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外文翻译
46 An Introduction to Modern Vehicle Design
composites and some ceramics materials. Electrical and particularly electronics engineers have far fewer problems of materials availability. Several factors or driving forces need to be considered in the materials selection process (Charles et al., 1989). The performance of the material must meet specific requirements. It is necessary to match the task, which the component or device may have to perform, with the material resources. It is important to consider the whole range of service requirements that are likely to arise, such as the mechanical loads and loading regimes, hardness, rigidity, flexibility and particularly weight, in vehicle design, as well as a range of physical properties. These can then be surveyed and matched with the properties and characteristics of suitable materials. The requirements of both properties and processing are often needed in various combinations for particular applications. Electrical, thermal or heat resistance may be linked with resistance to both wear and corrosion, in order to improve reliability and to increase the life span of the product. These and other requirements can now be explored and tested with computer software packages, particularly with plastics and polymers, so that comparisons can be made. In this way, the materials choice can be narrowed and a suitable selection becomes possible (Institute of Materials, 1995, Cebon et al., 1994). Quality and styling requirements may be considered as an extension of performance requirements. Factors such as noise and vibration could cause significant fretting failures, which may be significant. The aesthetic features of surface finish, static build up, colour, texture, feel and smell, such as for leather seats and wood veneers, which have a marketing and sales dimension in vehicle design, are also controlled by materials selection and processing. The method and scale of manufacture of the component or product are as significant, in the materials selection process, as the consideration of the in-service behaviour requirements. These processing factors are important in order to achieve the maximum effect with economy, precision and a high standard of finish. Thus, materials selection must take into account not only the in-service behaviour but also the influence, advantages and limitations, of the manufacturing process. For example, a car body panel may be made from timber, steel, aluminium or a GRP composite. Not only will the inherent properties of these materials differ but their fabrication into panels will involve different routes (Kalpakjian, 1991). Materials are available from suppliers in many regular or standardized forms. These include wire, round and square bar, film, sheet and plate, angles and other extruded sections, granules, chips and pellets and finally, viscous fluids. These forms come in standard, preferred sizes, which have been established by practice and demand. Standardization, affecting both quantity and size, is now applied to the specification of most types of material and component. Nonstandard sizes and quantities increase costs. Information on the structure, properties and behaviour of incoming materials and components will still require quality assurance, to ensure that the specifications are being met. It is common practice for larger companies, such as vehicle assembly plants, to purchase stock materials and components and then subject them to a quality audit. The assembly companies, such as Ford, Rover, Nissan, commonly known as the Original Equipment Manufacturer, OEM, are now reducing the size of their own design and development teams for work on new products, such as structural sub-assemblies, seats and body panelling. This work is now done in co-operation with their first-tier suppliers, who themselves cascade co-operative work down to third and fourth tier suppliers, such as raw materials manufacturers. Such simultaneous engineering down the product supply chain allows the OEMrsquo;s to concentrate on the problems of final product manufacture, such as the vehicle itself, which will need to satisfy all the customersrsquo; requirements.
Modern materials and their incorporation into vehicle design 47
Economics and commercial factors play a vital part in vehicle engineering design. The selling price of a component or product is made up of a number of parts, such as the costs of raw materials, manufacture, marketing, transportation, installation, maintenance and profit. Keeping the materials and manufacturing costs low will either maximize the profit or ensure sales at a realistic market price. However, the component specification must still be met using the correct materials and manufacturing methods. For similar vehicle parts, such as tyres, the specification can vary widely, leading to the use of different materials and methods of manufacture. Tyres may be used for family saloons, sports and racing cars, vans and lorries, farm tractors and earth moving vehicles. These applications use both high and low cost materials, together with hand crafted and mass-production techniques. Legislation requirements will influence the materials selection for a vehicle component. Health and safety factors govern such items as fuel tank integrity, windscreen vision, carbon and nitrogen oxides exhaust emissions, asbestos in friction materials and solvent/water based paints. Disposal methods, the cost of landfill and the economic necessity of recyclability now need serious consideration by the designer. Whilst the recycling of single material components is relatively easy, such as polypropylene copolymer bumpers, the recycling of multi-material products such as the starter battery, is a more complex affair. Both are being done at this time but the challenge is to actually design for recycling as well as for manufacture and behaviour in service. The life cycle analysis and total energy usage for a vehicle
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