Title: Development of Design Margin Decision System Based on Reliability.
Abstract:A fatigue curve for design in which the reliability is taken into consideration is generally obtained by ASME code. A constant safety factor is used for design in this code though the fatigue life sho...A fatigue curve for design in which the reliability is taken into consideration is generally obtained by ASME code. A constant safety factor is used for design in this code though the fatigue life shows some dispersion. Therefore, a design margin decision system based on reliability, which is capable of evaluating fatigue statistically, has been developed in this paper. In the developed system, the following assumptions are used: (i) the distribution of fatigue strength follows one of the normal, log-normal and Weibull, (ii) the distribution of fatigue life follows either log-normal or Weibull, and (iii) ηD, the coefficient of variance for cumulative cycle ratio, coincides with ηN, the coefficient of variance for fatigue life. By using the developed system, a design fatigue curve for a given failure probability and confidence level was obtained and compared with that of ASME code. As a result, it has been clarified that design margin can be calculated statistically for various materials with different dispersion of fatigue life by the developed system.Read More