Particle based topology optimization methods foradditive manufacturing technologies

Topology optimization (TO) is a robust design method that generates the best material distribution by improving an objective function (e.g., maximizing stiffness orminimizing strain energy) and satisfying design constraints (e.g., volume constraints,and minimum dimensions). Although TO is increasingly utilized in lightweight designs of various engineering structures, TO designs have usually been criticized forcausing complex forms, which makes obtained geometry difficult or even impossible to fabricate by using traditional manufacturing methods such as machining,casting, etc. Additive manufacturing (AM) is an effective approach to fabricatingthese intricate shapes obtained from topology optimization (TO). However, AMmethods, which entail multiple heating and cooling cycles, lead to the formationof concentrated local residual stresses in TO designs. Consequently, this results indiminished material properties in specific areas and increases the possibility of localfailures, such as cracks/defects. At this point, a non-local reformulation of classicalcontinuum mechanics, namely Peridynamics (PD), offers a practical way to modeldiscontinuities by only breaking the bonds between particles. The PD method canaccurately model the dynamic fracture behavior of the structures including crackbranching and coalescence thanks to the utilization of the integral form of balanceequations instead of partial derivatives.Overall, the main motivation of the present thesis is to develop novel 3D topologyoptimization methods based on peridynamics (i.e., peridynamic topology optimization or PD-TO) to maximize the structural performance of the final designs produced by AM processes. In this context, three different density-based TO algorithmsnamely bi-directional evolutionary structural optimization (BESO), optimality criteria (OC), and proportional approach (PROP) are coupled with the PD methodfor the optimization of three-dimensional structures. The developed methods areextensively validated by performing on various benchmark problems. Afterward,the PD-TO method is utilized for the TO of large-scale engineering structures (shipcross-section design). According to the obtained results, the viability and superior capabilities of the PD-TO methods are revealed. Furthermore, this method isperformed with a systematic optimization scheme for increased fracture resistanceunder the dynamic load by considering a classical continuum mechanics based failurecriteria. The comparisons showed the increased fracture resistance on the optimizeddesign by the proposed algorithms against the classical optimization results. Moreover, the PD-TO methods are utilized for decreasing residual stresses occurs onthe structures produced by metal AM processes. Thanks to embedding hypotetical cracks in the initial design domain and topologically optimizing via PD-TO,we achieved residual stress minimized light weighted structures and experimentallyvalidated the obtained numerical results.