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: huang@uta.edu

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