Torque Evaluation of Automotive Connecting-Rod Bolts Using Piezoelectric Sensors and Contact Acoustic Nonlinearity Methods

This work presents a nonlinear ultrasonic Structural Health Monitoring (SHM) approach for the non-destructive assessment of bolt torque in connecting rod assemblies. Variations in preload are captured through changes in higher harmonic components generated by Contact Acoustic Nonlinearity (CAN), which proved sensitive to different torque levels, excitation frequencies, and bio lubricants. The results demonstrate that nonlinear ultrasonic indicators offer a reliable basis for real-time monitoring of bolt tension in safety-critical mechanical joints.