Abstract
Adhesive bonded structures have been widely used in aerospace, automobile, and marine industries. Due to the complex nature of the failure mechanisms of bonded structures, cost-effective and reliable damage detection is crucial for these industries. Most of the common damage detection methods are not adequately sensitive to the presence of weakened bonding. This paper presents an experimental and analytical method for the in-situ detection of damage in adhesive-bonded structures. The method is fully non-contact, using air-coupled ultrasonic transducers (ACT) for ultrasonic wave generation and sensing. The uniqueness of the proposed method relies on accurate detection and localization of weakened bonding in complex adhesive bonded structures. The specimens tested in this study are parts of real-world structures with critical and complex damage types, provided by Hyundai Heavy Industries® and IKTS Fraunhofer®. Various transmitter and receiver configurations, including through transmission, pitch-catch scanning, and probe holder angles, were attempted, and the obtained results were analyzed. The method examines the time-of-flight of the ultrasonic waves over a target inspection area, and the spatial variation of the time-of-flight information was examined to visualize and locate damage. The proposed method works without relying on reference data obtained from the pristine condition of the target specimen. Aluminum bonded plates and triplex adhesive layers with debonding and weakened bonding were used to examine the effectiveness of the method.
Highlights
To fulfill the demand for lighter and more resistant materials in the aerospace, automobile, and marine industries, adhesive bonded structures have been widely adopted [1,2,3]
This paper presents a fully non-contact, baseline-free candidate method for the in-situ damage detection of adhesive-bonded structures using air-coupled ultrasonic transducers (ACT)
The overall velocity of the guided waves measured from the weakened bonding area was significantly lower than the velocity of the guided waves measured from the intact area
Summary
To fulfill the demand for lighter and more resistant materials in the aerospace, automobile, and marine industries, adhesive bonded structures have been widely adopted [1,2,3]. Improved uniform load transfer in adhesive bonded structures results in better damage tolerance and, more importantly, fatigue life extension, compared to conventional joining methods such as mechanical fastening [4]. Several damage detection methods have been developed and considered to address the challenges in the inspection of bonded structures These methods include neutron imaging radiography [7], thermography [8,9,10], and ultrasound [11,12,13]. This paper presents a fully non-contact, baseline-free candidate method for the in-situ damage detection of adhesive-bonded structures using ACTs. The method uses the time-of-flight (TOF) of the ultrasonic waves over a target inspection area to assess and visualize the presence of critical damage.
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