Bicycle Frame Design

Question 1

Factors for frame material? Split into 3 types

Answer 1

Physical – density, colour, electrical conductivity, magnetic permeability, thermal expansion
Mechanical – elongation, fatigue limit, hardness, stiffness, shear strength, tensile strength, toughness
Chemical – reactivity, corrosion resistance, electrochemical potential, irradiation resistance, resistance to acids and alkalis, solubility

Question 2

Material Properties 6 types?

Answer 2

• Density – weight per given volume
• Stiffness – Force deflection relationship
• Elongation – ductility
• Tensile Strength – load required per unit area to cause failure under a tension force
• Fatigue Strength – failure after a number of cycles. Fe alloys and Ti have a threshold. Al, Mg beware
• Toughness – ability to absorb energy and deform plastically

Question 3

Conventional Bicycle Frame

Answer 3

Diamond Shape Of Two Triangles
High static and Dynamic loads:
Rider and road misuse

Question 4

Determine the difference in time to get up a hill with a rider having the same power but a heavier frame?
“Assuming the same power output of the cyclist, what is the time difference to climb 300m on a 1 in 8 hill if the cyclist can maintain a steady 24 km/h on the lightweight frame?

Answer 4

Question 5

Advantages of triangulation in bike frames?

Answer 5

important loads are bending moments deforming tubes in plane of frame and axial forces (i.e. end loaf members or beams)
General: Tension or compression is less severe than bending

Question 6

Out of plane loading on bike frames?

Answer 6

Question 7

Bike Design Criteria

Answer 7

“Spending weight to purchase structural performance”
* Lightweight: support normal loads + safety factor stiffness sufficient to prevent distortion
* Torsional and bending response of individual elements
“Maximise the bending and torsional stiffness of the elements for a given weight structure without incurring and overload failure

Question 8

Types of tubes

Answer 8

• Welded tube (seamed tube) like orange
• Seamless tube

Question 9

Types of seamless tube manufacture?

Answer 9

• Hot working - Form tube shape - Plastic deformation above the recrystallisation temperature of metal
• Cold working - Plastic deformation below the recrystallisation temperature - Improve final dimensions and surface finish - Hardening through plastic deformation
• Heat treatment - Change the microscopic structure of the metal. Can be used to soften or harden the metal depending upon the process and metal chemistry

Question 10

Types of heat treatment? 4

Answer 10

• Annealing - above recrystallisation temperature. Slow cooling to room temperature. Softens the material.
• Quenching - above recrystallisation temperature. Fast cooling to room temperature. Forms dislocations in microstructure, resulting in hardening of the material.
• Tempering - below the recrystallisation temperature. Relieves internal stresses, reducing the brittleness. Often used after quenching or welding.
• Age/Precipitation hardening - Increased hardening after a period of time after quenching.

Question 11

Joining Techiques

Answer 11

• Brazing - Melts a filler material to bond the surfaces together (NOT the base metals) typically lowers the strength of the material to some extent.
• Welding - Melts both filler AND base material. Higher temperatures required relative to brazing.