Blade Layup Material Issue

[vacupenda]

For the two materials shown in the figure, when I applied the rated load (calculated by OpenFAST) to the blade and used a material mechanics analysis tool to calculate their strength ratios, I found them to be less than 1, indicating that both materials would fail. Additionally, a paper mentioned(The Impact of Bend–Twist Coupling on Structural Characteristics and Flutter Limit of Ultra-Long Flexible Wind Turbine Composite Blades), “The biaxial fibers [45/−45] and triaxial fibers [45/02/−45] can be represented by multiple uniaxial fibers in different directions.” Can I use the material “Glass_unin” to represent both “glass_biax” and “glass_triax”? When I perform the ply stacking using the aforementioned method rather than directly using the data shown in the figure, the calculated strength ratios are always greater than 1. However, I am not sure if this method is feasible.

[ptrbortolotti]

hi @vacupenda, the nominal blade did not undergo a detailed structural design, and so it is possible that some stress limits are exceeded. one word of caution is maybe around loads: in addition to material strength values, pay also attention to what loads you are using to compute the stresses.
Note that in the README you are going to see a couple of studies listed where a more rigorous structural design was performed. I would look into those
as for laminate theory, a triax can be seen as a combination of uniax and biax, but it's hard to say that it will be a 1-1 match. Triax fabrics have fibers at 45/0/-45 directions in specific percentages of volume, so you cannot just combine two random uniax and biax and you will get the properties of the triax

[vacupenda]

Thank you for your response. I found all the materials and layups in this file(https://github.com/IEAWindSystems/IEA-15-240-RWT/blob/master/WT_Ontology/IEA-15-240-RWT.yaml]. I used VABS to calculate stiffness and strength ratios. The stiffness results match correctly, but when calculating strength (with loads obtained from OpenFAST under rated conditions, providing forces and moments in three directions at different spanwise positions), the strength ratios for “glass_biax” and “glass_triax” are particularly low, while all other materials are normal. Therefore, I replaced these two materials with unidirectional fibers and applied layups of 45/-45 and 45/0/-45, respectively. I'm not sure if the issue originates from these two materials.Are glass_biax and glass_triax material properties that have already been mixed using unidirectional glass fibers? If I were to create the layup using unidirectional glass fibers myself, what proportions should I use for different fiber angles?

[ptrbortolotti]

The material properties are discussed in this article https://doi.org/10.5194/wes-7-19-2022, see Table 1. The values should be accurate and come from the open-source Montana State University composite database

I'm sorry, I don't have an immediate answer about the proportion of UD vs BX fibers in a TX laminate, I am sure commercially you will find different TX with different proportions

[vacupenda]

Thank you for your response. This literature has been very helpful to me. Additionally, when I use BeamDyn to calculate the loads at different spanwise positions of the blade, I need to input a BeamDyn.dat file, which contains the stiffness matrices at different spanwise positions. Currently, I am using VABS to calculate this stiffness matrix. However, when using VABS for the calculation, translating the cross-section to different reference points results in different stiffness matrices. Therefore, in order to obtain the stiffness matrix as required in the file, at which reference point should I define the cross-section?

[ptrbortolotti]

The K and I matrices are defined with respect to the reference axis. Airfoils are pinned along their chord according to the non dimensional field pitch_axis. This documentation should help https://windio.readthedocs.io/en/latest/source/blade.html
In addition to VABS, you can try the open-source ANBA code, which is called here https://github.com/ptrbortolotti/SONATA/tree/develop/examples/1_IEA15MW
This is how we generated the K and I matrices for the IEA15