Page 12 - 3D Fibre Reinforced Polymer Composites

Chapter 1

Introduction

1.1 BACKGROUND

Fibre reinforced polymer (FRP) composites have emerged from being exotic materials
used only in niche applications following the Second World War, to common
engineering materials used in a diverse range of applications. Composites are now used
in aircraft, helicopters, space-craft, satellites, ships, submarines, automobiles, chemical
processing equipment, sporting goods and civil infrastructure, and there is the potential
for common use in medical prothesis and microelectronic devices. Composites have
emerged as important materials because of their light-weight, high specific stiffness,
high specific strength, excellent fatigue resistance and outstanding corrosion resistance
compared to most common metallic alloys, such as steel and aluminium alloys. Other
advantages of composites include the ability to fabricate directional mechanical
properties, low thermal expansion properties and high dimensional stability. It is the
combination of outstanding physical, thermal and mechanical properties that makes
composites attractive to use in place of metals in many applications, particularly when
weight-saving is critical.
FRP composites can be simply described as multi-constituent materials that consist
of reinforcing fibres embedded in a rigid polymer matrix. The fibres used in FRP
materials can be in the form of small particles, whiskers or continuous filaments. Most
composites used in engineering applications contain fibres made of glass, carbon or
aramid. Occasionally composites are reinforced with other fibre types, such as boron,
Spectra@ or thermoplastics. A diverse range of polymers can be used as the matrix to
FRP composites, and these are generally classified as thermoset (eg. epoxy, polyester)
or thermoplastic (eg. polyether-ether-ketone, polyamide) resins.
In almost all engineering applications requiring high stiffness, strength and fatigue
resistance, composites are reinforced with continuous fibres rather than small particles
or whiskers. Continuous fibre composites are characterised by a two-dimensional (2D)
laminated structure in which the fibres are aligned along the plane (x- & y-directions) of
the material, as shown in Figure 1.1. A distinguishing feature of 2D laminates is that no
fibres are aligned in the through-thickness (or z-) direction. The lack of through-
thickness reinforcing fibres can be a disadvantage in terms of cost, ease of processing,
mechanical performance and impact damage resistance.
A serious disadvantage is that the current manufacturing processes for composite
components can be expensive. Conventional processing techniques used to fabricate
composites, such as wet hand lay-up, autoclave and resin transfer moulding, require a
high amount of skilled labour to cut, stack and consolidate the laminate plies into a
preformed component. In the production of some aircraft structures up to 60 plies of
carbon fabric or carbodepoxy prepreg tape must be individually stacked and aligned by
hand. Similarly, the hulls of some naval ships are made using up to 100 plies of woven