În vederea proiectării/reproiectării aparatului de ochire montat pe o armă automată, trebuie luat... more În vederea proiectării/reproiectării aparatului de ochire montat pe o armă automată, trebuie luate în consideraţie unele probleme legate de comportamentul dinamic sub sarcinile care apar pe timpul tragerii. Este analizată comportarea la vibraţii a structurii mecanice a aparatului de ochire, în conditiile unei excitaţii cu frecvenţa prescrisă de tragere. Studiul este efectuat experimental şi se prezintă o simulare numerică pentru determinarea frecvenţelor proprii ale structurii mecanice a aparatului. Afin de concevoir/reconcevoir l'appareil de visée monté sur une arme automatique, il est à prendre en considération certaines questions liées aux charges dynamiques pendant le tir. Il est analysé le comportement vibratoire de la structure mécanique d'un dispositif de visée, face à une excitation avec la fréquence de tir prescrite. L'étude est effectuée tant par calcul numérique, que expérimentalement, dans des conditions de laboratoire et dans des conditions de fonctionnement...
A method to extract macromodels for RF MEMS switches is proposed. The macromodels include both th... more A method to extract macromodels for RF MEMS switches is proposed. The macromodels include both the coupled structural-electric behavior of the switch as well as its RF behavior. The device with distributed parameters is subject to several analyses from which the parameters of the macromodel are extracted, by model reduction. From the coupled structural-electrostatic analysis the parametric capacitance and the effective stiffness coefficients of the switch are extracted. From the RF characteristics in the up stable state, the transmission line parameters are extracted. Finally, all parameters are combined in a Spice circuit model, which is controlled by the MEMS actuation voltage and is excited with the RF signal. The procedure is applied to a capacitive switch. Relative modeling errors with respect to the non-reduced model, considered as reference, of less than 3 % for the RF characteristics and less than 1 % for the mechanical characteristics are obtained.
Proceedings of the European Automotive Congress EAEC-ESFA 2015, 2015
The main issue in analyzing honeycomb structures is the substantial computational effort that has... more The main issue in analyzing honeycomb structures is the substantial computational effort that has to be spent in modeling and analyzing them with a multi-cell construction core by maintaining the actual geometry. Therefore, the common practice in the finite element modeling is to replace them by an equivalent orthotropic material. The determinations of these equivalent properties of the homogenized core are based on analytical or numerical relationships usually obtained from pure axial and shearing loads. By using these initial estimations of the equivalent properties, a homogenized model works well for in-plane deformations but may give large errors for out-of plane deformations which generally take place in panel or sandwich homogenized structures. This paper presents a numerical method that can be used to correct some of the equivalent elastic properties of the homogenized core to work properly in bending and torsion based on some modal analyses applied first for a real honeycomb panel, to obtain a reference solution, and then on the homogenized orthotropic panel where some of the equivalent elastic constant are iteratively improved by an optimization algorithm to fit the reference solution. The analyzed types of honeycomb cores are the commercial ones in three cell configurations: square, regular hexagonal and re-entrant shapes. The calculations show that some of the equivalent elastic properties obtained in the classical approach must be corrected with factors larger than five as to obtain correct results in bending and torsion loads.
In the paper are presented the results obtained by numerical simulations on composite plates, wit... more In the paper are presented the results obtained by numerical simulations on composite plates, with arrays of transducers able to create guided waves by appropriate management of the signal delay and topology of the transducers. Appropriate generation of the Lamb waves, using an adequately shaped burst signal and frequencies corresponding to quasi non-dispersive modes, proved to be able to detect barely visible defects in composites. The avoidance of reflected signals offered conditions to have an easier analysis task in evaluating the transmitted and reflected waves produced by a guided wave which was scanning the plate or pipe type structure.
ABSTRACT Because interactions between a PZT and a plate are a complicated process, it is necessar... more ABSTRACT Because interactions between a PZT and a plate are a complicated process, it is necessary to perform a multiphysics analysis in the numerical simulation to obtain accurate results. Recently, some papers reported an equivalent force method to replace PZT actuation in the finite element model and to transform a multiphysics analysis in a structural one. This paper presents an improved "two forces" model for replacing PZT actuation in the finite element model and also a general methodology to accurately describe the interaction between a PZT and the plate
The first part of this article presents a dynamic analysis of the fan of a generator connected by... more The first part of this article presents a dynamic analysis of the fan of a generator connected by rigid coupling to a diesel engine. The purpose of this analysis is to correlate the main components of the fan’s frequency response spectrum with the ones of the excitation source, i.e., the diesel engine. The second part describes a finite element analysis of the fan in order to find the best design solution.
Abstract The research work behind this paper focused a rather extensive assessment of hybrid comp... more Abstract The research work behind this paper focused a rather extensive assessment of hybrid composites made of pure aluminium sheets, alternating with GFRP and CFRP layers. Static, fatigue and low velocity impact tests were performed, combined with NDI on ...
The study had in view various aspects which can arise during the low velocity impact tests made o... more The study had in view various aspects which can arise during the low velocity impact tests made on composite pipes/tubes. It implied numerical simulations, made by ANSYS and LS-DYNA codes, on glass fiber/epoxy composite pipes. The geometry and material characteristics were taken from real pipes, which have been experimentally tested in parallel, using a drop weight impact tower. The main parameter in view was the impact force history, which gives most information upon the impact event and, accordingly, is used by most of researchers for characterizing the damages produced on the impacted body and for assessing the impact installation.
2014 49th International Universities Power Engineering Conference (UPEC), 2014
The design of RF MEMS switches is a challenging task due to the various multiphysics coupled phen... more The design of RF MEMS switches is a challenging task due to the various multiphysics coupled phenomena that have to be taken into consideration. In order to reach a configuration with specific requirements, dynamical compact models are needed, that should be accurate enough and have few degrees of freedom, so that the simulation of an entire system in which such a device is embedded need reasonable computer resources, measured in time and memory requirements. In order to allow the design and optimization tasks, these models have to be correlated with design parameters such as dimensions and material properties. This paper focuses on the path from coupled structural-electrostatic models to the extraction of relevant information for the design, namely the static pull-in voltage and the effective stiffness coefficient, for a capacitive switch of bridge type. The influence of the width of the actuation pads and the length of the bridge is investigated.
Polymeric layered composites exhibit a variety of damages following in service loading conditions... more Polymeric layered composites exhibit a variety of damages following in service loading conditions, like delamination, matrix cracking or even fibre breaking. Detection of such damages and assessing their extension and severity is vital during maintenance cycle, in view of keeping the normal operational reliability. For local inspections, IR thermography and ultrasonic scanning are among the best valued NDT methods. The paper describes the inspections performed by IR active thermography, in different variants, and pulse-echo ultrasonic scanning on GFRP. A variety of layered composites and defects/damages were inspected and the results are evaluated independently, in some cases being compared each other, with valuable conclusions for the users of the mentioned NDI techniques.
Static loading and impact tests of ceramic alumina tiles have shown a very interesting behaviour ... more Static loading and impact tests of ceramic alumina tiles have shown a very interesting behaviour of a tough, brittle, and high energy absorbing material. Strain gauges techniques and data acquisition were used throughout this research. A static-dynamic equivalence is done through a calibration procedure of the measuring system. The experimental strain history is completely acquired till the failure of the ceramic tile. Numerical simulation of impact tests gives additional insight on the complicated phenomena. Low velocity impact testing revealed different patters of failure, depending on the conditions of impact, and the capacity of this material to be used in particular purpose designed applications.
Low velocity impact is a frequent and inevitable in-service event, with higher occurrence in tran... more Low velocity impact is a frequent and inevitable in-service event, with higher occurrence in transportation structures. The damages following such an event are more diverse, extended and with more severe consequences in the case of composite materials and structures. The research work presented here concerns fibre reinforced polymeric composites in the forms of plates and pipes. It is continuing an effort meant to allow customers exploiting such structures to have a short cut in monitoring the integrity of this kind of structures. To this end, it is proposed a careful following of the impact force history recording, which can offer valuable and more direct information about the damage level produced under this insidious loading.
This paper presents a fast and reliable method, for obtaining all the range of dispersion curves ... more This paper presents a fast and reliable method, for obtaining all the range of dispersion curves for wave propagation usually used in practice, by numerical simulation only, via common commercial finite element codes. Essentially, the method is based on a simple and robust approach, consisting in a few series of modal analyses for a representative part of the inspected structure. In this way, for different wave lengths, one can find the mode shapes and corresponding natural frequencies by solving some real, symmetric and well numerically conditioned eigenvalue problems. The method allows the extraction of propagating modes only and, in spite of not producing continuous dispersion curves, it is not susceptible to aliasing effects, as some similar methods are. Additionally, complete graphical representations of guided waves are possible with some minor calculus effort.
In order to obtain a high bending stiffness in metallic structures subjected to vertical loads, h... more In order to obtain a high bending stiffness in metallic structures subjected to vertical loads, horizontal beams with increased height of the cross-section are used. For this reason, the study of the lateral buckling of such a beams becomes important in order to establish their ...
Composite materials are increasingly deployed in many industrial fields, into both the civilian a... more Composite materials are increasingly deployed in many industrial fields, into both the civilian and military sectors. Nondestructive evaluation (NDE) and damage assessment is essential for keeping high reliability of this class of materials. Several NDE/NDT methods ...
Structural integrity monitoring (SHM) and evaluation of residual mechanical performance are highl... more Structural integrity monitoring (SHM) and evaluation of residual mechanical performance are highly needed in assessing the post-impact behaviour of composite materials and structures. The link between impact force history and the damage level was not followed enough in research studies upon the SHM of composites. The authors put in evidence a clear link in this matter in a variety of layered composite materials. The link was assessed by evaluating the residual mechanical performance and by nondestructive inspection (NDI) – ultrasonics and infrared thermography (IRT) - on the impacted samples. Such a link may prove a very useful and reliable shortcut for backing the online SHM and condition based maintenance.
Lamb wave method is a long range inspection technique which is considered to have a nice future i... more Lamb wave method is a long range inspection technique which is considered to have a nice future in the field of structural health monitoring. In recent years, the applications are expanding towards composite structures. One of the main problems faced when using the ...
Composite pipes enjoy increasing interest in the sector of petroleum and gas transportation, due ... more Composite pipes enjoy increasing interest in the sector of petroleum and gas transportation, due to a number of qualities, concerning especially the corrosion resistance and light weight, face to the traditional steel pipes. As composite materials are prone to a various range of defects and damages which can seriously affect their service ability, reliable inspection methods have to be tested in order to assure the required in service reliability. The paper presents progress made in applying complementary global/local non-destructive inspection (NDI) methods, such as Lamb wave method and infrared thermography (IRT) method, to effective structural health (SHM) monitoring of composite pipes.
În vederea proiectării/reproiectării aparatului de ochire montat pe o armă automată, trebuie luat... more În vederea proiectării/reproiectării aparatului de ochire montat pe o armă automată, trebuie luate în consideraţie unele probleme legate de comportamentul dinamic sub sarcinile care apar pe timpul tragerii. Este analizată comportarea la vibraţii a structurii mecanice a aparatului de ochire, în conditiile unei excitaţii cu frecvenţa prescrisă de tragere. Studiul este efectuat experimental şi se prezintă o simulare numerică pentru determinarea frecvenţelor proprii ale structurii mecanice a aparatului. Afin de concevoir/reconcevoir l'appareil de visée monté sur une arme automatique, il est à prendre en considération certaines questions liées aux charges dynamiques pendant le tir. Il est analysé le comportement vibratoire de la structure mécanique d'un dispositif de visée, face à une excitation avec la fréquence de tir prescrite. L'étude est effectuée tant par calcul numérique, que expérimentalement, dans des conditions de laboratoire et dans des conditions de fonctionnement...
A method to extract macromodels for RF MEMS switches is proposed. The macromodels include both th... more A method to extract macromodels for RF MEMS switches is proposed. The macromodels include both the coupled structural-electric behavior of the switch as well as its RF behavior. The device with distributed parameters is subject to several analyses from which the parameters of the macromodel are extracted, by model reduction. From the coupled structural-electrostatic analysis the parametric capacitance and the effective stiffness coefficients of the switch are extracted. From the RF characteristics in the up stable state, the transmission line parameters are extracted. Finally, all parameters are combined in a Spice circuit model, which is controlled by the MEMS actuation voltage and is excited with the RF signal. The procedure is applied to a capacitive switch. Relative modeling errors with respect to the non-reduced model, considered as reference, of less than 3 % for the RF characteristics and less than 1 % for the mechanical characteristics are obtained.
Proceedings of the European Automotive Congress EAEC-ESFA 2015, 2015
The main issue in analyzing honeycomb structures is the substantial computational effort that has... more The main issue in analyzing honeycomb structures is the substantial computational effort that has to be spent in modeling and analyzing them with a multi-cell construction core by maintaining the actual geometry. Therefore, the common practice in the finite element modeling is to replace them by an equivalent orthotropic material. The determinations of these equivalent properties of the homogenized core are based on analytical or numerical relationships usually obtained from pure axial and shearing loads. By using these initial estimations of the equivalent properties, a homogenized model works well for in-plane deformations but may give large errors for out-of plane deformations which generally take place in panel or sandwich homogenized structures. This paper presents a numerical method that can be used to correct some of the equivalent elastic properties of the homogenized core to work properly in bending and torsion based on some modal analyses applied first for a real honeycomb panel, to obtain a reference solution, and then on the homogenized orthotropic panel where some of the equivalent elastic constant are iteratively improved by an optimization algorithm to fit the reference solution. The analyzed types of honeycomb cores are the commercial ones in three cell configurations: square, regular hexagonal and re-entrant shapes. The calculations show that some of the equivalent elastic properties obtained in the classical approach must be corrected with factors larger than five as to obtain correct results in bending and torsion loads.
In the paper are presented the results obtained by numerical simulations on composite plates, wit... more In the paper are presented the results obtained by numerical simulations on composite plates, with arrays of transducers able to create guided waves by appropriate management of the signal delay and topology of the transducers. Appropriate generation of the Lamb waves, using an adequately shaped burst signal and frequencies corresponding to quasi non-dispersive modes, proved to be able to detect barely visible defects in composites. The avoidance of reflected signals offered conditions to have an easier analysis task in evaluating the transmitted and reflected waves produced by a guided wave which was scanning the plate or pipe type structure.
ABSTRACT Because interactions between a PZT and a plate are a complicated process, it is necessar... more ABSTRACT Because interactions between a PZT and a plate are a complicated process, it is necessary to perform a multiphysics analysis in the numerical simulation to obtain accurate results. Recently, some papers reported an equivalent force method to replace PZT actuation in the finite element model and to transform a multiphysics analysis in a structural one. This paper presents an improved "two forces" model for replacing PZT actuation in the finite element model and also a general methodology to accurately describe the interaction between a PZT and the plate
The first part of this article presents a dynamic analysis of the fan of a generator connected by... more The first part of this article presents a dynamic analysis of the fan of a generator connected by rigid coupling to a diesel engine. The purpose of this analysis is to correlate the main components of the fan’s frequency response spectrum with the ones of the excitation source, i.e., the diesel engine. The second part describes a finite element analysis of the fan in order to find the best design solution.
Abstract The research work behind this paper focused a rather extensive assessment of hybrid comp... more Abstract The research work behind this paper focused a rather extensive assessment of hybrid composites made of pure aluminium sheets, alternating with GFRP and CFRP layers. Static, fatigue and low velocity impact tests were performed, combined with NDI on ...
The study had in view various aspects which can arise during the low velocity impact tests made o... more The study had in view various aspects which can arise during the low velocity impact tests made on composite pipes/tubes. It implied numerical simulations, made by ANSYS and LS-DYNA codes, on glass fiber/epoxy composite pipes. The geometry and material characteristics were taken from real pipes, which have been experimentally tested in parallel, using a drop weight impact tower. The main parameter in view was the impact force history, which gives most information upon the impact event and, accordingly, is used by most of researchers for characterizing the damages produced on the impacted body and for assessing the impact installation.
2014 49th International Universities Power Engineering Conference (UPEC), 2014
The design of RF MEMS switches is a challenging task due to the various multiphysics coupled phen... more The design of RF MEMS switches is a challenging task due to the various multiphysics coupled phenomena that have to be taken into consideration. In order to reach a configuration with specific requirements, dynamical compact models are needed, that should be accurate enough and have few degrees of freedom, so that the simulation of an entire system in which such a device is embedded need reasonable computer resources, measured in time and memory requirements. In order to allow the design and optimization tasks, these models have to be correlated with design parameters such as dimensions and material properties. This paper focuses on the path from coupled structural-electrostatic models to the extraction of relevant information for the design, namely the static pull-in voltage and the effective stiffness coefficient, for a capacitive switch of bridge type. The influence of the width of the actuation pads and the length of the bridge is investigated.
Polymeric layered composites exhibit a variety of damages following in service loading conditions... more Polymeric layered composites exhibit a variety of damages following in service loading conditions, like delamination, matrix cracking or even fibre breaking. Detection of such damages and assessing their extension and severity is vital during maintenance cycle, in view of keeping the normal operational reliability. For local inspections, IR thermography and ultrasonic scanning are among the best valued NDT methods. The paper describes the inspections performed by IR active thermography, in different variants, and pulse-echo ultrasonic scanning on GFRP. A variety of layered composites and defects/damages were inspected and the results are evaluated independently, in some cases being compared each other, with valuable conclusions for the users of the mentioned NDI techniques.
Static loading and impact tests of ceramic alumina tiles have shown a very interesting behaviour ... more Static loading and impact tests of ceramic alumina tiles have shown a very interesting behaviour of a tough, brittle, and high energy absorbing material. Strain gauges techniques and data acquisition were used throughout this research. A static-dynamic equivalence is done through a calibration procedure of the measuring system. The experimental strain history is completely acquired till the failure of the ceramic tile. Numerical simulation of impact tests gives additional insight on the complicated phenomena. Low velocity impact testing revealed different patters of failure, depending on the conditions of impact, and the capacity of this material to be used in particular purpose designed applications.
Low velocity impact is a frequent and inevitable in-service event, with higher occurrence in tran... more Low velocity impact is a frequent and inevitable in-service event, with higher occurrence in transportation structures. The damages following such an event are more diverse, extended and with more severe consequences in the case of composite materials and structures. The research work presented here concerns fibre reinforced polymeric composites in the forms of plates and pipes. It is continuing an effort meant to allow customers exploiting such structures to have a short cut in monitoring the integrity of this kind of structures. To this end, it is proposed a careful following of the impact force history recording, which can offer valuable and more direct information about the damage level produced under this insidious loading.
This paper presents a fast and reliable method, for obtaining all the range of dispersion curves ... more This paper presents a fast and reliable method, for obtaining all the range of dispersion curves for wave propagation usually used in practice, by numerical simulation only, via common commercial finite element codes. Essentially, the method is based on a simple and robust approach, consisting in a few series of modal analyses for a representative part of the inspected structure. In this way, for different wave lengths, one can find the mode shapes and corresponding natural frequencies by solving some real, symmetric and well numerically conditioned eigenvalue problems. The method allows the extraction of propagating modes only and, in spite of not producing continuous dispersion curves, it is not susceptible to aliasing effects, as some similar methods are. Additionally, complete graphical representations of guided waves are possible with some minor calculus effort.
In order to obtain a high bending stiffness in metallic structures subjected to vertical loads, h... more In order to obtain a high bending stiffness in metallic structures subjected to vertical loads, horizontal beams with increased height of the cross-section are used. For this reason, the study of the lateral buckling of such a beams becomes important in order to establish their ...
Composite materials are increasingly deployed in many industrial fields, into both the civilian a... more Composite materials are increasingly deployed in many industrial fields, into both the civilian and military sectors. Nondestructive evaluation (NDE) and damage assessment is essential for keeping high reliability of this class of materials. Several NDE/NDT methods ...
Structural integrity monitoring (SHM) and evaluation of residual mechanical performance are highl... more Structural integrity monitoring (SHM) and evaluation of residual mechanical performance are highly needed in assessing the post-impact behaviour of composite materials and structures. The link between impact force history and the damage level was not followed enough in research studies upon the SHM of composites. The authors put in evidence a clear link in this matter in a variety of layered composite materials. The link was assessed by evaluating the residual mechanical performance and by nondestructive inspection (NDI) – ultrasonics and infrared thermography (IRT) - on the impacted samples. Such a link may prove a very useful and reliable shortcut for backing the online SHM and condition based maintenance.
Lamb wave method is a long range inspection technique which is considered to have a nice future i... more Lamb wave method is a long range inspection technique which is considered to have a nice future in the field of structural health monitoring. In recent years, the applications are expanding towards composite structures. One of the main problems faced when using the ...
Composite pipes enjoy increasing interest in the sector of petroleum and gas transportation, due ... more Composite pipes enjoy increasing interest in the sector of petroleum and gas transportation, due to a number of qualities, concerning especially the corrosion resistance and light weight, face to the traditional steel pipes. As composite materials are prone to a various range of defects and damages which can seriously affect their service ability, reliable inspection methods have to be tested in order to assure the required in service reliability. The paper presents progress made in applying complementary global/local non-destructive inspection (NDI) methods, such as Lamb wave method and infrared thermography (IRT) method, to effective structural health (SHM) monitoring of composite pipes.
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Papers by Ştefan Sorohan