Torque Angle Signature Analysis of Joints with Thread Rolling Screws and Unthreaded Weld Nuts 2007-01-1665
Bolted joint separation occurs when components of a joint are no longer capable of maintaining a clamp load. The clamp load of a joint is the resultant of various factors such as the strength of joining components, geometry, and the surface condition of the joined parts. The fastener installation torque is a very critical parameter that contributes towards achieving the desired clamping force at the joint during the assembly process.
Thread rolling screws are increasingly being used in many automotive structural applications. The thread rolling screws are easy to install, are self aligning, and offer a torque prevailing feature with improved vibration resistance when mated with a un-threaded nut. This combination results in a robust joint and low field costs.
They also offer increased joint strength by work hardening the mating nut interface. This paper will describe the methodology of selecting the proper installation torque of bolted joints comprised of thread rolling screws and un-threaded weld nuts using torque to failure testing and torque angle signature analysis. The Torque-angle test is a very cost-effective method to determine the right installation torque of the bolted joints, thereby reducing the potential for joint failure.
The paper will also present a method to estimate the joint tension derived from the torque angle curve of the bolted joint.