Composites

FRP possess excellent mechanical properties:

• Impact resistance
• Strength
• Stiffness
• Flexibility
• Ability to carry loads

Typical tests used to measure the mechanical properties of FRP:

• Shear stiffness
• Tensile strength
• Flexible Modulus
• Impact resistance

The mechanical properties of FRP are determined by different factors including:

• the composition of the matrix: chemical composition, crystallinity, curing, presence of additives, etc.  
• Fibre composition (glass, carbon, aramid) and fineness
• textile structure: individual fibres, continuous yarns (rovings), fibre-based textiles including hybrid yarns, fibre mats, spunlaid yarn layers  (non crimp fabrics) 3D textiles (knits, braids...)
• Fibre concentration
• Fibre length
• Adhesion between matrix (resin) and fibre
• Fibre orientation
• Heat and humidity

Adding high strength fibres to the plastic (resin) matrix not only changes the strength of the FRP but also other properties:

Mechanical behaviour

Reduction of crimp and warping behaviour at high temperatures and of creep under (continuous) load.

Burning behaviour

Certain high strength fibres such as glass and basalt fibres are highly resistant to fire and are therefore suited to improve the burning behaviour of plastics.

Thermal and electric conductivity

Thermally and electrically conductive fibres (eg. carbon fibres) will affect the inherently good insulating properties of most plastics.

Carbon fibres in panels or structures may alter the detectability by radar waves (the radar transparency of CRP is used in military airplanes) and can also form a Faraday Cage to protect sensible electronic devices.

The presence of heat conductive fibres (eg. CF) can also accelerate the thermal process of forming and curing polymer systems.

• the thermal conductivity of the fibres can improve the heat transmission in conventional ovens to and within the composite structure
• carbon fibres can also capture electric waves allowing the application of inductive heating systems that will decrease the processing time.

Thermal insulation

Most plastics and high strength fibres do not conduct heat (or conduct it only very poorly). This thermal insulation of FRPs can be marketed as an advantage in contrast to materials reinforced with metal rods or cables. Many heat losses are indeed due to the presence of thermal bridges.

Corrosion resistance

In contrast to most metal reinforcing materials (metal reinforced concrete), most reinforcing fibres and polymer matrices are corrosion-free, which makes them very suited for several building applications (pipes, reservoirs...).

Colour and resistance to ageing

Fibres can of course influence the colour of the composite (carbon fibres are black and basalt fibres have a golden hue) as well as the resistance to ageing.

Affinity to functionalisation

Fibre reinforced plastics can be easily functionalised by means of coating, printing, laminating which may be advantageous in certain applications. It is possible to integrate smart materials and sensors.

RFID and other communication systems can be integrated by means of IML (In-Mould Labelling) techniques increasing the applicability of FRPs in new domains.

In a digitalised world governed by the "Internet of Things", functionalised composites will be playing a major role.
 

Wind energy

The first windmills of the 1980's had a rotor diameter of about 15m and a relatively small power output (50 to 100kW). In 2013, the average windmill rotor had a diameter of about 100m generating about 2,5MW. A two megawatt wind turbine generates an average of 4 million kWh/year, which corresponds with the energy consumption of 1300 households.

The increasing size of wind turbines has several consequences:

• Only a small number of companies are capable of producing these large (mainly offshore) wind turbines. Today, the European offshore wind energy market is dominated by Vestas Wind Systems and Siemens Wind Power (together they have realised 90% of the installed wind power). Other European companies are REpower, Bard and Areva.
• Due to the growing size, the glass fibre reinforcement has to be supplemented by carbon and aramid fibre reinforcement and with more performant core materials.
• The production techniques (in particular the infusion and prepreg technologies) and infrastructure need to be adapted to produce the very long blades (with a length of more than 60 m) economically and ecologically. One of the main challenges is avoiding the formation of voids in large surfaces and the homogeneous and quick curing of thermoset resins.
• Finally, the transportation and mounting of these very long blades require adapted procedures and working methods.

The use of appropriate FRP and core materials adapted to the task are essential in further developments of rotors and blades. 

Desirable material improvements:

1. Protection of the blade structure and its mechanical properties against lighting strikes by the integration of electric conductors in the blades. Damage by lightning is a major cause of standstill and loss of output. Some installations are equipped with monitoring systems to keep track of the number of lightning strikes. 
2. Integration of measuring systems in the composite material to enable online monitoring of tensions and impact. In principle, the minimal life span of windmills is twenty years, during which the desired output and a minimum of maintenance costs are to be expected.
3. Detection systems to rapidly detect damage to the components and the possible integration of self-healing systems to automatically repair damages.
4. Invisibility to radar waves. The communication of civil and military aircrafts can be disturbed by wind farms. To do this in a economical responsible way is a real challenge.

Solar energy systems

• Solar cells: PV (Photovoltaic) and PVT (Photovoltaic Thermal) panels convert solar energy (radiation) in electricity. In contrast to PV, a PVT panel also generates heat.
• Thermo-solar steam turbines: heat is formed by the concentration of solar light and transmitted to a fluid (thermal oil or water) to generate steam. This steam produces electricity. These systems are mainly used in southern Europe and Africa.
• Solar water heating (SWH): the harvested sun beams are used to heat water. By means of a heat exchanger and a pump the water is circulated.

In most solar energy systems, FRPs can be used. PV and PVT panels and SWH systems can be incorporated in lightweight FRP profiles reducing the load on the roof. It is also possible to use foam components (core materials also used to enhance the rigidity of FRPs) in the supporting composite structures to enhance the efficiency of the solar energy system.

Corrosion-free GRP composites are very suited for SWH: pipes and reservoirs made from composite materials are indeed highly resistant to (very) hot and mostly corrosive water.

Maritime energy

Seas and oceans enclose energy that can be harvested by

• Tidal power stations: Tidal forces are periodic variations in gravitational attraction exerted by celestial bodies. These forces create corresponding motions or currents in the world's oceans. Due to the strong attraction to the oceans, a bulge in the water level is created, causing a temporary increase in sea level.
• Wave power stations capture the energy generated by wind passing over the surface of the sea. As long as the waves propagate slower than the wind speed just above the waves, there is an energy transfer from the wind to the waves. Both air pressure differences between the upwind and the lee side of a wave crest, as well as friction on the water surface by the wind, making the water to go into the shear stress causes the growth of the waves.
• Ocean thermal energy conversion (OTEC) uses the temperature difference between cooler deep and warmer shallow or surface seawaters to run a heat engine and produce useful work, usually in the form of electricity. 

The enormous forces at sea and the influence of seawater can damage the floating (offshore) systems. Fibre reinforced plastics are stronger and more resistant to corrosion than steel are therefore very suited materials for these applications (stations, structures and piping...).
 

Innovation opportunities for FRPs for the construction market:

• Parking space floor with incorporated wireless inductive charging system for electric vehicles: A user-friendly method to charge a car's batteries is based on inductive energy transfer. The floor on top of the inductive charging system may not block the energy tranfer and may therefore contain no conductors. Carbon (and also glass) fibre reinforced concrete floors or road covering zones have already been proven very successful.
• Inductive energy transfer also allows the charging of battery-free automated guided vehicle (AGV) systems, making battery charging stations redundant in companies. The energy necessary to actuate these transportation systems is being supplied by inductive energy transfer systems that are embedded in the FRP floor covering.
• EMI-shielding by the integration of very thin electrically conductive FRP panels (based on carbon fibres) into building elements (walls, ceilings and floors).
• Energy storage materials by combining both conductive and insulating FRPs. Volvo already applies this principle to use the car body as a battery. The same system could be used to store energy generated by solar panels in FRP mural or ceiling panels.
• Co-extruded mural or ceiling profiles based on electrically conductive carbon fibre reinforced plastics (at the inside) and electrically insulating plastics (at the outside). This system allows to insert and connect several electric systems (LED, alarm systems...) in a single profile.
• Green building
• CF FRP-wrapping technology to repair and improve existing infrastructure (bridges, viaducts, railroads...) at lower costs
• Retrofitting with improved resistance to fire
• Integration of smart materials
  • PCM: energy storage and release based on phase change materials
  • conductive polymers (eg. in solar panels)
  • self-cleaning, self de-icing and self-healing FRP cladding
  • FRP coatings with sensor functions