Vocabulary

ability [э'biliti] способность

amount [a'maunt] количество

absorb [эb'zo:b] поглощать

amount [э'maunt] количество

application [,æpli'kei∫эn] применение

brittle ['britl] хрупкий, ломкий

car body кузов автомобиля

constituent [kэn'stitjuэnt] компонент

crack [kræk] трещина

creep resistance устойчивость к ползучести

definition [,defi'ni∫эn] определение

density ['densiti] плотность

ductility [dAk'tiliti] ковкость, эластичность

failure ['feiljэ] повреждение

gradual ['grædjuэl] постепенный

permanent ['pэ:mэnэnt] постоянный

rigid ['rid₃id] жесткий

to sink [siŋk] тонуть

square root ['skwεэ 'ru:t] квадратный корень

stiffness ['stifnis] жесткость

strain [strein] нагрузка, напряжение, деформация

strength [streŋθ] прочность

stress [stres] давление, напряжение

tensile strength прочность на разрыв

toughness ['tAfnis] прочность, стойкость

yield strength [ji:ld] прочность текучести

Young modulus модуль Юнга

Can you answer the following questions?

1. What is the density of a material?

2. What are the units of density? Where is low density needed?

3. What are the densities of water, aluminium and steel?

4. A measure of what properties is stiffness? When is stiffness important?

5. What is Young modulus?

6. What is strength?

7. What is yield strength? Why is fracture strength always greater than yield strength?

8. What is ductility? Give the examples of ductile materials. Give the examples of brittle materials.

8. What is toughness?

9. What properties of steel are necessary for the manufacturing of:

a) springs, b) car body parts, c) bolts and nuts, d) cutting tools?

10. Where is aluminium mostly used because of its light weight?

8. Machine-tools

Machine-tools are used to shape metals and other ma­terials. The material to be shaped is called the workpiece. Most machine-tools are now electrically driven. Machine-tools with electrical drive are faster and more ac­curate than hand tools: they were an important element in the development of mass-production processes, as they allowed individual parts to be made in large numbers so as to be interchangeable.

All machine-tools have facilities for holding both the workpiece and the tool, and for accurately controlling the movement of the cutting tool relative to the workpiece. Most machining operations generate large amounts of heat, and use cooling fluids (usually a mixture of water and oils) for cooling and lubrication.

Machine-tools usually work materials mechanically but other machining methods have been developed lately. They include chemical machining, spark erosion to machine very hard materials to any shape by means of a continuous high-voltage spark (discharge) between an electrode and a workpiece. Other machining meth­ods include drilling using ultrasound, and cutting by means of a laser beam. Numerical control of machine-tools and flexible manufacturing systems have made it possible for complete systems of machine-tools to be used flexibly for the manufacture of a range of pro­ducts.