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.