Monday, September 16, 2019
Engineering HSC Civil Structures
1. What development in motor cars led to the need to replace the block brake? What was the replacement? With the adoption of pneumatic rubber tyres for cars in 1895, the block brake became impractical and was replaced as an automobile brake, and was replaced by the contracting band brake. 2. Who invented the drum brake? In what year did this occur? In 1902 Louis Renault invented the internal expanding drum brake. 3. Why was the drum brake superior to its predecessors? First, the shoes are enclosed on the drum so the friction lining is away from water or dirt, so they last longer. The drum brake also exhibits servo-assistance, in both forward and reverse; the leading shoe exhibits servo assistance in forward travel, the trailing shoe in reverse travel. 4. Why are the disc brakes used extensively now? The disc brake offers better heat dissipation than the drum brake and also offers better weather performance as water is thrown off the disc by centrifugal force. 5. Why is asbestos still allowed in brake linings in Australia? Asbestos gave the break lining greater stability at higher temperatures, thus the linings are more resistant to break failure form the heat. 6. The coefficient of friction (Ã µ) is ratio between what two values? The coefficient of friction is the ratio of the frictional force present and the normal reaction to the matting surfaces. Ã µ=FFRN 7. What is the tensile stress in a brake cable of diameter 2 mm if the tensile force in the cable is 200N? 8. Draw a stress strain curve for mild steel; label the proportional limit, the upper and lower yield points and the UTS. . What is the difference between elastic and plastic deformation? 10. State Pascals principle. Why is it important to hydraulics? 11. What is steel? 12. What is the difference between austenite and ferrite? 13. What is pearlite? 14. What happens to the hardness of steel as the amount of cementite increases? 15. Describe what martensite is. 16. Why is manganese added to steels? 17. What effect will nickel have if added to a low alloy steel? 18. Why is molybdenum added to the nickel-chromium steels? 19. Why is Hadfield steel used for? What is different about its structure at room temperature as opposed to plain carbon steels? 20. There are three types of stainless steels available. List three and describe the uses of each? 21. Which stainless steel is non-magnetic? 22. What is the difference cast iron and steel? 23. Carbon appears in different forms in cast irons, how does it appear in white cast iron and grey cast iron? 24. Which type of grey cast iron is stronger, fine or course? 25. How do SG cast iron and CG cast iron differ? 26. Blackheart malleable cast iron has free carbon present in Whiteheart malleable cast iron? 27. Is free carbon present in Whiteheart malleable cast iron? 28. Why is copper added to break pads? 29. What type of resin is used to bind the break pad together? 30. Draw two stress strain diagrams, one showing high toughness, and one displaying high strength but a brittle failure. 31. What are the four hardness tests available? 32. Find the tension in the vertical and horizontal cables for the brake system shown. Slove this problem graphically then analytically.