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C O U R S E 
Materials Science: 10 Things Every Engineer Should Know
James Shackelford, University of California, Irvine
C O U R S E   L E C T U R E 
Dislocations Explain Plastic Deformation
Notes taken on January 17, 2016 by Edward Tanguay
six materials that engineers have to work with:
1. metals
2. polymers
3. ceramics
4. glass
5. fiberglass
6. semiconductors
in each case there is a difference at a very low level
e.g. in the case of fiberglass, the microscopic architecture of the fiber-reinforced composite
underlying principle
a mantra of material science: structure leads to properties
differences at the atomic or microscope level lead to differences at the macroscopic or engineering level
stress-strained curve
early concept of atomic bonding led to characteristic of stiffness
bonding force curve is the first derivative of the bonding energy curve
two carbon atoms in a polymer
two aluminum atoms in a aluminum alloy
the difference between an aluminum and oxygen ion in an aluminum oxide
at the atomic scale, we are trying to tear atoms apart
a macroscopic scale manifestations of atomic bonding
production of materials
make them fast or slow to affect desired properties
how a crystal-structure deformation is the basis of plastic deformation
edge dislocation
metallic crystal structure
a cubic arrangement of atoms
in the middle, we have squeezed in an extra half-plane of atoms
compare to perfect crystal
contrast it with the dislocation area
if you draw a loop around it, you don't come back to the same place: Burgers vector
Burgers vector
named after Dutch physicist Jan Burgers, is a vector, that represents the magnitude and direction of the lattice distortion resulting from a dislocation in a crystal lattice.
this is the basis of quantifying this structure in a mathematical way
the movement of those linear defects is the basis of plastic deformation
an object in the plastic deformation range will first have undergone elastic deformation, which is reversible, so the object will return part way to its original shape
deformation refers to any changes in the shape or size of an object due to:
1. an applied force
2. a change in temperature
as deformation occurs, internal inter-molecular forces arise that oppose the applied force
if the applied force is not too great, these forces may be sufficient to completely resist the applied force and allow the object to assume a new equilibrium state and to return to its original state when the load is removed
elastic deformation
elastomers and shape memory metals
plastic deformation
metal fatigue
occurs primarily in ductile metals
was originally thought that a material deformed only within the elastic range returned completely to its original state once the forces were removed
however, faults are introduced at the molecular level with each deformation
after many deformations, cracks will begin to appear, followed soon after by a fracture, with no apparent plastic deformation in between