In Search of Solutions

While many companies have robust R&D facilities trying to solve problems, higher education provides significant contributions, performing 13% of all U.S. research and development in 2017, according to the National Center for Science and Engineering Statistics, part of the National Science Foundation. In inflation-adjusted dollars, total academic R&D has grown every year since 1975, and in 2018, academic institutions performed $79.4 billion in R&D. One of the segments benefitting from university research is composites. This year’s annual university research and development article highlights five projects in crucial areas, including composite joining, recycling and computer aided process planning. Drilling Holes Without Damaging Fibers Project: Continuous Fiber Fastener Holes School: North Carolina Agricultural and Technical State University Location: Greensboro, N.C. Principal Investigators: Ajit Kelkar and Vishwas Jadhav Researchers at North Carolina A&T State University have developed a technique to create fastener holes in continuous carbon fiber composites without disrupting the fibers. Drilled holes are one of the primary causes of delamination in CFRP components. Drilling cuts the continuous fibers, reducing their strength and stiffness. “We are weakening the overall strength and stiffness of the laminate when we drill the holes, and this happens due to breakage of continuous fibers,” says Vishwas Jadhav, a graduate research assistant in the Joint School of Nanoscience and Engineering. Jadhav discussed this long-standing problem with his advisor Ajit Kelkar, a professor in the Department of Mechanical Engineering. Kelkar posed a simple question: “Can we make the holes without cutting the fiber?” Inspired, Jadhav devised a method to insert removable steel pins between continuous carbon fibers during fabrication. “The idea is similar to when we attach a button to textile fabric,” says Jadhav. “The inserted needle rarely breaks the fiber of the cloth.” When the steel pins are taken out of the carbon fabric, there is a circular fastener hole with intact continuous fibers – something that drilling is unable to achieve. During phase one of the project, which began in 2019, researchers fabricated 2.6 mm continuous CFRP panels using 12 layers of 0/90 plain weave carbon fabric supplied by Fibre Glast Developments Corp. Working one layer at a time, Jadhav measured and marked the hole locations, used tweezers to separate the fibers at each location and placed a ¼-inch steel pin between the fibers. The panels were vacuum infused with Hexion’s EPON™ 862 epoxy resin and EPIKURE™ Curing Agent W, then cured in an autoclave. Afterward, the pins were removed, leaving ¼-inch holes. Aligning the holes throughout the 12 layers was tricky. “The first two or three tries, we had some misalignment,” Jadhav says. “But then we got good panels.” Open hole compression testing revealed that the method increased compressive strength 25% to 30% in the adjacent area compared to panels with drilled or water jet cut holes. In the second phase, the team experimented with a quasi-isotropic lay-up. They used 40 layers of 190 gsm 0/-45 Chomarat non-crimp (NCF) continuous carbon fiber fabric to create the 2.6 mm panels. The team alternated 20 layers of the 0/-45 fabric with 20 layers of the same fabric rotated to 45/90. As before, Jadhav marked the hole locations, carefully separated the fibers and inserted the ¼-inch pin one layer at a time. This time, he also cut the fabric stitches before separating the fibers. It was a time-consuming process. “We had to be careful not to cut the fiber,” he recalls. Once completed, the panels were tested for compressive strength, static tension and tension-tension fatigue. The results again showed significant improvements in mechanical properties over panels with drilled or water jet cut holes. Microscopic images confirmed that the fibers remained intact. Jadhav says that future research may focus on creating different hole diameters and automating the process. For now, the team has applied for a patent and is gauging industry interest. Jadhav believes the new technique could benefit many industries, particularly aerospace. “The future is composites,” he says. “If this technique is used in aerospace whenever there is a joining of two structures, it will reduce delamination problems and help to enhance the life of the products.” Harnessing the Power of Big Data Projects: Machine Learning Algorithms School: University of Washington Location: Seattle Principal Investigators: Steve Brunton and Ashis Banerjee The machine learning industry is expected to hit $9 billion by 2022, up from $1 billion just five years earlier, according to AI Multiple, a technology industry analyst firm. It’s no wonder that schools such as the University of Washington are investing in machine learning research. The Boeing Advanced Research Center (BARC) in the College of Engineering at the University of Washington hosts joint research projects in which Boeing-employed affiliate instructors work side by side with faculty and students on a range of projects, including ones related to machine learning. Researchers are mining vast quantities of data to find patterns that can be used to accelerate aircraft production rates, streamline design and reduce costs. One BARC team is analyzing big data to help standardize aircraft brackets. Modern aircraft have thousands of custom brackets. “Brackets are everywhere, from critical structural components to those used to guide conduits and other electric and airflow systems throughout the aircraft,” says Steve Brunton, professor of mechanical engineering and adjunct professor of applied mathematics and computer science at the University of Washington. Brunton, doctoral student Emily Clark, her co-advisor Nathan Kutz and Boeing project engineer Angelie Vincent spent three years developing and deploying algorithms to sift through data from Boeing and its subcontractors and identify brackets that are similar enough to be standardized. Brunton says that defining a similarity metric to reveal how close two brackets are in design and functionality was surprisingly challenging. While the results are proprietary, Brunton says their work demonstrates that many brackets can be standardized, which will reduce manufacturing and inventory costs and streamline the design process. Another machine learning research team developed an automatic process for detecting tow boundaries in parts fabricated with automated fiber placement (AFP), which is crucial to ensuring acceptable structural properties. Currently, most composite aircraft parts, including fuselage sections, fairings and empennage components, are visually inspected with the aid of laser projection. Manual tow boundary inspections are extremely time-consuming. For instance, it might take several days to inspect an entire composite wing skin. Ashis Banerjee, associate professor of industrial and systems engineering and mechanical engineering, says that for a part with 100,000 tow ends, even state-of-the-art semi-automated inspection requires three to six hours of additional manual inspection. Banerjee is leading a BARC team that’s using machine learning to develop an automated tow boundary detection system that would minimize the need for extra manual inspection. Collaborators include two doctoral students at the university, Wei Guo and Ekta Samani, and Agnes Blom-Schieber, technical fellow at Boeing Commercial Airplanes – Product Development/Structures Division. For two years, the researchers gathered thousands of tow boundary inspection images, but they found it difficult to generate a sufficiently large training dataset for their machine learning model. “While we knew that the inspection images would be challenging to analyze, we were still surprised at the extent of the challenge due to variations in illuminating conditions, material processing parameters and ply geometry,” says Banerjee. “In fact, it was virtually impossible for non-experts like us to discern the tow boundaries visually in many images. Even traditional edge detection-based image processing methods failed miserably.” So, the team turned to domain experts at Boeing to examine each image and label the tow boundaries. It was a painstaking process that resulted in a training set of approximately 3,500 images. While the data set was smaller than the team would have liked, it was enough to demonstrate that the automated inspection method reduced post-processing manual inspection by 90%. Boeing is considering using a scaled-up version for its production lines, and a joint Boeing-UW patent has been filed. Banerjee says, “This research has the potential to save hours of manual inspection work for every large-scale aerospace component part.” Making New Composites from Obsolete Ones Project: Pyrolysis-Based Recycling Technology School: The University of Tennessee, Knoxville Location: Knoxville, Tenn. Principal Investigator: Ryan Ginder A major issue on the minds of not only composites manufacturers, but all global producers is sustainability. One drawback to widespread adoption of composites is the lack of an efficient way to break down the materials once they have reached end of life. Ryan S. Ginder, research assistant professor at the University of Tennessee, Knoxville has created a remedy to that. Ginder, along with colleagues at Carbon Rivers LLC, have developed a pyrolysis-based recycling technology to turn end-of-life composites into new composite applications. The venture began when Ginder discussed the technology with the founders of Carbon Rivers in 2018, and they were eager to bring him into the fold. A year later, they used Ginder’s research and plans to pursue funding from the U.S. Department of Energy for wind blade recycling. Flash forward to 2021, and they have successfully recovered fiberglass from polymer composites used in the window industry and turned it into nonwoven fabrics and injection molding pellets, which can be used to manufacture next-generation composite products. As a demonstration project, Ginder fabricated a small boat mold and radio-controlled boat made from nonwoven fabric with recycled fiberglass and epoxy resin using hand lay-up. “The input vinyl window production scrap was first size reduced to a wood chip consistency for both feeding into the pyrolysis system and to set the fiber length that would be eventually recovered,” says Ginder. “The scrap material was then put through a multistage pyrolysis process where heat energy is primarily used to break down all of the composite’s organic components followed by residual carbon removal and final glass rinsing.” He declined to explain precisely how the university’s proprietary pyrolysis technology works but noted that the recycled fibers can be used in place of traditional virgin fibers with no difference in tensile stiffness or comparable properties. Ginder cites several advantages to utilizing this technology over other pyrolysis-based methods. For example, it completely removes all previous organics or other fillers so as not to inhibit the mechanical properties of the new product. The recovered fibers have a high aspect ratio which allows them to be used in high-value composite applications, such as 3D printer filament. Lastly, the process is resin agnostic, so fiberglass from a broad array of applications can be recycled. “The process can, in principle, achieve economies of scale not possible with more niche recovery techniques,” says Ginder. The core equipment needed for this recycling process is already commercially available, and the technology has been rapidly scaled from “milligrams in 2019 to kilograms in 2020 and now metric tons this year,” says Ginder. He and his colleagues at Carbon Rivers plan to launch a full-scale facility in the next few years, commissioning a 20-ton per day reactor in 2022 and a 200-ton per day commercial fiberglass recycling facility in late 2024. Ginder adds that the scalability of the process should make it attractive to many market segments, from marine to automotive. His goal is for composites to achieve a truly circular materials economy. “Doing so creates a reliable, domestic materials supply chain that fuels local economic growth, creates jobs and reduces environmental impact by displacing the need for virgin materials,” he says. Closing the Gap Between Design and Production Project: Computer-Aided Process Planning Tool School: University of South Carolina Location: Columbia, S.C. Principal Investigator: Ramy Harik The chasm between designing a composite part and manufacturing it can be vast, especially for advanced composite parts fabricated with automated fiber placement (AFP). It’s the job of process planners to close that gap, but the task can be laborious. To remedy this, researchers at the University of South Carolina’s Ronald E. McNAIR Center for Aerospace Innovation and Research developed what they say is the first computer-aided process planning (CAPP) tool specifically for composites. “Using a computer-aided process planning tool, we can help eliminate some of the consuming time and reduce some of the complexity that process planners undergo when they sit in front of a design and try to match the optimal manufacturing process,” says Ramy Harik, associate professor in mechanical engineering at the University of South Carolina and resident researcher at the McNAIR Center. University researchers worked alongside a collaborative research team (CRT) funded by the NASA Advanced Composite Consortium (ACC). While developing the CAPP tool, Harik's team surveyed CRT partners, including Boeing, Spirit and Collier Aerospace, to ascertain the most important process planning functions. Based on input from the survey, the researchers identified 16 important functions, many of which fell into two main categories – process optimization and tool path optimization. Process optimization includes deciding where to begin lay-up, such as in the center of the part or toward an edge. The process planner must also decide which lay-up strategy to use based on surface geometry, such as constant angles or constant curvature. Together, these choices affect fiber coverage and help alleviate potential issues, including fiber overlap where the part is thicker and gaps where the AFP machine can’t place fibers. Process planners must also consider angle deviations and possible effects of steering fibers over distance, such as wrinkling. “The starting point of the lay-up, coupled with the lay-up strategy and coverage, creates an exponential influence on the final manufactured part,” says Harik. Use of the AFP machine, or its tool path, must also be optimized to reduce inertia and increase throughput. This includes choosing which axis to use and its range of movement. Process planners must think about tow width and whether to use unidirectional or bidirectional fiber placement. “This task is often very, very tedious,” Harik emphasizes. Using the CAPP tool, process planners begin by entering the part’s geometry and design parameters. Then, they access a menu of preloaded, scored options for each manufacturing decision. With the click of a mouse, they can explore each potential lay-up strategy, including an illustrated analysis of where gaps, overlaps, angle deviations and other defects will occur. The computer-aided tool will not only save time but will also provide traceability and justification for manufacturing decisions. A modified version of the software that requires less data entry to launch helps designers see how angles, plies, boundaries and other design parameters will play out. “Very often, you see a disconnect between the design and reality,” says Harik. “You can come up with the best design, but perhaps your design is unachievable … or it does not account for how the fibers will actually be laid.” The software will flag potential manufacturing hot spots. For example, if a design specifies a 45-degree ply angle but it will be 40 to 50 degrees in some areas due to geometry or machine limitations, the tool will highlight the discrepancy. “The software will help designers and engineers make better designs and make manufacturing-informed designs from the get-go,” says Harik. The computer-aided process planning tool is currently in testing and is expected to be released next year. Advancing Composites in the Construction Industry Project: Pultruded FRP Construction Framing School: The University of Notre Dame Location: Notre Dame, Ind. Principal Investigator: Kevin Walsh Structural framing, or the skeleton that supports a building, is critical for stability as it supports all other components, from drywall to windows and roofs. Traditionally, construction framing has been made from wood or steel. But researchers at the University of Notre Dame, working in collaboration with the structural design firm Frost Engineering and Consulting, have developed novel pultruded FRP framing configurations to expand the use of composites within the construction industry. Based on input from Frost’s clients, which include manufacturers, fabricators and installers of pultruded products, the team identified framing connections as a primary hindrance to widespread adoption of FRP. They pinpointed a need for semi-rigid, lapped joint connections. “Semi-rigid connections have been used in various other materials, such as steel and reinforced concrete, to solve one of the most fundamental challenges of structural framing, which is to provide lateral stability while avoiding clashes with access paths, utilities and architectural features,” says Kevin Walsh, assistant teaching professor in the Department of Civil and Environmental Engineering and Earth Sciences at Notre Dame. “By designing and testing lapped connections specifically, we are avoiding the issue of flange connection plates clashing with decking used for walking surfaces, as well as improving the efficiency of fabrication and installation.” The team developed, tested and analyzed a variety of rotationally semi-rigid, beam-column joint connections to ascertain the rotational strength and stiffness of laminated pultruded FRP surface materials under different surface preparation conditions and framing configurations, as well as how these unique stress conditions alter the performance needs of adhesives currently available. The corresponding construction project for this novel FRP structural framing was two low-rise, generator access platforms in a data center campus in Arizona, each measuring 52 x 167 feet and constructed in September 2021. Pultruded FRP profiles used for the installation included W columns, I beams, L angles for beam web connections and miscellaneous C channel shapes with adhesives and steel bolt hardware for transverse beam connections. Prior to the installation, the team tested 15 specimens to ensure they adhered to the American Society of Civil Engineers’ Load Resistance Factor Design Standard for Pultruded Fiber Reinforced Polymer Composite Structures, commissioned by ACMA. “While some fabricated items could be improved for future tests and similar projects, we validated that the configurations would have more than enough capacity for the design basis criteria for this particular project in Arizona,” says Walsh. The team plans to design and test specimens prior to the installation of similar framing configurations across the U.S. in the next year. Walsh believes the FRP lapped, semi-rigid connections will initially attract end users in sectors that require low-rise, personnel access platforms and utility support systems, such as industrial manufacturing, data centers and water and wastewater treatment facilities. But he envisions a broader market for composites in construction and is consulting with collaborators at Frost on approximately 40 other design needs the company’s engineers have identified. “With the ever-growing need for non-corrosive, lightweight and domestically produced construction materials in our built environment, I can see pultruded FRP having a great deal of growth potential in several market sectors,” says Walsh. Melissa O’Leary and Erin Turner are freelance writers in Cleveland. Email comments to mailto:melissa@good4you.org and erinjturner1066@gmail.com.