2,013 research outputs found
HYBRID STEEL FIBER REINFORCED CONCRETES: EFFECTS OF ELEVATED TEMPERATURE AND WATER RE-CURING ON THE MECHANICAL PERFORMANCE
No full textThis study investigated the effect of elevated temperatures and water re-curing on the mechanical response of hybrid steel fiber reinforced concretes. The first part of the study examines the effect of various steel fiber hybridizations on the compression, tension, shear and fracture behavior of fiber reinforced concretes at room temperature. The second part details the effects of elevated temperature and water re-curing on the compression performance and fracture process of hybrid steel fiber reinforced concretes. The results indicated an increase of the damage as the temperature increased. However, a considerable reduction of damage was obtained after water re-curing. Exposure to temperatures exceeding 200 °C had a negative impact on fracture toughness. The exposition to elevated temperatures and water re-curing modified the fracture process of hybrid fiber reinforced concrete. For temperatures above 200 °C, the branching fracture appeared around the peak load level. Water re-curing reduced the branching effect and prevented the formation of multiple cracks in thermally damaged hybrid fiber reinforced concrete
Tradução de uma disputa : Christophe versus Pétion em La tragédie du roi Christophe, de Aimé Césaire
No full textEsta contribuição propõe a tradução comentada da primeira cena da peça de teatro La Tragédie du roi Christophe (A tragédia do rei Christophe), de Aimé Césaire. O texto foi publicado pelo autor martinicano em 1963 e encenado a partir de 1964. A história aborda o embate histórico entre os dois líderes revolucionários haitianos, Alexandre Pétion (1770-1818) e Henry Christophe (1767-1820), após o estabelecimento da independência do Haiti, em 1804. O ex-escravizado Henry Christophe I, autoproclamado rei do Haiti em 1811, protagoniza, na peça, os impasses políticos decorrentes do processo de descolonização para a constituição de um novo estado haitiano livre e democrático. Optamos por traduzir a cena que anuncia e ilustra, na abertura do primeiro Ato, o caráter trágico que permeia o desenrolar dos eventos.This contribution proposes the commented translation of the first scene of the play La Tragédie du roi Christophe (The tragedy of King Christophe), by Aimé Césaire. The text was published by the Martinican author in 1963 and staged from 1964 onwards. The story addresses the historical clash between the two Haitian revolutionary leaders, Alexandre Pétion (1770-1818) and Henry Christophe (1767-1820), after the establishment of Haitian independence in 1804. The ex-enslaved Henry Christophe I, self-proclaimed King of Haiti in 1811, stars, in the play, political impasses resulting from the decolonization process, for the constitution of a new free and democratic Haitian state. We chose to translate the scene that announces and illustrates, in the opening of the first Act, the tragic character that permeates the unfolding of events
Dual-sinusoidal placement of fibre-optic sensors for fine SHM of composite structures
No full textThe integration of permanent distributed fibre-optic sensors (FOSs) into large-scale composite structures enables real-time remote monitoring of their internal health conditions. To address the drawbacks in employing embedded FOSs for accurate structural health monitoring (SHM), a new concept of dual sinusoidal
placement has been proposed to maximise monitoring coverage whilst minimising sensor count. Despite existing research, further simulation and testing are necessary to fully characterise the mechanical and sensing behaviour of the constructed smart composites across diverse loading conditions. Therefore, this work focuses on studying the strain patterns and sensing advantages resulting
from a dual-sinusoidal placement of FOSs in fibre reinforced composites. A detailed finite element modelling of coupon-level composite specimens with and without embedded FOSs assesses the dual sinusoidal placement in terms of its mechanical influence on host materials and monitoring advantages
across various loading scenarios. Results highlight the strain measurement advantages of the dual sinusoidal placement compared to linear and single sinusoidal patterns. This research benefits future applications in large-scale smart composite structures by discussing the balance between mechanical effects, sensing functions, and monitoring coverag
Experimental investigation of vertical human structure interaction for FRP footbridges
No full textFor the further development of prediction models for crowd-induced vibrations, it is imperative to
obtain realistic and detailed information regarding representative loading conditions. Current
guidelines only consider the force induced by crowds, neglecting the fact that the human body is a
mechanical system that interacts with the supporting structure. Recent research shows that these
human-structure interaction (HSI) effects, such as added mass and damping are significant when
assessing vibration levels for footbridges. HSI phenomena have been assessed for crowd‐to‐structure
mass ratios which are typical for steel footbridges. This work discusses a first step into the further
development of models considering HSI effects for higher crowd-to-structure mass ratios, as
encountered for fiber reinforced polymer (FRP) footbridges by experimentally investigating the
change in modal parameters due to the presence of persons on an FRP footbridge. The results show
that the largest changes in modal parameters is observed when the persons take on a posture with
slightly bent legs, similar to the body posture during walking. For a density of approximately
1 person/m², a decrease of 22% is found for the fundamental natural frequency and an increase up to
21% is found for the corresponding modal damping ratio. Compared to the damping ratio of 2.8% for
the empty footbridge, the increase in effective damping ratio is considerable and expected to have a
significant impact on the vibration serviceability assessment of this footbridge
DELAMINATION CLASSIFICATION IN COMPOSITE PLATES USING GUIDED WAVES AND 1D-CNN
No full textThis study assesses the effectiveness of Ultrasonic Guided Waves (UGWs) combined with a 1D Convolutional Neural Network (1D-CNN) for detecting and classifying delamination in carbon fiber reinforced polymer (CFRP) laminates. A dataset of 912000 waveforms from undamaged and damaged CFRP plates was analyzed using a shallow 1D-CNN with two convolutional blocks and a fully connected layer, designed for computational efficiency and robust generalization. The model processed data with a 70-30-10 split for training, validation, and testing, achieving an average accuracy of 90.27%. The analysis showed high recall and precision rates - over 90% in about 75% of classes and over 95% in about 40% of the classes. These metrics were particularly significant when the waveforms propagated parallel to the fiber direction: averaging Precision, Recall, and F1-Score at 96.2%. They highlighted the effectiveness of the model over a range of delamination depths and orientations. However, performance differences were observed in cases with deeper delamination and perpendicular wave propagation due to suboptimal wave excitation. These results highlight the potential of 1D-CNNs to effectively classify complex UGW signals for real-time health monitoring of structural composite components
Understanding Fatigue Delamination Crack Growth in a Wind Turbine Rotor Blade Through an Element Testing
No full textA novel element test specimen, considered to be representative of a thick composite laminate in a wind turbine rotor blade, is investigated in cyclic loading for fatigue delaminations. The element test specimen has an embedded artificial defect to mimic the delaminations in the spar cap of a 31 m wind turbine rotor blade. The aim was to measure the growth rate of delamination cracks and the temperature rise during the cracks propagation. It was noticed that four delamination cracks initiated and propagated, out of which two cracks were along the embedded defect interface planes and the other two originated from the crack-tips of a transvers tunneling crack in the resin pocket. The initial difference in the crack lengths of the four cracks translated throughout the cyclic loading. Initiation and propagation of multiple delamination cracks documented by the optical images were well correlated by the temperature distribution recorded from the thermal images
In-line monitoring of the fused filament fabrication additive manufacturing process for fibre-reinforced polymer matrix composites.
No full textIn the present work, a novel combination in-line monitoring methodology including Infrared Thermography (IR) and acoustic emission (AE), benchmarked against micro-computerised tomography was developed for the monitoring of the FFF AM process manufacturing pure polymer, short fibre-reinforced and continuous fibre reinforced polymer matrix composite samples. The method allows for the detection of anomalies during the printing process and the verification of their presence after printing without the need for destructive testing. For both the in-line monitoring, the correlation between the printing parameters and the presence of defects and anomalies was investigated.
It was found that the in-line monitoring method can detect anomalies during the printing process and can provide information on the efficacy of the printing. This is substantiated by the presence of defects found during the offline assessment. It was also concluded there was a correlation between the structural integrity and print quality of the printed samples and their printing parameters which was identified during the in-line monitoring work
Automated generation of labeled synthetic training data for machine learning based segmentation of 3D-woven composites
No full textA novel pipeline for the generation of synthetic tomograms of woven composite materials, to be used for training of machine learning based segmentation algorithms is presented. The pipeline is completely based on open source software and heavily utilizes the graphical processing unit for fast data generation. The proposed method generates a surface mesh of the woven geometry, scans it, reconstructs the scan, and generates a voxel labeling of the generated tomogram. It is demonstrated that the method can generate images that show good agreement with experimentally produced x-ray computed tomography images of a 3D-woven carbon fiber reinforced polymer composite
Fuzzy overbraids for improved structural performance
No full textOverbraiding is used as a reinforcement in two example systems. This includes both standard and ‘fuzzy’ overbraids, the latter created by braiding a brittle fibre at short lay length over a central component; when incorporated into a fibre-reinforced composite increases the resin-matrix contact zone. The fuzzy aspect is therefore expected to improve structural performance.Hierarchical composites, inspired by nature, can be created using pultruded rods as an element, with a hierarchy of fibres at the shorter length scale forming rods at the medium scale and a larger structure then created from these rods. Overbraiding of the pultruded rods is shown to improve their performance under compression.Microvascular channels, used for cooling, can be created in a composite laminate through a lost poly(lactic acid) process. Overbraiding of the poly(lactic acid) results in reinforced microvascular channels, with a fuzzy carbon overbraid demonstrating an order of magnitude increase in burst pressure of the microvascular channels compared to the unreinforced case
Finite element modelling of lithium-ion battery fires on composite structures
No full textThe use of composite materials, for lightweighting, and lithium-ion batteries (LIB), for electrification, has expanded across the transportation industry. A common failure mechanism for LIBs is thermal runaway (TR), i.e. when a battery enters a state of uncontrolled, self-heating which can result in very high temperatures, smoke, and even battery fire. Battery fire containment is generally achieved with metallic structures, but to-date Carbon Fibre Reinforced Polymer (CFRP) containment structures have not been investigated. This paper presents Finite Element (FE) models to assess thermal and mechanical damage and failure during and after a lithium-ion battery (LIB) thermal runaway (TR) event impinging on a CFRP composite specimen. A loading approach is developed using published experimental data for a cylindrical 18650 LIB fire. A trio of sequential simulations including heat transfer, thermo-mechanical and Compression after Thermal Runaway (CaTR) models are linked with python scripts to transfer damage states. Results have shown, for unprotected specimens, the presence of thermal damage from a single cell runaway can potentially reduce the residual strength by 20%. Application of a 0.5 mm coating reduced the thermal damage area from 10,587 mm2 to 1431 mm2.<br/
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