LOAD, STRESS AND STRAIN PROFESSIONAL ENGLISH IN USE FOR ENGINEERING

 

PROFESSIONAL ENGLISH IN USE FOR ENGINEERING UNIT 30. LOAD, STRESS AND STRAIN

 

A Load When engineers design a machine or structure, they need to know what forces will be exerted on it (put pressure on it). In engineering, forces are called loads. Usually, several different loads will act on – apply force to – the components in a machine, or the members (parts) of a structure. a component or member which is designed to carry (or bear) a load is called a load-bearing component or member. B Stress and strain The extract below is from an engineering textbook. In a test, a thick cable is used to pick up a heavy object. The cable stretches slightly, but lifts the weight. A second test is done using a thinner cable – one with only half the cross-sectional area of the thick cable. This time, the cable stretches, then breaks. Why did the thinner cable fail? Not due to a higher load, as the weight was the same. The failure was due to the stress. Stress is force per unit of area, and is measured in newtons per square metre, or Pascals (1 N/m2 = 1 Pa). The thinner cable was therefore stressed twice as much as the thick cable, as the same load was concentrated into a cross-sectional area that was 50% smaller. EXERCISES 30.1 Replace the underlined words and expressions with alternative words and expressions from A opposite and Appendix V. If you look at the objects around you. It’s difficult to find something that couldn’t be smashed with a hammer. But if you laid a hammer down carefully on any of those objects, the (1) force which it (2) put on them wouldn’t be sufficient to cause even the slightest damage. This comparison illustrates the difference between: ·         a (3) moving force. Which combines mass and movement to apply (4) a shock ·         a (5) still force, which consists only of an object’s (6) own mass. 30.2 Complete the technical checklist (1-7) based on the questions (a-g), using words from A and B opposite and Appendix V. The first one has been done for you. a. Which components need to carry load? b. What types of load will be carried by each part? Which loads will remain constant, and which will differ depending on use and circumstances. c. What amount of load will be exerted, in newtons?   1. Determine which components are _____load bearing ______. 2. Analyse the types of load that will ___________ on each part. Assess  ___________ loads and  ___________ loads.

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