smc-3714-90-Load-ext diagram

ENGINEERING, CS 2018 HSC 23b

The steel used in the chassis members was tested.

The load–extension graph represents the data collected during the testing of a specimen of the steel.

Before testing, the specimen was 1020 mm long with a cross-sectional area of 100 mm².

Calculate Young's modulus for this steel. (4 marks)

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Describe the physical changes that occur in the specimen tested in part (i) when a 20 kN load is applied and then removed, compared to when a 30 kN load is applied and then removed. (2 marks)

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i. Young’s modulus

`F = 20 xx 10^3\ text{N}, l = 1020\ text{mm}, e = 1\ text{mm}, text{A} = 100\ text{mm}^2`

`E`	`=(Fl)/(eA)`
	`=(20 xx 10^3 xx1020)/(1 xx 100)`
	`=204 xx 10^3`
	`=204\ text{GPa}`

ii. → Elastic deformation is produced by the 20 kN load.

→ After initial stretching the specimen returns to its original length.

→ Plastic deformation is produced by the 30 kN load.

→ The specimen stays deformed subsequent to release.

Show Worked Solution

i. Young’s modulus

`F = 20 xx 10^3\ text{N}, l = 1020\ text{mm}, e = 1\ text{mm}, text{A} = 100\ text{mm}^2`

`E`	`=(Fl)/(eA)`
	`=(20 xx 10^3 xx1020)/(1 xx 100)`
	`=204 xx 10^3`
	`=204\ text{GPa}`

♦ Mean mark (i) 51%.

ii. → Elastic deformation is produced by the 20 kN load.

→ After initial stretching the specimen returns to its original length.

→ Plastic deformation is produced by the 30 kN load.

→ The specimen stays deformed subsequent to release.

ENGINEERING, CS 2022 HSC 20 MC

For a particular material, specimens of different sizes were tested. A load-extension diagram and a stress-strain diagram are to be drawn for each specimen.

The shape of which diagram(s) will be affected by the size of the specimen tested?

Both diagrams
Neither diagram
The stress–strain diagram only
The load–extension diagram only

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`D`

Show Worked Solution

→ The stress–strain diagrams will be the same shapes as both stress and strain are calculated by dividing by constants (original area and original length).

`=>D`

♦♦ Mean mark 36%.