Macro-fiber composite–based structural health monitoring system for axial cracks in cylindrical structures

In cylindrical structures such as pipelines and pressure vessels, cracks are most likely to occur along the longitudinal (axial) direction, and they can be fatal to the serviceability of the structures. However, the conventional wave propagation–based crack detection techniques are not sensitive to this type of cracks. This article focuses on the identification of axial cracks in cylindrical structures using torsional wave generated by piezoelectric macro-fiber composite. The first-order torsional wave, which is a nondispersive pure shear wave propagating at a fixed wave speed, is utilized in this work because, intuitively, it is more sensitive to axial cracks than the longitudinal waves. The crack position is determined by the time of flight of the wave pack, while the crack propagation is monitored by measuring the variation in the crack-induced disturbances. Numerical simulations have been conducted to investigate the feasibility of the proposed method, and experimental tests on aluminum pipes have been carried out for verification. Macro-fiber composite transducers oriented at 45° against the axis of the specimen were used to generate and receive the torsional waves. The experimental results demonstrated that the crack position can be identified, and its growth can be well monitored with the proposed approach.