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The aluminium alloy wheel of a car, as shown, is subject to fatigue and must therefore be able to withstand shock and impact loads, such as striking kerbs and poor road conditions - Leaving Cert Engineering - Question 2 - 2015
Question 2
The aluminium alloy wheel of a car, as shown, is subject to fatigue and must therefore be able to withstand shock and impact loads, such as striking kerbs and poor r... show full transcript
Worked Solution & Example Answer:The aluminium alloy wheel of a car, as shown, is subject to fatigue and must therefore be able to withstand shock and impact loads, such as striking kerbs and poor road conditions - Leaving Cert Engineering - Question 2 - 2015
Step 1
Explain the term metal fatigue.
Answer
Metal fatigue refers to the phenomenon where a material undergoes failure after repeated loading and unloading cycles, leading to the development of small cracks. These cracks can grow under the action of fluctuating stresses, leading to structural failure even when the load is below the ultimate strength of the material.
Step 2
Describe in detail a suitable mechanical test to determine the aluminium alloy's ability to withstand shock or impact loads.
Answer
A suitable mechanical test to determine the ability of the aluminium alloy to withstand impact loads is the impact test. In this test, samples are clamped in a vice and a pendulum is released to strike the sample, imparting energy and assessing its toughness. The energy absorbed during fracture provides a numerical value for the material's toughness. The Charpy impact test, which uses a specific striking energy amount, is commonly applied, with values like 167 joules indicative of the material's impact resistance.
Step 3
Step 4
Analyse the effects of the tensile test on the shape of the test specimen shown at both B and C.
Answer
Up to point B, the specimen will elongate uniformly under load. At point B, it reaches the ultimate tensile strength before necking begins, leading to a localized reduction in area. At point C, the specimen likely fractures in a cup and cone shape, indicating that one side has a rough surface while the other has a hollow appearance due to the uneven stresses during fracture.
Step 5
Step 6
Describe, with the aid of a diagram, the non-destructive test to examine for internal flaws identified at (e) (i) above.
Answer
Ultrasonic testing involves transmitting high-frequency sound waves through the material. If internal flaws such as cracks or voids are present, they will reflect the sound waves back, indicating the location and size of the defects. A diagram illustrating a sound beam being sent through the material can show how reflections are interpreted to determine the presence of internal flaws.