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ABSTRACT: The work presented in this project is to evaluate tensile, flexural, chemical and thermal properties of Glass, Graphite and Kevlar fiber reinforced polymer matrix composites. Behaviour of different fibre-reinforced composite materials are studied with respect to their composition and the applications are discussed. The review looks into the studies on various types of Kevlar composites. It provides an orientation to optimise the present day Kevlar materials and a platform to explore and investigate new combinations
Introduction
Fibre-reinforced polymer (FRP), also Fibre-reinforced plastic, is a composite material made of a
polymer matrix reinforced with fibres. The fibres are usually glass, carbon, or aramid, although
other fibres such as paper or wood or asbestos have been sometimes used. The polymer is usually an epoxy, vinylester or polyester thermosetting plastic, and phenol formaldehyde
resins are still in use. FRPs are commonly used in the aerospace, automotive, marine, and construction industries.
Composite materials are engineered or naturally occurring materials made from two or more constituent materials with significantly different physical or chemical properties which remain separate and distinct within the finished structure. Most composites have strong, stiff fibres in a matrix which is weaker and less stiff. The objective is usually to make a component which is strong and stiff, often with a low density. Commercial material commonly has glass or carbon fibres in matrices based on thermosetting polymers, such as epoxy or polyester resins. Sometimes, thermoplastic polymers may be preferred, since they are mouldable after initial production. There are further classes of composite in which the matrix is a metal or a ceramic. For the most part, these are still in a developmental stage, with problems of high manufacturing
costs yet to be overcome [1]. Furthermore, in these composites the reasons for adding the fibres (or, in some cases, particles) are often rather complex; for example, improvements may be sought in creep, wear, fracture toughness, thermal stability, etc [2].
Fibre reinforced polymer (FRP) are composites used in almost every type of advanced engineering structure, with their usage ranging from aircraft, helicopters and spacecraft through
to boats, ships and offshore platforms and to automobiles, sports goods, chemical processing
equipment and civil infrastructure such as bridges and buildings. The usage of FRP composites continues to grow at an impressive rate as these materials are used more in their
existing markets and become established in relatively new markets such as biomedical devices and civil structures. A key factor driving the increased applications of composites over
the recent years is the development of new advanced forms of FRP materials. This includes
developments in high performance resin systems and new styles of reinforcement, such as
carbon nanotubes and nanoparticles[3]
Properties of FRP as a Composite Material
Composite materials can be defined as materials system combined of two or more micro- or macro-component that differ in form and chemical combination and which are fundamentally insoluble in each other. Usage of composite materials has a great importance in many engineering areas such as automotive industry, construction industry, manufacturing industry and new technology products. The purpose of the creating composite materials is to produce superior properties of a new material the production than existing components. In modern materials engineering, composite usually refers to a "matrix" material that is reinforced with fibers [4].
Classification of Composite Materials
Composite Materials generally have been classified in Metal Matrix Composites (MMC) or Ceramic Matrix Composites (CMC) or Polymer Matrix Composites (PMC) forms with the type of Fiber- reinforced, Particulate or Laminar Composites. The composites in most cases are useful materials.
Carbon Fibers (CFRP): Carbon fibers are anisotropic in nature Carbon fiber, is produced at 1300ºC. High strength, excellent creep level, resistance to chemical effects, low conductivity, low density and high elastic modulus are the advantages of carbon fibers. The weak sides of carbon fibers are being expensive and anisotropic materials with low compressive strength
Glass Fibers (GFRP): Glass fibers, typical are isotropic in nature and most widely used filament. Common types of glass fibers are E-Glass, S-Glass and C-Glass. The characteristic properties of glass fibers are high strength, low cost with good water resistance and resistance to chemicals
Aramid Fibers (AFRP): Aramid fibers widespread known as a Kevlar fiber in the markets as shown in Fig. 5. The structure of Aramid fiber is anisotropic in nature and usually yellow in colors. Aramid fibers are more expensive than glass moderate stiffness, good in tension applications (Cables and tendons) but lower strength in compression. Aramids have high tensile strength, high stiffness, high modulus and low weigh and density. Impact-resistant structures have been usually produced these materials. There are five classes of Kevlar with the different engineering properties Kevlar-29, Kevlar-49, Kevlar-100, Kevlar-119, and Kevlar-129
In general the mechanical properties of FRP vary with the type and orientation of the reinforcing fibers[6]. Fibers can be oriented in Continuous Form (Continuous and aligned fibers are generally long and straight also fibers distributed parallel to each other) or in Woven Form (Fibers come in cloth form and provide multidirectional strength) or Chopped Form (fibers are short and generally randomly and discontinuous arranged called fiber glass)
Aramid fibres characteristics
These are the first organic fibres used as reinforcements with high tensile modulus and strength. These fibers have 5-10% higher mechanical properties than other synthetic fibres. They perform better than steel or glass on equal weight basis and also have excellent heat and wear resistance.
Aramid fibres are characterized by medium to ultra high strength and medium to low elongation, and moderately high to ultra high modulus with densities for crystalline fibres ranging from 1.35g/cm3 to 1.45g/cm3 . They also have specific tensile strengths over twice that of nylon and polyester tire cord and five times that of steel wire. The specific ultimate tensile strength of reinforced epoxy composites is higher than that of high-strength inorganic fiber composites. The specific modulus of epoxies reinforced with Kevlar is roughly three times higher than that of S glass-epoxy and is equivalent to that of some graphite fibers and one-third that of boron epoxy. Kevlar has five times the strength of steel wire. They have fatigue life cycle of 107 cycles. The creep behavior at 50% of the break load and at107 cycles is around 0.3%.
Thermal Properties
Depending upon the selection of resin systems, aramid composites have a useful temperature range from -320 to 400°F (-196 to 204°C). They retain strength modulus even at a temperature of 300°C to 640°C.
Impact properties
The aramid composites in general resist shattering upon impact, and the presence of the fibers inhibits propagation of cracks. Impact strengths of the composite transverse to fiber alignment are about midway between that of E glass- epoxy and graphite-epoxy composites. [9]
Chemical Properties
Presence of Na2 SO4, Na2 CO3, and compounds of their mixtures is observed by x-ray diffraction of the fiber ash. Since the ash is found to be high in Na2 SO4 which is a known desiccant, this possibly contributes to water absorption. Only 6 to 10% of the total Na in the fibers is dissolved after 15 days, and more than 50% is dissolved within 6 h of exposure to water. The differences in the rates of Na dissolution and the percentages of the Total Na dissolved in water suggest either that the Na is distributed differently throughout the fibers, residing preferentially in the interior regions, or that the fibers differ in their porosities to water.
Examination of Kevlar-49 and Kevlar-29 fibers by x-ray photoelectron spectroscopy to evaluate the nature of the first few atomic layers of the fiber indicates that the surface composition differs from the theoretical composition of bulk PPTA
There appear to be no significant differences between
Kevlar-29 and Kevlar-49, and there is no evidence of an exudates caused by exposure to high temperatures. Fibers containing residual H2SO4 will rapidly darken, particularly at elevated temperatures (greater than 75°C, with associated 20 to 25% losses in strength. [10]
Advanced Composites
A wider adoption of emerging thermosetting composite materials using Boron and Kevlar-49 fibres will be facilitated by establishing their mechanical properties and production costs. This study aims to characterise these reinforced composites on the basis of performance and economic considerations that can be readily used by manufacturers and designers. Composites with polyimide and polyester thermosetting plastics were prepared and tested in tension, compression and bending. Consolidated results indicate that tensile strength values are similar to respective fibre composites since they are fibre dominated. The compressive strengths are lower and appear to be matrix dependent. From the cost analysis, Boron-polyester composite provides the best performance in terms of cost per unit tensile properties whereas Boron-polyimide composite provides the best performance in terms of cost per unit compressive and flexural properties. The results can serve as ready reference to designers to choose the most suitable composites during preliminary engineering design stage.[11]
Advanced composites application
• Aramid reinforced composites absorb 2-4 times more load than carbon fibre.
• Pressure vessels- they withstand 25-30% more pressure than glass and carbon fibre
• Combined Kevlar and carbon fibre form hybrid fibre are used in planes and aircrafts an example being BOEING 767.
• Used in construction and beams as reinforced concrete materials
• Ropes and cables use Kevlar 29 since its specific strength is 7 times more than steel and 20 times more in sea water
• Electro mechanical cables and fibre optics
• Due to fire resistive property it is used to create protective clothing in fire proof apparels and gloves
• Due to its excellent impact behavior its used for ballistic protections
• The short fibres are used in brake pads and clutches [12]
• Replace asbestos with 10% of Kevlar pulp will extend the life of these sheets by 3 to 5 times.
• Electronic circuit boards can be made lighter and thinner to low specific weight and high density characteristics [13]
Conclusion
We conclude that the Kevlar fibre with LY-556 Epoxy resin give good tensile strength, flexural strength and impact strength which are most useful in aircraft and automobile bodies that reduces weight and gives more strength. The studies further showed that with the variation in the fibre type and fillers used has a significant effect on the tensile and flexural properties of the specimens, the three varieties of fibres used are plain bi-woven glass fibre reinforced laminate, plain bi-woven graphite fibre reinforced laminate and plain bi-woven Kevlar Fibre reinforced laminate.