Evaluation of damaged composite materials using non-destructive testing

Abstract

Honeycomb composite sandwich structures are rapidly gaining popularity in the aerospace industry due to their superior structural properties over conventional materials. Hence the need to maintain its structural integrity becomes of utmost importance during inspection. This report discusses and evaluates Non-Destructive Testing techniques performed on honeycomb composite sandwich reference standards issued by Boeing. The reference standards comprises of carbon fibre reinforced polymer (CFRP) solid laminates sandwiched between a Nomex honeycomb core and include relevant damage types such as skin-to-core disbonds and interply delaminations. The two Non-Destructive Testing techniques evaluated are Ultrasonic Testing and Infrared Thermography. Ultrasonic Testing methods exploited on the reference standards were mainly Pulse Echo, Bond Testing and Resonance. Pulsed Thermography was chosen as the method of infrared thermography by using a collimated light as the heating source and with the aid of an infrared camera. The three different modes of Ultrasonic Testing and were critiqued on defect detection, sizing and depth estimation of the defects present in the reference standard. Pulsed thermography was critiqued mainly for defect detection and evaluation of the amount of heat energy versus skin thickness. Further evaluation parameters such as speed of inspection and sensitivities of the equipment used would also be briefly discussed. This report also gives an overview of the advantages and limitations of the different techniques explored, and concludes with general guidelines on proper instrumentation of each technique.