Carbon Fibre Reinforced Polymers - Assignment Example

Answer to Question a) Carbon fibre reinforced polymers are very vital in the structure strengthening applications. They have become more popular ininternal reinforcement. Carbon fibers have a high elastic modulus and a high tensile strength. Its use in structure strengthening applications has escalated owing to the fact that it has an elastic modulus higher than steel. The Carbon fibre reinforced polymers have acquired use in the aerospace industry because their strength to weight ratio is among the highest of the fiber reinforced polymers. (Prince 2011) The structural and mechanical properties of fiber reinforced materials may be discussed in two levels of scale, micromechanics and macro mechanics. (Hult & Rammersstorfer 1994) In analysing macro mechanical properties, analysis of material structural properties is done. Fiber reinforced polymers display a linear-elastic behaviour. Thus, it has properties related in a fashion described by Hooke’s law as follows. (Prince 2011) Where, ffu* is the Ultimate tensile strength. Ef is the Tensile Modulus of Elasticity. εfu* is the Ultimate Rupture Strain or Elongation at Break. (The strain of a material at the point of rupture.) Table 1.1 shows a comparison of the primary physical properties of a series of fibre reinforced polymers and Steel. Simple analysis shows that in comparison to steel and other fiber reinforced polymers, Carbon fibre reinforced polymers have the highest tensile strength. The elastic modulus of carbon reinforced polymers ranges between 15,900-84,000 ksi (GPa), while that of steel 29,000 ksi (GPa). This makes it a better Asset for use in the vehicle body structural applications as compared to the traditional metallic. (Prince 2011) Comparing the fibre reinforced polymers tensile and yield strength of steel;(fig.1.0) Our interest is on CFRP and steel. We see that carbon fiber reinforced polymer has the highest value of 3500 MPa while Steel has the lowest of value 500 MPa After the application of the reduction factor,(fig 2.0) it is observed that Carbon fiber reinforced polymer has the highest usable strength. High usable strength minimises material usage thus minimising labor cost. (Metalfe P. & Metalfe R. 2006) In further analysis of the mechanical properties, Carbon fiber reinforced polymers exhibit a wide range of mechanical properties including: impact resistance, stiffness, Ability to carry loads, Flexibility and Strength. Unlike the metals which display isotropic properties, Carbon fiber reinforced polymers exhibit isotropic properties. That is, some of their properties vary when measured when the direction of orientation (axes) are considered. For carbon fiber reinforced polymers to be isotropic, the reinforcing elements must be oriented in a random fashion. This, however, is not easily achieved with the carbon fiber reinforced polymers (CFRP) or any of the composites since the manufacture methods yield orientation to the discontinuous fibers. Continuous fibers are thus used in form of sheets to make the composites such as CFRP to be anisotropic in a particular plane. This enhances their strength in the direction of orientation of the force. This is particularly important since the resulting material will be stronger than the traditional metallic initially used in automotive applications. (Principally loaded axis.) 1(b) In the automotive manufacturing industry, a few considerations must be employed to ensure high production rates which are the core objective of any manufacturer. The automotive manufacturers must consider lightweightness of the materials used for manufacturing, the cost, crashworthiness, (the ability to absorb impact energy for the safety of the passengers.); resistance to impact and penetration resistance. The weight of the automotive dictates its fuel consumption behaviour. It is estimated that for every 10% of weight eliminated, a significant 7% of fuel is economised. For every Kilogram of weight reduced, 20% of carbon (IV) oxide is reduced. Composite materials prove to result in materials of significantly less weight that are much applicable in the automotive industry. The composite materials used for vehicle production must also meet the requirement of safety, particularly crashworthiness and Penetration resistance. In considering safety, legislation has been set which demands that in the case of impact at speeds of up to 5.5 m/s (35 mph) with a solid still object, the occupants of the vehicle in the passengers’ compartments must not feel a force that causes a net declaration bigger than 20g. Penetration resistance is concerned with total absorption without allowing projectile or fragment penetration. However, Composite materials in the form of pre-preg must be vacuum bugged and Auto claved in order to be used for the automotive applications. This whole process is costly and time consuming owing to the fact that the pre-preg undergoes a series of processing procedures to be finally useful. The pre-preg must be cut to shape defined in the design, layed up, bagged passed through the cure cycle and then demolded. Manufacturers must therefore adjust the final cost of the automotive to mach their design and manufacture demands. Cost is one of the consumer driven factors when they want to select an automotive for their use. A new material is normally compared to the one presently used and the variable for measure in this case is normally the cost. The cost of any product is determined by three factors, actual cost of raw material, cost incurred in designing and testing the product and the manufacturing value added. The sum of these three is the final cost of a product. Therefore, the high production rates required for the standard class of vehicles may not be adequately met due to the cost that will be incurred in producing the vehicles, thus alternatives must be employed which reduces the production rates considerably. Answer to question 2 Carbon Fiber reinforced polymers require detailed processing which consumes time and is also very costly. Some automotive manufacturers like Ferrari prefer the use of Aluminium to Carbon fiber reinforced Polymers (CFRP). Ferrari maintains that far from CFRP strength and weight, it proves difficult to use in automated production. Ferrari builds all her production models of vehicles from Aluminium. They do so not because they are unfamiliar with the processing of the CFRP but rather because of the time and cost involved in producing CFRP vehicles. The Maranello-based company prefers aluminium with a target of 30 cars in a day. Since CFRP technology requires a lot of labor and time; The Maranello-based Company uses a process that injects resin to the cloth after placement in the mould instead of the Pre-preg carbon fibre cloth. Ferrari argues that the potential which the high-volume carbon fiber offers is still not adequately exploitable unless low rate technologies are to be used. Ferrari argues that they avoid the use of CFRP since during the processing, the fibers are not used to their best advantage; they result to excess thickness and the use of high resin content makes the CFRP bulky. They on the other hand prefer Aluminium due to ability to use different alloys, biasing to the specific application of the car and ability to use heat treatment procedures for strengthening. They are able to use cast, steel and extruded aluminium joined by screws, welding, epoxy bonding and rivets. For instance, Ferrari employs 3 different alloys for the 458’s castings, three different sheet alloys and five different alloys for the 458’s extrusions. (SAE 2014) The company uses cold metal transfer welding, done by robots, that results in the welded material being minimally distorted by heat. They also use liquid and tape epoxy bonding material as well as mechanical methods of joining including screws and rivets. They however admit that screws and rivets are prone to the peeling forces and as such, they are not very efficient. They thus anticipate that in future, they will employ epoxy bonding fully as well as Aluminium mesh soaked in epoxy which results in stiffness at par with Steel. References Dan Carney. (2014). Ferrari prefers aluminum over carbon fiber. Available: http://articles.sae.org/10391/. Last accessed 03 April 2014. Jan A H Hult, F G Rammerstorfer (1994). Engineering mechanics of fibre reinforced polymers and composite structures. Wien ; New York: Springer-Verlag. 4. Peter Metcalfe, Roger Metcalfe (2006). Engineering studies. Year 11. Glebe, N.S.W: Pascal Press. 126. Richard E. Prince, PE. (2011). Fiber Reinforced Polymers Characteristics and Behaviors - See more at: http://www.build-on-prince.com/fiber-reinforced-polymers.html#sthash.V4njYTm5.4i5IsmeA.dpuf. Available: http://www.build-on-prince.com/fiber-reinforced-polymers.html#sthash.V4njYTm5.4i5IsmeA.dpbs. Last accessed 03 April 2014. Appendices Table 1.0 Reinforcing Material Yield Strength ksi (MPa) Tensile Strength ksi (MPa) Elastic Modulus ksi (GPa) Strain at Break percent Steel 40-75 (276-517) N/A 29,000 (200) N/A Glass FRP N/A 70-230 (480-1,600) 5,100-7,400 (35-51) 1.2-3.1 Basalt FRP N/A 150-240 (1,035-1,650) 6,500-8,500 (45-59) 1.6-3.0 Aramid FRP N/A 250-368 (1,720-2,540) 6,000-18,000 (41-125) 1.9-4.4 Carbon FRP N/A 250-585 (1,720-3,690) 15,900-84,000 (120-580) 0.5-1.9 Figure 1.0 Comparison of FRP Tensile and Steel Yield Strengths Figure 2.0 Factored FRP Tensile Strengths Read More