JEC COMPOSITES MAGAZINE - Issue #70 - January/February 2012 - 30

resin

the vinyl ester by approximately a factor of 3. Similarly, the polyurethane outperformed both the epoxy and vinyl ester samples in fatigue crack growth testing at all stress values.

State of the art
As the demand for longer wind turbine blades grows, so does the need to develop stronger, tougher composite materials. Today blades must endure 48 times the hourly fatigue of a commercial aircraft wing [1, 2] and are expected to log more than eight times its service hours. Thus, advances in blade composite material and process technologies are two of the top five needs of the industry. The development of stronger lightweight composite technology could enable up to a 35% increase in turbine energy output. In addition, new concerns over the carbon footprint of composite materials are emerging. There is a desire to consider composites with low or zero volatile components. Polyurethane-based systems are far superior to incumbent materials in this regard. Technologies using biobased components are well established in urethanebased composites, which offer the potential to reduce the footprint even further. Another identified need is to improve the ability to monitor blade performance in real time throughout its service life. Semiconductive fillers such as carbon nanotubes (CNTs) can be adapted to become passive sensors which provide feedback to operators regarding blade performance under varying environments. Initial investigation into the effect of carbon nanotubes in neat resin properties was reported [3,4].

m2, ±45 degree bias E-glass fabric cut to a 610 x 610 mm size. A 610 x 610 mm ply of Airtech flow media was placed on the top of each reinforcement stack. Then each reinforcement package was double bagged with 0.08-mm nylon film on a glass plate with an edge resin in port and a centre vacuum port. A vacuum of 60 millibars at room temperature was drawn on each reinforceFig. 1: 610 x 610 mm thin, flat plaque infusion set-up ment package. The thin, flat plaque infusion set-up is illustrated in Poisson’s ratio, and at -50°C for tensile Figure 1. strength and modulus. Each resin system was mixed by weight in accordance with the manufacturer’s recommended levels: Hexion EpiCote® 135i epoxy at 100 parts to Hexion EpiKure® 1366 hardener at 30 parts; Reichhold Dion® 9102-75 vinyl ester at 100 parts to Syrgis Norox® CHP at 1.5 parts; and Bayer 840871 polyol at 100 parts to Bayer 840859 isocyanate at 90 parts. Each mixed resin was degassed for 5 minutes at 23°C under 70 millibars vacuum prior to infusion. After the panel infusion by each resin system was complete, the resin inlet port and the vacuum port were clamped off and the resin infused panel was heated to 70°C and held at that temperature for 1 hour. Each panel was cooled to room temperature, the bagging removed, and then each panel was postcured for 6 hours at 80°C. After allowing each infused panel to condition for 24 hours at room temperature, panels were sectioned into test coupons in accordance with the ISO 527-4 Standard and were tested at 23°C for tensile strength and modulus and Long-flow, thin laminate infusion trials Two sets of long-flow, vacuum infusion experiments were conducted, one in a thin laminate construction and the other as a thick laminate. These experiments were designed to compare the flow rates of the different resins. These experiments were conducted on a large, flat, temperature-controlled steel table capable of accommodating three long-flow studies concurrently as shown in Figure 2. The thin laminate was constructed as follows: Vectorply E-BX-2400-5, 810 gm/m2, ±45 degree bias, E-glass fabric was cut to strips of 330 x 2,440 mm and stacked 4 high for each of the three resin

Experimentation
Composite preparation for testing To compare the properties of incumbent epoxy and vinyl ester resin systems to a polyurethane resin system, thin flat plaque infusion panels were prepared. The reinforcement package for each infusion trial consisted of either 4 or 6 plies of Vectorply E-BX-2400-5, 810 gm/

Fig. 2: 330 x 2,440 mm long-flow, thin and thick laminate infusion set-up

30 jec composites magazine / No70 January - February 2012

JEC COMPOSITES MAGAZINE - Issue #70 - January/February 2012

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #70 - January/February 2012