Note: This page contains sample records for the topic weld pool size from Science.gov.
While these samples are representative of the content of Science.gov,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of Science.gov
to obtain the most current and comprehensive results.
Last update: August 15, 2014.
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

Visualization of gas tungsten arc weld pools  

Microsoft Academic Search

Surface flow visualization of gas tungsten arc weld pools for HY-80 steel is presented using a pulsed laser light source and a conventional night vision image-intensifier tube equipped video camera. Visualization of the weld pool free surface is made possible by seeding a flow with alumina particles for both stationary and moving arc welds. These visualizations reveal several new features

Daniel C. Espinosa

1991-01-01

3

Obtaining weld pool vision information during aluminium alloy TIG welding  

Microsoft Academic Search

An image sensing system for the TIG (tungsten inert-gas arc) welding process of aluminium alloy was established. The relationships between the image sensing system and the characteristic of welding current were discussed in detail. Front and back images of the weld pool were obtained with different welding parameters. In order to process the image, the characteristics of an aluminium alloy

J. J. Wang; T. Lin; S. B. Chen

2005-01-01

4

The study of surface active element on weld pool development in A-TIG welding  

NASA Astrophysics Data System (ADS)

A 3D mathematical model was developed to simulate the weld pool development in a moving A-TIG weld pool with different oxygen and sulfur concentrations. It is shown that the surface active elements—oxygen and sulfur, which change the temperature coefficient of surface tension from a negative value to a positive one, can cause significant changes in fluid flow patterns and the weld penetration. When surface active element content increases, the weld penetration and depth/width ratio increase sharply and then remain nearly a constant. Positive temperature coefficient of surface tension dominates the fluid flow and the weld pool is narrow and deep. The further increasing surface active element content leads to an inappreciable difference in the weld pool size and shape when the oxygen content increases beyond 280 ppm and sulfur content beyond 125 ppm. Positive and negative temperature coefficients of surface tension co-exist in the weld pool when surface active element content is less than the critical value. The fluid flows in the weld pool change apparently with different surface active element. Depending upon the oxygen and sulfur concentrations, three, one or two vortexes that have different positions, strength and directions may be found in the weld pool. The vortexes with opposite direction caused by positive temperature coefficient of surface tension can efficiently transfer the thermal energy from the arc, creating a deep weld pool.

Zhao, Yuzhen; Zhou, Heping; Shi, Yaowu

2006-04-01

5

Numerical simulation on interaction between TIG welding arc and weld pool  

Microsoft Academic Search

The interface deformation between welding arc and weld pool is important in dynamic coupling numerical simulation on arc and pool. To reveal the interaction between welding arc and weld pool, unified mathematic model of TIG welding arc and pool was established in this paper. The moving interface was solved by updating the calculation region of arc and weld pool continually.

Fenggui Lu; Xinhua Tang; Hailiang Yu; Shun Yao

2006-01-01

6

Visualization of Gas Tungsten Arc Weld Pools.  

National Technical Information Service (NTIS)

Surface flow visualization of Gas Tungsten Arc weld pools for HY-80 steel is presented using a pulsed laser light source and a conventional night vision image-intensifier tube equipped video camera. Visualization of the weld pool free surface is made poss...

D. C. Espinosa

1991-01-01

7

Control of Gas Tungsten Arc welding pool shape by trace element addition to the weld pool  

DOEpatents

An improved process for Gas Tungsten Arc welding maximizes the depth/width ratio of the weld pool by adding a sufficient amount of a surface active element to insure inward fluid flow, resulting in deep, narrow welds. The process is especially useful to eliminate variable weld penetration and shape in GTA welding of steels and stainless steels, particularly by using a sulfur-doped weld wire in a cold wire feed technique.

Heiple, C.R.; Burgardt, P.

1984-03-13

8

Visualization of gas tungsten arc weld pools  

NASA Astrophysics Data System (ADS)

Surface flow visualization of gas tungsten arc weld pools for HY-80 steel is presented using a pulsed laser light source and a conventional night vision image-intensifier tube equipped video camera. Visualization of the weld pool free surface is made possible by seeding a flow with alumina particles for both stationary and moving arc welds. These visualizations reveal several new features not incorporated in the existing models for stationary welds. A strong clockwise stirring is observed contrary to the axisymmetric computational models. Also, the pool surface shows a bulge near the center. Complex flow patterns are observed for moving arc welding. Interpretations of the observed flows based on the driving forces are provided.

Espinosa, Daniel C.

1991-09-01

9

A keyhole volumetric model for weld pool analysis in Nd:YAG pulsed laser welding  

NASA Astrophysics Data System (ADS)

This study presents a new model for analyzing the temperature distribution and weld pool shape in Nd:YAG pulsed laser welding. In the proposed approach, a surface flux heat transfer model is applied in the low laser energy intensity region of the weld, while a keyhole heat transfer model based on a volumetric heat source is applied in the high laser energy intensity region of the weld. The correlation between the intensity of the laser input energy and the geometric parameters of the volumetric heat source is derived experimentally. A series of MARC finite element simulations based on the proposed single pulse model are performed to investigate the shape and size of the weld pool given different laser energy intensities. A good agreement is observed between the simulation results and the experimental results obtained under equivalent single pulse welding conditions. Thus, the basic validity of the proposed model is confirmed.

Kuang, Jao-Hwa; Hung, Tsung-Pin; Chen, Chih-Kuan

2012-07-01

10

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

11

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

12

Weld Pool Flow Visualization Studies during Gas Tungsten Arc Welding of Steel and Aluminum.  

National Technical Information Service (NTIS)

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 pa...

P. E. Schupp

1992-01-01

13

Neural network modeling of pulsed-laser weld pool shapes in aluminum alloy welds.  

National Technical Information Service (NTIS)

A model was developed to predict the weld pool shape in pulsed Nd:YAG laser welds of aluminum alloy 5754. The model utilized neural network analysis to relate the weld process conditions to four pool shape parameters: penetration, width, width at half-pen...

J. M. Vitek, Y. S. Iskander, E. M. Oblow, S. S. Babu, S. A. David

1998-01-01

14

Neural network modeling of pulsed-laser weld pool shapes in aluminum alloy welds.  

National Technical Information Service (NTIS)

A model was developed to predict the weld pool shape in pulsed Nd:YAG laser welds of aluminum alloy 5754. The model utilized neural network analysis to relate the weld process conditions to four pool shape parameters: (1) penetration width, (2) width at h...

J. M. Vitek, Y. S. Iskander, E. M. Oblow, S. S. Babu, S. A. David

1998-01-01

15

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

SciTech Connect

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 of turbulent nature are observed at higher currents. Autogenous welds on 17.75 cm by 28.0 cm by 1.27 cm thick 6061 aluminum plates are also studied to determine resulting surface flow characteristics and weld pool growth rates. Clockwise stirring in conjunction with a vertical undulation is noted in stationary welds. Solidified weld zone exhibits a profound crater that was not present in welds on HY-80 Steel.

Schupp, P.E.

1992-03-01

16

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

NASA Astrophysics Data System (ADS)

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 of turbulent nature are observed at higher currents. Autogenous welds on 17.75 cm by 28.0 cm by 1.27 cm thick 6061 aluminum plates are also studied to determine resulting surface flow characteristics and weld pool growth rates. Clockwise stirring in conjunction with a vertical undulation is noted in stationary welds. Solidified weld zone exhibits a profound crater that was not present in welds on HY-80 Steel.

Schupp, Peter E.

1992-03-01

17

Dynamic behavior of the weld pool in stationary GMAW  

NASA Astrophysics Data System (ADS)

Because hump formation limits welding productivity, better understanding of the humping phenomena during the welding process is needed to access to process modifications that decrease the tendency for hump formation and then allow higher productivity welding. From a physical point of view, the mechanism identified is the Rayleigh instability initiated by strong surface tension gradient which induces a variation of kinetic flow. But the causes of the appearance of this instability are not yet well explained. Because of the phenomena complex and multi-physics, we chose in first step to conduct an analysis of the characteristic times involved in weld pool in pulsed stationary GMAW. The goal is to study the dynamic behavior of the weld pool, using our experimental multi physics approach. The experimental tool and methodology developed to understand these fast phenomena are presented first: frames acquisition with high speed digital camera and specific optical devices, numerical library. The analysis of geometric parameters of the weld pool during welding operation are presented in the last part: we observe the variations of wetting angles (or contact lines angles), the base and the height of the weld pool (macro-drop) versus weld time.

Chapuis, J.; Romero, E.; Bordreuil, C.; Soulié, F.; Fras, G.

2010-06-01

18

Characterizing weld pool surfaces from polarization state of thermal emissions.  

PubMed

In this Letter, a vision-based remote sensing methodology is proposed to measure the topography of weld pool surfaces from one single view. Thermal radiations emitted by the hot liquid metal at a wavelength within the arc plasma blind spectral window are acquired by a wavefront division polarimetric system. The refractive index of the liquid metal and the topography of the weld pool surface are inferred from the polarimetric state of the thermal radiations. PMID:23938985

Coniglio, Nicolas; Mathieu, Alexandre; Aubreton, Olivier; Stolz, Christophe

2013-06-15

19

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

20

Measurement and prediction of weld pool shape during gas metal arc welding using a noncontact laser profiling system  

NASA Astrophysics Data System (ADS)

The main objective of this work is to provide detailed measurement of the full 3-dimensional weld pool shape for the Gas Metal Arc Welding (GMAW) process. Relationships between the welding process variables and important pool shape parameters have been established, and the measured profile is in an appropriate form for use in numerical models of the GMA welding process. A mechanical ejection device instantaneously emptied the molten metal from weld pool by rapidly accelerating and decelerating the test plate being welded. A non-contact laser profiling system is used for accurate measurement of the exposed weld pools. Welding speed and welding current are found to have the greatest influence on the length of a weld pool, and increasing heat input level yields higher values for all critical weld pool dimensions.

Wahab, M. A.; Painter, M. J.

1997-03-01

21

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

22

Optical spectral radiometric method for measurement of weld-pool surface temperatures.  

PubMed

A new experimental method has been developed for making weld-pool surface-temperature field measurements. The method requires spectral measurements of the directional emissive power and the directional emissivity of the weld pool. The technique has been successfully demonstrated for measuring the weld-pool surface-temperature field for gas tungsten arc thin-plate SS 304 welds. PMID:19738755

Kraus, H G

1986-12-01

23

Effects of surface active elements on weld pool fluid flow and weld penetration in gas metal arc welding  

NASA Astrophysics Data System (ADS)

This article presents a mathematical model simulating the effects of surface tension (Maragoni effect) on weld pool fluid flow and weld penetration in spot gas metal arc welding (GMAW). Filler droplets driven by gravity, electromagnetic force, and plasma arc drag force, carrying mass, thermal energy, and momentum, periodically impinge onto the weld pool. Complicated fluid flow in the weld pool is influenced by the droplet impinging momentum, electromagnetic force, and natural convection due to temperature and concentration gradients, and by surface tension, which is a function of both temperature and concentration of a surface active element (sulfur in the present study). Although the droplet impinging momentum creates a complex fluid flow near the weld pool surface, the momentum is damped out by an “up-and-down” fluid motion. A numerical study has shown that, depending upon the droplet’s sulfur content, which is different from that in the base metal, an inward or outward surface flow of the weld pool may be created, leading to deep or shallow weld penetration. In other words, it is primarily the Marangoni effect that contributes to weld penetration in spot GMAW.

Wang, Y.; Tsai, H. L.

2001-06-01

24

The study of surface active element on weld pool development in A-TIG welding  

Microsoft Academic Search

A 3D mathematical model was developed to simulate the weld pool development in a moving A-TIG weld pool with different oxygen and sulfur concentrations. It is shown that the surface active elements---oxygen and sulfur, which change the temperature coefficient of surface tension from a negative value to a positive one, can cause significant changes in fluid flow patterns and the

Yuzhen Zhao; Heping Zhou; Yaowu Shi

2006-01-01

25

Neural Network Modeling of Weld Pool Shape in Pulsed-Laser Aluminum Welds.  

National Technical Information Service (NTIS)

A neural network model was developed to predict the weld pool shape for pulsed-laser aluminum welds. Several different network architectures were examined and the optimum architecture was identified. The neural network was then trained and, in spite of th...

Y. S. Iskander, E. M. Oblow, J. M. Vitek

1998-01-01

26

Analysis of the transport phenomena in the interfacial region between TIG arcs and weld pools  

Microsoft Academic Search

It is of considerable practical interest in welding to provide a faithful representation of dynamic coupling between the welding arc and the weld pool surface. This paper introduces a three-dimensional model for fluid flow and heat transfer in the interfacial region between the TIG arc plasma and weld pool. It accounts for the interaction between the arc plasma and the

Z. Y. Li; C. S. Wu

1997-01-01

27

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

28

Visual sensing of weld pool in variable polarity TIG welding of aluminium alloy  

Microsoft Academic Search

The passive visual sensing method was successfully applied to monitor the weld pool in TIG welding of aluminium alloy. In order to reduce the disturbance from the arc and acquire clear image, two techniques were used: one was the own-developed computer-controlled variable polarity power(VPP), the other was the composite filter technology. The VPP source did not have high-frequency electromagnetic interference

Guang-jun ZHANG; Zhi-hong YAN; Lin WU

2006-01-01

29

Reflection of illumination laser from gas metal arc weld pool surface  

NASA Astrophysics Data System (ADS)

The weld pool is the core of the welding process where complex welding phenomena originate. Skilled welders acquire their process feedback primarily from the weld pool. Observation and measurement of the three-dimensional weld pool surface thus play a fundamental role in understanding and future control of complex welding processes. To this end, a laser line is projected onto the weld pool surface in pulsed gas metal arc welding (GMAW) and an imaging plane is used to intercept its reflection from the weld pool surface. Resultant images of the reflected laser are analyzed and it is found that the weld pool surface in GMAW does specularly reflect the projected laser as in gas tungsten arc welding (GTAW). Hence, the weld pool surface in GMAW is also specular and it is in principle possible that it may be observed and measured by projecting a laser pattern and then intercepting and imaging the reflection from it. Due to high frequencies of surface fluctuations, GMAW requires a relatively short time to image the reflected laser.

Ma, Xiaoji; Zhang, Yu Ming

2009-11-01

30

Influence of simulated high- G on the weld size of aL-lI alloy  

NASA Astrophysics Data System (ADS)

Whether welding processes are used on earth or in space, they have the same objective: to obtain defect-free welds. To fully understand the effect of gravity on the weld pool geometry and solidification one should perform experiments within a broad range of gravitational acceleration. High-gravity arc welding experiments were done on Al-Li alloy using the centrifuge called Multi-Gravity Research Welding System (MGRWS). At a high " g" level, buoyancy-driven flow is the dominant force in the weld pool over the Marangoni and the electromagnetic forces. Preliminary results show that the average grain size in the fusion zone at 1 g is smaller that at 5 g.

K. Aidun, Daryush

31

Detectability of penetration depth based on weld pool geometry and process emission spectrum in laser welding of copper  

NASA Astrophysics Data System (ADS)

Laser welding is a promising joining process for copper interconnections. A key criterion of quality for these welds is the penetration depth. The penetration depth is subject to intrinsic variation, i.e. by the nature of the welding process. Online detection of penetration depth enables quality assurance and furthermore welding of joint configurations with tighter tolerances via closed-loop control. Weld pool geometry and keyhole optical emission in the wavelength interval of 400-1100 nm are investigated with regard to how suitable they are for the detection of penetration depth in laser welding of copper Cu-ETP. Different penetration depths were induced by stepwise modulation of laser power in bead-on-plate welds. The welds have been monitored with illuminated high-speed videography of the work piece surface and spectrometry. Increase of the weld pool length (in direction of travel) corresponding to increase in penetration depth has been observed while no noticeable change was observed of the weld pool width (transverse to the direction of travel). No significant lines were observed in the spectrum. The radiant power in VIS-spectrum was observed to increase with increasing penetration depth as well. As future work, with increasing understanding and experimental data, online monitoring by indirectly measuring the penetration depth would be possible. The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement no 260153 (QCOALA: Quality Control for Aluminium Laser-Welded Assemblies).

Ã-zmert, Alp; Neisser-Deiters, Paul; Drenker, Alexander

2014-05-01

32

Three-dimensional reconstruction of specular surface for a gas tungsten arc weld pool  

NASA Astrophysics Data System (ADS)

Observing the weld pool and measuring its geometrical parameters are key issues for developing the next generation intelligent welding machine and modeling the complex welding process. In the past few years, different techniques have been applied, but the dynamic specular weld pool surface and the strong weld arc complicate these approaches and make observation difficult. To resolve the problem, a new three-dimensional sensing system using structured light is proposed for a gas tungsten arc welding (GTAW) process. In the system, a dot-matrix laser pattern is projected on the specular weld pool surface, which can reflect light onto an imaging plane. The reflected images are captured by a high-speed camera and can successfully be processed by image processing algorithms developed. With the acquired information, a three-dimensional reconstruction scheme is proposed and discussed in this paper. A surface reconstruction method with several slope-based algorithms is first developed to rebuild the region of weld pool surface which reflects the laser pattern. Then a two-dimensional piecewise model is provided to calculate weld pool boundary by utilizing the edge condition. Finally the optimal estimate of the three-dimensional weld pool surface is synthesized. The acceptable accuracy of the results verified the effectiveness of the reconstruction scheme.

Song, Hong Sheng; Zhang, Yu Ming

2007-12-01

33

In situ observations of weld pool solidification using transparent metal-analog systems  

Microsoft Academic Search

The dynamics of weld solidification were observed in situ using a laser welding process on transparent organic materials systems. Succinonitrile was used to simulate a pure metal system and succinonitrile with 1.2 wt. % acetone was used to simulate an alloy system. Observed weld pool shapes in succinonitrile were in good agreement with theoretical heat transfer calculations. The dynamics of

R. Trivedi; S. A. David; M. A. Eshelman; J. M. Vitek; S. S. Babu; T. Hong; T. Debroy

2003-01-01

34

Development of maintenance technology with underwater TIG welding for spent fuel storage pool  

Microsoft Academic Search

The core technology of an underwater TIG welding process has been developed and a welding equipment system has been manufactured for application to the maintenance of the spent fuel storage pool of Rokkasho reprocessing plant. Basic experiments for understanding the conditions of the dry area and the range of welding conditions was performed, and mock examination for simulation of the

Takeshi Obana; Yasumitsu Hamada; Toshihiro Ootsuka; Seiichi Toyoda; Atsushi Hosogane; Kaoru Ooeda; Masahide Katou

2009-01-01

35

Simulation of metal transfer and weld pool development in gas metal arc welding of thin sheet metals  

NASA Astrophysics Data System (ADS)

Gas metal arc welding (GMAW) is the most commonly used arc welding method in industry for joining steels and aluminum alloys. But due to the mathematical difficulties associated with the free surface motion of the molten droplet and the weld pool, the process is not well understood and the development of new welding procedures in the manufacturing industry highly depends on expensive, time-consuming and experience-based trial and error. In this dissertation, numerical methods are developed to overcome the difficulties and to simulate the metal transfer and weld pool development in the GMAW of sheet metals. The simulations are validated by experiments and used to study an industrial welding process. A numerical procedure is first developed to model the free surface motion in fusion welding processes. Thermal and electromagnetic models are integrated with the fluid models. Recommendations are made on the selection and improvement of publicly available numerical algorithms, while alternative methods are also reviewed. A model combining the enthalpy, effective-viscosity and volume-of-fluid methods is then developed to simulate the metal transfer process in globular, spray and short-circuiting transfer modes. The model not only describes the influence of gravity, electromagnetic force and surface tension on droplet profile and transfer frequency, but also models the nonisothermal phenomena such as heat transfer and phase change. The melting front motion, the droplet detachment and oscillation, the satellite formation and the fluid convection within the droplet are analyzed. It has been found that the taper formation in spray transfer is closely related to the heat input on the unmelted portion of the welding wire, and the taper formation affects the globular-spray transition by decelerating the transfer process. Experiments with a high-speed motion analyzer validate the simulation results. The model is then extended to simulate the initiation, development and solidification of the weld pool, with consideration of the droplet impingement on the pool surface. The characteristics of physical variables in the weld pool are analyzed. Burn-through of thin sheet metals and penetration of a multi-layered workpiece are also simulated. Experiments are used to verify the predicted weld penetration. Finally, numerical simulation is used to analyze an industrial welding process---the gas metal arc spot welding of multi-layered workpieces. The traditional spot welding and plug welding methods are simulated. It is shown that the plug method can ensure a stable short-circuiting transfer through a pre-made hole. Both the simulation and tensile-shear tests show that the plug method improves the penetration consistency by ensuring the effective joint diameter.

Wang, Fang

36

Vision detecting of arc welding pool surface topography based on projected grating  

NASA Astrophysics Data System (ADS)

A vision detecting of arc welding pool surface topography system was setup in this paper. A semiconductor laser as an active light-source which is projected laser on to the specialized grating and frost glass by collimating lens, deformed grating fringes are formed on the surface of arc welding pool, narrow band filter and neutral density filter are mounted on CCD for detecting pool surface topography at real time on the other side of the system. When projecting angle and shooting angle are selected properly, it can be avoided the interference of arc for pool image better, deformed grating fringes of pool surface can be detected. Deformed grating fringes are reflected the information of concave or convex of the pool. Two categories of stainless steel are experimented, deformed grating fringes of pool are got clearly under the condition of different welding current and different welding speed, pool edge is extracted by digital image processing technology, the geometric parameters of pool Front-side is obtained by demarcated and calculated successfully.

Wang, Yanfeng; Liu, Nansheng; Yuan, Youzhi; Luo, Wei; Liu, Xiaorui

2008-12-01

37

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

38

Numerical study of arc plasmas and weld pools for GTAW with applied axial magnetic fields  

NASA Astrophysics Data System (ADS)

A 3D numerical model containing the welding arc and the weld pool for gas tungsten arc welding (GTAW) with applied axial magnetic fields is established. The model is validated by comparing the calculated arc temperature with the measured ones. The influence of the magnetic field on the welding process is studied by changing the magnetic inductions, from 0 T to 0.06 T. For welding arcs, a radial spread is discovered, and a reverse flow appears over the anode. The distribution of temperature, heat flux, current density and pressure on the anode surface becomes double-peaked, while the voltage distributes in a double-valley type. For weld pools, the fluid flow cycle brings about a wide and shallow pool. In the circumferential direction, the fluid in the centre areas rotates in an opposite direction to that in the outer regions; in the axial direction, the fluid flows upwards at the centre while downwards in the edge area of the weld pool. All the driving forces including the surface tension, the shear stress from the arc plasma, the electromagnetic force and the buoyancy force that influence the fluid flow are analysed to explain these phenomena. The mechanism of how the applied axial magnetic field regulates the GTAW process is thus clarified.

Yin, Xianqing; Gou, Jianjun; Zhang, Jianxun; Sun, Jiangtao

2012-07-01

39

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

40

Melt pool and keyhole behaviour analysis for deep penetration laser welding  

NASA Astrophysics Data System (ADS)

One usually defines the main characteristic of the welding performances of a given laser system by its 'penetration curve' that corresponds to the welding depth as a function of the welding speed Vw for a given set of operating parameters. Analysis of a penetration curve is interesting and gives very fruitful results. Coupled with high-speed video imaging of melt pool surface and ejected plume behaviour, the analysis of this penetration curve on a very large range of welding speeds, typically from 0 to 50 m min-1, has allowed us to observe very different and characteristic regimes. These regimes are mainly characterized by the physical processes by which they impede the laser beam penetration inside the material. We show that it is only at rather high welding speeds that these limiting processes are reduced. Consequently, the scaling law of welding depth with welding speed is in agreement with adapted modelling of this process. On the other hand, as the welding speed is reduced, different effects depending on the weld pool dynamics and plume interaction strongly disturb the keyhole stability and are responsible for the deviation of the penetration curve from the previous modelling that agrees with a 1/Vw scaling law. A corresponding criterion for the occurrence of this effect is defined.

Fabbro, R.

2010-11-01

41

A three-dimensional sharp interface model for self-consistent keyhole and weld pool dynamics in deep penetration laser welding  

NASA Astrophysics Data System (ADS)

A three-dimensional sharp interface model is proposed to investigate the self-consistent keyhole and weld pool dynamics in deep penetration laser welding. The coupling of three-dimensional heat transfer, fluid flow and keyhole free surface evolutions in the welding process is simulated. It is theoretically confirmed that under certain low heat input welding conditions deep penetration laser welding with a collapsing free keyhole could be obtained and the flow directions near the keyhole wall are upwards and approximately parallel to the keyhole wall. However, significantly different weld pool dynamics in a welding process with an unstable keyhole are numerically found. Many flow patterns in the welding process with an unstable keyhole, verified by x-ray transmission experiments, were successfully simulated and analysed. Periodical keyhole collapsing and bubble formation processes are also successfully simulated and believed to be in good agreement with experiments. The mechanisms of keyhole instability are found to be closely associated with the behaviour of humps on the keyhole wall, and it is found that the welding speed and surface tension are closely related to the formation of humps on the keyhole wall. It is also shown that the weld pool dynamics in laser welding with an unstable keyhole are closely associated with the transient keyhole instability and therefore modelling keyhole and weld pool in a self-consistent way is significant to understand the physics of laser welding.

Pang, Shengyong; Chen, Liliang; Zhou, Jianxin; Yin, Yajun; Chen, Tao

2011-01-01

42

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

43

Reconstructing a three-dimensional P-GMAW weld pool shape from a two-dimensional visual image  

NASA Astrophysics Data System (ADS)

The online detection of the three-dimensional (3D) shape of a weld pool is a key unsolved question for weld shape control. In this paper, a method to reconstruct the 3D shape of a weld pool boundary from a two-dimensional (2D) visual image is proposed. Firstly, a new 3D model was developed to describe the weld pool geometry in pulsed gas metal arc welding (P-GMAW). In this model, four parameters could be used to determine the weld pool shape: the maximum width W, the length of the pool tail L, the height of the rear of the pool H and the projection of the rear angle onto the work piece plane ?L. Then, the clear weld pool images from the P-GMAW were captured from the upper side, and a series of algorithms were developed to extract the model geometrical parameters from these images. Finally, the 3D shape of the weld pool was reconstructed from the 2D images. The results were then validated with metallograph observations. The measurement error of this method was investigated, and methods for improvement were discussed.

Guangjun, Zhang; Zhihong, Yan; Lin, Wu

2006-07-01

44

Measurement of nugget size of spot weld by digital shearography  

NASA Astrophysics Data System (ADS)

Resistance spot welding is now widely used in the fabrication of sheet metals, mainly due to the cost and time considerations. Friction stir spot welding is getting more and more acceptance in the automotive industries. Such spot welds are found in nearly all products where sheet metal is joined. Obviously the quality of the spot weld has a direct impact on the quality of the product. The most important quality target of spot welds is the size of the weld nuggets. If the weld nuggets are improperly or incompletely formed, or the area surrounding the nugget is smaller than required, the structural integrity of the entire part may be uncertain. Furthermore these inconsistencies are usually internal and are seldom visible to optical inspection. This study is focused on the quality analysis of the spot welds by using "Digital Shearography". The paper mainly focuses on developing a novel, whole field technique for non-destructive inspecting the size of spot-welds, both for the resistance spot weld and the friction stir spot weld.

Yang, Lianxiang; Samala, Praveen R.; Liu, Sheng; Long, Kah Wah; Lee, Yung-Li

2005-08-01

45

Very low cycle fatigue properties of butt welded joints containing weld defects. Study of acceptable size of defects in girth welds of gas pipelines  

Microsoft Academic Search

This paper describes an investigation of the very low cycle fatigue strength of HT570 steel welded joints containing weld defects to determine the acceptable size of weld defects in girth welds of underground gas pipelines subjected to cyclic ground displacements due to earthquakes. Butt welded joints containing incomplete penetration (IP), blowholes (BH), lack of fusion in theintermedi?ate pass (LF), and

A. Seto; T. Masuda; S. Machida; C. Miki

2000-01-01

46

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

47

Phase-correction algorithm of deformed grating images in the depth measurement of weld pool surface in gas tungsten arc welding  

NASA Astrophysics Data System (ADS)

The principle and system structure of the depth measurement of weld pool surface in tungsten insert gas (TIG) welding are first introduced in the paper, then the problem of the common phase lines is studied. We analyze the causes and characteristics of the phase lines, and propose a phase correction method based on line ratio. The paper presents the principle and detail processing steps of this phase correction algorithm, and then the effectiveness and processing characteristics of the algorithm are verified by simulation. Finally, the algorithm is applied to phase processing in the depth measurement of the TIG weld pool surface and obtains satisfying results.

Wei, Yiqing; Liu, Nansheng; Hu, Xian; Ai, Xiaopu

2011-05-01

48

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

NASA Astrophysics Data System (ADS)

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.; Aubreton, O.; Stolz, C.

2014-03-01

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

Dynamic Approach Of The Keyhole And Melt Pool Behavior For Deep Penetration Nd-Yag Laser Welding  

NASA Astrophysics Data System (ADS)

This paper contains our last results concerning the understanding of fundamental processes occurring inside metallic melt pool produced during deep penetration CW Nd-Yag laser welding. When the welding speed varies from a few m/min to a few tens of m/min, one can observe that melt pool behavior has very different and complex hydrodynamics. At low welding speed, the keyhole appears to be quite vertical, embedded inside a large pool that fluctuates due to friction effects induced by the quite vertical ejected plume. At high welding speeds, laser interaction is only localized on the keyhole front whose inclination increases with the welding speed. Induced melt flow then dominates and can generate the humping regime, with severe undercuts. For intermediate welding speeds, it is the interaction of the vapor plume with the melt pool that controls its stability and the final quality of the weld seam. The vapor plume behavior that is ejected from the keyhole, such as its fluctuations or its dynamic pressure, has been also studied as a function of these different operating parameters. Also the behavior of the keyhole and more precisely its front wall is analyzed by using a simple modeling approach that allows us to reproduce its main characteristics such as the penetration depth or the keyhole front wall inclination dependences with operating parameters. The interpretation of these different experiments allows us to confirm that the dynamic pressure of the vapor plume, which is emitted with a variable intensity and direction perpendicularly from the inclined keyhole front, has an essential role for the melt pool stability and its dynamics in deep penetration laser welding.

Fabbro, Rémy

2008-09-01

51

Gravitational effects on the development of weld-pool and solidification microstructures  

SciTech Connect

This research effort has as its objective the development of a quantitative understanding of the effects of both low- and high-g environments on the solidification microstructures and morphologies that are produced in alloy single crystals during a variety of melting and solidification processes. The overall goal of the effort is to delineate the nature of the roles played by natural convection, surface-tension-driven convection, and mass transport effects due to interactions associated with various heating methods that are used to form melt pools in practical, commercially important alloy systems. The experimental and theoretical investigations comprising this effort encompass the study of configurations in which stationary heat sources are employed as well as melt pools formed by moving heat sources like those frequently used in fusion-welding processes.

Boatner, L.A.; David, S.A. [Oak Ridge National Lab., TN (United States); Workman, G. [Univ. of Alabama, Huntsville, AL (United States). Johnson Research Center

1994-09-01

52

Taurine Pool Sizes in the Rat: Effects of Vitamin B6 Deficiency and High Taurine Diet  

Microsoft Academic Search

The specific activity of taurine was measured in a number of tissues and body fluids of the rat at various times after injection of MS-taurine. The results provide evidence of separate taurine pools with different characteristics, and estimates of the sizes and half-lives of these pools. The results suggest that a 150 g rat has a rapidly miscible taurine pool

JOHN A. STURMAN

53

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

54

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

55

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

56

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

57

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

58

Cholesterol absorption in cirrhosis: the role of total and individual bile acid pool size.  

PubMed

Dietary cholesterol absorption was studied in patients with either "mild" (n = 23) or "severe" (n = 12) liver cirrhosis in relation to both total and individual bile acid pool size. Cholesterol absorption was significantly reduced in both groups of patients, and it was inversely related (r = -0.68; p less than 0.001) to the severity of the disease. Total, cholic acid, and deoxycholic acid p ool sizes were significantly reduced in cirrhosis, and a correlation was found between cholesterol absorption and cholic acid pool size (r = 0.78; p less than 0.001). In 5 patients, cholesterol absorption and bile acid pool size were estimated both before and after treatment with cholic acid (15 mg/kg/day) plus ampicillin (2 g/day). The treatment was followed by a mean threefold increase of cholic acid pool and by a sharp enhancement of cholesterol absorption in each patient. In conclusion, cholesterol absorption is often impaired in cirrhosis and is related to the severity of the disease. The correlation between cholic acid pool and cholesterol absorption and the constant increase of the absorption values after cholic acid pool expansion suggest that the size of cholic acid pool may be considered as an important factor in the regulation of cholesterol absorption. PMID:7227768

Ponz de Leon, M; Loria, P; Iori, R; Carulli, N

1981-06-01

59

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

60

Low-Temperature Sensitization Behavior of Base, Heat-Affected Zone, and Weld Pool in AISI 304LN  

NASA Astrophysics Data System (ADS)

Present investigations were focused on low-temperature sensitization (LTS) behavior of 304LN stainless steels considered from pipes of two different thicknesses. The specimens for the present study were taken from solution-annealed pipes (of varying thicknesses) and welded pipes (including the heat-affected zone (HAZ)). The specimens were subjected to thermal aging at 400 °C and 450 °C for different durations ranging from 125 to 8000 hours, to evaluate their sensitization susceptibility. The aging durations were worked out to simulate the 30-to-100-year life of the studied stainless steel at 300 °C using the Arrheneous equation and considering the activation energy of 150 kJ/mol. The thermally aged specimens were characterized for their degree of sensitization (DOS) and susceptibility to intergranular corrosion (IGC) by double-loop (DL) electrochemical potentiokinetic reactivation (EPR) and by methods given in the ASTM A262 practices A and E. It has been clearly shown that the weld pool is more sensitive to IGC than are the base and the HAZ at both the aging temperatures (LTS), because they showed IGC cracks during the bending subsequent to the boiling in H2SO4-CuSO4 solution. Both the base and the HAZ of the thicker pipe material showed susceptibility to sensitization, as indicated by the increasing DOS and “dual-type” microstructure during electrolytic oxalic acid (EOA) etching; however, they were found safe from IGC for the studied sensitization times. The susceptibility to sensitization and IGC in the weld pool is related to the presence of copious delta ferrite with chromium diffusivity that is accelerated compared to the austenite phase. The time-temperature-sensitization (TTS) curves were prepared accordingly, based on these results.

Singh, Raghuvir; Das, Gautam; Singh, P. K.; Chattoraj, I.

2009-05-01

61

Welding and lung cancer in a pooled analysis of case-control studies.  

PubMed

Several epidemiologic studies have indicated an increased risk of lung cancer among welders. We used the SYNERGY project database to assess welding as a risk factor for developing lung cancer. The database includes data on 15,483 male lung cancer cases and 18,388 male controls from 16 studies in Europe, Canada, China, and New Zealand conducted between 1985 and 2010. Odds ratios and 95% confidence intervals between regular or occasional welding and lung cancer were estimated, with adjustment for smoking, age, study center, and employment in other occupations associated with lung cancer risk. Overall, 568 cases and 427 controls had ever worked as welders and had an odds ratio of developing lung cancer of 1.44 (95% confidence interval: 1.25, 1.67) with the odds ratio increasing for longer duration of welding. In never and light smokers, the odds ratio was 1.96 (95% confidence interval: 1.37, 2.79). The odds ratios were somewhat higher for squamous and small cell lung cancers than for adenocarcinoma. Another 1,994 cases and 1,930 controls had ever worked in occupations with occasional welding. Work in any of these occupations was associated with some elevation of risk, though not as much as observed in regular welders. Our findings lend further support to the hypothesis that welding is associated with an increased risk of lung cancer. PMID:24052544

Kendzia, Benjamin; Behrens, Thomas; Jöckel, Karl-Heinz; Siemiatycki, Jack; Kromhout, Hans; Vermeulen, Roel; Peters, Susan; Van Gelder, Rainer; Olsson, Ann; Brüske, Irene; Wichmann, H-Erich; Stücker, Isabelle; Guida, Florence; Tardón, Adonina; Merletti, Franco; Mirabelli, Dario; Richiardi, Lorenzo; Pohlabeln, Hermann; Ahrens, Wolfgang; Landi, Maria Teresa; Caporaso, Neil; Consonni, Dario; Zaridze, David; Szeszenia-Dabrowska, Neonila; Lissowska, Jolanta; Gustavsson, Per; Marcus, Michael; Fabianova, Eleonora; 't Mannetje, Andrea; Pearce, Neil; Tse, Lap Ah; Yu, Ignatius Tak-Sun; Rudnai, Peter; Bencko, Vladimir; Janout, Vladimir; Mates, Dana; Foretova, Lenka; Forastiere, Francesco; McLaughlin, John; Demers, Paul; Bueno-de-Mesquita, Bas; Boffetta, Paolo; Schüz, Joachim; Straif, Kurt; Pesch, Beate; Brüning, Thomas

2013-11-15

62

Satellite-cell pool size does matter: Defining the myogenic potency of aging skeletal muscle  

Microsoft Academic Search

The deteriorating in vivo environment is thought to play a major role in reduced stem cell function with age. The capacity of stem cells to support tissue maintenance depends not only on their response to cues from the surrounding niche, but also on their abundance. Here, we investigate satellite cell (myogenic stem cell) pool size and its potential to participate

Gabi Shefer; Daniel P. Van de Mark; Joshua B. Richardson; Zipora Yablonka-Reuveni

2006-01-01

63

Method of Fusion Welding.  

National Technical Information Service (NTIS)

An Author Certificate has been issued for a method of fusion welding in which the welding pool is treated by a traveling stray magnetic field. To increase the welding speed and improve the quality of welds by moving the molten metal of the welding pool al...

B. E. Paton S. L. Mandelberg V. K. Lebedev B. G. Sidorenko V. E. Lopata

1970-01-01

64

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).

65

A preferentially segregated recycling vesicle pool of limited size supports neurotransmission in native central synapses.  

PubMed

At small central synapses, efficient turnover of vesicles is crucial for stimulus-driven transmission, but how the structure of this recycling pool relates to its functional role remains unclear. Here we characterize the organizational principles of functional vesicles at native hippocampal synapses with nanoscale resolution using fluorescent dye labeling and electron microscopy. We show that the recycling pool broadly scales with the magnitude of the total vesicle pool, but its average size is small (?45 vesicles), highly variable, and regulated by CDK5/calcineurin activity. Spatial analysis demonstrates that recycling vesicles are preferentially arranged near the active zone and this segregation is abolished by actin stabilization, slowing the rate of activity-driven exocytosis. Our approach reveals a similarly biased recycling pool distribution at synapses in visual cortex activated by sensory stimulation in vivo. We suggest that in small native central synapses, efficient release of a limited pool of vesicles relies on their favored spatial positioning within the terminal. PMID:23141069

Marra, Vincenzo; Burden, Jemima J; Thorpe, Julian R; Smith, Ikuko T; Smith, Spencer L; Häusser, Michael; Branco, Tiago; Staras, Kevin

2012-11-01

66

Detection and Sizing of Fatigue Cracks in Steel Welds with Advanced Eddy Current Techniques  

NASA Astrophysics Data System (ADS)

Butt-welded specimens were fatigued to produce cracks in the weld heat-affected zone. Advanced eddy current (AEC) techniques were used to detect and size the cracks through a coating. AEC results were compared with magnetic particle and phased-array ultrasonic techniques. Validation through destructive crack measurements was also conducted. Factors such as geometry, surface treatment, and crack tightness interfered with depth sizing. AEC inspection techniques have the potential of providing more accurate and complete sizing flaw data for manufacturing and in-service inspections.

Todorov, E. I.; Mohr, W. C.; Lozev, M. G.

2008-02-01

67

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.

68

Dynamics of space welding impact and corresponding safety welding study  

NASA Astrophysics Data System (ADS)

This study was undertaken in order to be sure that no hazard would exist from impingement of hot molten metal particle detachments upon an astronauts space suit during any future electron beam welding exercises or experiments. The conditions under which molten metal detachments might occur in a space welding environment were analyzed. The safety issue is important during welding with regards to potential molten metal detachments from the weld pool and cold filler wire during electron beam welding in space. 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. 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 determined for these detachment concerns from principles of impact and kinetic energies, surface tension, drop geometry, surface energies, and particle dynamics. A weld pool detachment parameter for specifying the conditions for metal weld pool detachment by impact was derived and correlated to the experimental results. The experimental results were for the most part consistent with the theoretical analysis and predictions.

Fragomeni, James M.; Nunes, Arthur C.

2004-03-01

69

Dynamics of space welding impact and corresponding safety welding study.  

PubMed

This study was undertaken in order to be sure that no hazard would exist from impingement of hot molten metal particle detachments upon an astronauts space suit during any future electron beam welding exercises or experiments. The conditions under which molten metal detachments might occur in a space welding environment were analyzed. The safety issue is important during welding with regards to potential molten metal detachments from the weld pool and cold filler wire during electron beam welding in space. 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. 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 determined for these detachment concerns from principles of impact and kinetic energies, surface tension, drop geometry, surface energies, and particle dynamics. A weld pool detachment parameter for specifying the conditions for metal weld pool detachment by impact was derived and correlated to the experimental results. The experimental results were for the most part consistent with the theoretical analysis and predictions. PMID:14740660

Fragomeni, James M; Nunes, Arthur C

2004-03-01

70

Experimental and numerical investigation of temperature distribution and melt pool geometry during pulsed laser welding of Ti6Al4V alloy  

NASA Astrophysics Data System (ADS)

This paper reports on a numerical and experimental investigation of laser welding of titanium alloy (Ti6Al4V) for modeling the temperature distribution to predict the heat affected zone (HAZ), depth and width of the molten pool. This is a transient three-dimensional problem in which, because of simplicity, the weld pool surface is considered flat. The complex physical phenomenon causing the formation of keyhole has not been considered. The temperature histories of welding process were studied. It was observed that the finite volume thermal model was in good agreement with the experimental data. Also, we predicted the temperature as a function of distance at different laser welding speeds and saw that at each welding speed, the temperature profile was decreased sharply in points close to the laser beam center, and then decreased slightly in the far region from the laser beam center. The model prediction error was found to be in the 2-17% range with most numerical values falling within 7% of the experimental values.

Akbari, Mohammad; Saedodin, Seyfolah; Toghraie, Davood; Shoja-Razavi, Reza; Kowsari, Farshad

2014-07-01

71

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

72

Size and age of the non structural carbohydrate pool in boreal trees  

NASA Astrophysics Data System (ADS)

Autotrophic respiration of trees is supposed to be closely linked to CO2 uptake by photosynthesis on a time scale of days. However, several studies have indicated that roots of boreal trees do not respired carbon (C) with a radiocarbon signature ?14C similar to that of CO2 in the atmosphere, but C that is 3-4 years old. Also, estimates of gross primary productivity obtained by eddy covariance flux measurements do often not correlate with tree ring width (growth). Both these findings point to the presences of a large non-structural C (NSC) pool within the tree, mainly sugars and starches. The concentration of NSC in tree tissue is considered a measure of C shortage or surplus for growth. Studies indicate that the NSC pool in trees is usually large and relatively constant throughout the year, not affected by e.g. leaf flushing. While estimates of the size of the NSC pool are available for a number of trees from various ecosystems, estimated of its turnover time are lacking. We tested if our finding that boreal trees respire 3-4 year old C is an artifact resulting from the depletion of the NSC pool in excised roots over time. We incubated roots with a diameter of 2-4 mm while they were still attached to the tree, and excised roots after 3 hours, and 1 to 4 days. We sampled CO2 for ?14C analysis of intact roots, freshly excised roots, and after 1 and 3 days. To obtain an estimate of the NSC pool size and its turnover time in roots of various diameter, we excised and incubated roots of 3 diameters: root hairs with mycorrhizal fungi, 2-4 mm, and 1-2 cm. We followed their respiration over the course of one full day. We will also compare the ?14C of respired CO2 of freshly root hairs to that of the NSC in the roots. To obtain an estimate of the size and turnover of the whole tree NSC pool, we will measure the ?14C of NSC in wood. Preliminary results indicate that CO2 fluxes were not correlated to temperature or the initial CO2 concentration in the chamber. While CO2 fluxes of medium and coarse roots remained relatively constant over 4 days, the respiration rates of root hairs declined sharply within the first 24 hours.

Czimczik, C. I.; Trumbore, S.

2005-12-01

73

Welding  

NSDL National Science Digital Library

Teachers' Domain presents this video as part of a series on advanced technological education. Around 500,000 people are currently employed in welding in the United States, and as more highways, bridges and other structures need crucial updates, welders will continue to be in demand. The video clip demonstrates welding techniques, including what constitutes a bad weld and how to recognize one. Careers in welding are also discussed. The video may be viewed online or downloaded. To download the clip, users must create a free login for Teachers' Domain. Running time for this QuickTime video is 3:56. Educators will also find a background essay, discussion questions, and standards alignment for the material.

2010-09-29

74

Increased cholesterol 7?-hydroxylase expression and size of the bile acid pool in the lactating rat  

PubMed Central

Maximal bile acid secretory rates and expression of bile acid transporters in liver and ileum are increased in lactation, possibly to facilitate increased enterohepatic recirculation of bile acids. We determined changes in the size and composition of the bile acid pool and key enzymes of the bile acid synthetic pathway [cholesterol 7?-hydroxylase (Cyp7a1), sterol 27-hydroxylase (Cyp27a1), and sterol 12?-hydroxylase (Cyp8b1)] in lactating rats relative to female virgin controls. The bile acid pool increased 1.9 to 2.5-fold [postpartum (PP) days 10, 14, and 19–23], compared with controls. A 1.5-fold increase in cholic acids and a 14 to 20% decrease in muricholic acids in lactation significantly increased the hydrophobicity index. In contrast, the hepatic concentration of bile acids and small heterodimer partner mRNA were unchanged in lactation. A 2.8-fold increase in Cyp7a1 mRNA expression at 16 h (10 h of light) demonstrated a shift in the diurnal rhythm at day 10 PP; Cyp7a1 protein expression and cholesterol 7?-hydroxylase activity were significantly increased at this time and remained elevated at day 14 PP but decreased to control levels by day 21 PP. There was an overall decrease in Cyp27a1 mRNA expression and a 20% decrease in Cyp27a1 protein expression, but there was no change in Cyp8b1 mRNA or protein expression at day 10 PP. The increase in Cyp7a1 expression PP provides a mechanism for the increase in the bile acid pool.

Wooton-Kee, Clavia Ruth; Cohen, David E.; Vore, Mary

2008-01-01

75

Investigation of mixing and diffusion processes in hybrid spot laser-MIG keyhole welding  

NASA Astrophysics Data System (ADS)

In hybrid laser-MIG keyhole welding, anti-crack elements can be added into the weld pool through a filler metal in anticipation of compensating mass loss, preventing porosity formation and improving compositional and mechanical properties of the welds. Understanding the mixing and diffusion of the filler metal in the molten pool is vital to achieve these desired objectives. In this study, mathematical models and associated numerical techniques have been developed to investigate the mixing and diffusion processes in hybrid laser-MIG keyhole welding. The transient interactions between droplets and weld pool and dynamics of the melt flow are studied. The effects of key process parameters, such as droplet size (wire diameter), droplet generation frequency (wire feed speed) and droplet impinging speed, on mixing/diffusion are systematically investigated. It was found that compositional homogeneity of the weld pool is determined by the competition between the mixing rate and the solidification rate. A small-size filler droplet together with high generation frequency can increase the latitudinal diffusion of the filler metal into the weld pool, while the large-size droplet along with the low generation frequency helps to get more uniform longitudinal diffusion. Increasing the impinging velocity of the filler droplet can improve the latitudinal diffusion of the filler metal. However, a high impinging velocity can cause a lower diffusion zone in the upper part of the welds. This study provides a good foundation for optimizing the hybrid laser-MIG keyhole welding process to achieve quality welds with desired properties.

Zhou, J.; Tsai, H. L.

2009-05-01

76

Testing for non-randomness in sizes and habitats of West Indian lizards: choice of species pool affects conclusions from null models  

Microsoft Academic Search

Summary Several null models are proposed for testing whether size or habitat differences in West IndianAnolis lizards are greater than expected ‘by chance’. The models differ primarily in choice of the pool from which species are sampled to form random communities. Regardless of choice of pool, size differences in the Lesser Antilles are greater than null models predict; the pool

Thomas W. Schoener

1988-01-01

77

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

78

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

79

Modeling of soil C-dynamics reveals different carbon pool sizes and decomposition rates under varying incubation temperatures  

NASA Astrophysics Data System (ADS)

Soils contain about two thirds of all organic carbon that is stored in terrestrial ecosystems. Annual release of soil carbon (C) to the atmosphere currently exceeds the rate of anthropogenic CO2 emissions by a factor of 10 demonstrating that even small changes in soil C cycling are highly relevant to the global C cycle. Total soil organic matter consists of different C pools with intrinsic turnover rates ranging from less than a year to thousands of years. The objectives of this study were to model soil C-dynamics of a long-term incubation study (336 days, Conant et al. 2008) under two different incubation temperatures (25°C and 35°C) to obtain i) soil CO2-efflux rates, ii) C-dynamics and iii) temperature sensitivities of C-pools with different turnover times. Respiration rates and soil C-dynamics of three different C-pools were modeled by a 1st order differential equation and data assimilation techniques were used to optimize parameter estimation. All C of the most labile pool (fast turnover time) was respired within the first ten days of the incubation study and pool size as well as absolute decline of the labile C-pool did not differ between temperatures. The intermediate C-pool (intermediate turnover time) was initially 70% larger at the higher temperature but as C was respired at a higher rate the intermediate pool was of equal size at both temperatures after 336 days of incubation. The most recalcitrant C-pool (slow turnover time) declined very slowly over time at both temperatures. However, the contribution of the recalcitrant C-pool to the whole CO2-efflux became more important towards the end of the incubation study. A 10K higher incubation temperature resulted in a larger intermediate C-pool and therefore in twice as much C released. This modeling study shows that higher temperatures increase the amount of easily decomposable C and that C-pool sizes vary at different temperatures. These results are of particular interest for high latitude regions as temperatures are predicted to increase more rapidly in arctic ecosystems and strong effects of higher temperatures on permafrost C are to be expected.

Schädel, C.; Luo, Y.; Schuur, E. A.; Zhou, J.

2011-12-01

80

The Bruchpilot cytomatrix determines the size of the readily releasable pool of synaptic vesicles  

PubMed Central

Synaptic vesicles (SVs) fuse at a specialized membrane domain called the active zone (AZ), covered by a conserved cytomatrix. How exactly cytomatrix components intersect with SV release remains insufficiently understood. We showed previously that loss of the Drosophila melanogaster ELKS family protein Bruchpilot (BRP) eliminates the cytomatrix (T bar) and declusters Ca2+ channels. In this paper, we explored additional functions of the cytomatrix, starting with the biochemical identification of two BRP isoforms. Both isoforms alternated in a circular array and were important for proper T-bar formation. Basal transmission was decreased in isoform-specific mutants, which we attributed to a reduction in the size of the readily releasable pool (RRP) of SVs. We also found a corresponding reduction in the number of SVs docked close to the remaining cytomatrix. We propose that the macromolecular architecture created by the alternating pattern of the BRP isoforms determines the number of Ca2+ channel-coupled SV release slots available per AZ and thereby sets the size of the RRP.

Matkovic, Tanja; Siebert, Matthias; Knoche, Elena; Depner, Harald; Mertel, Sara; Owald, David; Schmidt, Manuela; Thomas, Ulrich; Sickmann, Albert; Kamin, Dirk; Hell, Stefan W.; Burger, Jorg; Hollmann, Christina; Mielke, Thorsten

2013-01-01

81

The Bruchpilot cytomatrix determines the size of the readily releasable pool of synaptic vesicles.  

PubMed

Synaptic vesicles (SVs) fuse at a specialized membrane domain called the active zone (AZ), covered by a conserved cytomatrix. How exactly cytomatrix components intersect with SV release remains insufficiently understood. We showed previously that loss of the Drosophila melanogaster ELKS family protein Bruchpilot (BRP) eliminates the cytomatrix (T bar) and declusters Ca(2+) channels. In this paper, we explored additional functions of the cytomatrix, starting with the biochemical identification of two BRP isoforms. Both isoforms alternated in a circular array and were important for proper T-bar formation. Basal transmission was decreased in isoform-specific mutants, which we attributed to a reduction in the size of the readily releasable pool (RRP) of SVs. We also found a corresponding reduction in the number of SVs docked close to the remaining cytomatrix. We propose that the macromolecular architecture created by the alternating pattern of the BRP isoforms determines the number of Ca(2+) channel-coupled SV release slots available per AZ and thereby sets the size of the RRP. PMID:23960145

Matkovic, Tanja; Siebert, Matthias; Knoche, Elena; Depner, Harald; Mertel, Sara; Owald, David; Schmidt, Manuela; Thomas, Ulrich; Sickmann, Albert; Kamin, Dirk; Hell, Stefan W; Bürger, Jörg; Hollmann, Christina; Mielke, Thorsten; Wichmann, Carolin; Sigrist, Stephan J

2013-08-19

82

Naive pooled-data approach for pharmacokinetic studies in pediatrics with a very small sample size.  

PubMed

The objective of this study was to evaluate if the pharmacokinetic (PK) parameters (clearance, volumes of distribution, and half-life) from 1 blood sample per subject using naive pooled data (NPD) analysis can be obtained with reasonable accuracy with a very small sample size (n = 5). For this study, 7 drugs were selected from the literature. The PKs of these 7 drugs were studied in pediatrics, and plasma concentrations versus time data for individual subjects from extensive blood sampling were available. For this analysis, only 5 subjects were chosen, and each subject gave 1 blood sample. The estimated PK parameters from NPD analysis were compared with the mean PK parameters obtained from extensive sampling. The result of the study indicated that a fairly accurate estimate of PK parameters can be obtained with 1 blood sample each from a minimum of 5 subjects using NPD analysis. The NPD analysis with sparse-sampling scheme can be useful for PK studies in neonates and very young children, where sample size is small. PMID:22713529

Mahmood, Iftekhar

2014-01-01

83

Habitat stress, species pool size and biotic resistance influence exotic plant richness in the Flooding Pampa grasslands  

Microsoft Academic Search

Summary 1 Theory and empirical evidence suggest that community invasibility is influenced by propagule pressure, physical stress and biotic resistance from resident species. We studied patterns of exotic and native species richness across the Flooding Pampas of Argentina, and tested for exotic richness correlates with major environmental gradients, species pool size, and native richness, among and within different grassland habitat

SUSANA B. PERELMAN; ENRIQUE J. CHANETON; WILLIAM B. BATISTA; SILVIA E. BURKART; ROLANDO J. C. LEÓN

2007-01-01

84

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

85

Orphan G protein-coupled receptor GPR116 regulates pulmonary surfactant pool size.  

PubMed

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

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

2013-09-01

86

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

87

Influence of friction stir welding parameters on grain size and formability in 5083 aluminum alloy  

Microsoft Academic Search

Friction stir welding (FSW) has received a great deal of attention as a new solid-state welding technique. In the present study, the relationship between the microstructure of stir zone and the mechanical property of FS-welded 5083 aluminum alloy was investigated. The microstructures of the stir zones consisted of fine equiaxed grains at various FSW conditions in FS-welded 5083 Al alloy.

Tomotake Hirata; Taizo Oguri; Hideki Hagino; Tsutomu Tanaka; Sung Wook Chung; Yorinobu Takigawa; Kenji Higashi

2007-01-01

88

Litter pool sizes, decomposition, and nitrogen dynamics in Spartina alterniflora -invaded and native coastal marshlands of the Yangtze Estuary  

Microsoft Academic Search

Past studies have focused primarily on the effects of invasive plants on litter decomposition at soil surfaces. In natural\\u000a ecosystems, however, considerable amounts of litter may be at aerial and belowground positions. This study was designed to\\u000a examine the effects of Spartina\\u000a alterniflora invasion on the pool sizes and decomposition of aerial, surficial, and belowground litter in coastal marshlands, the

Cheng Zhang Liao; Yi Qi Luo; Chang Ming Fang; Jia Kuan Chen; Bo Li

2008-01-01

89

Pool-boiling critical heat flux of water on small plates: Effects of surface orientation and size  

Microsoft Academic Search

A series of experiments have been performed to understand the pool-boiling critical heat flux (CHF) behavior on small plates, varying the inclination angle and size of the heated surface under near atmospheric pressure: the first-phase experiment to clarify the CHF behavior at near the horizontal downward-facing position and the second-phase experiment to find out the general CHF behavior for overall

Soo Hyung Yang; Won-Pil Baek; Soon Heung Chang

1997-01-01

90

Size effects on the upper shelf energy of a neutron irradiated pressure vessel weld metal  

NASA Astrophysics Data System (ADS)

The methodologies published earlier for predicting the upper shelf energy (USE) of full size Charpy specimens based on subsize test data appear to work satisfactorily for either highly materials (USE > 200 J) or relatively brittle materials (USE ? 100 J). A methodology is proposed here that works well for pressure vessel weld materials in both unirradiated and irradiated conditions having USE in the intermediate region (100 J < USE < 200 J). The methodology uses partitioning of the USE into two components, USE p and ?USE ( = USE - USE p). USE p is the absorbed energy for a specimen fatigue-precracked to half the width. The predicted value of the USE of full-size specimens is a sum of two terms. The first term is equal to product of the normalized ?USE of the subsize specimen and the full-size normalization factor for ?USE. The second term is equal to the product of the normalized USE p of the subsize specimen and the fracture volume of the full-size precracked specimen. The predicted values were within about 10% of the measured values for both unirradiated and irradiated materials.

Kumar, A. S.; Schubert, L. E.; Hamilton, M. L.; Cannon, N. S.

1995-08-01

91

Optimal sizing of micro grid & distributed generation units under pool electricity market  

Microsoft Academic Search

This paper presents an optimized design of micro grid in a distribution system including various sources such as photovoltaic array, fuel cell, and battery bank with multiple distributed generation (DG) units under pool electricity market. In this research, an algorithm has been developed for the optimization of the micro grid cost. The costs include capital cost, replacement cost, operation and

M. Mohammadi; S. H. Hosseinian; G. B. Gharehpetian

2011-01-01

92

Expression of the pyrG gene determines the pool sizes of CTP and dCTP in Lactococcus lactis.  

PubMed

The pyrG gene from Lactococcus lactis encodes CTP synthase (EC 6.4.3.2), an enzyme converting UTP to CTP. A series of strains were constructed with different levels of pyrG expression by insertion of synthetic constitutive promoters with different strengths in front of pyrG. These strains expressed pyrG levels in a range from 3 to 665% relative to the wild-type expression level. Decreasing the level of CTP synthase to 43% had no effect on the growth rate, showing that the capacity of CTP synthase in the cell is in excess in a wild-type strain. We then studied how pyrG expression affected the intracellular pool sizes of nucleotides and the correlation between pyrG expression and nucleotide pool sizes was quantified using metabolic control analysis in terms of inherent control coefficients. At the wild-type expression level, CTP synthase had full control of the CTP concentration with a concentration control coefficient close to one and a negative concentration control coefficient of -0.28 for the UTP concentration. Additionally, a concentration control coefficient of 0.49 was calculated for the dCTP concentration. Implications for the homeostasis of nucleotide pools are discussed. PMID:15182359

Jørgensen, Casper M; Hammer, Karin; Jensen, Peter R; Martinussen, Jan

2004-06-01

93

Laser welding in space  

NASA Technical Reports Server (NTRS)

Autogenous welds in 304 stainless steel were performed by Nd-YAG laser heating in a simulated space environment. Simulation consists of welding on the NASA KC-135 aircraft to produce the microgravity and by containing the specimen in a vacuum chamber. Experimental results show that the microgravity welds are stronger, harder in the fusion zone, have deeper penetration and have a rougher surface rippling of the weld pool than one-g welds. To perform laser welding in space, a solar-pumped laser concept that significantly increases the laser conversion efficiency and makes welding viable despite the limited power availability of spacecraft is proposed.

Kaukler, W. F.; Workman, G. L.

1991-01-01

94

Heat Source - Materials Interactions during Fusion Welding.  

National Technical Information Service (NTIS)

This report summarizes the second year of research involving spectrographic and thermodynamic studies of vapor emission from welding arcs, infrared measurement of the weld pool surface temperature, electroslag welding of titanium, fracture toughness of HY...

T. W. Eagar A. Block-Bolten C. Allemand D. Hardt J. Katz

1982-01-01

95

NAD kinase regulates the size of the NADPH pool and insulin secretion in pancreatic ?-cells.  

PubMed

NADPH is an important component of the antioxidant defense system and a proposed mediator in glucose-stimulated insulin secretion (GSIS) from pancreatic ?-cells. An increase in the NADPH/NADP(+) ratio has been reported to occur within minutes following the rise in glucose concentration in ?-cells. However, 30 min following the increase in glucose, the total NADPH pool also increases through a mechanism not yet characterized. NAD kinase (NADK) catalyzes the de novo formation of NADP(+) by phosphorylation of NAD(+). NAD kinases have been shown to be essential for redox regulation, oxidative stress defense, and survival in bacteria and yeast. However, studies on NADK in eukaryotic cells are scarce, and the function of this enzyme has not been described in ?-cells. We employed INS-1 832/13 cells, an insulin-secreting rat ?-cell line, and isolated rodent islets to investigate the role of NADK in ?-cell metabolic pathways. Adenoviral-mediated overexpression of NADK resulted in a two- to threefold increase in the total NADPH pool and NADPH/NADP(+) ratio, suggesting that NADP(+) formed by the NADK-catalyzed reaction is rapidly reduced to NADPH via cytosolic reductases. This increase in the NADPH pool was accompanied by an increase in GSIS in NADK-overexpressing cells. Furthermore, NADK overexpression protected ?-cells against oxidative damage by the redox cycling agent menadione and reversed menadione-mediated inhibition of GSIS. Knockdown of NADK via shRNA exerted the opposite effect on all these parameters. These data suggest that NADK kinase regulates intracellular redox and affects insulin secretion and oxidative defense in the ?-cell. PMID:22550069

Gray, Joshua P; Alavian, Kambiz N; Jonas, Elizabeth A; Heart, Emma A

2012-07-15

96

Variation in adenylate energy charge and phosphoadenylate pool size in estuarine organisms after an oil spill  

SciTech Connect

Adenylate energy charge (AEC) is the proportion of the total phosphoadenylate pool charged with high-energy bonds. AEC values vary between zero and one by definition. Since AEC can be measured in any organism, decreases might be a universal measure of sublethal environmental stress. In some organisms which maintain high AEC while withstanding natural or anthropogenic stress, the absolute concentration of ATP and the total phosphoadenylate pool (TPP) decrease proportionally. However, in certain organisms the TPP shows dramatic natural fluctuations unrelated to pollution or stress. On 28 June 1983, a tanker spilled approximately 42,000 gallons of number6 diesel oil in the Cape Fear River, North Carolina, USA. Oil covered the tidal marshes on the east side of the river and provided an opportunity to determine if either the AEC or TPP in a variety of organisms would respond to this stress. Five test species were examined as long as one year after the spill. AEC and TPP values of the organisms were compared between contaminated and uncontaminated sites at all seasons. This is the first investigation to monitor AEC in a number of taxonomically distinct estuarine species during an extended period after an oil spill.

Shafer, T.H.; Hackney, C.T.

1987-05-01

97

Systematic Heterogeneity of Fractional Vesicle Pool Sizes and Release Rates of Hippocampal Synapses  

PubMed Central

Hippocampal neurons in tissue culture develop functional synapses that exhibit considerable variation in synaptic vesicle content (20–350 vesicles). We examined absolute and fractional parameters of synaptic vesicle exocytosis of individual synapses. Their correlation to vesicle content was determined by activity-dependent discharge of FM-styryl dyes. At high frequency stimulation (30 Hz), synapses with large recycling pools released higher amounts of dye, but showed a lower fractional release compared to synapses that contained fewer vesicles. This effect gradually vanished at lower frequencies when stimulation was triggered at 20 Hz and 10 Hz, respectively. Live-cell antibody staining with anti-synaptotagmin-1-cypHer 5, and overexpression of synaptopHluorin as well as photoconversion of FM 1-43 followed by electron microscopy, consolidated the findings obtained with FM-styryl dyes. We found that the readily releasable pool grew with a power function with a coefficient of 2/3, possibly indicating a synaptic volume/surface dependency. This observation could be explained by assigning the rate-limiting factor for vesicle exocytosis at high frequency stimulation to the available active zone surface that is proportionally smaller in synapses with larger volumes.

Welzel, Oliver; Henkel, Andreas W.; Stroebel, Armin M.; Jung, Jasmin; Tischbirek, Carsten H.; Ebert, Katrin; Kornhuber, Johannes; Rizzoli, Silvio O.; Groemer, Teja W.

2011-01-01

98

Regulation of memory CD4 T-cell pool size and function by natural killer T cells in vivo  

PubMed Central

To develop more effective vaccines and strategies to regulate chronic inflammatory diseases, it is important to understand the mechanisms of immunological memory. Factors regulating memory CD4+ T helper (Th)-cell pool size and function remain unclear, however. We show that activation of type I invariant natural killer T (iNKT) cells with glycolipid ligands and activation of type II natural killer T (NKT) cells with the endogenous ligand sulfatide induced dramatic proliferation and expansion of memory, but not naïve, CD4 T cells. NKT cell-induced proliferation of memory Th1 and Th2 cells was dependent largely on the production of IL-2, with Th2-cell proliferation also affected by loss of IL-4. Type II NKT cells were also required for efficient maintenance of memory CD4 T cells in vivo. Activation of iNKT cells resulted in up-regulation of IFN-? expression by memory Th2 cells. These IFN-?–producing memory Th2 cells showed a decreased capability to induce Th2 cytokines and eosinophilic airway inflammation. Thus, activated NKT cells directly regulate memory CD4 T-cell pool size and function via the production of cytokines in vivo.

Iwamura, Chiaki; Shinoda, Kenta; Endo, Yusuke; Watanabe, Yukiko; Tumes, Damon John; Motohashi, Shinichiro; Kawahara, Kazuyoshi; Kinjo, Yuki; Nakayama, Toshinori

2012-01-01

99

Simulation of Heat Flow During the Welding of Thin Plates  

Microsoft Academic Search

Based on the finite difference method and the enthalpy model of Shamsundar, a computer model was developed to describe the\\u000a steady state, two-dimensional heat flow during the welding of thin plates. In order to allow accurate computations of the\\u000a weld pool configuration, the size of the mushy zone and the temperature distribution near the heat source, a grid mesh of

Sindo Kou

1981-01-01

100

The effects of metal vapour in arc welding  

NASA Astrophysics Data System (ADS)

Metal vapour is formed in arc welding processes by the evaporation of molten metal in the weld pool, and in the case of gas-metal arc welding, in the wire electrode and droplets. The presence of metal vapour can have a major influence on the properties of the arc and the size and shape of the weld pool. Previous experimental and computational works on the production and transport of metal vapour in welding arcs, in particular those relevant to gas-metal arc welding and gas-tungsten arc welding, are reviewed. The influence of metal vapour on the thermodynamic, transport and radiative properties of plasmas is discussed. The effect of metal vapour on the distributions of temperature, current density and heat flux in arcs is examined in terms of these thermophysical properties. Different approaches to treating diffusion of metal vapour in plasmas, and the production of vapour from molten metal, are compared. The production of welding fume by the nucleation and subsequent condensation of metal vapour is considered. Recommendations are presented about subjects requiring further investigation, and the requirements for accurate computational modelling of welding arcs.

Murphy, Anthony B.

2010-11-01

101

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

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.

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

2011-01-01

103

Monitoring of Weld Penetration Using Arc Acoustics  

Microsoft Academic Search

The weld penetration monitoring is a challenging work in modern automated manufacturing industries. The weld quality can be improved with higher depth of penetration and less weld pool area. In this work, various pulse parameters have been varied to investigate their influence on weld penetration in pulsed metal inert gas (P-MIG) welding. The primary objective was to improve the depth

Kamal Pal; Surjya K. Pal

2011-01-01

104

Acoustic-Emission Weld-Penetration Monitor  

NASA Technical Reports Server (NTRS)

Weld penetration monitored by detection of high-frequency acoustic emissions produced by advancing weld pool as it melts and solidifies in workpiece. Acoustic emission from TIG butt weld measured with 300-kHz resonant transducer. Rise in emission level coincides with cessation of weld penetration due to sudden reduction in welding current. Such monitoring applied to control of automated and robotic welders.

Maram, J.; Collins, J.

1986-01-01

105

Active weld control  

NASA Technical Reports Server (NTRS)

Through the two phases of this contract, sensors for welding applications and parameter extraction algorithms have been developed. These sensors form the foundation of a weld control system which can provide action weld control through the monitoring of the weld pool and keyhole in a VPPA welding process. Systems of this type offer the potential of quality enhancement and cost reduction (minimization of rework on faulty welds) for high-integrity welding applications. Sensors for preweld and postweld inspection, weld pool monitoring, keyhole/weld wire entry monitoring, and seam tracking were developed. Algorithms for signal extraction were also developed and analyzed to determine their application to an adaptive weld control system. The following sections discuss findings for each of the three sensors developed under this contract: (1) weld profiling sensor; (2) weld pool sensor; and (3) stereo seam tracker/keyhole imaging sensor. Hardened versions of these sensors were designed and built under this contract. A control system, described later, was developed on a multiprocessing/multitasking operating system for maximum power and flexibility. Documentation for sensor mechanical and electrical design is also included as appendices in this report.

Powell, Bradley W.; Burroughs, Ivan A.

1994-01-01

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

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

108

First order decay models fail to represent soil organic carbon dynamics in both single-pool and in multiple-pool models based on size fractionation  

NASA Astrophysics Data System (ADS)

Soil organic carbon (SOC) models often rely on analytical solutions derived from litter bag experiments in which C losses follow first-order kinetics of the type (Ct= Co . e-kt). In this model, k is the decomposition or decay factor and is considered constant over time. Several authors pointed out that one-pool exponential SOC models fail to reproduce long-term SOC dynamics, and that multiple pools or time-dependent k values are needed to capture SOC behavior given its heterogeneous composition and turnover. As a consequence, models that separate organic matter in multiple pools with their own specific k values, expected to remain constant through time, have been proposed. Whether these multiple pool models with constant k values through time are able to represent SOC trajectories is unknown. We explored the stability of k values through time for total SOC and its more labile fraction known as particulate organic carbon (POC) across 15 grasslands sites in which shifts in the stable isotopic composition of C inputs after grazing exclosure (change from C4 to C3 dominated vegetation) allowed us to trace SOC dynamics. Time elapsed after grazing exclusion ranged from 4 to 30 years. We sampled soils and roots in grazed-ungrazed paired plots and measured SOC, POC and 13C composition. Using 13C and SOC changes we estimated k and carbon mean residence times (MRT) after grazing exclusion. As expected k (mass of annual C losses per unit of mass of C storage) values for total SOC were variable between sites but always lower (0.03 to 0.11) than k values of the POC fraction (0.09 to 0.19), and the opposite was true for MRT. For the total SOC, k values varied with time elapsed since grazing removal (r2= 0.71), suggesting that a variable k through time is needed to reproduce SOC dynamics with a one-pool model. Surprisingly, k values for the POC fraction were also significantly correlated with time (r2= 0.75), suggesting that even the POC fraction can not be accurately modeled with a first order kinetic model with a constant k that is successfully applied to litter bag decomposition experiments. Our results suggest that the widely used POC fraction does not separate a sufficiently homogenous pool with constant k values, or either that the exponential decay model does not apply for SOC dynamics.

Piñeiro, G.; Jobbágy, E. G.; Rizzotto, M. G.; Jackson, R. B.

2008-12-01

109

Mathematical modeling of heat transfer, fluid flow, and solidification during linear welding with a pulsed laser beam  

NASA Astrophysics Data System (ADS)

The evolution of temperature and velocity fields during welding of 304 stainless steel with a pulsed laser beam was simulated using a three dimensional numerical heat transfer and fluid flow model. The weld pool solidified between pulses and regions of the weld bead melted and solidified several times during welding. Short laser pulses restricted the width of the weld track and velocities in the weld pool. However, convection still remained an important mechanism of heat transfer in the weld pool. The computed high cooling rates during linear welding with neodymium-doped yttrium aluminum garnet pulsed laser operated at 140 W average power, 20 Hz frequency, and 5 ms pulse duration were consistent with those observed in typical laser welding. After the laser beam was switched off, the mushy zone expanded, reaching its maximum size when no pure liquid region remained. Calculations of solidification parameters indicated that the criterion for plane front solidification was not satisfied. The results demonstrate that the application of numerical transport phenomena can significantly improve the current understanding of linear welding with a pulsed laser beam.

Roy, G. G.; Elmer, J. W.; Debroy, T.

2006-08-01

110

Radiocarbon signatures and size-age-composition relationships of major organic matter pools within a unique California upwelling system  

NASA Astrophysics Data System (ADS)

Coastal upwelling zones are among the most productive regions in the world and play a major role in the global carbon cycle. Radiocarbon (as ?14C) is a powerful tool for tracing the source and fate of suspended particulate and dissolved organic matter (POM, DOM), and has the potential to reconcile key carbon budgets within upwelling systems. However, the extent to which upwelling processes influence the ?14C signature of surface DIC, or that of POM or DOM remains almost completely unknown. Here we present a time series of stable carbon (?13C) and ?14C isotopic data of major water column carbon pools, including dissolved inorganic carbon (DIC), large (0.7-500 ?m) and small (0.1-100 ?m) POM, and high molecular weight (HMW; ˜1 nm-0.1 ?m) DOM from an upwelling center along the Big Sur coast. We show that DIC ?14C values (ranging between +29‰ and -14‰) are strongly correlated to coastal upwelling processes, and that this 14C-signal readily propagates into both the POM and HMW DOM pool. However, the presence of negative POM and HMW DOM ?14C values (ranging between +46‰ and -56‰, +6‰ and -123‰ and -1‰ and -150‰, respectively) suggests contributions of “pre-aged” OM, complicating the direct use of “bulk” ?14C for tracing upwelling-derived carbon production/export. Using a triple-isotope mixing model (?13C, ?15N, ?14C) we estimate that 50-90% and 45-51% of large and small POM is newly-produced OM, while between 6-22% and 12-44% of large and small POM are derived from “pre-aged” re-suspended sediments. Finally, we observe quantitative relationships between OM size, composition (C:N ratio) and ?14C within this upwelling system, possibly representing a new tool for modeling ocean C and N biogeochemical cycles.

Walker, B. D.; Guilderson, T. P.; Okimura, K. M.; Peacock, M. B.; McCarthy, M. D.

2014-02-01

111

Effect of base plate thickness on wave size and wave morphology in explosively welded couples  

Microsoft Academic Search

The influence of plate thickness on the wave morphology generated in explosive welding is analysed by the use of mild steel base plates machined into steps of different thicknesses and a constant-thickness mild steel flyer plate, to ensure similar impacting conditions. It is found that wave shape, at the same distance from the collision point, remains unchanged for the different

D. Jaramillov; O. T. Inal; A. Szecket

1987-01-01

112

Elastic-Plastic Fracture Mechanics Analysis of Critical Flaw Size in ARES I-X Flange-to-Skin Welds  

NASA Technical Reports Server (NTRS)

NASA's Ares 1 Upper Stage Simulator (USS) is being fabricated from welded A516 steel. In order to insure the structural integrity of these welds it is of interest to calculate the critical initial flaw size (CIFS) to establish rational inspection requirements. The CIFS is in turn dependent on the critical final flaw size (CFS), as well as fatigue flaw growth resulting from transportation, handling and service-induced loading. These calculations were made using linear elastic fracture mechanics (LEFM), which are thought to be conservative because they are based on a lower bound, so called elastic, fracture toughness determined from tests that displayed significant plasticity. Nevertheless, there was still concern that the yield magnitude stresses generated in the flange-to-skin weld by the combination of axial stresses due to axial forces, fit-up stresses, and weld residual stresses, could give rise to significant flaw-tip plasticity, which might render the LEFM results to be non-conservative. The objective of the present study was to employ Elastic Plastic Fracture Mechanics (EPFM) to determine CFS values, and then compare these values to CFS values evaluated using LEFM. CFS values were calculated for twelve cases involving surface and embedded flaws, EPFM analyses with and without plastic shakedown of the stresses, LEFM analyses, and various welding residual stress distributions. For the cases examined, the computed CFS values based on elastic analyses were the smallest in all instances where the failures were predicted to be controlled by the fracture toughness. However, in certain cases, the CFS values predicted by the elastic-plastic analyses were smaller than those predicted by the elastic analyses; in these cases the failure criteria were determined by a breakdown in stress intensity factor validity limits for deep flaws (a greater than 0.90t), rather than by the fracture toughness. Plastic relaxation of stresses accompanying shakedown always increases the calculated CFS values compared to the CFS values determined without shakedown. Thus, it is conservative to ignore shakedown effects.

Chell, G. Graham; Hudak, Stephen J., Jr.

2008-01-01

113

The basics of semiautomatic welding  

SciTech Connect

By definition, gas metal arc welding (GMAW) and flux cored arc welding (FCAW) are semiautomatic processes in which a consumable electrode is fed into a weld at a controlled rate, while in most cases a continuous blanket of gas shields the weld zone from contamination by the atmosphere. Semiautomatic welding includes five distinctive techniques or process variations, known as short circuiting, spray transfer, pulsed spray, gas shielded flux cored, and self-shielded flux cored welding. Short circuiting welding operates on generally lower arc voltages and amperages than spray transfer. This process pinpoints the arc heat and produces a small fast-freezing weld pool. The spray transfer process provides an intensely hot, higher voltage arc and high deposition rates. The pulsed spray mode of metal transfer uses two weld current levels: low background and pulse peak. Droplet transfer usually occurs during the pulse peak portion of the cycle. The low current background allows reduced heat input and improved weld pool control. Flux cored welding transfers metal in a manner similar to spray transfer, but with larger droplets. The higher weld currents usable with flux cored welding result in higher deposition rates and deeper penetration. Self-shielded flux cored welding is similar to gas-shielded flux cored welding except that its weld shielding mechanism is self-contained in the wire. As a result, it can be used outdoors with less need for wind breaks.

Uttrachi, G.D. (Esab Group, Florence, SC (United States)); Meyer, D.W. (Esab Group, Hanover, PA (United States))

1993-08-01

114

71st American Welding Society annual meeting  

SciTech Connect

Detailed summaries are given for the 151 Technical and Brazing Conference papers presented at the 71st Annual Convention of the American Welding Society. Some of the topics covered were: computer technology for welding applications, weld testing, microstructure analysis, weld pool studies, electrode performance, welding processes and equipment development, thermal spraying, welding in marine and pipeline construction, weld cracking studies, aluminum welding, brazing, ceramic joining and low alloy steel welding. Also included are abstracts for the 29 poster sessions and 16 education session papers and the names and addresses of all professional program, poster session and education program participants.

Not Available

1990-01-01

115

A computationally efficient model of convective heat transfer and solidification characteristics during keyhole mode laser welding  

NASA Astrophysics Data System (ADS)

Computationally efficient heat transfer models of keyhole mode laser welding ignore fluid flow in the gas, liquid, and the two phase solid-liquid regions. These models cannot be applied to high Peclet number systems where convective heat transfer affects weld pool geometry, cooling rate, and other weld attributes. Here we show that by synthesizing features of an existing model to determine keyhole shape and size with rigorous fluid flow and heat transfer calculations in the liquid and the two phase solid-liquid regions, important features of both high and low Peclet number systems can be satisfactorily simulated. The geometry of the keyhole is calculated by assuming thermal equilibrium at the gas/liquid interface and point by point heat balance at the keyhole wall. The heat transfer outside the vapor cavity is calculated by numerically solving the equations of conservation of mass, momentum, and energy. A vorticity based turbulence model is used to estimate the values of effective viscosity and effective thermal conductivity of the liquid metal in the weld pool. It is shown that the temperature profile and the weld pool shape and size depend strongly on the convective heat transfer for low thermal conductivity alloys like stainless steel. For high thermal conductivity aluminum alloys, on the other hand, convection does not play a significant role in determining the shape and size of the weld pool. The computed solidification parameters indicated that the solidification structure becomes less dendritic and coarser with the decrease in welding velocity. The results demonstrate that a numerically efficient convective heat transfer model of keyhole mode laser welding can significantly improve the current understanding of weld attributes for different materials with widely different thermal properties.

Rai, R.; Roy, G. G.; Debroy, T.

2007-03-01

116

Peripheral "CD8 tuning" dynamically modulates the size and responsiveness of an antigen-specific T cell pool in vivo.  

PubMed

In this study, we suggest that CD8 levels on T cells are not static, but can change and, as a result, modulate CD8(+) T cell responses. We describe three models of CD8 modulation using novel weak-agonist (K1A) and super-agonist (C2A) altered peptide ligands of the HY smcy peptide. First, we used peripheral nonresponsive CD8(low) T cells produced after peripheral HY-D(b) MHC class I tetramer stimulation of female HY TCR transgenic and wild-type mice. Second, we used genetically lowered CD8(int) T cells from heterozygote CD8(+/0) mice. Finally, we used pre-existing nonresponsive CD8(low) T cells from male HY TCR transgenic mice. In CD8(low) and CD8(high) mice, presence of a lower level of CD8 greatly decreased the avidity of the peptide-MHC for HY TCR as reflected by avidity (K(D)) and dissociation constant (T(1/2)) measurements. All three models demonstrated that lowering CD8 levels resulted in the requirement for a higher avidity peptide-MHC interaction with the TCR to respond equivalently to unmanipulated CD8(high) T cells of the same specificity. Additionally, direct injections of wild-type HY-D(b) and C2A-D(b) tetramers into female HY TCR or female B6 mice induced a high frequency of peripheral nonresponsive CD8(low) T cells, yet C2A-D(b) was superior in inducing a primed CD8(+)CD44(+) memory population. The ability to dynamically modulate the size and responsiveness of an Ag-specific T cell pool by "CD8 tuning" of the T cell during the early phases of an immune response has important implications for the balance of responsiveness, memory, and tolerance. PMID:15634879

Maile, Robert; Siler, Catherine A; Kerry, Samantha E; Midkiff, Katherine E; Collins, Edward J; Frelinger, Jeffrey A

2005-01-15

117

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.

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

2013-01-01

118

Grain Refinement by Laser Welding of AA 5083 with Addition of Ti/B  

NASA Astrophysics Data System (ADS)

Grain refinement was reported to improve the mechanical properties and reduce the hot crack susceptibility of aluminum welds. Some of today's filler materials already contain grain refiners. However, their effectiveness will strongly depend on the boundary conditions of welding. The aim of this study is thus to determine the minimum content of Ti/B grain refiner, which is needed to achieve a small grain size with 100% globular grains of the weld metal for different welding conditions, particularly with respect to high welding speed and cooling rate by laser welding. Controlled amounts of TiborTM grain refiner (containing Ti and B in a ratio of 5:1) were introduced into the molten pool of AA 5083 by pre-deposited cast inserts under different welding conditions by laser welding. The results show that, despite the high cooling rate and great melt overheating, the laser weld could be grain refined to a mean grain size at ca. 22 ?m. The minimal required Tibor™ concentration for complete grain refinement increases with welding speed. The WDX analysis has confirmed that the titanium aluminides are the nucleation site for equiaxed grains.

Tang, Z.; Seefeld, T.; Vollertsen, F.

119

Effect of welding parameters on the solidification microstructure of autogenous TIG welds in an Al–Cu–Mg–Mn alloy  

Microsoft Academic Search

The weld metal microstructures of autogenous TIG welds have been investigated for a range of welding conditions using an Al–Cu–Mg–Mn alloy. It was found that a combination of high welding speeds and low power densities provide the thermal conditions required for the nucleation and growth of equiaxed grains in the weld pool, providing heterogeneous nucleation sites are available. The most

A. F. Norman; V. Drazhner; P. B. Prangnell

1999-01-01

120

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

121

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

122

SPOT WELDING OF INCONEL \\  

Microsoft Academic Search

Recommended welding schedules are outlined for spot welding Inconel ; X'' sheets of 0.032-, 0.062-, 0.093-, weld quality meets the requirements of ; Military Specification MIL-W-6858A. The work was performed on several sizes af ; welding machines which included the three-phase dry-disk rectifier type and ; single-phase type. The basic approach was to formulate two sets of schedules, ; one

J. Harris; J. J. Riley; M. D. Bellware

1958-01-01

123

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

124

Local fatigue strength parameters for welded joints based on strain energy density with inclusion of small-size notches  

Microsoft Academic Search

A fatigue strength parameter for (seam-)welded joints is presented which is based on the averaged elastic strain energy density (SED) criterion applied to full circle and semicircular ‘control volumes’, the latter centred by the expected crack path. The parameter is applicable both at weld toes and weld roots, at least in the medium-cycle and high-cycle fatigue range where elastic conditions

D. Radaj; F. Berto; P. Lazzarin

2009-01-01

125

Analysis of Weld Geometry Considering the Transferring Droplets in Gas Metal Arc Welding  

NASA Astrophysics Data System (ADS)

In the present study, depressions of the GMA weld pool due to the impact of droplets are numerically investigated. The numerical simulations is performed on the basis of the Navier-Stokes equation and the volume of fluid (VOF) functions. The kinetic energy of the transferring droplets produces a depression on the weld pool surface. The surface active element affects the depression of the weld pool. In GMAW, the droplet transferred to the surface of the weld pool is one of the factors to produce the finger shape penetration at high current.

Park, Hyunsung; Rhee, Sehun

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

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

128

Welding wire pressure sensor assembly  

NASA Technical Reports Server (NTRS)

The present invention relates to a device which is used to monitor the position of a filler wire relative to a base material being welded as the filler wire is added to a welding pool. The device is applicable to automated welding systems wherein nonconsumable electrode arc welding processes are utilized in conjunction with a filler wire which is added to a weld pool created by the electrode arc. The invention senses pressure deviations from a predetermined pressure between the filler wire and the base material, and provides electrical signals responsive to the deviations for actuating control mechanisms in an automatic welding apparatus so as to minimize the pressure deviation and to prevent disengagement of the contact between the filler wire and the base material.

Morris, Timothy B. (inventor); Milly, Peter F., Sr. (inventor); White, J. Kevin (inventor)

1994-01-01

129

Optical penetration sensor for pulsed laser welding  

DOEpatents

An apparatus and method for determining the penetration of the weld pool created from pulsed laser welding and more particularly to an apparatus and method of utilizing an optical technique to monitor the weld vaporization plume velocity to determine the depth of penetration. A light source directs a beam through a vaporization plume above a weld pool, wherein the plume changes the intensity of the beam, allowing determination of the velocity of the plume. From the velocity of the plume, the depth of the weld is determined.

Essien, Marcelino (Albuquerque, NM); Keicher, David M. (Albuquerque, NM); Schlienger, M. Eric (Albuquerque, NM); Jellison, James L. (Albuquerque, NM)

2000-01-01

130

Effect of particle size on the friction welding of Al 2O 3 reinforced 6160 Al alloy composite and SAE 1020 steel  

Microsoft Academic Search

The aim of this study is to investigate the feasibility of joining Al2O3reinforced Al alloy composite to SAE 1020 steel by rotational friction welding. The aluminum-based metal matrix composite (MMC) material containing 5, 10 and 15vol% Al2O3 particles with average particle sizes of 30 and 60?m was produced by powder metallurgy technique. The integrity of the joints has been investigated

Ahmet Hascalik; Nuri Orhan

2007-01-01

131

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

132

Impact Modeling of Spot Welds  

NASA Astrophysics Data System (ADS)

Resistance spot welds in most current finite element crash models are characterized as a rigid link at the location of the weld which transfers the load but is not designed to fail. Newer weld elements in the popular finite element analysis codes include the option of incorporating a failure criteria for the weld element. As many automotive companies move towards the use of high-strength steels, the dynamic behavior of the spot welds will become increasingly important and the failure of any welds should be incorporated during the simulation. The failure criteria will be influenced by mesh size, weld element properties, weld element type, surrounding material properties, strain rate, and weld placement. The influence of some of these parameters using current spot weld modeling techniques will be discussed along with recommendations for future work in this area.

Yancey, Robert N.

2004-06-01

133

Welded Kimberlite?  

NASA Astrophysics Data System (ADS)

Welding of pyroclastic deposits generally involves the sintering of hot glassy vesicular particles and requires the presence of a load and/or high temperatures. Welding can occur on various scales as observed in large welded pyroclastic flows, in small-volume agglutinated spatter rims, or as in coalesced clastogenic lava flows. In all these examples welding occurs mainly by reduction or elimination of porosity within the vesicular clasts and/or inter-clast pore space. The end result of welding in pyroclastic deposits is to produce dense, massive, coherent deposits. Here, we present a possible new end-member of the welding process: welding of non- vesicular pyroclasts in intra-crater kimberlite deposits. Kimberlite melt is a low-viscosity liquid carrying abundant crystals. Because of this, kimberlite eruptions generally produce non-vesicular pyroclasts. During welding, these pyroclast cannot deform by volume reduction to form typical fiamme. As a result, welding and compaction in kimberlites proceeds via the reduction of inter-clast pore space alone. The lack of porous pyroclasts limits the maximum amount of volumetric strain within pyroclastic kimberlite deposits to about 30%. This value is substantially lower than the limiting values for welding of more common felsic pyroclastic flows. The lower limit for volumetric strain in welded kimberlite deposits severely restricts the development of a fabric. In addition, pyroclastic kimberlite deposits commonly feature equant-shaped pyroclasts, and equant-shaped crystals. This, in turn, limits the visibility of the results of compaction and pore space reduction, as there are few deformable markers and elongate rigid markers that are able to record the strain during compaction. These features, together with the low viscosity of kimberlite magma and the stratigraphic position of these kimberlite deposits within the upper reaches of the volcanic conduit, call for careful interpretation of coherent-looking rocks in these settings. In this contribution we explore the possible welded origin for dark and competent kimberlite facies from the Victor Northwest pipe (Northern Ontario, Canada). This volumetrically extensive facies superficially resembles a coherent rock. The following observations on the dark and competent facies are suggestive of a pyroclastic, rather than intrusive or extrusive coherent origin: The facies is completely enveloped by pyroclastic facies; has gradational contacts with adjacent pyroclastic facies above and below; contains faint outlines of primary pyroclasts; shows diffuse grain size variations and rare bedding; shows systematic changes in components from the underlying pyroclastic facies to the dark and competent facies to the overlying pyroclastic facies implying a lack of a depositional break in this succession; and shows a faint, generally subhorizontal fabric despite the presence of an equant grain shape population. In addition, we present evidence that the original inter-clast porosity has been reduced or eliminated by syn-depositional welding rather than by precipitation of secondary minerals in the inter-clast pore spaces. We feel that the latter process (i.e., alteration) is highly unlikely because: The kimberlite package contains intervals with well crystallized groundmass similar to coherent kimberlite, this texture simply cannot be produced by alteration; the kimberlite is in fact the freshest rock within the pipe, containing mostly fresh olivines; and the dark and competent kimberlite does not show a patchy or vein-related heterogeneity typical of alteration. In summary, these deposits likely represent a variably welded succession of proximal spatter/fire fountaining kimberlite deposits.

van Straaten, B. I.; Kopylova, M. G.; Russell, J. K.; Scott Smith, B. H.

2009-05-01

134

The radial diffusivity and magnetization transfer pool size ratio are sensitive markers for demyelination in a rat model of type III multiple sclerosis (MS) lesions.  

PubMed

Determining biophysical sensitivity and specificity of quantitative magnetic resonance imaging is essential to develop effective imaging metrics of neurodegeneration. Among these metrics, apparent pool size ratio (PSR) from quantitative magnetization transfer (qMT) imaging and radial diffusivity (RD) from diffusion tensor imaging (DTI) are both known to relate to histological measure of myelin density and integrity. However their relative sensitivities towards quantitative myelin detection are unknown. In this study, we correlated high-resolution quantitative magnetic resonance imaging measures of subvoxel tissue structures with corresponding quantitative myelin histology in a lipopolysaccharide (LPS) mediated animal model of MS. Specifically, we acquired quantitative magnetization transfer (qMT) and diffusion tensor imaging (DTI) metrics (on the same tissue sample) in an animal model system of type III oligodendrogliopathy which lacked prominent lymphocytic infiltration, a system that had not been previously examined with quantitative MRI. We find that the qMT measured apparent pool size ratio (PSR) showed the strongest correlation with a histological measure of myelin content. DTI measured RD showed the next strongest correlation, and other DTI and relaxation parameters (such as the longitudinal relaxation rate (R1f) or fractional anisotropy (FA)) showed considerably weaker correlations with myelin content. PMID:23481461

Janve, Vaibhav A; Zu, Zhongliang; Yao, Song-Yi; Li, Ke; Zhang, Fang Lin; Wilson, Kevin J; Ou, Xiawei; Does, Mark D; Subramaniam, Sriram; Gochberg, Daniel F

2013-07-01

135

Grain Refinement Control in Tig Arc Welding.  

National Technical Information Service (NTIS)

A method for controlling grain size and weld puddle agitation in a tungsten electrode inert gas welding system to produce fine, even grain size and distribution is disclosed. In the method the frequency of dc welding voltage pulses supplied to the welding...

W. F. Iceland E. L. Whiffen

1975-01-01

136

Swimming Pool Guidelines. 1997 Edition.  

ERIC Educational Resources Information Center

The state of Alaska, which provides for swimming pools as an eligible project cost in projects approved for state aid, presents guidelines to assist school districts in planning swimming pools, and provides standards for swimming pool size based on the planned educational program and student population. The guidelines are intended to assist school…

Alaska State Dept. of Education, Juneau.

137

Tailoring weld geometry and composition in fusion welding through convective mass transfer calculations  

NASA Astrophysics Data System (ADS)

In the past two decades, numerical transport phenomena based models have provided useful information about the thermal cycles and weld pool geometry. However, no effort has been made to apply these concepts to design weld consumables, to study the weld bead shape on welding two plates with different sulfur contents and to tailor weld pool geometry to specified dimensions. The present research focuses on these unexplored areas. The research proposed here seeks to develop a quantitative understanding of mass transport during fusion welding, with special emphasis on the role of surface active elements and the effect of solute distribution on weld defects like liquation cracking. A comprehensive model, incorporating numerical three-dimensional calculations of temperature and velocity fields and solute distribution in the weld pool is developed for the proposed quantitative study. The study identifies the factors that affect the weld pool geometry on joining two plates with different sulfur contents, and predicts the susceptibility of an aluminum-copper alloy GMA weld to liquation cracking. The specific contributions of the present thesis research include (i) development of a numerical solute transport model for fusion welding; (ii) improving the reliability of output of the numerical model; (iii) achieving computational efficiency and economy by developing a neural network trained by data generated by the numerical model; (iv) creating a bi-directional methodology where a target weld attribute like weld pool geometry can be attained via multiple combinations of input process parameters like arc current, voltage and welding speed; (v) calculating sulfur distribution during gas tungsten arc welding of stainless steel plates with different sulfur contents and predicting the arc welding of aluminum-copper alloys by incorporating the heat and mass addition from filler metal and a non-equilibrium solidification model, and using the copper content of the mushy zone to predict the occurrence of liquation cracking.

Mishra, Saurabh

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

The particle size distribution, density, and specific surface area of welding fumes from SMAW and GMAW mild and stainless steel consumables.  

PubMed

Particle size distributions were measured for fumes from mild steel (MS) and stainless steel (SS); shielded metal arc welding (SMAW) and gas metal arc welding (GMAW) consumables. Up to six samples of each type of fume were collected in a test chamber using a micro-orifice uniform deposit (cascade) impactor. Bulk samples were collected for bulk fume density and specific surface area analysis. Additional impactor samples were collected using polycarbonate substrates and analyzed for elemental content. The parameters of the underlying mass distributions were estimated using a nonlinear least squares analysis method that fits a smooth curve to the mass fraction distribution histograms of all samples for each type of fume. The mass distributions for all four consumables were unimodal and well described by a lognormal distribution; with the exception of the GMAW-MS and GMAW-SS comparison, they were statistically different. The estimated mass distribution geometric means for the SMAW-MS and SMAW-SS consumables were 0.59 and 0.46 micron aerodynamic equivalent diameter (AED), respectively, and 0.25 micron AED for both the GMAW-MS and GMAW-SS consumables. The bulk fume densities and specific surface areas were similar for the SMAW-MS and SMAW-SS consumables and for the GMAW-MS and GMAW-SS consumables, but differed between SMAW and GMAW. The distribution of metals was similar to the mass distributions. Particle size distributions and physical properties of the fumes were considerably different when categorized by welding method. Within each welding method there was little difference between MS and SS fumes. PMID:7856513

Hewett, P

1995-02-01

140

Finite element models of laser welding  

NASA Astrophysics Data System (ADS)

A numerical study was undertaken in an effort to understand the complex heat and fluid flow during the laser beam welding process. The finite element method was applied, and a horizontal cross sectional model and a vertical cross sectional model have been suggested. In the horizontal cross sectional model, heat transfer in the deep penetration mode laser welding was discussed with the assumption that a keyhole has been formed and heat and fluid flow are two dimensional. Even though the driving forces of the weld convection are missing in the horizontal cross sectional model and the heat and fluid flow in the weld pool are more complicated than can be explained by it, the model included the penetration mode concept of the keyhole and is a helpful conceptual stepping stone toward the understanding of laser welding. It also served as a point of introduction for the enthalpy method in finite element analysis. The weld pool convection induced by the surface tension gradient in the conduction mode laser welding has been discussed in the vertical cross sectional model with and without a flat free surface assumption. It was found that a typical surface tension gradient during welding created violent convection in the weld pool. This model explains the elements of weld pool convection in conduction mode laser welding. Free surface problems with kinematic boundary conditions were also introduced as a part of the vertical cross sectional model. It was found that the presence of normal stress on the free surface places a severe restriction on the time step in the computations of time dependent problems. An enthalpy method has been shown to be useful in solving the Stefan problems with moving multi-phase interfaces. The presence of latent heat in the simulations of welding influences heat and fluid flow such that the weld pool is stretched in the direction of welding when the latent heat is included in the model.

Lee, Jinhee

141

Why to measure a broad range of city sizes? Analysis of globally pooled data of urban GHG measurements for sustainability  

NASA Astrophysics Data System (ADS)

We have assembled a database of urban GHG emissions from various published sources, including about 200 cities globally. Analyzing this CO2 emission inventory from multiple countries we find power-law relations between the emissions and city size, measured in population. The results suggest that in developing countries large cities emit more CO2 per capita compared to small cities, i.e. they tend to comprise super-linear correlations. For developed countries the results suggest the opposite, i.e. linear or sub-linear correlations, implying better efficiency of large cities. We derive how the total emissions of an entire country relate with the power-law correlations and find that the size of the most populated city is dominating in the case of linear and super-linear correlations, while a transition occurs to sub-linear correlations, where the size of the largest city has no influence. It is important to further substantiate an overview of city emission inventories across a broad range of city sizes and types to further clarify the complex relationships between cities and GHG emissions. On the one hand, we propose a minimum set of meta-information to be reported together with the emission inventories, e.g. for determining comparability among inventories. On the other hand, we propose to fill evident gaps with respect to regions (e.g. sub-Saharan African and South American cities) and types of cities (e.g. small medium and low-income country cities) to allow for a better global overview of city sizes, income, and emissions. We conclude that from the climate change mitigation point of view, urbanization is desirable in developed countries and should be avoided in developing countries, if effinciency increasing mechanisms can not be established. More data acquisition is needed to support our empirical findings.

Rybski, Diego; Sterzel, Till; Reusser, Dominik E.; Fichter, Christina; Kropp, Jürgen P.

2013-04-01

142

Daily consumption of orange-fleshed sweet potato for 60 days increased plasma ?-carotene concentration but did not increase total body vitamin A pool size in Bangladeshi women.  

PubMed

We assessed the effect of daily consumption of orange-fleshed sweet potatoes (OFSP), with or without added fat, on the vitamin A (VA) status of Bangladeshi women with low initial VA status. Women (n = 30/group) received one of the following for 6 d/wk over 10 wk: 1) 0 ?g retinol activity equivalents (RAE)/d as boiled white-fleshed sweet potatoes (WFSP) and a corn oil capsule, 2) 600 ?g RAE/d as boiled OFSP and a corn oil capsule, 3) fried OFSP and a corn oil capsule, or 4) boiled WFSP and a retinyl palmitate capsule in addition to their home diets. Plasma concentrations of retinol and ?-carotene and total body VA pool size were assessed before and after the 60-d intervention. Initial and final plasma retinol concentrations (mean ± SD) were 0.75 ± 0.18 ?mol/L and 0.84 ± 0.19 ?mol/L, respectively (P = 0.31); final means did not differ by group. Initial and final plasma ?-carotene concentrations were 0.10 ± 00 ?mol/L and 0.18 ± 0.09 ?mol/L, respectively (P < 0.0001); final mean plasma ?-carotene concentrations were higher in groups that received OFSP (P < 0.0001), and final mean plasma ?-carotene was marginally higher in the group that received fried OFSP compared with boiled OFSP (P = 0.07). Initial and final total body VA pool sizes were 0.060 ± 0.047 mmol and 0.091 ± 0.070 mmol, respectively (P = 0.05, n = 110) and did not differ by group. Despite an increase in plasma ?-carotene concentration, the impact of OFSP on VA status appears to be limited in Bangladeshi women residing in a resource-poor community. PMID:22933750

Jamil, Kazi M; Brown, Kenneth H; Jamil, Maleka; Peerson, Janet M; Keenan, Alison H; Newman, John W; Haskell, Marjorie J

2012-10-01

143

Fast, Nonspattering Inert-Gas Welding  

NASA Technical Reports Server (NTRS)

Proposed welding technique combines best features of metal (other than tungsten)/inert-gas welding, plasma arc welding, and tungsten/inert-gas welding. Advantages include: wire fed to weld joint preheated, therefore fed at high speed without spattering; high-frequency energy does not have to be supplied to workpiece to initiate welding; size of arc gap not critical, power-supply control circuit adjusts voltage across gap to compensate for changes; only low gas-flow rate needed; welding electrode replaced easily as prefabricated assembly; external wire-feeding manipulator not needed; and welding process relatively forgiving of operator error.

Gilbert, Jeffrey L.

1991-01-01

144

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

145

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

146

Increase in dNTP pool size during the DNA damage response plays a key role in spontaneous and induced-mutagenesis in Escherichia coli  

PubMed Central

Exposure of Escherichia coli to UV light increases expression of NrdAB, the major ribonucleotide reductase leading to a moderate increase in dNTP levels. The role of elevated dNTP levels during translesion synthesis (TLS) across specific replication-blocking lesions was investigated. Here we show that although the specialized DNA polymerase PolV is necessary for replication across UV-lesions, such as cyclobutane pyrimidine dimers or pyrimidine(6-4)pyrimidone photoproduct, Pol V per se is not sufficient. Indeed, efficient TLS additionally requires elevated dNTP levels. Similarly, for the bypass of an N-2-acetylaminofluorene-guanine adduct that requires Pol II instead of PolV, efficient TLS is only observed under conditions of high dNTP levels. We suggest that increased dNTP levels transiently modify the activity balance of Pol III (i.e., increasing the polymerase and reducing the proofreading functions). Indeed, we show that the stimulation of TLS by elevated dNTP levels can be mimicked by genetic inactivation of the proofreading function (mutD5 allele). We also show that spontaneous mutagenesis increases proportionally to dNTP pool levels, thus defining a unique spontaneous mutator phenotype. The so-called “dNTP mutator” phenotype does not depend upon any of the specialized DNA polymerases, and is thus likely to reflect an increase in Pol III's own replication errors because of the modified activity balance of Pol III. As up-regulation of the dNTP pool size represents a common physiological response to DNA damage, the present model is likely to represent a general and unique paradigm for TLS pathways in many organisms.

Gon, Stephanie; Napolitano, Rita; Rocha, Walter; Coulon, Stephane; Fuchs, Robert P.

2011-01-01

147

Development of Remote Control Welding System of Large Structures.  

National Technical Information Service (NTIS)

The authors have developed a remotely-controlled welding system. This system enables welding of large-size structures such as LNG storage tanks which particularly demand high quality welding by remote control while the operator monitors the arc condition ...

S. I. Tanioka N. Katayama A. Tejima M. Yamada T. Saito

1987-01-01

148

Analysis and validation of laser spot weld-induced distortion.  

National Technical Information Service (NTIS)

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 ...

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

1999-01-01

149

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

150

Study made to establish parameters and limitations of explosive welding  

NASA Technical Reports Server (NTRS)

It is theorized that metal jetting must be present for welding to occur, therefore an explosive weld interface may indicate the relation between the metal jet velocity and shock wave velocity in welding. Parameters for effecting explosive welding in patches of 3 or 4 inches in diameter were established, and found applicable to explosive welding of patches of various sizes.

Polhemus, F. C.

1967-01-01

151

Welding Research  

NASA Technical Reports Server (NTRS)

Welding fabrication and welding processes were studied. The following research projects are reported: (1) welding fabrication; (2) residual stresses and distortion in structural weldments in high strength steels; (3) improvement of reliability of welding by in process sensing and control (development of smart welding machines for girth welding of pipes); (4) development of fully automated and integrated welding systems for marine applications; (5) advancement of welding technology; (6) research on metal working by high power laser (7) flux development; (8) heat and fluid flow; (9) mechanical properties developments.

1982-01-01

152

Effect of Pin Length on Hook Size and Joint Properties in Friction Stir Lap Welding of 7B04 Aluminum Alloy  

NASA Astrophysics Data System (ADS)

Friction stir lap welding of 7B04 aluminum alloy was conducted in the present paper, and the effect of pin length on hook size and joint properties was investigated in detail. It is found that for each given set of process parameters, the size of hook defect on the advancing side shows an "M" type evolution trend as the pin length is increased. The affecting characteristics of pin length on joint properties are dependent on the heat input levels. When the heat input is low, the fracture strength is firstly increased to a peak value and then shows a decrease. When the heat input is relatively high, the evolution trend of fracture strength tends to exhibit a "W" type with increasing the pin length.

Wang, Min; Zhang, Huijie; Zhang, Jingbao; Zhang, Xiao; Yang, Lei

2014-05-01

153

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

154

Contribution to study of heat transfer and fluid flow during GTA welding  

NASA Astrophysics Data System (ADS)

In this paper, the effect of surface-active elements especially sulfur on weld pool shape has been reported. In our contribution, we analyze the influence of the weld pool chemical composition (Mn, Si, …), welding energy, sulphur gradient and electromagnetic effect. The computed results are in good agreement with the corresponding experimental results, indicating the validity of the modeling approach.

Koudadje, Koffi; Delalondre, Clarisse; Médale, Marc; Carpreau, Jean-Michel

2014-06-01

155

The mechanism of penetration increase in A-TIG welding  

NASA Astrophysics Data System (ADS)

The mechanism of the increasing of A-TIG welding penetration is studied by using the activating flux we developed for stainless steel. The effect of flux on the flow and temperature fields of weld pool is simulated by the PHOENICS software. It shows that without flux, the fluid flow will be outward along the surface of the weld pool and then down, resulting in a flatter weld pool shape. With the flux, the oxygen, which changes the temperature dependence of surface tension grads from a negative value to a positive value, can cause significant changes on the weld penetration. Fluid flow will be inward along the surface of the weld pool toward the center and then down. This fluid flow pattern efficiently transfers heat to the weld root and produces a relatively deep and narrow weld. This change is the main cause of penetration increase. Moreover, arc construction can cause the weld width to become narrower and the penetration to become deeper, but this is not the main cause of penetration increase. The effects of flux on fluid flow of the weld pool surface and arc profiles were observed in conventional TIG welding and in A-TIG welding by using high-speed video camera. The fluid flow behavior was visualized in realtime scale by micro focused X-ray transmission video observation system. The result indicated that stronger inward fluid flow patterns leading to weld beads with narrower width and deeper penetration could be apparently identified in the case of A-TIG welding. The flux could change the direction of fluid flow in welding pool. It has a good agreement with the simulation results.

Zhang, Rui-Hua; Pan, Ji-Luan; Katayama, Seiji

2011-06-01

156

Keyhole formation and collapse in plasma arc welding  

NASA Astrophysics Data System (ADS)

A mathematical model is developed to describe the heat transfer and fluid flow in stationary keyhole plasma arc welding. Using the volume of fluid method, the processes of heating, melting, collapsing and subsequent solidifying in the molten pool are dynamically studied. The predicted results have been compared with the experimental weld and keyhole shape. Using the LaserStrobe video system, the captured images of the upper surface of the weld pool are used to verify the predicted transient development of the weld pool. It is indicated that theoretical predictions and the experimental results are in close agreement.

Fan, H. G.; Kovacevic, R.

1999-11-01

157

Infrared Sensing Techniques for Adaptive Robotic Welding.  

National Technical Information Service (NTIS)

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 o...

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

1986-01-01

158

A novel visual image sensor for CO2 short circuiting arc welding and its application in weld reinforcement detection  

NASA Astrophysics Data System (ADS)

In this paper, a novel visual image sensor was designed to detect the weld pool images during CO2 short circuiting arc welding. Based on a charge coupled device (CCD) camera, the new sensor was smaller than the previous one. As a result, larger operation space is achieved for the welding torch which is attached to it. Moreover, the mismatching problem between the fixed shooting schedule of the CCD camera and the random short circuiting metal transfer during welding was successfully resolved. By eliminating the influences from welding arc and spatter, clear and complete welding pool images were acquired from different angles around the welding torch. Based on these images, the shape parameters of the welding pool were defined and the relationship between these parameters and weld reinforcement was analysed. In addition, the multiple linear regression (MLR) model and the artificial neutral network (ANN) model were proposed and trained, respectively, to detect weld reinforcement from weld pool images. Results of both the MLR model and the ANN model show that weld reinforcement can successfully be detected.

Sun, Zhenguo; Chen, Qiang; Zhang, Wenzeng; Cao, Yipeng; Liu, Pengfei

2006-12-01

159

Prevalence estimation from pooled samples.  

PubMed

Under certain conditions, prevalence can be estimated by testing samples from individual members or by pooling samples from members into a group and by testing the sample from the group as a single unit. Pooled tests are more accurate than individual tests when P is less than 10%. Optimal group size is 1.6/P. Efficiency decreases slowly with suboptimal size and rapidly with overly large size. PMID:2785780

Sacks, J M; Bolin, S R; Crowder, S V

1989-02-01

160

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.

161

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.

162

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

163

Automatic welding of stainless steel tubing  

NASA Technical Reports Server (NTRS)

The use of automatic welding for making girth welds in stainless steel tubing was investigated as well as the reduction in fabrication costs resulting from the elimination of radiographic inspection. Test methodology, materials, and techniques are discussed, and data sheets for individual tests are included. Process variables studied include welding amperes, revolutions per minute, and shielding gas flow. Strip chart recordings, as a definitive method of insuring weld quality, are studied. Test results, determined by both radiographic and visual inspection, are presented and indicate that once optimum welding procedures for specific sizes of tubing are established, and the welding machine operations are certified, then the automatic tube welding process produces good quality welds repeatedly, with a high degree of reliability. Revised specifications for welding tubing using the automatic process and weld visual inspection requirements at the Kennedy Space Center are enumerated.

Clautice, W. E.

1978-01-01

164

Computer integrated vision and neural network technologies for intelligent automatic laser butt joint welding  

Microsoft Academic Search

This paper discusses the integrated application of computer vision and neural technologies on laser welding to make welding processes more intelligent and automatic. Computer vision was employed to inspect a welding gap, to measure the welding gap size, and to trace the welding path for laser beam alignment. The NC code for the welding path was generated, and then the

Jeng-ywan Jeng; Tzuoh-fei Mau; Sh Yeu-ming Leu

2000-01-01

165

Joint tracking and adaptive robotic welding using vision sensing of the weld joint geometry  

SciTech Connect

An approach to the vision-guidance of welding robots and the in-process adjustment of welding conditions is presented. The implementation of a complete vision-guided adaptive robotic welding system is described. The vision-guided adaptive welding system described here has been used to track and weld a wide variety of test and production parts ranging in size from 1.6-mm (1/16-in.) sheet steel to 19.1-mm (3/4-in.) steel plate. Both conventional joint types, including square butt, lap, and V-groove, and special types, such as a multipass square butt submerged arc weld with pre-welded root passes or the axle joints were welded. Various welding procedures, such as GMA welding with a variety of shielding gases and submerged arc welding, have also been used.

Agapakis, J.E.; Katz, J.M.; Koifman, M.; Epstein, G.N.; Friedman, J.M.; Eyring, D.O.; Rutishauser, H.J.

1986-11-01

166

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

167

Grant pool  

Microsoft Academic Search

The Grant Pool, Harper County, Kans., is a structural trap in both the Mississippian and Simpson reservoirs. It has stong closure in all directions and is located on a weak, NE. trending regional Ordovician ridge. The Mississippian reservoir has very shallow weathering with chat grading to fresh chert in the top 15 ft. The Simpson reservoir consists of approximately 30

Devlin

1965-01-01

168

Weld Penetration Variability in Attachment Welds,  

National Technical Information Service (NTIS)

The weld penetration variability of a number of attachment weld samples, taken during production welding and laboratory experiments, were welded with manual and mechanized metal inert gas and manual and mechanized tungsten inert gas welding processes over...

P. J. Alberry R. R. L. Brunnstrom

1987-01-01

169

Mathematical modeling and experimental validation of gas metal arc welding of aluminum alloys  

NASA Astrophysics Data System (ADS)

Both mathematical modeling and experiments have been conducted on the GMAW of aluminum alloys. Transient weld shapes and distributions of temperature and velocity were calculated by a three-dimensional numerical model. The final weld bead shape and dimensions and peak temperature in the heat-affected zone (HAZ) were obtained. Metallurgical characterizations including microscopy and Knoop micro-hardness measurements were performed on experimental samples. The experimental weld bead shape and dimensions were in agreement with modeling predictions. It was found that a crater-shaped weld pool was formed as a result of weld pool dynamics. The combined effect of a series of droplet impingements and hydrostatic force caused the fluid level at the rear end of weld pool to vary periodically to form ripples on the weld bead. Also, the high peak temperature near the fusion line caused the HAZ softening. The lack of penetration in the cold weld is due to the lack of pre-heating by the welding arc. Three techniques were then proposed to increase the energy input at the initial stage of welding and improve cold weld penetration. The crater formation at the end of the welding process is due to the rapid solidification of the weld pool. The crater was filled and crater cracking was reduced by reducing welding current and reversing the welding direction at the same time before terminating the arc.

Guo, Hao

2004-11-01

170

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

171

Absorbed zinc and exchangeable zinc pool size are greater in Pakistani infants receiving traditional complementary foods with zinc-fortified micronutrient powder.  

PubMed

Adequacy of zinc intake from breast milk alone becomes marginal in relation to infant requirements by around 6 mo of age. Simple and cost-effective strategies are needed at the population level to ensure adequate intakes of zinc in infants and toddlers in populations at risk of zinc deficiency. We determined the amount of absorbed zinc (AZ) from a micronutrient powder (MNP) without and with 10 mg of zinc (MNP+Zn) added to local complementary foods used in Pakistan and the impact on the exchangeable zinc pool (EZP) size. As a nested study within a large, prospective, cluster randomized trial, 6-mo-old infants were randomly assigned to receive MNP or MNP+Zn. Stable isotope methodology was applied after ?3 and 9 mo of use to measure AZ from MNP-fortified test meals of rice-lentils (khitchri) and EZP. Nineteen infants per group completed the first metabolic studies and 14 and 17 infants in the MNP and MNP+Zn groups, respectively, completed the follow-up studies. AZs were (mean ± SD) 0.1 ± 0.1 and 1.2 ± 0.5 mg at the first point for the MNP and MNP+Zn groups, respectively (P < 0.001); results were nearly identical at the follow-up measurement. EZP did not differ between groups at the first measurement but was less in the MNP group (3.7 ± 0.6 mg/kg) than in the MNP+Zn group (4.5 ± 1.0 mg/kg) at the second measurement (P = 0.01). These data confirm that the MNP+Zn in khitchri were well absorbed and after 1 y of home fortification, zinc status assessed by EZP was significantly better for the MNP+Zn group. Additional field studies may be necessary to ascertain the adequacy of this dose for infants at high risk of deficiency. This trial was registered at ClinicalTrials.gov as NCT00705445. PMID:24225451

Ariff, Shabina; Krebs, Nancy F; Soofi, Sajid; Westcott, Jamie; Bhatti, Zaid; Tabassum, Farhana; Bhutta, Zulfiqar A

2014-01-01

172

Explosive Welding.  

National Technical Information Service (NTIS)

Explosive welding occurs when adjacent surfaces of appropriately positioned metals are properly thrust together by energy released from an explosive source. The procedure consists essentially of locating the metal members being welded between an explosive...

H. J. Addison

1964-01-01

173

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

174

Oscillation of Molten Pool by Pulsed Assist Gas Oscillating Method and Penetration Control Using Peculiar Frequency  

NASA Astrophysics Data System (ADS)

In automatic butt welding of relatively thin plates, it is important to control welding conditions in order to obtain a sound full penetration weld. Recently, it was reported that there was an intimate relationship between the oscillation of the molten pool and penetration. Therefore, the oscillation phenomena of the weld molten pool were analyzed and the estimation of penetration by detecting frequency of the molten pool was attempted. In this study, a new oscillating method, Pulsed Assist Gas (PAG) oscillating method is proposed. The natural frequency of molten pool was measured from the molten pool oscillation detected by arc sensor. A control system, which controled welding current on the basis of oscillation frequency measured, was constructed. Main results obtained are summarized as follows: 1) In order to oscillate molten pool during TIG arc welding of thin steel plate, Pulsed Assist Gas (PAG) oscillating method was proposed and effectiveness of this method was confirmed. 2) The PAG oscillating method was superior to conventional pulsed current oscillating (PC) method in amplitude of oscillation and robustness of frequency measurement. 3) Applying PAG oscillating method and detecting oscillation of arc voltage, the peculiar frequency of the oscillation of molten pool could be detected. 4) A system to control weld penetration using the principle of detecting the peculiar frequency of the molten pool was constructed and the effectiveness of the system was demonstrated.

Jianbin, Ju; Hasegawa, Hiroyuki; Suga, Yasuo

175

Resistance Welding of Motor Frames  

Microsoft Academic Search

Cost reduction calls for a continual revision of methods. The making of motor frames using rolled plate in place of castings formerly used, the object being to reduce cost is one such revision. The method of manufacture is briefly outlined including the rolling, welding, sizing, and other operations. The electric resistance welding method is emphasized and results of electrical tests

Malcolm Thomson

1931-01-01

176

Numerical modeling of keyhole dynamics in laser welding  

NASA Astrophysics Data System (ADS)

Mathematical models and the associated numerical techniques have been developed to study the following cases: (1) the formation and collapse of a keyhole, (2) the formation of porosity and its control strategies, (3) laser welding with filler metals, and (4) the escape of zinc vapor in laser welding of galvanized steel. The simulation results show that the formation of porosity in the weld is caused by two competing mechanisms: one is the solidification rate of the molten metal and the other is the speed that molten metal backfills the keyhole after laser energy is terminated. The models have demonstrated that porosity can be reduced or eliminated by adding filler metals, controlling laser tailing power, or applying an electromagnetic force during keyhole collapse process. It is found that a uniform composition of weld pool is difficult to achieve by filler metals due to very rapid solidification of the weld pool in laser welding, as compared to that in gas metal arc welding.

Zhang, Wen-Hai; Zhou, Jun; Tsai, Hai-Lung

2003-03-01

177

Optimization of Weld Conditions and Alloy Composition for Welding of Single-Crystal Nickel-Based Superalloys  

SciTech Connect

Calculations were carried out to identify optimum welding conditions and weld alloy compositions to avoid stray grain formation during welding of single-crystal nickel-based superalloys. The calculations were performed using a combination of three models: a thermal model to describe the weld pool shape and the local thermal gradient and solidification front velocity; a geometric model to identify the local active dendrite growth variant, and a nucleation and growth model to describe the extent of stray grain formation ahead of the advancing solidification front. Optimum welding conditions (low weld power, high weld speed) were identified from the model calculations. Additional calculations were made to determine potential alloy modifications that reduce the solidification temperature range while maintaining high gamma prime content. The combination of optimum weld conditions and alloy compositions should allow for weld repair of single-crystal nickel-based superalloys without sacrificing properties or performance.

Vitek, John Michael [ORNL; David, Stan A [ORNL; Babu, Sudarsanam S [ORNL

2007-01-01

178

Numerical simulation of humping phenomenon in high speed gas metal arc welding  

NASA Astrophysics Data System (ADS)

It is of great significance to obtain a thorough understanding of the physical mechanisms responsible for humping bead phenomenon in high speed gas metal arc welding (GMAW) in order to raise welding efficiency. Experiments were conducted to observe the weld pool behaviors in high speed GMAW, and it was found that both the severely deformed weld pool surface and strong backward flowing play a dominant role in humping bead formation. In this study, a mathematical model is developed to quantitatively analyze the forming mechanism of humping beads for high speed GMAW through considering both the momentum and heat content distribution of the backward flowing molten metal inside the weld pool. The transient development of temperature profiles in the weld pool with severe deformation demonstrates the humping bead forming process under some welding conditions. The predicted and measured humping bead dimensions are in agreement.

Chen, Ji; Wu, Chuan-Song

2011-06-01

179

Swimming pools soak up the sun  

SciTech Connect

Solar pool heaters survived the boom and bust solar years of the 1970s and 1980s. Today they are even popular and cost-effective in parts of the country where many people think solar is impractical. This article discusses the following topics: how solar pool heaters work; types of solar pool heater collectors; collector and pump sizing; collector siting and mounting; systems costs and economics; pool covers. 3 figs.

Cuoghi, D.; Hesse, P.; Schiller, T.

1996-05-01

180

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

181

Seam Tracking Monitoring Based on Adaptive Kalman Filter Embedded Elman Neural Network During High-Power Fiber Laser Welding  

Microsoft Academic Search

This paper proposes a method of seam tracking monitoring during high-power fiber laser welding. A visual sensor system was employed to capture the infrared images of molten pools and the surroundings in the laser welding process. A weld seam position variable was extracted by the image difference and centroid algorithms. The state and measurement equations for weld seam position were

Xiangdong Gao; Deyong You; Seiji Katayama

2012-01-01

182

Grain refinement control in TIG arc welding  

NASA Technical Reports Server (NTRS)

A method for controlling grain size and weld puddle agitation in a tungsten electrode inert gas welding system to produce fine, even grain size and distribution is disclosed. In the method the frequency of dc welding voltage pulses supplied to the welding electrode is varied over a preselected frequency range and the arc gas voltage is monitored. At some frequency in the preselected range the arc gas voltage will pass through a maximum. By maintaining the operating frequency of the system at this value, maximum weld puddle agitation and fine grain structure are produced.

Iceland, W. F.; Whiffen, E. L. (inventors)

1975-01-01

183

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

184

Effects of conventional welding and laser welding on the tensile strength, ultimate tensile strength and surface characteristics of two cobalt-chromium alloys: a comparative study.  

PubMed

The purpose of this study was to evaluate the efficacy of laser welding and conventional welding on the tensile strength and ultimate tensile strength of the cobalt-chromium alloy. Samples were prepared with two commercially available cobalt-chromium alloys (Wironium plus and Diadur alloy). The samples were sectioned and the broken fragments were joined using Conventional and Laser welding techniques. The welded joints were subjected to tensile and ultimate tensile strength testing; and scanning electron microscope to evaluate the surface characteristics at the welded site. Both on laser welding as well as on conventional welding technique, Diadur alloy samples showed lesser values when tested for tensile and ultimate tensile strength when compared to Wironium alloy samples. Under the scanning electron microscope, the laser welded joints show uniform welding and continuous molt pool all over the surface with less porosity than the conventionally welded joints. Laser welding is an advantageous method of connecting or repairing cast metal prosthetic frameworks. PMID:23858281

Madhan Kumar, Seenivasan; Sethumadhava, Jayesh Raghavendra; Anand Kumar, Vaidyanathan; Manita, Grover

2012-06-01

185

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

186

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

187

Understanding Bead Hump Formation in Gas Metal Arc Welding Using a Numerical Simulation  

NASA Astrophysics Data System (ADS)

Three-dimensional numerical simulations were conducted to study temperature distributions and fluid flows during formation of humped beads in high speed gas metal arc welding (GMAW). Based on simulation and experimental results, the physical mechanisms associated with humping phenomenon were investigated and two conditions responsible for hump formation were identified: the formation of thin liquid channel induced by surface tension pinching force and premature solidification of the melt in the thin channel that divides the weld pool into a front and rear portion. A strong backward fluid flow that produced an accumulation of melt at the rear of the weld pool increased the size of humps. Although surface tension was shown to be important in hump formation, Marangoni flow induced by negative surface tension gradients was not significant for hump formation. The simulation results clarified the fluid flow associated with two different hump shapes. Experimental welds without bead humping were made at a lower travel speed and were also simulated to illustrate the differences in heat and fluid flow from humped beads.

Cho, Min Hyun; Farson, Dave F.

2007-04-01

188

Structural and mechanical properties of welded joints of reduced activation martensitic steels  

NASA Astrophysics Data System (ADS)

Gas tungsten arc welding and electron beam welding methods were used to realise welding pools on plates of reduced activation martensitic steels. Structural and mechanical features of these simulated joints have been investigated in as-welded and post-welding heat-treated conditions. The research allowed to assess how each welding technique affects the original mechanical properties of materials and to find suitable post-welding heat treatments. This paper reports results from experimental activities on BATMAN II and F82H mod. steels carried out in the frame of the European Blanket Project - Structural Materials Program.

Filacchioni, G.; Montanari, R.; Tata, M. E.; Pilloni, L.

2002-12-01

189

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

190

Visualization of hump formation in high-speed gas metal arc welding  

NASA Astrophysics Data System (ADS)

The hump bead is a typical weld defect observed in high-speed welding. Its occurrence limits the improvement of welding productivity. Visualization of hump formation during high-speed gas metal arc welding (GMAW) is helpful in the better understanding of the humping phenomena so that effective measures can be taken to suppress or decrease the tendency of hump formation and achieve higher productivity welding. In this study, an experimental system was developed to implement vision-based observation of the weld pool behavior during high-speed GMAW. Considering the weld pool characteristics in high-speed welding, a narrow band-pass and neutral density filter was equipped for the CCD camera, the suitable exposure time was selected and side view orientation of the CCD camera was employed. The events that took place at the rear portion of the weld pools were imaged during the welding processes with and without hump bead formation, respectively. It was found that the variation of the weld pool surface height and the solid-liquid interface at the pool trailing with time shows some useful information to judge whether the humping phenomenon occurs or not.

Wu, C. S.; Zhong, L. M.; Gao, J. Q.

2009-11-01

191

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

192

Application research on multi-pulse laser used in micro laser welding fields  

Microsoft Academic Search

the metal's temperate field and fuse pool, and combine the multi-pulse compose method's process that cumulate laser energy in micro laser welding applications, designed the instrument which used in the micro laser welding, then makes some theoretic and validate experiments, educed some beneficial conclusions. It has been based the next step to research the automatic and intelligent micro laser weld

Rong Zhang; Qiue Zhang

2011-01-01

193

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.

Alfrey, Allen C.; Miller, Nancy L.

1973-01-01

194

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.

195

Resistance Welding  

Microsoft Academic Search

This paper is directed to engineers interested in the application of resistance welding to the industries. The discussion foreshadows some of the latest tendencies of development. It deals with some fundamentals of design though it is not written as a complete treatise on the subject, nor especially for those engaged in the designing of resistance welding machinery. Differentiation is made

Byron T. Mottinger

1930-01-01

196

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.

197

Simulation and Technology of Hybrid Welding of Thick Steel Parts with High Power Fiber Laser  

NASA Astrophysics Data System (ADS)

The article devoted to steady state and dynamic simulation of melt pool behavior during hybrid laser-arc welding of pipes and shipbuilding sections. The quasi-stationary process-model was used to determine an appropriate welding mode. The dynamical model of laser welding was used for investigation of keyhole depth and width oscillations. The experiments of pipe steel and stainless steel hybrid laser-MAG welding have been made with 15-kW fiber laser in wide range of welding mode parameters. Comparison of experimentally measured and simulated behavior of penetration depth as well as their oscillation spectra approved the self-oscillation nature of melt pool behavior. The welding mode influence of melt pool stability has also been observed. The technological peculiarities, which allow provide high quality weld seam, has been discussed also.

Turichin, Gleb; Valdaytseva, Ekaterina; Tzibulsky, Igor; Lopota, Alexander; Velichko, Olga

198

Modeling of transport phenomena during laser welding process  

NASA Astrophysics Data System (ADS)

This dissertation, consisting of three papers, presents the results of research investigations on laser welding of zinc-coated steel sheets and three-dimensional laser keyhole welding by numerical analysis. In the first paper, the mathematical model and numerical techniques are developed to simulate the keyhole formation, zinc vapor formation and zinc vapor escaping processes. In the study, the keyhole is used as an effective way to vent the high-pressure zinc vapor generated at the interface between the two zinc-coated metal sheets. The interaction between the weld pool and the escaping zinc vapor is investigated. It is the first comprehensive mathematical model for laser welding of zinc-coated steel sheets. In the second paper, the aforementioned model is employed to study the defect formation mechanisms in laser welding of zinc-coated steel sheets. Welding defects, such as voids at the root of welded metal, the undercut on the top surface and the bubbles trapped in the weld pool are simulated. The reasons causing these welding defects are given through the studies of the zinc vapor-weld pool interaction and the fluid flow and heat transfer during the keyhole collapse and metal solidification processes. In the third paper, the aforementioned stationary 2-D model is extended to modeling a 3-D moving laser keyhole welding process. The heat transfer and fluid flow in the welding pool around the keyhole are calculated. Also, the laser induced plasma inside the keyhole due to the Inverse Bremsstrahlung absorption is considered to calculate the temperature distribution inside the keyhole. Energy distribution inside the keyhole is computed by considering the Fresnel absorption and multiple reflections phenomena.

Zhou, Jun

199

Modeling cast IN738 superalloy gas tungsten arc welds  

Microsoft Academic Search

A three-dimensional finite-element thermal model has been developed to generate weld profiles, and to analyze transient heat flow, thermal gradients and thermal cycles in cast IN-738 superalloy gas tungsten arc welds. Outputs of the model (cooling rates, the thermal gradient G and the growth rate R) were used to describe solidification structures found around the weld pool for three different

E. A. Bonifaz; N. L. Richards

2009-01-01

200

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

201

Liquid Metal Oscillation and Arc Behaviour during Welding  

Microsoft Academic Search

The purpose of this research is to obtain insight into the oscillation behaviour of the liquid metal and the arc behaviour during GMA welding. Observations of the weld pool and the arc were undertaken by visual means using a high-speed video and by analysis of the voltage. To deal with the complex phenomena that take place, the research is performed

B. Y. B. Yudodibroto

2010-01-01

202

The importance of spatter formed in shielded metal arc welding  

Microsoft Academic Search

Spatter results when droplets of liquid metal that have been ejected from the weld pool by the impact of small droplets from the covered electrode solidify and weld to the surface of the base material. The present paper studies spatter and reveals why these small droplets do not oxidise during their short trajectory and accounts for why they arrive with

F. Molleda; J. Mora; J. R. Molleda; E. Mora; y B. G. Mellor

2007-01-01

203

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

204

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

205

Evaluation of Weld Porosity in Laser Beam Seam Welds: Optimizing Continuous Wave and Square Wave Modulated Processes.  

National Technical Information Service (NTIS)

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 associa...

C. M. Ellison J. T. Norris K. M. Faraone M. J. Perricone R. A. Roach

2007-01-01

206

An analytical thermodynamic model of laser welding  

NASA Astrophysics Data System (ADS)

An earlier model of deep-penetration laser welding has been simplified in order to provide a useful model of process analysis. This work involves the modelling of the various energy-absorption mechanisms which determine the keyhole shape and thus the dimensions of the melt pool. The penetration depth and weld width (top and bottom) predicted by the model are shown to be in close agreement with experimental results. The widening of the top of the weld seam as a result of Marangoni flow is accurately modelled by introducing an artificially enhanced value for the workpiece's thermal conductivity towards the top of the weld. The model allows analysis of the dependence of the weld profile on the process parameters.

Lampa, Conny; Kaplan, Alexander F. H.; Powell, John; Magnusson, Claes

1997-05-01

207

Yeast acyl-CoA-binding protein: acyl-CoA-binding affinity and effect on intracellular acyl-CoA pool size.  

PubMed Central

Acyl-CoA-binding protein (ACBP) is a 10 kDa protein characterized in vertebrates. We have isolated two ACBP homologues from the yeast Saccharomyces carlsbergensis, named yeast ACBP types 1 and 2. Both proteins contain 86 amino acid residues and are identical except for four conservative substitutions. In comparison with human ACBP, yeast ACBPs exhibit 48% (type 1) and 49% (type 2) conservation of amino acid residues. The amino acid sequence of S. carlsbergensis ACBP type 1 was found to be identical with the one ACBP present in Saccharomyces cerevisiae. A recombinant form of this protein was expressed in Escherichia coli and S. cerevisiae, purified, and its acyl-CoA-binding properties were characterized by isoelectric focusing and microcalorimetric analyses. The yeast ACBP was found to bind acyl-CoA esters with high affinity (Kd 0.55 x 10(-10) M). Overexpression of yeast ACBP in S. cerevisiae resulted in a significant expansion of the intracellular acyl-CoA pool. Finally, Southern-blotting analysis of the two genes encoding ACBP types 1 and 2 in S. carlsbergensis strongly indicated that this species is a hybrid between S. cerevisiae and Saccharomyces monacensis. Images Figure 3 Figure 4

Knudsen, J; Faergeman, N J; Sk?tt, H; Hummel, R; B?rsting, C; Rose, T M; Andersen, J S; H?jrup, P; Roepstorff, P; Kristiansen, K

1994-01-01

208

Welding Metals by Friction.  

National Technical Information Service (NTIS)

Contents: Features of friction welding; Mechanism of formation of a welded joint in solid phase; Basic information from the friction theory; Heat liberation during friction welding; Basic parameters and recommended regimes in friction welding process; Fri...

V. I. Vill

1972-01-01

209

A Convective Heat-Transfer Model for Partial and Full Penetration Keyhole Mode Laser Welding of a Structural Steel  

NASA Astrophysics Data System (ADS)

In the keyhole mode laser welding of many important engineering alloys such as structural steels, convective heat transport in the weld pool significantly affects temperature fields, cooling rates, and solidification characteristics of welds. Here we present a comprehensive model for understanding these important weld parameters by combining an efficient keyhole model with convective three-dimensional (3-D) heat-transfer calculations in the weld pool for both partial and full penetration laser welds. A modified turbulence model based on Prandtl’s mixing length hypotheses is included to account for the enhanced heat and mass transfer due to turbulence in the weld pool by calculating spatially variable effective values of viscosity and thermal conductivity. The model has been applied to understand experimental results of both partial and full penetration welds of A131 structural steel for a wide range of welding speeds and input laser powers. The experimentally determined shapes of the partial and full penetration keyhole mode laser welds, the temperature profiles, and the solidification profiles are examined using computed results from the model. Convective heat transfer was the main mechanism of heat transfer in the weld pool and affected the weld pool geometry for A131 steel. Calculation of solidification parameters at the trailing edge of the weld pool showed nonplanar solidification with a tendency to become more dendritic with increase in laser power. Free surface calculation showed formation of a hump at the bottom surface of the full penetration weld. The weld microstructure becomes coarser as the heat input per unit length is increased, by either increasing laser power or decreasing welding velocity.

Rai, R.; Kelly, S. M.; Martukanitz, R. P.; Debroy, T.

2008-01-01

210

Microstructure Improvement in Weld Metal under the Ultrasonic Application  

SciTech Connect

When considering the operational performance of weldments in the engineering projects, the most important issues to be considered are weld metal mechanical properties, integrity of the welded joint, and weldability 1 . These issues are closely related to the microstructure of the weld metal. A significant amount of research has been carried out to alter the process variables and to use external devices to obtain microstructure control of the weldments. It has been reported that grain refined microstructure not only reduces cracking behavior of alloys including solidification cracking, cold cracking and reheat cracking, 2 - 5 but also improves the mechanical properties of the weld metal, such as toughness, ductility, strength, and fatigue life. 6, 7 Weld pool stirring, 8 arc oscillation, 9, 10 arc pulsation, 11 , and magnetic arc oscillator 12, 13 have been applied to fusion welding to refine the microstructures. This article describes initial experimental results on the use of power ultrasonic vibration to refine the microstructure of weld metals.

Cui, Yan [University of Tennessee, Knoxville (UTK); Xu, Cailu [University of Tennessee, Knoxville (UTK); Han, Qingyou [ORNL

2007-01-01

211

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

212

Laser welding of selected aerospace alloys  

NASA Astrophysics Data System (ADS)

The study was aimed at developing an understanding of the microstructural effects of the laser welding process on the alloys, and assessing the structural integrity of the resultant welds. The effect of laser processing parameters such as laser power, laser beam traverse speed, lens focal length, and the manipulation of these parameters on the welding efficiency and weld area integrity was also investigated. Other tasks within the project included a study on the possibility of using an anodic film to enhance the laser weld ability of Al 6061. Finally, attempts were made to identify phases observed in the weld area of the composite materials. Nimonics C263 and PE11 exhibited laser welds free of cracks and porosity. The difference in composition between the two alloys did not result in any significant dissimilarities in their response to the laser welding process. The welds in both alloys exhibited a fine columnar dendritic microstructure, and while carbides were observed in the interdendritic regions of the welds, electron optical analysis did not reveal any gamma' precipitates in this region. It was concluded that for the welding of thin gage materials above a threshold laser power the resultant welding efficiency shows a greater dependence on laser beam mode, and laser spot size, than on laser power, and beam traverse speed. Aluminum 6061 was not easily welded with a laser in its as received form, and the welds showed some degree of porosity. Anodizing was found to improve the welding efficiency in this material. While the presence of an anodic film on the metal surface increased the welding efficiency of the alloy, no relationship was found between the thickness of the anodic film and welding efficiency in the range of film thicknesses investigated. Weld regions were observed to be cellular dendritic in structure, with narrow heat affected zones. No precipitates or low melting point phases could be identified in the weld region. Melt zones were successfully produced in the composite materials, with the main problem encountered being that of porosity adjacent to the weld bead. It was shown that manipulation of the laser welding parameters resulted in a decrease in this porosity.

Ebadan, Gracie E.

213

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

214

Marangoni convection and weld shape variation in A-TIG welding process  

Microsoft Academic Search

The flux effect on TIG weld shape variations is investigated by application of the heat transfer and fluid flow model. The simulation makes use of Nimonic 263 alloy, TiO, TiO2 and Ti2O3 as the flux. The arc constriction and the reversed Marangoni convection are considered to be the two main factors for increasing penetration of A-TIG weld pool. And the

Y. L. Xu; Z. B. Dong; Y. H. Wei; C. L. Yang

2007-01-01

215

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

216

Wonder Weld  

ScienceCinema

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.

217

17 CFR 229.1111 - (Item 1111) Pool assets.  

Code of Federal Regulations, 2010 CFR

...1) Number of each type of pool assets. (2) Asset size, such as original balance...includes different types, such as fixed and floating rates. (4) Capitalized...servicers service different pool assets. (7) If a loan or...

2010-04-01

218

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

219

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

220

Physicochemical and toxicological characteristics of welding fume derived particles generated from real time welding processes.  

PubMed

Welding fume particles have been well studied in the past; however, most studies have examined welding fumes generated from machine models rather than actual exposures. Furthermore, the link between physicochemical and toxicological properties of welding fume particles has not been well understood. This study aims to investigate the physicochemical properties of particles derived during real time welding processes generated during actual welding processes and to assess the particle size specific toxicological properties. A compact cascade impactor (Harvard CCI) was stationed within the welding booth to sample particles by size. Size fractionated particles were extracted and used for both off-line physicochemical analysis and in vitro cellular toxicological characterization. Each size fraction was analyzed for ions, elemental compositions, and mass concentration. Furthermore, real time optical particle monitors (DustTrak™, TSI Inc., Shoreview, Minn.) were used in the same welding booth to collect real time PM2.5 particle number concentration data. The sampled particles were extracted from the polyurethane foam (PUF) impaction substrates using a previously developed and validated protocol, and used in a cellular assay to assess oxidative stress. By mass, welding aerosols were found to be in coarse (PM 2.5–10), and fine (PM 0.1–2.5) size ranges. Most of the water soluble (WS) metals presented higher concentrations in the coarse size range with some exceptions such as sodium, which presented elevated concentration in the PM 0.1 size range. In vitro data showed size specific dependency, with the fine and ultrafine size ranges having the highest reactive oxygen species (ROS) activity. Additionally, this study suggests a possible correlation between welders' experience, the welding procedure and equipment used and particles generated from welding fumes. Mass concentrations and total metal and water soluble metal concentrations of welding fume particles may be greatly influenced by these factors. Furthermore, the results also confirmed the hypothesis that smaller particles generate more ROS activity and should be evaluated carefully for risk assessment. PMID:24592438

Chang, Cali; Demokritou, Philip; Shafer, Martin; Christiani, David

2013-01-01

221

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.

Huang, Wei; Kovacevic, Radovan

2011-01-01

222

A laser-based vision system for weld quality inspection.  

PubMed

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

223

Mechanisms giving increased weld depth due to a flux  

NASA Astrophysics Data System (ADS)

It is known that for 'tungsten inert gas' welding of stainless steel, the weld depth can be increased by a factor of two or more if a thin layer of flux powder is initially coated on the steel. Numerical predictions from a unified electrode-arc-weldpool model are made elucidating the possible role of three different mechanisms previously proposed to explain this effect, and we also examine a new fourth possible mechanism, namely the effect that the flux is an electrical insulator. (1) Calculations support the suggestion that if the dissolved flux in the weld pool changes the temperature dependence of the surface tension to increase rather than decrease with temperature, the direction of convective circulation within the weld pool can change from radially outwards to radially inwards, leading to an increased weld depth of the order of 2 mm. (2) The effect of electron attachment to flux vapour in the arc, if the vapour contains an attaching gas such as oxygen, is found to have a negligible effect in producing arc constriction and thus a higher current density to increase weld depth. (3) Our treatment assumes that the surface of the weld pool is undepressed by the arc, so that we have not examined the suggestion that increased weld depth is caused by the flux lowering surface tension and thus increasing depression of the weld pool surface. But experimental observations indicate that such depression is negligible for currents of less than 200 A. (4) If the flux produces an insulating layer on the metal surface, calculations indicate that there can be a marked increase in weld depth of the order of 5 mm or more due to the flux blocking the current in the outer regions of the arc thus producing a higher current density at the arc centre. Furthermore these calculations indicate that the flux causes an arc spot to form at the anode, in agreement with similar experimental observations of an anode spot in the presence of a flux.

Lowke, J. J.; Tanaka, M.; Ushio, M.

2005-09-01

224

Ferritic, martensitic, and precipitation hardening stainless steel laser weldings  

Microsoft Academic Search

Even if many steels and alloys have been welded on the last years, nowadays there are some other stainless steel alloys that need a further comprehension when they have to be welded. Typically these alloys are martensitic and precipitation hardening ones that still present some problems to be weld, i.e. hot cracks, fragile beads, an excessive grain size and other

Giuseppe Daurelio; Antonio D. Ludovico; Christos N. Panagopoulos; Corrado Tundo

1998-01-01

225

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

226

Characterization of a friction-stir-welded aluminum alloy 6013  

NASA Astrophysics Data System (ADS)

The aluminum alloy 6013 was friction-stir welded in the T4 and the T6 temper, and the microstructure and mechanical properties were studied after welding and after applying a postweld heat treatment (PWHT) to the T4 condition. Optical microscopy (OM), transmission electron microscopy (TEM), and texture measurements revealed that the elongated pancake microstructure of the base material (BM) was transformed into a dynamically recrystallized microstructure of considerably smaller grain size in the weld nugget. Strengthening precipitates, present before welding in the T6 state, were dissolved during welding in the nugget, while an overaged state with much larger precipitate size was established in the heat-affected zone (HAZ). Microhardness measurements and tensile tests showed that the HAZ is the weakest region of the weld. The welded sheet exhibited reduced strength and ductility as compared to the BM. A PWHT restored some of the strength to the as-welded condition.

Heinz, Beate; Skrotzki, Birgit

2002-06-01

227

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

228

Swimming pool granuloma  

MedlinePLUS

A swimming pool granuloma is a long-term (chronic) skin infection. It is caused by the bacteria Mycobacterium marinum . ... A swimming pool granuloma occurs when water containing Mycobacterium marinum bacteria enters a break in the skin. Signs of ...

229

Assessment of the origin of porosity in electron-beam-welded TA6V plates  

NASA Astrophysics Data System (ADS)

Experimental and theoretical analysis of the origin of porosity in electron-beam (EB) welding is detailed. The experiments are run with several surface treatments and reasonable welding parameters. The plate faces are characterized before welding with a number of methods, such as scanning electron microscope observation, X-ray photoemission spectroscopy (XPS) and, more significantly, secondary ion mass spectroscopy (SIMS) analysis, elastic-recoil detection analysis (ERDA) for hydrogen analysis, and surface roughness measurement. After welding, pores are sought with X-ray detection, phased-array ultrasonic (US) detection, and destructive control. An original comparison between ERDA and refined SIMS measurements allows a quantitative evaluation of surface pollution with hydrogen, oxygen, and carbon. The theoretical analysis is based on the literature concept that the cavities are nucleated from the adjacent plate faces in the solid state, just before melting. A less classical development is proposed in term of the evolution of bubbles in the weld pool. Once in the liquid, the cavities become bubbles. Their radius oscillates, according to Rayleigh-Plesset equations of bubbles, due to temperature and pressure driving forces. Solidification freezes them as they are, thus, forming pores. The extreme values of the oscillation give a good idea of the range of the size of pores in the weld joint, as the comparison between experiments and prediction states. A criterion of surface cleanliness is set, relating the surface pollution and the surface roughness. Above the criterion, the bubbles remain small during their oscillation. Below the criterion they tend to grow large. All the degraded-surface treatments are in dirty situation (large pores), and the reference surface treatment lies around the criterion for cleanliness.

Gouret, N.; Ollivier, E.; Dour, G.; Fortunier, R.; Miguet, B.

2004-03-01

230

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

231

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

232

Numerical models of in-service welding of gas pipelines  

Microsoft Academic Search

It is accepted that numerical methods have a useful role in the assessment of welding conditions for the safe in-service welding of high-pressure gas pipelines. Only limited published work has considered the direct calculation of burn-through using a combination of thermal and stress analysis. Using empirical relationships between welding process parameters, and weld bead size and shape is an appropriate

P. N. Sabapathy; M. A. Wahab; M. J. Painter

2001-01-01

233

Study on DC Double Pulse Metal Inert Gas (MIG) Welding of Magnesium Alloy  

Microsoft Academic Search

This article gives a preliminary research on direct current (DC) double pulse metal inert gas (MIG) welding of magnesium alloys. It will be an effort for broadening the application of this new MIG welding process. The unique parameters of DC double pulse MIG welding are selected to investigate their effects on weld bead geometry size and appearance of AZ31B Mg

Zhaodong Zhang; Xiangyu Kong

2012-01-01

234

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

235

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

236

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

237

Laser Keyhole Welding: The Vapour Phase  

NASA Astrophysics Data System (ADS)

Several aspects of the properties of the keyhole and its relationship to the weld pool in laser keyhole welding are considered. The aspect of most immediate importance is the exchange of energy between the laser beam itself and the molten material of the weld pool. Many mechanisms are involved, but the two considered here are the process of direct absorption at the keyhole wall (Fresnel absorption) and the two-stage process of absorption of energy by inverse bremsstrahlung into the ionised vapour that forms in the case of the longer-wavelength lasers such as the CO2, laser, followed by thermal conduction to the wall. Consideration is given to the role of the Knudsen layer at the boundary. The possibility that the exchange may be influenced by the vapour flow in the keyhole is considered. More generally, the dynamics of the flow is investigated and the balances necessary to keep the keyhole open are investigated. A simple model of the interaction of the vapour with the molten material in the weld pool is proposed which can be used to investigate their interaction. Order of magnitude estimates suggest that it is far from simple but that some simplifying approximations are possible.

Dowden, John

238

ARc Welding (Industrial Processing Series).  

National Technical Information Service (NTIS)

The bibliography comprises citations of unclassified reports dealing with arc welding in a series of bibliographies on industrial processing. Some of the topics included are: spot welding, gas metal arc welding, inert gas welding, pulsed arc welding, and ...

1973-01-01

239

Modeling of plasma and thermo-fluid transport in hybrid welding  

NASA Astrophysics Data System (ADS)

Hybrid welding combines a laser beam and electrical arc in order to join metals within a single pass at welding speeds on the order of 1 m min -1. Neither autonomous laser nor arc welding can achieve the weld geometry obtained from hybrid welding for the same process parameters. Depending upon the process parameters, hybrid weld depth and width can each be on the order of 5 mm. The ability to produce a wide weld bead increases gap tolerance for square joints which can reduce machining costs and joint fitting difficulty. The weld geometry and fast welding speed of hybrid welding make it a good choice for application in ship, pipeline, and aerospace welding. Heat transfer and fluid flow influence weld metal mixing, cooling rates, and weld bead geometry. Cooling rate affects weld microstructure and subsequent weld mechanical properties. Fluid flow and heat transfer in the liquid weld pool are affected by laser and arc energy absorption. The laser and arc generate plasmas which can influence arc and laser energy absorption. Metal vapors introduced from the keyhole, a vapor filled cavity formed near the laser focal point, influence arc plasma light emission and energy absorption. However, hybrid welding plasma properties near the opening of the keyhole are not known nor is the influence of arc power and heat source separation understood. A sound understanding of these processes is important to consistently achieving sound weldments. By varying process parameters during welding, it is possible to better understand their influence on temperature profiles, weld metal mixing, cooling rates, and plasma properties. The current literature has shown that important process parameters for hybrid welding include: arc power, laser power, and heat source separation distance. However, their influence on weld temperatures, fluid flow, cooling rates, and plasma properties are not well understood. Modeling has shown to be a successful means of better understanding the influence of processes parameters on heat transfer, fluid flow, and plasma characteristics for arc and laser welding. However, numerical modeling of laser/GTA hybrid welding is just beginning. Arc and laser welding plasmas have been previously analyzed successfully using optical emission spectroscopy in order to better understand arc and laser plasma properties as a function of plasma radius. Variation of hybrid welding plasma properties with radial distance is not known. Since plasma properties can affect arc and laser energy absorption and weld integrity, a better understanding of the change in hybrid welding plasma properties as a function of plasma radius is important and necessary. Material composition influences welding plasma properties, arc and laser energy absorption, heat transfer, and fluid flow. The presence of surface active elements such as oxygen and sulfur can affect weld pool fluid flow and bead geometry depending upon the significance of heat transfer by convection. Easily vaporized and ionized alloying elements can influence arc plasma characteristics and arc energy absorption. The effects of surface active elements on heat transfer and fluid flow are well understood in the case of arc and conduction mode laser welding. However, the influence of surface active elements on heat transfer and fluid flow during keyhole mode laser welding and laser/arc hybrid welding are not well known. Modeling has been used to successfully analyze the influence of surface active elements during arc and conduction mode laser welding in the past and offers promise in the case of laser/arc hybrid welding. A critical review of the literature revealed several important areas for further research and unanswered questions. (1) The understanding of heat transfer and fluid flow during hybrid welding is still beginning and further research is necessary. (2) Why hybrid welding weld bead width is greater than that of laser or arc welding is not well understood. (3) The influence of arc power and heat source separation distance on cooling rates during hybrid welding are not known. (4) Convect

Ribic, Brandon D.

240

A comparison between the back-propagation and counter-propagation networks in the modeling of the TIG welding process  

Microsoft Academic Search

The use of neural networks to model tungsten inert gas (TIG) welding is explored in this paper. Both the back-propagation and counter-propagation networks are used to associate the welding process parameters with the features of the weld-pool geometry. A comparison between the back-propagation and counter-propagation networks in the modeling of the TIG welding process is given. It is shown that

S. C Juang; Y. S Tarng; H. R Lii

1998-01-01

241

Effect of welding parameters on high-power diode laser welding on thin sheet  

NASA Astrophysics Data System (ADS)

High power diode laser (HPDL) is the newest laser tool for industrial manufacturing. The most promising areas of application of HPDL are thin sheet welding and hardening. The HPDL has several advantages and disadvantages compared to lasers CO2 and Nd:YAG lasers currently used for welding. There is quite a few industrial applications in which diode laser is the most suitable laser. A typical industrial installation consists of a HPDL, an industrial robot, work piece manipulation and safety enclosures. The HPDL welding process is at this moment conduction limited and has therefore different parameters than the keyhole welding. In this study the basic HPDL welding parameters and the effect of the parameters on the welding process, weld quality and efficiency are examined. Joint types tested are butt joint and fillet lap joint. The parameters tested are beam intensity, welding speed, spot size, beam impingement angle. The materials tested are common carbon steel and stainless steel. By the experiments carried out it can be seen that all of these parameters have an effect on the weld quality and the absorption of the laser power during welding. The higher the beam intensity is the shorter also the throughput time is. However, in case of fillet joint the maximum welding speed and best visual out look are achieved with totally different set of parameters. Based on these experiments it can, however, be seen that reliable welding parameters can be established for the welding of various industrial products. The beam quality of the diode laser is not optimum for high speed keyhole welding but it is a flexible tool to be used for different joint types.

Salminen, Antti; Jansson, Anssi; Kujanpää, Veli

2003-06-01

242

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

243

Welded solar cell interconnection  

SciTech Connect

The welding of solar cell interconnects has received increased attention in recent years. Welding is used routinely in Europe and is being investigated seriously by several solar array fabricators in the United States. Most of this welding has been made using parallel gap resistive heating. Hughes Aircraft Company has chosen to investigate ultrasonic welding as an alternate bonding method. The results of this work and the manner in which ultrasonic welding differs from parallel gap welding or soldering is herein summarized.

Stofel, E.J.; Browne, E.R.; Meese, R.A.; Vendura, G.J.

1982-09-01

244

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

245

A Quantitative Model of Keyhole Instability Induced Porosity in Laser Welding of Titanium Alloy  

NASA Astrophysics Data System (ADS)

Quantitative prediction of the porosity defects in deep penetration laser welding has generally been considered as a very challenging task. In this study, a quantitative model of porosity defects induced by keyhole instability in partial penetration CO2 laser welding of a titanium alloy is proposed. The three-dimensional keyhole instability, weld pool dynamics, and pore formation are determined by direct numerical simulation, and the results are compared to prior experimental results. It is shown that the simulated keyhole depth fluctuations could represent the variation trends in the number and average size of pores for the studied process conditions. Moreover, it is found that it is possible to use the predicted keyhole depth fluctuations as a quantitative measure of the average size of porosity. The results also suggest that due to the shadowing effect of keyhole wall humps, the rapid cooling of the surface of the keyhole tip before keyhole collapse could lead to a substantial decrease in vapor pressure inside the keyhole tip, which is suggested to be the mechanism by which shielding gas enters into the porosity.

Pang, Shengyong; Chen, Weidong; Wang, Wen

2014-06-01

246

Macroporosity free aluminum alloy weldments through numerical simulation of keyhole mode laser welding  

NASA Astrophysics Data System (ADS)

A transport phenomena-based numerical model is developed to predict the keyhole geometry and temperature profiles in the weldment during laser welding. The model can be used to prevent macroporosity formation during laser welding of aluminum alloys. The experimental results show that the weld metal contains large pores when the welding mode changes from conduction to keyhole mode or vice versa due to changes in welding variables. Based on this observation, the mathematical model predicts macroporosity formation when welding is conducted under conditions where small changes in welding parameters lead to a change in the welding mode. The model has been used to predict the geometry of the keyhole and the fusion zone, and the weldment temperature field for laser beam welding of aluminum alloys 5182 and 5754. The calculated weld pool depth, width, and shape for different welding speeds agreed well with the experimental results. The calculations showed that the keyhole profiles for high-speed welding were asymmetric. Negative beam defocusing resulted in a deeper keyhole than that obtained with positive beam defocusing. The transition from keyhole to conduction mode was more abrupt for negative beam defocusing. The model could predict the formation of macroporosity during laser welding of aluminum alloys 5182 and 5754. The results provide hope that transport phenomena-based models can be useful to prevent the formation of macroporosity during keyhole mode laser welding of aluminum alloys.

Zhao, H.; Debroy, T.

2003-06-01

247

Local properties of undermatched steel weld metal  

NASA Astrophysics Data System (ADS)

Samples from two undermatched, multipass welds on 50.8-mm-thick HY-100 steel were tested using a novel microtensile test machine and the local material properties were investigated using a chemical analysis, metallography, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The microtensile test technique allowed samples from individual weld beads and weldmetal heat-affected zones to be tested in three orthogonal directions. Relationships between local microhardness and tensile properties were established. The filler metals for the two welds were MIL-70S and MIL-100S. The MIL-70S weld formed ferritic microstructures; the weld-metal heat-affected sites were predominantly polygonal ferrite, while the as-deposited regions were a mixture of lath and polygonal ferrite. This weld showed a large variation in properties from the central weld bead to the outer ones. The outermost site exhibited significant anisotropy in strength that was not revealed by microhardness measurements. The yield strength specification was 483 MPa, while the average at the center of the weld was 675 MPa and the outer sites had an average of 445 MPa. Elongation for the samples from the center was significantly lower as well, 5 pct as compared to 18 pct for the outer sites. The yield strength showed a strong correlation with the size of inclusions measured by TEM. Microprobe analysis found no dilution of the base metal alloying additions into the weld metal. The MIL-100S filler formed predominantly fine acicular ferrite throughout the weld. The strength was much more uniform; the yield strength specification was 690 MPa, while the center of the weld was 756 MPa and the outer sites had an average of 616 MPa. The inclusion size did not play an important role in the variation in mechanical properties.

Lavan, David A.; Sharpe, W. N.

2001-04-01

248

Three-dimensional modeling of the plasma arc in arc welding  

NASA Astrophysics Data System (ADS)

Most previous three-dimensional modeling on gas tungsten arc welding (GTAW) and gas metal arc welding (GMAW) focuses on the weld pool dynamics and assumes the two-dimensional axisymmetric Gaussian distributions for plasma arc pressure and heat flux. In this article, a three-dimensional plasma arc model is developed, and the distributions of velocity, pressure, temperature, current density, and magnetic field of the plasma arc are calculated by solving the conservation equations of mass, momentum, and energy, as well as part of the Maxwell's equations. This three-dimensional model can be used to study the nonaxisymmetric plasma arc caused by external perturbations such as an external magnetic field. It also provides more accurate boundary conditions when modeling the weld pool dynamics. The present work lays a foundation for true three-dimensional comprehensive modeling of GTAW and GMAW including the plasma arc, weld pool, and/or electrode.

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

2008-11-01

249

Determination of Material Properties for Welding Models by Means of Arc Weld Experiments  

Microsoft Academic Search

Moving heat source solutions to the conduction heat flow equation are used to estimate the thermal diffusivity and thermal conductivity of nine engineering alloys. A technique is developed using gas tungsten arc edge weld data that enables least square fitting of the experimental weld size and heating parameters to the 2D and 3D conduction heat flow equations. Effective values of

Phillip W. Fuerschbach; G. Richard Eisler

250

Mathematical Modelling of Waves and Flows in Laser Welding.  

NASA Astrophysics Data System (ADS)

Available from UMI in association with The British Library. Requires signed TDF. This thesis describes mathematical models of certain interesting aspects of laser welding starting with discussion of the process of upwelling in the liquid region surrounding the keyhole in penetration welding with a laser. The pressure in the keyhole is in excess of atmospheric pressure producing a pressure gradient in the liquid region surrounding it and causing a flow parallel to the axis of the laser. The velocity of this flow is found as a function of the material constants, and the volume flow is calculated. From this it is possible to construct an estimate of elevation or depression of the weld. The shape of the surface cross section is discussed, and some deductions made about the pressure distribution in the liquid metal. Experimentally determined weld profiles were used to calculate this upwelling rate. This work then leads on to a mathematical model of the keyhole itself in penetration welding with a laser. A simple model was set up for the energy interchange as well as the vapour flow in the keyhole. The principal processes were identified and the model was used to calculate keyhole shapes. In penetration welding with a laser a plasma is formed in the keyhole. An essential step in the energy exchange between the beam and the workpiece is the interaction of the laser beam with the plasma. A simple model of this part of the process was described and its properties investigated. A very simple keyhole model was constructed which produced good predictions of weld shapes in agreement with experiment. In penetration welding with a laser, a ripple pattern is frozen into the weld-bed. The effect of oscillations on the weld pool forced by pulsation in the keyhole is also studied. In the case when a laser is used to weld thin sheets of material and has insufficient power to produce a keyhole, a molten pool is nevertheless formed and is seen to display the characteristic ripple pattern on its surface. The natural frequency of oscillation of the ellipsoidal weld-pool formed was calculated. The final sections of this thesis describe the thermo-capillary flow that results from the variation of the surface tension with temperature on the surface of the weld-pool. This process produces a so-called Marangoni flow which was studied using a boundary layer model. (Abstract shortened by UMI.).

Postacioglu, Mehmet Nazmi

251

Explosive welding  

Microsoft Academic Search

1.The results of our research have shown that when plane charges of granular explosives are employed it is necessary to take into account the change in detonation velocity D as a function of the initial density?0 and the thickness of the charged0.The relations D=f(?0), D=f(d0) have been obtained experimentally and used to determine the impact parameters in explosive welding.2.The use

A. A. Deribas; V. M. Kudinov; F. I. Matveenkov; V. A. Simonov

1967-01-01

252

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

253

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

254

Molten-region temperature distribution in laser welding  

NASA Astrophysics Data System (ADS)

When penetration welding in performed with a laser, the boundary of the keyhole formed in the weld-pool near to the surface of the workpiece experiences considerable variation of temperature; this variation could affect the dynamics of the flow in a number of ways. A simple mathematical model for the temperature distribution is investigated, and solutions obtained. These confirm that for values of the Peclet number of order one the variation of temperature at the keyhole surface can be very substantial.

Dowden, J.; Davis, M.; Kapadia, P.

1985-10-01

255

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

256

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

257

Hybrid Nd:YAG laser beam welding of aluminum in addition with an electric current  

NASA Astrophysics Data System (ADS)

A hybrid Nd:YAG laser beam welding technique has been investigated in welding of aluminum alloy. Connecting the filler wire with one pole of a DC power supply and the workpiece with the other, a closed electric circuit is built. By this means, the wire is resistively preheated, so that less energy from the laser beam is dissipated in melting the filler metal. On the other hand, the current flowing in the weld pool generates a magnetic field and electromagnetic forces which affect the fluid flow of the weld pool and then the welding process. It is found that the weld depth increases and the weld seam becomes slender when a certain current is supplied. To clarify which effect, the thermal effect or the electromagnetic effect, dominates, welding with pure hot wire was carried out. The experimental results demonstrate that the pure hot wire addition has no obvious affect on the welding efficiency and the weld cross section, but worsens the process instability. Thus we can conclude that the influences of the current do not result from the resistive heat from the wire, but the electromagnetic effects. This new approach provides a possibility to increase the processing efficiency and flexibility, improve the process stability and weld quality, and also shape the seam cross section.

Xiao, Rongshi; Zuo, Tiechuan; Leimser, Markus; Huegel, Helmut

2005-01-01

258

Optimal prediction pools  

Microsoft Academic Search

We consider the properties of weighted linear combinations of prediction models, or linear pools, evaluated using the log predictive scoring rule. Although exactly one model has limiting posterior probability, an optimal linear combination typically includes several models with positive weights. We derive several interesting results: for example, a model with positive weight in a pool may have zero weight if

John Geweke; Gianni Amisano

2011-01-01

259

Emission spectroscopy of plasma during laser welding of AISI 201 stainless steel  

Microsoft Academic Search

The rates of vaporization of alloying elements from the weld pool were related to the emission spectra of the plasma during\\u000a pulsed laser welding of AISI 201 stainless steel under various welding conditions. The temperature distribution in the plasma\\u000a was determined from the spectra obtained from various locations in the plasma plume. The extent of ionization of the plasma\\u000a was

M. M. Collur; T. Debroy

1989-01-01

260

Swimming pool. View of aisle between swimming pool and seating ...  

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

Swimming pool. View of aisle between swimming pool and seating area. Non-original spa pool is partially visible on right. - Jewish Community Center of San Francisco, 3200 California Street, San Francisco, San Francisco County, CA

261

Development of models for welding applications  

SciTech Connect

The modeling of welding processes offers considerable potential for help with manufacturing problems but a complete definition of any welding process offers many challenges. However, the modular structure of MARC, and the diverse range of capabilities offered, create a good opportunity for development in this area. This paper discusses these problems and describes techniques used to overcome some of them. Models have been developed to simulate gas tungsten arc (GTA) and electron beam (EB) welding with a moving heat source. Fortran routines for subroutines FLUX and FORCDT have been written to generate a moving heat source. Sequential element activation has permitted the simulation of GTA welding with cold wire feed (CWF), as in filling of a machined weld groove. A program which generates History Definition blocks necessary for this type of welding model is also described in this paper. Semi-infinite heat transfer elements were used to get accurate temperature histories while keeping the size of the model manageable. Time-temperature histories and isothermal contours compare well with experimental measurements, although many areas for improvement and refinement remain. Results have been used to anticipate the necessity for weld parameter changes after part redesign, and the electron beam model relates closely to situations in which information is needed for the minimization of peak temperatures on the underside of the welded part. 8 refs., 11 figs.

Roper, J.R.; Hayer, L.K.

1990-01-01

262

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

263

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

264

Micro laser welding of polymer microstructures using low power laser diodes  

Microsoft Academic Search

The use of laser welding for joining micro parts has experienced a substantial increase in popularity during recent years.\\u000a Specifically translucent microfluidic devices are assembled using laser welding; however, a major issue is the laser beam\\u000a size of commercially available laser-welding equipment and thus the resulting welding seam size, which may be orders of magnitude\\u000a larger than microfluidic channels and

T. Ussing; L. V. Petersen; C. B. Nielsen; B. Helbo; L. Højslet

2007-01-01

265

A Study on Analysis of Weld Distortion in Multi-pass Arc Welding  

NASA Astrophysics Data System (ADS)

Since prediction and control of welding deformation are one of an important problems connected with reliability of the manufactured structures, welding deformation should be measured and controlled with quickly and actively. Also, welding variables which have lots of effects on welding deformation such as arc voltage, welding current and welding speed can also be controlled. This study focuses on development of a simple 2D(a two-dimension) FEM(Finite Element Method) to calculate not only the transient thermal histories, but also the sizes of Fusion Zone(HZ) and Heat-Affected Zone (HAZ) in multi-pass arc welding including the butt weld type with dissimilar thickness, and to develop the new model for finding the parameters of Godak's heat source model based on a GA(Genetic Algorithm). The developed model included a GA program using MATLB and GA toolbox, and a batch mode thermal model using ANSYS software. The thermal model was verified by comparison with Goldak's work and the molten zone section from obtained the experimental data. In addition, the developed model could be applied the various welding types in order to employ for the manufacturing industries.

Lee, J. H.; Kim, I. S.; Jang, H. K.; Kim, H. J.; Kwak, S. K.; Ryoo, H. S.; Hong, S. H.; Shim, J. Y.

2011-01-01

266

Weld geometry strength effect in 2219-T87 aluminum  

NASA Technical Reports Server (NTRS)

A theory of the effect of geometry on the mechanical properties of a butt weld joint is worked out based upon the soft interlayer weld model. Tensile tests of 45 TIG butt welds and 6 EB beads-on-plate in 1/4-in. 2219-T87 aluminum plate made under a wide range of heat sink and power input conditions are analyzed using this theory. The analysis indicates that purely geometrical effects dominate in determining variations in weld joint strength with heat sink and power input. Variations in weld dimensions with cooling rate are significant as well as with power input. Weld size is suggested as a better indicator of the condition of a weld joint than energy input.

Nunes, A. C., Jr.; Novak, H. L.; Mcilwain, M. C.

1981-01-01

267

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

268

Numerical simulation of nanosecond pulsed laser welding of eutectoid steel components  

NASA Astrophysics Data System (ADS)

This paper considers the micro-closed seam laser welding of two nearly eutectoid carbon steel grades. These materials are difficult to weld due to their poor ductility. In particular, in closed seam welding, the laser beam starts and finishes in the same point thus increasing the risk of cracks. A numerical simulation of micro-welding of nearly eutectoid steels by nanosecond pulsed laser is carried out to evaluate the weld pool dimension and the heat-affected zone extension. Optimized welding parameters and strategy are determined by means of simulation and they are successfully applied in the welding of a 1.0%C shaft and a 0.7%C gear.

Fortunato, Alessandro; Ascari, Alessandro; Orazi, Leonardo; Cuccolini, Gabriele; Campana, Giampaolo; Tani, Giovanni

2012-10-01

269

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

270

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

271

Effect of Welding Consumables on Arc Welding Process Control and Weld Metal Structure and Properties.  

National Technical Information Service (NTIS)

The effect of welding consumables on arc welding process control and weld metal structure and properties was investigated. The first study demonstrated the potential use of exothermically (thermite) assisting steel arc welding consumables for field repair...

D. L. Olson R. H. Frost

1998-01-01

272

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

273

Resistance welding large parts  

SciTech Connect

An ongoing program at Savannah River to develop resistance welding techniques for fabrication of vessels will be described in this report. Resistance upset welding has advantages over the fusion welding techniques presently used to fabricate bodies of vessels. Advantages include the high reliability, quality, and yield experienced with our present resistance welding processes (<0.5% rejects for pinch and reclamation welds). The process is fast (about one second) and easily controlled (only three primary variables: current, force, and time). The metallurgical properties of these solid state welds are closer to those of the base metal since there is no resolidified zone and the heat affected zone is small. 4 figs.

Kanne, W.R. (Du Pont de Nemours (E.I.) and Co., Aiken, SC (USA). Savannah River Lab.)

1989-01-01

274

Fusion welding process  

DOEpatents

A process for the fusion welding of nickel alloy steel members wherein a ferrite containing pellet is inserted into a cavity in one member and melted by a welding torch. The resulting weld nugget, a fusion of the nickel containing alloy from the members to be welded and the pellet, has a composition which is sufficiently low in nickel content such that ferrite phases occur within the weld nugget, resulting in improved weld properties. The steel alloys encompassed also include alloys containing carbon and manganese, considered nickel equivalents.

Thomas, Kenneth C. (Export, PA); Jones, Eric D. (Salem, PA); McBride, Marvin A. (Hempfield Township, Westmoreland County, PA)

1983-01-01

275

Numerical simulation of dynamic development of keyhole in double-sided arc welding  

NASA Astrophysics Data System (ADS)

Double-sided arc welding (DSAW) is a novel process for joining metals that is capable of achieving deep narrow penetration in a single pass with minimized distortion. A clear understanding of the process fundamentals is critical in order to fully examine the potential of DSAW, to guide the further developments of the process, to direct the practicability study, and to design the process parameters. This paper aims at developing a numerical model for examining and simulating the dynamic keyhole establishment process, which will be a key in developing an effective control technology for DSAW. The model is used to determine the geometrical shape of the keyhole and the weld pool, and the temperature distribution in the workpiece. Quantitative information on the establishment of the keyhole in DSAW, such as the transient development of the keyhole and the weld pool, the increase rate of the depth of the surface depression, the time interval from full penetration to the keyhole establishment, the minimum span of the weld pool for describing the conditions required to complete the keyhole establishment, and variation of the overflow height of the weld pool surface on the plasma arc welding side, has been obtained through numerical analysis. The DSAW experiments show that the predicted weld cross-section is in agreement with the measured one. The results lay a foundation for guiding the further development of the DSAW process and its effective control.

Wu, C. S.; Sun, J. S.; Zhang, Y. M.

2004-05-01

276

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

277

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

278

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

279

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

280

An introduction to mid-Atlantic seasonal pools  

USGS Publications Warehouse

Seasonal pools, also known as vernal ponds, provide important ecological services to the mid-Atlantic region. This publication serves as an introduction to seasonal pool ecology and management; it also provides tools for exploring seasonal pools, including a full-color field guide to wildlife. Seasonal pools are defined as having four distinctive features: surface water isolation, periodic drying, small size and shallow depth, and support of a characteristic biological community. Seasonal pools experience regular drying that excludes populations of predatory fish. Thus, pools in the mid-Atlantic region provide critical breeding habitat for amphibian and invertebrate species (e.g., spotted salamander (Ambystoma maculatum), wood frog (Rana sylvatica), and fairy shrimp (Order Anostraca)) that would be at increased risk of predation in more permanent waters. The distinctive features of seasonal pools also make them vulnerable to human disturbance. In the mid-Atlantic region, land-use changes pose the greatest challenges to seasonal pool conservation. Seasonal pools are threatened by direct loss (e.g., filling or draining of the pool) as well as by destruction and fragmentation of adjoining terrestrial habitat. Many of the species that depend on seasonal pools for breeding spend the majority of their lives in the surrounding lands that extend a radius of 1000 feet or more from the pools; these vital habitats are being transected by roads and converted to other land uses. Other threats to seasonal pools include biological introductions and removals, mosquito control practices, amphibian diseases, atmospheric deposition, and climate change. The authors recommend a three-pronged strategy for seasonal pool conservation and management in the mid-Atlantic region: education and research, inventory and monitoring of seasonal pools, and landscape-level planning and management.

Brown, L.J.; Jung, R.E.

2005-01-01

281

Welding of Hermetic Connectors.  

National Technical Information Service (NTIS)

Certain systems use hermetically-sealed multipin connectors welded into a stainless steel support ring. Failure of these hermetic seals during welding continues to be a problem, and similar problems are anticipated on advanced systems. Since the assembly ...

D. E. Hieber

1976-01-01

282

Investment Policies and Concepts for Pools.  

ERIC Educational Resources Information Center

Investment and endowment policies for educational institutions are shown to be greatly influenced by the size of the endowment and of the school budget. Administration of pooled funds is discussed with particular reference to procedures at Smith College. Establishment of an independent investment committee, separate from the finance committee, is…

Ellis, Robert L.

1973-01-01

283

Possible implication of sterile connecting device in contamination of pooled platelet concentrates.  

PubMed

Considering the possibility that a pooled random donor platelet concentrate could become contaminated by welding with a sterile connecting device, we undertook a study to determine the influence of pooling on the contamination rate. As a control group, apheresis platelets were examined. Bacteriological testing was done with a sensitive CO2 detecting culture system, the BacT/ Alert. Out of 1105 pooled platelet concentrates prepared by the buffy coat method, 15 (1.4%) were confirmed as contaminated, all with Staphylococcus epidermidis and two with a second bacterial species, i.e. Staphylococcus capitis and Propionibacterium acnes, respectively. Median detection time by the BacT/Alert was 23 h. Twelve pools of five units were contaminated, which is significantly more than the three contaminated pools of four units. On the other hand, the reuse of the welding wafers proved not be a risk factor for contamination. One welded tubing segment of a contaminated platelet concentrate failed the air leakage test, an incident which was 73 times more frequent than with the sterile platelet concentrates. We found five pooled platelet concentrates containing Staphylococci from which no bacteria could be grown from the individual buffy coats that had been pooled. We suggest the contamination here to have occurred after separation of the buffy coat from the whole blood, possibly during the welding process. Finally, none out of 378 apheresis platelet concentrates was contaminated. All our observations highlight the potential risk for contamination when making pooled platelet concentrates with a sterile connecting device. For this type of transfusion product, we advocate bacteriological screening of all units before release. The incubation time for the sterility test should, however, be limited to 36 h, if logistical problems with the availability of platelets are to be avoided. PMID:10175151

Mertens, G; Muylle, L; Goossens, H

1997-09-01

284

Solidification microstructures in single-crystal stainless steel melt pools  

SciTech Connect

Development of microstructure of stationary melt pools of oriented stainless steel single crystals (70%Fe-15%Ni-15%Cr was analyzed. Stationary melt pools were formed by electron-beam and gas-tungsten-arc heating on (001), (011), and (111) oriented planes of the austenitic, fcc-alloy crystals. Characterization and analysis of resulting microstructure was carried out for each crystallographic plane and welding method. Results showed that crystallography which favors ``easy growth`` along the <100> family of directions is a controlling factor in the microstructural formation along with the melt-pool shape. The microstructure was found to depend on the melting method, since each method forms a unique melt-pool shape. These results are used in making a three-dimensional reconstruction of the microstructure for each plane and melting method employed. This investigation also suggests avenues for future research into the microstructural properties of electron-beam welds as well as providing an experimental basis for mathematical models for the prediction of solidification microstructures.

Sipf, J.B.; Boatner, L.A.; David, S.A.

1994-03-01

285

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

NASA Astrophysics Data System (ADS)

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.

2005-05-01

286

Welding-Current Indicator  

NASA Technical Reports Server (NTRS)

Light flashes on to indicate high current. Simple, inexpensive display circuit indicates when 3,000-A welding current flows in welding gun. Onset of welding current induces voltage and current in 1,000-turn, 28-gauge copper-wire coil. Single-transistor amplifier amplifies induced current, energizing light-emitting diode (LED) connected to collector of transistor. Light from LED gives simple, direct indication of welding current.

Hensley, Milton C.; Huston, Steven W.; Kroy, Ralph E.

1990-01-01

287

Infrared Thermography For Welding  

NASA Technical Reports Server (NTRS)

Infrared imaging and image-data-processing system shows temperatures of joint during welding and provides data from which rates of heating and cooling determined. Information used to control welding parameters to ensure reliable joints, in materials which microstructures and associated metallurgical and mechanical properties depend strongly on rates of heating and cooling. Applicable to variety of processes, including tungsten/inert-gas welding; plasma, laser, and resistance welding; cutting; and brazing.

Gilbert, Jeffrey L.; Lucky, Brian D.; Spiegel, Lyle B.; Hudyma, Russell M.

1992-01-01

288

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

289

Regression models for group testing data with pool dilution effects  

PubMed Central

Group testing is widely used to reduce the cost of screening individuals for infectious diseases. There is an extensive literature on group testing, most of which traditionally has focused on estimating the probability of infection in a homogeneous population. More recently, this research area has shifted towards estimating individual-specific probabilities in a regression context. However, existing regression approaches have assumed that the sensitivity and specificity of pooled biospecimens are constant and do not depend on the pool sizes. For those applications, where this assumption may not be realistic, these existing approaches can lead to inaccurate inference, especially when pool sizes are large. Our new approach, which exploits the information readily available from underlying continuous biomarker distributions, provides reliable inference in settings where pooling would be most beneficial and does so even for larger pool sizes. We illustrate our methodology using hepatitis B data from a study involving Irish prisoners.

McMahan, Christopher S.; Tebbs, Joshua M.; Bilder, Christopher R.

2013-01-01

290

Regression models for group testing data with pool dilution effects.  

PubMed

Group testing is widely used to reduce the cost of screening individuals for infectious diseases. There is an extensive literature on group testing, most of which traditionally has focused on estimating the probability of infection in a homogeneous population. More recently, this research area has shifted towards estimating individual-specific probabilities in a regression context. However, existing regression approaches have assumed that the sensitivity and specificity of pooled biospecimens are constant and do not depend on the pool sizes. For those applications, where this assumption may not be realistic, these existing approaches can lead to inaccurate inference, especially when pool sizes are large. Our new approach, which exploits the information readily available from underlying continuous biomarker distributions, provides reliable inference in settings where pooling would be most beneficial and does so even for larger pool sizes. We illustrate our methodology using hepatitis B data from a study involving Irish prisoners. PMID:23197382

McMahan, Christopher S; Tebbs, Joshua M; Bilder, Christopher R

2013-04-01

291

Coil Welding Aid  

NASA Technical Reports Server (NTRS)

Positioner holds coil inside cylinder during tack welding. Welding aid spaces turns of coil inside cylinder and applies contact pressure while coil is tack-welded to cylinder. Device facilitates fabrication of heat exchangers and other structures by eliminating hand-positioning and clamping of individual coil turns.

Wiesenbach, W. T.; Clark, M. C.

1983-01-01

292

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

293

Explosively Welded Scarf Joint.  

National Technical Information Service (NTIS)

This invention describes a method for producing a modified scarf weld which is not limited due to small gage of the parts to be welded. It uses the simple technique of explosive welding to bond and simultaneously shape sheet material so that an essentiall...

L. J. Bement

1972-01-01

294

Plasmas for Welding  

NSDL National Science Digital Library

To learn about an important plasma used in manufacturing, visit MIT's Plasmas for Welding. The text describes the arc, which is a plasma, and explains how the arc and the metal to be welded are part of an electric circuit. With photos, the site shows how high-power welding machines cut openings in large sheets of metal.

2006-08-05

295

Method of Laser Welding.  

National Technical Information Service (NTIS)

A method of welding two HY-steel members to produce a weld joint having improved impact toughness. The surface to be welded are first machined, roto-blasted and cleaned with acetone. Then, an inset of Inconel 600 is provided and cleaned with acetone. Next...

D. W. Moon E. A. Metzbower

1983-01-01

296

Fundamentals of Explosive Welding  

Microsoft Academic Search

An account is given of the basic mechanism of adhesion in all welding processes, and a brief review of fusion and pressure welding techniques is given. A completely new method of welding which employs high explosives is briefly described and explained in terms of the principle used in the hollow charge, which wm developed during days of war to defeat

B. Crossland; A. S. Bahrani

1968-01-01

297

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.

298

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

299

IMPROVEMENT OF PROPERTIES OF WELDED JOINTS OF CIRCULAR COMPONENTS FOR GAS TURBINE ENGINES  

Microsoft Academic Search

Method of electroslag welding with the combined electrode under ANF-21 flux, resulting in high-quality melting of the edges and satisfactory formation of the welded joint is described. In order to increase the properties of the weld metal, the latter was modified with the ultrafine powder of titanium carbonitride. The results of metallographic examination the zone or failure, the grain size,

E. N. Eremin

300

Residual stresses at weld repairs in pressure vessels. Quarterly progress report, September 1December 1, 1977  

Microsoft Academic Search

The objective of the research reported is to examine the residual stresses near a weld repair in view of the recent developments in computational modeling for predicting weld-induced residual stresses. A framework for such a study exists through the results of the Heavy Section Steel Technology (HSST) program. Specifically, weld repairs have been conducted on intermediate sized test vessels and

E. F. Rybicki; R. B. Stonesifer

1978-01-01

301

Polymictic pool behavior in Sierra Nevada Streams  

NASA Astrophysics Data System (ADS)

Pools in streams and meadows in the mid to high Sierra Nevada (1800-2300 m) in low flow scenarios were observed to exhibit polymictic behavior during summer months. Although daily thermal stratification has been observed in pools of various sizes and in multiple locations, the degree and timing of stratification is highly variable and not well understood. Previous studies have shown that thermally stratified stream pools can provide cold water refugia for thermally sensitive species, specifically salmonid fish. Diel temperature patterns demonstrating daily thermal stratification and nightly mixing of small (1-4 m diameter and 1-2 m deep) pools in the Long Meadow complex (Sequoia National Park, CA) were observed during the deployment of a distributed temperature sensor (DTS) in 2008. Similar behavior was also noted in stream pools along Chilnualna Creek, a tributary of the South Fork of the Merced River, Yosemite National Park, CA. To further investigate this polymictic behavior, we developed a two-dimensional model of water temperature and flow using Fluent, a computational fluid dynamics solver. The model successfully simulated thermal patterns similar to those observed and indicated that groundwater inflow has a significant influence on pool stratification, consistent with observed low temperatures and raised Radon-222 activity in highly localized areas in the pool bottoms. Similar polymictic behavior was observed in larger (4-10 m diameter and 1.5-2 m deep) stream pools on Chilnualna Creek in the late summer under baseflow conditions. The significant factors that determine stratification or mixing conditions are stream flow velocity, groundwater influence, and density variations due to radiative heating. We use the Richardson number, which was originally developed for assessing thermal stratification in lakes and reservoirs, to develop a one-dimensional tool for prediction of stream pool stratification at multiple scales. This application allows us to assess the stream velocity versus the density discrepancy dictated by the thermal gradient of a given stream pool. Using approximations of stream velocity, stream and groundwater temperatures, we can predict the potential for a stream pool to provide a refuge of cold water.

Lucas, R. G.; Conklin, M. H.; Tyler, S. W.; Suarez, F. I.; Moran, J. E.; Esser, B. K.

2010-12-01

302

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

303

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

304

The study of surface-active element oxygen on flow patterns and penetration in A-TIG welding  

NASA Astrophysics Data System (ADS)

A three-dimensional mathematical model was developed to simulate the flow patterns and temperature distributions in a moving A-TIG weld pool of 304 stainless steels with different oxygen content using PHOENICS software. It is shown that the surface-active element, oxygen, is important, because it affects the weld shape by changing the flow patterns in the weld pool. The weld bead penetration and the depth/width ratio increase first sharply and then remain nearly a constant with increasing oxygen content. Depending upon the oxygen contents, three, one, or two vortexes that have different positions, strength, and directions may be found in the weld pool. Oxygen can cause significant changes in the weld shape by varying the sign of the surface tension coefficient. The situation with the maximum surface tension moves from the edge to the center with increasing oxygen content. As oxygen content exceeds a critical value, a positive surface tension coefficient dominates the flow patterns. The vortexes with opposite directions caused by positive surface tension coefficient can efficiently transfer the thermal energy from the arc, creating a deep weld pool. The critical oxygen content increases with the increase of the welding current.

Zhao, Yuzhen; Shi, Yaowu; Lei, Yongping

2006-06-01

305

Exposures from Thorium Contained in Thoriated Tungsten Welding Electrodes  

Microsoft Academic Search

Information provided in this article can be used for estimating the radiation dose associated with the use of thoriated tungsten electrodes in tungsten inert gas welding. Area and breathing zone concentrations of Th generated by welding and electrode sharpening along with particle size information; isotopic composition of electrodes from two domestic manufacturers and one European manufacturer; and process variables and

J. T. Jankovic; W. S. Underwood; G. M. Goodwin

1999-01-01

306

Determination of welding heat source parameters from actual bead shape  

Microsoft Academic Search

Analytical and numerical approaches are used to model a gas metal arc welding (GMAW) process. In order to simulate the detailed aspects of material changes during the process, it is important to implement the correct size and distribution of the heat source. In this study the dimensions of a heat source model in a welding case will be calculated based

Amin S. Azar; Sigmund K. Ås; Odd M. Akselsen

307

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

308

Stochastic pooling networks  

NASA Astrophysics Data System (ADS)

We introduce and define the concept of a stochastic pooling network (SPN), as a model for sensor systems where redundancy and two forms of 'noise'—lossy compression and randomness—interact in surprising ways. Our approach to analysing SPNs is information theoretic. We define an SPN as a network with multiple nodes that each produce noisy and compressed measurements of the same information. An SPN must combine all these measurements into a single further compressed network output, in a way dictated solely by naturally occurring physical properties—i.e. pooling—and yet cause no (or negligible) reduction in mutual information. This means that SPNs exhibit redundancy reduction as an emergent property of pooling. The SPN concept is applicable to examples in biological neural coding, nanoelectronics, distributed sensor networks, digital beamforming arrays, image processing, multiaccess communication networks and social networks. In most cases the randomness is assumed to be unavoidably present rather than deliberately introduced. We illustrate the central properties of SPNs for several case studies, where pooling occurs by summation, including nodes that are noisy scalar quantizers, and nodes with conditionally Poisson statistics. Other emergent properties of SPNs and some unsolved problems are also briefly discussed.

McDonnell, Mark D.; Amblard, Pierre-Olivier; Stocks, Nigel G.

2009-01-01

309

The effect of the welding direction on the plasma and metal transfer behavior of CO2 laser+GMAW-P hybrid welding processes  

NASA Astrophysics Data System (ADS)

During laser–arc hybrid welding, the welding direction exerts direct effects on the plasma properties, the transient behavior of the droplet, the weld pool behavior, and the temperature field. Ultimately, it will affect the welding process and the weld quality. However, the behavior of the CO2 laser+GMAW-P hybrid welding process has not been systematically studied. In this paper, the current–voltage characteristics of different welding processes were analyzed and compared. The dynamics of the droplet transfer, the plasma behavior, and the weld pool behavior were observed by using two high-speed camera systems. Moreover, an optical emission spectroscopy was applied to analyze the plasma temperature and the electron number density. The results indicated that the electrical resistance of the arc plasma reduced in the laser leading mode. For the same pulse duration, the metal transfer mode was the spray type with the laser leading arrangement. The temperature and electron density distribution showed bimodal behavior in the case of arc leading mode, while this phenomenon does not exist in the caser of laser leading mode. The double elliptic-planar distribution which conventional simulation process used was not applicable in the laser leading mode.

Zhang, Wang; Hua, Xueming; Liao, Wei; Li, Fang; Wang, Min

2014-07-01

310

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

311

Stress corrosion cracking susceptibility of friction stir welded AA7075–AA6056 dissimilar joint  

Microsoft Academic Search

Two aluminium alloys, AA7075 and AA6056, were friction stir welded, with the AA7075 alloy placed on the advancing side of the welding tool. Microstructural observations revealed the development of a recrystallised fine-grained weld nugget, with two different grain sizes, resulting from the two different base materials. Slow strain rate tensile (SSRT) tests in air have shown that the weld nugget

P. Bala Srinivasan; W. Dietzel; R. Zettler; J. F. dos Santos; V. Sivan

2005-01-01

312

Evaluation of solar cell welds by scanning acoustic microscopy  

NASA Technical Reports Server (NTRS)

Scanning laser acoustic microscopy was used to nondestructively evaluate solar cell interconnect bonds made by resistance welding. Both copper-silver and silver-silver welds were analyzed. The bonds were produced either by a conventional parallel-gap welding technique using rectangular electrodes or new annular gap design with a circular electrode cross section. With the scanning laser acoustic microscope, it was possible to produce a real time television image which reveales the weld configuration as it relates to electrode geometry. The effect of electrode misalinement with the surface of the cell was also determined. A preliminary metallographic analysis was performed on selected welds to establish the relationship between actual size and shape of the weld area and the information available from acoustic micrographs.

Klima, S. J.; Frey, W. E.; Baraona, C. R.

1982-01-01

313

Stitch-Bond Parallel-Gap Welding for IC Circuits: Stitch-bonded flatbacks can be superior to soldered dual-in-lines where size, weight, and reliability are important.  

National Technical Information Service (NTIS)

This citation summarizes a one-page announcement of technology available for utilization. Flatback integrated circuits installed by stitch-bond/parallel-gap welding can be considerably more economical for complex circuit boards than conventional solder-in...

1981-01-01

314

On-line inspection of weld quality based on dynamic resistance curve in resistance spot welding and weldbonding  

NASA Astrophysics Data System (ADS)

In order to reduce destructive testing of car sub-assemblies, on-line inspection of weld quality has gained more and more concern in terms of both resistance spot welding (RSW) and weldbonding. Dynamic resistance directly determines the amount of heat generated by current flow and consequently reflects nugget formation and growth, which is one of the most effective technologies for quality inspection. Under the measurements of voltage and current at the secondary circuit of a welding transformer, this paper proposes a method for on-line inspection of weld quality based on two indicators from dynamic resistance curve: time to nugget initiation and durable time to nugget expansion. Firstly, during the welding process of RSW and weldbonding, the proper range of time to nugget initiation and durable time to nugget expansion for good welds is set up. Then on-line inspection of weld quality on the basis of the developed proper range of these two indicators is carried out. The experimental results show the following conclusions: it is clearly able to separate accepted welds without expulsion from the welds of unaccepted nugget size in both RSW and weldbonding; the proper range for good welds, independent of electrode wear, is obtained only for a new electrode.

Sun, Haitao; Zhang, Yansong; Lai, Xinmin; Chen, Guanlong

2008-12-01

315

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

316

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

317

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

318

Finite-element modeling of heat flow in deep-penetration laser welds in aluminum alloys  

NASA Astrophysics Data System (ADS)

A two-dimensional finite-element nonlinear transient heat conduction model was developed and used to simulate deep-penetration keyhole laser welds in aluminum alloys. The weld thermal profiles were calculated in an arbitrary plane as the laser beam approached and passed the plane. From the calculated thermal profiles, three-dimensional quasi-steady-state shapes of the weld pools were determined. The predicted weld bead shape and dimensions were in good agreement with the experimental results. The experimental laser welds in aluminum alloys contained large amounts of porosity. The model predicted large mushy zones for aluminum laser welds during solidification, which in turn increase the probability of porosity formation by increased bubble entrapment.

Sonti, N.; Amateau, M. F.

1989-10-01

319

Three-dimensional modelling of heat transfer and fluid flow in laser full-penetration welding  

NASA Astrophysics Data System (ADS)

Modelling results are presented concerning the laser full-penetration welding characteristics. The effects of welding speed, Marangoni convection and natural convection on melt flow and heat transfer are all included in the modelling, and thus a three-dimensional (3-D) approach is employed. Comparison of the present 3-D modelling results with corresponding two-dimensional ones shows that besides the welding speed, Marangoni convection also plays critical role in determining the temperature distribution in the workpiece and melt flow in the weld pool and cannot be ignored even for the full-penetration welding of a thin plate. A method is described concerning how to use the present 3-D modelling results to estimate the keyhole radius or predict the energy efficiency in the laser full-penetration welding.

Ye, Xiao-Hu; Chen, Xi

2002-05-01

320

Mechanism of laser welding on dissimilar metals between stainless steel and W-Cu alloy  

NASA Astrophysics Data System (ADS)

CO2 laser is employed to join a piece of powder metallurgical material (PMM) to a stainless steel in butt joint welding mode. The powder Ni35, as a filler powder, is used. The weld metal comes from three parts of stainless steel, powder Ni35, and Cu in W-Cu PMM. It is indicated that some parts of the W-Cu base metal are heated by laser and the metal Cu at the width of 0.06-0.12 mm from the edge is melted into the melting pool in the laser welding process. The formation of firm weld joint is just because that the melting liquid metal could fill the position occupied by metal Cu and surround the metal W granules fully. The analysis results indicate that the mechanism of the laser welding for stainless steel and W-Cu alloy is a special mode of fusion-brazing welding.

Chen, Kai; Wang, Zhiyong; Xiao, Rongshi; Zuo, Tiechuan

2006-05-01

321

Reserve Growth of Alberta Oil Pools  

USGS Publications Warehouse

This Open-File Report is based on a presentation delivered at the Fourth U.S. Geological Survey Workshop on Reserve Growth on March 10-11, 2008. It summarizes the results of a study of reserve growth of oil pools in Alberta Province, Canada. The study is part of a larger effort involving similar studies of fields in other important petroleum provinces around the world, with the overall objective of gaining a better understanding of reserve growth in fields with different geologic/reservoir parameters and different operating environments. The goals of the study were to: 1. Evaluate historical oil reserve data and assess reserve growth. 2. Develop reserve growth models/functions to help forecast hydrocarbon volumes. 3. Study reserve growth sensitivity to various parameters ? for example, pool size, porosity, oil gravity, and lithology. 4. Compare reserve growth in oil pools/fields of Alberta provinces with those from other large petroleum provinces.

Verma, Mahendra K.; Cook, Troy

2008-01-01

322

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

323

Measurement and modelling of residual stresses in a TIG weld  

NASA Astrophysics Data System (ADS)

Residual stresses due to TIG welding have been measured using neutron diffraction and the results compared with a finite element model calculation. Measurements were made on a single-pass, autogenous, bead-on-plate TIG weld made along the centre line of an aluminium alloy rectangular plate of dimensions 172×150×3mm3. The weld is 150mm long with the start and end pools centred approximately 12mm from the plate edges. There is an 8mm wide molten band on the crown surface of the weld. Measurements were made at a neutron wavelength of 1.51Å using the aluminium (311) reflection and a gauge volume 2×2×2mm3. Scans were made along three transverse lines, across the centre of the weld, 40mm from the start and 40mm from the end at mid-thickness. Stresses were derived using data collected in the three orthogonal symmetry directions. A finite-element model was generated using ABAQUS. The agreement between the calculated and measured results is good. Longitudinal residual stresses are strongly tensile (approaching 200MPa) in the weld, falling to zero at around 15mm from the weld line with balancing compression towards the edges.

Webster, P. J.; Ananthaviravakumar, N.; Hughes, D. J.; Mills, G.; Preston, R. V.; Shercliff, H. R.; Withers, P. J.

324

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

325

Laser welding of INCONEL 600  

Microsoft Academic Search

Laser beam welding exhibits features typical of autogenous welding by fusion with very concentrated heat sources: narrow deep weld, restrict heat affected zone (HAZ), negligible residual.stresses etc. All these aspects are of great importance in welding special purpose alloys such as corrosion resistant nickel base alloys. In this work, a nickel base alloy INCONEIl 600 has been welded by means

G. Daurelio; G. Dionoro; F. Memola Capece Minutolo

1991-01-01

326

Dual wire weld feed proportioner  

NASA Technical Reports Server (NTRS)

Dual feed mechanism enables proportioning of two different weld feed wires during automated TIG welding to produce a weld alloy deposit of the desired composition. The wires are fed into the weld simultaneously. The relative feed rates of the wires and the wire diameters determine the weld deposit composition.

Nugent, R. E.

1968-01-01

327

13 CFR 120.1704 - Pool Loans eligible for Pooling.  

Code of Federal Regulations, 2011 CFR

...six-month-period immediately prior to the date the Pool is formed or for the life of the Pool Loan, whichever time period is shorter; ...business within NAICS code 713940 covering Fitness and Recreational Sports Centers; (If SBA determines that a Pool Loan has had...

2011-01-01

328

13 CFR 120.1704 - Pool Loans eligible for Pooling.  

Code of Federal Regulations, 2010 CFR

...six-month-period immediately prior to the date the Pool is formed or for the life of the Pool Loan, whichever time period is shorter; ...business within NAICS code 713940 covering Fitness and Recreational Sports Centers; (If SBA determines that a Pool Loan has had...

2010-01-01

329

Non-metallic oxide inclusion formation in C-Mn low alloy steel welds.  

National Technical Information Service (NTIS)

Inclusion characteristics influence weld metal microstructure development, especially the formation of high toughness acicular ferrite phase. Important inclusion characteristics are: size distribution, number density, volume fraction, composition. Previou...

S. S. Babu K. Mundra T. DebRoy S. A. David J. M. Vitek

1995-01-01

330

Effect of changes in testing parameters on the cost-effectiveness of two pooled test methods to classify infection status of animals in a herd  

Microsoft Academic Search

Monte Carlo simulation was used to determine optimal fecal pool sizes for identification of all Mycobacterium avium subsp. paratuberculosis (MAP)-infected cows in a dairy herd. Two pooling protocols were compared: a halving protocol involving a single retest of negative pools followed by halving of positive pools and a simple protocol involving single retest of negative pools but no halving of

Locksley L. Mc V. Messam; Joshua M. O’Brien; Sharon K. Hietala; Ian A. Gardner

2010-01-01

331

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

332

Weld procedure development with OSLW - optimization software for laser welding.  

National Technical Information Service (NTIS)

Weld procedure development can require extensive experimentation, in-depth process knowledge, and is further complicated by the fact that there are often multiple sets of parameters that will meet the weld requirements. Choosing among these multiple weld ...

P. W. Fuerschbach G. R. Eisler R. J. Steele

1998-01-01

333

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

334

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

335

Optimal pooled testing  

Microsoft Academic Search

This paper first characterizes three pooled testing techniques for generic testing conditions. It then applies these methods\\u000a to demonstrate potential costs savings for universal HIV screening in the United Stated and Thailand. The success of these\\u000a techniques in general is shown to be dependent on the prevalence as well as the disparity in prevalence between high and low\\u000a risk groups.

Brett A. Saraniti

2006-01-01

336

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

337

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

338

Influence of the weld conditions on the forming-limit strains of tailor-welded blanks  

Microsoft Academic Search

The main objective of the present work is to study experimentally the influence of just the weld conditions, namely the weld region, weld orientation, and weld location, on the forming-limit strains of steel laser-welded blanks. Transverse and longitudinal weld orient- ations are considered for this study. The weld location includes both centre and offset weld positions in the transverse weld

R Ganesh Narayanan; K Narasimhan

2008-01-01

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

Automated Weld Characterization Using the Thermoelectric Method  

NASA Technical Reports Server (NTRS)

The effective assessment of the integrity of welds is a complicated NDE problem that continues to be a challenge. To be able to completely characterize a weld, detailed knowledge of its tensile strength, ductility, hardness, microstructure, macrostructure, and chemical composition is needed. NDE techniques which can provide information on any of these features are extremely important. In this paper, we examine a seldom used approach based on the thermoelectric (TE) effect for characterizing welds and their associated heat affected zone (HAZ). The thermoelectric method monitors the thermoelectric power which is sensitive to small changes in the kinetics of the conduction electrons near the Fermi surface that can be caused by changes in the local microstructure. The technique has been applied to metal sorting, quality testing, flaw detection, thickness gauging of layers, and microscopic structural analysis. To demonstrate the effectiveness of the technique for characterizing welds, a series of tungsten-inert-gas welded Inconel-718 samples were scanned with a computer controlled TE probe. The samples were then analyzed using a scanning electron microscope and Rockwell hardness tests to characterize the weld and the associated HAZ. We then correlated the results with the TE measurements to provide quantitative information on the size of the HAZ and the degree of hardness of the material in the weld region. This provides potentially valuable information on the strength and fatigue life of the weld. We begin the paper by providing a brief review of the TE technique and then highlight some of the factors that can effect the measurements. Next, we provide an overview of the experimental procedure and discuss the results. Finally, we summarize our findings and consider areas for future research.

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

1992-01-01

341

Trailer-Mounted Welding Shop.  

National Technical Information Service (NTIS)

This technical information report describes a lightweight, mobile welding shop designed to provide field forces with a previously unavailable facility for both gas and electric arc welding. The shop contains a 300-amp DC, gasoline-driven welding machine d...

1968-01-01

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

Welding skate with computerized controls  

NASA Technical Reports Server (NTRS)

New welding skate concept for automatic TIG welding of contoured or double-contoured parts combines lightweight welding apparatus with electrical circuitry which computes the desired torch angle and positions a torch and cold-wire guide angle manipulator.

Wall, W. A., Jr.

1968-01-01

344

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

345

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

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

Friction Stir Welding  

NSDL National Science Digital Library

Probably the best resource to learn about friction stir welding (FSW) comes from the entity that developed the technology. The Welding Institute (1) offers a thorough overview of FSW and its advantages over other types of welding. The University of Cambridge (2) maintains another informative Web site about FSW. This is a more visual resource, allowing the visitor to view images and video clips that show FSW equipment and how the process works. Three introductory slide presentations are also available. For those who are unfamiliar with other types of welding, the Joining Technologies company (3) has an online welding reference center. Of particular interest is the Weld Defects section, which describes many of the problems of conventional welding that FSW solves. The American Welding Society published this research paper (4) in the January 2003 issue of the Welding Journal. The nine-page document presents experimental results of FSW tests, showing that defect-free welds can be achieved with a material such as mild steel. Automobile design is a prime application area for FSW, as is noted in a fact sheet from the National Transportation Research Center (5). It states that while other welding methods are suitable for standard metals in automobiles, new lightweight materials cannot be effectively joined unless a technique like FSW is used. A research paper that will be presented at an international conference in July 2003 (6) discusses the residual stresses resulting from a weld created with the FSW process. While welds of this type are typically much stronger than others, it is important to note how the performance of a weld is degraded by such residual stresses. NASA has devised a new technique, called thermal stir welding, that improves upon FSW. This breakthrough is presented in a two-page summary (7) that briefly explains the differences between thermal stir welding and other advanced methods. A new friction stir welding center was announced in November 2002, and it will be used in the construction of a new jet airplane. FSW will replace over half of the rivets traditionally used to hold planes together. This development, and its importance for jet manufacturing, are outlined in a press release from Eclipse Aviation (8).

Leske, Cavin.

348

Associations of welding and manganese exposure with Parkinson disease  

PubMed Central

Objective: To examine associations of welding and manganese exposure with Parkinson disease (PD) using meta-analyses of data from cohort, case-control, and mortality studies. Methods: Epidemiologic studies related to welding or manganese exposure and PD were identified in a PubMed search, article references, published reviews, and abstracts. Inclusion criteria were 1) cohort, case-control, or mortality study with relative risk (RR), odds ratio (OR), or mortality OR (MOR) and 95 confidence intervals (95% CI); 2) RR, OR, and MOR matched or adjusted for age and sex; 3) valid study design and analysis. When participants of a study were a subgroup of those in a larger study, only results of the larger study were included to assure independence of datasets. Pooled RR/OR estimates and 95% CIs were obtained using random effects models; heterogeneity of study effects were evaluated using the Q statistic and I2 index in fixed effect models. Results: Thirteen studies met inclusion criteria for the welding meta-analysis and 3 studies for the manganese exposure meta-analysis. The pooled RR for the association between welding and PD for all study designs was 0.86 (95% CI 0.80–0.92), with absence of between-study heterogeneity (I2 = 0.0). Effect measures for cohort, case-control, and mortality studies were similar (0.91, 0.82, 0.87). For the association between manganese exposure and PD, the pooled OR was 0.76 (95% CI 0.41–1.42). Conclusions: Welding and manganese exposure are not associated with increased PD risk. Possible explanations for the inverse association between welding and PD include confounding by smoking, healthy worker effect, and hormesis.

Borenstein, Amy R.; Nelson, Lorene M.

2012-01-01

349

Role of surface-active elements during keyhole-mode laser welding  

NASA Astrophysics Data System (ADS)

During high power density laser welding of mild steel, the keyhole depth, liquid metal flow, weld geometry and weld integrity are affected by base-metal sulfur content and oxygen (O2) present in the atmosphere or shielding gas. The role of these surface-active elements during keyhole-mode laser welding of steels is not well understood. In order to better understand their effects, welding of mild steel specimens containing various concentrations of oxygen and sulfur are examined. In addition, a numerical model is used to evaluate the influence of the surface-active elements on heat transfer and fluid flow in keyhole-mode laser welding. Increase in base-metal sulfur concentration or O2 content of shielding gas results in decreased weld widths. Sulfur results in a negligible increase in penetration depth whereas the presence of O2 in shielding gas significantly affects the weld penetration. It has earlier been proposed that oxygen, if present in the shielding gas, can get introduced into the weld pool resulting in formation of carbon monoxide (CO) at the keyhole surface and additional pressure from CO can result in increased penetration. Numerical modelling has been used in this work to understand the effects of formation of CO on the keyhole and weld geometries.

Ribic, B.; Tsukamoto, S.; Rai, R.; DebRoy, T.

2011-12-01

350

LWRHU GTA Weld Development  

SciTech Connect

Nineteen LWRHU Development Welds have been made. Welds WD-1 through WD-4 were made early in the program to obtain preliminary joint design data. Welds WD-5 through WD-10 were made with the vertical leg of the shim located toward the closure end cap. A decision was made to locate the shim with the vertical leg on the fuel side of the capsule; therefore, the data obtained on the above capsule welds will not be included in this report. A tantalum pellet machined to the configuration of the fuel pellet was placed inside each development capsule. O.D. shrinkage measurements were taken across the stand-off ring nearest the weld. A small increase in capsule length resulted from the weld bead on the end of the capsule.

Burgan, C.E.

1979-12-13

351

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

352

Bond formation in ultrasonically welded aluminum sheet metal  

NASA Astrophysics Data System (ADS)

Ultrasonic welding (USW), a solid state joining technology, has been used to bond aluminum alloys commonly used in the automotive industry. Bonding occurs due to USW's high frequency (˜20 kHz) in-plane vibration of sample interfaces while being held under moderate clamp pressure normal to the plane of vibration. Vibration and clamp pressure are transmitted into bond formation via contact with a weld-tip. To better understand how weld-tip geometry affected bond formation, experiments were conducted to quantify how tip geometry influenced plastic deformation characteristics between fully welded coupons of 0.9mm thick AA6111-T4 aluminum alloy. Weld-interface microstructure features were documented by optical microscopy and features quantified in a 19 point matrix. Correlation between microstructure features, such as rolling-wakes, and resulting weld bond strengths of more than 3.0kN is made. Weld zone microstructure features appear to result from deformation at and severe migration of the original weld interface during USW. To confirm this hypothesis, intrinsic and extrinsic markers were employed to monitor weld interface deformation characteristics. Various physical and analytical techniques were used in conjunction with these markers to show that joining of "like" and "dislike" aluminum samples is achieved through mechanical mixing of mating interfaces and not by elemental diffusion. It is also hypothesized that severe deformation of the original interface would result in areas of high residual strain within a formed weld zone. To investigate this and the influence that tip geometry may have on residual strain, fully welded samples were annealed at 500°C for a controlled period of time and recovery, recrystallization and grain growth characteristics were monitored. In all welds, initial recrystallization and grain growth occurred at the outer ends of weld zones and along weld interfaces where the most turbulent mixing and grain size reduction was observed. Similarity in how all welds responded to annealing indicates that the tip geometries investigated had little influence on resulting weld formation. This claim is further supported by lap-shear failure load data for welds made with these tips being within statistical error of each other.

Wilkosz, Daniel Edward

353

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

354

Detection of defects in laser welding of AZ31B magnesium alloy in zero-gap lap joint configuration by a real-time spectroscopic analysis  

NASA Astrophysics Data System (ADS)

The effect of surface oxide layer existing at the lap-joint faying surface of magnesium sheets is investigated on the keyhole dynamics of the weld pool and weld bead qualities. It is observed that by removing the oxide layer from the faying surface of the lap joint, a high quality weld can be achieved in the laser welding process. However, the presence of an oxide layer deteriorates the quality of the weld by forming pores at the interface of the two overlapped sheets. The purpose of this paper is to identify the correlation between the integrity of the weld and the interaction between the laser and material. A spectroscopy sensor was applied to detect the spectra emitted from a plasma plume during the laser welding of AZ31B magnesium alloy in a zero-gap lap joint configuration. The electron temperature was calculated by applying a Boltzmann plot method based on the detected spectra, and the correlation between the pore formation and the spectral signals was studied. The laser molten pool and the keyhole condition were monitored in real-time by a high speed charge-coupled device (CCD) camera. A green laser was used as an illumination source in order to detect the influence of the oxide layer on the dynamic behavior of the molten pool. Results revealed that the detected spectrum and weld defects had a meaningful correlation for real-time monitoring of the weld quality during laser welding of magnesium alloys.

Harooni, Masoud; Carlson, Blair; Kovacevic, Radovan

2014-05-01

355

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

356

Hybrid laser-arc welding of galvanized high-strength steels in a gap-free lap-joint configuration  

NASA Astrophysics Data System (ADS)

In order to meet the industry demands for increased fuel efficiency and enhanced mechanical and structural performance of vehicles as well as provided excellent corrosion resistance, more and more galvanized advanced high-strength steels (AHSS) have been used to fabricate automobile parts such as panels, bumpers, and front rails. The automotive industry has shown tremendous interest in using laser welding to join galvanized dual phase steels because of lower heat input and higher welding speed. However, the laser welding process tends to become dramatically unstable in the presence of highly pressurized zinc vapor because of the low boiling point of zinc, around 906°C, compared to higher melting point of steel, over 1500°C. A large number of spatters are produced by expelling the liquid metal from the molten pool by the pressurized zinc vapor. Different weld defects such as blowholes and porosities appear in the welds. So far, limited information has been reported on welding of galvanized high strength dual-phase steels in a gap-free lap joint configuration. There is no open literature on the successful attainment of defect-free welds from the laser or hybrid welding of galvanized high-strength steels. To address the significant industry demand, in this study, different welding techniques and monitoring methods are used to study the features of the welding process of galvanized DP steels in a gap-free lap joint configuration. The current research covers: (i) a feasibility study on the welding of galvanized DP 980 steels in a lap joint configuration using gas tungsten arc welding (GTAW), laser welding, hybrid laser/arc welding with the common molten pool, laser welding with the assistance of GTAW preheating source and hybrid laser-variable polarity gas tungsten arc welding (Laser-VPGTAW) techniques (Chapter 2-4); (ii) a welding process monitoring of the welding techniques including the use of machine vision and acoustic emission technique (Chapter 5); (iii) Modeling of hybrid laser-GTAW as a preheating source welding process of galvanized steels in a gap-free lap joint configuration (Chapter 6). Experimental results demonstrated that completely defect-free lap joints in galvanized high strength steels can be obtained in a gap-free configuration by using the laser welding process with the GTAW torch preheating and hybrid laser-VPGTAW welding technique. Effects of the welding parameters on the weld quality are discussed. The mechanical properties of the welded joints are studied. A machine vision system and an acoustic emission (AE) signal acquisition system are employed to acquire the images of the molten pool and the emitted AE signals on-line. Furthermore, image processing and Short Time Fourier Transform (STFT) techniques are employed to analyze the acquired images of the molten pool and the collected AE signals. The acquisition attempts are composed of (1) monitoring the weld defects by machine vision; (2) monitoring the formation of spatters from the AE signals; (3) detecting the weld modes by the induced plume; and (4) monitoring the instability of the welding process by machine vision. In addition, the numerical results have been validated by the experimental data.

Yang, Shanglu

357

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

358

Welded preforms for forging  

Microsoft Academic Search

While tailor-welded preforms are commonly used in sheet forming, to date, similar technology has not been developed for bulk forming. In the present paper, the results of a study that was conducted to investigate the feasibility of solid-state welded preforms in forging is presented. Both same-metal and bi-metal combinations were considered and results indicate that in general friction welded preforms

Joseph Domblesky; Frank Kraft; Benjamin Druecke; Bart Sims

2006-01-01

359

Vibrations in friction welding  

Microsoft Academic Search

For more than 50 years rotational friction welding has been successfully used for joining metallic materials. Since lightweight\\u000a structures became established in industry new challenges emerge to rotational friction welding, that have not yet been studied.\\u000a This report considers vibrations in rotational friction welding in order to identify possibilities and means and to avoid\\u000a damage of the component structure by the

M. F. Zaeh; A. Poehler

2011-01-01

360

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.

2013-08-02

361

Simplified explosive-weld evaluation  

NASA Technical Reports Server (NTRS)

Weld surfaces, coated with commercially available molybdenum disulfide, allow visual inspection of significant indications of bond quality. Process reduces number of trial welds, making explosive bonding more competitive.

Mclarty, D. M.

1976-01-01

362

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

363

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

364

Evaluation of pooled rapid HIV antibody screening of patients admitted to a San Diego Hospital  

Microsoft Academic Search

Current HIV screening guidelines in the United States recommend expanding the scope of HIV screening to include routine screening in health care settings; however, this will require increased resources. Since testing of pooled samples can decrease costs, the test characteristics of pooled rapid antibody testing were determined and optimal pool sizes were estimated for populations with HIV prevalence ranging from

Sanjay R. Mehta; Vu T. Nguyen; Georgina Osorio; Susan Little; Davey M. Smith

2011-01-01

365

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

366

Robot welding process control  

NASA Technical Reports Server (NTRS)

This final report documents the development and installation of software and hardware for Robotic Welding Process Control. Primary emphasis is on serial communications between the CYRO 750 robotic welder, Heurikon minicomputer running Hunter & Ready VRTX, and an IBM PC/AT, for offline programming and control and closed-loop welding control. The requirements for completion of the implementation of the Rocketdyne weld tracking control are discussed. The procedure for downloading programs from the Intergraph, over the network, is discussed. Conclusions are made on the results of this task, and recommendations are made for efficient implementation of communications, weld process control development, and advanced process control procedures using the Heurikon.

Romine, Peter L.

1991-01-01

367

Physics of Fusion Welding  

NASA Technical Reports Server (NTRS)

Applicabilities and limitations of three techniques analyzed. NASA technical memorandum discusses physics of electron-beam, gas/ tungsten-arc, and laser-beam welding. From comparison of capabilities and limitations of each technique with regard to various welding conditions and materials, possible to develop criteria for selecting best welding technique in specific application. All three techniques classified as fusion welding; small volume of workpiece melted by intense heat source. Heat source moved along seam, leaving in wake solid metal that joins seam edges together.

Nunes, A. C., Jr.

1986-01-01

368

Superplastic Forming of Aluminum Multisheet Structures Fabricated Using Friction Stir Welding and Refill Friction Stir Spot Welding  

SciTech Connect

Superplastically-formed structural panels are growing in their applications in aerospace, aircraft, automotive, and other industries. Generally, monolithic sheets are employed, limiting the size and complexity of the final part. However, more complex and larger final geometries are possible if individual sheet materials can be joined together through an appropriate joining technology, then SPF formed to final shape. The primary challenge in this type of SPF fabrication has been making a joint between the sheets that will survive the SPF forming event and display the correct amount of elongation in the joint relative to the base materials being formed. Friction Stir Welding is an ideal joining technology for SPF applications because the forming response of the weld metal at SPF conditions is adjustable by selecting different weld process parameters during initial joining. This allows the SPF deformation in the weld metal to be “tuned” to the deformation of the parent sheet to prevent early failure from occurring in either the weld metal or the parent sheet due to mismatched SPF flow stresses. Industrial application of the concept of matching flow stresses is currently being pursued on a program at the Pacific Northwest National Laboratory on room temperature formed friction stir welded tailor welded blanks for heavy truck applications. Flow stress matching and process parameter “tuning” is also important in the fabrication of SPF multisheet structural panels. These panels are fabricated by joining three sheets together with alternating welds top and bottom, so that each weld penetrates only two of the three sheets. This sheet pack is then sealed with a weld seam around the outside and hot gas is introduced between the sheets through a welded tube. Under SPF conditions the sheet pack inflates to produce an internally supported structure. In this paper we presents results on an investigation into using FSW and Refill Friction Stir Spot Welding to fabricated 5083 aluminum multisheet packs that can be SPF formed into 3-D structural or integrally stiffened panels. Several configurations of 3-sheet egg crate and truss structures were friction stir welded and hot gas SPF formed in a parallel-platen SPF press. Data on weld conditions for optimum SPF forming as well as pre- and post- forming microstructures will be presented. It is found that FSW process conditions are a key feature of a successful SPF forming operation and the nugget microstructures and other features of the weld zone can be optimized to produce a wide range of weld region elongations. Friction Stir Welding may prove to be the enabler that allows aluminum to be considered in multisheet and integrally stiffened SPF Aluminum structures.

Grant, Glenn J.; Herling, Darrell R.; Arbegast, William J.; Allen, Casey D.; Degen, Cassandra M.

2006-12-20

369

Permanent refueling pool seal  

SciTech Connect

This patent describes a permanent pool seal and neutron shield for providing an effective water barrier over the annular space between a nuclear reactor vessel flange and a surrounding annular ledge. It comprises an annular space-spanning deck structure supported underneath by circumferentially spaced radially disposed ribs spanning the annular space with the inner ends of the ribs supported by the vessel flange and the outer ends of the ribs supported by the ledge; and flexible seals between the deck structure and the vessel flange and the deck structure and the ledge.

McDonald, M.S.; Siegel, E.A.; Roebelen, G.J.; Schukei, G.E.; Brookins, R.H.; Ayres, D.J.

1992-04-07

370

The Swimming Pool  

NSDL National Science Digital Library

This problem provides an opportunity for introducing and raising children's awareness of negative numbers. The first part of the problem is moving up and down a ladder or steps into a swimming pool. Students are counting along a number line, but in this case it is vertical rather than the more usual horizontal orientation. The final part of the activity encourages children to be creative and invent their own way of numbering the steps below the water level. The Teachers' Notes page offers suggestions for implementation and discussion as well as ideas for extension and support.

2008-01-01

371

Capabilities of Ultrasonic Phased Arrays for Far-Side Examinations of Austenitic Stainless Steel Piping Welds  

SciTech Connect

A study was conducted to assess the ability of advanced ultrasonic techniques to detect and accurately determine the size of flaws from the far-side of wrought austenitic piping welds. Far-side inspections of nuclear system austenitic piping welds are currently performed on a “best effort” basis and do not conform to ASME Code Section XI Appendix VIII performance demonstration requirements for near side inspection. For this study, four circumferential welds in 610mm (24inch) diameter, 36mm (1.42inch) 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 ranged 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 phased array technology at 2.0 MHz, and compared to conventional ultrasonic techniques as a baseline. The examinations showed that phased-array methods were able to detect and accurately length-size, but not depth size, the notches and flaws through the welds. The ultrasonic results were insensitive to the different welding techniques used in each weld.

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

2006-10-01

372

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

373

Particle Emission from Welding of Painted Steel  

Microsoft Academic Search

The particulate emission caused by welding of steel plates covered with 29 diversified shop primers has been investigated. The investigation includes the determination of particle mass, particle size distribution, and of the contents of heavy metals such as lead and cadmium. The results show that all investigated primers except those with high concentration of zinc pigment produce mass emissions which

D. Körber; H. J. Fißan

1981-01-01

374

Defect distributions in weld-deposited cladding  

SciTech Connect

Defect distributions in stainless steel and nickel-chromium alloy weld-deposited cladding over a low alloy steel base were characterized by destructive evaluation (DE). An evaluation of the observed defects was conducted to characterize the defects by type or classification. Size distributions of cladding defect types were developed from the information obtained. This paper presents the results of the cladding evaluation.

Li, Y.Y.; Mabe, W.R.

1998-11-01

375

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

376

Detection of West Nile virus in large pools of mosquitoes.  

PubMed

We conducted a laboratory evaluation of the ability of commercial antigen-capture assays, the Rapid Analyte Measurement Platform (RAMP) and the VecTest wicking assay, as well as Real Time reverse transcriptase polymerase chain reaction (RT-PCR, Taqman) and Vero cell plaque assay to detect West Nile virus (WNV) in large mosquito pools. Real-Time PCR (Taqman) was the most sensitive, detecting WNV ribonucleic acid (RNA) in 100% of samples containing a single infected mosquito in pool sizes of up to 500 mosquitoes. Mosquito body tissues minimally impacted the ability of Real Time RT-PCR to detect WNV in a pool size of 500, reducing sensitivity by 0.6 log10 plaque-forming units (PFU)/ml. Vero cell plaque assay detected live virus from a single infected mosquito in 100% of pools containing up to 200 mosquitoes, but was unreliable at larger pool sizes. VecTest detected 100% of positive pools containing 50 mosquitoes with 5.8 log10 PFU/ml virus, 100 mosquitoes with 5.9 log10 PFU/ml, and 200 mosquitoes with 5.2 log10 PFU/ ml. The RAMP assay detected 100% of positive pools containing 50 mosquitoes with 3.3 log10 PFU/ml virus, 100 mosquitoes with 3.7 log10 PFU/ml, and 200 mosquitoes with 4.0 log10 PFU/ml. Results indicate that WNV can be reliably detected by all 4 assays in pools of mosquitoes exceeding 50 specimens, though there is some loss of sensitivity with very large pool sizes. PMID:18240515

Sutherland, Genevieve L; Nasci, Roger S

2007-12-01

377

Strain Rates and Grain Growth in Al 5754 and Al 6061 Friction Stir Spot Welds  

Microsoft Academic Search

The stir zone temperature and microstructures are compared in friction stir spot welds produced in Al 5754 and Al 6061 alloys.\\u000a Electron backscattered diffraction was used to determine the relationship between tool rotation speed during welding and final\\u000a stir zone grain size. Comparison of the grain sizes in rapidly quenched welds with those in air-cooled joints confirmed that\\u000a grain growth

A. Gerlich; M. Yamamoto; T. H. North

2007-01-01

378

Nine Ball Pool Model  

NSDL National Science Digital Library

The Nine Ball Pool Model is set up as a game of nine-ball (nine balls in a diamond formation with a cue ball), and the player may hit the balls in any order. With normal play (the player selecting "Nine-Ball"), the goal of the game is to sink all of the balls in as little time as possible, with the least number of possible turns, and with the least possible number of scratches (sinking of the cue ball). The player may see these statistics at the bottom-right corner of the play screen and will get a final report upon sinking the last non-cue ball. (The back arrow is a total reset button for the simulation.) This form of play is essentially a free-for-all. The Nine Ball Pool Model was created using the Easy Java/JavaScript Simulations (EjsS) modeling tool. It is distributed as a ready-to-run (compiled) Java archive.

Kozlowski, Ryan

2014-03-09

379

[Treatment of thermal pool waters].  

PubMed

No laws currently exist regarding the treatment of spa pool water, since it is not completely logical that these should have the same requirements as normal swimming pools. The problem arises especially with regards to the use of chlorine as a disinfectant, which may actually annulate the therapeutic effects of spring waters by altering their physical-chemical characteristics. Possible choices may be represented by frequent replacement of pool water, which may be easily achievable for small pools but more difficult to implement for larger pools, or by alternative disinfection methods such as ozone or ultraviolet rays. The efficacy of these methods must be shown through frequent chemical and microbiological analyses and future, to be hoped-for laws or guidelines, will need to be aimed at defining safety performance standards rather than prescribing analytical intervention and control methods. Beyond the choice of disinfection method, it is extremely important to highlight some relevant hygienic measures that bathers should take and that play a fundamental role in preventing infectious diseases which may be acquired in pools. The most important of these include: showering before entering the pool, wearing slippers around the pool, not urinating in the pool, not bathing if affected by diarrhea, wearing a bathing cap, avoiding the use of contact lenses while bathing and avoiding exchanging towels. Pool managers have the important role of avoiding overcrowding of the facilities and ensuring that all technological systems function properly. PMID:17206228

Signorelli, Carlo; Pasquarella, Cesira; Saccani, Elisa; Sansebastiano, Giuliano

2006-01-01

380

Control of Weld Quality in Large Welded Populations,  

National Technical Information Service (NTIS)

The use of factorial experimental design during weld procedure development, as a statistical tool for the control of weld quality in large welded populations, is investigated. It is applied to single pass welds made in the laboratory using the spacer to t...

P. J. Alberry R. R. L. Brunnstrom J. A. Lambert R. A. Willgoss

1988-01-01

381

On line sensing of weld penetration using infrared thermography  

SciTech Connect

The objective of this research is to apply new sensing techniques, artificial intelligence, and robotics to improve the welding process through control of penetration depth and width parameters. By producing a constant depth and width of penetration through on line control, the quality and strength of welds may be improved to a new level of reliability previously unobtainable. Experimental data presented in this paper indicate that depth and width of penetration can be monitored by infrared thermography and hence controlled dynamically during the weld process. Infrared thermography is used to monitor surface temperature distributions in the vicinity of the molten metal pool. Characteristics of temperature distributions perpendicular to the direction of arc travel are analyzed and correlated with weld bead width and depth as measured by destructive examination after the weld production. The results show that there is a linear relationship between peak weld plate surface temperature and depth of penetration. Additionally, surface puddle width is found to be directly correlated to measured distance separating solidus temperatures of the molten metal as measured by infrared thermography.

Wang, Y.; Chin, B.A.

1986-01-01

382

Experimental detection and theoretical prediction of laser welding plasma oscillations  

NASA Astrophysics Data System (ADS)

In deep penetration laser welding the keyhole plays an important role in the energy transfer from the laser beam to the work-piece. Its dynamic behaviour influences the quality of the welded joint since fluctuations of process parameters may induce keyhole instabilities that result in weld defects and volume fluctuations of the thermal plasma filling it. In this work we present an experimental study of the plasma optical emission in the UV-VIS range measured by means of photodiodes. We real-time investigated the intensity oscillations of the emission performing a FFT power spectrum of the acquired signal in the 0.4-20 kHz range. The influence of the variation of the main process parameters (incident power, welding speed, beam focus position and gas flow rate) on the joint quality and on the recorded FFT spectrum was analysed. A comparison of these results with those predicted by a theoretical study of the dynamic behaviour of the keyhole has shown good agreement. The theoretical model is based on a pressure and energy balance between the different forces acting on the keyhole walls, which is assumed to be cylindrical. Any distortion of this balance induces radial, axial and azimuthal oscillations of the cavity and of the weld pool surrounding it, whose eigen-frequencies have been calculated. These preliminary results can be used in order to assemble an innovative photodiode-based sensor for real-time welding process quality monitoring.

Ancona, Antonio; Sibillano, Teresa; Maggipinto, Tommaso; Ottonelli, Fabio; Lugarà, Pietro Mario

2003-12-01

383

Voluminal defects observed in laser spot welding of tantalum  

NASA Astrophysics Data System (ADS)

Significant problems in deep laser spot welding are formation of welding defects, and particularly porosities in the case of tantalum joining. In this study, we investigate and model porosities forming and trapping. Two types of porosity are observed: (1) Small porosities are round shape bubbles of less than 250 micrometer diameter. These defects may come from gas bubbles generated following hydrogen rejection during solidification or they may come from bubbles induced by both an intense evaporation inside the keyhole and a turbulent flow in the molten pool. (2) Large porosities are voids generated in the bottom of the welded zone. They arise from a lack of matter inside the weld as if the molten metal have not had enough time to fill up the keyhole completely before it solidifies. We elaborated a numerical model for the comprehension of little porosities trapping by comparing the calculated spot weld solidification time to the rising time of bubbles in the liquid phase. We also studied the melt flow back into the keyhole in order to explain the formation of the observed large voids. These two models are in good agreement with experimental observations, in particular with X-ray radiographs achieved during the solidification of tantalum spot welds.

Girard, Karen; Jouvard, Jean-Marie; Boquillon, Jean-Pierre; Bouilly, Philippe; Naudy, Ph.

2000-02-01

384

Stochastic modelling of plasma reflection during keyhole arc welding  

NASA Astrophysics Data System (ADS)

Keyhole arc welding (KAW), including the keyhole double-sided arc welding process being developed at the University of Kentucky and keyhole plasma arc welding, can achieve much deeper narrower penetration than all other arc welding processes. If it could be controlled such that the heat input and weld pool are minimized while at the same time the desired full penetration is guaranteed, it could become an effective yet affordable technology to improve productivity in welding thick materials. However, the key in developing such a controlled KAW technology is the sensor which can detect the evolution of the keyhole. Preliminary study shows that the plasma reflection could lead to a practical yet accurate sensor. In this study, the dynamic behaviour of the plasma reflection is described using the reflection arc angle (RAA). It is found that the RAA series can be considered an autoregressive moving-average (ARMA) process. The orders of the ARMA model are determined using auto-correlation and partial auto-correlation functions. The parameters of the ARMA are recursively estimated using the extended least squares algorithm. It is found that the recursive estimates of the model parameters change as the state of the keyhole changes. A discriminator has been proposed to determine the state of the keyhole based on the recursive estimates of the model parameters.

Zhang, Y. M.; Ma, Y.

2001-11-01

385

Monitoring Welding Images And Data Simultaneously  

NASA Technical Reports Server (NTRS)

Video/computer subsystem of welding system produces overlay, on video image, containing numerical data on parameters of welding operation being viewed. Operator watches weld bead simultaneously with instantaneous values of such data as elapsed time, welding current, and processed sensor measurements of weld area. Pertinent weld data always available to viewer and correlated in time with image of weld.

Delcher, Ray C.; Smith, Matthew A.

1991-01-01

386

Use of Metallographic Analysis and Strength Testing to Improve Ultrasonic Phased-Array Evaluation of Resistance SPOT Welds  

Microsoft Academic Search

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

Deborah L. Hopkins

2008-01-01

387

USE OF METALLOGRAPHIC ANALYSIS AND STRENGTH TESTING TO IMPROVE ULTRASONIC PHASED-ARRAY EVALUATION OF RESISTANCE SPOT WELDS  

Microsoft Academic Search

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

Deborah L. Hopkins

2008-01-01

388

The influence of pin geometry on bonding and mechanical properties in friction stir weld 2014 Al alloy  

Microsoft Academic Search

Friction stir tool is the key art of friction stir welding process. The influence of the welding structure and the mechanical properties has been investigated. For this purpose, four different stir pins, two of them are column pin and taper pin and the other two are the same size but with screw thread, were used to carry out a welding

Yan-hua Zhao; San-bao Lin; Lin Wu; Fu-xing Qu

2005-01-01

389

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

390

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.

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

2010-01-01

391

Fine welding with lasers.  

PubMed

The need for micro joining metallic alloys for surgical instruments, implants and advanced medical devices is driving a rapid increase in the implementation of laser welding technology in research, development and volume production. This article discusses the advantages of this welding method and the types of lasers used in the process. PMID:18557404

MacLellan, D

2008-01-01

392

NASA welding assessment program  

NASA Technical Reports Server (NTRS)

A program was conducted to demonstrate the cycle life capability of welded solar cell modules relative to a soldered solar cell module in a simulated low earth orbit thermal environment. A total of five 18-cell welded (parallel gap resistance welding) modules, three 18-cell soldered modules, and eighteen single cell samples were fabricated using 2 x 4 cm silicon solar cells from ASEC, fused silica cover glass from OCLI, silver plated Invar interconnectors, DC 93-500 adhesive, and Kapton-Kevlar-Kapton flexible substrate material. Zero degree pull strength ranged from 2.4 to 5.7 lbs for front welded contacts (40 samples), and 3.5 to 6.2 lbs for back welded contacts (40 samples). Solar cell cross sections show solid state welding on both front and rear contacts. The 18-cell welded modules have a specific power of 124 W/kg and an area power density of 142 W/sq m (both at 28 C). Three welded and one soldered module were thermal cycle tested in a thermal vacuum chamber simulating a low earth orbit thermal environment.

Patterson, R. E.

1985-01-01

393

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

394

Weld Energy Monitor  

SciTech Connect

A weld energy monitor has been developed to measure electrical energy delivered to resistance welds. The monitor combines the measurement of voltage, current, and time into an energy measurement with accuracy traceable to the National Bureau of Standards. This paper discusses this development.

Clayton, J.D.

2002-08-26

395

Welding Over Paint Primer.  

National Technical Information Service (NTIS)

When welding is performed over primer-coated steels such as in the shipbuilding and offshore structures fabrication industry, significant amounts of hydrogen and other gases, e.g., CO and Zn(v) are generated as the welding arc causes the primer to decompo...

D. L. Olson K. S. Johnson S. Liu

1998-01-01

396

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

397

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.

398

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

399

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

400

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

401

Welding Sensor System  

NASA Technical Reports Server (NTRS)

A system originally designed for welding components of the huge Space Shuttle external tank led to a laser-based automated welder for industrial use. A laser sensor tracks the seam where two pieces of metal are to be joined, measures gaps, misfits and automatically corrects welding of torch distance and height. A small industrial computer translates the sensor's information to the weld head and records and displays weld data for control purposes and analysis. The system was modified for commercial use by Marshall Space Flight Center (MSFC), Martin Marietta and Applied Research, Inc., which produces the commercial system. Applications are in industrial welding processes that require repetitive operations and a high degree of reliability.

1993-01-01

402

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

403

Welds in thermoplastic composite materials  

Microsoft Academic Search

Welding methods are reviewed that can be effectively used for joining of thermoplastic composites and continuous-fiber thermoplastics. Attention is given to the use of ultrasonic, vibration, hot-plate, resistance, and induction welding techniques. The welding techniques are shown to provide complementary weld qualities for the range of thermoplastic materials that are of interest to industrial and technological applications.

N. S. Taylor

1990-01-01

404

Welds in thermoplastic composite materials  

NASA Astrophysics Data System (ADS)

Welding methods are reviewed that can be effectively used for joining of thermoplastic composites and continuous-fiber thermoplastics. Attention is given to the use of ultrasonic, vibration, hot-plate, resistance, and induction welding techniques. The welding techniques are shown to provide complementary weld qualities for the range of thermoplastic materials that are of interest to industrial and technological applications.

Taylor, N. S.

405

Single crystals for welding research  

Microsoft Academic Search

Most welds last for many years, but a few fail after a relatively short time. Knowing the reasons why welds fail is important because cracks in welds can threaten the safety of people in buildings, airplanes, ships, automobiles, and power plants. Bad welds can lead to costly, extended shutdowns of industrial facilities such as petroleum refineries. Thus, research on this

S. A. David; L. A. Boatner

1991-01-01

406

Welding Torch Arc Light Reflector.  

National Technical Information Service (NTIS)

A welding torch arc light reflector is disclosed for welding torches having optical viewing systems. A schematic of a welding torch having an internal coaxial viewing system consisting of a lens which focuses the field of view of the weld scene of the wor...

S. S. Gordon

1985-01-01

407

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

408

MODELING of WELDING SEAM SEQUENCES  

Microsoft Academic Search

This paper explores simulation techniques for prognosis residual strains of welded structures taking into account welding seam sequences. Simplified approaches of welding stress and strain theories were used and implemented on SKIF-family supercomputers. The elaborated program options allow to apply the fictitious shrinkage forces to the weld models of arbitrary space location. The results of the experimental computational verification of

Sergey Medvedev; Maria Petrushina; Oleg Tchij

409

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

410

Problems of Welding Dissimilar Metals.  

National Technical Information Service (NTIS)

The article does not exhaust all aspects of the complex problem of welding dissimilar metals. More effort is needed to bring the welding of dissimilar metals to the level of sophistication employed in welding metals of the same type. In welding the majori...

B. E. Paton D. Rabkin V. Ryabov

1972-01-01

411

New England salt marsh pools: A quantitative analysis of geomorphic and geographic features  

USGS Publications Warehouse

New England salt marsh pools provide important wildlife habitat and are the object of on-going salt marsh restoration projects; however, they have not been quantified in terms of their basic geomorphic and geographic traits. An examination of 32 ditched and unditched salt marshes from the Connecticut shore of Long Island Sound to southern Maine, USA, revealed that pools from ditched and unditched marshes had similar average sizes of about 200 m2, averaged 29 cm in depth, and were located about 11 m from the nearest tidal flow. Unditched marshes had 3 times the density (13 pools/ha), 2.5 times the pool coverage (83 m pool/km transect), and 4 times the total pool surface area per hectare (913 m2 pool/ha salt marsh) of ditched sites. Linear regression analysis demonstrated that an increasing density of ditches (m ditch/ha salt marsh) was negatively correlated with pool density and total pool surface area per hectare. Creek density was positively correlated with these variables. Thus, it was not the mere presence of drainage channels that were associated with low numbers of pools, but their type (ditch versus creek) and abundance. Tidal range was not correlated with pool density or total pool surface area, while marsh latitude had only a weak relationship to total pool surface area per hectare. Pools should be incorporated into salt marsh restoration planning, and the parameters quantified here may be used as initial design targets.

Adamowicz, S.C.; Roman, C.T.

2005-01-01

412

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

413

Solar heater for swimming pools  

SciTech Connect

A solar heater for swimming pools is provided having one or more heating panels installable on a roof or the like and arranged to discharge into a pool equipped with an apron without need for disturbing or obstructing the apron. This is accomplished by the provision of an elevated bistable dumper adjacent the perimeter of the apron having a dispensing spout normally inclined upwardly but pivoting at intervals to discharge into the pool across the apron without obstructing it. Water to be heated is diverted from the pool filtering system to the solar heater via a pressure regulator and a solar responsive flow control.

Babcock, H.W.

1984-12-04

414

Novel low-cost vision-sensing technology with controllable of exposal time for welding  

NASA Astrophysics Data System (ADS)

In the process of robot Welding, position of welding seam and welding pool shape is detected by CCD camera for quality control and seam tracking in real-time. It is difficult to always get a clear welding image in some welding methods, such as TIG welding. A novel idea that the exposal time of CCD camera is automatically controlled by arc voltage or arc luminance is proposed to get clear welding image. A set of special device and circuits are added to a common industrial CCD camera in order to flexibly control the CCD to start or close exposal by control of the internal clearing signal of the accumulated charge. Two special vision sensors according to the idea are developed. Their exposal grabbing can be triggered respectively by the arc voltage and the variety of the arc luminance. Two prototypes have been designed and manufactured. Experiments show that they can stably grab clear welding images at appointed moment, which is a basic for the feedback control of automatic welding.

Zhang, Wenzeng; Wang, Bin; Chen, Nian; Cao, Yipeng

2005-02-01

415

Vaccum Gas Tungsten Arc Welding, phase 1. Technical report, October 1993-March 1995  

SciTech Connect

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.

1995-03-01

416

Grinding Parts For Automatic Welding  

NASA Technical Reports Server (NTRS)

Rollers guide grinding tool along prospective welding path. Skatelike fixture holds rotary grinder or file for machining large-diameter rings or ring segments in preparation for welding. Operator grasps handles to push rolling fixture along part. Rollers maintain precise dimensional relationship so grinding wheel cuts precise depth. Fixture-mounted grinder machines surface to quality sufficient for automatic welding; manual welding with attendant variations and distortion not necessary. Developed to enable automatic welding of parts, manual welding of which resulted in weld bead permeated with microscopic fissures.

Burley, Richard K.; Hoult, William S.

1989-01-01

417

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

418

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

419

Parameters controlling microstructure and hardness during friction-stir welding of precipitation-hardenable aluminum alloy 6063  

Microsoft Academic Search

The aluminum (Al) alloys 6063-T5 and T4 were friction-stir welded at different tool rotation speeds (R), and then distributions of the microstructure and hardness were examined in these welds. The maximum temperature of the\\u000a welding thermal cycle rose with increasing R values. The recrystallized grain size of the weld increased exponentially with increasing maximum temperature. The relationship\\u000a between the grain

Yutaka S. Sato; Mitsunori Urata; Hiroyuki Kokawa

2002-01-01

420

Microstructural and mechanical properties of friction-stir-welded and post-heat-treated Inconel 718 alloy  

Microsoft Academic Search

This study was performed to investigate the microstructural and mechanical properties of friction-stir-welded and post-heat-treated Inconel 718 alloy. Friction stir welding (FSW) was performed at a rotation speed of 200rpm and welding speed of 150mm\\/min; heat treatment was performed after welding at 720°C for 8h in vacuum. As a result, the grain size due to FSW was significantly refined from

K. H. Song; K. Nakata

2010-01-01