Chemical and physical properties of carbon-fibre reinforced composites - Coursework Example

Chemical and physical properties of carbon-fibre reinforced composites Composite materials are materials that constitute two or more materials with significantly different chemical and physical properties merged together. These materials are blended together in specific ratios to produce materials that that are different from the original materials based on chemical and physical properties. There are many important reasons behind the desire to have composite materials. These include, the need for stronger materials, the need for lighter materials to be used in automobile and aviation industries, wind turbines and the gradual rising need to reduce cost and improve efficiency of target applications (Werfelman, 2007). These composites are more resistant to fatigue and strain from repeated use in various devices such as aircrafts or car bodies, therefore, reducing maintenance costs and increase lifespan of vehicles (Price, 1997). Examples of composite materials include fibre-reinforced polymer, carbon-fibre-reinforced composites, and ceramic composites among others. Carbon-fibre reinforced composite is the common form of composite used today. These type of composite is made by heating rayon or other types of fibre to extremely high temperatures usually above 2000 degree Celsius in an oxygen deprived environment such as an oven (NASA, 2010). The tremendous heat in combination to lack of oxygen ensures that there is no combustion and that the strands are converted into pure carbon atoms. These strands produced are then spun into a thread and woven into appropriate sheets. The sheets are then hardened by addition of resins to produce a material that is not only strong, but also stiff. Composite materials consist of materials of stronger materials usually called reinforcement and a weaker material commonly known as a matrix. The reinforcement material provides the rigidity and strength required to support the whole structure while the matrix assists in maintaining orientation and position of the reinforcement (Brent, 2008). Figure 1 shows a simple diagram showing how composition of composites is done. Composite materials are continuously replacing traditional materials like aluminium in construction of vehicle body structural applications. There has been a rising concern for the load capability of these materials, damage tolerance and reparability of the structures. The advantage of carbon- fibre reinforced composites is that they do not rust. This property ensures that they stay for a relatively longer life span compared to the traditional metallic body structures that are prone to corrosion. The fact that most composite materials like carbon fibre reinforced composites makes them preferred materials in construction of vehicle body structures among other components in the automobile industry. Another unique feature of carbon reinforced composites is that they contain high internal damping (Mallick, 1993). This property provides them with better vibrational energy absorption within the material and also provide little transmission of noise to the neighbouring structures. High damping capacity of this carbon reinforced materials are of significant importance in the manufacture of vehicle body structures in which noise vibration and harshness due to the no uniform status of roads is a crucial issue for passengers comfort. Therefore, the car industry market prefer automobiles that produce limited noise pollution hence the desire to have vehicles made of composites. There are other safety concerns in the automobile industry that call for the desire to use composite materials in place of metals. Among this safety, concern is crash-worthiness that is defined as the potential for energy absorption through controlled failure mechanisms that offer gradual decay in the load profile during absorption. Some materials that for a long time have been involved in the manufacture of body structures lack this safety concern and in case of an accident the probability of survival of the passengers is minimum. Therefore, Material progressive failure and deformation behaviour defined by stiffness yield, elongation and strain at break are equally important in energy absorption capacity of the automobile. The second safety concern that demands the use of carbon- fibre composite materials is penetration resistance that refers to the total absorption without fragment penetration (Jacob et al., 2002). This property defines the ability of an external force to tunnel into the inside of the vehicle body if the material is used to create vehicle body structures. Traditional metallic structural materials are always considered isotropic because the exhibit nearly equal properties regardless of the direction of measurement. For example, the Young's modulus of elasticity is constant irrespective of the direction of measurement for pure steel. However, carbon-fibre reinforced materials are anisotropic meaning that their properties strongly depend on the direction of measurement. A good example of the features is the modulus and strength of tensile strength that are maximum when measured in the longitudinal orientation of the fibre (Mallick, 1993; Brent 2008). The design of these carbon-fibre composites is harder than a metallic structure, but the anisotropic properties of these materials provide a unique ability to change the properties according to the manufacturer's requirement. Hence, their preferred use in the automobile industry. Prepreg refers to composite reinforcement materials that have been mixed with activated resin usually epoxy. Making composites from prepreg reinforcement is commonly done by layering prepreg into a mould, vacuum bag the mould, laminate it and cure it in the oven often called octave. Vacuum bagging technique has been developed for fabricating a large variety of complex shapes and relatively large components. Figure 2 in the appendix illustrates simple vacuum bag layup. There is substantial competition of materials for automobile applications in the market. This is mainly due to the size of the market. The need for lighter vehicles for lighter fuel consumption and the need for recycling have become major concerns in the environment. In addition efficiency of machines together with their lifespan are properties that customers cannot ignore when purchasing automobiles. These concerns continually provide avenues for composite materials like carbon-fibre composites as alternative for heavy metals such as steel that make automobiles consume more fuel. Traditional market holders such as steel are always adopting innovations and gradual improvement in making their alloys in order to produce lighter material and structures (Mallick, 1993). There still lies a great challenge in production of carbon-fibre composites because of the expensive raw materials and the complex, time consuming and labour intensive processes. However, the current state of technology is heavily investing on research that is dedicated towards finding lasting solutions to the cost of carbon reinforced fibres and adopt them more proportionally in the manufacture of vehicle body structures. Conventional metals are cheaper than composite materials whose cost is usually high. This means that the main targets for future development should be the use of hybrid composites that take into account the cost and apply expensive carbon composites in specific areas of the vehicle body where damage tolerance and stiffness is desired. Carbon-fibre reinforcement technology for long time has been understood as a proper combination of strength and weight. The difficult and long processing time together with its high prices have given aluminium preference in the manufacture of vehicle body structures. The production speed for the carbon fibres is relatively low compared to the use of aluminium. In addition carbon fibre composites are time and labour intensive techniques that waste material because excess material is used during the manufacturing process. The high volume carbon-fibre technique, therefore, fails to realise the materials weight saving potential. However, Aluminium is better suited to high production rates that consist of numerous material tailored to many specific applications. In addition, heat treatment is used to ensure strength of the product. This heat treatment is important for appropriate deformation of the front and rare crash boxes and therefore aluminium is preferred over steel that was traditionally used because it provides a better moment of inertia contributing to better handling. In conclusion, therefore, composites are gaining a better position in the automobile industry compared to the traditional heavy materials that for a long time have been used to manufacture automobile structures. There is a continuous rising concern in the amount of fuel consumed in automobile and aviation industries. The weight of the automobile body structures being the primary factor contributing to excess fuel consumption. The operators and agents of these industries desire light, hard a stiff materials that provide sufficient safety in case of an accident apart from improving efficiency of the devices using them. Although the carbon reinforced composites possess the above properties, the processes involved in the manufacture of this composites are time-consuming, labour intensive and the final products are quite expensive. However, with the current state of technology, there is intensive research geared towards reducing the general cost of these materials and improving efficiency of automobiles in the industry. References Price, T. L. (1997). Handbook: manufacturing advanced composite components for airframes. Washington, D.C., Federal Aviation Administration, Office of Aviation Research Werfelman L. 2007, The composite Evolution, Aero Safety World, accessed 5 December, 2014, < https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0CB8QFjAA&url=http%3A%2F%2Fflightsafety.org%2Fdownload_file_iframe.php%3Ffilepath%3D%2Fasw%2Fmar07%2Fasw_mar07.pdf&ei=VP2BVP2jD4XmUtrhgNAP&usg=AFQjCNE5tQaXDyCog_c5wovVd8kejiSygg&bvm=bv.80642063,d.d24 Brent A. Strong 2008, Fundamentals of composite manufacturing: Materials, methods and application, Society of manufacturing Engineers pg1-640. STRONG, A. B. (2008). Fundamentals of composites manufacturing: materials, methods and applications. Dearborn, Mich, Society of Manufacturing Engineers. Mallick, P. (1988). Fiber reinforced composites: materials, manufacturing and design. New York, Marcel Dekker. Crouch, T. D. (1990). The National Aeronautics and Space Administration. New York, Chelsea House Publishers. Appendix Read More