Core research programme 2007 - 2009:
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Technical area |
Sector |
The objectives of the work to be carried out within the scope of this proposal are to:
It is proposed to extend the library of elastic-plastic finite element (FE) analysis for determining crack driving forces (J, CTOD) for surface flaws as functions of applied strain to include the effects of weld-parent strength mismatch and residual stress. Selected combinations of pipe sizes (diameter and thickness), loading types (axial tension, bending, internal pressure), flaw sizes and aspect ratios, and tensile properties will be investigated. The crack driving force solutions will be analysed and parametric equations and curves will be derived so intermediate values can be obtained.
In parallel, the project will also examine alternative ways in which the FAD based procedures in BS7910 can be modified for assessments at high strains. This may include modifying the fracture parameters to be strain based. Current links with work by British Energy will be maintained.
The work will provide guidance on estimation of fracture toughness (critical CTOD and J) for assessment of flaws in pipe welds at large strains (referred to as structural fracture toughness). It is well known that fracture toughness is geometry (or constraint) dependent. Full scale testing is the definitive method for obtaining structural fracture toughness, but is usually impracticable.
As an alternative to structural fracture testing, it is proposed that local approaches be used to estimate structural fracture toughness from conventional specimen data. Several local approaches will be considered including the cohesive zone model, GTN model and critical strain model. Because of its complexity, the aim will be to demonstrate the predictive capabilities of these local approaches. It will, therefore, focus on 2D and axi-symmetrical specimens, components and structures, but will include plain pipe material as well as girth welds. This task should provide enough information for an evaluation of the suitability of these local approaches for future applications.
A framework for an ECA procedure at large strains will be established on the basis of fracture mechanics principles and limit state design. These will include ductile tearing initiation, instability of ductile tearing, plastic collapse, and fracture.
It is envisaged that there will be a third phase of this project that will start July 2008. An indicative budget for this phase is given below. While the scope cannot be defined until Phase 2 is complete, it is anticipated that it will involve validation of the new procedure including some further pipe testing.
Oil and Gas
A state-of-the-art ECA procedure to meet specific needs of the oil and gas and other industries industry for the design, fabrication and in-service assessment of flaws in pipe girth welds subject to axial straining.
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The aim of this project will be to prepare a system design and business case for the introduction of computer-based weld distortion prediction and control in a manufacturing company, and hence to pioneer the widespread use of this technology as an integral part of the design and manufacturing process, with particular reference to transport applications.
This work will concentrate on the validation and improvement of numerical models for predicting distortion for selected application, on management systems for the implementation of weld distortion prediction and control in industry, and on the cost benefits of using distortion prediction technology. Weld modelling will be performed at TWI using FEA'S servers and software.
Aerospace, Rail and Shipbuilding
Limitations in the use of weld distortion prediction technology in industry are currently associated with lengthy solution times, high cost (high price of software), complexity of user interface and doubts over the accuracy of the results. The proposed project will address these issues which are the main barriers to the future growth of this much-needed technology. It is anticipated that in the first instance TWI will receive income for carrying out distortion prediction work for its Members. There will also be scope to help members set-up their own in-house methods for distortion prediction. Finally, methods for converting the methods developed in the project into software products will be investigated.
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The focus for 2007-2008 will be the experimental investigation of material behaviour during the early stages of environment assisted cracking. Tests will be carried out to determine data for a chosen material-environment system, as described within the review published in June 2007. Experimental data will be analysed to determine whether proposed assessment methodologies accurately describe the observed behaviour.
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The project will initially identify problem areas and where existing testing and assessment methods are inadequate. It is proposed that results of the Phase 1 review are published and recommendations discussed with members. The next phase will involve the development of testing and evaluation procedures on selected materials so that recommendations can be made for improving current procedures. Separate funding will be sought at this stage.
The review will provide a clear statement of the limitation of current testing and fitness-for-service assessment pipelines and dissimilar metal joints. It will identify the ways in which the problems can be addressed and eventually avoid expensive subsea failures.
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This proposal is for work to develop and apply welding residual stress prediction and measurement methods. Initially, the work will concentrate on girth welds in pipes.
User friendly methods of computer prediction will be developed for use in a design environment for fatigue and fracture assessments. Faster computers and advanced programming languages now permit more efficient modelling. The effect on reducing welding residual stresses of including in-service loads and crack growth will be investigated.
The project will make a comparative study of different residual stress measurement techniques to develop the state of the art and to validate the numerical models. Axial and hoop residual stresses will be measured and compared to the modelling results. The techniques would be surface and through thickness measurement.
As well as centre hole drilling and layer removal techniques, which already available for TWI, other through thickness measurements such as ring core may be considered. Non- destructive measurement will also be considered by applying for use of the ENGIN-X instrument at the ISIS facility located at the Rutherford Appleton Laboratory at Oxford, UK. The residual stress measurement method in this project will be chosen based on geometry and scale (length) of residual stress field and measurement cost.
Oil and Gas, Nuclear.
There are numerous engineering calculations conducted every year for the Oil and Gas industry in which the unknown residual stresses make the difference between go and no go, so the potential savings are significant (easily £500k pa). Similarly, TWI was recently involved in a safety critical application where predicted residual stresses were used to justify continued operation of plant.
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Welded joints of the same geometry but with different section thickness for which there are fatigue test data will be analysed using finite element analysis to determine the structural hot-spot stress by through wall integration. The results of the fatigue tests will be converted into SHS versus cycles. The data will be plotted and the variability of the curves for different thickness observed.
A multi-variable regression-based method will be applied to generate correction factors to account for the effects of thickness. The result will be a Master or Reference SHS-N curve for the joint which, when multiplied by a function F(t,N), allows for the thickness effect over the cycle range, where t is the thickness. The approach will be applied to joints of different geometry and other variables are the same, where suitable test data exist. It is hoped that a single function F(t,N) can be derived.
Oil and Gas, Construction, Power.
Welded structures in all industries are being withdrawn from service or reassessed unnecessarily on the grounds of current design calculations of fatigue life, when in fact there is adequate fatigue life left. Improvements in design methods will allow such structures to continue to operate for longer, thereby saving industry considerable costs. Revised fatigue guidance may result in new structures being allowed to operate at higher stresses to achieve a certain fatigue design life than would otherwise have been the case. There are significant technical and economic benefits to Members from this work.
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Finite element analysis has been shown to be a valuable tool in understanding the propagation of guided waves in pipes. In the first phase of the project it is proposed that finite element analysis is used to understand and develop new excitation and signal processing techniques for both defect sizing and inspection beyond features such as pipe bends. In the second phase, new test loops (with various dimensions) will be designed and constructed. These loops (made of several pipes) will have artificial flaws and corrosion. At this stage, suitable types of ultrasonic transduction techniques will also be studied. This will include an assessment of flexible piezo-composite transducers, which are lighter and more efficient in terms of transmission of energy from the transducer onto the pipe.
In third phase of the project, experimental trials will be conducted to validate the models and quantify the effectiveness of the new techniques. In phase four the results of the experimental trials will be used in combination with further finite element analysis to refine the techniques.
Oil and Gas, Chemical and Power.
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Stage 1
Use ultrasonic models to establish the optimum probe specifications for the supplied weld test pieces. The intended test blocks are ferritic with Inconel welds based upon the power industry steam line pipes. Using this data obtain and purchase
the appropriate ultrasonic probes. It is intended to use the TWI owned CIVA beam and defect interaction ultrasonic modelling software for this stage. This model can provide accurate simulation dissimilar metal weld conditions and their interaction
with complex ultrasonic beams.
Stage 2
Generate the appropriate time delay curves for the inspection probes and test these probes on a conventional test block to establish their optimum operating parameters.
Stage 3
Inspect the supplied test blocks with conventional best practice ultrasonic probes to establish the base line capability for detection and sizing of the implanted defects. Inspect the same test blocks with the new techniques and probes and again
establish the defect detection and sizing capability for these probes.
Power, Oil and Gas, Nuclear and Construction.
This project will provide detailed knowledge of the use of phased array TRL probes, self tandem and swept focused TOFD for the inspection of transition welds. Because industry is working with more complex structures and in harsher environmental conditions these transition welds are now commonplace in most heavy industries. Because the inspection quality is currently restricted due to poor signal to noise capabilities of conventional NDT the inspection regimes the construction and inspection is expensive. By providing better signal to noise and defect sizing capability inspection regimes can be lengthen and generous engineering to compensate for poor inspection large cost savings can be achieved.
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The project will first identify the applications areas where pulsed eddy current is a more appropriate technique to use than other proprietary systems (such as rapid ultrasonic scanning, digital radiography and guided waves). The development of the technique will then be targeted at these areas (for example small diameter pipes and welds). The prototype pulsed eddy current system developed in the Pipescan project will be used.
A range of test samples will be acquired or manufactured and the technique optimised for the application. New sensor types such as fluxgate magnetometers will be used to enhance the performance of the technique, and advanced signal processing methods will also be tried. A range of sensor arrays for different pipe diameters will be manufactured. The inspection of large areas, possibly by automated application, will be considered.
In addition, a liaison with Huddersfield University will be maintained. They are currently developing mathematical models of the pulsed eddy current technique for corrosion under insulation and these could be helpful in this project. This will add useful gearing to the project.
Oil and Gas, Power, Process and Chemicals.
The technical benefit is a new NDT technique for difficult-to-inspect areas.
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The objective of this project is to establish the capabilities of CT for the detection and sizing of defects within various complex components through the use of the two advanced CT systems based at TWI Wales; a low- energy system for small components, and a high-energy system for larger components. Several case studies will be produced that concentrate on applications for the microelectronic, automotive and aerospace industry sectors. A variety of components will be inspected that may include integrated circuits, sensors, cables, glow plugs, turbine blades, welds and castings. In particular, the ability of CT to improve on traditional 2D radiography and other NDT techniques to accurately measure defect dimensions in different planes and thus gain a better understanding of the effects of defects on the structural integrity of components will be explored.
Stage 1
A variety of samples will be acquired and/or produced that will include industry representatives from the microelectronics, automotive and aerospace sectors. This will require work with other TWI departments and will involve the relevant
industry groups.
Stage 2
Validated CT of microelectronic components, such as integrated circuits, cables and sensors, will be carried out using the low-energy CT system.
Stage 3
Validated CT of automotive components, such as spark plugs and welds and will be carried out using a combination of the low-energy and high-energy CT systems.
Stage 4
Validated CT of aerospace components, such as turbine blades, castings and welds, will be carried out using the high-energy CT system.
Stage 5
Several case studies relevant to each industry sector will be produced in a final report that will highlight the capabilities of CT for detection and sizing of defects within various industry representative samples. It will also include relevant
procedures, standards and publications produced during the project.
This project will concentrate on the Microelectronics, Aerospace and Automotive industry sectors. However, the results of this project will be relevant to all industry sectors.
This project will promote the use of CT over other less quantitative NDT methods used in the targeted industries. As CT systems and experts are rare, this project will increase business opportunities for TWI Wales with TWI members, re-enforcing the 'centre of excellence' for NDT. It is predicted that, as a direct result of this project, an income of £500k per year will be generated.
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Oil and Gas, Power, Aerospace.
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Stage 1
A theoretical investigation will be carried out to quantitatively analyse the effect of a defect on the surface strain profile of a component under generic circumstances. This involves certain simplifications on the mechanical and geometrical
conditions.
Stage 2
Generating FE mesh models representing typical structures/components. They will comprise of several layers with different materials, including a thin layer representing glue-like material that can be used to simulate different types of defect
such as dis-bond, void, crack etc.
Stage 3
A series of FEM simulations will be conducted by (1) introducing artificially a defect with varying types, locations, sizes; and (2) applying different geometric and stress boundary conditions or loading to simulate possible physical loading
means such as vacuum chamber, thermo-shock or heating, mechanically point pressing, compressing, bending etc. In the meantime, certain experimental tests will be performed to verify the theoretical and FEM simulation results. In addition, results of
shearography and thermography can be used for cross verification.
Stage 4
Through these systematic works, detailed capabilities of defect detection for shearography, thermography will be established in terms of the type, location and size of defect, the optimal means and magnitude of stressing the component, the
optimal operational procedure of carrying out NDT inspection for all relevant optical/thermal techniques.
Oil, Gas and Chemicals, Power, Aerospace, Automobile, Electronics and Sensors, Construction and Engineering.
This project will provide detailed defect detection capabilities of certain NDT techniques (shearography, thermography etc) and the corresponding optimal operation procedures for them being applied to all relevant industrial sectors. These in turn would help carrying out NDT inspections effectively in industries with the benefits of reducing failure costs and enhancing the reliability and safety of in-service structures/components.
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Oil and Gas, Power.
Failure of such critical joints can have severe safety, environmental and economic consequences. A better understanding of the failure mode(s) and development of methods for proving fitness-for-purpose will mitigate the risks. This will be of benefit for subsea, refinery, chemical processing and power generation applications.
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Oil and Gas, Power.
An improved fundamental understanding of sustained load strain development and associated failure modes should ultimately reduce the incidence of high strength CRA failures, saving millions of pounds in lost revenue and improving the safe operation of subsea systems.
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Industrially relevant classes of materials will be selected. These are likely to include: aluminium alloys (including mixtures) as alternatives to cadmium plating, copper alloys suitable as lead-free bearing linings and iron and nickel alloys for corrosion resistant layers. Procedures will be developed for the deposition of these materials, and the role of key process variables on the deposit microstructure and properties determined. Key variables include powder size and microstructure, process gas type (helium/nitrogen), working gas pressure, gas pre-heating and spraying distance. These will be varied and different deposit microstructures produced. In addition, each material will be deposited on to different, but industrial relevant substrate types, including polymer composites if appropriate.
The deposit microstructures will be characterised using light and electron microscopy and micro analysis to determine particle deformation, porosity, oxide level (if any), grain structure and nature of both the inter-particle and deposit-to-substrate interfaces. Attempts will also be made to measure the bond strength between the deposit to the substrate cohesive strength within the deposit and residual stress. If appropriate, limited wear and corrosion testing will be undertaken on selected cold sprayed coatings to establish indications of performance, benchmarked against coatings deposited by alternative processes.
All industry sectors have the potential to use cold spray metal deposition, but those of particular relevance are aerospace, automotive, electronics and medical devices.
The successful implementation of this project would broaden the potential use of cold spray deposition in industry. This project aims to provide data on cold sprayed deposits of industrially relevant materials. The specific benefits are:
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Exposure to nitrous gases will be measured in simulations and in workplace situations. In simulations, activities will be performed under controlled conditions that would be difficult to achieve in the workplace. For example draughts will be excluded by performing the work in an enclosure. The size of the enclosure, duty cycle, orientation of the operator to the work, process and process parameters will all be controlled, allowing the effect of selected parameters on exposure to be evaluated systematically.
Work places where on-site sampling may be carried out will be identified. As far as possible, different fabrication sites and work locations e.g. shipbuilding, pressure vessels, open workshop, enclosed space etc will be selected and exposure measurements performed. It will not be possible to exercise control over all parameters, as in laboratory simulations, because the parameters will be determined by production requirements. However, 'true' exposure measurements will be made to record the range of exposures occurring in real working situations. Given the relationships between various parameters and exposure developed in simulations, it is expected that it will be possible to extrapolate 'true' exposure measurements to provide values that would be obtained if the work situation were slightly different.
The efficacy of local exhaust ventilation in controlling exposure to appropriate levels will be investigated and the availability of RPE to remove nitrous gases will be investigated.
The results will be recorded by process, activity, location etc and any control requirements noted. The results will be used for risk assessment and in assessing the costs of implementing control procedures.
The work is relevant to the entire fabrication industry.
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Welds in 316L austenitic stainless steel and alloy 825 made with and without argon back purging will be obtained. Samples from the welds will be tested in the as-welded and pickled conditions, and compared with parent steel samples. Pitting temperatures will be obtained for each condition in environments selected to be representative of typical oil and gas industry service, ie deoxygenated brine acidified with CO 2 and possibly H 2 S, although there are difficulties associated with the presence of H 2 S, which masks the electrochemical response of the sample. This is being addressed in GSP 15944 and if methods for inclusion of this are developed, it will be included in this project. For comparison, pitting potentials at room temperature will be established. The effect of early service exposure on the surface oxide and subsequent pitting resistance will be established via testing of samples that have been 'pre-conditioned'.
After test, the samples will be examined by scanning electron microscopy and metallographic sectioning to establish the nature and location of the pits developed.
Oil and Gas.
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The selected welding processes are electron beam welding and narrow gap submerged arc welding. The work will determine if these processes offer improved weldment long-term creep performance, ie improved resistance to type IV creep cracking, due to reduced over-tempering to which parts of the HAZ are subjected. In the remaining 18months of this programme, the long-term weldment creep rupture behaviour will be investigated in cross-weld specimens.
Power.
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Aerospace, Power.
Utilisation of lower cost materials will enable saving of millions of pounds in the aerospace sector and provide a competitive advantage to TWI members. Higher performance materials could yield greater long-term savings due to increased life or justify higher material costs.
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Year 1
Year 2
Year 3
Aerospace, Construction and Engineering, Electronics and Sensors, Equipment, Consumables and Materials, Oil and Gas, Power, Road Transport.
All industry sectors will be affected by this legislation, as all use EuP.
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Vision system development
Improvements to the existing vision system capability will be sought through an investigation of the following:
This task will be carried out by the University of Liverpool with support from TWI. Process parameter monitoring and integration High-speed data acquisition systems will be investigated for the monitoring and recording of arc welding parameters. The possibility of integrating arc parameter data with weld pool/metal transfer images will be investigated.
Vision system application
The capability of the vision system for determination of weld pool dimensions will be evaluated. In particular its capacity to determine weld pool width for different process techniques and materials will be assessed. This information can then be used for process control.
The potential for the vision system for developing improved process understanding will be assessed. For example, advances in process control for MIG/MAG welding and fume emission in arc welding are candidate studies.
Aerospace, Automotive, Defence, Heavy Construction, Light Manufacture, Oil and Gas, Power Generation, Nuclear, Shipbuilding.
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The programme of work will investigate the following process techniques.
Advanced MIG and TIG Welding
Improved process control has been achieved for short circuit metal transfer MAG welding. Several commercial equipments are available which utilise either electronic control of the current waveform and/or the use of reciprocating wire feed to achieve more precise control of the metal transfer characteristics. These commercial equipment developments include 'Surface Tension Transfer', 'Cold Metal Transfer', etc. The net benefits include reduced heat input, minimal spatter and more reliable weld fusion characteristics, particularly for thin material. The TOPTIGTM process, which involves feeding the filler wire vertically and directly into the TIG arc, claims to achieve welding speeds close to that possible with the MAG process. The alternative welding process equipments will be evaluated in order to provide guidelines on their effective exploitation.
Novel Process Techniques
The following novel approaches will be investigated:
Aerospace, Automotive, Defence, Heavy Construction. Light Manufacture, Oil and Gas, Power Generation, Nuclear, Shipbuilding.
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TWI will work closely with a welding consumable supplier to develop tubular flux cored wires with improved welding characteristics. The aim will be to produce weld deposits which meet the requirements of *AWS D3.6M Class B. The consumable development programme will investigate the following:
Initial consumable evaluation will be carried out as weld bead on plate trials in the flat and vertical positions. Subsequently using the most promising filler wires, welding procedures will be developed for fillet and butt joints in up to 20mm thick C-Mn steel plate, in both the flat and vertical positions. The test welds will be assessed in accordance with AWS D3.6M Class B.
Oil and Gas, Shipbuilding/repair.
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Welding trials will be carried out on 5083 aluminium and S275 grade C-Mn steel, both commonly used in structural applications. Material thicknesses between 2 and 10mm will be assessed. Laser sources with beam qualities ranging from 25mm.mrad (e.g. lamp-pumped Nd:YAG) down to 2mm.mrad (e.g. latest 5kW Yb-fibre laser) will be used in combination with focussing systems producing spot sizes between 0.1 and 0.6mm in diameter and beam brightnesses ranging from those with Nd:YAG laser and electron beam. TWI's Nd:YAG (25mm.mrad) and Yb-fibre (18mm.mrad) laser will be used and, as well as higher beam quality/brightness systems installed elsewhere in Europe at other research institutes and/or laser manufacturers. It is important that welding with the different lasers is carried out under identical conditions, including power at workpiece, material preparation, clamping (heat sink) and shielding.
Initial welding trials will aim at confirming initial findings with respect to the influence of spot size, beam quality and brightness on welding performance when welding with 4kW of laser power. Lasers and focussing systems will be chosen to provide additional data points, thereby strengthening the confidence in the trend lines observed for spot size and brightness on welding performance (welding speed and depth of penetration) in the initial study (1). Subject to availability of the laser and focussing systems, this will be repeated at a workpiece power of 6kW to verify the trends and compare with 4kW. A limited gain in depth of penetration was observed from this initial study when welding with a smaller Yb-fibre laser spot size, below speeds of 7.5m/min. Possible reasons for this include the presence of a plasma above the weld pool (not normally observed for this wavelength at lower power densities), the misalignment of the keyhole front wall with the incident laser beam (linked to the inclination of the plasma/plume above the weld pool) or convection of the air above the weld pool. All three of these change the absorption of the incident laser beam into the material, impacting on keyhole behaviour, performance (speed/penetration) and weld quality. This will be investigated through the use of an IR camera (thermal convection), spectrometer (plume or plasma) and high-speed camera (plume/plasma and keyhole behaviour).
All sectors which use high-power lasers for keyhole welding, including Automotive; Aerospace; Oil, Gas and Chemicals; Power Generation; Construction and Engineering.
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As a fundamental study this work would concentrate on butt joints in materials up to 10mm in thickness. A real industrial driver for the work is for the laser welding of titanium alloy. Because of the relative expense of this material it is proposed to work also with aluminium alloy. Other materials such as nickel and magnesium will only be introduced into the programme depending on progress with the other alloys and availability of material. Due to a general move in industrial laser welding, to the use of fibre delivered laser beams, it is proposed to work only with this type of laser beam. One of the experimental variables in the tests would be the beam quality of the laser used, and the focussed spot size used for welding. TWI has recently found that in some circumstances, use of a directed gas jet, to blow away the 'plume' of metallic vapour emerging from the laser keyhole, has had a significant positive influence on porosity formation. However, critical parameters in this process have not been fully quantified and the mechanisms by which this effect can reduce porosity are not understood. Further work on understanding the effects of directed gas jets will be conducted. It would be hoped to use high speed video of the keyhole and weldpool, to observe both keyhole and weldpool stability during welding. It is also possible that, because of the different power densities which might be employed using fibre delivered laser beams, that the non-ionised plumes, found at modest power densities become plasmas at higher power density. If so this would have a considerable effect on the choice of optimum 'shielding' gas used. Spectroscopy measurements would be useful to determine if plasma is generated by the welding process. Other aspects considered to effect weld porosity, such as welding speed, weld profile, humidity material surface properties would also be investigated. Analytical tools such as radiography, sectioning and possibly pore gas analysis would be used to evaluate the welds produced This would lead to a series of 'best practice' recommendations for consistent achievement of weld quality.
Aerospace, Automotive, Transport, Power Generation.
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This project would identify a small number of industrially relevant materials, likely to be types of tool steel and types of Inconel or titanium alloys. Previous work carried out in the CRP, and other accessible programmes such as Laser Advanced Manufacturing, have developed procedures for the laser deposition of a range of materials, as well as some procedures for the generation of functionally graded parts. These procedures will be used and altered to produce specimens with several different microstructures per material. Key variables, such as heat input, will be varied and different microstructures produced. These properties will then be compared to wrought material.
These procedures will then be used to deposit blocks, or cylinders, that will be machined into specimens for testing and evaluation. Mechanical testing, such as tensile, fatigue, shear, impact and other regimes, including residual stress analysis and creep resistance, will then be conducted to establish the performance of the deposited material. Control specimens, machined from wrought material, will also be tested and the results from the laser deposition work will be compared to these results.
The main objective of the modelling part of the work would be to develop a model of laser direct metal deposition, that predicts the quality of the deposited material, founded on a fundamental, physics based model of the process. A combination of thermo-fluid flow, dynamic impact and thermal stress analyses will be used to predict the particle speeds at impact, the shape of the impacted particles and the underlying residual stresses. The work will be combined with the Engineering Critical Analysis (ECA) methods used by TWI to predict the strength of deposited material. The thermo-fluid modelling will be undertaken with the Computational Fluid Dynamics (CFD) program, CFX, that is currently being used by TWI for modelling of supersonic flows, particle behaviour in blast nozzles and for modelling of material flow during FSW. The predicted particle velocities will then be passed to the Finite Element Analysis software ABAQUS. TWI presently uses ABAQUS for impact and dynamic loading modelling. ABAQUS will also be used to predict the heat flow in the underlying component and hence ultimately to predict the thermal stresses and residual stresses in the deposited layers. The combined set of modelling methods will therefore predict defect development and loading.
All industry sectors have the potential to use laser direct metal deposition, but those of particular relevance would be Aerospace, and Power Generation.
The successful implementation of this project could result in a step change in the confidence in the laser deposition technique. This project aims to provide such a link for several materials and also develop a modelling capability in this area, whilst providing valuable mechanical data for laser deposited material. The specific benefits are:
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A range of common materials, including structural steel, stainless steel, and aluminium in various thicknesses suitable for the laser cutting trials will be sourced. The cutting trials will be carried out using a fibre delivered, high beam quality laser. A standard sample will be used for all cuts, and all cutting parameters recorded. Cuts will be produced in the flat (PA) position, and also other positions to investigate the tolerance of the process to changes in position. Methods of improving cut quality, when active assist gases are used, will include investigation of nozzle designs for improved flow in the kerf and also through the use of two and three part gas mixtures. The improved beam quality available with these lasers allows opportunity for designing more parallel-sided gas feed delivery co-axial with the laser beam. Some samples will also be produced by conventional CO 2 laser cutting at a selected job shop, for comparison of cut quality. The cutting performance will be analysed in terms of cut edge roughness and squareness, kerf width, cutting speeds, and maximum cut thickness.
The results will be used to produce guideline procedures for laser cutting with fibre delivered lasers, and a comparison of cutting performance with that of conventional CO 2 lasers.
Structural, Shipbuilding, Steel producers, Yellow goods, Automotive, Aerosopace, Laser manufacturers and Gas suppliers.
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The approach to this work would be, in the first place, to better understand the basis of the laser based Surfi-Sculpt TM process, and compare this to the mechanisms believed in operation using electron beams. In the electron beam process it is felt that instantaneous volumetric substrate heating occurs. A requirement is that a suitably thick layer of material is heated to a temperature between its melting and its boiling point as the heat source is translated. In the laser process it is felt that the high opacity of a metal in its solid and even liquid phase, would limit heating to the surface, volumetric melting therefore occurring in the first instance, only from the surface downwards. Using a laser beam, the formation of a molten layer of finite thickness might require more time for the process to occur, as well as the creation of higher peak surface temperatures. The first part of this project will therefore investigate the process fundamentals, using fibre delivered laser beams, of wavelength close to 1 micron, and of different beam qualities, on a single material surface. In this work the use of high speed video is considered necessary to understand the formation method of features, as a function of the number of scans of the laser beam, and other variables, such as the atmosphere in the region of the process.
Once these fundamentals are better understood, further work will be undertaken to produce a particular type of surface feature, of a more complex nature, selected for comparison with the electron beam process. In this work, it is thought that use of a galvanometer driven laser beam scanning device will be required.
Aerospace, Automotive, Electronics, Power Generation.
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The steels used for the work will include TWIP and boron treated martensitic grades with a thickness in the range 1.2 to 2.0mm, depending on availability and typical application expectations. The TWIP steel will be zinc coated and the hot formable boron steels either uncoated or aluminium coated, typical of the conditions in which the material is supplied. Additional zinc coated low carbon and HS steels will be used for mixed material combinations.
Resistance spot welding work will include the development of welding procedures appropriate to the materials used. Static joint properties will be examined using standard shear and cross tension tests. A limited examination of fit-up effects will be conducted.
Laser weldability and weld performance of TWIP and boron alloyed steels will also be established. The high carbon content of TWIP steels plus the fast cooling rate of laser welding are likely to cause excessive weld hardening, particularly when it is welded to a ferritic steel. Therefore, laser welding procedures will be developed to achieve fully penetrating welds in lap joints using twin-spot laser welding. The elongated weld pool in twin spot welding will reduce the cooling rate during welding, for example. For boron-alloyed steels, laser-welding procedures will be developed to minimize the thermal effect in the HAZ and assess the effect of the aluminised coating.
For both materials, the effect of dissimilar material combinations on weldability and weld performance will be examined. Weld static tensile properties will be measured.
The work is relevant primarily the Automotive and Aerospace industry sectors.
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The preliminary stage of the project will be to further develop all aspects of the High Intensity EB equipment in order to optimise its performance. Extensive tests need to be carried out on working distance, coil positioning, viewing apparatus and the high speed scanning techniques.
Control of the beam parameters at low powers and in a manner suitable for micro-processing will be addressed. This will involve review and development of control of the beam current, focus and deflection on the prototype equipment. The near beam axis viewing system provided by the visual optics has shown major advantages towards understanding fine scale engineering. Viewing techniques need to be optimised further so alignment to the beam is more readily adjustable.
The fusion of data from the back-scattered electron imaging system and the CCTV system to give a better depiction of intense electron beam processing will be investigated. This combination will give a 'real time' representation, and will enable the beam to be used as a self-monitoring device, both processing at fine scales and guiding the operator.
Industrial applications such as cutting, drilling and sculpturing will be studied for a wealth of different materials relevant to the focus of the enquiries from our members. Studies of the quality and ability to replicate micro features on metal foils, polymers, fine wires, and substrates using micro beam diameters will be established to address market requirements.
Electronics and Sensors, Medical, Chemical, Pharmaceutical.
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The NVEB equipment has recently been upgraded to include a new 100kW switch mode power supply and more robust beam pulsing equipment is currently being designed and manufactured. In parallel with this work, advances in gas dynamic and electron scattering calculations have enabled a significantly improved beam delivery system to be devised. By means of these equipment improvements and design advances it is anticipated that the average beam power delivered to the workpiece can be extended up to 60kW. Also advanced beam pulsing capability is expected to permit peak powers in excess of 80kW to be applied The effect of these upgrades on penetration performance will be explored for both flat position and horizontal-vertical welding. The main thrust of the programme would be to optimise welding parameters for typical material and joint designs where the outstanding benefits of electron beam welding at atmospheric pressure can be used to best advantage. As part of this programme the effect of beam transport gas and shielding gas types would be explored. It would be important to minimise the cost of these consumables whilst noting the effect on beam penetration and weld quality. The work would involve a study of gas flow characteristics for a range of output devices, beam scattering calculations as well as practical tests on a range of material types and thickness.
Power Generation, Nuclear, Oil and Gas, Pressure Vessel, Chemical Plant, Rolled and Forged Products, Aerospace, Marine, Turbine Manufacture, Automotive, Medical.
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The existing facility will be modified to accept a commercial electron beam generator and welding trials will be performed to establish the range of materials and joint configurations that can be accommodated with this technology. The performance of the current seals will be tested under welding conditions and if necessary the design and materials employed will be re-visited.
Power, Aerospace, Road Transport, Construction and Engineering, Oil, Gas and Chemicals.
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Work will commence with a review of LFW system manufacturers, sub-contractors, and end users throughout the world. This exercise will collect published information/data on LFW, including process performance, available resources, and current and potential industrial applications. The project will continue with a series of experimental trials to directly compare the characteristics and performance of LFW samples produced under the same global conditions, using the two variants of LFW machine.
Project work will then move on to the application of TWI's new hydraulically actuated LFW machine to the production of welds for challenging applications, including dissimilar materials, fine feature components, and LFW with relatively low levels of applied force. This work will investigate the limits of current LFW technology, and will showcase the capabilities of this relatively unknown, but highly capable, friction welding technology.
Aerospace, Power, Construction and Engineering, Road Transport.
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Work on FSW process management will commence with a review of the capabilities of TWI's new process monitoring system, and an investigation of its performance in a range of common FSW applications. A series of welding trials will be undertaken to simulate the occurrence of weld defects during FSW, such as: tool failure, tool wear, incomplete weld penetration, and void formation (due to inappropriate welding parameters). For each defect case the process monitoring system will be applied in an attempt to detect/predict the occurrence of these defects based on the process data that is collected. The effectiveness and sensitivity of the process monitoring system will be assessed.
Work on FSW process control will commence with a review of published information/data and TWI experience relating to known control methods for FSW. A summary of the characteristics and capabilities of each approach will be produced, including recommendations of the most suitable approach for common FSW applications. Work will continue with experimental development and assessment of a weld temperature control system for FSW. A series of experimental trials will be conducted, both with and without thermal control, in order to demonstrate the effectiveness of the approach.
Aerospace, Power, Construction and Engineering, Road Transport, Oil, Gas and Chemical, Electronics and Sensors.
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Initial work will focus on generating a database of suitable high temperature materials, this will be performed in conjunction with the relevant departments within TWI and material suppliers. A number of appropriate tool materials and/or coatings will be selected for assessment in friction stir welding trials. Selection criteria will incorporate not only the salient physical properties but also the material cost, availability and ease of processing. Welding trials will focus on ranking the wear resistance of these tool materials in a number of high temperature workpiece materials. Further studies will aim to improve the lifetime of best performing tool material by incorporating tool cooling.
Oil and Gas, Power Generation, Automotive and Construction and Engineering.
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The project will primarily involve understanding the synthesis of nanotubes and ways of controlling their length and dimensions followed by understanding the science of coupling carbon nanotubes with IR radiation. This will aid the understanding of a range of structural forms and distribution of nanotubes and their interaction with incident IR radiation. The energy generated by the interaction of the CNT with the radiation will be measured as a function of nanotubes, type, dimension and concentration. The project will aim to evaluate and optimise this relationship to increase the efficiency of energy download. This will be demonstrated by the use of CNT in both welding and disassembly of a range of materials. The project will also investigate the role of intense pulses in oxidising and degrading CNTs to develop the ability to remove residual CNT as well as demonstrating possibility of causing micro-explosions which could find use in a variety of applications including initiation of spontaneous welds at interfaces.
The project will support a staff member who will be undertaking a PhD in this technical area at Cambridge University.
Oil, Gas & Chemicals, Power Generation, Aerospace, Road Transport, Construction & Engineering, Electronics & Sensors.
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To achieve the development of Comeld technology a program of work is suggested that will focus on Titanium carbon fibre reinforced polymer composite joints. A variety of Surfi-Sculpt treatments will be applied and the effect of these will be analysed. These will be compared directly to conventional adhesively bonded metal to composite joints, and conclusions made.
Surfi-Sculpt treatments will developed with the aim of designing surfaces for specific purposes, for example stress transfer. Different geometries will be explored, in combination with different composite processing methods. Demonstrator products will aim to be produced with appropriate industry collaborations.
Developments or identification of suitable surface pre-treatments, which are effective and acceptable for two application areas will be undertaken. The selection of a number of commercially available adhesives generally used in these application areas will be undertaken. The adherends or the substrates will be selected from a range of materials (titanium, stainless steel, PEEK and UHMPE) which are directly relevant to specific end-uses. Specific environmental factors such as the effects of body fluids, mechanical forces, high saline levels etc will be evaluated. As well as joint properties the degree of sealing performance of the selected materials will be assessed.
Road transport, Aerospace, Construction & Engineering, Electronics & Sensors, Oil & Gas.
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To develop process and materials know-how in through-transmission laser welding consisting of:
- Part tolerances for through-transmission laser welding.
- Identification of effective clamping of samples for through-transmission laser welding.
Modelling of the welding process will be conducted, using currently available software models, to identify the thickness of the molten region for various processes:
Defects of various sizes will be introduced into moulded parts and used to assess their effects on the process parameters required to manufacture high-strength, hermetic welds. Appropriate fixturing for effective laser welding of complex joint geometries will be developed. Finite element analysis of the load transfer from a local clamp to the joint region will be carried out to assess the stress distribution at the joint. This will be compared with experimental trials using different clamps, different processing procedures (single pass verses multiple pass scanning methods), and materials of different thickness.
Trials will be conducted to identify through-transmission laser welding conditions for the following materials combinations:
A set of guidelines will be prepared to allow product designers to select appropriate combinations of materials and process.
Oil, Gas and Chemicals, Construction and Engineering, Power Generation, Aerospace, Road Transportation, Electronics & Sensors.
Technical benefits for TWI Members will arise from greater exploitation of through-transmission laser welding of plastics across a range of industry sectors. The benefits of a high-strength, hermetic joint can be used both in development of new products, and in re-designing the manufacturing process for existing products.
Economic benefits will be seen in a number of areas, including, but not limited to:
These benefits cannot be quantified in advance. However, if we guess that ten organisations every year can each save 40 days development time at £750 per day from a project by using the guidelines, this provides an immediate benefit of £300k per year.
Economic benefits to TWI will arise from:
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The project will be undertaken on two parallel pathways in the first eighteen months. One activity will identify the critical pathways for adoption of thin coatings in a number of applications areas. Included in this will be an assessment of both technical and economic sensitivities for existing technical solutions and the drivers for new coating systems. Three application areas will be selected as case studies. The criteria for selection will include consideration of a significant or potentially significant marketplace, a highly demanding set of performance criteria requiring an alternative approach to that conventionally used in this sector. The second activity will be the modification of an existing model sol-gel system which yields high corrosion protection to steels. Modification to the fabrication sequence will be undertaken to give a coating with a lower solvent content without viscosity loss so giving lower drying related stresses. Methods will also be investigated to reduce the temperature and time of cure.
The third phase of the project will involve the preparation and evaluation of sol-gel coatings using the synthesis approach pioneered by TWI. Coatings will be deposited onto three commercially important components and compared directly with the class leading competitor coatings. Testing will be carried out both at TWI and on-site with participating Industrial Members.
Oil, Gas and Chemical, Road Transportation, Construction & Engineering, Aerospace, Electronics, Sensors and Medical Devices.
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Initially, a series of industrially relevant materials will be selected. These may include high temperature nickel alloys, FeCrAl alloys (which may be oxide dispersion strengthened) and engineering ceramics. For each material, diffusion bonding trials will be performed using a Design of Experiment approach to map the time/temperature/pressure surface for successful bonding of the material to itself. Bonding conditions will then be established for relevant material combinations.
Oil, Gas and Chemicals, Power Generation, Aerospace.
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The project will undertake a critical review of the existing test methods for reliability determination. Using software methods for failure mechanism and lifetime prediction (such as the CALCE software used in project 0405-3), predictive models for a range of test vehicles will be produced. The test vehicles will contain critical elements common to many industrial requirements such as power semi-conductors, high-density grid array devices, solderless lead joints, and sealant materials. These case studies will be identified with Industrial Member end users for applications selected from, for example, aero engines, power conversion, portable communications and sterilisable medical products. Precision reliability tests will be performed to allow refinement of the models, to validate the predictive methods, and guide development of more highly accelerated tests. The latter will be evaluated as a method for product assessment at lower cost and with reduced 'time to market' capability. Where necessary materials data will be acquired or new data will be produced for the construction of a consistent database of materials properties for use with the software tools. A range of experimental and analytical methods will be used to identify the failure mechanisms of the test vehicles.
In addition to the reliability of soldered and adhesive joints the project will investigate selected brazed joints, material combinations will include aluminium-aluminium, stainless steel-stainless steel, stainless steel-alumina and aluminium-silicon carbide. The effect of bonding parameters will be determined using a range of brazes, including Ag-Cu, as well as Au/Si and Au/Ge, directly relevant to high temperature electronic devices. The joints will be assessed after exposure to elevated temperature and static creep testing. The joints will also be subjected to corrosion testing using high temperature oxidation techniques as well as by electrochemical means.
The project will also include significant activity from Suite 0702 via project 0702-8 'Application of Advanced Failure Analysis Techniques' which will develop failure analysis methods in support of the test vehicle programme (eg Phase Contrast X-ray) and raise TWI's core expertise in micro-sectioning of electronics and sensor components. Further cross-departmental support will be provided by the FEA section which will provide FEA analysis and development of predictive models for typical failure mechanisms (eg thermal mismatch fatigue).
Electronics, Sensors and Medical Devices, Aerospace, Road Transport, Power Generation.
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