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(a) (i) What are the advantages of mechanical testing? Mechanical tests are carried out on materials to assess how they might perform when they are put into use - Leaving Cert Engineering - Question 2 - 2007
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(a) (i) What are the advantages of mechanical testing? Mechanical tests are carried out on materials to assess how they might perform when they are put into use. Ma... show full transcript
Worked Solution & Example Answer:(a) (i) What are the advantages of mechanical testing? Mechanical tests are carried out on materials to assess how they might perform when they are put into use - Leaving Cert Engineering - Question 2 - 2007
Step 1
What are the advantages of mechanical testing?
Answer
Mechanical tests are carried out on materials to assess how they might perform when they are put into use. Many of these tests destroy the sample material but are carried out for several reasons, including:
- Values for properties such as strength, ductility, hardness, toughness, elasticity, fatigue, creep, etc. can be ascertained.
- Standardisation of components can be achieved.
- Quality control is maintained.
- The success of heat treatments can be measured.
Step 2
Compare Izod and Charpy impact tests.
Answer
Both tests involve striking a notched bar with a pendulum from a predetermined height to deliver a specific impact, with the following distinctions:
| Izod Test | Charpy Test |
|---|---|
| 167 joules striking energy | 300 joules striking energy |
| Test specimen held vertically | Test specimen held horizontally |
| Test specimen is clamped at one end | Test specimen is clamped at both ends |
| Notch on test specimen faces striker | Notch on test specimen faces away from striker |
Step 3
Identify the basic information that can be obtained from a tensile test.
Answer
The following information can be obtained from a tensile test:
- Young's Modulus
- Proof or yield stress
- Tensile strength
- Percentage elongation
- Percentage reduction in area
- Properties such as ductility and shear strength can also be ascertained.
Step 4
Outline the properties associated with materials A, B and C.
Answer
Material A exhibits a small amount of elasticity with minimal ductility, characterizing it as a brittle material, such as cast iron.
Material B shows good ductility with a definite elastic limit, typical of low carbon steel.
Material C is quite ductile, demonstrating significant stretching with only a small increase in load, exemplified by copper.
Step 5
Why are non-destructive tests used in the manufacture of engine parts?
Answer
Non-destructive tests are employed to ensure:
- That parts can be tested for quality.
- That expensive components need not be destroyed during testing.
- That tests can be carried out for flaws at surface level or internally.
Step 6
Describe, with the aid of a diagram, a suitable non-destructive test for assessing welds for internal faults.
Answer
A suitable non-destructive test for assessing welds for internal faults would be X-ray testing. In this method:
- Radiation from an x-ray tube is passed through the weld.
- To detect defects, the radiograph is produced consistently with the x-ray beam.
- A defect in the weld results in less absorption of rays, causing variations in the computed image intensity. This is captured on film.
A negative film will show defects as dark spots.