There is no doubt that fiber-reinforced materials have high strength-to-weight ratios which make them appealing for many applications, especially aviation and automotive. However, the high-cost of carbon fiber and the limits of mass production of fiber-reinforced materials which require lay-up remain a barrier to these industries. On-going research by Pepin Associates is leading to mechanisms which will lower the cost barrier for carbon fiber applications.
Pepin Associates has developed a formable, aligned, discontinuous fiber fabric called DiscoTex® which may be made from carbon, glass, quartz or ceramic fibers. The material is highly formable as compared to continuous-fiber fabrics due to the ability of DiscoTex® to stretch in the direction of reinforcement, a capability which can reduce or even eliminate the need to cut and dart the material during lay-up.
DiscoTex® fabric can be pre-pregged with thermosets. However, Pepin Associates is learning from previous research how to best create a carbon fiber DiscoTex® fabric combined with a thermoplastic such as Nylon 6. Pepin Associates previously developed an energy absorption crush rail demonstration part for a subcompact car using an E glass/polyethylene terephthalate (PET) DiscoTex® fabric. The PET fibers were spun from recycled soft drink bottles (100% post-consumer). The use of this material demonstrated that readily-available waste materials may be recycled to form parts of value to the automotive industry.
The part was formed by pressurizing an internal bladder to consolidate the DiscoTex® fabric against the walls of the female tool. The PET melted and wet out the glass fiber very effectively. "The compelling attribute of this part is the use of discontinuous glass fiber in the hoop direction of the structure", stated John Pepin, President of Pepin Associates. "Consolidating the layup into the corners of the part would be very difficult with continuous hoop fibers", Pepin added.
Thermoplastics are commonly used in many industries due to the ease by which they may be used to form parts of various sizes and functions. But structural parts require the greater strength which fiber-reinforced plastics provide. As even greater strength and stiffness are needed in fiber-reinforced thermoplastics, such as in the replacement of metal automotive components to thermoplastic composites to achieve weight savings, random fiber alignment for composite reinforcement meets limitations. When reinforcing thermoplastics with continuous fibers, however, the manufacturing issues for forming complex shapes and structures can be very challenging.
DiscoTex® aligned, discontinuous fiber fabric may be a solution for this problem. Pepin Associates is currently fabricating a tow (an untwisted bundle of continuous filaments) which combines discontinuous carbon fiber segments with continuous nylon tows. Pepin Associates refers to this combined, continuous / discontinuous tow as "cd tow".
DiscoTex® is designed to help manufacturers more easily form parts which contain complex shapes. The ability of this material to stretch in the reinforcement direction allows for time savings in production. For example, when DiscoTex® fabric is prepregged with epoxy, a flat layup can be stretch-formed into complex shapes such as a hemisphere. The ability to stretch-form the prepreg eliminates the need to cut or dart such complex parts. Demonstration parts for military aircraft using DiscoTex® resulted in 35% overall cost savings as compared to production of parts using continuous fibers.
Production of parts commercially requires speed and efficiency, regardless of the industry. For fiber reinforced thermoplastic composite parts with a constant cross-section, pultrusion can be an ideal production method. However, the process of pulling continuous fibers through a die to compress the layed up material can make this method unsuitable for any structure which has fiber reinforcement in the hoop direction. Again, the cd tow used to make DiscoTex® fabric may be a solution.
"When woven into fabric, the use of discontinuous carbon fiber in a thermoplastic matrix will allow for faster production times for fabricating parts with complex contours", said John Pepin. "Even faster would be the use of pultrusion to form thermoplastic parts with discontinuous carbon fibers aligned in the hoop direction. Incorporation of CD Tow in an input material form for pultrusion could enable high speed fabrication of pultruded parts with hoop reinforcement", Pepin added.
The high cost of carbon fiber and its application to automotive part production has been a significant barrier to its use in the automotive field. However, researchers at the Oak Ridge National Laboratory (ORNL) are working to devise lower-cost precursors for carbon fiber as well as processing methods which use less energy. The intended result is lower cost carbon fiber for use by manufacturers in various sectors, with a focus on automotive applications.
The Oak Ridge National Laboratory is seeking to form a consortium of carbon fiber composite manufacturers and research entities to work together toward the common aim of lowering the cost of carbon fiber applications in the automotive sector, as well as others. Pepin Associates looks forward to joining this multi-disciplinary effort led by the researchers at ORNL.
Pepin Associates, Inc.
15 Log Home Road
Greenville, Maine 04441
Director of Business Development