# Experimental Evaluation of Mixed Mode Stress Intensity Factor for Prediction of Crack Growth by Phoelastic Method

## Abstract

Determination of stress intensity factors *K* _{I}, *K* _{II}, and constant stress term, *σ* _{ ox } is investigated. A theory of determining the stress intensity factors using photo-elastic method is formulated taking three stress terms. Three-parameter method of fracture analysis for determining the mixed mode stress intensity factors under biaxial loading conditions from photo-elastic isochromatic fringe data is used. A special biaxial test rig is designed and fabricated for loading the specimen biaxially. A simplified and accurate method is proposed to collect the data from isochromatic fringes. Taking specimen geometry and boundary conditions into account, regression models are developed for estimation of fracture parameters.

## Keywords

Mixed mode fracture Stress intensity factor Biaxial load Crack angle## List of Symbols

- 2
*a* Crack length

*C*_{n}Experimental constant

- \( f_{\sigma } \)
Material fringe value

*E*Modulus of elasticity

*L*Length of the specimen

*W*Width of the specimen

*N*Fringe order

*t*Specimen thickness

*r, θ*Polar coordinates

*K*_{I},*K*_{II}Mode I and mode II stress intensity factor

*β*_{1, k}Biaxial load factor

*α*Crack angle

*f*_{i}(..)Function

*n*Number of stress terms

*σ*_{1},*σ*_{2}Principal stresses

*σ*_{x},*σ*_{y,}*τ*_{xy}Stress components

*τ*_{m}Maximum shear stress

*σ*_{0}Yield strength

*υ*Poisson’s ratio

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