Experimental determination of crack-tip fields: holographic interferometry method and digital image correlation method

The problems of reconstruction of the stress field at the crack tips of a system of horizontal and inclined cracks in a linear isotropic elastic medium using the results of experimental studies conducted by interference-optical methods: the method of holographic interferometry and the digital image correlation are considered. The experiments are aimed at constructing a multi-component asymptotic expansion of M. Williams with the retention of regular (nonsingular) series terms for plates weakened by two interacting cracks. To restore the coefficients of the M. Williams series the interference patterns of the absolute retardation fringes (isodromes) are used. Favre's law allows us to determine the main stresses in the vicinity of the crack tip. The strain and displacement fields were determined using the digital image correlation method for a number of cracked specimens. The experimental data obtained by two interference-optical methods was used to calculate the coefficients of the multi-point asymptotic expansion of M. Williams. A new variation of the over-deterministic method is proposed, focused on the linearized Favre's law, and allowing us to find the coefficients of the asymptotic series of M. Williams (generalized stress intensity coefficients) by means of an iterative procedure, based on the results of polarization-optical measurements. To verify the results of processing all the experimental data, a computational experiment was additionally carried out using the finite element method, which made it possible to calculate generalized stress intensity factors based on the stress fields found by the finite element method. A modification of the over-deterministic method based solely on the application of stress fields associated with the crack tip is proposed. It is shown that the generalized coefficients of the M. Williams series, determined using a full-field and computational experiment, are in good agreement.