Eddy Current Testing of Thick Aluminum Plates with Hidden Cracks (original) (raw)
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As a result of cyclic fatigue, cracks may develop around ferrous fasteners found on aircraft such as the F/A-18 Hornet, CC-130 Hercules and CP-140 Aurora. Normally, fastener removal is required for inspection by bolt hole eddy current techniques, since the presence of the fastener would otherwise confound detection of cracks propagating from the inner bore. However, the removal of fasteners introduces additional down time as well as the risk of collateral damage. Transient eddy currents generated by probe designs that utilize the ferrous fastener as a flux conduit have demonstrated the capability of detecting subsurface cracks at depth within conducting structures. On the aluminum surface, differentially connected pickup coils are used to sense the differences in response due to variations in the induced eddy current field arising from the presence of the cracks. The resulting signal is analyzed using Principal Components Analysis (PCA) to extract scores that are used to determine t...
Studies to Optimize the Probe Response for Velocity Induced Eddy Current Testing in Aluminium
Measurement, 2015
This paper presents an enhancement in the probes to be used on a new nondestructive testing method with eddy currents induced by velocity. In this method, a permanent magnet that is attached to a moving carriage creates eddy currents in the conductive material to be inspected. By measuring the opposing magnetic field generated by the eddy currents, it is possible to obtain information regarding the presence of defects. Different magnetic field sensors, such as, differential pick-up coils, giant magneto resistors (GMR) and Hall sensors have been used and compared. A permanent magnet moving above a plate was studied using a numerical model to allow further improvements to be made in the probe. Depending on each sensor's geometry, sensing axis and range, its position and orientation must be strategically chosen in order to increase defect sensitivity.
A Study of the Automated Eddy Current Detection of Cracks in Steel Plates
Journal of Nondestructive Evaluation, 2019
Applying life estimation approaches to determine in-service life of structures and plan the inspection schedules accordingly are becoming acceptable safety design procedures in aerospace. However, these design systems shall be fed with reliable parameters related to material properties, loading conditions and defect characteristics. In this context, the role of non-destructive (NDT) testing reliability is of high importance in detecting and sizing defects. Eddy current test (ECT) is an electromagnetic NDT method frequently used to inspect tiny surface fatigue cracks in sensitive industries. Owing to the new advances in robotic technologies, there is a trend to integrate the ECT into automated systems to perform NDT inspections more efficiently. In fact, ECT can be effectively automated as to increase the coverage, repeatability and scanning speed. The reliability of ECT scanning, however, should be thoroughly investigated and compared to conventional modes of applications to obtain ...
Metals, 2019
The use of eddy currents for detecting flaws in specimens is of considerable significance in the industrial sector. In this study, a new design of a rotating uniform eddy current (UEC) probe, termed the rotating butterfly probe, is presented. The probe consists of two pairs of excitation coils arranged perpendicular to each other, positioned in two layers, and in a detection coil. The excitation and detection coils were installed the pancake orientation, which provides larger induction and enhances the sensitivity of flaws detection. In addition, to generate a rotating UEC distribution with same amplitude in all directions, the number of turns between first and second layers of the excitation coils and the amplitude of excitation current were arranged. Finite element simulations were conducted to confirm that rotating UEC distribution has the same amplitude in all directions. The experiment with the rotating butterfly probe was then conducted. In the experiment, the measured results with the probe was indicated the self-differential and self-nulling properties. Moreover, the probe was successful in detecting flaws in all directions on an aluminum plate. This attribute can be used for the effective inspection of test pieces.
Investigate of the Effect of Width Defect on Eddy Current Testing Signals under Different Materials
Indian Journal of Science and Technology, 2017
Objectives: Non-Destructive Evaluation (NDE) is the inspection of an object to determine its properties without destroying its usefulness. It is used, for example, to detect cracking in steam generator tubing in nuclear power plants and aircrafts. Eddy Current NDE is a commonly used method of NDE. This study creates a sample calibration block with different materials and investigates the effect of width defects in these materials on the Eddy Current signal. Method/Statistical: The materials of the artificial defect block are mild steel, brass and copper with dimensions of 260 mm (length) × 30 mm (width) × 10 mm (height). A total of 12 artificial defects are located 20 mm parallel to the length of the block. The distance of the defect is located in between 1 mm up to 2.5 mm from the surface of the artificial defect block. A weld probe was used to inspect the block. The wire cut machines were utilized to add defects to the sample block. Findings: Results prove that the deviation of Eddy Current Testing measurement was influenced by the width and material of the objective. Application/Improvement: The results showed that the signal of the Eddy Current was affected by the size of the defect and the type of specimen.
Non-Destructive Techniques Based on Eddy Current Testing
Non-destructive techniques are used widely in the metal industry in order to control the quality of materials. Eddy current testing is one of the most extensively used non-destructive techniques for inspecting electrically conductive materials at very high speeds that does not require any contact between the test piece and the sensor. This paper includes an overview of the fundamentals and main variables of eddy current testing. It also describes the state-of-the-art sensors and modern techniques such as multi-frequency and pulsed systems. Recent advances in complex models towards solving crack-sensor interaction, developments in instrumentation due to advances in electronic devices, and the evolution of data processing suggest that eddy current testing systems will be increasingly used in the future.
Non-destructive testing of Al-Mg alloys by using the eddy-current method
The measuring system based on subminiature eddy-current transducers has been developed to carry out local investigations of aluminum-magnesium alloy plates for flaws. The Delianna filter has been modified to allow the significant increase of signal-to-noise ratio. A scheme that uses a computer as a generator and receiver of signals from windings is proposed. It is capable of automatically changing the filtering cutoff frequency and operating frequency of the device. The transducer has been tested on a number of aluminum-magnesium alloy plates with flaws. The article presents data on the relationship of eddy-current transducer response to the presence of flaws in alloys as hidden holes at signal frequencies comprised between 300÷700 Hz on an exciting winding.
Detection and measurement of surface cracks in ferromagnetic materials using eddy current testing
NDT & E International, 2006
Eddy current testing is used to detect and quantify defects in electric conductive materials. Defects investigated are specifically mechanical, chemical and microstructural heterogeneities. In this scope, artificial defects simulating superficial cracks have been achieved in order to establish an eventual relationship between the orientation, the shape and the size of the defect in one hand, and the signature that it generates in the impedance plane on the other hand. We determine in the first stage the operating conditions for the minimization of all signals that may perturb the crack signal such as the background one. We have been able to detect easily a surface crack on ferromagnetic steel in a large range of the frequency. Curves allowing the discrimination between signals corresponding to the presence of cracks and those corresponding to a lift-off have been established. The limit depth has as well been determined and we found that this limit has no relationship with the depth of penetration of the eddy current. The operative parameters such as the diameter and the working mode of the probe, the excitation frequency and the setting of the measurement equipment have been optimized for the testing of the quality and the reliability of critical ferromagnetic steel parts.