2. Materials Flashcards
Force on a spring equation
Force = spring constant (k) x extension
What does a larger spring constant mean
The spring is stiffer
Equation for stress
Stress = Force / Area
Equation for strain
Strain = extension / original length
Youngs modulus equation
Stress / strain
What are the conditions to calculate youngs modulus
That the material is obeying hookes law
What does the area under a force extension graph represent
The work done
If a material has gone over the limit of elasticity then what happens
It will not return to its original shape or length
Equation for Elastic Potential Energy
EPE = 1/2 x k x X^2
EPE = 1/2 x F x X
What are the three classifications of solids
Crystalline
Amorphous
Polymeric
What are the properties of a crystalline material
Ductile
Tough
Made from a lattice structure
What are the properties for an Amorphous structure
This has a non ordered structure
Rigid
Strong
What are the properties of a Polymeric structure
Long chained polymers
Strong
Flexible
Give an example of a Crystalline structure
Diamonds, Sugar, Most metals
Give an example of an amorphous structure
Glass or ceramics
Give an example of a polymeric structure
Plastics, Clothing and Meats
Define necking
When the cross sectional area of a material becomes so small that it deforms plastically and could create a ductile fracture at that point
What are edge dislocations
When crystalline structures are put under strain the gaps in between atoms allow a row of to slip out of formation, spreading the dislocation throughout the metal. This makes it much weaker
How can you prevent or reduce the effects of edge dislocation
Create a compound of different metals which introduces different sized atoms into the structure which stops edge dislocation from spreading.
What does introducing more grain boundaries do to a metal
This means that there are more boundaries so then edge dislocation is more contained and cannot spread in the metal
What causes brittle fractures
Crack Propagations
What is crack propagations
When small imperfections in the surface of a metal come under stress the cracks become bigger until it fractures open
What do the imperfections on a metal decrease
The breaking stress of a material
What does a graph of a brittle material look like
They have a steep gradient so a large young modulus
But also they are not strong so they fracture before they can stretch further
What does a graph of a rubber material look like
It creates a hysteresis graph meaning the loading curve is above the unloading curve
What does the area on a hysteresis graph represent
The energy per unit volume stored as thermal energy
Does a rubber material have a low or high youngs modulus
Very low as it isnt a stiff material
What happens to rubber materials when it is overloaded
The rubber then cannot return back to its original form or breaks
