Colloquia

Summary

The European Commission estimates between upto 450 GW of offshore wind power is needed by 2050 to keep global temperature rises below 1.5°C. Electricity will represent at least 50% of the total energy mix in 2050 and 30% of the future electricity demand will be supplied by offshore wind. To achieve this goal, wind turbines manufactured using durable and stronger material become necessary. This is more important for wind turbines having longer wind blades as energy conversion efficiency is higher. Failing blades cause major accidents if they cant resist the loads acting on them. A solution to this is the introduction of spar caps within wind blades which withstand heavy loads and provide structural solidity to the blades. The spar cap plays an important role in transferring the load to the root of the blade which results in electricity generation. This is bonded to the shell of the blade and the quality of this bonding is very important for overall stability of the blade. A weak bond can result in the blade fracturing and reduced load transfer can lead to defects due to fatigue which eventually lead to a failure of the blade. As longer blades are used to increase the power output, they need to be more stable, which means that the bonding between the shell and spar cap needs to be stronger. Hence study is conducted into the strength of bonding between the shell and spar cap.

In this thesis, the effect of different surface treatment on the bonding strength of pultruded spar cap with the blade shell are studied. Adhesion mechanisms are brought into action through surface treatment, and mechanisms studied here include mechanical interlocking, adsorption and chemical adhesion. The surface treatments considered are peel ply treatment, grit blasting, sanding and plasma treatment. Pultruded carbon fibre reinforced vinyl ester is selected for the spar cap (substrate) and the shell is represented by polyester-glass fibre (skin). Initially, suitable settings for each treatment are determined and after each surface treatment on the substrate, they are studied for the changes in surface energy through contact angle measurements and surface parameters are determined through confocal microscopy. Then, the substrates undergo co-bonding under vacuum through which the spar cap and shell are bonded in a real scenario and then the bond strength between the skin and substrate is evaluated through a fracture toughness test. Next, all the obtained data is analysed and the nature of fracture in each case is studied via optical microscopy and scanning electron microscopy. Finally, relevant surface parameters are linked to fracture toughness and the nature of the fracture.