materials Flashcards
What is an elastic material ?
A material that does not have a limit of proportionality/can return to original shape
What is a plastic material ?
Material that can be permanently altered by applying force
What is the area under loading curve ?
Work done in stretching a spring
What is the area under unloading curve ?
energy released/stored
difference due to thermal
Where is the limit of proportionality ?
Where the graph is no longer a straight line
What is the limit of proportionality ?
Where a spring no longer obeys Hooke’s law
What is the elastic limit / Yield point ?
Where an object no longer returns to original length when force is removed
What does it mean if the loading and unloading curves end in the same place ?
the material behaves elastically
What does it mean if the loading and unloading curves don’t end in the same place ?
the material behaves plastically
How to calculate spring constant of 2 springs ‘in series’
spring constant of 1 spring / 2
How to calculate spring constant of 2 springs ‘in parallel’
spring constant of 1 spring x 2
What is tensile stress ? (and units)
F / A
Force per cross sectional area
Pa
What is tensile strain ? (and units)
(ΔL) / L
Extension per unit length
No Units
How to find the cross sectional area for tensile stress ?
Use a micrometer at several points and find a mean radius
- use A = πr²
How do you find the Youngs Modulus graphically ?
The gradient / Use values given with equation
How to find the Yield Stress ?
Stress at Yield Point / Elastic Limit
What does it mean if a material is ductile ?
Can deform without breaking
eg. Gelatine
What does it mean if a material is Brittle ?
Experiences no deformation before breaking
eg. carrot, pasta
What is the ultimate tensile stress / breaking stress ?
Amount of stress needed to break an object (highest point of stress on a graph)
What properties does glass have ?
brittle, no plastic deformation
What properties does copper have ?
ductile, undergoes significant plastic deformation
What happens when a material deforms plastically ?
energy/force aplies rearranges atoms -> can’t be recovered when force removed
work done ≠ energy stored
energy stored ≠ area under graph
In what conditions is the area under a graph equal to energy stored ?
When Hooke’s law is obeyed
What to do if a material is made of an alloy ?
Calculate them separately
