Materials Flashcards
What is a compressive force
Forces that shorten an object
What is a Tensile Force
Forces that produce an extension
What is elastic deformation
A change in extension of an object where once the forces are removed, the object will return to its original length.
What is plastic deformation
When an object has permanent structural changes due to external forces and does not return to its original shape once forces are removed.
What is the elastic limit
The most extension an object can undergo before being plastically deformed.
What is Hookes Law
For a material within its elastic limit, the force
applied is directly proportional to the extension of the material.
What is Force constant
The measure of stiffness of an object. A spring with a large force constant is referred to as a stiff spring
What are the characteristics of a Force - Extension graph
Force is on the Y - Axis
Extension is on the X-Axis
Linear slope is the region of elastic deformation
Gradient of graph is the force constant of the spring.
Where linear slope ends is the elastic limit.
Area under graph is equal to work done on spring.
What happens to the work done on a spring when it is stretched or compressed
The work done is transferred to elastic potential energy. If the object is compressed or extended beyond its elastic limit, work done is transferred to changing the positions of atoms in the object.
Equation for elastic potential energy
Deriving from the area under force-extension graph, E=1/2Fx. Also known as Work done = Average force * Final extension. Also known as E=1/2kx^2
What is a loading curve
The curve that shows an objects extension due to force.
What is an unloading curve
The curve that shows an objects extension as force is removed.
What are the characteristics of a force extension graph of a metal wire
The loading graph follows hookes law until the elastic limit of the wire. The unloading graph will be identical for forces less than the elastic limit. If the Loading graph passes the elastic limit, it will not follow hookes law and the unloading graph will be parallel to it but not identical. Wire will be plastically deformed and will be permanently extended
What are the characteristics of a force extension graph of a rubber
Rubber bands do not obey hookes law. Both loading and unloading graphs are curved and different, and the rubber returns to its original shape after the forces are removed. A hysteresis loop is formed by the loading and unloading graph. More work is done loading rubber band then unloading. Thermal energy is released when unloading, given by the area inside the loop.
What are the characteristics of a force extension graph for polythene
Polythene does not obey hookes law. Low elastic limit and does not return to original size after being stretched.
