Module 3 - Section 4 - Stress, Strain And Elastical Potential Energy Flashcards
What might happen to an object if it’s subject to a pair of opposite forces ?
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
What is Tensile Stress ?
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
What tensile strain ? And what’s the equation ?
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
What does a stress cause ?
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
Are tensile forces negative or positive ? And are compressive forces negative or positive ?
Tensile forces are regarded as positive
Compressive forces are regarded as negative
What does UTS stand for ?
Ultimate tensile strength
What is ultimate tensile strength ( UTS ) ?
It is the maximum stress that a material can take
What happens to a material when a greater and greater tensile force is applied to it ?
If the tensile forces applied to the material are increased then the stress on the material increases
What is the effect of stress on a material ( object ) ?
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
When the material breaks from too much stress - how is this represented on a stress - strain graph ?
The line starts to dip after the UTS - this indicates that the material has broke
The UTS being the highest point on the graph
What do engineers have to consider about the materials when designing a structure ?
Engineers have to consider the UTS and the breaking stress of a material when designing a structure
What is elastic potential energy ?
Elastic potential energy is the energy stored in a stretched material
What has to be done in order to deform a material ?
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
How can you figure out work done on a force extension graph ?
On a force against extension graph - work done is given by the area under the graph
Where does all the work done get stored before the material reaches its elastic limit ?
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 )
