Question

Composite materials often times consist of fibers imbedded in a matrix material. What role does the fiber length, fiber orientation and fiber and matrix clastic properties play in determining the mechanical properties of the composite?

Answer 1

Composites , as the name suggests, comprise of different type of constituents. Clearly this results into better properties than the constituents. Fibers are usually put as reinforcements in the composite.

Some fiber length is important for good reinforcement. Here comes the concept of critical fibre length which is : product of ultimate tensile strength and diameter divided by two times the Fibre bond matrix strength. Maximum fibre load will be at the centre of fibre once stress is applied once length is same as critical length. Stress vs position behaviour will be affected if length is more or less than the critical length.

Orientation:

Uniformity in orientation means better properties. As a rule, if fibers are aligned well, properties will be anisotropic viz dependent of direction they are measured. Loading behaviour and stress strain curve will also be impacted by the orientation( Total alignment/ randomness/etc).

If all fibers are parallel, reinforcement efficiency is one When stress is parallel to fibers and zero when stress is perpendicular to fibers. For randomly distributed fibers, reinforcement efficiency will be 0.2

Properties of both fibre and matrix will be reflected later. Matrix will bind the fibre together and impart some protection from surface abrasions.

Whiskers( fibers will thin crystals) have very high strength. Properties like specific gravity/tensile strength of fibre/matrix will be key for the composite.