12,712 research outputs found
Integrated digital survey methodologies for the knowledge and enhancement of the ancient city walls. The “Curtain” of Santa Chiara in Cagliari (Italy)
No full textThe contribution shows some results of a multidisciplinary research in which architectural surveying and representation methods are supported by archival documents analysis. The procedure is applied in a limited area of the ancient walls of Cagliari (Sardinia, Italy). The sector consists in the meet point between the sixteenth century bastion called “Curtain” of Santa Chiara realized in the period 1575-1578 by the military engineer Giorgio Paleari and the curtain of de Cardona commissioned by the Viceroy in the 30s of the same century. The historical documents indicates the presence of medieval structures, vaulted chamber and passages designed and built during this period. This source, supported by the knowledge of construction techniques indicated in the military treaties, allows a first graphic representation of the sixteenth century bastion, of which today we can only recognize a part of the vaulted gun chamber positioned along the curtain of de Cardona
Investigation on Homogeneous Modeling of Gyroid Lattice Structures: Numerical Study in Static and Dynamic Conditions
No full textThe TPMS (triply periodic minimal surface) are receiving great attention for production of open cell scaffold structures, for example in biomedical applications. In this paper stretch-dominated lattice structures have been considered. The Gyroid cell made of epoxy resin by DLP technology was analyzed. The compression test results in quasi-static (10-3 s-1) and dynamic (4x102 s-1) conditions have been used to compute the macroscopic cellular material properties by the homogenization methods. Finally, in order to evaluate the behaviour of the unit cell under multi-axial stress state, combined shear-compression tests have been carried out as well.</jats:p
High Strain Rate Tests by a 90 m Long Tension-Torsion Hopkinson Bar
No full textThis work describes the design, construction, and first experimental results of an innovative device of the Hopkinson bar type with a length of 90 m for performing high strain rate tests on metals in a combined tension-torsion state. Analogously to the classic split Hopkinson bar technique, the system configuration consists of three bars: a pre-stressed bar, an input bar, and an output bar; the measurement is also based on the classical three-wave method, where the incident, transmitted, and reflected waves are measured. The length of the bars is designed so that the tensile wave reaches the sample from the output bar side at the same time as the torsion wave comes from the input bar. A successful test has been conducted on a hollow aluminum sample; it has been possible to measure the tension-torsion stress-strain curves; in addition, the dynamic equivalent stress-equivalent strain curves have been evaluated
Simple multiaxial tests to assess dynamic ductility of 17-4PH
No full textTo investigate material ductility, the use of simple multiaxial specimens which can be
tested through a common tensile machine or by a Split Hopkinson bar facility would allow
avoiding the use of more complex equipment to induce different stress states in the investigated
material. In this work, experimental dynamic tests have been performed on four different specimen
geometries on a 17-4PH steel by a direct Split Hopkinson Bar (SHB). Finite element models of
the experiments are set up and used jointly with experimental data to calibrate and validate a strain
rate dependent plasticity model, and to extract the local values of stress and ultimate strain in the
most critical point of the samples, at fracture. These latter results allowed the calibration of a
ductile damage model, whose predictions, compared with a previous calibration using tests carried
out in quasi-static conditions, confirmed the effectiveness of the proposed specimens and test
methodology to assess material ductility under dynamic conditions
3D Printed PEI Cellular Materials: Mechanics, Performances and Piezoresistive Properties
No full textL'attività di ricerca ha l'obiettivo di valutare le potenzialità meccaniche e multifisiche di materiali cellulari in polietereimmide ottenuti tramite manifattura additiva. Un'estesa ricerca in letteratura sulla polietereimmide e sui suoi compositi indroduce l'attività di ricerca su questo polimero a dimostrazione dell'attualità e dell'importanza dello studio intrapreso.
L'attività di ricerca propone la stampa 3D di strutture cellulari tramite tecnologia a deposizione di filamento fuso e ne studia le loro prestazioni meccaniche confrontandole con la letteratura.
Successivamente, lo studio della meccanica del materiale ottenuto con questa tipologia di stampa viene affrontata e sfruttata per predire il comportamento meccanico tramite simulazioni numeriche delle strutture stampate. I risultati numerici vengono pertanto confrontati con i risultati sperimentali ottenuti in precedenza.
L'attività di ricerca si conclude arricchendo il lavoro con l'introduzione di una modellazione numerica del comportamento piezoresistivo di strutture composite in polietereimmide sulla base del precedente. Il modello multifisico permette di valutare le potenzialità piezoresistive di queste strutture cellulari e discutere sulle possibili migliorie da apportare. In conclusione, strutture cellulari in composito di polietereimminide vengo stampate e un confronto dei risultati numerici e sperimentali in termini di prestazioni meccaniche e piezoresistività viene affrontato.The research activity aims to evaluate the mechanical and multiphysics properties of cellular materials in polyetherimide obtained through additive manufacturing. An extensive literature review on polyetherimide and its composites drives research on this polymer, demonstrating the relevance and importance of the study undertaken. The research activity proposes the 3D printing of cellular structures by fused filament fabrication technology and studies their mechanical performances by comparing them with the literature. Subsequently, the study of the mechanics of the material obtained with this type of 3D printing is faced and exploited to predict the mechanical behaviour through numerical simulations of the printed structures. The numerical results are therefore compared with the experimental results previously obtained. The research activity concludes by enriching the work by introducing numerical modelling of the piezoresistive behaviour of composite structures in polyetherimide based on the previous one. The multiphysics model allows us to evaluate the piezoresistivity of these cellular structures and discuss possible improvements to be made. In conclusion, cellular structures in polyetherimide composite are 3D printed and a comparison of the numerical and experimental results in terms of mechanical performance and piezoresistivity is addressed
Multiscale experiments and predictive modeling for failure mitigation in additive manufacturing of lattices
No full textAdditive Manufacturing (AM) empowers the creation of high-performance cellular materials, underscoring the increasing need for programmable and predictable energy absorption capabilities. This study evaluates the impact of a precisely tuned fused filament fabrication (FFF) process on the energy absorption and failure characteristics of 2D-thermoplastic lattice materials through multiscale experiments and predictive modeling. Macroscale in-plane compression testing of both thick- and thin-walled lattices, along with their µ-CT imaging, reveal relative density-dependent damage mechanisms and failure modes, prompting the development of a robust predictive modeling framework to capture process-induced performance variation and damage. For lower relative density lattices, an FE model based on the extended Drucker–Prager material model, incorporating Bridgman's correction with crazing failure criteria, accurately captures the crushing response. As lattice density increases, interfacial damage along bead-bead interfaces becomes predominant, necessitating the enrichment of the model with a microscale cohesive zone model to capture interfacial debonding. The predictive modeling introduces an enhancement factor, offering a straightforward method to assess the impact of the AM process on energy absorption performance, thereby facilitating the inverse design of FFF-printed lattices. This approach provides a critical evaluation of how FFF processes can be optimized to achieve the highest attainable performance and mitigate failures in architected materials
Inverse FE Analysis of Combined Tension–Torsion Tests Performed with a 90 m Hopkinson Bar
No full textIn this work, the results coming from the recently developed Split Hopkinson Tension–Torsion Bar have been post-processed according to finite element model updating approach. The aim is to assess the elastoplastic constitutive behaviour of the material subjected to a multiaxial state of stress in the framework of large deformations. The experimental test consists in the application of a simultaneous tensile and torsional load to a hollow cylindrical-shaped sample; pure tension and pure torsion tests have been conducted as well. Both displacement (elongation and twist angle) and load (axial force and torque) values are measured. In the tests with the Split Hopkinson Tension–Torsion Bar, an average strain rate of 100/s was reached. In addition, analogous tests with similar load-torque ratios were performed with a quasi-static multiaxial machine. The experimental test was replicated in an Abaqus/Explicit FEM model, where the constitutive parameters are iteratively varied until an adequate match was obtained with the experimental observations in terms of force–displacement law. In particular, a power law was used for the strain hardening description, combined with the classical von Mises yield criterion. The material of the sample was AA7075T6, whose Johnson–Cook strain rate sensitivity parameters were borrowed from the literature. A reasonably good matching was achieved between the numerical and experimental load–displacement and torque-rotation, meaning that the classical von Mises plasticity describes quite well the plastic behaviour of the material; the model was also able to capture the effect of the non-proportional loading path applied in the combined tension–torsion test
Inverse Identification of the Post-Necking Behavior of Metal Samples Produced with Additive Manufacturing
No full textAdditive manufacturing (AM) is undoubtedly the fastest-growing technology in the field of component productions. In particular, metal AM is rapidly emerging thanks to its enormous potentiality in manufacturing components with complex shapes and high structural performances. Although the precision and the rapidity of the production process is continuously improving, the performance of the final components in terms of crashworthiness and mechanical properties is still under evaluation. In this work, several specimens were manufactured using metal AM, in particular the Selective Laser Melting (SLM) method was employed. The used material is steel. All specimens have the same dimensions, but they were created using different paths of the laser source with respect to the metal powder layers during the AM process. Afterwards, the specimens were subjected to tensile test and the deformation field was measured using Digital image Correlation. The post-necking behavior as well as the anisotropy were evaluated using the Virtual Fields Method. It turned out that the laser paths used during the forming process have an impact on the plastic flow at large deformation up to the final fracture. The variance of the mechanical properties and the experimental uncertainties are discussed thoroughly
Dynamic Piezoresistive Behaviour of Composite Materials: Experimental Testing and Analytical Modelling
No full textNowadays, additive manufacturing technologies allow coupling peculiar material properties with complex shapes to obtain cellular materials capable of exhibiting advanced multi-functionalities. Among them, self-sensing materials are increasingly valuable for applications where structural integrity monitoring is needed without external measurement instru- ments. This study exploits the piezoresistive properties of composite materials coupled with their own 3D-printed shapes. Therefore, understanding and modelling piezoresistive behaviour is getting a need. The piezoresistive behaviour of 3D printed composite material has been investigated under quasi-static and dynamic compression loadings. An innovative split Hopkinson bar set-up is introduced in order to measure the change in electrical resistance of composite material during the high strain rate compression. The strain rate and temperature effects on the material’s piezoresistivity behaviour are discussed. Based on experimental evidence, a strain rate-dependent parameter is introduced into piezoresistivity analytical theory. The analytical findings are compared with the experimental ones
Rappresentare l’architettura militare tra ‘antichi’ linguaggi e nuove frontiere. Le mura di Cagliari in Età Moderna
No full textLa cinta muraria di Cagliari costituisce un importante esempio di architettura militare, tutelata per il suo valore storico-ambientale e paesaggistico, della quale conserva la forma impostata dagli Spagnoli nella metà del Cinquecento e le opere volute dai Piemontesi nel corso del Settecento. In particolare la sequenza di opere “alla moderna”, che dal bastione Santa Croce si susseguono lungo l’asse nord-sud in direzione del bastione Balice, e gli ampliamenti situati nel settore nord e nel settore orientale costituiscono il risultato di una serie di trasformazioni che hanno ridisegnato e ampliato la linea difensiva sostenendo logiche insediative, religiose e militari.
L'attuale conformazione di sito pluristratificato custodisce le testimonianze dei diversi passaggi che hanno " ridisegnato e scolpito" le forme dei luoghi e creato un paesaggio che connota fortemente il quartiere Castello e la città stessa.
Una tutela consapevole di un patrimonio storico caratterizzato da valori e criticità richiede una conoscenza approfondita delle trasformazioni avvenute e un'analisi delle dinamiche in atto, affidata ad indagini multidisciplinari. Lo studio dei diversi aspetti utili a garantire una consapevole gestione del patrimonio storico è tuttavia nelle mani degli specialisti, padroni di un linguaggio -a volte di difficile comprensione per i profani- che necessita di mezzi di rappresentazione appropriati al fine di favorire una più ampia diffusione e una maggiore consapevolezza dei valori.
Una rappresentazione che fino all'Ottocento è stata principalmente finalizzata alla descrizione del progetto architettonico oltre che alla documentazione dei luoghi, come nei taccuini dei viaggiatori.
Tuttavia, la complessità della stratificazione storica della città contemporanea richiede l'utilizzo di un linguaggio strettamente tecnico e di un'illustrazione scientifica che a volte sacrifica gli aspetti legati alla divulgazione.
Il passaggio dal modello puramente tecnico a un modello di facile lettura diviene uno degli obiettivi di una più ampia ricerca -presentare e illustrare le trasformazioni urbane- che trova nella piazzaforte di Cagliari un'opportunità per esplorare le diverse modalità di analisi grafica e di linguaggi affidati a strumenti tradizionali e digitali, anche integrati.The city walls of Cagliari are an important example of military architecture protected for its historical-environmental and landscape value.
The actual conformation of a multi-layered site preserves the signs of the different changes that have "redefined and sculpted" the shapes of the places creating a landscape that strongly characterize the Castello district and the city itself.
The sequence of bastions located in the north and in the western sector of Castello, in particular, is the result of a series of urban transformations that have redesigned and expanded the defensive line by supporting settlement, religious and military reasons.
A conscious protection of a landscape characterized by values and criticalities requires an in-depth knowledge of the transformations happened and an analysis of the dynamics in progress, entrusted to multidisciplinary investigations. However, the knowledge of the many aspects useful to guarantee a mindful management of the historical heritage is in the hands of specialists, masters of a language -sometimes difficult to understand for the layman- that needs appropriate means of representation to support a wider dissemination aimed to a bigger awareness of values.
A representation that until the nineteenth century was mainly aimed to describe the architectural project as well as the documentation of the places in travelers' notebooks.
However, the complexity of the historical stratification of the contemporary city requires the use of a strictly technical language and a scientific illustration that sometimes sacrifices the aspects related to disclosure.
The transition from the pure technical model to a model easy to read is one of the objectives of a broader research -representing and illustrating urban transformations- which finds in the stronghold of Cagliari an opportunity to explore the different ways of graphic analysis and languages entrusted to traditional and IT tools, including integrated ones
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