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Following an analysis of a road accident black-spot, it has been decided to reinforce the crash barrier shown with an additional post - Leaving Cert Engineering - Question Question 1 - 2014
Question Question 1
Following an analysis of a road accident black-spot, it has been decided to reinforce the crash barrier shown with an additional post. The post is to be centered bet... show full transcript
Worked Solution & Example Answer:Following an analysis of a road accident black-spot, it has been decided to reinforce the crash barrier shown with an additional post - Leaving Cert Engineering - Question Question 1 - 2014
Step 1
Analyse the main properties of metals A, B and C.
Answer
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Metal A:
- High ductility, allowing for significant elongation under load.
- Suitable for applications requiring flexibility but may not handle high loads well due to its comparatively small load capacity.
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Metal B:
- Can withstand reasonable loads, making it good for moderate stress applications.
- However, it is brittle and may fracture under excessive stress.
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Metal C:
- Exhibits strength in tension and does not show excessive brittleness.
- Its ability to withstand impact without stretching makes it a strong candidate for safety applications like crash barriers.
Step 2
Select the most suitable metal from A, B and C for the additional post and outline two reasons for your selection.
Answer
The most suitable metal for the additional post is Metal C.
- Reason 1: Metal C is strong in tension, which is critical for the structural integrity of the crash barrier as it will endure various forces during an impact.
- Reason 2: It is not excessively brittle and can withstand impacts, ensuring that it will perform well under the stress encountered in real-world scenarios.
Step 3
Using the graph paper supplied, plot the Stress-Strain diagram for the alloy and determine:
Answer
To plot the Stress-Strain diagram, follow these steps:
- Mark the axes: Label the x-axis as 'Strain (× 1000)' and the y-axis as 'Stress (N/mm²)'.
- Plot the points: Using the stress and strain values provided, plot each corresponding point on the graph.
- Connect the points: Once all points are plotted, connect them smoothly to form the Stress-Strain curve.
After plotting the graph:
- For Young’s modulus of elasticity, calculate it using the formula:
ext{Young's Modulus} = rac{ ext{Stress}}{ ext{Strain}}
Using the initial linear portion of the graph, Young's modulus is determined to be 90 kN/mm².
- For 0.1% proof stress, identify the point on the graph where the offset of 0.1% strain intersects with the curve. This value is found to be 332 N/mm².
Step 4
Evaluate the quality of a weld.
Answer
The weld shows signs of porosity, which is a common weld defect caused by insufficient shielding during welding. The presence of contaminants or inadequate weld settings can lead to gas entrapment, reducing the overall strength of the weld. It is essential to ensure proper surface preparation and shielding techniques to avoid such defects.
Step 5
Describe, with the aid of a diagram, a non-destructive test suitable for testing weld quality.
Answer
One suitable non-destructive test for evaluating weld quality is X-ray Radiography. This method involves passing X-ray radiation through the weld. Here’s a simplified description:
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Diagram: In the diagram, illustrate the X-ray source on one side and a film or digital sensor on the opposite side. Indicate the weld area in the middle.
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Process: If the weld is sound, the amount of radiation absorbed is uniform, showing no significant dark areas on the film. However, if defects such as cracks or porous areas exist, they absorb less radiation, resulting in darker spots on the film, indicating potential failure points.
This test is essential for verifying the integrity of welds without damaging the material.