bluuebunny/crossref_metadata_2025 huggingface dataset:
Design of electric mechanism system based on Hall zero position sensor
Authors: Pengtao Mou , Liguoqiang  , Jiyuan
Published: October 2020

Based on the electromagnetic induction Hall zero position sensor, a multi‐stage reducer motor structure system with a brush DC motor is designed using an aviation fuel on–off valve. The output shaft of the motor structure can respond to commands, rotate double directions, and lock the brake shaft after reaching the designated position. After that, the current position and on/off situation of pipeline fuel can be derived accurately. The system has the advantages of light weight, small volume, fast response, high precision, high reliability, and integration.
Analysis of proportional valve flow field in common rail system
Authors: Yazhou Li , Du Huang , Jian Fu , Guihu Zhang , Kang Wang , Hui Xu , Sirui Chen
Published: October 2020

A certain type of proportional valve has been optimised in design by adding a damping hole in its structure, which solves the problem of pressure rise in the fuel chamber due to gap leakage when closing. An integrated circuit electromagnetic model is used to mesh the model. Based on FLUENT software, the flow characteristics of the proportional valve at different valve opening have been analysed to get the curve of turbulent kinetic energy, pressure, and flow in internal field changing with different valve opening. The results show that the proportional valve with a damping hole has faster response speed and less pressure loss at the inlet and outlet of the valve. The data and conclusion obtained in this study are very important for the performance improvement of the proportional valve.
Design and simulation of hydraulic auto‐brake‐valve of unmanned aerial vehicle
Authors: Feng Gu , Bo Zhu , Fu Ju Hong
Published: October 2020

This study designs one kind of hydraulic auto‐brake‐valve calculates its driving force and velocity, simulates its braking force and stability, in order to accomplish auto brake in the landing condition and keep braking in cruising condition of the unmanned aerial vehicle. The auto‐brake‐valve uses a servo motor to drive lead screw and nut. The output press of the auto‐brake‐valve is changed by the variation of rotate speed and direction of servo motor, that can be completed the control of the brake device.
Sodium–Calcium Exchanger Reverse Mode Sustains Dichotomous Ion Fluxes Required for Procoagulant COAT Platelet Formation
Authors: Aliotta Alessandro , Bertaggia Calderara Debora , Zermatten Maxime G. , Alberio Lorenzo
Published: October 2020

Procoagulant collagen-and-thrombin (COAT)-activated platelets represent a subpopulation of activated platelets, which retain a coat of prohemostatic proteins and express phosphatidylserine on their surface. Dichotomous intracellular signaling generating procoagulant platelet activity instead of traditional aggregating endpoints is still not fully elucidated. It has been demonstrated that secondary messengers such as calcium and sodium play a critical role in platelet activation. Therefore, we developed a flow cytometric analysis to investigate intracellular ion fluxes simultaneously during generation of aggregating and procoagulant platelets. Human platelets were activated by convulxin-plus-thrombin. Cytosolic calcium, sodium, and potassium ion fluxes were visualized by specific ion probes and analyzed by flow cytometry. We observed high and prolonged intracellular calcium concentration, transient sodium increase, and fast potassium efflux in COAT platelets, whereas aggregating non-COAT platelets rapidly decreased their calcium content, maintaining higher cytosolic sodium, and experiencing lower and slower potassium depletion. Considering these antithetical patterns, we investigated the role of the sodium–calcium exchanger (NCX) during convulxin-plus-thrombin activation. NCX inhibitors, CBDMB and ORM-10103, dose-dependently reduced the global calcium mobilization induced by convulxin-plus-thrombin activation and dose-dependently prevented formation of procoagulant COAT platelets. Our data demonstrate that both NCX modes are used after convulxin-plus-thrombin-induced platelet activation. Non-COAT platelets use forward-mode NCX, thus pumping calcium out and moving sodium in, while COAT platelets rely on reverse NCX function, which pumps additional calcium into the cytosol, by extruding sodium. In conclusion, we described for the first time the critical and dichotomous role of NCX function during convulxin-plus-thrombin-induced platelet activation.
Improving the taxonomy of fossil pollen using convolutional neural networks and superresolution microscopy
Authors: Romero Ingrid C. , Kong Shu , Fowlkes Charless C. , Jaramillo Carlos , Urban Michael A. , Oboh-Ikuenobe Francisca , D’Apolito Carlos , Punyasena Surangi W.
Published: October 2020

Significance

We demonstrate that combining optical superresolution imaging with deep learning classification methods increases the speed and accuracy of assessing the biological affinities of fossil pollen taxa. We show that it is possible to taxonomically separate pollen grains that appear morphologically similar under standard light microscopy based on nanoscale variation in pollen shape, texture, and wall structure. Using a single pollen morphospecies,
Striatopollis catatumbus
, we show that nanoscale morphological variation within the fossil taxon coincides with paleobiogeographic distributions. This new approach improves the taxonomic resolution of fossil pollen identifications and greatly enhances the use of pollen data in ecological and evolutionary research.
A Critical Review of Damage and Failure of Composite Wind Turbine Blade Structures
Authors: Chen Xiao , Eder Martin A.
Published: October 2020

Advancing beyond the historic feasibility limits deemed by designers, wind turbine rotor blades have eventually surpassed the 100m milestone, making them reside among the largest single components in the world made of fiber composite materials. In the development of wind energy, aerodynamics has been an essential field of research, just as it will still be, the recent two decades witnesses structures becoming more critical due to the ever-increasing size of the rotor blades. The fact is simple: for wind turbines to operate continuously and cost-efficiently, rotor blades must maintain their structural integrity and reliability. This study reviews recent advances in the field of the structural integrity of large scale composite wind turbine blades. A particular focus is placed on damage and failure in such structures from the triad of field observations, laboratory experiments and numerical modeling. This study also identifies the established knowledge, the latest achievements, the topical research fields and the current challenges for future research and development.
Microscale testing and modelling for damage tolerant composite materials and structures
Authors: Sørensen Bent F
Published: October 2020

There is a need for damage tolerant composite material for very large engineering structures such as wind turbine rotor blades. The development of improved composite materials with higher damage tolerance will be most efficiently guided by models of the relevant damage modes. Two damage modes are considered in the present paper: Fatigue damage due to in-plane tensile stresses in the fibre direction and cyclic delamination crack growth from a ply drop. For both failure modes the damage evolution is considered at macro- and microscale. Micromechanical models are used to illustrate how changes in the mechanical properties of fibre, matrix and the fibre/matrix interface can lead to an increased damage tolerance material. Also, micromechanical testing methods for characterizing the relevant micromechanical parameters are discussed.
State-of-the-art models for mechanical performance of carbon-glass hybrid composites in wind turbine blades
Authors: Swolfs Yentl , Fazlali Babak , Melnikov Arsen , Mesquita Francisco , Feyen Vincent , Breite Christian , Gorbatikh Larissa , Lomov Stepan V
Published: October 2020

Wind turbine blades are a key growth market for fibre-hybrid composites, as they offer the potential for higher turbine efficiency at a reduced cost. This paper therefore overviews the developments of KU Leuven models for mechanical properties relevant to wind turbine blades, including fibre-hybridisation, size scaling effects, flexure, transverse cracking, stress relaxation and fatigue. The strengths and limitations of the models will be highlighted with a particular focus on relevance for wind turbine blades. While significant steps forward have been made, the various developments still need to be incorporated in one all-encompassing model, and further work is needed on gathering the required input data and detailed experimental validation studies.
ReliaBlade Project: A Material’s Perspective towards the Digitalization of Wind Turbine Rotor Blades
Authors: Sayer F , Antoniou A , Goutianos S , Gebauer I , Branner K , Balzani C
Published: October 2020

In many industries, digitalization is expected to have a significant economic potential. The digitalization of wind turbine rotor blades including their materials could contribute to accelerate the development of novel and tailored materials, to improve the blades’ reliability, and to make wind energy more cost efficient. However, the digitalization of the blades through their entire life cycle is challenging e.g. due to the dependence of the material properties on the manufacturing process parameters, the complex structural health monitoring and the challenging modelling of blade response under complex loading. In the presented work based on the results of the ReliaBlade project, a theoretical approach is attempted towards describing the blade in-situ structural performance, based on the material properties, the blade manufacturing processes and loading history. In the first phase of the ReliaBlade project, an experimental blade for full-scale testing with three pre-defined internal damage modes is designed. Based on these damage modes the digitalization approach towards increasing the blade structural reliability is exemplarily shown.
Proof of concept: elliptical biaxial rotor blade fatigue test with resonant excitation
Authors: Melcher David , Rosemann Heiko , Haller Bernd , Neßlinger Sebastian , Petersen Enno , Rosemeier Malo
Published: October 2020

Rotor blades of wind turbines are subjected to high-cycle fatigue during their lifetime of 20-25 years. To show that a blade design fulfils the normative requirements, the test campaign usually consists of two consecutive cyclic tests, i.e., in the flapwise and lead-lag directions. The fatigue test excites the blade close to its corresponding natural frequency. Combining the two uniaxial tests into one biaxial test excites the blade in both directions simultaneously. Using the same excitation frequency for both directions results in the blade cross-sections describing an elliptical deflection path. To realize such a test while still exciting close to resonance, the natural frequencies for the two directions need to be equalized with the aid of decoupled masses and stiffness elements. This approach reduces the testing time, and induces a more realistic loading which is comparable with field conditions while keeping the energy consumption of the hydraulic actuation low. This work describes the concept of the elliptical biaxial rotor blade fatigue test with resonant excitation using a commercial blade design. To this end, the design model, which uses both a transient and a harmonic simulation, is validated with the experimental results of the test. The simulation model and the experiment agree well with each other in terms of displacements and loads along the blade.
On the composite design of wood branches leading to improved bending strength
Authors: Hartwig M , Gamstedt E K
Published: October 2020

Wooden branches are designed to carry large bending moments, and so are longer composite structures, e.g. rotor blades for wind turbines. Being a natural fibrous composite material, wood is made from relatively simple biopolymer building blocks. In this preliminary work, we describe the composition and structure of softwood branches, including 3D images from X-ray computed tomography. The main difference in branch structure compared with other wood tissues is the reaction wood formed on the compressive side in e.g. spruce and pine. A simple beam is used to show that maximum bending moment is multiplied several times solely from the reaction wood. This is noteworthy, since chemical composition of the reaction wood does not differ significantly from the rest of the wood. The tissue gradients in the branch resulting from variation in density, microfibrillar angle and cell geometry contribute to the strength improvements. In composite structures, sandwich design is used to improve the load carrying capacity. From a general perspective, also local features as found in wood, such as smooth gradients and controlled cellular structure, could be further explored to improve bending strength in engineered composite materials.
The influence of different glass fiber/epoxy matrix combinations on the durability under severe moisture impact
Authors: Gibhardt D , Fleschhut C , Fiedler B
Published: October 2020

The growing success of fiber reinforced polymers (FRP) as material for the construction of high-performance lightweight structures used under maritime environmental conditions, requires foremost the knowledge about their long term durability. As the supplier market is still growing fast, methods which allow manufacturers to distinguish between suitable and less suitable composites are needed. In this study, the effects of moisture on the mechanical properties of glass fiber reinforced polymers (GFRP) using different glass fiber fabrics are investigated under several ageing and testing conditions. Focusing on the fabrics and introducing an ageing method prior to composite manufacturing, allows to describe the proportions of fiber, matrix, sizing and interphase damage to the composites durability in more detail. Absorption quantity related testing after ageing at temperatures between 8°C and 50 °C highlights the resulting effects on the tensile strength of mostly unidirectional GFRPs. The strength of composites based on fabrics with high resistance to moisture degradation decreases steady but moderate during absorption. This effect is mainly associated with changes of matrix properties. However, less durable composites show a two-stage behavior. In this case, severe interphase damage and cracking leads to an additional drastic strength decrease when exceeding a defined amount of water absorption.
Mechanical properties characterization of the Ichu fibers composites
Authors: Charca S , Candiotti S
Published: October 2020

In the recent years, natural fibers are gaining an outstanding position as a reinforcement material, due to diverse advantages like high specific properties, low cost and low environmental impact. On the other hand, according to the market studies, in the next years the offer of the natural fibers will be in deficit; therefore, exploration of new natural fibers from new resources can be an alternative to fill this gap. Along the Andean region there are diverse natural resources from which cellulosic fibers can be extracted, like the Stipa obtusa grass, also commonly known as Ichu. The main purpose of this research was to determine the mechanical properties of unidirectional composite laminates made from Ichu fibers mixed with polyester resin; tensile, compressive and shear properties were evaluated. Results show that the stiffness in the principal direction (E1 ∼ 16 GPa) and the transverse direction (E2 ∼ 4.7 GPa) are over the average values compared to the composites made from the commercial fibers; similar behavior was observed in its shear and compression characteristics. Strength shows values around σ
1 ∼ 118 MPa, σ
2∼ 13 MPa, τ
12∼ 46 MPa and τ
21∼ 18 MPa, which is similar to the values reported in the literature for the commercial natural fiber composites. Based on these results, the Ichu fiber has a great potential as a reinforcement in composites materials.
A comparison of surface preparation techniques for wind turbine field repairs
Authors: Lusty Ariel , Cairns Douglas , Miller David , Samborsky Daniel
Published: October 2020

Wind turbine service lifetimes can exceed 20 years. This extreme operational demand necessitates reliable and consistent field repairs; however, the effects of current wind turbine field repair surface preparation techniques are not well-documented and are thus not well-understood. This leads to reliance on technician experience rather than scientific data for repair procedures, which causes variability in the quality of repairs. Solvent wiping is a common procedure for contaminant removal after damaged material is removed from a wind turbine blade, but it was unknown if solvent wiping reduced the surface energy and consequently the likelihood of a durable repair. The goal of this study was to quantify the effects that various surface preparation techniques have on the overall strength and reliability of wind turbine repairs. Type of reagent-grade solvent, fiber direction, matrix, and adhesive were varied for contact angle, lap shear, Double Cantilever Beam (DCB), and End-Notch Flexure (ENF) testing. The type of solvent used did not affect surface energy, maximum lap shear stress, or modes I and II fracture toughness values. However matrix-adhesive combinations significantly affected maximum lap shear stress and fracture toughness values.
Recyclable epoxy systems for rotor blades
Authors: Dubey Pradip K , Mahanth Satish K , Dixit Amit , Changmongkol Sirirat
Published: October 2020

The global energy demand is largely met by power generated from fossil fuels (Thermal Power plants) and nuclear means (Nuclear Power plants). Even though both these technologies have been used for decades, they have huge environmental impact and severe sustainability issues with depleting fossil fuel and serious concerns about the spent nuclear rods disposal. With growing awareness of impact on the environment and finding a sustainable solution for power generation, wind energy offers a lasting solution that addresses both issues, however it is still not truly sustainable as the primary materials used for manufacturing of rotor blades are non-recyclable. A new revolutionary technological solution has been invented where in, the epoxy thermoset can be recovered as thermoplastic and the reinforcement in composite can be re-used, making it a first of its kind in the thermoset industry segment. The Recyclable Epoxy Systems for rotor blades provide a path breaking solution that enables recycling of epoxy thermoset, recovery and re-use of the reinforcement and the matrix in a fibre reinforced composite. Leveraging from the proprietary Recyclamine® platform technology, series of recyclable epoxy systems are developed for wet lay-up and infusion processes to meet the requirements for both on-shore and off-shore rotor blades, including next generation rotor blades. The systems are characterized by determining process and performance properties and found to provide distinct advantages in comparison to the conventional non-recyclable epoxy systems. The recycling of composites made from recyclable epoxy systems is successfully demonstrated by low energy solvolysis followed by recovery of the reinforcement and epoxy matrix as thermoplastic. The recovered reinforcement and epoxy thermoplastic are re-used to make composite and representative thermoplastic object respectively, deriving value from the waste and closing the loop to make the wind energy industry sustainable for a circular economy.
Re-use of wind turbine blade for construction and infrastructure applications
Authors: André A , Kullberg J , Nygren D , Mattsson C , Nedev G , Haghani R
Published: October 2020

To achieve a more resource-efficient society with a future with reduced carbon dioxide emissions, new technological challenges must be dealt. One way to reach a more sustainable world is to start re-using end-of-life structures and waste and give them a ‘Second Life” with a new function in the society. As composite structures are lightweight, strong, stiff and durable materials, there is great potential to re-use decommissioned composite for new resource-efficient solutions in the building and infrastructure sector. The present paper investigates innovative solutions in re-using wind turbine blades as elements in new bicycle and pedestrian bridge designs. Several conceptual bridge designs where wind blades utilized as load bearing elements were developed and studied. The main design requirements for pedestrian bridges were considered and assumptions regarding wind blades quality and their mechanical properties addressed based on interviews with industries working with wind turbine blades repair and recycling. The aim of this paper is to contribute to a sustainable use of fibre reinforced polymer (FRP) waste and at the same time provide a more cost-effective FRP bridges. In a larger perspective, the authors would like to highlight the economically profitable potential of recovering and reusing / re-manufacturing end-of-life glass FRP composites.
Composite wind turbine blade recycling - value creation through Industry 4.0 to enable circularity in repurposing of composites
Authors: Geiger Raphael , Hannan Yasser , Travia William , Naboni Roberto , Schlette Christian
Published: October 2020

Composite waste, especially from wind turbine blades will increase foreseeably. The motivation of this paper is to develop new solutions to repurpose the global material stream coming from wind turbine blades at their end of use. Its suggested to use the composite structure for repurposing, differing from the available recycling methods that aim for a separation of the composite into fibre and matrix fractions. One key factor towards circularity in composite materials is converting significant amounts of composite material into multiple meaningful applications and products. Industry 4.0 can offer a systemic solution utilising robots and digital tools, such as a digital twin of a composite wind turbine blade. The digital handling of relevant material information can offer a new affordable material source to multiple industries, such as building industry or manufacturing businesses. Based on a digital platform the composite material can be made available for architects, designers and developers to repurpose composites into multiple new products.
Micromechanical and spectroscopic characterisation of the curing performance of epoxy resins in the microbond test
Authors: Bryce David , Thomason James , Yang Liu
Published: October 2020

In the present work, the microscale curing performance of two epoxy resin systems was investigated. It was shown that the degree to which these resins formed cured axisymmetric droplets suitable for microbond testing was influenced by the inclusion of a room-temperature pre-cure stage. Immediate curing at elevated temperature of these systems resulted in the formation of under-cured, soft droplets that deformed under loading. The introduction of a protracted room temperature standing time increased the apparent interfacial shear strength substantially. Fourier-transform infrared spectra generated by a novel technique allowed for the glass transition temperature of microdroplet samples to be determined and detected deviations from stoichiometry. Good correlation was shown between the two methods, in that an increase in IFSS was commensurate with spectra indicating droplets were closer to the ideal stoichiometric ratio, and had both higher degrees of cure and glass transition temperatures.
Multiaxial stress and strain analysis on laminated plates under different flexural loading rates
Authors: Horta Muñoz S , Serna Moreno M C
Published: October 2020

The occurrence of events associated with Low-Velocity Impacts (LVI) is analysed by drop-weight impact tests on carbon fibre reinforced polymer laminates, comparing the response in these tests with Quasi-Static Indentation (QSI). A laminate sequence of interest, the angle-ply [±45]4S, is tested in both testing procedures with a simply supported configuration on a circular fixture. Both methodologies show similarities in the critical points for change of behaviour in terms of energy, while the strain rate effect is verified to influence the higher apparent stiffness of the laminate submitted to the LVI test compared with the QSI test. The effect of multiaxiality in loads existing in these tests is addressed in the quasi-static experiment by applying Digital Image Correlation (DIC), comparing the results with numerical simulations using the Finite Element Method (FEM). The orthotropy of the material generates strain and displacement fields which allow understanding the dissimilar response of the laminate in the different radial directions, also giving explanation to the initiation and evolution of different damage mechanisms.
Rain droplet erosion behavior of a thermoplastic based leading edge protection system for wind turbine blades
Authors: Hoksbergen T.H. , Baran I. , Akkerman R.
Published: October 2020

This paper discusses the rain droplet erosion mechanisms of an acrylonitrile butadiene styrene (ABS). Rain droplet impingement was modeled based on a coupled smoothed particle hydrodynamics and finite element method (SPH/FEM). Using linear elastic material parameters at low strain rates, the dynamic stress behavior was studied and the location of damage initiation was predicted. Experiments using a pulsating jet erosion tester were performed and the resulting erosion behavior was analyzed using confocal microscopy. The damage was expected to initiate at the surface and remain superficial during propagation. It was shown that a pitting behavior occurred at the surface after the first few impacts. This pitting continued until 100.000 impacts. After this, the pits connected through a cracking mechanism and finally, at 300.000 impacts, cratering was observed which led to the onset of material loss. The depth of these craters was observed to be approximately 80µm, which was relatively low as compared to the material thickness of 4mm, indicating superficial damage. The resulting volume loss curve showed an initial period where no volume loss occurred, called the incubation period, followed by a linear relation between the volume loss and the number of impacts. This behavior agreed well with behavior found for other materials in literature. The surface roughness parameters were determined for each amount of impacts and the mean roughness value corresponded well to the volume loss behavior. Earlier stages of damage could be detected by analyzing the skewness value.
A practical approach for the peel stress prediction in the trailing-edge adhesive joint of wind turbine blades
Authors: Rosemeier M , Gebauer T , Antoniou A
Published: October 2020

Wind turbine blades consist of thin-walled cylindric and airfoil-shaped structures, which are prone to “breathing” or “pumping” when subjected to cyclic loading. The “pumping” induces a peel stress in the adhesive layer of the trailing-edge bond line. To take account of this peel stress in the design phase, adequate models are required. State-of-the-art blade finite element (FE) models are usually implemented using shell elements. The trailing-edge joint is often represented by solid elements that are connected with the shell elements. The peel stress peak of interest occurs at the edge of the adhesive joint, which is, subject to a singularity, however. This study proposes a practical approach to estimate the peel stress peak in the adhesive joint with the help of the analytical solution which approximates and extrapolates the FE results. Moreover, different modeling techniques are benchmarked in respect of the peel stress prediction.
On the potential of particle engineered anti-erosion coatings for leading edge protection of wind turbine blades: Computational studies
Authors: Jespersen K M , Monastyreckis G , Mishnaevsky L
Published: October 2020

The potential of particle and fiber reinforced anti-erosion coatings for the protection of wind turbine blades is explored through computational modelling. A hypothesis that stiff disc-shaped particle or fiber reinforcements embedded in viscoelastic coatings ensure better erosion protection is validated numerically, and mechanisms of this effect are analyzed. A computational unit cell model of coatings with embedded fibers (fiber pulp) or disc particles subject to rain droplet impact is developed, and series of computational experiments is carried out. The distribution and scattering of stress waves from the rain droplet impact and damping properties are analyzed for homogeneous viscoelastic polyurethane coatings, coatings with discshaped particles, and fiber pulp. It is shown that the stress waves are increasingly scattered, and the damping is increased with higher volume percentage of the fibers. The mechanism of such increased energy dissipation is found to be related to the high local viscoelastic deformation in the regions between closely located fibers and the higher stiffness of the unit cell. The current work demonstrates the high potential of fiber engineered coatings for the improvement of anti-erosion protection of wind turbine blades.
Characterisation of fibre/matrix interfacial fracture energy using the single fibre peel experiment
Authors: Hottentot Cederløf Daan J , Sørensen Bent F
Published: October 2020

An experimental method for determining the interfacial fracture energy of a single fibre undergoing peeling is presented. Peeling of a partially embedded single fibre is observed under scanning electron microscopy. The fracture energy of the fibre/matrix interface is determined by analysis of the measured curvature of the fibre near the crack tip. This study serves as a demonstration of concept for the characterization of fibre/matrix interfaces through the single fibre peel experiment. A glass fibre/vinylester interface is used as an initial test case, from which obtained interfacial fracture energies was found to be in the range from 2 Jm−2 to 14 Jm−2.
The effect of environmental ageing in the interphase of a glass fibre/vinyl ester composite designed for wind turbine applications
Authors: Xypolias G , Thomason J , Yang L
Published: October 2020

The use of advanced fibre reinforced polymer (FRP) composites in the renewable energy sector has significantly increased over the last decade. However, the durability and damage tolerance of such materials when exposed to environmental conditions still remains under investigation. This creates some uncertainty for their introduction and development in the sector. The scope of the present work is the assessment of the durability of composite laminates and structures through providing a fundamental understanding of the micromechanical performance of the glass fibre/vinyl ester fibre-matrix interphase as a function of the environmental history. An accelerated ageing study has been conducted in order to create a correlation between the moisture sorption at the interphase and its effect in the micromechanical performance of the composite system. The composite interphase performance has been assessed by measuring the Interfacial Shear Strength (IFSS) using the microbond test. An estimation of the moisture sorption of each microbond sample has been obtained by the gravimetric analysis of thin film neat resins specimens of similar thickness to the microbond sample diameter. These results have also been coupled to results obtained by Fourier-transform Infrared Spectroscopy (FTIR). Additionally, moisture induced degradation has been characterised by recording the change in the Tg of the vinyl ester resin as a function of environmental ageing by a number of thermal analysis techniques.
Design of lamina orientation for biaxially loaded off-axis tunnelling cracks
Authors: Bangaru Ashish K , Mikkelsen Lars P , Sørensen Bent F
Published: October 2020

The primary objective of this work is to demonstrate how the condition for biaxially loaded off-axis tunnelling crack growth can be reproduced in a modified laminate under uniaxial loading. More specifically, laminates with the stacking sequences [0/θ/0/-θ]
s
and [0/α/0/-α]
s
have been considered for the biaxial and uniaxial loadings, respectively. A steady-state crack growth condition is analysed for an isolated off-axis tunnelling crack. The crack tip stress state is expressed in terms of a through thickness averaged mode mixity and energy release rate. The presented framework uses an energy accounting method with the crack opening displacements extracted from a finite element analysis. Results shows that the tunnelling crack tip stress state of the modified laminate under uniaxial loading matches with the biaxially loaded laminate. With a modified off-axis lamina orientation and the additional load amplitude from the biaxially loaded laminate, a simplified uniaxial testing laminate can be designed that yields the same biaxial tunnelling crack tip conditions.
Investigations of the carbon fibre cross-sectional areas and their non-circularities by means of laser diffraction
Authors: Huether Jonas J. , Liebig Wilfried V.
Published: October 2020

Laser diffraction is a commonly used tool to measure the fibre diameter of carbon fibres prior to mechanical testing. However, non-circularities of carbon fibres need to be considered in order to minimise measuring errors. As the work at hand demonstrates, using a single measurement of the fibre diameter may cause deviations as high as 30% from a computationally determined value. It appears that the error can be minimised by acquiring a data set of several apparent diameters as a function of the angle around the fibre axis. Based on this data, the cross-sectional area can be calculated as a circle with an averaged diameter or as an ellipse by applying an elliptical fitting procedure.
Evolution of CFRP stress cracks observed by in-situ X-ray refractive imaging
Authors: Kupsch A , Trappe V , Müller B R , Bruno G
Published: October 2020

Modern air-liners and wind turbine rotor blades are made up primarily of fiber reinforced plastics. Failure of these materials heavily impairs the serviceability and the operational safety. Consequently, knowledge of the failure behavior under static and cyclic loads is of great interest to estimate the operational strength and to compare the performance of different materials. Ideally, the damage evolution under operational load is determined with in-situ non-destructive testing techniques. Here, we report in-situ synchrotron X-ray imaging of tensile stress induced cracks in carbon fiber reinforced plastics due to inter-fiber failure. An in-house designed compact tensile testing machine with a load range up to 15 kN was integrated into the beamline. Since conventional radiographs do not reveal sufficient contrast to distinguish cracks due to inter-fiber failure and micro cracking from fiber bundles, the Diffraction Enhanced Imaging (DEI) technique is applied in order to separate primary and scattered (refracted) radiation by means of an analyzer crystal. This technique allows fast measurements over large fields-of-view and is ideal for in-situ investigations. Imaging and the tensile test are run at the highest possible frame rate (0.7 s−1) and the lowest possible strain rate (5.5·10−4 s−1). For 0°/90° non-crimp fabrics, the first inter-fiber cracks occur at 380 MPa (strain 0.8 %). Prior to failure at about 760 MPa (strain 2.0 %), we observe the evolution of nearly equidistant (1 mm distance) cracks running across the entire sample in the fully damaged state.
Comparison of the damage evolution in glass fiber-reinforced polyurethane and epoxy in the HCF and VHCF regimes investigated by intermittent in situ X-ray computed tomography
Authors: Hülsbusch D , Helwing R , Mrzljak S , Walther F
Published: October 2020

The aim of this work is the comparative characterization of the fatigue and damage behaviors of GFR-polyurethane and GFR-epoxy with application-relevant quasi-isotropic layer setup in the high cycle and very-high cycle fatigue regimes. Therefore, a high-frequency test method based on a resonant testing system (1 kHz) has been further developed and assessed with special consideration of self-heating. In intermittent test procedures, the damage state has been explored by in situ X-ray computed tomography analysis after certain numbers of cycles. It was shown that the overall damage state in the VHCF regime is reduced by a factor of three compared to the HCF regime and accompanied by delayed initiation and propagation of delamination. The latter was proven to be the main reason for a decreased inclination of the S/N-curve in the VHCF regime by 50-60%.
Does age matter? Impact on fire safety properties of composite materials from ageing
Authors: Sandinge Anna , Blomqvist Per , Dederichs Anne
Published: October 2020

When materials are tested and classified before entering the market, they are mainly tested as newly produced. However, it is known that material properties change with time and when exposed to temperature, humidity, wind and light. As a result, it is important to have knowledge of how material age and which parameters are affected in order to retain safety. Studies show how the mechanical properties change when the materials age. But not much can be found in literature about the ageing effect on fire properties. In the present study, accelerated ageing testing was made with a composite material of phenolic resin and basalt fibres. Selected ageing methods applied were thermal ageing at 90 °C and moisture ageing at 40 °C and 90 % Relative Humidity. Samples were collected from ageing chambers after one, two and four weeks. To investigate the ageing effect on the fire properties of the composite, fire testing was conducted using cone calorimetry according to ISO 5660-1. The test results showed that ageing does matter. There was an impact on the material and the fire properties were affected. The ignition time decreased for the aged samples and the heat release rate slightly increased. Also, the smoke production increased with ageing.
Strength analysis of a 5-m composite wind turbine blade under static and fatigue loading conditions
Authors: Muyan C , Coker D
Published: October 2020

This study focuses on the static and fatigue strength analysis of the existing 5-m RUZGEM composite wind turbine blade with and without defect in the form of debonding. Puck progressive damage analysis is used to investigate the effect of defect introduced to the spar/pressure side interface on the ultimate strength under extreme flap-wise (min) by single-loading point application. In addition, fatigue life according to the Germanischer Lyod (GL) guidelines is determined. For the original blade, collapse is observed after 85% loading, whereas due to defect, failure region changes and the blade collapses after 69% loading. Blade is found to exhibit sufficient resistance against fatigue. However, the inclusion of defect decreases the fatigue life of the blade significantly.
AHR Conversation: Black Internationalism
Authors: Bedasse Monique , Butler Kim D. , Fernandes Carlos , Laumann Dennis , Nagaraja Tejasvi , Talton Benjamin , Thurman Kira
Published: October 2020

This annual AHR Conversation focuses on the issues and historiographic debates raised by the term “Black Internationalism.” Participants Monique Bedasse, Kim D. Butler, Carlos Fernandes, Dennis Laumann, Tejasvi Nagaraja, Benjamin Talton, and Kira Thurman bring a wide array of interests and areas of expertise to bear on the origins, evolution, and meaning of the concept of Black Internationalism; its application within Africa, the U.S., and the African diaspora more generally; and its relationship to gender, nationalism, and anticolonialism. In addition to tracing the deep roots of this framework for writing the history of Black resistance to slavery, colonialism, and white supremacy as global phenomena, they insist on seeing Black Internationalism from multiple points on the compass. Perspectives derived from the history—and intellectual production—of Africa, Europe, South America, and the Caribbean prove just as important, if not more so, than those emanating from the United States.
From Counterpublics to Contentious Publicness: Tracing the Temporal, Spatial, and Material Articulations of Popular Protest Through Social Media
Authors: Kavada Anastasia , Poell Thomas
Published: October 2020

This article presents a new approach to the study of public contestation through social media. Developing this approach, we make three conceptual moves. First, to capture the dynamic character of contemporary contestation, we shift attention from publics to publicness as an interactive process. Second, we turn the focus from the “counter,” as a public or space distinct from the dominant sphere, towards distributed forms of contention. Finally, instead of considering media as arenas of claims, we investigate how media are constitutive of contentious publicness, which can be studied along its material, spatial, and temporal dimensions. These moves lead to an analytical framework through which trajectories of contentious publicness can be systematically traced and evaluated. Through case studies on the 2011 Egyptian uprising and the Occupy protests, we demonstrate how this framework can be employed to examine the construction of new contentious actors and evaluate their democratic legitimacy as claim-makers.
Exploratory Survey of Spotted Lanternfly (Hemiptera: Fulgoridae) and Its Natural Enemies in China
Authors: Xin Bei , Zhang Yan-long , Wang Xiao-yi , Cao Liang-ming , Hoelmer Kim A , Broadley Hannah J , Gould Juli R
Published: October 2020

An invasive population of spotted lanternfly (SLF), Lycorma delicatula White, was first noted in North America in Pennsylvania in 2014, and by September 2020 populations had spread to six additional states. To develop a biocontrol program to aid in the management of the pest, exploratory surveys for SLF natural enemies in its native range were carried out in 27 provinces and other administrative regions of China from 2015 to 2019. Naturally laid egg masses were collected and sentinel SLF egg masses were deployed to attract egg parasitoids, and yellow sticky traps were used to collect SLF nymphs to discover and determine the parasitism rates of nymphal parasitoids. Results show that SLF is widely distributed in China (22 provinces and regions) and that the population densities in northeast China are higher than in southern and western China. An egg parasitoid, Anastatus orientalis Yang (Hymenoptera: Eupelmidae), and a nymphal parasitoid, Dryinus sinicus Olmi (Hymenoptera: Dryinidae), were collected. Anastatus orientalis was reared from SLF eggs in seven provinces in China with parasitoid emergence rates ranging from 4.0 to 15.5% (or 17.6 to 37.3% if including only egg masses that had at least some parasitism). There were significant differences in parasitoid emergence rates between sites associated with factors including habitat and host plants. Dryinus sinicus was discovered in eight cities across six provinces. The percentage of SLF nymphs parasitized by D. sinicus were 31.1, 23.3, and 0% in Tai’an, Shandong Province, Beijing City, and Yan’an, Shaanxi Province, respectively. These two parasitoids are promising natural enemies that are being considered as potential biocontrol agents of invasive populations of SLF.
Antibacterial action of acriflavine hydrochloride for eradication of the gastric pathogen Helicobacter pylori
Authors: Tehlan Ankita , Karmakar Bipul Chandra , Paul Sangita , Kumar Raghwan , Kaur Inderjeet , Ghosh Amit , Mukhopadhyay Asish K , Dhar Suman Kumar
Published: October 2020

Helicobacter pylori, a type 1 carcinogen, accounts for numerous gastric cancer-related deaths worldwide. Repurposing existing drugs or developing new ones for a combinatorial approach against increasing antimicrobial resistance is the need of the hour. This study highlights the efficacy of acriflavine hydrochloride (ACF-HCl) in inhibiting the growth of H. pylori reference strain and antibiotic-resistant clinical isolates at low concentrations. ACF-HCl inhibits H. pylori growth at MIC value 10 times less than that in Escherichia coli, another Gram-negative bacteria. Furthermore, ACF-HCl demonstrates synergistic effect with clarithromycin, a commonly used antibiotic against H. pylori. ACF-HCl treatment also eradicates H. pylori infection in the mice model efficiently. Our in vitro data indicate that bacterial membrane is the prime target. The novel action of ACF-HCl against antibiotic-resistant clinical isolates, synergistic effect with the conventional antibiotic clarithromycin and eradication of H. pylori from infected mice highlight the potential of ACF-HCl as a promising therapeutic agent against H. pylori by itself as well as for combinatorial therapy.
Large-Scale Phylogenetic Analysis of Trypanosomatid Adenylate Cyclases Reveals Associations with Extracellular Lifestyle and Host–Pathogen Interplay
Authors: Durante Ignacio Miguel , Butenko Anzhelika , Rašková Vendula , Charyyeva Arzuv , Svobodová Michaela , Yurchenko Vyacheslav , Hashimi Hassan , Lukeš Julius
Published: October 2020

Receptor adenylate cyclases (RACs) on the surface of trypanosomatids are important players in the host–parasite interface. They detect still unidentified environmental signals that affect the parasites’ responses to host immune challenge, coordination of social motility, and regulation of cell division. A lesser known class of oxygen-sensing adenylate cyclases (OACs) related to RACs has been lost in trypanosomes and expanded mostly in Leishmania species and related insect-dwelling trypanosomatids. In this work, we have undertaken a large-scale phylogenetic analysis of both classes of adenylate cyclases (ACs) in trypanosomatids and the free-living Bodo saltans. We observe that the expanded RAC repertoire in trypanosomatids with a two-host life cycle is not only associated with an extracellular lifestyle within the vertebrate host, but also with a complex path through the insect vector involving several life cycle stages. In Trypanosoma brucei, RACs are split into two major clades, which significantly differ in their expression profiles in the mammalian host and the insect vector. RACs of the closely related Trypanosoma congolense are intermingled within these two clades, supporting early RAC diversification. Subspecies of T. brucei that have lost the capacity to infect insects exhibit high numbers of pseudogenized RACs, suggesting many of these proteins have become redundant upon the acquisition of a single-host life cycle. OACs appear to be an innovation occurring after the expansion of RACs in trypanosomatids. Endosymbiont-harboring trypanosomatids exhibit a diversification of OACs, whereas these proteins are pseudogenized in Leishmania subgenus Viannia. This analysis sheds light on how ACs have evolved to allow diverse trypanosomatids to occupy multifarious niches and assume various lifestyles.