Luca Esposito

Enhancing the long-term reliability and durability of solid oxide fuel cells is crucial to ensure the high-performance standards required in modern applications. For this purpose, high-resolution modelling that accurately captures the critical phenomena affecting cell operation is needed. The cells’ long-term performance can be significantly impacted by degradation processes arising from intense stress fields induced by high operating temperatures, creep deformation and oxide growth on interconnects. This study introduces a predictive tool to enhance the cells’ long-term reliability and durability. A finite element thermo-mechanical model accounting for the operating temperature distribution, mechanical stresses and creep was developed to assess cell structural integrity. A predictive model for the evaluation of oxide growth on the solid interconnects was integrated in the model via subroutine. The whole cell efficiency estimation as a function of the oxide thickness was assessed by introducing a dedicated local degradation function. This research contributes to advancing SOFC design and operational stability, thereby enhancing their long-term viability in energy applications.

Tire puncturing is one of the main causes of accidents and/or traffic interruptions, leading to unsafe and unsustainable mobility scenarios. Insert-supporting Run-Flat systems can be a strategic technology to improve tire performance, but further developments are needed to improve system reliability, modularity, and efficiency. A novel Run-Flat system was proposed in the present study to address specific features. The concept was developed by exploiting numerical simulation tools, enabling a comprehensive system assessment. In addition, a technological demonstrator was manufactured employing rapid prototyping techniques based on 3D printing processes.

The VITAL-E (Versatile Innovative Testing Low-Cycle Fatigue for Elastomers) project introduces a shift in low-cycle fatigue (LCF) testing by replacing traditional hydraulic systems with an electromechanical solution. Hydraulic machines, although widely used, present issues such as fluid leakage, environmental impact, high maintenance, and complex feedback control. In contrast, VITAL-E incorporates a zero-backlash linear actuator, addressing a key challenge in electromechanical systems: backlash. This issue, caused by axial movement between the nut and screw during load reversals, can disrupt load application and compromise test accuracy. By eliminating backlash, the chosen actuator ensures continuous and precise load application, especially during critical cycle reversals, enhancing both the accuracy and reliability of LCF testing. Beyond technical improvements, the electromechanical system reduces component complexity, wear, and maintenance needs while offering easier upgrades and adaptability to evolving testing demands. Compared to conventional hydraulic systems, VITAL-E’s design offers an innovative industrial solution, promoting a new generation of LCF test machines that excel in accuracy, reliability, and operational efficiency. This innovation aligns with the growing demand for sustainable and adaptable testing solutions, particularly in the automotive industry, ensuring that LCF testing remains relevant for future research and industrial needs.

In this work, the stress relaxation behavior of 3D printed PLA was experimentally investigated and analytically modeled. First, a quasi-static tensile characterization of additively manufactured samples was conducted by considering the effect of printing parameters like the material infill orientation and the outer wall presence. The effect of two thermal conditioning treatments on the material tensile properties was also investigated. Successively, stress relaxation tests were conducted, on both treated and unconditioned specimens, undergoing three different strains levels. Analytical predictive models of the viscous behavior of additive manufactured material were compared, highlighting and discussing the effects of considered printing parameters.

By the term, lattice structures are intended topologically ordered open-celled structures consisting of one or more repeating unit cells. Technological development and especially the growth of the additive manufacturing (AM) industry allows innovative structural design, including complex lattice structure. Selective laser melting (SLM) is an AM process that enables the manufacture of space filling structures. This work investigated the influence of the most important process parameter settings on lattices printability, focusing on the geometrical accuracy, the quantity of powders adhered to the main frame (satellites) and their compression behaviour. The process parameters such as the laser power, scan speed and layer height affect vigorously the design, quality and mechanical properties of the part. The aim of the paper is to evaluate how different parameter combinations affect the cellular structures’ printing. Twenty-four lattice structures with cubic and rhombic dodecahedron unit cells made of stainless steel 17-4PH (AISI-630) were printed using different combinations of SLM process parameters. Each structure was analysed considering its geometrical, topological and mechanical properties. Finally, the best parameter combination was evaluated comparing results achieved. Although this work investigated the 17-4PH stainless steel, physical principles related to the printing process described are generally true for the SLM process. Therefore, the adopted approach could still be suitable also for all the other materials commonly used with this AM technology.

The recent increase of train speed and frequency determines a rise of the loads transmitted to the superstructure. Therefore, railway components might experience service loads that have not considered at the design stage. Moreover, wear and backlash modification between components of a mechanical system might be able to modify the internal boundary conditions of the assembly. According to damage tolerance philosophy, an initial flaw is assumed to exist in the fatigue critical location of a structural component, and the analysis of the crack propagation life for such component needs accurate Stress Intensity Factor (SIF) evaluations. In this study, the effects of the boundary conditions on the crack propagation life have been evaluated for a semi-elliptical surface crack having semi-axes a and c and growing from the root of a shoulder fillet notch in a round bar loaded in bending. Two cases have been analyzed: - the shoulder is free from external forces; - the shoulder is in contact with an adjacent generic body. At first, the SIF distribution has been calculated with the Virtual Crack Closure Technique, considering or not the nonlinear effect induced by the contact forces arising from the interaction between the shoulder and the neighboring component. Successively, in both the above cases a two-parameters propagation law has been utilized to predict the evolution of both crack shape and crack depth when a cyclic bending load is applied to the rod. For this purpose, different values of the Stress Concentration Factor at the root of the fillet, and of the initial aspect ratio of the crack front, were considered in the calculations. It is found that the aspect ratio evolves to a unique asymptote, taking or not into account the non-linearity introduced by the contact at the shoulder, and this value depends on the notch severity. The ratio between the dimensionless SIFs obtained with and without the unilateral constraint at the shoulder, βcs / βfs, does not depend on the relative crack depth and crack shape. Also, the effect of the notch severity on the dimensionless SIF appears to be evident only for the portion of the crack front in the vicinity of the free surface.