composite material

Composite Material by moses dhilipkumar

Abstract

Composite materials are continuously gaining more importance in the field of engineering. In this paper we have focused mainly on natural fiber reinforced polymer composite materials. This natural fiber composite are having some special advantages such as high strength to weight ratio and stiffness. These fiber composites are also claimed to offer environmental advantages such as lower pollutant emission and replaces metals because of their high strength-to-weight ratio and stiffness properties. This work concentrate on fiber extracted from banyan tree (Natural fiber) as a reinforcement for the Polyester matrix. These banyan fibers have some added advantage such as low cost, lesser weight and no medical application. The most important advantage of this fiber is that the wasted fiber can be used effectively (recycling).

Tensile strength of the Banyan Fiber Reinforced Composite is studied. Specimens are prepared as per ASTM Standards. Computer assisted UTM is used for testing the Tensile Strength of the prepared composite structure. Fabrication of the pure and hybrid composite is done by simple hand lay-up method. The Banyan short fiber reinforced composites shown a better performance when it is hybrid with the    E-Glass fiber. The performance of the prepared composite is also studied in moisture environment.

Introduction 

Composite material is not a newly developed field mankind knows it since several hundred years before Christ and applied innovation to improve the quality of life. Although it is not clear has to how man understood the fact that mud brick make sturdier houses if lined with straw, he used them to make building that lasted. Ancient pharaohs made their slaves use bricks with straw to enhance the structural integrity of their buildings, some of which testify to wisdom of the dead civilization even today.

 Contemporary composite results from research and innovation from past few decades have progressed from glass fiber for automobile bodies to particulate composites for aerospace and range other applications. Fiberglass, developed in the late 1940s, was the first modern composite and is still the most common. It makes up about 65 percent of all composites produced today. More recently, fiber reinforced resin composites that have high strength to weight and stiffness-to-weight ratios have become important in weight sensitive application such as aircraft and space vehicles. This kind of fiber or particle embedded in the matrix of another material would be the best example of modern-day composite materials, which are more structural.

Composite Theory

In its most basic form a composite material is one, which is composed of at least two elements working together to produce material properties that are different to the properties of those elements on their own. In practice, most composites consist of a bulk material (the ‘matrix’), and a reinforcement of some kind, added primarily to increase the strength and stiffness of the matrix. This reinforcement is usually in fiber form. Today, the most common man-made composites can be divided into three main groups:

    Polymer Matrix Composites (PMC’s) – These are the most common and will be discussed here. Also known as FRP - Fiber Reinforced Polymers (or Plastics) – these materials use a polymer-based resin as the matrix, and a variety of fibers such as glass, carbon and aramid as the reinforcement.

Metal Matrix Composites (MMC’s) - Increasingly found in the automotive industry, these materials use a metal such as aluminium as the matrix, and reinforce it with fibers such as silicon carbide.

 Ceramic Matrix Composites (CMC’s) - Used in very high temperature environments, these materials use a ceramic as the matrix and reinforce it with short fibers, or whiskers such as those made from silicon carbide and boron nitride.

Composite Material

 Ironically, despite the growing familiarity with composite material and ever-increasing range of application, the term defines a clear definition. Loose terms like “material composed of two or more distinctly identifiable constituents” are used to describe natural composites like timber, organic materials, like tissue surrounding the skeletal system, soil aggregates, mineral and rock. The properties that can be improved by forming a composite material include strength, stiffness, less weight and corrosion resistance.

Fiber Reinforced Composites

Fibers are the important class of reinforcement, as they satisfy the desired conditions and transfer strength to the matrix constituent influencing and enhancing their properties as desired.  The orientation of the fiber in the matrix is an indication of the strength of the composite and the strength is greatest along the longitudinal directional of fiber. This doesn’t mean the longitudinal fiber can take the same quantum of load irrespective of the direction in which

 it is applied. Optimum performance from longitudinal fibers can be obtained if the load is applied along its direction. The slightest shift in the angle of loading may drastically reduce the strength of the composite.

 Long fibers in various forms are inherited much stiffer and stronger than the same material in bulk form. For example, ordinary plate glass fractures at stresses of only few thousand pounds per square inch, yet glass fibers have strength of 400,000 to 700,000 psi in commercially available forms and about 1,000,000 psi in laboratory prepared forms obviously then, the geometry of a fiber is somehow crucial to the evaluation of its strength and must be considered in structural applications.

Banyan and Glass Fiber Composites

Our paper deals with Banyan and Glass Fiber composites. It is one of the natural fiber polymer reinforced composites. Banyan and Glass are used as reinforcement and the polymer-based resin is used as a matrix. These fibers are been chosen because of their low weight, easily available, waste can be used effectively, no medical application.

Polymer Matrix Composites

Resin systems such as epoxies and polyesters have limited use for the manufacture of structures on their own, since their mechanical properties are not very high when compared to, for example, most metals. However, they have desirable properties, most notably their ability to be easily formed into complex shapes. Materials such as glass, aramid and boron have extremely high tensile and compressive strength but in ‘solid form’ these properties are not readily apparent. This is due to the fact that when stressed, random surface flaws will cause each material to crack and fail well below its theoretical ‘breaking point’. To overcome this problem, the material is produced in fiber form, so that, although the same number of random flaws will occur, they will be restricted to a small number of fibers with the remainder exhibiting the material’s theoretical strength. Therefore a bundle of fibers will reflect more accurately the optimum performance of the material. However, fibers alone can only exhibit tensile properties along the fiber’s length, in the same way as fibers in a rope.

It is when the resin systems are combined with reinforcing fibers such as glass, carbon and aramid those exceptional properties can be obtained. The resin matrix spreads the load applied to the composite between each of the individual fibers and also protects the fibers from damage caused by abrasion and impact. High strengths and stiffness, ease of moulding complex shapes, high environmental resistance all coupled with low densities, make the resultant composite superior to metals for many applications. Since PMC’s combine a resin system and reinforcing fibers, the properties of the resulting composite material will combine something of the properties of the resin on its own with that of the fibers on their own.

Fabrication Procedure

 Fabrication of Composite Material

 The materials used to prepare the Banyan Fiber and Hybrid Glass-Banyan composite are,

   General Purpose Resin (G.P. Resin Chemically polyester).

   Accelerator (Methyl Ethyl Ketone).

   Catalyst (Cobalt).

    Poly vinyl.

    Polythene Sheets & Glass Plates.

    Banyan and Glass fiber.

Overall, the properties of the composite are determined by:

      The properties of the fiber

   The properties of the resin

   The ratio of fiber to resin in the composite (Fiber Volume Fraction (FVF))

    The geometry and orientation of the fibers in the composite

The ratio of the fiber to resin derives largely from the manufacturing process used to combine resin with fiber. However, it is also influenced by the type of resin system used, and the form in which the fibers are incorporated. In general, since the mechanical properties of fibers are much higher than those of resins, the higher the fiber volume fraction the higher will be the mechanical properties of the resultant composite. In practice there are limits to this, since the fibers need to be fully coated in resin to be effective, and there will be an optimum packing of the generally circular cross-section fibers. In addition, the manufacturing process used to combine fiber with resin leads to varying amounts of imperfections and air inclusions.

Typically, with a common hand lay-up process as widely used in the boat-building industry, a limit for FVF is approximately 30-40%. With the higher quality, more sophisticated and precise processes used in the aerospace industry, FVF’s approaching 70% can be successfully obtained. The geometry of the fibers in a composite is also important since fibers have their highest mechanical properties along their lengths, rather than across their widths. This leads to the highly anisotropy properties of composites, where, unlike metals, the mechanical properties of the composite are likely to be very different when tested in different directions. This means that it is very important when considering the use of composites to understand at the design stage, both the magnitude and the direction of the applied loads. When correctly accounted for, these anisotropy properties can be very advantageous since it is only necessary to put material where loads will be applied, and thus redundant material is avoided. It is also important to note that with metals the material supplier largely determines the properties of the materials, and the person who fabricates the materials into a finished structure can do almost nothing to change those ‘in-built’ properties. However, a composite material is formed at the same time, as the structure is itself being fabricated. This means that the person who is making the structure is creating the properties of the resultant composite material, and so the manufacturing processes they use have an unusually critical part to play in determining the performance of the resultant structure.

Fabrication Using Hand-layup method

The hand lay-up or wet lay-up method is one of the oldest and most commonly used methods for manufacturing of composite parts. Hand lay-up composites are a case of continuous fiber reinforced composites. Resin is impregnated by hand in to fiber, which are in the form of woven, knitted, stitched or bonded fabrics this is usually accomplished by rollers or brushes.

 The fiber reinforced resin matrix composite material is fabricated as follows, Fibers are prepared for the required size of 5 mm length. 30g of fiber is taken in a container and it is gradually mixed with 150ml of resin in beaker. Then accelerator about 2.5% of volume of resin is added to it and stirred well.

Then catalyst about 1.5% volume of resin is added to it and stirred well. Then the mixture is transferred to mould setup. Now the mould is left for 24 hours for setting. After dying we can obtain the required composite.The various types of fibers in the fabrication process are Banyan. Banyan and Glass.

Result and Discussion

Tensile Test

             Tensile test is done by Universal Testing Machine. Tensile test is done by applying tensile load on the specimen. We have carried out our studies on the specimen with and without application of moisture.

Tensile Test without Moisture

Test is done on a specimen with a size of 24cm x 3cm x 0.3cm. The specimen is tested in dry condition as we are performing the test without moisture. When the load is applied above 14.5 KN, the specimen begins to deform. As the load increases, the deformation begins to increase.

We have done a comparison of tensile nature of Banyan and combination of Banyan and Glass fiber.

Load (KN)

This chart shows the tensile strength of the Banyan and Banyan-Glass combination For different load conditions.

Tensile Test for Specimen with Moisture

 To carry out the tensile test on the specimen with moisture, then the specimen is immersed in water for one day and the testing is carried out. This testing is done by UTM (Universal Testing Machine). During testing the composites begins to deform at the load of 12 KN. As the load increases the deformation also increases.

 We have also performed the tensile test on specimen with moisture for different combinations and a sample tensile graph is obtained as shown below.

Load (KN)

Comparison Between with and without Moisture

We have done a comparison of tensile nature of various fibers and their combination in wet and dry condition. Below chart shows the comparison of specimen for both wet and dry condition.

It is observed from the graph that Banyan and Glass fiber reinforced resin matrix composite material have maximum peal load in wet condition and it is about 15.95 KN. Peak load increases in wet condition when compared with dry condition for Banyan and Glass combination.

Comparison with Other Structural Materials

Due to the factors described above, there is a very large range of mechanical properties that can be achieved with composite materials. Even when considering one fiber type on its own, the composite properties can vary by a factor of 10 with the range of fiber contents and orientations that are commonly achieved. The comparisons that follow therefore show a range of mechanical properties for the composite materials. The lowest properties for each material are associated with simple manufacturing processes and material forms (e.g. spray lay-up glass fiber), and the higher properties are associated with higher technology manufacture (e.g. autoclave moulding of unidirectional glass fiber prepreg), such as would be found in the aerospace industry.

Composites in the aerospace industry

The aerospace industry’s unrelenting quest to enhance the performance of its products is constantly driving the development of improved structural materials. EADS companies have always been at the cutting edge of advanced materials development.

Fiber-based composite materials play an ever-increasing role in the construction of aircraft, helicopters, missiles, rocket launchers and satellites. The most common composites used in aerospace are carbon fiber reinforced plastics (CFRP), a mix of 60 percent carbon fiber and 40 percent resin. Other types include sandwich and honeycomb structures, fiber/metal laminates and glass fiber materials, while ceramic carbon fiber composites are used in high-temperature applications such as rocket motors.
The advantages of composites in aircraft design are their high strength-to-weight ratio, excellent fatigue endurance, corrosion resistance and a malleability that allows tailoring them to meet design requirements. Composites can be more easily formed into complex shapes (such as spheres) than their metallic counterparts. This not only reduces the number of parts making up a given component, but also reduces the need for fasteners and joints – often the weakest points of a structure.
Composite structures do, however, have a few drawbacks. For example, they tend to have higher manufacturing costs than metallic structures. Composites have stiffness and strength properties that may vary with temperature and moisture content and which depend on the thickness of a component. In some circumstances they may also be more sensitive to damage such as hail or bird strikes, not to mention accidental impact by servicing vehicles at airports.
Several different techniques are used in the production of CFRP aircraft parts. The most common method uses rolls of carbon fiber that have been pre-impregnated with resin, which are then cut and shaped as required and built into a series of layers. Pressure is then applied and the part is cured at high temperatures in an autoclave. In another commonly used method, the carbon fiber is shaped in a mould or by using sewing or braiding techniques. The liquid resin is added to this textile pre-form in the next step. This can be done using several processes, some of which involve placing the part in a vacuum and then curing it at room temperature.
A switch from metal to composites can make parts up to 40% lighter. The weight savings, which have a positive effect on both fuel consumption and the aircraft’s payload, are particularly important in a market environment characterized by high fuel

prices and the prospect of ever more stringent aircraft emission standards. Besides being lighter than traditional materials, composites offer significant advantages in terms of operational reliability, leading to lower in-service operating costs.
As already mentioned, however, composite structures have a major drawback in terms of their higher manufacturing costs compared to metallic structures. Consequently, much research continues to be directed at reducing these costs by developing methods that do not require the use of an autoclave and by increasing the automation of manufacturing processes such as automated tape lay-up, robotic fiber placement, resin transfer moulding and resin film infusion.

 

Conclusion 

At present there are the technical and economic prerequisites for broad use of composite materials in large-scale machine building industries. Replacement of traditional metallic materials by composite ones provides a reduction in material consumption for machine parts of up to 2.5 times with an increase in their operating life of up to 3 times and decreases the labor requirement for production by up to 10 times with a reduction in the time for organization of production of a new part of up to 2.5 times. The reliability of composite materials parts is 1.5 times greater than of hose of traditional materials. The unquestionable advantages of composite materials make it possible to confidently predict a steady broadening of their use in advanced models of transportation machinery in the very near future.