Bio-based resins, obtained from renewable raw materials, are a more sustainable alternative to oil-based resins for fiber-reinforced polymer (FRP) composites. The incorporation of lignin in those ...resins has the potential to enhance their performance. This paper presents results of an experimental study about the effects of Lignoboost lignin incorporation on a partially bio-based vinyl ester (VE) resin. Two resins were prepared—without (reference) and with lignin addition (4% by weight) to its main chain—and their chemical, thermophysical, and mechanical properties were compared using Fourier transform infrared (FTIR) spectroscopy, gel permeation chromatography (GPC), dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), and tensile and shear tests. Results suggest that the addition of lignin to the base resin resulted in a copolymer of increased heterogeneity and higher molecular weight, incorporating stiff and complex aromatic structures in the polymer chain. While requiring high-temperature curing, the VE–lignin copolymer presented improvements of 27% in tensile strength, 4% in shear strength, and increased glass transition temperature by about 8 °C, thus confirming the potential of this natural biopolymer for FRP composite applications.
Abstract
Corrugated steel-sheet culvert systems were extensively applied in the construction of hydraulic and agricultural highways underpasses from the 1980s until the beginning of the 21st century. ...Less than 30 years after being built, the level of corrosion in the steel sheets was found to be higher than expected, potentially compromising the structural safety and service life of these structures. In this context, it is urgent to develop durable solutions for both the rehabilitation of such underpasses and the construction of new ones. Recently, structural systems based on glass fiber–reinforced polymer (GFRP) culvert sections have been proposed as an answer to this issue and have already been used in a few rehabilitations, installed inside of existing steel culverts. However, doubts have been raised about the performance of this new solution, mainly due to the lack of consolidated knowledge about its structural behavior in this specific type of work. This paper presents an experimental and numerical investigation of the performance of a commercially available GFRP culvert system. The experimental program comprised coupon tests and full-scale flexural tests up to failure on GFRP culverts, with a 60-mm-thick wall, produced by filament winding, with a height of ∼2.15 m and a width of ∼3.40 m. Conventional finite-element (FE) models were developed with commercial FE packages to simulate the structural behavior of the GFRP culverts. Following validation, a design parametric analysis was carried out with those FE models, demonstrating that this structural solution is able to comply with serviceability and ultimate-limit states requirements. Finally, this paper presents a case study of the rehabilitation of an underpass originally built with corrugated steel sheets, using this new GFRP culvert. Overall, the results obtained in this study show the feasibility of applying GFRP culverts—both in new structures and when rehabilitating existing underpasses—and of using conventional FE tools in their design.
The HeartWare (HeartWare International, Inc. Framingham, MA) ventricular assist device (HVAD) is approved for implantation through a sternotomy with cardiopulmonary bypass. We report on our initial ...experience with this device implanted off-pump via thoracotomy.
A total of 26 patients were included in this review. All patients were Interagency Registry for Mechanically Assisted Circulatory Support categories 2 or 3 and underwent implantation of an HVAD as an elective procedure via thoracotomy and mini sternotomy approach. Three-dimensional echocardiography was used to assess the ventricle and was also used to facilitate proper pump positioning. Patients were managed during follow-up using anti-coagulants at a target international normalized ratio 2.0 to 2.5 as well as anti-platelet agents.
Implantation was performed without the use of cardiopulmonary bypass, but 1 patient did require conversion to on-pump surgery. There were no perioperative deaths or right heart failure events. The mean intensive care unit stay was 1.5 days. Transfusions of 1 to 3 units of packed red blood cells were required in 16 patients, whereas 10 patients maintained a stable perioperative hematocrit of at least 30% and did not require transfusion. Survival through 90 days was 100%, and survival through 180 days was 87%.
Our experience was favorable in respect to outcome, safety, and use of blood products. Our technique can be used as an alternative approach for left ventricular assist device implantation using the HVAD.
•Sandwich panel concept for structural and thermal retrofit of existing RC-buildings;•Extensive laboratory characterization of the panel’s individual components;•Use of recycled steel fibres as ...discrete reinforcement of thin concrete wythes;•Pullout tests for selection of insulation layer and GFRP connectors;•Numerical simulation of pullout test using 3D surface interface finite elements.
This paper presents an experimental and numerical study aiming at the development of a sustainable and multifunctional composite sandwich panel for the rehabilitation of reinforced concrete (RC) buildings from the 1960s to the mid-1980s. The sandwich panel, which was designed for the structural, thermal and acoustic refurbishment of building facades, comprises three main components: (i) thin outer layers of Recycled Steel Fibre Reinforced micro–Concrete (RSFRC) that fulfil the strength, ductility and durability requirements of the panel; (ii) a lightweight core made of polystyrene that provides thermal insulation; and (iii)internally distributed glass fibre reinforced polymer (GFRP) connectors that join the different layers of the panel, providing an adequate structural behaviour to the composite system. The mechanical characterization tests highlighted the viability of using RSFRC for the production of structural sandwich facade panels, as relatively high post-cracking tensile capacity was obtained for thin RSFRC layers. Pushout and pullout tests were carried out on intermediate-scale specimens representative of the sandwich panel solution for assessing the overall composite behaviour of the sandwich panels and analysing the influence of the type of core insulation layer (expanded/extruded polystyrene cores, with different surface finishing), of the anchoring conditions (25 and 35 mm of embedment depth) and diameter of the GFRP connectors (8 and 12 mm). These tests showed that the structural GFRP connectors with diameters of 8 and 12 mm are able to ensure shear load transfer between RSFRC layers, exhibiting better composite behaviour when combined with anchorage depths of 25 and 35 mm, respectively. The numerical part of this study aimed at modelling the failure mechanisms observed at the interface between RSFRC and polystyrene, showing good agreement between experimental and numerical results, with important conclusions being drawn regarding cohesion and friction angle between these materials.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
45.
Local Probing ErCrO3 Oliveira, Gonçalo N. P.; Rodrigues, Pedro R.; Correia, João G. ...
Crystals,
01/2023, Volume:
13, Issue:
1
Journal Article
Peer reviewed
Open access
Local distortions in perovskite-like orthochromites are of extreme importance for the properties they exhibit. Here, we present the results of structural and DC magnetisation measurements combined ...with local probe studies in polycrystalline ErCrO3. The electric field gradient (EFG) parameters’ evolution with temperature shows two clear signals of local environment changes, one at the ferroelectric phase transition (TFE) and the other below 250 K. At the claimed TFE, the EFG changed from a slightly distorted axial symmetric to an EFG with axial symmetry (evidence that the local point-symmetry of the crystal might have changed). At a temperature around 250 K, we observed the development of a magnetic hyperfine field (MHF) and a change in the EFG to an axial slightly distorted one. These observations are rather in line with our magnetisation measurements, as a relatively strong coercive field was observed well above the Cr sub-lattice ordering temperature.
Part 1 1 of this two-part paper presented an experimental study of the cyclic behaviour of a novel beam-to-column sleeve connection system for pultruded glass fibre reinforced polymer (GFRP) tubular ...profiles, and the numerical simulation of such behaviour. This Part 2 presents an experimental and numerical study on the sway behaviour of full-scale GFRP plane frames comprising the same tubular profiles and the aforementioned connection system. The GFRP frames were tested under quasi-static monotonic and cyclic loading, with and without infill walls, materialized by composite sandwich panels. The results of the tests show that high-load carrying capacity infill walls have a remarkable effect on the frames’ structural behaviour, significantly increasing their stiffness and load carrying capacity, as well as their cyclic performance, namely regarding energy dissipation. On the other hand, such improvement involved extensive damage in the frame elements, particularly in the beams, which at some point compromised their structural integrity. The numerical study included the simulation of the cyclic tests of the unfilled walls, by means of relatively simple finite element (FE) models, comprising frame elements and spring joints simulating the behaviour of the connections, in which the Pivot hysteresis model calibrated in Part 1 1 was used. The comparison between experimental and numerical results shows that these simple and design-oriented FE models can provide an effective (and conservative) tool for the simulation of pultruded GFRP frames under horizontal cyclic loads.
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•SCM-FEMIX provide more accurate results mostly due to absence of dynamic effects.•DPM-ABAQUS residual stresses showed great influence on SFlex beams.•Small loading steps ABAQUS/Explicit ensures ...stability during crack formation.•In SDur beams, threshold angle and SCM showed a great influence on crack patterns.
Several reinforcing strategies have recently been developed to overcome glass brittleness and numerical simulations are essential to investigate the structural behaviour of such hybrid systems. Based on previous experimental results from monotonic quasi-static tests, this paper presents a numerical study about the flexural behaviour of glass beams reinforced with glass fibre reinforced polymer (GFRP) laminates bonded with two different adhesives: polyurethane and epoxy. The main objective of this study is to evaluate the efficiency of different constitutive models to simulate the non-linear behaviour of glass, considering the following factors: initial stiffness, cracking load, post-cracking stiffness, crack pattern and progressive failure. The glass is simulated using smeared crack (SCM) and damaged plasticity (DPM) models with static and dynamic numerical approaches. Particular attention is paid to the influence of the several parameters that influence the structural behaviour of glass (e.g. threshold angle), as well as to the interfaces between all the materials involved (e.g. thickness of the adhesive layer). In relation to static numerical approaches, dynamic numerical approaches require more computational effort and their dynamic effects may influence the structural responses obtained; however, they also show to be able to capture all the stages of cracking in greater detail, because stability during cracking formation is guaranteed even at smaller loading stages. Since DPM models do not allow considering a maximum absolute damage factor of 1.0, the smeared crack models simulate better the non-linear behaviour of glass.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The fundamental objective of the present work consists of the improvement of the plastic strain ratio (R-values) of AA-5182 aluminium alloy through improving the crystallographic texture by ...asymmetric rolling (ASR). The ASR process imposes intense shear deformation across the thickness of the sheet samples, leading to shear texture development. Finite element (FE) simulations of the ASR were first performed in order to investigate the impact of process parameters on the onset and growth of shear deformation throughout the thickness of sheet samples. In the present work, polycrystal simulations were also done to predict the texture evolutions and the mechanical response of the sheets deformed by different rolling processes. Afterwards, experimental studies were conducted. Conventional rolling (CR) as well as two types of ASR processes was carried out to reduce the thickness of the sheet samples. After each process, the rolled sheet samples were annealed. The crystallographic textures achieved in CR and ASR processes and annealing were measured. Furthermore, uniaxial tensile tests on the rolled sheets were also carried out in order to consider the effects of crystallographic texture on the macroscopic anisotropy. In agreement with the FE predictions, the experimental results showed that the shear strain spreads throughout the thickness of sheet samples during ASR and develops the shear texture. The mechanical behaviour and texture evolution predicted by numerical models are in good agreement with the experimental results. The modified texture leads to an increase of normal anisotropy as well as an increase of absolute value of planar anisotropy.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Conspectus Metalloproteins are essential to numerous reactions in nature, and constitute approximately one-third of all known proteins. Molecular dynamics of proteins has been elucidated with great ...success both by experimental and theoretical methods, revealing atomic level details of function involving the organic constituents on a broad spectrum of time scales. However, the characterization of dynamics at biomolecular metal sites on nanosecond time scales is scarce in the literature. The aqua ions of many biologically relevant metal ions exhibit exchange of water molecules on the nanosecond time scale or faster, often defining their reactivity in aqueous solution, and this is presumably also a relevant time scale for the making and breaking of coordination bonds between metal ions and ligands at protein metal sites. Ligand exchange dynamics is critical for a variety of elementary steps of reactions in metallobiochemistry, for example, association and dissociation of metal bound water, association of substrate and dissociation of product in the catalytic cycle of metalloenzymes, at regulatory metal sites which require binding and dissociation of metal ions, as well as in the transport of metal ions across cell membranes or between proteins involved in metal ion homeostasis. In Perturbed Angular Correlation of γ-rays (PAC) spectroscopy, the correlation in time and space of two γ-rays emitted successively in a nuclear decay is recorded, reflecting the hyperfine interactions of the PAC probe nucleus with the surroundings. This allows for characterization of molecular and electronic structure as well as nanosecond dynamics at the PAC probe binding site. Herein, selected examples describing the application of PAC spectroscopy in probing the dynamics at protein metal sites are presented, including (1) exchange of Cd2+ bound water in de novo designed synthetic proteins, and the effect of remote mutations on metal site dynamics; (2) dynamics at the β-lactamase active site, where the metal ion appears to jump between the two adjacent sites; (3) structural relaxation in small blue copper proteins upon 111Ag+ to 111Cd2+ transformation in radioactive nuclear decay; (4) metal ion transfer between two HAH1 proteins with change in coordination number; and (5) metal ion sensor proteins with two coexisting metal site structures. With this Account, we hope to make our modest contribution to the field and perhaps spur additional interest in dynamics at protein metal sites, which we consider to be severely underexplored. Relatively little is known about detailed atomic motions at metal sites, for example, how ligand exchange processes affect protein function, and how the amino acid composition of the protein may control this facet of metal site characteristics. We also aim to provide the reader with a qualitative impression of the possibilities offered by PAC spectroscopy in bioinorganic chemistry, especially when elucidating dynamics at protein metal sites, and finally present data that may serve as benchmarks on a relevant time scale for development and tests of theoretical molecular dynamics methods applied to biomolecular metal sites.
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Systemic lupus erythematosus (SLE), antiphospholipid syndrome (APS), and Sjögren's syndrome (SS) are heterogeneous autoimmune diseases. Severe manifestations and refractory/intolerance to ...conventional immunosuppressants demand other options, namely biological drugs, and small molecules. We aimed to define evidence and practice-based guidance for the off-label use of biologics in SLE, APS, and SS. Recommendations were made by an independent expert panel, following a comprehensive literature review and two consensus rounds. The panel included 17 internal medicine experts with recognized practice in autoimmune disease management. The literature review was systematic from 2014 until 2019 and later updated by cross-reference checking and experts' input until 2021. Preliminary recommendations were drafted by working groups for each disease. A revision meeting with all experts anticipated the consensus meeting held in June 2021. All experts voted (agree, disagree, neither agree nor disagree) during two rounds, and recommendations with at least 75% agreement were approved. A total of 32 final recommendations (20 for SLE treatment, 5 for APS, and 7 for SS) were approved by the experts. These recommendations consider organ involvement, manifestations, severity, and response to previous treatments. In these three autoimmune diseases, most recommendations refer to rituximab, which aligns with the higher number of studies and clinical experience with this biological agent. Belimumab sequential treatment after rituximab may also be used in severe cases of SLE and SS. Second-line therapy with baricitinib, bortezomib, eculizumab, secukinumab, or tocilizumab can be considered in SLE-specific manifestations. These evidence and practice-based recommendations may support treatment decision and, ultimately, improve the outcome of patients living with SLE, APS, or SS.
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