Reinforcement Fibres Flashcards
Define Composite Materials
Definition: A combination of two or more materials
(reinforcing elements, fillers, and composite matrix binder), differing in form or composition on a macro-scale. Normally, the components can be physically identified and exhibit an interface between one another.
REINFORCEMENT + RESIN = COMPOSITE
Three main types of composites
Polymer Matrix Composites (PMC’s) Most common
composites. Usually Fibre Reinforced Polymers or Plastics (FRP) - polymer-based resin as matrix plus fibres as reinforcement
Metal Matrix Composites (MMC’s) - Increasingly found
automotive industry, metal (e.g. aluminium) matrix plus fibres as reinforcement (eg SiC)
Ceramic Matrix Composites (CMC’s) – Used in very high
temperature environments, ceramic matrix with short fibre reinforcement (eg SiC)
Four main factors that govern the fibre’s reinforcement
The basic mechanical properties of the fibre itself
The surface interaction of fibre and resin (the ‘interface’)
The amount of fibre in the composite (‘Fibre Volume
Fraction’) – above 60-70% FVF tensile stiffness may
continue to increase BUT laminate’s strength will reach a peak, then decrease, due to lack of resin to hold fibres together
The orientation of the fibres in the composite - fibres are designed to be loaded along their length, and not across their width
Main types of Fibrous Reinforcement:
Carbon, Glass, Aramids (Kevlar, Twaron etc), Natural (hemp, flax etc)
Properties of Carbon Fibre (5)
Industrial processing perfected in 1960s
Outstanding stiffness and strength
Very expensive due to price of precursor, Polyacrylonitrile (PAN) – linked to price of
oil (can also be made from pitch or cellulose but quality is worse)
Very expensive production process (large investment – hundreds of millions £) so
supply is relatively fixed
Not so good under impact
Properties of Aramids (5)
Invented by Polish-American chemist Stephanie Kwolek while working for DuPont in 1964
Larger elongation to break gives it excellent toughness and energy absorption properties for impact protection
Stiffer than glass
Low density gives good specific properties
Expensive due to processing and once again linked to price of oil (polymer based)
Properties of Glass Fibres
Industrial manufacture process developed in
1930s by Owens-Corning Fiberglas Corp
Good mechanical properties (stiffness and strength)
Good toughness
Low cost compared to carbon and aramid
Two main glass fibres E-glass and S-glass:
- E-glass (electrical insulator)
- S-glass (high strength) more expensive, better properties
Properties of Natural Fibres
Jute fibres used since 300BC, evidence for flax
fibres dating back 30,000 years!!
A ‘green’ material with zero greenhouse gas impact
Fibre properties are OK but interface with resin is often poor so restricted to low-tech applications – properties can depend on growing conditions!
Low density gives good specific properties
Low cost alternative to E-glass
Typical Impact properties of laminates
Order: HS Carbon (very low), E-Glass, Aramid, S-Glass
Forms of (Aligned and Continuous = Advanced Composite) Fibre Reinforcement
Roving Uniaxial tape Uniaxial sheet Woven sheet Stitched fabric 3D - textiles
Fibre Cost
Order: ( E-glass, S-Glass, Aramid, HS Carbon, IM Carbon)
Fibre cost depends on bundle size (tex), smaller bundles are
more expensive
Forms of (Random Alignment / Chopped / Recycled) Fibre Reinforcement
Chopped fibres
Random chopped mat
Random continuous mat
Length and Alignment of Fibre Reinforcement
Longer more aligned fibres provide better mechanical properties but more difficult and slower processing – higher cost parts
Shorter fibre reinforcement permits easier and faster
processing but lower mechanical properties –lower cost parts
Thus, the choice between long and short fibre reinforcement depends on application
