1) Micromechanics of Lamina

Question 1

Are ply’s anisotropic or isotropic and why?

Answer 1

Anisotropic, they are different properties in different directions.

Question 2

Define a fibre phase of an FRP?

Answer 2

Fibre phase consists of individual micrometer-diameter individual filaments.

Question 3

List 3 FRP’s?

Answer 3

Glass Fibres
Carbon Fibres
Aramid Fibres

Question 4

What are polymer resins and what are they also known as?

Answer 4

They bond the fibres together. This is also known as the matrix or binder.

Question 5

Give 3 examples of resins?

Answer 5

1) Epoxy resin
2) Vinylester resins
3) Phenolic resins

Question 6

List two properties, when compared to other FRP’s, of carbon-fibres?

Answer 6

1) Highest average tensile strength
2) Highest average tensile modulus
3) Lowest density

Question 7

What is notable when looking at carbon fibres in an epoxy matrix under a microscope?

Answer 7

The fibres are randomly distributed

Question 8

Why can the volume fractions and volume matrixes not sum to 100%?

Answer 8

Because if you have circular fibres you will have gaps between them.

Question 9

Wha are the two arrangements for fibre packing?

Answer 9

1) In unidirectional material, fibres are aligned.
2) Two ideal models Hexagonal and square packing.

Question 10

What happens to the strength and stiffness to the material if you increase the number of fibres?

Answer 10

They increase.

Question 11

What happens as a result of clustering of fibres?

Answer 11

Voids appear making it difficult for the resin to penetrate through a dense pack of fibres.

Question 12

Define micromechanics?

Answer 12

Determining unknown effective properties of the composite based on known properties of the fibre and matrix.

Question 13

Are FRP’s anisotropic or isotropic and why?

Answer 13

Anisotropic because the properties depend on the direction.

Question 14

What is the fibre strain equal to according to the direct rule of mixtures?

Answer 14

The matrix strain.

Question 15

What is the stress acting on the reinforcement equal to, according to the inverse rule of mixtures? Is this the case in reality?

Answer 15

The stress acting on the matrix but in reality this is not the case because the stresses and strains are not uniformly distributed.

Question 16

Finish the sentence:
“The true effective properties……”

Answer 16

Always higher than the prediction using the rule of mixtures.

Question 17

Define the poissons ratio nu12.

Answer 17

It it the ratio of strain being applied in direction one and being measured in direction 2.

Question 18

What is the name of Nu12 and Nu21?

Answer 18

1) Nu12 is called the major Poisson’s ratio.
2) Nu21 is called the minor Poisson’s ratio because E2 is much smaller than E1.

Question 19

What method was developed as a replacement for the inaccuracy of the inverse rule of mixtures?

Answer 19

Halphin-Tsai Method