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Öğe Design of fiber reinforced laminates for maximum fatigue life(Elsevier Science Bv, 2010) Ertas, Ahmet H.; Sonmez, Fazil O.Composite materials are used in many structural applications due to their superior properties, e. g., strength-to-weight ratio. Composite structures also offer great flexibility and stiffness in design, allowing change of the material system in many ways like number of fibers, different lay-up configurations, etc. With the increased use of composites it has been understood that their deformations in terms of fatigue is more complex than that of metals. Because of the major deficiencies in life prediction methodologies for composite materials resulting from their complexities, composite structures, used in fatigue applications for example, are generally over-designed to eliminate catastrophic and fatal failures and are therefore heavier and more costly. In this study, a methodology was proposed to find globally optimum designs of composite laminates subject to given in-plane loads for maximum fatigue life. For this purpose, a parametric fatigue life prediction model, proposed by Fawaz and Ellyin, was coupled with a global optimization technique called Direct Simulated Annealing (DSA) which is the improved version of Simulated Annealing (SA). The number of distinct fiber orientation angles and the number of plies each lamina contains were predetermined. The fiber orientation angles in each layer were taken as design variables and determined in the design process. A computer code was developed in ANSYS parametric language and results were obtained for different configurations and loading conditions. A number of problems were solved to demonstrate the effectiveness and reliability of the proposed method. (C) 2010 Published by Elsevier Ltd.Öğe Design optimization of fiber-reinforced laminates for maximum fatigue life(Sage Publications Ltd, 2014) Ertas, Ahmet H.; Sonmez, Fazil O.Composite structures are usually subjected to fluctuating loads in service leading to fatigue failure. Because it is one of the main failure modes, fatigue behavior of composites has been extensively studied to be able to design fatigue-resistant composite structures. However, little attention has been paid to their design optimization under fatigue loading. In this study, a methodology is proposed to find the optimum fiber orientation angles of composite laminates under various in-plane loads to achieve maximum fatigue life. Fawaz-Ellyin's model is used to predict the fatigue life of the laminates. A variant of simulated annealing algorithm is used as the search algorithm in the optimization procedure. A number of problems are solved to demonstrate the effectiveness of the proposed method.Öğe Design optimization of spot-welded plates for maximum fatigue life(Elsevier Science Bv, 2011) Ertas, Ahmet H.; Sonmez, Fazil O.Resistance spot welding is the most preferred and widely used method for joining metal sheets in automotive and many other industrial assembly operations. Spot-welded joints are usually the weakest parts of structures leading to fatigue failure under fluctuating loads. Increasing the fatigue strength of the joints through geometrical changes will also increase the overall integrity of the whole structure. In this study, a methodology is proposed to find the optimum locations of spot welds and the optimum overlapping length of the joined plates for maximum fatigue life. Minimum weld-to-weld and weld-to-edge distances recommended by the industry are considered as side constraints. The total strain life equation is used to predict the fatigue life. In order to use this model, the strain state in the structure developed under cyclic loading is required. For this purpose, a nonlinear finite element analysis is carried out, taking into account residual stresses due to localized plastic deformations around the spots. Nelder-Mead (Sequential Simplex) is employed as the search algorithm in the optimization procedure. A number of problems are solved to demonstrate the effectiveness of the proposed method. (C) 2010 Elsevier B.V. All rights reserved.
