Fatigue crack quantification approach based on multi-path unit-cell concept in sensor network

A major safety and maintenance concern in aerospace structures are fatigue induced cracks for which quantification is a very critical component for achieving design performance. Such incipient damages, once initiated, can grow extremely fast and can lead to catastrophic failure of the structure. Traditional nondestructive inspection (NDI) techniques offer solutions which are offline, time consuming and quite expensive. Structural Health Monitoring (SHM) techniques are known to overcome some of these drawbacks. However, in SHM the challenges associated with quantification of fatigue cracks come mainly from the differential structural acoustic-ultrasonic response in similar material due to system installation errors or are caused by environmental usage conditions. Studies have shown that these variations in acoustic response come primarily from sensor positioning and the characteristics of crack e.g. orientation, crack length etc. This study presents a robust, multipath and scalable unit-cell approach for quantification of fatigue cracks. Multiple paths from a sensor configuration with a four sensor unit called a unit-cell is used along with an adaptive weighted averaging method to mitigate the effects of sensor positioning errors and/or uncertainties associated with crack orientation for quantification in SHM systems. Coupon tests that have been conducted to verify and validate the performance of this unit-cell approach for quantification purposes.