Photo AI
(a) (i) Describe the principle of operation of any one impact test - Leaving Cert Engineering - Question 2 - 2012
Question 2
(a) (i) Describe the principle of operation of any one impact test. Impact testing will determine the toughness of the material. Test pieces are notched and held in... show full transcript
Worked Solution & Example Answer:(a) (i) Describe the principle of operation of any one impact test - Leaving Cert Engineering - Question 2 - 2012
Step 1
Describe the principle of operation of any one impact test.
Answer
Impact testing is used to determine the toughness of a material by measuring the energy absorbed during fracture. The test piece, typically notched, is fixed in a machine where it's struck by a pendulum. The energy absorbed during the impact is quantified, providing an evaluation of the material's toughness. For example, the Izod impact test involves a specific setup where the test specimen is positioned vertically and has a designated striking energy, such as 167 joules.
Step 2
Compare the two impact tests represented in diagrams A and B.
Answer
Impact test A (Charpy Test) and Impact test B (Izod Test) differ in their setups and applications:
-
Impact test A (Charpy Test):
- Utilizes 300 joules striking energy.
- The test specimen is held horizontally.
- Clamped at both ends.
- Notch faces the striker directly.
-
Impact test B (Izod Test):
- Uses 167 joules striking energy.
- The specimen is held vertically.
- Clamped at one end.
- The notch facing the striker is oriented differently.
Step 3
Describe the degree of brittleness in each of the metals shown.
Answer
The degree of brittleness in each of the metals is as follows:
- Brass: Characterized as a brittle metal with no ductility, meaning it tends to break without significant deformation.
- Copper: Considered not brittle; it is a ductile metal, allowing for extensive deformation before breaking.
- Mild Steel: Not classified as a brittle metal, showing good ductility and toughness.
Step 4
Explain the difference between the elastic state and the plastic state when mild steel is subjected to a tensile test.
Answer
In the tensile testing of mild steel, two distinct phases are observed:
- Elastic State: During this stage, the material elongates proportionately with the applied load. If the load is removed, the material returns to its original dimensions.
- Plastic State: Beyond the elastic limit, the material undergoes plastic deformation, where it does not return to its original shape upon unloading. In this phase, load increments yield considerable strain with minimal load increase, leading to necking and potential fracture.
Step 5
Identify two NDTs that examine surface imperfections and two NDTs that detect internal flaws.
Answer
Surface imperfections can be examined using methods such as:
- Visual inspection: A straightforward method to detect surface faults.
- Penetrant test: This technique identifies surface-breaking flaws using liquid penetrants.
For detecting internal flaws, the following methods are used:
- Radiography (x-ray) test: Utilizes x-rays to identify internal defects in the material.
- Ultrasonics: Employs high-frequency sound waves to locate internal flaws.
Step 6
Describe, with the aid of suitable diagrams, one non-destructive test used to check for internal faults in welded joints.
Answer
One common non-destructive testing method for internal faults in welded joints is X-ray / Radiography testing. This technique involves passing X-rays through the weld joint to create a film on the opposite side:
- If no defects are present, the absorption is consistent.
- If defects exist, they cause variations in absorptive properties, creating darker spots on the film indicating flaws. This method provides an effective way to assess the integrity of welds without damaging the material.