Tatjana Lazovic | University of Belgrade, Faculty of Mechanical Engineering (original) (raw)
Papers by Tatjana Lazovic
Machines. Technologies. Materials., 2021
Additional manufacturing (AM), commonly known as 3D printing, exists for 40 years, still evolving... more Additional manufacturing (AM), commonly known as 3D printing, exists for 40 years, still evolving and improving. AM has gained great popularity in modern industries due to many advantages concerning conventional manufacturing technologies. Consequently, AM is one of nine pillars of the currently dominating industry trend-Industry 4.0. Initially, AM was mostly used for making models. Now, objects made by AM technologies, often are physical parts ready to be used as final products or to be installed as parts of asse mblies in more complex systems. Because of that, in more applications, the mechanical properties of these parts have to be known for the purpose to determine load carrying capacity essential for their functionality. Mechanical properties are being tested using appropriate methods, specimens, and equipment. In order to obtain comparable and evaluable test results, the test procedures and means should be s tandardized. Therefore, there was a need to develop standards for testing materials used for AM. International standardization in the field of AM started 10 years ago. The international body for standardization ISO developed and published a certain number of standards, but this is just beginning. This paper discusses aspects of AM standardization in the field of testing the mechanical properties of materials for 3D printing using fused deposition modelling (FDM). As an illustration of the standard application, specimens were prepared for testing t he tensile properties of plastic materials widely used in AM: PLA, PETG and ABS+.
Machine and Industrial Design in Mechanical Engineering, 2022
Engineering Failure Analysis, 2010
Traction shafts and axles of railway vehicles are designed to be safe and reliable in normal serv... more Traction shafts and axles of railway vehicles are designed to be safe and reliable in normal service conditions. Accidental and unpredictable conditions including bad exploitation (rail tracks, maintenance and extreme long service life) make the probability of shaft and axle fracture realistic. This article contains the experience and analysis of the traction shafts and axles fractures and fracture processes. Research
Machines. Technologies. Materials., 2021
Additional manufacturing (AM), commonly known as 3D printing, exists for 40 years, still evolving... more Additional manufacturing (AM), commonly known as 3D printing, exists for 40 years, still evolving and improving. AM has gained great popularity in modern industries due to many advantages concerning conventional manufacturing technologies. Consequently, AM is one of nine pillars of the currently dominating industry trend-Industry 4.0. Initially, AM was mostly used for making models. Now, objects made by AM technologies, often are physical parts ready to be used as final products or to be installed as parts of asse mblies in more complex systems. Because of that, in more applications, the mechanical properties of these parts have to be known for the purpose to determine load carrying capacity essential for their functionality. Mechanical properties are being tested using appropriate methods, specimens, and equipment. In order to obtain comparable and evaluable test results, the test procedures and means should be s tandardized. Therefore, there was a need to develop standards for testing materials used for AM. International standardization in the field of AM started 10 years ago. The international body for standardization ISO developed and published a certain number of standards, but this is just beginning. This paper discusses aspects of AM standardization in the field of testing the mechanical properties of materials for 3D printing using fused deposition modelling (FDM). As an illustration of the standard application, specimens were prepared for testing t he tensile properties of plastic materials widely used in AM: PLA, PETG and ABS+.
The operational ability of a rolling bearing selected for a specific application is assessed base... more The operational ability of a rolling bearing selected for a specific application is assessed based on service life. The basic formula for bearing rating life was established more than 70 years ago by A. Palmgren. The first standard presenting a basic mathematical model for rating life calculation was published in 1962 (ISO/R281). The content of this standard has been revised and the next version was published in 1977 (ISO 281-1). The novelty was the introduction of adjustment factors for reliability other than 90%. This standard was replaced by the ISO 281 standard in 1990, which introduced additional adjustment factors for special bearing properties and operating conditions. The latest version of the ISO 281 standard was published in 2007. This standard provides a procedure for calculating the modified service life by taking into account the additional impacts of lubrication condition, lubricant contamination and limit fatigue load. Furthermore, the document ISO/TS 16281 was publis...
The influence of the bolt size and the width of the joint members/bolt diameter ratio (relative c... more The influence of the bolt size and the width of the joint members/bolt diameter ratio (relative clamped length) on the stiffness coefficient of the bolt and joint members, as well as on the ratio of these stiffness coefficients are discussed in this paper. The individual stiffness coefficients of the bolt and the joint members decrease with the increase of the relative clamped length and the decrease of the bolt size. However, the stiffness ratio of the joint members and the bolt increases with the increase of the relative clamped length. Of the considered bolts M6 ... M24, the bolted joint with the M6 bolt has the highest stiffness ratio of the joint members and the bolt, and the bolted joint with the M12 bolt has the lowest stiffness ratio. When a bolted joint is loaded with a variable working load, then the dynamic safety factor (DSF) is used for evaluating the joint load capacity. The DSF increases with a decrease in the stiffness of the bolted joint, i.e. by increasing the relative clamped length of the bolted joint. For the same conditions analyzed, the bolted joint with M6 bolt has the largest DSF, and the bolted joint with M12 bolt has the smallest DSF. The obtained result can be used by engineers to evaluate the load-carrying capacity of dynamically tension-loaded bolted joints.
Biomimetics
During the last few decades, the requirements for modern machine elements in terms of size reduct... more During the last few decades, the requirements for modern machine elements in terms of size reduction, increasing the energy efficiency, and a higher load capacity of standard and non-standard gears have been very prevalent issues. Within these demands, the main goals are the optimization of the gears’ tooth profiles, as well as the investigation of new tooth profile designs. The presented design idea is based on the optimal solutions inspired by nature. Special attention is paid to the new design of the tooth root zones of spur gears in order to decrease the stress concentration values and increase the tooth root fatigue resistance. The finite element method is used for stress and strain state calculations, and the particular gear pair is modeled and optimized for these purposes. For tooth root strength analysis, the estimations are based on the theory of critical distances and the stress gradients obtained through finite element analysis. The obtained stress gradients have shown im...
The construction variation of packing machine in food processing is shown in this paper. By the t... more The construction variation of packing machine in food processing is shown in this paper. By the techno-economic analyses it is shown that original and new construction has the same construction value, but the new construction has a better economic value – validity. Better economic value has achieved with new construction and engaging domestic components and production technology.У раду је приказано варијантно конструкционо решење машине за паковање прехрамбених производа. На основу техно-економске анализе показано је да оригинално и варијантно конструкционо решење имају приближно исту техничку вредност, с тим што варијантна конструкција има већу економску вредност - оправданост. Економска оправданост постигнута је погодним конструкционим решењем и применом домаћих компоненти и технологије израде
The load distribution in machine elements is the first step in the analysis of their operating co... more The load distribution in machine elements is the first step in the analysis of their operating condition. Because of influence of many various factors, constructional and technological, it is very difficult to determine precisely a real condition – real load distribution without the approximations – hypotheses. The load distribution is basic input in mechanical and mathematical modelling with the purpose of the analysis of machine parts operating conditions from different relevant aspects: durability, stiffness, reliability and stability. Because of that, the modelling of load distribution is a very responsible and difficult task. The existing models of load distribution in rolling bearings [1], gear transmissions, chain transmissions etc. contain many approximations and empirical coefficients, which have no the appropriate physical basis. Load distribution in rolling bearings, which operate in condition of the time limited endurance, has a dominant influence on bearing durability. ...
machine design, 2018
The aim of this paper is to determine deformations and stresses in the statically loaded thrust b... more The aim of this paper is to determine deformations and stresses in the statically loaded thrust ball bearing subjected to a centric external axial load. In this case, all balls in the bearing are equally engaged in the transmission of the operational load. The influence of the load on the stresses and deformations in the bearings of different series has been analysed. The obtained results are the basis for further research of the load distribution in an eccentrically loaded axial ball bearing in order to determine the reduction of the static load bearing capacity in relation to the values determined in appropriate standard and also to the values prescribed by manufacturers’ catalogues.
INFLUENCE OF INTERNAL RADIAL CLEARANCE ON THE BALL BEARING SERVICE LIFE, 2010
external load of ball bearing is transferred from one ring to other one through balls. in the rad... more external load of ball bearing is transferred from one ring to other one through balls. in the radially loaded bearing all balls are not simultaneously active. simultaneously active balls participating in load transfer are in loaded zone. Load distribution between balls in loaded zone is unequal. Width of loaded zone depends on bearing internal radial clearance. The loaded zone decreases with increasing clearance. consequently, the load distribution between balls becomes more unequal. it leads to decreasing of ball bearing service life. The analysis of influence of internal radial clearance on the radially loaded deep groove ball bearing service life is carried out in this paper. For this purpose a new mathematical model is derived respecting classic ball bearing life theory and by introduction of a new parameter – reduced load distribution factor.
seth.asc.tuwien.ac.at
The universal joint -U-joint is type of mechanical coupling which consists of two shaft yokes con... more The universal joint -U-joint is type of mechanical coupling which consists of two shaft yokes connected with cross. The cross arms rides inside four needle bearings pressed into the yokes bores. With good lubrication and sealing, the life of U-joint is determined by material fatigue after more than million reversals. However, U-joint often does not achieve its predicted (calculated) fatigue life. When the lubrication is inappropriate and/or the sealing is not efficient enough, the U-joint service life is limited by the corrosion and wear. As U-joint loses its operational ability due to intensive wear it has to be replaced by a new one or to be repaired. The U-joint repair implies additional machining of worn out needle bearing parts. Therefore, dimensions are changed and entire needle bearing internal geometry is changed, as well. The internal geometry affects dynamics and load carrying capacity of the needle bearing, and appropriate geometrical and mathematical relations, primarily based on limited radial and circular internal clearance, must not be disturbed by repair process. Hence, it is necessary to establish a mathematical model of the needle bearing internal geometry and the corresponding algorithm for determining appropriate dimensions and it was carried out in this paper. This is the basis for further mathematical modelling of U-joint needle bearing dimensions, mechanical behaviour and load distribution, in order to optimize the geometry and increasing load carrying capacity.
In case of contaminated machine environment with dust, sand or minerals, small solid debris parti... more In case of contaminated machine environment with dust, sand or minerals, small solid debris particles could be involved into rolling bearing lubricant. Solid and very sharp non-metal particles cause intensive abrasive wear of rolling bearing parts. This process could leads to change of rolling bearing macro geometry and contact surfaces micro geometry. This paper analyzes an influence of abrasive particles size and concentration on the rolling bearing micro geometry (contact surfaces roughness). The results presented for this tribosystem as an example are emphasing the importance of lubrication system innovations aimed to produce advance eco-oriented tribosystems.
Proceedings of the 3rd Wseas International Conference on Engineering Mechanics Structures Engineering Geology, Jul 22, 2010
The methods of structural dynamic modification, especially those with their roots in finite eleme... more The methods of structural dynamic modification, especially those with their roots in finite element models, have often been described as reanalysis. The present paper deals with the problem of improving of dynamic characteristics some structures. New dynamic modification procedure is given as using distribution of potential and kinetic energy in every finite element is used for analysis. The main goal of dynamic modification is to increase natural frequencies and to increase the difference between them. Some information should be prepared, before setting up the FE model. The first pack of information includes referent pieces of information about the structure: size, material, and boundary conditions. It should be noticed that dynamic response is given primarily through corresponding eigenfrequencies and main oscillation forms as characteristic (typical) variables. Changing them by changing the design parameters of a structure it is possible to achieve (can bring about) requested structural dynamic response. Sensitivity analysis is an important point within the dynamical modification process. Sensitivity analysis represents a collection of mathematical methods for reanalyzing constructions which is, within dynamical modification, related to sensitivity of eigenvalues and eigenvectors. Therefore, the application of sensitivity analysis is limited to construction of segments for which necessary mathematical relations can be determined. If this is not possible, sensitivity analysis is only partially applicable. Dynamical analysis of complex structures can easily be conducted via finite elements modeling. Therefore, while finite element analysis method is highly adequate for modeling complex structures, one of its major drawbacks lies in the usage of large number of degrees of freedom in calculating the exact eigenpairs. This number can amount to few tens of thousands, or even more. To reduce the calculation time it is possible to divide the complex structure into connected substructures and analyze each one separately. The dynamical behavior of each substructure is represented only by a reduced set of eigenpairs of interest, which contributes to significant problem simplification. A more general problem of structural dynamic analysis has three important aspects. Firstly, the observed physical structure is represented by initial finite element model. Modeling is based on numerous idealizing approximations within an exaggerated elaboration of details, which in essence does not significantly improve the accuracy of output data, especially having available powerful computers and appropriate software packages. Optimal alternative is to have the possibility of verifying outputted data that were measured on a prototype or real structure. Secondly, the dynamic characteristics of construction under reanalysis are analyzed. What is basically observed are eigenvalues and main forms of oscillations as characteristic variables that can invoke inadequate actual dynamic behavior. Thirdly, on the basis of analysis of actual dynamic behavior, modification steps are proposed after which a modified model is obtained. Having in mind that mechanical structures are most often very complex, the most convenient modification steps are not easily obtained. shows a simplified triangle of fine reanalysis. Choosing the structural parts most suitable for reanalysis requires the analysis of sensitivity for separate segments to changes in construction. Most importantly, the best result should be obtained with minimal changes. This most frequently involves the increase in frequency and distance between two neighboring frequencies.
The universal joint -U-joint is type of mechanical coupling which consists of two shaft yokes con... more The universal joint -U-joint is type of mechanical coupling which consists of two shaft yokes connected with cross. The cross arms rides inside four needle bearings pressed into the yokes bores. With good lubrication and sealing, the life of U-joint is determined by material fatigue after more than million reversals. However, U-joint often does not achieve its predicted (calculated) fatigue life. When the lubrication is inappropriate and/or the sealing is not efficient enough, the U-joint service life is limited by the corrosion and wear. As U-joint loses its operational ability due to intensive wear it has to be replaced by a new one or to be repaired. The U-joint repair implies additional machining of worn out needle bearing parts. Therefore, dimensions are changed and entire needle bearing internal geometry is changed, as well. The internal geometry affects dynamics and load carrying capacity of the needle bearing, and appropriate geometrical and mathematical relations, primarily based on limited radial and circular internal clearance, must not be disturbed by repair process. Hence, it is necessary to establish a mathematical model of the needle bearing internal geometry and the corresponding algorithm for determining appropriate dimensions and it was carried out in this paper. This is the basis for further mathematical modelling of U-joint needle bearing dimensions, mechanical behaviour and load distribution, in order to optimize the geometry and increasing load carrying capacity.
FME Transactions
External load of rolling bearing is transferred from one ring to the other one through the rollin... more External load of rolling bearing is transferred from one ring to the other one through the rolling elements. Load distribution between rolling elements is unequal. Degree of load distribution unequality depends on internal geometry of bearing and magnitude of external load. Two boundary load distributions in radially loaded ball bearing were defined and discussed in this paper. These are ideally equal and extremely unequal load distribution. Real load distribution is between these boundary cases. The new mathematical model of load distribution is developed respecting classic rolling bearing theory and by introduction of new, original value defined as load distribution factor. Developed mathematical model includes all main influences on load distribution in rolling bearing (number of rolling elements, internal radial clearance and external load).
The methods of structural dynamic modification, especially those with their roots in finite eleme... more The methods of structural dynamic modification, especially those with their roots in finite element models, have often been described as reanalysis. The present paper deals with the problem of improving of dynamic characteristics some structures. New dynamic modification procedure is given as using distribution of potential and kinetic energy in every finite element is used for analysis. The main goal of dynamic modification is to increase natural frequencies and to increase the difference between them. Some information should be prepared, before setting up the FE model. The first pack of information includes referent pieces of information about the structure: size, material, and boundary conditions. It should be noticed that dynamic response is given primarily through corresponding eigenfrequencies and main oscillation forms as characteristic (typical) variables. Changing them by changing the design parameters of a structure it is possible to achieve (can bring about) requested str...
The universal joint is one of the oldest of all flexible couplings, designed to compensate for th... more The universal joint is one of the oldest of all flexible couplings, designed to compensate for the misalignment between shafts. The simplest form of universal joint consists of two shaft yokes at right angle to each other and cross which connects the yokes. The cross arms situated at right angle to each other rides inside four needle rolling bearings pressed into the yokes bores. The bearing assembly consists of cap and set of needle rollers without cage. Universal joint is commonly known for its use on automobiles and trucks. A failed universal joint is the most common vehicles drive line problem. With good lubrication and sealing the life of universal joint is limited by fatigue of the material after millions of reversals. However, in many cases universal joint does not achieve its predicted (calculated) fatigue life. When the lubrication is inappropriate and/or the sealing is not efficient enough the entry of water and dirt, as well as the leakage of grease can occur. Consequentl...
Machines. Technologies. Materials., 2021
Additional manufacturing (AM), commonly known as 3D printing, exists for 40 years, still evolving... more Additional manufacturing (AM), commonly known as 3D printing, exists for 40 years, still evolving and improving. AM has gained great popularity in modern industries due to many advantages concerning conventional manufacturing technologies. Consequently, AM is one of nine pillars of the currently dominating industry trend-Industry 4.0. Initially, AM was mostly used for making models. Now, objects made by AM technologies, often are physical parts ready to be used as final products or to be installed as parts of asse mblies in more complex systems. Because of that, in more applications, the mechanical properties of these parts have to be known for the purpose to determine load carrying capacity essential for their functionality. Mechanical properties are being tested using appropriate methods, specimens, and equipment. In order to obtain comparable and evaluable test results, the test procedures and means should be s tandardized. Therefore, there was a need to develop standards for testing materials used for AM. International standardization in the field of AM started 10 years ago. The international body for standardization ISO developed and published a certain number of standards, but this is just beginning. This paper discusses aspects of AM standardization in the field of testing the mechanical properties of materials for 3D printing using fused deposition modelling (FDM). As an illustration of the standard application, specimens were prepared for testing t he tensile properties of plastic materials widely used in AM: PLA, PETG and ABS+.
Machine and Industrial Design in Mechanical Engineering, 2022
Engineering Failure Analysis, 2010
Traction shafts and axles of railway vehicles are designed to be safe and reliable in normal serv... more Traction shafts and axles of railway vehicles are designed to be safe and reliable in normal service conditions. Accidental and unpredictable conditions including bad exploitation (rail tracks, maintenance and extreme long service life) make the probability of shaft and axle fracture realistic. This article contains the experience and analysis of the traction shafts and axles fractures and fracture processes. Research
Machines. Technologies. Materials., 2021
Additional manufacturing (AM), commonly known as 3D printing, exists for 40 years, still evolving... more Additional manufacturing (AM), commonly known as 3D printing, exists for 40 years, still evolving and improving. AM has gained great popularity in modern industries due to many advantages concerning conventional manufacturing technologies. Consequently, AM is one of nine pillars of the currently dominating industry trend-Industry 4.0. Initially, AM was mostly used for making models. Now, objects made by AM technologies, often are physical parts ready to be used as final products or to be installed as parts of asse mblies in more complex systems. Because of that, in more applications, the mechanical properties of these parts have to be known for the purpose to determine load carrying capacity essential for their functionality. Mechanical properties are being tested using appropriate methods, specimens, and equipment. In order to obtain comparable and evaluable test results, the test procedures and means should be s tandardized. Therefore, there was a need to develop standards for testing materials used for AM. International standardization in the field of AM started 10 years ago. The international body for standardization ISO developed and published a certain number of standards, but this is just beginning. This paper discusses aspects of AM standardization in the field of testing the mechanical properties of materials for 3D printing using fused deposition modelling (FDM). As an illustration of the standard application, specimens were prepared for testing t he tensile properties of plastic materials widely used in AM: PLA, PETG and ABS+.
The operational ability of a rolling bearing selected for a specific application is assessed base... more The operational ability of a rolling bearing selected for a specific application is assessed based on service life. The basic formula for bearing rating life was established more than 70 years ago by A. Palmgren. The first standard presenting a basic mathematical model for rating life calculation was published in 1962 (ISO/R281). The content of this standard has been revised and the next version was published in 1977 (ISO 281-1). The novelty was the introduction of adjustment factors for reliability other than 90%. This standard was replaced by the ISO 281 standard in 1990, which introduced additional adjustment factors for special bearing properties and operating conditions. The latest version of the ISO 281 standard was published in 2007. This standard provides a procedure for calculating the modified service life by taking into account the additional impacts of lubrication condition, lubricant contamination and limit fatigue load. Furthermore, the document ISO/TS 16281 was publis...
The influence of the bolt size and the width of the joint members/bolt diameter ratio (relative c... more The influence of the bolt size and the width of the joint members/bolt diameter ratio (relative clamped length) on the stiffness coefficient of the bolt and joint members, as well as on the ratio of these stiffness coefficients are discussed in this paper. The individual stiffness coefficients of the bolt and the joint members decrease with the increase of the relative clamped length and the decrease of the bolt size. However, the stiffness ratio of the joint members and the bolt increases with the increase of the relative clamped length. Of the considered bolts M6 ... M24, the bolted joint with the M6 bolt has the highest stiffness ratio of the joint members and the bolt, and the bolted joint with the M12 bolt has the lowest stiffness ratio. When a bolted joint is loaded with a variable working load, then the dynamic safety factor (DSF) is used for evaluating the joint load capacity. The DSF increases with a decrease in the stiffness of the bolted joint, i.e. by increasing the relative clamped length of the bolted joint. For the same conditions analyzed, the bolted joint with M6 bolt has the largest DSF, and the bolted joint with M12 bolt has the smallest DSF. The obtained result can be used by engineers to evaluate the load-carrying capacity of dynamically tension-loaded bolted joints.
Biomimetics
During the last few decades, the requirements for modern machine elements in terms of size reduct... more During the last few decades, the requirements for modern machine elements in terms of size reduction, increasing the energy efficiency, and a higher load capacity of standard and non-standard gears have been very prevalent issues. Within these demands, the main goals are the optimization of the gears’ tooth profiles, as well as the investigation of new tooth profile designs. The presented design idea is based on the optimal solutions inspired by nature. Special attention is paid to the new design of the tooth root zones of spur gears in order to decrease the stress concentration values and increase the tooth root fatigue resistance. The finite element method is used for stress and strain state calculations, and the particular gear pair is modeled and optimized for these purposes. For tooth root strength analysis, the estimations are based on the theory of critical distances and the stress gradients obtained through finite element analysis. The obtained stress gradients have shown im...
The construction variation of packing machine in food processing is shown in this paper. By the t... more The construction variation of packing machine in food processing is shown in this paper. By the techno-economic analyses it is shown that original and new construction has the same construction value, but the new construction has a better economic value – validity. Better economic value has achieved with new construction and engaging domestic components and production technology.У раду је приказано варијантно конструкционо решење машине за паковање прехрамбених производа. На основу техно-економске анализе показано је да оригинално и варијантно конструкционо решење имају приближно исту техничку вредност, с тим што варијантна конструкција има већу економску вредност - оправданост. Економска оправданост постигнута је погодним конструкционим решењем и применом домаћих компоненти и технологије израде
The load distribution in machine elements is the first step in the analysis of their operating co... more The load distribution in machine elements is the first step in the analysis of their operating condition. Because of influence of many various factors, constructional and technological, it is very difficult to determine precisely a real condition – real load distribution without the approximations – hypotheses. The load distribution is basic input in mechanical and mathematical modelling with the purpose of the analysis of machine parts operating conditions from different relevant aspects: durability, stiffness, reliability and stability. Because of that, the modelling of load distribution is a very responsible and difficult task. The existing models of load distribution in rolling bearings [1], gear transmissions, chain transmissions etc. contain many approximations and empirical coefficients, which have no the appropriate physical basis. Load distribution in rolling bearings, which operate in condition of the time limited endurance, has a dominant influence on bearing durability. ...
machine design, 2018
The aim of this paper is to determine deformations and stresses in the statically loaded thrust b... more The aim of this paper is to determine deformations and stresses in the statically loaded thrust ball bearing subjected to a centric external axial load. In this case, all balls in the bearing are equally engaged in the transmission of the operational load. The influence of the load on the stresses and deformations in the bearings of different series has been analysed. The obtained results are the basis for further research of the load distribution in an eccentrically loaded axial ball bearing in order to determine the reduction of the static load bearing capacity in relation to the values determined in appropriate standard and also to the values prescribed by manufacturers’ catalogues.
INFLUENCE OF INTERNAL RADIAL CLEARANCE ON THE BALL BEARING SERVICE LIFE, 2010
external load of ball bearing is transferred from one ring to other one through balls. in the rad... more external load of ball bearing is transferred from one ring to other one through balls. in the radially loaded bearing all balls are not simultaneously active. simultaneously active balls participating in load transfer are in loaded zone. Load distribution between balls in loaded zone is unequal. Width of loaded zone depends on bearing internal radial clearance. The loaded zone decreases with increasing clearance. consequently, the load distribution between balls becomes more unequal. it leads to decreasing of ball bearing service life. The analysis of influence of internal radial clearance on the radially loaded deep groove ball bearing service life is carried out in this paper. For this purpose a new mathematical model is derived respecting classic ball bearing life theory and by introduction of a new parameter – reduced load distribution factor.
seth.asc.tuwien.ac.at
The universal joint -U-joint is type of mechanical coupling which consists of two shaft yokes con... more The universal joint -U-joint is type of mechanical coupling which consists of two shaft yokes connected with cross. The cross arms rides inside four needle bearings pressed into the yokes bores. With good lubrication and sealing, the life of U-joint is determined by material fatigue after more than million reversals. However, U-joint often does not achieve its predicted (calculated) fatigue life. When the lubrication is inappropriate and/or the sealing is not efficient enough, the U-joint service life is limited by the corrosion and wear. As U-joint loses its operational ability due to intensive wear it has to be replaced by a new one or to be repaired. The U-joint repair implies additional machining of worn out needle bearing parts. Therefore, dimensions are changed and entire needle bearing internal geometry is changed, as well. The internal geometry affects dynamics and load carrying capacity of the needle bearing, and appropriate geometrical and mathematical relations, primarily based on limited radial and circular internal clearance, must not be disturbed by repair process. Hence, it is necessary to establish a mathematical model of the needle bearing internal geometry and the corresponding algorithm for determining appropriate dimensions and it was carried out in this paper. This is the basis for further mathematical modelling of U-joint needle bearing dimensions, mechanical behaviour and load distribution, in order to optimize the geometry and increasing load carrying capacity.
In case of contaminated machine environment with dust, sand or minerals, small solid debris parti... more In case of contaminated machine environment with dust, sand or minerals, small solid debris particles could be involved into rolling bearing lubricant. Solid and very sharp non-metal particles cause intensive abrasive wear of rolling bearing parts. This process could leads to change of rolling bearing macro geometry and contact surfaces micro geometry. This paper analyzes an influence of abrasive particles size and concentration on the rolling bearing micro geometry (contact surfaces roughness). The results presented for this tribosystem as an example are emphasing the importance of lubrication system innovations aimed to produce advance eco-oriented tribosystems.
Proceedings of the 3rd Wseas International Conference on Engineering Mechanics Structures Engineering Geology, Jul 22, 2010
The methods of structural dynamic modification, especially those with their roots in finite eleme... more The methods of structural dynamic modification, especially those with their roots in finite element models, have often been described as reanalysis. The present paper deals with the problem of improving of dynamic characteristics some structures. New dynamic modification procedure is given as using distribution of potential and kinetic energy in every finite element is used for analysis. The main goal of dynamic modification is to increase natural frequencies and to increase the difference between them. Some information should be prepared, before setting up the FE model. The first pack of information includes referent pieces of information about the structure: size, material, and boundary conditions. It should be noticed that dynamic response is given primarily through corresponding eigenfrequencies and main oscillation forms as characteristic (typical) variables. Changing them by changing the design parameters of a structure it is possible to achieve (can bring about) requested structural dynamic response. Sensitivity analysis is an important point within the dynamical modification process. Sensitivity analysis represents a collection of mathematical methods for reanalyzing constructions which is, within dynamical modification, related to sensitivity of eigenvalues and eigenvectors. Therefore, the application of sensitivity analysis is limited to construction of segments for which necessary mathematical relations can be determined. If this is not possible, sensitivity analysis is only partially applicable. Dynamical analysis of complex structures can easily be conducted via finite elements modeling. Therefore, while finite element analysis method is highly adequate for modeling complex structures, one of its major drawbacks lies in the usage of large number of degrees of freedom in calculating the exact eigenpairs. This number can amount to few tens of thousands, or even more. To reduce the calculation time it is possible to divide the complex structure into connected substructures and analyze each one separately. The dynamical behavior of each substructure is represented only by a reduced set of eigenpairs of interest, which contributes to significant problem simplification. A more general problem of structural dynamic analysis has three important aspects. Firstly, the observed physical structure is represented by initial finite element model. Modeling is based on numerous idealizing approximations within an exaggerated elaboration of details, which in essence does not significantly improve the accuracy of output data, especially having available powerful computers and appropriate software packages. Optimal alternative is to have the possibility of verifying outputted data that were measured on a prototype or real structure. Secondly, the dynamic characteristics of construction under reanalysis are analyzed. What is basically observed are eigenvalues and main forms of oscillations as characteristic variables that can invoke inadequate actual dynamic behavior. Thirdly, on the basis of analysis of actual dynamic behavior, modification steps are proposed after which a modified model is obtained. Having in mind that mechanical structures are most often very complex, the most convenient modification steps are not easily obtained. shows a simplified triangle of fine reanalysis. Choosing the structural parts most suitable for reanalysis requires the analysis of sensitivity for separate segments to changes in construction. Most importantly, the best result should be obtained with minimal changes. This most frequently involves the increase in frequency and distance between two neighboring frequencies.
The universal joint -U-joint is type of mechanical coupling which consists of two shaft yokes con... more The universal joint -U-joint is type of mechanical coupling which consists of two shaft yokes connected with cross. The cross arms rides inside four needle bearings pressed into the yokes bores. With good lubrication and sealing, the life of U-joint is determined by material fatigue after more than million reversals. However, U-joint often does not achieve its predicted (calculated) fatigue life. When the lubrication is inappropriate and/or the sealing is not efficient enough, the U-joint service life is limited by the corrosion and wear. As U-joint loses its operational ability due to intensive wear it has to be replaced by a new one or to be repaired. The U-joint repair implies additional machining of worn out needle bearing parts. Therefore, dimensions are changed and entire needle bearing internal geometry is changed, as well. The internal geometry affects dynamics and load carrying capacity of the needle bearing, and appropriate geometrical and mathematical relations, primarily based on limited radial and circular internal clearance, must not be disturbed by repair process. Hence, it is necessary to establish a mathematical model of the needle bearing internal geometry and the corresponding algorithm for determining appropriate dimensions and it was carried out in this paper. This is the basis for further mathematical modelling of U-joint needle bearing dimensions, mechanical behaviour and load distribution, in order to optimize the geometry and increasing load carrying capacity.
FME Transactions
External load of rolling bearing is transferred from one ring to the other one through the rollin... more External load of rolling bearing is transferred from one ring to the other one through the rolling elements. Load distribution between rolling elements is unequal. Degree of load distribution unequality depends on internal geometry of bearing and magnitude of external load. Two boundary load distributions in radially loaded ball bearing were defined and discussed in this paper. These are ideally equal and extremely unequal load distribution. Real load distribution is between these boundary cases. The new mathematical model of load distribution is developed respecting classic rolling bearing theory and by introduction of new, original value defined as load distribution factor. Developed mathematical model includes all main influences on load distribution in rolling bearing (number of rolling elements, internal radial clearance and external load).
The methods of structural dynamic modification, especially those with their roots in finite eleme... more The methods of structural dynamic modification, especially those with their roots in finite element models, have often been described as reanalysis. The present paper deals with the problem of improving of dynamic characteristics some structures. New dynamic modification procedure is given as using distribution of potential and kinetic energy in every finite element is used for analysis. The main goal of dynamic modification is to increase natural frequencies and to increase the difference between them. Some information should be prepared, before setting up the FE model. The first pack of information includes referent pieces of information about the structure: size, material, and boundary conditions. It should be noticed that dynamic response is given primarily through corresponding eigenfrequencies and main oscillation forms as characteristic (typical) variables. Changing them by changing the design parameters of a structure it is possible to achieve (can bring about) requested str...
The universal joint is one of the oldest of all flexible couplings, designed to compensate for th... more The universal joint is one of the oldest of all flexible couplings, designed to compensate for the misalignment between shafts. The simplest form of universal joint consists of two shaft yokes at right angle to each other and cross which connects the yokes. The cross arms situated at right angle to each other rides inside four needle rolling bearings pressed into the yokes bores. The bearing assembly consists of cap and set of needle rollers without cage. Universal joint is commonly known for its use on automobiles and trucks. A failed universal joint is the most common vehicles drive line problem. With good lubrication and sealing the life of universal joint is limited by fatigue of the material after millions of reversals. However, in many cases universal joint does not achieve its predicted (calculated) fatigue life. When the lubrication is inappropriate and/or the sealing is not efficient enough the entry of water and dirt, as well as the leakage of grease can occur. Consequentl...