Dynamic analysis of cracked pipe elbows: Numerical and experimental studies

This study aims to investigate the dynamic behaviors of fluid-delivering cracked pipe elbows (FDCPEs), thereby providing theoretical and methodological guidance for vibration-based crack detection in pipe elbows. Specifically, an efficient spectral element-finite element (SE-FE) based modeling method for the FDCPEs is proposed firstly, which considers fluid-structure coupling and breathing effect. For the SE-FE method, the spectral element (SE) and finite element (FE) are constructed to simulate the healthy straight segments and cracked elbows of the pipe, respectively, and a penalty function method is adopted to simulate interface coupling and breathing effects. Furthermore, the computational accuracy and efficiency of the SE-FE method are verified through numerical and experimental studies. Finally, the effects of the elbow and crack parameters on the dynamic behaviors of FDCPE are analyzed. The results indicate that changes in the bending radius and angle may trigger frequency veering behaviors, leading to in-plane and out-plane vibration mode switching. Moreover, the even-mode harmonics of the stress responses can effectively detect cracks in the elbow. Most importantly, the strength of nonlinearity at different measuring locations can be used to predict the crack location and size.