unit 2 Flashcards
what are the four main categories of Engineering Materials?
-metals and alloys
-polymers
-ceramics and glass
-composites
What are the qualities of Metals and Alloys
Bonding: Metallic
Microstructure: crystal grains
Advantages: strong, stiff, ductile, and conductive
disvantages:
-fracture
-fatigue
What are the qualities of polymers?
Bonding: covalent and secondary
Microstructure: chain molecules
Advantages:
low cost
-low weight
-resists corrosion
Disadvantages:
-low strength
-low stiffness
-creep prone
What are the qualities of ceramics and glass
bonding:
-ionic -covalent
microstructure:
-crystal grains
-amorphous
advantages
-strong, stiff, hard
-resist temperature
-resist corrosion
disadvantages
-brittleness
What are the qualities of composites?
bonding: various
microstructure: matrix and fibre
advantages:
-strong
-stiff
-lightweight
disadvantages
-high cost
-delamination
what are the different types of microstructure?
-IRREGULAR ORDER- monoatomic gases have irregularly ordered atoms
-SHORT RANGE ORDER - water vapor, nitrogen, amorphous silicon have short range order
-CRYSTALLINE ORDER-metals, alloys, and ceramics and some polymers have regular square shaped ordering of atoms
What is crystal structure in solids
crystal structure = space crystal lattice + basis
crystal lattice - a mathematical abstraction, regular pariodic arrangement of points in space
-crystal structure: formed by placing identical atoms in the points of the space lattice
what is the formula for atomic packing factor (APF)?
((# of atoms in unit cell)(4/3Pir^3))/a^3
I.e. (# atoms) x (spherical volume with given radius) / (unit volume)
The denominator volume may be calculated differently depending on the shape of the compound in questions
apf formulas for each type of structure
simple cubic : a=2r, APF=0.52
body centred cubic: a=4r/sqrt3, APF=0.68
face-centred cubic:
a=4r/sqrt2, APF = 0.74
What types of defects are present in crystals
-point defects (0 dimensional)
-dislocations (line defects: 1 dimensional)
-grain boundaries (planar defects: 2-dimensional)
what are line defects in microstructure?
-dislocations
-happen as material solidifies or when it deforms
what happens during inelastic deformation?
-known as yielding
-behavioural change in the material
-material begins to shear along planes at 45 degree angles at an atomic level
-material deforms noticeably without any increase in stress
what happens after inelastic deformation?
-atoms change neighbours and return to a new stable configuration
-elastic strains are recovered, but plastic strains remain
