Health Monitoring of Aerospace Structures Utilizing Novel Health Indicators Extracted from Complex Strain and Acoustic Emission Data

Abstract

The development of health indicators (HI) of diagnostic and prognostic potential from generally uninformative raw sensor data is both a challenge and an essential feature for data-driven diagnostics and prognostics of composite structures. In this study, new damage-sensitive features, developed from strains acquired with Fiber Bragg Grating (FBG) and acoustic emission (AE) data, were investigated for their suitability as HIs. Two original fatigue test campaigns (constant and variable amplitude) were conducted on single-stringer composite panels using appropriate sensors. After an initial damage introduction in the form of either impact damage or artificial disbond, the panels were subjected to constant and variable amplitude compression–compression fatigue tests. Strain sensing using FBGs and AE was employed to monitor the damage growth, which was further verified by phased array ultrasound. Several FBGs were incorporated in special SMARTapesTM, which were bonded along the stiffener’s feet to measure the strain field, whereas the AE sensors were strategically placed on the panels’ skin to record the acoustic emission activity. HIs were developed from FBG and AE raw data with promising behaviors for health monitoring of composite structures during service. A correlation with actual damage was attempted by leveraging the measurements from a phased array camera at several time instances throughout the experiments. The developed HIs displayed highly monotonic behaviors while damage accumulated on the composite panel, with moderate prognosability.

Multi-level damage diagnosis on stiffened composite panels based on a damage-uninformative digital twin

“…46,52,[58][59][60] Also, model-independent methodologies are followed where solely experimental data are utilized. [61][62][63][64][65] Methods for damage identifications based on strains recorded from zero-strain trajectories are also employed. 35,66,67 Lately, strain-based SHM methodologies utilizing the inverse FE method are emerging.…”

Damage Diagnostics on Post-buckled Stiffened Panels Utilizing the Digital-Twin Concept

“…The proposed SHM methodology is tested for the case of two SSPs subjected to block loading compression-compression fatigue [5,6]. The load limits per block are presented in Table 1.…”

Acoustic emission applied to mode I fatigue damage monitoring of adhesively bonded joints

“…Since SHM methods can assess the joints' integrity under in-service life, giving the possibility of their on-demand or real-time diagnosis and prognostic, implementing a condition-based maintenance system that saves time and maintenance costs of the structures, the interest of the scientific community in their application is increasing. Among the different SHM methods, Acoustic Emission (AE) is a promising alternative due to its possibility of assessing the elastic waves produced within the monitored material when their strain energy is released during the deformation or damage initiation and propagation (even in small increments) [4]. The assessed elastic waves are then recorded and have their time-domain features (i.e., amplitude, duration, counts, energy and rise time) and waveform saved by the acquisition system as detailed in the flowchart of Figure 1.…”