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By combining the elasticity and strength of materials, a single mono-form component can be made to take different shapes, which is referred to as shape-shifting or morphing.
Inspired by nature, Dr. Sridhar Kota, of the University of Michigan Mechanical Engineering Dept and Director of the Compliant Systems Design Laboratory, is developing ways to design objects that are strong, yet flexible. One piece, “hinge-less” mechanisms can replace complex assemblies of arms, springs, pins and hinges. In search of co-development partners for product application, these methods and capabilities are being presented for the first time in a commercial forum by FlexSys, Inc.“Legacy GFRP and thermoplastic composites are actually ideal for these applications because of their high strength/stiffness ratio attributes. They can also be customized with fiber orientation and localized thickness changes, unlike isotropic metals and stampings,” explains Bob Schartow the VP Business Development at FlexSys.Partnering with Nasa and the Air Force, FlexSys developed morphing wing technology that allows in-flight shape optimization for changing conditions of weight, altitude and wind speed. After $20 million and 15 years of tests, it has recently led to a Joint Venture with Aviation Partners Inc of Seattle WA. But now by using composites, this technology is being adapted to shape changing applications for automobiles, sailboat rigid sails and underwater foils; and a new area of focus – Elasto-Monolithic Mechanisms for industry and product application.By using their proprietary design methods, FlexSys was able to design a single piece wiper arm and blade that costs less, out lasts and out performs traditional metal assemblies. FlexSys developed software to determine shape and thicknesses, and determined that a composite thermoplastic of 30% glass filled PBT provided the needed strength/stiffness ratio. Dr. Sridhar Kota, Founder of FlexSys and Professor of Mechanical Engineering at the University of Michigan says, “The single piece molded design reduces part count by 75% and associated assembly, it came in at half the weight, and can be made in the USA at two thirds less cost than the legacy metal design.”Unlike the traditional hinged blade, this wiper provides constant spring pressure through each of its arms. Bob further explains that, “In compliant or Elasto-Monolithic design, the elasticity of materials must be embraced and used to create motion, but current design tools and methods create rigid members, hinges and springs.” To surmount this obstacle FlexSys, with the help of a grant from the National Science Foundation, is developing unique software called FlexWorks.FlexWorks allows for the input of desired motions and magnitudes, and will run through 1000’s of compliant mechanism iterations to find one to most closely deliver the desired output. It considers the max stress/strain capability of the material in each iteration. The output provides required thickness variation of each bending member. It also performs compliant mechanism simulation and stress analysis. The final design can be further tweaked in the edit mode, reevaluated, then saved in a file to either 3D Print or import to Solidworks, Ansys, etc. FlexSys believes this software could eventually become a module available in 3D modeling programs.
FlexSys Iris mechanism illustrates the principle of designing with distributed compliance.By distributing the material optimally, large deformations can be realized while limiting the material strains to lie within a very small linear elastic range.
3D printing provides FlexSys with quick conceptual confirmations and the ability to create iterations to optimize their designs. FlexSys also found unexpected synergy between compliant design and 3D printing. Their Iris demo design is an excellent example of Elasto-Monolithic Design and perfectly suited for 3D printing in one piece. In fact, many compliant designs can be 3D printed allowing for its application without the high costs of molds. Spring forces can be tailored through material choice, thickness and width. Thus, even a constant force, non-linear spring can be achieved. For example, the Iris spring force can be customized by changing material and the arm width and thickness.Advancements in additive manufacturing materials and in customization of composite materials will fuel the future of compliant and morphing structures. Additives can increase the strength/flexibility ratio allowing for higher load applications and greater travel without stress fatigue. FlexSys is a technology company that is looking to license their Intellectual Property to be integrated into products. More compliant design concepts can be seen in the JEC-Atlanta Demo Zone including applications in automotive, medical, robotics and prosthetics.Photo: FlexSys Iris mechanism illustrates the principle of designing with distributed compliance - by distributing the material optimally, large deformations can be realized while limiting the material strains to lie within a very small linear elastic range.More information:www.flxsys.com