Problem Set 2 - Materials Selection | EMA 4714, Assignments of Materials science

Download Problem Set 2 - Materials Selection | EMA 4714 and more Assignments Materials science in PDF only on Docsity! Problem Set 2 EMA 4714 Materials Selection and Failure Analysis January 16, 2008 [Due Wednesday January 23, 2008]. 1. Deiter 1.4 The need for material conservation and decreased cost has increased the desirability of corrosion-resistant coatings on steel. Develop several design concepts for producing 12-inch wide low carbon steel that is coated on one side with a thin layer - e.g. 0.001-inch of nickel. There are several techniques available for producing thin layers on steel: electroless coating, diffusion bonding, chemical vapor deposition (CVD), electrodeposition, electrophoretic deposition and aqueous colloidal processing. Of these techniques, the most common for lower cost is electrodeposition (electroplating). Electroless coating can also be used. Aqueous colloidal processing also offers lower cost, but generally results in a porous coating and would not be ideal for corrosion resistance. One design concept would be to coat one side of the 12 in sheets with an insulator such as a polymer coating and then draw the sheet through a bath of sulfanate electrolyte. A rectifier would supply the current for the electroplating. After coating the polymer can be removed by heating or dipping in a solvent. It is important that the surface to be coated is cleaned thoroughly before processing. Another design concept is to use electrophoretic deposition. A characteristic feature of this process is that colloidal particles suspended in a liquid medium migrate under the influence of an electric field (electrophoresis) and are deposited onto an electrode. All colloidal particles that can be used to form stable suspensions and that can carry a charge can be used in electrophoretic deposition. Therefore, a solution containing commercial nickel powder of ~ 2.5 microns in size, stabilizing material of ammonium salt of polyacrylic acid, and binder solution of latex emulsions are used in an electric field. The solution can be applied to one side of the sheet Electroless coating of nickel is another design concept and can be obtained by first coating the one side with a polymer coating to prevent adherence to one side. The coated plate would then be dipped in a plating solution. The plating solution chosen would be an acid, hypophosphite-reduced bath, which is a combination of nickel chloride (NiCl2), sodium hypophosphite (NaH2PO2) and hydroxyacetic acid (C2H4O3). The pH value of the plating solution is set at 5 by controlling with sodium hydroxide (NaOH). The working temperature of the plating solution should be kept at 90°C. The plating time is set at 25 min. After the plating process, the electroless plating Ni specimens are immediately rinsed in flowing deionized (DI) water for 2 min, followed by alcohol rinsing and drying. The polymer coating would then be removed by either heating or using an appropriate solvent. 2. Dieter 1.7. Consider the design of aluminum [alloy] bicycle frames. A prototype model failed in fatigue after 1600 km of riding, whereas most steel frames can be ridden [??] For over 60,000 km. Describe a design program that will solve this problem. ******************************************************************** [1] analysis of failure - failure mechanism [e.g. Fatigue, SCC, whatever] including design factors influencing failure mode and time to failure [bending, torsional moments, stress concentrations, joining procedures, etc. Important to determine why this reduced service life was not anticipated - What wrong with evaluation/testing procedures. [2] stress distribution analysis on prototype design - Why did failure occur when and where it did? - remember, the object is not necessarily to eliminate failure but to postpone it. [3] redesign options to at least extend time to failure to where it can compete with steel. [4] some simulation of performance - computer modeling, FEA, whatever to test the various redesign concepts. [5] develop a prototype testing procedure/device which will allow some estimation of service life. [6] Manufacture/construct and assemble prototype. [7] Test prototype and redesign if necessary [iterative/feedback design process] 3 Pressure vessels, from the simplest aerosol can to the largest boiler, are designed for safety, to yield or to leak before break or the equivalent. List the merits and drawbacks of the following materials as potential pressure vessels: (1) aluminum, (2) steel, (3) silica glass and (4) glass fiber reinforced polymer (GFRP). Note that it is up to each team to find a source of properties upon which you base your analysis. You can start with: http://www.matls.com ******************************************************************** The leak before break criterion assumes that the crack can grow (in a semi-circular pattern) to the point at which it “breaks through” to the surface. Thus, the stress intensity at that point is: KI = Y  (t)1/2 where t is the thickness of the vessel. Now, if KI < KC (or KIC), then fracture would not take place even though leaking has begun. Based on this analysis we can evaluate the different materials. (1) Aluminum can act as a pressure vessel for some applications because the toughness values ( 23 – 45 MPam1/2) are large enough for thin vessels under