Detection of crack initiation and propagation in ceramic composites using piezoelectric acoustic sensors

This paper investigates the applications of the piezoelectric acoustic sensors for real time detection of crack initiation and propagation in ceramic composites. In the first case this paper presents a smart method to detect and track the ceramic cell crack initiation and propagating in real time when the solid oxide fuel cell (SOFC) system is in operation with extremely high temperature (>750 deg. C). The main sources of fracture and delamination are the ceramic cell interlayers and interfaces during high temperature thermocycling. This research work is to successfully discern the damages during assembly, initial damages at first thermocycle and damage propagation, if any, at later cycles. This paper demonstrates that the AE signals generated from cell cracking and fracture in the stack modules can be successfully captured by commercially off the shelf (COTS) AE experimental hardware. The distinguishing characteristics of the cell crack AE signal and the metal impact AE signals will be presented in the paper. The second case successfully demonstrates the application of acoustic emission sensors to detect the first crack initiated due to crushing load on ceramic balls. A comprehensive strategy to capture the crushing load with respect to first crack initiation has been developed and would be presented in this paper. The crack is initiated when the Hertzian contact stresses are higher than the crushing load limit. Some initial results on signal processing to distinguish between first and second crack initiation would be presented.