Damage detection from changes in curvature mode shapes

This paper gives a survey of frequency domain identification methods for rational transfer functions in the Laplace (s) or z-domain. The interrelations between the different approaches are highlighted through a study of the (equivalent) cost functions. The properties of the various estimators are discussed and illustrated by several examples. >

Parametric identification of transfer functions in the frequency domain-a survey

Machine tool spindle units

This paper was originally presented at the first IMAC Conference in 1982 [6]. Its abstract was a follows, This is a new formulation that overcomes many of the numerical analysis problems associated with an old least squared error parameter estimation technique. Overcoming these problems has made this technique feasible for implementation on mini-computer based measurement systems. This technique is not only useful in modal analysis applications for identifying the modal parameters of structures, but it can also be used for identifying poles, zeros and resonances of combined electro-mechanical servo-systems. Our early development of this method took place in the late 1970’s, and it was first implemented (as an SDOF fitter) in a modal testing instrument, the Hewlett Packard 5423A Structural Dynamics Analyzer. Since then it has been used in a variety of other analyzers and modal analysis software packages (as an MDOF & Global fitter), and is still widely used today. In this paper, we will review other IMAC papers that have been written about this method during the past twenty years. We will also discuss remaining curve fitting challenges and opportunities for further research.

Parameter estimation from frequency response measurements using rational fraction polynomials (twenty years of progress)

Simplified models for the location of cracks in beam structures using measured vibration data

Experimental modal analysis has grown steadily in pop ularity since the advent of the digital FFT spectrum analyzer in the early 1970’s. Today, impact testing (or bump testing) has become widespread as a fast and economical means of finding the modes of vibration of a machine or structure. In this paper, we review all of the main topics associated with experimental modal analysis (or modal testing), including making FRF measurements with a FFT analyzer, modal excitation techniques, and modal parameter estimation from a set of FRFs (curve fitting).

EXPERIMENTAL MODAL ANALYSIS By

This is a new formulation which overcomes many of the numerical analysis problems associated with an old least squared error parameter estimation technique. Overcoming these problems has made this technique feasible for implementation on mini-computer based measurement systems. This technique is not only useful in modal analysis applications for identifying the modal parameters of structures, but it can also be used for identifying poles, zeros and resonances of combined electro-mechanical servo-systems.

Parameter estimation from frequency response measurements using rational fraction polynomials

Mode shapes and operating "deflection" shapes are related to one another. In fact, one is always measured in order to obtain the other. Yet, they are quite different from one another in a number of ways. This article discusses the relationships between modal testing, modal analysis and operating deflection shape measurements.

Is It a Mode Shape, or an Operating Deflection Shape?

Modal testing has become commonplace in many industries today as a research and development tool. In this capacity, it is used primarily during product prototype development and for trouble-shooting noise and vibration problems in general. Very little use has been made of this technology to date, though, for detecting faults in mechanical structures. By "faults," we mean any of the following occurrences: • Failure of the structural material, e.g., cracking or breaking. • Loosening of assembled parts. • Flaws, voids, cracks, thin spots, etc. caused during manufacturing. • Improper assembly of parts during manufacturing. In this paper, the correlation between a physical change and changes in the structure's modal parameters is investigated. A flat plate structure with a rib stiffener bolted to it is used as the test specimen and modal tests are performed on it using an impact hammer. This paper not only includes discussion about the advantages of using experimental modal data as a means of detecting structural faults, but also includes demonstrations of the sensitivity of modal parameters to physical changes. Specifically, it is shown how modal parameters can detect variations in the bolt tightness between the plate and the rib.

Fault detection in structures from changes in their modal parameters

Mode shapes and operating deflection shapes (ODS’s) are related to one another. In fact, ODS’s are always measured in order to obtain mode shapes. Yet, they are quite different from one another in a number of ways. In this paper, we will discuss ODS measurements, and their relationship to experimental modal parameters.

Mark Richardson

Papers

EXPERIMENTAL MODAL ANALYSIS By

Parameter estimation from frequency response measurements using rational fraction polynomials

Is It a Mode Shape, or an Operating Deflection Shape?

Fault detection in structures from changes in their modal parameters

INTRODUCTION TO OPERATING DEFLECTION SHAPES By