bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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.