Identification of linearised joint structural parameters by combined use of measured and computed frequency responses

doi:10.1016/0888-3270(91)90028-4

Mechanical Systems and Signal Processing

Volume 5, Issue 4, July 1991, Pages 267-277

https://doi.org/10.1016/0888-3270(91)90028-4 Get rights and content

Abstract

The necessity of accurate prediction of structural dynamics has led to extensive studies on identification of joint structural parameters. The present paper proposes an effective identification scheme for linearised joint parameters of a structure, which makes use of not only the measured frequency response functions (FRFs) of the structure but also the computed FRFs of an auxiliary model. The auxiliary model is constructed such that it possesses the same properties as the test structure except the joint structural parameters to be determined. The fundamental assumption is that the dynamic properties of the structure other than the joint parameters to be identified are completely known. The proposed identification scheme is straighforward and cost-effective, requiring neither modal parameters nor any condensation techniques for the model.

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Cited by (42)

Nonlinear vibration mechanism and modeling for flange-bolted joints
2024, Mechanical Systems and Signal Processing
Nonlinear modeling of bolted joints is an extremely challenging task in structural dynamics. Considering the contact nonlinearity of joint interfaces, this study presents a new nonlinear dynamic model for flange-bolted joints. Firstly, the elastostatic properties of the flange are studied through finite element (FE) analysis. It is found that the axial stiffness shows significant differences under tension and compression, and the flange exhibits axial deformation under bending loads. Subsequently, through modeling the vibration mechanism of the axial and bending behavior of the flange, the longitudinal coupled vibrations subjected to bending impacts are analytically predicted. Meanwhile, the relevant nonlinear dynamic model for the flange is further developed, which reveals the mapping relations between the vibration properties and the preload performances. Finally, an experimental investigation is performed to validate the presented model.
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The advantages of FRF based approaches over modal based approaches in joint parameter identification were discussed by Nobari [18]. Hong and Lee [19] proposed a hybrid method which employs the experimentally measured and numerically simulated FRFs and identifies the structural joint parameters. Hwang [20] identified the joint parameters by employing the FRFs of a structure with joint and the FRFs of a structure without joint.
The stiffness characteristics of the contact interfaces in joints or boundary conditions have a great effect on dynamic response of assembled structures. Predictive analytical/numerical modeling of mechanical structures is not possible without representing the contact interfaces accurately. Because of the complex mechanisms involved, contact interfaces introduce difficulties both in modeling the inherent dynamics and identification of the model parameters. In this paper an identification approach employing the dynamic characteristic equation is proposed for linear interface parameters. The proposed method is applicable to both analytical and numerical problems. The accuracy of the proposed method is investigated by simulation results of a beam with elastic boundary support and experimental results of a bolted lap-joint.
FRF based joint dynamics modeling and identification
2013, Mechanical Systems and Signal Processing
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The CMS method is therefore more applicable for the finite element (FE) environment but it may be difficult to use for the experimental data. As a result of these limitations, another methodology (i.e. response-based methods) is introduced, which directly deals with the frequency response properties of the structure and does not require the extraction of modal data [6]. The receptance coupling (RC) method, which is a response-based method, couples substructures using experimentally or analytically obtained frequency response functions (FRFs) [7].
Complex structures, such as machine tools, are comprised of several substructures connected to each other through joints to form the assembled structures. Joints can have significant contributions on the behavior of the overall assembly and ignoring joint effects in the design stage may result in considerable deviations from the actual dynamic behavior. The identification of joint dynamics enables us to accurately predict overall assembled dynamics by mathematically combining substructure dynamics through the equilibrium and compatibility conditions at the joint. The essence of joint identification is the determination of the difference between the measured overall dynamics and the rigidly coupled substructure dynamics. In this study, we investigate the inverse receptance coupling (IRC) method and the point-mass joint model, which considers the joint as lumped mass, damping and stiffness elements. The dynamic properties of the joint are investigated using both methods through a finite element (FE) simulation and experimental tests.
Identification of dynamic stiffness matrices of elastomeric joints using direct and inverse methods
2013, Mechanical Systems and Signal Processing
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Joints such as fasteners, welds, bearings, and elastomers present many challenges in modeling, and thus, the development of identification methods has drawn much attention [1–11].
New experiments are designed to permit direct comparison between direct and inverse identification methods of the dynamic stiffness matrices of elastomeric joints, including non-diagonal terms. The joints are constructed with combinations of inclined elastomeric cylinders to control non-diagonal terms in the stiffness matrix. The inverse experiment consists of an elastic metal beam end-supported by elastomeric joints coupling the in-plane transverse and longitudinal beam motion. A prior method is extended to identify the joint dynamic stiffness matrices of dimension 3 from limited modal measurements of the beam. The dynamic stiffness and loss factors of the elastomeric cylinders are directly measured in a commercial elastomer test machine in shear, compression, and inclined configurations and a coordinate transformation is used to estimate the kinematic non-diagonal stiffness terms. Agreement is found for both dynamic stiffness and loss factors between the direct and inverse methods at small displacements. Further, the identified joint properties are employed in a model that successfully predicts the modal parameters and accelerance spectra of the inverse experiment. This article provides valuable insight on the difficulties encountered when comparing system and elastomeric component test results.
Identifying joints from measured reflection coefficients in beam-like structures with application to a pipe support
2010, Mechanical Systems and Signal Processing
Citation Excerpt :
Some techniques arrive at a frequency domain description of the joint without making any a priori assumptions about the physical form of the joint [1,2]. Other techniques presuppose a parametric joint model (e.g. masses, springs and dampers) and tune the parameter values so as to best match experimental data [3–5]. In the case of FE models, modal or frequency response data are frequently used as they are often readily measurable [6].
The properties of joints in mechanical systems are notoriously uncertain causing corresponding uncertainty in the systems’ dynamic responses. A piping system is one such example where an accurate knowledge of joint properties is useful for the purposes of structure-borne sound transmission, fatigue considerations and structural health monitoring. This paper presents an inverse technique that is applicable to joint estimation in one-dimensional structures such as a pipe. Measured wave reflection coefficients are used which have several advantages over modal information. First, they characterise just the joint and adjacent pipes and are independent of the rest of the built-up system. Second, they are potentially more sensitive to the joint parameters in question than are modal parameters.
The method is illustrated by means of an experimental case study featuring a straight pipe suspended by a cantilevered hanger. The stiffness and inertia of the hanger are accurately identified from measured data at frequencies significantly higher than the fundamental modes of the structure.
Uncertainties and dynamic problems of bolted joints and other fasteners
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This review article provides an overview of the problems pertaining to structural dynamics with bolted joints. These problems are complex in nature because every joint involves different sources of uncertainty and non-smooth non-linear characteristics. For example, the contact forces are not ideally plane due to manufacturing tolerances of contact surfaces. Furthermore, the initial forces will be redistributed non-uniformly in the presence of lateral loads. This is in addition to the prying loading, which is non-linear tension in the bolt and non-linear compression in the joint. Under environmental dynamic loading, the joint preload experiences some relaxation that results in time variation of the structure's dynamic properties. Most of the reported studies focused on the energy dissipation of bolted joints, linear and non-linear identification of the dynamic properties of the joints, parameter uncertainties and relaxation, and active control of the joint preload. Design issues of fully and partially restrained joints, sensitivity analysis to variations of joint parameters, and fatigue prediction for metallic and composite joints will be discussed.

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Identification of linearised joint structural parameters by combined use of measured and computed frequency responses

Abstract

Journal of Sound and Vibration

Journal of Sound and Vibration

Mechanical Systems and Signal Processing

Journal of Sound and Vibration

Identification of the joint structural parameters of machine tool by DDS and FEM

Transactions ASME, Journal of Engineering for Industry

Optimal weight orthogonalization of measured modes

AIAA Journal

Optimal correction of mass and stiffness matrices using measured modes

AIAA Journal

Parameter adjustment of a finite element model by means of measured natural frequencies

Analytical model improvement using modal test results

AIAA Journal