Discrete optimisation of truss and beam structures subjected to fatigue life

The goal of design optimization is to find a technically feasible design of machinery, respectively its parts as the best solution of all possible. The optimal result is quantified through the extreme value of a suitably selected objective function while adhering to the constraint conditions defined by the designer. The objective function is often presented as the weight of the optimized design, resp. its volume. We also encounter tasks where the objective function is price, in which case the functions defined in the restrictive conditions are also affected. Depending on the type of engineering problem, the objective function can also be the value of maximum deformation or stress. In the case of dynamics, this can be prescribed the eigenvalues of the dynamic system, etc. In the paper, the authors present selected methods of discrete optimization in terms of the mass minimization of truss and beam structures subject to the limiting condition of limited fatigue life. The load of the structure is modelled by the forces in the given nodes and directions and the number of operating cycles with the appropriate load period. The calculation of fatigue damage accumulation was performed by applying the Corten-Dolan hypothesis. The whole calculation process was realized in MATLAB using a files compiled by the authors.