A SIMPLE METHOD FOR DETERMINATION OF THE FRACTURE-MECHANICS GEOMETRIC PARAMETER KI

The method discussed in this paper describes a three parameter method of analysis for accurate detrmination of the stress intensity factor (SIF) using the crack tip stress field information given by photoelasticity. The sole objective is, in fact, to determaine a specific parameter or set of parameters which when used with the experimental results provide, the best match between the experimental and analytical results. A new three parameter method is using information from only one fringe loop is introduced which followes the method developed by Fattah, flj for determination of mixed mode stress intensity factors (K1 and KII). The three parameter used in the present method are, σox= αK/√2πa, which acts parallel to the direction of the crack extension, the stress intensity factor (KI) and a parameter β which is a term added to the Westergaard stress function to provide one more degree of freedom. A new simple formula for β determination has been introduced in this analysis to take care of fare field stresses, finite dimension, crack tilt angle and curvature effects. A method of solution based on measurements rm , θm and r at θ= π/2 from only one fringe loop is given. A systematic experimental study on finite CCT, SEN and DEN plates has been carried out for various value of λ(=-2a/W) with fringe data collected from near the crack tip. The results obtained for Dobeckote-505 show good agreement with the analtical results.