Deformation

1. What is the ultimate tensile stress of a material?

• 1. the stress at which the material becomes ductile

• 1. the stress at which the material breaks

• the stress at which the material deforms plastically

• 1. the stress at which the material reaches its elastic limit

1. Two materials with the same dimensions were loaded to fracture; the graph shows the force-extension of these.

• 1. Both materials are plastic

• 1. Both materials have the same ultimate tensile stress

• 1. Both materials are brittle

• 1. Both materials obey Hooke’s law

1. The variation of the extension x of a spring with applied force F is shown.

2. Which shaded area represents the work done when the extension is increased from x1 to x2?

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The graph shows how the extension of a spring varies with the force used to stretch it.

What is the strain energy stored in the spring when the extension is 4.0 cm?

• 60 J

• 120 J

• 600 J

• 1200 J

What is the Young modulus of a metal?

• extension/force

• force/extension

• strain/stress

• stress/strain

In describing the behavior of a spring, the spring constant is used. Different loads are used to extend the spring by different amounts. To find the spring constant, which quantities are required?

• the elastic limit and the loads

• the elastic limit, extensions and the length of the spring

• the loads and the extensions of the spring

• the loads and the length of the spring

What is represented by the gradient of a graph of force (vertical axis) against extension (horizontal axis)?

• elastic limit

• spring constant

• stress

• the Young modulus

What is plastic deformation?

• Plastic deformation occurs when strain is not proportional to stress but when the load is removed the material returns to its original length.

• Plastic deformation occurs if, when the load is removed, the material contracts but a permanent stretching has occurred.

• Plastic deformation occurs until the extension is no longer proportional to the load

• Plastic deformation occurs when the material extends so that strain is directly proportional to stress.

The graphs show how force varies with extension and stress varies with strain for the loading of a metal wire.

The Young modulus for this wire is equal to

• the gradient of the force-extension graph

• the area between the force-extension graph and the extension axis.

• the gradient of the stress-strain graph.

• the area between the stress-strain graph and the strain axis

In stress-strain experiments on metal wires, the stress axis is often marked in units of 108 Pa and the strain axis is marked as a percentage. This is shown for a particular wire in the diagram.

What is the value of the Young modulus for the material of the wire?

• 6.0 × 10^7Pa

• 7.5 × 10^8Pa

• 1.5 × 10^9Pa

• 6.0 × 10^9 Pa