The algorithm of crack and crack tip coordinates detection in optical images during fatigue test

S V Panin,P S Lyubutin,V V Titkov,V O Chemezov

doi:10.1088/1757-899x/177/1/012019

Abstract

An algorithm of crack detection during fatigue testing of materials, designed to automate the process of cyclic loading and tracking the crack tip, is proposed and tested. The ultimate goal of the study is aimed at controlling the displacements of the optical system with regard to the specimen under fatigue loading to ensure observation of the ‘area of interest’. It is shown that the image region that contains the crack may be detected and positioned with an average error of 1.93%. In terms of determining the crack tip position, the algorithm provides the accuracy of its localization with the average error value of 56 pixels.

Highlights

When studying the fatigue fracture of solids, the problem of estimating crack growth parameters is one of the most important
The commercial systems, like VIC 3D, Strain Master [3, 4] and others first of all in their stereoscopic realization have become very popular for appreciable aiding the experimental mechanics. These systems comprise a pair of TV cameras operating in a macro shooting mode. They are usually aimed at obtaining the macroscale pattern of strain distribution on the surface of the specimen under loading
From the point of view of physical mesomechanics and fracture mechanics, the studies involving the crack with the length not exceeding tens of microns are of particular interest

Summary

Introduction

When studying the fatigue fracture of solids, the problem of estimating crack growth parameters (length, growth rate, crack opening displacement, etc.) is one of the most important. The commercial systems, like VIC 3D, Strain Master [3, 4] and others first of all in their stereoscopic realization have become very popular for appreciable aiding the experimental mechanics These systems comprise a pair of TV cameras operating in a macro shooting mode. From the point of view of physical mesomechanics and fracture mechanics, the studies involving the crack with the length not exceeding tens of microns are of particular interest. In this case, the crack growth observation at macroscale is impossible because the spatial resolution does not resolve the crack as well as the processes developing at its tip

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