Composites

Question 1

What are the component phases in a composite?

try name the two phases in a composite

Answer 1

• A composite: a multiphase component having two or more dissimilar constituents to provide improved properties.
  -Reinforcement
  ->Generally high quality (flaw-free) and good performance.
  ->May incorporate coating to enhance interfacial properties.-Matrix:
  ->Generally provides load transfer medium
  ->Protects reinforcement from surface damage
  ->Generally absorbs damage in service
  ->Provides environmental protection
• Properties are defined by materials, reinforcement distribution, design and processing route.
• Composite, two materials that are combined, that have different materials. These provide better overall properties, like lighter in weight, etc.
• Having a good interface between the matrix and reinforcement is what affects the quality often of the composite.
• Matrix seem like the least important of the two, but is also surprisingly key.

Question 2

What are some composite classfications and how do we name them?

Answer 2

• See diagram and points
• Convention dictates the expensive filler materials are named first in the pairing.
• ============================================= Particle-reinforced examples:
• WC-Co (tungsten carbide) cutting tool material
  -WC - brittle and hard, in a particular form.
  -Co (cobalt) - ductile matrix.This provides the impact resistance so the tungsten won’t generate flaws and break.
• Rubber reinforced with C particles:
  -Tyre application.

Question 3

What are the different types of fibre reinforcement?

Answer 3

The different types:
* Continuous and aligned (mostly interested in this one)
* Discontinuous and aligned
* Discontinuous and randomly oriented

Question 4

How do the two phases in a composite act to make the mechanics behind a composite?

Answer 4

• The Fibres alone will have a long elastic modulus and little deformation before failure (brittle).
• The matrix we will see some plastic deformation and more ductile response.
• The composite will have a response, somewhere in between the two of those. Seen on the right. We get a blended response of the two.

Question 5

What is the equation for composite stiffness, Ec, (youngs moduls) in the longitudinal direction (Load is parrallel to the fibre directions)?

What is an assumption we make?

Answer 5

• Stiffness, E, for continuous fibre reinforcement in the longitudinal direction:
  -Isostrain situation, i.e. assume a good interface between fibre and matrix.
• The strain in the matrix and the fibres and composite are all equal
• Force on the composite, is the force on the matrix and fibres. Therefore we can work out the Force based on the area of the fibre, and matrix, and their respective areas.
• We can then re-arrange to work out the stress on the matrix.
• We see the stress on the composite, is equal to the stress on the matrix and fibres multiplied by their volumes now respectively.
• Understanding we are in this isostrain situation, we can then get the stiffness (the modulus) of the composite using the modulus of the matrix and fibres and volumes of each. Shown in the equation.
• This equation, shows us how we can then still get the required mechanics while altering matrix and fibre volumes, etc.

Question 6

What is the equation for composite stiffness, Ec, (youngs moduls) in the transverse direction (Load is perpendicular to the fibre directions)?

What is an assumption we make?

Answer 6

• Stiffness, E, for continuous fibre reinforcement in transverse direction:
  -Isostress situation, i.e. assume complete load transfer between the fibre and matrix.
• The stress in the fibres, matrix and composite are all equal
• Therefore we can work out the stiffness, E, (or modulus) of the composite.
• You can see that the modulus of the matrix now affects the stiffness, being weighted more.
• This shows how the fibre alignment will need to be considered.

Question 7

What is meant by composite anistropy and why do we consider it?

Answer 7

• Anisotropy is the structural property of non-uniformity in different directions
• We may need to consider what loading our material will be going to then align fibres or make alternating alignments to make our material stiffer.
• Stiffness in the longitudinal direction is greater than stiffness in the transverse direction (seen in the equations), significant anisotropy in stiffness and strength.
• If isotropic properties are required then cross-ply laminates can be constructed.