A Method to Measure Fatigue Crack Growth Using Discontinuity in the Displacement Field

Digital Image Correlation is an increasingly popular tool for measuring displacement and strain fields in experimental investigations. Recent studies use the strain field to determine fatigue crack growth, e.g. by edge detection in the principal strain field or by measurement of compliance. However, when a strain field is used, a threshold value is needed which is potentially material dependent. This study presents a method to measure crack size, and hence fatigue crack growth, by means of the displacement field. In particular, the discontinuity in the displacement field induced by the crack is determined using the Chow test. The presence of the crack is determined by comparing the results of the Chow test obtained along the perspective crack path before and after crack growth. This does not require a predetermined threshold value to be selected by the user. The method is verified against experiments and compared with fatigue crack growth prediction using a compliance-based method. The results show that the proposed method can accurately determine the fatigue crack growth.