermal conductivity and viscosity. The effect of metal vapour on the arc and weld pool properties is assessed. The most important effect of the metal vapour is found to be the increased electrical conductivity at low temperatures, which leads to lower heat flux density and current density at the weld pool, implying a shallower weld pool.

Murphy, A. B.; Tanaka, M.; Yamamoto, K.; Tashiro, S.; Sato, T.; Lowke, J. J.

2009-10-01

357

Gaseous hydrogen embrittlement of T-250 laser welds  

SciTech Connect

The tensile properties of laser-welded T-250 maraging steel are measured, with attention paid to the influence of strain rate and gaseous hydrogen on the fracture behavior of welded specimens. Post-weld heat treatments are performed on laser-welded specimens to obtain underaged (WU), peak-aged (WP), and overaged (WO) specimens. Hydrogen embrittlement (HE) affects the tensile fracture behavior of the welded specimens; HE changes not only the fracture mode but also the fracture location. Without the influence of hydrogen, the fracture location is at the softest region, the weld metal (WM), and the fracture appearance reveals a ductile dimple fracture. For welds sensitive to HE, the fracture is initiated at the heat-affected zone (HAZ) with coarse grain size, and the associated fracture surface exhibits intergranular and quasi-cleavage fractures that are brittle in nature. In addition, the HAZ with coarse grain size is more prone to HE, as compared to other regions in the welded specimens. The WU specimens are susceptible to HE in air under a low strain rate, while the WP specimens are only susceptible to gaseous hydrogen embrittlement (GHE). However, the WO specimens are immune to GHE and insensitive to strain rate.

Tsay, L.W.; Huang, W.B. [National Taiwan Ocean Univ., Keelung (Taiwan, Province of China). Inst. of Materials Engineering; Chen, C. [National Taiwan Univ., Taipei (Taiwan, Province of China). Inst. of Materials Science and Engineering

1997-04-01

358

Effects of Sealing Run Welding with Defocused Laser Beam on the Quality of T-joint Fillet Weld  

NASA Astrophysics Data System (ADS)

Fillet weld is the predominant weld type used for connecting different elements e.g. in shipbuilding, offshore and bridge structures. One of prevalent research questions is the structural integrity of the welded joint. Post weld improvement techniques are being actively researched, as high stress areas like an incomplete penetration on the root side or fluctuations in penetration depth cannot be avoided. Development of laser and laser-arc hybrid welding processes have greatly contributed to increase of production capacity and reduction of heat-induced distortions by producing single pass full penetration welds in thin- and medium thickness structural steel parts. Present study addresses the issue of how to improve the quality of the fillet welds by welding the sealing run on the root side with defocused laser beam. Welds having incomplete or excessive penetration were produced with several beam angles and laser beam spot sizes on surface. As a conclusion, significant decrease or even complete elimination of the seam irregularities, which act as the failure starting points during service, is achieved.

Unt, Anna; Poutiainen, Ilkka; Salminen, Antti

359

Through Weld Inspection of Wrought Stainless Steel Piping Using Phased-Array Ultrasonic Probes.  

SciTech Connect

A study was conducted to assess the ability of phased-array ultrasonic techniques to detect and accurately determine the size of flaws from the far-side of wrought austenitic piping welds. Far-side inspections of these welds are currently performed on a “best effort” basis and do not conform to ASME Code Section XI Appendix VIII performance demonstration requirements. For this study, four circumferential welds in 610mm diameter, 36mm thick ASTM A-358, Grade 304 vintage austenitic stainless steel pipe were examined. The welds were fabricated with varied welding parameters; both horizontal and vertical pipe orientations were used, with air and water backing, to simulate field welding conditions. A series of saw cuts, electro-discharge machined (EDM) notches, and implanted fatigue cracks were placed into the heat affected zones of the welds. The saw cuts and notches range in depth from 7.5% to 28.4% through-wall. The implanted cracks ranged in depth from 5% through wall to 64% through wall. The welds were examined with two phased-array probes, a 2.0 MHz transmit-receive longitudinal wave array and a 2.0 MHz transmit-receive shear wave array. These examinations showed that both phased-array transducers were able to detect and accurately length-size, but not depth size, all of the notches and flaws through the welds. The phased-array results were not strongly affected by the different welding techniques used in each weld.

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

2004-08-05

360

Manually Operated Welding Wire Feeder  

NASA Technical Reports Server (NTRS)

A manual welding wire feeder apparatus comprising a bendable elongate metal frame with a feed roller mounted at the center thereof for rotation about an axis transverse to the longitudinal axis of the frame. The frame ends are turned up as tabs and each provided with openings in alignment with each other and the mid-width center of the roller surface. The tab openings are sized to accommodate welding wire and each extends to a side edge of the tab, both opening on the same side of the frame, whereby welding wire can be side-loaded onto the frame. On the side of the frame, opposite the roller a lock ring handle is attached tangentially and is rotatable about the attachment point and an axis perpendicular to the frame. The device is grasped in the hand normally used to hold the wire. A finger is placed through the loop ring and the frame positioned across the palm and lower fingers. The thumb is positioned atop the wire so it can be moved from the back of the frame across the roller, and towards the front. In doing so, the wire is advanced at a steady rate in axial alignment with the tab openings and roller. To accommodate different wire diameters the frame is bendable about its center in the plane of the frame axis and wire so as to keep the wire in sufficient tension against the roller and to keep the wire fixed when the frame is tilted and thumb pressure released.

Rybicki, Daniel J. (Inventor)

2001-01-01

361

LPT. EBOR (TAN646) interior, installing reactor in STF pool ("vault"). ...  

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

LPT. EBOR (TAN-646) interior, installing reactor in STF pool ("vault"). Pressure vessel shows core barrel and outlet nozzle (next to man below) to inner duct weld, which is prepared and in position for stress relieving. Camera facing southeast. Photographer: Comiskey. Date: January 20, 1965. INEEL negative no. 65-239 - Idaho National Engineering Laboratory, Test Area North, Scoville, Butte County, ID

362

Determination of pool boiling Critical Heat Flux enhancement in nanofluids  

E-print Network

Nanofluids are engineered colloids composed of nano-size particles dispersed in common fluids such as water or refrigerants. Using an electrically controlled wire heater, pool boiling Critical Heat Flux (CHF) of Alumina ...

Truong, Bao H. (Bao Hoai)

2007-01-01

363

Gravitational Effects on the Gas Tungsten Arc Welds of 304 Stainless Steels  

Microsoft Academic Search

Gravitational effects on gas tungsten arc welding (GTAW) of 304 stainless steels were studied to determine the behavior of the weld pool geometry, and its impact on microstructure and solute distribution. This was accomplished through both a KC-135 flight experiment and a ground-based experiment. Gravitational level variation from low gravity (LG) (?1.2 g) to high gravity (HG) (?1.8 g) caused a 10%

Namhyun Kang; Jogender Singh; Anil. K. Kulkarni

2003-01-01

364

Pulsed Nd-YAG laser welding of A SiC particulate reinforced aluminium alloy composite  

NASA Astrophysics Data System (ADS)

This paper examines the laser welding behaviour of a SiC particulate reinforced Al-alloy 2124 composite using a pulsed Nd-YAG laser. The influences of laser welding parameters of laser intensity, pulse duration and the beam's focus position on the depth of weld penetration as well as the size of fusion zone were investigated. These investigations have led to an optimum welding condition proposed for pulsed laser welding of SiC particulate reinforced aluminium alloy composites with minimum defects.

Yue, T. M.; Xu, J. H.; Man, H. C.

1997-01-01

365

DC arc weld starter  

DOEpatents

A system for starting an arc for welding uses three DC power supplies, a high voltage supply for initiating the arc, an intermediate voltage supply for sustaining the arc, and a low voltage welding supply directly connected across the gap after the high voltage supply is disconnected.

Campiotti, Richard H. (Tracy, CA); Hopwood, James E. (Oakley, CA)

1990-01-01

366

Welding blades to rotors  

NASA Technical Reports Server (NTRS)

A process is described to form T-joints between dissimilar thickness parts by magnetic force upset welding. This type of resistance welding is used to join compressor and turbine parts which thereby reduces the weight and cost of jet engines.

Hoklo, K. H.; Moore, T. J. (inventors)

1973-01-01

367

Welding: Scope and Sequence.  

ERIC Educational Resources Information Center

Intended for use by all welding instructors in the Metropolitan Nashville Public Schools, this guide provides a sequential listing of course content and scope. A course description provides a brief overview of the content of the courses offered in the welding program. General course objectives are then listed. Outlines of the course content are…

Nashville - Davidson County Metropolitan Public Schools, TN.

368

Laser Welding in Space  

NASA Technical Reports Server (NTRS)

Solidification type welding process experiments in conditions of microgravity were performed. The role of convection in such phenomena was examined and convective effects in the small volumes obtained in the laser weld zone were observed. Heat transfer within the weld was affected by acceleration level as indicated by the resulting microstructure changes in low gravity. All experiments were performed such that both high and low gravity welds occurred along the same weld beam, allowing the effects of gravity alone to be examined. Results indicate that laser welding in a space environment is feasible and can be safely performed IVA or EVA. Development of the hardware to perform the experiment in a Hitchhiker-g platform is recomended as the next step. This experiment provides NASA with a capable technology for welding needs in space. The resources required to perform this experiment aboard a Shuttle Hitchhiker-pallet are assessed. Over the four year period 1991 to 1994, it is recommended that the task will require 13.6 manyears and $914,900. In addition to demonstrating the technology and ferreting out the problems encountered, it is suggested that NASA will also have a useful laser materials processing facility for working with both the scientific and the engineering aspects of materials processing in space. Several concepts are also included for long-term optimization of available solar power through solar pumping solid state lasers directly for welding power.

Workman, Gary L.; Kaukler, William F.

1989-01-01

369

Vocational Preparation Curriculum: Welding.  

ERIC Educational Resources Information Center

Designed to be a workable guide for instructors serving the occupational needs of various categories of disadvantaged and handicapped students, this welding curriculum contains fourteen units of self-paced and self-contained instructional materials. The instructional units cover the following topics: job opportunities in welding, safety rules in…

Usoro, Hogan

370

Explosive Welding of Pipes  

NASA Astrophysics Data System (ADS)

For connection by welding it is suggested to use the explosive welding method. This method is rather new. Nevertheless, it has become commonly used among the technological developments. This method can be advantageous (saving material and physical resources) comparing to its statical analogs (electron-beam welding, argon-arc welding, plasma welding, gas welding, etc.), in particular, in hard-to-reach areas due to their geographic and climatic conditions. The suggestion is to use water as filler. The principle of non-compressibility of liquid under quasi-dynamic loading is used. In one-dimensional gasdynamic and elastic-plastic calculations we determined non-deformed mass of water (perturbations, which are moving in the axial direction with sound velocity, should not reach the layer end boundaries for 5-7 circulations of shock waves in the radial direction). Linear dimension of the water layer from the zone of pipe coupling along axis in each direction is >= 2R, where R is the internal radius of pipe. Model experiments with pipes having radii R = 57 mm confirmed results of the calculations and the possibility in principle to weld pipes by explosion with use of water as filler. Reduction of pipe diameter after dynamic loading and explosive welding was ˜2%.

Burtseva, Olga

2007-06-01

371

Cable Pool - Cherryfield  

USGS Multimedia Gallery

The USGS monitors the Narraguagus River at Cherryfield, Maine at a location called Cable Pool. This spot was once renowned for Atlantic salmon, where anglers would line the banks, waiting their turn to cast a line into the water. In fact, posts along the river bank to hold the waiting anglers rods e...

372

NEW APPROACHES: Pool table  

NASA Astrophysics Data System (ADS)

This article explains a novel way of demonstrating the principle of conservation of energy. This can be difficult to demonstrate in the laboratory, but if students have been convinced of the conservation of momentum, two-dimensional collisions on a pool table may be used.

Parry, Malcolm

1998-05-01

373

Low cycle fatigue behavior of electron beam and friction welded joints of an α-β titanium alloy  

Microsoft Academic Search

Fusion welds in titanium alloys, with intermediate β stabilizing additions, show poor mechanical properties due to large fusion zone grain size coupled with a brittle plate martensitic microstructure and hydrogen induced microporosity. These problems, associated with fusion welding, have been reported to be overcome by friction welding. The alloy used in this study is a Soviet composition (VT9) of the

T. Mohandas; V. K. Varma; D. Banerjee; V. V. Kutumbarao

1996-01-01

374

Method for welding beryllium  

DOEpatents

A method is provided for joining beryllium pieces which comprises: depositing aluminum alloy on at least one beryllium surface; contacting that beryllium surface with at least one other beryllium surface; and welding the aluminum alloy coated beryllium surfaces together. The aluminum alloy may be deposited on the beryllium using gas metal arc welding. The aluminum alloy coated beryllium surfaces may be subjected to elevated temperatures and pressures to reduce porosity before welding the pieces together. The aluminum alloy coated beryllium surfaces may be machined into a desired welding joint configuration before welding. The beryllium may be an alloy of beryllium or a beryllium compound. The aluminum alloy may comprise aluminum and silicon. 9 figs.

Dixon, R.D.; Smith, F.M.; O`Leary, R.F.

1997-04-01

375

Method for welding beryllium  

SciTech Connect

A method is provided for joining beryllium pieces which comprises: depositing aluminum alloy on at least one beryllium surface; contacting that beryllium surface with at least one other beryllium surface; and welding the aluminum alloy coated beryllium surfaces together. The aluminum alloy may be deposited on the beryllium using gas metal arc welding. The aluminum alloy coated beryllium surfaces may be subjected to elevated temperatures and pressures to reduce porosity before welding the pieces together. The aluminum alloy coated beryllium surfaces may be machined into a desired welding joint configuration before welding. The beryllium may be an alloy of beryllium or a beryllium compound. The aluminum alloy may comprise aluminum and silicon. Beryllium parts made using this method can be used as structural components in aircraft, satellites and space applications.

Dixon, R.D.; Smith, F.M.; O`Leary, R.F.

1995-12-31

376

Degrees that Work: Welding  

NSDL National Science Digital Library

This video provides an inside look at the lives of professional welders. From artistic welder Mike Patterson to manufacturing specialist Jennifer Brikley-Cruz this video covers a wide range of possibilities within the welding industry. The video covers the Fabtech International and American Welding Society Welding Show in Chicago and showcases interviews with industry representatives. Viewers can download the 158 MB video to their computer, or stream it directly from the website. Welding is an ever needed but stigmatized industry with a diminishing work force; but this high-quality video truly explores the opportunities and benefits of welding. It would be an excellent resource in high schools or colleges to introduce students to an otherwise unknown or overlooked career possibility.

377

Analysis and validation of laser spot weld-induced distortion  

SciTech Connect

Laser spot welding is an ideal process for joining small parts with tight tolerances on weld size, location, and distortion, particularly those with near-by heat sensitive features. It is also key to understanding the overlapping laser spot seam welding process. Rather than attempting to simulate the laser beam-to-part coupling (particularly if a keyhole occurs), it was measured by calorimetry. This data was then used to calculate the thermal and structural response of a laser spot welded SS304 disk using the finite element method. Five combinations of process parameter values were studied. Calculations were compared to experimental data for temperature and distortion profiles measured by thermocouples and surface profiling. Results are discussed in terms of experimental and modeling factors. The authors then suggest appropriate parameters for laser spot welding.

Knorovsky, G.A.; Kanouff, M.P.; Maccallum, D.O.; Fuerschbach, P.W.

1999-12-09

378

Multi-Canister overpack ultrasonic examination of closure weld  

SciTech Connect

The method used for non-destructive examination of the closure weld must provide adequate assurance that the weld is structurally sound for the pressure and lifting loads to be imposed, and must be consistent with NRC equivalency requirements established for the SNF Project. Given the large flaw size that would need to exist before the structural integrity of the weld is challenged, liquid penetrant testing of the root and final passes provides adequate assurance of weld quality to meet structural loads. In addition, the helium leak test provides confirmation that the containment boundary is intact and leaktight. While UT examination does provide additional evidence of weld integrity, the value of that additional evidence for this particular application does not justify performing UT examination, given the additional financial and ALARA costs associated with performing the examination.

SMITH, K.E.

1998-11-03

379

A combined enthalpy / front tracking method for modelling melting and solidification in laser welding  

NASA Astrophysics Data System (ADS)

The authors present an integrated meso-scale 2D numerical model for the simulation of laser spot welding of a Fe-Cr-Ni steel. The melting of the parent materials due to the applied heating power is an important phenomenon, leading to the formation of the weld pool and the subsequent conditions from which solidification proceeds. This model deals with the dynamic formation of the weld pool whereby melting may be occurring at a given location while solidification has already commenced elsewhere throughout the weld pool. Considering both melting and possible simultaneous solidification in this manner ensures a more accurate simulation of temperature distribution. A source based enthalpy method is employed throughout the calculation domain in order to integrate the melting model with the UCD front tracking model for alloy solidification. Melting is tracked via interpolation of the liquidus isotherm, while solidification is treated via both the tracking of the advancing columnar dendritic front, and the nucleation and growth of equiaxed dendrites using a volume-averaging formulation. Heterogeneous nucleation is assumed to take place on TiN grain refiner particles at a grain refiner density of 1000 particles per mm2. A mechanical blocking criterion is used to define dendrite coherency, and the columnar-to-equiaxed transition within the weld pool is predicted.

Duggan, G.; Mirihanage, W. U.; Tong, M.; Browne, D. J.

2012-07-01

380

Exploring infrared sensoring for real time welding defects monitoring in GTAW.  

PubMed

This paper presents an evaluation of an infrared sensor for monitoring the welding pool temperature in a Gas Tungsten Arc Welding (GTAW) process. The purpose of the study is to develop a real time system control. It is known that the arc welding pool temperature is related to the weld penetration depth; therefore, by monitoring the temperature, the arc pool temperature and penetration depth are also monitored. Various experiments were performed; in some of them the current was varied and the temperature changes were registered, in others, defects were induced throughout the path of the weld bead for a fixed current. These simulated defects resulted in abrupt changes in the average temperature values, thus providing an indication of the presence of a defect. The data has been registered with an acquisition card. To identify defects in the samples under infrared emissions, the timing series were analyzed through graphics and statistic methods. The selection of this technique demonstrates the potential for infrared emission as a welding monitoring parameter sensor. PMID:22219697

Alfaro, Sadek C A; Franco, Fernand Díaz

2010-01-01

381

Exploring Infrared Sensoring for Real Time Welding Defects Monitoring in GTAW  

PubMed Central

This paper presents an evaluation of an infrared sensor for monitoring the welding pool temperature in a Gas Tungsten Arc Welding (GTAW) process. The purpose of the study is to develop a real time system control. It is known that the arc welding pool temperature is related to the weld penetration depth; therefore, by monitoring the temperature, the arc pool temperature and penetration depth are also monitored. Various experiments were performed; in some of them the current was varied and the temperature changes were registered, in others, defects were induced throughout the path of the weld bead for a fixed current. These simulated defects resulted in abrupt changes in the average temperature values, thus providing an indication of the presence of a defect. The data has been registered with an acquisition card. To identify defects in the samples under infrared emissions, the timing series were analyzed through graphics and statistic methods. The selection of this technique demonstrates the potential for infrared emission as a welding monitoring parameter sensor. PMID:22219697

Alfaro, Sadek C. A.; Franco, Fernand Díaz

2010-01-01

382

Alternating-Polarity Arc Welding  

NASA Technical Reports Server (NTRS)

Brief reversing polarity of welding current greatly improves quality of welds. NASA technical memorandum recounts progress in art of variable-polarity plasma-arc (VPPA) welding, with emphasis on welding of aluminum-alloy tanks. VPPA welders offer important advantages over conventional single-polarity gas/tungsten arc welders.

Schwinghamer, R. J.

1987-01-01

383

Argon Welding Inside A Workpiece  

NASA Technical Reports Server (NTRS)

Canopies convert large hollow workpiece into inert-gas welding chamber. Large manifold serves welding chamber for attachment of liner parts in argon atmosphere. Every crevice, opening and passageway provided with argon-rich environment. Weld defects and oxidation dramatically reduced; also welding time reduced.

Morgan, Gene E.

1988-01-01

384

Vacuum Gas Tungsten Arc Welding  

NASA Technical Reports Server (NTRS)

A two-year program investigated vacuum gas tungsten arc welding (VGTAW) as a method to modify or improve the weldability of normally difficult-to-weld materials. After a vacuum chamber and GTAW power supply were modified, several difficult-to-weld materials were studied and key parameters developed. Finally, Incoloy 903 weld overlays were produced without microfissures.

Weeks, J. L.; Todd, D. T.; Wooten, J. R.

1997-01-01

385

Multihole Arc-Welding Orifice  

NASA Technical Reports Server (NTRS)

Modified orifice for variable-polarity plasma-arc welding directs welding plume so it creates clean, even welds on both Inconel(R) and aluminum alloys. Includes eight holes to relieve back pressure in plasma. Quality of welds on ferrous and nonferrous alloys improved as result.

Swaim, Benji D.

1989-01-01

386

Weld overlay coatings for erosion control  

SciTech Connect

A literature review was made. In spite of similarities between abrasive wear and solid particle erosion, weld overlay hardfacing alloys that exhibit high abrasion resistance may not necessarily have good erosion resistance. The performance of weld overlay hardfacing alloys in erosive environments has not been studied in detail. It is believed that primary-solidified hard phases such as carbides and intermetallic compounds have a strong influence on erosion resistance of weld overlay hardfacing alloys. However, relationships between size, shape, and volume fraction of hard phases in a hardfacing alloys and erosion resistance were not established. Almost all hardfacing alloys can be separated into two major groups based upon chemical compositions of the primary solidified hard phases: (a) carbide hardening alloys (Co-base/carbide, WC-Co and some Fe base superalloys); and (b) intermetallic hardening alloys (Ni-base alloys, austenitic steels, iron-aluminides).

Levin, B.; DuPont, J.N.; Marder, A.R.

1993-03-03

387

Heat Treatment of Friction-Stir-Welded 7050 Aluminum Plates  

NASA Technical Reports Server (NTRS)

A method of heat treatment has been developed to reverse some of the deleterious effects of friction stir welding of plates of aluminum alloy 7050. This alloy is considered unweldable by arc and high-energy-density beam fusion welding processes. The alloy can be friction stir welded, but as-welded workpieces exhibit low ductility, low tensile and yield strengths, and low resistance to stress corrosion cracking. Heat treatment according to the present method increases tensile and yield strengths, and minimizes or eliminates stress corrosion cracking. It also increases ductility. This method of heat treatment is a superior alternative to a specification-required heat treatment that caused the formation of large columnar grains, which are undesired. Workpieces subjected to the prior heat treatment exhibited elongations <2 percent, and standard three-point bend specimens shattered. The development of the present heat treatment method was guided partly by the principles that (1) by minimizing grain sizes and relieving deformation stresses, one can minimize or eliminate stress corrosion cracking and (2) the key to maximizing strength and eliminating residual stresses is to perform post-weld solution heating for as long a time as possible while incurring little or no development of large columnar grains in friction stir weld nuggets. It is necessary to perform some of the solution heat treatment (to soften the alloy and improve machine welding parameters) before welding. The following is an example of thickness- dependent pre- and post-weld heat treatments according to the present method: For plates 0.270 in. (approx.6.86 mm) thick milled from plates 4.5 in. (114.3 mm) thick, perform pre-weld solution heating at 890 F (477 C) for 1 hour, then cool in air. After friction stir welding, perform solution heating for 10 minutes, quench, hold at room temperature for 96 hours, then age at 250 F (121 C) for 5 hours followed by 325 F (163 C) for 27 hours.

Petter, George E.; Figert, John D.; Rybicki, Daniel J.; Burns, Timothy

2006-01-01

388

Adaptive weld control for high-integrity welding applications  

NASA Astrophysics Data System (ADS)

Adaptive, closed-loop weld control is necessary to maintain high-integrity, zero-defect welds. Conventional weld control techniques using weld parameter feedback control loops are sufficient to maintain set points, but fall short when confronted with unexpected variations in part/tooling temperature and mechanical structure, weldment material, arc skew angle, or calibration in weld parameter feedback measurement. Modern technology allows closed-loop control utilizing input from real-time weld monitoring sensors and inspection devices. Weld puddle parameters, bead profile parameters, and weld seam position are fed back into the weld control loop which adapts for the weld condition variations and drives them back to a desired state, thereby preventing weld defects or perturbations. Parameters such as arc position relative to the weld seam, puddle symmetry, arc length, weld width, and bead shape can be extracted from sensor imagery and used in closed-loop active weld control. All weld bead and puddle measurements are available for real-time display and statistical process control analysis, after which the data is archived to permanent storage or later retrieval and analysis.

Powell, Bradley W.

389

Mechanical Properties, Microstructure and Crystallographic Texture of Magnesium AZ91-D Alloy Welded by Friction Stir Welding (FSW)  

NASA Astrophysics Data System (ADS)

The objective of the study was to characterize the properties of a magnesium alloy welded by friction stir welding. The results led to a better understanding of the relationship between this process and the microstructure and anisotropic properties of alloy materials. Welding principally leads to a large reduction in grain size in welded zones due to the phenomenon of dynamic recrystallization. The most remarkable observation was that crystallographic textures appeared from a base metal without texture in two zones: the thermo-mechanically affected and stir-welded zones. The latter zone has the peculiarity of possessing a marked texture with two components on the basal plane and the pyramidal plane. These characteristics disappeared in the thermo-mechanically affected zone (TMAZ), which had only one component following the basal plane. These modifications have been explained by the nature of the plastic deformation in these zones, which occurs at a moderate temperature in the TMAZ and high temperature in the SWZ.

Kouadri-Henni, A.; Barrallier, L.

2014-10-01

390

Capabilities of infrared weld monitor  

SciTech Connect

A non-obtrusive pre-aligned, solid-state device has been developed to monitor the primary infrared emissions during laser welding. The weld monitor output is a 100-1000 mV signal that depends on the beam power and weld characteristics. The DC level of this signal is related to weld penetration, while AC portions of the output can be correlated with surface irregularities and part misalignment or contamination. Changes in DC behavior are also noted for both full and deep penetration welds. Full penetration welds are signified by an abrupt reduction in the weld monitor output. Bead on plate welds were made on steel, aluminum, and magnesium with both a CW CO{sub 2} laser and a pulsed Nd:YAG laser to explore the relationships between the weld characteristics and the weld monitor output.

Sanders, P.G.; Keske, J.S.; Leong, K.H.; Kornecki, G.

1997-11-01

391

EFFECT OF MINOR ADDITIONS OF HYDROGEN TO ARGON SHIELDING GAS WHEN WELDING AUSTENITIC STAINLESS STEEL WITH THE GTAW PROCESS  

SciTech Connect

This paper provides the technical basis to conclude that the use of hydrogen containing shielding gases during welding of austenitic stainless steels will not lead to hydrogen induced cracking (HIC) of the weld or weld heat affected zone. Argon-hydrogen gas mixtures, with hydrogen additions up to 35% [1], have been successfully used as the shielding gas in gas tungsten arc welding (GTAW) of austenitic stainless steels. The addition of hydrogen improves weld pool wettability, bead shape control, surface cleanliness and heat input. The GTAW process is used extensively for welding various grades of stainless steel and is preferred when a very high weld quality is desired, such as that required for closure welding of nuclear materials packages. The use of argon-hydrogen gas mixtures for high-quality welding is occasionally questioned, primarily because of concern over the potential for HIC. This paper was written specifically to provide a technical basis for using an argon-hydrogen shielding gas in conjunction with the development, at the Savannah River Technology Center (SRTC), of an ''optimized'' closure welding process for the DOE standardized spent nuclear fuel canister [2]. However, the basis developed here can be applied to other applications in which the use of an argon-hydrogen shielding gas for GTAW welding of austenitic stainless steels is desired.

CANNELL, G.R.

2004-12-15

392

Characterisation of fume from hyperbaric welding operations  

NASA Astrophysics Data System (ADS)

We report preliminary work characterising dust from hyperbaric welding trials carried out at increased pressure in a helium and oxygen atmosphere. Particle size and concentration were measured during welding. Samples for quartz and metal analysis and toxicity assessment were taken from a filter in the local fume extraction system. The residue of dust after metal extraction by nitric acid in hydrogen peroxide predominantly a non-metallic white powder assumed to be dust from welding rod coatings and thermal insulation material. Metallic analysis showed predominantly calcium, from the welding rod coating, and period 4 transition metals such as iron, manganese, magnesium and titanium (inductively coupled mass spectrometry, Agilent 7500c). The presence of zirconium indicated a contribution from grinding. The fume was nanoparticulate in nature with a mean particle diameter of 20-30 nm (MSI Inc WPS 1000XP). It showed an intermediate level of oxidative potential regarding the low-molecular weight respiratory tract lining fluid antioxidants ascorbate and glutathione and caused release of the inflammatory marker IL-8 in a human lung A 549 epithelial cell culture with no indication of cytotoxicity. The study findings have strong implications for the measurement techniques needed to assess fume exposure in hyperbaric welding and the provision of respiratory protection.

Ross, John A. S.; Semple, Sean; Duffin, Rodger; Kelly, Frank; Seldmann, Joerg; Raab, Andrea

2009-02-01

393

Robotic weld overlay coatings for erosion control  

NASA Astrophysics Data System (ADS)

Research is being conducted to develop criteria for selecting weld overlay coatings for erosion mitigation in circulated fluidized beds. Twelve weld overlay alloys were deposited on 1018 steel substrates using plasma arc welding. Ten samples from each coating were prepared for erosion testing. All selected coatings were erosion tested at 400C and their erosion resistance and microstructure evaluated. Steady state erosion rates were similar for several weld overlay coatings (Ultimet, Inconel-625, Iron-Aluminide, 316L SS, and High Chromium Cast Iron) and were considerably lower than the remaining coating evaluated. These coatings had different base (Co, Fe, Ni-base). No correlations were found between room temperature microhardness of the weld overlay coatings and their erosion resistance at elevated temperature, although this criteria is often thought to be an indicator of erosion resistance. It was suggested that the coatings that showed similar erosion rates may have similar mechanical properties such as fracture strength, toughness and work hardening rates at this temperature. During the past quarter, Iron-Aluminide, Inconel-625, and 316L SS coatings were selected for more detailed investigations based upon the preliminary erosion test results. Microhardness tests were performed on eroded samples to determine the size of the work hardened zone and change in coatings hardness due to erosion. The work hardened zone was correlated with erosion resistance of the coatings. Additional Iron-Aluminide, Inconel-625, and 316L SS coatings were deposited on 1018 steel substrates.

Levin, B. F.; Dupont, J. N.; Marder, A. R.

1994-01-01

394

Use of Metallographic Analysis and Strength Testing to Improve Ultrasonic Phased-Array Evaluation of Resistance SPOT Welds  

NASA Astrophysics Data System (ADS)

Results are summarized for a series of experiments in which one hundred spot welds were inspected using a high-frequency phased-array ultrasonic probe, and then sectioned, polished and etched to reveal the microstructure of the welds. The ultrasonic and metallographic results are analyzed in conjunction with the results of strength tests and the size of the weld buttons obtained from destructive tear-down of the welded samples.

Hopkins, Deborah L.

2008-02-01

395

Role of Welding Parameters Using the Flux Cored Arc Welding Process of Low Alloy Steels on Bead Geometry and Mechanical Properties  

NASA Astrophysics Data System (ADS)

Welding parameters have direct effects on the bead geometry, microstructure, and mechanical properties of low alloy steels. A series of experiments have been carried out to examine some of these parameters using the flux cored arc welding process (FCAW). In this article, an experimental study was conducted to investigate the influence of welding parameters in FCAW process particularly welding voltage and travel speed on weld bead dimensions. The study also includes the effects of bead overlap and deposition sequence on the parent material and the heat-affected zone (HAZ) properties. It was found that an increase in the welding voltage leads to an increase in the weld bead width, and the increase in the welding traverse speed leads to a decrease in the weld bead width. When studying the bead overlap percentages, it was found that the 50% bead overlap can be considered to be practically a better option than the higher percentages of bead overlap (i.e., 70-90%). The experimental investigation of studying the deposition sequence showed that there were no significant differences in the microstructure, hardness, and the size of the refined HAZ between the two proposed deposition sequences. However, a significant improvement in the microstructure and the size of the refined HAZ, and a reduction in the hardness were achieved after depositing the second welding bead, irrespective of the depositing sequence.

Aloraier, A.; Almazrouee, A.; Shehata, T.; Price, John W. H.

2012-04-01

396

Analysis of ripple formation in single crystal spot welds  

NASA Technical Reports Server (NTRS)

Stationary spot welds have been made at the (001) surface of Fe-l5%Ni-15%Cr single crystals using a Gas Tungsten Arc (GTA). On the top surface of the spot welds, very regular and concentric ripples were observed after solidification by differential interference color microscopy. Their height (typically 1--5 micrometers and spacing, typically approximately 60 micrometers) decreased with the radius of the pool. These ripples were successfully accounted for in terms of capillary-wave theory using the fundamental mode frequency f(sub 0) given by the first zero of the zero-order Bessel function. The spacing d between the ripples was then equated to v(sub s)/f(sub 0), where v(sub s) is the solidification rate. From the measured ripple spacing, the velocity of the pool was deduced as a function of the radius, and this velocity was in good agreement with the results of a heat-flow simulation.

Rappaz, M.; Corrigan, D.; Boatner, L. A.

1997-01-01

397

Laser Welding of Copper Using Multi Mode Fiber Lasers at Near Infrared Wavelength  

NASA Astrophysics Data System (ADS)

Due to the increasing electrification of automotive drives and the expansion of decentralized renewable energygeneration, the consumption of copper for the fabrication of electrical components such as electric motors or conducting paths increases. To jointhese components, laser welding is more frequently used since it represents a flexible and fully automatable joining process. Because of the high thermal conductivity, the low absorption coefficient forinfrared wavelength of common laser beam sources and the resulting limited process efficiency, welding of copper alloys represents a major challenge for laser assisted processes. In this paper, experimental investigationsare presented to identify arising process limits during laser welding of pure copper materials with multi-mode fiber lasers at near infrared wavelength depending on the applied laser power and welding velocity. In addition, a potential stabilization of the welding process by shielding gas support was examined. Further investigations were focused on the influence of shielding gas on the molten pool geometry.

Liebl, S.; Wiedenmann, R.; Ganser, A.; Schmitz, P.; Zaeh, M. F.

398

Argon-Hydrogen Shielding Gas Mixtures for Activating Flux-Assisted Gas Tungsten Arc Welding  

NASA Astrophysics Data System (ADS)

Using activating flux for gas tungsten arc welding (GTAW) to improve penetration capability is a well-established technique. Argon is an inert gas and the one most widely used as a shielding gas for GTAW. For the most austenitic stainless steels, pure argon does not provide adequate weld penetration. Argon-hydrogen mixtures give a more even heat input to the workpiece, increasing the arc voltage, which tends to increase the volume of molten material in the weld pool as well as the weld depth-to-width ratio. Great interest has been shown in the interaction between activating flux and the hydrogen concentration in an argon-based shielding gas. In this study, the weld morphology, the arc profile, the retained delta ferrite content, the angular distortion, and the microstructures were examined. The application of an activating flux combining argon and hydrogen for GTAW is important in the industry. The results of this study are presented here.

Huang, Her-Yueh

2010-11-01

399

SUMMER BAT ACTIVITY AT WOODLAND SEASONAL POOLS IN THE NORTHERN GREAT LAKES REGION  

Microsoft Academic Search

Woodland seasonal pools in the northern Great Lakes region, limited in this study to northern Wisconsin and Michigan's Upper Peninsula, are potentially important sites for bat feeding and drinking. In order to determine the influence of pool size, hydroperiod, and structural complexity on relative bat activity, I surveyed pools (17 in 2004, eight in 2005 and 2006) at approximately two-week

Karen E. Francl

2008-01-01

400

Item Pool Design for an Operational Variable-Length Computerized Adaptive Test  

ERIC Educational Resources Information Center

For computerized adaptive tests (CATs) to work well, they must have an item pool with sufficient numbers of good quality items. Many researchers have pointed out that, in developing item pools for CATs, not only is the item pool size important but also the distribution of item parameters and practical considerations such as content distribution…

He, Wei; Reckase, Mark D.

2014-01-01

401

Exposure to inhalable, respirable, and ultrafine particles in welding fume.  

PubMed

This investigation aims to explore determinants of exposure to particle size-specific welding fume. Area sampling of ultrafine particles (UFP) was performed at 33 worksites in parallel with the collection of respirable particles. Personal sampling of respirable and inhalable particles was carried out in the breathing zone of 241 welders. Median mass concentrations were 2.48 mg m(-3) for inhalable and 1.29 mg m(-3) for respirable particles when excluding 26 users of powered air-purifying respirators (PAPRs). Mass concentrations were highest when flux-cored arc welding (FCAW) with gas was applied (median of inhalable particles: 11.6 mg m(-3)). Measurements of particles were frequently below the limit of detection (LOD), especially inside PAPRs or during tungsten inert gas welding (TIG). However, TIG generated a high number of small particles, including UFP. We imputed measurements welding fume. Concentrations were mainly predicted by the welding process and were significantly higher when local exhaust ventilation (LEV) was inefficient or when welding was performed in confined spaces. Substitution of high-emission techniques like FCAW, efficient LEV, and using PAPRs where applicable can reduce exposure to welding fume. However, harmonizing the different exposure metrics for UFP (as particle counts) and for the respirable or inhalable fraction of the welding fume (expressed as their mass) remains challenging. PMID:22539559

Lehnert, Martin; Pesch, Beate; Lotz, Anne; Pelzer, Johannes; Kendzia, Benjamin; Gawrych, Katarzyna; Heinze, Evelyn; Van Gelder, Rainer; Punkenburg, Ewald; Weiss, Tobias; Mattenklott, Markus; Hahn, Jens-Uwe; Möhlmann, Carsten; Berges, Markus; Hartwig, Andrea; Brüning, Thomas

2012-07-01

402

Large-scale pool fires   

E-print Network

A review of research into the burning behaviour of large pool fires and fuel spill fires is presented. The features which distinguish such fires from smaller pool fires are mainly associated with the fire dynamics at low ...

Steinhaus, Thomas; Welch, Stephen; Carvel, Ricky O; Torero, Jose L

2007-03-29

403

Contribution to arc plasma modeling for welding TIG application  

NASA Astrophysics Data System (ADS)

In this paper we present a numerical model that simulates transferred energy by a welding thermal plasma to the weld pool. This energy transfer allows materials melting. The originality of our model is to include the modeling of transition zones and the vaporization of the anode. The cathodic and anodic areas are taken into account in the model by means of heat balance at the gas-solid interfaces. We report the heating and cooling effects they induce on the solid (cathode, anode) and plasma. Code_Saturne® the CFD software developed at EDF R&D is used for this work Comparisons between simulations and measurements of temperature and electron density confirm the model assumptions for TIG welding.

Borel, Damien; Delalondre, Clarisse; Carpreau, Jean-Michel; Chéron, B. G.; Boubert, J.-P.

2014-06-01

404

Numerical simulation of full-penetration laser beam welding of thick aluminium plates with inductive support  

NASA Astrophysics Data System (ADS)

A three-dimensional laminar steady-state numerical model was developed to investigate the influence of an alternating current (ac) magnetic field during high-power full-penetration laser welding on the weld pool dynamics and weld cross section of a 20 mm thick aluminium plate in flat position. Three-dimensional heat transfer, fluid dynamics including phase transition and electromagnetic field partial differential equations were solved iteratively with the commercial finite element software COMSOL Multiphysics using temperature-dependent material properties up to evaporation temperature. Thermocapillary convection at the weld pool surfaces, natural convection and latent heat of solid-liquid phase transition were taken into account in this model. Solidification was modelled by the Carman-Kozeny equation for porous media morphology. The ac magnet was mounted on the root side of the weld specimen. The magnetic field was aligned perpendicular to the welding direction. The flow pattern in the melt and thus also the temperature distribution were significantly changed by the application of oscillating magnetic fields. It was shown that the application of an ac magnetic field to laser beam welding allows for a prevention of the gravity drop-out. The simulation results are in good qualitative agreement with the experimental observations.

Bachmann, Marcel; Avilov, Vjaceslav; Gumenyuk, Andrey; Rethmeier, Michael

2012-01-01

405

Solar pool heater  

SciTech Connect

A solar pool heater is defined by a submersible tubular ring attached to the perimeter of a transparent or translucent sheet. Floatation of the heater is obtained through an air bubble captured by the sheet and maintained by the ring. The ring is perforated to permit the entry of water within the ring to induce partial submersion and thereby establish a peripheral seal about the captured air bubble. The submersed ring also prevents overlapping of adjacent heaters and reduces the likelihood of the heaters being blown off the pool by wind. By developing the sheet from material transparent to at least a spectrum of the solar rays, the air space intermediate the sheet and the underlying water surface will provide a ''greenhouse'' effect to heat the water through direct impingement by the received radiant energy; additionally, radiation of heat from the water will be reduced by the sheet, whereby, the heater not only collects but retains the impinged radiant energy.

Acker, L.C.

1980-09-16

406

Investigation of the effect of welding parameters on weld quality of plasma arc keyhole welding of structural steels  

SciTech Connect

In the present investigation, the individual and interactive effects of the main welding parameters on weld quality of plasma arc keyhole welding of conventional structural steel, high strength microalloyed steel and strong formable microalloyed steel have been examined using welding of butt joints with a square groove in various welding positions, and welding of joint roots with a single-V-groove and the root face in the flat position. The most important welding parameters are welding current, welding speed and welding gases, especially plasma gas flow rate. Welding parameter combinations producing the best quality welds are presented. It is shown that it is possible to achieve defect-free high-quality welds with good strength and toughness properties, but the allowable range of variation of welding parameters, especially for the highest weld quality, is narrow. An argonhydrogen mixture for the plasma gas together with argon as shielding and backing gases give the best results with respect to weld quality.

Martikainen, J.K.; Moisio, T.J.I. (Lappeenranta Univ. of Technology, Lappeenranta (Finland). Welding Technology Lab.)

1993-07-01

407

Pooled Genomic Indexing Miklos Csuros  

E-print Network

& Human Genome Sequencing Center Baylor College of Medicine #12;Pooled shotgun reads developed at Baylor College of Medicine Human Genome Sequencing Center 1. DNA from genomic clones are pooled together 2Pooled Genomic Indexing Mikl´os Csur¨os Department of Computer Science and Operations Research

Csürös, Miklós

408

Prediction of weld strength and seam width for laser transmission welding of thermoplastic using response surface methodology  

NASA Astrophysics Data System (ADS)

In the present work, a study is made to investigate the effects of process parameters, namely, laser power, welding speed, size of the laser beam and clamp pressure, on the lap-shear strength and weld-seam width for laser transmission welding of acrylic (polymethyl methacrylate), using a diode laser system. Response surface methodology (RSM) is employed to develop mathematical relationships between the welding process parameters and the output variables of the weld joint to determine the welding input parameters that lead to the desired weld quality. In addition, using response surface plots, the interaction effects of process parameters on the responses are analyzed and discussed. The statistical software Design-Expert v7 is used to establish the design matrix and to obtain the regression equations. The developed mathematical models are tested by analysis-of-variance (ANOVA) method to check their adequacy. Finally, a comparison is made between measured and calculated results, which are in good agreement. This indicates that the developed models can predict the responses adequately within the limits of welding parameters being used.

Acherjee, Bappa; Misra, Dipten; Bose, Dipankar; Venkadeshwaran, K.

2009-11-01

409

Acoustic microscopy of internal structure of resistance spot welds.  

PubMed

Acoustic microscopy, although relatively new, has many advantages within the industrial quality control process. Its high degree of sensitivity, resolution, and reliability make it ideal for use in resistance spot weld analysis, aiding in visualization of small-scale nugget failures, as well as other defects, at various depths. Acoustic microscopy makes it possible to inspect fine detail of internal structures, providing reliable inspection and characterization of weld joints. Besides weld size measurements, this technique is able to provide high resolution, three-dimensional images of the weld nuggets, revealing possible imperfections within its microstructure that may affect joint quality. The high degree of accuracy allows one to consider the results of acoustic microscopy an authoritative measure of weld size, particularly in the case of high strength steels, dual phase steel, USIBOR steel, etc. Indeed, this technique is effective even when both conventional ultrasound and hammer and chisel methods are not. In this paper, the potential of scanning acoustic microscopy as a means to provide qualitative and quantitative information about the internal microstructure of the resistance spot welds is demonstrated. Thus, acoustic microscopy is shown to be a unique and effective laboratory instrument for the evaluation and calibration of weld quality. PMID:17703655

Chertov, Andrey M; Maev, Roman G; Severin, Fedar M

2007-08-01

410

Robotics for welding research  

SciTech Connect

The welding metallurgy research and education program at Colorado School of Mines (CSM) is helping industries make the transition toward automation by training students in robotics. Industry's interest is primarily in pick and place operations, although robotics can increase efficiency in areas other than production. Training students to develop fully automated robotic welding systems will usher in new curriculum requirements in the area of computers and microprocessors. The Puma 560 robot is CSM's newest acquisition for welding research 5 references, 2 figures, 1 table.

Braun, G.; Jones, J.

1984-09-01

411

Thermal stir welding apparatus  

NASA Technical Reports Server (NTRS)

A welding method and apparatus are provided for forming a weld joint between first and second elements of a workpiece. The method includes heating the first and second elements to form an interface of material in a plasticized or melted state interface between the elements. The interface material is then allowed to cool to a plasticized state if previously in a melted state. The interface material, while in the plasticized state, is then mixed, for example, using a grinding/extruding process, to remove any dendritic-type weld microstructures introduced into the interface material during the heating process.

Ding, R. Jeffrey (Inventor)

2011-01-01

412

WELDING RESEARCH -s55WELDING JOURNAL  

E-print Network

process is assessed in this research. A Laser Engineered Net Shaping (LENS®) unit was used to prepare of this approach in actual service conditions. Introduction Failure of Dissimilar Metal Welds Many applications be found in power generation applications. The pri- mary boilers and heat exchangers in coal- fired power

DuPont, John N.

413

Microstructure of Laser-MAG Hybrid Welds of Sintered P/M Steel  

NASA Astrophysics Data System (ADS)

The microstructure and mechanical properties of iron-based powder metallurgical steels jointed by CO2 laser-metal active gas (MAG) hybrid welding were investigated. The cross-sectional morphology of hybrid weld bead consisted of arc zone and laser zone. The microstructure of arc zone consisted of columnar dendrite and fine acicular dendrite between the columnar dendrites, but that of laser zone was composed of fine equiaxed dendrite. The MAG weld had obvious heat-affected zone (HAZ) zone, while hybrid weld had very narrow HAZ zone because of the rapid cooling rate. The phase constitutions of the joint determined by x-ray diffraction were ?-Fe (ferrite) and Cu. The 2? value of ?-Fe (200) peaks of hybrid weld was smaller than that of sintering compact. Compared to MAG weld, hybrid weld had finer grain size, higher micro-hardness, and higher micro-strain, which was caused by the difference of cooling rate and crystallizing.

Liu, Shuangyu; Zhang, Hong; Hu, Jiandong; Shi, Yan

2013-01-01

414

A Three-Pool Model Dissecting Readily Releasable Pool Replenishment at the Calyx of Held  

PubMed Central

Although vesicle replenishment is critical in maintaining exo-endocytosis recycling, the underlying mechanisms are not well understood. Previous studies have shown that both rapid and slow endocytosis recycle into a very large recycling pool instead of within the readily releasable pool (RRP), and the time course of RRP replenishment is slowed down by more intense stimulation. This finding contradicts the calcium/calmodulin-dependence of RRP replenishment. Here we address this issue and report a three-pool model for RRP replenishment at a central synapse. Both rapid and slow endocytosis provide vesicles to a large reserve pool (RP) ~42.3 times the RRP size. When moving from the RP to the RRP, vesicles entered an intermediate pool (IP) ~2.7 times the RRP size with slow RP-IP kinetics and fast IP-RRP kinetics, which was responsible for the well-established slow and rapid components of RRP replenishment. Depletion of the IP caused the slower RRP replenishment observed after intense stimulation. These results establish, for the first time, a realistic cycling model with all parameters measured, revealing the contribution of each cycling step in synaptic transmission. The results call for modification of the current view of the vesicle recycling steps and their roles. PMID:25825223

Guo, Jun; Ge, Jian-long; Hao, Mei; Sun, Zhi-cheng; Wu, Xin-sheng; Zhu, Jian-bing; Wang, Wei; Yao, Pan-tong; Lin, Wei; Xue, Lei

2015-01-01

415

Effects of shielding gas hydrogen content on the arc behavior in gas tungsten arc welding  

SciTech Connect

The primary role of the shielding gas in gas tungsten arc welding (GTAW) is to protect the weld pool and tungsten electrode from the oxygen and nitrogen in the surrounding atmosphere. Traditionally inert gases such as argon and helium have been used, either as pure gases or mixed with each other. However, additions of small amounts of hydrogen have been reported to improve weld bead penetration and enable higher welding speeds to be used. The present work was performed to investigate the effect of small hydrogen additions on the arc behavior in GTAW, and to further the fundamental understanding of the effect of shielding gas on arc characteristics. GTAW bead-on-plate welds were made on 12.5 mm x 150 mm x 75 mm Type 304 stainless steel test coupons. The welding current, voltage, and their variations were continuously monitored during welding. After welding, each test coupon was sectioned and prepared using standard metallographic techniques and etched in Vilella`s etch for macroexamination of the weld bead cross section. Bead width, depth, and cross-sectional area were measured using a LECO image analysator system. The influence of hydrogen content in an argon has tungsten arc was characterized. The electrical behavior of the arc, including the arc resistance, was measured as a function of current and hydrogen content. A better fundamental understanding of arc behavior and energy transfer was achieved using these experimental gas mixes. The results allow the following conclusions to be drawn: (1) Small additions of hydrogen in the argon based shielding gas in gas tungsten arc welding significantly change the weld bead geometry due to changes in the arc column. (2) Selection of the right argon, hydrogen shielding gas mixture to give the optimum arc column characteristics for a given condition can improve weld quality and increase productivity. (3) The resistance of the arc column was found to be an adequate parameter to describe the arc column behavior.

Onsoien, M.I.; Olson, D.L.; Liu, S. [Colorado School of Mines, Golden, CO (United States)] [and others

1994-12-31

416

Eddy current inspection of weld defects in tubing  

NASA Technical Reports Server (NTRS)

An approach using differential probes for the inspection of weld defects in tubing is studied. Finite element analysis is used to model the weld regions and defects. Impedance plane signals are predicted for different weld defect types and compared wherever possible with signals from actual welds in tubing. Results show that detection and sizing of defects in tubing is possible using differential eddy current techniques. The phase angle of the impedance plane trajectory gives a good indication of the sizing of the crack. Data on the type of defect can be obtained from the shape of the impedance plane trajectory and the phase. Depending on the skin depth, detection of outer wall, inner wall, and subsurface defects is possible.

Katragadda, G.; Lord, W.

1992-01-01

417

49 CFR 179.300-9 - Welding.  

Code of Federal Regulations, 2010 CFR

...Welding. (a) Longitudinal joints must be fusion welded. Head-to-shell joints must...subchapter). (b) Fusion-welded joints must be in compliance with...radiotaped. (c) Forge-welded joints shall be thoroughly...

2010-10-01

418

49 CFR 179.300-9 - Welding.  

Code of Federal Regulations, 2011 CFR

...Welding. (a) Longitudinal joints must be fusion welded. Head-to-shell joints must...subchapter). (b) Fusion-welded joints must be in compliance with...radiotaped. (c) Forge-welded joints shall be thoroughly...

2011-10-01

419

Fiber Laser Welded AZ31 Magnesium Alloy: The Effect of Welding Speed on Microstructure and Mechanical Properties  

NASA Astrophysics Data System (ADS)

This study was aimed at characterizing microstructural change and evaluating tensile and fatigue properties of fiber laser welded AZ31B-H24 Mg alloy with special attention to the effect of welding speed. Laser welding led to the formation of equiaxed dendrites in the fusion zone and columnar dendrites near the fusion zone boundary along with divorced eutectic Mg17Al12 particles and recrystallized grains in the heat-affected zone. The lowest hardness across the weld appeared in the fusion zone. Although the yield strength, ductility, and fatigue life decreased, the hardening capacity increased after laser welding, with a joint efficiency reaching about 90 pct. A higher welding speed resulted in a narrower fusion zone, smaller grain size, higher yield strength, and longer fatigue life, as well as a slightly lower strain-hardening capacity mainly because of the smaller grain sizes. Tensile fracture occurred in the fusion zone, whereas fatigue failure appeared essentially in between the heat-affected zone and the fusion zone. Fatigue cracks initiated from the near-surface welding defects and propagated by the formation of fatigue striations together with secondary cracks.

Chowdhury, S. H.; Chen, D. L.; Bhole, S. D.; Powidajko, E.; Weckman, D. C.; Zhou, Y.

2012-06-01

420

Thermal plasma properties for Ar-Al, Ar-Fe and Ar-Cu mixtures used in welding plasmas processes: I. Net emission coefficients at atmospheric pressure  

NASA Astrophysics Data System (ADS)

This article is devoted to the calculation of the net emission coefficient (NEC) of Ar-Al, Ar-Fe and Ar-Cu mixtures at atmospheric pressure for arc welding processes. The results are given in data tables for temperatures between 3 kK and 30 kK, for five plasma thicknesses (0, 0.5, 1, 2, 5 mm) and ten concentrations of metallic vapours (pure gas, 0.01%, 0.1%, 1%, 5%, 10%, 25%, 50%, 75% and pure metal vapours in mass proportions). The results are in good agreement with most of the works published on the subject for such mixtures. They highlight the influence of three parameters on the radiation of the plasma: the NEC is directly related to temperature and inversely related to plasma radius and is highly sensitive to the presence of metal vapours. Finally, numerical data are supplied in tables in order to develop accurate computational modelling of welding arc and to estimate both qualitatively and quantitatively the influence of each metallic vapour on the size and on the shape of the weld pool.

Cressault, Y.; Gleizes, A.

2013-10-01

421

Weld failure detection  

DOEpatents

Method and apparatus for detecting failure in a welded connection, particrly applicable to not readily accessible welds such as those joining components within the reactor vessel of a nuclear reactor system. A preselected tag gas is sealed within a chamber which extends through selected portions of the base metal and weld deposit. In the event of a failure, such as development of a crack extending from the chamber to an outer surface, the tag gas is released. The environment about the welded area is directed to an analyzer which, in the event of presence of the tag gas, evidences the failure. A trigger gas can be included with the tag gas to actuate the analyzer.

Pennell, William E. (Unity Township, Westmoreland County, PA); Sutton, Jr., Harry G. (Mt. Lebanon, PA)

1981-01-01

422

Investigation of electromagnetic welding  

E-print Network

We propose several methodologies to study and optimize the electromagnetic process for Electromagnetic Forming (EMF) and Welding (EMW), thereby lowering the necessary process energy up to a factor of three and lengthening ...

Pressl, Daniel G. (Daniel Gerd)

2009-01-01

423

Friction stir welding tool  

DOEpatents

A friction stir welding tool is described and which includes a shank portion; a shoulder portion which is releasably engageable with the shank portion; and a pin which is releasably engageable with the shoulder portion.

Tolle, Charles R. (Idaho Falls, ID); Clark, Denis E. (Idaho Falls, ID); Barnes, Timothy A. (Ammon, ID)

2008-04-15

424

Online NIR diagnostic of laser welding processes and its potential for quality assuring sensor systems  

NASA Astrophysics Data System (ADS)

We have integrated an imaging thermographic sensor into commercial welding optics for observation of the weld zone. Key element of the sensor is an InGaAs-camera that detects the thermal radiation of the welding process in the wavelength range of 1,200 to 1,700 nm. This is well suited to record images of the keyhole, the melt pool and the thermal trace. The sensor was integrated to the welding heads for on-axis observation to minimize the interfering contour to ensure easy adaption to industrial processes. The welding heads used were established industrial-grade TRUMPF optics: a BEO fixed optics with 280 mm focal length, or a TRUMPF PFO-3D scanner optics with 450 mm focal length. We used a TRUMPF TruDisk 16002 16kW-thin disk laser that transmits its power through a 200 ?m core diameter light cable. The images were recorded and features of the various process zones were evaluated by image processing. It turns out that almost all weld faults can be clearly detected in the NIR images. Quantitative features like the dimension of the melt pool and the thermal trace can be derived from the captured images. They are correlated to process input parameters as well as to process results. In contrast to observation in the visible spectrum the NIR camera records the melt pool without auxiliary illumination. As an unrivaled attribute of the NIR sensor it supports an online heat flow thermography of the seam and allows identifying missing fusion ("false friends") of lap joints virtually during the welding process. Automated weld fault detection and documentation is possible by online image processing which sets the basis for comprehensive data documentation for quality assurance and traceability.

Dorsch, Friedhelm; Braun, Holger; Keβler, Steffen; Pfitzner, Dieter; Rominger, Volker

2014-02-01

425

13 CFR 120.1706 - Pool Originator's retained interest in Pool.  

Code of Federal Regulations, 2013 CFR

...interest will decline with Loan Interest payments, prepayments, defaults and any other early termination. At Pool formation, the CSA will issue the Pool Originator a Pool Originator Receipt evidencing the Pool Originator's retained interest in the Pool....

2013-01-01

426

13 CFR 120.1706 - Pool Originator's retained interest in Pool.  

Code of Federal Regulations, 2010 CFR

...interest will decline with Loan Interest payments, prepayments, defaults and any other early termination. At Pool formation, the CSA will issue the Pool Originator a Pool Originator Receipt evidencing the Pool Originator's retained interest in the Pool....

2010-01-01

427

13 CFR 120.1706 - Pool Originator's retained interest in Pool.  

Code of Federal Regulations, 2011 CFR

...interest will decline with Loan Interest payments, prepayments, defaults and any other early termination. At Pool formation, the CSA will issue the Pool Originator a Pool Originator Receipt evidencing the Pool Originator's retained interest in the Pool....

2011-01-01

428

13 CFR 120.1708 - Pool Certificates.  

Code of Federal Regulations, 2010 CFR

...backing a Pool Certificate, SBA, through the CSA, will make advances to maintain the schedule... (e) Pool Certificate form. The CSA prepares the Pool Certificate. SBA must...Certificate must be registered with the CSA. (g) Face amount of Pool...

2010-01-01

429

13 CFR 120.1708 - Pool Certificates.  

Code of Federal Regulations, 2013 CFR

...backing a Pool Certificate, SBA, through the CSA, will make advances to maintain the schedule... (e) Pool Certificate form. The CSA prepares the Pool Certificate. SBA must...Certificate must be registered with the CSA. (g) Face amount of Pool...

2013-01-01

430

13 CFR 120.1708 - Pool Certificates.  

Code of Federal Regulations, 2011 CFR

...backing a Pool Certificate, SBA, through the CSA, will make advances to maintain the schedule... (e) Pool Certificate form. The CSA prepares the Pool Certificate. SBA must...Certificate must be registered with the CSA. (g) Face amount of Pool...

2011-01-01

431

13 CFR 120.1708 - Pool Certificates.  

Code of Federal Regulations, 2012 CFR

...backing a Pool Certificate, SBA, through the CSA, will make advances to maintain the schedule... (e) Pool Certificate form. The CSA prepares the Pool Certificate. SBA must...Certificate must be registered with the CSA. (g) Face amount of Pool...

2012-01-01

432

13 CFR 120.1708 - Pool Certificates.  

Code of Federal Regulations, 2014 CFR

...backing a Pool Certificate, SBA, through the CSA, will make advances to maintain the schedule... (e) Pool Certificate form. The CSA prepares the Pool Certificate. SBA must...Certificate must be registered with the CSA. (g) Face amount of Pool...

2014-01-01

433

Weld braze technique  

DOEpatents

High-strength metal joints are formed by a combined weld-braze technique. A hollow cylindrical metal member is forced into an undersized counterbore in another metal member with a suitable braze metal disposed along the bottom of the counterbore. Force and current applied to the members in an evacuated chamber results in the concurrent formation of the weld along the sides of the counterbore and a braze along the bottom of the counterbore in one continuous operation.

Kanne, Jr., William R. (Aiken, SC); Kelker, Jr., John W. (North Augusta, SC); Alexander, Robert J. (Aiken, SC)

1982-01-01

434

Welding and joining techniques.  

PubMed

There is a welding solution for most applications. As products must meet more stringent requirements or require more flexible processes to aid design or reduce cost, further improvements or totally new processes are likely to be developed. Quality control aspects are also becoming more important to meet regulation, and monitoring and control of welding processes and the standardised testing of joints will meet some if not all of these requirements. PMID:11521652

Chipperfield, F A; Dunkerton, S B

2001-05-01

435

Friction Stir Weld Tools  

NASA Technical Reports Server (NTRS)

A friction stir weld tool sleeve is supported by an underlying support pin. The pin material is preferably selected for toughness and fracture characteristics. The pin sleeve preferably has a geometry which employs the use of an interrupted thread, a plurality of flutes and/or eccentric path to provide greater flow through. Paddles have been found to assist in imparting friction and directing plastic metal during the welding process.

Carter, Robert W. (Inventor); Payton, Lewis N. (Inventor)

2007-01-01

436

Friction stir weld tools  

NASA Technical Reports Server (NTRS)

A friction stir weld tool sleeve is supported by an underlying support pin. The pin material is preferably selected for toughness and fracture characteristics. The pin sleeve preferably has a geometry which employs the use of an interrupted thread, a plurality of flutes and/or eccentric path to provide greater flow through. Paddles have been found to assist in imparting friction and directing plastic metal during the welding process.

Carter, Robert W. (Inventor); Payton, Lewis N. (Inventor)

2007-01-01

437

Investigation of transport phenomena and defect formation in pulsed laser keyhole welding of zinc-coated steels  

NASA Astrophysics Data System (ADS)

Lasers are being used to weld zinc-coated steels due to high welding speed, high aspect ratio, and narrow heat affected zone. However, escape of high-pressure zinc vapour in the welding process can damage the weld pool continuity and cause large voids and serious undercuts in the final welds. In this paper, a mathematical model and the associated numerical techniques have been developed to study the transport phenomena and defect formation mechanisms in pulsed laser keyhole welding of zinc-coated steels. The volume-of-fluid (VOF) method is employed to track free surfaces. The continuum model is used to handle the liquid phase, the solid phase and the mushy zone of the metal. The enthalpy method is employed to account for the latent heat during melting and solidification. The transient heat transfer and melt flow in the weld pool during the keyhole formation and collapse processes are calculated. The escape of zinc vapour through the keyhole and the interaction between zinc vapour and weld pool are studied. Voids in the welds are found to be caused by the combined effects of zinc vapour-melt interactions, keyhole collapse and solidification process. By controlling the laser pulse profile, it is found that the keyhole collapse and solidification process can be delayed, allowing the zinc vapour to escape, which results in the reduction or elimination of voids. The good agreement between the model predictions and the experimental observations indicates that the proposed model lays a solid foundation for future study of laser welding of zinc-coated steels.

Zhou, J.; Tsai, H. L.; Lehnhoff, T. F.

2006-12-01

438

Weld radiograph enigmas  

NASA Technical Reports Server (NTRS)

Weld radiograph enigmas are features observed on X-ray radiographs of welds. Some of these features resemble indications of weld defects, although their origin is different. Since they are not understood, they are a source of concern. There is a need to identify their causes and especially to measure their effect on weld mechanical properties. A method is proposed whereby the enigmas can be evaluated and rated, in relation to the full spectrum of weld radiograph indications. Thie method involves a signature and a magnitude that can be used as a quantitive parameter. The signature is generated as the diference between the microdensitometer trace across the radiograph and the computed film intensity derived from a thickness scan along the corresponding region of the sample. The magnitude is the measured difference in intensity between the peak and base line values of the signature. The procedure is demonstated by comparing traces across radiographs of a weld sample before and after the introduction of a hole and by a system based on a MacIntosh mouse used for surface profiling.

Jemian, Wartan A.

1986-01-01

439

Concurrent ultrasonic weld evaluation system  

DOEpatents

A system for concurrent, non-destructive evaluation of partially completed welds for use in conjunction with an automated welder is disclosed. The system utilizes real time, automated ultrasonic inspection of a welding operation as the welds are being made by providing a transducer which follows a short distance behind the welding head. Reflected ultrasonic signals are analyzed utilizing computer based digital pattern recognition techniques to discriminate between good and flawed welds on a pass by pass basis. The system also distinguishes between types of weld flaws. 5 figs.

Hood, D.W.; Johnson, J.A.; Smartt, H.B.

1987-12-15

440

Concurrent ultrasonic weld evaluation system  

DOEpatents

A system for concurrent, non-destructive evaluation of partially completed welds for use in conjunction with an automated welder. The system utilizes real time, automated ultrasonic inspection of a welding operation as the welds are being made by providing a transducer which follows a short distance behind the welding head. Reflected ultrasonic signals are analyzed utilizing computer based digital pattern recognition techniques to discriminate between good and flawed welds on a pass by pass basis. The system also distinguishes between types of weld flaws.

Hood, D.W.; Johnson, J.A.; Smartt, H.B.

1985-09-04

441

Lasers of All Sizes  

NASA Astrophysics Data System (ADS)

* Introduction * The Laser in All Its Forms * Gas lasers * Dye lasers * Solid-state lasers * Lasers for Every Taste * The rise of lasers * Lasers of all sizes * The colors of the rainbow... and beyond * Shorter and shorter lasers * Increasingly powerful lasers * Lasers: A Universal Tool? * Cutting, welding, and cleaning * Communicating * Treating illnesses * Measuring * Supplying energy? * Entertaining * Understanding * Conclusion

Balcou, Philippe; Forget, Sébastien Robert-Philip, Isabelle

2015-10-01

442

Mitigating Abnormal Grain Growth for Friction Stir Welded Al-Li 2195 Spun Formed Domes  

NASA Technical Reports Server (NTRS)

Formability and abnormal grain growth (AGG) are the two major issues that have been encountered for Al alloy spun formed dome development using friction stir welded blanks. Material properties that have significant influence on the formability include forming range and strain hardening exponent. In this study, tensile tests were performed for two 2195 friction stir weld parameter sets at 400 F to study the effects of post weld anneal on the forming range and strain hardening exponent. It was found that the formability can be enhanced by applying a newly developed post weld anneal to heat treat the friction stir welded panels. This new post weld anneal leads to a higher forming range and much improved strain hardening exponent. AGG in the weld nugget is known to cause a significant reduction of ductility and fracture toughness. This study also investigated how AGG may be influenced by the heating rate to the solution heat treatment temperature. After post-weld annealing, friction stir welds were strained to 15% and 39% by compression at 400 F before they were subjected to SHT at 950 F for 1 hour. Salt bath SHT is very effective in reducing the grain size as it helps arrest the onset of AGG and promote normal recrystallization and grain growth. However, heat treating a 18 ft dome using a salt bath is not practical. Efforts are continuing at Marshall Space Flight Center to identify the welding parameters and heat treating parameters that can help mitigate the AGG in the friction stir welds.