Self healing interfaces in composites

Composite structures failure starts most often from interfaces or adhesive joints. Thus, if we suppress interface defects, we can prevent the overall failure of structures, long before it even started. The attractive idea is to initiate self-healing of interface defects. In ideal case, it will lead to permanent prevention of defects at early stages, and (in ideal case) to infinite life time of composite structures (or until next crash/typhoon). How to make the interfaces self-healing? Dr. Yulin Sun, Dr. Laura Simonini, Dr. Xing and I published a new paper “Self-healing interfaces in fiber reinforced polymers “, where we studied the self-healing of composite interfaces. Link: https://doi.org/10.1016/j.compscitech.2025.111269 . 

In our earlier work “Healable polymer blends for structural applications”, Dr. Sun and I also studied self-healing of structural polymer composites, https://doi.org/10.1016/j.ijmecsci.2025.109938 . The mechanisms of self-healing in these two cases are different, and we carrying out investigations now how to combine them. 

Chemical recycling of wind turbine blades

In our new paper “Multifield computational model of chemical recycling of polymer composites: Temperature effects on solvolysis efficiency and energy consumption” (https://doi.org/10.1016/j.jclepro.2025.145313), we proposed a multifield computational model of chemical recycling (solvolysis), that integrates diffusion, chemical reaction, temperature distribution, and mechanical responses. What is the problem? It was demonstrated in many works, that wind turbine blades can be recycled, using solvolysis (and also some other technologies) (https://www.mdpi.com/1996-1944/14/5/1124). The problem is that the depolymerization is still expensive process, and the recycled fibers can come damaged at the end, with reduced strength and residues. In other words, the process is expensive, and the output is of low quality. How to optimize this process? For this, we (Yi, Justine, Asger and I) developed this model. Analyzing the temperature effect, we observed that while higher temperatures reduce the time required for matrix dissolution, they also increase energy consumption and reduce the mechanical strength of recovered fibers. The next step will be to optimize the recycling regimes, using the quantitative model of solvolysis. This computational model can be also expanded for pyrolysis, and other recycling technologies. This model is based on our previous works, ”Modeling the solvolysis of composite materials of wind turbine blades” (https://doi.org/10.1002/adem.202302150) and ”Recycling carbon fibers by solvolysis” (https://doi.org/10.1016/j.compositesa.2024.108667), where we observed the link between the availability of manufacturing defects in compoites and the recycling efficiency, and recycled fiber quality. Summarizing: If we have high quality composite, and recycle it, using  intelligent control  of thermal regime, one can get relatively high quality fibers, with reasonably low costs. Further, with this model, we can comoare different recycling technologies. 27.3.2025

Nanoengineered composites and coatings for multifunctional smart structures

New research publication on nanoengineered coatings for corrosion protection, “Layered double hydroxides reinforced epoxy composites” (https://doi.org/10.1016/j.commatsci.2025.113816 ), our long term collaboration with Kaunas University of Technology, Sigitas Kilikevičius and Professor Daiva Zeleniakiene. In this article, the effect of nanoparticle reinforcements on the strength of polymer nanocomposites is explored. This article continues the series of investigationss on the effect of various nanoreinforcements (carbon, graphene, Mxenes) on the properties of composites, and possibility to add additional functionalities to the composites (like self-sensing, explored in our recent publication by Daiva Zeleniakiene, Gediminas Monastyreckis and Gabrielė Jovarauskaitė , ”Self-sensing composites with damage mapping using 3D carbon fibre grid”, https://doi.org/10.1016/j.compositesb.2025.112182). In the earlier works, hybrid polymer composites with graphene and Mxene nanoreinforcements (https://doi.org/10.3390/polym13071013) and MXene-polymer composites (https://doi.org/10.1016/j.carbon.2020.02.070 ) were studied. In our even earlier project, we studied and tested, carbon fiber/carbon nanotube based hierarchical composites (https://doi.org/10.1016/j.compositesb.2015.10.035) and graphene/polymer interfaces (https://doi.org/10.1016/j.commatsci.2014.08.011). There is huge potential in nanoengineering of composite materials, to develop new generations of multifunctional smart materials and structures. 20.3.2025

Self-healing wind turbine blades - is it possible?  

Blades are made from stiff and durable composites, with glass or carbon fibers and thermoset matrices. How to heal defects in such materials?  If one can repair defects at early stages of the material degradation, one can avoid expensive composite repair at later stages. In our new article ”Healable polymer blends for structural applications”, Yulin Sun and I investigate the potential of thermoset/thermoplastic polymer blends as a basis for healable composites for challenging service conditions. We developed a computational model of damage healing in materials. Link:  https://doi.org/10.1016/j.ijmecsci.2025.109938 - 10.1.2025

2025 is starting soon. Looking back - what did we achieve in 2024? 

• New computational model of chemical recycling of composites, which allows optimization of recycling technologies, was published in “Advanced Engineering Materials” (“Modeling the solvolysis of composite materials of wind turbine blades”, https://doi.org/10.1002/adem.202302150), by Yi Chen and me,

• New research project “PREMISE “Preventing MIcroplastic pollution in SEa water from offshore wind” started in May 2024 (https://wind.dtu.dk/newsarchive/2024/06/project-premise),

• I started my course “Micromechanics of composites: from computational modelling to new materials and technbologies”, for Master Students of Mechanical Engineering at the Technical University of Darmstadt, https://www.linkedin.com/posts/mishn_micromechanics-of-composites-modelling-activity-7229394329637703681-NABN?utm_source=share&utm_medium=member_desktop

• Investigation of microplastic emission due to the surface erosion of wind blades, and estimation of the volume of eroded plastic, published in “Energies” (“Microplastic emission from eroding wind turbine blades”, https://www.mdpi.com/1996-1073/17/24/6260

• Collaboration with IIT Delhi: We studied residual stresses and viscoelastic effects in repaired wind turbine blades. The article was published in Composites Part C (“Cure-induced residual stresses and viscoelastic effects in repaired wind turbine blades: Analytical-numerical investigation”, https://doi.org/10.1016/j.jcomc.2024.100521),

• Organized International Conference on Sustainable Wind Turbine Blades: New Materials, Recycling and Future Perspectives, 18-20.11.2024, https://www.conferencemanager.dk/recyc2,

• 5th  International  Symposia on Leading Edge Erosion of Wind Turbine Blades took place at February 6-8, 2024 https://www.conferencemanager.dk/5lee. Now, Charlotte and I prepare 6th Symposium: https://www.conferencemanager.dk/6lee,

• Collaboration with ORE Catapult: Antonios Tempelis, Kristine, I and OREC colleagues published an article ., How leading edge roughness influences rain erosion of wind turbine blades?, in “Wear” (https://doi.org/10.1016/j.wear.2024.205446),

• Collaboration with Sapienza University Roma: Daniele Tortorici stayed at DTU several months, and the paper “Recycling carbon fibers by solvolysis: effects of porosity and process parameters” has been accepted at Composites Part A.

• And several more publications.

It was quite a productive year.

Merry Christmas and Happy New Year! 🎄 20.12.2024

Microplastic emission due to offshore wind turbine blades

There are some wild rumors about hashtag#microplastic hashtag#emission from wind energy. We decided to calculate, how much microplastic can fall into water due to wind turbine blade erosion. Two new estimation methods were developed: direct and indirect. Direct method is based on modelling of rain erosion, as multiple liquid impacts, leading to the stress waves and local damage of polymers. Indirect method is based on empirical data from wind turbine service companies. If a blade needs to be repaired N times per year (in real life, N varies from 0.15 to 0.4), and, when each repair starts, a technician sees that volume V was worn out from the blade surface, then the volume of eroded microplastic is N*V. Our estimations shows that between 30 and 600 gramm per blade per year are removed, which yields 1.7 tonnes for all wind turbines in all of Denmark. Is it a lot? Let us compare it with other plastic emission sources. Car tires can emit up to 1700 tones plastic per year into the sea. Textiles bring 60 tones per year. Paints bring 390 tones per year. All this is one, two or three orders of magnitude larger, than the estimated hashtag#plastic hashtag#emission from wind turbines. Our new articles was published in the journal “Energies”: https://www.mdpi.com/1996-1073/17/24/6260 . The project PREMISE is funded by VELUX FONDEN. 15.12.2024

Maintenance and repair of wind turbne blades: Danish-Indian collaboration

With the expansion of wind energy industry, maintenance and repair of wind turbines acquire special significance. How to optimize the repair technology, reduce costs, ensure quick and efficient maintenance, improve quality of blade repair and post-repair lifetime? In our current project Maintainergy ("Maintenance and Repair Strategy for Wind Energy Development"), the strategy, technology and solutions for maintenance and repair of wind turbines in Europe and in India are investigated. Here is the overview of the project results. The partners are DTU Wind and Energy Systems (coordinator), Clobotics Wind Services, WiSH Energy Solutions Private Ltd, Windcare India, IIT Delhi, CSIR India and National Institute of Wind Energy. The project is supported by the Ministry of Foreign Afairs of Denmark, in the framework of Danida Fellowship Centre grant. The main directions included understanding the wind turbine failure mechanisms, methods of extension of the blade lifetime and prevention of defects, improvement of repair, bonding and curing technologies, and optimization of maintenance and repair strategies. The project webpage is here.  6.2024.

How to reduce the maintenance and repair costs of wind turbine blades? 

First, by reducing time and increasing efficiency of each blade repair. Second, by improving repair quality, so that the next repair is needed not in 2, 5 or 7 years, but rather in decades. Physically, repair represents a rather complex process, including composite grinding, adhesive bonding, flow and curing of polymers, heat flow, phase transitions. If a technician increases the curing temperature during the blade repair, it can shorten the repair time (reducing costs), but it leads to higher residual stresses in the composite, ultimately reducing post repair lifetime. If the curing temperature is reduced, longer curing might be necessary, leading to larger voids in the composite and higher costs. This is the process, which we study and optimize in several projects. In our newest publication “Cure-induced residual stresses and viscoelastic effects in repaired wind turbine blades” (https://doi.org/10.1016/j.jcomc.2024.100521 ), we analyze the residual stresses induced during repair of wind turbine blades, and the post-repair mechanical behaviour. It was observed that temperature cycles of adhesive curing can have significant effect on the post-repair lifetime. Our other publications in this area:

• L. Mishnaevsky Jr., How to repair the next generation of wind turbine blades, Energies 2023 (about repair of recyclable wind blades, https://doi.org/10.3390/en16237694 )

• D. Paul et al., Post-repair residual stresses and microstructural defects in wind turbine blades, Int J Adhesion & Adhesives, 2023 (residual stresses and effect of voids, https://doi.org/10.1016/j.ijadhadh.2023.103356 )

• L. Mishnaevsky Jr. et al, Technologies of wind turbine blade repair: practical comparison. Energies. 2022 (comparing different repair technologies, https://doi.org/10.3390/en15051767 )

• R. Muthu et al, Repair of wind turbine blades: Experience and observations from India – A Review. Wind Energy Science (practical observations in India) (https://wes.copernicus.org/preprints/wes-2024-55/)

• L. Mischnaewski, L. Mishnaevsky Jr., Structural repair of wind turbine blades: Effects of adhesive and patch properties on the repair quality, Wind Energy, 2021 (modelling of repair and effect of voids, https://onlinelibrary.wiley.com/doi/10.1002/we.2575)

• L. Mishnaevsky Jr., Kenneth Thomsen, Costs of repair of wind turbine blades: Influence of technology aspects, Wind Energy, 2020 (costs of repair and optimization, https://onlinelibrary.wiley.com/doi/epdf/10.1002/we.2552)

• L. Mishnaevsky Jr., Repair of wind turbine blades: Review of methods and related computational mechanics problems, Renewable Energy, 2019  (overview, https://doi.org/10.1016/j.renene.2019.03.113 ). 3.2024

Course "Micromechanics of composites, smart composites and sustainable technologies" (MSc students, TU Darmstadt)

I teach a course ”Micromechanics of composites” for master students at the  Technische Universität Darmstadt, Department of Lightweight Engineering and Structural Mechanics (LSM). Here are the slides of the last, overview lecture, summarizing the ideas and concepts, which were studied at this course. 2.2024