Adhesive Bonding

Question 1

What is the definition of Adhesive Bonding?

Answer 1

The state at which two surfaces are held together by interfacial forces, which may consist of all known chemical attraction forces, as well as mechanical interlocking action, or both.

Question 2

What are the advantages of mechanical fastening?

Answer 2

• No surface preparation.
• Disassembly possible.
• Simpleinspection.
• Better for thick sections.
• No ‘chemistry’.

Question 3

What are the disadvantages of mechanical fastening?

Answer 3

• High stress concentration at holes.
• Additional weight/parts.
• Loss of smooth surface.
• Possible galvanic corrosion.

Question 4

What are the advantages of adhesives?

Answer 4

• Sealing as well as jointing.
• Better in fatigue loading.
• Good damping.
• Low weight penalty.
• Reduced part count.
• Can reduce assembly time.
• Can improve fatigue and corrosion resistance.
• Reduced stress concentration (no bolt/rivet holes). • Can join very dissimilar materials.

Question 5

What are the disadvantages of adhesives?

Answer 5

• Disassembly is difficult/impossible.
• Good surface preparation required.
• Accurate assembly may be required (jigs, fixtures).
• Non-destructive testing (ND T) difficult.
• Possible sensitivity to environment (both during assembly and in use).
• Can be affected by age.

Question 6

What factors should you consider when designing a joint (ie welded/adhesive etc)?

Answer 6

• Cost.
• Is skilled labour required?
• Is machinery required?
• Heat and distortion.
• Heat affected zone (H AZ)
• On-site work.
• Electrical conductivity/insulation.

Question 7

What are the main types of adhesives?

Answer 7

• Epoxy resin (superior bonds for a wide range of materials, excellent environmental resistance)
• Polyurethane (resistant to low temps, low shirnkage, elasticity, good fatigue and ageing)
• Acrylic (high toughness, minimal surface prep, wide range of materials)
• Cyanoacrylate (fast bonding, good resistance to weather)
• Anaerobic (cure in absence of air, good resistance to temp changes, can be disassembled)

Question 8

What two types of failure mechanisms should be avoided for adhesives?

Answer 8

Peeling and cleavage

Question 9

What is ageing?

Answer 9

The ageing of an adhesive or adhesive bond is defined as the change in the quality of adhesive bonding as a function of time and the external effects that provoke the change.

Question 10

what are the three factors that cause ageing?

Answer 10

1) Mechanical effects (static, dynamic, cyclic)
2) Chemical effects (humidity, oxygen)
3) Physical effects (temp, UV radiation)