R. P. L. Nijssen

Knowledge Centre WMC · Materials Research

This paper investigates the viscoelastic/viscoplastic/fracture behavior of an epoxy resin. A state-of-the-art pressure-dependent elastoplastic constitutive model (Melro et al. 2013) is expanded to include viscoelasticity, viscoplasticity and a modified damage formulation with linear softening and shrinking pressure-dependent fracture surface. A wat...

This work investigates hygrothermal aging degradation of unidirectional glass/epoxy composite specimens through a combination of experiments and numerical modeling. Aging is performed through immersion in demineralized water. Interlaminar shear testes are performed after multiple conditioning times and after single immersion/redrying cycles. Degrad...

Integrated Research Programme on Wind Energy (IRPWind) Work Package 7.1: Efficient blade structure The research leading to these results has received funding from the European Union Seventh Framework Programme under the agreement 609795

A combined experimental and numerical investigation is conducted on the anisotropic water diffusion behaviour of unidirectional glass/epoxy composites. Experimental diffusivity values are obtained by immersing thin material slices for each of its planes of orthotropy extracted from a thick composite panel and interphase measurements are performed u...

In this work, a glass/epoxy material system applied in wind turbine blades was used to evaluate degradation processes induced by water ingression. Composite and neat epoxy specimens were conditioned in demineralised water at 50°C for 4800h and tested quasi-statically and in fatigue. Comparing results from mechanical tests in composite specimens, si...

In this work, a numerical framework for modelling of hygrothermal ageing in laminated composites is proposed. The model consists of a macroscopic diffusion analysis based on Fick's second law coupled with a multiscale FE2 stress analysis in order to take microscopic degradation mechanisms into account. Macroscopic material points are modelled with...

Fibre-reinforced plastics used in rotor blade composites are characterised by the fact that they are exposed to extreme high-cycle fatigue loads, while architecture and manufacturing methods are to a large extent driven by investment cost.

In this work a glass/epoxy composite commonly used in wind turbine blades is exposed to a humid environment at an elevated temperature. To research the anisotropic diffusion behaviour observed in unidirectional composite specimens, experimental results of slices cut along the three directional planes of the laminate immersed in demineralised water...

In this paper, a method has been developed to use thermography for the quantitative analysis of a delamination area under dynamic loading. To demonstrate this method, a coupon was developed with double shear configuration and an initial delamination consisting of a PTFE insert. The coupon was tested under fatigue loading and an infrared (IR) camera...

Mechanical properties of glass fibre reinforced polymers are dependent on the manufacturing curing cycles. During the laminate manufacturing process, each thickness position experiences a different local curing cycle. Therefore, it can be expected that mechanical properties vary through the thickness, particularly for thick laminates. To study the...

The European Academy of Wind Energy (eawe), representing universities and institutes with a significant wind energy programme in 14 countries, has discussed the long-term research challenges in wind energy. In contrast to research agendas addressing short- to medium-term research activities, this eawe document takes a longer-term perspective, addre...

Abstract Thick laminates can be found in different wind turbine blade sections, such as the root or the spar caps. However, static and fatigue design of thick laminate components is based on thin coupons tests (around 4 mm thick) and safety coefficients determined by the guidelines and standards. The aim of this work is to study the size effect in...

Abstract Due to the poor thermal conductivity of composites and the material heating that occurs during fatigue loading, high temperatures may appear in the laminate. Since the mechanical properties of composites are dependent on temperature, the fatigue performance may be affected negatively. This effect will occur when local temperatures approach...

Effects of cold climate exposure on structures made of composite materials are scarcely documented. As a result, even if exceptional wind conditions prevail in some cold regions, uncertainties related to composite materials durability at low temperatures may hinder development of wind energy projects in those regions. Therefore, as part of the Wind...

Fatigue characterization of composite materials is based on thin laminates with thicknesses between 1 to 5 mm. The measured performance of these materials may not be representative for thick laminates (up to 150 mm) in structures such as wind turbine blades. Accurate and reliable design of tests on thick laminates is subject of ongoing investigatio...

Thick laminate sections can be found from the tip to the root in most common wind turbine blade designs. Obtaining accurate and reliable design data for thick laminates is subject of investigations, which include experiments on thick laminate coupons. Due to the poor thermal conductivity properties of composites and the material self-heating that o...

The effect of Constant Life Diagram (CLD) formulation on the fatigue life prediction under variable amplitude (VA) loading was investigated based on variable amplitude tests using three different load spectra representative for wind turbine loading. Next to the Wisper and WisperX spectra, the recently developed NewWisper2 spectrum was used. Based o...

Thick laminates can be found in different wind turbines blade sections, such as the root or the spar caps. For 40 meter long blades, thicknesses between 30 to 50 mm are typical. Root and cap thicknesses between 100-150 mm can be considered as common for 60 to 70 meter long blades. The aim of the project is to study the thickness effect in composit...

The aim of this work is to study the thickness effect in static and fatigue tests of glass-fibre unidirectional compression coupons. For this purpose, the self-heating effect, the effect of specimen geometry, and the influence of the manufacturing processes have been minimized. A scaled thickness compression coupon has been designed with the intent...

Wind turbines have seen a strong growth in the rotor size and new lighter and stiffer materials would be useful to improve the structural design of wind turbine blades. This research analyses the potential of carbon glass hybrid composites. Three laminates typical of the laminates used in the spar caps and in the trailing edge reinforcement are man...

As wind turbines are likely to be installed in a wide variety of environments, knowledge of their materials mechanical properties under extreme environments is needed. The project presented herein aims at evaluating the effects of temperatures of -40 °C, 23 °C, and 60 °C on the static properties and fatigue lives of unidirectional glass-epoxy compo...

This paper aims to provide the building blocks for fatigue simulations on glass-fibre reinforced polymer (GRFP) coupons. To this end, 3D simulations of Multiple-Fibre (MF) unit cells consisting of 7 or 45 fibres are used, including the prediction of fibre failure. These simulations are part of a multi-scale simulation approach. The MF unit cells ar...

An accurate model for constant amplitude description can be used as a tool to obtain a more reliable life prediction of wind turbine composites under variable amplitude loading. Such a fatigue model describes fatigue behavior under all possible loading conditions. Experimental data are typically only available for selected load types. The accuracy...

x Wind turbine rotor blades experience in excess of 10(7) significant load cycles, which makes them an exceptionally demanding application of composites, in terms of fatigue loading. Typical wind turbine rotor blade composites were tested in fatigue, and strength after fatigue. These experiments provide input data for strength degradation models. S...

This paper outlines the WP 3.1 of the EU 6th framework project UPWIND, which was started in 2006. In this unique integrated project on wind energy in the 6th framework, a large number of material tests will be conducted. These are mainly fatigue tests on relatively small material specimens. In a previous project, OPTIMAT BLADES, a material for wind...

In a major European research project, OPTIMAT BLADES, a large number of material tests have been conducted. For the first time, a material for wind turbines has been characterised in full detail in a single consistent project in terms of static, fatigue and residual strength as well as stiffness. The extensive investigation of the material, a glass...

This paper looks at modern wind turbine rotor blades from the point of view of material fatigue. Characteristics of the rotor blades and loads are discussed and a simple commonly used lifetime prediction method is reviewed. Also, possible modifications to the various components of the fatigue calculations are discussed.

The present paper describes a benchmarking programme to compare different lifetime prediction methodologies. Lifetime prediction is still a complex task and the results depend on many factors. Thus, it is very important to know which factors have a decisive effect on the results. The main objective of this investigation is not to proof the validity...

Possible alternative fatigue formulations to predict lifetime under variable-amplitude loading are investigated. Test results of WISPER and WISPERX variable-amplitude tests on a material representative for wind turbine rotor blades are used. All fatigue calculations are performed using Rainflow counting of the WISPER(X) load histories and employing...

A subcomponent which represents a structural detail of a blade can be a cost-effective addition prior to full scale blade tests. Such a subcomponent can be used for various purposes, like material testing, modelling and validation and investigating the influence of manufacturing and repair methods. A generic I-beam assembly is suggested, which can...

Blade designers are in need of accurate strength and stiffness data for the materials used in their design. In some parts of the blade, loading is dominated by shear. For accurate modeling of the design, an appropriate description of the shear characteristics of the material is required, including the non-linearity in shear/strain responses. The ob...

This paper describes the tests, results and analysis carried out in the first phase of the UPWIND project, Work Package 3 (Rotor Structures and Materials). This phase focuses on testing methodologies for strength and fatigue. A universal reference geometry is defined, and its behaviour is extensively predicted, tested and documented. The reference...

This paper presents new residual strength data, which were collected to aid the development and validation of a residual strength based lifetime prediction method for fatigue of wind turbine rotor blade composites. Residual strength tests were done on one multi-directional glass-fiber/polyester material, which is representative for the material use...

Final report of the European Project NNE5-2001-00174