Abstract
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 a better understanding of the advantages and shortcomings related to this technique. In this contribution, a series of manual and automated ECT tests are carried out on a set of samples using a split-D reflection differential surface probe. The study investigates the level of noise recorded in each technique and discuss its dependency on different parameters, such as surface roughness and frequency. Afterwards, a description of the effect of crack orientation on ECT signal amplitude is provided through experimental tests and finite element simulations. Finally, the reliability of each ECT technique is investigated by means of probability of detection (POD) curves. POD parameters are then extracted and compared to examine the effect of scanning index, frequency and automation on detection reliability.
Highlights
Fatigue failure is the most important source of damage in systems subjected to cyclic loads
Journal of Nondestructive Evaluation (2020) 39:6 intervals would be set based on more realistic results, and unexpected failure could be avoided [3]
The signal response Probability of detection (POD) is considered as the quantitative tool for this comparison study, where only the most influential parameters, namely the test frequency, the crack orientation, the index of automated raster scan and the inspector are considered
Summary
Fatigue failure is the most important source of damage in systems subjected to cyclic loads. In order to make decisions on the continuation of operation and on the maintenance intervals, risk assessment programs have been introduced [1]. In this framework, probabilistic physical models are used to estimate the remaining fatigue life of in-service components. Probabilistic physical models are used to estimate the remaining fatigue life of in-service components These models are mostly developed based on the damage tolerance approach, which requires several input parameters including flaw characteristics, material properties and loading conditions [2]. Optimal definition of these input parameters considering their uncertainty would lead to more accurate remaining life estimation; the maintenance
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