N. M. M. Maia

A review of vibration-based structural health monitoring with special emphasis on composite materials

Structural health monitoring and damage detection techniques are tools of great importance in the off-shore, civil, mechanical and aeronautical engineering communities, both for safety reasons and because of the economic benefits that can result. The need to be able to detect damage in complex structures has led to the development of a vast range of techniques, of which many are based upon structural vibration analysis. In the present article, some of the latest advances in Structural Health Monitoring and Damage Detection are reviewed, with an emphasis on composite structures on the grounds that this class of materials currently has a wide range of engineering applications. FOREWORD-It should be noted that this review is not intended to be a general, all-encompassing review covering the whole range of structural health monitoring (SHM); it was planned as the starting point for a study focusing on damage detection, localization and assessment for certain kinds of structure. Thus, the line of thought behind the search and the structure of this review is a result of objectives beyond the scope of the paper itself. Nevertheless, it was considered that, once the above was understood, an updated synopsis such as this could also be useful for other researchers in the same field. ©2006 SAGE Publications.

Modal analysis identification techniques

The objective of this paper is to give a general panorama of the subject of modal analysis identification techniques, as a detailed explanation is not possible due to the vast amount of available information concerning the many existing methods. Beginning with an introduction, followed by the various types of classification and a short historical note, the reader is led into the subject, although he or she needs much more information to delve deeper into specific details and developments of individual methods. This information is provided in the fundamental works and textbooks we have cited.

Modal analysis and testing

An Overview of the Fundamentals of Modal Analysis.- to Signal Processing.- 1: Fundamentals of Signal Processing.- 2: Advanced Signal Processing.- Rules for the Exchange and Analysis of Dynamic Information.- I: Basic Definitions and Test Scenarios.- II: Numerically Simulated Results for a Deterministic Excitation with no External Loads.- III: Numerically Simulated and Experimental Results for a Deterministic Excitation with External Loads.- IV: Numerically Simulated and Experimental Results for a Random Excitation.- V: Q-Transmissibility Matrix vs. Single Point Transmissibility in Test Environments.- PartVI: Current Practice and Standards.- Theoretical Models for Modal Analysis.- Fundamentals of Time Domain Modal Identification.- Modal Identification Methods in the Frequency Domain.- Parametric Identification Based on Pseudo-Tests.- Updating of Analytical Models - Basic Procedures and Extensions.- Model Quality Assessment and Model Updating.- Damage Detection and Evaluation I.- Damage Detection and Evaluation II Field Applications to Large Structures.- Structural Modification.- Damping: an Introduction to Viscoelastic Models.- Description of Damping and Applications.- Existence and Normalization of Complex Modes for Post Experimental Use in Modal Analysis.- Active Control of Structures.- Acoustic Modal Analysis.- Neural Networks for Modal Analysis.- Advanced Optimisation Methods for Model Updating.- Modal Analysis for Rotating Machinery.- Nonlinearity in Modal Analysis.

Transmissibility matrix in harmonic and random processes

The transmissibility concept may be generalized to multi-degree-of-freedom systems with multiple random excitations. This generalization involves the definition of a transmissibility matrix, relating two sets of responses when the structure is subjected to excitation at a given set of coordinates. Applying such a concept to an experimental example is the easiest way to validate this method.

Structural damage detection using transmissibility together with hierarchical clustering analysis and similarity measure

Maintenance and repairing in actual engineering for long-term used structures, such as pipelines and bridges, make structural damage detection indispensable, as an unanticipated damage may give rise to a disaster, leading to huge economic loss. A new approach for detecting structural damage using transmissibility together with hierarchical clustering and similarity analysis is proposed in this study. Transmissibility is derived from the structural dynamic responses characterizing the structural state. First, for damage detection analysis, hierarchical clustering analysis is adopted to discriminate the damaged scenarios from an unsupervised perspective, taking transmissibility as feature for discriminating damaged patterns from undamaged ones. This is unlike directly predicting the structural damage from the indicators manifestation, as sometimes this can be vague due to the small difference between damaged scenarios and the intact baseline. For comparison reasons, cosine similarity measure and distance measure are also adopted to draw out sensitive indicators, and correspondingly, these indicators will manifest in recognizing damaged patterns from the intact baseline. Finally, for verification purposes, simulated results on a 10-floor structure and experimental tests on a free-free beam are undertaken to check the suitability of the raised approach. The results of both studies are indicative of a good performance in detecting damage that might suggest potential application in actual engineering real life.

Damage Detection and Quantification Using Transmissibility Coherence Analysis

A new transmissibility-based damage detection and quantification approach is proposed. Based on the operational modal analysis, the transmissibility is extracted from system responses and transmissibility coherence is defined and analyzed. Afterwards, a sensitive-damage indicator is defined in order to detect and identify the severity of damage and compared with an indicator developed by other authors. The proposed approach is validated on data from a physics-based numerical model as well as experimental data from a three-story aluminum frame structure. For both numerical simulation and experiment the results of the new indicator reveal a better performance than coherence measure proposed in Rizos et al., 2008, Rizos et al., 2002, Fassois and Sakellariou, 2007, especially when nonlinearity occurs, which might be further used in real engineering. The main contribution of this study is the construction of the relation between transmissibility coherence and frequency response function coherence and the construction of an effective indicator based on the transmissibility modal assurance criteria for damage (especially for minor nonlinearity) detection as well as quantification.

Estimation of the Rotational Terms of the Dynamic Response Matrix

The dynamic response of a structure can be described by both its translational and rotational receptances. The latter ones are frequently not considered because of the difficulties in applying a pure moment excitation or in measuring rotations. However, in general, this implies a reduction up to 75% of the complete model. On the other hand, if a modification includes a rotational inertia, the rotational receptances of the unmodified system are needed. In one method, more commonly found in the literature, a so called T-block is attached to the structure. Then, a force, applied to an arm of the T-block, generates a moment together with a force at the connection point. The T-block also allows for angular displacement measurements. Nevertheless, the results are often not quite satisfactory. In this work, an alternative method based upon coupling techniques is developed, in which rotational receptances are estimated without the need of applying a moment excitation. This is accomplished by introducing a rotational inertia modification when rotating the T-block. The force is then applied in its centroid. Several numerical and experimental examples are discussed so that the methodology can be clearly described. The advantages and limitations are identified within the practical application of the method.

A new approach for the modal identification of lightly damped structures

Abstract A new approach for the modal identification of lightly damped structures is proposed, being derived from, and a particular case of, the Rational Fraction Polynomial Method. The novelty of the new method lies in the fact that the results are obtained with the minimum of intervention and experience of the user: the method is automatic and can be made “intelligent”, in that it makes judgements and takes decisions. Some examples are presented and discussed in order to illustrate the method.

Evaluation of the Performance of Three Different Methods Used in the Identification of Rigid Body Properties

The identification of the rigid body properties of a structure is an important matter in various structural dynamic applications, namely in structural modification (coupling/uncoupling), optimization and vibration control. In most situations, the experimental route is the only via to obtain the desired dynamic properties. This goal is achieved by an inverse process which starts from the measurement of Frequency Response Functions (FRFs) and ends on matrices describing the mass distribution of a rigid body.

Using the Detection and Relative Damage Quantification Indicator (DRQ) with Transmissibility

The Detection and Relative Damage Quantification Indicator (DRQ) was presented previously as a reliable damage detection indicator when used with Operational Deflection Shapes (ODS). The DRQ was computed from the Response Vector Assurance Criterion (RVAC) between the damaged and the initial ODS and the resulting value proved to be a good indicator of the presence of damage. The use of the ODS implies that the loads applied to the structure with and without damage are either known or, at least, the same. If the forces are not deterministic but still ergodic, the power spectrum could be used to evaluate the ODS, but still the above conditions hold, in a statistical sense. When a structure is subjected to ambient excitation, those conditions can hardly be assured. The loads may vary quite significantly and the ODS changes may be due to those changes instead of the presence of damage. To avoid this handicap, the authors explore here the use of the Transmissibility functions. If properly defined, the Transmissibility is invariant with respect to the amplitude of the loads. Since the Displacement Transmissibility is load invariant, a picked set of responses can be measured in service and used to predict another set; the result will then be correlated to the actual values using the RVAC and the DRQ will be computed. Numerical and experimental examples illustrate the proposed technique.