Whole field evaluation of stress components in digital photoelasticity—Issues, implementation and application

Digital photoelasticity has rapidly progressed in the last few years and has matured into an industry-friendly technique. This review thematically classifies all the developments in digital photoelasticity and highlights the relative merits and drawbacks of the various techniques. The overall objective is to provide enough information and guidance to allow an end-user to make an informed choice on the type of technique to be used in a particular situation.

Digital photoelasticity – A comprehensive review

Review of RGB photoelasticity

Digital photoelasticity: Recent developments and diverse applications

With advancements in digital image processing and data acquisition, a separate branch of photoelasticity namely digital photoelasticity came into existence. Here, intensity information of the acquired image is used for the evaluation of whole-field photoelastic parameters. Digital photoelasticity provides only wrapped phasemaps of isoclinics and isochromatics and they have to be unwrapped in different ways for getting the continuous-phase values. In the case of the isochromatic phasemap, ambiguity removal prior to unwrapping is essential. In this paper, a 10-step phase-shifting methodology is proposed and a new strategy for obtaining the isochromatic phasemap free of ambiguity is demonstrated. Isoclinic unwrapping is performed by a new adaptive quality guided algorithm. Adaptive in the sense that isoclinic phase unwrapping is done autonomously even in the presence of isotropic points/π jumps occurring in the isoclinic phasemap. The isochromatic phasemap is also unwrapped using the quality guided path follower. The methodology is validated for the problem of a ring under diametral compression and later shown for three other models which have complex stress fields. Wherever possible, the parameters obtained by the new methodology are compared with analytical or numerical methods and the comparison is quite good.

Adaptive Quality Guided Phase Unwrapping Algorithm for Whole-Field Digital Photoelastic Parameter Estimation of Complex Models

Noise removal in three-fringe photoelasticity by adaptive colour difference estimation

Three fringe photoelasticity (TFP) can give the total fringe order from a single colour isochromatic fringe field by suitably comparing the colour with a calibration specimen. The fringe order evaluation can be erroneous when the materials for the calibration specimen and the application specimen are different. This is because of the colour variation between the two materials. This is conventionally handled by preparing individual calibration tables for each application. A new methodology to tune the calibration table obtained for a single material to accommodate the tint variation in TFP is proposed for the use of different specimen materials. Discontinuities in fringe order variation are smoothed using the refined TFP (RTFP) procedure. The elegance of the new methodology for solving a multi-material system is bought out by solving the problem of a bi-material Brazilian disc. The results obtained are compared with the phase shifting technique.

Colour Adaptation in Three Fringe Photoelasticity

New Boundary Information Encoding and Autoseeding for Effective Phase Unwrapping of Specimens with Cutouts

Phasemaps obtained by phase-shifting techniques contain ambiguous zones. To obtain total fringe order by phase unwrapping, the phasemap should be corrected for ambiguity. Each available ambiguity removal method can resolve ambiguity for only a class of problems. Appropriate selection of these algorithms and their combination for a specific case can give a better result. A comprehensive ambiguity removal methodology is demonstrated in this paper. Disturbance in the intensity pattern of the phase shifted images due to lines and marks on the models lead to noise in phasemaps. This in turn affects the ambiguity removal and unwrapping procedures. A methodology has also been proposed to remove the lines and marks from the phase-shifted images.

New initiatives in phase unwrapping in digital photoelasticity

The global marine ornamental fish trade is dominated by wild collected fishes, and the contribution from hatchery production is less than 10% of the total. Hatchery production is considered to be the only long-term sustainable option to reduce the fishing pressure on the wild population and also to safeguard the delicate coral reef ecosystem, which houses most of the marine ornamental species. Among the hatchery-produced fishes that are being traded, clown fishes form a dominant group, and a recent addition to this list is the designer clown fishes, which are costlier than other clown fishes due to their rare and attractive color patterns. However, ambiguities about designer clown fish such as its production (wild caught, captive bred, or genetically modified) and taxonomic identity still exist among the general public and hobbyists, as scientific reports on these aspects have not yet been published, even though few aquaculture companies display the photos of designer clown fishes in their websites. The common names for designer clown fishes (such as Platinum, Picasso, and snowflake) have been given by the aquaculture companies/traders solely based on the color patterns or designs on the fish body. The paper describes in detail the production of designer clown fish through captive breeding, followed by elucidating the taxonomic identity of two easily distinguishable designer clown fishes, viz., Picasso and Platinum. Both classical taxonomic tools and molecular methods were employed to elucidate the taxonomic identity. The morpho-merisitic characteristics of Picasso and Platinum were similar to those of Amphiprion percula. The partial cytochrome c-oxidase subunit I (COI) sequences of Picasso and Platinum clown fishes were submitted to the National Center for Biotechnology Information (NCBI) GenBank with accession numbers MT947238 and MT947239, respectively, which had maximum similarity to sequences of A. percula already deposited in the NCBI GenBank. The designer clown fishes exhibited protandrous hermaphroditism with monogamous mating behavior. Their egg incubation period ranged from 7 to 8 days, and the larval rearing was carried out with live feeds such as rotifers and Artemia under the greenwater technique using microalgae, Nannochloropsis oculata. This paper can thus unravel the ambiguities related to the production of designer clown fishes as well as their taxonomy.

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K. R. Madhu

Papers

Noise removal in three-fringe photoelasticity by adaptive colour difference estimation

Colour Adaptation in Three Fringe Photoelasticity

New Boundary Information Encoding and Autoseeding for Effective Phase Unwrapping of Specimens with Cutouts

New initiatives in phase unwrapping in digital photoelasticity

Designer clown fishes: Unraveling the ambiguities