Background

Nuclear power currently supplies some 17% of world electricity production from over 400 power stations. In addition, advanced nuclear systems are under development with the potential to make a significant contribution to future energy demands in an environmentally acceptable manner.
Materials R&D in The Nuclear Field

The safe, reliable and economic operation of such plant is critically dependent on good materials performance and, in particular, on understanding and mitigating specific environmental degradation processes (e.g. mechanical, corrosion and radiation effects). Materials R & D effort in the nuclear field has spanned some 40 years but, interestingly, has resulted in much detailed understanding of many generic aspects of materials behaviour, in areas such as crystal defects, diffusion and solute segregation, phase evolution and deformation and fracture processes etc outside the nuclear field. Such advances have been of both direct and indirect benefit to many other industries, including fossil fuel power generation, chemical plant, aerospace etc., and extending into such diverse areas as novel welding techniques, tribology, liquid metal technology, high purity alloy specification and production, structural integrity etc.
Materials and nuclear Power – Euromat ‘96

This is the background against which The Institute of Materials organised Euromat ‘96, under the conference title ‘Materials and Nuclear Power’ on behalf of The Federation of European Materials Societies (FEMS), and (for the first time) in association with the American Society of Metals (ASM). This international conference, one of a continuing series promoted by FEMS under the Euromat title, was held at the Bournemouth International Conference Centre on 21-23 October 1996, attracting over 130 delegates and speakers from 20 countries. The purpose of the meeting was not only to address the current status of materials for nuclear plant but also to highlight the potential for technology transfer to other industries. The content of the conference embraced a whole range of materials topics, from the design and construction of advanced systems through to aspects of nuclear fuels and finally to backend issues of waste management and decommissioning.
Materials For Light Water Reactors and Boiling Water Reactors

Light water reactors (the pressurised water reactor or PWR and the boiling water reactor or BWR) account for over 80% of an installed nuclear capacity, and thus materials aspects of these system were the dominant theme of Sessions 1 and 2. Manfred Erve (Siemens AG, Germany) reviewed materials choices for PWRs. Low alloy ferritic steels are selected for heavy section components principally the reactor pressure vessel (RPV), the steam generator (SG), the pressuriser and the reactor containment. For example, the RPV in modern plant is constructed of monoblock ring forging of A508 Class 3 - a high toughness Mn-Mo-Ni bainitic steel. Austenitic stainless steels of the 18Cr-10Ni type are used for core internals, small diameter primary loop systems and, in some designs, for main coolant pump casings. In some cases Nb-stabilised AISI 347 or other stabilised grades are selected whereas non-stabilised grades are specified with low (< 0.02%) carbon to minimise problems from intergranular stress corrosion cracking (SCC). Finally, high nickel alloys are used in heat exchanger tubing for the SC, and for small components in core internals. SCC has been problem in Inconel 600, but selection Inconel 690 and 800 has proved beneficial in this respect.
Development of High Grade A508 Ring Forgings for Reactor Pressure Vessels

G A Honeyman (Forgemasters Steel and Engineering Ltd, UK) traced the development of high grade A508 ring forgings for RPVs and, in particular, the specifications needed to confer high toughness and radiation resistance. The former is achieved by tailoring C, Ni, Mn levels and keeping sulphur levels low - 0.003% is now routinely obtained. Radiation embrittlement is associated with the presence of residual Cu in the steel, and is a problem at levels above 0.1%; again levels at or below 0.05% are now routinely obtained; in addition, any thermal ageing embrittlement due to P is also minimised by ensuring levels are below 0.005%.
Radiation Embrittlement

Other contributions in the first two sessions reviewed aspects of environmental degradation in support of lifetime management (L Valibus, EdF, France) and described the degradation mechanisms caused by the neutron irradiation environment. The role of Cu in the radiation embrittlement of RPV steels at the coolant inlet temperature of 290°C is now well understood; although Cu retained in solid solution is thermally immobile at this temperature, radiation induced formation of fine epsilon-Cu particles occurs. These retain a bcc structure and act as potent matrix strengtheners. The routine specification of low-Cu A508 steel, however, has essentially solved the RPV embrittlement problem in new plant. Furthermore, in the latest on-going designs, such as the European pressurised water reactor (EPR) being undertaken by a FrancoGerman (Framatome/Siemens) consortium, the lifetime neutron dose even for a proposed extended 60 year life is significantly reduced compared with standard plant by specifying a larger than usual gap between the RPV and the core barrel.
Irradiation Assisted Stress Corrosion Cracking

Austenitic core internals also experience loss of fracture toughness during irradiation to high doses at the coolant outlet temperature of 325°C, but the toughness saturates at levels compatible with the relatively low stresses experienced by these components; however, there is concern for advanced PWRs with lifetimes extending to 60 years for which further data is required. Nickel-base alloys also exhibit more severe radiation embrittlement and their use may need to be re-evaluated. Irradiation-assisted stress corrosion cracking (IASCC) may also be a problem in PWR core internals and certainly more so in BWRs. IASCC in austenitic steels is a relatively newly understood phenomena in which grain boundary depletion of Cr together with enrichment of minor elements (e.g. Si) occurs by a process of radiation-induced non-equilibrium segregation (RIS) in which solute element fluxes are driven by coupling to the point defect fluxes. The Cr-depleted boundary is susceptible to anodic dissolution in reactor water and, because the boundary is also weakened by segregants, a form of SCC occurs. Several instances of both IASCC and SCC in core components were reported, whilst the theoretical basis of RIS was covered by the presentations of G Martin (CEA, France) and R G Faulkner (Loughborough University, UK).
Advanced Fuel Cycles

A number of important aspects of advanced fuel cycles were covered in Session 3. The use of MOX (i.e. mixed oxide or (Pu,U)O2) fuel for PWRs as a means of recycling plutonium was reviewed by H Bernard (CEA, France) and fast reactor fuels including high-Pu U-free non-conventional variants were also discussed. The development of zircalloy fuel cladding for LWRs was highlighted by A Seibold (Siemens AG, Germany) and the benefits of restricted compositional specifications and/or exceeding ASTM elemental specifications to improve corrosion resistance were described. The elements with the largest effect on corrosion are Sn, Fe and Cr.
Radioactive Waste Management

The development of technology for safe and responsible radioactive waste management is a key issue for on-going confidence in nuclear power, and this aspect was considered in Session 4. Encapsulation of high level waste by vitrification was a central theme in the presentation by C Scales (BNFL, UK) while investigations of the potential of glass‑ceramics (K M Garrett, University of Warwick) and cementitious systems (E J Butcher, BNFL) for immobilisation of certain waste forms was described. From a different viewpoint, Henderson (Swedish Institute of Metals Research) presented creep test data on various grades of copper used in Sweden for radwaste canisters.
Structural Materials for Fast Breeder Reactors and Fusion Reactors

The final session covered structural materials for fast breeder reactor (FBR) and fusion reactor (FR) systems, and opened with a survey by W Dietz (Lindlar, Germany). In sodium-cooled FBRs, operating temperatures are in the range 350-550°C (excluding transients) and austenitic steels have been developed for primary system components (reactor vessel, core support, sodium coolant piping). Around the world there has been convergence to a low-C grade with added N, i.e. Type 316L(N), for resistance to intergranular attack during fabrication and improved ductility and strength during operation. There are trends away from Alloy 800 towards ferritic steels (initially 2.25Cr1Mo and now modified 9Cr1Mo) for FBR steam generators. Materials selection for first wall applications in FRs is still broad-based due to the conceptual nature of fusion systems, which thus permits a wide range of options for operating conditions. Martensitic stainless steels with 9-12%Cr, vanadium alloys and even fibre-reinforced ceramic composites based on SiC are under consideration. Current research is centred on low induced radioactivity (LA) materials for safe waste disposal purposes.
The Future

Despite the current downturn in new nuclear plant construction, the buoyant atmosphere evident at this conference indicated considerable optimism for the future. Attention is now focussed on plant life extension, which clearly requires a detailed understanding of material degradation processes, and on decommissioning of existing plant and radwaste issues. The continuing research effort on materials for advanced LWRs for near-term applications and for fusion reactor systems designed to operate early in the next century clearly implies that nuclear power will continue to play a key role in future electricity generation.

Background

Checking the cleanness of a sample of steel can be a time consuming business. The usual way of going about it is to use metallographic techniques to prepare a thin slice of the material being analysed. Several chemical or mechanical preparation steps can be required. The surface of the sample is then inspected optically or using particle interactions to determine the level of inclusions. A new technique promises to take some of the work out of this quality control process, reducing analysis time to just a couple of minutes. The technique is known as single spark evaluation spectroscopy.
How Does Single Spark Evaluation Work?

Single spark evaluation (SSE) involves the time resolved multispectral detection of individual emission intensities from the spark plasma. In other words, each individual spark is logged by the system to build up a histogram of the intensities of the emissions. This histogram can provide details about the distribution of an element in the sample, so picking out inclusions and measuring, for example, the levels of both soluble and insoluble aluminium in steel samples.
Determining Compositions of Metal Samples

Spark optical emission spectroscopy is normally used in an integrating mode for measuring line emission intensities. This type of analysis provides a value for the concentration of an element within a sample. However, this value is an average for the ‘burning spot’ - the area over which the hundreds of spark discharges have occurred.

Individual sparks only form craters of approximately 10-30µm in diameter, and so the emission line intensities represent a sample amount of only 30-500ng. By registering and evaluating the line intensities from each spark, SSE therefore gives access to the local concentration of elements within sample portions of about 20μm or 100ng in diameter. This makes SSE potentially very useful for measuring the size and distribution of non-homogeneities in a material, and for measuring the chemical constitution of inclusions.
Identifying Inhomogeneities in Metal Samples

The SSE method for detecting inhomogeneities in an element’s distribution relies on a simple approximation. The histogram of individual spark emission intensities from a homogeneously distributed element can be represented satisfactorily as a Gaussian curve. So if any sparks are picked up that do not fit into the Gaussian distribution, these must be the result of inhomogeneities. The relative amounts of the element in the homogeneous phase and inhomogeneous phase can be calculated by the number of sparks under and outside the Gaussian curve. SSE applied to a number of selected elemental emission lines allows the identification of those elements in an inclusion, and calibration graphs can be used to calculate the amounts of each element present.
Steps in a Single Spark Evaluation Process

The essential steps in the SSE process are as follows:

· Register all spark intensities for selected spectral lines

· Select the most suitable section of the sparking sequence to give an accurate representation of the material’s composition• calculate the best Gaussian fit for each spectral line and separate the non-Gaussian parts, known as ‘outliers’

· Calculate the intensity of the homogeneous and non-homogeneous parts of the elements being analysed, and calibrate for each element if reference samples are available

· Calculate the relative numbers and intensities of the `outliers' of a selected element to another element

· Use this data to identify the inclusions by their elemental composition.

Inclusions can then be characterised by calculating the number of atoms within an inclusion, assuming an average spark crater is represented by a hemisphere of 30μm diameter. Inclusion size can be worked out, and the overall analysis used to show the frequency of occurrence of each inclusion.
Determining Aluminium Content in Low Alloyed Steel

SSE has already been successfully applied to the measurement of the soluble and insoluble components of aluminium in low alloyed steel, and for the characterisation of inclusions in low alloyed steel. For determining insoluble aluminium, the first ‘diffuse discharges’ in the sparking series that contain very low iron intensities must be ignored. Once the level of iron has stabilised, the next 500 sparks are relevant for picking out the insoluble aluminium component.

The tests carried out by Spectro Analytical on 40mm diameter steel rods showed that the level of the insoluble aluminium varied considerably through the sample, by as much as 30%. Soluble aluminium levels varied by only a few percent. The technique proved successful, correlating well with the levels of aluminium in the sample and providing an improved analytical facility for distinguishing the soluble and insoluble phases.
Analysis of Inclusions in Low Alloyed Steels

SSE has also been used to analyse inclusions in rolled bars of low alloyed steel, with particular attention paid to certain element combinations that occur frequently. One search looked for any combination of aluminium, calcium, magnesium, oxygen and silicon. Another looked for any combination of calcium, manganese, oxygen, sulphur and zirconium, and a final search looked for combinations of aluminium, titanium and nitrogen.

Using correlation analysis of the ‘outliers’ found for each element, the SSE system was able to pick out the inclusion species and also show the size and frequency of occurrence of each inclusion. Frequency and size both varied considerably, but the system highlighted several relationships between the frequency of occurrence of certain species and the size of the inclusions. Sulphides, oxides and nitrides were all picked up easily, demonstrating that SSE could be used to perform a quick cleanness test in less than a minute on a sample of steel.

The levels of the dominant inclusion species found using SSE qualitatively agree with those determined using standard metallographic techniques. This augurs well - if further studies and agreement between SSE and metallographic techniques are shown, SSE will become a time-saving alternative to existing practices. Quality and process control will benefit greatly from the new technique.

Background

Maney Publishing is an independent academic publisher of titles in materials science, languages, literature, archaeology and social history. Founded in 1900, the company has offices in Leeds and London in the UK, and in Boston, USA. Maney offers academic societies, editors, authors and members outstanding service in the publication of their books and journals.

Since 2001 Maney has been publisher to the Institute of Materials, Minerals and Mining (IOM³) and has developed a leading international materials science and engineering journal portfolio, including titles such as International Materials Reviews, Materials Science and Technology, Corrosion Engineering, Science and Technology and Powder Metallurgy. Maney continues to expand this subject portfolio, and 2007 will see the launch of a brand new journal, Tribology – Materials, Surfaces & Interfaces.

Maney offers individual and institutional subscriptions that include online access via Ingenta where applicable. Also available are the MORE (Maney Online Research E-journals) packages providing online journal collections.
Journals

Maney publishes a range of journals. Some of these include:

· Advances in Applied Ceramics

· Applied Earth Science

· Corrosion Engineering, Science and Technology

· Energy Materials

· The Imaging Science Journal

· Interdisciplinary Science Reviews

· International Journal of Cast Metals Research

· International Materials Reviews

· Ironmaking & Steelmaking

· Journal of the Energy Institute

· Materials Science and Technology

· Mineral Processing and Extractive Metallurgy

· Mining Technology

· Packaging, Transport, Storage and Security of Radioactive Material

· Plastics Rubber and Composites

· Powder Metallurgy

· Science and Technology of Welding and Joining

· Surface Engineering

· Transactions of the Institute of Metal Finishing

· Tribology - Materials, Surfaces & Interfaces

The Cambridge-MIT Institute is pleased to announce the achievement of one of its researchers.

Dr Athina Markaki, from Cambridge University’s Department of Materials Science & Metallurgy, has been awarded one of the 2004 SET (Science, Engineering and Technology) for Britain awards for her work arising from the CMI-funded project on ‘Developing an ultra-light stainless steel sheet material’, which has developed and patented a lightweight metal 'sandwich' of microscopic stainless steel fibres bonded between two very thin stainless steel faceplates.

As a spin-off from the project, Dr Markaki conducted research into another possible application for the metal fibres, after a magnetic field has been applied to them, to connect prostheses to bone more effectively.

Replacement of hip, knee and other joints, usually as a treatment for degenerative arthritis, has a worldwide market of $5 billion and a growth rate of about 10%. These operations bring relief from pain to millions of people every year, but there is a serious problem. Prosthetic implants are attached to bone either with cement or later via bone growth into a rough surface. Loosening between bone and implant can cause problems, reducing the average prosthesis lifetime to less than 15 years. An effective method to improve the durability of implant-bone joints is urgently required.

Loosening has two main causes - poor bonding and “stress shielding”. The latter arises because conventional (metal) prostheses are stiffer than surrounding bone, which inhibits bone from being strained, and straining is essential for healthy bone growth.

Dr Markaki was one of several hundred young researchers who submitted a poster about her work to this year's SET for Britain scheme. On March 15, at the House of Commons, she was honoured with the De Montfort Award for her work, which has been published in the April edition of Biomaterials.

The team behind the CMI-funded project on 'Developing an ultra-light stainless steel sheet material' is working with an industrial consortium to develop and test the metal further, with a view to encouraging its use by vehicle manufacturers, as it could help to help cut down the body weight, and therefore the fuel consumption, of cars and trucks.

MAGNETO-MECHANICAL STIMULATION OF BONE GROWTH

A.E. Markaki and T.W. Clyne, Department of Materials Science & Metallurgy, Cambridge University, Pembroke Street, Cambridge CB2 3QZ, UK

This work introduces a completely new approach to the crucial problem of interfacial loosening, which commonly occurs with prosthetic implants. This arises partly because bone adjacent to a conventional, fully dense metallic prosthesis often fails to bond well to it. Additionally, since the metal is much stiffer than the bone, stress shielding occurs, so that straining of bone adjacent to an implant is strongly inhibited. Such straining is essential for healthy bone growth it is responsible for the beneficial effects of exercise on bone physiology. Strain levels of at least about 1millistrain (0.1%) are needed in order to stimulate significant beneficial effects.

The proposal relates to the introduction of a relatively thick layer, strongly attached to the prosthesis. This layer is highly porous, being composed of an array of metallic fibres bonded together. Bone growth into such material is known to occur readily.

The fibres are made of a magnetic material, such as ferritic stainless steel (which has excellent biocompatibility). When a magnetic field is applied, a fibrous array of this type deforms elastically, as a result of the tendency for such fibres to align with the field. In-growing bone tissue filling the inter-fibre space would be mechanically strained during such deformation. Subjecting a newly implanted prosthesis to an externally imposed magnetic field for suitable periods would thus be expected to stimulate bone growth and to promote healthy bone physiology.

A simple analytical model has been developed to predict the expected levels of deformation. This demonstrates that, using magnetic field strengths already employed for diagnostic purposes, it should be possible to generate strain levels sufficient to stimulate bone growth, provided the architecture of the fibre array conforms to certain (achievable) requirements.

Experimental measurements confirm the broad validity of the model, although no work has been done so far involving bone tissue. It may also be noted that, by suitable choice of the layer thickness, stress shielding could be reduced or eliminated, so that the long-term health of adjacent bone would be improved. Application of the magnetic field would only be required during the short period immediately after implantation, when bone-in-growth occurs.

The proposed concept should not be confused with that of an externally-applied magnetic field itself directly stimulating bone growth, which has often been suggested, but which lacks both a clear mechanistic explanation and convincing experimental evidence for its efficacy. It also differs from the idea of magnetic fields being used to generate forces within cells and tissues implanted with magnetic micro-particles, which suffers from similarly uncertainties and also presents practical difficulties.

In contrast to these two suggestions, the mechanistic basis for the proposed approach is simple, clear and well founded. A paper outlining the work done so far has recently been published in Biomaterials. No IPR protection has been sought, since it was felt that this might inhibit systematic study and development of the concept.

Background

Macor is a tradename for a machinable glass ceramic grade from Corning. Glass Ceramics Glass ceramics are formed by the careful heat treatment of glasses to induce crystallisation. Glass ceramics are fully dense materials which can contain up to 98 vol% crystals, where the crystals are typically less than 1µm in diameter. The remainder of the material will be residual glassy phase. Composition Macor is composed of approximately 55% fluorophlogopite and 45% borosilicate glass. Its composition is given in table 1. Table 1. Composition of Macor. Material Approx wt% SiO2 46 MgO 17 Al2O3 16 K2O 10 B2O3 7 F 4

Key Properties

· Key properties include: · Macor is white in appearance and looks very similar to porcelain · Continuous usage temperature limit of 800°C · Peak usage temperature of 1000°C · Has a similar co-efficient of thermal expansion to most sealing metals and glasses · It is non-wetting · It is non-porous · Excellent insulator at high voltages, various frequencies and high temperatures · Properly heat treated materials will not outgas in vacuum environments · It can be machined with high speed steel and carbide tools · Can be machined into complex shapes · Can be machined to tight tolerances (up to 0.005”) · Can be machined to a surface finish of 20µin · It can be joined and sealed to itself and other materials using processes such as metallising, sputtering, soldering and brazing, as well as adhesives such as epoxies. · It has no known toxicological effects, but exposure to dust should be avoided as much as possible as it can be an irritant

Applications

Macor has been used in the following areas: · Vacuum seals and in vacuum environments · Aerospace · Nuclear and radiation environments · Welding nozzles · Engineering components · Medical equipment.

Background

What do you do after you have slashed the weight of a steel car structural body through the use of state-of-the-art materials, manufacturing technologies and design? Do you sit back and admire the lighter, more environmentally friendly vehicle you have created? No, you apply the same principles to other parts of the car. Following on from the ultra-light steel auto body (ULSAB) project, which was aimed at optimising the use of steel in a car body, an international consortium of steel producers, including British Steel, has embarked upon the ultra-light steel auto closures (ULSAC) project. The project is intended to demonstrate the potential for steel-based car closure panels that offer major weight savings without penalties to structural performance or cost.

Target Areas for Weight Reduction

ULSAC focuses on four closure panels - doors, bonnets (hoods), bootlids (decklids) and tailgates (hatchbacks). The first phase of the project involved generating design concepts for lightweight steel closures that can be made affordably using current vehicle manufacturing technologies. The new closures also had to meet pre-defined targets for their key structural parameters.

The designs produced in the first phase of the project form the basis for building demonstration closure panels in phase two. The ULSAC consortium contracted Porsche Engineering Services (PES) of Troy, Michigan, to provide engineering management for the project and worked with the company in defining the goals of the project.

Project Approach

The ULSAC approach comprised benchmarking, target setting, conceptual design, FEA calculations on the concept designs and cost analysis. Benchmarking was performed on 18 upper-medium size 1997 North American, European and Japanese cars to define current state-of-the-art design concepts. The study established mass, dimensional and structural performance standards for each of the four closures. Structural performance test methods and specifications were defined from a survey of carmakers, so as to represent OEM internal targets.

Following benchmarking, PES developed the targets for each closure. Dimensional targets for doors, bonnets and bootlids were based on the dimensions used in the ULSAB car body. Structural performance targets were set at the midpoint of the range derived from the OEM survey, and mass targets for each closure were set as 10% lower than the best of the benchmarked parts.

Materials and Design Concepts

Steels

The balance between lower weight, structural performance and cost was achieved using state-of-the-art steels and manufacturing techniques combined with an iterative holistic approach to design. In this approach, the structure is treated as an integrated system rather than as an assembly of individual components. For the doors, efforts to optimise design were directed at the sheet metal panels and the components. Weight savings were achieved in both areas, whereas savings in the other less-sophisticated closures came about through attention to design, materials and the manufacturing of the inner and outer panels. High-strength steels were used for all outer panels. Bake-hardenable steel with a minimum yield stress of 210MN.m^-2 has excellent formability in the as-delivered condition and gains additional strength and dent resistance after press forming and paint baking. Higher strength steels were chosen for other components, such as hinge areas of the inner door panels, and a 1200MN.m^-2 yield stress ultra high-strength steel was used for side intrusion bars to give good impact resistance at low weight.

Sandwich Panels

Steel sandwich material can also be used for mass reduction. The ULSAC design study showed that using it for bonnet and bootlid inners can increase weight savings by 3%. Steel sandwich material can withstand bake ovens so that parts can be assembled prior to painting. However, it increases the cost of the closure compared to current designs.

Sheet Metal Hydroforming

Sheet metal hydroforming was used in the manufacturing of the outer panels to increase dent resistance through better strain distribution and added work hardening. All four closures could be produced using a sheet-hydroformed outer panel made from bake-hardenable steel. High-strength hydroformed tube also reduced the weight of the frame-integrated and frameless door and the tailgate designs.

Tailored Blanks

As in the ULSAB project, the use of tailored blanks was crucial to reducing weight and cost. All the door design concepts used tailored blanks for inner and/or outer panels. This allowed reinforcement of the belt area of the roof-integrated door design through the use of thicker material. More sophisticated blank construction involving non-linear welds meant that laser welds could be located for optimum formability, while still giving weight savings.

Assembly Methods

Assembly methods giving continuous joints increase stiffness and provide the opportunity for mass savings compared to spot welded assemblies. Therefore, adhesive bonding and laser welding were specified where possible in the closure designs. Bonnet and bootlid inner-to-outer hemmed joints were formed using adhesive bonding and reinforcements were bonded to the bonnet inner. Laser welding was used extensively in the door and tailgate designs to join the tubular hydroformed parts, and for attaching the hinges and impact beam.

Project Performance

Weight Reduction Techniques

Various techniques were used to reduce mass and/or improve structural stiffness. These included part consolidation, functional integration, incorporating feature lines in outer panels and designing inners to support outer panels. For example, in the frameless door design, a thin wall die casting was used as a structural node to connect the upper and lower frame. This incorporated the mirror patch, upper hinge and joint node into one part. The bonnet and bootlid inners were designed with triangular beams in a ‘V’ pattern supporting the outer panel.

Overall Weight Reduction

The weight savings achieved in the design study are summarised in table 1. This shows that the door designs were between 21% and 27% lighter than the benchmarked average. The bonnet designs were 26% or 32% lighter than the benchmark depending on whether sandwich steel was used. Similarly, with the bootlid, a weight saving of 23% or 29% could be obtained depending on the use of sandwich steel. The tailgate designs were 22-32% lighter than the benchmark average.

Table 1. Summary of weight savings achieved by ULSAC

Part	Benchmark	Target	ULSAC design	Weight Saving (%)
Roof integrated door	19.7	15.5	15.1	23
Frame integrated door	19.7	15.5	15.5	21
Frameless door	19.7	15.5	14.3	27
Bonnet	11.6	8.0	7.9-8.5	26-32
Bootlid	11.2	8.0	8.0-8.6	23-29
Tailgate	13.9	11.3	9.5-10.9	22-32

FEA and Stiffness

Finite element analysis calculations were performed on each part to confirm that the design would give acceptable structural performance. For the doors, frame rigidity, door sag, torsional rigidity, check load and side intrusion load were evaluated. Torsional rigidity and bending stiffness were looked at for the bonnet, bootlid and tailgate designs, while data on side beam stiffnesses were obtained for both the bonnet and bootlid. All designs met the set targets derived from the OEM survey.

Cost Analysis

To conclude the study, PES performed a preliminary cost analysis on each of the ULSAC closure concepts. To create a baseline with which to compare the ULSAC closures, PES developed cost estimates for current closures made from similar materials in similar sizes and geometries. The costs were estimated based on manufacturing experience and knowledge of business economics.

This economic analysis showed no discernible difference between the costs of the ‘concept’ and ‘baseline’ in two of the three designs of doors. The frame-integrated door was estimated to cost about 7% more than the baseline. For bonnets, there was no additional cost for the sheet steel solution and an increase of about 10% for the steel sandwich design. Similarly, for bootlids the study revealed no additional cost compared with baseline for the steel sheet solution and a 16% increase for the steel sandwich design. Costs for the concept tailgates were estimated to be between 12% and 24% above the baseline.

Company Background

Leco Instruments originally started business in 1936 and were the first company to produce a Rapid Carbon Analyser for the steel industry using the combustion technique. Business grew very quickly as most steel companies worldwide purchased the Leco Carbon Analyser that immediately transformed the time that it took them to do a carbon analysis down to a matter of minutes. The name Leco has now become synonymous with this type of analysis with operatives referring to “doing a Leco” on the sample.

Built on the success of the rapid Carbon Analyser, Leco went on to build more rapid analysers for the analysis of Sulphur, Oxygen, Nitrogen and Hydrogen, all elements critical to the production of high grade steel.

The technology utilised in these analysers was then put to use analysing other products such coal, coke, petroleum etc therefore dramatically expanding the customer base of the company.
Instrumentation and Equipment Supplied by Leco

Leco Instruments is now one of the leading companies in the world supplying analytical and laboratory instrumentation to most types of industries. Products include:

· Metallographic

· Hardness Testing

· Image Analysis

· Elemental Analysis

· Optical Emission Spectrometers (OES)

· Thermogravimetric Analysis Equipment (TGA)

· Surface Depth Coating/Treated Analysers

· Mass Spectrometers

Leco of course also supply the service along with consumables to support this full range of products. In addition Leco also provide many OEM products that compliment our range of products allowing customers a “one stop shop”.
Products for the Organics Based Industries

In addition to these products, Leco has successfully developed and sells to the market, a wide range of analysers and instrumentation for the Organics based industries, our most popular instrument being the FP range of instrument for analysing Protein in food and agricultural products. More lately we have introduced a full range of “Time of Flight” Mass Spectrometers aimed at the organic chemistry market which includes pharmaceutical, pesticides, food, flavours, fragrances etc. The important feature of these instruments being very rapid analysis and data acquisition.
The Leco Worldwide Network

Leco has subsidiary companies along with agents and distributors worldwide allowing access to our products and services from any country or industry all of which provide vital feedback to Leco providing them with information for product development and future markets.

In addition to new lightweight vehicle bodies, a new weight saving design is available for commercial vehicles. This time it is the turn of the suspension unit, the weight of which is reduced through a spring design that optimises the use of the properties of the steel from which it is made.

Parabolic tapered leaf springs are designed to offer a significant and cost effective weight reduction in previously very high weight components (figure 1). They provide an alternative to traditional laminated leaf springs, offering:

· Approximately 40% weight reduction

· Optimised use of material properties

· Minimum inter-leaf friction and contact, and so the ability to use more durable corrosion protection and improved ride characteristics.

Other benefits include improved fuel economy or load carrying capacity, and reduced road damage for an equivalent axle weight.

In conventional uniform thickness leaf springs, the mid length is the highest stressed region and the thickness of the leaves is designed to accommodate this maximum stress. However, to either side the stress decreases with distance from the centre and the strength of the steel is progressively under used.

Parabolic tapered leaf springs, on the other hand, are designed with a reducing thickness from the centre outwards. The regions to either side operate at a uniform stress level, similar to that at the centre. This allows for maximum use of the material properties, and reducing the section thickness minimises the weight of the spring.

Parabolic tapered leaf springs can be fitted in place of standard laminated leaf springs with very little change to the design of vehicle attachment fixtures. They are produced using conventional metallurgical techniques and spring steels, including 0.6%C-Cr (SAE 5160, BS970:525A58) for thinner sections and 0.6%C-CrMo (SAE 4161, BS970:705A60) for thicker sections. The leaves are produced by hot rolling the tapered section, and then after roll forming they are hardened and tempered to a hardness of approximately 450HB.

For maximum fatigue resistance the leaves are stress peened to develop a high level of beneficial compressive residual stress in the surface. This involves deflecting individual leaves and shot peening while they are in the strained condition. Then they are assembled into the final component, which may comprise a number of parabolic leaves, figure 1. Typical weight savings per spring are shown in table 1.

Table 1. Typical weight savings using parabolic tapered leaf springs.

Application	Weight (kg) Parallel multi leaf	Weight (kg) Parabolic	Weight Saving (%)
Van	7.8	4.4	44
Articulated Vehicle -
Front Axle	103	71	38
Rear Axle	162	90	44

A further development, currently under evaluation to introduce additional weight saving, involves the use of a lower carbon steel that is hardened and tempered to a higher strength level. This lower carbon steel offers a higher heat treated strength combined with the retention of good ductility and toughness. The objective is to use these features to provide improved fatigue resistance and a possible additional 15% weight saving. Increased fatigue resistance is obtained from a combination of higher strength and an improved sub surface compressive stress profile following shot peening.

The hardenability of the new steel is adjusted to ensure a fully martensitic microstructure on hardening, thus producing a ductility level at least equal to that of a traditional spring steel, despite the higher heat treated strength. The spring can be produced with a similar form to that of a standard parabolic tapered leaf spring. Typical heat treated properties, compared with those of a conventional spring, are shown in table 2. In addition, a Weibull analysis of laboratory results shows an improvement it bending fatigue properties obtained from the development grade, compared with a 0.6%C-Cr steel (SAE 5160).

Table 2. Mechanical properties of steel for reduced weight springs.

Steel	0.2% P.S. (N mm-2)	Tensile Str (N mm-2)	Elong (%)	R of A (%)	Charpy Impact 2mm V
SAE 5150	1290	1430	11	37	10
New Grade	1530	1750	11	41	10

Parabolic tapered leaf springs are produced by Tinsley Bridge of Sheffield (UK), under the name of Taperlite. The latest development described above has the code name Extralite. Both types of spring highlight the potential for component improvement when the use of steel is optimised for a particular application.