Photoelastic determination ofK I andK II : A numerical study on experimental data

Abstract

ABSTRACT--The most efficient photoelastic methods to obtain stress intensity factors are those based on stress functions series expansions. The coefficients of these expansions are fitted to the experimental isochromatic pattern using an overdeterministic Newton-Raphson least squares method. In this paper, a study has been carried out to analyze the influence on the results of several numerical and experimental factors. It is shown that accurate values of the stress intensity factors K/and KI/can be obtained by following some recommendations given in the text and summarized in the conclusions at the end of the paper.

Crack paths under mixed mode loading

“…Several methods have been developed to determine K I and K II using the full field of data surrounding the slit tip [18,19]. Nurse and Patterson [16] also developed a photoelastic method to predict the direction of crack growth using the theory that long cracks usually grow under mode I loading in direction perpendicular to maximum tangential stress.…”

Use of automated photoelasticity to determine stress intensity factors of bimaterial joints

“…Photoelasticity has been widely used by various authors to evaluate the SIFs of cracked homogeneous [18][19][20][21] and bimaterial components subjected to static [22][23][24][25] or dynamic loading [41,42] because, as has been shown in numerous applications [43], the isochromatic fringes are very sensitive to the parameters that govern a singular stress field. Unfortunately, all the methods proposed in the literature do not exploit the full field data available from modern automated photoelasticity techniques [44] and do not allow the user a previous evaluation of the SDZ extension.…”

“…having < 3 or r < 0:5. It then allows the user to locate the SDZ interactively by fitting the log () curve relative to specimens T1 and M1 with a linear function and the 2 curve relative to specimens T2 and M2 with the polynomial function (21). Successively, for each selected radial line a third routine computes the SIFs by using the q constant of the fitting curves and equation (16) for specimens T1 and M1, and equations (22) and (23) for specimens T2 and M2.…”

“…In this context, various techniques, mainly based on the finite element method (FEM) [6][7][8][9][10][11][12][13][14][15], have been proposed by several authors, but only a few experimental methods have been properly implemented [16,17]. Although the experimental methods proposed in the literature to determine the SIFs for a crack in a homogeneous material [18][19][20][21] and at the interface of bimaterial joints [22][23][24][25][26][27][28][29][30] can be potentially extended to evaluate the SIFs of bimaterial joints, its use generally leads to approximate results because all these methods do not allow the user either to determine the actual extension of the singularity dominated zone (SDZ) or to optimize the model zone where data have to be collected to minimize the influence of the main error sources. In fact, unlike cracked components, the extension of the SDZ in bimaterial joints is not only related to the extension of the notch but is also strictly related to material properties and the local geometry of the joint.…”

A method for determining mixed mode stress intensity factors using strain gage data

“…The method has been shown to yield high quality results on models but has the inherent limitation of optical viewing of the test article by the polaroscope. Paris, Picon, Marin, and Cana [13] The moire technique is capable of measuring displacements with a resolution in the sub-wavelength of light. The method uses a reference grid, or array, of lines or points and an identical grid, or array, placed on the specimen to be analyzed [9].…”