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Hanshan - Golf and Bicycles :golfer: :bicyclist: - Coggle Diagram
Hanshan - Golf and Bicycles :golfer: :bicyclist:
Coefficient of restitution
Measure of energy transfer/energy retention between two objects in collision
R=0 is perfect plastic collision (no energy transfered)
R=1 is perfect elastic collision (full energy transfer)
CoR of clubhead
M is head mass and m is ball mass
High CoR drivers need lower stiffness so greater elastic deformation during impact
Deflection of a club face (circular disk)
For high CoR:
:arrow_up: Planar area (A)
:arrow_down: Thickness (t)
:arrow_down: Modulus (E)
Must be below yield stress when impacted - limits how thin head can be
Stiffness is dependent on face and
crown
Sole does not contribute to CoR as it has to be thick
Hollow Ti vs Solid wood
:check: Large hitting surface
:check: Low young's modulus
:check: High strength
Alternative alloys
Steels: :arrow_up: strength, :arrow_up: modulus
Al-based: :arrow_down: strength, :arrow_down: modulus
Alternative alloys and CoR
Steel can have thinner walls, but high modulus means bad CoR
Metallic glasses
No crystalline structure means high strength
Amorphous Zr has highest strength to modulus ratio
Amorphous Zr would have high CoR but requires welding which causes crystallisation and cracking
Friction
Ball spin
Energy lost as drag and friction
Reduced distance
Back Spin
Essential for lift
:check: Short games: direction control (gyro effect) and soft landing
:red_cross: Long games: energy loss
Side spin
Mis-hit sweet spot
Energy loss
No directional accuracy
Friction tailoring
Reduce friction/long game
Liquid lubricants (SiO2, PTFE, waxes, water based lube)
Solid coatings (PVD coatings, TiN, DLC)
Increase friction/short game
Softer ball covers (PU)
Grooved hitting surface
Sand/bead blasting (deteriorates quickly)
Ti/Diamond particle composite surface
Metallic Tubes
Thin walled tubes have :arrow_up: strength and modulus
Butting - Centre of tube sections is thinner, ends are thicker
Stiffness
Stiffness of a tube
Tube dimensions can be changed = :red_cross: weight
L is fixed by bike dimensions
High modulus is good
Material merit index:
E/ \(\rho\) in tension
E/\(\rho^2\) in compression
Stiffness of a bike
Torsional Stiffness:
High modulus is good
Materials
Considerations
Road bicycles need good damage tolerance (fatigue and corrosion)
Good formability and weldability
Must be lightweight/low density
Joining methods
Brazing
Use of lower melting temperature metals to join tubes
:check: No melting of tubes = no microstructure changes
TIG
Tungsten inert gas welding
Design flexibility
Non-ferrous metals
Intergranular cracking around weld
Tube materials
Road/mountain bikes
Steel
Ti alloy
Al alloy
Mg alloy
CFRP composites
Track cycles
High strength steel
CFRP composites
Composites can be engineered to give directional specific modulus
Best performance comes from single shell structure
Merit index: E/ \(\rho^3\)
