NDE: An effective approach to improved reliability and safety. A technology survey

Technical abstracts are presented for about 100 significant documents relating to nondestructive testing of aircraft structures or related structural testing and the reliability of the more commonly used evaluation methods. Particular attention is directed toward acoustic emission; liquid penetrant; magnetic particle; ultrasonics; eddy current; and radiography. The introduction of the report includes an overview of the state-of-the-art represented in the documents that have been abstracted

Fusion of Microwave and Eddy Current Data for a Multi-Modal Approach in Evaluating Corrosion under Paint and in Lap Joints

Critical aircraft structures are susceptible to hidden corrosion. Find-it and fix-it approaches are inefficient as it relates to managing the problems associated with corrosion. More comprehensive corrosion information may be obtained using data fusion from several detection and evaluation methods. To this end, microwave, conventional and pulsed eddy current data from a multi-layer corroded panel, representing an aircraft lap joint, are fused and used as inputs to a structural analysis model to obtain a comprehensive snapshot of the corroded environment. This paper presents the data fusion algorithm and the structural analysis model along with a discussion of the results

Imaging subsurface defects using SQUID magnetometers

Over the last several years, SQUID magnetometers have been utilized for detection of defects in metal structures by measuring the magnetic field produced by injected current or permanent magnetization [1,2,3]. Because the amplitude of the output signal from the SQUID magnetometer is independent of the frequency of the magnetic field to be measured, SQUIDs are suitable for dc or low frequency measurements as required for detection of subsurface flaws inside a conductor

Development of a pulsed eddy current instrument and its application to detect deeply buried corrosion

Eddy current techniques have historically been valuable to nondestructive evaluation and testing. They allow detection of cracks, corrosion, and other inhomogeneities in conducting materials. However, due to the fact that traditionally eddy currents only use one frequency to excite the coil, limited information about the detected flaw is available. Swept frequency eddy current methods, which sweep the frequency of excitation over a specified range, allow much more information about the flaw to be extracted from the data. This method is much slower due to the amount of time required to sweep the frequency. The pulsed eddy current method was developed to decrease the time required for swept frequency measurements while retaining the ability to extract more information from the data.;The technique is a broadband measurement which requires the coil to be excited by a step function and the response of the coil monitored. Since the coil is excited with a spectrum of frequencies contained in the step function, similar information content to the swept frequency method is available. In this thesis, the electronic hardware for a pulsed eddy current system with the ability to operate a probe in the absolute or reflection mode using a step voltage drive waveform was developed and demonstrated. The system consists of a portable computer with three expansion boards to control the probe drive and signal amplification, digitize the signal, and control the scanner.;The system is controlled by custom designed software based on the Windows[Superscript TM] operating system. The capabilities of the pulsed eddy current system were then extended to allow for a step current drive waveform. The experimental results for corrosion detection in a two-layer structure of 1 mm thick aluminum plates simulating an aircraft lap joint are compared with theory and are found to be in good agreement. The ability to use the instrument with a magnetic sensor capable of sensing the magnetic field threading the coil was also added to the instrument. Using theory and experiment, it is demonstrated that a magnetic sensor is superior to the coil sensor at detecting deeply buried corrosion in aluminum