1

Fiber Reinforced Polymer

(FRP) Composites

Dr Antonis Michael

Department of Civil Engineering

Frederick University Cyprus

Composite Materials: Introduction

A composite material is formed by the combination of two or more distinct materials to form a new material with enhanced properties

Early manmade composites:

� Straw-reinforced clay

� Early mortars

� Reinforced concrete

2

Advanced Composite Materials in

Construction

Variety of Composite materials or material systems available:

� FRP Composites: Structural shapes, external and internal reinforcement of construction materials (concrete, masonry etc), pre-stressing elements

� FRP Hybrids: FRP+wood, FRP+concrete, FRP+masonry etc.

FRP Composite Materials

Combination of two or more materials to achieve properties that are superior to those of the constituents (fibers and matrix).

3

Classification

� Reinforcement

� Continuous long fibers: unidirectional, bidirectional

(woven, stitched mat), random (continuous strand

mat)

� Discontinuous fibers: random (chopped strand

mat), preferential orientation

� Particles and whiskers: random, preferential

orientation

Classification (Cont.)

� Laminate Configuration

� Unidirectional

� Lamination

� Hybrid Structure

� Different materials in various layers (FRP+wood)

� Different reinforcement in a layer (glass+carbon)

4

Constituent Materials

� Fibers

� Provide stiffness and strength

� Fibers stronger than bulk materials

� Matrix

� Binds fibers together

� Provides load transfer

� Protects against environmental attack

Advantages of FRP Composites

� Weight reduction

� Corrosion resistance

� Electromagnetic transparency

� Wear resistance

� Enhanced fatigue life

� Thermal, acoustical insulation

� Low thermal expansion and conductivity

5

Advantages (Cont.)

� For loads in multiple directions

� Can add layers with various orientations

� Short-fibers randomly oriented in the matrix (lower

properties)

� Fillers in the matrix

� Reduce weight

� Delay flame and reduce smoke

� Protect against UV degradation

Typical Properties of Unidirectional

Composites

1.291.82.3Long. Tens. Strain ε1t (%)

228138140Trans. Comp. Str. F2c (MPa)

1096586620Long. Comp. Str. F1c (MPa)

7144.160Inplane Shear Str. F6 (MPa)

5734.540Trans. Tens. Str. F2t (MPa)

183013801020Long. Tens. Str. F1t (MPa)

10.35.512Trans. Modulus E2 (GPa)

14275.845Long. Modulus E1 (GPa)

Carbon AS4 / Epoxy 3501-6

Kevlar 49 / Epoxy

E-Glass / Epoxy

Property

6

Materials

� Fiber: provides stiffness and strength

� Matrix: binds the fibers together

� Fillers: improve processability and dimensional stability

Fiber Reinforcement

� Tensile strength of bulk E-glass is low (1.5 -5.8 GPa)

� Tensile strength of E-glass fibers is high (72.3 GPa)

� Why?

� Due to reduction of surface defects in fibers

7

Fiber Reinforcement

� Fiber alignment

� Lamina (layer or ply): maximum properties in fiber

direction and minimum in perpendicular direction

� Randomly oriented fibers: same properties in

every direction on a plane

� Common fibers

� Glass, carbon and organic (Kevlar)

� Choice of fibers

� Mechanical, environmental properties and cost

Glass Fibers

� Properties

� Hardness

� Corrosion resistance

� Flexible

� Inexpensive

� Most common in low-cost industrial and construction applications

8

Glass Fibers

Glass CSM Woven Unidirectional Glass Fabric

Types of Glass Fibers

Several types with similar stiffness but different strength and environmental resistance� E-Glass (electrical): preferred for structural

application

� S-Glass (strength): Highest strength

� C-Glass (corrosion): corrosion-resistant applications

� A-Glass (alkaline resistant): surfacing veils and mats

� Fiber diameters: 9.5 to 24.77 microns

9

Factors Affecting Glass Fibers

� High temperatures: tensile strength reduction of fibers (strength remains the same for temperature range of matrices)

� Chemical corrosion: reduction of tensile strength for example exposure to high PH levels (alkaline environment)

� Sustain loads: tensile strength reduces with time (static fatigue or stress corrosion). Such a failure called creep rapture

Carbon (Graphite) Fibers

10

Carbon (Graphite) Fibers

� Properties

� Lightweight

� High Strength

� Excellent chemical resistance

� Mostly used in the aerospace industry

� Broad range of stiffness values. Properties depend on raw material (precursor) and processing

Types of Precursors

� PAN (Polyacrylonitrile)

� Dominate high performance market (High strength

fibers)

� Pitch:

� Less expensive but lower strength

11

Classification of Carbon Fibers

� High strength (HS)

� High modulus (HM)

� Ultra high modulus (UHM)

Production

12

Comparison with Glass Fibers

� Carbon fibers stiffer than glass fibers

� Better fatigue characteristics due to reduction in

the amount of strain in the matrix

� Less stress corrosion compared to glassfibers

� Reduction in strength due to sustain loads smaller

in carbon than glass

� Carbon more expensive than glass

� Problem: Cost

Uses for Carbon Fibers

� Weight critical structures requiring high performance properties

� Airplanes (new military aircraft made from carbon

composites)

� Aerospace vehicles and structures

13

Organic Fibers

� Aramid Fibers

� Kevlar

� Technora

� Twaron

� High energy absorption

� Ideal for impact and ballistic protection (military

helmets, bulletproof vests etc)

� Low density

� High strength to weight and modulus to weight

ratios

Aramid Fibers

� Aramid fibers are polymers

� Low compressive strength

� Creep

� Absorb moisture

� Sensitive to UV light

� Mechanical properties vary with temperature!!!!

14

Polyethylene Fibers

� Limited use for structural applications

� Low maximum operating temperature (120º C)