Subject: Composite Materials Science and Engineering Subject code: 0210080060. Prof. C. H. XU School of Materials Science and Engineering Henan University of Science and Technology Chapter 7: Polymer Matrix Composites (PMCs). Polymer Matrix Composites (PMCs). This chapter covers
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Subject: Composite MaterialsScience and Engineering Subject code: 0210080060
Prof. C. H. XU
School of Materials Science and Engineering
Henan University of Science and Technology
Polymer Matrix Composites (PMCs)
This chapter covers
The most common matrix materials for composites are polymeric.
Polyester resin (聚酯树脂) Acetyle
Epoxy resin（环氧树脂） polypropylene
Phyenolics (酚醛树脂) Nylon
Polyimides (聚酰亚胺) Polyetheretherketone (PEEK)
Most widely used matrix (¾) Less used matrix
For large parts for small parts
Specific strength 103 s/r(MPa)/(Mg/m3)
0 50 100 150 200
Specific modulus E/r (GPa)/(Mg/m3)
Manufacturing Process of PMCs
4) Molding compound
5) Core structures
(a) Spooled fiber
(b) A thin film of heated resin solution of relatively low viscosity is coated on release paper
(c) Sandwich and press fibers between release sheets and carrier paper using heated rollers
(d) Remove release paper
(e) Spooled prepreg tape
Molding compounds are made of short or long fibers impregnated with resins. The compound contains uncured thermosetting resins and uniformly distributed short fibers. They are raw materials for compression molding. A resin paste is placing on a polyethylene(聚乙烯） moving films, Continuous strands of glass fibers are chopped and dispersed over the moving resin paste. Top and bottom film with paste and fibers pass compaction rollers.
Schematic of molding compound manufacturing
Aluminium Nomex thermoplastic honeycombs
Methods vary from simple labor intensive for one-offs to automated methods for rapidly producing large numbers of complex components.
The method of product selected by a manufacture depends on factors, such as cost, shape of components and required performance
There are four steps in manufacturing composites:
Hand(manual) Lay-up Technique
Advantages of hand lay-up technique:
Disadvantages of hand lay-up technique:
Description:Fibre is chopped in a hand-held gun. Chopped fibres, resin, and catalyst are fed into a gun which spray of resin directed at the mould. The deposited materials are left to cure under standard atmospheric conditions. The sprayed composite has to be rolled to remove entrapped air and to give a smooth surface finish.
Basic Processing Steps
Release agent is applied to the mold
Prepreg is laid on the mold surface until to applied all the prepreg sheets. Air between prepreg sheets is removed by using a squeezing roller after applying each prepreg sheet.
Employing a vacuum bag in special equipment for curing (solidify the composite).
(a) Vacuum forming
(b) Autoclave (高压锅)molding
(c) Pressure bagging
After cooling, removing vacuum bag and take out parts.
Prepregs commonly come in various widths (3 to 72 inches) and have a leathery feel. They are slightly tacky so that they will stick when formed. The prepreg materials degrade over time, and should be kept in cool environments.
Vacuum forming uses atmospheric pressure to press the cloth tightly. This technique requires a vacuum bag, vacuum pump capable of pulling a significant vacuum (at least 25 inches of mercury) and various accessories. Thus vacuum forming has been mostly restricted to large commercial use.
Vacuum Bag Molding in step 3(b)
Basically an oven that also uses pressure.
Pressure bagging: A flexible bag is placed over the lay-up components on the mould. Inflation of the bag by compressed air forces the lay-up into mould.
Advantages of vacuum baggingmould technique:
Disadvantages of vacuum bagging mould technique:
Compression molding process
Compression molding process
Compression molding is very popular in the automotive industry because of its high volume capabilities.
Car composite parts
Resin Transfer Moulding (RTM)
(a) A mould is filled with fibre and it is closed. (b) The mould is often in vacuum before injection. (c) Resin is injected at high pressure and high temperature (curing). The pressure of injection wets the fibres.
Resin Transfer Moulding (RTM)
This process was used to make car body panels. The fibre in the mould can be any that holds its shape during the injection. Layers are often stitched, and bonded. Inserts/ribs/etc can easily be put into the mould before it is closed.
Most resins can be used, but low viscosities are useful.
Glass fibre-reinforced polyesters
the largest proportion of the market
Less cost, lower strength, less heat and weather resistant, shrinkage of 4-8% during curing
Glass fibre-reinforced epoxy
Better properties, shrinkage of 1-5% during curing.
Good bond between matrix and glass fiber
Properties of unidirectional glass reinforced epoxy and polyester
Reinforcement: Glass fiber or fabric
Coupling agent (VOLAN) enhances the wetting and bond between glass and polyesters
Mechanism of coupling
(a) Volan hydrolyze （水解）
(b) Absorb water on the surface of glass
(c) Reaction between volan-volan and volan - the absorbed water’ glass
(e) Bond between C=H2 and polyesters
Water reduces the strength of the composites. The reasons are
The effects of water on glass transition T (Tg) of six cured epoxy resins ●caculated ○experimental
The strength of epoxy laminates versus time exposed to boiling water ( 4 coupling agents)
Mechanical properties of epoxy with various fibers
Impact characteristics of fiber reinforced epoxies
Effects of T on stiffness & strength of PEEK matrix composites
Creep modulus against time
Polymer matrix (rubber) + carbon black particles
Composite Materials: Engineering and Science (pages179-207).
Introduction to Materials (page 241-283)
Lecture note 7