Materials State Awareness (MSA) goes beyond traditional NDE and SHM in its challenge to characterize the current
state of material damage before the onset of macro-damage such as cracks. A highly reliable, minimally invasive system
for MSA of Aerospace Structures, Naval structures as well as next generation space systems is critically needed.
Development of such a system will require a reliable SHM system that can detect the onset of damage well before the
flaw grows to a critical size. Therefore, it is important to develop an integrated SHM system that not only detects macroscale
damages in the structures but also provides an early indication of flaw precursors and microdamages. The early
warning for flaw precursors and their evolution provided by an SHM system can then be used to define remedial
strategies before the structural damage leads to failure, and significantly improve the safety and reliability of the
structures. Thus, in this article a preliminary concept of developing the Hybrid Distributed Sensor Network Integrated
with Self-learning Symbiotic Diagnostic Algorithms and Models to accurately and reliably detect the precursors to
damages that occur to the structure are discussed. Experiments conducted in a laboratory environment shows potential of
the proposed technique.
Fatigue crack detection and quantification is by far the most challenging task in Structural Health Monitoring (SHM). In
the past decade numerous techniques were developed to detect and quantify fatigue damages. Fatigue loading leads to
fatigue crack development in metals and delamination growth in composites. It has been found that different techniques
are suitable for different damage development. Hence, the selection of the appropriate analysis methodologies pertaining
to different problems is crucial. At the same time there has been an effort to reduce the power requirement for data
analysis. This in turn triggered the idea of developing low power damage detection algorithms. In this paper a comparison between different damage detection techniques are presented and problems with different materials and structural geometries are considered. Three damage detection techniques were selected and evaluated.
In order to take full advantages of composites and enable future composite structures to operate at their physical limits
rather than limits predetermined from computational design assumptions and safety factors, there is a need to develop an
embeddable sensing system to allow a structure to "feel" and "think" its structural state. In this paper, the concept of
multi-modal sensing capabilities using a network of multifunctional sensors integrated with a structure has been
developed. Utilizing this revolutionary concept, future structures can be designed and manufactured to provide multiple
modes of information that when synthesized together can provide capabilities for intelligent sensing, environmental
adaptation and multi-functionality. To demonstrate the feasibility of multi-modal sensing capabilities with built-in sensor
network, one single type of piezoelectric sensor was selected to perform the measurements of dynamic strain,
temperature, damage detection and impact monitoring. The uniqueness of the sensing system includes (1) Flexible,
multifunctional sensor networks for integration with any type of composite structural component, (2) Scalable sensor
network for monitoring of a large composite structure, (3) Reduced number of connecting wires for sensors, (4) Hybrid
diagnostics with multiple sensing capabilities, (5) Sensor network self-diagnostics and self-repair for damaged sensor
Composites are increasingly used in numerous structural applications because of their low weight-to-strength and
weight-to-stiffness ratios. However, the performance and behavior characteristics of nearly all in-service composite
structures can be affected by degradation resulting from sustained use as well as from exposure to severe environmental
conditions or damage resulting from external conditions such as impact, loading abrasion, operator abuse. These factors
can have serious consequences on the structures relative to safety, cost, and operational capability. In this paper, a
SmartComposite system is introduced for monitoring the integrity of large composite structures. Key features of the
system include miniaturized lightweight hardware, self-diagnostics and an adaptive algorithm to automatically
compensate for damaged sensors, reliable damage detection under different environmental conditions, and generation of
POD curves. Tests were conducted on composite test article with sensor network embedded inside the composite skin or
surface mounted to demonstrate the impact damage detection capability of the SmartComposite System. It is clear from
the test results that the SmartComposite system can successfully detect impact damages, including both damage location
and probability of damage size.
Acellent Technologies, Inc. developed a smart structural health monitoring (SHM) sensor network that can autonomously assess in real time the structural stability of buildings. The sensor network uses piezoelectric actuators and sensors to characterize damage in, and monitor the
rigidity of components of the building primary structure. Additionally, temperature sensors are integrated into the proposed sensor network to
monitor the temperature of the structural components. Acellent's existing sensor network SMART Layer technology was used as the basis for
the proposed development. The modifications to our existing technology included a redesigned sensor/actuator arrangement, the development
of a SmartDAQ sensor package with the required sensor and electronics, and additional software that provides a map of the structural damage,
temperature and rigidity information. This will be useful to provide a real time assessment of the building structural integrity. The data will be
available for display to provide and early warning to first responders and emergency personnel to ensure their safety prior to entering the
The Air Force Research Laboratory/Space Vehicles Directorate (AFRL/RV) is developing Structural Health Monitoring
(SHM) technologies in support of the Department of Defense's Operationally Responsive Space (ORS) initiative. Such
technologies will significantly reduce the amount of time and effort required to assess a satellite's structural surety.
Although SHM development efforts abound, ORS drives unique requirements on the development of these SHM
systems. This paper describes several technology development efforts, aimed at solving those technical issues unique to
an ORS-focused SHM system, as well as how the SHM system could be implemented within the structural verification
process of a Responsive satellite.
Structural Health Monitoring (SHM) that uses integrated sensor network to provide real-time monitoring of in-service
structures can improve the safety and reliability of the structures significantly. Acellent Technologies' SHM systems
based on SMART technology consists of the integrated sensor network, diagnosis hardware platform and the diagnosis
software. This paper introduces the latest SMART damage detection hardware platform - ScanGenie and the new
analysis software for damage detection in composite and metal structures. The ScanGenie is a portable high-performance
hardware that provides many features such as through-transmission, pulse-echo, temperature measurement,
self-diagnosis, sensor diagnosis, etc. The new analysis software is based on the ScanGenie hardware to provide
functions such as temperature compensation, auto-gain adjustment, impedance-based diagnosis and probability of
detection. The system can be used for damage detection in most composite and metal structures such as aircraft,
spacecraft and civil infrastructures.
It is essential to ensure the safety and reliability of in-service structures such as unmanned vehicles by detecting
structural cracking, corrosion, delamination, material degradation and other types of damage in time. Utilization of an
integrated sensor network system can enable automatic inspection of such damages ultimately. Using a built-in network
of actuators and sensors, Acellent is providing tools for advanced structural diagnostics. Acellent's integrated structural
health monitoring system consists of an actuator/sensor network, supporting signal generation and data acquisition
hardware, and data processing, visualization and analysis software.
This paper describes the various features of Acellent's latest SMART sensing system. The new system is USB-based
and is ultra-portable using the state-of-the-art technology, while delivering many functions such as system self-diagnosis,
sensor diagnosis, through-transmission mode and pulse-echo mode of operation and temperature
measurement. Performance of the new system was evaluated for assessment of damage in composite structures.
The United States is striving to develop an Operationally Responsive Space capability. The goal is to be able to deliver
tailored spacecraft capabilities to the warfighter as needs arise. This places a premium on the timespan between
generating that requirement and having a functioning satellite performing its mission on orbit. Although there is lively
debate regarding how to achieve this responsive space capability, one thing remains undeniable; the satellite flight
qualification and launch vehicle integration process needs to be dramatically truncated. This paper describes the Air
Force Research Laboratory's attempts to validate the use of Structural Health Monitoring (SHM) in lieu of traditional
structural flight qualification testing schemes (static and shock loads, random vibration, coupled loads analysis, thermal
vacuum testing, etc.) for potential Responsive Space (RS) satellites.
Composites are becoming increasingly popular materials used in a wide range of applications on large-scale structures
such as windmill blades, rocket motor cases, and aircraft fuselage and wings. For these large structures, using
composites greatly enhances the operation and performance of the application, but also introduces extraordinary
inspection challenges that push the limits of traditional NDE in terms of time and cost. Recent advances in Structural
Health Monitoring (SHM) technologies offer a promising solution to these inspection challenges. But efficient design
methodologies and implementation procedures are needed to ensure the reliability and robustness of SHM technologies
for use in real-world applications. This paper introduces the essential elements of the design and implementation
process by way of example. State-of-the-art techniques to optimize sensor placement, perform self-diagnostics,
compensate for environmental conditions, and generate probability of detection (POD) curves for any application are
discussed. The techniques are presented in relation to Acellent's recently developed SmartComposite System that is
used to monitor the integrity of large composite structures. The system builds on the active sensor network technology
of Acellent that is analogous to a built-in acousto-ultrasonic NDE system. Key features of the system include new
miniaturized lightweight hardware, self-diagnostics and adaptive algorithm to automatically compensate for damaged
sensors, reliable damage detection under different environmental conditions, and generation of POD curves. This paper
will provide an overview of the system and demonstrate its key features.
This manuscript includes information from test evaluations and development of a smart event detection system for use
in monitoring composite rocket motor cases for damaging impacts. The primary purpose of the system as a sentry for
case impact event logging is accomplished through; implementation of a passive network of miniaturized piezoelectric
sensors, logger with pre-determined force threshold levels, and analysis software. Empirical approaches to structural
characterizations and network calibrations along with implementation techniques were successfully evaluated, testing
was performed on both unloaded (less propellants) as well as loaded rocket motors with the cylindrical areas being of
primary focus. The logged test impact data with known physical network parameters provided for impact location as
well as force determination, typically within 3 inches of actual impact location using a 4 foot network grid and force
accuracy within 25%of an actual impact force. The simplistic empirical characterization approach along with the robust
/ flexible sensor grids and battery operated portable logger show promise of a system that can increase confidence in
composite integrity for both new assets progressing through manufacturing processes as well as existing assets that may
be in storage or transportation.
Monitoring the continued health of aircraft subsystems and identifying problems before they affect airworthiness has
been a long-term goal of the aviation industry. Because in-service conditions and failure modes experienced by
structures are generally complex and unknown, conservative
calendar-based or usage-based scheduled maintenance
practices are overly time-consuming, labor-intensive and expensive. Metal structures such as helicopters and other
transportation systems are likely to develop fatigue cracks under cyclic loads and corrosive service environments. Early
detection of cracks is a key element to prevent catastrophic failure and prolong structural life.
Furthermore, as structures age, maintenance service frequency and costs increase while performance and availability
decrease. Current non-destructive inspection (NDI) techniques that can potentially be used for this purpose typically
involve complex, time-intensive procedures, which are labor-intensive and expensive. Most techniques require access to
the damaged area on at least one side, and sometimes on both sides. This can be very difficult for monitoring of certain
inaccessible regions. In those cases, inspection may require removal of access panels or even structural disassembly.
Once access has been obtained, automated inspection techniques likely will not be practical due to the bulk of the
required equipment. Results obtained from these techniques may also be sensitive to the sweep speed, tool orientation,
and downward pressure. This can be especially problematic for
hand-held inspection tools where none of these
parameters is mechanically controlled. As a result, data can vary drastically from one inspection to the next, from one
technician to the next, and even from one sweep to the next.
Structural health monitoring (SHM) offers the promise of a paradigm shift from schedule-driven maintenance to
condition-based maintenance (CBM) of assets. Sensors embedded permanently in aircraft safety critical structures that
can monitor damage can provide for improved reliability and streamlining of aircraft maintenance. Early detection of
damage such as fatigue crack initiation can improve personnel safety and prolong service life.
This paper presents the testing of an acousto-ultrasonic piezoelectric sensor based structural health monitoring system for
real-time monitoring of fatigue cracks and disbonds in bonded repairs. The system utilizes a network of distributed
miniature piezoelectric sensors/actuators embedded on a thin dielectric carrier film, to query, monitor and evaluate the
condition of a structure. The sensor layers are extremely flexible and can be integrated with any type of metal or
composite structure. Diagnostic signals obtained from a structure during structural monitoring are processed by a
portable diagnostic unit. With appropriate diagnostic software, the signals can be analyzed to ascertain the integrity of
the structure being monitored. Details on the system, its integration and examples of detection of fatigue crack and
disbond growth and quantification for bonded repairs will be presented here.
Currently, there exist several different types of structural health monitoring (SHM) systems that are in the stage of development and/or are being tested for use in real-world applications. For a number of years, Structural Health Monitoring (SHM) systems have demonstrated feasibility in laboratory and controlled testing environments. Acellent has been developing and testing strategies to bring the SHM field to the next level. These include issues involved with system installation, calibration, reliability and connections for structures fabricated with composite materials. Composite structures are susceptible to hidden or barely visible damage caused by impacts and/or excessive loads that if unchecked may lead to lower structural reliability, higher life-cycle costs, and loss in operational capability. Current maintenance and inspection techniques for in-service composite structures can be labor-intensive and time-consuming. Utilization of an integrated sensor network system such as that developed by Acellent can greatly reduce the inspection burden through fast in-situ data collection and processing. Using a built-in network of actuators and sensors, Acellent Technologies is providing the tools required for a practical SHM system. In this paper, key development and testing issues concerning real-world implementation of the SHM system on composite structures are presented.
The SMART Layer (reg. TM) manufactured by Acellent is a thin flexible layer with a network of miniature piezoelectric actuators
and sensors that can be embedded inside or mounted onto metal and composite structures to acquire information on
structural integrity. Currently, SMART Layers (reg. TM) are used to assess the condition of structures and to monitor impact
events. The layers can be used to perform built-in structural inspection by exciting the devices with a periodic or
transient burst controlled input and analyzing the corresponding structural response. The technology can also be applied
to areas concerned with Homeland Security. For example, the technology can be used for motion monitoring and
monitoring of structures used in defense applications. By having a network of sensors that monitor loads on a structure, it
is possible to monitor the movement of people by measuring the loads exerted by them. The SMART Layer (reg. TM) technology
can be used to enhance the readiness of structures used for homeland defense such as manned and unmanned aircraft,
missiles and radar systems. It can also be used to monitor a pipeline network for any terrorist related activity that can
potentially damage the pipe system. A brief overview of such potential applications is presented here.
Monitoring the integrity of filament wound composite structures such as solid rocket motors and liquid fuel bottles is important in order to prevent catastrophic failures and to prolong the service life of these structures. To ensure the safety and reliability of rocket components, they require frequent inspection for structural damages that might have occurred during manufacturing, transportation, and storage. The timely and accurate detection, characterization and monitoring of structural cracking, delamination, debonding and other types of damage is a major concern in the operational environment. Utilization of a sensor network system integrated with the structure itself can greatly reduce this inspection burden through fast in-situ data collection and processing. Acellent Technologies, Inc. is currently developing integrated structural monitoring tools for continuous monitoring of composite and metal structures on aircraft and spacecraft. Acellent's integrated structural monitoring system consists of a flexible sensor/actuator network layer called the SMART Layer, supporting diagnostic hardware, and data processing/analysis software. Recently, Acellent has been working with NASA Marshall Space Flight Center to develop ways of embedding the SMART Layer inside filament wound composite bottles. SMART Layers were designed and manufactured for the filament wound bottles and embedded in them during the filament winding process. Acellent has been working on developing a complete structural health monitoring system for the filament wound bottles including data processing tools to interpret the changes in sensor signal caused by changes in the structural condition or material property. A prototype of a filament wound composite bottle with an embedded sensor network has been fabricated and preliminary data analysis tools have been developed.
Structural health monitoring is a new technology that has been increasingly evaluated by the industry as a potential approach to improve the cost and ease of structural inspection. By improving structural inspection, structures can be made safer and more reliable, thus reducing the cost of structure ownership. Acellent Technologies is developing tools for structural health monitoring. The tools Acellent is offering are the SMART Layer and the SMART Suitcase. The SMART Layer is a flexible layer with a distributed array of piezoelectric transducers made using the printed circuit process that allows easy installation onto structures for in-situ sensing. The SMART Suitcase is an instrument that can interact with the SMART Layer and process the information collected from the structures. Acellent has been providing the system to researchers and companies to try out this new technique. Currently, this system is being evaluated by aircraft manufacturers for monitoring fatigue cracks from rivet holes, by an automotive company for inspecting flaws in composite/foam components, and by aerospace companies for detecting damages in composite/honeycomb sandwich structures. Other recent developments include the addition of fiber-optic sensors onto the SMART Layer and proving the SMART Layer for composite RTM process.
Knowledge of integrity of in-service structures can greatly enhance their safety and reliability and lower structural maintenance cost. Current practices limit the extent of real-time knowledge that can be obtained from structures during inspection, are labor-intensive and thereby increase life-cycle costs. Utilization of distributed sensors integrated with the structure is a viable and cost-effective means of monitoring the structure and reducing inspection costs. Acellent Technologies is developing a novel system for actively and passively interrogating the health of a structure through an integrated network of sensors and actuators. Acellent's system comprises of SMART Layers, SMART Suitcase and diagnostic software. The patented SMART Layer is a thin dielectric film with an embedded network of distributed piezoelectric actuators/sensors that can be surface-mounted on metallic structures or embedded inside composite structures. The SMART Suitcase is a portable diagnostic unit designed with multiple sensor/actuator channels to interface with the SMART Layer, generate diagnostic signals from actuators and record measurements from the embedded sensors. With appropriate diagnostic software, Acellent's system can be used for monitoring structural condition and for detecting damage while the structures are in service. This paper enumerates on the SMART Layer and SMART Suitcase and their applicability to composite and metal structures.