Tensile load measurement of titanium bolts with detailed uncertainty analysis based on acoustoelastic theory by using an ultrasonic sensor

Abstract Titanium alloy fasteners are widely used in the aerospace industry. The assembly quality is critical to the reliability and safety of different kinds of components. Limited by the precision and detection efficiency, traditional methods such as the torque coefficient method and the strain gauge method can no longer meet the requirements of rapid, high-precision measurement. The acoustoelasticity method is a fast, precise, and non-destructive method that provides a solution to the above problems. This study focuses on the measurement of tensile load applied to Ti-6Al-4V (TC4) bolts. Stepwise loads are gradually and accurately applied on TC4 bolts, high-frequency echo signals are recorded, and the time-of-flight (TOF) can be calculated correspondingly. Supplemented by a precise calibration procedure, the linear fitting equation of tensile load and TOF based on acoustoelastic theory has been established. Experiment results show that, within (5 – 45) kN tensile load range, the typical relative error is below 5%. The calculated relative expanded uncertainty is around 6.0% ( k = 2). Taking sample dispersion into consideration, the relative expanded uncertainty of the bolt population can be statistically calculated within 8.5% ( k = 2).