A comprehensive collection of news and information about composites.
Posted by: Jeff Sloan4. February 2016
This five-plus passenger, single-engine, V-tailed personal jet will sport an OOA-composites-enabled low maximum takeoff weight of 2,722 kg.
We here at CW put together a supplement published with the February issue of the regular magazine that focuses on the technologies, tools and materials being used today in out-of-autoclave (OOA) processing for aerocomposites. If you're a CW subscriber you will receive the supplement in the mail, but if you're not, or if you don't want to wait for the postal service, you can find the supplement here: cw.epubxp.com/i/630867-autoclave-2016, or just click any of the images.
The A350 XWB window frame preforms, made by Advanced Composite Engineering GmbH, use vertical structural stitching and selective stitching to achieve an L-cross-sectioned oval without any wrinkles and a glass fiber lining to prevent galvanic corrosion in contact with metal.
Although OOA processing in aerospace applications has been employed for decades in the manufacture of thermoset composite parts for unmanned spacecraft and, more recently, in the manufacture of substructures for commercial passenger aircraft, the autoclave remains the curing technology of choice for the world’s large aircraft OEMs, primarily because of its brute strength — its ability to definitively consolidate composite parts and remove the voids that can compromise struc- tural performance. Such robust consolidation, however — <1% void content — comes at a high price in terms of capital expense, operational costs and time. As composites move further into aircraft, it’s clear the autoclave cannot be the only process available to aerocomposites fabricators. Today, OOA alternatives include vacuum bag-only (VBO) prepregs, dry fiber placement, infusion processes (which rely on oven cure), resin transfer molding (RTM) and thermoplastic composites.
Development of this helicopter driveshaft by Automated Dynamics helped dispel the notion that porosity is paramount when it comes to thermoplastic composites performance. It offered a 35% weight reduction compared to its aluminum predecessor, with 150% post-ballistic torque to failure — with thermoset-unacceptable 4% porosity.
From a technical viewpoint the question is simple: Can OOA options be matured sufficiently to yield parts with <1% void content? The answer, based in part on the reports in this supplement, is yes, but there is a larger question: Can OOA processes match this parameter and demonstrate enough overall savings in capital expense and time to justify the process development/recertification efforts that a move to OOA will require?
At GE Aviation in the UK, a vacuum bagged Upper Panel 12 for the A350 XWB is in oven, ready for cure, with thermocouples (mounted on the underside of the toolface) wired for cure-temperature control.
We may have that answer sooner than later. As the stories in this OOA Supplement demonstrate, the activity level in OOA process development is substantial, involving structures on flying aircraft. And the composites professionals involved with each, as you’ll find, are strongly invested in making OOA not only feasible, but successful.
Posted by: Ginger Gardiner1. February 2016
Spirit AeroSystems’ Inflexion technology enables manufacture of large, complex composite aerostructures in one continuous piece that are lighter, more affordable and more efficient.
SOURCE: Spirit AeroSystems
In 2013, Spirit AeroSystems (Wichita, KS, US) announced that it was working with Spintech (Xenia, OH, US) to develop new tooling technology for manufacturing complex composite aircraft structures. Trademarked as Inflexion, the technology is based on re-formable, reusable mandrels, and touted as enabling integrated composite structures with features not possible to achieve using traditional tooling.
Traditional composite structures manufacturing uses rigid tooling that must be removed from inside the part. But this limits the size and complexity of structures. Inflexion tooling can be transitioned between rigid and flexible states for easy removal, regardless of part size and complex geometries. As explained by Spintech engineering director Tom Margraf in a 2013 interview:
“The composites manufactured using Inflexion are structures that integrate engineering stiffeners such as frames, stringers, spars, and longerons with skin panels that are co-cured in a single cure process. The inflexion process eliminates the need for secondary bonding and/or fastening of engineering stiffeners, which enables lower cost, lighter weight, and more damage tolerant structures.”
Years in the Making
Spirit AeroSystems began working on Inflexion in 2005, collaborating with Cornerstone Research Group (CRG, Dayton, OH, US), which had developed tooling using its patented shape memory polymer (SMP) materials. CRG spun off Spintech Ventures LLC in 2010 to refine the technology and scale it up for industrial aerostructures production. Spintech offers the technology under the trade name Smart Tooling (follow the link to see videos of how the technology works). Spirit’s version reportedly includes enhancements it has developed for producing large, integrated structures with singled-sided reinforcements (e.g., stiffeners).
Spirit's Inflexion technology is based on Smart Tooling which uses
shape memory polymer (SMP) materials to enable rigid layup tools
that become elastomeric after cure for easy extraction.
SOURCE: Cornerstone Research Group (CRG) and Spintech/Smart Tooling.
CRG completed a Phase II Small Business Innovation Research (SBIR) project with NAVAIR, demonstrating Smart Tooling’s benefits. During the 2011 Navy Opportunity Forum, Spintech summarized these as including increased throughput, which reduces total process time; increased repeatability from part to part due to a rigid, net-shaped, layup tool; and up to an 80% reduction in manufacturing cost.
"Smart Tooling's patented technology allows composite manufacturers to significantly reduce a combination of labor, material, and capital cost, while significantly increasing production throughput of composite parts with trapped features and/or complex shapes," said previous Spintech president Craig Jennings.
According to a 2013 press release, Spirit Aerosystems acting director of technology Bill Smith explained that Inflexion allows “extraction of the tool in spite of trapping features which would hinder current tooling methods. This enables, for example, the full integration of skins, stringers, and frames or ribs in one step."
Investment for Future Contracts
In the 2013 The Wichita Eagle article “Spirit’s ShadowWorks, a technology investment,” author Molly McMillin asserts that Spirit AeroSystems’ investment into innovative technologies like Inflexion is aimed at helping the company win new programs and retain customers. Quoting Spirit research and development engineer Allison Wright, Madison writes that Spirit “looks to provide customers the capabilities they need in their products — lower weight, more efficiency or better manufacturing processes.” She notes that cost is also key as Spirit competes with other large firms for contracts from aerospace OEMs.
This article too quoted Spirit’s technology/R&D director Bill Smith: “It’s not about putting in ‘gee whiz’ technology for the sake of technology. It’s for the requirements and capabilities that an airplane needs. ... It’s about, ‘Can you offer more cost-effective solutions than your competitors?’ ” He pointed out that there are consequences to missing out on new programs. “If you lose one, you don’t wait until next week for a new airplane program to come in. The winner takes it all.”
Inflexion was then described in the article as an example of Sprit AeroSystems’ investment in innovation: The tooling made from the [shape memory] polymers remains rigid for winding and curing the materials, but additional heat allows it to become flexible, where it can be stretched, reshaped and pulled away. The article quotes Spirit research and design engineer Carl Fiegenbaum, “It goes from a hard tool to a soft tool during the curing process.” He explains that ability lets the composite stringers, frames or other components be integrated into a single structure. Smith added, “The more I can integrate composite features, the lower the cost. The idea is to do everything at once.”
The article goes on to say Spirit was testing the process on a 40-inch fuselage barrel and that the Inflexion Smart Tooling could be reused and formed back to that shape or another shape for multiple cycles. Spintech said in a 2014 article that it had demonstrated a life of 40 cycles for Smart Tooling vs. 6-10 cycles for the baseline tooling systems. Spirit actually showed off a cylindrical composite structure at the 2012 Farnborough International Airshow, as reported by Jeff Sloan and Bob Griffiths:
Spirit AeroSystems (Wichita, Kan.) had two technically intriguing parts on its stand. … The second part was a cylindrical structure with internal stiffeners. Historically, parts with trapping geometries have required multipart tools that can be disassembled to permit postcure removal. These come at great expense and require constant maintenance. Spirit claims to have developed a “reconfigurable” tooling process called Inflexion that has reduced its tooling costs.
McMillin winds up the Inflexion section of her article by quoting Smith as saying Spirit would roll out the Inflexion technology on “fairly near-term programs in smaller ways,” and then build up to larger applications. Figgenbaum added, “There’s a variety of architectures and design philosophies and configurations that we believe would be well suited” for the process. “It’s not the perfect thing for everything. But there are places where it’s really well suited.”
Posted by: Ginger Gardiner28. January 2016
FiberCore Europe’s InfraCore Inside composite technology enables this 142m span bridge/viaduct over the A27 motorway near Utrecht (left) and 13m tall by 6m wide lock gates in the Wilhelminakanaal near Tilburg (right). SOURCE: FIberCore Europe
Established in 2008, FiberCore Europe (FCE, Rotterdam, Netherlands) has produced over 500 fiber-reinforced composite bridge and lock gate structures worldwide. Among its impressive claims:
and fiber-reinforced plastic (FRP) structures that won’t crack, debond or delaminate thanks to its patented InfraCore Inside technology.
The company also claimed the world’s largest infusion — 6,200 kg of resin in one shot — in 2009. (The Oyster 125 sailboat hull broke this in 2010 with a single shot of 6,300-kg and a 62m Russian minesweeper hull used two shots in 2011, one totaling 14,685 kg). The company has since infused 6.2m-wide deck sections for the A27 hybrid bridge/viaduct (see below) that used 10.2 metric tonnes of resin in a single shot.
FiberCore Europe completes longest FRP-decked hybrid bridge over A27 motorway near Utrecht. SOURCE: FiberCore Europe.
Hybrid Steel-Composite Construction
FCE also won the Outstanding Paper Award 2015 from the International Association for Bridge and Structural Engineering (IABSE, c/o ETH Zurich, Zurich, Switzerland) for "Hybrid Bridge Structure Composed of Fibre Reinforced Polymers and Steel" which describes design and construction of the 142m span hybrid steel/composite bridge across the A27 motorway near Utrecht, the Netherlands. Comprised of seven prefabricated InfraCore composite bridge deck segments joined and subsequently coupled to a steel support truss to achieve a EuroCode traffic rating of 60 metric tonnes (60,000 kg), the deck weighed only 140 kg/m2 compared to 220 kg/m2 for a steel deck, saving 72,000 kg. The InfraCore deck sections were molded to include not only accurately-dimensioned recesses for slotting connections, but also a water drainage gutter and integrated cable tray. Dry noncrimp E-glass fabrics and foam core — the latter acts as a mandrel and is not structural — were infused with polyester resin per a design that orients fibers in multiple directions to provide a semi-plastic failure mode with redundant load paths for residual load bearing capacity. Fabrication were achieved quickly and cost-effectively at the project site with minimal disruption to traffic — only portions of two subsequent evenings, as self-propelled modular transporters moved the completed span into place.
“The news here is the size,” says FCE founder Simon de Jong. “We had to realize a 71m span between supports, which was not possible with FRP only. So we combined an FRP deck with a steel truss as the primary load-bearing structure, achieving an overall weight savings of 800 metric tonnes vs. the concrete bridge used before.” De Jong points out that this composite bridgedeck’s 60-tonne traffic rating is also a first, and made possible by the company’s InfraCore system.
InfraCore as Backstory
“In 1997, my associate Jan Peeters designed and built the first FRP bridge in Nederland,” recalls De Jong. He notes that hundreds of bridges and other infrastructure were built using FRP in the 1990s. “But then many of these structures cracked and delaminated,” says De Jong. He explains that the Rijkswaterstaat, part of the Dutch Ministry of Infrastructure and the Environment (Utrecht, Netherlands), was very interested in using composites in infrastructure but advised it wasn’t possible “unless you solve this problem of delamination, debonding and cracking.” Now FiberCore Europe’s chief technology officer, Jan Peeters had worked with aerospace composites at TU Delft (Delft, Netherlands), which would prove useful as he began developing a more robust design solution. “The problem was the weakness after impact loading in combination with fatigue due to rolling wheels,” says Peeters. “In sandwich construction, the skin bounces back, but the core material and/or beams underneath are no longer connected to the skin. Subsequent loading from truck wheels then spread this delamination.”
With InfraCore, there is no adhesive bonding between the core and skin. The polyurethane foam core acts only as a permanent formwork and is not structural. The skin-stringer construction thus, is not formed by box beams glued to faceskins, but instead by multiple Z-shaped two-flanged web structures which are overlapped and then faced to form an extremely robust construction. “There is no longer a resin-dominated crack area,” says Peeters. “The fibers in the upper and lower skins and in the reinforcing ribs run in all directions seamlessly so that local damage cannot extend.” A feat, he claims, that even bridges using composite pultrusions cannot achieve. The durability endowed by InfraCore has been proven by large-scale laboratory tests at TU Delft, where 1:1 scale bridge deck sections were tested in three-point bending at loads up to 45 tonnes with no failure. In further testing, the InfraCore deck section was impact damaged locally to simulate a cargo container drop, and then areas at the size of wheel prints were loaded up to 13.5 tonnes, as part of the typical load pattern of a vehicle weighing 60 tonnes. After 30 million cycles, there was no propagation of damage and the strength and stiffness were the same vs. pre-damage evaluation. “This simulates a service life of over 100 years,” says De Jong.
The reduced weight of the 13m tall by 6m wide FRP lock gates in the Wilhelminakanaal reduce friction and load on the actuation system during gate operation as well as much lower maintenance costs. SOURCE: FiberCore Europe.
This same construction used for a helicopter deck on a luxury yacht has shown excellent fire resistance performance in improvised tests by Lloyds Register (London, UK). It also absorbs energy well, showing potential benefits in fenders and other structures for large ships. Meanwhile, eight FRP lock gates, measuring 13m tall, 6m wide and bridging an 8m difference in water height, have been installed in the Wilhelminakanaal (Tilburg, Netherlands) for the client Rijkswaterstaat. Touted by FiberCore Europe as the largest FRP lock gates in the world, their composite construction offers reduced weight and accordingly reduced friction in gate operation, resulting in less load on the actuating mechanism. They also provide a 100-year service life with much reduced maintenance costs vs. traditional materials, and increased sustainability including less CO2 emissions during production.
Rijkswaterstaat made a presentation on the FRP lock gates at the 7th International PIANC-SMART Rivers Conference (Sep. 7-11, 2015, Buenos Aires, Argentina). The audience of water authorities and international businesses responded so enthusiastically, that the event organizer PIANC (the World Association for Waterborne Transport Infrastructure, Brussels, Belgium) was prompted to establish the international working group: Composites for Hydraulic Structures.
Another benefit of InfraCore is its potential for cost-savings in bridge renovation. There are roughly one million bridges in the EU that require renovation at an estimated cost totaling 50 billion Euros. “We have engineered a renovation process with InfraCore that could save more than 10% of this, or 7 billion Euros” says De Jong. FIberCore Europe will complete engineering and testing over the next two years in order to validate this financial savings as part of the SUREBRIDGE project, one of only nine infrastructure innovation projects chosen from 100 candidates to be completed within the multinational INFRAVATION program. Organizations worldwide will be watching the results of this program, including the US Army Corps of Engineers and Federal Highway Administration.
FiberCore Europe is using the InfraCore technology to continue innovating future infrastructure, including bridges with integrated lighting (top and bottom right), floating roadways (bottom left), and FRP catenary systems for high-speed trains (top left) where the whole structure acts as an insulator, eliminating the need for insulating and voltage limiting devices which also reduces stray currents. The high strength of composites enables novel designs with fewer parts and their lighter weight allow for simpler foundations, for overall systems that are easier and faster to install. The environmental costs are significantly reduced with zinc or paint no longer required for conservation and minimal need for maintenance and inspection.
Posted by: Jeff Sloan22. January 2016
Walking the North American International Auto Show (NAIAS; aka, the Detroit Auto Show) last week in Detroit, MI, US, it was not difficult to get excited about the automotive industry — or, as some automakers are calling it, the mobility industry. The bright lights, loud music, big crowds, attractive concept cars and the latest and greatest production vehicles ranging from two-seater all-electrics to gargantuan pickups concentrated the automotive industry's energy to convey a distinct sense of optimism about where this market is headed.
Carbon fiber wheel for the Ford GT350
It was also not difficult, walking the show, to detect the influence of composites, for any automaker that uses carbon fiber on a visible part apparently is duty-bound — very likely for aesthetic and marketing reasons — to make sure that the tell-tale black (and in one case, blue) weave is highly visible. Indeed, carbon fiber could be found in rearview mirrors, in interior trim parts, in roofs, and in the exterior trim of concept cars (see photos). And then there was the carbon fiber you could not see (or not see as easily), including in the monocoques of the BMW i8 and i3 and the Alfa Romeo 4C Coupe and Cabriolet. And probably others that I couldn't see.
Alfa Romeo 4C Coupe, with carbon fiber composite monocoque.
What struck me, looking at all of the 2016 model year vehicles at the show, was that I was seeing automotive technology that is, for the most part, about two years old. That is, the design cycle of the automotive industry forces automotive OEMs to work ahead of itself, which means that much of the material technology on the floor in Detroit was conceived of in 2013-2014. So, for all of the talk of late about the incursion of composites into automotive structures, it will likely be a year or two before we see more vehicles with more composites in more structural applications.
Carbon fiber in Mercedes Benz sideview mirror.
Then again, it's likely that whatever we see of composites in 2018 at the NAIAS will look a lot like it did in 2016, with visible carbon fiber emphasized, and all of the other carbon fiber (likely a lot more of it) out of direct sight. And this, I suppose, is the point. Composites, to have a seat at the table, must perform with adaptability, flexibility and speed. If, in fact, automakers are becoming "material agnostic," then all of the materials at their disposal must be adaptable to a variety of designs and applications. The consumer, after all, is buying a vehicle to meet their transportation needs, regardless of material.
So, we'll check in with the NAIAS from time to time for a holistic view of how the automotive world is evolving, but for composites professionals like you, we'll stay focused on those structures that are a little harder to see.
Nissan TDS concept car, with carbon fiber trim under a transluscent blue gelcoat.
Posted by: Sara Black20. January 2016
This demonstration wingskin is a 21m-long hat-stiffened, monolithic part built by The Boeing Co.’s (Chicago, IL, US) facility in St. Louis, MO, US. Materials used in the wingskin were Cytec’s trademarked CYCOM 5320 unidirectional and fabric out of autoclave (OOA) prepregs. Photo source: DARPA
The quest for prepreg materials capable of being processed without an autoclave, but able to produce autoclaved part performance properties, began in the mid-1990s. It was driven, in part, by the US Air Force and the US National Aeronautical and Space Admin. (NASA), which envisioned composite launch vehicle components far too large for any autoclave.
You may not know that CW has prepared a Supplement to the upcoming February 2016 issue that examines out of autoclave processing in detail. It asks the question: Can OOA options be matured sufficiently to yield parts with <1% void content, outside of the autoclave? The answer, based on detailed applications where OOA processing is in place, is yes, but there is a larger question: Can OOA processes match this <1% void parameter and demonstrate enough overall savings in capital expense and time to justify the process development/recertification efforts that a move to OOA will require?
I learned a lot while researching the efforts being made by many to improve current OOA processing methods. One illuminating development is work done by Cytec Solvay Group (Tulsa OK, US and Woodland Park, NJ, US) on out of autoclave (OOA) prepregs, often called VBO prepregs.
As most of you already know, VBO prepregs allow lower-cost tooling that doesn’t have to withstand autoclave pressure, and lower processing costs (parts are vacuum bagged and oven cured). Coefficient of thermal expansion issues between part and tooling are fewer, because the cure temperature can be lower. But thorny technical issues can include high void content, surface pitting on the tool side surface, insufficient out time for fabricating large parts, and compatibility issues with ancillary materials including adhesives.
When early investigators attempted VBO processing with traditional prepregs, they found that, without the autoclave’s pressure, air became trapped in the layup causing voids. OOA-optimized prepregs for hand layup, sometimes called semi-pregs, have since been designed with lower resin impregnation levels, which leaves dry fiber paths for evacuation of air and any moisture that is absorbed by the epoxy resin when exposed to air during layup. To ensure that the air can be pulled out, in the plane of the laminate, an “edge breathing” vacuum bagging technique is employed, which keeps at least one laminate edge in contact with breather material. Because semi-preg is not fully saturated with resin and contains open air evacuation paths, it is bulkier than conventional prepreg, and care must be taken to mitigate bridging and wrinkling especially in shaped parts with corners.
Most important, air evacuation must occur before resin crosslinking and viscosity increase to the point that the air pathways become blocked. Many fabricators, therefore, employ long vacuum “dwells” at low-to-moderate temperatures — 16 hours or more — to ensure full evacuation of air before the oven temperature is elevated to cure (crosslink) temperature, a procedure now shown to be unnecessary. “The need for long dwells is a common misconception, since much published literature on VBO prepregs has been associated with development programs on low-cost tooling where cure time wasn’t an issue,” says Chris Ridgard, associate technical fellow at Cytec Solvay Group. “We’ve developed a method called super-ambient dwell that can significantly shorten cure cycles by 50%, for production settings.”
Super-ambient dwell employs a high level of vacuum, at least 60 cm Hg (using a dedicated vacuum pump), and a resin temperature typically between 50° and 60°C, which together, says Ridgard, exceeds the boiling point of water — thus driving off the entrapped moisture — without causing the resin to flow sufficiently that the air evacuation channels are closed off. He cites monolithic (uncored) carbon/epoxy panels, one made with super-ambient dwell of 4 hours and the other in a 16-hour room temperature dwell, which ultimately showed equal cured porosity (around 2%). “Cure times comparable to those of autoclaved prepregs have now been demonstrated,” he adds. New, second and third generation OOA prepregs have now also resolved the issue of out time, which currently is typically 21 days at room temperature, or longer.
In the case of cored parts made with OOA prepreg, care must be taken to prevent air trapped within core cells from causing laminate porosity; venting the core through the use of a breather ply is necessary. And because autoclave pressure is lacking, adhesive foaming during cure can affect face skin/core bond quality due to the high vacuum levels, which act to lower the boiling point of water in the adhesive. Ridgard says a number of core adhesives compatible with OOA cure conditions have been developed.
It turns out that in addition to epoxy resin, OOA prepregs have been developed for bismaleimide, polyimide and benzoxazine resins for higher temperature applications. While numerous production parts are likely being made using VBO methods, details aren’t available for many, but our Supplement does describe some notable examples. The VBO demonstrator wingskin shown in the photo is a 21m-long hat-stiffened, monolithic part built by The Boeing Co.’s (Chicago, IL, US) facility in St. Louis, MO, US. Materials used in the wingskin were Cytec’s trademarked CYCOM 5320 unidirectional and fabric OOA prepregs.
So watch for the Supplement; I’m sure you’ll find much of interest there.