System and method for detecting structural damage

Abstract

A system and method for detecting structural damage is provided that utilizes a general order perturbation methodology involving multiple perturbation parameters. The perturbation methodology is used iteratively in conjunction with an optimization method to identify the stiffness parameters of structures using natural frequencies and / or mode shape information. The stiffness parameters are then used to determine the location and extent of damage in a structure. A novel stochastic model is developed to model the random impact series produced manually or to generate a random impact series in a random impact device. The random impact series method or the random impact device can be used to excite a structure and generate vibration information used to obtain the stiffness parameters of the structure. The method or the device can also just be used for modal testing purposes. The random impact device is a high energy, random, and high signal-to-noise ratio system.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a method and apparatus for detecting structural damage, and, more specifically, to a method and apparatus for detecting structural damage using changes in natural frequencies and / or mode shapes. 2. Background of the Related Art Damage in a structure can be defined as a reduction in the structure's load bearing capability, which may result from a deterioration of the structure's components and connections. All load bearing structures continuously accumulate structural damage, and early detection, assessment and monitoring of this structural damage and appropriate removal from service is the key to avoiding catastrophic failures, which may otherwise result in extensive property damage and cost. A number of conventional non-destructive test (NDT) methods are used to inspect load bearing structures. Visual inspection of structural members is often unquantifiable and unreliable, especially in instances wh...

AI Technical Summary

Benefits of technology

The invention is a system and method for detecting structural damage based on changes in natural frequencies and mode shapes. It can be applied to large operating structures with millions of degrees of freedom. It can accurately detect small to large levels of damage and is useful for detecting a large level of damage with severe mismatch between the eigenparameters of the damaged and undamaged structures. It can work with a limited number of measured vibration modes and can handle structures with slight nonlinearities or closely spaced vibration modes. It can handle different levels of measurement noise and can automate damage detection and assessment. It can also be used in the field to monitor structural health and optimize useful service life. The random impact series method enables the modal parameters such as natural frequencies and mode shapes to be measured for a large structure or a structure in the field when there are noise effects such as those arising from the wind or other ambient excitation.

Problems solved by technology

Visual inspection of structural members is often unquantifiable and unreliable, especially in instances where access to damaged areas may be impeded or damage may be concealed by paint, rust, or other coverings.

PT reveals only surface cracks and imperfections, and can require a large amount of potentially hazardous dye be applied and disposed of.

Further, due to the current required to generate a strong enough magnetic field to detect cracks, MT is not practically applied to large structures.

Likewise, eddy current testing (ET) uses changes in the flow of eddy currents to detect flaws, and only works on materials that are electrically conductive.

Results generated by all of these methods can be skewed due to surface conditions, and cannot easily isolate damage at joints and boundaries of the structure.

Unless a general vicinity of a damage location is known prior to inspection, none of these methods are easily or practically applied to large structures which are already in place and operating.

On the other hand, resonant inspection methods are not capable of determining the extent or location of damage, and is used only on a component rather than a assembled structure.

None of the above NDT methods are easily or practically applied to large structures requiring a high degree of structural integrity.

However, this type of vibration based damage testing does not work for most structures.

Because of the single iteration, these methods are not accurate in detecting a large level of damage.

The third category includes control-based eigenstructure assignment methods, which have the similar limitation to that of the direct methods indicated above and are not accurate in detecting a large level of damage.

None of these current vibration based methods have been incorporated into an iterative algorithm that can detect small to large levels of damage, and the vibration based approach for structures remains an immature technology area which is not readily available on a commercial basis.

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