PhotoelasticityYang Dai

Introduction

• Initiated at turn of 20th century• Experimental stress analysis method• Widely used

Photoelastic Material

• Transparent Material– Glass– Plastic– Epoxy resin

• Double refraction

Experimental Equipment

• Polarized light• Vibrate along principal

stress direction• Speed proportional to

stress magnitude• Interference Pattern

Fringe Pattern

• Isochromatic fringe– Related to stress

difference• Isoclinic fringe

– Related to stress direction

Analysis

• Stress-optic law

n- the reflective indexC-stress-optical

coefficientσ -the principle stress

)( 21 σσ −= Cn

Pattern Interpretation

• More lines-higher stress

• Close lines-more concentrated stress

3D Analysis

• Stress freezing• Section model• 2D analysis of each

section• Build 3D stress

picture

Disadvantage

• Not real model• Impossible to model perfectly• Need separate model for each

load,appliance

Application

• Overshadow by FEM

• Validate the FEM • Verify the stress

concentration site

Reference

• Ramesh,K. Digital Photoelasticity Springer,2000• Lau,C.Y.;Teoh,S.H. 3D Photoelastic Stress Analysis of the

femur• http://www.msm.cam.ac.uk/doitpoms/tlplib/photoelasticity/Introd

uction to Photoelasticity