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AE5301-Sensor Technologies for Structural AE5301-Sensor Technologies for Structural Health MonitoringHealth Monitoring
Spring 2007
Monday,Wednesday 9:00 - 10:20 am
Room 110, Nedderman Hall
Instructor: Prof. Haiying Huang
Office hour: 1:30-2:30pm MW@ WH315
Email: [email protected]
Course website: webct.uta.edu
• Introduction (Major, MS or PhD, Research experience, Research interests)
• Survey of Academic Background Matlab Programming Data acquisition (hardware, Labview) Structural Dynamics Finite Element Analysis Fracture and fatigue
• Syllabus and tentative schedule
Course IntroductionCourse Introduction
Definition:In-service evaluation of structural health status by measuring key structural and environmental parameters on a continuous base at real-time.
Purposes of SHM: Detect structure damages• Safety, Safety, Safety• Provide maintenance and rehabilitation advices• Improve design guidelines• Disaster mitigation
What is Structural Health Monitoring?What is Structural Health Monitoring?
Current Safety Assurance PracticesCurrent Safety Assurance Practices
• Design with large safety factors-overdesign• Design for damage tolerance
– Life prediction (material damage, fracture mechanics)– Quality control (material processing, manufacturing,
assembly)– Accurate specification of operational conditions
• Periodic Inspection– Manual– Nondestructive Evaluation (visual, ultrasound, eddy
current)
Infamous Disasters due to Structural Infamous Disasters due to Structural Failures Failures
Question: IF all structures are designed properly, do we still need Structural Health Monitoring?
• Design uncertainties– Loading conditions
• Manufacturing uncertainties• Material variations• Environmental effects
• Aging Infrastructures– Civil infrastructures– Spacecrafts
– Airplanes
Why Do Disaster Happen?Why Do Disaster Happen?
Conventional Structural SystemsConventional Structural Systems
Conventional Structural Systems are dumb, very dumb
– Designed to achieve a set of intended functions under pre-selected loads and forces.
– Large safety factor is employed to account for the uncertainty in external loads
– Unable to adapt to structural changes and to varying usage patterns and loading conditions.
Both pictures were taken from the 1995 Kobe Earthquake
Design, Build, and Cross-your-fingers
Future Structural SystemsFuture Structural Systems
“Smart” Structures-structures that are able to sense and response/adapt to changes in their environment
Characteristics of SS– Integrated with many sensors
and control devices through information network
– To achieve an enhanced performance at a reduced life-cycle cost
Image courtesy of USA Today & Ken P. Chong at NSF
Biological Analogy to Smart Structural Biological Analogy to Smart Structural SystemSystem
A smart structural system can be considered as a mimicking of biological systems, possessing its own sensory and nervous systems, brain, and muscular system, with the goal of being autonomous and adaptable as living things
Information Processing (brain)
Actuators
(Muscular)
Sensors
(visual, olfactory, hearing, mechanosensory)
Courtesy of T. Kobori, Kajima Corp.
Core Components of Smart Structural Core Components of Smart Structural SystemSystem
Core components of a smart structural system (equipping structures with an integrated system of the following elements to make them adaptive to environment changes):
– Sensor (network)– Data/information processing
and interpretation– Controller and Actuating Device
(sometimes called effector)
Networked Sensors
Control & Actuator
Information Processing
Structural System
SSS
Smart
Materials
Smart Structural SystemSmart Structural System
• A smart structural system is roughly defined as a system with sensors, data processing unit, control and actuating devices, and therefore is adaptive to the change in external operating conditions.
Control effect under the November 19, 1991 Chiba City Coast earthquake (Tokyo, Magnitude: 4.9)
Typical SHM SystemTypical SHM System
Sensor System
Prognosis
Data ProcessingSystem
Health Evaluation System
Simulation Model
Life Prediction Model
Maintenance Scheduling
Self-healing
Benefits of SHMBenefits of SHM
• Better safety ensurance
• Cost-saving– Cost of inspection (e.g. 40% saving on
airplane inspection)– Early detection
• Autonomous damage detection for disaster mitigation
Aerospace Structures (Airframe, engine components, composite materials, etc.)Civil Structures (Bridge, Dam, Skyscraper, Earthquake impact, etc.)Mechanical Systems (bearing, engine, etc.)Human (elderly, people with health problems, fatigue of mission critical personnel, etc.)
Applications of SHMApplications of SHM
Structural DamagesStructural Damages
Definition: any structural condition that is different from its normal/design condition
Examples of Structural Damages
Typical Damages in AirplanesTypical Damages in Airplanes
• Fatigue cracking, particularly in joints at countersunk hole edges
• Corrosion, particularly inside joints and closed compartments
• Paint damage as an impact event signal• Debonding, due to corrosion in joints• Impact damages in composite materials• Manufacturing damages in composite materials• Debonding in stiffened composite panels
Four Levels of Damage DetectionFour Levels of Damage Detection
1. Detection of whether damage is present in the structure;
2. Identification of the location of the damage;
3. Quantification of the severity of the damage;
4. Evaluation of remaining structural integrity and risk assessment.
Damage Detection Requirement for Damage Detection Requirement for AirplanesAirplanes
Detection Sensitivity• 1-2mm cracks in Aluminum sheet• 5 mm cracks in a metallic frame• 100 mm cracks in a large area• 10% of sheet thickness in corrosion• 15X15mm debonding
Detection reliability: 90% reliability with 95% confidence level
Damage Detection MechanismsDamage Detection Mechanisms
• Local & direct measurement– Check for damage types (crack, corrosion,
delamination) – Acoustic Emission
• Global & indirect measurement– Measure structural behavior
Usage based SHM: measure the usage of the structure and determine if abnormal usage occurred
Vibration-based SHM – Natural frequency and frequency response functions– Mode shape and mode shape curvature– Damping– Wave propagation (guided wave, ultrasonic, etc.)
Strain-based SHM– Strain-energy distribution
SHM MechanismsSHM Mechanisms
SHM Techniques for AirplanesSHM Techniques for Airplanes
Sensors Used for SHMSensors Used for SHM
Vibration measurement sensors – Accelerometer– Deflection/bending sensor– Strain gauge– Acoustic sensor
Environmental sensors– Pressure sensor– Temperature sensor– Moisture sensor– Corrosion sensor
Different Stages of Fatigue Damages For Different Stages of Fatigue Damages For Metallic MaterialsMetallic Materials
• Substructural and microstructural damages• Microscopic cracks• Formation of dominate cracks• Stable propagation of dominated cracks• Structural instability and/or complete fracture
Question: at what stages should we detect the fatigue damages to save repair cost?
Aging Civil AircraftAging Civil Aircraft