Impact of Site-Specific Thermal Residual Stress on the Fatigue of Wind-Turbine Blades

Antoniou, Alexandros; Rosemeier, Malo; Tazefidan, Kutlualp; Krimmer, Alexander; Wolken-Möhlmann, Gerrit

doi:10.2514/1.j059388

Cited by 20 publications

(7 citation statements)

References 25 publications

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“…As simultaneously the water content and the external activation energy by the environment are the highest, it can be hypothesized that the amount of strongly bound water is likewise very high. Furthermore, the drop in stiffness and increase in T g show analogies to the development of these properties as a function of the curing degree identified by Antoniou et al (2020) for a similar epoxy system. In this regard, the type II bound water could be expected to act like a secondary cross-linking, depressing the stiffness but increasing the T g compared with sub-T g aged conditions.…”

Section: Comparison Of Specific Time-temperature Historiessupporting

confidence: 56%

Hygrothermal Aging History of Amine-Epoxy Resins: Effects on Thermo-Mechanical Properties

et al. 2022

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Epoxy systems are widely used as matrix resins for fiber reinforced polymers (FRP) and, therefore, often have to withstand harsh environmental conditions. Especially in marine and offshore environments, moisture or direct water contact leads to water absorption into the epoxy resin. As a result, the mechanical properties change during application. Since diffusion at room or colder temperatures is slow, industry and academia typically use accelerated aging methods at elevated temperatures for durability prediction. However, as the water-polymer interaction is a complex combination of plasticization, physical aging, and molecular interaction, all of these mechanisms are expected to be affected by the ambient temperature. To reveal the impact of aging time and temperature on the thermo-mechanical properties of an amine-epoxy system, this publication includes various hygrothermal aging conditions, like water bath and relative humidity aging at temperatures ranging from 8°C to 70°C and relative humidity from 20% to 90%. Thus, it is demonstrated via long-term aging, DMTA and FTIR investigations that, e.g., strength, stiffness, strain to failure, and the glass transition temperature (Tg) can differ significantly depending on aging time and temperature. For example, it can be shown that water absorption at cold temperatures leads to the strongest and longest-lasting reduction in strength, although the maximum water absorption amount is lower than at higher temperatures. For the application, this means that strength differences of up to 26% can be obtained, depending on the aging method selected. Furthermore, it can be shown that conventional prediction models, such as Eyring correlation, which consider the mobility of the molecular structure for the prediction of thermo-mechanical properties, can only be used to a limited extent for prediction in hygrothermal aging. The reasons for this are seen to be, in particular, the different characteristics of the water-polymer interactions depending on the aging temperature. While plasticization dominates in cold conditions, relaxation and strong water-molecule bonds predominate in warm conditions.

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Section: Comparison Of Specific Time-temperature Historiessupporting

confidence: 56%

Hygrothermal Aging History of Amine-Epoxy Resins: Effects on Thermo-Mechanical Properties

et al. 2022

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“…The validated crack initiation model can be applied for design purposes taking into account the operating-temperature-dependent [31] and manufacture-induced multi-axial mean stress-states, and the multi-axial mean and amplitude stress-states due to field operating conditions, e.g., by using a simplified engineering approach as proposed in [7,32], i.e., a deterministic wind plus lead-lag gravity loads to predict the crack initiation in the field.…”

Section: Applicability Of Modelmentioning

confidence: 99%

Validation of crack initiation model by means of cyclic full-scale blade test

Rosemeier

Melcher

Krimmer³

et al. 2022

J. Phys.: Conf. Ser.

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Wind turbine rotor blades are subject to highly dynamic loads and designed for life cycles of at least 20 years, which means that materials are subjected to high-cycle fatigue. Fatigue is a design-driving loading for current and future blades. Bond lines of blades are exposed to a multi-axial stress-state due to the anisotropic thin-walled blade structure and curved, tapered, twisted, and airfoil-shaped blade geometry. To eliminate undesirable failure modes and thus increase the reliability of wind turbine rotor blades, standards and guidelines recommend that the multi-axial stress-states be taken into consideration for the limit state analysis. In addition, thermal residual stresses that develop during manufacture can have a significant impact on the fatigue life of the bond line. By means of a cyclic full-scale blade test of a commercial 81.6m long offshore blade, we validate a crack initiation model, which takes into account multi-axial thermal and mechanical stress-states, as well as the probabilistic stress-life, to predict the edge of crack initiation in the adhesive as well as the span-wise position. Both observations agreed well with the simulations. All residual normal stress components and cross-sectional plane shear stress made up the major part of the mean equivalent stress, while the mechanical stress amplitude components - longitudinal, peel, and cross-sectional plane shear stress - made up the major part of the equivalent stress amplitude.

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“…The matrix itself makes a substantial contribution to the damage onset of an FRP [1], however, particularly when the load axis is transverse to the fiber direction. Besides the matrix's mechanical performance as a function of the degree of cure [4], its viscoelastic nature (i.e., strain rate dependency, creep behavior, and relaxation behavior [5,6]) and its fracture toughness [7] also have an effect on the fatigue resistance.…”

mentioning

confidence: 99%

“…For design purposes, it is essential to accurately describe the mechanical loading of the FRP matrix [9]. The FRP matrix in wind turbine blades is subjected to more than 100 million load cycles during an operational life of at least 20 years with various combinations of mean stresses and stress amplitudes that stem from aerodynamic and gravitational loads [10] in addition to the thermal residual stress [4].…”

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confidence: 99%

Probabilistic Approach for the Fatigue Strength Prediction of Polymers

Rosemeier

Antoniou

2022

AIAA Journal

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Impact of Site-Specific Thermal Residual Stress on the Fatigue of Wind-Turbine Blades

Abstract: to initiate your request. See also AIAA Rights and Permissions www.aiaa.org/ randp. *Technical Head, Department of Rotor Blades, Am Seedeich 45.

Cited by 20 publications

References 25 publications

Hygrothermal Aging History of Amine-Epoxy Resins: Effects on Thermo-Mechanical Properties

Hygrothermal Aging History of Amine-Epoxy Resins: Effects on Thermo-Mechanical Properties

Validation of crack initiation model by means of cyclic full-scale blade test

Probabilistic Approach for the Fatigue Strength Prediction of Polymers

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