Dottorato in INGEGNERIA INDUSTRIALE E GESTIONALE

Titolo della tesi: Study on the Benefits of Lattice Structures within the Framework of High-Performance Structural Design: A Case Study.

The design and development of the innovative structures require rigorous and robust efforts when they are based on complex geometries, involving multi-physics functionalities/behavior, subjected to other assembly components, and to be prototyped with additive manufacturing. Additive manufacturing allows us to explore new topologies that may fulfill many functional requirements. Lattice structures are part of these new topologies, providing abundant promising advantages, such as lightweight design, functional graded solutions, etc. In this work we investigate the state of the art of lattice structures in respect of their related field of applications and we apply this knowledge to support the design of a high-performance device, such as next-generation cryogenic detectors for particle physics research. Lattice structures pose many challenges in the field of the CAD-CAE approaches, since it requires managing a multiscale modelling domain. This may reduce the capability of young engineers to completely accomplish the design workflow with efficiency. This thesis aims to investigate a design-development workflow suitable to guarantee this efficiency, and subsequently facilitates the development of innovative structures with virtual prototyping and additive manufacturing. The followed approach was: ▪ To investigate the state of the art of lattice design modelling and simulation. ▪ To define a design-development workflow suitable to accomplish functional, performance and process requirements. ▪ To test the design-development workflow through the design of a high-performance device. The proposed design-development workflow is based on a comprehensive list of requirements engulfing all the design, functional, assembly, and manufacturing requirements to fulfill the desired objectives. This list of requirements is then successfully translated into the initial design phase to facilitate the subsequent 3D modelling, manufacturing, and assembly phases. The validation case study is a real application of BULLKID Project, provided by the industrial partner INFN (Istituto Nazionale di Fisica Nucleare/Italian National Institute of Nuclear Physics) Rome (Italy). BULLKID is developing the next-generation cryogenic detectors for Particle Physics research, in the field of neutrino and dark matter. The detectors are operated at 10 mK temperature in a high vacuum and light-tight environment. This case study is basically a multi-physics problem, and it is based on multi-objective design optimization. Main challenges concerning the research work are to hold the detector with the least possible mechanical vibrations, excellent thermal contact, and stacking up several of them in a closely packed structure. In addition, the proposed design should be lightweight, thermal efficient, and the protype of the wafer holders and the wafer holding ring should be developed with additive manufacturing (AM) technology (SLM technique) to ensure maximum flexibility in the design and to obtain the fine features required for the final structure. The design optimization is carried out in two stages: first without the lattice structure, and second with the lattice structure. In the first optimization stage, it is ensured that the optimized design (without lattice) has the capability to stack up three wafer assemblies successfully in the prototype, withstand a fail-safe cryogenic operation (ensuring an improved rigidity with respect to vibration issues detected during the experimental run of the previous design), and the prototyping of complex components with AM in accordance with the stipulated requirements. In the second optimization stage, the infill volume lattice (with an optimal cell structure) is employed in the wafer holding ring, under the consideration of the assembly constraints, to further reduce the structural weight, reduce the mechanical vibrations, and improve the thermal efficiency. In addition, to facilitate the AM of the desired component and minimize the possible thermal distortion, the support structure for the AM is also designed with an optimized lattice structure. The proposed design is initially validated through numerical simulations (structural, modal, and thermomechanical analysis), and virtual 3D CAD assembly. However, it is physically validated through prototyping and subsequent experimental tests. In addition, 3D scanning of the additively manufactured components is also performed through the reverse engineering technique of photogrammetry, as a quality check of the AM process. In conclusion, the proposed design successfully supports up to three detector assemblies. It also reduced the structural weight, mechanical vibrations, and improved thermal efficiency, as warranted by the design requirements.