Fatigue crack growth identification in bonded joints by using carbon nanotube doped adhesive films - IOPscience
An investigation on fatigue crack growth monitoring of bonded joints has been conducted employing a novel carbon nanotube (CNT) adhesive film, chosen for their proven exceptional properties for sensing purposes. Single lap shear fatigue tests have been carried out at a 7 kN load, load ratio 0.1 and 10 Hz frequency. A correlation between the electrical response of the adhesive joints and the fatigue crack growth has been established by means of voltage acquisition through the thickness in combination with crack length monitoring by microscopy analysis. Three phases can be distinguished during the fatigue tests: phase one without crack initiation with a steady electrical response; phase two in which cracks start propagating, with a slight increase of the electrical resistance, and phase three, corresponding to final propagation to failure with a drastic increase of the electrical resistance. A correlation between the electrical response, the estimated crack area and the measured edge-crack size is achieved, allowing to get a deeper understanding of crack growth phenomenon as a function of the number of cycles. Thus, the potential and the applicability of the proposed technique for monitoring crack growth in lap joint fatigue tests have been demonstrated.
5 février 2020
29 janvier 2020
Innovation Fields for Sustainable Development of Wind Power | SpringerLink
Innovation Fields for Sustainable Development of Wind Power | SpringerLink
This chapter intends to elucidate technical routes for sustainable development of wind power industry. However, the most prominent bottleneck for the target evidently comes from intermittent and stochastic source, which very likely causes extensive wind power curtailment. To cope with this challenging issue, the innovation technologies proposed in this chapter are generally divided into two categories......
This chapter intends to elucidate technical routes for sustainable development of wind power industry. However, the most prominent bottleneck for the target evidently comes from intermittent and stochastic source, which very likely causes extensive wind power curtailment. To cope with this challenging issue, the innovation technologies proposed in this chapter are generally divided into two categories......
(PDF) A Unified Formulation for Fatigue Crack Onset and Growth via Cohesive Zone Modelling
A Unified Formulation for Fatigue Crack Onset and Growth via Cohesive Zone Modelling
This paper presents a unified cohesive zone formulation for describing the fatigue-driven crack onset and propagation in quasi-brittle materials. This approach is based on formulating a modified traction-displacement law involving linear softening, which accounts for the onset of fatigue failure described by materials S-N curves. The fatigue crack propagation in a steady-state regime is described as a sequence of initiation stages that progressively take place within the process zone ahead of the zero-stress fracture tip. It is demonstrated that the damage distribution within the process zone under cyclic load is governed by a non-linear Fredholm integral equation of the second kind, which is solved numerically using an iterative scheme. It is also shown that the Paris-Erdogan law for fatigue crack growth can be directly obtained from engineering S-N curves via the linear traction displacement model introduced here. The Paris-Erdogan propagation regime is attained when the crack propagation rate is much smaller that the length of the process zone. The exponent of the Paris-Erdogan law is equal to half the inverse of that characterising the material S-N curve. The main advantage of the cohesive zone model introduced here is that it does require neither ad-hoc additional parameters nor calibration constant to obtain the Paris-Erdogan law from material S-N data. It is also proved that the cohesive zone length in fatigue depends on the exponent of the S-N curve and it always shorter than its static counterpart. The unified cohesive zone model is validated against experimental data for the specific cases of mode I and mode II fatigue delamination growth in the carbon/epoxy composite material IM7/8552. Finally, an analysis of the role played by size effects is presented, with emphasis on the influence of the laminate thickness on the fatigue damage accumulation within the process zone and the ensuing propagation rates of cohesive cracks.
This paper presents a unified cohesive zone formulation for describing the fatigue-driven crack onset and propagation in quasi-brittle materials. This approach is based on formulating a modified traction-displacement law involving linear softening, which accounts for the onset of fatigue failure described by materials S-N curves. The fatigue crack propagation in a steady-state regime is described as a sequence of initiation stages that progressively take place within the process zone ahead of the zero-stress fracture tip. It is demonstrated that the damage distribution within the process zone under cyclic load is governed by a non-linear Fredholm integral equation of the second kind, which is solved numerically using an iterative scheme. It is also shown that the Paris-Erdogan law for fatigue crack growth can be directly obtained from engineering S-N curves via the linear traction displacement model introduced here. The Paris-Erdogan propagation regime is attained when the crack propagation rate is much smaller that the length of the process zone. The exponent of the Paris-Erdogan law is equal to half the inverse of that characterising the material S-N curve. The main advantage of the cohesive zone model introduced here is that it does require neither ad-hoc additional parameters nor calibration constant to obtain the Paris-Erdogan law from material S-N data. It is also proved that the cohesive zone length in fatigue depends on the exponent of the S-N curve and it always shorter than its static counterpart. The unified cohesive zone model is validated against experimental data for the specific cases of mode I and mode II fatigue delamination growth in the carbon/epoxy composite material IM7/8552. Finally, an analysis of the role played by size effects is presented, with emphasis on the influence of the laminate thickness on the fatigue damage accumulation within the process zone and the ensuing propagation rates of cohesive cracks.
US20200018292A1 - Nacelle cover for wind turbines - Google Patents
US20200018292A1 - Nacelle cover for wind turbines - Google Patents
Provided is a nacelle for a wind turbine, the nacelle including an support frame and a nacelle cover coupled to the support frame, wherein the nacelle cover comprises a self-supported nacelle roof comprising a plurality of panels made of a composite, the panels being connected to each other by means of connection flanges integral to the panels, wherein the self-supported nacelle roof extends, while being unsupported by the support frame at least in a center section of the self-supported nacelle roof, from a first lateral side of the nacelle to a second lateral side of the nacelle. A wind turbine including the nacelle, a wind park including a plurality of wind turbines and methods is also provided.
Provided is a nacelle for a wind turbine, the nacelle including an support frame and a nacelle cover coupled to the support frame, wherein the nacelle cover comprises a self-supported nacelle roof comprising a plurality of panels made of a composite, the panels being connected to each other by means of connection flanges integral to the panels, wherein the self-supported nacelle roof extends, while being unsupported by the support frame at least in a center section of the self-supported nacelle roof, from a first lateral side of the nacelle to a second lateral side of the nacelle. A wind turbine including the nacelle, a wind park including a plurality of wind turbines and methods is also provided.
US20200018284A1 - Wind turbine blade and a wind turbine - Google Patents
US20200018284A1 - Wind turbine blade and a wind turbine - Google Patents
Provided is a wind turbine blade for a wind turbine, the wind turbine blade including an electrical conductor extending in a longitudinal direction of the wind turbine blade, and a carbon fiber material being electrically conductive and having a first portion which is arranged beside the electrical conductor, a second portion which is connected to the first portion and is attached and electrically connected to the electrical conductor, and a third portion which is connected to the second portion and at least partially overlaps with the first portion. Due to such an electrical connection between the electrical conductor and the carbon fiber material arcing and, thus, delamination of carbon can be avoided when conducting current of a lightning strike.
Provided is a wind turbine blade for a wind turbine, the wind turbine blade including an electrical conductor extending in a longitudinal direction of the wind turbine blade, and a carbon fiber material being electrically conductive and having a first portion which is arranged beside the electrical conductor, a second portion which is connected to the first portion and is attached and electrically connected to the electrical conductor, and a third portion which is connected to the second portion and at least partially overlaps with the first portion. Due to such an electrical connection between the electrical conductor and the carbon fiber material arcing and, thus, delamination of carbon can be avoided when conducting current of a lightning strike.
Fracture mechanics of polymer composites in aerospace applications - ScienceDirect
Fracture mechanics of polymer composites in aerospace applications - ScienceDirect
Fiber-reinforced polymer-matrix composites find increasing use in high performance aerospace structures and elements due to their light-weight and the related high specific strength and stiffness. Over the last 30 to 40 years, fracture mechanics test method development for these materials has yielded several standards and additional standard procedures are in preparation. The current status of standardisation is briefly reviewed and the applicability of fracture mechanics data for composites design and other uses in aerospace is discussed. Major issues are laminate lay-up, fatigue behaviour, and service conditions. These are illustrated by selected data from fracture mechanics literature......
Fiber-reinforced polymer-matrix composites find increasing use in high performance aerospace structures and elements due to their light-weight and the related high specific strength and stiffness. Over the last 30 to 40 years, fracture mechanics test method development for these materials has yielded several standards and additional standard procedures are in preparation. The current status of standardisation is briefly reviewed and the applicability of fracture mechanics data for composites design and other uses in aerospace is discussed. Major issues are laminate lay-up, fatigue behaviour, and service conditions. These are illustrated by selected data from fracture mechanics literature......
Structured interfaces and their effect on composite performance: computational studies - ScienceDirect
Structured interfaces and their effect on composite performance: computational studies - ScienceDirect
Nanostructuring and nanoengineering of interfaces, phase and grain boundaries of materials have strong influence on the mechanical properties and strength of materials. In this chapter, the potential of interface nanostructuring and its effect to enhance the materials properties are described. Several groups of materials (composites, nanocomposites, nanocrystalline metals, wood) are considered with view on the effect of nanostructured interfaces on their properties, The structures of various nanostructured interfaces and the methods of their modeling are discussed. It is demonstrated that structuring of interfaces is a powerful tool for controlling the material deformation and strength behavior, and allows to enhance the mechanical properties and strength of the materials.....
Nanostructuring and nanoengineering of interfaces, phase and grain boundaries of materials have strong influence on the mechanical properties and strength of materials. In this chapter, the potential of interface nanostructuring and its effect to enhance the materials properties are described. Several groups of materials (composites, nanocomposites, nanocrystalline metals, wood) are considered with view on the effect of nanostructured interfaces on their properties, The structures of various nanostructured interfaces and the methods of their modeling are discussed. It is demonstrated that structuring of interfaces is a powerful tool for controlling the material deformation and strength behavior, and allows to enhance the mechanical properties and strength of the materials.....
Experimental and numerical analysis of a multilayer composite ocean current turbine blade - ScienceDirect
Experimental and numerical analysis of a multilayer composite ocean current turbine blade - ScienceDirect
Ocean environmental corrosion and mechanical load vibration introduce considerable negative effects caused by the fluid-structure-environment interaction. A new design scheme for a blade with salinity corrosion resistance and mechanical fatigue resistance is proposed, based on numerical simulation and fatigue tests. The one-way fluid-structure interaction (FSI) model for an ocean current turbine blade was established and calculated by a computational fluid dynamics (CFD) solver and finite element method (FEM) solver....
Ocean environmental corrosion and mechanical load vibration introduce considerable negative effects caused by the fluid-structure-environment interaction. A new design scheme for a blade with salinity corrosion resistance and mechanical fatigue resistance is proposed, based on numerical simulation and fatigue tests. The one-way fluid-structure interaction (FSI) model for an ocean current turbine blade was established and calculated by a computational fluid dynamics (CFD) solver and finite element method (FEM) solver....
Aerospace engineering requirements in building with composites - ScienceDirect
Aerospace engineering requirements in building with composites - ScienceDirect
The growing use of composite material has arisen from their high specific strength and stiffness when compared to the more conventional materials, and the ability to tailor their structure to produce aerodynamically more efficient structural configurations. In this introductory chapter, it is argued that fiber-reinforced polymers, especially carbon fiber-reinforced plastics can and will, in the near future, contribute more than 50% of the structural mass of an aircraft
The growing use of composite material has arisen from their high specific strength and stiffness when compared to the more conventional materials, and the ability to tailor their structure to produce aerodynamically more efficient structural configurations. In this introductory chapter, it is argued that fiber-reinforced polymers, especially carbon fiber-reinforced plastics can and will, in the near future, contribute more than 50% of the structural mass of an aircraft
Structured interfaces and their effect on composite performance: computational studies - ScienceDirect
Structured interfaces and their effect on composite performance: computational studies - ScienceDirect
Nanostructuring and nanoengineering of interfaces, phase and grain boundaries of materials have strong influence on the mechanical properties and strength of materials. In this chapter, the potential of interface nanostructuring and its effect to enhance the materials properties are described.....
Nanostructuring and nanoengineering of interfaces, phase and grain boundaries of materials have strong influence on the mechanical properties and strength of materials. In this chapter, the potential of interface nanostructuring and its effect to enhance the materials properties are described.....
Experimental and numerical analysis of a multilayer composite ocean current turbine blade - ScienceDirect
Experimental and numerical analysis of a multilayer composite ocean current turbine blade - ScienceDirect: Ocean environmental corrosion and mechanical load vibration introduce considerable negative effects caused by the fluid-structure-environment interaction. A new design scheme for a blade with salinity corrosion resistance and mechanical fatigue resistance is proposed, based on numerical simulation and fatigue tests. The one-way fluid-structure interaction (FSI) model for an ocean current turbine blade was established and calculated by a computational fluid dynamics (CFD) solver and finite element method (FEM) solver.
21 janvier 2020
Le vent soulevé par les Creusois souffle toujours dans le sens contraire de l'éolien - Guéret (23000)
Le vent soulevé par les Creusois souffle toujours dans le sens contraire de l'éolien - Guéret (23000)
Ils étaient près d’une centaine de Creusois à manifester devant la mairie de Guéret, ce matin, pour protester contre les projets d’éoliennes industrielles qui s’implantent dans le département et demander un moratoire à la préfecture de la Creuse.
Ils étaient près d’une centaine de Creusois à manifester devant la mairie de Guéret, ce matin, pour protester contre les projets d’éoliennes industrielles qui s’implantent dans le département et demander un moratoire à la préfecture de la Creuse.
14 janvier 2020
Determination of gel point and completion of curing in a single fiber/polymer composite - ScienceDirect
Determination of gel point and completion of curing in a single fiber/polymer composite - ScienceDirect
By embedding both a single fiber Bragg grating (FBG) sensor and a thermocouple during the cure cycle of a room temperature cure epoxy, a novel in-situ approach was developed to identify certain properties of the polymer. Residual strains during curing and cooling of the epoxy were determined as a function of time for three different ambient curing temperatures. Comparing the thermocouple based temperatures to those of the ambient environment allowed for the calculation of the degree of cure and the full cure time of the epoxy. Analyzing the wavelengths of the FBG sensor and compensating for the temperature measured by the internal thermocouple, the gel point was precisely identified and validated using Flory-Stockmayer theory. As expected the residual strains increased with the curing temperature while the gel time and the completion of curing time decreased with temperature. The integrated approach of using both FBG sensors and embedded thermocouples presented in this study could be used for other polymer systems and polymer matrix composites during their manufacturing.
By embedding both a single fiber Bragg grating (FBG) sensor and a thermocouple during the cure cycle of a room temperature cure epoxy, a novel in-situ approach was developed to identify certain properties of the polymer. Residual strains during curing and cooling of the epoxy were determined as a function of time for three different ambient curing temperatures. Comparing the thermocouple based temperatures to those of the ambient environment allowed for the calculation of the degree of cure and the full cure time of the epoxy. Analyzing the wavelengths of the FBG sensor and compensating for the temperature measured by the internal thermocouple, the gel point was precisely identified and validated using Flory-Stockmayer theory. As expected the residual strains increased with the curing temperature while the gel time and the completion of curing time decreased with temperature. The integrated approach of using both FBG sensors and embedded thermocouples presented in this study could be used for other polymer systems and polymer matrix composites during their manufacturing.
Impact of Site-Specific Thermal Residual Stress on the Fatigue of Wind Turbine Blades | AIAA SciTech Forum
Impact of Site-Specific Thermal Residual Stress on the Fatigue of Wind Turbine Blades | AIAA SciTech Forum
Thermal residual stresses can have a substantial impact on the bond line fatigue of wind turbine blades and the initiation of tunneling cracks in the adhesive layer early in their operational life. Thermal residual stresses develop during the manufacture of the blade as a consequence of the temperature difference between the curing conditions and the operating environmental conditions. Polymers are used as adhesive or matrix material for fiber rein-forced materials. Their physical properties, e.g., the coefficient of thermal expansion, Young’s modulus, and the tensile strength, depend on the curing process, i.e., the degree of cure and the temperature. Moreover, the ambient temperature for the blade during its operational life underlies a statistical distribution, which is site-specific. Traditionally, the design evaluation is conducted with material properties obtained at room temperature of 23°C. Taking into account the variability of temperature at a specific site, e.g., from −35°C to 25°C, will increase the fidelity of the design evaluation. This research investigates the impact of thermal residual stress on the fatigue stress exposure along the trailing-edge bond line during operational blade life. A simplified approach using temperature-independent material properties for different temperature sites at Northern, Central, and Southern European wind farm sites is compared to an advanced approach using temperature-dependent properties. It was found that the simplistic approach yields more conservative results.
Thermal residual stresses can have a substantial impact on the bond line fatigue of wind turbine blades and the initiation of tunneling cracks in the adhesive layer early in their operational life. Thermal residual stresses develop during the manufacture of the blade as a consequence of the temperature difference between the curing conditions and the operating environmental conditions. Polymers are used as adhesive or matrix material for fiber rein-forced materials. Their physical properties, e.g., the coefficient of thermal expansion, Young’s modulus, and the tensile strength, depend on the curing process, i.e., the degree of cure and the temperature. Moreover, the ambient temperature for the blade during its operational life underlies a statistical distribution, which is site-specific. Traditionally, the design evaluation is conducted with material properties obtained at room temperature of 23°C. Taking into account the variability of temperature at a specific site, e.g., from −35°C to 25°C, will increase the fidelity of the design evaluation. This research investigates the impact of thermal residual stress on the fatigue stress exposure along the trailing-edge bond line during operational blade life. A simplified approach using temperature-independent material properties for different temperature sites at Northern, Central, and Southern European wind farm sites is compared to an advanced approach using temperature-dependent properties. It was found that the simplistic approach yields more conservative results.
Enhanced damping characteristics of carbon fiber reinforced polymer–based shear thickening fluid hybrid composite structures - Jaehyeong Lim, Sang-Woo Kim,
Enhanced damping characteristics of carbon fiber reinforced polymer–based shear thickening fluid hybrid composite structures - Jaehyeong Lim, Sang-Woo Kim
Lightweight carbon fiber reinforced polymer composite structures with high stiffness are at risk of resonant vibration. Our study proposes a methodology to reduce this risk by passively improving the damping ratio of carbon fiber reinforced polymer composite structures. We developed shear thickening fluid hybrid composite structures by applying polyimide tubes filled with shear thickening fluid having rheological properties into a composite laminate. In order to verify the proposed methodology, carbon fiber reinforced polymer–based shear thickening fluid hybrid composite beams were fabricated, and modal tests were subsequently performed to investigate their dynamic characteristics.
Lightweight carbon fiber reinforced polymer composite structures with high stiffness are at risk of resonant vibration. Our study proposes a methodology to reduce this risk by passively improving the damping ratio of carbon fiber reinforced polymer composite structures. We developed shear thickening fluid hybrid composite structures by applying polyimide tubes filled with shear thickening fluid having rheological properties into a composite laminate. In order to verify the proposed methodology, carbon fiber reinforced polymer–based shear thickening fluid hybrid composite beams were fabricated, and modal tests were subsequently performed to investigate their dynamic characteristics.
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