Giurgiutiu Structural Health Monitoring with Piezoelectric Wafer Active Sensors

2. Auflage 2014
ISBN: 978-0-12-420102-6
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 1024 Seiten

Structural Health Monitoring with Piezoelectric Wafer Active Sensors, Second Edition provides an authoritative theoretical and experimental guide to this fast-paced, interdisciplinary area with exciting applications across a range of industries. The book begins with a detailed yet digestible consolidation of the fundamental theory relating to structural health monitoring (SHM). Coverage of fracture and failure basics, relevant piezoelectric material properties, vibration modes in different structures, and different wave types provide all the background needed to understand SHM and apply it to real-world structural challenges. Moving from theory to experimental practice, the book then provides the most comprehensive coverage available on using piezoelectric wafer active sensors (PWAS) to detect and quantify damage in structures. Updates to this edition include circular and straight-crested Lamb waves from first principle, and the interaction between PWAS and Lamb waves in 1-D and 2-D geometries. Effective shear stress is described, and tuning expressions between PWAS and Lamb waves has been extended to cover axisymmetric geometries with a complete Hankel-transform-based derivation. New chapters have been added including hands-on SHM case studies of PWAS stress, strain, vibration, and wave sensing applications, along with new sections covering essential aspects of vibration and wave propagation in axisymmetric geometries. - Comprehensive coverage of underlying theory such as piezoelectricity, vibration, and wave propagation alongside experimental techniques - Includes step-by-step guidance on the use of piezoelectric wafer active sensors (PWAS) to detect and quantify damage in structures, including clear information on how to interpret sensor signal patterns - Updates to this edition include a new chapter on composites and new sections on advances in vibration and wave theory, bringing this established reference in line with the cutting edge in this emerging area

Dr. Giurgiutiu is an expert in the field of Structural Health Monitoring (SHM). He leads the Laboratory for Active Materials and Smart Structures at the University of South Carolina. He is a regular contributor of papers to leading conferences in the area, received the award Structural Health Monitoring Person of the Year 2003 and is Associate Editor of the international journal, Structural Health Monitoring.

Autoren/Hrsg.

Giurgiutiu, Victor

Leseproben

Chapter 1 Introduction
This chapter introduces the reader to the concept of structural health monitoring (SHM) and articulates the need for developing SHM systems in order to increase the safety and readiness of our current and future engineering systems while decreasing the life-cycle costs. The chapter briefly reviews some fundamental concepts such as structural fracture and failure, linear elastic fracture mechanics principles and analysis of crack propagation. The principles of aircraft structural integrity program (ASIP), damage-tolerant design and fracture control methodology are reviewed together with component life prediction and airframe life prediction in the context of fatigue testing, aircraft usage, and in-service nondestructive inspection/evaluation (NDI/NDE). The potential for improving diagnosis and prognosis through the application of SHM principles is discussed. The chapter ends with an overview of the book with a brief presentation of the book chapters. It also gives a statement about the book’s purpose and intended audience. This textbook can be used for both teaching and research by students, researchers, practicing engineers, and industry specialists. Comprehensive teaching tools (workout examples, experiments, homework problems, and exercises) and an on-line instructor manual containing lecture plans and homework solutions are offered on the publisher’s website. Keywords
structural health monitoring; SHM; nondestructive inspection/evaluation; NDI; NDE; fracture control; fracture mechanics; aircraft structural integrity program; ASIP; diagnosis; prognosis; life-cycle costs; fatigue testing; crack propagation; airframe life prediction Outline 1.1 Structural Health Monitoring Principles and Concepts 1 1.2 Structural Fracture and Failure 4 1.2.1 Review of Linear Elastic Fracture Mechanics Principles 4 1.2.2 Fracture Mechanics Approach to Crack Propagation 5 1.3 Aircraft Structural Integrity Program (ASIP) 8 1.3.1 Terminology 9 1.3.2 Damage Tolerance and Fracture Control 10 1.3.3 Component Life Prediction 11 1.3.4 Airframe Life Prediction 13 1.3.5 Aircraft Usage 13 1.3.6 In-service NDI/NDE 14 1.3.7 ASIP Inspection Intervals 15 1.3.8 Fatigue Tests and Life-cycle Prognosis 15 1.4 Improved Diagnosis and Prognosis through Structural Health Monitoring 17 1.5 About this Book 18 References 19 1.1 Structural Health Monitoring Principles and Concepts
Structural health monitoring (SHM) is an area of growing interest and worthy of new and innovative approaches. The United States spends more than $200 billion each year on the maintenance of plant equipment and facilities. Maintenance and repairs represent about a quarter of commercial aircraft operating costs. Out of approximately 576,600 bridges in the US national inventory, about a third are either “structurally deficient” and in need of repairs, or “functionally obsolete” and in need of replacement. The mounting costs associated with the aging infrastructure have become an ongoing concern. The increasing age of our existing infrastructure makes the cost of maintenance and repairs a growing concern. Structural health monitoring may alleviate this by replacing scheduled maintenance with as-needed maintenance, thus saving the cost of unnecessary maintenance, on one hand, and preventing unscheduled maintenance, on the other hand. For new structures, the inclusion of structural health monitoring sensors and systems from the design stage is likely to greatly reduce the life-cycle cost. Structural health monitoring systems could ensure increased safety and reliability while reducing maintenance costs. Structural health monitoring has multiple applications. Structural health monitoring assesses the state of structural health and, through appropriate data processing and interpretation, may predict the remaining life of the structure. Many aerospace and civil infrastructure systems are at or beyond their design life; however, it is envisioned that they will remain in service for an extended period. SHM is one of the enabling technologies that will make this possible. It addresses the problem of aging structures, which is a major concern of the engineering community. SHM allows condition-based maintenance (CBM) inspection instead of schedule-driven inspections. Another potential SHM application is in new systems; that is, by embedding SHM sensors and associate sensory systems into a new structure, the design paradigm can be changed and considerable savings in weight, size, and cost can be achieved. A schematic representation of a generic SHM system is shown in Figure 1.1.
Figure 1.1 Schematic representation of a generic airliner SHM system consisting of active sensors, data concentrators, wireless communication, and SHM central unit. Structural health monitoring can be performed in two main ways: (a) passive SHM; and (b) active SHM. Passive SHM is mainly concerned with measuring various operational parameters and then inferring the state of structural health from these parameters. For example, one could monitor the flight parameters of an aircraft (airspeed, air turbulence, g-factors, vibration levels, stresses in critical locations, etc.) and then use the aircraft design algorithms to infer how much of the aircraft useful life has been used up and how much is expected to remain. Passive SHM is useful, but it does not directly address the crux of the problem, i.e., it does not directly examine whether the structure has been damaged or not. In contrast, active SHM is concerned with directly assessing the state of structural health by trying to detect the presence and extent of structural damage. In this respect, the active SHM approach is similar to the approach taken by nondestructive evaluation (NDE) methodologies, only that active SHM takes it one step further: active SHM attempts to develop damage detection sensors that can be permanently installed on the structure and monitoring methods that can provide on-demand structural health bulletins. Recently, damage detection through guided-wave NDE has gained extensive interest. Guided waves (e.g., Lamb waves in plates) are elastic perturbations that can propagate for long distances in thin-wall structures with very little amplitude loss. In Lamb-wave NDE, the number of sensors required to monitor a structure can be significantly reduced. The potential also exists for using phased array techniques that use Lamb waves to scan large areas of the structure from a single location. However, one of the major limitations in the path of transitioning Lamb-wave NDE techniques into SHM methodologies has been the size and cost of the conventional NDE transducers, which are rather bulky and expensive. The permanent installation of conventional NDE transducers onto a structure is not feasible, especially when weight and cost are at a premium such as in aerospace applications. The recently developed piezoelectric wafer active sensors (PWAS) have the potential to improve significantly structural health monitoring, damage detection, and nondestructive evaluation. PWAS are small, lightweight, inexpensive, and can be produced in different geometries. PWAS can be bonded onto the structural surface, can be mounted inside built-up structures, and can even be embedded between the structural and nonstructural layers of a complete construction. Studies are also being performed to embed PWAS between the structural layers of composite materials, though the associated issues of durability and damage tolerance have still to be overcome. Structural damage detection with PWAS can be performed using several methods: (a) wave propagation, (b) frequency response transfer function, or (c) electromechanical (E/M) impedance. Other methods of using PWAS for SHM are still emerging. However, the modeling and characterization of Lamb-wave generation and sensing using surface-bonded or embedded PWAS has still a long way to go. Also insufficiently advanced are reliable damage metrics that can assess the state of structural health with confidence and trust. The Lamb-wave-based damage detection techniques using structurally integrated PWAS are still in their formative years. When SHM systems are being developed, it is often found that little mathematical basis is provided for the choice of the various SHM parameters involved such as transducer geometry, dimensions, location and materials, excitation frequency, bandwidth, etc. Admittedly, the field of structural health monitoring is vast. A variety of sensors, methods, and data reduction techniques can be used to achieve the common goal of asking the structure “how it feels” and determining the state of its “health”, i.e., structural integrity, damage presence (if any), and remaining life. Attempting to give an encyclopedic coverage of all such sensors, methods, and techniques is not what this book intends to do. Rather, this book intends to present an integrated approach to SHM using the PWAS as a case study and then taking the reader through a step-by-step presentation of how the PWAS transducers can be used to detect and quantify the presence of damage in a given...