Lecture 11: Polymer Matrix Composites

Polymer Matrix Composites (PMC)

Modern Ski Construction

• Complex composite structure.
• Materials used:
  • Carbon: Light, lively, strong under compression, very expensive.
  • Kevlar: Strong, light, good under tension, good dampener.
  • Aluminum Honeycomb: Light, strong, expensive, reduced damping.
  • Fiberglass: Relatively strong, light, inexpensive.
  • Titanium: Light, strong, good damping, expensive.
  • Air: Decreases weight without affecting strength.
  • Foam: Used with a composite torsion box for strength and flex.

Principle of Combined Action

• Composites extend material property combinations.
• Composite: Multiphase material exhibiting properties of constituent phases.
• Better properties achieved by combining distinct materials.
• Property trade-offs are common.
• Composite: Artificially made multiphase material with chemically dissimilar phases separated by a distinct interface.
• Metals, ceramics, and polymers are used.

Matrix Phase and Dispersed Phase

• Many composites have two phases: matrix (continuous) and dispersed phase.
• Composite properties depend on:
  • Properties of constituent phases.
  • Relative amounts.
  • Geometry of the dispersed phase (shape, size, distribution, orientation).

Polymer-Based Composites

• Properties depend on constituent phases, amounts, and geometry.
• Polymer embedded with reinforcing items (fibers or powders).

Applications of Polymer-Based Carbon Fiber Composites

• Textile and Paper Industry
• Acoustics
• Aerospace and Aircraft Industry
• Portable power sources
• Automotive Parts
• Energy Production
• Civil Engineering
• Sports Equipment

Polymer Matrix

• Thermosetting (TS) polymers are common matrix materials.
  • Phenolics (particulate reinforcing phases).
  • Polyesters and epoxies.
  • Rubbers reinforced with carbon black.
• Reinforcing Agents: Ceramics, metals, polymers, elements (carbon, boron).
• Geometries: Fibers, particles, flakes.
  • Fibers are of most engineering interest.

Types of PMCs

• Particle-reinforced
• Fiber-reinforced
• Structural (laminates, sandwich panels)
• Continuous (aligned)
• Discontinuous (short) - Aligned, Randomly oriented

Particle-Reinforced Composites

• Particle dimensions are approximately the same in all directions
• Fiber-reinforced polymer composites: Dispersed phase has geometry of a fiber (large length-to-diameter ratio).
• E-glass (electrical glass) is the standard glass composition used for most glass fibers.

Particle-Reinforced Polymer Composites

• Small-particle reinforcement (dispersion-strengthened composites).
• Particle diameter between $0.01$ and $0.1$ mm ($10$ and $100$ nm).
• Particle–matrix interactions occur on the atomic/molecular level.
• Matrix bears the load, dispersed particles hinder dislocation motion.
• Rubbers with particulate materials (e.g., carbon black) enhance tensile strength, toughness, and tear/abrasion resistance.
• Automobile tires contain 5-30 vol% carbon black.
• Automobile Rire matrix: rubber (compliant) particles: carbon black (stiff).

Fiber-Reinforced Polymer Composites

• Glass Fiber-Reinforced Polymer (GFRP) Composites
• Glass fibers (E-glass) + polymer matrix
• Fiber diameters: $3-20$ μm
• Temperature limit: below $200$ °C
• Carbon Fiber-Reinforced Polymer (CFRP) Composites
  • Carbon fibers + polymer matrix
  • High specific modulus & strength
  • Retain properties at high temperatures
  • Resistant to moisture, solvents, acids
• Aramid Fiber-Reinforced Polymer Composites
  • Outstanding strength-to-weight ratios (e.g., Kevlar™, Nomex™).
  • Toughness, impact resistance, resistance to creep and fatigue.
  • Used in ballistic products, sporting goods, tires, ropes, missile cases, pressure vessels, automotive brakes.

Fiber-Reinforced Polymer Composites - Properties

• Dispersed phase is a fiber.
• Fibers are strong in tension.
• Characteristics depend on:
  • Fiber properties
  • Load transmission by the matrix
• Polymer matrix:
  • Holds fibers in place
  • Protects fiber surfaces from abrasion
  • Transfers load to fibers
  • No load transmittance from the matrix at each fiber extremity.

Alignment of Fibers

• Continuous and aligned
• Discontinuous and aligned
• Discontinuous and randomly oriented.

Fiber-Reinforced Polymer Composites - Discontinuous Fibers

• Random in 2 dimensions
• Carbon fiber fabrication: carbon fibers in polymer resin matrix, resin pyrolyzed at up to $2500$ °C.
• Uses: Disk brakes, gas turbine exhaust flaps, missile nose cones.

PROCESSING OF FIBER-REINFORCED COMPOSITES

• Fibers should be uniformly distributed and oriented.
• Techniques:
  • Pultrusion
  • Filament winding
  • Prepreg production processes

Pultrusion Processes

• Extrusion-like process where workpiece is pulled through die.
• Produces continuous straight sections of constant cross section.
• Continuous fiber rovings are dipped in resin and pulled through a shaping die for curing.
• Limited to straight sections of constant cross section.

Pultrusion Processes - Materials and Products

• Common resins: Unsaturated polyesters, epoxies, silicones (TS polymers).
• Reinforcing phase: E-glass (30-70%).
• Products: Solid rods, tubing, long flat sheets, structural sections, tool handles, third rail covers.

Filament Winding Process

• Resin-impregnated continuous fibers are wrapped around a rotating mandrel.
• Resin is cured, and the mandrel is removed.
• Fiber rovings are pulled through a resin bath and wound in a helical pattern.
• Layers with crisscross patterns are formed.

Other PMC Shaping Processes

• Centrifugal casting
• Tube rolling
• Continuous laminating
• Cutting of FRPs
• Thermoplastic shaping processes (blow molding, thermoforming, extrusion) applicable to FRPs with short fibers based on TP polymers

Tube Rolling

• Wrapping FRP prepreg around mandrel.
• Completed tube after curing and mandrel removal.
• Prepreg: Fibrous material pre-impregnated with synthetic resin.