Fibre Reinforced Plastics - Essay Example

?Fibre Reinforced Plastics 518545) Introduction Fibre Reinforced Plastics are gaining in prominence due to their increased scope of applications and also due to their strength capabilities. These are replacing areas which were earlier dominated by carbon steel materials. A Fibre Reinforced Plastic is considered a composite material made up of a combination of resins, fibre material and core. These set of additions impart a new identity to the composite in terms of heat resistance, strength and stiffness. Individually the mechanical properties of these additives might not be of an appreciable value but on combining to form a composite matrix these properties are magnified. The ultimate mechanical property of the composite of course depends upon the manner in which these fibres are arranged in the matrix and the manufacturing method followed in producing the composite. FRP in Aerospace and Formula-1applications Both these applications; Aerospace and Formula-1 deal with mechanisms to reduce the weight of the body and increase the aerodynamic profile of the surface. These functions would ultimately define the fuel efficiency and the speed of the aircraft or the Formula-1 car. (Cripps David, 2000) Research currently being undertaken seeks to refine the existing manufacturing processes to reduce the weight of the composite further but at the same time maintaining structural integrity. Advantages of using FRP 1. This offers a wide range of corrosion resistance over acids, chlorides and other oxidizers. 2. Since its offer no galvanic potential it negates the requirement of sacrificial anodes for cathodic protection. (The composite advantage, 2004) 3. The strength to weight ratio is quite large. 4. It can operate over a wide range of temperatures; from low temperature cryogenic temperature applications to high temperatures in the range of 350 to 400? F. (The composite advantage, 2004) 5. It provides safe working environment as it is fire resistant. 6. The inherent nature of the material and the adaptability of the manufacturing process make it suitable for creating large complex shapes in situ. 7. Both the installation costs and maintenance costs are lower. (The composite advantage, 2004) The Manufacturing Process There are number of manufacturing processes that are used in producing Fibre Reinforced Plastics. These include the 1. Hand Lay-Up process 2. Spray Lay-Up process 3. Vacuum Bagging 4. Filament Winding 5. Pultrusion However the manufacturing process that is usually used in the manufacturing of components and structural parts of aircrafts and F1 racing cars include the following (Cripps David, 2000) 1. Resin Transfer Molding (RTM) 2. Vacuum Assisted Resin Transfer Moulding (VARTM) 3. Prepegs 4. Resin Film Infusion. (RFI) 1. Resin Transfer Moulding (RTM) - This is a closed moulding process done under low pressure. The volume of composite produced is somewhere between that generated in a contact moulding process and that of a compression moulding process. The strands of reinforcement that is completely dried out are neatly arranged in the lower part of the mould. Glass reinforcements of various shapes can also be used along with the fiber matrix to ensure that complex mould shapes can be generated. Source: Cripps David, 2000, Reinforced Transfer Moulding The mating part or the upper portion of the mould is then closed onto the bottom half of the bold leaving a cavity which eventually takes the shape of the structure this process is trying to manufacture. The thermosetting resin is then injected into this cavity space. It is necessary to ensure that sufficient amount of this resin is used to avoid the formation of voids, cavities or edge imperfections caused due to low quantity of resin. (Rice Brian and Lee William, n.d ) To assist in this filling process and guarantee that all areas of this cavity are filled, vacuum can be used which draws the resin to all parts of the cavity and ensures a perfect fill. This process is also known as the Vacuum Assisted Resin Injection or VARI. Vents are also located at certain points on the mould so that any air that is trapped in the cavity can escape as the resin begins filling up the cavity. Formations of voids, pores and laminations are thus avoided. A static mixer is also utilized to mix the resin and the catalyst at preset design ratios which are then fed into this mould cavity. The ratio of the resin and catalyst depends on the strength of the structural part that is being moulded. (Rice Brian and Lee William, n.d) The resin inlets are closed as soon as some part of this wet resin comes out of the vents. The laminate matrix is then allowed to cure at the ambient temperature or at a higher temperature. This is defined by the constraints set up by the manufacturing process. Typical applications of this material include small components of aircraft and automobiles. The materials that are usually considered in this manufacturing process include (i) Resins- Some of the commonly used resins are vinyl ester, epoxy and polyester materials. At higher temperatures resins such as bismalemides can also be used. (Cripps David, 2000) (ii) Fibres- Fibres that are stitched together are particularly efficient since these assist in smooth flow of the resin. (iii) Cores- This process does not encourage the use of honeycomb structures since the pressure generated within this cavity have a tendency to destroy the honeycomb structure. Advantages of this Process (i) It has been estimated that composites used in the aerospace applications require a fiber volume in excess of 50% with the application of high quality resins. The RTM process very effectively achieves this criteria. ( Rice Brian and Lee William, n.d) (ii) There is no safety aspect associated with this process as it is taking place in an enclosed space. Environmental problems associated with this process are also minimal. (iii) Since this process involves injecting the resin into the mould cavity the degree of skill required to carry out the process is not too high if the mould has already been manufactured. The number of man-hours required for labour is also reduced considerably. (Rice Brian and Lee William, n.d) (iv) Excellent surface finish that is attained on both sides of the final product. Disadvantages of this Process (i) The degree of pressure that this mould is subjected to calls for the requirement of a heavy, sturdy and robust setup. This is therefore quite an expensive procedure requiring expensive tools and a substantial initial capital investment. (ii) This method of manufacture is usually restricted to generating small components of the automotive and aerospace parts. (iii) There can be areas in the final mould product having portions that are not fully impregnated. Various reasons including incorrect mould dimensions, faulty setting of parameters like curing temperature and viscosity of the resin can also contribute in not getting a perfect mould product. Such areas would then always need to be discarded as scrap. Incorrect setting up of the moulding process could therefore lead to wastage of expensive scrap pieces. (Cripps David, 2000) 2. The Vacuum Assisted Resin Transfer Moulding (VARTM) This follows the similar procedure as in Resistance Transfer Moulding with a few variations. The fibres are similarly arranged dry in the mould. This arrangement is then covered with a resin distribution fabric. This whole setup is then vacuum bagged which means the air that is present underneath the bag is extracted using a vacuum pump. However it needs to be ensured that there are no leaks present in the bagging since the vacuum atmosphere can be disrupted leading to lower quality of product. The resin is then injected into the cavity space and its flow is further eased out due the vacuum existing in the space. (Song Xiaolan, 2003) Source: Cripps David, 2000, Vacuum assisted Resin Transfer Moulding The materials that can be used in this process are similar to the ones used in the RTM process. Epoxy and vinyl ester resins, stitched conventional fibres and cores that do not have honeycomb structures work well with the VARTM process. Advantages (i) The tooling cost involved in this exercise is less compared to the RTM process since one section of the process is controlled using the vacuum bag. (ii) The amount of strength to be applied to the main tool assembly is less compared to the RTM process. (iii) Since the vacuum bag can be arranged for large sizes and since the tooling load applied is also minimal, this process can be used in the fabrication of large components and structural parts.( Song Xiaolan, 2003) (iv) Structures with integral core can be fabricated in one piece. (v) The standard wet layup devices which include chopper gun that is used to spray chopped fibres along with resin into the mould can be utilized in the VARTM process with a few modifications. Disadvantages (i) The vacuum bag must be laid very accurately so as not to entrain any air for the process to work accurately. (ii) Since the amount of load applied externally is of a lower value, the resin must have excellent flow ability characteristics to fill up the entire available cavity. In other words the viscosity of the resin must be lower than the RTM process. (iii) There are chances of areas in the mould existing without sufficient quantity of resin and hence can result in these parts being relegated to scrap. These are generally used in the production of body panels of smaller aircraft and also of formula-1 cars. 3. Prepegs As the name suggests these fibers and fabrics are impregnated with the resin long before the actual manufacture of the component takes place. The resin and the fibre reinforcements are prefabricated at the required design temperature and pressure. These materials can exist in such a state at ambient temperatures. However the prepegs are defrosted to increase its shelf life and also ensure that this prefabricated prepeg is available as when there is an actual demand for manufacturing the product. (Cripps David, 2000) Source: Cripps David, 2000, Prepegs When the actual moulding process into a complex shapes needs to be carried out these prepegs of standard shapes are laid out in the mould and heated to 120? C to 180? C. The resin breaks down on the application of heat and again flows into the cavity spaces that are provided in the mould. This also allows the resin to get cured. (Cripps David, 2000) An autoclave is a device used to pressurize a compartmental space at high temperatures. This also ensures removal of any trapped air. This autoclave is therefore used to generate a pressure of 5 atmospheres to act on the laminar matrix.(Briefing Autoclaving, 2008) A vacuum pump provided additionally is used to remove any trapped air and also assist in the flowing of the resin. The materials used in this process include the following (i) Resins- High temperatures resins like polymides, bismaleimides and phenolic are very effectively used in this process. (ii) Fibres- The fabric that can be laid out from a reel are generally used for this process. (iii) Foam materials of special chemical properties need to be used in the process due to the high temperature involved. Advantages (i) Since the material is preset without the requirement of a complex shape, the resin manufacturer can very accurately control the amount of fibres, resins and catalyst levels that are required in the prepeg. (ii) These prepegs have excellent properties and are extremely safe to work with. (iii) Since fibers can be directly used in the prepegs there is no requirement to further convert the fiber in to a fabric for resin laying. Source: www.Reinforcedplastics.com, 2009, A super sized autoclave with an inside working diameter of 30ft (9.14m) and length of 76 ft (23.2m) fabricated by ASC Process system for Vought Aircraft. (iv) Since the process involves the use of an autoclave which generates high temperatures and pressure, high viscosity resins can be easily used in the process. Hence the mechanical and thermal properties achieved in the final end product are of a higher value. Also, more number of resins of varying viscosities can be accommodated in this process due to the better control of system parameters. (Cripps David, 2000) (v) The degree of flexibility achieved in this process is huge and generating complex shapes is an advantage of this process. (vi) The degree of automation therefore achieved is far greater since the initial manufacture of the prepegs of a simple shape is quite easy. Disadvantages (i) The capital cost involved in the production of these prepegs is high. (ii) To cure the component which involves heating the same at elevated temperature require the services of an autoclave; a device that consumes a lot of time in completing the process. The additional cost incurred in operating the Autoclave also adds to the capital cost. (Cripps David, 2000) (iii) Both the tool setup of the mould and the core materials need to be sturdy enough to endure the elevated temperature and pressure. The Prepegs are typically used for fabricating the wing and tail section of the aircrafts and the body of F1 racing cars. 4. Low Temperature Oven curing Prepegs This is an off shoot of the Prepeg process. This is similar to the Prepeg processes except that the temperatures at which curing can be undertaken are much lower at 60? C to 100 ?C. (Cripps David, 2000) Autoclaves required to generate high temperatures and pressures to achieve the necessary curing along with the flowing characteristics of the resin can be easily avoided. (Briefing Autoclaving, 2008) A vacuum bag can therefore very easily achieve the process parameters. Advantages (i) The low temperature curing prepegs have all the advantages that are associated with the standard regular prepeg with a few additions. Source: Cripps David, 2000, Low Temperature Prepegs (ii) The lower cure temperatures allow the use of low temperature heating resources thus reducing heating cost. (iii) Large structures can be easily fabricated since temperatures required are low and the resin flow is maintained using a vacuum bag; the size of which can be increased to accommodate increased flow. (iv) Foam core can be used due lower temperature and pressure. Disadvantages (i) The only disadvantage is that the system is still higher in capital cost compared to the RTM process. This process is typically used in the fabrication of the large turbine blades of the aircraft propeller. 5. Resin Film Infusion (RFI) This process involves the arrangement of layers of semi solid resin that are interspersed with fabric material kept in dry condition. The vacuum bag in conjunction with the vacuum pump removes the air from the cavity space. (Muller Marcelo, 2000) The heating process is subsequently carried out to melt the semi solid resin and allow it flow into the empty spaces. This heating also assists in the curing of the resin mix. Source: Cripps David, 2000, Resin Film Infusion Advantages (i) The fibre volume achieved in this process is of a higher degree while at the same time porous spaces due to entrapped air are minimal. (ii) The process is extremely clean and poses no health hazards. (iii) The mechanical property of the final product that is fabricated is of a higher quality. (Muller Marcelo, 2000) (iv) The capital cost of this process compared to a prepeg is lower. Disadvantages (i) These are limited to aerospace industry applications (ii) The mould setup needs to be able to withstand temperatures up to 100? C. Source: Rice Brian and Lee William, n.d, Comparison of actual and reconstructed flow front progression Some of the commonly used materials include the Hexcel Lyvertex G808 and Cramer Style 473 that are used as fabrics and the Hexcel M36 Resin Film that are generally used as the semi solid resin films. (Muller Marcelo, 2000) The applications of the Resin Film Infusion (RFI) Process include the fabrication of the aircraft radomes or the front nose portion of the aircraft. The process ensures that the finish of this portion is excellent since this area involves maximum drag when the aircraft is in motion. Source: Rice Brian and Lee William, n.d, Viscosity profile of PR520 during a heating rate of 2?C/min Conclusion The Fibre reinforced plastics are therefore used extensively in the aircraft and the Formula-1 industry. The reinforced injection moulding process and the resin film infusion process are suited to this industry since this industry does not require churning out volumes of sales every year. The increased time taken to carry out these processes does not act as a hindrance as far as this industry is concerned. However, the FRP industry is carrying out extensive researches to reduce the time of manufacture, impart better strength to its products and also find out new areas where this manufacturing technology can be utilised. Recent manufacturing trends have shown that almost fifty percent of the weight of Boeing 787 is being manufactured using fibre reinforced composites which reduce its weight considerably. Almost 21% of the FRP that is being manufactured is for the aviation sector. (Stewart Richard, 2009) The key players who utilise the services of FRP in the manufacturing include the Boeing and the Airbus which accounts for 60 percent. The racing car industry is also witnessing new trends in manufacturing. Since this is not a large volume sector a lot of research can be undertaken to fine tune processes to obtain optimum surface profiles. Toray Industries have developed methods that combine the Resin transfer moulding process with better hardening mechanisms that can reduce the moulding cycle from 160 minutes to 10 minutes. (Stewart Richard, 2009) The parts thus generated are 50 percent lighter compared to their steel counterpart and its collision strength 50 percent higher. Source: www.Reinforcedplastics.com, 2009, A hybrid perform produced using American GFM binder combines carbon and glass fibres. Oxeon AB another Swedish player that use tow carbon fibres which are essentially fibres that are made of jute or flax in their manufacturing process. This has successfully managed to bring down the weight of the body panels of F1 cars by 30 percent. (Stewart Richard, 2009) Reference Lists 1. Muller Marcelo, 2000, Resin Film Infusion for net shaped composite stiffened panels, Structures and materials division, National Aerospace Laboratory NLR 2. Cripps David, 2000, FRP Composites Processing, Available at http://www.gurit.com, [Accessed on 1st April 2011] 3. Rice Brian and Lee William, n.d, Resin Transfer Moulding Process Monitoring and Control, University of Dayton 4. Stewart Richard, 2009, Carbon fibre composites poised for dramatic growth, Available at http://www.reinforcedplastics.com, [Accessed on 1st April 2011] 5. Briefing Autoclaving, 2008, Autoclaving, Friends of the Earth 6. Song Xiaolan, 2003, Vacuum assisted Resin Transfer Moulding: Model Development and Verification. 7. The composite advantage, 2004, Fiber-Tech Engineering Inc, Available at http://www.fibertecheng.com, [Accessed on 1st April 2011] Read More