Composite Material Introduction

Composite Material Introduction

• Composites contain two or more distinct constituents or phases.
• Constituents must have differing physical or chemical properties.
• Composites are made of two or more materials at a microscopic level with chemically distinct phases.
• They are heterogeneous at the microscopic scale yet statically homogeneous at the macroscopic scale.
• Individual constituent materials each have significantly different properties.
• Constituents are constructed into complex structures at different levels or scales.
• Composites offer improved performance versus their constituent materials.
• The aerospace and defense industries triggered composite design in the 1950s and 1960s.
• Composites are still target structural materials, with industrial technology driving advancements.
• Composites are combined for strength, stiffness, toughness, corrosion/wear resistance, reduced weight, fatigue life, insulation, and acoustic and tailorable properties.
• Desired properties are enhanced by combining composite materials including:
• Strength and Stiffness
• Toughness and Reduced weight
• Corrosion and Wear resistance
• Fatigue life and Acoustic insulation
• Thermal/Electrical conductivity and Tailorable properties.

Reasons for Composites

• Military aircraft use composites for lighter, stronger, and stiffer builds with up to 20% improved strength to weight ratio.
• Over 50% of the Boeing 787 airframe and Airbus A350XWB are carbon fiber composite.
• Piping and tanks use advanced composites for environmental resistance, advanced composites are stronger, corrosion resistant, and lighter than steel.
• Industries experiencing metal piping corrosion benefit, with corrosion costing about $20 billion annually.
• F1 cars utilize composite impact structures for crashworthiness, absorbing kinetic energy, limiting forces on the driver, and meeting FIA requirements.

Constituents of Composites

• Reinforcement: -Is discontinuous. -Is stronger and harder.
• Matrix: -Is continuous.
• Reinforcement functions: -Contributes desired properties. -Carries load. -Transfers strength to matrix.
• Matrix functions: -Holds fibers together. -Protects fibers from the environment and abrasion. -Helps maintain fiber distribution. -Distributes loads evenly. -Enhances material and structural properties. -Provides better finish.
• Composite matrices can be polymer, ceramic, metal, or carbon.
• Commercial and high-performance aerospace applications use polymer matrices most widely.
• Matrixes: Usually ductile or tough, provides low density to a composite.
• Offers strength of around 1/10 of the fibers used.
• Holds the filler in a favorable orientation.
• Transfers stress to other phases and protects phases from the environment.
• Fiber Reinforcements: Stronger and stiffer than the matrix and have low densities with high load bearing properties.
• Fiber reinforcements are used due to being lightweight, stiff and strong.
• Fiber reinforcements are stronger than the bulk material due to: -Preferential molecule orientation along the fiber direction. -Reduced number and sizes of defects versus bulk material.
• E-glass is low in tensile strength at 1.5 GPa.
• Fibers of the same material can reach 3.5 GPa.
• Continuous reinforcements in unidirectional composites are aligned in lamina or ply.
• Unidirectional laminas have maximum stiffness and strength along the fiber direction.
• When uniform properties are needed, random fiber orientation is considered.
• Fiber selection involves trade-offs for mechanical criteria, environmental factors and cost.
• Fibers are classified by length, short, long, or continuous, strength/stiffness(low, medium, high,or ultrahigh modulus) and chemical composition (organic or inorganic).
• Common inorganic fibers are glass, carbon, boron, ceramic, mineral, and metallic.
• Organic fibers are polymeric.

Fiber Reinforcement Types

• Key fibre reinforcements include: -Glass fibres -Silica & quartz fibres -Carbon fibres -Aramid fibres -Boron -Polyester -Natural fibres
• Glass fibers are made from bulk glass and comprises a blend of sand, limestone, and oxidic compounds.
• Silica (SiO2) is the main chemical constituent in glass fibers (46-75%).
• Glass Fibers are typically flexible, lightweight, inexpensive and possess hardness, corrosion resistance, and inertness.
• Glass fiber's chemical composition and manufacturing process yields various types with similar stiffness with differing strength and environmental degradation resistance.
• E-glass fibers are preferred for structural reinforcement and their good chemical resistance.
• E-glass fibres mechanical behavior is influenced by environmental conditions
• E-glass tensile strength tends to decrease at elevated temperatures.
• Silica and Quartz Fibers distinguished from classical glass fibers of high silica concentration (SiO2).
• Silica fibers Concentrations range from 96-98%, quartz fibers concentration range from 99.95–99.97%.
• Silica & quartz fibers cost 25–50% more than glass fibers with enhanced physical and mechanical properties.
• They have comparable or better stiffness and strength than glass fibers, and thermal stability.
• Long-term working temperatures reach up to 900°C for silica and up to 1050°C for quartz fibers.
• Silica & Quartz Fibers offer good thermal and electrical insulation, with very good stability under different chemicals and are virtually insensitive to humidity.
• They are widely applied in high temperatures, and highly corrosive environments.
• Due to better radio-frequency transparency, they're antenna applications.
• Carbon Fibers, lightweight with excellent chemical resistance, Also called graphite fibres.
• They are widely used in the aerospace industry.
• Mechanical properties are determined by the atomic configuration of carbon chains and their connections.
• Strength in carbon fibres is controlled by orienting the carbon atomic structures with their strongest atomic connections along the carbon fibre direction.
• Boeing 787 is made of 50% composite, 15% aluminium, 12% titanium.
• Use of barrel section removes 50,000 rivets.
• Boeing 787 exhibits fuel efficiency, lower maintenance costs, elimination of metal fatigue and corrosion, and 60% smaller noise footprint.
• Carbon fibres are used in sports equipment and musical instruments
• Carbon fibers create wing leading edge structures against foreign object impact and composite sandwich structures.
• Composite sandwich structures are SLM built lattice cores.
• SLM built lattice cores offer reduced damage area, increase energy absorption and are higher weight.
• Carbon fibers are produced by the controlled oxidation, carbonisation and graphitisation of carbon-rich organic precursors in fiber form.
• Fiber surfaces are give surface treatment to improve matrix bonding, as well as a protection during handling.
• Carbon fiber advantages include high strength and high modulus, creep and fatigue resistance, and good energy absorption used in structural panels in F1 cars.
• Carbon fiber disadvantages include cost, poor impact resistance, and electrical conductivity.
• Compared to other fibres, carbon fibres can offer:
• Strength between 3500 and 5300 (MPa) tensile strength.
• Modulus Tensile between 160 - 440+ (GPa).
• Typical density of 1.8-2.0 (g/cc).
• Specific modus of 90 - 200+ .
• The most common precursor for carbon fiber is polyacrylonitrile (PAN),
• PAN fibers are stretched by 500-1300% to improve molecular alignment during manufacturing.
• Then, they are stabilised in air at 300°C and carbonised at 1500°C for crystallinity and nitrogen release.
• Fibers are about 90% carbon after the heat treatment, and further graphitized by heating and stretching up to 3000°C.

Other Types of Fibres

• Polyester fibres: Low-density, good impact resistance but low modulus.
• Typically used as a surfacing material because gives smooth finishing.
• Polyethylene fibers are made when Ultra-high molecular weight polyethylene molecules have very low mechanical properties in random orientation.
• Dissolving and drawing from solution creates disentangled and aligned molecules.
• Polyethylene fibers manufacturing includes:
• Dissolving polymer in solvent and heating.
• Spun then quenched viscous liquid.
• Heated and stretched fibres up to 100 times their original length.
• Solvent is removed by heating.
• High tensile strength fiber is created.
• Quartz Fibres exhibit good mechanical properties and high temperature resistance.
• They have lower density, higher strength and modulus then E-glass.
• Twice the elongation-to-break as E glass.
• Manufacturing process and the low volume production gives high prices of between 74 and 120 pounds per KG.
• Quartz Fibres has a near-zero CTE which can maintain performance properties under high temp as high as 1050-1250C.
• Offers great electromagnetic properties for fabricating parts such as aircraft radomes.
• Boron fibres created from coating carbon or metal fibres with boron via vapour deposition.
• This can create fibres are five times as strong, twice as stiff versus steel.
• Boron offers strength, stiffness, and light weight with excellent compressive properties/buckling resistance.
• Boron fibres have extremely high cost, this can restrict uses in high temp aerospace applications and/or is used in specialized sporting equipment.
• Offering high beam stiffness, torsional stiffness, low density, and high strength.
• Ceramic fibres utilized when high temperature resistance is need and it is associated with metal alloys (MMC’s).
• Has high to very high temperature resistance, low impact resistance, and poor room temperature properties.
• Usually more expensive than other fibres, but used whenever great advantages can justify the cost.
• The ceramic composites considered for components in high-heat aircraft engine applications.
• Natural fibres such as abaca, coconut, flax, hemp, jute, sisal are reinforcements in 'low-tech' applications.
• Fibres low specific gravity (0.5-0.6) means achieve high strengths can be achieved.
• They possess “green” attributes (less energy to produce), light weight, recyclability, good insulation and are carbon dioxide neutral.
• Natural fibre-reinforced thermosets/thermoplastics found in door panels, package trays, seat backs, and trunk liners of vehicles.
• European fabricators lead for materials that require automobiles can be recycable in their component parts.
• Hybrid Composites has advantages of combining different fibre types to produce a hybrid, improving its properties and reducing raw material costs.
• Hybrids a fabric with more than one structural fiber.
• Carbon/aramid or carbon/glass fibres is utilized in aircraft engine thrust reversers, telescope mirrors and column-wrapping for concrete support.