AE5301-Sensor Technologies for Structural Health Monitoring Spring 2007 Monday,Wednesday 9: :20 am Room 110, Nedderman Hall Instructor: Prof. Haiying Huang Office hour: 1:30-2:30pm WH315 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 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?

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?

Design uncertainties –Loading conditions Manufacturing uncertainties Material variations Environmental effects Aging Infrastructures –Civil infrastructures –Spacecrafts –AirplanesAirplanes Why Do Disaster Happen?

Conventional 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 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 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 Information Processing (brain) Actuators (Muscular) Sensors (visual, olfactory, hearing, mechanosensory) 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 Control & Actuator Information Processing Structural System SSS Smart Materials

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 Sensor System Prognosis Data Processing System Health Evaluation System Simulation Model Life Prediction Model Maintenance Scheduling Self-healing

Benefits of SHM Better safety ensurance Cost-saving –Cost of inspection (e.g. 40% saving on airplane inspection) –Early detectionEarly 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 SHM

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

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 Mechanisms

SHM Techniques for Airplanes

Sensors 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 Metallic 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 Aircraft