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Various prediction methods have been proposed for evaluating the fatigue life of welded joints by combining finite element analysis (FEA) with an experimental database. However, to obtain more universal and accurate fatigue life predictions, it is necessary to have criteria for making integrated evaluations of the fatigue strength of welded joints. This paper presents a study that focuses on the local cyclic plastic zone size (ω*) as the criterion of fatigue strength and investigates its validity. The definition of ω* was given by the relationship between the stress state at the notch tip and the elastic strain which was defined along the strain-life fatigue curve (ε - N diagram) of a base metal. As a result of using ω*, it was found that an integrated fatigue life prediction was possible to a certain extent for notch and arc-welded joint specimens.

A new method was developed to help determine the conditions that would create adhesion strength of heat-resisting coatings formed in plasma spraying. This method is a combination of an experiment design that uses a Latin square and multiple regression analysis. Since it allows the direct analysis of experimental data, conditions can be determined in one third of the number of tests required by conventional experimental methods. The multiple regression equation gained through this study is also effective in comparing the heat resistance of the heat-resisting coating.