In-Flight Fatigue In-Flight Fatigue Crack Monitoring in Crack Monitoring in Aircraft Aircraft Using Acoustic Emission and Neural Using Acoustic Emission and Neural Networks Networks Eric. v. K. Hill Eric. v. K. Hill Samuel G. Vaughn Samuel G. Vaughn Christopher L. Rovik Christopher L. Rovik
56
Embed
In-Flight Fatigue Crack Monitoring in Aircraft Using Acoustic Emission and Neural Networks Eric. v. K. Hill Samuel G. Vaughn Christopher L. Rovik.
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
In-Flight Fatigue Crack In-Flight Fatigue Crack Monitoring in AircraftMonitoring in Aircraft
Using Acoustic Emission and Neural NetworksUsing Acoustic Emission and Neural Networks
Brittle failure in a normally ductile material Brittle failure in a normally ductile material due to cyclic loads below yield stressdue to cyclic loads below yield stress
Plastic deformation plus cyclic loads leads Plastic deformation plus cyclic loads leads to strain hardening, then fatigue crackingto strain hardening, then fatigue cracking
Small cyclic loads can cause significant Small cyclic loads can cause significant damage over timedamage over time
Notable Fatigue FailuresNotable Fatigue Failures
1988 Aloha Airlines flight: a piece of a B-737 1988 Aloha Airlines flight: a piece of a B-737 fuselage tore off during flight due to fuselage tore off during flight due to corrosion/fatigue crackingcorrosion/fatigue cracking
Aging aircraft are progressively accumulating Aging aircraft are progressively accumulating fatigue damagefatigue damage
This leads to costly mandatory inspections and This leads to costly mandatory inspections and parts replacement at “safe” intervalsparts replacement at “safe” intervals
Goal:Goal: In-flight fatigue crack detection systems In-flight fatigue crack detection systems promote maintenance schemes based on promote maintenance schemes based on replacement for causereplacement for cause rather than rather than replacement at replacement at conservatively calculated intervalsconservatively calculated intervals using linear using linear elastic fracture mechanics.elastic fracture mechanics.
Relevant M.S. ThesesRelevant M.S. Theses 1994 A.F. de Almeida: Neural Network Detection of 1994 A.F. de Almeida: Neural Network Detection of
Fatigue Crack Growth in Riveted Joints Using Fatigue Crack Growth in Riveted Joints Using Acoustic Acoustic EmissionEmission
1995 W.P. Thornton: Classification of Acoustic Emission 1995 W.P. Thornton: Classification of Acoustic Emission Signals from an Aluminum Pressure Vessel Using Signals from an Aluminum Pressure Vessel Using
a a Self-Organizing MapSelf-Organizing Map 1996 M.L. Marsden: Detection of Fatigue Crack Growth 1996 M.L. Marsden: Detection of Fatigue Crack Growth
in a Simulated Aircraft Fuselagein a Simulated Aircraft Fuselage 1998 S.G. Vaughn III: In-Flight Fatigue Crack Monitoring 1998 S.G. Vaughn III: In-Flight Fatigue Crack Monitoring
of an Aircraft Engine Cowlingof an Aircraft Engine Cowling 1998 C.L. Rovik: Classification of In-Flight Fatigue 1998 C.L. Rovik: Classification of In-Flight Fatigue
Cracks in Aircraft Structures Using Acoustic Cracks in Aircraft Structures Using Acoustic Emission Emission and Neural Networksand Neural Networks
4 acoustic emission transducers 4 acoustic emission transducers symmetrically mounted on engine symmetrically mounted on engine cowlingcowling
2 transducers monitoring crack growth 2 transducers monitoring crack growth and the other 2 recording the noiseand the other 2 recording the noise
3 Flights with 5 particular maneuvers 3 Flights with 5 particular maneuvers monitored on each flightmonitored on each flight
Testbed 2: Vertical TailTestbed 2: Vertical Tail
Cessna Crusader N106ER
Equipment Setup (Flight)Equipment Setup (Flight)
Equipment Setup (Lab)Equipment Setup (Lab)
Acoustic EmissionAcoustic Emission
Acoustic Emission (AE)Acoustic Emission (AE)
Definition:Definition:
The transient elastic waves generated by The transient elastic waves generated by the rapid release of energy within a material the rapid release of energy within a material due to flaw growth mechanismsdue to flaw growth mechanisms
AE Signal (Voltage vs. Time) AE Signal (Voltage vs. Time) Waveform ParametersWaveform Parameters
AE Duration vs. Amplitude PlotAE Duration vs. Amplitude Plot
Source LocationSource Location
Source Location PlotSource Location Plot
Finite Element Analysis (FEA) Finite Element Analysis (FEA) AnalysisAnalysis
Data AcquisitionData Acquisition
AE source (e.g., fatigue crack) emits acoustic AE source (e.g., fatigue crack) emits acoustic emission energy in the form of stress wavesemission energy in the form of stress waves
Piezoelectric crystal within AE transducer senses Piezoelectric crystal within AE transducer senses the signalthe signal
AE signal amplified and transmitted to a computer AE signal amplified and transmitted to a computer where its waveform quantification parameters are where its waveform quantification parameters are digitized and storeddigitized and stored
Records signals in the frequency range 100 kHz to Records signals in the frequency range 100 kHz to 1 MHz1 MHz
Kohonen Self-Organizing Map (SOM) neural Kohonen Self-Organizing Map (SOM) neural network uses mathematical processes to classify network uses mathematical processes to classify “things” based on a set of inputs: six AE “things” based on a set of inputs: six AE quantification parameters (amplitude, duration, quantification parameters (amplitude, duration, counts, energy, rise time, and counts-to-peak) counts, energy, rise time, and counts-to-peak)
SOM Neural Network ArchitectureSOM Neural Network Architecture
SOM Data ProcessingSOM Data Processing
Two primary steps in implementing a Two primary steps in implementing a Kohonen SOM neural network:Kohonen SOM neural network:
Training the SOM – sample of dataTraining the SOM – sample of data Testing the SOM – remainder of dataTesting the SOM – remainder of data
Training the SOMTraining the SOM
Create a training fileCreate a training file 5 steps to training:5 steps to training: 1.1. Randomly set weights between 0 and 1Randomly set weights between 0 and 1 2.2. Introduce first input vector ( 6 signal Introduce first input vector ( 6 signal
parameters for AE hit)parameters for AE hit) 3.3. Find minimal planar distance between the Find minimal planar distance between the
input vector and Kohonen neuronsinput vector and Kohonen neurons 4.4. Identify the neuron with the minimal distanceIdentify the neuron with the minimal distance 5.5. Adjust/update the weights Adjust/update the weights
Testing the SOMTesting the SOM
Create testing fileCreate testing file Pass test file through the trained neural Pass test file through the trained neural
network and it will be classifiednetwork and it will be classified
ResultsResults
Anticipated ResultsAnticipated Results
Neural network classifies lab test data into 3 Neural network classifies lab test data into 3 categories: fatigue cracking, plastic deformation, categories: fatigue cracking, plastic deformation, and rubbing (mechanical noise)and rubbing (mechanical noise)
Trained neural network classifies the entire lab Trained neural network classifies the entire lab test file with a high degree of accuracytest file with a high degree of accuracy
In-flight data verifies fatigue crack growth between In-flight data verifies fatigue crack growth between Channels 1 & 2 on Piper Cadet cowling Channels 1 & 2 on Piper Cadet cowling
Fatigue crack growth activity associated with Fatigue crack growth activity associated with stressful maneuvers on Cessna Crusader vertical stressful maneuvers on Cessna Crusader vertical tailtail
Lab Test ConfigurationLab Test Configuration
Lab Test ResultsLab Test Results
Over twenty AE files were recorded during Over twenty AE files were recorded during the lab fatigue teststhe lab fatigue tests
File twenty: 3 minutes 30 seconds in length; File twenty: 3 minutes 30 seconds in length; recorded fatigue cracking for the last minuterecorded fatigue cracking for the last minute
Duration vs. Amplitude plot of file twenty Duration vs. Amplitude plot of file twenty shows good separation between failure shows good separation between failure mechanismsmechanisms
Duration vs. Amplitude (File 20)Duration vs. Amplitude (File 20)
ATPOST Filtering LimitsATPOST Filtering Limits
AE sources filtered into individual files:AE sources filtered into individual files:
100 hits each of fatigue cracking, plastic 100 hits each of fatigue cracking, plastic deformation, and rubbing for a total of 300 deformation, and rubbing for a total of 300 hits were used for traininghits were used for training
Trained neural network tested 99% accurate Trained neural network tested 99% accurate when testing the remaining 70,000+ hitswhen testing the remaining 70,000+ hits
One column by three row (1x3) matrix One column by three row (1x3) matrix Kohonen classification layer gave the most Kohonen classification layer gave the most concise output concise output
detected on both sides of the aircraft detected on both sides of the aircraft cowlingcowling
Inspection revealed cracking between Inspection revealed cracking between Channels 3 - 4 as well as 1 - 2Channels 3 - 4 as well as 1 - 2
Cracking in the engine cowling occurred Cracking in the engine cowling occurred predominantly during ground predominantly during ground operations: taxi, take-off, and final operations: taxi, take-off, and final approach/landingapproach/landing
from both engine cowling of the Piper PA-28 Cadet from both engine cowling of the Piper PA-28 Cadet and vertical tail of the Cessna T-303 Crusader using and vertical tail of the Cessna T-303 Crusader using AE parameter dataAE parameter data
Engine cowling fatigue cracking occurred mostly Engine cowling fatigue cracking occurred mostly during ground-based operations while vertical tail during ground-based operations while vertical tail fatigue cracking occurred predominantly in-flight, fatigue cracking occurred predominantly in-flight, especially during rolls and Dutch rollsespecially during rolls and Dutch rolls
In-flight crack detection systems should help to In-flight crack detection systems should help to minimize maintenance costs and extend the service minimize maintenance costs and extend the service lives of aging aircraft.lives of aging aircraft.
Problem: Data Overlap in AE Problem: Data Overlap in AE Parameter PlotsParameter Plots