Fatigue crack detection with estimation of stress fields near a notch root of thin plate structures in in-plane loading

A practical method is proposed for in situ fatigue crack detection in actual notched structures. This method is available for the cases where the initiation position and propagation direction of a crack are uncertain and the load direction or the load mode changes. In the present method, the stress fields near a notch root are estimated using the general stress function in a polar coordinate system and the stress values obtained from strain gages around the notch root. The stress fields are characterized by the residual stress due to plastic deformation around a fatigue crack. Not only a propagating crack but also a nonpropagating crack can be detected from the characteristic stress field. Moreover, the detection limitation is subject to the strength of the residual stress field relative to an elastic stress field due to external loads. The fatigue experiment of a notched specimen of steel was carried out. In the present experiment, a 0.33-mm-long crack could be detected in the notch whose root radius was 12.5 mm.