Gabriel Andrei - Academia.edu (original) (raw)
Papers by Gabriel Andrei
The Annals of "Dunarea de Jos" University of Galati. Fascicle IX, Metallurgy and Materials Science, 2013
This paper presents the effect of different contents of single-wall carbon nanotubes (SWCNT) on t... more This paper presents the effect of different contents of single-wall carbon nanotubes (SWCNT) on the specific heat and coefficient of thermal expansion of polyester composites. By adding small content of SWCNT in the matrix of the polyester, the specific heat increase compared to pure polyester. For a content higher than 0.15 wt% SWCNT, the coefficient of thermal expansion increases compared with pure polyester on cooling curve.
The Annals of "Dunarea de Jos" University of Galati. Fascicle IX, Metallurgy and Materials Science, 2013
This paper covers some aspects related to the structure of natural cellulose fibers as well the s... more This paper covers some aspects related to the structure of natural cellulose fibers as well the sources, obtaining methods, properties and their applications. In contrast with aramide and other materials resulted from fossil fuels, nanocellulose is completely renewable. The tensile strength of crystalline cellulose is similar to aluminum's. Its stiffness has been shown to be in the order of magnitude which is similar to aramide and better than glass fibers. Nananocellulose may be prepared as films which are expected to show high strength, high stiffness and high strain. Its strength/weight ratio is 8 times greater than that of stainless steel.
MATEC Web of Conferences, 2017
This paper presents an analysis of the power losses due to the friction between the components of... more This paper presents an analysis of the power losses due to the friction between the components of the spherical joints, belonging to a 6RSS parallel mechanism. The determination of power losses in spherical joints has been done with an application where the characteristic point follows a closed space curve. The trajectory of the point on the convex semicuple in contact with the concave semicuple it has been determined by using facilities of the CATIA software. 2 Geometrical modeling of the spherical joint Let us consider a kinematic chain of a 6RSS parallel mechanism (Figure 1). The kinematic chain is composed of rotational joints in the points k and spherical joints in the points k and k , respectively. The actuating arms k = k k = 254 mm are rotated at an angle k around the axis passing through the k point, by means of actuators mounted on the base plate. The position of the k point relative to the {R} system, the length of the actuating arms and the value of the angle k are known. In Figure 2, has been shown the position of the k points.
The paper presents results on wear after testing a class of composites (PA +1% black carbon and d... more The paper presents results on wear after testing a class of composites (PA +1% black carbon and different 5 concentrations of micro glass spheres) and discussions about damaging processes within the superficial layer, grouped in two categories: one favouring the material remove and the other the reduction of wear intensity. The analysis points out that tribological behaviour should be interpreted only by putting together information about wear, friction, temperature in contact, pair of materials in contact in order to obtain sustainable results that could be useful in engineering design.
It is well-known the fact that carbon nanotubes (CNTs) contain carbon atoms in different hybridiz... more It is well-known the fact that carbon nanotubes (CNTs) contain carbon atoms in different hybridization states (sp 3 and sp 2 ), that generates complex structures (diamond and graphite respectively). These multiple connections generate strong interaction of forces between particular CNTs, that means Van der Waals forces and also π-π type those immediate result in the agglomerates obtaining and, singularizing the composite materials, the first effect is clusters generation process. The physical-chemical properties of nanocomposite materials are influenced by the appropriate CNTs dispersion obtaining in the matrix. This fact is efficiently obtained when the interactions energy between CNTs themselves is lower than the dispersion energy cumulated with the interactions energy between CNTs and the matrix. The dispersion energy considers CNTs blending techniques inside the matrix and the interactions energy between CNTs and the matrix supposes the chemical bond obtaining and physical-chemi...
Polyester belongs to the thermoset group of polymers. Polyester and his composites are used in in... more Polyester belongs to the thermoset group of polymers. Polyester and his composites are used in industry mainly because of the lowest price, but also because of their mechanical performance. This paper aims to be a review of the tribological behavior of the polymer and its composites studied to date. In the recent years, the research trend is to improve the properties of polymers by adding nanoscale materials. The paper highlighted some aspects of the tribological characteristics of the polyester nanocomposites.
The mechanical properties of neat polyetherether ketone (PEEK), and reinforced PEEK with 30 (wt%)... more The mechanical properties of neat polyetherether ketone (PEEK), and reinforced PEEK with 30 (wt%) carbon fibre (PEEK CF 30) and 15.8 (wt%) carbon nanotube (PEEK Nano) was investigated at compression tests at different strain rate. The G’Sell – Jonas phenomenological model was used to describe the mechanical behavior of the composite materials.
Journal of Clinical and Investigative Surgery, 2021
Introduction. Gastric cancer remains among the top three digestive diseases with the highest mort... more Introduction. Gastric cancer remains among the top three digestive diseases with the highest mortality rates in the world. Treatment of gastric cancer is multidisciplinary, gastric resection being essential for the best result. Anemia is one of the most common comorbidities present in patients diagnosed with gastric cancer. Materials and Methods. This is a retrospective analytical study over a period of 6 years (2014-2019). It is based on 114 consecutive gastric resections for cancer performed by a single team using exclusively resection and reconstruction stapling methods. The study aims to investigate a correlation between the presence of preoperative anemia and the incidence of postoperative morbidity and mortality. Results. Preoperative anemia was found in 70% of patients, with about half of these patients presenting with mild anemia. Most postoperative complications were grade I and II according to the Clavien Dindo scale. Anemia was correlated with an increase in infectious co...
Energy Reports, 2021
Abstract This paper focuses on the energy potential of the Black Sea wind, with the ultimate goal... more Abstract This paper focuses on the energy potential of the Black Sea wind, with the ultimate goal of evaluating a possible location of a wind farm near the Western coast of the Black Sea. The model taken into account for the research investigation is based on the existing wind farms from North Sea geographical area. The study aims to evaluate the wind energy potential based on three parameters, according to existing mathematical models, namely wind speed, wind power density and annual electricity production. The calculation of wind speed, wind power density, and annual electricity production, for all geographical points considered in the North Sea and the Black Sea, was made on the basis of existing information in the ERA-Interim and SMHI databases, using own codes written in Matlab. The period analyzed was of about 20 years, between 1999 and 2018. Comparing the data obtained from the calculations, for the annual energy production, with those made available by the statistics, one could see that the results obtained are close. Following the calculations we noticed that the location of the wind farm could achieve a sufficiently large amount of energy, greater than the productivity of the current model farm, in term of the past values, but with lower efficiency than those obtained for the future of the current farm. One can conclude that such a wind farm can produce enough energy to supply an entire city, having a population up to 290000 inhabitants, and for which the energy consumption is about 0.42 TWh .
DAAAM Proceedings, 2011
It is well known that the quality of a composite depends not only in its components quality but a... more It is well known that the quality of a composite depends not only in its components quality but also in forming technology. Regarding particulate polymer composites the mentioned dependence is stronger. This study is about how the filler's dispersion into the matrix is influencing the basic properties of filled composites. In the case of moulded thermosetting based composites three ways to disperse the powders into the matrix are available leading, probably, to different final properties. In this study the epoxy system EPIPHEN RE 4020-DE 4020 was used as matrix and Starch, Clay, Talc, CNT, Aluminium titanate, Lithium titanate as fillers.
Archives of the Balkan Medical Union, 2020
Systèmes de grading histologique chez les patients atteints de colite ulcéreuse: une perspective ... more Systèmes de grading histologique chez les patients atteints de colite ulcéreuse: une perspective pratique de routine Introduction. La guérison histologique est devenue un objectif thérapeutique chez les patients atteints de colite ulcéreuse. Cependant, un consensus sur sa définition précise n'a pas encore été atteint. Un grand nombre de systèmes de grading histologique complexes pour la colite ulcéreuse sont disponibles dans la littérature, ce qui rend la standardisation compliquée. L'objectif de l'étude était d'identifier un système de grading histologique adapté à la pratique de routine et de contribuer ainsi à la standardisation du rapport histologique de l'activité inflammatoire dans la colite ulcéreuse. Matériaux et méthodes. Nous avons examiné rétrospectivement et noté 64 lames colorées H&E en utilisant l'index de Nancy (NI), le score Geboes (GS) et l'indice histopathologique Robarts (RHI) par trois pathologistes indépendants. Le niveau d'accord
IOP Conference Series: Materials Science and Engineering, 2019
The study of the kinematic performances of a parallel mechanisms an important aspect in terms of ... more The study of the kinematic performances of a parallel mechanisms an important aspect in terms of analysis and design. This paper presents a study on the kinematic manipulability and kinematic efficiency of a 6RSS parallel mechanism. The parallel mechanism consists of a fixed plate and a mobile platform connected by six independent kinematic chains. Each of the six kinematic chains has an actuated rotational joint and two spherical joints. The motion equations for the six kinematic chains of the parallel mechanism are defined when the characteristic point P moves on the spatial curve with constant speed. Based on the global Jacobian matrix determinant and the angular speeds of actuated arms was graphically represented the variation of the two kinematic indices. Kinematic indices allow for assessing the quality of the mechanism motion; they also help us avoid those critical configurations encountered in the case of parallel mechanisms.
Mechanism and Machine Theory, 2018
The paper presents a method of determining the optimal trajectory of the characteristic point bel... more The paper presents a method of determining the optimal trajectory of the characteristic point belonging to the end effector of a parallel robot with six degrees of freedom type 6 R SS. The parallel robot is composed of a fixed plate and a mobile platform connected by six independent kinematic chains. Each of the six kinematic chains was part of one rotational actuating joint and two spherical joints. Based on the kinematic analysis, the motions of the end effector element were defined for manipulation operations using polynomial expressions of geometric parameters as time functions. By means of computational programs the polynomial variation of the motion parameters was determined. The data obtained were analysed on the basis of CAD programs through which the angular velocities of the actuating arms were determined when the end effector followed the trajectory described by the Hermite function. Using the same Hermite polynomials, two methods for optimizing the trajectory of the characteristic point were developed, the first intended to minimize its length and the second to minimize the runtime of the trajectory.
Applied Mechanics and Materials, 2015
Friction coefficient and linear wear rate of polyester-carbon nanotubes composites were investiga... more Friction coefficient and linear wear rate of polyester-carbon nanotubes composites were investigated through ball-on-flat reciprocating test, under dry sliding contact. Three types of nanoscopic fillers were used: multiwall carbon nanotubes (MWCNT), functionalized multiwall carbon nanotubes (MWCNT-COOH) and singlewall carbon nanotubes (SWCNT), with three values of weight content 0.1, 0.15 and 0.2 wt%. Comparative analysis was done for polyester and its composites tested over 14 m sliding distance, under three values of load, 30 N, 40 N and 50 N. Composites containing MWCNT underwent a decrease in friction coefficient and linear wear rate only in case of 50N loading. An improvement of wear behavior under 50N loading was obtained for the composite with 0.10 wt% functionalized carbon nanotubes. Generally, better values of wear rate at 50 N loading were recorded in case of composites with 0.15 wt% and 0.20 wt% MWCNT and SWCNT, respectively. Optical and electronic investigation of the wo...
Applied Mechanics and Materials, 2015
This paper presents an experimental evaluation of friction and wear properties of a composite mat... more This paper presents an experimental evaluation of friction and wear properties of a composite material-moglice - made by Diamant Metallplastic GmbH company, from Germany. This material is a polymeric matrix reinforced with particles of cristobalite (αSiO2) and molybdenum disulphide (MoS2). The material is recommended by the manufacturer for repairing metal parts. This material was tribologically tested in dry friction conditions, on a ball on flat configuration, using the reciprocating method, on a CETR UMT-2 tribometer (Bruker Corporation). The counterpart was a steel ball. The tests were performed at room temperature in normal conditions of relative humidity of 40-60% using an average sliding speed of 3.5 mm/s. The tests were carried out at normal loads of 20, 30, 40 and 50N over a sliding distance of 100 m. The wear traces obtained were optically examined with μSCAN laser profilometer (NANOFOCUS).
Applied Mechanics and Materials, 2015
The wear behaviour of poly (ether-ether-ketone) (PEEK) composite was investigated according to th... more The wear behaviour of poly (ether-ether-ketone) (PEEK) composite was investigated according to the load and test speed. Three types of materials were studied: first, neat PEEK, PEEK with 30 wt. % carbon fiber (PEEK CF30), and third, PEEK with carbon nanotubes (PEEK ELS NANO). Tribological tests were performed on the universal tribometer UMT-2, using a pin-on-disc device. The friction coefficient and wear rate for the composites studied were analysed. Tests carried out have allowed the examination of the influence of load and speed on the friction coefficient and wear rate under dry sliding regime. Also, structural changes were noticed by optical and SE microscopy, and wear types of surface were discussed. As a result of experimental tests, it was established that PEEK composite with carbon fiber/carbon nanotubes exhibit good wear behaviour under operating conditions.
It is known that an important factor in nanocomposites obtaining technology is the dispersion of ... more It is known that an important factor in nanocomposites obtaining technology is the dispersion of nanoparticles in the matrix. The paper proposes a new technology in the dispersion of carbon nanotubes in a polymer matrix. It was used multiwall carbon nanotubes (MWCNT) that based on a particular technology, have been coated with iron oxide (III) resulting so-called plated or coated nanotubes (MWCNT-F3). MWCNT-F3 carbon nanotubes were used to obtain a polymer/MWCNT-F3 nanocomposite material by dispersion in a polymer matrix represented by polyester resin. Oscillating magnetic field interacting with carbon nanotubes coated with iron oxide (III) own fields performs a vibrating movement thereof. Dispersion was carried out in steps by mechanical and ultrasonic mixing, with and without applying an oscillating magnetic field in polyester resin curing phase. The dispersion degree was qualitatively analyzed by SEM analysis. Influence of dispersion on the mechanical and thermal properties was p...
This paper presents an analysis of several 3D parameters based on bearing area curve in order to ... more This paper presents an analysis of several 3D parameters based on bearing area curve in order to use the information for establishing the influence of sliding regime against steel on the tribological behavior of a composite class with polyamide matrix and 1% of black carbon. There were done pin-on-disk tests for different concentrations of micro glass spheres (MGS): 2.5, 5, 10, 20, 30 and 50% (wt), respectively. The polymer was tested under similar conditions in order to have a reference basis and to point out the improvement in tribological behavior when adding this reinforcement material. The surface topographies were registered with the help of PRO500 3D (stylus) Profilometer. The test parameters in dry regime were: sliding speed 0.5, 1.0 and 1.5 m/s, average pressure 1, 2 and 3 MPa, respectively. There were analyzed the influence of MGS concentration and sliding regime on wear as mass loss of the composite discs, after 10,000 m of sliding, the friction coefficient and several 3D parameters related to the bearing area curve, determined from raw profiles (surface bearing index – Sbi, core fluid retention index – Sci, valley fluid retention index, Svi, reduced summit height, Spk, core roughness depth, Sk, and reduced valley depth, Svk).
Applied Mechanics and Materials, 2014
This paper presents the results of the profilometric analysis of wear tracks from tribological te... more This paper presents the results of the profilometric analysis of wear tracks from tribological tests of a composite material made by Diamond Metallplastic GmbH, Germany. This material has a polymer matrix reinforced with Cu, Zn, Sn particles, and various allotropic forms of SiO2. The material belongs to Multimetall Messing category and is recommended by the manufacturer for repairing brass made parts. This composite material was tribologically tested in dry friction reciprocating conditions, in ball-on-flat configuration, using the tribotester CETR-UMT-2 (Bruker Corporation). The counterpiece was a steel ball. The tests were conducted at normal loads of 20, 30, 40 and 50N, over a distance of 100 m, at an average sliding speed of 3,50 mm/s, at room temperature and relative humidity of 40-60%. The wear tracks were examined with the help of a laser profilometer and the profilometric module of the tribotester CETR-UMT-2 (Bruker Corporation). The profilometric analysis results for the co...
Applied Mechanics and Materials, 2014
Phenomenological constitutive equations are applied successfully to predict stress-strain relatio... more Phenomenological constitutive equations are applied successfully to predict stress-strain relationship for semi-crystalline polymers at high strain rates encountered in mechanical tests. The parameters of mechanical behaviour law for polymer composites with nanoscopic additives and carbon fibres can be identified by applying a known law over a lot of data obtained from compressive tests. The objective of this study is to investigate the applicability of the model G'Sell - Jonas in the case of poly (ether-ether-ketone) composites with carbon nanotubes and carbon fibres.
The Annals of "Dunarea de Jos" University of Galati. Fascicle IX, Metallurgy and Materials Science, 2013
This paper presents the effect of different contents of single-wall carbon nanotubes (SWCNT) on t... more This paper presents the effect of different contents of single-wall carbon nanotubes (SWCNT) on the specific heat and coefficient of thermal expansion of polyester composites. By adding small content of SWCNT in the matrix of the polyester, the specific heat increase compared to pure polyester. For a content higher than 0.15 wt% SWCNT, the coefficient of thermal expansion increases compared with pure polyester on cooling curve.
The Annals of "Dunarea de Jos" University of Galati. Fascicle IX, Metallurgy and Materials Science, 2013
This paper covers some aspects related to the structure of natural cellulose fibers as well the s... more This paper covers some aspects related to the structure of natural cellulose fibers as well the sources, obtaining methods, properties and their applications. In contrast with aramide and other materials resulted from fossil fuels, nanocellulose is completely renewable. The tensile strength of crystalline cellulose is similar to aluminum's. Its stiffness has been shown to be in the order of magnitude which is similar to aramide and better than glass fibers. Nananocellulose may be prepared as films which are expected to show high strength, high stiffness and high strain. Its strength/weight ratio is 8 times greater than that of stainless steel.
MATEC Web of Conferences, 2017
This paper presents an analysis of the power losses due to the friction between the components of... more This paper presents an analysis of the power losses due to the friction between the components of the spherical joints, belonging to a 6RSS parallel mechanism. The determination of power losses in spherical joints has been done with an application where the characteristic point follows a closed space curve. The trajectory of the point on the convex semicuple in contact with the concave semicuple it has been determined by using facilities of the CATIA software. 2 Geometrical modeling of the spherical joint Let us consider a kinematic chain of a 6RSS parallel mechanism (Figure 1). The kinematic chain is composed of rotational joints in the points k and spherical joints in the points k and k , respectively. The actuating arms k = k k = 254 mm are rotated at an angle k around the axis passing through the k point, by means of actuators mounted on the base plate. The position of the k point relative to the {R} system, the length of the actuating arms and the value of the angle k are known. In Figure 2, has been shown the position of the k points.
The paper presents results on wear after testing a class of composites (PA +1% black carbon and d... more The paper presents results on wear after testing a class of composites (PA +1% black carbon and different 5 concentrations of micro glass spheres) and discussions about damaging processes within the superficial layer, grouped in two categories: one favouring the material remove and the other the reduction of wear intensity. The analysis points out that tribological behaviour should be interpreted only by putting together information about wear, friction, temperature in contact, pair of materials in contact in order to obtain sustainable results that could be useful in engineering design.
It is well-known the fact that carbon nanotubes (CNTs) contain carbon atoms in different hybridiz... more It is well-known the fact that carbon nanotubes (CNTs) contain carbon atoms in different hybridization states (sp 3 and sp 2 ), that generates complex structures (diamond and graphite respectively). These multiple connections generate strong interaction of forces between particular CNTs, that means Van der Waals forces and also π-π type those immediate result in the agglomerates obtaining and, singularizing the composite materials, the first effect is clusters generation process. The physical-chemical properties of nanocomposite materials are influenced by the appropriate CNTs dispersion obtaining in the matrix. This fact is efficiently obtained when the interactions energy between CNTs themselves is lower than the dispersion energy cumulated with the interactions energy between CNTs and the matrix. The dispersion energy considers CNTs blending techniques inside the matrix and the interactions energy between CNTs and the matrix supposes the chemical bond obtaining and physical-chemi...
Polyester belongs to the thermoset group of polymers. Polyester and his composites are used in in... more Polyester belongs to the thermoset group of polymers. Polyester and his composites are used in industry mainly because of the lowest price, but also because of their mechanical performance. This paper aims to be a review of the tribological behavior of the polymer and its composites studied to date. In the recent years, the research trend is to improve the properties of polymers by adding nanoscale materials. The paper highlighted some aspects of the tribological characteristics of the polyester nanocomposites.
The mechanical properties of neat polyetherether ketone (PEEK), and reinforced PEEK with 30 (wt%)... more The mechanical properties of neat polyetherether ketone (PEEK), and reinforced PEEK with 30 (wt%) carbon fibre (PEEK CF 30) and 15.8 (wt%) carbon nanotube (PEEK Nano) was investigated at compression tests at different strain rate. The G’Sell – Jonas phenomenological model was used to describe the mechanical behavior of the composite materials.
Journal of Clinical and Investigative Surgery, 2021
Introduction. Gastric cancer remains among the top three digestive diseases with the highest mort... more Introduction. Gastric cancer remains among the top three digestive diseases with the highest mortality rates in the world. Treatment of gastric cancer is multidisciplinary, gastric resection being essential for the best result. Anemia is one of the most common comorbidities present in patients diagnosed with gastric cancer. Materials and Methods. This is a retrospective analytical study over a period of 6 years (2014-2019). It is based on 114 consecutive gastric resections for cancer performed by a single team using exclusively resection and reconstruction stapling methods. The study aims to investigate a correlation between the presence of preoperative anemia and the incidence of postoperative morbidity and mortality. Results. Preoperative anemia was found in 70% of patients, with about half of these patients presenting with mild anemia. Most postoperative complications were grade I and II according to the Clavien Dindo scale. Anemia was correlated with an increase in infectious co...
Energy Reports, 2021
Abstract This paper focuses on the energy potential of the Black Sea wind, with the ultimate goal... more Abstract This paper focuses on the energy potential of the Black Sea wind, with the ultimate goal of evaluating a possible location of a wind farm near the Western coast of the Black Sea. The model taken into account for the research investigation is based on the existing wind farms from North Sea geographical area. The study aims to evaluate the wind energy potential based on three parameters, according to existing mathematical models, namely wind speed, wind power density and annual electricity production. The calculation of wind speed, wind power density, and annual electricity production, for all geographical points considered in the North Sea and the Black Sea, was made on the basis of existing information in the ERA-Interim and SMHI databases, using own codes written in Matlab. The period analyzed was of about 20 years, between 1999 and 2018. Comparing the data obtained from the calculations, for the annual energy production, with those made available by the statistics, one could see that the results obtained are close. Following the calculations we noticed that the location of the wind farm could achieve a sufficiently large amount of energy, greater than the productivity of the current model farm, in term of the past values, but with lower efficiency than those obtained for the future of the current farm. One can conclude that such a wind farm can produce enough energy to supply an entire city, having a population up to 290000 inhabitants, and for which the energy consumption is about 0.42 TWh .
DAAAM Proceedings, 2011
It is well known that the quality of a composite depends not only in its components quality but a... more It is well known that the quality of a composite depends not only in its components quality but also in forming technology. Regarding particulate polymer composites the mentioned dependence is stronger. This study is about how the filler's dispersion into the matrix is influencing the basic properties of filled composites. In the case of moulded thermosetting based composites three ways to disperse the powders into the matrix are available leading, probably, to different final properties. In this study the epoxy system EPIPHEN RE 4020-DE 4020 was used as matrix and Starch, Clay, Talc, CNT, Aluminium titanate, Lithium titanate as fillers.
Archives of the Balkan Medical Union, 2020
Systèmes de grading histologique chez les patients atteints de colite ulcéreuse: une perspective ... more Systèmes de grading histologique chez les patients atteints de colite ulcéreuse: une perspective pratique de routine Introduction. La guérison histologique est devenue un objectif thérapeutique chez les patients atteints de colite ulcéreuse. Cependant, un consensus sur sa définition précise n'a pas encore été atteint. Un grand nombre de systèmes de grading histologique complexes pour la colite ulcéreuse sont disponibles dans la littérature, ce qui rend la standardisation compliquée. L'objectif de l'étude était d'identifier un système de grading histologique adapté à la pratique de routine et de contribuer ainsi à la standardisation du rapport histologique de l'activité inflammatoire dans la colite ulcéreuse. Matériaux et méthodes. Nous avons examiné rétrospectivement et noté 64 lames colorées H&E en utilisant l'index de Nancy (NI), le score Geboes (GS) et l'indice histopathologique Robarts (RHI) par trois pathologistes indépendants. Le niveau d'accord
IOP Conference Series: Materials Science and Engineering, 2019
The study of the kinematic performances of a parallel mechanisms an important aspect in terms of ... more The study of the kinematic performances of a parallel mechanisms an important aspect in terms of analysis and design. This paper presents a study on the kinematic manipulability and kinematic efficiency of a 6RSS parallel mechanism. The parallel mechanism consists of a fixed plate and a mobile platform connected by six independent kinematic chains. Each of the six kinematic chains has an actuated rotational joint and two spherical joints. The motion equations for the six kinematic chains of the parallel mechanism are defined when the characteristic point P moves on the spatial curve with constant speed. Based on the global Jacobian matrix determinant and the angular speeds of actuated arms was graphically represented the variation of the two kinematic indices. Kinematic indices allow for assessing the quality of the mechanism motion; they also help us avoid those critical configurations encountered in the case of parallel mechanisms.
Mechanism and Machine Theory, 2018
The paper presents a method of determining the optimal trajectory of the characteristic point bel... more The paper presents a method of determining the optimal trajectory of the characteristic point belonging to the end effector of a parallel robot with six degrees of freedom type 6 R SS. The parallel robot is composed of a fixed plate and a mobile platform connected by six independent kinematic chains. Each of the six kinematic chains was part of one rotational actuating joint and two spherical joints. Based on the kinematic analysis, the motions of the end effector element were defined for manipulation operations using polynomial expressions of geometric parameters as time functions. By means of computational programs the polynomial variation of the motion parameters was determined. The data obtained were analysed on the basis of CAD programs through which the angular velocities of the actuating arms were determined when the end effector followed the trajectory described by the Hermite function. Using the same Hermite polynomials, two methods for optimizing the trajectory of the characteristic point were developed, the first intended to minimize its length and the second to minimize the runtime of the trajectory.
Applied Mechanics and Materials, 2015
Friction coefficient and linear wear rate of polyester-carbon nanotubes composites were investiga... more Friction coefficient and linear wear rate of polyester-carbon nanotubes composites were investigated through ball-on-flat reciprocating test, under dry sliding contact. Three types of nanoscopic fillers were used: multiwall carbon nanotubes (MWCNT), functionalized multiwall carbon nanotubes (MWCNT-COOH) and singlewall carbon nanotubes (SWCNT), with three values of weight content 0.1, 0.15 and 0.2 wt%. Comparative analysis was done for polyester and its composites tested over 14 m sliding distance, under three values of load, 30 N, 40 N and 50 N. Composites containing MWCNT underwent a decrease in friction coefficient and linear wear rate only in case of 50N loading. An improvement of wear behavior under 50N loading was obtained for the composite with 0.10 wt% functionalized carbon nanotubes. Generally, better values of wear rate at 50 N loading were recorded in case of composites with 0.15 wt% and 0.20 wt% MWCNT and SWCNT, respectively. Optical and electronic investigation of the wo...
Applied Mechanics and Materials, 2015
This paper presents an experimental evaluation of friction and wear properties of a composite mat... more This paper presents an experimental evaluation of friction and wear properties of a composite material-moglice - made by Diamant Metallplastic GmbH company, from Germany. This material is a polymeric matrix reinforced with particles of cristobalite (αSiO2) and molybdenum disulphide (MoS2). The material is recommended by the manufacturer for repairing metal parts. This material was tribologically tested in dry friction conditions, on a ball on flat configuration, using the reciprocating method, on a CETR UMT-2 tribometer (Bruker Corporation). The counterpart was a steel ball. The tests were performed at room temperature in normal conditions of relative humidity of 40-60% using an average sliding speed of 3.5 mm/s. The tests were carried out at normal loads of 20, 30, 40 and 50N over a sliding distance of 100 m. The wear traces obtained were optically examined with μSCAN laser profilometer (NANOFOCUS).
Applied Mechanics and Materials, 2015
The wear behaviour of poly (ether-ether-ketone) (PEEK) composite was investigated according to th... more The wear behaviour of poly (ether-ether-ketone) (PEEK) composite was investigated according to the load and test speed. Three types of materials were studied: first, neat PEEK, PEEK with 30 wt. % carbon fiber (PEEK CF30), and third, PEEK with carbon nanotubes (PEEK ELS NANO). Tribological tests were performed on the universal tribometer UMT-2, using a pin-on-disc device. The friction coefficient and wear rate for the composites studied were analysed. Tests carried out have allowed the examination of the influence of load and speed on the friction coefficient and wear rate under dry sliding regime. Also, structural changes were noticed by optical and SE microscopy, and wear types of surface were discussed. As a result of experimental tests, it was established that PEEK composite with carbon fiber/carbon nanotubes exhibit good wear behaviour under operating conditions.
It is known that an important factor in nanocomposites obtaining technology is the dispersion of ... more It is known that an important factor in nanocomposites obtaining technology is the dispersion of nanoparticles in the matrix. The paper proposes a new technology in the dispersion of carbon nanotubes in a polymer matrix. It was used multiwall carbon nanotubes (MWCNT) that based on a particular technology, have been coated with iron oxide (III) resulting so-called plated or coated nanotubes (MWCNT-F3). MWCNT-F3 carbon nanotubes were used to obtain a polymer/MWCNT-F3 nanocomposite material by dispersion in a polymer matrix represented by polyester resin. Oscillating magnetic field interacting with carbon nanotubes coated with iron oxide (III) own fields performs a vibrating movement thereof. Dispersion was carried out in steps by mechanical and ultrasonic mixing, with and without applying an oscillating magnetic field in polyester resin curing phase. The dispersion degree was qualitatively analyzed by SEM analysis. Influence of dispersion on the mechanical and thermal properties was p...
This paper presents an analysis of several 3D parameters based on bearing area curve in order to ... more This paper presents an analysis of several 3D parameters based on bearing area curve in order to use the information for establishing the influence of sliding regime against steel on the tribological behavior of a composite class with polyamide matrix and 1% of black carbon. There were done pin-on-disk tests for different concentrations of micro glass spheres (MGS): 2.5, 5, 10, 20, 30 and 50% (wt), respectively. The polymer was tested under similar conditions in order to have a reference basis and to point out the improvement in tribological behavior when adding this reinforcement material. The surface topographies were registered with the help of PRO500 3D (stylus) Profilometer. The test parameters in dry regime were: sliding speed 0.5, 1.0 and 1.5 m/s, average pressure 1, 2 and 3 MPa, respectively. There were analyzed the influence of MGS concentration and sliding regime on wear as mass loss of the composite discs, after 10,000 m of sliding, the friction coefficient and several 3D parameters related to the bearing area curve, determined from raw profiles (surface bearing index – Sbi, core fluid retention index – Sci, valley fluid retention index, Svi, reduced summit height, Spk, core roughness depth, Sk, and reduced valley depth, Svk).
Applied Mechanics and Materials, 2014
This paper presents the results of the profilometric analysis of wear tracks from tribological te... more This paper presents the results of the profilometric analysis of wear tracks from tribological tests of a composite material made by Diamond Metallplastic GmbH, Germany. This material has a polymer matrix reinforced with Cu, Zn, Sn particles, and various allotropic forms of SiO2. The material belongs to Multimetall Messing category and is recommended by the manufacturer for repairing brass made parts. This composite material was tribologically tested in dry friction reciprocating conditions, in ball-on-flat configuration, using the tribotester CETR-UMT-2 (Bruker Corporation). The counterpiece was a steel ball. The tests were conducted at normal loads of 20, 30, 40 and 50N, over a distance of 100 m, at an average sliding speed of 3,50 mm/s, at room temperature and relative humidity of 40-60%. The wear tracks were examined with the help of a laser profilometer and the profilometric module of the tribotester CETR-UMT-2 (Bruker Corporation). The profilometric analysis results for the co...
Applied Mechanics and Materials, 2014
Phenomenological constitutive equations are applied successfully to predict stress-strain relatio... more Phenomenological constitutive equations are applied successfully to predict stress-strain relationship for semi-crystalline polymers at high strain rates encountered in mechanical tests. The parameters of mechanical behaviour law for polymer composites with nanoscopic additives and carbon fibres can be identified by applying a known law over a lot of data obtained from compressive tests. The objective of this study is to investigate the applicability of the model G'Sell - Jonas in the case of poly (ether-ether-ketone) composites with carbon nanotubes and carbon fibres.