Materials, Tribotechnology, and Surface Engineering - Assignment Example

MATERIALS TRIBOTECHNOLOGY AND SURFACE ENGINEERING [Name] [Institutional Affiliation] [Date] Table of Contents Question 1 3 Question 2 4 Question 3 5 Question 4 5 Question 5 6 Question 6 9 Question 1 Young’s modulus is 97GPa whereas Poisson’s ratio is 0.34 Thus, effective modulus is given by the formula: Where; Effective modulus, Elastic modulus, and Poisson’s ratio Elastic modulus, Shear modulus, 97GPa Poisson’s ratio, But = = 156.61 x Pa Elastic strain in copper at yield strength Hardness = 150 MPa and Young’s modulus = 140GPa = = 0.00107 Elastic Modulus = stress/strain = 140 x 109 Pa Question 2 According to Torbacke, Rudolphi & Kassfeldt (2014), the lubrication regimes are largely determined by the conformity levels in terms of geometry and the lubricant film’s thickness. Under this consideration, the Ra value of 0.4μm is rotating in a brass bush and the Ra value for its inner diameter of 0.7μm. Further, both the shaft and the bush have been immersed in oil and an oil film thickness of 5μm has developed during the operation. From the description given, the lubrication regime that applies is elastohydrodynamic lubrication. Here, the value of R falls in the following ranges:. Theoretically, the smallest thickness of the oil film depends on the speed of sliding and the pressure viscosity coefficient. What is more, in the elastohydrodynamic regime, the minimum thickness ranges between 80-90 percent for central film thickness. Lubrication Regimes as shown on Stribeck’s Curve Question 3 Limitations of liquid lubricants A liquid lubricant poses a number of limitations due to their physical and chemical properties. Broadly, these limitations can be categorized into thermal stability, flammability, oxidation stability, and volatility challenges (Roark, Young & Budynas 2002). Liquid lubricants pose higher molecular weight resulting in volatility problems. When liquid lubricants get oxidized, the lubricant fails. Therefore, oxygen supply should be controlled in order to manage the effect of oxidation. Vegetable oils are easily affected even by low oxidation. Higher temperatures make the liquid lubricants thermally unstable (Hamrock, Schmid & Jacobson, 2004). Lubricants such as vegetable oils can vaporized or change into gas at high temperatures, making them less useful or not useful at all. The lubricants become more viscous with temperature increases. For some oils, they become flammable at high temperatures (Frène 1997). Question 4 The wear rate depth for a polymer-based bearing that supports a rotating steel shaft is 0.25mm in 1000 hours whereas the bearing pressure and speed are 10MPa and 10-1ms-1 respectively. At a pressure of 1 MPa, speed is 1ms-1. (a) Illustrating that the bearing operates within the range where specific rate of wear is constant The expression for estimated wear dimensions (mm), W, is given by: From this expression, K stands for the specific amount of wear, P stands for bearing load surface pressure (N/mm2), V stands for bearing sliding velocity (m/s), whereas T stands for sliding hours (hours). Thus, = 2.5 x10-7 (b) If we assume a pressure of 2 MPa and wear speed of 0.2 ms-1, the time, T, for sliding hours is given by: T = T = Thus, sliding hours =2.5 (c) Determination as to whether it is safe to calculate the wear rate at 10MPa and speed of 1ms-1. In order to determine whether it is safe to calculate wear rate at 10MPa and speed of 1ms-1, the factors that affect the wear rate should be considered. These factors include the bearing sliding velocity, the sliding hours, the wear dimensions and the bearing load surface pressure (Ashby 1999). The mount of wear decreases with an increase in the sliding velocity and loading surface pressure. (d) The specific wear will be affected in different ways if a polished steel shaft is used in the environment of a laboratory and room temperature. At room temperature and environment, the polished steel is not prone to environmental corrosion easily and that means its specific wear will remain constant for some time. Question 5 (a) What it means by the statement: “To reduce wear on a steel component, a hard ware resistant ceramic coating is applied” When steel components are exposed to high temperature and other environmental conditions, they wear easily. In order to reduce this, a material that is resistant to corrosion, such as ceramics, are used to coat the steel components to increase their life by lowering friction and protecting steel from thermal fatigue. However, steel components can only be coated with ceramics but cannot be substituted altogether. They are more strong that ceramic and therefore, only coating by ceramics can be applied to resist some unique environmental conditions under the environment where the steel component is working (Wachtman & Haber 1993). The thermal coatings offer the steel coatings with a thermal barrier. The thickness of the ceramic coatings applied varies from one component to another and takes into consideration the environment the coating is intended to resist. The properties of ceramics that make is suitable for steel coatings include their ability to resist corrosion, and the reduce friction. (b) Three techniques for ceramic coating and explaining why ceramic coating is used and what are the advantages of ceramic coating techniques. Generally, ceramic coatings are applied by dipping and spraying, physical vapour deposition (PVD), Chemically Formed Processes (CFP) and Chemical Vapour Deposition (CVD). The selection of the coating method depends on the coating material, cost, substrate material, service conditions and shape and size of the component to be coated. Physical Vapour Deposition Physical Vapour Deposition (PVD) technique make use of surface coating methods for tool coating, decorative coating and other techniques used for coating the equipments (Turner, 2009). Fundamentally, this is a vaporization coating process where basic mechanisms entail atom by atom material transfer from the solid phase to vapor phase and then back to solid phase leading to gradual development of a film on the surface being coated. The advantages of PVD coating is that it is more resistant to corrosion and harder than coatings applied through the electroplating processes. The technique makes use of some organic and inorganic coating materials and uses a variety of finishes. The process is also friendlier to the environment and several techniques can be used in deposition of any given film. Chemical Vapour Vaporization Chemical Vapour Vaporization (CVC) process takes place in a vacuum chamber at high temperatures of about 1000°C. In the chamber, the gases are disassociated and react on the surface of the workpiece in order to form a coating. It forms thin films for different materials. The CVD process has several advantages. It is versatile and can be used to produce powders and coatings by depositing any compound or element. The method is economical in its production and the formation of material is near the melting point. Further, coatings of high density and high purity are obtained. Chemically Formed Processes Chemically Formed Processes (CFP) helps in offering resistance to corrosion and wear on the metallic components covered. The thickness of the coating is about 10 to 100mm thick. After the desired temperature has been achieved, thin ceramic coatings form and the process is repeated continuously till the desired shape is obtained. This process has the advantage of coating even for lines that are not on sight. Further, the ceramic coatings can be bonded to the substrate at high density and achieve sufficient resistance to corrosion. Question 6 The diagram bellow stands for a Tungsten Carbide ball whose diameter is 50 mm and is loaded under a normal force increasingly applied against the stainless steel plate with a hardness of 200 GPa and entails the following calculations. The relevant Hertz equations for this contact are: Radius of the circle of contact, a = (3PR/4E*)1/3 (equation 1) Maximum pressure, p0 = 3P/2πa2 = (6PE*2/π3R2)1/3 (equation 2) P = the normal load, R = the radius of the ball and E*= the composite modulus at the contact. i) The force at which the plate material first yields The Maximum pressure, p0 is given by = 3P/2πa2 = (6PE*2/π3R2)1/3 = (6 x P x (700 x 109)2) / 3.1423 x 0.052)1/3 =333800000 P Thus, = = 0.001669 N (i) Contract width According to Roark, Young & Budynas (2002), pressure = Young’s modulus x Strain = 54 x 109 Pa Contact area = = 0.03 m If we assume the contact area is square, then contact width = Square root of area = Sq. Root 0.03 = 0.170 m (ii) Pressure = Young’s modulus x strain = 54 GPa At the point of pressure application for the tungsten Carbine Pressure = 700 x 109 Pa x 0.27 = 189 GPa From the two values of pressure obtained, minimum pressure is 54 GPa (iii) Mean Pressure is the average of the maximum and minimum pressures = = 54 GPa + 189 GPa = 121.5 GPa (iv) Maximum pressure is applied on the side of the tungsten carbine and is equal to 189GPa. References Top of Form Bottom of Form Top of Form Top of Form Top of Form Top of Form Top of Form Top of Form ASHBY, M. F. (1999). Materials selection in mechanical design. Oxford, OX, Butterworth-Heinemann. FRÈNE, J. (1997). Hydrodynamic lubrication bearings & thrust bearings. Amsterdam [Netherlands], Elsevier. http://www.sciencedirect.com/science/book/9780444823663. HAMROCK, B. J., SCHMID, S. R., & JACOBSON, B. O. (2004). Fundamentals of fluid film lubrication. New York, Marcel Dekker. ROARK, R. J., YOUNG, W. C., & BUDYNAS, R. G. (2002). Roark's formulas for stress & strain. New York, McGraw-Hill. TORBACKE, M., RUDOLPHI, A. K., & KASSFELDT, E. (2014). Lubricants: introduction to properties and performance. http://catalogimages.wiley.com/images/db/jimages/9781118799741.jpg. TURNER, A. (2009). Ceramic sculpture inspiring techniques. Westerville, Ohio, American Ceramic Society. http://search.ebscohost.com/login.aspx?direct=true&scope=site&db=nlebk&db=nlabk&AN=420378. WACHTMAN, J. B., & HABER, R. A. (1993). Ceramic films and coatings. Park Ridge, N.J., U.S.A., Noyes Publications. http://app.knovel.com/web/toc.v/cid:kpCFC00001. Bottom of Form Read More