Module 3 - Section 4 - Stress, Strain And Elastical Potential Energy Flashcards

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1
Q

What might happen to an object if it’s subject to a pair of opposite forces ?

A

The object might deform i.e change shape

If the forces stretch the material they are tensile forces
If the forces squash the material they are compressive forces

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2
Q

What is Tensile Stress ?

A

Tensile stress is the force exerted per unit cross-sectional area on an object

The units of stress are Nm*-2 or pascals, Pa

O = F/A

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3
Q

What tensile strain ? And what’s the equation ?

A

It is defined as the change in length - the extension divided by the original length of the material

E = x / L

X=extension (m)

L= original length (m)

Strain has no units - its just a number

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4
Q

What does a stress cause ?

A

A stress causes a strain

A stress is caused when a force is applied to a material - while a strain is a deformation or change in shape of the material which is caused by the force exerted on the material

So when a force is applied this is stress —> and then this force extorted on the material cause a change in shape of the material —> this is called strain

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5
Q

Are tensile forces negative or positive ? And are compressive forces negative or positive ?

A

Tensile forces are regarded as positive

Compressive forces are regarded as negative

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6
Q

What does UTS stand for ?

A

Ultimate tensile strength

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7
Q

What is ultimate tensile strength ( UTS ) ?

A

It is the maximum stress that a material can take

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8
Q

What happens to a material when a greater and greater tensile force is applied to it ?

A

If the tensile forces applied to the material are increased then the stress on the material increases

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9
Q

What is the effect of stress on a material ( object ) ?

A

The effect of stress is that it starts to pull the atoms apart from one and other

So when stress is applied to a material - the atoms start to get pulled apart from each other and the more stress applied to it the more it gets closer to the materials UTS ( ultimate tensile strength ) and when it goes past the materials UTS then the material breaks

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10
Q

When the material breaks from too much stress - how is this represented on a stress - strain graph ?

A

The line starts to dip after the UTS - this indicates that the material has broke

The UTS being the highest point on the graph

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11
Q

What do engineers have to consider about the materials when designing a structure ?

A

Engineers have to consider the UTS and the breaking stress of a material when designing a structure

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12
Q

What is elastic potential energy ?

A

Elastic potential energy is the energy stored in a stretched material

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13
Q

What has to be done in order to deform a material ?

A

In order to deform a material - work has to be done in order to deform the material

Therefore anytime a material is stretched or compressed, work is done in deforming the material - because a stretch or compression in the material is a deformity

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14
Q

How can you figure out work done on a force extension graph ?

A

On a force against extension graph - work done is given by the area under the graph

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15
Q

Where does all the work done get stored before the material reaches its elastic limit ?

A

Before the elastic limit has been reached - all the work done in stretching and compressing the material gets stored in the elastic potential energy store of the material ( the potential energy in the material )

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16
Q

What is the work done on the wire ( in stretching it ) equal to ?

A

The work done on the wire by stretching it - is equal to the energy stored

17
Q

What are the 2 equations for elastic potential energy ?

A

E = 1/2 fx

E = 1/2 kx*2

18
Q

If the material is stretched beyond its elastic limit, where does some of the work get done ?

A

If the material is stretched beyond the elastic limit, some work is done separating atoms

This will not be stored as elastic potential energy and so its wont be released when the force is removed

19
Q

What is the point called when the material breaks ?

A

Breaking stress

20
Q

Why is the work done when stretching a wire 1/2Fx ?

A

This is because the force on the material isn’t constant - it rises from zero up to force F