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Traditional adhesive joints with straight edged adherends suffer from a significant stress concentration in the composite coincident with the edge of the metal adherend, which can lead to accelerated translaminar failure of the substrate. In this work, we developed a novel profiling concept which improves the mechanical performance of adhesive joints between metallic adherends and composite substrates. We conducted quasi-static four-point bending (4PB) tests which showed that profiling the edge of the metallic adherend could improve the peak load by at least 27%, and that the stability of failure was simultaneously improved. We investigated varying the profile parameters and were able to conclude that further significant mechanical performance gains could be achieved by increasing any of the profile: amplitude, frequency, or number of fractal length-scales. By analysing in-situ acoustic emission (AE) monitoring data we were able to observe that profiling of the metallic adherend results in failure initiation occurring at higher loads, which suggests that the concept is successful in providing better stress distributions and lowering peak stresses. By analysing the fracture surfaces, it is apparent that the profiling concept is successful in deflecting the translaminar fracture path; and additionally that a debonding mechanism occurs at the profile tips which is thought to be an important additional mechanism for creating damage tolerant joints.

Background Ventricular arrhythmias (VA) include a spectrum that ranges from premature ventricular beats (VPBs) to ventricular fibrillation (VF) and account for approximately 50% of all cardiovascular deaths. Echocardiography is commonly used to identify structural heart disease (SHD), the most frequent substrate of VA. Cardiovascular magnetic resonance (CMR) is recommended to complement echocardiography when image quality is suboptimal. Purpose This study sought to determine whether CMR may identify SHD in patients (pts) with VA, who had normal baseline ECGs and whose echocardiogram with fair technical conditions, ruled out pathological findings. Methods We included consecutive pts followed in arrythmia outpatient clinic of one clinical center from June 2014 to June 2021 for significant VA; this was categorized as >1,000 but Results A total of 75 pts were included (no SHD: N=59; 45±15 years old; SHD: N=16, 53±15 years). All pts performed CMR, and Table 1 shows pts' baseline characteristics, VA diagnosis and CMR measurements. Definite SHD was diagnosed in 8 patients (11%): ischemic cardiopathy (three pts), myocarditis (1 pt), hypertrophic cardiomyopathy (1 pt), right ventricle arrhythmogenic disease (1 pt), non-compaction cardiomyopathy (1 pt); 1 patient presented higher myocardial T2 signal and was later diagnosed with sarcoidosis. Furthermore, abnormal findings not specific for a definite SHD diagnosis were found in other 8 pts (10%) who showed unspecific intra-myocardium enhancement. Discussion and conclusion CMR imaging identified SHD in around 20% of patients with normal ECG and echocardiogram. Among patients with identified SHD, ischemic cardiopathy was the most common finding, differently from the largest study that showed myocarditis as the main diagnosis. This may be associated to higher age in the SHD group. In conclusion, CMR allowed diagnosis of clinically relevant SHD even when echocardiography excluded it. Funding Acknowledgement Type of funding sources: None.

Complex fluids exist in nature and are continually engineered for specific applications involving the addition of macromolecules to a solvent, among other means. This imparts viscoelasticity to the fluid, a property responsible for various flow instabilities and major modifications to the fluid dynamics. Recent developments in the numerical methods for the simulation of viscoelastic fluid flows, described by continuum-level differential constitutive equations, are surveyed, with a particular emphasis on the finite-volume method. This method is briefly described, and the main benchmark flows currently used in computational rheology to assess the performance of numerical methods are presented. Outstanding issues in numerical methods and novel and challenging applications of viscoelastic fluids, some of which require further developments in numerical methods, are discussed.

Direct numerical simulations (DNS) of turbulent fronts spreading into an irrotational flow region are used to analyse the turbulent entrainment mechanism for viscoelastic fluids. The simulations use the FENE-P fluid model and are initiated from DNS of isotropic turbulence with Weissenberg and turbulence Reynolds numbers varying in the ranges $1.30 \le Wi \le 3.46$ and $206 \le Re_{\lambda }^{0} \le 404$, respectively. The enstrophy dynamics near the turbulent/non-turbulent interface (TNTI) layer, that separates regions of turbulent and irrotational flow, includes a new mechanism – the viscoelastic production – caused by the interaction between the vorticity field and the polymer stresses. This term can be a sink or a source of enstrophy in the turbulent core region of the flow, depending on the Weissenberg number, and contributes to the initial growth of the enstrophy in the viscous superlayer, together with the viscous diffusion, which is the only mechanism present for Newtonian fluids. For low and moderate Weissenberg numbers the scaling of the TNTI layer is similar to the scaling of TNTI layers for Newtonian fluids, but this is no longer the case at high Weissenberg numbers where the enstrophy tends to be concentrated into thin vortex sheets instead of vortex tubes. Finally, it is shown that the substantial decrease of the entrainment rates observed in turbulent flows of viscoelastic fluids, compared with Newtonian fluids, is caused by a reduction of the surface area and fractal dimension of the irrotational boundary, originated by the depletion of ‘active’ scales of motion in the fluid solvent caused by the viscoelasticity.

SUMMARY Maxillary lateral incisor agenesis (MLIA) is a condition that significantly compromises smile esthetics and is a particular concern in younger patients. The treatment options include orthodontics for space opening with rehabilitation or space closure with canine camouflage. Currently, there is some controversy regarding the most appropriate treatment. In this case report, we propose a multidisciplinary approach through the combination of orthodontic treatment, frenectomy, and a restorative finishing stage with composite resin and dental implants. More specifically, this treatment was planned to orthodontically close the anterior space by opening the premolar area for subsequent placement of implants and enameloplasty with a composite resin. The replacement of a missing lateral incisor by an implant is a predictable treatment approach, but it might best be deferred until dental maturity and then accurately placed in a well-developed site through a multidisciplinary approach. Precluding the closure of the anterior spaces and the opening of the posterior zone for implant placement, allows for a more stable and appealing esthetic and functional rehabilitation for young patients, in whom esthetic appearance and self-esteem play a primary role.

Single-walled carbon nanotube (SWCNT)/epoxy composites were cured under external electric fields and the influence of the processing parameters (electric field magnitude and frequency, SWCNT concentration and curing temperature) on the electrical response of the system was evaluated. A mold for the electric field application was designed and manufactured, allowing in situ measurements of the electrical resistivity of the composite, during and after the curing process. The resulting electrical properties revealed a strong dependence on the processing parameters. By rising the curing temperature, the solid bulk resistivity was decreased by one order of magnitude. Further reduction was observed with electric fields, up to an additional order of magnitude. Such improvements can be related with the decrease in viscosity and improvement of interconnected-nanotube paths within the polymer matrix. The effect of the electric field on the rotation and interconnection of the SWCNTs was investigated using a classical mechanics model based on the dielectrophoretic theory for the liquid state. The influence of inter-nanotube distances on the bulk electrical properties was calculated at different particle concentrations, using finite element models of the microstructure. This processing technique presents promising results for enhancing the electrical conductivity of polymer composites with carbon-based nanoparticles.

Industrial applications of conductive polymer composites with carbon nanotubes require precise tailoring of their electrical properties. While existing theoretical methods to predict the bulk conductivity require fitting to experiments and often employ power-laws valid only in the vicinity of the percolation threshold, the accuracy of numerical methods is accompanied with substantial computational efforts. In this paper we use recently developed physically-based finite element analyses to successfully train an artificial neural network to make predictions of the bulk conductivity of carbon nanotube-polymer composites at negligible computational cost.

This paper investigates whether the toughening mechanisms of a biological crossed-lamellar microstructure can be reproduced in a synthetic high-performance carbon fibre/epoxy matrix composite. The mechanics of the failure process in synthetic crossed-lamellar microstructures was investigated using the Finite Element Method. This enabled the design of a high-performance carbon-fibre reinforced polymer (CFRP) with such microstructure. Two different procedures were then developed to synthesise the first crossed-lamellar microstructures in CFRP in the literature. Test specimens were subsequently manufactured. Three-point bend tests were carried out in an SEM environment, showcasing the damage diffusion capability of the microstructure under stable conditions. The results show that the crossed-lamellar microstructure can be synthesised in CFRP with good accuracy, and that the mechanical toughening mechanisms associated with the natural crossed-lamellar microstructures can be reproduced in this synthetic material.

In this paper, the non-linear mechanical response of triaxial braided composites under multiple loading conditions was investigated with a meso-scale simulation strategy. Numerical predictions made by three-dimensional finite element unit cells with a realistic internal geometry in two nesting configurations correlated well with experimental stress–strain curves and damage mechanisms. Although the investigated braid topologies exhibited considerable geometric variability, the unit cell modelling approach with a compacted geometry model built from average input parameters was capable of correctly predicting the homogenised constitutive response, localisation, and damage evolution. Further, the mechanical response was predicted under variable uni-axial off-axis load cases and the effect of the textile topology on the ultimate strength of the material was investigated. Aside from providing a valuable insight into how damage propagation is affected by the meso-structure, the predicted stress–strain curves can be used to calibrate macroscopic material models suitable for large-scale crash simulations of textile composites.

This work presents new semi-analytical solutions for the combined fully developed electro-osmotic pressure-driven flow in microchannels of viscoelastic fluids, described by the generalised Phan-Thien–Tanner model (gPTT) recently proposed by Ferrás et al. (Journal of Non-Newtonian Fluid Mechanics, 269:88–99, 2019). This generalised version of the PTT model presents a new function for the trace of the stress tensor—the Mittag–Leffler function—where one or two new fitting constants are considered in order to obtain additional fitting flexibility. The semi-analytical solution is obtained under sufficiently weak electric potential that allows the Debye–Hückel approximation for the electrokinetic fields and for thin electric double layers. Based on the solution, the effects of the various relevant dimensionless numbers are assessed and discussed, such as the influence of εWi2, of the parameters α and β of the gPTT model, and also of κ¯, the dimensionless Debye–Hückel parameter. We conclude that the new model characteristics enhance the effects of both εWi2 and κ¯ on the velocity distribution across the microchannels. The effects of a high zeta potential and of the finite size of ions are also studied numerically., A.M. Ribau would like to thank FCT - Fundacao para a Ciencia e a Tecnologia, for financial support through scholarship SFRH/BD/143950/2019. A.M. Ribau, A.M. Afonso, M.A. Alves and F.T Pinho also acknowledge FCT for financial support through projects UIDB/00532/2020 and UIDP/00532/2020 of CEFT (Centro de Estudos de Fenomenos de Transporte), and project PTDC/EMS-ENE/3362/2014-POCI-01-0145-FEDER-016665-funded by FEDER funds through COMPETE2020-Programa Operacional Competitividade e Internacionalizacao (POCI) and by national funds through FCT. L.L. Ferras would also like to thank FCT for financial support through scholarship SFRH/BPD/100353/2014 and projects UIDB/00013/2020 and UIDP/00013/2020. M.L. Morgado acknowledges funding by FCT through project UID/Multi/04621/2019 of CEMAT/IST-ID, Center for Computational and Stochastic Mathematics, Instituto Superior Tecnico, University of Lisbon. This work was partially supported by Fundacao para a Ciencia e a Tecnologia (Portuguese Foundation for Science and Technology) through project UIDB/00297/2020 (Centro deMatematica e Aplicacoes). The authors also acknowledge financial support from COST Action CA15225, a network supported by COST (European Cooperation in Science and Technology).

The effect of a spatially uniform magnetic field on the shear rheology of a dilute emulsion of monodispersed ferrofluid droplets, immersed in a non-magnetizable immiscible fluid, is investigated using direct numerical simulations. The direction of the applied magnetic field is normal to the shear flow direction. The droplets extra stress tensor arising from the presence of interfacial forces of magnetic nature is modeled on the basis of the seminal work of G. K. Batchelor, J. Fluid Mech., 41.3 (1970) under the assumptions of a linearly magnetizable ferrofluid phase and negligible inertia. The results show that even relatively small magnetic fields can have significant consequences on the rheological properties of the emulsion due to the magnetic forces that contribute to deform and orient the droplets towards the direction of the applied magnetic vector. In particular, we have observed an increase of the effective (bulk) viscosity and a reversal of the sign of the two normal stress differences with respect to the case without magnetic field for those conditions where the magnetic force prevails over the shearing force. Comparisons between the results of our model with a direct integration of the viscous stress have provided an indication of its reliability to predict the effective viscosity of the suspension. Moreover, this latter quantity has been found to behave as a monotonic increasing function of the applied magnetic field for constant shearing flows ("magneto-thickening" behaviour), which allowed us to infer a simple constitutive equation describing the emulsion viscosity., Peer-reviewed version: Added new arguments throughout the whole manuscript. Revised arguments in Section 5.2. Addition of a new section dedicated to the comparison with previous theoretical models (Sect. 5.3)

Background Each year, 23 million people get ill from unsafe food in Europe. Food safety refers to the absence or safe acceptable levels of hazards in food that may harm the health of consumers. The Public Health Unit of Baixo Vouga Primary Healthcare Cluster (Aveiro region) developed a programme to identify hazards and promote implementation of corrective measures in community canteens that serve children and elderly. It has three fields of action: qualitative evaluation of the installation and operating conditions, based on the legislation; microbiological surveillance of food and utensils; training of food handlers and managers. This study aims to describe the results of such programme in 2018 and 2019. Methods This cross-sectional study used data from qualitative evaluation and microbiological results for a descriptive analysis. Additionally, an assess of the compliance of the critical points was performed to identify the main barriers in achieving the proposed targets. Results From a total of 420 registered canteens, 211 and 294 were evaluated in 2018 and 2019, respectively. For these years, only 87 (41.2%) and 124 (33.3%) fully complied with all critical points. The main problems were the lack of non-manual activation system in wash basins and faucets and inadequately instructed food handlers about required hygiene measures. Microbiological surveillance results of 371 and 393 samples had a proportion of satisfactory or acceptable results of: 93.5% and 91.3% for the main dish; 56.1% and 46.6% for the salads and 82.4% and 79.8% for the utensils. Coliform bacteria were the most common agent. Conclusions The compliances with critical points were low, accounting for the fact they are legislation-based. The microbiological results were worst for the salads' samples. Deviations give us hints of what should be reinforced. Education of the food handlers and consulting with companies to improve procedures and equipment could be of great use. Key messages Community canteens’ compliances with legislated criteria were low. This programme is useful in identifying vulnerabilities and may lead to the implementation of corrective measures.

Chlamydia (CT), gonorrhoea (NG) and syphilis (TP) infections are rising and have an important burden in the EU/EEA. This study aims to describe the epidemiology of these infections in Portugal, between 2015 and 2018, in order to set a baseline for the recently created National Strategy for STI Control and to generate hypothesis on areas for improvement. We analysed data from the national system of epidemiological surveillance (SINAVE®) and described all probable and confirmed cases of CT, NG and TP notified in Portugal between January 1st, 2015 and December 31st, 2018.This reports the overall case evolution as well as specific characteristics of different groups. Throughout the analysed 4-year period there were 1267 cases of CT, 1917 of NG and 3240 of TP (probable and confirmed). Of CT cases, 70% (n = 891) occurred in males, 66.3% (n = 840) in people aged 18-35, 52.9% (n = 670) in heterosexuals and 42.9% (n = 543) in men who have sex with men (MSM). Of NG cases, 87.9% (n = 1686) were males, 90.8% (n = 1741) were In similarity to European trends, CT, NG and TP infections seem to be rising in Portugal. Changes in patient behaviour, clinical practice, screenings, settings of diagnosis and notification should be further explored to better understand this trend, including clinical features. From our results, MSM and people aged Key messages The number of chlamydia, gonorrhoea and syphilis reported cases in Portugal raised in the four-year period between 2015 and 2018, with MSM accounting for 54.6% (1312/2403) of the cases in 2018. This sets up a baseline to guide the adoption of specific measures and the prioritisation of interventions. MSM should be given special attention when addressing new prevention strategies.

Direct numerical simulations (DNS) of spatially evolving turbulent planar jets of viscoelastic fluids described by the FENE-P model, such as those consisting of a Newtonian fluid solvent carrying long chain polymer molecules, are carried out in order to develop a theory for the far field of turbulent jets of viscoelastic fluids. New evolution relations for the jet shear-layer thickness is the coordinate in the streamwise direction. It is shown that, compared with a classical (Newtonian) turbulent jet, the effect of the polymers is to reduce the spreading rate, centreline velocity decay, Reynolds stresses and viscous dissipation rate. The self-preserving character of the flow is analysed and it is shown that profiles of mean velocity, Reynolds stresses and polymer stresses are self-similar provided the proper scales are used in the normalisation of these quantities. A fundamental difference from the Newtonian jet in this regard is the necessity for two, instead of only one, different velocity and length scales to properly characterise the evolution of the turbulent flow. These extra velocity and length scales are directly related to a time scale associated with the characteristic fading memory property of viscoelastic fluids.

Design and optimisation of large structures, including the positioning of lower-level components, typically require extensive user involvement and sequential mechanical analysis/optimisation iterations. This paper presents an original method that enables adaptive positioning of lower-level models (such as components) within higher level-models (such as large structures), and that achieves a combined mechanical/optimisation problem for the design of structures with various hierarchical levels (such as the positioning of stiffeners within a wingbox). As the position of the lower-level model evolves, our proposed method does not require re-generating of the geometry, remeshing or modifying the stiffness matrix of the elements corresponding to the various hierarchical levels. Instead, we achieve the adaptive positioning via an original concept that we propose here: Floating Connector (FC) elements. In this paper, we validate the FC elements against reference purely-mechanical solutions, show that they can be combined with gradient-descent method and genetic algorithms, and that they can be applied to optimise the positioning of a stiffener runout taking into account a debonding manufacturing defect.

This paper proposes a novel biomimetic Carbon Fibre Reinforced Polymer (CFRP) with a microstructure inspired by fish scales. The aim of the novel microstructure is to improve the perforation resistance of CFRP without compromising its flexibility. To this end, we prototype the first ever CFRP laminate with scales and test it in quasi-static indentation on a soft backing material. We compare the mechanical behaviour of the CFRP with scales to two baseline configurations with conventional lay-ups. The results presented in this paper suggest that the CFRP with scales significantly outperforms the two baseline configurations in terms of force and displacement at penetration, while being flexible. This makes CFRPs with scales an attractive alternative for applications where perforation resistance is paramount, such as body armour against low velocity strikes.

In this work, we present a systematic numerical investigation of the 1:4 planar expansion creeping flow under the influence of slip boundary conditions for Newtonian and viscoelastic fluids, the latter modeled by the simplified Phan-Thien-Tanner constitutive model. The linear and nonlinear Navier slip laws were considered with the dimensionless slip coefficient kl* varying in the range mml:mfenced close="]" open="["0,4500 mml:mfenced> and the slip exponents m = 0.5, 1, and 2. The simulations were carried out for a low Reynolds number, Re = 0.001, and for Deborah numbers (De) between 0 and 100. Convergence could not be achieved for higher values of the Deborah number and large values of the slip coefficient due to the large stress gradients near the singularity point (reentrant corner). The results obtained allow us to conclude that for all De, the increase in slip velocity leads to vortex suppression. The flow characteristics are described in detail for low values of the Deborah number, De, A. M. Afonso acknowledges the support of CEFT (Centro de Estudos de Fenomenos de Transporte) and through Project Nos. PTDC/EMS-ENE/3362/2014 and POCI-01-0145-FEDER-016665-funded by FEDER funds through COMPETE2020-Programa Operacional Competitividade e InternacionalizacAo (POCI) and by national funds through FCT-FundacAo para a Ciencia e a Tecnologia, I.P. A. M. Afonso, M. M. Alves, and F. T. Pinho are also grateful to FCT for funding through projects UIDB/00532/2020 and UIDP/00532/2020.The research of L. L. Ferras was partially financed by Portuguese Funds through FCT within the Project Nos. UIDB/00013/2020 and UIDP/00013/2020 and the scholarship Grant No. SFRH/BPD/100353/2014. J. M. Nobrega acknowledges the funding by FEDER funds through the COMPETE 2020 Program and National Funds through FCT-Portuguese Foundation for Science and Technology under the Project No. UID/05256/2020.

This paper investigates the role of dynamic stress concentrations, and of fracture mechanics-driven growth of critical clusters of fibres, on the longitudinal tensile failure of fibre-reinforced composites. For this purpose, we developed a semi-analytical fibre bundle model to simulate the longitudinal tensile failure of large composite bundles of continuous fibres. The model uses shear-lag to calculate the stress recovery along broken fibres, and an efficient field superposition method to calculate the stress concentration on the intact fibres, which has been validated against analytical and Finite Element (FE) results from the literature. The baseline version of the model uses static equilibrium stress states, and considers fibre failure driven by strength of materials (stress overload) as the only damage theory which can drive bundle failure. Like other models in the literature, the baseline model fails to capture the correct size effect (decreasing composite strength with bundle size) shown by experimental results. Two model variants have been developed which include dynamics stress concentrations and a fracture mechanics failure criterion respectively. To the knowledge of the authors, it is the first attempt in the literature to investigate these two effects in a fibre bundle model by direct simulation of large composite bundles. It is shown that, although the dynamic stress concentration significantly decreases the predicted bundle strength, it does not allow to predict the correct trend of the size effect. Finally, the results suggest that fracture mechanics may be the physical mechanism which is necessary to include to correctly predict the decreasing composite strength with bundle size shown by experimental results.

The use of interlaminar reinforcement units, containing an interlocked tab-and-slit geometry, is a new concept for improving interlaminar fracture toughness. It was recently shown that such reinforcement units are capable of substantially increasing mode I fracture toughness, but mode II fracture toughness was unaffected. This paper presents an investigation into the effect of tab orientation on the toughening mechanisms, comparing the experimentally determined Mode I and II interlaminar fracture toughness for different tab orientations. The results show that the previously reported lack of mode II toughness increase was due to an unsuitable tab orientation. With a better choice of tab orientation a mode II propagation toughness increase (of 23.5%) could be obtained, while simultaneously increasing the mode I propagation toughness further than previously reported (up to a 109% improvement). Fractography was used to investigate the toughening mechanisms. It was found that the two main toughening mechanisms are crack bridging (in mode I) and deflection of the delamination path (in both mode I and II). The relationship between the tab orientation and the obtained increase of fracture toughness can be explained by the effect of tab orientation on these mechanisms.

This work is concerned with time-dependent axisymmetric free surface flows of Oldroyd-B fluids for any value of β, the ratio of solvent to total viscosities. The Oldroyd-B constitutive equation is dealt with by employing a novel technique to calculate the conformation tensor while an EVSS transformation allows the solution of the momentum equations coupled with the free surface stress conditions: this avoids numerical instabilities that can arise when using small values of β. The convergence of this new methodology is verified on pipe flow and also by comparing results from the literature for the time-dependent impacting drop problem. This approach is then used to predict the time-dependent free surface flow after a viscoelastic drop impacts a solid surface for β values in the range [0, 1]. The impacting drop problem is investigated for polymer solutions containing a small solvent contribution ( β ⟶ 0 ) or without any solvent viscosity ( β = 0 ). In addition, a study of the bouncing drop problem for different values of β, Weissenberg and Reynolds numbers is undertaken.

In this work, we demonstrate for the first time that the inherent low performance to out-of-plane loading of thin-ply Carbon Fibre Reinforced Plastics (CFRPs) can be overcome with tailored bio-inspired Bouligand microstructures. To this end, we designed, manufactured ultra-thin-ply CFRP Bouligand laminates and conducted an original study which combines full-penetration quasi-static indentation tests, in situ three-point bending tests conducted under a SEM and detailed analytical modelling. We investigated a wide range of mismatch (pitch) angles [2.5°, 5°, 10°, 20°, 45°], showing that decreasing pitch angles simultaneously achieved a larger (i) load-bearing capability, (ii) delay in catastrophic failure and (iii) total dissipated energy. We then investigated the role of the pitch angle on the activation of the highly dissipative sub-critical failure mechanisms responsible for the high mechanical performances achieved by small pitch angles laminates. Our investigation clearly shows that, with ultra-thin-ply CFRP, smaller pitch angles achieve higher damage tolerance and structural integrity.

Postponement of infrastructure investment is often regarded as a potential benefit of distributed PV generation. However, PV has questionable impact on the postponement of investments for infrastructure capacity increase. This paper evaluates under which conditions and to which extent distributed photovoltaics and energy storage systems are able to aid the distribution system in terms of alleviating the loading of feeders. The methodology consists of a sensitivity analysis, in different demand and generation scenarios, on the impacts that photovoltaic generation and energy storage systems would have in alleviating distribution feeders. In each scenario, the synergy between energy storage and PV generation is evaluated by estimating the amount of energy storage capacity needed to reduce the peak demand to a desired level. Results show that the existence of PV generation may reduce the storage capacity needed (and consequently the cost) to achieve a desired peak demand reduction only if proper conditions are found in the demand curve.

In this paper, a carbon-fibre/epoxy (CF) composite with nacre-inspired tiled micro-structure is designed and synthesised. The aim is to investigate the interaction between the CF discontinuous micro-structure and continuous glass-fibre/epoxy (GF) layers, which are intended to act as crack stoppers, similarly to the organic interlayers that separate layers of ceramic tiles in natural nacre. Firstly, we use a GF skin to trigger unstable failure in nacre-like mesolayers, and show how the damage mode in the latter changes from pull-out to brittle fibre fracture due to the interaction with the GF skin. Secondly, we demonstrate how continuous GF interlayers can succeed in arresting unstable crack propagation in the nacre mesolayers. Furthermore, we show that they can also change the morphology of damage in the nacre, promoting a transition from brittle tile fracture to more damage-tolerant tile pull-out.

Carbon fiber layer failure is vital for the tensile behavior of interlayer hybrid carbon fiber (CF)/self-reinforced polypropylene (SRPP) composites. Introducing cuts, termed here as discontinuities, into the carbon layer is a promising way to tailor its failure behavior. Inspired by structural features of biological composites, we designed and produced hybrid composites with hierarchical and polygonal arrangements of discontinuities in the carbon layer. Increasing the number of levels in the hierarchical patterns delayed the onset of carbon layer failure, hence improving the damage resistance of the hybrid composites. A progressive carbon layer failure was achieved with the polygonal patterns by creating a transition from fiber bundle pull-out to fiber bundle fracture. Spreading the polygonal patterns throughout the specimen resulted in a unique diffused delamination distribution that has not been reported in the literature. Pseudo-ductile behavior was achieved by creating dispersed fiber bundle pull-out with the fully dispersed polygonal patterns. The resulting hybrid CF/SRPP composites demonstrated a rare combination of stiffness (10 GPa) and ductility (~16% failure strain) with a pseudo-ductile strain over 14%. This paper delivers and proves the concept of utilizing discontinuities to engineer the tensile behavior of hybrid composites.

We present finite element simulations to predict the conductivity, elastic response and strain-sensing capability of conductive composites comprising a polymeric matrix and carbon nanotubes. Realistic representative volume elements (RVE) of the microstructure are generated and both constituents are modelled as linear elastic solids, with resistivity independent of strain; the electrical contact between nanotubes is represented by a new element which accounts for quantum tunnelling effects and captures the sensitivity of conductivity to separation. Monte Carlo simulations are conducted and the sensitivity of the predictions to RVE size is explored. Predictions of modulus and conductivity are found in good agreement with published results. The strain-sensing capability of the material is explored for multiaxial strain states.

In this work, we developed a film-casting technique to deposit thin ( ∼ 13 μm) layers of poly(lactic acid) (PLA) on the interface of carbon/epoxy prepregs, with the aim of increasing the interlaminar toughness. PLA patches with fractal shape were explored, based on preliminary results showing that the toughening effect increases when PLA is deposited at multiple scales simultaneously. Double Cantilever Beam (DCB) and 4-point End-Notched Flexure (4ENF) tests showed an increase in interlaminar toughness of, respectively, up to 80% for Mode I and 12% for Mode II. This is specially remarkable because the interface thickness is only 13 μm. Moreover, it was demonstrated that this technique can promote interaction between neighbouring layers where PLA has been cast, thus triggering fibre bridging and leading to a further enhancement of toughness.

In this paper, a bio-inspired carbon-fibre/epoxy composite with nacre-like tiled microstructure is designed, synthesised and tested. Analytical models are developed to predict the energy dissipation and crack deflection properties of such composite, and the predictions for the stress-strain response during tile pull-out are validated against direct numerical simulation. Suitable configurations for tile geometry with interlocks are then identified (with dimensions of the order of 0.6 mm) and used for the subsequent prototyping. In-situ three-point bend tests are then carried out in a SEM environment, showing the capability of the interlocking micro-structure in deflecting the crack, avoiding sudden failure in the most highly loaded cross-section of the specimen. The results suggest that further damage diffusion could in principle be achieved by additionally modifying the interface between tiles.

This work presents a detailed numerical investigation on the required development length (L=L/B) in laminar Newtonian fluid flow in microchannels with rectangular cross section and different aspect ratios (AR). The advent of new microfluidic technologies shifted the practical Reynolds numbers (Re) to the range of unitary (and even lower) orders of magnitude, i.e., creeping flow conditions. Therefore, accurate estimations of L at Re≤O(1) are important for microsystem design. At such low Reynolds numbers, in which inertial forces are less dominant than viscous forces, flow characteristics become necessarily different from those at the macroscale where Re is typically much larger. A judicious choice of mesh refinement and adequate numerical methods allowed obtaining accurate results and a general correlation for estimating L, valid in the ranges 0≤Re≤2000 and 0.1≤AR≤1, thus covering applications in both macro and microfluidics., The authors acknowledge the support by CEFT (Centro de Estudos de Fenómenos de Transporte) and Project PTDC/EMS-ENE/3362/2014—POCI-01-0145-FEDER-016665, funded by FEDER funds through COMPETE2020 “Programa Operacional Competitividade e Internacionaliza” (POCI) and by national funds through FCT “Fundac ao para a Ciência e a Tecnologia”, I.P. L.L. Ferrás would also like to thank FCT for financial support through scholarship SFRH/BPD/100353/2014 and projects UIDB/00013/2020 and UIDP/00013/2020. A. Sucena, A. M. Afonso, M. M. Alves and F. T. Pinho are also grateful to FCT for funding through projects UIDB/00532/2020 and UIDP/00532/2020. A. Sucena thanks FCT for the Ph.D. Grant SFRH/BD/115547/2016

Over millions of years Nature has attained highly optimized structural designs with remarkable toughness, strength, damage resistance and damage tolerance - properties that are so far difficult to combine in artificial high-performance fibre-reinforced polymers (HPFRPs). Recent studies, which have successfully replicated the structures and especially the toughening mechanisms found in flora and fauna, are reviewed in this work. At the core of the manufacturing of damage-tolerant bio-inspired composites, an understanding of the design principles and mechanisms is key. Universal and naturally-inherent design features, such as hierarchical- and organic-inorganic-structures as well as helical or fibrous arrangements of building blocks were found to promote numerous toughening mechanisms. Common to these features, the outstanding ability of diffusing damage at a sub-critical state has been identified as a powerful and effective mechanism to achieve high damage tolerance. Novel manufacturing processes suitable for HPFRP (such as tailored high-precision tape placement, micro-moulding, laser-engraving and additive manufacturing) have recently gained immense traction in the research community. This stems from the achievable and required geometrical complexity for HPFRPs and the replication of subtly balanced interaction between the material constituents. Even though trends in the literature clearly show that a bio-inspired material design philosophy is a successful strategy to design more efficient composite structures with enhanced damage tolerance and mechanical performance, Nature continues to offer new challenging opportunities yet to be explored, which could lead to a new era of HPFRP composites.

Background and purpose Although cerebrovascular disorders are the main cause of epilepsia partialis continua (EPC) in adulthood, the frequency of EPC after stroke is unknown. The aim was to prospectively ascertain its frequency 1 year after an ischaemic stroke. Methods This was a prospective study of consecutive acute anterior circulation ischaemic stroke patients, previously independent, with an admission National Institutes of Health Stroke Scale score ≥4, an acute ischaemic lesion on imaging and no previous epileptic seizures. During admission patients received standardized diagnostic and medical care and were submitted to a neurophysiological evaluation protocol. One year after stroke, patients were re-evaluated by an epilepsy expert neurologist and performed a video-electroencephalogram with electromyography co-registration whenever myoclonus was observed during neurological examination for jerk-locked back averaging analysis (JLBA). EPC was defined as continuously repeated fragments of epileptic seizures, with preserved consciousness, lasting at least 1 h, and representing locally restricted epileptic activity. Results In all, 151 acute anterior circulation stroke patients were consecutively included and prospectively evaluated, but 23 died in the first year. One year after stroke, from 127 patients alive, 117 (92.1%) underwent clinical and neurophysiological evaluation. In two (1.7%) patients, EPC diagnosis was made both by clinical and electroencephalographic criteria, namely JLBA. Both patients had a history of remote symptomatic seizures and one of them acute symptomatic seizures and non-convulsive status epilepticus criteria during the first 7 days after stroke. Conclusions Despite its low frequency, the high stroke incidence makes post-stroke EPC relevant. This study draws attention to this recognizable condition with therapeutic and eventually prognostic implications.

The concept of translaminar fracture toughness of 0° plies has enabled the development of a considerable number of ply-level numerical models for structural failure of laminated composites. Using thin-ply pre-pregs, this paper demonstrates that this translaminar toughness is not an absolute, but rather in-situ, property and depends strongly on the 0° ply-block thickness, even in situations where delamination and diffuse damage are inhibited. We used two different grades of a thin-ply carbon-epoxy system to produce four different 0° ply-block thicknesses ranging from 0.03 mm to 0.12 mm, and measured the respective translaminar fracture toughness using compact tension tests. SEM and X-ray analysis showed no delamination nor diffuse damage. Yet, the translaminar fracture toughness increased from 46 to 104 kJ/m2 (initiation), and from 49 to 160 kJ/m2 (propagation), for the thickness range above. This finding has significant implications for the development and use of ply-level numerical failure models, for structural design with thin-ply composites, and for the development of thin-ply material systems.

We present a new hybrid CFRP concept, aimed at increasing the energy absorption capacity of the material by diffusing damage through-out the laminate. To achieve this, we combine thin-ply CFRP layers, cut into interlocking tiles, with titanium interlayers. Uniaxial tension tests and bending tests on a preliminary design iteration showed that damage initiation and initial propagation were successfully achieved, but damage propagation localized during further loading. Final failure was triggered by strain concentrations in the titanium layers, which caused the titanium failure strain to be locally exceeded. The key to achieving higher laminate ultimate strain is to prevent or ameliorate these strain concentrations in the titanium layers.

The flows of two semi-dilute surfactant solutions (CTAB and CPyCl) through several micro contractions/expansions are experimentally investigated, following an extensive rheological characterization in both shear and extensional flows. The shear rheology of the solutions shows strong shear thinning and shear banding, whereas Small Amplitude Oscillatory Shear and Capillary Break-up Extensional Rheometry indicate that they have high shear and extensional elasticities. Flow visualizations and micro-particle image velocimetry measurements show that the surfactant solutions exhibit three established types of flow patterns in contraction flows: Newtonian-like, asymmetric and disordered. Newtonian-like flow occurs at low flow rates and is preceded by a long transient flow in experiments starting from rest, which seems to be related to shear banding and the alignment of wormlike micelles. The asymmetric flow regime occurs at moderate flow rates and is characterized by an asymmetric upstream central jet with two adjacent vortices, features that change non-periodically, but slowly, in time. This flow pattern seems to be related with the high elasticity of the semi-dilute solutions. The disordered flow pattern is similar to the asymmetric flow in terms of broad characteristics, but the flow asymmetry changes with time much faster than in the asymmetric flow regime, resembling a chaotic-like flow. The disordered flow seems to be related with the breakdown of micellar structures. We concluded also that the flows in both the asymmetric and disordered flow regimes are globally stable in terms of flow patterns, but locally unstable in terms of flow characteristics, with power spectra of the velocity fluctuations having slopes that differ from those typically encountered in elastic turbulence. [GRAPHICS] .

In this paper, we demonstrate that a novel hybrid composite of aluminium and Carbon Fibre Reinforced Polymer (CFRP) with a microstructure inspired by a biological crossed-lamellar microstructure is an attractive alternative for applications where structural integrity is paramount. Composites with such microstructure are prototyped and tested using both standard and thin-ply CFRP prepreg. Three-point bend tests are carried out in an SEM environment, showing extensive diffuse damage in the CFRP and yielding in the aluminium. This is the first hybrid crossed-lamellar-inspired microstructure in the literature and the results demonstrate that this novel microstructure can be loaded up to record large curvatures (in comparison with other CFRPs and hybrid CFRPs) while retaining its structural integrity and dissipating energy under stable conditions.

Translaminar fracture toughness is a vital property governing the notch sensitivity and damage tolerance of composites. Nature has shown that incorporating material transitions can increase toughness significantly. This work presents finite element models demonstrating that such transitions can indeed increase the translaminar fracture toughness. The designed microstructures were then 3D printed using continuous glass and carbon fibres. The specimens consisted primarily of glass fibres, but with local carbon fibre strips. A new compact tension specimen with a side groove was designed to ensure proper failure. When the strips were sufficiently large, toughness improvements of 20–60% were found after the crack had grown through the strips. These results reveal a powerful strategy for locally increasing the toughness in areas where it is needed the most.

In this work we investigate the role played by viscoelasticity on the thermocapillary motion of a deformable Newtonian droplet embedded in an immiscible, otherwise quiescent non-Newtonian fluid. We consider a regime in which inertia and convective transport of energy are both negligible (represented by the limit condition of vanishingly small Reynolds and Marangoni numbers) and free from gravitational effects. A constant temperature gradient is maintained by keeping two opposite sides of the computational domain at different temperatures. Consequently the droplet experiences a motion driven by the mismatch of interfacial stresses induced by the non-uniform temperature distribution on its boundary. The departures from the Newtonian behaviour are quantified via the “thermal” Deborah number, De T , and are accounted for by adopting either the Oldroyd-B model, for relatively small De T , or the FENE-CR constitutive law for a larger range of De T . In addition, the effects of model parameters, such as the concentration parameter c = 1 − β (where β is the viscoelastic viscosity ratio), or the extensibility parameter, L 2 have been studied numerically using a hybrid volume of fluid-level set method. The numerical results show that the steady-state droplet velocity behaves as a monotonically decreasing function of De T , whilst its shape deforms prolately. For increasing values of De T , the viscoelastic stresses show the tendency to be concentrated near the rear stagnation point, contributing to an increase in its local interface curvature.

© 2019 Elsevier Ltd In this work, we investigate the toughness of an inter-layer Self-Reinforced Polypropylene/Carbon Fibre Polypropylene (SRPP/CFPP) cross-ply hybrid composite and devise strategies to improve two aspects of its damage tolerance: (i) increasing the energy dissipation capability and (ii) enhancing the impact damage tolerance. To this end, we introduced discontinuities in the form of laser-cuts across the fibres of the CFPP plies, tailoring two patterns of laser-cuts to meet each specific damage tolerance requirement. We conducted penetration impact and Double Edge Notched Tensile (DEN-T) tests. The DEN-T tests, analysed via the Essential Work of Fracture method, show that engineering the microstructure successfully diffused damage. This resulted in a great increase in energy dissipation capability — 90% higher than a reference non-engineered structure. Engineering the microstructure of impact samples has led to enhanced impact damage tolerance with increased energy dissipation at a sub-critical level and delayed critical failure. ispartof: COMPOSITES PART A-APPLIED SCIENCE AND MANUFACTURING vol:121 pages:341-352 status: published

This work presents an analytical solution for electro-osmotic flow (EOF) in small amplitude oscillatory shear (SAOS) as a measuring tool suitable to characterize the linear viscoelastic properties of non-Newtonian fluids in microchannel flow. The flow in the straight microchannel is driven by applying oscillating sinusoidal electric potentials. Fourier series are used to derive an expression for the velocity field, under an externally imposed generic potential field aimed at the practical application of SAOS in characterizing the rheological properties of viscoelastic fluids. This extensive investigation covers a wide range of parameters and considers the multi-mode upper-convected Maxwell (UCM) model, which represents the rheology of viscoelastic fluids in the limit of small and slow deformations. Particular focus is given to two cases of practical interest: equal wall zeta potentials at both channel walls and negligible zeta potential at one of the walls. The results show that in flows with thin electric double layers (EDL), Reynolds numbers below 0.001, and Deborah numbers below 100, corresponding to a viscoelastic Mach number of 0.32, the velocity field outside the EDLs is linear and has a large enough amplitude of oscillation, which may allow the quantification of the storage and loss moduli in the linear regime. This technique requires the use of significantly smaller sample sizes than the traditional SAOS in a rotational rheometer.