1,720,971 research outputs found
3D Printed PEI Cellular Materials: Mechanics, Performances and Piezoresistive Properties
Full text linkL'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
Autonomous sensing architected materials
Full text linkIntegrating autonomous sensing materials into future applications necessitates developing advanced multiscale multiphysics predictive models. This study introduces an experimentally informed predictive framework for autonomous sensing architected materials, combining theoretical and computational methodologies. By incorporating stress-dependent electrical resistivity through anisotropic piezoresistive constitutive effects, alongside considering material, geometric, and contact nonlinearities, the proposed multiscale model captures the architecture-dependent piezoresistive responses of lattice composites produced via additive manufacturing of polyetherimide (PEI)/carbon nanotube (CNT) nanoengineered feedstock. The PEI/CNT composite exhibits exceptional strength (105 MPa), stiffness (3368 MPa), and strain sensitivity (gauge factor ≈13), translating into remarkable piezoresistive characteristics for the PEI/CNT lattice composites, surpassing existing works (gauge factor ≈3 to 11). This multiscale finite element model accurately predicts both macroscopic piezoresistive responses and the influence of architectural and topological variations on electric current paths, validated via infrared thermography analysis. Additionally, an Ashby chart for the gauge factor of PEI/CNT lattice composites suggests their prediction through a scaling law similar to mechanical properties, underscoring the tunable strain and damage sensitivity of these materials. The combined experimental, theoretical, and numerical findings offer critical insights into optimizing piezoresistive composites through architected design, with profound implications for smart orthopedics, structural health monitoring, sensors, batteries, and other multifunctional applications
Multiscale experiments and predictive modeling for failure mitigation in additive manufacturing of lattices
Full text linkAdditive 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
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
DLP printed 3D gyroid structure: Mechanical response at meso and macro scale
No full textRapid prototyping (RP) technology enables the fabrication of complex geometries, making lattice structures increasingly popular. Lattice structures, known as cellular materials, have garnered significant attention over the past two decades due to their ability to optimise mass distribution in components. These structures excel in mechanical properties, catering to energy absorption (bending-dominated structures) and structural performance (stretch-dominated structures). In this paper, we investigate the behaviour of stretch-dominated lattice structures using periodic surface models, specifically focusing on sheet-based Gyroid cells, to allow for a more efficient macroscale modelling. We study cells and scaffolds of different sizes, considering various triply periodic minimal surface thicknesses and relative densities ranging from approximately 0.2 to 0.65. We explore load applications in directions different from the unit cell's principal axes and analyse the strain rate effect on both bulk and cellular material. The lattice structures are manufactured using epoxy resin and digital light processing (DLP) technology. In the range of relative density investigated, both in quasi-static and dynamic conditions, a linear trend is observed for Young's modulus and compression yield strength. To extend the quasi-static results to the dynamic regime, we employ a more generalized normalization technique. This approach divides Young's modulus and compression yield strength by the behaviour of the base material at a specific strain rate, facilitating the correlation of mechanical properties across the two loading regimes. Based on experimental findings, we implemented and calibrated a bi-linear material model for describing, in macroscale, triply periodic minimal surface (TPMS) Gyroid structures. The model coefficients are parameterized with respect to relative density. In addition, the presented material law was compared with that proposed by Gibson-Ashby. Furthermore, we evaluated the anisotropy of both the base material and the unit cell. The first one is done by testing the 3D printed samples in directions different from the printing one, the latter by using the Zener factor. The anisotropy evaluation confirmed the isotropic behaviour of the unit cell within the range of relative density and test conditions investigated. Finally, we perform linear elastic 3D macroscopic and mesoscopic model simulations for combined shear-compression tests using the implemented bi-linear material model and the anisotropic stiffness matrix (obtained through the homogeneous formulation) for the macroscale, and the base material for the mesoscopic one. The results demonstrate the suitability of the proposed equivalent material model for studying the TPMS Gyroid structure in the elastic regime, both in quasi-static and dynamic states. This allows for an efficient FE modelling process of complex lattice structures
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
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
Topology-engineered piezoresistive lattices with programmable strain sensing, auxeticity, and failure modes
Full text linkThis study investigates the programmable strain sensing capability, auxetic behaviour, and failure modes of 3D-printed, self-monitoring lattices made from in-house-engineered polyetheretherketone (PEEK) reinforced with multi-walled carbon nanotubes (MWCNTs). A skeletally parametrized geometric modelling framework, combining Voronoi tessellation with 2D wallpaper symmetries, is used to systematically explore a vast range of non-traditional, non-predetermined topologies. A representative set of these architectures is realized via fused filament fabrication, and multiscale characterization—including macroscale tensile testing and microstructural analysis—demonstrates tuneable multifunctional performance as a function of MWCNT content and unit cell topology. Real-time electrical resistance measurements track deformation, damage initiation, and progression, with the sensitivity factor increasing from below 1 in the elastic regime (strain sensitivity) to as high as 80 for PEEK/MWCNT at 6 wt% under inelastic deformation (damage sensitivity). Architecture–topology tailoring further allows fine-tuning of mechanical properties, achieving stiffness values ranging from 9 MPa to 63 MPa and negative Poisson's ratios between −0.63 and −0.17 at ∼3 wt% MWCNT and 25% relative density. Furthermore, a novel piezoresistive finite element model, implemented in Abaqus via a user-defined subroutine, accurately captures stress-induced intrinsic piezoresistivity, geometry-driven deformation, and damage evolution up to the onset of ligament failure. Together, the experimental results and predictive modelling enable “design for strain-sensitivity” and “design for failure”, demonstrating how architecture–topology tuning can be leveraged to tailor strain sensitivity, auxeticity, and failure modes—ultimately guiding the development of multifunctional piezoresistive architected composites for applications such as smart orthopaedic implants, aerospace skins, and impact-tolerant systems
Adaptive twisting metamaterials
Full text linkNext-generation protective systems require adaptive materials capable of reconfiguring their response to impact type and severity, thereby offering multiple force–displacement pathways. Here, the study introduces twisting metamaterials, a subclass of architected lattices whose mechanics are captured by micropolar elasticity. Derived from twisting operations on primitive lattices, these structures exhibit geometry-induced torsional actuation and nonlinear responses, enabling adaptive crashworthiness. A multiscale predictive framework—combining Cosserat continuum mechanics, finite element modeling, and experiments—demonstrates its viability. Twisting sheet-based gyroid structures (10% relative density) are additively manufactured in FE7131 steel and tested under quasi-static and dynamic compression with varied torsional constraints, revealing adaptive energy absorption. When rotation is constrained, the structures achieve high axial stiffness (4.8 GPa), collapse stress (21 MPa), and specific energy absorption (15.36 J g⁻¹), while free-to-twist and over-rotation conditions reduce these values by up to 25%, 24%, and 33%, respectively. A macroscale model captures both axial and torsional responses, while SEM and µCT analyses of process-induced defects inform a parametric finite element study extended to 5% and 15% relative densities. Mapping their performance onto an Ashby chart highlights twisting metamaterials as a promising class of mechanically adaptive, crashworthy materials for advanced protection systems in automotive, rail, aerospace, and defence applications
Exploring Tensile and Compressive Properties of SLMed CuCrZr Alloy at High Strain Rates
No full textThe CuCrZr alloy has garnered significant interest as a promising material for additive manufacturing, particularly in applications requiring high strain rate performance. Such applications include vertical targets like heat sinks in the ITER divertor and actively cooled plasma-facing components, where these alloys serve as structural materials. Although the dynamic behaviour of additively manufactured materials is an expanding area of study, the high strain rate properties of CuCrZr remain not exhaustive and require further investigation. This study presents the results of quasi-static and dynamic tension–compression tests conducted at various strain rates on CuCrZr alloy specimens in their as-built condition. The alloy was fabricated using laser powder bed fusion (L-PBF) with selective laser melting (SLM) technology. Compression samples were designed with standard cylindrical shapes, whereas tensile sample geometry was tailored to meet dynamic testing requirements. The study involves the calibration of an improved Johnson–Cook constitutive model through inverse analytical and numerical procedures. Dynamic increase factors (DIFs) were also evaluated using phenomenological and physical model parameters. The findings indicate that CuCrZr alloy exhibits strain rate sensitivity, which activates above a certain threshold. This was confirmed by a reconstructed dynamic fracture locus, which was consistently higher than the quasi-static locus across all stress triaxiality values
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