Materiels Flashcards
Define what a bulk property is
mechanical properties that arise from the atoms or molecules acting together after bonding
Give the equation for density
Density = Mass / Volume
Define Hookes Law
The force needed to stretch a spring is directly proportional to it’s extension from its natural length giving rise to Force = Spring Constant x Extension
In a Force - Extension graph what happens when the constant gradient suddenly slopes downward
The spring has reached the limit of proportionality
What happens to a spring after it passes the limit of proportionality
- The spring elastically deforms causing hookes law to no longer apply as force is no longer directly proportional to extension and less force is able to cause larger extensions
When does a spring reach its elastic limit
At the point of elastic deformation, the limit of proportionality of the string
What happens when a spring reaches its elastic limit
The spring will begin to behave and deform plastically, so the shape changes cannot be reversed
Define Plastic deformation
Where an object deforms to the point that it will not return back to its original shape
When 2 springs are connected in parallel how do you calculate their combined spring constant
K(Total) = K(1) + K(2)
When 2 springs are connected in series how do you calculate their combined spring constant
1/K(Total) = 1/K(1) + 1/K(2)
Describe the equation for work done on springs
Work done = 1/2 x Force x extension
Define what a tensile force is
A pulling force on an object
In a Force-Extension graph what does the area under the loading curve equal?
Work done
Why on the Force-extension graph for loading and unloading rubber different
As it deforms and energy is also wasted in the thermal store
Give the equation for stress
Stress = Force / Cross Sectional Area
Give the equation for Strain
Strain = Extension / Original Length
Give the equation for Youngs Modulus
Youngs Modulus = Stress / Strain = (Force x Length) / (Area x Extension)
Define Youngs Modulus
The measure of stiffness of a material and ability to withstand a force without an extension
In order, list the stages of change on a Stress-Strain Graph
- P - Limit of proportionality where stress is no longer directly proportional to strain
- E - The material becomes elastically deformed
- Y1 - Yeild point 1 where the material weakens temporarily
- Y2 - Yeild point 2 where a small increase in stress causes a larger increase in strain as the wire undergoes plastic flow
- UTS - Ultimate Tensile Stress - Maximum tensile stress that can be reached
- B - Breaking point where the wire looses its strength, extends, becomes narrower at its weakest point and finally fractures
