Crack identification at welding joint with a new smart coating sensor and entropy

Abstract

Abstract A damage identification module is designed and studied to realize the both close and open crack detection and severity increment estimation at a welding joint area using a new smart coating sensor and entropy measurement. A new piezoelectric composite coating sensor is developed and applied at a welding joint of an operating structure to send warning and dynamic signals for the damage identification, when the crack occurs. Entropy calculation is introduced to measure the weak dynamic perturbations, which is caused by the strain concentration and/or crack breathing at the crack tip and hidden in the dynamic signal at the welding joint of the operating structure. A finite element model (FEM) of a welded beam experiencing dynamic base motions is established as a case study to show the efficiency of the proposed smart coating design and the entropy measurement method. The effects of strain concentration and crack breathing on the structural dynamic response are simulated by creating the nonlinear material property around the crack area and contact pair of crack walls, respectively. After obtaining the time domain vibration signal, crack severity increment is estimated using Sample Entropy. From simulations, it is found that even at very early stages of the crack (5% of the beam thickness), the entropy variation is significant for both closed and open cracks compared with the healthy beam indicating the high crack identification sensitivity with the smart coating and entropy. In addition, the variation ratio increases corresponding to the increment of the strain level at the crack tip, and it reaches a limit at a critical strain value. Different case studies are presented to prove the feasibility of the damage identification methodology on different beam structures. After that, an experimental study of an open crack with strain singularity at the crack tip is conducted to validate the simulation studies. The results show a consistent trend with the simulations. In this way, the augmentation of the damage severity or possibility to further propagate during operation of the structure can be noticed with the help of the new sensor and the entropy measurement. Detection and estimation of the open crack and its induced local strain concentration are realized by the new sensor, wavelet and entropy measurement of vibration signal for the first time.