From the viewpoint of engineering, fatigue is an important issue as most of the mechanical failures are associated with fatigue damage. In fact, these disastrous events had occurred unexpectedly during the regular working conditions and most of the time the applied stresses are well below the yield strength of the material. Thus, it makes the prediction of fatigue damage a challenging task in the field of engineering, especially when the manmade structures and machines are getting more complex than before. Even though fatigue has been studied extensively in the past 170 years, many limitations are still being found within the current fatigue analysis, testing and the non-destructive inspection. Hence, there is a great need to develop a precise and yet efficient inspection technique in quantifying the fatigue cracks. Therefore, the objective of this study is to develop a quantifiable approach in monitoring the fatigue cracks using digital image correlation technique. 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 (Grade: 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 translations, normal and shear strains 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.
Applying the digital-image-correlation technique to measure the deformation of an old building’s column retrofitted with steel plate in an in situ pushover test
