Mechanical Design in Sport

Mechanical Design in Sport

1. Material Science

   • Copper
     • Biological properties = antibacterial
     • High stiffness
     • Ductility
     • High fracture toughness
     • Good electrical and thermal conductors
     • Susceptible to corrosion and oxidation
   • Ceramics main properties:
     • Resistance to chemical attack
     • Brittle
     • Hard and wear-resistant
     • Good thermal and electrical insulators
     • Poor fracture toughness
     • High compressive strength
     • Low tensile strength
   • Polymers main properties:
     • Low stiffness
     • Low thermal and electrical conductivities
     • Corrosion resistant
     • Generally low cost
   • Density = mass / unit volume
   • Metals = high density
     • heavy atoms packed close together
   • Ceramics = density lower than metal
     • light atoms arranged in regular structure
   • Polymers = low density
     • light atoms arranged in low density amorphous/semi-crystalline structure
   • Amorphous -- characterised by atomic or molecular structures are relatively complex and become ordered only with some difficulty
   • Output of tensile tests is force vs elongation
   • Load ==> stress
   • Elongation ==> strain
   • Elastic deformation -- stress and strain are proportional
   • Elastic deformation is non-permenant
   • Plastic deformation is permenent
   • Brittle -- very little/no plastic deformation upon fracture
   • Ductile -- metal experiences plastic deformation upon fracture
   • Hooke's law
   • Fracture toughness -- measure of material's resistance to brittle fracture
   • Charpy impact test
   • Solvent -- compound present in greatest amount
   • Solute -- compound in minor concentration
   • Pros of ferrous materials
     • Abundant quantities
     • Relatively economical extraction
     • Wide range of properties
   • Cons of ferrous materials
     • Susceptible to corrosion
     • Relatively high density
     • Low electrical conductivity
   • Titanium alloy
     • Resistant to corrosion
     • Strong and lightweight
     • High tensile strength
     • V expensive
   • Linear
   • Crosslinked
   • Branched
   • Polymerisation -- process of converting a monomer/mixture into polymer
     • 1. Addition
     • 2. Condensation
   • Mi = mean molecular weight of size range i
   • Xi = fraction of total number of chains within corresponding size
   • Degree of Polymerisation
   • Mn = number average molecular weight
   • m = molecular weight of repeat unit
   • ps = density of sample
   • pa = density of amorphous polymer
   • pc = density of crystalline polymer
   • Ceramics
     • Types of ceramics:
       • 1. Tiles
       • 2. Bricks
       • 3. Concrete
       • 4. Glass
     • Electroceramics -- electronic safety components made of ceramics
       • E.g. Voltage dependent resistor
     • Functional ceramics -- used for specialist properties, extremely purity dependent
     • Bioceramics -- beneficial properties e.g. bioactivity (HA)
       • HA -- synthetic version of bone mineral encourages bone in-growth
     • Additives = dopants
     • Types of carbon structure:
       • 1. 3D covalent diamond structure
       • 2. Single-layer -- graphene
       • 3. Layered -- graphite
       • 4. Amorphous -- coal
     • Ceramics have 2-3 times less density than metals
     • Directional bonding
       • 1. Bond angles are fixed and rigid
         • = brittle behaviour
       • 2. Bonds are very storng
         • = high melting point
       • 3. Electrons strongly bonded
         • = electrical insulators
     • Ceramic properties:
       • Hard
       • Superior compressive strength
       • Stiff
       • Low coeffeicnt of friction
       • Wear resistance
       • Chemical resistance
       • Very heat resistant
       • Low density
       • Brittle
       • Weak in tension
     • Golden triangle
       • 1. Properties
       • 2. Proceesing
       • 3. Microstructure

2. Sean's lectures

3. Andy's lectures

   • Particle -- a body of negliable dimensions
   • Newton's law
     • 1. Particle remains at rest or moves with uniform velocity if there is no force acting on it
     • 2. Acceleration of particle is proportional to resultant force and is in direction of the force
     • 3. Forces of action and reaction are equal in magnitude, opposite in direction and collinear
   • Work done = F*s
   • Energy -- total wprk required to bring particle from rest to velocity
   • Energy = 0.5*m*v^2
   • Momentum = m*v
   • Impulse = change in momentum
   • Laminar flow
     • Stationary ball and moving air = moving ball and stationary air
     • Ball passes through viscous fluid at low velocity
     • Velocity increases and pressure drops at b&c
     • Fast moving air has a lower pressure
     • Drag force caused enitrely due to viscous shear force, given by Stokes Law
   • Semi-turbulent flow
     • Appropriate to most ball games
     • Velocity of ball is sufficient to drag some fluid behind the wake
     • Higher viscous shear forces at b&c
     • Pressure at a > d
   • Semi-turbulent flow (bigger wake)
     • Velocity increases, viscous shear forces at b&c increase
     • Creates larger wake = larger drag force
     • Inefficient way of travelling
   • Fully turbulent flow
     • Boundary layer becomes turbulent at higher velocity
     • Viscous shear forces at b&c decrease
     • Extra layer of air makes journey smoother/more efficient
     • Wake becomes smaller = drag force becomes less
   • Drag coefficient is a function of:
     • 1. Shape
     • 2. Surface texture
     • 3. Velocity
     • 4. Fluid viscosity
   • Increased surface roughness causess less sudden transition and lowers threshold velocity of boundary layer turbulence
   • Reynold's number used to equate similar flows around objects
   • Surface texture
   • Drag opposes directon of velocity
   • Retardation -- how quickly something slows down
   • Effect of drag on trajectory:
     • 1. Different landing angles from same launch angle
     • 2. Different peak height
   • Ballistic performance = drag insensitivity
   • Environmental effects including drag:
     • 1. Pressure
     • 2. Temperature
     • 3. Humidity
     • 4. Altitude
   • Head and tail winds -- not mathematically linear so no equation to solve offset

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