Issue 30

R. Baptista et alii, Frattura ed Integrità Strutturale, 30 (2014) 118-126; DOI: 10.3221/IGF-ESIS.30.16 125 Figure 6 : Center stress differences. Figure 7 : Stress distribution in the optimized geometry, t=5mm, Load Case 1. Figure 8 : Stress distribution in the optimized geometry, t=5mm, Load Case 2. Figure 9 : Maximum center stress, Load Case 1. C ONCLUSIONS he Direct Multi-Search model was able to produce several Pareto Fronts for a very complicated Finite Element problem, which included two objective function and five active design variables. Each Pareto Front was obtained for each arms thickness, based on the Renard series of preferred numbers, and therefore the specimen designer can obtain the optimal geometry as a function of the desired material thickness. Within the Pareto Front all the specimen geometries configurations are mathematically equal, therefore the ones chosen in this paper represent the best possible correlation between the design variables and the arms thickness. It was possible to achieve a correlation between the arms thickness and the specimen elliptical fillet variable. On the other hand the relationship between the center spline radius or the spline exit angle and the arms thickness still need to be worked on. Both these variables have the same effect on the maximum stress level and stress uniformity level on the specimen center. Decreasing their value leads to an increase on the maximum stress level and a decrease on the stress uniformity level. Therefore different combinations lead to similar results. Decreasing the specimen center reduced thickness value leads to higher stress levels, but is was found that this is a dominating variable. Therefore the center thickness was assumed constant, sa ratio of the arms thickness, in the optimization process. Future work will require to achieve a correlation between this variable and the other specimen design variables. Two different loading conditions were studied, and it is possible to report that the second load case produces higher stress levels on the specimen center. .As expected increasing arms thickness decreases the maximum stress level on the specimen. R EFERENCES [1] Shanyavskiy, A., Fatigue cracking simulation based on crack closure effects in Al-based sheet materials subjected to biaxial cyclic loads, Eng. Fract. Mech., 78 (8) (2011) 1516–1528. T