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# To select a material using a computer database called 'Cambridge Engineering Selector' (C.E.S).

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Introduction

Object To select a material using a computer database called 'Cambridge Engineering Selector' (C.E.S) Apparatus - Computer - 'Cambridge Engineering Selector' database program Theory The Problem Below is a brief description of the theory regarding this lab: - Oars are light, stiff beams. They must also have reasonable fracture toughness (KIC) and acceptable price per unit mass (Cm). The performance index for a light, stiff beam is: M1 = E1/2/? Where E is the Young's modulus and ? is the density. To select the best materials, perform two selection stages: (i) In stage 1, select materials with M1 > 7 (GPa) /(Mg/m) (ii) In stage 2, select materials with KIC > 1 MPa.m and Cm < 100 GBP/kg. CES Selector Materials for Oars: The solution The performance index for a light, stiff beam (M1) is plotted in stage 1. 'Density' is plotted on the x-axis and 'Young's Modulus' on the y-axis. A selection line of gradient 2, through the point (1.0, 49) is plotted. The constraints on adequate fracture toughness and price are plotted in stage 2. 'Fracture Toughness' is plotted on the x axis and 'Density' on the y axis. A selection box whose upper left corner is at (1.0, 100) is defined. In stage 1, the line representing the performance index is moved 'up' until only a small subset of records remains in the selection. Magnified views of the two selection charts are shown in figures M5.3.1 and M5.3.2 (results intersection and hide failed records on), and the materials passing both stages are shown in figure M5.3.3. ...read more.

Middle

CALCULATION OF THE GRADIENT FOR BOTH GRAPHS The gradient of the lines in both graphs were calculated using the performance index for the bending of rods, the formula used was: - E/P = Young's Modulus / Density In order to get the above equation into the correct term for a gradient or a curve (y=m x + c) both sides of the equation had to be logged: LOG E - LOG ? = LOG C Transpose for LOG E LOG E = LOG ? + LOG C The equation for a straight line is y = mx + c From the above it is fair to mention that: - Y = LOG E X = LOG ? M = 1 The performance used in this lab was E 1/2 / P = C If you take log on both sides of the equation above: 1/2 LOG E - LOG ? = LOG C Transpose for 1/2 LOG E: LOG C + LOG ? = 1/2 LOG E Multiply both sides by 2 to get LOG E LOG E = 2 LOG ? + 2 LOG C From the above it can be assumed that: Y = LOG E M = 2 X = LOG ? C = 2 LOG C M (The gradient) = 2 The gradient in the first graph of Density Vs. Young's Modulus is 2. If another performance index is used: K IC / p = c The log of both sides of the equation gives: - 2/3 LOG K ic = LOG ? ...read more.

Conclusion

). But in the economical end of manufacturing rowing boat oars, both the wood materials would be selected, as they are reasonably cheap to buy, whereas carbon fibre is more expensive. Costs of materials are not the only concern, as the usage of each material is just as important. Questions could be asked; such as, how often is the boat going to be used? Is it going to be used on a regular basis? All of these questions should be taken into consideration before a decision is made. If an average person who is not a professional rower was going to consume a rowing boat ore, he/she would be better off opting for the one made from low density wood as the wooden ore is a great deal cheaper. On the other hand if the same question was asked to a professional rower, then the rower would pick the ore made of carbon fibre since the price does not come at the top of the list of concern and winning the race is the major objective. Basically, there is a good point and a bad point on each material. This largely depends on the object of buying the ore. If it is to win a race then money is not an option and the consumer would be better off buying the one made from carbon fibre but if the object is to just go rowing for a weekend then the best option would be to go for the oar made from wood simply because there is no likely consistent further use for the ore. YHAREES KHAN BSc Mechanical Engineering ...read more.

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