Wind energy

Invisible weaknesses in wind turbine blades can be prevented

The wind turbine industry can cut millions in costs by minimizing errors during the casting of wind turbine blades. DTU develops and tests new production methods for this purpose.

Associate Professor Philipp Ulrich Haselbach has helped to make it possible, through simulations with "digital twins", to predict exactly where air pockets in wind turbine blades are at risk of occurring before the actual casting begins. Photo: Bax Lindhardt

Wednesday 08 July 2026

Magnus Stenaa Jensen

The forces of nature put super heavy wind turbine blades to the test. The longest blades are 100 metres long and achieve a rotation speed of around 250 km/h when the wind hits the hardest. Even though the blades are built to withstand the rigours of nature, even the smallest production errors can have major impact—at worst, the blades may break. However, the defects usually result in expensive repairs or that the blades must be discarded. 

Manufacturing the massive blades is an extensive process, and even though the blade is hollow, it consists of many tonnes of load-bearing material. The largest wind turbine blades are cast in moulds more than 100 metres long, which are moved around the huge production halls using gantry cranes. 

One of the biggest challenges in manufacturing is avoiding air pockets when moulding the blade.

Air pockets that weaken

When a wind turbine blade is produced, many layers of carbon fibre or fibreglass cloth are placed on top of each other with other material in a mould. Liquid resin (a form of hardening plastic) is then added through a so-called vacuum infusion. The resin spreads between the layers and binds the components together. However, if the resin flows too quickly in parts of the process, air can get trapped, creating air pockets that weaken the bond between the materials.

“It’s hard to monitor what’s happening inside the casting. If the resin does not saturate the fibres sufficiently, air pockets will occur, weakening the blade and—at worst—leading to it breaking. It’s very expensive for a manufacturer to discard what is easily many tonnes of material,” says Philipp Ulrich Haselbach, Associate Professor at DTU Wind.

He has participated in the AIOLOS project to develop sophisticated production methods that enable simulations with ‘digital twins’ to predict exactly where air pockets risk occurring before the actual casting begins.

“We simulate the casting process to identify better infusion strategies and modifications that can prevent air pockets and other errors from occurring,” explains the associate professor.

By testing alternative methods digitally, manufacturers can optimize resin flow through the materials before they even touch the physical raw materials.

The innovative methods are developed in close interaction between computer and reality. At DTU Risø Campus, the researchers use ComponentLab, which is a key facility in the process, making it possible to cast and produce the researchers’ own 12.6-metre-long wind turbine blades under controlled conditions.

Associate Professor Philipp Ulrich Haselbach (left), Research Technician Jonas Kreutzfeldt Heininge and Development Engineer Maksim Larionov from DTU Wind are inspecting a wind turbine blade (a single shell) following vacuum infusion. They are examining the material’s structure and quality, including the interaction between the layers. Photo: Bax Lindhardt
The blade (shell) after vacuum infusion, viewed from the root – that is, the end that is bolted to the wind turbine's rotor hub. Photo: Bax Lindhardt
The image shows a cured sandwich construction where a transparent layer of fiberglass composite is bonded to a foam core. The checkered pattern in the core reveals the channels that have ensured that the resin has fully penetrated and created a homogeneous bond between the materials. Photo: Bax Lindhardt

Prevents wrinkles

Once the resin is added during casting, it must be cured from liquid to solid form. This happens through gradually increasing temperatures of up to 90 °C. However, during the heating process, there is a risk of the fibres wrinkling due to residual stress during curing. A bit like when the skin shrinks on a grape that lies in the sun and turns into a raisin, the contraction and expansion of the materials risk forming inconsistencies if the heating occurs too quickly or unevenly.

Avoiding such wrinkles is critical, as they are often the cause of delamination. Delamination is when layers that make up the composite start to separate, so they lose the ability to fit snugly, and the layers can begin to separate. This separation significantly weakens the blade structure and can cause the inner layers to yield to the enormous wind pressure, ultimately destroying the blade’s load-bearing capacity.

Therefore, the researchers behind the project are developing models that predict the risk of wrinkles occurring. This allows manufacturers to adjust the production process before such errors occur. 
Even though the AIOLOS project has been completed, DTU Wind’s researchers and PhD students continue the experiments in ComponentLab, where new production methods, changes in fibre structures, and the production of sustainable alternatives to the current material in the blades are constantly evolving.

Facts

About the AIOLOS project

  • Together with Aalborg University and the companies FORCE Technology and Pontis Engineering as well as Siemens Gamesa, DTU worked to increase the production output of wind turbine blades. 
  • The focus of the project was to reduce the cycle time in production so more blades can be manufactured faster, which a more uniform casting process and a more uniform production quality. 
  • This is done, among other things, through simulations to detect errors before production launch.

Contact

Philipp Ulrich Haselbach

Philipp Ulrich Haselbach Associate Professor Department of Wind and Energy Systems Mobile: +45 50156403