Use Of Kevlar As A Composite In Aerospace

History

Discuss about the Use of Kevlar as a Composite in Aerospace.

Composite materials are key materials since their invention due to their continued advantages from individual materials. Composite materials are composed of several materials in order to enhance some key aspect of the final product. Aramid – Kevlar is one of the key composite material which has been used in aerospace industry in order to increase several characteristics and enhance the industry. Kevlar is a synthetic fiber which was developed in 1960’s by Stephanie Kwolek (2002). The major characteristic since its invention is the high strength, was used to replace steel in the 1970 in high racing tires, and has evolved it use to the aerospace industry. Kevlar was found due to the demand of a lightweight material which would perfectly replace the steel in its use (Kwolek, Mera and Takata, 2002). In its chemical composition, Kevlar is made of poly-p-phenylene-terephthalate and polybenzamide, which is made from liquid crystal. Initially, before its invention, this cloudy, opalescent material, which is known to have low viscosity, was being thrown away. On the process, Kwolek persuaded one of the technician to run a test on the material and through the test; he discovered that the material was not breaking as it was in the case of nylon (Kwolek, 2009). Therefore, through this discovery, the seniors took the initiative to develop the discovery and come up with the polymer. Nevertheless, through the process Kwolek was not much involved in the development of the Kevlar material to its final stages and helping it to attain its current characteristics.

The composite materials are always made of several mixture of materials in order to make their composition. In these mixtures, the materials are chosen in order to bring out the required characteristics, which are meant for specific purpose. The Kevlar is a synthentised material which is made from the monomers 1,4-phenylene-diamine (para-phenylenediamine) and terephthaloyl chloride through a condensation process, which leads to the formation  of hydrochloric acid as a by product (Quintanilla, 1990). The major process for the synthetic process in pol;ymerization and  Hexamethylphosphoramide (HMPA) was used as a solvent initially. Nevertheless, the safety issues led to the abortion of the use of the HMPA and DuPont is used instead, which is used and it is a solution of N-methyl-pyrrolidone and calcium chloride (Kwolek, 2009). The production of Kevlar is expensive due to the use of the sulfuric acid, which is needed to keep it soluble in water as a polymer during the synthesis and spinning process. In addition, the protection of the Kevlar against sunlight is key since the ultraviolet component of the sunlight is able to lead to the UV degradation. This lead to the degradation and decomposition of the Kevlar and therefore the composite is mostly made indoors.

Synthesis of Both Fibers

The mechanical properties of Kevlar is able to change at different temperatures. More specifically, the strength of the composite is related to the temperatures at the different stages. Kevlar is more stronger at low temperatures as it is compared at high temperature. When the temperatures increase, the strength is able to reduce and the reduction is able to change considering the different level of temperature. At high temperature for instance, the tensile strength of Kevlar is able to reduce immediately and the reduction ranges between 10 and 20 percent (Kwolek, Mera and Takata, 2002). After some hours, further reduction of the tensile strength is experienced. In addition, the tensile strength of Kevlar is about 3,620 MPa when it is spun well and a relative density of 1.44.

the bond type for the Kelver (Kwolek, Mera and Takata, 2002)

As noted, the composites have their advantages and disadvantages as well. nevertheless, regardless of the shortfalls, the advantages of the material are able to outdo the disadvantages and this has led to their continued usage in the past few years.

Reduction of weight is one of the major advantage of Kevlar as a composite material.  The use of steel and aluminum have been the major materials which have been used for long is aerospace industry. Nevertheless, the use of the composites and more specifically Kevlar has been able to reduce the weight of the airplanes. The weight of aerospace bodies is a key factor which is able to dictate several factors such as fuel consumption and efficiency of the machines. The usage of the Kevlar composite in this industry is able to reduce the fuel consumption for the airplanes since they are lighter than before (Quintanilla, 1990). This helps to increase the efficiency and therefore increase the economic factors in terms of profit generation. In addition, the Kevlar material is formed through high number of bond inter-chains, which lead to higher strength of the composite material. The hydrogen bonds in the Kevlar material are able to increase the strength of the material and this enhances their usage in aerospace industry.

(Shepherd et al., 2013).

The airplanes are able to move at high speed and the need of a high strength material has been required for a long time. The introduction of the Kevlar composite material has been able to solve the problem and therefore enhancing the use and efficiency of this industry. The high strength of the material is able to reduce the number of casualties, which are experiences in case of any accidents. For instance, in the F18 Midair Collision the use of the Kevlar composite led to zero casualties (Circa 2002, no injuries) (Shepherd et al., 2013). In addition, the Kevlar composite has a stiffness factor of close to 125 GPA in tension. This enhances its usage on different positions and therefore able to withstand strong tension forces without breaking. This is another vital key advantage, which has led to the continued use of the material since its invention (Gong, 2011). In addition, the weak interface is able to act as impact protection in airplanes and therefore making the material useful in the aerospace industry. This helps to create the air and other material resistance and therefore increasing the usage factors of the material. In addition, in terms of the chemical resistance, the Kevlar composite is able to act inert and therefore does not react with most of the chemicals. This means that the life cycle of the material is increased and therefore promoting its usage in the aerospace industry.

Mechanical Properties

Nevertheless, the Kevlar composite has its shortfall as well. First and foremost, the properties of the properties of Kevlar is highly affected by impurities such as salts and this affects the effectiveness of the material. For instance, the presence of calcium is able to lower the strength of Kevlar and therefore affecting the effectiveness and life cycle of the material. This is a key property, which is considered in the use of the material, and therefore when the factor is altered the effectiveness is affected. In addition, these impurities are able to affect the bonds and this leads to the change of the strength of the matters. This means that the life of the airplanes and other materials made from this composite is able to reduce and therefore making its use expensive (Meyer, 2015). Another major disadvantage, which is experience, is on the production stage of the Kevlar. Its production is much more expensive than other available composites and therefore this makes the materials much more expensive. This makes the material rarely used and therefore affects its usage in the aerospace industry. At the end, the cost is transferred to the consumers and this makes it uneconomical to use.

Another major disadvantage of the Kevlar composite is its degradation when exposed to the sun UV rays and moisture. This means that its usage is altered and therefore cannot be used under some circumstances. This limits the full exposure of the material potential and therefore able to offer limitation during the usage (Fink, 2010).  In addition, during the production process, the material is as well skeptical to the UV rays and this means there is a limitation of the areas of production since it cannot be manufactured outdoors. Additionally, at times, the fibers fail to bond well and this creates a point of weakness leading to weak fiber or even matrix interface. This limits the usage and lead to the failure of the parts when much loading is done (Pagen, 1990). This is a key factor that leads to continued analysis of the material and therefore making it expensive to use the material. All the analysis has to be done before the go ahead to use it is reached and this increases the cost of production and at most limiting its usage.

Apart from the aerospace industry usage, the Kevlar material is also used in manufacturing of the bulletproof vests and helmets. This is because the material can resist other introduced tensional forces by a large factor. All these fall on the personal protection category for the usage of the material. In addition, Kevlar is used in the cryogenic field due to its low thermal conductivity and high strength (Quinn, 2009). This is due to the enhanced suspension rate of the material as compared to other materials. The material is also used as a personal armor in the military industry. The ability to withstand tensional forces makes it suitable to be adopted in this category (Michael, 2007). Other areas where this composite is used is in the shoe industry, the musical category and fire dancing among other areas. Reinforced composite material are used to enhance the quality of the composite materials. These elements are usually added to enhance the qualities of the composite material, which has been already formed.

The environmental impact of any manufactured material is given a great weight in the current days through the green engineering aspect. The environment degradation and climatic changes are led to the increased through concerning the materials being manufactured and this does happen for the Kevlar as well (Fink, 2010). The transportation factor of the material is one of the environmental issue which the use of the composite and especially Kevlar is looked at. Transporting heavier materials lead to high consumption of fuel and this lead to higher release of greenhouse gases and thus increasing global warming. Using Kevlar therefore reduces the fuel consumption and the amount of greenhouse gases released to the atmosphere. This leads to less depletion of the ozone layer and therefore leading to it’s enhance use due to the environmental conservation (Quinn, 2009). In addition, Kevlar is carrion resistant and therefore unable to react with most of the chemicals. This means that it is friendly to the environment and helps to conserve the environment. Nevertheless, the material does not decompose easily and this offers a environmental challenge when the material is already out of use. This means that the material end up in landfills and it can stay there for many years and therefore affecting the soil composition.

References

Kwolek S. , Mera H. and Takata T. (2002) "High-Performance Fibers" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim.

Fink J. K., (2010). Handbook of Engineering and Specialty Thermoplastics: Polyolefins and Styrenics, Scrivener Publishing, p. 35 

Kwolek S. (May 24, 2009).  "Inventing Modern America: Insight —:". Lemelson-MIT program. Archived from the original on May 24, 2009. 

Quinn, J. (May 24, 2009). "I was able to be Creative and work as hard as I wanted". American Heritage Publishing. Archived from the original on May 24, 2009.

Quintanilla, J. (1990). "Microstructure and properties of random heterogeneous materials : a review of theoretical results". Polymer engineering and science. 39: 559–585.

Michael C. P. (2007). Molecular electronics: from principles to practice, John Wiley & Sons, p. 310 

Pagen, D. (1990), Paragliding Flight: Walking on Air, Pagen Books, p. 9, ISBN 0-936310-09-X

Shepherd, Robert; Stokes, Adam; Nunes, Rui; Whitesides, George (October 2013). "Soft Machines That are Resistant to Puncture and That Self Seal". Advanced Materials. 25 (46): 67

Gong (Ed), RH (2011). Specialist Yarn and Fabric Structures: Developments and Applications. Woodhead Publishing. p. 349. ISBN 9781845697570.

Meyer, B. (November 9, 2015). "Unaflex adding space, capacity at S.C. plant". Rubber & Plastics News.09–6713.