Detection of the Crack Initiation by Means of AE Method Under Low Cycle Fatigue of Elbow Pipe Having Local Wall Thinning

This paper describes the detectability of the crack initiation by means of the AE method under low cycle fatigue of the elbow pipe having local wall thinning to clarify the crack growth behavior for the pipes. Elbow specimens having local wall thinning were prepared, and local wall thinning due to flow accelerated corrosion was simulated by machined pipe wall thinning. Low cycle fatigue tests for the specimens were then carried out. AE method during low cycle fatigue tests was conducted to evaluate the crack initiation and location. In AE measurement, wide band AE sensors of 5mm in diameter were used to attach to the convex surfaces of the specimens. The circumference and axial strain of the specimens and the cross head displacement were also stored to the digital AE system signal. As a result, it is clear that the AE signals indicated the crack initiation in small circumference strain.