4+5 Revision Flashcards
What is Hooke’s law?
Extension is proportional to force (when elastic limit is not exceeded)
F=Kx
In Hooke’s law what is k?
The spring constant/stiffness
In Hooke’s law what is x?
The extension
What happens to the spring constant in series?
1/kt=1/k1+1/k2+1/k3…
What happens to the spring constant in parallel?
k=k1+k2+k3
What are the four kinds of deformation?
tension, compression, torsion, shear
In an F/X graph what is the area under the graph?
The work done to stretch the object
What is the formula for elastic potential energy?
PE=1/2kX^2
Is the young modulus an object or material property?
material
What is the area under a stress v strain graph?
The energy absorbed per unit volume
What is the structure of MOST materials?
crystalline
What is a crystalline structure?
A regularly repeating pattern of atoms or ions
What structure do polymers have?
Can be either crystalline or amorphous
What is an amorphous structure?
Irregular, jumbled structure
Name two amorphous materials
Cross linked rubber
Glasses
What four things give evidence of the size of an atom?
- Rayleigh’s oil drop experiments
- X-ray diffraction
- modern electron microscopes
- Atomic force or tunneling microscopes
What is the size of one atom?
about 0.5*10^-9m
In theoretical perfect structures what stress is needed for a whole plain of atoms to slip?
roughly E/3 Pa
In actual structures what stress is needed to move a whole plane of atoms?
roughly E/1000 Pa
What are dislocations?
Essentially an extra half plane of atoms
How can metallurgy be used to control the properties of materials?
- alloying
- thermal treatments
- mechanical deformation
How does alloying affect material properties?
Foreign atoms obstruct dislocation movement to raise the yield stress
How do thermal treatments affect the properties of metals?
It makes precipitates and modifies the number and mobility of dislocations
How does mechanical deformation affect the mechanical properties of metals?
Dislocations multiply and become entangled
What is annealing?
Heating to a very high temperature
Causes more plastic deformation (easier to shape)
What is quenching?
cooling very fast after heating to very high temperatures
makes material very brittle
What is tempering?
Heating with a lower flame and then cooling slowly
Original properties should be recovered
