Papers by Author: K. Ramesh

Abstract: The stresses and its distribution in complex shape chain plate geometry play a critical role in the fatigue life performance of a chain assembly. However, it is difficult to identify the stress distribution and stress concentration zones precisely using only the conventional industrial friendly tools such as routine quality control test, breaking load test and numerical computations. In this context the transmission photoelastic technique has made it possible to identify the stress distribution, its concentration and also to quantify the stress and strain at any point in the chain plate. This paper explains how transmission photoelastic technique is used to estimate the stress distribution and its concentration zones in a complex chain plate when it is loaded.

Abstract: Digital photoelasticity is an experimental method for determining stresses in 2D and 3D models. In digital photoelasticity one gets a wrapped isoclinic phasemap. The main issue with wrapped isoclinic phasemaps is that the isoclinic values obtained do not uniformly represent the principal stress direction of one of the principal stresses consistently over the entire domain. These zones are labelled as inconsistent zones. Such zones need to be identified and corrected to get unwrapped values of continuous isoclinic phase values. In this paper, a method is developed to plot the simulated wrapped and unwrapped isoclinic phasemap from 2D Finite Element (FE) results so that one can use this as a convenient tool for identification and correction of inconsistent zones in isoclinic phasemaps obtained experimentally for complex problems. The method is explained by using the problem of a circular disc under diametral compression. The application of this method for handling complex problems is demonstrated by solving the cantilever bending of a binocular specimen.

Abstract: Photoelasticity is one of the most widely used techniques for experimental stress and strain analysis. With the availability of low cost digital image processing systems, a separate branch of photoelasticity known as digital photoelasticity came into existence providing whole-field values of the isoclinics (θ) and isochromatics (N) in a true sense. Among the several methods available for data acquisition, phase shifting / polarization stepping techniques are most widely used for their simplicity and accuracy. In this paper a new digital photoelastic method based on phase shifting using monochromatic light source is presented. It provides full field values of θ and N. The arrangement is carefully chosen with the intention of reducing the influence of quarter wave mismatch error in the evaluation of θ and N. The methodology is validated for the benchmark problem of a disk under diametral compression.

Abstract: The main sources of error in the determination of stress intensity factors (SIFs) for an interface crack in a bi-material by conventional photoelasticity are the measurement of the positional co-ordinates of the data point and the fringe order. In the present work, use of two digital photoelasticity methods for collecting these data is discussed. SIFs are evaluated using constant radius method and a least squares approach based on the singular stress field equation. The need for developing a multi-parameter stress field solution for evaluating SIF is highlighted.