Today’s engineers have a vast range, comprising of several thousand materials available to them. Some of these, timbers, stone and clay products, some cast irons and copper alloys have been in use as constructional materials for centuries. At the other hand of the scale, many polymers, high temperature superalloys, industrial ceramics and fibre reinforced composite materials have come into use in recent decades, while other materials of great potential interest, including new alloy compositions, new polymers, metallic glasses and metal-matrix composites are currently in the development stage. Running parallel to the invention of new and improved materials there have been equally important developments in materials processing including vacuum melting and casting, new moulding techniques for polymers, ceramics and composites, and new joining technologies.
今天的工程师拥有广泛的范围，包括数千种可用的材料。其中一些木材、石材和粘土产品、一些铸铁和铜合金几个世纪以来一直被用作建筑材料。另一方面，近几十年来，许多聚合物、高温高温合金、工业陶瓷和纤维增强复合材料已投入使用，而其他具有巨大潜在兴趣的材料，包括新合金成分、新聚合物、金属玻璃和金属基复合材料，目前正处于开发阶段。在发明新材料和改进材料的同时，材料加工也取得了同样重要的发展，包括真空熔炼和铸造、聚合物、陶瓷和复合材料的新成型技术以及新的连接技术。

In addition to the need for an increased knowledge of materials and processing technology, other challenges are having to be met by our design engineers. In earlier times, with a much smaller number of materials available, engineers often produced their designs and products by a process of trial and error, in many cases using far more material than was really necessary. Today there is a requirement to use materials more effectively and efficiently in order to manufacture quality products which can compete in world markets and to minimize cost. Also, the advent of product liability legislation places an increased burden on design and materials engineers and they now need to foresee and cater for possible misuse of the product in addition to normal usage by customers. For example, the materials and corrosion protection treatments specified and used in the production of a small car may be adequate for the normal user but a few vehicles may be purchased by inshore fishermen who will leave them for long periods on quaysides exposed to salt water spray.
除了需要增加材料和加工技术知识外，我们的设计工程师还必须应对其他挑战。在早期，由于可用的材料数量要少得多，工程师们经常通过反复试验的过程来生产他们的设计和产品，在许多情况下，使用的材料远远超过实际需要的材料。今天，需要更有效地使用材料，以制造能够在世界市场上竞争的优质产品，并最大限度地降低成本。此外，产品责任立法的出现给设计和材料工程师带来了更大的负担，除了客户的正常使用之外，他们现在还需要预见并满足可能的产品滥用。例如，在小型汽车生产中指定和使用的材料和防腐蚀处理可能足以满足普通用户的需求，但近海渔民可能会购买一些车辆，他们将把它们长期留在暴露在盐水喷雾下的码头上。

There is a complex inter-dependence between design, material and manufacture, and the design engineer, material engineer and manufacture engineer need to function as a close-knit team. Many factors have to be considered when selecting possible material to fit a design and manufacturing requirement.
设计、材料和制造之间存在复杂的相互依存关系，设计工程师、材料工程师和制造工程师需要作为一个紧密团结的团队发挥作用。在选择适合设计和制造要求的可能材料时，必须考虑许多因素。

Does the material possess the necessary mechanical, electrical and thermal properties?
材料是否具有必要的机械、电气和热性能？
Can the material be formed to the desired shape?
材料能否成型成所需的形状？
Will the properties of the material alter with time during service?
在使用期间，材料的特性会随着时间的推移而改变吗？

Will the material be adversely affected by the environmental conditions and resist corrosion and other forms of attack?
材料是否会受到环境条件的不利影响并抵抗腐蚀和其他形式的侵蚀？

Will the material be acceptable on aesthetic grounds?
这种材料在美学上是可以接受的吗？
Will the material give sufficient degree of reliability and quality?
材料是否提供足够的可靠性和质量？
Can the product be made at an acceptable cost?
商品能否以可接受的成本生产？

The complete range of material can be classified into the categories: metals, polymers, ceramics, inorganic glasses, composites.
整个材料系列可分为以下几类：金属、聚合物、陶瓷、无机玻璃、复合材料。

The classification, composites, contains materials with constituents from any two of the first three categories, for example, fibre reinforced polymers. A broad comparison of the properties of metals, ceramics and polymers is given in Table 1.1.
复合材料分类包含成分来自前三类中任意两类的材料，例如纤维增强聚合物。表 1.1 给出了金属、陶瓷和聚合物性能的广泛比较。

Table 1.1 Comparison of properties of metals, ceramics and polymers
表 1.1 金属、陶瓷和聚合物的性能比较

Composite materials have been developed to overcome some of the deficiencies of members of a particular class of materials and there are examples of ceramic/metal, polymer/ceramic and metal/polymer composites in current use. Ceramics, though strong in compression, generally are weak in tension, but metals tend to have equal strength in
复合材料已经开发出来以克服特定类别材料成员的一些缺陷，目前使用的陶瓷/金属、聚合物/陶瓷和金属/聚合物复合材料的例子。陶瓷虽然压缩强度高，但张力通常较弱，但金属往往具有相同的强度
both tension and compression. Reinforced and prestressed concretes are composites designed to improve the tensile characteristics of concrete structural members. Polymers have low densities but also have low strength and stiffness. The use of glass, carbon or other fibre reinforcement gives greatly increased strength and stiffness without adding an excessive weight penalty. The load bearing characteristics of metals and the low friction characteristics of polymer such as PTFE are combined to good effect in metal particle/ PTFE composites developed as bearing materials.
拉伸和压缩。钢筋混凝土和预应力混凝土是旨在改善混凝土结构构件的拉伸特性的复合材料。聚合物密度低，但强度和刚度也低。使用玻璃、碳或其他纤维增强材料可大大提高强度和刚度，而不会增加过多的重量损失。金属的承载特性和 PTFE 等聚合物的低摩擦特性相结合，在作为承载材料开发的金属颗粒/PTFE 复合材料中效果很好。

Very many properties, or qualities, of materials have to be considered when choosing a material to meet a design requirement (see table 1.2). These include a wide range of physical, chemical and mechanical properties together with forming, or manufacturing characteristics, cost and availability data and, in addition, more subjective aesthetic qualities such as appearance and texture.
在选择满足设计要求的材料时，必须考虑材料的许多特性或质量（见表 1.2）。这些包括广泛的物理、化学和机械特性，以及成型或制造特性、成本和可用性数据，此外，还包括更主观的美学品质，如外观和质地。

Table 1.2  表 1.2

One of the most important aspects affecting the selection and use of materials is cost and availability. In many cases purchase cost of materials accounts for about one-half of the total works cost of the finished product. It follows from this that the use of a cheaper raw material should have a significant effect on the final product cost. This is not always true as, in some cases, the choice of an expensive material may permit the use of relatively simple and low cost processing methods whereas a cheaper material may require lengthy, complex and expensive production methods.
影响材料选择和使用的最重要方面之一是成本和可用性。在许多情况下，材料采购成本约占成品总工程成本的一半。由此可见，使用更便宜的原材料应该对最终产品成本产生重大影响。但情况并非总是如此，因为在某些情况下，选择昂贵的材料可能允许使用相对简单和低成本的加工方法，而更便宜的材料可能需要冗长、复杂和昂贵的生产方法。

It is usual to see the cost of materials quoted per unit mass, for example $\pounds 100$$\pounds 100$£100£ 100 per tonne. This may give a misleading picture as often it is the volume of material which is important rather than the mass. The relative position of material in league table of cost
通常可以看到每单位质量的材料报价，例如 $\pounds 100$$\pounds 100$£100£ 100 每吨。这可能会给出一个误导性的画面，因为通常重要的是材料的体积而不是质量。材料在成本排行榜中的相对位置