Introduction 

Glass fiber reinforced polymers (GFRPs) are one of the most widely used composite materials and are e.g. chosen as material for wind turbine blades (WTBs). The life time of onshore wind turbines is typically approximately 20 years (Ziegler et al. 2018). During this time, wind turbines, especially the WTBs, are exposed to natural weathering conditions, such as changing temperatures, ultraviolet (UV) radiation, and moisture exposure. These weathering phenomena result in aging and degradation of the composite materials used (Kjærside Storm 2013). Thereby, the term degradation describes all processes which lead to a decline of polymer’s and composite’s properties, and the term aging denotes a long-term change of polymer properties and may involve degradation processes (Yousif and Haddad 2013). The different weathering conditions result in degradation, aging and could change the morphology of the GFRP (Blaga 1972). The degradation of polymers and polymer based composites starts at the outer surface and gradually penetrates into the interior of the material (Yousif and Haddad 2013) (Fig. 1). To avoid the negative influence of different weathering phenomena, the surfaces of WTBs are protected with gelcoat or paint (Kjærside Storm 2013; Sørensen et al. 2010). In the near-surface regions and in the case of a missing coating, all kinds of weathering phenomena lead to a change of the composite’s mechanical material properties. The exposure to ultraviolet (UV) radiation may cause significant degradation of polymeric materials (Joustra et al. 2021; Kepir et al. 2021). UV light has the ability to damage the composite’s polymeric surface, exposing the fibers and boosting water absorption (Kepir et al. 2021). Most of the solar radiation is classified as UV-B which is filtered by the stratosphere and therefore does not reach the Earth’s surface. The solar radiation UV-A has a wavelength of 315 to 400 nm and reaches the surface of the Earth. It results in photochemical degradation of polymeric materials (Yousif and Haddad 2013). The term photochemical degradation is denoted as the degradation of photodegradable molecules caused by the absorption of photons from sunlight (Yousif and Haddad 2013). Furthermore, WTBs are exposed to water in the form of steam due to the humidity of air and soil moisture or in the form of liquid water due to precipitation in the form of rain or snow. The presence of moisture can lead to degradation of mechanical properties, especially in non-surface treated GFRP. The combined influence of temperature and moisture ingression, particularly in combination with fatigue loading may impact the mechanical properties of composite materials (Rocha et al. 2017; Rocha et al. 2019). This effect is described as hydrothermal degradation.

Fig. 1
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Segment of a decommissioned E-40 wind turbine blade with different kinds of damages: a shell debonding tail edge, b gelcoat cracks, c leading edge erosion, d mechanical damage 

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In the literature, there are several experimental studies focusing the individual or combined effect of changing temperature, UV radiation, and moisture on the mechanical properties of composites (Kepir et al. 2021; Dogan et al. 2019; Bazli et al. 2020; Bazli et al. 2019; Shin et al. 2003; Martins et al. 2011; Mouzakis et al. 2008; Sousa et al. 2016). Bazil et al. analyzed the resulting ultimate strength of different configuration of GFRP laminates for different environmental conditions including freeze and thaw cycles with and without the presence of moisture, UV radiation, and water vapor condensation (Bazli et al. 2019). They further investigated the degradation of GFRP pultruded profiles after exposure to various weathering cycles using bending, tensile, and compression tests (Bazli et al. 2020). Dogan et al. figured out that coated materials are less sensitive to hygrothermal strength degradation than uncoated composite materials (Dogan et al. 2019). Shin et al. investigated the correlation of accelerated aging test to natural aging test on graphite-epoxy composite materials (Shin et al. 2003). Martins carried out a comparative study of the phenomenological behavior of silica-polytetrafluoroethylene matrix reinforced composite before and after accelerated ageing with exposure to UVB radiation and water vapor (Martins et al. 2011). Mouzakis et al. performed dynamic mechanical analysis (DMA) for a range of temperatures and frequencies under tensile and three-point bending loadings of glass fiber reinforced polyester and revealed that the aged material’s stiffness increases, whereas a small deterioration in the composite’s strength was determined (Mouzakis et al. 2008). Sousa et al. analyzed the mechanical properties of pultruded profiles made of E-glass fiber reinforced vinylester and polyester and compared different accelerated exposures to natural weathering in a Mediterranean climate (Sousa et al. 2016). These experimental studies largely represent the mechanical behavior of composites before and after accelerated exposure, natural weathering or both, but do not cover the full range of weathering conditions which are required for the assessment of composite applied in WTBs. Furthermore, the investigation did not only focus on glass fiber reinforced epoxy resins.

To overcome the lack of knowledge concerning the elastic properties of composites under accelerated exposure or natural weathering, a micromechanical modeling approach is used in the current study. For consideration including fiber misalignment or an inelastic material behavior of composites’ components, numerical micromechanical modeling provide more accurate results (Mishnaevsky and Brøndsted 2013). In this context, finite element analyses (FEA) are particularly widespread. Therefore, the microstructure of the composite material is described by means of representative volume element (RVE). The mechanical properties of the individual components and the boundary layer are modeled and the effective properties of the composite are calculated numerically with the aid of a suitable homogenization technique. This micromechanical modeling allows a fast and effective investigation of different fiber arrangement and fiber volume ratios which can be used to assess the structural behavior of composite structures. Furthermore, it enables a better design, lifetime assessment of WTBs and the quantification of GFRP’s degradation. This information allows an assessment of WTB’s structural integrity, a decision on life extension and planning for the decommissioning of WTBs in the sense of a circular economy system (compare e.g. (Association and “Wind in power - 2015 European statistics”. 2015)). Furthermore, this quantification of the composite’s mechanical properties at their end-of-life (EoL) enable the choice of suitable waste-treatment strategies, such as the so-called R6-strategy (Johst et al. 2023).

Due to the lack of experimental data considering the dependencies of all relevant weathering phenomena and for the required range of weathering conditions, the aim of the current study is to numerically investigate the elastic property’s degradation of glass fiber reinforced epoxy resin according to changing temperatures within the relevant temperature range, moisture absorption and the exposure of UV radiation. Using a numerical micromechanical modeling approach, the dependencies of these phenomena on the composite effective elastic properties are estimated and analyzed. Therefore, the elastic properties of the composite were determined using a finite elements analysis of the composite’s microstructure. Based on available literature values, the degradation of E-glass fiber and cold-curing epoxy resin according to the individual weathering conditions was quantified. Using these elastic properties of the composite’s components, the elastic properties of the composite were estimated. A set-theoretic accumulation approach for the determination of the composite component’s degradation was applied. Finally, the composite’s resulting elastic constants and their degradation according to changing temperatures, moisture absorption and UV radiation was numerically investigated. Using suitable experimental data including all considered weathering phenomena and the interactions, the used micromechanical modeling approach can be used to quantify the degradation of glass fiber reinforced polymers under weathering conditions.

Methodology

Wind Turbine Blade and Visual Damage Analysis

A segment of a WTB (E-40, Enercon, Aurich, Germany) with the dimensions of approximately 1.1 m in width direction and 2.0 m in length direction was used for the identification of typical damages (Katnam et al. 2015; Katsaprakakis et al. 2021; Reddy et al. 2019; Shihavuddin et al. 2019). The decommissioned blade was segmented with the help of an industrial excavator using a wire saw. Before the visual inspection, soiling caused by storage was removed and the segment was cleaned with a mild soap solution. After the segment was completely dried, the entire surface was inspected visually and individual damages were documented including length scales of the individual damages. The considered WTB segment consists of typical damages, such as shell debonding tail edge, gelcoat cracks, leading edge erosion, mechanical damage, could be detected in the examined WTB segment (Fig. 1).

The dimensions of the available WTB segment (Fig. 1) was manually measured by means of different length measures. Based on these measurements, the generation of the three-dimensional model was carried out using the multi-platform software suite (CATIA V5-6R2018, Dassault Systems, Velizy-Villacoublay, France). For the consideration of the cross-sectional dimensions of the WTB, a scaled sectional view of the composite structure including the WTB’s individual materials was generated (Fig. 2b). This cross section was used for the set-theoretical accumulation approach of the individual weathering phenomena presented in the following.

Fig. 2
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Set-theoretical accumulation of individual weathering phenomena

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Set-Theoretical Accumulation Approach of the Different Weathering Phenomena

The individual weathering conditions according to changing temperatures, UV radiation, and moisture absorption influence the material properties of the used composite materials. In practice, there can be interactions between these phenomena which have to be intensively examined. One possible approach to define these interactions is a set-theoretical accumulation (Fig. 2a). Each weathering condition represents its own set, defined as set \(E\), set \(R\) and set \(M\) for the changing temperatures, moisture absorption, and UV radiation, respectively. According to basic set-theoretical considerations, different combinations of this conditions can be defined (compare Fig. 2a).

Microstructure Analysis of Spar Cap

To determine the required diameter of GFs and to estimate the practically relevant fiber volume ratio \(\varphi\) defined as \(\varphi = {V}_{\text{f}}/{V}_{\text{c}}\), a microstructural analysis of an upper spar cap’s section was carried out (compare Fig. 2b). Therefore, microscopic images of this section were evaluated using an image processing program (ImageJ 1.53t, National Institutes of Health, USA). For the investigated unidirectional (UD) glass fiber reinforced epoxy resin (Fig. 3), a fiber diameter of 15.7 ± 1.8 µm was measured. Considering the microscopic images, the unequal distribution of the fibers, holes, and non-impregnated areas are visible. Due to the low contrast between GF and epoxy resin, the fibers were masked manually and the fiber volume ration was determined which result in a value of \(\varphi\) = 0.52. However, this ratio can only be seen as a representative value since the unequal fiber distribution (compare Fig. 3).

Fig. 3
figure 3

Microscopic images of spar cap section: a schematic of WTB cross section, b spar cap section, c unidirectional glass fiber reinforced section at a magnitude of 50, d unidirectional glass fiber reinforced section at a magnitude of 500

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Micromechanical Modeling

To determine the effects of the degradation of the individual components on the effective properties of the composite and for the sake of simplicity, a unidirectional (UD) laminate is analyzed. Therefore, the following subscripts \({\text{f}}\) is used for glass fibers, \({\text{m}}\) for epoxy resin matrix, and \({\text{c}}\) for the resulting composite. Using a numerical micromechanical modeling approach, the composite’s effective elastic constants of the composite are obtained. For the considered transversely isotropic linear elastic material behavior, the strain stress relation can be written in the Voigt notation (Altenbach et al. 2001; Schürmann 2007), consisting of engineering constants denoted by \(||\) for the fiber’s longitudinal direction and \(\perp\) for the transversal direction. This yields the longitudinal modulus \({E}_{||}\), the transversal modulus \({E}_{\perp }\), the shear modulus \({G}_{\perp ||}\) in the orthogonal plane, the Poisson’s ratio \({\nu }_{\perp ||}\) due to longitudinal elongation, the Poisson’s ratio \({\nu }_{\perp \perp }\) due to transversal elongation and shear modulus \({G}_{\perp \perp }\) in the isotropic plane (compare e.g. (Altenbach et al. 2001; Schürmann 2007)). To determine these five engineering constants, the numerical micromechanical modeling approach is carried out by means of a simulation software (Ansys 2019 R2, Ansys, Canonsburg, PA, USA). For the considered small dimensions of the RVEs, volume loads were neglected. Furthermore, the following modeling assumptions for a UD composites were assumed according to reference (N. N. 2023):

  • The fiber volume ratio has a constant value.

  • The composite consists of isotropic linear-elastic matrix and fiber materials (Table 1).

  • The fibers have an infinite length and are ideal cylindrical with a constant fiber diameter of \({d}_{\text{f}}\).

  • There is a perfect bonding between the fibers and matrix material.

  • All fibers are perfectly oriented in longitudinal direction without any misalignment.

  • Periodic boundary conditions are defined for the RVE.

Table 1 Mechanical properties of epoxy resin and E-glass fiber according to reference (Schürmann 2007)
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Taking the degradation of fibers’ and polymeric matrix’ stiffness into consideration, the resulting degraded elastic properties of UD composite were determined. For E-glass fibers and cold-curing epoxy resin, generally valid material parameters and not the material parameter of a certain supplier were used according to Schürmann et al. (Schürmann 2007). The material parameters of the individual constituents used in the current study are summarized in Table 1.

In order to exclude an influence of the microstructure on the resulting mechanical properties, the Monte Carlo method of different fiber arrangements was used and the mean values of the individual simulation were calculated. The random fiber distribution was generated using the sequential addition and migration method according to Schneider (Schneider 2017) which considers a repeated count \({c}_{\text{RVE}}\) of the geometry. Using the tool “Material Designer,” the FEA software periodic and conformal meshes were automatically generated to ensure the assumptions of periodic RVEs (Fig. 4). As elements, SOLID187 elements were used which have a quadratic displacement behavior and are well suited for the modeling of irregular meshes. For the considered fiber volume ratio of \(\varphi\) = 0.52, a fiber diameter of \({d}_{\text{f}}\) = 15.7 µm and a repeat count of \({c}_{\text{RVE}}\) = 5, the resulting RVEs consist of a number of 26 glass fibers and had the main dimensions of 179 µm \(\times\) 90 µm \(\times\) 90 µm. In this RVE, all fibers are oriented in \({x}_{1}\) direction (Fig. 4). It should be noted that the fiber volume ratio slightly differs compared to value determined by microstructural analysis due to the applied sequential addition algorithm for the generation of symmetric fiber distribution.

Fig. 4
figure 4

Exemplary RVE of the investigated unidirectional composite with a fiber volume ratio of φ = 0.52

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Data Collection Procedure of Stiffness Degradation

The stiffness degradation of the E-glass fibers and of the polymer matrix epoxy resin according to the weathering phenomena changing temperatures, UV radiation, and moisture was taken from different literature sources. The measured data was determined by digitizing the existing diagrams. Since the properties of the particular kind of used epoxy resin vary due to the wealth of different resin systems, hardener contents and processing parameters, only the relative changes of the properties according to the individual weathering phenomena were examined for polymer matrix. Analogously, this consideration was used for the properties of glass fibers. Therefore, an initial tensile modulus \({E}_{0}\) at 20 °C, not exposed to UV radiation and completely dry was considered as reference value. Using this value, the relative changes of materials’ elastic properties were quantified.

For the micromechanical modeling, the degradation of the elastic properties according to moisture absorption for a relative humidity of 60% was analyzed in dependency of the time \(t\). The change of stiffness properties was related to the ambient temperatures \(\vartheta\) which were considered in the range between − 50 and 70 °C (Kjærside Storm 2013). The photochemical degradation was affected by the time \(t\) exposed to UV light. The time-dependent effects of changing stiffness \(E(t)\) were linearly interpolated between the existing data points using the numerical computing software (MATLAB version 9.12.0, MathWorks, Natick, MA, USA). This data was used to explain the material’s stiff degradation for the individual phenomena which are required for the determination of the composite’s stiffness as described in the “Wind Turbine Blade and Visual Damage Analysis” section. Using the stiffness degradation and the elastic properties of the composite components (Table 1), the engineering constants of the compliance matrix were determined. The determined data sets and their related references are presented in the following.

According to the set-theoretical accumulation (compare the “Set-Theoretical Accumulation Approach of the Different Weathering Phenomena” section), the change of the composite components’ elastic properties to all individual weathering phenomena is required. For this purpose, it was assumed in the current study that the individual effects accumulate and that interactions between the individual effects neither lead to an increase nor to a decrease of the resulting degradation. Considering the sets mentioned in the “Set-Theoretical Accumulation Approach of the Different Weathering Phenomena” section as subscripts E, M, and R, the resulting degradation represented by the damage parameter (compare e.g. (Mao and Mahadevan 2002)) \(D = ({E}_{0}-E)/{E}_{0}=\Delta E/{E}_{0}\) of the polymer matrix and the reinforcement fibers are denoted as

$${D}_{\text{m}}={D}_{\text{E},\text{m}}+{D}_{\text{M},\text{m}}+{D}_{\text{R},\text{m}}$$
(1)
$${D}_{\text{f}}={D}_{\text{E},\text{f}}+{D}_{\text{M},\text{f}}+{D}_{\text{R},\text{f}}$$
(2)

where \({D}_{\mathrm{E}}\), \({D}_{\mathrm{M}}\), and \({D}_{\mathrm{R}}\) are of degradation values according to changing temperatures, moisture absorption, and UV radiation. Using Eq. (1) and Eq. (2), the components’ elastic properties for the numerical calculations were determined.

Results and Discussion

Individual Stiffness Degradation of Fiber Reinforcement and Polymer Matrix

The gelcoats used as coating of WTBs are exposed to all weathering phenomena (compare e.g. (Kjærside Storm 2013; Sørensen et al. 2010)). In particular, damage to this surface coating allows moisture to penetrate the structure and thus alter the mechanical properties of the outer laminates. In the case of a destroyed protection layer, the outer layers consisting of bidirectional (BD) reinforced epoxy resin are exposed to all weathering conditions including changing temperatures, moisture absorption and UV radiation (Fig. 2a, area \(E\cap M\cup R\)). Since these areas are considered small, the full combination of changing temperatures, moisture absorption and UV radiation has only a small influence area. More relevant for the resulting elastic behavior of WTBs is the interaction of moisture absorption due to precipitations and changing temperatures (Fig. 2a, area \(E\cap M\backslash R\)). This affects in particular the outer layers of the WTB. For a constant temperature distribution over the entire cross section, the remaining inner materials are only exposed to changing temperatures (Fig. 2a, area \(E\backslash (R\cup M\))).

According to Niederstadt (Niederstadt 1997), mainly synthetic fibers, such as aramid, are subjected to photochemical degradation due to radiation above the UV B range between 280 and 315 nm. The photochemical degradation was not mentioned for glass fiber and is more critical for polymeric matrices. Thus, since this effect was small compared to polymer’s degradation, no photochemical degradation of E-glass fibers was considered in current study. Glass fibers are incombustible, temperature-resistant up to a temperature of approximately 400 °C and resistant to weathering (Niederstadt 1997). For the standard operating temperatures up to 70 °C, E-glass fibers show a slightly increase of the elastic properties (Kessler et al. 2016; Otto 1961; Thomason et al. 2014). In the current study, the elastic properties of E-glass fiber are assumed to have a constant value of \(E/{E}_{0}\) = 1 for all investigated weathering conditions.

For the polymeric matrix, the different weathering conditions has a significant effect on the elastic modulus (Fig. 5). The change of the material’s temperature results in the highest change (Fig. 5a). Comparing three different epoxy resins according to references (Arena et al. 2019; Gibhardt et al. 2022; Hübner et al. 2021), similar curve can be observed (Fig. 5a). The presented data was obtained from DMA of different epoxy resins at different temperature ranges. The approach of taken experimental data from different literature sources was applied since no referenceable data of the identical resin system was available. It enables the comparison of the different individual weathering phenomena in terms of their magnitude and the usage of the exiting experimental data from several studies.

Fig. 5
figure 5

Elastic modulus of epoxy resin: a at temperatures between 20 and 100 °C (Arena et al. 2019; Gibhardt et al. 2022; Hübner et al. 2021), b for a certain time in a admophere with relative humidity of 60% (Ji et al. 2019), c exposed to UV radiation (Nikafshar et al. 2017)

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For the numerical modeling, the measurements of Arena et al. (Ji et al. 2019) were used who analyzed the whole investigated temperature range. The absorption of moisture also influences the elastic properties of epoxy resin (Fig, 5b). Comparing the individual weathering phenomena of epoxy resin, it can be seen that the influence of photochemical degradation is small compared to the other phenomena. Furthermore, it should be noted that the composite is protected against the exposure of UV radiation in the case of an unbroken coating (see Fig. 2b). Only in the case of damages, small areas are exposed to UV radiation which have a considerable small influence of the structural behavior (compare the “Set-Theoretical Accumulation Approach of the Different Weathering Phenomena” section). Due to before mentioned reasons, the photochemical degradation of epoxy resin was not further considered in the current study.

Degradation of Epoxy Resin

Using the changes of the resin’s elastic modulus due to temperature changes (Fig. 5a) and the increasing time for the absorption of moisture (Fig. 5b), the resulting degradation of the polymer matrix according to Eq. (1) was determined (Fig. 6). The resulting degradation at a temperature of \(\vartheta =\) 20 °C and at time \(t\) = 0 of the moisture absorptions reaches by definition a value of \(({E}_{\text{m}} - {E}_{0,{\text{m}}})/{E}_{0,{\text{m}}}\) = 0. With increasing time, the modulus decreases \(({E}_{\text{m}}-{E}_{0,{\text{m}}})/{E}_{0,{\text{m}}}<0\). At the upper limit of the considered temperature range of \(\vartheta = -\) 50 °C, the elastic modulus of epoxy resin is higher than the reference value \(({E}_{\text{m}}-{E}_{0,{\text{m}}})/{E}_{0,{\text{m}}}>0\) (compare Fig. 6). This effect is known as low temperature embrittlement in the epoxy matrix (Arena et al. 2019; Hübner et al. 2021). It should be noted that the used damage parameter \({D}_{\mathrm{m}}\) is not identical to the damage parameter for the fatigue damage modeling of composite materials (Mao and Mahadevan 2002) or for biaxial load application of textile reinforced composites (Düreth, et al. 2020). In the current study, only the degradation due to weathering and not to fiber or matrix damage was considered.

Fig. 6
figure 6

Resulting degradation of epoxy resin \(({E}_{\text{m}}-{E}_{0,{\text{m}}})/{E}_{0,{\text{m}}}\) for temperatures \(\vartheta\) between − 50 and 70 °C and for a certain time \(t\) in a atmosphere with relative humidity of 60%

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Stiffness Degradation of Composite

Especially the exposure to high temperatures results in a significant reduction of the tensile strength of GFRP (see e.g. (Yang and Yao 2018)). This effect can be seen as result of the high temperature dependency of the polymer matrix (compare Fig. 5). Additionally, it can be seen that due to low-temperature embrittlement of epoxy resin, the tensile moduli increase as the temperature decreases (Fig. 7b).

Fig. 7
figure 7

a Tensile modulus in fiber direction \({E}_{||}\) and b in transversal direction of glass fiber reinforced epoxy resin obtained from micromechanical modeling for temperatures \(\vartheta\) between − 50 and 70 °C and for a certain time \(t\) in a atmosphere with relative humidity of 60%

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Considering all elastic constants of the investigated UD GFRP, it can be seen that the matrix-dominated constants, such as the transversal tensile modulus \({E}_{\perp }\), strongly depend on temperature. The fiber-dominated tensile modulus \({E}_{||}\) change only slightly due to varying temperatures and the moisture absorption (Fig. 8a) since the fiber properties show only very small variations for the investigated weathering phenomena (compare the “Individual Stiffness Degradation of Fiber Reinforcement and Polymer Matrix” section).

Fig. 8
figure 8

Degradation of the uniderectional composite’s elastic moduli for temperatures \(\vartheta\) between − 50 and 70 °C after a time of \(t\) = 200 h in a atmosphere with relative humidity of 60%: a tensile moduli \(E\), b shear modulus \({G}_{\perp ||}\), c Poisson’s ratios \({\nu }_{\perp ||}\), \({\nu }_{\perp \perp }\)

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Limitations and Future Work

The used micromechanical modeling approach enables the estimation of the composite’s elastic properties according to the environmental-based degradation phenomena. In particular, the outer layers of a WTB with damaged coating are most exposed to all weathering phenomena. Currently, there are no studies that simultaneously analyze the full range of the individual dependencies of changing temperatures in the relevant range, moisture absorption, and UV radiation of the elastic properties of GFRP for applications in WTBs. Investigations of the resulting effects for all combinations of weathering conditions, including also intermediate states, require a high experimental effort (Dogan et al. 2019; Bazli et al. 2020; Bazli et al. 2019; Shin et al. 2003; Martins et al. 2011; Mouzakis et al. 2008; Sousa et al. 2016). To overcome this high experimental effort, accelerated exposure tests were carried out to simulate natural weathering conditions (Shin et al. 2003; Sousa et al. 2016). An alternative approach is the use of numerical modeling methods including RVEs to determine the individual dependencies (compare e.g. (Mishnaevsky and Brøndsted 2013)). However, for this numerical approach, the complex interactions between the individual weathering phenomena and the influence on the fiber-matrix interface have to be characterized experimentally and suitable modeled. However, for the determination of the elastic properties, the component’s elastic properties and a perfect bonding between the fibers and matrix material result in a good approximation of these dependencies. Nevertheless, experimental measurements are indispensable for a reliable quantification of the individual weathering effects and a micromechanical modeling. Nevertheless, the set-theoretical accumulation of the individual phenomena and the numerical micromechanical modeling approach used here provides valuable insights into the design of these experiments and can enable quantification of the maximum weathering-induced degradation of the elastic properties of GFRP as part of preliminary estimations.

Concluding Remarks

The introduced micromechanical modeling approach enables a better understanding of the environmental-based natural degradation phenomena of glass fiber reinforced epoxy resin. The obtained results could be used as basis for the planning of experimental investigations. As a result of the current study, the composite elastic properties are strongly dependent on the material’s temperature and the current moisture absorption. The effects of photochemical degradation are minor compared to other weathering phenomena. Overall, the finding of the current study will help to accelerate and improve the preliminary design processes of wind turbine blades by providing a first estimation of the composite’s elastic properties and its degradation which will enable a preliminary quantification of new composite materials.