Colour adaptation techniques are useful in extending the method of Twelve fringe photoelasticity (TFP) to solve problems in industries as one can minimise the generation of specific calibration tables for each experiment. Image artefacts affect the functioning of existing colour adaptation techniques affecting the fringe order demodulation. Colour transfer is a popular technique in the field of image processing to tackle colour mismatch between images. In this paper, the applicability of two colour transfer strategies in the context of TFP is explored, of which one is selected for implementation. A comparative study on the performance of the novel colour transfer method with the existing colour adaptation techniques is carried out. © 2019 Elsevier Ltd

Krishnamurthi Ramesh

Department of Applied Mechanics

Color

ELASTICITY

Image processing

Photoelasticity

Physical optics

Principal component analysis

ADAPTATION TECHNIQUES

Comparative studies

DIGITAL PHOTOELASTICITY

FRINGE ORDERS

IMAGE ARTEFACTS

TRANSFER METHOD

TRANSFER STRATEGIES

TRANSFER TECHNIQUE

Color image processing

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Optics and Lasers in Engineering

In white light photoelasticity, the fringe order at a point of interest is resolved by comparing the colour data with a calibration table recorded experimentally. Recently, some researchers have proposed the idea of using a theoretical calibration table if the application image is normalized. In this paper, a systematic study is carried out on the applicability of the theoretical calibration table for fringe demodulation. A novel normalization methodology is developed to improve the dynamic range in both low and high fringe density areas. It is demonstrated that while applying normalization for stretching the dynamic range, one has to use only an experimentally recorded calibration table that is normalized. Specific advantages of using colour adaptation or fringe demodulation by normalization in certain practical situations is discussed. © 2018 Elsevier Ltd

An improved normalization technique for white light photoelasticity

Varied spatial resolution of isochromatic fringes over the domain influences the accuracy of fringe order estimation using TFP/RGB photoelasticity. This has been brought out in the first part of the work. The existing scanning schemes do not take this into account, which leads to the propagation of noise from the low spatial resolution zones. In this paper, a method is proposed for creating a whole field map which represents the spatial resolution of the isochromatic fringe pattern. A novel scanning scheme is then proposed whose progression is guided by the spatial resolution of the fringes in the isochromatic image. The efficacy of the scanning scheme is demonstrated using three problems – an inclined crack under bi-axial loading, a thick ring subjected to internal pressure and a stress frozen specimen of an aerospace component. The proposed scheme has use in a range of applications. The scanning scheme is effective even if the model has random zones of noise which is demonstrated using a plate subjected to concentrated load. This aspect is well utilised to extract fringe data from thin slices cut from a stereo-lithographic model that has characteristic random noise due to layered manufacturing. © 2016 Elsevier Ltd

Scanning schemes in white light photoelasticity – Part II: Novel fringe resolution guided scanning scheme

The use of single-colour image for determining the fringe orders in digital photoelasticity has gained importance in recent years, and in this, the fringe orders are obtained by comparing the colour information at each pixel of the model image using a calibration table. They were originally used for identifying fringe orders of up to 3, and there have been attempts to extend this to higher fringe orders. The methods proposed were tested only for the special case of the application specimen where the fringe signature is similar to that in the calibration specimen for fringe orders beyond 3. In this article, various colour difference formulae are studied, and a new colour difference formula is proposed to handle fringes beyond 3. The advantage of the new colour difference formula is illustrated for the problem of a thick ring subjected to internal pressure and a finite plate with a hole. A new multi-directional smoothing methodology is proposed to smooth the fringe order obtained. The results are compared with those obtained by 10-step phase shifting technique. Advancing front scanning approach coupled with multiple seed points is used to solve a variety of problems in which both the geometry and the fringe signature are quite different from the calibration specimen. The influence of seed point selection is brought out by solving the problem of a plate with a hole having up to 15 fringe orders. New approaches to handle noisy industrial images are also dealt with. © Institution of Mechanical Engineers 2015.

Journal of Strain Analysis for Engineering Design

New initiatives in single-colour image-based fringe order estimation in digital photoelasticity

A new technique used to tune the color code table developed for one specimen in three fringe photoelasticity (TFP) for another specimen that may have some color variation was investigated. A calibration table needs to be generated with RGB values assigned with known fringe orders in TFP/refined three fringe photoelasticity (RGBP). A beam under 4-point bending was conventionally used to generate the calibration table as the variation in fringe order is known to be linear across the depth of the beam. The use of a single calibration table could help to simplify the use of TFP in an industrial environment. It can be done by suitably modifying the RGB variation of the calibration table in such a way that it matches the application specimen. The proposed method finds applicability in analyzing stress-frozen slices and could be extended for transient problems. The validity of the proposed technique was demonstrated using a 4-point bend specimen and the benchmark problem of a disc under diametral compression.

Experimental Techniques

Colour adaptation in three fringe photoelasticity using a single image

In three fringe photoelasticity, a single colour isochromatic image is used to estimate the total fringe order by comparing the colour at each point with that of a calibration table. The generation of the calibration table is critical, and certain nuances involved therein are brought out in this paper. Ideally, the same specimen material and lighting conditions must be used for both the calibration and application experiments, which are often not possible in an industrial scenario, and colour adaptation is a simple way of suitably modifying the calibration table. Till date, only experimental analyses of the colour adaptation procedures are available in the literature; in this paper, the colour adaptation procedures are investigated from an analytical viewpoint. This study has brought out that a two-point colour adaptation scheme accounts not only for tint variation between the calibration and application specimens, but also for ambient illumination. This finding has also been experimentally verified for a benchmark problem, and thereafter extended for reflection photoelastic analyses. © 2010 Elsevier Ltd. All rights reserved.

Journal	Data powered by TypesetOptics and Lasers in Engineering
Publisher	Data powered by TypesetElsevier Ltd
ISSN	01438166
Open Access	No