Distinct Boundaries between Strong Carbon Fibers and a Polymer Matrix - Assignment Example

THE USE OF CARBON FIBER REINFORCED COMPOSITES IN MANUFACTURING VECHICLES by Presented to Dr. City Name, State Name Due Date Question 1 a) The safety of a passenger is determined by the acceleration a he or she experiences in the frame of reference associated with the car. From the second Newtons law, it follows that a = F/m (1) where F is the net force that acts on the car bumper in this frame of reference and m is the mass of the bumper. Assuming that the bumper is flat one can estimate F as (2) where S is the area of the bumper contact surface, is the thickness of the bumper, is the deformation, and is modulus if the deformation is elastic or tensile strength if the deformation is maximal. Since where is the density of the material the bumper made from, from equations (1) and (2) it follows that . (3) Obviously, for a given acceleration the smaller is, the safer the vehicle is. On Figure 1, “the modulus–weight ratio and the strength–weight ratios are obtained by dividing” respectively the modulus and the tensile strength “with the specific weight of the respective material”. As for specific weight, “it is obtained by multiplying density with the acceleration due to gravity” (Mallick, 2007, p. 20). According to Figure 1, carbon fiber reinforced polymers (CFRPs) have much higher strength–weight and modulus–weight ratios than the traditional metals have. Besides, “fatigue strength as well as fatigue damage tolerance of” CFRPs are very good (Mallick, 2007, p. 20). Therefore, from equation (3) it follows that a car with a bumper made from CFRP is going to be safer than the car with the bumper made from a traditional metal if other conditions are identical. The vehicle weight determines the fuel consumption of the car: 100 kg reduction in the weight of a car results in saving from 0.2 to 0.4 liters of fuel during 100 km trip (Kelly, 2004, p. 1). From Figure 1, it follows that the densities of CFRPs are lower than those of traditional metals. Therefore, the fuel consumption of the car can be reduced without detriment to passenger safety through replacement of traditional metals in vehicles with CFRPs. Figure 1 (Mallick, 2007, p. 21). In CFRPs, there are distinct boundaries between strong carbon fibers and a polymer matrix. However, a set of CFRP properties can not be replicated “with either of the constituents acting alone” (Mallick, 2007, p. 19). Carbon fibers determine the strength of the composite. As for polymer matrix, it “keeps them in the desired location and orientation, acts as a load transfer medium between them, and protects them from environmental damages” (Mallick, 2007, p. 19). However, the carbon fibre fabric is not rigid at all if it is not placed inside the polymer (Buttler, 2013). Traditional metals are isotropic. As for CFRPs, their properties significantly depend on the direction at which they are measured. “For example, the tensile strength and modulus of a unidirectionally oriented fiber-reinforced polymer are maximum when these properties are measured in the longitudinal direction of fibers. At any other angle of measurement, these properties are lower. The minimum value is observed when they are measured in the transverse direction of fibers, that is, at 90° to the longitudinal direction” (Mallick, 2007, p. 20). Moreover, in this direction the material is so weak that it can be used to create innate hinges. At first glance, it seems that the possibility of the replacement of traditional metals with CFRPs in vehicles is an issue because most often vehicle parts have to be strong in all directions to guarantee safety of a driver and passengers. However, multidimensional reinforcement easily resolves it because such the reinforcement generates properties that “represent a considerable advantage over common structural metals on a unit weight basis" (Mallick, 2007, p. 20). Thanks to this anisotropy, CFRPs with properties that meet requirements imposed beforehand can be created. For example, a structure made from CFRP can be reinforced “in the directions of major stresses”. As for its stiffness, it can be increased “in a preferred direction”. Using CFRPs, one can “fabricate curved panels without any secondary forming operation” (Mallick, 2007, p. 22). Thus, advantages of the replacement of traditional metals in production vehicles with CFRPs are the following: It improves the safety of the car. It reduces the fuel consumption of the car. It allows tailoring properties of the material the car is made from “according to the design requirements” (Mallick, 2007, p. 22). Question 1 b) A material can be successfully used in an application only if it is produced by using a “cost-effective and reliable manufacturing method”. The material production rate determines the costeffectiveness whereas reliability implies “a uniform quality from part to part” (Mallick, 2007, p. 395). “Autoclave molding” is too slow to be used for a vehicle mass production (Mallick, 2007, p. 33). This technique assumes “the placing and sealing of a flexible bag over a composite lay-up” (see Figure 2) followed by “evacuating all the air from under the bag” and placing “the completed assembly” in the autoclave (Hexcel, 2005, p. 14). Figure 2 (Hexcel, 2005, p. 14). On Figure 2, the prepreg is “a combination of a matrix (or resin) and fibre reinforcement” (Hexcel, 2005, p. 4). As for autoclave, it “is a pressure vessel which provides the curing conditions for the composite where the application of vacuum, pressure, heat up rate and cure temperature are controlled” (Hexcel, 2005, p. 14). Usually, CFRP is produced in the form of laminate which is a consolidated set of layers of the polymer filled with carbon fibers. Laminate properties depend on how fibers are oriented in the layers. “Transformation of uncured or partially cured fiber-reinforced thermoset polymers into composite parts or structures involves curing the material at elevated temperatures and pressures for a predetermined length of time. High cure temperatures are required to initiate and sustain the chemical reaction that transforms the uncured or partially cured material into a fully cured solid. High pressures are used to provide the force needed for the flow of the highly viscous resin or fiber–resin mixture in the mold, as well as for the consolidation of individual unbonded plies into a bonded laminate. The magnitude of these two important process parameters, as well as their duration, significantly affects the quality and performance of the molded product. The length of time required to properly cure a part is called the cure cycle. Since the cure cycle determines the production rate for a part, it is desirable to achieve the proper cure in the shortest amount of time”. (Mallick, 2007, pp. 395–396) In autoclave molding, it is important to choose such the cure pressure and the cure temperature at which “the temperature at any position inside the prepreg does not exceed a prescribed limit during the cure” (Mallick, 2007, p. 411). Estimates obtained by using “a theoretical model for the complex thermomechanical phenomenon that takes place in a vacuum bag-molding process” developed by Loos and Springer (1983 cited in Mallick, 2007, p. 411) indicate that “the time needed for completing the desired degree of cure is reduced by increasing the cure temperature” or “the heating rate” (Mallick, 2007, pp. 411–412). “The maximum cure temperature is usually prescribed by the prepreg manufacturer for the particular resin–catalyst system used in the prepreg and is determined from the time–temperature–viscosity characteristics of the resin–catalyst system. At low heating rates, the temperature distribution remains uniform within the layup. At high heating rates and increased layup thickness, the heat generated by the curing reaction is faster than the heat transferred to the mold surfaces and a temperature ‘overshoot’ occurs”. (Mallick, 2007, p. 411) As a consequence “long cure cycles are required because the large autoclave mass takes a long time to heat up and cool down” (Hexcel, 2005, p. 14). The mass production of vehicles assumes producing the parts at the rate in the range from “100 to 200 pieces per hour”, which is too high for autoclave molding (Mallick, 2007, p. 33). Question 2 The usage of fossil fuels gives rise to building up carbon dioxide in the air. Unfortunately, current state of technology does not allow capturing carbon in the atmosphere on a large scale. Modern estimates suggest that irreversible climate changes are likely to occur if the concentration of this gas in the atmosphere will keep increasing at the current rate during next ten years (Lewis, 2009). However, reduction in motor vehicle emissions can significantly delay these changes. For example, “transportation produces almost thirty percent of all U.S. global warming emissions” (Union of Concerned Scientists, 2014). One way to achieve this reduction is to impose various regulations and legislations on car manufacturers. Lowering the weight of the vehicles is an efficient way to reduce CO2 emissions in the atmosphere. Specifically, get riding of 1 kg of the weight of a vehicle is equivalent to removing “20 kg of carbon dioxide” from the air (Ghassemich, 2011, p. 366). Ferrari considers CFRP technology to be too complicated for its usage in vehicle mass production and “builds all its current production models—the 458 Italia, 458 Spider, 599 GTB, California, and the FF—from aluminum” (Carney, 2011). However, recent technological advances such as the ones presented in reference (Nguyen, et al., n. d.) allowed BMW to announce “the first all carbon fiber production car” in 2013 (Buttler, 2013). Moreover, “it is well recognized that significant vehicle weight reduction needed for improved fuel efficiency can be achieved only with carbon fiber-reinforced polymers, since they have much higher strength–weight and modulus– weight ratios” than various aluminum materials have as it can be seen on Figure 1 (Mallick, 2007, p. 34).One of core competencies of the Society of Automotive Engineers (SAE) International is “voluntary consensus standards development” (SAE International, n. d.). Hence, developing standards regarding levels of greenhouse emissions, the SAE International has to care about providing automakers with incentives to adopt technological innovations that allow using CFRPs in vehicle mass production. Reference List Buttler, W., 2013. The use of carbon fibre in automotive engineering. [online] Prezi, Inc. Available at: [Accessed 6 March 2014]. Carney, D. 2011. Ferrari prefers aluminium over carbon fiber. [online] SAE International. Available at: [Accessed 8 March 2014]. Ghassemich, E., 2011. Materials in automotive application, state of the art and prospects. In: M. Chiaberge, ed. 2011. New trends and developments in automotive industry. [e- book] InTech. Ch. 20. Available at: [Accessed 6 March 2014]. Hexcel, 2005. Prepreg technology [pdf] Hexcel. Available at: [Accessed 7 March 2014]. Kelly, G., 2004. Joining of carbon fibre reinforced plastics for automotive applications [pdf] Stockholm: Department of Aeronautical and Vehicle Engineering, Royal Institute of Technology. Available at: [Accessed 6 March 2014]. Lewis, N. S. 2009. Powering the planet, the Roger Revelle centennial symposium series. [video online] Available at: [Accessed 8 March 2014]. Loos, A. C. and Springer, G. S., 1983. Curing of epoxy matrix composites. Journal of Composite Materials, 17(2), pp. 135-169. Mallick, P. K., 2007. Fibre-reinforced composites: Materials, manufacturing, and design. [pdf] Boca Raton: CRC Press. Available at: [Accessed 6 March 2014]. Nguyen, F. N., Yoshioka, K., Kamae, T., Taketa, I., and Kitano, A. n. d. Fast-cycle CFRP manufacturing technologies for automobile applications [pdf]. Available at: [Accessed 6 March 2014]. SAE International, n. d. About SAE international [online] SAE International. Available at: [Accessed 7 March 2014]. Union of Concerned Scientists, 2014. Car emissions and global warming. [online] Union of Concerned Scientists. Available at: [Accessed 9 March 2014]. Read More