A comprehensive collection of news and information about composites.
North American Windpower reported this week that a third 48.7m/160-ft blade has broken off a GE 1.6-100 turbine. All three breaks happened either during or shortly after turbine commissioning. No one was injured in any of the breaks.
The most recent occurred at Invenergy’s (Chicago, Ill.) Orangeville Wind Farm in New York. A blade on turbine #34 snapped near the hub, with most of it falling to the ground, leaving a jagged stub.
Though the first and second breaks in 2013 — both in Michigan wind farms operated by DTE Energy (Detroit, Mich.) — sound similar, they look very different from the one in Orangeville. The Nov. 7 break of a blade on Echo Wind Park’s #60 turbine and the Mar. 11 break on one of 40 turbines in Thumb Wind Park’s Sigel Township installation (officially dedicated October 2012) both show separation of the blade along its length. The Orangeville blade showed more of a clean snap.
In fact, the earlier 2013 breaks look more similar to two GE 1.6-100 turbine blade breaks in 2012, both in Illinois. In an image from the California Ridge Wind Farm, the carbon spar used in GE’s 48.7m blades can be clearly seen. According to GE Renewable Energy spokesperson Lindsay Theile, an “isolated manufacturing issue was the cause of the two blade fault occurrences.” Though the precise nature of the issue was not disclosed, the Mar. 11 break at DTE’s Thumb Wind Park was attributed to a failure in the carbon fiber spar “at the 19-meter mark” caused by an accidental 2-hour oven shutdown during cure.
RechargeNews.com stated the Echo Wind Park blade was made in Brazil. Tecsis (Sorocaba, Sao Paulo state, Brazil) had a $1 billion contract to supply blades to GE for U.S. wind power projects from 2006-2010. In a 2012 Wind Turbine Overview for the World Bank, GE presented its 1.6-100 turbine blade testing overview with a photo beside “Certification Requirements” titled “GE-Tecsis Collaboration”. Thus, GE and Tecsis have had a close relationship, and it is possible, if not likely, that the five GE 1.6-100 blades that have failed in 2012-2013 were produced by Tecsis in Brazil.
Tecsis was founded in 1995 by aeronautical engineer Bento Koike. In 2012 it was listed as the second largest blade manufacturer in the world, behind LM Wind Power. A 2009 article by PIB magazine claimed Tecsis had supplied half the blades in operation in North America and held more than 40 international patents on blade technology. A Sep. 2012 article from Valor explained that the company filed bankruptcy in 2010 but has emerged stronger, with positive earnings in 2012 based on revenue of US$700, a doubling over 2011. It also increased production from 10 to 12 blades per day to 30 and said it supplied “besides GE,” Alstom, Gamesa, Impsa and Siemens. 2012 production was slated at 5,500 blades. The company described its largest blade as 50m (i.e. the 48.7m for GE) and weighing roughly 9 tons (19,842 lb). Interestingly, Tecsis director of operations Ventura Pobre, previously from a maintenance services subsidiary in the U.S., is credited with developing a new solution for carbon fiber application in the “record time” of one year, which reduced blade weight from 9 to 6 tons. The article explains, “The base material is not simple at all and needs to be transported and stored under special conditions.” This seems to point to a recent switch to prepreg for the spar caps. In a 2008 presentation, GE showed carbon fiber spar caps being infused, layed into the fiberglass and balsa core blade shell layups and then infused. Meanwhile, Composites Technology magazine (Oct 2013) reported the blades are E-glass/epoxy sandwich construction with a hybrid core using balsa wood plus PVC and SAN foams.
Time will tell what these blade failures have in common, and why they’re occurring, but in the meantime it is important to note that they are quite different from the previous blade failures experienced by Gamesa in 2007 and Siemens earlier this year. For Gamesa, a defect in a foot-long applicator produced an irregular line of adhesive, causing splintering and breakage in 13 of nearly 400 blades produced at its Ebensburg, Pa. plant that year. Seven blade failures were first observed at the Allegheny Ridge Wind Farm in Pennsylvania. The problem was corrected and the blades were replaced.
Siemens responded quickly to two B53 (53m/174 ft long) blade failures in its SWT-2.3-108 turbines at the Eclipse wind farm in Iowa and the Ocotillo Wind project in Calilfornia. It immediately curtailed production of that turbine, performed a root-cause analysis and determined the cause was adhesive bonding failure between pre-cast root segments and the main blade fiberglass laminate due to insufficient surface preparation. All B53 blades have been inspected and most are back in operation. Siemens will replace a number of blades due to delamination and will apply a minor modification in the field to all B53 blades that are not replaced, incurring $131 million in charges toward 3rd quarter 2013 results.
The GE 1.6-100 turbine was touted as the most popular U.S. wind turbine installation in 2012 by Navigant Research and was named 2012 Turbine of the Year by Windpower Monthly for kick-starting the large-rotor trend, which, when combined with modest generator power, has reduced the cost of energy. It has also helped GE to surpass Vestas as the number one turbine supplier in the world.
It’s important to keep these blade failures in perspective. According to published GE announcements, it expects to install 1,500 1.6-100 turbines by the end of 2013, for a total of 4,500 blades. Including the two failures in 2012, a total of five failures translates into 0.1 percent of production. As comparison, the 10 largest automobile recalls in 2013 (as of July) reported by the U.S. National Highway Transportation Safety Administration (NHTSA) totaled 8,471,045 vehicles, which represents 27 percent of the 31.4 million vehicles produced in North America during 2012-2013. Realize, these recalls were all for serious issues with brakes, airbags and potential for fires. Granted, the comparison is not direct because the car models affected can date back before 2012. However, just the portion of recalls that affect mainly 2012-2013 model years totals more than 2 million vehicles, or 6.5 percent of North American production.
Yes, there have been failures, but so far, they have affected a very small percentage of the total blades produced and installed. If GE follows Gamesa and Siemens in conducting a swift investigation and correction, it should be able to maintain the industry confidence it has duly earned.
The number of large composite surfaces requiring sanding before bonding or painting is increasing rapidly as the Boeing 787, Airbus A350 XWB and next-generation single-aisle jetliners enter service.
The Easily Manipulated Mechanical Arm, or EMMA, is a pneumatic, mechanical arm developed by Temple Allen Industries (Rockville, Md.) during the 787 program to enable surface preparation of large composite wing and fuselage areas, where chemical solvent and stripper use is not allowed. EMMA is written into the 787 specifications as the only acceptable alternative to manual sanding and is approved for use on most commercial aircraft.
EMMA is a mechanized tool and not a robot to replace the worker. Instead, it improves worker productivity and eliminates the pain and injuries that surface preparation/finish personnel too often must endure. Vibration white finger (VWF, more typically known as hand-arm vibration syndrome or HAVS) occurs when capillaries in the fingers close down after hours of holding a sander or grinder. HAVS affects tens of thousands of workers and can damage blood vessels, nerves, muscles, and joints in the hand, wrist and arm. Its effects are cumulative, and become permanent with continued exposure.
In Europe, Occupational Safety and Health Administration (OSHA)-equivalent agency regulations limit vibration exposure. For example, U.K. workers cannot hold a sander past defined exposure limits, which are often less than half a shift. Though no such regulations exist in the U.S., most high-tech manufacturers are interested in reducing worker injuries and increasing sanding and machining quality and productivity.
Many people think that sanding composite surfaces is fairly simple, holding a tool while bending over a part on a table. But increasingly, the surface to be sanded is a fuselage or nacelle in front of the worker or the underside of a wing overhead. Combine that awkward position with the weight of the tool and the force required to make sure the surface is abraded adequately but not excessively, as well as the extended time periods required, and it is easy to see the potential for injuries, need for frequent breaks that slow productivity and factors that could produce inconsistency.
EMMA bears the weight of the tool, absorbs vibration, and holds the tool flat on the workpiece surface while applying a consistent contact force. The worker can sit or stand comfortably using a joystick to control direction and movement.
EMMA is used by Boeing (Renton, Wash.), Airbus (Broughton, U.K.), Northrop Grumman (Palmdale, Calif., USA), Embraer (São José dos Campos, Brazil), British Airways (Heathrow), Triumph Aerostructures - Vought Aircraft Division (Milledgeville, Ga., USA), and the US Air Force and Navy, among others. A unit is being installed now at a large wind blade manufacturing facility.
Thanks to a variety of deployment options (e.g. rail-mounted, telescoping stand, or belly system for sanding the underside of aircraft) EMMA can be integrated into various processes and operational set-ups. Watch EMMA in operation: http://www.templeallen.com/Videos.html
Pierre Harter, engineering manager – M&P, technology readiness and structural certification Learjet, was the featured speaker on the last day of SAMPE Tech (Oct. 20-24, Wichita, Kan., USA) and provided a great deal of information about the composite materials and manufacturing processes being used to fabricate aerostructures for the forthcoming Learjet 85 business jet.
Wing skins and spars for the plane are manufactured in Belfast, Ireland, using an in-autoclave resin transfer infusion (RTI) process. Fuselage and empennage are manufactured in Querétaro, Mexico, via an out-of-autoclave process. Harter reported that the plane, which is expected to make its first flight in the next few weeks, is the first FAR Part 25 aircraft with composites in the fuselage and wing. He also said that the Learjet 85’s use of composites was not driven chiefly by lightweight, but instead to significantly reduce part count by manufacturing large, integrated structures. In the process, Bombardier learned much about materials characterization, materials management, process development and certification.
Harter described the RTI process to make the wing skins and spars as using dry carbon fiber non-crimp fabric (NCF) that can be quickly cut (by Gerber machines) and placed. The NCF has a binder, which is used in preforming on a male tool, followed by infusion in a female tool. The tool is preheated, the part is bagged and the resin (Cytec’s Cycom 890, for resin transfer molding) is injected under autoclave cure. Stringers are co-cured with the upper and lower wing skins. Harter said the process/material combination is certified by the U.S. Federation Aviation Administration (FAA) for the application.
More challenging, said Harter, was the out-of-autoclave (OOA) material and process development for the fuselage. This was done in close cooperation with Cytec, which provided the resin (Cycom 5320) for this application as well; Harter described the company’s assistance as crucial to the plane’s development.
The fuselage is manufactured in three sections: the nose, the main fuselage and the tail. The main fuselage is 30 ft/9.1m long and represents one of the largest of its kind to be fabricated OOA. Challenges included the fact that the Bombardier facility in Querétaro is at an elevation of more than 6,000 ft/1,829m, which reduces available vacuum pressure compared to lower altitude locations. Further, although Bombardier is adept at developing composite material parameters for autoclave cure, Harter said OOA changed many of the company’s cure management assumptions. Compaction, air removal, resin flow and ply placement had to be adjusted, managed and fine-tuned much differently than they would have been for autoclave-based curing, he said. In addition, the OOA process proved uncommonly sensitive to difficult design features.
Bombardier also had to evaluate breathing methods, bulk and debulk cycles, dwell times and rheology to achieve desired porosity. If the part was cured too quickly, many small voids were generated in the composite. Combating porosity required perfecting the management of resin viscosity over time, Harter said, and was achieved only after extensive trial and error. “Legacy flow and gel times are not adequate,” he noted. Bombardier eventually developed an OOA manufacturing process that produced voids of less than or near 1 percent.
Harter related that after processes were optimized, Bombardier faced the daunting task of achieving FAA certification. Much like the Boeing 787 and the Airbus A350 XWB, intensive use of composites on the Learjet 85 meant Bombardier had to perform extensive testing to satisfy the FAA’s special conditions for certification. Much of this, Harter said, focused on in-flight flammability, post-crash flammability, crashworthiness, durability, toxicity in burn, damage tolerance and thermal expansion at interactions with metals. Results, across the board, were positive. In fact, noted Harter, composite materials on the Learjet 85 outperformed aluminum in flammability and crashworthiness tests — a fact that he believes needs to be emphasized more by the aerospace composites professionals. Composite readiness testing is now complete and certification testing has begun.
Bombardier has committed five full-size Learjet 85 aircraft for testing, which represents significant investment for the company. When asked why Bombardier was going to such effort and expense in regards to material and process development, and certification, Harter said, “Bombardier management knows that composites are the way to go. This is the future.”
Wind blades currently use epoxy paste adhesive to bond top and bottom composite blade shells together around a prefabricated shear web, which also typically includes a bonded spar cap. The epoxy requires significant time to cure, and because the shell halves are mated blindly, without visual access to the bonding areas, the bondline thickness can vary wildly.
General Electric’s (Schenectady, N.Y., USA) patent US0027610, awarded in 2012, describes (underline added), “This configuration, however, often results in the use of excess bond paste to achieve the bond width . . . contributes unnecessary weight to the blade and can break off and result in blade “rattling” during operation . . . Also, air voids and unpredictable squeeze-out of the bond paste in the typical construction can result in areas of decreased bond strength, which is particularly problematic in sections of the blade where repair is not possible from within the blade. Accordingly, the industry would benefit from an improved bond configuration . . .”
SCIGRIP (Durham, N.C., USA) — one of the largest suppliers of methyl methacrylate (MMA) structural adhesives for composites and assembly adhesives used to bond dissimilar substrates, including composites, metals, and plastics — has a long history of technical development and working with customers to achieve productivity gains.
Sales and marketing director, Karen Brock Amoah, explains: “Our SG 747 structural adhesive has been evaluated to replace epoxy and other traditional adhesives at two large wind blade manufacturers, with qualification complete at one and nearing completion at the other. We have developed SG 747 with tensile strength and high temperature performance [up to 150˚F/66˚C] approaching that of epoxy, but with much better toughness at cold temperatures [down to -40˚F/-40˚C] — where epoxies become brittle — and an order of magnitude improvement in fatigue resistance, especially important for service in wind turbines.”
Amoah showed a thick wedge section bonded with SG 747 to demonstrate its thick-section capability at the far extreme. “No one would ever make a bondline this thick, but it shows that at 4.5 inches of adhesive thickness the SciGrip material provided good bond without any voids or boiling (due to exotherm).” Amoah notes that MMA chemistry is inherently moisture resistant and offers quick cure times without having to add heat, predicting a 40 percent reduction in production time for typical blade assembly operations.
Midnight Express Boats (Hollywood, Fla., USA) started in the 1980s and became known for indestructible, high-speed powerboats. “We have large contracts with Homeland Security and for overseas patrol boats, for example, the Trinidad & Tobago Coast Guard,” says production manager, Tague Estes. He adds that the boats are also overbuilt and solid, with some customers using four engines. “Now we can keep that strength and smooth ride, but pull the weight out,” Estes says. “We’ve cut close to 4,000 lb from our newest model, the 39S, by using infusion and better optimized laminates — hull and deck are still fiberglass — but the strength is six times greater than what we were getting with hand layup.” Owners may still use four engines, but it’s to reach new levels of speed. “Today’s customers are all about performance,” Estes explains. “If you don’t have a center console running 80 mph, you aren’t in the game.”
The Midnight Express 39S will be on display at the Ft. Lauderdale Intl. Boat Show this week (Oct. 31-Nov. 4) and features a hull and longitudinal stringers (plus aft bulkhead) that were resin infused simultaneously to save weight and time. Estes details, “We eliminated additional surface prep. and adhesive bonding, plus it addressed one of our biggest time challenges with hand layup, which is getting everything layed into the stringer grid. With co-infusion, we use jigs during the infusion process and make sure everything is perfect.” Overall build time was reduced by almost two days. Estes adds, “The more you can put into one shot, the better. You’re using the same resin, molded at the same time, and under the same conditions. It simply eliminates potential for inconsistencies.”
“This is a big boat,” says Estes, “39-ft long with a 9.6-ft beam and all the toys, yet it is probably the fastest center console in the world.” He adds that the only way to achieve that kind of performance is to drop weight. Selective use of infused carbon fiber was also key, cutting the console door weight from 150 lb to 35 lb and lightening the hard top from 335 lb to under 100 lb.
Midnight Express boats already had a reputation for standing out, with many featuring black hulls and decks. “We’ve never had any problem,” says Estes. The skin is 100 percent vinylester. Half of the boats are painted and half use gel coat. The 39S for the Ft. Lauderdale Show was painted to match the owner’s Lamborghini, using a special PPG automotive system with two types of pearl additives and silver matte finish. It also features a stepped bottom for high performance planing and speed. “It’s all about what the owner wants,” Estes remarks. “I try not to say no.” But he admits, that becomes difficult when customers want to add more gensets and special equipment without losing performance. Co-infused structures and carbon fiber help him to say yes, and still hit speed and durability targets.
Midnight Express uses vinylester resin from Interplastic Corp. (St. Paul, Minn.), non-crimp fabrics from Vectorply (Phenix City, Ala.) and woven reinforcements from BGF Industries (Greensboro, NC). It also worked with Composites Consulting Group (CCG, DeSoto, Tex.) to develop its hull-stringer co-infusion process, which is discussed in the upcoming IBEX show review in the December issue of CT magazine.