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hassan jalali

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Caglar Baslamisli

Hacettepe University

University of Basrah

Saiful Amri Mazlan

Universiti Teknologi Malaysia - UTM

ESPOL (Escuela Superior Politécnica del Litoral)

Pakharuddin Samin

Universiti Teknologi Malaysia - UTM

spyros G tzafestas

National Technical University of Athens

University of East London

Gwen Robbins Schug

University of North Carolina at Greensboro

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Papers by hassan jalali

Bolt-Jointed Structural Modelling by Including Uncertainty in Contact Interface Parameters

Springer eBooks, Jul 29, 2022

A generalization of the Valanis model for friction modelling

Mechanical Systems and Signal Processing

Model identification and dynamic analysis of ship propulsion shaft lines

Dynamic response analysis of mechanical structures is usually performed by adopting numerical/ana... more Dynamic response analysis of mechanical structures is usually performed by adopting numerical/analytical models. Finite element (FE) modeling as a numerical approach plays an important role in dynamic response analysis of complex structures. The calculated dynamic responses from FE analysis are only reliable if accurate FE models are used. There are many elements in real mechanical structures which make constructing accurate FE models difficult. For example, modeling the boundary supports of mechanical structures are usually challenging because of the uncertainties existing in their stiffness values. The stiffness values of boundary supports can be identified by using experimental natural frequencies and hence the FE model can be corrected. In this paper, the FE modeling and updating of propulsion shaft lines in a ship structure is considered by employing experimental modal parameters, i.e. natural frequencies. Natural frequencies of shaft lines are measured by performing experiment...

Modelling the Effect of Preload in a Lap-Joint by Altering Thin-Layer Material Properties

Nonlinear Structures & Systems, Volume 1, 2021

The joints in an assembled structure represent a significant source of energy dissipation and may... more The joints in an assembled structure represent a significant source of energy dissipation and may lead to overall stiffness variation, which may affect high cycle fatigue failure. Many approaches have been developed to model and simulate the dynamics of bolted joint structures. However, the inherent dynamics of the contact interfaces still need further investigation in order to be able to generate accurate models to predict the behaviour in the contact interface. In this paper, the modelling of the contact interface of a bolted lap-joint and the prediction of its pressure distribution are considered using 2D and 3D FE models. A 3D finite element model with solid elements is developed to simulate the behaviour of the contact interface. The model is a modified thin-layer element where the material properties of a thin layer are distributed over the contact interface. Due to the high computational cost of the 3D model, a reduced-order model is proposed for the lap-joint in which beam elements are used. The material properties are introduced in these models to account for the variability in the contact parameters. Finally, experimental modal properties were used to identify the joint parameters. A good agreement is obtained between the detailed model and the reduced order model in the prediction of the pressure distribution in the contact interface.

The effect of preload and surface roughness quality on linear joint model parameters

Journal of Sound and Vibration, 2019

The physical parameters of the contact interfaces, such as preload and surface roughness quality,... more The physical parameters of the contact interfaces, such as preload and surface roughness quality, significantly affect the stiffness of joints. Knowledge of the relationship between these interface parameters and the equivalent stiffness allows joints to be considered in the design stages of complex structures. Hence, this paper considers the effect of contact interface parameters on the identified equivalent stiffness parameters of joint models. First, a new generic joint model is proposed to model the contact interfaces. Then, the ability of three different joint models, including the new model proposed in this paper, to capture the linear effects of contact interfaces under different preloads and surface roughness qualities is investigated. Finally, it is concluded that the preload and surface roughness quality control the normal and shearing stiffness of the joint models respectively. Experimental investigations also reveal that a complex mechanism governs the energy dissipation in the contact interface.

Boundary Condition Identification of a Plate on Elastic Support

The International Journal of Acoustics and Vibration, 2014

The behaviour of mechanical structures in low frequencies is strongly affected by the existence o... more The behaviour of mechanical structures in low frequencies is strongly affected by the existence of the boundary conditions. It is not usually possible to provide ideal boundary conditions, i.e. simply supported or clamped, for structures. Therefore the real structures are mostly constrained by elastic supports. Constructing an accurate mathematical or numerical model for a structure requires the knowledge of the support parameters. In this paper, a new method is proposed for the parameter identification of a rectangular plate constrained by elastic support. The method relies on the free vibration solution of the plate dynamics subjected to elastic boundary conditions and employs the optimization toolbox of MATLAB.

Identification of nonlinear bolted lap-joint parameters by force-state mapping

International Journal of Solids and Structures, 2007

Joints and fasteners often have a significant effect on the dynamical behaviour of assembled mech... more Joints and fasteners often have a significant effect on the dynamical behaviour of assembled mechanical structures and the analytical prediction of structural responses therefore depends upon the accuracy of joint modelling. Detailed constitutive models that fully describe the behaviour of frictional interfaces are often unduly complicated; in which case simpler phenomenological models having parameters identified from vibration tests may be preferable. Unfortunately the direct measurement of forces transmitted between two contacting surfaces and their relative displacements are not possible in practice and it is therefore necessary to rely on measurements remote from joints. In this paper, the parameters of an assumed nonlinear joint model are identified by force-state mapping from time-domain acceleration records in response to single-frequency excitation close to the first natural frequency. The problem of lack of accessibility for measurement at the joint is overcome by casting the governing equation of the system in modal coordinates so that modal parameters are identified to represent the nonlinear behaviour of the joint. A particular result from the experimental programme is the identification of viscous damping coefficients dependent upon displacement amplitude. The significance of this result is that the complex phenomenon of energy dissipation in lap joints can be represented by a simple analytical model capable of producing accurate results.

Identification of micro-vibro-impacts at boundary condition of a nonlinear beam

Mechanical Systems and Signal Processing, 2011

Under high amplitude vibrations, contact interfaces experience micro-vibro-impacts and frictional... more Under high amplitude vibrations, contact interfaces experience micro-vibro-impacts and frictional slips. These nonlinear mechanisms can introduce response nonlinearity and energy dissipation into the structures containing them. Beams are widely used in engineering structures and almost in every application they are subjected to boundary conditions. Boundary conditions may contain nonlinear contact interfaces. Therefore, modeling accurately the micro-vibro-impacts and frictional slips developing at the boundary condition of a beam is important in structural dynamics. Ignoring this may result in major discrepancies between experimental observations and theoretical calculations. In this paper identification of micro-vibro-impacts and frictional slips at boundary condition of a nonlinear beam is considered. The structure, being modeled as an Euler-Bernoulli beam, is analyzed using nonlinear normal modes. A reduced-order model governing the dynamic response of the beam near its first resonant point is resulted from the analysis. Identification of the nonlinear boundary condition parameters can be performed by means of the reduced order model and using experimental results.

Identification of bolted lap joints parameters in assembled structures

Mechanical Systems and Signal Processing, 2007

Bolted lap joints have significant influence on the dynamical behaviour of the assembled structur... more Bolted lap joints have significant influence on the dynamical behaviour of the assembled structures due to creation of strong local flexibility and damping. In modelling the dynamical behaviour of assembled structures the joint interface model must be represented accurately. A nonlinear model for bolted lap joints and interfaces is proposed capable of representing the dominant physics involved in the joint such as micro/macro-slip. The joint interface is modelled using a combination of linear and nonlinear springs and a damper to simulate the damping effects of the joint. An estimate of the response of the structure with a nonlinear model for the bolted joint under external excitations is obtained using the method of multiple scales. The parameters of the model, i.e. the spring constants and the damper coefficient, are functions of normal and tangential stresses at the joint interface and are identified by minimizing the difference between the model predictions and the experimentally measured data.

Nonlinearity identification using sensitivity of frequency response functions

Journal of Vibration and Control, 2012

Nonlinearities in mechanical systems demand extensive efforts both in modeling their dynamics and... more Nonlinearities in mechanical systems demand extensive efforts both in modeling their dynamics and identification of their parameters. In this paper an identification approach is proposed for nonlinear multi-degree-of-freedom systems when there is a single nonlinear element in the system and its location is known. The proposed method is an extension of the frequency response function (FRF) sensitivity method used in the linear systems. The method uses measured nonlinear FRFs and employs a reduced order model for sensitivity calculations. Numerical and experimental case studies are used to verify the accuracy of the proposed method.

Micro/macro-slip damping in beams with frictional contact interface

Journal of Sound and Vibration, 2012

Friction in contact interfaces of assembled structures is the prime source of nonlinearity and en... more Friction in contact interfaces of assembled structures is the prime source of nonlinearity and energy dissipation. Determination of the dissipated energy in an assembled structure requires accurate modeling of joint interfaces in stick, micro-slip and macro-slip states. The present paper proposes an analytical model to evaluate frictional energy loss in surface-to-surface contacts. The goal is to develop a continuous contact model capable of predicting the dynamics of friction interface and dissipation energy due to partial slips. To achieve this goal, the governing equations of a frictional contact interface are derived for two distinct contact states of stick and partial slip. A solution procedure to determine stick-slip transition under single-harmonic excitations is derived. The analytical model is verified using experimental vibration test responses performed on a free-frictionally supported beam under lateral loading. The theoretical and experimental responses are compared and the results show good agreements between the two sets of responses.

Modelling mechanical interfaces experiencing micro-slip/slap

Inverse Problems in Science and Engineering, 2011

Surface-to-surface contact interfaces significantly affect structural behaviour. Therefore, accur... more Surface-to-surface contact interfaces significantly affect structural behaviour. Therefore, accurate modelling of the stiffness and damping characteristics of such interfaces is crucial for dynamic response analysis of assembled structures. Due to the development of nonlinear interactions, such as slip and slap mechanisms, modelling and analysis of the contact interfaces is a challenging task. The nonlinear effects of the slip and slap mechanisms need to be considered in interface models particularly when the amplitude of the structural response is high. This article considers finite element (FE) modelling of a compound structure containing a surface-to-surface contact interface, i.e. a bolted lap-joint. The joint, modelled using thin-layer element theory, experiences micro-slips/slaps under extreme loading conditions of the structure and to take into account these behaviours, the thin-layer element is assumed to behave in a nonlinear manner. In order to identify the nonlinear uncertainties in the joint interface, the real structure is subjected to vibrational testing, and its dynamical behaviour at different loading levels is extracted. The parameters of interfacial elements are tuned in such a way that the resultant FE model predicts the experimental results with a high accuracy.

Characterization of dominant mechanisms in contact interface restoring forces

International Journal of Mechanical Sciences, 2012

Accurate representation of different parts of a mechanical system is important in construction of... more Accurate representation of different parts of a mechanical system is important in construction of mathematical models for structural dynamic analysis. There are usually elements in structures-for example joints or boundary conditions-which demand more efforts for precise modeling. This is due to development of the contact mechanisms-i.e. linear or nonlinear-in normal and tangential directions of their surfaces. In this paper a method for multiple nonlinearity detection and identification is proposed. The method is applied to characterize the state of the contact mechanisms in normal and tangential directions of a nonlinear beam subjected to a frictional contact support.

Identification of Weakly Nonlinear Systems Using Describing Function Inversion

Experimental Mechanics, 2010

In this paper describing functions inversion is used and the restoring force of a nonlinear eleme... more In this paper describing functions inversion is used and the restoring force of a nonlinear element in a MDOF system is characterized. The describing functions can be obtained using linearized frequency response functions (FRFs). The response of the system to harmonic excitation forces at distinct frequencies close to the resonant frequency results in linearized FRFs. The nonlinear system can be approximated at each excitation frequency by an equivalent linear system. This approximation leads to calculation of the first-order describing functions. By having the experimental describing functions calculated and the system's responses corresponding to the nonlinear element (measured or interpolated), nonlinear parameter identification can be performed. Two numerical and experimental case studies are provided to show the applicability of this method.

Identification of Joint Interface Model Usnig Modal Testing Data

INTERNATIONAL JOURNAL OF INDUSTRIAL ENGINEERING AND PRODUCTION MANAGEMENT (IJIE) (INTERNATIONAL JOURNAL OF ENGINEERING SCIENCE) (PERSIAN), 2004

Dynamic behavior of a structure is significantly affected by the properties of its joints. This e... more Dynamic behavior of a structure is significantly affected by the properties of its joints. This effect is more important in light weight structures with low damping such as airspace structures. In this paper two models for joint inteiface are presented and their properties are identified using modal testing results. In the identification procedure the characteristic equation of motion is used to obtain joint parameters. A good correlation between identified model and the modal testing results is obtained.

Identifying slip-slap forces in the contact interface using dual-mode excitation

International Conference on Noise and Vibration Engineering (ISMA 2010), Leuven, Belgium, Sep 1, 2010

Frictional contact interfaces play a key role in dynamic behavior of mechanical systems. Various ... more Frictional contact interfaces play a key role in dynamic behavior of mechanical systems. Various nonlinear mechanisms such as micro slap, micro and macro slippage develop at the frictional interface depending on the vibration amplitude at the contact surface. Majority of experimental studies consider the dynamic characteristics of the contact only in one direction, either tangential or normal. In the present paper, a procedure is proposed in which both components of the contact forces in these directions are ...

Modeling and identification of frictional forces at a contact interface experiencing micro-vibro-impacts

Journal of Sound and Vibration, 2012

Modeling and identification of restoring forces at contact interfaces is an inevitable part of in... more Modeling and identification of restoring forces at contact interfaces is an inevitable part of investigating the dynamic characteristics of mechanical systems. As the vibration amplitude increases, various nonlinear mechanisms such as micro/macro-slip and micro-impacts activate in the interface. This paper considers the nonlinear behavior of a frictional contact in situations where micro-impacts develop in the normal direction to the friction surface. It investigates the effect of variable normal load on the contact frictional forces, and defines a friction model capable of taking into account this effect. In an experimental case study, the contact is excited using a dual sine force to allow a reliable dual-mode identification procedure. The measured data and the normal modes of the corresponding linear system are employed to define the system nonlinear modes used to expand the system response. This provides a reduced order model containing dominant nonlinear effects in the contact interface. Force state mapping method is employed to identify the contact restoring forces. The experimentally obtained forces are employed to determine the parameters of a new friction law defied by modifying the Valanis model. It is shown the model is capable of predicting the main nonlinear characteristics of the contact interface and regenerates the experimental results at different vibration response levels.

Bolt-Jointed Structural Modelling by Including Uncertainty in Contact Interface Parameters

Springer eBooks, Jul 29, 2022

A generalization of the Valanis model for friction modelling

Mechanical Systems and Signal Processing

Model identification and dynamic analysis of ship propulsion shaft lines

Dynamic response analysis of mechanical structures is usually performed by adopting numerical/ana... more Dynamic response analysis of mechanical structures is usually performed by adopting numerical/analytical models. Finite element (FE) modeling as a numerical approach plays an important role in dynamic response analysis of complex structures. The calculated dynamic responses from FE analysis are only reliable if accurate FE models are used. There are many elements in real mechanical structures which make constructing accurate FE models difficult. For example, modeling the boundary supports of mechanical structures are usually challenging because of the uncertainties existing in their stiffness values. The stiffness values of boundary supports can be identified by using experimental natural frequencies and hence the FE model can be corrected. In this paper, the FE modeling and updating of propulsion shaft lines in a ship structure is considered by employing experimental modal parameters, i.e. natural frequencies. Natural frequencies of shaft lines are measured by performing experiment...

Modelling the Effect of Preload in a Lap-Joint by Altering Thin-Layer Material Properties

Nonlinear Structures & Systems, Volume 1, 2021

The joints in an assembled structure represent a significant source of energy dissipation and may... more The joints in an assembled structure represent a significant source of energy dissipation and may lead to overall stiffness variation, which may affect high cycle fatigue failure. Many approaches have been developed to model and simulate the dynamics of bolted joint structures. However, the inherent dynamics of the contact interfaces still need further investigation in order to be able to generate accurate models to predict the behaviour in the contact interface. In this paper, the modelling of the contact interface of a bolted lap-joint and the prediction of its pressure distribution are considered using 2D and 3D FE models. A 3D finite element model with solid elements is developed to simulate the behaviour of the contact interface. The model is a modified thin-layer element where the material properties of a thin layer are distributed over the contact interface. Due to the high computational cost of the 3D model, a reduced-order model is proposed for the lap-joint in which beam elements are used. The material properties are introduced in these models to account for the variability in the contact parameters. Finally, experimental modal properties were used to identify the joint parameters. A good agreement is obtained between the detailed model and the reduced order model in the prediction of the pressure distribution in the contact interface.

The effect of preload and surface roughness quality on linear joint model parameters

Journal of Sound and Vibration, 2019

The physical parameters of the contact interfaces, such as preload and surface roughness quality,... more The physical parameters of the contact interfaces, such as preload and surface roughness quality, significantly affect the stiffness of joints. Knowledge of the relationship between these interface parameters and the equivalent stiffness allows joints to be considered in the design stages of complex structures. Hence, this paper considers the effect of contact interface parameters on the identified equivalent stiffness parameters of joint models. First, a new generic joint model is proposed to model the contact interfaces. Then, the ability of three different joint models, including the new model proposed in this paper, to capture the linear effects of contact interfaces under different preloads and surface roughness qualities is investigated. Finally, it is concluded that the preload and surface roughness quality control the normal and shearing stiffness of the joint models respectively. Experimental investigations also reveal that a complex mechanism governs the energy dissipation in the contact interface.

Boundary Condition Identification of a Plate on Elastic Support

The International Journal of Acoustics and Vibration, 2014

The behaviour of mechanical structures in low frequencies is strongly affected by the existence o... more The behaviour of mechanical structures in low frequencies is strongly affected by the existence of the boundary conditions. It is not usually possible to provide ideal boundary conditions, i.e. simply supported or clamped, for structures. Therefore the real structures are mostly constrained by elastic supports. Constructing an accurate mathematical or numerical model for a structure requires the knowledge of the support parameters. In this paper, a new method is proposed for the parameter identification of a rectangular plate constrained by elastic support. The method relies on the free vibration solution of the plate dynamics subjected to elastic boundary conditions and employs the optimization toolbox of MATLAB.

Identification of nonlinear bolted lap-joint parameters by force-state mapping

International Journal of Solids and Structures, 2007

Joints and fasteners often have a significant effect on the dynamical behaviour of assembled mech... more Joints and fasteners often have a significant effect on the dynamical behaviour of assembled mechanical structures and the analytical prediction of structural responses therefore depends upon the accuracy of joint modelling. Detailed constitutive models that fully describe the behaviour of frictional interfaces are often unduly complicated; in which case simpler phenomenological models having parameters identified from vibration tests may be preferable. Unfortunately the direct measurement of forces transmitted between two contacting surfaces and their relative displacements are not possible in practice and it is therefore necessary to rely on measurements remote from joints. In this paper, the parameters of an assumed nonlinear joint model are identified by force-state mapping from time-domain acceleration records in response to single-frequency excitation close to the first natural frequency. The problem of lack of accessibility for measurement at the joint is overcome by casting the governing equation of the system in modal coordinates so that modal parameters are identified to represent the nonlinear behaviour of the joint. A particular result from the experimental programme is the identification of viscous damping coefficients dependent upon displacement amplitude. The significance of this result is that the complex phenomenon of energy dissipation in lap joints can be represented by a simple analytical model capable of producing accurate results.

Identification of micro-vibro-impacts at boundary condition of a nonlinear beam

Mechanical Systems and Signal Processing, 2011

Under high amplitude vibrations, contact interfaces experience micro-vibro-impacts and frictional... more Under high amplitude vibrations, contact interfaces experience micro-vibro-impacts and frictional slips. These nonlinear mechanisms can introduce response nonlinearity and energy dissipation into the structures containing them. Beams are widely used in engineering structures and almost in every application they are subjected to boundary conditions. Boundary conditions may contain nonlinear contact interfaces. Therefore, modeling accurately the micro-vibro-impacts and frictional slips developing at the boundary condition of a beam is important in structural dynamics. Ignoring this may result in major discrepancies between experimental observations and theoretical calculations. In this paper identification of micro-vibro-impacts and frictional slips at boundary condition of a nonlinear beam is considered. The structure, being modeled as an Euler-Bernoulli beam, is analyzed using nonlinear normal modes. A reduced-order model governing the dynamic response of the beam near its first resonant point is resulted from the analysis. Identification of the nonlinear boundary condition parameters can be performed by means of the reduced order model and using experimental results.

Identification of bolted lap joints parameters in assembled structures

Mechanical Systems and Signal Processing, 2007

Bolted lap joints have significant influence on the dynamical behaviour of the assembled structur... more Bolted lap joints have significant influence on the dynamical behaviour of the assembled structures due to creation of strong local flexibility and damping. In modelling the dynamical behaviour of assembled structures the joint interface model must be represented accurately. A nonlinear model for bolted lap joints and interfaces is proposed capable of representing the dominant physics involved in the joint such as micro/macro-slip. The joint interface is modelled using a combination of linear and nonlinear springs and a damper to simulate the damping effects of the joint. An estimate of the response of the structure with a nonlinear model for the bolted joint under external excitations is obtained using the method of multiple scales. The parameters of the model, i.e. the spring constants and the damper coefficient, are functions of normal and tangential stresses at the joint interface and are identified by minimizing the difference between the model predictions and the experimentally measured data.

Nonlinearity identification using sensitivity of frequency response functions

Journal of Vibration and Control, 2012

Nonlinearities in mechanical systems demand extensive efforts both in modeling their dynamics and... more Nonlinearities in mechanical systems demand extensive efforts both in modeling their dynamics and identification of their parameters. In this paper an identification approach is proposed for nonlinear multi-degree-of-freedom systems when there is a single nonlinear element in the system and its location is known. The proposed method is an extension of the frequency response function (FRF) sensitivity method used in the linear systems. The method uses measured nonlinear FRFs and employs a reduced order model for sensitivity calculations. Numerical and experimental case studies are used to verify the accuracy of the proposed method.

Micro/macro-slip damping in beams with frictional contact interface

Journal of Sound and Vibration, 2012

Friction in contact interfaces of assembled structures is the prime source of nonlinearity and en... more Friction in contact interfaces of assembled structures is the prime source of nonlinearity and energy dissipation. Determination of the dissipated energy in an assembled structure requires accurate modeling of joint interfaces in stick, micro-slip and macro-slip states. The present paper proposes an analytical model to evaluate frictional energy loss in surface-to-surface contacts. The goal is to develop a continuous contact model capable of predicting the dynamics of friction interface and dissipation energy due to partial slips. To achieve this goal, the governing equations of a frictional contact interface are derived for two distinct contact states of stick and partial slip. A solution procedure to determine stick-slip transition under single-harmonic excitations is derived. The analytical model is verified using experimental vibration test responses performed on a free-frictionally supported beam under lateral loading. The theoretical and experimental responses are compared and the results show good agreements between the two sets of responses.

Modelling mechanical interfaces experiencing micro-slip/slap

Inverse Problems in Science and Engineering, 2011

Surface-to-surface contact interfaces significantly affect structural behaviour. Therefore, accur... more Surface-to-surface contact interfaces significantly affect structural behaviour. Therefore, accurate modelling of the stiffness and damping characteristics of such interfaces is crucial for dynamic response analysis of assembled structures. Due to the development of nonlinear interactions, such as slip and slap mechanisms, modelling and analysis of the contact interfaces is a challenging task. The nonlinear effects of the slip and slap mechanisms need to be considered in interface models particularly when the amplitude of the structural response is high. This article considers finite element (FE) modelling of a compound structure containing a surface-to-surface contact interface, i.e. a bolted lap-joint. The joint, modelled using thin-layer element theory, experiences micro-slips/slaps under extreme loading conditions of the structure and to take into account these behaviours, the thin-layer element is assumed to behave in a nonlinear manner. In order to identify the nonlinear uncertainties in the joint interface, the real structure is subjected to vibrational testing, and its dynamical behaviour at different loading levels is extracted. The parameters of interfacial elements are tuned in such a way that the resultant FE model predicts the experimental results with a high accuracy.

Characterization of dominant mechanisms in contact interface restoring forces

International Journal of Mechanical Sciences, 2012

Accurate representation of different parts of a mechanical system is important in construction of... more Accurate representation of different parts of a mechanical system is important in construction of mathematical models for structural dynamic analysis. There are usually elements in structures-for example joints or boundary conditions-which demand more efforts for precise modeling. This is due to development of the contact mechanisms-i.e. linear or nonlinear-in normal and tangential directions of their surfaces. In this paper a method for multiple nonlinearity detection and identification is proposed. The method is applied to characterize the state of the contact mechanisms in normal and tangential directions of a nonlinear beam subjected to a frictional contact support.

Identification of Weakly Nonlinear Systems Using Describing Function Inversion

Experimental Mechanics, 2010

In this paper describing functions inversion is used and the restoring force of a nonlinear eleme... more In this paper describing functions inversion is used and the restoring force of a nonlinear element in a MDOF system is characterized. The describing functions can be obtained using linearized frequency response functions (FRFs). The response of the system to harmonic excitation forces at distinct frequencies close to the resonant frequency results in linearized FRFs. The nonlinear system can be approximated at each excitation frequency by an equivalent linear system. This approximation leads to calculation of the first-order describing functions. By having the experimental describing functions calculated and the system's responses corresponding to the nonlinear element (measured or interpolated), nonlinear parameter identification can be performed. Two numerical and experimental case studies are provided to show the applicability of this method.

Identification of Joint Interface Model Usnig Modal Testing Data

INTERNATIONAL JOURNAL OF INDUSTRIAL ENGINEERING AND PRODUCTION MANAGEMENT (IJIE) (INTERNATIONAL JOURNAL OF ENGINEERING SCIENCE) (PERSIAN), 2004

Dynamic behavior of a structure is significantly affected by the properties of its joints. This e... more Dynamic behavior of a structure is significantly affected by the properties of its joints. This effect is more important in light weight structures with low damping such as airspace structures. In this paper two models for joint inteiface are presented and their properties are identified using modal testing results. In the identification procedure the characteristic equation of motion is used to obtain joint parameters. A good correlation between identified model and the modal testing results is obtained.

Identifying slip-slap forces in the contact interface using dual-mode excitation

International Conference on Noise and Vibration Engineering (ISMA 2010), Leuven, Belgium, Sep 1, 2010

Frictional contact interfaces play a key role in dynamic behavior of mechanical systems. Various ... more Frictional contact interfaces play a key role in dynamic behavior of mechanical systems. Various nonlinear mechanisms such as micro slap, micro and macro slippage develop at the frictional interface depending on the vibration amplitude at the contact surface. Majority of experimental studies consider the dynamic characteristics of the contact only in one direction, either tangential or normal. In the present paper, a procedure is proposed in which both components of the contact forces in these directions are ...

Modeling and identification of frictional forces at a contact interface experiencing micro-vibro-impacts

Journal of Sound and Vibration, 2012

Modeling and identification of restoring forces at contact interfaces is an inevitable part of in... more Modeling and identification of restoring forces at contact interfaces is an inevitable part of investigating the dynamic characteristics of mechanical systems. As the vibration amplitude increases, various nonlinear mechanisms such as micro/macro-slip and micro-impacts activate in the interface. This paper considers the nonlinear behavior of a frictional contact in situations where micro-impacts develop in the normal direction to the friction surface. It investigates the effect of variable normal load on the contact frictional forces, and defines a friction model capable of taking into account this effect. In an experimental case study, the contact is excited using a dual sine force to allow a reliable dual-mode identification procedure. The measured data and the normal modes of the corresponding linear system are employed to define the system nonlinear modes used to expand the system response. This provides a reduced order model containing dominant nonlinear effects in the contact interface. Force state mapping method is employed to identify the contact restoring forces. The experimentally obtained forces are employed to determine the parameters of a new friction law defied by modifying the Valanis model. It is shown the model is capable of predicting the main nonlinear characteristics of the contact interface and regenerates the experimental results at different vibration response levels.