LM Glasfiber’s material mechanics experts are always on the lookout for details that will help us improve our blade designs. It’s only by being completely familiar with the outer limits of these materials’ capabilities – and then expanding the envelope all the time – that we can ensure that each blade is reliable, durable and cost-effective. And do so without using more than is really needed, and without using materials that are more expensive than really necessary.
It’s often the small details that lead to major technology breakthroughs. That’s why we examine the microstructure of the materials we use in the lab, as part of our analysis of their overall properties. This helps reveal how these materials will perform when used in large-scale composite structures, paving the way to achieving the best possible quality.
To study these properties, we produce a special test model, which then undergoes a range of different tests. Part of these involves a special pull-and-push testing machine that uses computer-controlled servo-hydraulics to test the strength and stiffness of a particular material. The test unit is then inspected under a microscope. Any signs of damage always make their first appearance in the microstructure.
Different combinations of glass fibre and resin, under different process conditions, result in a wide range of different properties and strengths. The combination of testing and examination under a microscope enables us to map these in great detail so that we can adjust the properties of each laminate to any specific requirement, at the same time as making sure that any potential weaknesses are eliminated.
Boundary areas, such as glued joints and interfaces between laminates and the core material, have a critical influence on the overall structural strength of a wind turbine blade. LM Glasfiber has worked with the Risø National Laboratory in Denmark to develop a method for testing mechanical breaking strength. This introduces different loadings using force moments, which makes it possible to apply well-defined loads in several different axes at once. These correspond to the forces that act on the blade while in real-life operation. These test procedures are carried out in our own specially developed mixed-mode test machine.
Microscopic examination is part of our systematic examination of so-called “scale effects”. This involves studying and testing materials at different levels so that we can take maximum advantage of the properties of each material, and also ensure that the final product is as reliable as possible in operation.
Testing takes place at different scales, from nano level – focusing on the structure and surface of the individual fibre – upwards. This provides us with a more in-depth understanding of how single fibres interact with the resin. At the other end of the scale is full-scale testing of the complete blade, in which the aim is to test material composition and the sum total of the material properties. These tests examine the ways that blade structure and material characteristics interact, as this is crucial for the success of the final blade.
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