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The engine crankshaft pictured opposite has failed due to metal fatigue - Leaving Cert Engineering - Question 3 - 2022
Question 3
The engine crankshaft pictured opposite has failed due to metal fatigue. (i) Explain the term metal fatigue. (ii) Outline two design considerations which will help... show full transcript
Worked Solution & Example Answer:The engine crankshaft pictured opposite has failed due to metal fatigue - Leaving Cert Engineering - Question 3 - 2022
Step 1
Explain the term metal fatigue.
Answer
Metal fatigue is the initiation and propagation of cracks in a material due to cyclic loading (on/off loading). Once a fatigue crack forms, it grows incrementally with each loading cycle. The crack will continue to expand until it reaches a critical size, leading to total failure of the structure.
Step 2
Outline two design considerations which will help minimise metal fatigue in the manufacture of crankshafts.
Answer
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Component Size: Ensuring that the size of the component is sufficient to withstand the expected loading conditions without excessive stress concentrations.
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Material Choice: Selecting materials with high fatigue resistance and durability, and incorporating surface treatments that enhance material properties.
Step 3
Explain the importance of quality control (QC) in engineering manufacture.
Answer
Quality control (QC) is a systematic approach to ensure that manufactured products meet specified standards and criteria. It involves regular inspections and testing of materials and products throughout the manufacturing process, ensuring that any defects are identified and rectified, ultimately leading to safe and reliable end products.
Step 4
Using the graph supplied, plot the stress-strain diagram for metal A and the stress-strain diagram for metal B on the same graph axes, as shown.
Answer
To plot the stress-strain diagrams:
- Metal A graph begins at (0, 0) and increases steeply, reaching the maximum stress of 425 N/mm² around a strain of 4.0.
- Metal B graph starts lower at a stress of 30 N/mm², with its curve gradually rising to a stress of 155 N/mm² with a corresponding higher strain, demonstrating its ductility.
Step 5
With reference to metal B, describe with the aid of a diagram, the profile of the tensile test specimen when subjected to a load value of 158N/mm².
Answer
At a load of 158N/mm², metal B exhibits necking, which is evident in the diagram:
- The test specimen will show a pronounced narrowing in the middle section, indicating the onset of plastic deformation.
This necking leads eventually to fracture, as the load can no longer be supported due to the reduced cross-sectional area.
Step 6
Step 7
Describe, with the aid of a suitable diagram(s), the process of magnetic particle testing.
Answer
Magnetic particle testing involves the following steps:
- Preparation: The metal surface is cleaned to remove any contaminants.
- Magnetization: A magnetic field is applied to the ferromagnetic component.
- Application of Particles: Magnetic particles are applied. Any surface cracks will show a distortion in the magnetic field, leading to a visible accumulation of particles over defects.
A diagram can depict a test setup featuring a magnetic yoke and a specimen being inspected.
Step 8
Outline two benefits of using NDT, such as magnetic particle testing, in the gas and oil industries.
Answer
- Product Safety: NDT ensures that products do not have internal or hidden defects, preventing potential failures that could lead to accidents.
- Cost Effectiveness: NDT methods are generally less expensive than destructive testing, allowing for more extensive inspections with minimal downtime.