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Dumitru Bolcu

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Universitatea Petrol si Gaze, Ploiesti, Romania

Nicolae Dumitru

Cosmin Mihai Miritoiu

Universitatea din Craiova

Sabin Vasile Rizescu

Evgeny Barkanov

Ivan Kernytskyy

Gennadi Mikhasev

Belarusian State University

Abdelouahed Tounsi

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Papers by Dumitru Bolcu

Determination of Damping Factor at the Vibrations of Composite Bars Reinforced with Carbon and Kevlar Texture

In this paper, it is showed that a mechanical model with one degree of freedom can be used to stu... more In this paper, it is showed that a mechanical model with one degree of freedom can be used to study the vibrations of a bar in a certain point. The considered structures were made of epoxy resin reinforced with carbon and carbon-kevlar texture. The vibrations in the free end of the bar, clamped at the other end, were determined experimentally for four different lengths. Eigenfrequencies and damping factor for the first modes of vibration were obtained for each bar. Relationships for the eigenfrequency and damping factor are proposed, as a function of the length of the bar, for each of the studied materials.

About the Mechanical Properties for a Type of Green Composites with Hybrid Dammar/Sandarac Matrix and Natural Reinforcements

Macromolecular Symposia

This paper presents the mechanical properties for sandwich core strips with a 60% sandarac combin... more This paper presents the mechanical properties for sandwich core strips with a 60% sandarac combination core and 40% Resoltech 1050 epoxy resin with 1055 hardener, and the upper and lower layers reinforced with cotton, silk and linen fabric, and the matrix is a combination of 60% dammar resin and 40% Resoltech 1050 epoxy resin with 1055 hardener. For these materials, there is determined: static mechanical properties from tensile stress (Young elastic modulus, yield strength, breaking strength) and chemical composition by energy dispersive spectroscopy analysis with an scanning electron microscope. It is observed that the dammar resin, in all the cases, has increased mechanical characteristics compared to sandarac. Also, the samples reinforced with cotton show better mechanical properties compared to the ones reinforced with flax and silk.

Study About Some Mechanical Properties for Composites Reinforced with Corn Cob Powder

Materiale Plastice

In this paper we have created some composites reinforced with corn cob powder and the matrix was ... more In this paper we have created some composites reinforced with corn cob powder and the matrix was made by a combination between Resoltech 1050 resin with its Resoltech 1058 hardener. For the composites manufacturing, we have used the manual casting technique. For the new manufactured composites, we have determined the mechanical properties from the tensile test according to ASTM D3039: Young modulus, breaking strength and elongation at break. We have also molded samples for the compression test according to ASTM D695-15 and we have determined the breaking strength. The tensile and compression tests were made on universal testing machines. In the end, we have determined also the dynamic mechanical properties for the studied material by clamping the samples at one edge and leaving the samples unconstrained at the other edge. At the unconstrained edge we have placed a Bruel&Kjaer accelerometer which recorded the samples free vibrations. From the free vibrations recording and Euler-Berno...

Chemical and Mechanical Properties for Rosin-based Hybrid Resins

Materiale Plastice, Apr 5, 2023

Study of Composite Bar Damping from Dammar Hybrid Resin Reinforced with Natural Fibers

Materiale Plastice

At the moment, the tendency in the composites field, is to use natural resins and fibers to obtai... more At the moment, the tendency in the composites field, is to use natural resins and fibers to obtain �environmental friendly� materials, that are compostable and biodegradable. In this paper there is an experimental study of the depletion capacity of the vibration from the composite beams, using the hardener made of cotton, flax, hemp, silk textile and the three types of the Dammar hybrid resin matrix. The damping factor and the eigenfrequency of the vibrations was determined experimentally for these bars. Based on the acquired results, the dynamic elasticity modulus and the loss factor were calculated, for each composite material studied.

Determination of Damping Coefficients for Sandwich Bars with Polypropylene Honeycomb Core and the Exterior Layers Reinforced with Metal Fabric

We deduced the equation of motion for free vibrations using Mohr-Maxwell method, considering that... more We deduced the equation of motion for free vibrations using Mohr-Maxwell method, considering that the bar is requested to bending by the inertial forces and by the damping forces. We experimentally obtained the dynamic response for sandwich bars with polypropylene honeycomb core, which have the exterior layers made of epoxy resin reinforced with steel fabric. In addition, we determined the damping coefficients per unit mass and per unit length of the bar, for bar with core thicknesses equal to 10, 15, 20 mm; width of 40 and 60 mm, and the free length of embedded bar equal to 200, 250, 300 and 350 mm. For each type of bar studied, we determined the relationships of exponential type for the calculus damping coefficients (mentioned above), according to the free length of the embedded bar.

A Discrete ( ) D Θ Algorithm Designed to Increase the Convergence Speed in Solving Transport-Type Problems

In this article, we propose a discrete algorithm that can be used to solve transport-type problem... more In this article, we propose a discrete algorithm that can be used to solve transport-type problems. The real improvement brought by applying this original algorithm consists in obtaining a completely filtered and kind of optimal program, following a small number of steps, comparing with other existing algorithms. The outcome will be that the computer memory and the implementation costs will be reduced. The solution is based upon combinatorial methods, and it addresses a certain transport capacity X that is bounded both above and below () D X d ≤ ≤. As a concrete example, we also present a () () 3 , 3 , = m n numerical application corresponding to a situation of 3 suppliers and 3 of their beneficiaries.

A Method for the Analysis of Vibrations Occurring Within Some Mechanical Systems Which Contain Spur Gears

Starting from the mathematical model created for the relative displacement of two cog wheels insi... more Starting from the mathematical model created for the relative displacement of two cog wheels inside of a gearing (model which is expressed under the form of a second-order system of differential equations with parameter'shaped or possibly non-linear excitations) we will present in this work an original method of integrating the matrix movement equation which does make use of the procedure of rendering discrete the time interval during which the concerned movement is observed. The applying of the Laplace integrated transformations which are unilateral in respect to time should lead us towards rendering algebraic the concerned model. This fact could hugely simplify the problem. Furthermore, we should be as well able to provide the graphical representations of the relative displacements for the considered gearing mechanism.

Spectral Decomposition of the Elasticity Matrix

În Teoria Elasticităţii Anizotrope, matricea coeficienţilor elastici este, până la urmă, o transf... more În Teoria Elasticităţii Anizotrope, matricea coeficienţilor elastici este, până la urmă, o transformare liniară, simetrică, pe spaţii vectoriale 6-dimensionale. Deci, orice asemenea matrice admite o descompunere spectrală. Structura unei descompuneri spectrale este determinată de mulţimile spaţiilor invariante, specifice tipului de simetrie elastică a materialului studiat. Vectorii proprii, cel puţin parţial, nu depind de valorile constantelor elastice, în schimb, valorile proprii depind de aceste constante. Sunt prezentate matricile coeficienţilor elastici pentru categoriile semnificative de simetrie cristalină. Sunt calculate matricile coeficienţilor elastici pentru cazuri concrete de materiale reprezentative pentru fiecare categorie de simetrie cristalină.

The Vibratory Behaviour of a Lathe with Continious Variator of High Speed and Dynamic Absorber

Proceedings of the 23rd International DAAAM Symposium 2012, 2012

In this paper, a lathe with continuous variator of high speed and dynamic absorber is studied. Th... more In this paper, a lathe with continuous variator of high speed and dynamic absorber is studied. The machine, which is a complex system with a great number of freedom degrees, has a corresponding number of freedom degrees, which is why in the dynamic study, there will be taken into account only those vibratory modes that, according to the required precision and the main purpose, have a great influence in the development of the studied vibratory phenomenon.

Comparisons between some composite materials reinforced with hemp fibers

Materials Today: Proceedings, 2019

For this research we have built original composite materials that have a dammar-based bio-resin a... more For this research we have built original composite materials that have a dammar-based bio-resin as matrix and are reinforced with hemp fibers. These composite materials have been subjected to tensile tests to find their mechanical characteristics and elastic constants: ultimate tensile strength, Young's modulus, Poisson's ratio and elongation at break. In the second part of the paper we have studied other composite samples with dammar-based resin/hemp fibers and classical composite samples epoxy/hemp fibers. By recording their free vibrations, we have determined the damping factor with respect to their mass, length, loss factor, dynamic flexural stiffness and dynamic Young's modulus respectively. In the end, we have compared the studied samples with other composite materials reinforced with hemp fibers that have been studied in the scientific literature.

Considerations on Computational Accuracy of the Solution for a Partial Differential Equation

Applied Mechanics and Materials, 2020

In this paper, we will compare the methods of solving with explicit or implicit finite difference... more In this paper, we will compare the methods of solving with explicit or implicit finite difference of the partial differential equations that define the mechanical models of hydrodynamics movements, thermodynamics or those that define the vibration movements with the ones that use integral transforms. By applying the Laplace and Fourier transforms, finite in sine or cosine, depending on the boundary conditions of the real physical problem, it leads to the algebraic approach of the problem, which reduces the difficulty of solving partial differential equations. The errors obtained for the solution of partial differential equations using different methods are within the standard norms. However, in terms of calculus precision, the use of integral transforms is more advantageous.

Considerations Regarding the Dynamic Behavior of Composite Sandwich Bars with Polystyrene Core Reinforced with Fiber-Glass

Applied Mechanics and Materials, 2020

In this paper some sandwich bars made from classical materials (polystyrene core, glass fiber) bu... more

Study of some mechanical properties of Dammar matrix reinforced with hemp fabrics composites

THE 9TH INTERNATIONAL CONFERENCE ON STRUCTURAL ANALYSIS OF ADVANCED MATERIALS - ICSAAM 2019, 2019

In the last decades a great attention is paid to bio-composites due to their low cost and renewab... more In the last decades a great attention is paid to bio-composites due to their low cost and renewability. Until now, mostly natural fiber reinforced composites with a synthetic resin matrix have been studied. Composites with natural matrix were less studied. In this paper, some mechanical properties of composite materials with Dammar matrix with a reinforcement consisting in hemp fabrics have been studied. More specifically, the authors studied four types of resins where Dammar was the major component, its volume ratio varying between 50% and 80%. From each type of resin different composites were performed using as reinforcement two types of hemp fabrics. Based on tensile tests, the stress-strain curves and elastic or mechanical properties such as elastic modulus, ultimate tensile strength and breaking elongation were determined.In the last decades a great attention is paid to bio-composites due to their low cost and renewability. Until now, mostly natural fiber reinforced composites with a synthetic resin matrix have been studied. Composites with natural matrix were less studied. In this paper, some mechanical properties of composite materials with Dammar matrix with a reinforcement consisting in hemp fabrics have been studied. More specifically, the authors studied four types of resins where Dammar was the major component, its volume ratio varying between 50% and 80%. From each type of resin different composites were performed using as reinforcement two types of hemp fabrics. Based on tensile tests, the stress-strain curves and elastic or mechanical properties such as elastic modulus, ultimate tensile strength and breaking elongation were determined.

Study on transverse vibrations of a lathe

IOP Conference Series: Materials Science and Engineering, 2019

This paper is focused on the importance of applying integral transforms in the determining of the... more

A Study on the Mechanical Properties of Some Green-Composites

Environmental Engineering and Management Journal, 2018

In this paper, we determined some mechanical properties of a new category of green composites, ba... more In this paper, we determined some mechanical properties of a new category of green composites, based on tensile tests. More precisely, we selected a set of samples from a new bio-resin based on Dammar and two sets of samples from green-composites with matrix by bio-resin and reinforced with almost compact layers of Typha latifolia or Schoenoplectus lacustris. For these built materials, we obtained the characteristic curve, tensile strength, percentage elongation after fracture and elasticity modulus. In addition, for each sample, we observed the breakage area with an electronic microscope. The roughness profile parameters for a bio-resin specimen were determined. Based on the EDS analysis we obtained the chemical structure of the bio-resin. Finally, based on the properties of these green-composites, we proposed a few applications in civil engineering and medical fields.

A discrete θ(D) algorithm designed to increase the convergence speed in solving transport-type problems

Upb Scientific Bulletin Series a Applied Mathematics and Physics, 2014

Experimental Determinations of the Damping Factor for Composite Sandwich Bars Reinforced with Two Carbon Fiber Layers

Applied Mechanics and Materials, 2015

In this paper we will build some new and original composite sandwich bars reinforced with two lay... more In this paper we will build some new and original composite sandwich bars reinforced with two layers of carbon fiber, with the core made of polypropylene honeycomb. Starting from the dynamic response of these bars that are in free vibration, we will establish a procedure to determine their damping factor per unit mass and per unit length. We will also determine the bars eigenfrequencies (for the first eigenmode). The bars will have the core with 10, 15 and 20 mm and the free lengths of: 200, 230, 260, 290, 320 and 350 mm. The eigenfrequencies can be used in a future research to determine the bars stiffness. The stiffness values are important if these type of composite bars are used as frames for concrete forming, because the displacements when the concrete is molded are smaller if the stiffness has high values.

The Damping Study for Dammar Composites Reinforced with Natural Fibers

Applied Mechanics and Materials, 2015

In this paper we have studied the vibration damping for composite bars made by dammar based natur... more In this paper we have studied the vibration damping for composite bars made by dammar based natural resin, the reinforcement being made by flax, cotton, silk and hemp fibers. There were made rectangular section samples (5x10 mm) with 220 mm length. The bars were clamped, the free length being 100 mm, 120 mm, 140 mm, 160 mm and 180 mm. For each bar, the free vibrations made by an initial deformation, obtained by inserting an external force in the free end, were recorded. In each case, the measured vibration was under-damped.

Finite element method in modal analysis of the IO 220 kV high voltage circuit breaker structure

This paper present a Finite Element model of the high-voltage circuit breaker type IO-240 kV made... more This paper present a Finite Element model of the high-voltage circuit breaker type IO-240 kV made by using ANSYS program and the modal analysis of this model. The study was made in order to simulate the behavior of this type of circuit breaker during different types of earthquakes. The modal analysis is the first step in earthquake F.E.M. simulation. The results presented are the first 8 natural frequencies and the corresponding vibration modes. This F.E.M. model was validated by experimental results and can be used in earthquake simulation by performing a F.E.M. spectrum analysis.

Determination of Damping Factor at the Vibrations of Composite Bars Reinforced with Carbon and Kevlar Texture

In this paper, it is showed that a mechanical model with one degree of freedom can be used to stu... more In this paper, it is showed that a mechanical model with one degree of freedom can be used to study the vibrations of a bar in a certain point. The considered structures were made of epoxy resin reinforced with carbon and carbon-kevlar texture. The vibrations in the free end of the bar, clamped at the other end, were determined experimentally for four different lengths. Eigenfrequencies and damping factor for the first modes of vibration were obtained for each bar. Relationships for the eigenfrequency and damping factor are proposed, as a function of the length of the bar, for each of the studied materials.

About the Mechanical Properties for a Type of Green Composites with Hybrid Dammar/Sandarac Matrix and Natural Reinforcements

Macromolecular Symposia

This paper presents the mechanical properties for sandwich core strips with a 60% sandarac combin... more This paper presents the mechanical properties for sandwich core strips with a 60% sandarac combination core and 40% Resoltech 1050 epoxy resin with 1055 hardener, and the upper and lower layers reinforced with cotton, silk and linen fabric, and the matrix is a combination of 60% dammar resin and 40% Resoltech 1050 epoxy resin with 1055 hardener. For these materials, there is determined: static mechanical properties from tensile stress (Young elastic modulus, yield strength, breaking strength) and chemical composition by energy dispersive spectroscopy analysis with an scanning electron microscope. It is observed that the dammar resin, in all the cases, has increased mechanical characteristics compared to sandarac. Also, the samples reinforced with cotton show better mechanical properties compared to the ones reinforced with flax and silk.

Study About Some Mechanical Properties for Composites Reinforced with Corn Cob Powder

Materiale Plastice

In this paper we have created some composites reinforced with corn cob powder and the matrix was ... more In this paper we have created some composites reinforced with corn cob powder and the matrix was made by a combination between Resoltech 1050 resin with its Resoltech 1058 hardener. For the composites manufacturing, we have used the manual casting technique. For the new manufactured composites, we have determined the mechanical properties from the tensile test according to ASTM D3039: Young modulus, breaking strength and elongation at break. We have also molded samples for the compression test according to ASTM D695-15 and we have determined the breaking strength. The tensile and compression tests were made on universal testing machines. In the end, we have determined also the dynamic mechanical properties for the studied material by clamping the samples at one edge and leaving the samples unconstrained at the other edge. At the unconstrained edge we have placed a Bruel&Kjaer accelerometer which recorded the samples free vibrations. From the free vibrations recording and Euler-Berno...

Chemical and Mechanical Properties for Rosin-based Hybrid Resins

Materiale Plastice, Apr 5, 2023

Study of Composite Bar Damping from Dammar Hybrid Resin Reinforced with Natural Fibers

Materiale Plastice

At the moment, the tendency in the composites field, is to use natural resins and fibers to obtai... more At the moment, the tendency in the composites field, is to use natural resins and fibers to obtain �environmental friendly� materials, that are compostable and biodegradable. In this paper there is an experimental study of the depletion capacity of the vibration from the composite beams, using the hardener made of cotton, flax, hemp, silk textile and the three types of the Dammar hybrid resin matrix. The damping factor and the eigenfrequency of the vibrations was determined experimentally for these bars. Based on the acquired results, the dynamic elasticity modulus and the loss factor were calculated, for each composite material studied.

Determination of Damping Coefficients for Sandwich Bars with Polypropylene Honeycomb Core and the Exterior Layers Reinforced with Metal Fabric

We deduced the equation of motion for free vibrations using Mohr-Maxwell method, considering that... more We deduced the equation of motion for free vibrations using Mohr-Maxwell method, considering that the bar is requested to bending by the inertial forces and by the damping forces. We experimentally obtained the dynamic response for sandwich bars with polypropylene honeycomb core, which have the exterior layers made of epoxy resin reinforced with steel fabric. In addition, we determined the damping coefficients per unit mass and per unit length of the bar, for bar with core thicknesses equal to 10, 15, 20 mm; width of 40 and 60 mm, and the free length of embedded bar equal to 200, 250, 300 and 350 mm. For each type of bar studied, we determined the relationships of exponential type for the calculus damping coefficients (mentioned above), according to the free length of the embedded bar.

A Discrete ( ) D Θ Algorithm Designed to Increase the Convergence Speed in Solving Transport-Type Problems

In this article, we propose a discrete algorithm that can be used to solve transport-type problem... more In this article, we propose a discrete algorithm that can be used to solve transport-type problems. The real improvement brought by applying this original algorithm consists in obtaining a completely filtered and kind of optimal program, following a small number of steps, comparing with other existing algorithms. The outcome will be that the computer memory and the implementation costs will be reduced. The solution is based upon combinatorial methods, and it addresses a certain transport capacity X that is bounded both above and below () D X d ≤ ≤. As a concrete example, we also present a () () 3 , 3 , = m n numerical application corresponding to a situation of 3 suppliers and 3 of their beneficiaries.

A Method for the Analysis of Vibrations Occurring Within Some Mechanical Systems Which Contain Spur Gears

Starting from the mathematical model created for the relative displacement of two cog wheels insi... more Starting from the mathematical model created for the relative displacement of two cog wheels inside of a gearing (model which is expressed under the form of a second-order system of differential equations with parameter'shaped or possibly non-linear excitations) we will present in this work an original method of integrating the matrix movement equation which does make use of the procedure of rendering discrete the time interval during which the concerned movement is observed. The applying of the Laplace integrated transformations which are unilateral in respect to time should lead us towards rendering algebraic the concerned model. This fact could hugely simplify the problem. Furthermore, we should be as well able to provide the graphical representations of the relative displacements for the considered gearing mechanism.

Spectral Decomposition of the Elasticity Matrix

În Teoria Elasticităţii Anizotrope, matricea coeficienţilor elastici este, până la urmă, o transf... more În Teoria Elasticităţii Anizotrope, matricea coeficienţilor elastici este, până la urmă, o transformare liniară, simetrică, pe spaţii vectoriale 6-dimensionale. Deci, orice asemenea matrice admite o descompunere spectrală. Structura unei descompuneri spectrale este determinată de mulţimile spaţiilor invariante, specifice tipului de simetrie elastică a materialului studiat. Vectorii proprii, cel puţin parţial, nu depind de valorile constantelor elastice, în schimb, valorile proprii depind de aceste constante. Sunt prezentate matricile coeficienţilor elastici pentru categoriile semnificative de simetrie cristalină. Sunt calculate matricile coeficienţilor elastici pentru cazuri concrete de materiale reprezentative pentru fiecare categorie de simetrie cristalină.

The Vibratory Behaviour of a Lathe with Continious Variator of High Speed and Dynamic Absorber

Proceedings of the 23rd International DAAAM Symposium 2012, 2012

In this paper, a lathe with continuous variator of high speed and dynamic absorber is studied. Th... more In this paper, a lathe with continuous variator of high speed and dynamic absorber is studied. The machine, which is a complex system with a great number of freedom degrees, has a corresponding number of freedom degrees, which is why in the dynamic study, there will be taken into account only those vibratory modes that, according to the required precision and the main purpose, have a great influence in the development of the studied vibratory phenomenon.

Comparisons between some composite materials reinforced with hemp fibers

Materials Today: Proceedings, 2019

For this research we have built original composite materials that have a dammar-based bio-resin a... more For this research we have built original composite materials that have a dammar-based bio-resin as matrix and are reinforced with hemp fibers. These composite materials have been subjected to tensile tests to find their mechanical characteristics and elastic constants: ultimate tensile strength, Young's modulus, Poisson's ratio and elongation at break. In the second part of the paper we have studied other composite samples with dammar-based resin/hemp fibers and classical composite samples epoxy/hemp fibers. By recording their free vibrations, we have determined the damping factor with respect to their mass, length, loss factor, dynamic flexural stiffness and dynamic Young's modulus respectively. In the end, we have compared the studied samples with other composite materials reinforced with hemp fibers that have been studied in the scientific literature.

Considerations on Computational Accuracy of the Solution for a Partial Differential Equation

Applied Mechanics and Materials, 2020

In this paper, we will compare the methods of solving with explicit or implicit finite difference... more In this paper, we will compare the methods of solving with explicit or implicit finite difference of the partial differential equations that define the mechanical models of hydrodynamics movements, thermodynamics or those that define the vibration movements with the ones that use integral transforms. By applying the Laplace and Fourier transforms, finite in sine or cosine, depending on the boundary conditions of the real physical problem, it leads to the algebraic approach of the problem, which reduces the difficulty of solving partial differential equations. The errors obtained for the solution of partial differential equations using different methods are within the standard norms. However, in terms of calculus precision, the use of integral transforms is more advantageous.

Considerations Regarding the Dynamic Behavior of Composite Sandwich Bars with Polystyrene Core Reinforced with Fiber-Glass

Applied Mechanics and Materials, 2020

In this paper some sandwich bars made from classical materials (polystyrene core, glass fiber) bu... more

Study of some mechanical properties of Dammar matrix reinforced with hemp fabrics composites

THE 9TH INTERNATIONAL CONFERENCE ON STRUCTURAL ANALYSIS OF ADVANCED MATERIALS - ICSAAM 2019, 2019

In the last decades a great attention is paid to bio-composites due to their low cost and renewab... more In the last decades a great attention is paid to bio-composites due to their low cost and renewability. Until now, mostly natural fiber reinforced composites with a synthetic resin matrix have been studied. Composites with natural matrix were less studied. In this paper, some mechanical properties of composite materials with Dammar matrix with a reinforcement consisting in hemp fabrics have been studied. More specifically, the authors studied four types of resins where Dammar was the major component, its volume ratio varying between 50% and 80%. From each type of resin different composites were performed using as reinforcement two types of hemp fabrics. Based on tensile tests, the stress-strain curves and elastic or mechanical properties such as elastic modulus, ultimate tensile strength and breaking elongation were determined.In the last decades a great attention is paid to bio-composites due to their low cost and renewability. Until now, mostly natural fiber reinforced composites with a synthetic resin matrix have been studied. Composites with natural matrix were less studied. In this paper, some mechanical properties of composite materials with Dammar matrix with a reinforcement consisting in hemp fabrics have been studied. More specifically, the authors studied four types of resins where Dammar was the major component, its volume ratio varying between 50% and 80%. From each type of resin different composites were performed using as reinforcement two types of hemp fabrics. Based on tensile tests, the stress-strain curves and elastic or mechanical properties such as elastic modulus, ultimate tensile strength and breaking elongation were determined.

Study on transverse vibrations of a lathe

IOP Conference Series: Materials Science and Engineering, 2019

This paper is focused on the importance of applying integral transforms in the determining of the... more

A Study on the Mechanical Properties of Some Green-Composites

Environmental Engineering and Management Journal, 2018

In this paper, we determined some mechanical properties of a new category of green composites, ba... more In this paper, we determined some mechanical properties of a new category of green composites, based on tensile tests. More precisely, we selected a set of samples from a new bio-resin based on Dammar and two sets of samples from green-composites with matrix by bio-resin and reinforced with almost compact layers of Typha latifolia or Schoenoplectus lacustris. For these built materials, we obtained the characteristic curve, tensile strength, percentage elongation after fracture and elasticity modulus. In addition, for each sample, we observed the breakage area with an electronic microscope. The roughness profile parameters for a bio-resin specimen were determined. Based on the EDS analysis we obtained the chemical structure of the bio-resin. Finally, based on the properties of these green-composites, we proposed a few applications in civil engineering and medical fields.

A discrete θ(D) algorithm designed to increase the convergence speed in solving transport-type problems

Upb Scientific Bulletin Series a Applied Mathematics and Physics, 2014

Experimental Determinations of the Damping Factor for Composite Sandwich Bars Reinforced with Two Carbon Fiber Layers

Applied Mechanics and Materials, 2015

In this paper we will build some new and original composite sandwich bars reinforced with two lay... more In this paper we will build some new and original composite sandwich bars reinforced with two layers of carbon fiber, with the core made of polypropylene honeycomb. Starting from the dynamic response of these bars that are in free vibration, we will establish a procedure to determine their damping factor per unit mass and per unit length. We will also determine the bars eigenfrequencies (for the first eigenmode). The bars will have the core with 10, 15 and 20 mm and the free lengths of: 200, 230, 260, 290, 320 and 350 mm. The eigenfrequencies can be used in a future research to determine the bars stiffness. The stiffness values are important if these type of composite bars are used as frames for concrete forming, because the displacements when the concrete is molded are smaller if the stiffness has high values.

The Damping Study for Dammar Composites Reinforced with Natural Fibers

Applied Mechanics and Materials, 2015

In this paper we have studied the vibration damping for composite bars made by dammar based natur... more In this paper we have studied the vibration damping for composite bars made by dammar based natural resin, the reinforcement being made by flax, cotton, silk and hemp fibers. There were made rectangular section samples (5x10 mm) with 220 mm length. The bars were clamped, the free length being 100 mm, 120 mm, 140 mm, 160 mm and 180 mm. For each bar, the free vibrations made by an initial deformation, obtained by inserting an external force in the free end, were recorded. In each case, the measured vibration was under-damped.

Finite element method in modal analysis of the IO 220 kV high voltage circuit breaker structure

This paper present a Finite Element model of the high-voltage circuit breaker type IO-240 kV made... more This paper present a Finite Element model of the high-voltage circuit breaker type IO-240 kV made by using ANSYS program and the modal analysis of this model. The study was made in order to simulate the behavior of this type of circuit breaker during different types of earthquakes. The modal analysis is the first step in earthquake F.E.M. simulation. The results presented are the first 8 natural frequencies and the corresponding vibration modes. This F.E.M. model was validated by experimental results and can be used in earthquake simulation by performing a F.E.M. spectrum analysis.