Decide whether the sentences below are true or false, and correct the false sentences.

1. The elements that make up a compound are chemically bound.

2. Alloys are chemical compounds that are frequently used in engineering.

3. Alloys can contain both metallic and non-metallic constituents.

4. In an alloy, an alloying metal is the biggest constituent, by percentage.

5. Steel is a metallic element.

3. Complete the extract about concrete and steel, using suitable forms of the word reinforce. Sometimes there is more than one possible answer.

1)…………..concrete is one of the most widely used construction materials, and one we take for granted. However, using steel bars to (2)…………..concrete structures located outdoors is only possible thanks to a fortunate coincidence: concrete and steel have practically the same coefficient of thermal expansion - in other words, as atmospheric temperature varies, the concrete and the steel (3)………….expand and contract at the same rate, allowing uniform movement. Using a (4)……………. material with a different coefficient of expansion would not be feasible. For example, (5)………… aluminium-..concrete would quickly disintegrate.

Read the text below and find two elements, two compounds, an alloy and a composite.

Generally, the steel used in reinforced concrete will have previously been exposed to water and to the oxygen in the air. As a result, it will usually be partly corroded, being covered with a layer of iron oxide (rust). However, once the steel is inside the hardened concrete, it will be protected from air and water, which prevents further rusting. Additionally, the cement in concrete does not react aggressively with the iron in steel.

 

Metals

Read about metals and be prepared to discuss with your partner different features metals possess.

Metals

Metals owe their versatility as engineering materials to the fact that they can be plastically deformed and can be strengthened by a variety of methods which, by and large, act by inhibiting the motion of dislocations. As a consequence of the non-directional nature of the metallic bond, dislocations are highly mobile in pure metals which are therefore very soft. But by controlling the number and distribution of dislocations the materials scientist can adjust the properties of a metal or alloy system to suit specific requirements. There are limitations, however. Increases in strength can usually be achieved only at the expense of the capacity for plastic deformation, with the consequence that the strongest alloys often lack tolerance of defects or other stress-concentrators. Since brittleness is a drawback no designer dares underestimate, this leads to the use of large safety factors which, in turn, means that the full potential of high-strength alloys are often not utilisable in practice.

Many conventional metallic materials are relatively heavy. For land-based engineering projects this may be of no consequence, but economic arguments relating to pay-loads (in civil aircraft) and tactical arguments relating to maneuverability (in military aircraft) have always been a powerful incentive for the use of low-density materials in aerospace engineering, and in these energy-conscious times the economic incentive for lightening automobiles has considerably influenced the motor car designer.

For structural applications involving compression rather than tensile loads, the relevant structural stiffness index is not simply Young's modulus, E, but the modulus/density ratio.

These features show why it is worthwhile to attempt to use light, strong, stable fibres to reinforce some of the lighter engineering metals and alloys.

Read about metals and be prepared to discuss with your partner different features metals possess.

M. Ibbotson Professional English in Use. Engineering, - Cambridge, 2009