American Journal of Mechanical Engineering, 2014, Vol. 2, No. 7, 239-243 Available online at http://pubs.sciepub.com/ajme/2/7/13 © Science and Education Publishing DOI:10.12691/ajme-2-7-13 Characteristic Entities in PhotoStress Method Peter Frankovský 1,* , František Trebuňa 2 , Ján Kostka 2 , František Šimčák 2 , Oskar Ostertag 2 , Władysław Papacz 3 1 Department of Mechatronics, Faculty of Mechanical Engineering, Technical University of Košice, Košice, Slovakia 2 Department of Applied Mechanics and Mechatronics, Faculty of Mechanical Engineering, Technical University of Košice, Košice, Slovakia 3 Instytut Budowy i Eksploatacji Maszyn, Uniwersytet Zielonogórski, Zielona Góra, Poland *Corresponding author: peter.frankovsky@tuke.sk Received September 15, 2014; Revised October 01, 2014; Accepted October 30, 2014 Abstract The presented paper describes characteristic entities in PhotoStress method - isoclinic fringes, singular points, isostatic lines, and isochromatic fringes. These entities are used in PhotoStress method to visualise and quantify deformation and stress fields of various photoelastically coated structural elements. Keywords: isoclinic fringes, singular points, isostatic lines, isochromatic fringes Cite This Article: Peter Frankovský, František Trebuňa, Ján Kostka, František Šimčák, Oskar Ostertag, and Władysław Papacz, “Characteristic Entities in PhotoStress Method.” American Journal of Mechanical Engineering, vol. 2, no. 7 (2014): 239-243. doi: 10.12691/ajme-2-7-13. 1. Introduction Reflection photoelasticity or PhotoStress method is an experimental method of mechanics which allows quantitative as well as qualitative analysis of directions and magnitudes of principal strains or principal normal stresses on a variety of structural elements. Being universal, this method can be used in a variety of engineering applications such as structural analysis of engines, analysis of architectural structure solutions, development of prosthetic implants, development of structural components of planes, machines etc. A photoelastic coating is used for the evaluation of deformation. This coating is applied with a special two- component adhesive on the analysed surface of the object under examination. When the object, which is subjected to loads, is illuminated with light from the reflection polariscope, it is possible to view isoclinic or isochromatic fringes, based on the polariscope settings. For the purposes of a quantitative evaluation it is necessary to be familiar with parameters of isoclinic and isochromatic fringes in points of measurements. This paper presents the procedure of obtaining individual photoelastic entities, as well as a description of these entities. 2. Isoclinic Fringes Isoclinic fringes (Figure 1) are defined as geometrical points in which directions of principal normal stresses are parallel to intersected polarisation planes of the polariser and the analyser. They occur at plane-polarised white light. Isoclinic fringes of a particular angle parameter α are related to a chosen direction of intersected polarisation planes of the polariser and the analyser, which is given by angle α or /2 α π + [1,2]. The creation of isoclines with regards to angle parameter α is a periodical phenomenon with period /2 π . With synchronous rotation of the polariser and the analyser, isoclinic fringes continuously change from the isoclines of angle parameter 0 α = ° up to angle parameter 90 α = ° in line with rotation angle of the polariser and the analyser. Figure 1. Isoclinic fringes The creation of isoclines with regards to angle parameter α is a periodical phenomenon with period /2 π . With synchronous rotation of the polariser and the analyser, isoclinic fringes continuously change from the isoclines of angle parameter 0 α = ° up to angle parameter 90 α = ° in line with rotation angle of the polariser and the analyser. They are distributed along whole analysed surface of the object under examination simultaneously according to the changes in directions of principal normal stresses. The isoclinic fringe runs through every point of