Severity Estimation of Defects on Interpretation of Eddy-Current Defectograms

Abstract

To ensure traffic safety of railway transport, non-destructive tests of rails are regularly carried out by using various approaches and methods, including eddy-current flaw detection methods. An automatic analysis of large data sets (defectograms) that come from the corresponding equipment is an actual problem. The analysis means a process of determining the presence of defective sections along with identifying structural elements of railway tracks in defectograms. At the same time, severity estimation of defined defects is also of great interest. This article continues the cycle of works devoted to the problem of automatic recognition of images of defects and rail structural elements in eddy-current defectograms. In the process of forming these images, only useful signals are taken into account, the threshold levels of amplitudes of which are determined automatically from eddy-current data. The article is devoted to the issue of constructing severity estimation of found defects with various lengths. The construction of the severity estimation is based on a concept of the generalized relative amplitude of useful signals. A relative amplitude is a ratio of an actual signal amplitude to a corresponding threshold level of useful signals. The generalized relative amplitude is calculated by using the entropy of the half-normal distribution, which is assumed to be a model for a probability distribution of an appearance of certain relative amplitudes in an evaluated defect. Tuning up the formula for calculating severity estimation of a defect is carried out on the basis of eddy-current records of structural elements. As a reference of the most dangerous defect, the bolted rail joint is considered. It models a fracture of a rail. A reference weak defect is a flash butt weld, a defectogram of which contains signals with low amplitude values. The proposed approach to severity estimation of defects is shown by examples.