Showing papers on "Structural health monitoring published in 1993"
08 Sep 1993
TL;DR: The basic system architecture, program assumptions and constraints, the analytic methods used to monitor aircraft structural integrity, and the potential payoffs of an on-board structural health monitoring system (SHMS) are investigated.
Abstract: A computer program entitled SHARP (structural health assessment and review program) has been developed to demonstrate smart structures concepts for automated aircraft health monitoring. SHARP is an object-oriented design, combining C++ and FORTRAN routines d veloped and implemented on a Motorola 68030 platform. SHARP combines unique analytic flaw generation algorithms with more traditional durability and damage tolerance routines to process data from a variety of sensors (acoustic emission, strain, acceleration etc.) and assess the aircraft's structural integrity. This paper outlines the basic system architecture, program assumptions and constraints. The analytic methods used to monitor aircraft structural integrity are then discussed in the context of current military aircraft structural integrity programs (ASIP). Finally, the potential payoffs of an on-board structural health monitoring system (SHMS) are investigated.
6 citations
01 Jan 1993
TL;DR: In this article, a structural integrity assessment approach based on the measured eigenmodes is proposed, which is completed by a new method which supplies an independent diagnosis only on the basis of the measured Eigenfrequencies.
Abstract: Among the new perspectives opened by the recent developments in the field of adptive structures is an interesting future for structural health monitoring. A structure with embedded actuators and sensors represents the best environment for an integrity assessment device based on the monitoring of the systems's vibrational behavior. For this purpose, an algorithm is needed that is able to extract reliable information from vibration measurements about the position and extent of damage in a structural system. This idea is not new; many contributions can be found in the literature. Nevertheless, until now no approach has established itself as the way to be followed. On the contrary, the opinion has become more and more popular that damage detection by modal techniques would be possible only with extremely accurate measurement results. The techniques examined in this paper give confidence to the possiblility of realizing a reliable modal damage diagnosis under normal measurement conditions and also when a small amount of measured modal data is available. A recently proposed detection approach, based on the measured eigenmodes, is completed here by a new method which supplies an independent diagnosis only on the basis of the measured eigenfrequencies. Both approaches require the availability of a reliable mathematical model of the undamaged structure. Numerically and experimentally tested on a cantilever beam, the approaches are virtually able to operate on all structurtes for which a modelization with the Finite Element is possible. The damage localization is supplied with a resolution that is correlated with the element dimensions in the model. Some of the results are presented in the paper; the information on.
4 citations
19 Apr 1993
TL;DR: In this article, the concept of the minimum rank perturbation theory (MRPT) is adopted to determine the damage extent on the mass properties of an undamped structure, and the MRPT is extended to the case of proportionally damped structures.
Abstract: Recently, the authors proposed computationally attractive algorithms to determine the location and extent of structural damage for undamped structures assuming damage results in a localized change in stiffness properties. The algorithms make use of a finite-element model and a subset of measured eigenvalues and eigenvectors. The developed theories approach the damage location and extent problem in a decoupled fashion. First, a theory is developed to determine the location of structural damage. With location determined, a damage extent theory is then developed. The damage extent algorithm is a minimum rank perturbation, which is consistent with the effects of many classes of structural damage on a finite-element model. In this work, the concept of the minimum rank perturbation theory (MRPT) is adopted to determine the damage extent on the mass properties of an undamped structure. In addition, the MRPT is extended to the case of proportionall y damped structures. For proportionally damped structures, the MRPT is used to find the damage extent in any two of the three structural property matrices (mass, damping, or stiffness). Finally, illustrative case studies using both numerical and actual experimental data are presented. HE advent of the Space Shuttle has prompted considerable attention to the design and control of large space structures. Due to the large size and complexity of envisioned structures, as well as the use of advanced materials to reduce structural weight, it may become necessary to develop a structural health monitoring system to detect and locate structural damage as it occurs. From experience gained in the machinery health monitoring field, one would expect the vibration signature of the structure, either frequency response functions and/or modal parameters, to provide useful information in determining the location and extent of structural damage. Assume that a refined finite element model (FEM) of the structure has been developed before damage has occurred. By refined, we mean that the measured and analytical modal properties are in agreement. Next, assume that at a later date some form of structural damage has occurred. If significant, the damage will result in a change in the structures modal parameters. The question is: can the discrepancy between the original FEM modal properties and postdamage modal properties be used to ascertain structural damage? Most prior work in damage detection has used the general framework of FEM refinement (system identification) in the development of damage assessment algorithms. The motivation behind the development of FEM refinement techniques is based on the need to validate engineering FEMs before their acceptance as the basis for final design analysis. The standard problem has been to seek a refined FEM that is as close to the original FEM and whose modal properties are in agreement with those that are measured subject to various constraints such as symmetry and sparsity preservation. A considerable amount of work in this area has been
4 citations
01 Jan 1993
TL;DR: In this article, a modal approach for structural health monitoring is proposed, which performs the damage detection on the basis of measured modal properties of the structure, with the prerequisite that a reliable mathematical model of the undamaged structure is available.
Abstract: The dynamic behavior of a structural system is influenced by damage to the structure. Extraction of reliable information about the position and extent of damage from vibration measurement results would transform modal analysis into an attractive tool for non-destructive assessment of structural integrity. The advantages of a modal approach for structural health monitoring would be remarkable for a wide range of applications: aircraft, space structures, off-shore platforms, and basically all systems characterized by limited accessibility and high inspection costs. Therefore, it is no wonder that in the last few decades much research has been done in this field. In spite of the simplicity of the basic idea, until now no approach has established itself as the way to be followed. On the contrary, the opinion that damage detection by modal techniques would be possible only with extremely accurate measurement results has become more and more popular. The new technique proposed in this paper performs the damage detection on the basis of measured modal properties of the structure, with the prerequisite that a reliable mathematical model of the undamaged structure is available. The method is virtually able to operate on all structures for which a modelization with the finite element method is possible. The damage localization is supplied with a resolution which is correlated with the element dimensions in the model. The quality of the detection is influenced by the accuracy of the measured modal parameters, as well as by the amount of available data. In order to verify the proposed method, some numerical simulations and experimental tests were performed on a cantilever beam. This paper presents some of the results. Not only large zones of stiffness degradation, but also small cracks are successfully detected in the test structure.
1 citations
01 Jan 1993
TL;DR: In this article, the feasibility of improving spatial resolution by incorporating the zeros of cross transfer functions is demonstrated, and the frequency based procedure was developed specifically to support structural health monitoring in an environment that is less than ideal for modal testing.
Abstract: Frequency based localization is a technique which locates structural flaws by monitoring changes in transfer function pole and zero frequencies. This technique has been successfully applied to isolate simulated structural flaws in a modal database representation of a spacecraft using transfer function poles and driving point zeros. However, the number of usable frequencies and, therefore, the achievable spatial resolution, was limited by high modal density and narrow excitation bandwidth. In this paper, the feasibility of improving spatial resolution by incorporating the zeros of cross transfer functions is demonstrated. The frequency based procedure was developed specifically to support structural health monitoring in an environment that is less than ideal for modal testing. For spacecraft on-orbit, testing to detect structural flaws is constrained by the limited availability of sensors and excitation sources, and by the requirement for minimal impact on mission operations. Frequency based localization is well suited for this application, since measurements of input forces and modal frequencies only are required. This greatly reduces the requirements for sensors and data acquisition compared to localization techniques that rely on measurements of mode shapes.
TL;DR: In this article, the feasibility of a health monitoring system for crack form damage of metal ship structures is discussed, and the significance of health monitoring on structural safety and the cost of a system in comparison with in-service inspections based on reliability analysis are also discussed.
Abstract: In this paper, the feasibility of a health monitoring systems for crack form damage of metal ship structures is discussed. In order to carry out a wide range of monitoring, experiments were carried out using three types of line sensors: an electro-conductive film sensor, an electro-conductive paint sensor and a plastic optical fibre sensor. The sensors were bonded to the surfaces of a welded joint model and a notched plate specimen and fatigue tests were carried out. The sensors were monitored for crack detection performance, the possibility of false indication, the influence of a corrosive environment and the time and cost required for installation. The significance of health monitoring on structural safety and the cost of a system in comparison with in-service inspections based on reliability analysis are also discussed.