Chapter14 - Case studies: use of data sources 14.1...

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Case studies: use of data sources 14.1 Introduction and synopsis Screening requires data sources with one structure, further information, sources with another. This chapter illustrates what they look like, what they can do and what they cannot. The procedure follows the flow-chart of Figure 13.2, exploring the use of handbooks, databases, trade-association publications, suppliers data sheets, the Internet, and, if need be, in-house tests. Examples of the use of all of these appear in the case studies which follow. In each we seek detailed data for one of the materials short-listed in various of the case studies of earlier chapters. Not all the steps are reproduced, but the key design data and some indication of the level of detail, reliability and difficulty are given. They include examples of the output of software data sources, of suppliers data sheets and of information retrieved from the World-wide Web. Data retrieval sounds a tedious task, but when there is a goal in mind it can be fun, a sort of detective game. The problems in Appendix B at the end of this book suggests some to try. 14.2 Data for a ferrous alloy - type 302 stainless steel An easy one first: finding data for a standard steel. A spring is required to give a closing torque for the door of a dishwasher. The spring is exposed to hot, aerated water which may contain food acids, alkalis and salts. The performance indices for materials for springs MI = 6 - E M2 = ~ 4 (small springs) or (cheap springs) ECR, a2 -1- E MI = (small springs) or 0-" f M2 = :Ec; (cheap springs) A screening exercise using the appropriate charts, detailed in Case Study 6.8, led to a shortlist which included elastomers, polymers, composites and metals. Elastomers and polymers are elimi- nated here by the additional constraint on temperature. Although composites remain a possibility, the obvious candidates are metals. Steels make good springs, but ordinary carbon steels would corrode in the hot, wet, chemically aggressive environment. Screening shows that stainless steels can tolerate this. The detailed design of the spring requires data for the properties that enter M lor M 2, -the strength at (in the case of a metal, the yield strength ay), the modulus E, the density p and the cost C m -and data for the resistance to corrosion. The handbooks are the place to start.
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Case studies: use of data sources 335 Table 14.1 Data for hard drawn type 302 stainless steels* Property Density (Mg/m3) Modulus E (GPa) 0.2% Strength oy (MPa) Tensile strength (MPa) Elongation (%) Corrosion resistance cost Source A* B* C’ 7.8 210 965 1280 9 ‘Good’ No information 7.9 215 1000 1466 6 ‘Highly resistant’ 7.86 193 1345 - - ~ ~ *Source A: ASMMerals Handbook, 10th Edition, Vol. 1 (1990); Source B: Smithells (1987); Source C: http.//www.matweb.com. All data have been converted to SI units. Source A, the ASM Metals Handbook and Source B Smithells (1987) both have substantial entries listing the properties of some 15 stainless steels. Hard-drawn Type 302 has a particularly high yield strength, promising attractive values of the indices M1 and M2.
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This note was uploaded on 04/26/2008 for the course M&AE 212 taught by Professor Miller during the Spring '07 term at Cornell.

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Chapter14 - Case studies: use of data sources 14.1...

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