Dear Dr. Sajan Sukumaran,

I think the wind industry has the following specific tendency. Lightness and mechanical properties play a pivot role to the future for wind turbine blade applications.

The currently available solution, in the simplest case, are E-glass/epoxy composites but carbon fibers represent a very promising alternative to the traditional E-glass fibers. There is virtually no alternative to lightweight constructions: carbon fibres, the black wonder fibres that are superior to steel and aluminium in almost all respects when it comes to cutting weight. And, in terms of stability and lightness, carbon-reinforced plastic is simply unbeatable. Carbon fibers ensure higher stiffness while their disadvantages are higher costs, lower compressive strength and high sensitivity to local defects. In several studies, the combination of carbon and E-glass fibers was recommended as a promising solution, which allows to achieve the combination of higher stiffness (due to carbon fibers) with limited cost increase. The quantity of CF (Carbon Fiber) to other structural material is a little, but the use in many specific area play a pivot role.

Best regards, Pierluigi Traverso

dear Sajan Sukumaran

in the history of the turbine, the Gedser wind turbine which installed at Gedser coast in Denmark in 1956–1957 designed by Johannes Juul, with three composite blades built from steel spars, with aluminum shells supported by wooden ribs.

and recently, glass fibre is manufactured from glass manufacturing materials such as silicate, colemanit with aluminum oxide

Article Materials for Wind Turbine Blades: An Overview

Using of Composite Material in Wind Turbine Blades

Bulent Eker, Aysegul Akdogan and Ali Vardar

https://scialert.net/fulltextmobile/?doi=jas.2006.2917.2921

Aluminum could be used, but it has the disadvantage of corrosion. This is particularly pronounced in saltwater environments, but can also be a problem in regular atmosphere.

Pure aluminum rarely corrodes, but high-strength aluminum alloys contain galvanic cells, especially alloys containing copper. For example, 7075 aluminum has Zn as its primary alloying element, but also contains 1.4% Cu, and is susceptible to stress corrosion cracking:

https://www.onepetro.org/conference-paper/NACE-06496

SCC is a problem for structures that are generally in tension (as wind turbine blades would be.) This is typically mitigated by overaging (e.g. -T7 condition), but this reduces the strength of the final product and plating or painting.

Plating reduces the fatigue strength of a material because it induces stress at the interface. Aerospace applications use cadmium because it is less noble than aluminum and the corrosion product tends to inhibit further corrosion. This likely would not be an option for a wind turbine. Paint might be an option, but would need excellent adhesion and a wear-resistant layer to prevent hail and other types of damage.

It was proposed and tried in past. It has many limitations. Now a days plastic composite is a best option.

For more details you can reefer my Chapter 3. 'Materials for Small Wind Turbine Blades' in the book " Renewable Energy and Sustainable Development ".

http://www.novapublishers.org/catalog/product_info.php?products_id=52355

A fundamental aspect in the wind blades design is the choice of the correct materials, because several parameters (weight, load and fatigue behaviour, physical properties, etc.) are influenced by this basic decision.

Several years ago materials as varied as wood, steel and aluminium where used to produce wind blades.

The first wind blades where made using wood, a low cost, low density material with a good resistance to fatigue. However, wood has a strong anisotropy and a huge potential variation of his properties, together with a notable tendency to water absorption that can lead to a reduction of resistance.

Steel was used in the first years of the 80’s in turbines as Growian ("Große Windkraftanlage" – big wind turbine), a Goliath for his times with steel spars and fibreglass skin. The structural properties of this material are exceptional, while the main drawback is its elevated density, leading to an increase of inertial and gravitational loads.

Aluminium was the initial choice for the MOD-0 prototype. Blades were developed by Lockheed, but were removed do to problems at the root caused by the rapidly changing loads (the WTG was downwind). It has a low density and a good resistance to corrosion, but a low fatigue resistance. It has been traditionally used in vertical axis wind turbines.

It must be observed that several variables influence the choice of the materials: cost, weight, resistance, number of blades of the rotor (3 blades WTGs with fixed hubs are more robust than 2 blades WTGs with tilting hubs). An important parameter is the specific weight, the relation between the weight of the rotor and the swept area (in kg/m²).

As mentioned by Thomas Anthony Troszak "ACM panels as currently manufactured are very light and strong, but they are also rectangular, flat, have a constant thickness, and are extremely rigid. So the currently available sheets of ACM are perhaps not ideally suited to the fabrication of very long, very curved structures that vary greatly in material thickness from root to tip.

I think one of the guiding principles of blade design is the achievement of a single, continuous 'shell' that is free of structural joints and bonding discontinuities to the greatest extent possible. So adapting the current ACM sheet production methods to this 'continuously curved structural envelope' application would be a challenge, especially when bonding aluminum to aluminum - which would also be an issue for in-service repairs (patches). Others have already mentioned the issues with atmospheric corrosion potential for the aluminum skin - which can be significant, depending on the service environment. The expected lifetime of presently existing blades is highly dependent on their geographic location of deployment - as temperature, sunlight, dust, salt, water, and variability of wind loads all have their respective and combined effects upon the blade materials and structure. Blades in service (over land) in Denmark (steady wind, cool temperatures) can easily outlast those in Texas (blazing heat, dust storms) or the Gulf of Mexico (salt spray, hurricanes) by a factor of three times or more.""

Therefore ACM is not a very good choice for turbines.

Instead of ACM, KEVLAR is the most promising material for turbines.

Dear Sajan,

According to a report from the National Renewable Energy Laboratory, wind turbines are predominantly made of steel (71-79% of total turbine mass), fiberglass, resin, or plastic (11-16%), iron or cast iron (5- 17%), copper (1%), and aluminum (0-2%). Earlier it is made composite blades built from steel spars, with aluminum shells supported by wooden ribs, installed at Gedser coast in Denmark in 1956–1957.Lightness, stiffness is ok, but main problem is oxide deposition on the turbine blade. It has a disadvantage of intergranular and pit corrosion attack on the blade.

Ashish

No

Because it can not withstand the load

If your mean is the fiber metal laminates (FMLs) consisting of the layers of composite bonded to aluminum sheets, it is an innovative desision. Regarding fatigue is one of the most important issues in wind turbines, using the FML as a fatigue-resistance material for blades is strongly recommended.

Dear Sajan Sukumaran The answer to that question is yes. But there are a few things to consider:

The answer to that question is yes. But there are a few things to consider:

Due to its excellent proprietary features, aluminum is one of the most widely used metals in the world. Being light and inexpensive is the most important commercial features of this invaluable metal.

Aluminum is one of the most important foundations of the aircraft body. Ti-6Al-2Sn-4Zr-6Mo alloy is the main component of the boing 747.

The main point that engineers always deal with is balancing efficiency and cost. The engineer must not only technically consider the feasibility of using a device or process, but economics should be an integral part of all these decisions.