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a) (i) Outline two reasons for the mechanical testing of metals to the point of destruction - Leaving Cert Engineering - Question 2 - 2010
Question 2
a) (i) Outline two reasons for the mechanical testing of metals to the point of destruction. 1. It can give specific data to determine the degree of properties such... show full transcript
Worked Solution & Example Answer:a) (i) Outline two reasons for the mechanical testing of metals to the point of destruction - Leaving Cert Engineering - Question 2 - 2010
Step 1
Outline two reasons for the mechanical testing of metals to the point of destruction.
Answer
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Mechanical testing provides specific data regarding the material's properties, which include hardness, toughness, ductility, and strength. These properties are crucial for understanding how a material will perform under various conditions.
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This testing helps to assess the suitability of materials before their application in actual products, ensuring that the right materials are used for the right purposes.
Step 2
Describe the main features of the mechanical test represented in the diagram, with reference to the following: Purpose of the test.
Answer
The purpose of the test is to determine the toughness of the material being tested. Toughness is a critical property that indicates how well a material can absorb energy before failing.
Step 3
Describe the main features of the mechanical test represented in the diagram, with reference to the following: Principle of operation.
Answer
In the impact testing machine, test pieces are notched and secured in a vice. A pendulum is released, striking the notched specimen, and the energy absorbed by the specimen during fracture is measured. This value indicates the toughness of the material, often expressed in Joules.
Step 4
Using the graph paper supplied, plot the load-extension diagram and determine: (i) The ultimate tensile strength (UTS).
Answer
To determine the UTS, the maximum load from the load-extension diagram is identified. In this case, the maximum load is given as 139 kN. Next, calculate the Ultimate Tensile Strength using the formula:
ext{UTS} = rac{ ext{Max Load}}{ ext{C.S.A}} = rac{139}{ rac{ ext{π}}{4} (16^2)}
Calculate the cross-sectional area (C.S.A.) using the diameter of the specimen (16 mm). Thus, the UTS is approximately:
Step 5
Using the graph paper supplied, plot the load-extension diagram and determine: (ii) The 0.1% proof stress.
Answer
To determine the 0.1% proof stress, first identify the proof load, which is given as 85 kN. The calculation is performed using the formula:
ext{0.1% Proof Stress} = rac{ ext{Proof Load}}{ ext{C.S.A}} = rac{85}{ rac{ ext{π}}{4} (16^2)}
This results in a 0.1% proof stress of approximately 0.42 kN/mm².
Step 6
Describe, with the aid of suitable diagrams, each of the following non-destructive tests (NDT): (i) Eddy current testing.
Answer
Eddy current testing is a method used primarily for non-ferrous metals with uniform sections. A coil carrying a high-frequency alternating current creates a magnetic field, which induces eddy currents in the tested material. The flow of these currents can highlight defects, enabling the identification of flaws within the material that can be recorded electronically.
Step 7
Describe, with the aid of suitable diagrams, each of the following non-destructive tests (NDT): (ii) Radiography (x-ray) testing.
Answer
Radiography involves passing radiation from an x-ray tube through a material. If defects are present, the radiation absorption varies according to the material’s density and integrity. A photographic film placed on the opposite side captures the radiation. Areas with defects will appear darker on the film. This technique allows for non-invasive inspection and evaluation of internal flaws.