When designing various projects for a client, an engineer is concerned with different aspects of the design. For instance, the aesthetic value of the design is very important to the engineer. Other factors that concern the engineer are the durability of the product and the cost effectiveness in both the design and production processes. However, and without belittling the importance of these factors, safety is ultimately the major concern of the engineer. Safety as a factor is incorporated into all designs, for both the client and the environment (including other people who might not necessarily use the product but stand in arms way). The one thing that is critical to the achievement of all these factors is the choice of materials used in the construction of the prospective product. This paper considers two materials for the construction of a portable safety walkway the two materials in consideration are stainless steel and aluminum.
The two materials under consideration will be used to construct a portable safety walkway. It is important to note that a portable safety walkway is exposed to environmental factors. This means that one has to consider these environmental factors, especially with regard to how they affect the degradation of the materials under consideration. Degradation of the material has adverse effects on the properties mentioned erstwhile. While the other factors are also of concern, perhaps the most concerning with regard to degradation of materials is the safety of the structure. Degradation can be cause by spillages of corrosive liquids like acid, corrosion due to moisture from the environment and other chemical attacks on the material. Additionally, and since the material under consideration will be used to make the steps and the walking platform component of the structure, it is important to consider the exposure to tensile, compressive and shear forces as these also contribute to the degradation of the material (Allen, 2013).
Mechanical properties of Aluminum
` The weight of aluminum is one of its best properties. Its density is one thirds compared to that of steel. The low density (2.700kg /m3) make the material very light. Nonetheless, its light nature does not influence its strength. Alloys of aluminum have tensile strengths that range from 70 to 700 Mpa. This property compares positively to steel. This is because aluminum is not brittle when exposed to low temperatures, more precisely, the strength of aluminum increases at low temperatures. Of concern is the fact that at constant temperatures of 100oC and above, the strength of aluminum decreases to extent designer engineers should consider.
With regards to linear expansion, aluminum has large linear expansion coefficients when compared to other metals. Aluminum can be worked with relative ease using a variety of machining methods like punching, milling, bending, cutting and drilling. The energy input during these processes is also low. The superior malleability of the material means that it can be curved and bent with relative ease. Aluminum has features that facilitate easy jointing. Fusion welding, taping, friction stir welding and binding are some of the jointing techniques that can be used with aluminum. Aluminum is also corrosive resistant. It reacts with oxygen from the atmosphere to form a microfilm of aluminum oxide, a layer that is dense and excellently protects the material from corrosion (Kaufman & Rooy, 2007).
Mechanical properties of stainless steel
Yield strength and the tensile strength are important factors to consider in stainless steel as a material for construction. Cold work on stainless steel increases the yield strength of stainless steel to a greater extent when compared to the tensile strength. The ductility of stainless steel is also a property worth considering. Steel is highly ductile, meaning that they can be used in fabrication operations without fracturing. The resistance to penetration of steel that is hardness is also of importance. When compared to aluminum, stainless steel has a higher harness. This means that harder indenters my not penetrate large distances. This affects the working of the material using methods like punching, drilling, use of rivets and cutting. Stainless steel is also corrosion resistant when exposed to water. This is because the chromium in the material forms a passive film containing chromium oxide. The passive film prevents surface corrosion (Bertolini, 2004). It also prevents the spreading of corrosion to the internal structure of the metal by blocking oxygen. The material is not stain-proof when exposed to high-salinity, low oxygen and poor circulation environments (Khatak & Raj, 2002).
Cost comparisons of Aluminum and Stainless steel
The price and cost of materials is a very important factor for a design engineer to consider when assembling any product. On the global market, the prices of aluminum and stainless steel are always fluctuating depending on the global forces of supply and demand. The other factors that affect the prices of aluminum and stainless steel include the cost of fuel, availability of bauxite and iron ore and the prices of these precursors. Nonetheless, stainless steel is cheaper for every pound when compared to aluminum. The cost of the raw materials used to spin the two materials has an impact on the price of similar units of the two materials.
Both materials are susceptible to degrading forces both in the environment and those that occur spontaneously due to the use of structures made of the material. For instance, galvanic corrosion degrades aluminum. This happens when aluminum is exposed to more noble metals or electron conductors that have a chemical potential that is higher than that of aluminum (Ghali, & Revie, 2010). Stainless steel, copper and carbon steel are some of the metals that can initiate galvanic corrosion in aluminum. Galvanic corrosion can be prevented through electrical insulation. This means that when aluminum is used together with these metals, all contact must be broken using insulation (Kaufman, 2000). On the other hand, galling is one of the degradation forces that affect steel. This occurs when nuts and bolts made of stainless steel are forced together. This causes the chromium oxide layer to peel off, thereby allowing the two parts to weld. When the parts are disassembled forcibly, the material may be pitted or torn. This degradation can be prevented by using materials that are different together with stainless steel
Both materials have mechanical properties that are very appropriate for this particular structure. I therefore make the following recommendations: -
- The use of both materials in order to combine the mechanical properties of both materials in order to achieve durability, structural integrity, aesthetic value and safety.
- That electrical insulation be used when aluminum is combined with stainless steel so as to avoid galvanized corrosion of the two materials.
- I also recommend that bolts and nuts of the alternate material be used when binding the metals in order to avoid pitting.
References
Allen, E. (2013). Fundamentals of Building Construction: Materials and Methods. Hoboken: John Wiley & Sons.
Bertolini, L. (2004). Corrosion of steel in concrete: Prevention, diagnosis, repair. Weinheim: Wiley-VCH.
Ghali, E., & Revie, R. W. (2010). Corrosion and Its Control of Aluminum and Magnesium Alloys: Understanding, Engineering, and Performance. Hoboken: John Wiley & Sons.
Kaufman, J. G. (2000). Introduction to aluminum alloys and tempers. Materials Park, OH: ASM International.
Kaufman, J. G., & Rooy, E. L. (2007). Aluminum alloy castings: Properties, processes, and applications. Schaumburg, IL: American Foundry Soc.
Khatak, H. S., & Raj, B. (2002). Corrosion of austenitic stainless steels: Mechanism, mitigation and monitoring. Cambridge [u.a.: Woodhead Publ. [u.a..
