0. Introduction
Moto-cars are made from metals. This very common opinion was almost entirely true during almost all the previous century though opposite solitary examples (displayed at images below) are very well known for car likers: wooden bulks, a rubber car, a fiberglass sport car, a car with plastic bulk facias based on soybeans, a concept of a ceramic car, a glass car, and so on.
All those examples are just very rare exceptions. Moreover, the probably refer rather to arts than to industry. However, in the current century, metals lost their monopoly. In the present essay, several material groups quite important for the contemporary car industry are reviewed.
1. Ceramic materials
Car industry (both now and in the future) is inconceivable without collars. Ceramic ones have the following advantages compared with the traditional steel ones:
The low chemical activity, which is the main characteristic of ceramic materials, leads to very low adhesive wear-out of mating parts. This property allows car designers to implement new constructive and technical solutions to produce collars exploited under low grease (or even without greasing materials at all). Therefore, ceramic collars stably work even in emergency situations and do not cause sudden technique failures.
The low friction coefficient guarantees (provided that the grease is sufficient) a high productivity of systems with mounting bearer parts. The friction is essentially lower, which decreases the temperature, which allows us to increase the rotational speed-limit.
The very high corrosion resistance allows us to exploit ceramic collars in hostile environment and in zones, where the application of traditional steel collars is impossible.
Another example of the usage of ceramic materials to produce car parts is gland rings. To ensure their fine work, it is crucially important to select the material. In car industry, ceramic gland rings for rotating cylinders is propagated very broadly. The reason is as follows. Since ceramic materials are polycrystalline materials, even absolutely smooth (visibly) surfaces have moats ideally fitting to preserve the grease layer. The application of ceramic materials grows in electronic schemes of modern cars. Ceramic materials are used in car systems reducing the toxicity of exhaustion: they serve as catalytic neutralizers, gages of the exhaustion content, and electronic control blocks for those systems.
Application of ceramic materials in car motors allows car makers to increase the operational temperature in muffs, to reduce heat losses and fuel consumption, and to improve the operational characteristics. Selected parts of car motors are already manufactured of the silicium nitride: parts of the rotor and adjutage for car gas turbine, buckets, cylinder sleeves, forehearthes, etc. In particular, the application of a ceramic forehearth reduces the Diesel noise level at its launching and low load.
Even more interesting R&D direction is the design of fully ceramic car motors. This is based on the advanced manufacturing technology for parts of combustion engines of the same silicium nitride. This perspective is especially attractive regarding to Diesel motors: its main advantages are the expected increase of the fuel efficiency, decrease of the toxicity of exhaustion and the noise level, decrease of the weight and size of the motors, and to increase their resource. Also, it should be taken into account that raw materials for such motors (argil, arenaceous quartz, etc.) are substantially easier accessible than the ones for motors of traditional materials. It is expected that the prospective ceramic Diesel motor with an adiabatic combustion chamber (adiabatic motor) will substantially increase the efficiency (compared with contemporary motors) and will be able to use not only Diesel fuel, but low-bracket gasoline, broad-fraction fuels, and fuels of degraded content. This is caused by the circumstance that the walls of the ceramic combustion chamber have much more high temperature that steel ones. In average, the strength-to-weight ratio of ceramics two times exceeds the one for steel and its working temperature range exceeds the one for steel two times too.
However, this technical development faces principal challenges in front of car makers. For example, the allowed porous size for ceramic parts is much less than the one for steel parts. This requires to develop nondestructive inspection methods for ceramic materials. As a whole, this means that ceramic car motors are still an issue of the future, while any single sample would be too expensive to be affordable nowadays.
2. Plastic materials
In the contemporary car industry, the usage of plastics continuously and essentially grows. Nowadays, a great variety of types of plastics is used in car industry; several dozens of them are used to produce bulk parts such as bumpers, moldings, fenders, heat radiator grids, etc. For many cars, traditional metallic parts are replaced by plastic ones. This is caused by the circumstance that, regarding such key parameters as the corrosion resistance, heat resistance, humidity resistance, resistance, and elasticity, plastic materials are not worse than traditional materials of car industry. On the other hand, plastics have additional advantages:
The low weight of plastic parts leads to the decrease of the fuel consumption and environment pollution.
Polymers are easily processed so it is possible to produce parts of very complex shapes (including parts that cannot be produced from metal due to their shape and size).
The production costs go down because it is frequently cheaper (both with respect to money and man-hours) to produce parts from plastic materials.
All those properties provide car makers a possibility to prefer plastics to traditional materials.
Plastic materials are divided into two types (with respect to the nature of the polymer): thermoplastics and thermosets (Automotive Composites Alliance, 2000). The former ones, unlike the latter ones, can transit to a high-elastic state under the heating. This transition is invertible and can be repeated many times. Examples of thermoplastics are polythene (PE), polypropylene (PP), polymethylmethacrylate (PMMA), polystyrene (PS or ABS), polyamide (PA), vinyl chloride polymer (PVC), and polycarbonate (PC). Thermosets have a linear structure. Being cooled, they acquire a net structure due to a noninvertible chemical reaction. The material becomes infusible and insoluble. Plastics of this type are destroyed under the heating and, being cooled afterwards, do not acquire their original properties. Thus, traditional repair methods using the heating of the surface do not fit for such plastic parts. Examples of thermosets are phenol-formaldehyde oleoresins, polyurethane, poly oleoresins, and carbamide oleoresins. Also, poly glass fiber plastics (such as BMC and SMC or prepregs) are broadly propagated in car industry: they are used to produce cowl facias, roofs, and baggage holds.
Among all above types of plastics, the most frequent for the contemporary car industry is polypropylene or modified polypropylene (EPDM or ethylene-propylene masterbatch). Most frequently, the last material is used to produce bumpers and other car parts undergo various buff loads.
Particular examples of applications of plastic materials in car industry are as follows.
Quartzous, silicate, and organic (one-layer and multi-layer) glasses are used for glass cover of car cabins.
Rubbers from masterbatch strengthened by cord fabric are used to produce car wheels and various (stationary and mobile) glands.
Organic plastics based on high-resistance aramid fiber possess high resistance and elasticity characteristic, resilience, high chemical withstandability, and strong heat-insulating and dielectric properties. They burn badly and they extract low fume. They are the lightest polymer composite materials (Cole & Sherman, 1995). They have high values of such parameters crack resistance, resource period, and the exploitation reliability under the impact of mechanical or acoustic shock, fretting flows, and vibration. That is why organic plastics are used to sheathe passenger compartments of cars.
Carbon plastics are used to produce supporting elements of bulk and bracket, transmission nodes, power frames of seats, motor parts, and bumpers: this decreases the mass and corrosion and increase operational characteristics of cars.
However, polymer materials have their disadvantages too. They are still more expensive, and their production is generally slower than for traditional materials. Also, the recyclability issue is not finally solved in behalf of polymers yet. The main challenges faced by the further development of that direction are to intensify the use of hybrid composites and to achieve highly automated and fast manufacturing processes.
One more important issue is the comparison between polymer composites and metals regarding of the behavior of failure in compression (see, e.g., Wallentowitz & Adam, 1996). Tests show that composites response to load rather as a brittle than ductile. To the contrary, metal structures crush-collapse is characterized rather by buckling and/or folding (in particular, this includes extensive plastic deformation). Which behavior is preferable from the safety viewpoint, is still an open question.
3. Nanocomposites
Nanotechnologies cause changes throughout all the car industry. Almost any car produced in USA contains nanocomposite materials. New dough of fluoropolymer with nanotubes (cylindrical nanograins) is used to produce car gland rings. A composite of nanoargil and nylon is used to obtain an abrasive heat-resistant coverage for car cogged belts. In recent years, the application of conductive polymers in cars grows. The area of their application is very broad: from external bulk facias to optic microchangers, nano-size intellectual changers, and gages. Thermoplastic nanocomposites became the main composite materials for fuel line tubes, where polymers replace the traditional steel. Also, conductive polymers are developed to use them in external bulk facias; they can be colored at the same electrostatic coloring lines as the replaced steel parts, which essentially reduce the investments to the mount of new equipment (compared with special coloring lines for plastic facias). For the near future of car industry, it is anticipated to apply nanocomposites for hydrogen storage systems, fuel elements, and batteries of supercondensers. Those directions promise an essential impact to the creating of new energy-produce and energy-storage devices applied in car industry. The flame resistance of nanocomposites provides one more application area. They can be applied to design passenger compartments. On the other hand, nanocomposites based on bioplastics allow car producers to change their mind regarding to the secondary usage and biodeterioration of materials (Mohanty, Misra, & Drzal, 2005).
Materials that can be used to design new types of car motors possess a great potential. Requirements to motor efficiency and to the toxicity reduction of exhaustion grow each year. That is why car designers actively seek materials able to replace steel and iron. For that purpose, the most promising material is the plastic modified by nanocomposite materials: it might become the base to create newest car models. From the theoretical point of view, this material can substantially simplify all the production workflow for various motor parts and (simultaneously) to increase their precision. The resistance and rigidity of the modified polymer are close to the same characteristics of metals. However, the plastic has a lower weight and improved corrosion resistance. Also, it provides a possibility to reduce the noise level and technology limits.
Nanocrystalline components of parts exploited under high-temperature conditions (fuel spray nozzles, spark plugs, and so on) essentially extend their useful life.
One more composite material popular in car industry is the fiberglass. It is broadly used to produce (fore and back) external bulk facias of buses and trolley-buses, interior design elements, elements of aerodynamic bypasses, bumpers, roof baggage holds, and control panels. Its popularity is caused by higher physics-mechanical properties compared with other types of plastics such as
higher resistance and scratch-resistance;
structure stability under high and low temperatures;
relatively low weight;
resistance against vibration and stroke loads.
4. Final conclusions
The competition on the car parts materials market is very strong. This is natural because this market is very broad and its value is enormously high. A new trend related to the environmental issue has appeared at the end of the previous century and its impact becomes more and more important: it is clear that, to win the competition, car makers must offer lighter cars with lower fuel consumption and easier possibilities to recycle. This opens great possibilities for new materials such as ceramic materials, plastics, and composites. However, it is not sufficient to replace a metal by a plastic to win the competition: one has to ensure low (or, at least, decreasing) prices and modern and rapid production run. But this way should be passed because the transition to new materials is the core of the research and innovations on our way to cars of our future.
References
Automotive Composites Alliance (2000). 2000 Model Year Passenger Car and Truck Thermoset Composite Components. Troy, MI: ACA.
Cole G.S. & Sherman, A.M. (1995). Light weight materials for automotive applications. Mater. Charact., 35, 3–9.
Mohanty A.K, Misra M., & Drzal L.T. (2005). Natural Fibres, Biopolymers, and Biocomposites. Boca Raton, FL: CRC Press.
Wallentowitz, H. & Adam, H. (1996). Predicting the crashworthiness of vehicle structures made by lightweight design materials and innovative joining methods. International Journal of Crashworthiness, 1(2), 163–180.
