Sustainable design has become a key objective in modern engineering, as early design decisions largely determine a product’s environmental impact. In this context, this thesis presents a framework that enables directional disassembly through the use of topology optimization. The approach integrates geometric modeling via the level set method with numerical analysis using the eXtended Finite Element Method to design structures that can be separated along prescribed directions. A disassembly constraint is introduced through the concept of shading, which models geometric obstruction between parts in a given removal direction. Two different shading formulations are considered and validated: a distance-based method originally proposed by Allaire et al. (2023), which is adopted in this work, and an alternative gradient based formulation. Shading is computed in both cases from a heat diffusion problem, either using the difference between two generated distance fields or gradient misalignment. The former yields a more accurate shade but is more computationally expensive, whereas the latter is more efficient but prone to boundary effects. Both single-material and two-material formulations are considered. The shading formulations are subsequently used in a multi-objective topology optimization framework that incorporates perimeter penalization and level set regularization, ensuring smooth, manufacturable, and disassemblable designs. Optimization studies show that the proposed framework can generate disassemblable designs. The methodology is further extended to incorporate structural performance objectives, enabling the creation of designs that are both mechanically efficient and easily disassemblable.

In various engineering fields it is required to design material layouts with improved performance or tai- lored properties. Hereby, the structural integrity should not be compromised, such that material failure is avoided. Topology optimization enables the systematic design of structures presenting enhanced performance with respect to criteria, such as mass, volume, stiffness, or eigenfrequencies. In the majority of research works in topology optimization, material failure is addressed by constraining or minimizing the stress state in simplified analyses, in which the material is modeled as isotropic linear elastic. However, brittle and quasi-brittle materials, such as concrete and rock, progressively degrade on a micro-scale, before material rupture occurs macroscopically. Using continuum damage mechan- ics, the state of material degradation may be modeled through one or multiple internal variables that are thermodynamically irreversible. However, modeling damage leads to a computationally intensive, non-linear and path-dependent optimization problem. The limited previous research suggests, though, that accounting for material degradation throughout the design phase can significantly improve the per- formance and reliability of the resulting designs. In this work, a level set-based topology optimization approach is proposed to generate steel- reinforced concrete layouts with enhanced damage resistance. Additionally, a thorough comparison of addressing material failure in a linear stress-based and a non-linear damage-based TO approach is conducted. The geometry of the designs is represented implicitly through a level set function. The level set and state fields are discretized using the extended finite element method, which alleviates the need to remesh in each optimization iteration. Assuming isotropic damage, strain softening degradation in the concrete material is modeled through a single scalar damage variable. The steel as well as the un- damaged concrete are modeled as isotropic linear elastic materials. To avoid instability and localization of deformation, non-locality is introduced through a gradient-enhanced damage model. Boundary and interface conditions are imposed weakly using Nitsche’s method. Numerical instabilities due to small material subdomains are mitigated through face-oriented ghost stabilization. The optimization prob- lems are solved through mathematical programming using the globally convergent method of moving asymptotes. Accounting for the irreversibility of damage, the required shape-sensitivities are evaluated semi-analytically through an adjoint approach. The proposed optimization approach is applied to two-dimensional numerical problems from the literature. The results show that resorting to a simplified linear analysis is insufficient to generate struc- turally reliable designs of brittle material. When modeling the non-linear damaged material behavior throughout the optimization process, though, resulting layouts show an enhanced load-bearing capacity and resistance to damage. It is further demonstrated that the maximum damage level in steel-reinforced concrete layouts can be controlled, through an optimized distribution of reinforcing steel material.