Showing papers by "K. Ramesh published in 2000"

Digital Photoelasticity: Advanced Techniques and Applications

Abstract: Transmission Photoelasticity.- Reflection Photoelasticity.- Digital Image Processing.- Fringe Multiplication.- Fringe Thinning and Fringe Clustering.- Phase Shifting, Polarization Stepping and Fourier Transform Methods.- Phase Unwrapping and Optically Enhanced Tiling in Digital Photoelasticity.- Colour Image Processing Techniques.- Evaluation of Contact Stress Parameters and Fracture Parameters.- Stress Separation Techniques.- Fusion of Digital Photoelasticity, Rapid Prototyping and Rapid Tooling Technologies.- Recent Developments and Future Trends.

Recent Developments and Future Trends

Abstract: The application of digital techniques for data acquisition in 2-D transmission photoelasticity and reflection photoelasticity is well developed and these were discussed in the earlier chapters. The extension of digital techniques for data acquisition to integrated photoelasticity and scattered light photoelasticity have just made a beginning. In integrated photoelasticity, one has to determine three parameters experimentally and these are known as characteristic parameters. In scattered light photoelasticity, the illumination levels are quite low due to light scattering. This necessitates the use of high-resolution CCD cameras. The ultimate aim of integrated photoelasticity or scattered light photoelasticity is to evaluate the stress field interior to the model. The current developments on tensorial tomography are discussed in this chapter.

Stress Separation Techniques

Abstract: Photoelasticity directly provides the information of principal stress difference and the orientation of the principal stress direction at the point of interest. Using these, one can find the normal stress difference and in-plane shear stress by invoking equations in mechanics of solids or Mohr’s circle.

Evaluation of Contact Stress and Fracture Parameters

Abstract: In many mechanical devices, there exist contact between two or more parts such as in gears, rolling element bearings, locomotive wheels and rails etc. The stresses caused by the pressure distribution between the bodies in contact are of importance in the design of these parts. Hertz [1] pointed out that in the absence of friction, the maximum shear stress occurs beneath the surface of contacting bodies. This leads to pitting of the contacting surfaces. The material lost from the surface due to pitting may get trapped into the contacting surfaces, causing abrasive wear. Smith and Liu [2] studied the effect of friction between the contacting surfaces. They reported that under certain conditions, the point of maximum shear stress could also occur at the surface of contacting bodies. The knowledge of contact zone and coefficient of friction between the contacting bodies is essential for evaluating the design of such contacting elements.

Phase Shifting, Polarization Stepping and Fourier Transform Methods

Abstract: In the previous chapter, data acquisition by fringe skeleton identification was discussed. The skeleton identification became much simpler and effective if intensity variations over the fringe field were also taken into account. In view of skeleton identification, the data being collected is restricted to these zones. In the early stages of automatic acquisition of photoelastic data, several point-by-point methods were proposed which also utilised intensity information for automation. In these techniques, either the analyzer/polarizer or the compensator is rotated continuously to produce a modulated intensity signal at the point of interest. Data is recorded based on either the intensity signal is monitored for its minimum value or the phase of the modulated signal is compared with that of a reference signal [1-11]. Thus, the use of intensity information in some form has always attracted researchers to improve the methodology of data acquisition in photoelasticity.

Colour Image Processing Techniques

Abstract: With rapid advancements in computer technology, colour image processing systems are now available at affordable prices. A proper understanding of the colour image processing techniques requires an understanding of the various models for colour representation. Apart from this, one needs to know the spectral response of the colour camera and the light source. The type of colour image processing hardware used for transmission or reflection photoelastic analysis has an influence on the quality of data acquisition. Data interpretation and analysis requires the understanding of the intensity of light transmitted, for various polariscope arrangements, in white light

Fringe Multiplication, Fringe Thinning and Fringe Clustering

Abstract: Isochromatics and isoclinics are the two fringe contours obtained in a photoelastic experiment. Isochromatics are contours of constant principal stress difference and isoclinics are the loci of points along which the principal stress orientation (with respect to a reference axis) is a constant. For stress analysis at any point, the photoelastic data required are, 1. The isochromatic fringe order and 2. The isoclinic parameter at that point.

Phase Unwrapping and Optically Enhanced Tiling in Digital Photoelasticity

Abstract: In the previous chapter, various techniques to obtain fractional retardation over the complete model domain have been presented. In these techniques, the fractional retardation is represented as a phase map. In the phase map, the fractional fringe orders in the range of 0-1 are represented as an intensity map of 0-255. For practical utilisation of the data, one has to find the total fringe order over the domain. This is achieved by a process called phase unwrapping. For phase unwrapping to be effective, the phase map should be free of noise and discontinuities.