Simple crack tip and stress intensity factor determination method for model I crack using digital image correlation

Abstract

In the past three decades, quantitative characterization of cracks attracted much attention with the development of digital image correlation (DIC), especially for estimation of crack tip position (CTP) and stress intensity factor (SIF). Quantifying CTP and SIF is of great importance in the damage tolerance assessment of fracture-critical components and structures. In previous research, multivariate fitting is performed on the displacement field to determine CTP and SIF. However, high gradient deformation near the crack tip causes inaccurate results and an involving complex estimation process. In this paper, a simple method is proposed to determine the CTP and SIF based on the displacement field calculated by DIC. Instead of the full-field fitting method, two lines symmetrically distributed on both sides of the crack tip are selected to fit the CTP. Vertical displacement differences between two lines are fitted with the theoretical solutions of mode I crack. Compared with the actual position observed by the micrograph, the estimation error is less than 2 pixels (about 6 μm). Additionally, a similar method is proposed to estimate the SIF utilizing the CTP results. To avoid the bias errors caused by the plastic zone, two lines are selected in the elastic zone away from the crack tip. Vertical displacements on two lines are fitted with the theoretical solutions to obtain SIF. The fitting results of the proposed method are close to that of the full-field fitting method. Compared with the previous methods, the computation burden of the proposed method is greatly reduced while the accuracy is not affected.