MATERIAL PROPERTIES 2 PROFESSIONAL ENGLISH IN USE FOR ENGINEERING

 

PROFESSIONAL ENGLISH IN USE FOR ENGINEERING UNIT 19. MATERIAL PROPERTIES 2

 

A Hardness The hardness of a material affects its durability – that is, how long it will last. Generally, hard materials are more durable than soft materials, because they are better at resisting wear – progressively worsening damage – to their surfaces. Hardness can be defined in two main ways: B Fatigue, fracture toughness and creep The article below is from an aviation magazine. In aircraft construction, special attention must be paid to two materials problems that are well understood by mechanical and structural engineers. One is fatigue, often called metal fatigue in metals. This problem is cause by cyclic leads- forces that continually vary. In aircraft, the wings are affected by cyclic loading as they frequently flex, continually bending up and down due to air turbulence. The consequence of fatigue is micro-cracking – the formation of cracks too small to see with the eye, C Basic thermal properties Some materials conduct (carry or transmit) heat better than others. Therefore, thermal conductivity varies, depending on the material. Copper, for example, is an excellent thermal conductor. Polystyrene, on the other hand, is an excellent thermal insulator (and so a very poor thermal conductor). EXERCISES 19.1 Complete the design brief for part of a cutting machine using four of the words in the box. Look at A opposite to help you. abrasion durability durable hard indentation scratch soft The cutting wheel will be surrounded by transparent guards. These will allow the operator to see the cutting wheel at all times, and will shield the operator from flying metal fragments. The guards must therefore be constructed from material with a high degree of (1) ___________ hardness, to 19.2 Match the descriptions (1-4) to the technical terms (a-d). look at B opposite to help you. 1 the cause of fatigue a creep 2 the consequence of fatigue b cyclic loads 19.3 Complete the extract from an electrical design handbook using words and expressions from C opposite. When comparing copper and aluminium as materials for electrical wires, it is necessary to consider their thermal properties. For instance, in situations where high temperatures are involved, it is important to understand how quickly wires (1)___________ heat along their length-for example away from hot parts, such as motors, towards heat-sensitive electrical

ANSWER KEY