Practical solutions for multi-objective optimization: An application to system reliability design problems

For multiple-objective optimization problems, a common solution methodology is to determine a Pareto optimal set. Unfortunately, these sets are often large and can become difficult to comprehend and consider. Two methods are presented as practical approaches to reduce the size of the Pareto optimal set for multiple-objective system reliability design problems. The first method is a pseudo-ranking scheme that helps the decision maker select solutions that reflect his/her objective function priorities. In the second approach, we used data mining clustering techniques to group the data by using the k-means algorithm to find clusters of similar solutions. This provides the decision maker with just k general solutions to choose from. With this second method, from the clustered Pareto optimal set, we attempted to find solutions which are likely to be more relevant to the decision maker. These are solutions where a small improvement in one objective would lead to a large deterioration in at least one other objective. To demonstrate how these methods work, the well-known redundancy allocation problem was solved as a multiple objective problem by using the NSGA genetic algorithm to initially find the Pareto optimal solutions, and then, the two proposed methods are applied to prune the Pareto set.     

Surface modification of ferrous alloys with boron

This paper presents the effects of boronizing on ferrous alloys such as plain-carbon steel AISI 1018, high-strength alloy steel AISI 4340, and austenitic stainless steel AISI 304. The coatings were produced by thermochemical treatment with powder mixtures at temperatures of 850°C for 4 h. The microstructure of obtained coatings was investigated, the microhardness was measured, and the corrosion resistance and oxidation resistance were tested. By metallographic analyses, the thickness of the coatings was measured. Microhardness of the boron coatings was measured using loads of 10 gf, 25 gf, and 50 gf. Corrosion tests were performed in 5% HCl, 10% HCl, and 15% HCl at room temperature. To determine the oxidation resistance of the coatings, the isothermal method was used to observe the weight change at a temperature of 600°C for 12 h. Results indicated that the presence of boronized coatings on ferrous alloys greatly improved their microhardness, oxidation resistance, and corrosion resistance.