Multipass Techniques Research Articles

Carbide evolution and its effect on the impact toughness of the 9Cr/CrMoV dissimilar welded joint during the aging treatment

The microstructure evolution in the weld metal (WM) and its effect on the impact toughness for the 9Cr/CrMoV dissimilar welded joint with various aging time was systematically investigated. With the aging time increased from 0 h to 3,000 h, the specimen aged at 470 ℃ for 1,000 h revealed the lowest impact energy (13.5 J). Moreover, the impact fracture morphology details were obtained by scanning electron microscopy (SEM). The results showed that the quasi-cleavage fracture appeared for the specimens in the original and aged (aged at 470 °C for 3,000 h) states, while the cleavage fracture could be observed for the specimen aged at 470 °C for 1,000 h. Besides, the microstructure observation exhibited that the main microstructure in the WMs for the specimens in the original and aged states were all the tempered martensite. The columnar and equiaxed grain zones formed owing to the multi-layer and multi-pass techniques. Based on the characterization analysis of the precipitates for the aged specimens, the coarsening of the carbides was determined as the crucial factors to decrease the impact energy. On the contrary, with the aging time increased, the newly precipitated fine carbides could produce the positive effects on the impact toughness. In the original state, the impact energy of the specimens was about 29.2 J. With the aging time increased to 1,000 h and 3,000 h, the impact energy became 13.5 J and 21.0 J, respectively.

Advanced THz MIMO Sparse Imaging Scheme Using Multipass Synthetic Aperture Focusing and Low-Rank Matrix Completion Techniques

This article proposes an advanced THz multiple-input-multiple-output (MIMO) near-field sparse imaging scheme for target detection that uses single-pass synthetic aperture focusing and multipass interferometric synthetic aperture focusing techniques to improve imaging effectiveness and efficiency. It benefits from the MIMO of the linear sparse periodic array (SPA) and random undersampling sparse imaging to reduce sampling data and system cost. Both simulated and proof-of-concept experimental results have verified the scheme, revealing that the single-pass synthetic aperture imaging approach is sufficient to identify pure metallic targets with 3.87% of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda /2$ </tex-math></inline-formula> sampling data. The multipass interferometric synthetic aperture imaging approach is capable of improving image quality on the image signal-to-noise ratio (SNR) and contrast, which is ideal for detecting more challenging targets. The random sparse imaging with help of the low-rank matrix completion (LRMC) technique has shown the promising potential of achieving equivalent image quality when further reducing 43.75% data in the experiment of five-pass imaging on a complex target; this corresponds to 82.51% data reduction compared to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda /2$ </tex-math></inline-formula> sampling.

Squeezed-Light Enhancement and Backaction Evasion in a High Sensitivity Optically Pumped Magnetometer.

We study the effect of optical polarization squeezing on the performance of a sensitive, quantum-noise-limited optically pumped magnetometer. We use Bell-Bloom (BB) optical pumping to excite a ^{87}Rb vapor containing 8.2×10^{12} atoms/cm^{3} and Faraday rotation to detect spin precession. The sub-pT/sqrt[Hz] sensitivity is limited by spin projection noise (photon shot noise) at low (high) frequencies. Probe polarization squeezing both improves high-frequency sensitivity and increases measurement bandwidth, with no loss of sensitivity at any frequency, a direct demonstration of the evasion of measurement backaction noise. We provide a model for the quantum noise dynamics of the BB magnetometer, including spin projection noise, probe polarization noise, and measurement backaction effects. The theory shows how polarization squeezing reduces optical noise, while measurement backaction due to the accompanying ellipticity antisqueezing is shunted into the unmeasured spin component. The method is compatible with high-density and multipass techniques that reach extreme sensitivity.

Orbital Hybrid Laser-arc Welding Using a High-power Fibre Laser for Pipeline Construction

Recently developed fibre lasers provide multi-kilowatt beam power with high quality at impressive energy efficiency. Combined with gas metal arc welding (GMAW) equipment these lasers can be used in a hybrid process to weld thick-walled constructions single-pass, that are currently welded using multi-pass techniques. The main benefits are a reduction of heat induced distortions, due to the low heat input, as well as savings in filler material and process time. Probable applications can be found in power generation, ship building and pipeline constructions. An orbital (girth) laser-hybrid process using a 20 kW fibre laser and a GMAW torch is currently examined at the BAM, Berlin. The aim of this research is to obtain a stable and crack free girth welding process and to demonstrate its application in pipeline construction. The experiments are carried out on 16 mm thick plates as well pipe rings with 36 (914 mm) pipe diameter of X65. Particular welding parameters, such as welding speed, GMAW power, arc length are varied and their influence on the appearance of the weld in the different welding positions is analyzed. Even though issues remain that demand further research it could already be shown that the rings can be welded using a girth hybrid process that is divided into two half girth processes in downward direction.

Transition and fracture shift behavior in LCF test of dissimilar welded joint at elevated temperature

This work focused on the low-cycle fatigue (LCF) behavior of modified 9Cr/CrMoV dissimilar welded joint at elevated temperature. Narrow gap submerged arc welding (NG-SAW) process via multi-pass and multi-layer techniques was employed to fabricate the welded joint. LCF tests at different strain amplitude range from 0.22% to 0.75% were performed at strain ratio R=−1. The two-slope behavior based on fracture location shift was presented both on the cyclic stress-strain (CSS) curve and Manson-Coffin (M-C) curve, which could be applied to predict the fatigue life more precisely especially at relatively low strain amplitude. The results indicated that the joint failed in CrMoV-base metal (BM) at relatively low strain amplitude below 0.4% while failure shifted to CrMoV-over tempered zone (OTZ) at higher strain amplitude above 0.4%. Fatigue failure occurred in CrMoV-BM at low strain amplitude could be attributed to temperature softening effect in CrMoV-BM combined with cyclic strengthening in CrMoV-OTZ. While CrMoV-OTZ with a comparable number of grain boundaries and much lower hardness than that of CrMoV-BM was deemed to be the weakest zone across the welded joint at higher strain amplitude. EBSD investigations also revealed that CrMoV-BM experienced more fatigue damage at relatively low strain amplitude, while CrMoV-OTZ accumulated more plastic strain at higher strain amplitude.

Study on the microstructure and toughness of dissimilarly welded joints of advanced 9Cr/CrMoV

Abstract

Tree Representation: Knowledge Discovery from Uncertain Data

Most of the real-world data is gathered locally, organized regionally leading to distributed environment. The analysis of such data will assist decision makers for promoting their business. Most of the data mining strategies are multi-pass techniques employed for mining and discovering the knowledge. Hence, the paper focuses on developing two pass data mining constructs to handle uncertain data. One of the simplest and feasible item-pattern representations is transactional tree. The developed methodology for constructing transactional trees is studied in detail and apt technological solutions is proposed. It is proposed to construct transactional tree from uncertain data which is usually associated with existential probabilities and to establish distributed computing environment for developing transactional trees. This paper aims at bringing out the knowledge valid for a given location through which it is expected to derive global knowledge.

Joint Sparsity in SAR Tomography for Urban Mapping

With meter-resolution images delivered by modern synthetic aperture radar (SAR) satellites satellites like TerraSAR-X and TanDEM-X, it is now possible to map urban areas from space in very high level of detail using advanced interferometric techniques such as persistent scatterer interferometry and tomographic SAR inversion (TomoSAR), whereas these multi-pass techniques are based on a great number of images. We aim at precise TomoSAR reconstruction while significantly reducing the required number of images by incorporating building a priori knowledge to the estimation. In the paper, we propose a novel workflow that marries the freely available geographic information systems (GIS) data (i.e., 2-D building footprints) and the joint sparsity concept for TomoSAR inversion. Experiments on bistatic TanDEM-X data stacks demonstrate the great potential of the proposed approach, e.g., highly accurate tomographic reconstruction is achieved using six interferograms only.

Single point and asymmetric incremental forming

This paper presents an update on single point incremental forming (SPIF) of sheet metal since 2005. It includes a description of the process with new information on the maximum forming angle, \(\phi_{ \hbox{max} }\), for 5052-H32. An in-depth example of the successful design and production of parts is given for industry. This includes discussion on production times and surface roughness with details that will help designers. A general design guide for users of SPIF is provided. It is based upon experience gained in the last decade. In general, materials show a trend of decreasing formability with increasing initial thickness. It is shown that for thicker sheet metal, it is recommended using large spherical tools (12.7 mm or larger), or a large flat-ended tool. The flat-ended tool provides the best combination of good formability and very low surface roughness. For aluminum, galvanized steel and stainless steel, it is recommended using a flat-ended tool. Advances in multi-pass techniques and information on successful and useful numerical models which predict forming behaviour are included. Finally, there is a discussion on future work needed in SPIF.

Process-parameter interactions in ultra-narrow gap laser welding of high strength steels

S960 and S700 are two new high strength steels recently developed by Tata Steel, UK. Due to the high power densities that can be achieved, small component distortion, and fast welding speeds, laser welding of thick section steels has been widely used in offshore construction and shipbuilding. However, the penetration depth is typically limited in single pass welding to 1–2 mm/kW laser power. Melt sagging is a typical defect for single pass autogenous laser welding of thick section materials. Multi-pass narrow gap laser welding techniques become more attractive because they can weld thicker sections of material with a moderate laser power and suppress the melt sagging problem. In addition, this approach requires less filler material, and the cumulative heat input to the material is reduced when compared with traditional arc welding techniques. However, there are many variables involved in this narrow gap laser welding technique, which makes this process more complicated than single pass autogenous laser welding. In this study, the effects of multi-pass ultra-narrow gap laser welding parameter interactions (i.e. laser power, welding speed and wire feed rate) on laser weld quality and the welding efficiency for S960 high strength steel plates were investigated. Moderate laser powers of 1 to 2 kW were used to weld S960 high strength steel plates with a very narrow parallel groove (1.2 mm). Statistical design of experiments was carried out to assess the process parameter interactions and to optimise the ultra-narrow gap laser welding parameters. Validation experiments indicate that the proposed models predict the responses adequately within the range of welding parameters that were used. Defect-free welds in 6 mm thick S960 steel were obtained with only two passes, using the optimised welding parameters, and these optimised parameters were successfully transferred to the welding of 8 mm thick S960 steel. In addition, they were also successfully transferred to the welding of 13 mm thick S700 steel with a small modification. The optimised narrow gap laser welded joints show almost the same tensile properties as the base material, with failures occurring in the base material away from the weld.

High spatial resolution laser cavity extinction and laser-induced incandescence in low-soot-producing flames

Abstract Accurate measurement techniques for in situ determination of soot are necessary to understand and monitor the process of soot particle production. One of these techniques is line-of-sight extinction, which is a fast, low-cost and quantitative method to investigate the soot volume fraction in flames. However, the extinction-based technique suffers from relatively high measurement uncertainty due to low signal-to-noise ratio, as the single-pass attenuation of the laser beam intensity is often insufficient. Multi-pass techniques can increase the sensitivity, but may suffer from low spatial resolution. To overcome this problem, we have developed a high spatial resolution laser cavity extinction technique to measure the soot volume fraction from low-soot-producing flames. A laser beam cavity is realised by placing two partially reflective concave mirrors on either side of the laminar diffusion flame under investigation. This configuration makes the beam convergent inside the cavity, allowing a spatial resolution within 200 μm, whilst increasing the absorption by an order of magnitude. Three different hydrocarbon fuels are tested: methane, propane and ethylene. The measurements of soot distribution across the flame show good agreement with results using laser-induced incandescence (LII) in the range from around 20 ppb to 15 ppm.

Distortion Analysis on Multipassed Butt Weld Using FEM and Experimental Study

This paper investigates the simulation technique for analyzing the distortion behavior induced by welding process on welded plate which was clamped on one side. This clamping method is intended to enable the investigation of the maximum distortion on the other side. FEA software SYSWELD was employed to predict multipassed butt weld distortion of low carbon steel with thicknesses of 6 mm and 9 mm. The simulation begins with the development of model geometry and meshing type followed by suitable selection of heat source model represented by the Goldak’s double ellipsoid model. Other parameters such as travel speed, heat input, clamping method etc. were determined. The model is dedicated for multipass welding techniques using Gas Metal Arc Welding (GMAW). The experimental works were conducted by using Robotic welding process.

Data maximization by multipass analysis of protein mass spectra

With the proliferation of search engines for the analysis of MS data, multisearch techniques aimed at boosting the discriminating power of the search engines' score functions have recently become popular. Much statistical and algorithmic work has been done, therefore, in order to be able to combine and parse multiple search streams. However, multisearch techniques suffer from long run times, and may have little impact on false negatives because of similar peptide filtering heuristics between searches. This review focuses, rather, on multipass techniques, which use the results of one search to guide the selection of spectra, parameters and sequences in subsequent searches. This reduces the number of false-negative peptide identifications due to peptide candidate filtering while preserving statistical significance of existing (correct) identifications. Furthermore, this technique avoids substantial increases in running time and, by limiting the search space, does not reduce the statistical significance of correct identifications or introduce a statistically significant number of false-positive identifications. However, we argue that the existing combiner tools are not reliably applicable to these multipass situations, because of algorithmic assumptions about search space and statistical assumptions about the rate of true positives. Here we provide an overview of the advantages of and issues in multipass analysis techniques, the existing methods and workflows available to proteomic researchers, and the unsolved statistical and algorithmic issues amenable to future research.

DEM by Ground-Based SAR Interferometry

In this letter, a ground-based synthetic aperture radar (SAR) interferometer was used to generate digital elevation maps (DEMs) of the illuminated area. With respect to other ground-based data processing techniques, here, the effect of the propagation through the atmosphere is considered. An algorithm similar to multipass satellite SAR techniques was developed in accordance with the phase model used in the ground-based interferometry. Many images taken from different viewing angles were collected and combined to form different interferograms at a test site in Austria. Results from this technique have been compared with an existing geographic model of the test area.

ENEA Activities in the Field of Laser Spectroscopic Techniques for Environmental Trace Analysis with Perspectives of Applications to Nuclear Safeguards

The ENEA (Italian National Agency for New Technologies, Energy and the Environment) laser spectroscopic activities carried on at the Laser Application Section of the Frascati Research Center are presented with main emphasis given to the additional capabilities of environmental monitoring of hidden nuclear activities or possible nuclear disasters. High resolution linear spectroscopies based on photo-acoustic or multipass detection techniques, together with nonlinear in-situ and remote sensing stand-off instruments are reviewed. The current results have been presented upon invitation at the IAEA Safeguards Technical Meeting [1].

Coincident wire and powder deposition by laser to form compositionally graded material

In this paper a new surface coating technique is reported. The method combines powder and wire feed laser cladding to produce a functionally graded material in a single pass. The technique is demonstrated and material distributions in the clads are investigated using H13 tool steel as a substrate, copper powder and nickel wire as feedstock and a 1.5 kW diode laser as a power source. Electron probe microanalysis, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction and optical microscopy were used to analyse deposited clads in terms of elemental composition, microstructure and flow characteristics in the deposition melt pool. It was found that by varying the feed rates of copper powder and nickel wire, the composition gradients within a layer and overall clad properties could be controlled, avoiding the need for multipass techniques.

The effects of pulse dye laser double‐pass treatment intervals on depth of vessel coagulation

Multi-pass treatments with pulse dye lasers (PDLs) are avoided due to perceived side effects. Proper multi-pass techniques allow for deeper vascular injury. New extended PDLs allow use of multi-pass procedures. This study evaluates how the time between pulses, inter-pulse interval [IPI] affect extent of vascular treatment. Sixteen subjects were exposed to a series of exposures on normal skin to determine depth of injury for various IPI. Subjects were exposed to single pass, and 4 double-pass intervals. Tests included exposures at 0.5 milliseconds, 2-7 j/cm(2). Exposures included one and two passes, IPI of 1, 10, 30, and 60 seconds; 5 and 30 minutes. Treatments were done with PhotoGenica V-Star (595-nm), SmartCool air cooling. Biopsies were taken: single pass and double pass purpuric thresholds; and at 7 j/cm(2) to determine depth of vascular coagulation. Histology revealed increased vascular coagulation depth at purpura threshold for intervals of 1, 10, 30, and 60 seconds between passes compared to single pass treatment, and a significant monotonic increase in depth of vascular injury at 7 j/cm(2) with increasing IPI. The use of multiple passes increases depth of vascular injury, which may increase the efficacy of treatment without significant increase in purpura or risk of scarring for treatments at purpura threshold. At purpura threshold, the depth of vascular injury increases with increasing IPI up to 60 seconds. Above purpura threshold, there is a monotonic increase in depth of vascular injury for IPI up to 30 minutes. These observations suggest multi-pass treatment methods may be beneficial when employed with PDLs.

Henry Granjon Prize Competition 2005 Winner, Category A “Joining and fabrication technology” Novel Ways of Using Nd:YAG Laser for Welding Thick Section Austenitic Stainless Steel

Hybrid welding has been introduced as a process that combines one laser and one arc welding process to work together. These advanced joining processes are effective and outweigh several drawbacks of mere single methods. Hot spots, made by laser to the joint, have been reported to stabilise the arc and change the way of material transfer in the arc. The arc is also attracted and constricted by the hot spot. This phenomenon has been utilised in this study in order to get the process adaptable inside very narrow grooves. This novel approach, combined with multipass techniques, enables a considerable increase in the thickness of the parts to be welded. Welding continues to employ rather low total heat input levels and, consequently, results in very low thermal distortions in joining thick sections. As the process retains a keyhole typical of high energy density welding, the process is also very effective for joining thick sections. Based on the above argument, the process further developed in this study should be considered when evaluating welding processes for joining vacuum vessel sectors of ITER. The same certainly applies to many other demanding thick sections and hence heavy high precision components.

P-59: Thin-beam Crystallization Method for Fabrication of LTPS

Thin film transistors fabricated using Low Temperature Polycrystalline Silicon (LTPS) have several well-known advantages over those made with amorphous Silicon: higher electron mobility, smaller size, higher speed. However, LTPS has not been widely adopted due to the relatively high cost and low yield of the process relative to a-Si. We have investigated a laser annealing process that offers an improvement for both throughput and yield when compared to existing processes. The process uses a very narrow laser beam (∼5 microns) at high repetition rates to create large poly-Si crystals via lateral growth. The beam length is long enough to allow the substrate to be scanned in a single pass, resulting in better uniformity without any seams seen in multi-pass techniques. In this presentation, we will present results from a prototype system used to validate the critical elements of the process.

Spectroscopy of Matrices and Thin Films with an Integrating Sphere

The paper describes a novel experimental approach to improving sensitivity to weak absorption in matrix isolation and thin film spectroscopy. The matrix or film is grown on the surface of an integrating sphere, in which the multiply reflected light correspondingly multipasses the sample film. The quantitative photometric behavior of the sphere is satisfactorily described by extending standard theory. Enhancement of absorption by a factor of at least 20 is possible and is demonstrated. The sphere has a number of useful advantages over other multipass techniques, particularly in matrix isolation spectroscopy.