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Improved Corner Detection by Ultrasonic Testing using Phase Analysis
University West, Department of Engineering Science, Division of Mechanical Engineering. (PTW)ORCID iD: 0000-0001-7748-0565
University West, Department of Engineering Science, Division of Mechanical Engineering. (PTW)ORCID iD: 0000-0001-6933-375X
University West, Department of Engineering Science, Division of Mechanical Engineering. (PTW)
2013 (English)In: Ultrasonics, ISSN 0041-624X, E-ISSN 1874-9968, Vol. 53, no 2, p. 630-634Article in journal (Refereed) Published
Abstract [en]

In ultrasonic testing, corners are used for sensitivity calibration in the form of notches, for measuring the sound velocity in the material, and as known reference points during testing. A 90° corner will always reflect incoming waves in the opposite direction due to a double reflection and therefore give a strong echo. This article presents a method for separating the echo from a corner from other echoes and more accurately find the position of the corner. The method is based on analysing the phase of the reflected signal. The proposed method was tested on a steel calibration block and the width of the indication was reduced by up to 50% compared to the amplitude signal. This results in a more accurate positioning of the corner. Using the phase instead of the amplitude will also improve the reliability, since reflections other than from corners will disappear.

Place, publisher, year, edition, pages
Elsevier, 2013. Vol. 53, no 2, p. 630-634
Keywords [en]
phase, ultrasound, non-destructive testing, corner, calibration, WIL, Work-integrated Learning
Keywords [sv]
AIL
National Category
Signal Processing
Research subject
ENGINEERING, Physics; Work Integrated Learning
Identifiers
URN: urn:nbn:se:hv:diva-4112DOI: 10.1016/j.ultras.2012.10.015ISI: 000311488800039Scopus ID: 2-s2.0-84870250647OAI: oai:DiVA.org:hv-4112DiVA, id: diva2:483833
Projects
ANDTEAvailable from: 2012-01-26 Created: 2012-01-26 Last updated: 2017-12-08Bibliographically approved
In thesis
1. Towards Automation of Non-Destructive Testing of Welds
Open this publication in new window or tab >>Towards Automation of Non-Destructive Testing of Welds
2011 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

All welding processes can give rise to defects that will weaken the joint and can lead to failure of the welded structure. Because of this, non-destructive testing (NDT) of welds have become increasingly important to ensure the structural integrity when the material becomes thinner and stronger and welds become smaller; all to reduce weight in order to save material and reduce emissions due to lighter constructions.

Several NDT methods exists for testing welds and they all have their advantages and disadvantages when it comes to the types and sizes of defects that are detectable, but also in the ability to automate the method. Several methods were compared using common weld defects to determine which method or methods were best suited for automated NDT of welds. The methods compared were radiography, phased array ultrasound, eddy current, thermography and shearography. Phased array ultrasound was deemed most suitable for detecting the weld defects used in the comparison and for automation and was therefore chosen to be used in the continuation of this work. Thermography was shown to be useful for detecting surface defects; something not easily detected using ultrasound. A combination of these techniques will be able to find most weld defects of interest.

Automation of NDT can be split into two separate areas; mechanisation of the testing and automation of the analysis, both presenting their own difficulties. The problem of mechanising the testing has been solved for simple geometries but for more general welds it will require a more advance system using an industrial robot or similar. Automation of the analysis of phased array ultrasound data consists of detection, sizing, positioning and classification of defects. There are several problems to solve before a completely automatic analysis can be made, including positioning of the data, improving signal quality, segmenting the images and classifying the defects. As a step on the way towards positioning of the data, and thereby easing the analysis, the phase of the signal was studied. It was shown that the phase can be used for finding corners in the image and will also improve the ability to position the corner as compared to using the amplitude of the signal. Further work will have to be done to improve the signal in order to reliably analyse the data automatically.

Place, publisher, year, edition, pages
Luleå: Luleå tekniska universitet, 2011. p. 42
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
Keywords
Welding, non-destructive testing, NDT
National Category
Computer Vision and Robotics (Autonomous Systems) Fluid Mechanics and Acoustics Applied Mechanics
Research subject
ENGINEERING, Industrial engineering
Identifiers
urn:nbn:se:hv:diva-4122 (URN)978-91-7439-352-1 (ISBN)
Presentation
2011-12-19, E246, Luleå tekniska universitet, Luleå, 10:00 (Swedish)
Opponent
Supervisors
Available from: 2012-02-08 Created: 2012-02-02 Last updated: 2018-01-12Bibliographically approved
2. Imaging and analysis methods for automated weld inspection
Open this publication in new window or tab >>Imaging and analysis methods for automated weld inspection
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

All welding processes can give rise to defects, which weakens the joint and can eventually lead to the failure of the welded structure. In order to inspect welds for detects, without affecting the usability of the product, non-destructive testing (NDT) is needed. NDT includes a wide range of different techniques, based on different physical principles, each with its advantages and disadvantages. The testing is often performed manually by a skilled operator and in many cases only as spot-checks. Today the trend in industry is to move towards thinner material, in order to save weight for cost and for environmental reasons. The need for inspection of a larger portion of welds therefore increases and there is an increasing demand for fully automated inspection, including both the mechanised testing and the automatic analysis of the result. Compared to manual inspection, an automated solution has advantages when it comes to speed, cost and reliability. A comparison of several NDT methods was therefore first performed in order to determine which methods have most potential for automated weld inspection. Automated analysis of NDT data poses several difficulties compared to manual data evaluation. It is often possible for an operator to detect defects even in noisy data, through experience and knowledge about the part being tested. Automatic analysis algorithms on the other hand suffer greatly from both random noise as well as indications that originate from geometrical variations. The solution to this problem is not always obvious. Some NDT techniques might not be suitable for automated inspection and will have to be replaced by other, better adapted methods. One such method that has been developed during this work is thermography for the detection of surface cracks. This technique offers several advantages, in terms of automation, compared to existing methods. Some techniques on the other hand cannot be easily replaced. Here the focus is instead to prepare the data for automated analysis, using various pre-processing algorithms, in order to reduce noise and remove indications from sources other than defects. One such method is ultrasonic testing, which has a good ability for detecting internal defects but suffers from noisy signals with low spatial resolution. Work was here done in order to separate indications from corners from other indications. This can also help to improve positioning of the data and thereby classification of defects. The problem of low resolution was handled by using a deconvolution algorithm in order to reduce the effect of the spread of the beam.The next step in an automated analysis system is to go beyond just detection and start characterising defects. Using knowledge of the physical principles behind the NDT method in question and how the properties of a defect affect the measurement, it is sometimes possible to develop methods for determining properties such as the size and shape of a defect. This kind of characterisation of a defect is often difficult to do in the raw data, and is therefore an area where automated analysis can go beyond what is possible for an operator during manual inspection. This was shown for flash thermography, where an analysis method was developed that could determine the size, shape and depth of a defect. Similarly for laser ultrasound, a method was developed for determining the size of a defect.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2014. p. viii, 68 s.
Series
Doctoral thesis / Luleå University of Technology, ISSN 1402-1544
Keywords
Welding, materials
National Category
Materials Engineering
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-6696 (URN)978-91-7439-931-8 (ISBN)978-91-7439-932-5 (ISBN)
Opponent
Available from: 2014-09-17 Created: 2014-09-17 Last updated: 2016-02-08Bibliographically approved

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Broberg, PatrikRunnemalm, Anna

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