This open access book presents established methods of structural health monitoring (SHM) and discusses their technological merit in the current aerospace environment. While the aerospace industry aims for weight reduction to improve fuel efficiency, reduce environmental impact, and to decrease maintenance time and operating costs, aircraft structures are often designed and built heavier than required in order to accommodate unpredictable failure. A way to overcome this approach is the use of SHM systems to detect the presence of defects. This book covers all major contemporary aerospace-relevant SHM methods, from the basics of each method to the various defect types that SHM is required to detect to discussion of signal processing developments alongside considerations of aerospace safety requirements. It will be of interest to professionals in industry and academic researchers alike, as well as engineering students. This article/publication is based upon work from COST Action CA18203 (ODIN - http://odin-cost.com/), supported by COST (European Cooperation in Science and Technology). COST (European Cooperation in Science and Technology) is a funding agency for research and innovation networks. Our Actions help connect research initiatives across Europe and enable scientists to grow their ideas by sharing them with their peers. This boosts their research, career and innovation.

In the last two decades, the emphasis in aircraft maintenance has been on developing online structural health monitoring systems to replace conventional non destructive inspection techniques which require considerable down-time, human effort and cost. Vibration based damage detection is one of the most promising techniques for implementation in Structural Health Monitoring (SHM). In vibration based methods, the presence of damage is detected by monitoring changes in one of the dynamic parameters of the structure, resonant frequencies, modeshapes or damping characteristics. Compared to modeshape based methods, frequency based methods have the advantage that measurements need to be taken only at a single location. Previous developments on frequency based techniques have relied on Finite Element Model updating; analytical techniques have hitherto been restricted to beams due to the complexity in developing equations for cracked two dimensional structures. In this thesis the analytical approach using an energy formulation is extended to plates with through-thickness cracks, where modeshapes from either numerical modelling or experimental measurements can be employed to determine the energy of vibration. It is demonstrated that by using a hybrid approach, incorporating experimentally measured modeshapes along with measured changes in frequencies, the damage parameters can be estimated without resorting to theoretical modelling or numerical analysis. The inverse problem of finding the crack location, size and orientation from measured changes in frequencies is addressed using minimisation techniques. The forward problem and the inverse algorithm is first validated using numerical simulation and experimental testing of beams with edge cracks and centre cracks. The application of the methodology to the two dimensional case is then validated by numerical simulation and experimental modal analysis of plates with through thickness cracks. A statistical procedure is developed for determination of the 90/95 probability of crack detection and the minimum detectable crack size in both cases. It is demonstrated that the measurement of frequency changes can be successfully employed to detect and assess the location and size of cracks in beams and plates, using modeshapes from theory, Finite Element Analysis (FEA) or measurements.

Two methods for detecting the location of structural damage in an aircraft fuselage using modal test data are presented. Both methods use the dynamically measured static flexibility matrix, which is assembled from a combination of measured modal vectors, frequencies, and driving point residual flexibilities. As a consequence, neither method requires a mode-to-mode correlation, and both avoid tedious modal discrimination and selection. The first method detects damage as a softening in the point flexibility components, which are the diagonal entries in the flexibility matrix. The second method detects damage from the disassembled elemental stiffnesses as determined using a presumed connectivity. Vibration data from a laser vibrometer is used to measure the modal mechanics of a DC9 aircraft fuselage before and after induced weakening in a longitudinal stringer. Both methods are shown to detect the location of the damage, primarily because the normal stiffness of the reinforced shell of the fuselage is localized to a few square centimeters.

Non destructive testing aimed at monitoring, structural identification and di- nostics is of strategic importance in many branches of civil and mechanical - gineering. This type of tests is widely practiced and directly affects topical issues regarding the design of new buildings and the repair and monitoring of existing ones. The load bearing capacity of a structure can now be evaluated using well established mechanical modelling methods aided by computing facilities of great capability. However, to ensure reliable results, models must be calibrated with - curate information on the characteristics of materials and structural components. To this end, non destructive techniques are a useful tool from several points of view. Particularly, by measuring structural response, they provide guidance on the validation of structural descriptions or of the mathematical models of material behaviour. Diagnostic engineering is a crucial area for the application of non destructive testing methods. Repeated tests over time can indicate the emergence of p- sible damage occurring during the structure's lifetime and provide quantitative estimates of the level of residual safety.

Organized by the International Association for Structural Control(IASC), and sponsored by the European Association for the Controlof Structures (EACS), the recent world conference on structuralcontrol (3WCSC) brought together engineers, scientists, architects,builders and other practitioners interested in the general fieldsof active, hybrid and passive vibration control, health monitoringand damage detection, intelligent/smart materials and systems.Applications included buildings, bridges, space structures andcivil infrastructures under the action of dynamic environments(earthquake, wind, traffic...) and man-made loads. It provideda valuable forum for the discussion of the most pressing concernsin structural control and its related topics. The conference covered a wide range of topics including activeand semi-active control devices, passive control devices, controlalgorithms for linear and non-linear systems, modeling andidentification of structural systems, sensors, health monitoringand damage detection, benchmark test of building and bridges,innovative materials for structural control, applications toaerospace structures, applications to bridges, applications tocritical structures, external dynamic force characteristics andcontrollability issues, implications of severe ground motions, windforces, codes for structural control, and so forth. Suchcomprehensive treatment of the most innovative developments instructural control will make these volumes an informative referencefor all researchers and engineers interested in this area. Proceedings of the US - Europe Workshop On Sensors andSmart Structures Technology Como and Somma Lombardo, Italy In the last few years, significant progress has been made in thearea of sensing technology and structural healthmonitoring/condition assessment in the US and Europe. Innovativeconcepts involving new hardware, algorithms, and software have beenproposed. There have also been several full-scale trialimplementations of densely sensor-instrumented infrastructures andhealth monitoring systems, as well as case studies on bridges inEurope and in the US. Much can be learnt through US/European collaboration in the areaof experimental verification on small, medium, large and full-scaleprojects. Moreover, a common framework for expanded future jointresearch can be developed on the increased understanding achievedthrough mutual learning. This workshop consisted of seminar sessions on several themeswhich included innovative sensing hardware, advances in wirelesstechnology, and damage detection/characterization and conditionassessment methodologies. In addition, there were several workshopsessions devoted to summarizing the status of the sensors and smartstructures technologies in these topics, identifying the compellingresearch issues, and formulating an action plan withrecommendations for development and implementation through possiblecollaborative research projects and sharing of scientific data.