smc-3715-40-Cracking

ENGINEERING, CS 2025 HSC 22b

A building is being partially demolished and replaced. Part of the original structure will be retained.

Engineers want to retain some steel components of the building.

Describe a suitable process which could be used to detect surface cracks in ONE steel component of the building. (3 marks)

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Magnetic particle inspection (MPI) is a non-destructive testing method suitable for detecting surface cracks in steel components.
The steel component is first cleaned and then magnetised using an electromagnet or permanent magnet. Iron oxide particles suspended in a liquid carrier are then applied to the surface.
Where surface cracks exist, magnetic flux leaks outward and attracts the particles, forming a visible cluster that clearly marks the location and extent of any defect.
The component is then inspected under white or ultraviolet light, and the severity of any cracking is assessed before a repair or replacement decision is made.

Show Worked Solution

Magnetic particle inspection (MPI) is a non-destructive testing method suitable for detecting surface cracks in steel components.
The steel component is first cleaned and then magnetised using an electromagnet or permanent magnet. Iron oxide particles suspended in a liquid carrier are then applied to the surface.
Where surface cracks exist, magnetic flux leaks outward and attracts the particles, forming a visible cluster that clearly marks the location and extent of any defect.
The component is then inspected under white or ultraviolet light, and the severity of any cracking is assessed before a repair or replacement decision is made.

A highly stressed steel plate develops a fatigue crack while in service.

Which of the following is the most effective temporary method to slow or stop the crack's growth?

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`B`

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A and D are possible permanent solutions, but as the question requests the most effective temporary method it must be B or C.
Drilling a hole at the tip of the crack is a more effective solution as it prevents the crack from penetrating further, while drilling a hole at the start would not prevent the cracks growth.

`=>B`

The diagram shows a steel plate with a crack developing.

Which of the following would best prevent the crack from growing?

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`C`

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Drilling a stop hole at the end of a crack can be effective in arresting crack growth as it reduces stress concentration at the crack tip.

`=>C`

Mean mark 59%.