Problem Solving on Materials Tribotechnology and Surface Engineering - Report Example

Problem Solving on Materials Tribotechnology and Surface Engineering [Name] [Institutional Affiliation] [Date] Question 1 (a) Effective Modulus at Interface, given Young’s modulus as 97GPa and Poisson’s ratio as 0.34. Shear modulus, G = E/2(1+v) = 97 x 109Pa Poisson’s ratio, v= E / 2G -1 = 0.34 Elastic modulus, E = 2G (1+v) = = 259.96 GPa Effective = E / (1-2v)(1+v) = = = = 156.60 GPa (b) Estimating the Elastic strain in the copper at its yield stress, given the modulus of 140 GPa and a hardness of 150 MPa. Elastic Modulus = stress/strain = 140 x 109 Pa Hardness (stress) = F/A where F = force applied and A = cross sectional area. Thus, Hardness = 150 x 106 Pa Thus, Elastic strain = stress (hardness)/ elastic modulus = 150 x 106 Pa /140 x 109 Pa = 1.0714 x 10-3 Question 2 In order to determine the lubrication regimes, the Ra value shall be considered. In this case, the Ra value of 0.4μm is rotating in a brass bush with a Ra value in its inner diameter of 0.7μm. The shaft and bush are immersed in oil and, during operation, an oil film thickness of 5μm is developed. The thickness of the lubricant’s film and the level of conformity in terms of geometry determine the different modes of lubrication which are regarded as the lubrication regimens. The main lubrication regimes are hydrodynamic lubrication, the elastohydrodynamic lubrication, the quasihydrodynamic lubrication and boundary lubrication (George and Hong, 2004). The lubrication regime for the sliding interface falls under elastohydrodynamic lubrication. In elastohydrodynamic lubrication, . In theory, the minimum thickness of the film largely depends on the sliding speed, and the co-efficient of pressure viscosity. Further, the minimum thickness of the film in elastohydrodynamic regime is about 80% to 90% for central thickness for the parallel film. In the Figure bellow, II represents elastohydrodynamic lubrication. Stribeck’s Curve & Lubrication Regimes Question 3 Four Limitations of the liquid lubricants Liquid lubricants have limitations imposed by the properties of liquid lubricants such as their viscosity, oxidation stability, volatility, thermal stability and flammability. Oxidation results in failure of liquid lubricants and therefore, oxygen supply should be controlled to manage oxidation. For example, low oxidation affects the vegetable oils. Further, high temperature may result in vaporizition of the liquid lubricant, thus changing it to gas. The more the temperature, the more viscous the lubricant becomes. The molecular weight for liquid lubricants, especially the mineral oils, is wide and this results in volatility problems. Some liquid lubricants are biodegradable. For example, vegetable oils biodegrade more than the petroleum oils in a tune of up to about 15-35 percent. Liquid lubricants exhibit a high pour pouring, especially the vegetable oils. When the temperatures increases, some liquid lubricants such as the oils become flammable and may evaporate. Question 4 It is found that a polymer-based bearing supporting a rotating steel shaft has a depth wear rate of 0.25mm in 1000 hours both at a bearing pressure of 10MPa and speed of 10-1ms-1, and at a pressure of 1 MPa and a speed of 1ms-1. (a) Bearing is operating in a range where the specific rate of wear is constant This can be illustrated by the following calculation: The formula for wear is given: Where W = Estimated wear dimensions (mm) K = Specific amount of wear P = Bearing load surface pressure (N/mm2) V = Bearing sliding velocity (m/s) T = Sliding hours (hours) Thus, K = W / P.V.T = 0.25mm/ (10000000Pa x 1m/s x 1000hr) =2.5 x10-7 (b) Time taken to reach wear depth of 0.25 mm given a pressure and wear speed of 2 MPa and 0.2 ms-1. Where; W = Estimated wear dimensions (mm) K = Specific amount of wear P = Bearing load surface pressure (N/mm2) V = Bearing sliding velocity (m/s) T = Sliding hours Therefore, T = W/ K.P.V = 0.25/ (2.5 x10-7 x 2 x 106 Pa x 0.2 ) = 0.25/0.1 =2.5 hours (c) Wear rate depends on a number of factors such as the wear dimensions, bearing load surface pressure, the bearing sliding velocity and sliding hours. An increase in the loading surface pressure and sliding velocity decreases the amount of wear, which also lowers the wear rate. Therefore, it would be safe to calculate the wear rate at 10MPa and a speed of 1ms-1. Where W = Estimated wear dimensions (mm) K = Specific amount of wear P = Bearing load surface pressure (N/mm2) V = Bearing sliding velocity (m/s) T = Sliding hours (d) If polished steel shaft is used in the environment of a laboratory and room temperature, the specific wear will be affected as explained herein. The pressure of the bearing load surface, which largely depends on the material used, the sliding hours which also depend on the material used, and finally the sliding velocity of the bearing which is a function of time. Thus, since the wear rate depends on such factors, the specific wear rate would also be different from the original value. The factors that affect the amount of wear and subsequent wear rate are represented by the formula shown below: Where W = Estimated wear dimensions (mm) K = Specific amount of wear P = Bearing load surface pressure (N/mm2) V = Bearing sliding velocity (m/s) T = Sliding hours Question 5 (a) Meaning of the statement “To reduce wear on a steel component, a hard ware resistant ceramic coating is applied” The ceramic coatings are suitable for metallic areas that have been exposed to severe high temperature conditions such as the exhaust pipes. The ceramic coatings the life of a steel component, lowers its friction and help in production of useful power and offers protection to the steel components and other metallic parts from thermal fatigue. In most cases, most components are considered to be worn out just because the surfaces have already degraded more that the predetermined limits. The limits vary from one level to another. Some steel components cannot be substituted by the ceramic material in order to gain the useful duration required out of them. Therefore, such material are manufactures out of the steel components but coated with ceramics in order to resist the specific environment under which the material is working. Therefore, thermal coatings are employed to give a thermal barrier and low friction. Although production of the ceramic parts may not be a good approach in solving of corrosion problems, it is still the best option in protection of some of the steel components. The original metallic part is coated and the thickness of the coating applied varies from one component to another. Further, the thickness of the coating deposited depends on the product usage and the environment the product is intended to resist. (B) Illustration of the three different techniques used in ceramic coating and explanation as to why ceramic coating is used alongside the advantages of the techniques used. Ceramic coatings vary in size depending on the technique used. Some of the commonly used techniques include the Chemical Vapour Deposition (CVD), Physical Vapour Deposition(PVD) & Chemically Formed Processes(CFP). Some of these techniques are capable of developing worn parts on the original tolerances and thus creating both replacement cost and waste associated costs. Physical Vapour Deposition (PVD) The PVD technique is applied in depositing of thin layers of the ceramic material in order to reduce both wear and friction or to prevent the instance of cold welding. For instance, the figure bellow, the PVD process of coating has been represented in form of a schematic diagram. The Titanium Nitride (TiN) gets deposited in the partial vacuum by way of feeding the ionized titanium to plasma of nitrogen and argon that has been ionized. The operation is carried out at a temperature range of between 350 - 450°C. Some of the materials that can be produced include the Chromium Nitride, Titanium Carbo Nitride, and Tungsten Carbide through the process of changing the material within the crucible and the type of reactive gases used. The section of PVD coating shown illustrates that a thin section of the coating is produced and bonded to the substance. The coating contours to the original surface in a manner that is accurate. The entire of this process is carried out within the vacuum chamber where the issues to do with the limitations of the work piece size come into play. The bores and deep holes cannot be coated that easily since the process works effectively for a line of sight. The entire process can be represented by the diagrams bellow: . Chemical Vapour Vaporization (CVC) The CVC process requires high temperatures of about 1000°C (Bharat, 2000). Further, this process takes place in the vacuum chamber where gases are disassociated and then allowed to reach at the surface of the workpiece, thus forming a coating that is solid. Through the CVC process, coatings such as the diamond coatings can be produced. The main limitation of this technique is that the temperatures required are very high. Chemically Formed Processes (CFP) CFP coatings are usually about 10 -100 thick and can be used to improve corrosion or offer resistance to wear since the components are covered in a material that acts as a precursor for fore heating between 350 -600°C (Bharat, 1999). Once the required temperature of the reaction has been reached, a thin coating forms and the process can be repeated several times to obtain the required shape. The main advantage of this process is that it includes coating of holes since it is not for lines on sight. Further, large components can be coated through this process. What is more, the coatings can be bonded to a substrate and be fully dense, thus affording good resistance to corrosion. Question 6 Considering the case of a Tungsten carbide ball 50mm in diameter that is loaded under an increasing normal force against a stainless steel plate whose hardness is 200 GPa, the following calculation are done: 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) Where P is the normal load, R is the radius of the ball and E* is the composite modulus at the contact. (i) At what force does the material of the plate first yield; Maximum pressure, p0 = 3P/2πa2 = (6PE*2/π3R2)1/3 = (6 x P x (700 x 109)2) / 3.1423 x 0.052)1/3 = (2.9 x 1024P/0.078)1/3 = 142.6 x106/0.427 =333.75 x 106P Thus, P = 333.75 x 106/ p0 = 333.75 x 106/ 200x 109 =1.669 x 10-3 N (ii) Corresponding Contract width Contact Area = Force/Pressure But Pressure = Young’s modulus x Strain = 200 x 109 Pa x 0.27 = 54 x 109 Pa Area = 1.669 x 10-3 / 54 x 109 = 0.03m For a square are of contact, L = W = L Therefore, L2 = 0.03 m L = 0.17m (iii) In contact areas, Pressure = E x strain = 54 x 109 Pa For the tungsten Carbine Pressure = 700 x 109 Pa x 0.27 = 189 x 109 Pa Thus, minimum pressure is 54 x 109 Pa (iv) Mean Pressure = ( Minimum Pressure + Maximum Pressure )/2 = 54 x 109 Pa + 189 x 109 Pa = 121.5 x 109 Pa (v) Magnitude of the maximum pressure is = 189 x 109 Pa and and applies to the side of the tungsten carbide. References Bharat B. (1999). Principles and Applications of Tribology. New York: Wiley and Sons. Bharat B. (2000). Modern Trobogy Handbook, Two Vol Set. New York: CRC Press George E.T. and Hong, L. 2004. Mechanical Tribology: Materials, Characterization, & Applications. CRC Press. Read More

The pressure of the bearing load surface, which largely depends on the material used, the sliding hours which also depend on the material used, and finally the sliding velocity of the bearing which is a function of time. Thus, since the wear rate depends on such factors, the specific wear rate would also be different from the original value. 

The ceramic coatings are suitable for metallic areas that have been exposed to severe high-temperature conditions such as exhaust pipes. The ceramic coatings the life of a steel component, lowers its friction and help in the production of useful power, and offers protection to the steel components and other metallic parts from thermal fatigue.

 In most cases, most components are considered to be worn out just because the surfaces have already degraded more than the predetermined limits. The limits vary from one level to another.

Some steel components cannot be substituted by the ceramic material to gain the useful duration required out of them. Therefore, such materials are manufactures out of steel components but coated with ceramics to resist the specific environment under which the material is working. Therefore, thermal coatings are employed to give a thermal barrier and low friction.

Although production of the ceramic parts may not be a good approach in solving corrosion problems, it is still the best option for the protection of some of the steel components. The original metallic part is coated and the thickness of the coating applied varies from one component to another. Further, the thickness of the coating deposited depends on the product usage and the environment the product is intended to resist.

(B) Illustration of the three different techniques used in ceramic coating and explanation as to why ceramic coating is used alongside the advantages of the techniques used.

Ceramic coatings vary in size depending on the technique used. Some of the commonly used techniques include the Chemical Vapour Deposition (CVD), Physical Vapour Deposition(PVD) & Chemically Formed Processes(CFP). Some of these techniques are capable of developing worn parts on the original tolerances and thus creating both replacement cost and waste associated costs.

Physical Vapour Deposition (PVD)

The PVD technique is applied in depositing thin layers of the ceramic material to reduce both wear and friction or to prevent the instance of cold welding. For instance, in the figure below, the PVD process of coating has been represented in form of a schematic diagram. The Titanium Nitride (TiN) gets deposited in the partial vacuum by way of feeding the ionized titanium to plasma of nitrogen and argon that has been ionized. The operation is carried out at a temperature range of between 350 - 450°C.

Some of the materials that can be produced include Chromium Nitride, Titanium Carbo Nitride, and Tungsten Carbide through the process of changing the material within the crucible and the type of reactive gases used. The section of PVD coating shown illustrates that a thin section of the coating is produced and bonded to the substance. The coating contours to the original surface in an accurate manner.

The entire process is carried out within the vacuum chamber where the issues to do with the limitations of the workpiece size come into play. The bores and deep holes cannot be coated that easily since the process works effectively for a line of sight.

The entire process can be represented by the diagrams below. The main advantage of this process is that it includes a coating of holes since it is not for sightlines. Further, large components can be coated through this process. What is more, the coatings can be bonded to a substrate and be fully dense, thus affording good resistance to corrosion. Considering the case of a Tungsten carbide ball 50mm in diameter that is loaded under an increasing normal force against a stainless steel plate whose hardness is  200 GPa, some calculations are done.

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