Composite Micromechanics

Question 1

Explain the matrix assumption - imperfections

Answer 1

• Assume perfect bonding between the fibre and the matrix
• High adhesion between resin and reinforcement fibres is necessary for any resin system.

This will ensure that the loads are transferred efficiently and will prevent cracking or fibre/resin debunking when stressed.

Question 2

Explain the matrix assumption - fibre size

Answer 2

• Diameter of the fibres in a composite are tightly controlled - but there is still a distribution in the fibre diameter
• This will result in different strengths for each fibre.

Question 3

Explain the matrix assumption - stress and strain

Answer 3

• Assume uniform strain and stress in the individual components
• Essentially we simplify the geometry of the composite.

Question 4

Explain the concept of “isostrain”

Answer 4

As we load the composite, two blocks move together.

• For unidirectional composite loaded in the fibre direction: Strain in fibres = Strain in matrix = Overall strain in composite.

Question 5

Explain the concept of “isostress”

Answer 5

In transverse loading, stresses are equal (strain can vary)

Strain in the composite = Strain in matrix = Strain in fibre