Joan Baiges

Qualification of repair and remanufacturing operations through directed energy deposition (DED) offers a sustainable pathway to restore and even enhance the performance of high-value metallic components. By employing additive manufacturing techniques to deposit material onto damaged parts, this approach minimizes downtime and extends the lifecycle of critical components such as molds, dies and tooling. However, integrating newly deposited material with the original substrate poses challenges related to residual stress formation, distortion, and alterations of the microstructural. In this study, qualification is addressed from two interrelated perspectives: (1) the qualification of the component-ensuring dimensional accuracy, minimal residual stresses and preserved metallurgical integrity; and (2) the qualification of the DED process-focusing on buildability through optimized power supply, scanning speed and dwell times. Because extensive experimental testing on high-value parts is impractical and often destructive, simulation studies are the only viable means to qualify repair operations. A simulation-assisted dynamic power control strategy is developed to maintain consistent melt-pool behavior through feedback-based power modulation. The model is calibrated and validated using finite element simulations and targeted experiments. Results demonstrate that power modulation and inter-layer dwell time effectively stabilize the melt-pool and reduce heat accumulation, improving dimensional accuracy, microstructural uniformity, and hardness distribution. However, these benefits are accompanied by increased inter-layer residual stresses due to enhanced thermal gradients. The study therefore establishes the trade-offs between thermal control, mechanical response, and microstructural control in DED-based remanufacturing, providing practical insight into selecting appropriate process parameters for qualification.

This paper presents mixed finite element formulations to approximate the hyperelasticity problem using as unknowns the displacements and either stresses or pressure or both. These mixed formulations require either finite element spaces for the unknowns that satisfy the proper inf‐sup conditions to guarantee stability or to employ stabilized finite element formulations that provide freedom for the choice of the interpolating spaces. The latter approach is followed in this work, using the Variational Multiscale concept to derive these formulations. Regarding the tackling of the geometry, we consider both infinitesimal and finite strain problems, considering for the latter both an updated Lagrangian and a total Lagrangian description of the governing equations. The combination of the different geometrical descriptions and the mixed formulations employed provides a good number of alternatives that are all reviewed in this paper.

In this work, an algorithm for topology optimization of incompressible structures is proposed, in both small and finite strain assumptions and in which the loads come from the interaction with a surrounding fluid. The algorithm considers a classical block-iterative scheme, in which the solid and the fluid mechanics problems are solved sequentially to simulate the interaction between them. Several stabilized mixed finite element formulations based on the Variational Multi-Scale approach are considered to be capable of tackling the incompressible limit for the numerical approximation of the solid. The fluid is considered as an incompressible Newtonian fluid flow which is combined with an Arbitrary-Lagrangian Eulerian formulation to account for the moving part of the domain. Several numerical examples are presented and discussed to assess the robustness of the proposed algorithm and its applicability to the topology optimization of incompressible elastic solids subjected to Newtonian incompressible fluid loads.

In this work a new methodology for finite strain solid dynamics problems for stress accurate analysis including the incompressible limit is presented. In previous works, the authors have presented the stabilized mixed displacement/pressure formulation to deal with the incompressibility constraint in finite strain solid dynamics. To this end, the momentum equation is complemented with a constitutive law for the pressure which emerges from the deviatoric/volumetric decomposition of the strain energy function for any hyperelastic material model. The incompressible limit is attained automatically depending on the material bulk modulus. This work exploits the concept of mixed methods to formulate stable displacement/pressure/deviatoric stress finite elements. The final goal is to design a finite element technology able to tackle simultaneously problems which may involve incompressible behavior together with a high degree of accuracy of the stress field. The variational multi‐scale stabilization technique and, in particular, the orthogonal subgrid scale method allows the use of equal‐order interpolations. These stabilization procedures lead to discrete problems which are fully stable, free of volumetric locking, stress oscillations and pressure fluctuations. Numerical benchmarks show that the results obtained compare very favorably with those obtained with the corresponding stabilized mixed displacement/pressure formulation.