Turning Ideas into Innovations

Perhaps now more than ever, university research is critical. Inquisitive researchers on campuses across the U.S. are working on projects related to materials, technologies, processes and applications in the composites industry that have the potential to not only shape the industry itself, but also bolster an economy weakened by the COVID-19 pandemic and offer solutions to help strengthen systems that are vital to the country, such as infrastructure and transportation. In this year’s annual report on university research and development, Composites Manufacturing magazine highlights five potentially ground-breaking innovations, from new manufacturing processes to novel materials. While the lightweighting advantages of multi-material components are attractive to many industries, such as automotive, there are significant challenges to their use. Mixing materials typically necessitates additional manufacturing processes and joining techniques, which hike up the costs for components. Researchers in the Clemson Composites Center think they have a solution with their single-shot manufacturing process for dissimilar materials. “Most current technologies use multi-stage manufacturing processes,” says Saeed Farahani, a postdoctoral fellow in Clemson’s Department of Automotive Engineering. “You need to first form the metal in a stamping process, then insert it in an overmolding process. Or, you can laminate a sheet metal with a layer of polymer, then use a cold or hot forming process to form the laminated structure. But these have limitations and challenges.” Farahani and Srikanth Pilla, Jenkins Endowed Professor in the Department of Automotive Engineering, developed a process they call hybrid single-shot manufacturing, which integrates manufacturing of metals and composites in one piece of equipment using a single tooling system. The researchers opted to use injection molding equipment for the technique because it’s readily available in industrial manufacturing settings. “The general idea behind the integration is to use the pressure of the melt during the injection to form the sheet metal,” says Farahani. “Then, the polymer is injected onto the sheet metal, and the two materials are bonded during the solidification.” Another option is to pre-form the sheet metal while the mold is closing, then inject the polymer after it is closed to make the final formation. The first materials that Farahani and Pilla tested a few years ago were aluminum and a simple polypropylene. Next, they moved to advanced steel. They have also tested several composite materials, including carbon fiber prepreg sheets with epoxy resin. “In that case, we manufactured a hybrid thermoset/thermoplastic structure in a single shot,” says Farahani. “From the composite standpoint, as long as you can put the material inside the injection molding equipment, we can make it work.” The researchers faced several challenges along the way. The first was related to modeling and simulation for the process, which is a combination of sheet metal forming and injection molding. Existing software for sheet metal forming processes can’t model the flow of the polymer, while packages for injection molding processes can’t account for deformation of components. “We had to develop custom models for our process and, based on those models, create our own simulation tools to better understand the process,” says Farahani. The team has also addressed tactical challenges for potential industrial applications, such as the opposing phenomena of “spring back” in metals during the deformation process and shrinkage of materials during injection molding. Farahani and Pilla developed a patent-pending method to prevent the ensuing delamination and debonding. They also have integrated sensors in the tooling and utilized advanced modeling and artificial intelligence to better control the process and monitor the final quality of the hybrid component. “We now believe this process is mature enough to be implemented in industrial applications,” says Farahani. He adds that hybrid single-shot manufacturing can not only reduce the aforementioned difficulties and limitations in manufacturing multi-material structures, but also opens up new opportunities to cost-effectively produce multi-functional, smart components. The added functionality can be diverse, and the emerging applications can go beyond automotive, including aerospace, consumer markets, biomedical and construction. “We foresee applications in any domain where there is a necessity for complex geometries with diverse functionalities,” says Pilla. CNT Curing for Aerospace Parts Project: Carbon nanotube porous networks School: Massachusetts Institute of Technology Location: Boston Principal Investigator: Brian L. Wardle More than a decade ago, researchers at MIT and Metis Design were testing sensors made with carbon nanotube (CNT) networks under funding from the Air Force Office of Scientific Research when they noticed something interesting. Depending on how they were measured, the CNT heated up. This tangential discovery led the researchers to investigate CNT films as lightweight resistive heaters, which the Naval Air Systems Command (NAVAIR) funded to develop into an embedded deicing system for aircraft. During that project, Brian L. Wardle, professor of aeronautics and astronautics at MIT, says the team realized the technology might work for curing: “We’re placing a heater on this aerostructure for ice protection. Why don’t we use that heat to actually cure the part underneath in the first place? It sure gets plenty hot.” Fast forward to today and that is exactly what MIT and Metis Design are doing on behalf of NAVAIR – developing a CNT-based conductive heating technique that, when combined with carbon nanoporous network (NPN) film, can be used to manufacture aerospace-grade composite materials. To begin, the team developed an out-of-oven (OoO) process that uses carbon nanotube film to heat and cure out-of-autoclave prepreg materials. In the early years, MIT grew vertically aligned carbon nanotubes and “knocked them down” to create the horizontally aligned CNTs this process requires. Now, they are commercially purchased in large format sheets. Researchers then created a NPN that provides capillary pressure to enable curing traditional autoclave-required graphite epoxy prepreg materials. The NPN film is made of 8-nanometer diameter, multi-walled, vertically aligned carbon nanotubes that are grown at MIT. While the largest part cured so far is a x 30-centimeter flat panel, Estelle Cohen, lead researcher for the collaboration at Metis Design, plans to make a 60 x 60-centimeter flat panel and a curved part by the fall, with customers talking about scaling to much larger and complex parts early next year. The technique has many advantages. Foremost are reduced energy costs. This resistive heating technique uses just 1% of the energy that would be required to cure large composite parts in an autoclave. “That’s a step change in energy efficiency,” says Jeonyoon Lee, a postdoctoral researcher leading the project at MIT. The process is also faster. Seth Kessler, president of Metis Design, says that because CNTs heat more rapidly and uniformly than an oven or autoclave, the technique can be used to cure parts in roughly half the time. Most recently, the team documented a 90-minute reduction in cure time, which is good news for throughput. “That’s going to translate into making more parts per hour, per day, which is obviously going to translate into increased margins,” says Kessler. CNT-based resistive curing could significantly reduce barriers to entry for companies that can’t afford an autoclave. “All you need is enough shop floor space for the tool,” says Kessler. “That means that any medium or even small-sized business that can afford to get a warehouse would possibly be able to make large composite parts. This technology really has the opportunity to revolutionize the way that composites enter non-traditional markets.” Tools will also be far cheaper – perhaps a fraction of the cost of a traditional mold – spurring further market entry and faster innovation. “Right now it is very difficult to iteratively design and test composite parts, especially after production begins because traditional molds can cost millions of dollar, take six months to fabricate and can be virtually impossible – or at least financially impractical – to re-work,” Kessler explains. “Pressure-free curing outside of an autoclave allows you to rapidly prototype parts and go through design iterations much more easily.” Wardle sums up the benefits: “A lot of parts are bottlenecked by the autoclave process. This technique absolutely gets you to a lighter infrastructure and much lighter, flexible and robust manufacturing processes.” Healing Broken Bones with CFRP Project: Braided carbon fiber tubes and polymer cement School: The University of Arizona Location: Tucson, Ariz. Principal Investigators: Hamid Saadatmanesh and Ehsan Mahmoudabadi Structural engineers at the University of Arizona are adapting a CFRP process used to reinforce ailing infrastructure columns to repair broken bones. “When supporting a structure – whether it is a bridge or the body of a person – the mechanics are more or less the same,” says Hamid Saadatmanesh, professor of structural engineering. Saadatmanesh, who has focused on composite-reinforced infrastructure projects for decades, hadn’t considered biomedical applications until a cardiologist asked him to examine the viability of CFRP heart valves. That sparked another idea: “It came to me that we could make a direct transfer from this proven civil engineering technique that has worked well for bridges and convert the technology for use in the human body,” he says. To repair degraded concrete and steel supports on bridges, piers and highways, a braided CFRP tube is inserted into the hollow column and filled with polymer concrete, creating a new structural column inside the existing form. Saadatmanesh believes surgeons could stabilize broken bones in the same way, by aligning broken bones, inserting a braided CFRP tube into the bone cavity and filling it with bio-compatible polymer. As the polymer fills the CFRP sleeve, it would expand and take the form of the bone’s cavity. “The whole system works like steel-reinforced concrete,” says Ehsan Mahmoudabadi, professor of structural engineering. “But here we have carbon fiber as the tensile material and polymer concrete as the compression part.” The hope is that the new technique will allow patients to avoid either invasive repair surgeries to implant plates, rods, wires and screws or external frames with steel pins drilled into the bone. In contrast, the new technique is expected to require two small incisions – one to insert the CFRP tube and another to pull it through the bone cavity. The inherent antioxidant properties of carbon may also promote faster healing than titanium or other metal implants. “We want to minimize the healing period and the trauma and make it as non-invasive as possible,” says Saadatmanesh. Current research is focused on 4- to 5-millimeter diameter, multiaxial braided CFRP tubes that are manufactured to specifications by an outside vendor. The tubes are pre-impregnated with zinc phosphate or resin modified glass ionomer (RMGI). While it was easy to locate a manufacturer to produce the tubes, finding the right polymer to fill the sleeve presented a challenge. The team is investigating multiple bio-grade polymers – or “bone cements” – that are already approved for use in the human body. They may also consider dental composites. Regardless of the final choice, the polymer must harden quickly and bond well with the CFRP tube. “We are in the process of investigating which one would fuse better with the carbon fiber to make the two materials work together as one,” says Saadatmanesh. While the project was initially aimed at repair of large bones, such as leg femurs, other potential applications have emerged, including stabilization of hard-to-set ribs and collarbones. “[For these bones] there is no other option,” says Saadatmanesh. “They are just left to heal by themselves, and it takes a long time and is very painful.” Researchers are also considering preventative reinforcement of bones weakened by osteoporosis and veterinary uses, including fracture repair for horses and other large animals that must bear weight as they heal. The proposed technique is so promising that UA Venture Capital (UAVC), an investment firm that helps finance faculty-led innovations from the University of Arizona, has invested millions of dollars in MediCarbone, the company Saadatmanesh founded to accelerate commercialization. “We look for unique, world-changing technology, and clearly MediCarbone fits that description,” says Fletcher J. McCusker, UAVC founder and CEO. “The opportunity to repair bone intracorpus with minimum invasion could drastically change how broken bones are treated.” Creating a New Class of Prepregs Project: Semi-pregs with through-thickness permeability School: University of Southern California Location: Los Angeles Principal Investigator: Steven Nutt and Mark Anders (co-investigator) Through the years, researchers at the M.C. Gill Composites Center at the University of Southern California (USC) have studied ways to make composites manufacturing more cost effective and efficient. “Although autoclaves impart robustness to prepreg processing, their high cost creates a bottleneck in production capacities,” says Mark Anders, a postdoctoral fellow at USC. “Therefore, manufacturers have looked to alternative, out-of-autoclave options, such as vacuum-bag-only (VBO) oven cure.” One of the concerns with VBO processing is that it lacks the high pressures of autoclaves to suppress defects, so removal of entrapped air is critical to production of high-quality laminates. “Any time you lay up prepreg plies on top of each other, inevitably there will be air in and between them,” says Anders. “So the question then is how can you reliably get the air back out?” Partial impregnation enhances air evacuation, but the concept hasn’t yet been fully optimized, says Anders. Partial impregnation is typically achieved by laminating resin films onto either side of a fiber reinforcement without fully saturating through the thickness, leaving dry evacuation channels at the ply center. These VBO prepregs utilize in-plane evacuation, or “edge breathing,” but the time required to evacuate air scales to the breathe-out distance squared. “For larger parts, debulking becomes impractically long,” says Anders. Under the direction of Steven Nutt, M.C. Gill Professor and director of the M.C. Gill Composites Center, the team at USC has been working on a solution: promote extraction of gases in the through-thickness direction of laminates, which is much shorter than the planar direction. This paradigm shift for prepreg formats relies on discontinuities or openings in the resin films coated onto the fibers, through which entrapped gases can be evacuated. “The relatively simple idea is to get the air flow out of the plane in the Z direction,” says Anders. “It really improves the robustness of out-of-autoclave prepregs if you have that feature – that out-of-plane breathability or through-thickness gas permeability.” These prepregs – known as semi-pregs – have several advantages, according to Anders. They reduce debulk times from hours to minutes without sacrificing part quality. In addition, semi-pregs exhibit a much lower sensitivity to adverse process conditions, such as humidity and embedded ply drops, than conventional VBO prepregs. To further development of this new class of prepregs, Nutt’s team has set out to answer three primary questions: Does extraction of gases in the through-thickness direction work? How can you make these semi-preg materials? What is the best design? The first question has been answered. “Our lab has fabricated semi-pregs with through-thickness permeability using various reinforcement architectures and resin types, demonstrating the feasibility and versatility of the concept,” says Anders. To date, the team has done lab-scale work, making small quantities of laminates measuring 12 square inches or less and conducting in-situ diagnostics to better understand how the gas transport happens. Recently, Anders has examined how to make prepreg with through-thickness permeability, testing a variety of methods in the lab. One system his team built is a printer that programs any desired pattern and could potentially make prepreg on demand. However, it’s slower than traditional prepreg manufacturing machines. Another method the team has pursued is retrofitting existing prepreg equipment to make semi-pregs. “We are looking at how to translate these ideas into something that can be done at scale and won’t cost an arm and a leg,” he says. Finally, the researchers are looking at design options. “Suddenly, you have this whole new design space,” says Anders. “Before, you were only considering the through-thickness degree of impregnation, but now you are considering in-plane patterns in the resin.” The team has tried numerous patterns, resins and fabrics, such as stripes of resin on plain weave fabrics and “islands” or separate dots of resin on spread tows. “The work is promising,” says Anders. “We have conceived, designed and demonstrated scalable prepregging methods.” Now the researchers are pivoting their efforts to transition the technology from the lab into commercial products. Next Generation Military Applications Project: Cold spray processes for polymers and composites School: Rowan University Location: Glassboro, N.J. Principal Investigators: Francis Haas and Joseph Stanzione, III Researchers at Rowan University are leading a project to pioneer cold spray of polymers and composites for potential use in next-generation military applications. The five-year, $14.5 million dollar project is a collaborative effort with the U.S. Army Combat Capabilities Development Command’s Army Research Laboratory (CCDC ARL), the Kostas Research Institute (KRI) at Northeastern University, Clemson University, Drexel University, University of Massachusetts Amherst and PPG Inc. Cold spray processing involves spraying of powdered material at extremely high velocities, generally hundreds of meters per second. When the sprayed particles make contact with the substrate, they flatten out and can chemically and mechanically interlock with the structure. Despite its name, cold spray is anything but cold. As Francis “Mac” Haas, Rowan University assistant professor of mechanical engineering explains, “You can get a cold spray that starts off at 700 degrees Celsius – so it is in no way cold – but it’s cold relative to its melting point.” While cold spray processes are well-developed for metals, they represent a new frontier for polymers and composites. Adapting the technology involves several fundamental challenges. For polymers, the processing temperatures are much lower (generally between 70 and 200 degrees Celsius) and are likely to be governed by the glass transition temperature of the sprayed polymeric material. In addition, polymers can become tacky when heated, which hinders flow for spraying. Polymers also react differently when they impact the surface. For example, deposition efficiency rates for polymers – the amount of sprayed powder that “sticks” to the substrate – are generally quite low. “You get a tiny amount of powder to stick, and even then, that doesn’t necessarily mean it will do a particularly good job, whether structurally or as a coating. That just means it’s stuck to the wall,” says Haas. “So there’s a lot of basic science that needs to be done.” Cold spraying processes for polymers and composites are expected to enable the manufacture of functionally-graded composites that have different materials layered into the same part. Researchers believe that by changing the powder mixture they can create varied composite layers with different resins, fibers and fiber-to-resin content. Joseph Stanzione III, associate professor of chemical engineering and founding director of the Advanced Materials & Manufacturing Institute (AMMI) at Rowan, says that the layers could be made from a variety of materials, including polymer-on-polymer, polymer-on-metal or metal-on-polymer. “That’s the beauty of this project!” he says. John La Scala, division chief for material and manufacturing sciences at CCDC ARL agrees. “It would allow you to have a layer-by-layer differentiation of properties, which could be really useful to achieve high performance,” he says. For example, combat vehicle parts could contain a hard outer shell with softer inner layers for damage tolerance – all achieved through the single process of cold spraying. The technology could also be used for rapid, in-theater repair of combat vehicles. Hypersonic weapons, which travel at more than five times the speed of sound, are another potential application. La Scala says that cold spray processes could potentially be used to create light, strong, high-temperature resistant carbon-carbon composite hypersonic casings. Among other benefits, this would allow for pyrolysis of each carbon-carbon layer, which would reduce the voids caused by the carbonization process. Initially, researchers worked with polystyrene because it is a well-characterized material. Now, they are focused on thermoplastics such as polycarbonate and PEEK. Next, they hope to tackle thermosets like vinyl resin and epoxy systems. Since commercially available powder polymers and composites are limited, the team is synthesizing polymers in-house, as well as adding fibers and fill and reducing particle sizes with milling, grinding and microfluidics techniques. In the long run, this developing technology could benefit numerous industries, including aerospace, automobile and petrochemical. Stanzione and Haas are particularly excited about potential biomedical applications, such as lighter weight, more advanced prosthetics.