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(a) The design and manufacture of the engine crankshaft in high performance sports cars must take into account both metal fatigue and metal hardness - Leaving Cert Engineering - Question 2 - 2019
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(a) The design and manufacture of the engine crankshaft in high performance sports cars must take into account both metal fatigue and metal hardness. (i) Describe t... show full transcript
Worked Solution & Example Answer:(a) The design and manufacture of the engine crankshaft in high performance sports cars must take into account both metal fatigue and metal hardness - Leaving Cert Engineering - Question 2 - 2019
Step 1
Describe the terms metal fatigue and metal hardness.
Answer
Metal fatigue refers to the progressive structural damage that occurs in materials subjected to cyclic loading. It begins with the formation of small cracks under fluctuating stresses, which can grow and propagate over time, eventually leading to material failure. The phenomenon is critical in applications like engine components, where repeated stress cycles are common.
Metal hardness is a material's ability to withstand deformation, particularly indentation. It indicates the resistance of a material to scratching, abrasion, or penetration. Hardness can be measured using various methods, such as the Vickers, Brinell, or Rockwell tests, with each method employing specific techniques for quantifying the material's hardness.
Step 2
Describe, with the aid of a diagram(s), a test for metal hardness.
Answer
The Vickers hardness test is commonly used to assess the hardness of materials. In this test, a diamond indenter with a square pyramid shape is pressed into the material's surface under a specific load. The depth of the resulting indentation is measured and converted into a hardness value. The test is suitable for both hard and thin materials, which makes it versatile across various applications.
In the diagram, the angle of the indenter is typically set at 136 degrees, and the resilience of the material to indentation is evaluated through the length of the diagonal formed by the indentation.
Step 3
Using the graph paper supplied, plot the stress-strain diagram for metal A and the stress-strain diagram for metal B using the same graph axes.
Answer
To plot the stress-strain diagrams:
- Label the x-axis as 'Strain (x 1000)' and the y-axis as 'Stress (N/mm²)'.
- Plot the data points for metal A and metal B on the same axes:
- For Metal A, plot points: (0, 0), (0.5, 125), (1.0, 260), (1.5, 400), (2.0, 425).
- For Metal B, plot points: (0, 0), (0.5, 30), (1.0, 60), (1.5, 110), (2.0, 135).
- Draw smooth curves connecting the points to represent the stress-strain behavior of both metals.
Step 4
Describe, with the aid of a diagram, the type of fracture which will occur when metal A breaks and the type of fracture which will occur when metal B breaks.
Answer
When metal A breaks, it is likely to exhibit a brittle fracture characterized by a sudden failure with little to no plastic deformation. This type of fracture often occurs in materials that are hard and low ductility.
Conversely, metal B is expected to demonstrate a ductile fracture, which is characterized by significant plastic deformation prior to failure. This type of fracture typically shows necking and a cup-and-cone appearance at the fracture surface.
Step 5
Give one example of a metal that is consistent with the graph of metal A and one example of a metal that is consistent with the graph of metal B.
Answer
An example of a metal that is consistent with the graph of metal A is cast iron, known for its brittleness. On the other hand, aluminum or copper would be examples consistent with metal B, as these metals typically exhibit ductile behavior under loading.
Step 6
Outline one application for each of the following methods of NDT: Visual inspection, Dye penetrant testing, Magnetic particle testing, Eddy current testing.
Answer
- Visual Inspection: Used for assessing surface defects in components, such as cracks or corrosion, by direct observation.
- Dye Penetrant Testing: Employed to reveal surface defects in non-porous materials; a colored dye is applied and the excess is wiped off, allowing defects to be highlighted.
- Magnetic Particle Testing: Suitable for detecting surface and near-surface defects in ferromagnetic materials by applying a magnetic field and using magnetic particles to outline the flaws.
- Eddy Current Testing: Utilized for identifying surface and subsurface defects in conductive materials by inducing eddy currents and analyzing the response signal.
Step 7
Describe, with the aid of a diagram(s), one suitable radiography (x-ray) NDT method.
Answer
Radiographic testing (x-ray NDT) evaluates the integrity of materials by producing an internal photographic image. X-rays penetrate the test object, and a film placed behind it captures the radiation. Areas of the object that have flaws will appear darker on the processed film, indicating defects like voids or cracks.
In the diagram, the radiation source, test object, and resulting film image are illustrated, showcasing how the process is conducted.