Inspections of Helicopter Composite Airframe Structures using Conventional and Emerging Nondestructive Testing Methods

This paper presents nondestructive testing (NDT) results and analysis from the inspection of composite specimens representing typical helicopter parts. The specimens include monolithic laminates produced from carbon fiber reinforced plastic (CFRP), Nomex honeycomb core sandwich panels with CFRP skins, and CFRP frame-skin joint panels. External protection layers comprising copper mesh and fiberglass were also included in the specimens. These panels were fabricated with a wide range of defects to simulate helicopter in-service damage including delamination and skin-core disbond along with barely visible impact damage. The study aims to assess a number of conventional and emerging NDT techniques suitable for rapid in situ and off-site inspection of helicopter composite structures. The techniques considered are flash and sonic thermography, radiography, and different ultrasonic inspection modes including pulse-echo, through-transmission, and phased array. These techniques are compared on their ability to detect and characterize the fabricated defects.