The prediction of the micromechanical response of fibre-reinforced polymer composites with numerical models relies on the assumption that the matrix behaves like a bulk sample of the same polymer. Yet, the presence of fibres likely impacts the thermochemical history and mechanical behaviour of the matrix (e.g. formation of an interphase during processing). In this work, micromechanical analysis of a thermoplastic polymer matrix is performed on glass fibre-reinforced composite samples manufactured by vacuum infusion and in-situ polymerisation. The interphase thickness and mechanical behaviour are assessed by atomic force microscopy (AFM). The mechanical properties of the matrix beyond the interphase are measured by nanoindentation and AFM in intra- and inter-tow matrix pockets, for different levels of natural physical ageing. While the distance to the nearest fibre does not significantly impact the polymer properties at a given ageing time, fibre proximity affects the rate and extent of physical ageing experienced by the polymer.

Near-surface axial tensile residual stresses (from manufacturing) are reportedly detrimental to the yield strength of cold-drawn wires. Therefore, a reliable evaluation of their magnitude is necessary. The size and geometry of electrical wires can pose challenges for experimental measurement of those residual stresses. For that reason, the finite element analysis can prove useful. However, great care must be taken with the right choice of strain hardening law for a sound assessment of residual stresses. Given the complex loading condition during cold drawing, cyclic loading arises through the wire cross section even in single-pass drawing. As a result, it is of crucial importance to account for associated backstresses. The current study makes a comparison between two different hardening laws’ prediction of axial residual stress profiles in numerically cold-drawn Cu–Al composite wires of various Al volume fractions. The impact of die geometry on this prediction was also examined for a 25%Al-wire. To that end, a combined isotropic-kinematic law and a pure isotropic constitutive equation were considered. The results imply a possible overestimation of residual stresses by the pure isotropic model at relatively low Al volume fractions. The difference between the maximum magnitudes of tensile or compressive residual stresses (predicted by the two models) could be as large as about 100 MPa (larger than the yield strength of the starting materials). Furthermore, the tooling geometry minimally affects the prediction of the hardening models. In conclusion, backstresses are not to be overlooked for accurate estimations of drawing residual stresses at low Al volume fractions.

The present study investigates the tensile behavior of the two bimetallic composite wires Cu-Al and Fe-Al. The purpose is to understand the deviation their tensile strengths show from the Rule of Mixtures’ prediction. To that end, an experimental-numerical approach was adopted. Following tensile testing of the above cold-drawn composite wires, the manufacturing process (wire drawing) was simulated via finite element analysis. The prominent role of processing-induced residual stresses on the yield strength of cold-drawn products is known. Therefore, a discussion based on the axial tensile residual stress profile was developed. It was concluded that the higher-magnitude-near-surface tensile residual stresses in the Fe-Al wire causes its tensile curve to show a negative deviation from the Rule of Mixtures (RoM). The Cu-Al wire, on the contrary, exhibits a slight positive deviation.

The present study is concerned with the mechanical properties of Cu-Al wires manufactured via cold drawing. The common approach for improving the tensile strength of drawn wires is to optimize the operational parameters. Those parameters include the die geometry, amount of area reduction at each pass, drawing speed, lubrication and so on. Optimization helps homogenize the plastic deformation during wire drawing. That in turn minimizes the undesirable effect of processing-induced tensile residual stresses forming near the wire surface. The current investigation introduces a novel optimization approach to modify the residual stress distribution with a focus on the fiber-matrix configuration rather than the operational parameters. To that end, residual stress distributions in the two configurations I- conventional copper-clad aluminum and II- so-called “Architectured” wires were compared at the same Cu/Al volume fraction. The comparison was performed using the finite element analysis. Experimental stress–strain curves, numerical residual stress profiles, and equivalent plastic strain contours were then plotted for both conventional and novel configurations. The findings suggest that the novel composite wires offer remarkably better tensile behavior along with other already-known electrical and thermal advantages. This could be ascribed to their architectural features such a continuous copper network and fine Al fibers. Therefore, the new fiber-matrix configuration could remove the need for optimization of various operational parameters or post-drawing treatments for a given wiredrawing set-up.

Abstract Near-surface axial tensile residual stresses (from manufacturing) are reportedly detrimental to the yield strength of cold-drawn wires. Therefore, a reliable evaluation of their magnitude is necessary. The size and geometry of electrical wires can pose challenges for experimental measurement of those residual stresses. For that reason, the finite element analysis can prove useful. However, great care must be taken with the right choice of strain hardening law for a sound assessment of residual stresses. Given the complex loading condition during cold drawing, cyclic loading arises through the wire cross section even in single-pass drawing. As a result, it is of crucial importance to account for associated backstresses. The current study makes a comparison between two different hardening laws’ prediction of axial residual stress profiles in numerically cold-drawn Cu-Al composite wires of various Al volume fractions. The impact of die geometry on this prediction was also examined for a 25%Al-wire. To that end, a combined isotropic-kinematic law and a pure isotropic constitutive equation were considered. The results imply a possible overestimation of residual stresses by the pure isotropic model at relatively low Al volume fractions. The difference between the maximum magnitudes of tensile or compressive residual stresses (predicted by the two models) could be as large as about 100 MPa (larger than the yield strength of the starting materials). Furthermore, the tooling geometry minimally affects the prediction of the hardening models. In conclusion, backstresses are not to be overlooked for accurate estimations of drawing residual stresses at low Al volume fractions.

The present study investigates the mechanical behavior of severely plastic-deformed Cu-Al composite wires with different diameters and heat-treatments. Each composite holds 61 restacked copper-clad aluminum wires. The bimetal composites were cold-worked up to diameters ranging from 1 mm to 3 mm, without any intermediate heat treatment. All the wires contain 61 hexagonal Cu-Al fibers with a continuous copper network extended from the outer surface into the center of the samples. Tensile tests were then performed on the as-drawn and heat treated wires. The latter were treated at 400 degrees C for 30 min and 6 h. The heat treatments firstly induce recrystallization in both constituents, giving rise to a fine-grained microstructure and secondly prompt the formation of several intermetallics. Without heat treatment after processing, the architectured composites exhibit a ductility value similar to the conventional copper-clad aluminum wires and larger yield stresses compared to them, regardless of the diameter. The intermetallic compounds, forming as a result of heat treatment, affect the yield stress, ductility and strain hardening mechanisms. Finally, the results are discussed in terms of grain size, texture, intermetallics volume fraction and mechanical coupling between the phases.

The present study investigates, experimentally and numerically, the tensile behavior of copper-clad aluminum composite wires. Two fiber-matrix configurations, the conventional Al-core/Cu-case and a so-called architectured wire with a continuous copper network across the cross-section, were considered. Two different fiber arrangements with 61 or 22 aluminum fibers were employed for the architectured samples. Experimentally, tensile tests on the two types of composites show that the flow stress of architectured configurations is markedly higher than that of the linear rule of mixtures' prediction. Transverse stress components and processing-induced residual stresses are then studied via numerical simulations to assess their potential effect on this enhanced strength. A set of elastic-domain and elastoplastic simulations were performed to account for the influence of Young's modulus and volume fraction of each phase on the magnitude of transverse stresses and how theses stresses contribute to the axial stress-strain behavior. Besides, residual stress fields of different magnitude with literature-based distributions expected for cold-drawn wires were defined. The findings suggest that the improved yield strength of architectured Cu-Al wires cannot be attributed to the weak transverse stresses developed during tensile testing, while there are compelling implications regarding the strengthening effect originating from the residual stress profile. Finally, the results are discussed and concluded with a focus on the role of architecture and residual stresses.

This work is devoted to investigate the structural and electrical properties of the Ce, Gd-doped YBCO superconductors bulk ceramics. YBa2-xRExCu3O7-delta (x = 0, 0.01, 0.05, 0.1) (RE = Gd, Ce) samples were prepared by means of conventional solid-state reaction. X-ray diffraction analysis was carried out to identify the present phases in the as-prepared samples followed by the determination of their lattice parameters. Fourier Transform Infrared Spectroscopy (FTIR) was used to identify the functional groups. Furthermore, the morphology and the surface roughness of the studied samples were characterized using Scanning Electronic Microscopy (SEM) and Atomic Force Microscopy (AFM). Vickers Micro-hardness of the as-prepared samples was examined. Besides, the electrical resistivity measurements were achieved to determine the critical transition temperature T-C and the critical current density J(C). The effect of Ce and Gd additions is clearly noticed in the obtained results, where all the prepared samples are superconductors with the presence of Y123 as a major polycrystalline phase. From the XRD patterns, the intensities of the Y123 corresponding peaks decrease with further increasing the Ce and Gd contents. In addition, the variation of the cell parameters was significant after additions of both Ce and Gd, which affect the grain size and the oxygen content of the YBa2-xRExCu3O7-delta system. An improvement of the structure and surface roughness is observed on SEM and AFM images. Likewise, Vickers micro-hardness has increased after the Ce and Gd additions. Although, the critical transition temperature T-C was not further increased upon Ce or Gd additions compared to the undoped YBCO samples. Nevertheless, an exception has been recorded with an increase of T-C for YBa2-xRExCu3O7-delta with (RE = Gd, x=0.01) to reach 88 K. In contrary, an improvement of the deduced critical current density J(C) was achieved for all Ce-doped YBCO samples unlike those of Gd-doped samples.

Abstract Learning biology, and in particular systematics, requires learning a substantial amount of specific vocabulary, both for botanical and zoological studies. While crucial, the precise identification of structures serving as evolutionary traits and systematic criteria is not per se a highly motivating task for students. Teaching this in a traditional teaching setting is quite challenging especially with a large crowd of students to be kept engaged. This is even more difficult if, as during the COVID‐19 crisis, students are not allowed to access laboratories for hands‐on observation on fresh specimens and sometimes restricted to short‐range movements outside their home. Here, we present QuoVidi, a new open‐source web platform for the organization of large‐scale treasure hunts. The platform works as follows: students, organized in teams, receive a list of quests that contain morphologic, ecologic, or systematic terms. They have to first understand the meaning of the quests, then go and find them in the environment. Once they find the organism corresponding to a quest, they upload a geotagged picture of their finding and submit this on the platform. The correctness of each submission is evaluated by the staff. During the COVID‐19 lockdown, previously validated pictures were also submitted for evaluation to students that were locked in low‐biodiversity areas. From a research perspective, the system enables the creation of large image databases by the students, similar to citizen science projects. Beside the enhanced motivation of students to learn the vocabulary and perform observations on self‐found specimens, this system allows instructors to remotely follow and assess the work performed by large numbers of students. The interface is freely available, open‐source and customizable. Unlike existing naturalist platforms, allows the educators to fully customize the quests of interest. This enables the creation of multiple teaching scenarios, without being bound to a fixed scope. QuoVidi can be used in other disciplines with adapted quests and we expect it to be of interest in many classroom settings.

This work focusses on the link between microstructure and creep properties for heat-resistant austenitic alloys with high aluminum content (3-5 wt %). An emphasis was put on the coupling of thermodynamic simulations, microstructural characterizations by scanning electron microscopy and transmission electron microscopy, and creep testing. The phase predictions performed by the calculation of phase diagrams method are in good agreement with the observed microstructure after creep at 1000 degrees C and 1050 degrees C. Correlation between creep properties and microstructure characterizations at 1000 degrees C and 1050 degrees C revealed that NiAl and alpha' (chromium-rich base centered cubic phase) phases are deleterious for the creep properties at service temperature. Several high Al-content alloys are selected in order to replace the chromia-forming alloys standardly used in cracking furnaces.

This prospective cohort study investigated the distribution pattern of carious lesions diagnosed by visual tactile and radiographic examinations, assessed the radiographic yield for clinical caries diagnosis, and estimated how accurately commonly used indicators for caries identified young adults who would benefit from radiographs at different thresholds. Overall, 576 patients aged 16-32 years seeking a first consultation were included. Patients were examined for caries and answered a validated questionnaire on sociodemographics and oral health behavior. Almost 10% of clinically sound approximal surfaces presented radiolucency in enamel/dentine. Of the clinically diagnosed noncavitated approximal and occlusal lesions, 22.5 and 17.7%, respectively, presented radiolucency reaching dentine at the radiographic examination. Noncavitated/enamel lesions detected radiographically were mainly at approximal surfaces (73.2%), while at occlusal surfaces these were negligible (0.7%). More than half of approximal dentine lesions were only detected radiographically (61.3%), while more than half of occlusal dentine lesions were only clinically diagnosed (57.1%). The hierarchical logistic regression analysis showed that patient's caries activity, D1MFS scores ≥17, and frequent consumption of soft drinks were significantly associated with detection of approximal enamel/dentine lesions. Also, patient's caries activity and frequent consumption of soft drinks were significantly associated with occlusal dentine caries (p ≤ 0.05). The indicator power of grouping these indicators as a predictor for the presence of radiographically detected lesions showed high sensitivity (0.84-0.91) and moderate specificity (0.64-0.73) for all surfaces and thresholds tested. In conclusion, radiographs increased significantly the number of approximal enamel/dentine and occlusal dentine lesions diagnosed. The ability to identify young adults with approximal lesions from the predictor was satisfactory. Bearing in mind that an essential contribution of bitewing radiographs to clinical examination is the detection of approximal noncavitated/enamel lesions that can be inactivated by nonoperative interventions, our results support the prescription of radiographs in young adults seeking a first consultation. Updating of current guidelines' recommendation of radiographs is warranted.

BackgroundPaediatric complex chronic conditions (CCCs) are life-limiting conditions requiring paediatric palliative care, which, in Belgium, is provided through paediatric liaison teams (PLTs). Like the number of children and adolescents with these conditions in Belgium, their referral to PLTs is unknown.ObjectivesThe aim of the study was to identify, over a 5-year period (2010–2014), the number of children and adolescents (0–19 years) living with a CCC, and also their referral to PLTs.MethodsInternational Classification of Disease codes (ICD-9) corresponding to a CCC, as described by Feudtneret al, and national registration numbers were extracted from the databases of all hospitals (n=8) and PLTs (n=2) based in the Brussels region. Aggregated data and pseudonymised national registration number were transmitted to the research team by a Trusted Third Party (eHealth). Ages and diagnostic categories were calculated using descriptive statistics.ResultsOver 5 years (2010–2014) in the Brussels region, a total of 22 721 children/adolescents aged 0–19 years were diagnosed with a CCC. Of this number, 22 533 were identified through hospital registries and 572 through PLT registries. By comparing the registries, we found that of the 22 533 children/adolescents admitted to hospital, only 384 (1.7%) were also referred to a PLT.ConclusionIn Belgium, there may be too few referrals of children and adolescents with CCC to PLTs that ensure continuity of care.

The present study relates to Polymers Additive Manufacturing (PAM) traditionally used for rapid prototyping operations. The use of PAM components as functional parts is still marginal compared to injection molded components. This is due to the uncertainty on their mechanical properties and to the present knowledge on PAM products. A new additive manufacturing technology has been integrated in the free former-Arburg machine. It was inspired by injection molding technology and creates plastic parts using layers built up from tiny droplets of polymer. In this work, the mechanical characterization of thermoplastic polymer parts obtained by Arburg Plastic Free forming (APF) is studied. Additionally the mechanical properties of polymer specimens obtained by injection molding as a conventional process are studied in order to evaluate the influence of the manufacturing process on the parts mechanical behavior. The tensile mechanical properties are evaluated by varying some manufacturing parameters, such as the printing path. Microstructural analyses have been performed to better understand the relationship between the manufacturing process and the final mechanical properties.

The thermal behavior of Phase Change Materials (PCMs) is a major issue for cooling, heat storage and thermal management of various systems in general. Unfortunately many PCMs present supercooling which is a major drawback regarding the efficiency of cooling systems. Various solutions were proposed to model the thermal kinetics, in particular using the apparent specific heat Cp(T) technique. But among them only few consider the supercooling effect. The present work considers this issue by focusing on the representation of the different steps of the supercooling phenomenon. This leads to different formulations of the apparent capacity Cp (T,fsuper). The presented algorithm uses the lumped system analysis approach that is widely spread for first-order and multi-scale resolutions. The apparent capacity laws are explicitly presented for the different melting-crystallization steps. In particular, the punctually negative Cp formulation, a helpful mathematical artifact, permits to reproduce the thermal dynamics during the local crystallization. The formulations and the models are discussed. Eventually, the temperature evolutions of an experimental system are compared to calculated data and the crystallization rate is compared to the literature.

Architectured wires containing 61 restacked Copper Clad Aluminum (CCA) wires were cold-drawn down to a diameter of 1mm without intermediate annealing. Samples were taken at intermediate diameters of 3mm and 1.7mm to observe the wire structure at different steps. Independently of the wire diameter, the structure did not exhibit any porosity and initial CCA wires were uniformly distributed inside the structure with constant equivalent diameters. Post-elaboration annealing treatments performed on CCA and architectured wires led to the formation of Al2Cu, AlCu and Al4Cu9 intermetallic compounds (IMC). It was shown that IMC growth kinetics do not depend on the wire diameter, indicating no marked influence of the plastic deformation. The volume fraction of IMC strongly increased with the reduction of the diameter and impacted the electrical resistivity of the architectured wire. The equivalent resistivity has been easily computed by a linear rule of mixture model, with three electrical resistances in parallel (Al, Cu and IMC), weighted by their respective volume fraction. This model allowed extracting a mean resistivity of IMCs of 4.5μΩ·cm. It also demonstrated that this restacking drawing process, without any intermediate annealing treatment is an interesting method for the elaboration of architectured wires with optimized functional properties.

Architectured copper clad aluminium composites processed by a restacking drawing method at room temperature are reported in this work. Wires were drawn to severe plastic strain without any intermediate annealing. Three different diameters were studied in order to examine the influence of a different plastic deformation level on the structure of the different wires. Thanks to image processing it has been shown that independently of the plastic deformation, inserted fibers remain continuous and are homogeneous in size and shape. Furthermore, XRD and TEM characterizations confirm that there is no significant intermetallic growth during the deformation. Thus, the improvement and/or degradation of the functional properties of the wires can be well controlled by performing an appropriate post-processing annealing treatment. Keywords: Cu/Al composite, architectured wire, drawing, microscopy, image processing

In the particular case of finite orders, we investigate the notion of faithful extension among relations introduced in 1971 by R. Fraisse: an order Q admits a faithful extension relative to an order P if P does not embed into Q and there exists a strict extension of Q into which P still does not embed. For most of the known order classes, we prove that if P and Q belong to a class then Q admits a faithful extension in this class. For the class of distributive lattices, we give an infinite family of orders P and Q such that P does not embed into Q and embeds in every strict extension of Q.

Characterization of honeys produced in the region of Djelfa steppe land in Algeria. Description of the subject. This paper deals with the quality of honeys produced in the steppe areas of Algeria and discusses the possibility of their valorization. Objectives. The objective was to characterize and compare the physical and chemical quality of honeys and to determine their pollen composition according to their geographical origin in three areas of the Djelfa semi-arid region of Algeria. Method. Thirty-eight samples of honey produced in 11 localities in the north, centre and south of the Djelfa semi-arid steppe region were harvested in July for two consecutive years. Pollen analyses were performed and the following properties of the honey samples were determined: water content, pH level, electrical conductivity, color, hydroxymethylfurfural content, saccharase index, diastase index and carbohydrate profile. Results. The results of the pollen analyses identified 34 taxa of pollen. The most abundant pollens were from the Ziziphus lotus, which were present in 97.12% of the samples. The pollens from this shrub were dominant in 27 of the honey samples tested, with a pollen percentage of greater than 45%. Over 55% of the pollen frequencies found came from plants belonging to Asteracae, Brassicaceae, Cistaceae and more particularly to Euphorbia bupleuroides, Peganum harmala, Thapsia garganica, Echium sp. and Retama retam. Conclusions. The physicochemical parameters of the honey samples studied comply with European and international quality standards, which opens up perspectives for their valorization.

This paper presents an original contribution for the establishment of the high-cycle fatigue curves ε–Nf (strain versus cycle number to failure) of low carbon steel under vibratory testing. These curves are obtained thanks to a vibrational fatigue bench composed of an electrodynamic shaker and a closed loop vibration control system. The main advantage of this is the high frequency excitation compared to conventional fatigue systems. Three criteria based on strain gauge measurements are implemented to provide cycle numbers to failure Nf and to plot the fatigue curves. Furthermore, cycle numbers to failure are also assessed from two modal parameters (resonant frequency and loss damping factor) and compared with the results obtained from these three criteria. Some micrographies of fractured samples observed by scanning electron microscope reveal fatigue striations but also intergranular fracture.

Brain blood barrier breakdown as assessed by contrast-enhanced (CE) T1-weighted MR imaging is currently the standard radiological marker of inflammatory activity in multiple sclerosis (MS) patients. Our objective was to evaluate the performance of an alternative model assessing the inflammatory activity of MS lesions by texture analysis of T2-weighted MR images. Twenty-one patients with definite MS were examined on the same 3.0T MR system by T2-weighted, FLAIR, diffusion-weighted and CE-T1 sequences. Lesions and mirrored contralateral areas within the normal appearing white matter (NAWM) were characterized by texture parameters computed from the gray level co-occurrence and run length matrices, and by the apparent diffusion coefficient (ADC). Statistical differences between MS lesions and NAWM were analyzed. ROC analysis and leave-one-out cross-validation were performed to evaluate the performance of individual parameters, and multi-parametric models using linear discriminant analysis (LDA), partial least squares (PLS) and logistic regression (LR) in the identification of CE lesions. ADC and all but one texture parameter were significantly different within white matter lesions compared to within NAWM(p < 0.0167). Using LDA, an 8-texture parameter model identified CE lesions with a sensitivity Se = 70% and a specificity Sp = 76%. Using LR, a 10-texture parameter model performed better with Se = 86%/Sp = 84%. Using PLS, a 6-texture parameter model achieved the highest accuracy with Se = 88%/Sp = 81%. Texture parameter from T2-weighted images can assess brain inflammatory activity with sufficient accuracy to be considered as a potential alternative to enhancement on CE T1-weighted images.