Automated Crawler-Based Ultrasonic Investigation to Monitor the Structural Integrity of Composite Liquid Hydrogen Tanks

Abstract

Inspection of composite liquid hydrogen tanks (LH2) for aviation is very challenging using existing non-destructive testing (NDT) technology. This is due to the external insulation layer and limited access to the inside of the tank. New inspection technology is urgently needed for the LH2 tank inspection and maintenance of these LH2 tanks. This work presents the development of a compact high-payload ratio ultrasonic inspection automatic robotic crawler designed for the inspection of the inner curved surfaces of a carbon fiber reinforced polymer (CFRP) composite. The robot is equipped with wheeled locomotion and uses wheel encoders for precise localization on the irregular inner surfaces of the composite LH2 tank. The crawler carries an ultrasonic flaw detector payload housed in a specially designed enclosure, which securely holds a 5 MHz wheel probe for ultrasonic inspection. This study investigates Proportional- Integral-Derivative (PID) tuning for a crawler integrated with an ultrasonic phased array probe, executing straight-line motion on a CFRP composite surface under dynamic conditions at various speeds. The system is designed to operate through tank openings as small as 250-300 mm in diameter, providing a practical solution for challenging inspection scenarios of the LH2 tank.