Transcript Slide 1

AE5301-Sensor Technologies for Structural
Health 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
Course Introduction
• 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
What is Structural Health Monitoring?
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
Current 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
Failures
Question: IF all structures are designed
properly, do we still need Structural Health
Monitoring?
Why Do Disaster Happen?
• Design uncertainties
– Loading conditions
• Manufacturing uncertainties
• Material variations
• Environmental effects
• Aging Infrastructures
– Civil infrastructures
– Spacecrafts
– Airplanes
Conventional Structural Systems
Conventional Structural
Systems are dumb, very dumb
– Designed to achieve a set of
intended functions under preselected 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.
Design, Build, and Cross-your-fingers
Both pictures were taken from
the 1995 Kobe Earthquake
Future 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 lifecycle cost
Image courtesy of USA Today & Ken P. Chong at NSF
Biological Analogy to Smart Structural
System
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
Sensors
(visual, olfactory,
hearing,
mechanosensory)
Information
Processing (brain)
Actuators
(Muscular)
Courtesy of T. Kobori, Kajima Corp.
Core Components of Smart Structural
System
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
Information
Processing
Smart
SSS
Materials
Control &
Actuator
Structural
System
Smart 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 System
Data Processing
System
Sensor
System
Self-healing
Simulation Model
Prognosis
Life Prediction
Model
Health Evaluation
System
Maintenance
Scheduling
Benefits 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
Applications of SHM
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.)
Structural Damages
Definition: any structural condition that is
different from its normal/design condition
Examples of Structural Damages
Typical 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 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
Airplanes
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 Mechanisms
• Local & direct measurement
– Check for damage types (crack, corrosion,
delamination)
– Acoustic Emission
• Global & indirect measurement
– Measure structural behavior
SHM Mechanisms
Usage based SHM: measure the usage of the structure
and determine if abnormal usage occurred
Vibration-based SHM
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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 Techniques for Airplanes
Sensors Used for SHM
Vibration measurement sensors
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–
–
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Accelerometer
Deflection/bending sensor
Strain gauge
Acoustic sensor
Environmental sensors
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Pressure sensor
Temperature sensor
Moisture sensor
Corrosion sensor
Different Stages of Fatigue Damages For
Metallic Materials
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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 Aircraft