One simple tool that has been developed to assist in materials selection is a comparison chart, such as the one shown in Figure 9-A. The various desired properties are weighted as to their significance, and candidate materials are evaluated on a scale such as 1 to 5 or 1 to 10 with regard to their ability to provide that property. A rating number is then computed by multiplying the property rating by its weighted significance and summing the results. Potential materials can then be compared in a uniform, unbiased manner, and the best candidates can often be identified. In addition, by placing all the requirements on a single sheet of paper, the designer is less likely to overlook a major requirement. Finalist materials should then be reevaluated to assure that no key requirement has been overlooked or excessively compromised.
Three materials, X, Y, and Z, are available for a certain use. Any material selected must have good weldability. Tensile strength, stiffness, stability, and fatigue strength have also been identified as key requirements. Fatigue strength is considered the most important of these requirements, and stiffness is least important. The three materials can be rated as follows:

Use a rating chart such as that in Figure 9-A to determine which material you would recommend.

Weldability Tensile strength Good Excellent Fair Stiffness Stability Fatigue strength Fair Excellent Poor Good Good GoodGood Good Excellent Good Good Excellent