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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.
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Non-destructive material investigation: advanced techniques across disciplines
(Università della Calabria, 2025-01-03) Crocco, Maria Caterina; Cipparrone, Gabriella; Agostino, Raffaele Giuseppe; Guzzi, Rita
The advancement of experimental physical techniques has significantly improved the study of materials across a range of scales, from micro to macro, and has allowed for probing various material characteristics with remarkable precision. Among these techniques, X-ray microtomography and Fourier transform infrared (FTIR) spectroscopy stand out as powerful tools that provide critical insights into the structural and molecular properties of materials. This thesis investigates the complementary applications of these techniques across multiple scientific disciplines, including biology, engineering, and photonics. X-ray microtomography offers high-resolution, non-destructive imaging capabilities, enabling the detailed visualization of internal structures of materials. In contrast, FTIR spectroscopy provides molecular-level information through the identification of vibrational modes, offering a deeper understanding of chemical composition and bonding environments. By combining these techniques, it is possible to bridge the gap between structural and chemical analysis, thus achieving a more holistic characterization of complex systems. This thesis presents a detailed exploration of how the integration of X-ray microtomography, FTIR spectroscopy, and other experimental methods can lead to a more comprehensive understanding of diverse classes of materials. Through case studies in biological sample analysis, defect analysis in engineering materials, and the characterization of optical fibers, this work demonstrates the synergistic potential of these techniques. The overall findings underscore that a multidisciplinary and integrated approach, utilizing advanced physical techniques, not only enriches scientific understanding but also fosters technological innovation across various fields. Keywords: X-ray microtomography, Fourier transform infrared spectroscopy, biological systems, engineering, photonics research, multiple sclerosis, hearts, cells.
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Late pleistocene coastal sea surface temperature and environmental reconstruction for a post global-warming climate modelling in the central mediterranean
(Università della Calabria, 2024-07-30) Santagati, Pierluigi; Critelli, Salvatore; Perri, Edoardo; Bernaconi, aria Pia
The Last Interglacial (MIS 5) is a warm period within the Late Pleistocene. In particular, its first substage (MIS 5e) is the last warmer than today period before the present-day Interglacial, therefore it is considered a good analogue for assessing future climate responses to global warming. The present work focuses on two shallow marine deposits cropping out along the Ionian Sea coastline, central Mediterranean: 1) a MIS 5e fossiliferous calcarenite from Taranto (Apulia), and 2) MIS 5a/c bioconstructed deposits from Capo Colonna (Calabria). These deposits were studied for a paleoenvironmental characterization, which included the paleoecology of benthic associations, paleotemperature estimates and early diagenetic phenomena, with the aim of providing new data on the response of these systems to climatic variations. The MIS 5e calcarenite from Taranto, sampled in three related sites cropping out along the Mar Piccolo (MP) coastline (Masseria La Penna, Mass. S. Pietro, and Il Fronte), returned a rich molluscan fauna consisting of 120 extant species and 5174 individuals, including four of the tropical Senegalese Fauna, today absent in the Mediterranean. The molluscan assemblages were used for a refined quantitative palaeoenvironmental reconstruction; as a whole, the fauna represents an autochthonous-parautochthonous assemblage coming from a sandy-vegetated infralittoral bottom, locally accompanied by coarser and less finer sediment fractions, and characterized by slight lateral variability, shifting from more sheltered and exposed areas, and from finer and coarser bottoms, suggesting a heterogeneous and well-structured palaeoenvironment during MIS 5e. The same molluscan assemblage was used for a multi-proxy palaeoclimatic study. The biogeographic-climatic affinity of the assemblage shows, compared to today, a double percentage of warm affinity species, while the cold affinity species are similarly represented, indicating a warmer but not strictly tropical Sea Surface Temperature (SST). This is confirmed by the most recurring preferred SST ranges of the assemblage, indicating an average of 20 °C. The skeletal compositions of five well-preserved molluscan and coral specimens were analyzed for trace elements and stable isotopes for further mean SST estimations. From the comparison of the results of several equations available in literature, it appears that only some SST estimations are realistic, converging into similar values of, on average, 20.8 ± 0.9 °C. Considering all the used proxies, the MIS 5e SST difference compared to today falls in the range 1.2 - 2.0 °C for the Gulf of Taranto (GT) (being a more reasonable scenario) and 2.0 - 2.8 °C for the MP. This is not a firmly tropical-like SST setting as suggested by the sole Senegalese fauna, indicating at least 2.7 °C to 3.5 °C more than to today’s GT and MP, respectively. The approximations and assumptions made for obtaining SST values with any single proxy indicates the need of a multi-proxy approach to define the best SST estimation. Cemented samples of the same MIS 5e calcarenite were analyzed through optical and SEM analyses. Clasts mostly consist in medium to coarse sandy size skeletons and fragments of skeletons of a variegated biota together with mainly large mollusks shells that inhabited the sediment and a very minor amount of siliciclastic. Micritization variably affects most of the bioclasts while cements are constituted by a microcrystalline texture with various micro-morphologies and fabrics: not-isopachous aphanitic and filamentous rims, vacuolar peloidal meniscus, aphanitic micro-mounds, and aphanitic porosity-filling matrix. Cements are constituted by sub-micron sized anhedral to nanospheroidal crystals of low Mg calcite, mixed with a minor amount of irregular platy crystals of saponite. All fabrics of cement are rich of mineralized filamentous, tubular, and sub-spherical bacteria bodies that imply the presence of a microbial community forming an epilithic to endolithic biofilm that stabilized the incoherent sediment and mediated the early precipitation of cements. This process led to the synsedimentary hardening of some parts the mobile sandy substrate, allowing the settlement of sessile taxa - such as Spondylus gaederopus, oysters, serpulids and barnacles. The Last Interglacial (MIS 5) transgressive-regressive deposits of the Capo Colonna marine terrace provide a good fossil example of a Central Mediterranean infra/circa-littoral setting, characterized by both calcareous coralline algae-dominated low-relief bioherms and biostromes, analogous respectively to the present coralligenous and mäerl habitats. The skeletal primary framework of the bioherms consists of laminar to massive encrusting coralline red algae acting as main bioconstructors, with minor bryozoans, encrusting foraminifera and serpulids as secondary frame-builders. Whereas the autochthonous mäerl tabular beds are mainly composed of free-branched coralline red algae rudstones. A variable amount of sandy bioclastic sediment is laterally interbedded with the bioconstructions and tends to be entrapped in their cavities and pockets. All sedimentary sub-facies of the bioconstructions and associated sediment, are rich in autochthonous syn-sedimentary microbial-mediated micrite, forming aphanitic, peloidal, clotted peloidal, and filamentous fabrics. Microbial micrite can also trap and bind a variable amount of grains or being a secondary component of the sandy detrital sediment with micritic rims surrounding the clasts. All these early-lithified micrites show the typical nanostructure of the primary microbial-mediated carbonates, rather than a detrital mud particles accumulation, as they consist of nanospheres coalescing into subhedral microcrystals, replacing, and mineralizing both microbial cells (present with several morphological types) and extracellular substances. This in turn implies the widespread presence of benthic lithifying microbial biofilms that colonized both the cavities of the skeletal framework of the bioconstructions, and the intergranular space of the associated sediment. These microbial communities, thanks to the metabolic processes of the microorganisms that induced the carbonate precipitation, significantly contributed to the early cementation of all the studied deposits. In conclusion, the results of the work were used to infer possible effects of climate change in similar Mediterranean contexts. The diversity and temperature preferences of the MIS 5e molluscan assemblage from Taranto show no significant differences compared to modern analogous faunas from some Southern Italy sites reported in the literature, which could show a resilient response to an SST increase of +2 °C, already experienced during MIS 5e and expected in the next decades. This, however, does not consider the different causes, the current higher warming rates, as well as the human impact, which could affect faunas more than the temperature itself. Today, microbial induced micritic cementation processes, similar to those reported in the studied MIS 5 deposits, are observed in tropical/subtropical carbonate platform realms and have not been indicated for similar infra-circalittoral beds of the modern Mediterranean. Their occurrence in MIS 5 deposits confirms the warmer SST during MIS 5e and suggests a persistently warm SST at the end of MIS 5. However, as these cements have been associated with an estimated SST of just +2 °C compared to modern times, it is suggested that early cementation could become common in the Mediterranean mobile bottoms already in the near future as an effect of the global warming.
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Risks and impacts of mercury use in gold mining in Ecuador
(Università della Calabria, 2024-04-30) Mestanza Ramón, Carlos; Critelli, Salvatore; Straface, Salvatore; D'orio, Giovanni; Montoya, Alex V. Gavilanes
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Definition and application of methodological protocols for the conservation and protection of cultural heritage: case studies
(Università della Calabria, 2024-04-15) Donato, Antonio; La Russa, Mauro; Costanzo, Antonio; Buongiorno, Maria F.; Critelli, Salvatore