Advantages of Fiber Polymers over Metals - Essay Example

APPLICATION OF FIBRE REINFORCED POLYMERS BY Advantages of fibre polymers over metals Currently, fibre reinforced polymers are increasingly used in the automotive industry and other industries due to their benefits that over conventional metals. In addition use of polymer materials in automotive industry, they are increasing applied in the construction, aerospace industries, among other applications. This implies that fibre reinforced polymers are gradually replacing metals in various industries due to their inherent advantages over metals as indicated below. The use of fibre reinforced composite materials in the vehicle industry offers more advantages in reducing the weight of the vehicle. Reduced weight increases fuel consumption efficiency and reduces the amount of carbon compounds produced (Das 2001, 1). Reducing the weight of a vehicle by about 100kgs would lead to a reduction of about 0.3 to 0.4 liters of fuel per 100km (Yu & Dean 2006, 580). For example, the Ford Explorer model by Ford has a scratch resistance and corrosion proof cargo area made from integrated liners and side panels, reducing the vehicle’s weight by up to 20% compared to its conventional metal model. In addition, using composites makes it possible to reduce the number of parts required in fabrication of vehicles, compared to use of steel or aluminum (Calister 2007, 582). This leads to achievement of high volume composite concept in vehicle manufacturing, which leads to increased cost effectiveness. The use of natural based fibre has further improved fibre applications in the vehicle industry. Natural fibres are environmentally sustainable to use compared to metals. These fibres are processed from natural plants, making them biodegradable and environmentally friendly. Table of usages of fiber reinforced polymers (Mair, 1999) Currently, natural fibres are mostly used in making of seat liners, equipment panels, carpets, among other applications in vehicles (Riaz 2012, 9). Natural fibres such as jute, sisal, hemp, and kenaf offer good acoustic properties to vehicles, high stability, less splintering in case of accidents, and reduced forging behavior compared to metals (Sanadi et al 1994, 469). Through the use of fibre reinforced composites, many parts of different shapes can be produced with much ease, and at high speed compared to use of metallic materials. The ability to configure and produce complex shapes inexpensively makes the use of polymers to considerably reduce the cost of a vehicle, making them more affordable to customers. (Source: http://www.compun.com/CompositeBenefits.html) Composites offer increased stiffness, toughness, and strength over structural metal alloys. These superior properties come along with vehicle weight reduction. The specific strength and modulus per unit weight is almost five times that offered by steel or aluminum (Chung 2004, 22). Composites have increased resistance to rusting especially in environments susceptible to metal corrosion and rusting. Resistance to environmental degradation offers increased life cycle of vehicles in corroding environments, though the fibre reinforced polymer may be costly to produce initially. In addition, carbon fibre reinforced polymers offer superior properties to any vehicle parts that need sliding friction, example being the engine pistons. The properties obtained in this case are almost those of lubricated steel. Carbonated integrity application carbon fibre matrices have been used in making piston heads in engines to take advantage of the sliding properties (AVK, 2010). Fibre reinforced composites can be used in some vehicle parts that need high heat resistance and dimensional stability at elevated temperatures. The use of composites in making fuselages in vehicle engines takes advantage of this property; composites do not loose stability at elevated temperatures, and are also used as flame retardants in vehicles. Graph stress-strain curves for mild steel, CFRP, AFRP and GFRP (Source: http://www.rjdindustries.com/Products/Rebar/rebar.html) Using metals that would result in the same properties would require expensive alloys, which have to be treated to increase their thermal stability, making the use of composites much cheaper. The need for environmental sustainability is driving many automobile companies to rethink their use of materials, specifically due to strict regulations imposed in the European market. For example, in Europe, vehicles are currently supposed to be made of 95% recyclable materials. This has driven many companies to seek new ways of designing and using cost effective and lightweight materials, with bio-composites offering the best alternative. The use of natural fibres in motor vehicles offers increased biodegradability and high performance in vehicles (Zhu et al, 2012). Natural fibres used ensure the end of life of each vehicle is environmentally sustainable; a challenge being faced with the conventional materials currently. Composites increasingly offer better impact resistance to vehicle structures, improving the safety of vehicle users. In racing vehicles, companies such as McLaren employ crush structures made from carbon fibre reinforced matrix (Savage & Oxley 2008, 758). This increases the safety of drivers, a factor that would be hard to achieve using metals. Composites in the same case offer improved energy absorption properties for noise dumping, door sealants, and other vehicle linings that make it possible to reduce vehicle’s noise especially at high speeds. Carbon-fibre BMW i3 (Source: http://www.goauto.com.au/mellor/mellor.nsf/story2/A971B8128B6974B4CA25790D001C9C6D) Manufacture of a vehicle bonnet using Carbon based fibres Car bonnets are mostly made from metal, specifically steel or aluminum alloys. The use of steel in making car bonnets leads to certain drawbacks that need to be addressed. In high speeds, bonnets tend to make much noise due to the low dumping properties of the materials, making the vehicle noisy. Moreover, engine heating affects metallic bonnets due to the high thermal conductivity of steel alloys. In addition, the low impact resistance in steel makes bonnets prone to damage in case of slight crush or impact. All the same, the use of fibre reinforced polymers can solve all these drawbacks, leading to a better bonnet with higher impact resistance and better noise dumping properties. Mechanical properties Fibres have much higher strengths and stiffness values than a matrix (Malkapuram, Kumar & Yuvraj 2008, 1170). The use of short fibre matrix has portrayed high performance in reinforced polymers (Ahmed, Baharum & Abdullah 2006, 959). The anisotropy of fibres in the manufacture of such a vehicle bonnet will largely affect its tensile properties. In making the bonnet, fibres have to be arranged in a parallel and not perpendicular direction, which offers 40% increased tensile strength to the bonnet (Hajnalka, Racz & Anandjiwala 2008, 167). To increase the Young modules of the bonnet, the fibre content has to be increased. For example, research has shown that at 50% hemp fibre loading, the young modulus of the manufactured part will increase by two and a half times (Hajnalka, Racz & Anandjiwala 2008, 168). Increasing the fibre content will thus increase the young modulus of the bonnet, making it to perform much better. The energy absorption of the fibre component will depend on the types of fibre, the matrix type, the fibre orientation, and the fibre volume fraction; decreasing the density of the fibres used will greatly increase the energy absorption of the component (Jacob et al, 2005). In manufacturing the bonnet, short fibres will be used in parallel orientation to ensure increased tensile strength of the bonnet, to increase the energy absorption of the bonnet in case of an impact, in addition to reducing the excess noise from bonnet vibrations. This results from concentration of stress in shot fibre specimens (Jacob et al, 2005), improving the dumping properties of such materials. Manufacturing methods Fibre length, orientation, and density to volume ratio all have a bearing on the manufacturing process of a composite. In manufacturing of a vehicle bonnet, the issue of discontinues long fibre reinforced composites offers a great alternative to non-reinforced polymers and continuous fibre laminates in terms of the mechanical properties obtained (Joules et al, 2004). For example, using long glass fibre Polypropylenes (LGFPP), the resulting composites would be of low cost production, which is suitable for mass production (Joules et al, 2004). They lead to reduced mass of the produced part and superior mechanical properties in terms of durability, stiffness, and impact resistance, the same qualities required in making a vehicle bonnet. On the other hand, short fibres were observed to offer greater energy absorption properties compared to long fibres (Jacob et al, 2005). Manufacturing of composite plates from chopped carbon fibres mixed with an epoxy resin to offer superior bonding qualities would thus form the best laminate plates to use in bonnets. These plates can only be manufactured through compression molding due to the small fibre length, high fibre fraction, and the fibre tow size required to offer superior energy absorption properties to the bonnet (Thomason 2009, 117). In addition, Jacob et al (2005) noted that forming fibres in tube structures would make them easy to fabricate and ensure they are close to the geometry of actual crashworthy structures. Manufacturing the fibres in form of tubes makes it possible to absorb impact energy in a controlled way through progressive triggering, a property required in energy dissipation (Feraboli 2009, 1967). Therefore, for a vehicle bonnet to have high energy absorption properties resulting from short fibres in parallel, high fibre fraction to volume ratio, fibre tow size; compression molding would be the most ideal manufacturing method. Manufacturing cycle times Due to the relatively low build rates of carbon fibre parts especially in Europe, carbon fibres in composite molds require typically short cycle times. The molds have a life span of thousands of cycles for a single part, and many more cycles where simple geometries are concerned (Brosious, 2003). Invar and steel molds have considerable low thermal expansivity, and can be used for hundreds of parts. In the making of the carbon fibre bonnet, the compression molding used will require such molds to reduce the cycle times needed. The use of short fibre lengths and high volume fibre plates in compression molding would facilitate further joining of small plates using resins, and then curing the complete bonnet. This will require several different molds according to the shape of the bonnet, where compression molding would be done at very low cycle times leading to production of hundreds of parts per day. Compression molding offers short cycle times especially due to the short fibre length and high volume content, and has proved to be efficient in production of different profiles (Sahari & Sapuan 2011, 172). Vehicle Recycling and Recovery In the last 20 years, automobile manufacturing has drastically increased to about 58 million vehicles. The organization for Economic Cooperation and development, (OECD) estimates the number of vehicles in OECD countries to increase by about 32% from 1997 to 2020 (Kanarai, Pineau & Shallari, 2010). Most vehicles are either manufactured in Germany, Britain, France, Italy or Spain. The motor vehicle industry is currently facing the biggest challenge related to its impact to the environment, particularly after the service life of vehicles. Though vehicles affect the environment in their entire life in waste generation, consumption of energy sources, disposal, and greenhouse gases, the end of their lives becomes the greatest problem in ensuring environmental sustainability. To ensure such environmental sustainability is achieved, reduced vehicle pollution and ultimately ease of disposal and recyclability at the vehicle’s end life, vehicles manufacturers are constantly employing the use of recyclable materials and other non-hazardous materials, which would ensure less impact on environmental pollution once the vehicle attains its end life. This makes more vehicle manufacturers to shift towards sustainable waste management in vehicle production. Vehicle manufacturing has been shifting towards the use of much lighter materials compared to conventional materials. For example, in 1965 a European car had 82% ferrous and non-ferrous materials, and 2% plastic; in the 1980s, the ferrous and non-ferrous materials in vehicles averaged 74 to 75%, aluminum about 4.5%, and plastics estimated to range between 8 to 10% of any European’s car weight (Zebori et al, 2000). The gradual change in materials reduced the overall weight of the vehicle further saving on fuel used, which reduces the impact of the vehicle to the environment. By 1998, the average composition of a vehicle in Europe had increased to about 8% aluminum of the total weight, reduction of both ferrous and non-ferrous metals to about 67.5% of the vehicle, and increasing plastic content increasing to about 9.3% (Kanarai, Pineau & Shallari, 2010). Currently companies such as Toyota have complied with Europeans regulations on increasing the reuse and recovery of end of life vehicles (ELV) to a minimum of 85% by 2006, and reuse and recovery of ELVs at a minimum if 95% by average weight of a vehicle, and a reuse and recycling minimum of 85% by 2015 (Kanarai, Pineau & Shallari, 2010). Toyota has set up an Environmental Committee and Working Group dedicated to recycling through research on dismantling technologies of all ELV, seeking ways to promote usage of the shredder residual, and boosting the reuse of recycled materials in their vehicle manufacturing parts (Toyota Motor Marketing, 2009). For example, instead of using the conventional reinforced composite polypropylene (PP), the company adopted the use of the Super Olefin Polymer (TSOP), a thermoplastic that can be recovered and reused much more easily than PP (Toyota Marketing, 2009). This material is currently being used in modeling and manufacturing the front and rear bumper of the new Toyota corolla. The same material is being used for air conditioning, insulating pads, as a sealing material, and instrument panels, all which are connected using friction welding compared to using screws or metal clips (Toyota Marketing , 2009). This reduces the amount of materials used, while at the same time improving on the dismantling operations of the vehicle. Toyota is currently phasing out any use of leaded materials, and the use of sodium azide in airbags. The Toyota LS430 model is one of the most environmentally sustainable vehicles due to extensive use of sustainable and recyclable materials. The vehicle contains large amounts of super Olefin polymers, thermoplastic Urethane, thermoplastic olefins, recyclable sound proofing products, recyclable polypropylene, and kenaf , a natural fibre (Toyota Marketing , 2009). The use of these materials in the vehicle body parts, seats, airbags, and other parts makes the company attain an almost 90% reuse of recyclable materials, greatly reducing the impact of ELVs to the environment. The company is also credited for developing the world’s first rubber recycling technology in 1997, recycling more than 200 tons of waste rubber. The recycled rubber is then used in Toyota vehicle production as weather stripping material to make water proof vehicle doors and trunks. Moreover, Ford in its campaign to ensure environmental sustainability has developed the use of natural products in its vehicles. The postindustrial cuttings from coffee beans are processed and made into interior padding, postindustrial yams made into seat fabrics, and post-consumer nylon carpeting processed and made into resin for making cylinder head covers in engines (Ford, 2012). The company uses soy based polyurethane foams as seat cushions, headliners and seatbacks, while wheat straw and plant fibre reinforced plastics are used for interior door panels. In other words, Ford in ensuring sustainability of its vehicles and ELV sustainability. Much has been employed in research and development of natural based composites, most of which can be recycled, while others are biodegradable. The new plan is to ensure steel, aluminum, or thermoplastic materials used are effectively recycled. Currently, about 85% of materials used in most Ford vehicles are recyclable, while more than 95% are recoverable. Limitations of High end Carbon Fibre Processing Though BMW and McLaren will sell a good number of vehicles similar to Ferrari, the company insists that it can produce about 30 cars daily when using aluminum composites, compared to using carbon fibre composite. This is because; aluminum is much less labor intensive making vehicles manufactured by aluminum much less labor intensive compared to those built with carbon fibre reinforced matrix (SAE international, 2011).The aim would be to replace the hand pre-impregnation of carbon fibre cloth to a much faster process of injecting resin into a cloth after setting it in a mold. This implies that the use of fibre reinforced matrix is hampering mass production of vehicle units due to a manual process that is more time consuming compared to aluminum, which is easier to work with and possible to automate the process. Vehicle manufacturers such as McLaren and BMW have expressed intension to refocus from carbon fibre based polymers to other alternative fibres due to these limitations. Despite the need for manual work, carbon fibres are brittle due to the strong conventional bonds between them. In addition, once the body made extensively from carbon fibre is cracked or dented, it is not possible to beat it back into shape compared to steel or aluminum, or adding a glass fibre layer as done in most panel beating operations. Once such a part cracks, the tensile strength and young modulus of the structure becomes flawed and need to be replaced. This makes vehicles made from carbon fibre much expensive and demanding in maintenance, which might not be economical for a company to produce. The manufacturing process especially in making and treating carbon fibres for use in sensitive or integrity parts becomes lengthy and expensive. High performance carbon fibre use a mesosphase pitch fibre, which differs in terms of pyrolysis, hydrogenation, catalyst modification and solvent extraction (Morgan 2005, 89). The elongated process in preparing mesophase pitch carbon fibres makes use of carbon fibres in high integrity parts that require high performance experience non economical for companies. For example, during oxidation, the mesophase or high performance carbon fibre requires 6% increase in mass over general use carbon fibre to achieve adequate stabilization, which is achieved in 40 minutes at 260degrees. The several processes required in making and treating the high quality level increases the processing time of high end use carbon fibre (Morgan 2005, 90). The cost of the solvent precursor in addition to the lengthy processing times makes the use of high performing carbon fibre too lengthy and expensive. In spinning, the mesophase pitch precursor is melted and then sprayed through spinning jets. The fibre at this stage is drawn and stretched in maintaining a certain degree of tension in fibre. To make carbon fibre to have a better molecule alignment along the fibre axis and a small diameter, this offers the fibre good dimensional qualities (Liu, 2010). Stabilization of carbon fibres occurs at temperatures between 150 and 400, in areas with tension; heat is needed in the entire stabilization process to ensure fibres have a better alignment of molecules (Gerstle1991, 653). In addition, the stabilized fibres have to be heated at between 1000 to 3000 degrees centigrade in an inert atmosphere, with short duration exposure of nitrogen or argon. Graphitization is then carried out at temperatures between 2000 and 3000 degrees. The oxidized fibres are then surface treated through either carbon dioxide exposure, nitric acid, or any other methods that would impact better adhesion to resins (Liu, 2010). This process is expensive and lengthy in producing carbon fibres that are fit to be used in parts demanding integrity and high performance. The problem of a labor intensive and lengthy process makes mass production of carbon fibres for high end performance components impossible, in addition to the high cost involved in carbon fibre processing. As SAE Intentional (2013) explains using such a process in manufacture of high performing vehicles at mass production is not possible, calling vehicle manufacturers to opt for better process cycle times, overall reduced costs in the production process, ease of mass production, and automation, as well as a process that would lead to production of high performance materials. Therefore, the use of aluminum alloys treated with resins thus offers the best alternative. Aluminum once treated with resins attains the strength and qualities similar to steel. The ease of aluminum production and resin treatment process is ideal for high preforming vehicle components at much lower costs and facilitates mass production of vehicles. The use of resin treated aluminum will thus make vehicle manufacturers to move from using carbon fibres in high performing components to the use of the easier to make aluminum based polymers. List of References Brosius, D., 2003. Carbon fiber: The automotive material of the twenty-first century starts fulfilling the promise http://speautomotive.com/SPEA_CD/SPEA2003/pdf/f01.pdf [Accessed 7th April 2013] Callister, W. D., Jr. 2007. Material Science and Engineering. An introduction. Seventh Edition. John Wiley and Sons, Inc. Chung D.L, 2004. Composite Materials: Functional Materials for Modern Technologies, NY: Springer Das S, 2001.The cost of automotive polymer composites: A review and assessment of does lightweight materials composites research TE: Energy Division Oak Ridge National Laboratory Feraboli P., 2009. Development of a Modified Flat-plate Test Specimen and Fixture for Composite Materials Crush Energy Absorption, Journal of Composite Materials, 43(19) Gerstle, P.L, 1991. Composites Encyclopedia of Polymer Science and Engineering, NY: Wiley New York Hajnalka, H, Racz, I and Anandjiwala, R D, 2008. Development of HEMP Fibre Reinforced Polypropylene Composites, Journal of Thermoplastic Composite Materials, 21, 165-174 Jacob G.C., Starbuck M.J., Fellers J.F., & Simunovic S., 2005. Effect of Fiber Volume Fraction, Fiber Length and Fiber Tow Size on the Energy Absorption of Chopped Carbon Fiber–Polymer Composites, Polymer Composites, DOI 10.1002/pc.20100 Joules E,J., Tsujikami T., Lomov S.V., & Verpoest I.,2004. Effect of fibres length and fibres orientation on the predicted elastic properties of long fibre composites, http://www.mtm.kuleuven.be/Onderzoek/Composites/Research/meso-macro/textile_composites_map/textile_modelling/downloads/sl-modelling-micro-mech-random-fibres-paper.pdf [Accessed 7th April 2013] Kanari N., Pineau L., & Shallari S., 2010. End-of-Life Vehicle Recycling in the European Union, The Minerals, Metals & Materials Society, http://www.sae.org/events/green/reference/2010/End%20of%20Life%20Vehicle%20Recycling.pdf [Accessed 7th April 2013] Liu C., 2010.Mesophase Pitch-based Carbon Fiber and Its Composites: Preparation and Characterization. Masters Thesis, University of Tennessee, http://trace.tennessee.edu/utk_gradthes/8162010.http://trace.tennessee.edu/utk_gradthes/816 Malkapuram, R, Kumar, V and Yuvraj, S N., 2008. Recent Development in Natural Fibre Reinforced Polypropylene Composites, Journal of Reinforced Plastics and Composites, 28, pp. 1169-1189 Morgan P., 2005. Carbon fibers and their composites. Boca Raton: CRC Press SAE International, 2013. Ferrari prefers aluminum over carbon fiber http://www.sae.org/mags/SVE/10391[Accessed 7th April 2013] Sahari J, & Sapuan S.M., 2011 Natural fibre Reinforced Biodegradable Polymer Composites, Rev.Adv. Mater. Sci. 30, 166-174 Savage G, & Oxley M., 2008. Damage Evaluation and Repair of Composite Structures, Anales de Mecánica de la Fractura 25 (2) http://www.gef.es/Congresos/25/pdf/10-8.pdf Thomason, J.L. 2009, The influence of fibre length, diameter and concentration on the impact performance of long glass-fibre reinforced Polyamide 6,6. Composites Part A: Applied Science and Manufacturing, 40 (2). 114-124 Yu L.; Dean K, Li L.2006. Polymer blends and composite from renewable resources. Prog Polym Sci 31: 576-602. Zhu J. et al, Abhyankar H, & Njuguna J., 2012 Tannin-based flax fibre reinforced composites for structural applications in vehicles, IOP Conf. Ser.: Mater. Sci.Eng. 40 012030 doi:10.1088/1757-899X/40/1/012030 Zoboli R et al., 2000. Regulation and Innovation in the Area of End-of-Life Vehicles, EUR 19598 EN, ed. F. Leone Milan, Italy: IDSE-CNR Read More