Session: 05-01-02: Condition Monitoring, Metrology & Instrumentation

Paper Number: 173018

Development and Validation of a Novel Method to Measure Residual Preload Using the Torque Angle Signature Method 

Residual clamp force is a critical parameter for ensuring the structural integrity of bolted joints that are exposed to various mechanical environments. In our particular case, we needed to conduct a study of a specific bolted joint that consistently lost preload during dynamic testing. However, the existing measurement methods available were not suitable for meeting our specific needs and requirements.

This abstract presents our development and validation of the Torque-Angle Signature Logger (TASL), a novel tool designed to measure the remaining preload force in fasteners during their removal by utilizing the torque-angle signature method. While this method is well-established in controlled environments, its application to real-world scenarios introduces complexities arising from nonlinear effects such as surface variations and thread-locking compounds as well as bulky lab setups making real-world use unfeasible. The TASL addresses these challenges through novel data processing techniques and a hardware configuration optimized for constrained environments and small fasteners.

Existing methods for measuring residual clamp force are accurate but have specific limitations. Ultrasonic methods require smooth surfaces and are size-constrained; micrometer techniques need direct access to both bolt ends; clamped load cells need extra space; embedded strain gauges are only available in large fastener sizes. Other methods, like optical distortion measurements, require precise lab setups and are not suitable for field use. These limitations are especially significant for small fasteners, such as #10 screws, treated with thread-locking compounds, where conventional techniques often fail to provide reliable data.

The TASL was designed to address these limitations. We incorporated a rotary torque transducer and a high-resolution incremental encoder into a flexible configuration for accurate torque and angle measurements. By initially calibrating the TASL model in the lab through collecting torque-angle data across various preload forces measured by a load cell, we can predict the residual preload in any fastener that matches the lab conditions in a real assembly. This is achieved by simply measuring the release torque-angle signature during fastener removal. We validated the TASL using a lab setup which exactly emulated our bolted joint of interest. We measured torque-angle data by tightening these fasteners to and from a range of 400 to 1200 lbF with cured Loctite. We collected the same data on our gold standard fixtures (calibrated rotary test frame with torque and angle transducers). Through rigorous testing and analysis, we demonstrated an average TASL error of 6.4% and a 95% confidence interval of 14.5%, confirming the reliability and accuracy of our innovative approach in practical applications.

Presenting Author: Camden Boston Sandia National Labs

Presenting Author Biography: Camden is a mechanical systems engineer with a strong academic foundation and hands-on experience in robotics. He earned both his Bachelor of Science and Master of Science degrees in Mechanical Engineering from Purdue University.

During his graduate studies, Camden focused on advanced submersible robotics, contributing to cutting-edge research that aimed to enhance the capabilities and efficiency of underwater exploration technologies. His work involved designing and testing robotic systems capable of operating in challenging environments.

Currently, Camden applies his expertise at Sandia National Laboratories, where he plays a pivotal role in developing and optimizing mechanical systems for various applications.

Authors:

Ross Schneider Sandia National Labs
Camden Boston Sandia National Labs
Yousef Saed Sandia National Labs