T. Kasimayan

Abstract: 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.

Abstract: 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.

Abstract: In digital photoelasticity, one gets whole field information of isoclinic and isochromatic parameters based on intensity processing. Isoclinic values are undefined at isochromatic fringe contours and this appears as noise in the isoclinic phasemap which affects stress separation adversely. A new adaptive smoothing algorithm to remove the noise due to isochromatic-isoclinic interaction that automatically takes care of the isotropic points and π jumps present in the isoclinic phasemap is proposed. It is validated for the benchmark problem of a ring under diametral compression and verified for an angled bracket.

Abstract: Digital photoelasticity is a whole field experimental technique which can analyze both 2-D and 3-D models. In this paper, stress frozen 3-D models are sliced mechanically and the whole field principal stress differences (Isochromatics) and principal stress directions (Isoclinics) are evaluated by capturing only five images using the standard optical arrangements of a conventional polariscope. The wrapped isoclinic values obtained by processing the first four colour polarization stepped images in the range -π/4 to +π/4 are unwrapped using adaptive quality guided phase unwrapping algorithm to get isoclinics in the range of -π/2 to +π/2. The total fringe order is evaluated by three fringe photoelasticity or RGB photoelasticity with its latest developments like colour adaptation combined with refined three fringe photoelasticity. The methodology is validated for two slices cut from aero-structural components.

Abstract: 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.

Abstract: Gear mesh stiffness plays a very important role in gear dynamics and it varies in the presence of gear fault such as crack. The measurement of stress intensity factor can lead to the determination of gear tooth mesh stiffness variation in the presence of crack in a spur gear system. In this paper, the technique of conventional photoelasticity has been revisited to explore the possibility of using it as a supplementary technique to experimentally measure the variation of gear mesh stiffness. An attempt has been made to calculate the variation of mesh stiffness for a pinion having a cracked tooth and a gear tooth with no crack of a spur gear pair. An analytical methodology based on elastic strain energy method in conjunction with total potential energy model has been adopted and implemented within the mesh stiffness calculations. To visualize the state of stress in a structure using finite element and other currently available methods, photoelasticity is considered to be one of the oldest and most developed experimental technique. An experimental methodology based on conventional photo-elasticity technique for computing stress intensity factor (SIF) for cracked spur gear tooth is presented for different single tooth contact position and crack length. The relation between contact position, crack length, crack configuration, SIF and the variation of total effective mesh stiffness have been quantified. Finally, a comparison has been made and the results obtained from finite element method (FEM) based on linear elastic fracture mechanics (LEFM), analytical method and proposed experimental method has been outlined.

Abstract: Automatic methods of photoelasticity have had a significant progress with the development of automatic acquisition and image processing methods. This article concerns RGB photoelasticity, which allows the determination of the photoelastic retardation using, usually, a single acquisition of the isochromatic fringes in white light by a colour camera. In particular, the article presents an overview of the main characteristics of RGB photoelasticity that is influence of the quarter-wave plate error, number of acquisitions, type of light source, determination of low and high fringe orders, methods for searching the retardation, scanning procedures, calibration on a material different from that under test, combined use of the RGB and phase shifting methods. A short section on the applications of RGB photoelasticity completes the article.

Abstract: Characterization of the three-dimensional stress field of concrete materials is crucial to understanding their mechanical properties and failure mechanisms, but their hidden and complex meso-scale structure makes physically extracting and visualizing this information intractable. This paper therefore presents a new approach that uses 3D printed models based on X-ray microfocus computed tomography (CT) imaging of a concrete sample to replicate its complex aggregate structure in a transparent matrix. The associated three-dimensional stress field is visually characterized at mesoscale through uniaxial compression tests and photoelastic techniques that incorporate a three-dimensional frozen-stress test to analyse the effects of randomly distributed aggregates. These results are used to validate the accuracy of simulated data created using the finite element method, which allows a comparison to be made between two-dimensional and three-dimensional heterogeneous aggregated models. The study indicates that meso-heterogeneity has more influence on the stress state of localized areas than the entire field. Compared to 2D structures, 3D structures possess a lower stress concentration due to the lateral inertial confinement effect. The difference in stress field between the two structure types is therefore attributable to a combination of structural heterogeneity and lateral inertial confinement.

Abstract: Keywords: Speckle interferometry ; Digital holographic interferometry ; Digital image correlation ; Fringe projection profilometry ; Digital photoelasticity Reference EPFL-ARTICLE-222716doi:10.1016/j.optlaseng.2016.05.002View record in Web of Science Record created on 2016-10-26, modified on 2017-03-09