A novel way to determine crack tip stress field parameters involving displacement field estimated using digital image correlation technique

Harilal, R (2015) A novel way to determine crack tip stress field parameters involving displacement field estimated using digital image correlation technique. Masters thesis, Indian Institute of Technology Hyderabad.

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Abstract

In the present work, an experimental study is carried out to estimate the mixed-mode stress intensity factors (SIF) for different cracked specimen configurations using digital image correlation (DIC) technique. For the estimation of mixed-mode SIFs using DIC, a new algorithm is proposed for the extraction of crack tip location and coefficients in the multi parameter displacement field equations. The required displacement data surrounding the crack tip has been obtained using 2D-DIC technique. An open source 2D DIC software Ncorr is used for the displacement field extraction. To compare its capabilities with the existing commercial code, various experiments are conducted and results have been compared with commercial software Vic 2D. There is good coherence in results obtained from both the software. An additional SIF estimation module has been developed in MATLAB for SIF estimation from the displacement data obtained from Ncorr open source 2D DIC software. The presented methodology has been used to extract SIF's for specimen configurations like single edge notch (SEN) specimen and center slant crack (CSC) specimens made out of Al-2014 T6 alloy. The experimental results have been compared with the analytical values and they are found to be in good agreement, thereby confirming the accuracy of the algorithm being proposed. As an additional visual confirmation, the experimental displacement contours are superimposed over the theoretically reconstructed displacement contours obtained using extracted crack tip parameters. They are found to be in coherence with each other. Further, the same algorithm has been intelligently extended to fatigue crack growth study as well. Two types of specimens namely, un-repaired and single sided carbon fiber reinforced polymer (CFRP) patch repaired cracked aluminum panel under fatigue loading are considered. The mixed mode SIFs are estimated from the displacement field data at various crack lengths and they are compared with their nite element analysis (FEA) estimates based on a previous study. The numerical and experimental SIFs are found to be in coherence with each other.

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