Fasteners such as bolts, nuts, studs, washers and rivets, are used in innumerable structures and machines. Fastener failure has led to many costly documented failures in a wide range of application and for many different causes.
NASA has also experienced a number of fastener problems as were compile during a technical exchange meeting in the mid-90 (Gamwell 1995). Out of 240 lots of fasteners period, 42 lots were rejected.
Fastener failure analysis has shown that the causes include improper tightening, fatigue, tensile fracture, galling, insufficient preload, thread stripping, creep, stress relaxation, and self-loosening.
NASA has invented a smart fastener to ensure that fastener failure can be detected in time to avoid huge losses. The technology offers the ability to remotely, quickly, and inexpensively verify that any number of fasteners are torqued properly upon initial installation. Further, it allows low cost monitoring over the life of the fastener.
The smart fasteners include an RFID-based torque sensor that can be used to quickly monitor off the shelf fasteners including fasteners that are used in expensive satellites or other uses where fastener failure can be very costly.
The sensor includes an antenna, an RFID ring and a spring. The sensor can be interrogated with an interrogation signal produced by an interrogator device. When sufficient torque is applied to the fastener, an RFID circuit is connected, and produces a radio frequency (RF) signal that can be read by the interrogator. If the RFID circuit does not transmit when the spring member is not compressed, it indicates insufficient tensioning of the fastener.
Publication number: US 9,483,674
Patent Title: RFID torque sensing tag system for fasteners
Publication date: 1 Nov 2016
Filing date: 7 Mar 2014
Inventors: Patrick W. Fink; Gregory Y. Lin; Phong H. Ngo; Timothy F. Kennedy;
Original Assignee: The United States of America as represented by the Administrator of the National Aeronautics and Space