Uncover the story behind the blade failure using advanced testing and high-fidelity modeling

Significance 

Composite wind turbine blades undergo various structural failures which affect their performance. In particular, trailing edge failures have been widely reported in rotor blades. As such, several experimental and numerical based studies have been conducted to explore the mechanisms and causes of the training edge failures.

In a recently published literature, buckling effects due to the ultimate static loading has been identified as the main cause of the failures. Additionally, subcomponent testing has also been carried out to examine the structural behaviors of composite blades. In addition to the full-scale blade tests, this is also an important element in the certification of wind turbine blades.

Unlike the full-scale tests, subcomponents can be used to effectively evaluate the structural integrity of different trailing edges sections thus providing more understanding of the failure mechanisms. However, despite the available knowledge on the structural response of the trailing edge sections in the subcomponent tests, the entire failure sequence in the trailing edge section has not been fully explored. This should further take into account the buckling response in both the pre-peak and post-peak regimes. Considering the significance of the post-peak regime especially in determining the failure modes and characteristics, investigation of the post-peak response of the trailing edge sections will enable understanding of the failure sequences and the underlying mechanisms which facilitate damage-tolerant blade designs.

On the other hand, predicting the failure modes and sequences have remained a challenging task due to the presence of multiple structural nonlinearities induced by the changes in the boundary and load conditions. Even though finite element models have been used to predict the buckling response and stress-strain distribution, it is not suitable for predicting highly nonlinear structural behaviors associated with failures of different materials.

Recently, scientists at Technical University of Denmark: Dr. Xiao Chen, Mr. Peter Berring, Mr. Steen Hjelm, Dr. Kim Branner and Mr. Sergei Semenov explored the structural failure of a trailing edge section to understand the failure sequence and the buckling modes taking into account the multiple structural nonlinearities. Specifically, an advanced finite element model was developed to investigate the entire failure sequence of a blade subcomponent specimen. Furthermore, Digital Image Correlation (DIC) was used to measure strain distributions and buckling deformation during the loading history.

The developed finite element modeling technique exhibited good capability for predicting strain distributions, buckling deformation and post-peak responses that constitute the key influencers of the failure modes and characteristics in trailing edge sections. Additionally, both the buckling-driven failure phenomenon and the surface contact of sandwich panels were found to significantly contribute to the failure process of the trailing edge sections. For instance, composite and adhesive materials failed in the post-peak regime while foam materials failed in the pre-peak regime.

In summary, Technical University of Denmark researchers presented a detailed study on the failure of trailing edge sections by evaluating the critical loading conditions. In general, the authors pointed out that failure behavior in different blades will vary depending on the material properties, geometric profiles, and loading conditions. Altogether, the presented numerical method will pave the way for advancing structural analysis and evaluation of composite rotor blades. “By combining advanced subcomponent testing and high-fidelity numerical modeling, we can reshape the conventional testing pyramid of composite rotor blades.” Dr. Xiao Chen said in a statement to Advances in Engineering, “Eventually, this allows us to develop more reliable and cost-effective composite structures in a highly efficient way despite the ever-increasing sizes of rotor blades.” The work is currently published in the journal, Composite Structures.

Uncover the story behind the blade failure using advanced testing and high-fidelity modeling - Advances in Engineering Uncover the story behind the blade failure using advanced testing and high-fidelity modeling - Advances in Engineering

About the author

Xiao Chen is currently a Senior Researcher at Technical University of Denmark (DTU). He received his doctoral degree in structural engineering in 2011 from Nagoya University in Japan and then worked as a Postdoctoral Research Fellow in National Wind Energy Center at University of Houston, TX, US. From 2013, he was an Assistant Professor and later an Associate Professor at Chinese Academy of Sciences in Beijing before he joined DTU in 2017.

Xiao’s research field is experimental investigations and advanced numerical modeling of the structural response of large composite and offshore steel structures, with a primary focus on damages, failures and fractures driven by nonlinear buckling, multiple material failures, manufacturing-induced defects and extreme load conditions. Xiao is currently the work package leader in the DARWIN project funded by the Innovation Fond of Denmark and the ReliaBlade project supported by the Danish Energy Agency through the Energy Technology Development and Demonstration Program (EUDP) and several industry partners. He is also the author of more than 20 journal articles and the supervisor of two Ph.D. students.

About the author

Peter Berring, MSc ME, has been a senior development engineer at Wind Energy Department at Technical University of Denmark since 2006.

Peter’s primary field of research is in the area of analytical, numerical and experimental methods for structural design of wind turbines with the main focus on ultimate strength, fatigue and failure mechanisms in composite and sandwich structures.

Peter has extensive experience in numerical modelling and simulations of wind turbine blades using linear and non-linear, static and dynamic FEA, furthermore Peter has developed Pre-processing procedures for detailed and complex FE-models of wind turbine blades. Within the experimental field, Peter has been involved in testing of composite structures and wind turbine blades applying advanced test and measuring methods as well as design and development of test setups at various scales.

About the author

Steen Hjelm Madsen, MSc ME, has been a development engineer at Wind Energy Department (former Risø National Laboratory for Sustainable Energy) at Technical University of Denmark since 2016.

He is operations manager for the DTU Large Scale Facility and works with testing of full scale wind turbine blades as well as subcomponent of segments of blades. He is also involved in design and development of subcomponent test methods and test rigs.

About the author

Kim Branner, Ph.D., is senior research scientist at the Wind Energy Department at Technical University of Denmark (DTU). He is heading the Structural Design & Testing team, which primarily is doing research in the areas of experimental, numerical and analytical design in order to develop more reliable and exact methods for structural design, manufacturing and testing of wind turbine blades and other large composite and metal structures.

He is also Lab manager for DTU Large Scale Facility, which is a unique research and demonstration test facility for studying strength and fatigue of large structures exposed to complex loading. The facility is in operation since January 2019 and is able to test wind turbine blades up to 45 m with advanced loading and measuring equipment.

Kim studied at Cornell University, NY, USA 1984-85 and got his MSc in Naval Architecture and Physics from Technical University of Denmark in 1991. He obtained his PhD from Technical University of Denmark in 1995 after spending part of the studies at Royal Institute of Technology in Stockholm, Sweden. He worked in industry as marine consultant and research engineer from 1995 until he joined Risø National Laboratory for Sustainable Energy (now DTU) in 2003. Kim is currently the project manager for two large research, development and demonstration project supported by the Danish Energy Agency through the Energy Technology Development and Demonstration Program (EUDP) and several industry partners. The first project BLATIGUE runs until 2020 and the objective is to develop fast and efficient fatigue test methods for large wind turbine blades and to develop equipment to excite the blades under such tests. The second project ReliaBlade runs until 2022 and the objective is to improving blade reliability through application of Digital Twins over the entire life cycle. The ReliaBlade project is also unique in the sense that it composes of two national funded projects (Danish and German), which are strongly aligned and coordinated.

About the author

Sergei Semenov, MSc ME, had joined Wind Energy Department at Technical University of Denmark as a development engineer in 2017.

His primary research fields are nonlinear mechanics of materials and structures, experimental methods of parameters identification and model prediction validations, development of efficient numerical implementations of the models for structural design of wind turbines.

Sergei has extensive experience in numerical modelling and FE simulations, designing and performing advanced coupon and structure testing with multiple DAQ systems, development of the simulation tools. He is one of the core developers of BECAS software.

Links:

ORCID , SCOPUSDTU

Reference

Chen, X., Berring, P., Madsen, S., Branner, K., & Semenov, S. (2019). Understanding progressive failure mechanisms of a wind turbine blade trailing edge section through subcomponent tests and nonlinear FE analysis. Composite Structures, 214, 422-438.

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