Experimental Mechanics DOI 10.1007/s11340-016-0134-5 A Revisit to the Frozen Stress Phenomena in Photoelasticity D. Swain 1 · J. Philip 1 · S.A. Pillai 1 · K. Ramesh 2 Received: 17 April 2015 / Accepted: 19 January 2016 © Society for Experimental Mechanics 2016 Abstract Stress freezing in photoelasticity is regularly employed for 3-D elastic stress analysis of geometrically complex models, wherein the models under load are soaked at the stress freezing temperature and slowly cooled to room temperature. During this process, a model may distort or fail undergoing large deformations at the stress freezing temperature owing to thermo-mechanical interactions. The contribution of thermal deformation to the model distortions is neglected in the available literature of stress freezing. This aspect of stress freezing is investigated in this paper, wherein Digital Image Correlation (DIC) is used to study the strain behavior during a complete stress freezing cycle for an epoxy made of CY230 resin cured with HY951 hard- ener. The results show that the thermal contributions to the model distortions at the critical temperature must be taken care of to estimate the failure margins. The distor- tions and failures would mainly depend upon the thermal and mechanical response of the model material and the complexity of the model. Keywords Photoelasticity · 3-D Stress analysis · Stress freezing · Digital image correlation (DIC) · Thermal deformations · Model distortion and failure K. Ramesh is a SEM Member  D. Swain digendranath@gmail.com 1 Experimental Mechanics Division, Vikram Sarabhai Space Center, Indian Space Research Organization, Thiruvananthapuram, Kerala, 695 022, India 2 Department of Applied Mechanics, Indian Institute of Technology Madras, Chennai, India Introduction Photoelasticity is one of the popular techniques for experi- mental stress analysis. Stress analysis with two-dimensional (2-D) models in photoelasticity is often sufficient for spec- imen level and simple model studies. However, real life mechanical components are more complex to carry out stress analysis using simple 2-D models [1]. Hence, three- dimensional (3-D) stress analysis is practised to measure the stresses at interior critical locations of geometrically complex models [2, 3]. With the advent of modern manufac- turing capabilities such as rapid tooling, rapid prototyping, and stereolithogrphy [4, 5] and digital photoelasticity [6], 3- D stress analysis using photoelasticity would be an attractive alternative to finite element analysis (FEA). Nevertheless, photoelasticity is currently used as a valuable experimen- tal tool to verify and validate critical and complex designs wherein joints, tolerances and gaps have to be analyzed accurately [7], which are otherwise difficult to handle with analytical and computational techniques. Three-dimensional stress analysis in photoelasticity uses a unique technique of locking the birefringence and defor- mations permanently into a model known as ‘frozen stress technique’ [3, 8]. The models undergo a temperature cycle to achieve this, wherein the models under the desired loads are heated to and soaked at the stress freezing temperature, then slowly cooled to the room temperature to avoid ther- mal quenching. Subsequently the models are unloaded at the room temperature. After stress freezing, the desired slices are sawed out and interrogated in a polariscope to measure the stresses [9]. These stresses are known as model stresses, which are then scaled up/down to find prototype stresses. For such a scaling, the geometric deviations due to model deformations during stress freezing must be minimal [8, 10]. Furthermore, the locked in deformations in the model