Showing papers by "K. Ramesh published in 2009"

An adaptive scanning scheme for effective whole field stress separation in digital photoelasticity

Abstract: In photoelasticity, the method of obtaining the individual values of principal stresses/normal stresses separately is referred to as stress separation. Shear difference method is one of the widely used techniques for stress separation in digital photoelasticity. Normally a simple raster scanning approach is used in shear difference method in which stress separation is carried out for all the lines within the model domain by either row-wise horizontally or column-wise vertically starting from the boundary pixels. This requires the presence of a free boundary to start the integration scheme for every row of interest, which is not always possible in most of the practical problems. In order to overcome this, in this paper, an adaptive scanning scheme is proposed so that stress separation can be carried out even if there is only one free boundary pixel available in the model. The new scanning scheme is validated using the theoretically generated data for the problem of a ring subjected to internal pressure. Later, the applicability of this scheme is demonstrated by using two other example problems.

Transient thermal stress intensity factors of bimaterial interface cracks using refined three-fringe photoelasticity

Abstract: Transient thermal stresses of a bimaterial specimen with interface edge cracks subjected to heating along an edge is analysed by refined three-fringe photoelasticity (RTFP). Whole-field, noise-free, fringe order estimation using a single colour image is made possible using RTFP combined with colour adaptation. The stress intensity factors (SIFs) of the interface crack are determined through a multiparameter overdeterministic system of equations by a least-squares approach using experimental data collected automatically. The transient SIFs are found to peak to a higher value than in steady state, and the opening mode is found to be dominant. An increase in thermal load causes the crack to propagate, and this is easily visualized on the basis of quantitative fringe order data available for the whole field. The SIFs of a propagating crack are found to be low. The study shows that the crack propagates easily when the opening mode is dominant.

Effect of error in crack tip identification on the photoelastic evaluation of SIFs of interface cracks

Abstract: Digital photoelastic evaluation of stress intensity factors (SIFs) of bimaterial interface cracks using the method of least squares and the multi-parameter stress field equations is of current interest. For this, positional coordinates (with crack tip as origin) and corresponding fringe orders of data points are collected along isochromatic fringe contours in such a way that the geometric features of the fringe field are captured. Whole-field evaluation of isochromatic parameter is now made possible by various techniques of digital photoelasticity, enabling automation of the data collection procedure and collection of data points along fractional fringe orders as well. However, the identification of the crack tip, still done interactively, is prone to error. When the crack tip location is inaccurately identified, the evaluated SIFs are considerably different. The effect of error in precise identification of the crack tip on the evaluated SIFs is analyzed with the help of theoretically simulated fringe fields, in order to arrive at a technique by which the crack tip could be detected in a semiautomated fashion reducing this error in the evaluated SIFs.

Inspection of assembly stresses in an industrial chain plate using reflection photoelasticity

Abstract: Assembly stresses developed in a chain plate assembly play a critical role in the fatigue performance of the industrial chain. However, it is difficult to identify precisely the stress concentration zones and estimate its values using conventional industry-friendly tools such as the routine quality control test, pull out force test and numerical computations. In this context, reflection photoelasticity proves to be an excellent industry-friendly tool. Use of reflection photoelasticity technique has made it possible not only to instantly identify the stress concentration zones but also to quantify the stress and strain at any point on the chain plate.

Photoelastic analysis of stress frozen slices using five-step method

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.

Digital Photothermoelastic and Numerical Analysis of Transient Thermal Stresses in Cracked Bimaterial Interfaces

Abstract: Transient thermal stresses of a bimaterial specimen with interface cracks, under uniform cooling by convection, are analyzed by photothermoelasticity and a coupled temperature-displacement, finite element scheme. The stress intensity factors of the interface crack are determined by a multiparameter overdeterministic system of equations in a least-squares sense using the experimental data and by J-integral, numerically. The study showed that a normal temperature variation can lead to significant stresses due to the mismatch of thermal expansion coefficients.