Engineering materials metals

Chemical bonding and electrical conductivity provide five major categories of engineered materials metals, polymers, ceramics/glasses, composites, and semiconductors. The properties of these materials are dependent on atomic- and microscopic-scale stmcture, as well as on the way in which a given material is processed. Materials science enables the selection of the optimal material for a given application, see also Ceramics Glass Physical Chemistry Polymers, Synthetic Semiconductors. 

In principle, there are as many combinations of fibre and matrix available for textile-reinforced composites as there are available for the general class of composite materials. In addition to a wide choice of materials, there is the added factor of the manufacturing route to consider, since a valued feature of composite materials is the ability to manufacture the article at the same time as the material itself is being processed. This feature of composite materials contrasts with the other classes of engineering materials (metals, ceramics, polymers), where it is usual for the material to be produced first (e.g. steel sheet) followed by the forming of the desired shape. 

H. A. Miska, Engineering Materials Handbook, Vol. 4, Ceramics and Glasses, ASM International, Metals Park, Ohio, 1991. 

About 20% of the total import bill of a country like Britain is spent on engineering materials. Table 2.2 shows how this spend is distributed. Iron and steel, and the raw materials used to make them, account for about a quarter of it. Next are wood and lumber - still widely used in light construction. More than a quarter is spent on the metals copper, silver, aluminium and nickel. All polymers taken together, including rubber, account for little more than 10%. If we include the further metals zinc, lead, tin, tungsten and mercury, the list accounts for 99% of all the money spent abroad on materials, and we can safely ignore the contribution of materials which do not appear on it. 

As we saw in the first chapter, polymers have become important engineering materials. They are much more complex structurally than metals, and because of this they have very special mechanical properties. The extreme elasticity of a rubber band is one the formability of polyethylene is another. 

The densities of common engineering materials are listed in Table 5.1 and shown in Fig. 5.12. These reflect the mass and diameter of the atoms that make them up and the efficiency with which they are packed to fill space. Metals, most of them, have high densities because the atoms are heavy and closely packed. Polymers are much less dense because the atoms of which they are made (C, H, O) are light, and because they generally adopt structures which are not close-packed. Ceramics - even the ones in which atoms are packed closely - are, on average, a little less dense then metals because most of them contain light atoms like O, N and C. Composites have densities which are simply an average of the materials of which they are made. 

Rubbers are exceptional in behaving reversibly, or almost reversibly, to high strains as we said, almost all materials, when strained by more than about 0.001 (0.1%), do something irreversible and most engineering materials deform plastically to change their shape permanently. If we load a piece of ductile metal (like copper), for example in tension, we get the following relationship between the load and the extension (Fig. 8.4). This can be... 

In Chapter 5 we said that many important engineering materials (e.g. metals) were normally made up of crystals, and explained that a perfect crystal was an assembly of atoms packed together in a regularly repeating pattern. 

Engineering Materials 2 Table 1.6 Properties of the generic metals... 

This book has been written as a second-level course for engineering students. It provides a concise introduction to the microstructures and processing of materials (metals, ceramics, polymers and composites) and shows how these are related to the properties required in engineering design. It is designed to follow on from our first-level text on the properties and applications of engineering materials," but it is completely self-contained and can be used by itself. 

From the time that formaldehyde was first isolated by Butlerov in 1859 polymeric forms have been encountered by those handling the material. Nevertheless it is only since the late 1950s that polymers have been available with the requisite stability and toughness to make them useful plastics. In this period these materials (referred to by the manufacturers as acetal resins or polyacetals) have achieved rapid acceptance as engineering materials competitive not only with the nylons but also with metals and ceramics. 

The acetal resins may best be considered as engineering materials. They therefore become competitive with a number of plastics materials, nylon in particular, and with metals. 

Many thermoplastics are now accepted as engineering materials and some are distinguished by the loose description engineering plastics. The term probably originated as a classiflcation distinguishing those that could be substituted satisfactorily for metals such as aluminium in small devices and structures from those with inadequate mechanical properties. This demarcation is clearly artificial because the properties on which it is based are very sensitive to the ambient temperature, so that a thermoplastic might be a satisfactory substitute for a metal at a particular temperature and an unsatisfactory substitute at a different one. 

Definition of corrosion in the context of Corrosion Engineering the reaction of an engineering constructional metal (material) with its environment with a consequent deterioration in properties of the metal (material). 

As a light, strong metal, beryllium holds considerable promise as a useful engineering material, but because of an inherent directional brittleness, a really significant commercial use, e.g. in the aircraft industry, has not proved possible. It has been used to a limited extent in aerospace applications, and it was employed as heat shields for the Project Mercury space capsule. It has also found use in precision guidance systems when fairly pure environmental conditions can be assured. 

Cheiius, J., Understanding the Refractory Metals , Chemical Engineering, Dec. 10, 178 (1962) Cooper, M.J. and Mannox, D.J., Tantalum and its Alloys as Engineering Materials , Proc. 

In principle, all metals may be protected by cathodic protection. In practice, it is not always relevant either because the metals are, to all intents and purposes, naturally immune to corrosion (the noble metals) and often not used as engineering materials or, being base metals, they are well protected by... 

Designers with a background in using other materials will recognize both the similarities and the differences in the behavior of the plastics discussed. As an example, impact resistance has been a continuing issue with engineering materials, particularly certain metals with similarities to many of the phenomena observed in plastics. 

---