Dipartimento di Ingegneria Civile - Tesi di Dottorato

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Questa collezione raccoglie le Tesi di Dottorato Dipartimento di Ingegneria Civile dell'Università della Calabria.

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ADVANCED MODELING APPROACHES FOR THE FAILURE ANALYSIS OF HETEROGENEOUS MATERIALS AND STRUCTURES
(Università della Calabria, 2024-07-30) Gaetano, Daniele; Greco, Fabrizio; Critelli, Salvatore
The development of new engineered materials and the introduction of innovative design techniques have led researchers in the field of structural engineering to focus their attention on the mechanical behavior of these materials to develop optimal and innovative design procedures to improve the structural performance of new and existing buildings, especially concerning their seismic behavior. The most investigated aspects are, on the one hand, the mechanical characterization of complex microstructures, such as those of composite reinforced with fibers and/or particles, to be carried out taking into account the influence of the micro-constituents on the global properties, and, on the other hand, the study of the interactions between these materials and the structural elements to which these composites are applied for mechanical reinforcement, considering the damage and fracture phenomena that can potentially occur. From a mechanical point of view, both innovative materials (e.g. composite laminates) and conventional materials (e.g. concrete, reinforced concrete, and masonry) can be considered heterogeneous materials, as they are composed of a more or less complex microstructure, made up of different constituents, usually distinguishable at very small scale compared to the dimensions of the whole structure, known as microscopic scale [1]. Being formed by the combination of distinct phases, such materials often have different (even better) mechanical properties than those of the individual constituents, but at the same time are subject to failure phenomena including: • fiber/matrix debonding, for composites, or FRP/substrate debonding for FRP-strengthened structures; • delamination between the different constituents for layered composites; • matrix cracking; • damage and plasticity phenomena; • growth of voids in the matrix phase; •As a characteristic feature of materials with heterogeneous microstructure, the different failure mechanisms may interact with each other, especially if coupled with additional effects related to unilateral contact (with or without friction) between the surfaces of the cracks or due to the presence of imperfect interfaces between the different phases [2]. As a consequence, the analysis of these non-linear phenomena and the associated structural response, results in the solution of highly non-linear problems, which make the study of the behavior of heterogeneous materials extremely challenging, requiring highly specialized theoretical and numerical knowledge as well as accurate and computationally efficient tools. In recent decades, different theoretical and numerical models have been developed to study the collapse mechanisms in heterogeneous materials and their influence on the overall properties in terms of strength and stiffness. Among these, for example, multiscale approaches that make it possible to analyze the response by considering the interaction that occurs between the various phenomena at different involved scales, or methods that use damage and fracture mechanics to describe the behavior of heterogeneous solids subject to damage phenomena. Besides the study of these issues, research interest in recent years has been focusing on structural health monitoring and damage identification within existing structures; the aim is to reduce the risk of collapse mechanisms within the materials so that the structural integrity is no longer compromised and premature and catastrophic collapses of the structures are avoided. This thesis aims to develop a series of advanced numerical methods for the failure analysis of heterogeneous materials and structures, both at the meso- and micro-scale. All the developed models use a cohesive/volumetric finite element method, based on an inter-element fracture approach [3]. In particular, two models have been developed: • A first model combining the cohesive fracture approach with a hierarchical multiscale model used to study the collapse phenomena of materials at a microscopic scale; • A second model, based exclusively on the inter-element cohesive approach, to analyze the structural behavior of FRP-strengthened reinforced concrete elements subjected to cyclic loading conditions for structural health monitoring, as well as to investigate the failure mechanisms in masonry elements. The key aspect of this work is to illustrate the models developed, to show the different strategies and procedures required to adapt them to different scales, and to the different materials and structures in the engineering fields. Chapter 1 contains the introduction and a review of the technical literature, as well as the aims and objectives of the work. Chapter 2 presents the theoretical formulation of the proposed models, while Chapters 3 and 4 review the obtained numerical results. Finally, Chapter 5 outlines the conclusions and the future perspective of the present work. microscopic and macroscopic instabilities due to finite deformations.
Assessing and managing the relationship between urban growth and greening goals for sustainable urban development. An innovative methodological approach.
(Università della Calabria, 2024-02-02) Salvo, Carolina; Francini, Mauro; Tondelli, Simona; Mundo, Domenico
As part of the transformation and qualifying processes of cities and territories, considering the challenges posed by climate change and the ecological transition in progress, the need to define new methods for sustainable urban planning capable of analyzing, evaluating, and managing the complex relationship between urban growth and greening processes to guarantee adequate levels of urban liveability and sustainability has emerged in an increasingly evident way. The thesis deals with the complex relationship between urban growth and urban greening processes. Precisely, after the analysis of the state-of-the-art on the topics of urban growth, compact and dispersed, and greening processes, such as urban green areas, ecosystem services, and nature-based solutions, and the innovative methods and tools employed in urban planning to pursue this purpose, an innovative methodological approach based on innovative information technologies, such as artificial intelligence models and remote sensing techniques, and advanced geospatial analysis techniques, also shared via the web, for assessing and managing urban growth and greening processes is defined. The proposed methodological approach is applied to specific case studies, demonstrating that planners can employ this approach to make informed decisions regarding evaluating and managing urban growth and greening processes to make these processes truly sustainable. The analyses and experiments led within the thesis bring out the need for flexible, innovative, and integrated urban planning approaches that appropriately direct the urban and territorial planning decision-making processes for achieving sustainable and liveable development.
Materials, Processing and Assessment for Bioengineering Applications
(Università della Calabria, 2024-02-02) Sanguedolce, Michela; Mundo, Domenico; Filice, Luigino
Titanium alloys, in particular Ti6Al4V, are the current standard of care for orthopedic implants due to their good biological response. But issues such as infection susceptibility and implant failure due to poor osteointegration and stress shielding persist. Furthermore, orthopedic implant infections are challenging to detect and not always completely solved by systemic antibiotic delivery. Thus, it is essential to develop implants with antibacterial properties to prevent infections and antibiotic resistance due to frequent antibiotic delivery, while promoting integration with surrounding tissues and reducing the revision surgeries rate. Biomaterial-tissue interactions at the implant interface play a crucial role in its operation, influencing tissue attachment. The surface of an implant also affects how bacterial pathogens interact and create biofilms. The complexity of the relationship between biomaterial composition, device design, and biological response in living organisms presents challenges in predicting the outcome of the implant. In vitro methods are valuable but have limitations, necessitating the improvement of predictive models. The focus of this work is modifying the surface of the Ti6Al4V titanium alloy, commonly used in skeletal fixation devices. The goal is to address issues related to poor integration, infection, and metal sensitivity. Surface modification techniques, involving mechanical and thermal mechanisms, are herein explored to provide some guidelines for the prediction and modulation of performance. The studied techniques include grit blasting, milling, electrical discharge machining, laser texturing, and coating deposition. The aim is to deepen the influence of implant surface properties on its performance and biological response, with a multi-level approach: (i) modulate the integration of the implants with surrounding bone tissues by acting on surface properties (i.e. surface roughness, microstructure, chemistry, contact angle), employing material deformation and removal techniques, and studying the effects on in vitro bone cells response; (ii) improve the to date insufficient adhesion of biopolymer coatings made of chitosan by: tuning film properties through different deposition techniques, coating composition, and substrate properties; (iii) preliminary analyze the effect of surface modification techniques on in vitro bacterial response.
Shape Memory Alloy (SMA) connectors for ultra-high vacuum applications: modeling and testing
(Università della Calabria, 2024-06-02) Giovinco, Valentina; Maletta, Carmine; Garion, Cedric; Mundo, Domenico
Shape Memory Alloy (SMA) connectors have been developed at CERN in recent years for Ultra-High-Vacuum (UHV) applications in the Large Hadron Collider (LHC) as an alternative to the traditional coupling provided by metallic flanges tightly connected by several screws or heavy collars. SMA couplers offer many advantages, including low cost, compact size, ease of assembly and maintenance, ability to make bi-material connections, and ability to be remotely controlled by temperature variation, limiting the need for human presence in highly radioactive areas of the accelerator. The working principle of a SMA connector is based on thermoelastic martensitic transformations between two crystallographic structures, austenite and martensite. The object of this project is the testing and modelling of SMAs in order to investigate and describe the macroscopic behaviour of the material. Methods and measurements of an extensive experimental campaign on Nickel-Titanium (NiTi) alloy specimens are herein presented and discussed. Different stress and temperature conditions are investigated, as well as the thermomechanical training of different shaped connectors (rings, ovals, C-shaped) and the constrained recovery capability of ring couplers. Two analytical models based on the elastic-plastic theory of axial-symmetric bodies have been developed to describe the pre-expansion and constrained recovery of SMA rings. Systematic comparisons between the analytical predictions with Finite Element Analysis (FEA) and experimental measurements show very good agreement. Finally, SMA constitutive modelling and FE simulations by a user-defined material model have been performed. Models and results are herein presented. This thesis provides robust tools to be used for the design of SMA couplers with shape recovery capabilities. Keywords: Shape memory alloys, NiTi alloys, vacuum connections, constrained recovery.
Architettura e approccio parametrico. Visioni, invarianti, identità e codici per il progetto
(Università della Calabria, 2024-06-02) Canestrino, Giuseppe; Conte, Enrico; Lucente, Roberta
Development of advanced strategies for modeling, design and virtual sensing of multimaterial metallic-composite robots
(Università della Calabria, 2023-10-10) Capalbo, Enrico; Conte, Enrico; Carbone, Giuseppe; Tamarozzi, Tommaso
Robotic manipulators with lightweight design are becoming increasingly popular given their superior mobility, ease of setup and reduced dangers in case of collisions with humans. In contrast with what traditionally done for bulky manipulators, design of lightweight manipulators requires to take compliance of the components into account. Compliance should in fact be minimized in order to ensure accuracy, while keeping energy usage as low as possible to ensure efficient actuation. The requirements for energy efficiency and stiffness are often contrasting and difficult to address with traditional materials and design methodologies. Great performance improvements can be achieved employing advanced materials such as composites, thanks to their low specific weight and high stiffness. Lightweight manipulators made of composite materials would allow for better dynamic performances, improved safety and reduction of actuation power. The use of composites in robotic applications has been particularly limited both in research and industry, mainly due to the high cost and complex design choices required to avoid damage during machining. Hybrid multimaterial designs have been proposed in literature to solve these issues, with few components in composite materials and the most complex ones in traditional materials. The design of multimaterial mechanical systems results in a complex challenge. Given a set of requirements, their dependency on design parameters is often highly nonlinear and complicated to extract. Furthermore, the solutions require high quality while satisfying numerous and often contrasting requirements. Simulation based on numerical models can predict the performances and in turn enable automated design methods based on optimization algorithms. The numerical models employed in the design phase can then be updated based on experimental data to closely match any physical instance of the systems, constituting a Digital Twin (DT). The availability of a DT enables in turn applications in the operation phases such as Virtual Sensing (VS), which allows to indirectly estimate quantities that can result difficult, expensive or even impossible to directly measure. Models employed for optimization and VS need to satisfy two often contrasting requirements: high accuracy and computational efficiency. Common industrial-level numerical models require large sizes in order to guarantee accuracy, resulting in inefficient simulation and model updating procedures. This work aims at the development of accurate and efficient numerical modeling strategies for multimaterial mechanical systems that enable design optimization and VS applications. The systems on which the methodologies are applied are multimaterial robotic manipulators in which composite materials are employed to achieve high performance and energy savings. The work initially focuses on modeling strategies based on the Finite Element (FE) and Flexible MultiBody (FMB) methodologies. The use of component-level parametric Model Order Reduction (pMOR) techniques allows to define component-level and system-level models with high accuracy and efficiency both in terms of performance evaluation and design update. The proposed methodology is validated showing good results, with particular focus on the model of a 5-DOF robotic manipulator. A multimaterial version of the robotic manipulator is then designed through a MultiObjective Optimization (MOO) technique. The use of the developed efficient system-level models proves fundamental in this phase to grant efficiency and accuracy. The results demonstrate the gains in terms of maneuver accuracy and energy consumption resulting from the use of composite materials. The final part of the thesis employs the models for VS applications based on the Kalman Filter (KF) framework for the joint estimation of states, inputs and material parameters. The methodology is developed both for component-level and system-level applications, allowing to track the evolution of the system in time through a limited set of output-only measurements. A wide set of numerical and experimental validations shows good results.
Numerical modeling of fracture phenomena by means of moving mesh method
(Università della Calabria, 2023-07-15) Ammendolea, Domenico; Critelli, Salvatore; Lonetto ,Paolo
In recent years, the impact of crack evolution on the bearing capac-ity of a structure has become one of the most important features in mod-ern design processes to choose the best structural intervention, which must be as “sustainable” as possible both in terms of the materials used and from an economic point of view. The important advances in computational fields have led to several numerical methods that can accurately reproduce crack propagation phenomena. Most of them have been developed in the framework of the Finite Element (FE) method because of its simplicity and flexibility in analyzing complex structures. Commonly, FE methods are classified into (i) smeared crack models and (ii) discrete crack approaches. Dis-crete crack approaches reproduce internal defects, including strain or discontinuity fields, into finite element formulations. In contrast, smeared crack models account for the presence of cracks at the consti-tutive level by using proper damage laws that degrade the mechanical properties of the material once crack conditions occur. Each method presents negative and positive features, thus denoting that it is some-what challenging to find the best one. Developing advanced approaches ensuring a suitable compromise between low computational costs and reliable predictions is attracting considerable attention from national and international research communities. The present thesis aims to develop a numerical model for reproduc-ing crack propagation mechanisms in different structural components under generalized loading conditions. The proposed methodology com-bines the Moving Mesh (MM) technique and the Interaction integral method (M-integral) in an FE framework. In particular, based on the Arbitrary Lagrangian-Eulerian (ALE) formulation, the MM approach is used for tracing the variation in the geometry of the computational do-main due to the crack advance. More precisely, the mesh node associ-ated with the crack tip is moved consistently with the conditions dic-tated by classic fracture criteria developed in the context of Fracture Mechanics. To ensure the consistency of the mesh point's motion, the proposed strategy uses mesh regularization techniques based on proper rezoning equations. This feature drastically reduces the overall amount of re-meshing events, which typically affect the computational effi-ciency of standard crack propagation procedures, thereby saving rele-vant computational resources meanwhile avoiding convergence issues. Useful solutions to overcome the major issues of traditional FEM pro-cedure for studying crack propagation mechanisms are much sought. Another key aspect of the present thesis is a novel strategy for ex-tracting fracture variables at the crack front, which are necessary for defining crack onset conditions, the direction of propagation, and the crack tip velocity. Specifically, the proposed model uses the M-integral method to extract Stress Intensity Factors (SIFs) at the crack front. In particular, in the framework of the MM strategy adopted, this work in-troduces the ALE formulation of the M-integral. Comparisons with predictions of other numerical methodologies, analytical formulations, and, especially, experimental results are devel-oped to check the reliability and efficacy of the proposed method. In this context, parametric analyses regarding mesh discretization and pa-rameters involved in the numerical model serve to assess the computa-tional efficiency and accuracy in predicting fracture variables and crack trajectories. The results show that the proposed approach is an efficient and robust and numerical tool for reproducing complex crack propaga-tion phenomena. The thesis is organized as follows: chapter 1 contains the introduc-tion, which reports a brief literature review on the fracture phenomena and modeling approaches, the aims and scope. Chapters 2 and 3 present the developed method in a static framework. In particular, chapter 2 depicts the theoretical formulation, the numerical implementation, and the computational procedure, while chapter 3 shows numerical results to assess the proposed strategy's reliability and efficacy. Chapter 4 gen-eralizes the proposed modeling approach to the context of dynamic Fracture Mechanics. Finally, chapter 5 outlines the conclusions and fu-ture perspectives of this work.
Metodi innovativi per la modellazione e la progettazione in zona sismica delle tamponature di edifici in C.A.
(Università della Calabria, 2022-07-20) Donnici, Angelo; Conte, Enrico; Mazza, Fabio
New on-line model for shoreline evolution at beaches composed of not cohesive grains of any size
(Università della Calabria, 2020-02-12) Francone, Antonio; Furgiuele, Franco; Tomasicchio, Giuseppe Roberto; Frega, Ferdinando
Over recent decades, efforts have been made to find robust methods for predicting shoreline evolution near to the coastal structures. This requires a rigorous understanding of the key coastal processes that drive sediment transport, and how they are impacted by the presence of structures. Once this understanding is reached, a method for predicting morphological shoreline evolution is required. In this context, numerical modelling plays an important role. A new one-line model for shoreline evolution at beaches composed of not cohesive grains of any size is proposed: the General Shoreline beach (GSb). GSb model is based on the one-line theory, for which it is assumed that the equilibrium beach profile remains unchanged (Dean, 1990), thereby allowing beach change to be described uniquely in terms of the shoreline position. The longshore sediment transport rate is estimated by means of a general formula/procedure (Tomasicchio et al., 1994; Lamberti and Tomasicchio, 1997; Tomasicchio et al., 2013; Tomasicchio et al., 2015) combining an energy flux approach with an empirical/statistical relationship between the waveinduced forcing and the number of moving units. The uniqueness of the proposed new one-line model consists in the possibility to simulate beach change, including the effects of coastal structures (i.e. groynes, detached breakwaters), at a mound composed of not cohesive grains of any size, from sand to rock units. Despite other existing models, the GSb model presents a calibration factor, KGSb solely and it has been calibrated and verified against field and laboratory data on sandy and mixed beach (sand and gravel) referring to simple groyne and detached breakwater (Ming and Chiew, 2000; Hamilton et al., 2001; Martin-Grandes et al., 2009; Medellin et al., 2018;). Optimal values of KGSb, valid for different types of not cohesive grains and coastal structures, have been reported. It is showed that the GSb model can be considered a reliable engineering tool to conduct morphodynamics studies. A demo version of the GSb model, for Mac and Windows systems, has been released for the scientific community and is available at www.scacr.eu.
A Comprehensive analysis of hydrological benefits of low impact development techniques: experimental investigation and numerical modeling
(Università della Calabria, 2020-03-05) Palermo, Stefania Anna; Furgiuele, Franco; Piro, Patrizia
Urban floods, recently increasing due to the combine effect of climate change and urbanization, represent a potential risk to human life, economic assets and environment. In this context, the traditional urban drainage techniques seem to be inadequate for the purpose, therefore a transition towards an innovative sustainable and resilient urban stormwater management is a valid solution. One promising strategy is the implementation of decentralized stormwater controls, also known as Low Impact Development (LID) systems that provide several benefits at multiple scales. Despite several studies demonstrated the LIDs’ capability in terms of surface runoff reduction, the transition towards a sustainable urban drainage system, which includes these techniques, seems to be very slow. One of the key scientific limiting factors can be found in the lack of comprehensive analyses able to highlight the hydrological performance and the physical processes involved in LID systems at multiple spatial scale and by considering long-term experimental data. The complexity of the physical processes, involved in each specific LIDs stratigraphy, requires modeling tools able to accurately interpret their hydraulic behaviour, as well as to correlate their hydrologic efficiency with the management of stormwater in the surrounding urban area. For these reasons, so far different empirical, conceptual and mechanistic models have been proposed, however in many of these studies, the hydrological parameters, as well as the physical ones were not properly investigated, limiting the analysis only to specific factors, or by considering literature values for the numerical modeling. Thus, principal aim of this thesis is to present a comprehensive analysis of the hydrological benefits of LID techniques by experimental investigation and numerical modeling. To achieve this goal, several analyses were carried out by considering different: LID systems, spatial scales, weather conditions, modeling investigation, as well as mathematical optimization approaches. Monitored data at the full scale implementation and laboratory measurements were used to support the numerical modeling. More in detail, first a global sensitivity analysis (GSA), based on the Elementary Effect Test (EET) was applied to a PCSWMM hydrodynamic model of the University Campus Innsbruck, which combines traditional drainage infrastructures and low impact development techniques, as Rain Gardens. In this regard, main findings have showed that soil hydraulic parameters considered in the model, (i.e., principally Soil Hydraulic Conductivity and Seepage Rate) were the most sensitive parameters. Therefore, the identification of these properties for LID systems is crucial in order to correctly evaluate their hydraulic performance. Starting from this finding the analysis of the hydrological efficiency of a full-scale extensive green roof, located at University of Calabria in Mediterranean Climate was assessed, by considering field monitored hydrological data, as well as soil hydraulic properties evaluated in lab, and a modeling analysis. Thus, first a field monitoring campaign for one year was carried out, and then hydrological performance indices on an event scale were evaluated. The findings have revealed the optimal behaviour of the specific green roof in Mediterranean climate, which presents an average value of Subsurface Runoff Coefficient of 50.4% for the rainfall events with a precipitation depth more than 8 mm. Later, to evaluate the influence of increasing values of substrate depths (6 cm, 9 cm, 12 cm, 15 cm) on green roof retention capacity, the hydraulic properties of the soil materials were first investigated in Laboratory, by the simplified evaporation method, and then considered for the implementation of the mechanistic model HYDRUS 1D. The results obtained in this phase have showed how the considered substrate depths were able to achieve a runoff volume reduction of 22% to 24%. Thus, as the outflow volume reduction achieved by increasing the soil depth was not significant, the ideal depth for specific soil substrate would be 6 centimetres. Following this study, and based on the findings obtained at building scale, next phase was focused on the analysis of hydrological effectiveness of Low Impact development solutions at largeurban scale in a south Italian case study. This investigation was carried out by considering different LID conversion scenarios by a predictive conceptual model (PCSWMM). In this regards, a specific permeable pavement and green roof, developed and installed at University of Calabria, were considered for the model implementation. Globally, modeling results have confirmed the suitability of these LID solutions to reduce surface runoff even if just a small percentage (30%) of the impervious surfaces is converted. By considering all of the findings, previous achieved by experimental and modelig investigation, it emerged that many aspects related to LIDs design and operation, as well as the choice of the facility and its location can affect the results in terms of hydraulic efficiency. In this regard, a mathematical optimization approach to consider several aspects together could be a suitable tool for designers of LID systems and experts in the field. Therefore, in the last part of the work, new Mathematical Optimization Approaches for LID techniques were evaluated. More in detail, the optimization of rainwater harvesting systems, by using TOPSIS (Technique for Order Preference by Similarity to Ideal Solution) and Rough Set method as Multi-Objective Optimization approaches, was carried out. The results have demonstrated that these approaches could provide an additional tool to identify the ideal system. In conclusion, main findings of this thesis confirm the suitability of LID systems for urban stormwater management providing useful suggestions for their design and tools for assessing their hydrological effectiveness, analysing physical and hydrological parameters that affect their operation, introducing advanced concepts for the optimization of LID systems, therefore providing a significant and innovative contribution for the improvement of scientific research in the field and the spread of these sustainable techniques.

Dipartimento di Ingegneria Civile - Tesi di Dottorato

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