Development of a quantifiable approach in monitoring the fatigue cracks using digital image correlation

The prediction of fatigue damage is a challenging task in the field of engineering. Therefore, the objective of this study is to develop a quantifiable approach in monitoring the fatigue cracks using digital image correlation technique. Technically, this can be achieved by using a developed two-dimensional sub-pixel accuracy deformation measurement algorithm which determines the deformation parameters of the first-order shape function of a material subjected to cyclic loading. Next, fatigue tests for samples made of mild steel (JIS G 3101 SS400) were conducted in accordance to the ASTM E466. Simultaneously, an industrial grade camera was used to capture the fatigue crack's region at a specific interval until the sample broke into two pieces. The captured images were then analysed and the deformation parameters such as translation, normal strain and shear strain values were determined by using the developed digital image correlation algorithm. Based on the determined deformation patterns, a specific trend was observed throughout the graphs of respective deformation parameters against the number of cycles. Besides, drastic changes were observed when the average number of cycles was approaching 95.5% (min. loading) and 93.8% (max. loading) of the total fatigue life. In conclusion, the digital image correlation technique was proven to be capable in monitoring the severity of a fatigue crack and the proposed monitoring system would serve as an inspection technique in examining the fatigue damage of a structural component throughout its operational period.