24SEE10-Structural Health Monitoring
Dr. S. Vinodhkumar
Assistant Professor
Dept. of Civil Engg.
Kongu Engineering College, Perundurai
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
Current Safety Assurance Practices
Why Do Disaster Happen?
Conventional Structural Systems
Conventional Structural Systems are dumb, very dumb
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
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):
Networked Sensors
Control & Actuator
Information Processing
Structural System
SSS
Smart
Materials
Smart Structural System
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
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
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
Detection reliability: 90% reliability with 95% confidence level
Damage Detection Mechanisms
SHM Mechanisms
SHM Techniques for Airplanes
Sensors Used for SHM
Different Stages of Fatigue Damages For Metallic Materials
Question: at what stages should we detect the fatigue damages to save repair cost?
Aging Civil Aircraft
Introduction to Nondestructive Testing
What is nondestructive testing?
NonDestructive Testing (NDT) is the process of doing inspections, testing, or evaluating materials, components or assemblies for defects without destroying the material or component.
Or the use of noninvasive techniques to determine the integrity of a material, component or structure”.
In other words, “Inspect or measure without doing harm.”
Introduction to Nondestructive Testing
Who Uses NDT?
Introduction to Nondestructive Testing
What are Some Uses of NDT?
Introduction to Nondestructive Testing
When is NDT Used?
There are NDT application at almost any stage in the production or life cycle of a component.
Introduction to Nondestructive Testing
Introduction to Nondestructive Testing
NDT Methods
Test methods are the type of penetrating medium or the equipment used to perform that test. Some of the current NDT methods are:
- Acoustic Emission Testing (AE) - Liquid Penetrant Testing (PT)
- Electromagnetic Testing (ET) - Magnetic Particle Testing (MT)
- Guided Wave Testing (GW) - Neutron Radiographic Testing (NR)
- Ground Penetrating Radar (GPR) - Radiographic Testing (RT)
- Laser Testing Methods (LM) - Thermal/Infrared Testing (IR)
- Leak Testing (LT) - Ultrasonic Testing (UT)
- Magnetic Flux Leakage (MFL) - Vibration Analysis (VA)
- Microwave Testing - Visual Testing (VT)
Introduction to Nondestructive Testing
The most frequently used test methods are:
Visual Testing (VT)
Liquid Penetrant Testing (PT)
Magnetic Particle Testing (MT)
Ultrasonic Testing (UT)
Electromagnetic Testing (ET) (Eddy Current)
Radiographic Testing (RT) (X-ray)
Acoustic Emission Testing (AE)
Each of these test methods and some of the other methods will be discussed later in this presentation and more detail provided in subsequent presentations.
Introduction to Nondestructive Testing
Visual Testing (VT)
VT is the visual observation of the surface to evaluate the presence of surface discontinuities. Corrosion, misalignment of parts, physical damage and cracks are some of the discontinuities that may be detected by VT.
VT is the most commonly used test method in industry as most test methods require that the operator look at the surface of the part being inspected. VT inspections may be by direct looking, or may be by use of optical instruments such as magnifying glasses, mirrors, borescopes, and remote Viewing.
Introduction to Nondestructive Testing
Liquid Penetrant Testing (PT)
PT uses a liquid with high surface wetting characteristics is applied to the surface and allowed to seep into defects and then excess liquid is removed.
A developer is applied the trapped penetrant is pulled out of the defect where it can be seen.
Visual inspection is then performed.
The penetrant used is often loaded�with a fluorescent dye and�the inspection is done under UV�light to increase test sensitivity.
Introduction to Nondestructive Testing
Magnetic Flux Leakage (MFL)
MFL detects anomalies in normal flux patterns created by discontinuities in ferrous material saturated by a magnetic field. This technique can be used for piping and tubing inspection, tank floor inspection and other applications. This technique can be done without removing the insulation, resulting in a fast, economic way to inspect long runs of pipe or tubing.
Introduction to Nondestructive Testing
Ultrasonic Testing (UT)
UT uses the same principle as is used in naval SONAR and fish finders. Ultra-high frequency sound is introduced into the part being inspected and if the sound hits a material with a different acoustic impedance (density and acoustic velocity), some of the sound will reflect back to the sending unit and can be presented on a visual display.
Introduction to Nondestructive Testing
Electromagnetic Testing (ET)
Electromagnetic testing is a general test category that includes Eddy Current testing (ECT), Alternating Current Field Measurement (ACFM) and Remote Field testing. While magnetic particle testing is also an electromagnetic test, due to its widespread use it is considered a stand-alone test method rather as than an electromagnetic testing technique. All of these techniques use the�induction of an electric current or magnetic field�into a conductive part, then the resulting effects
are recorded and evaluated.
Introduction to Nondestructive Testing
Radiographic Testing (RT)
RT involves exposing a test object to radiation so that the radiation passing through the object is recorded on a medium placed against the opposite side. The recording media can be industrial x-ray film or one of several types of digital radiation detectors. If there is a void or defect in the part, more �radiation passes through, �causing a darker image on the �film or detector.
Top view of developed film
X-ray film
= more exposure
= less exposure
Introduction to Nondestructive Testing
Acoustic Emission Testing (AE)
AE is performed by applying a localized external force such as an abrupt mechanical load or rapid temperature or pressure change to the part being tested. The resulting stress waves in turn generate short-lived, high frequency elastic waves in the form of small material displacements, or plastic deformation, on the part surface that are detected by sensors that have been attached to the part surface. When multiple sensors are used, the resulting data can be evaluated to locate
discontinuities in the part.
Introduction to Nondestructive Testing
Guided Wave Testing (GW)
GW uses controlled excitation of ultrasonic waves that travel along the length of a pipe, reflecting from changes in the pipe stiffness or cross section. A transducer ring or exciter coil is used to introduce the guided wave into the pipe and each transducer/exciter. Control and analysis software is used to drive the transducer/exciter and to analyze results. The transducer/exciter is designed specifically for the�diameter of the pipe, and can inspect the pipe �wall over long distances without having to �remove coatings or insulation. GW can locate �both ID and OD discontinuities but cannot �differentiate between them.
Introduction to Nondestructive Testing
Ground-penetrating Radar (GPR)
GPR is a geophysical method that uses radar pulses to image the subsurface. This nondestructive method uses electromagnetic radiation in the microwave band (UHF/VHF frequencies) of the radio spectrum, and detects the reflected signals from subsurface structures. GPR can have applications in a variety of media, including rock, soil, ice, fresh water, pavements and structures. In the right conditions, practitioners can use GPR to �detect subsurface objects, changes in �material properties, and voids and cracks.
Introduction to Nondestructive Testing
Laser Testing Methods (LM)
LM includes three techniques, Holography, Shearography and Profilometry. As the method name implies, all three techniques user lasers to perform the inspections.
Introduction to Nondestructive Testing
Leak Testing (LT)
LT as the name implies, is used to detect through leaks using one of the four major LT techniques:
Bubble,
Pressure Change,
Halogen Diode and
Mass Spectrometer Testing.
Introduction to Nondestructive Testing
Microwave Nondestructive Testing (MNDT)
MNDT techniques have advantages over other NDT methods (such as radiography, ultrasonics, and eddy current) regarding low cost, good penetration in nonmetallic materials, good resolution and contactless feature of the microwave sensor (antenna).
Introduction to Nondestructive Testing
Magnetic Particle Testing (MT)
In MT the part is magnetized. Finely milled iron particles coated with a dye pigment are then applied to the specimen. These particles are attracted to magnetic flux leakage fields and will cluster to form an indication directly over the discontinuity. This indication can be visually detected under proper lighting conditions.
Crack
Introduction to Nondestructive Testing
Neutron Radiographic Testing (NR)
NR uses an intense beam of low energy neutrons as a penetrating medium rather than the gamma- or x-radiation used in conventional radiography. Generated by linear accelerators, betatrons and other sources, neutrons penetrate most metallic materials, rendering them transparent, but are attenuated by most organic materials (including water, due to its high hydrogen content) which allows those materials to be seen within the component being inspected. When used with conventional radiography, both the structural and internal�components of a test piece can be viewed.
Introduction to Nondestructive Testing
Thermal/Infrared Testing (IR)
IR, or infrared thermography, is used to measure or map surface temperatures based on the infrared radiation given off by an object as heat flows through, to or from that object. The majority of infrared radiation is longer in wavelength than visible light but can be detected using thermal imaging devices, commonly called "infrared cameras.“ For accurate IR testing, the part(s) being investigated should be in direct line of sight with the camera. Used properly, thermal imaging can be used to detect corrosion damage, delamination's,�disbonds, voids, inclusions as well as �many other detrimental conditions.
Introduction to Nondestructive Testing
Vibration Analysis (VA)
Vibration analysis refers to the process of monitoring the vibration signatures specific to a piece of rotating machinery and analyzing that information to determine the condition of that equipment. Three types of sensors are commonly used: displacement sensors, velocity sensors and accelerometers.
Introduction to Nondestructive Testing
Common Application of NDT
Inspection of Raw Products
Forgings Castings Extrusions
Introduction to Nondestructive Testing
Common Application of NDT
Inspection Following Secondary Processing
Machining Welding Grinding Heat Plating
treating
Introduction to Nondestructive Testing
Common Application of NDT
In-Services Damage Inspection
Cracking Corrosion Heat Damage Erosion/Wear
Introduction to Nondestructive Testing
Examples of NDT
Power Plant Inspection - Periodically, power plants are shutdown for inspection. Inspectors feed eddy current probes into heat exchanger tubes to check for corrosion damage
Introduction to Nondestructive Testing
Examples of NDT
Wire Rope Inspection - Electromagnetic devices and visual inspections are used to find broken wires and other damage to the wire rope that is used in chairlifts, cranes and other lifting devices.
Introduction to Nondestructive Testing
Examples of NDT
Storage Tank Inspection - Robotic crawlers use ultrasound to inspect the walls of large above ground tanks for signs of thinning due to corrosion. Cameras on long articulating arms are used to inspect underground storage tanks for damage
Introduction to Nondestructive Testing
Examples of NDT
Aircraft Inspection - Nondestructive testing is used extensively during the manufacturing of aircraft. NDT is also used to find cracks and corrosion damage during operation of the aircraft. A fatigue crack that started at the site of a lightning strike is shown.
Introduction to Nondestructive Testing
Examples of NDT
Jet Engine Inspection Aircraft engines are overhauled after being in service for a period of time. They are completely disassembled, cleaned, inspected and then Reassembled. Fluorescent penetrant inspection is used to check many of the parts for cracking.
Introduction to Nondestructive Testing
Examples of NDT
Pressure Vessel Inspection - The failure of a pressure vessel can result in the rapid release of a large amount of energy. To protect against this dangerous event, the tanks are inspected using radiography and ultrasonic testing.
Introduction to Nondestructive Testing
Examples of NDT
Rail Inspection - Special cars are used to inspect thousands of miles of rail to find cracks that could lead to a derailment.
Introduction to Nondestructive Testing
Examples of NDT
Bridge Inspection - The US has 578,000 highway bridges. Corrosion, cracking and other damage can all affect a bridge’s performance. Bridges get a visual inspection about every 2 years. Some bridges are fitted with acoustic emission sensors that “listen” for sounds of cracks growing.
Introduction to Nondestructive Testing
Examples of NDT
Pipeline Inspection - NDT is used to inspect pipelines to prevent leaks that could damage the environment. Visual inspection, radiography and electromagnetic testing are some of the NDT methods used.