Jozef Bocko | Technical University of Kosice (original) (raw)

Papers by Jozef Bocko

Engineering Failure Analysis

Materials

Isogeometric analysis (IGA) represents a relatively new method of problem-solving in engineering ... more Isogeometric analysis (IGA) represents a relatively new method of problem-solving in engineering practice. A huge advantage of this method over the finite element method (FEM), is the reduction of the simulation execution time. Non-uniform rational B-splines (NURBS) allow the use of higher-order basis functions, thus increasing the accuracy of the solution. This paper deals with the comparison of structural analysis of thin-walled structural elements using isogeometric analysis and the finite element method. The investigated objects are modelled using a single patch in MATLAB. The basic functions are created from NURBS, which were previously used in the creation of an accurate geometric model. The paper contains a comparison of the results obtained by the above-mentioned methods. All computations are performed in the elastic domain.

International Journal of Applied Mechanics and Engineering

When designing structures, it is often necessary to re-analyse a structure that is different in s... more When designing structures, it is often necessary to re-analyse a structure that is different in some parts from the original one. As real structures are often complex, their analysis is therefore very challenging. In such cases, reanalysis methods are advantageously used. The aim of this paper is to approach the problem of solving the constructions using reanalysis method in which the time taken in solving algebraic equations is reduced. In particular, the purpose of this work is to demonstrate on a chosen system the time savings and the advantages of the chosen direct efficient reanalysis method for a given design problem. A basic condition for meeting these criteria is the modernization of computational procedures in the mechanics of compliant solids.

Materials

The present paper discusses a new approach for the experimental determination of modal parameters... more The present paper discusses a new approach for the experimental determination of modal parameters (resonant frequencies, modal shapes and damping coefficients) based on measured displacement values, using the non-contact optical method of digital image correlation (DIC). The output is a newly developed application module that, based on a three-dimensional displacement matrix from the experimental measurement results, can construct a frequency response function (FRF) for the purpose of experimental and operational modal analysis. From this frequency response function, the modal parameters of interest are able to be determined. The application module has been designed for practical use in Scilab 6.1.0, and its code interfaces directly with the ISTRA4D high-speed camera software. The module was built on measurements of a steel plate excited by an impact hammer to simulate experimental modal analysis. Verification of the correctness of the computational algorithm or the obtained modal p...

IOP Conference Series: Materials Science and Engineering, 2021

In this paper, the elastic modulus of single-layered graphene sheets (SLGSs) with and without def... more In this paper, the elastic modulus of single-layered graphene sheets (SLGSs) with and without defects is investigated using the finite element method. The SLGSs with two chiralities (armchair and zigzag) are modeled by beam elements. At first, the SLGSs without defects are investigated then the carbon atoms and corresponding beam elements are removed and the elastic modulus of SLGSs is determined. The increasing number of defects apparently decreased the elastic modulus of graphene sheets.

American journal of mechanical engineering, 2017

The paper deals with geometric imperfections, which are defined as the deviation of the mid-surfa... more The paper deals with geometric imperfections, which are defined as the deviation of the mid-surface of the shell. A parametric model of the axially symmetrical shell was created which was loaded with axial compressive load. The task was to determine the decrease in critical force causing loss of stability. The finite element method was used in order to find solution.

American journal of mechanical engineering, 2016

The paper deals with the description of methodology for performing of drop test of smartphones us... more The paper deals with the description of methodology for performing of drop test of smartphones using high-speed digital image correlation method. This method allows capturing the impact of the phone at high sampling frequencies and thus the stresses in each surface point can be computed. The measurement was realized in laboratory conditions, in which the phone was fallen down from the height of one meter, which is a distance, which the mobile phones are dropped out from the being’s hand. Five different possibilities of the phone impact were investigated. The acquired results are in a form of deformation as well as von Mises stress computed in chosen locations of the touchscreen area.

American journal of mechanical engineering, 2015

Nonlinear analysis of the enclosure of the pulley is described in this paper. Three different mat... more Nonlinear analysis of the enclosure of the pulley is described in this paper. Three different materials were used for the enclosure. Polyethylene, aluminium alloy and titanium alloy were used for model of the enclosure. The enclosure was pressed on the pulley and this frictional contact with friction coefficient was used in nonlinear finite element analysis. The maximal von Misses stress of the enclosure was higher than tensile strength of the materials used for the enclosure so three different variants were proposed. The maximal stress level of the three new variants was smaller than the yield point of the materials.

During the operation of the tank its shell was deformed in plastic area. In order to assess its f... more During the operation of the tank its shell was deformed in plastic area. In order to assess its further operation there were determined residual stresses in the shell and by the finite element method as well as by the experimental methods the analysis of stresses was performed. On the base of these results were suggested simple improvements of design that allow further operation of tank.

American journal of mechanical engineering, 2016

This paper deals with the description of methodology for experimental non-contact investigation o... more This paper deals with the description of methodology for experimental non-contact investigation of stress fields in the area of contact mechanics using digital image correlation method. The measurement was realized in laboratory conditions via low-speed digital image correlation system. As the control software of mentioned digital image correlation system does not allow investigate and visualize stress fields, the authors used an additional application called Q-STRESS v.1.0 allowing compute several types of stress. The paper also briefly described the creation of numerical model in Ansys software. The Von Mises stress levels were in chosen location compared, whereby the results show agreement adequate for comparison of experimental and numerical modeling.

American journal of mechanical engineering, 2017

The contribution deals with describing of two experimental approaches leading to assumption of mo... more The contribution deals with describing of two experimental approaches leading to assumption of modal parameters in a form of natural frequencies, mode shapes and damping of freely supported steel pipe. In the first approach, the model of the pipe was created in common way using planar elements. In the second one, the model of the pipe was simplified using line elements, which should lead to the increasing of time needed for realization of experimental investigation. The results obtained by both approaches as well as their pros and cons are described in the paper.

American journal of mechanical engineering, 2015

The paper deals with application of Bodner-Partom material model for description of material beha... more The paper deals with application of Bodner-Partom material model for description of material behavior. The results from experimental measurements of test specimens of given material were used for identification of parameter of Bodner-Partom model by using procedures based on genetic algorithms. The parameters of material were then used in computations by procedure UMAT of finite element program ABAQUS. The results of computations demonstrate ability of model to simulate material behavior with satisfied accuracy.

American journal of mechanical engineering, 2016

This paper deals about a buckling analysis of composite plates with four different layers orienta... more This paper deals about a buckling analysis of composite plates with four different layers orientations and with three, six and twelve layers. Composite plate was modeled by the finite element method. Compression load, shear load and combination of both loads were applied to the composite plate. Then the computational buckling analysis for the all combinations of load was performed for four different orientations of layers and for plates with different numbers of layers. The computed critical buckling loads for the applied loads were compared for all orientations of layers. From the results the inappropriate orientations of layers for different loads were obtained. The critical buckling load increased almost ten times for the composite plates with two times higher thickness.

American journal of mechanical engineering, 2016

The paper deals with the analysis of stress and deformation conditions that occur in bolted joint... more The paper deals with the analysis of stress and deformation conditions that occur in bolted joints with prestress. The stress and deformation states are significantly influenced by the grooves made in nuts. The grooves affect stress distribution in the nut – bolt connection and accordingly the shape of groove is very important for the knowledge of stress conditions in threads as well as in the whole bolted joint. In the paper is described a parametric study of grooves and corresponding stress states in bolted connections. Several types of grooves of different dimensions are studied. The grooves and corresponding results of computations can serve as material for better understanding of stress states inside joint assembly and consequently for better design of bolted joints. The computations of parametric studies were accomplished by the finite element method.

Applied Optics, 2020

This paper deals with the visualization and analysis of interaction of a cutting wedge disintegra... more This paper deals with the visualization and analysis of interaction of a cutting wedge disintegrator with plastic at low loads. For exploratory research, a contactless optical holographic interferometry method was used, allowing a comprehensive picture of the stress state when opening microcracks. An experimental model was set up for the purposes of the research. The structure of the model as well as its geometric parameters had to comply with the applied optical method. The method of holographic interferometry enabled us to record even the initial stages of the crack. Pictures of holographic interferograms allowed us to observe stress fields on the cutting wedge as well as on the loaded body in the form of interference fringes. In order to record the interferograms, we used the method of two exposures so that we gained double-exposure interferograms, which represent the state of the object during the second exposure. The first exposure was caused by superposition of object-related ...

IOP Conference Series: Materials Science and Engineering, 2020

In this paper, the techniques of modelling bolts in program ANSYS are investigated. Several types... more In this paper, the techniques of modelling bolts in program ANSYS are investigated. Several types of the bolt models are proposed and compared. The finite element models with solid bolt with and without thread, and no-solid model. The pretension effect is applied for all types of bolts. Different types of connections and finite elements are used for modelling. In addition, the assembled mechanical structure is loaded by pretension effect and the field of stress and displacement of points around holes for bolts are investigated. Moreover, the stresses in the bolts computed by three-dimensional finite elements are investigated.

Journal of Engineering Sciences, 2019

The article dials with studying of the gas-dispersed systems classification process in gravitatio... more The article dials with studying of the gas-dispersed systems classification process in gravitation pneumoclassifiers of prismatic shape. The aim of the research is to determine operating parameters of the investigated process. Recent research is based on the previously developed mathematical model of hydrodynamics for a gasdispersed flow in a vertical channel with variable cross-section. As a development of this study, a physical model based on the process of kinetic removal from the mixture was used. This process is caused by the removal of fine particles from the weighed layer in the case of theirs low velocities in comparison with the average gas flow velocity. This model also considers the inertial effect due to the kinetic energy of fine particles removed from the surface of the weighted later. The first order linear nonhomogeneous partial differential equation describing the unsteady process of changing the dispersed phase concentration in the gas-mechanical mixture by channel height was solved by mathematical modeling using the combination of direct and inverse Laplace transforms. As a result, for the first time the general solution was obtained for for non-trivial boundary and initial conditions. This fact allowed developing the mathematical model of the nonstationary problem for the disperse phase concentration during the pneumoclassification process of mechanical mixtures in pneumoclassifiers. The model allows determining the concentration of fine fraction of the gas-dispersed mixture by channel height in operating volume of the device, as well as evaluating time of the pneumoclassification process. Particularly, it was found that the dispersed phase concentration decreases by the height of the apparatus with respect to time. This fact proves the possibility of effective separation of components in gas-mechanical mixtures. Finally, the achieved results allow proposing the engineering technique for calculations of vertial-type gravitation pneumoclassifiers.

Acta Mechatronica, 2018

The paper deals with a description of the aspects of stress analysis performed by 2D or 3D digita... more The paper deals with a description of the aspects of stress analysis performed by 2D or 3D digital image correlation system. It describes the differences between the types of smoothing used in Istra4D that is a software commercially delivered with correlation systems Dantec Dynamics. The analysis was performed on flat specimen made from PSM-1 material used in photoelasticity method. By loading of the specimen in form of three-point bending, a proper dependence between the facet size set for correlation of the images and level of local regression filter (characterized by a kernel size) was found. The finding for mentioned dependence was realised by comparison of the results with the results obtained numerically in Ansys Workbench 17.0.

Mechanical Sciences, 2018

In this work, a recently proposed nonlocal theory of bending is used in the analysis of eigenfreq... more In this work, a recently proposed nonlocal theory of bending is used in the analysis of eigenfrequencies of single-walled carbon nanotubes (SWCNTs). The nanotube vibration is analyzed in the form of a homogenized continuum. Classical treatment where a nanotube is approximated by standard beam theory, is replaced by the more sophisticated nonlocal method of material interactions where a nonlocal parameter is used. The eigenfrequencies are computed by the combination of analytical as well as numerical methods for four different carbon nanotube (CNT) supports. Various types of supports are considered for the analysis: fixed-simply supported, fixed-free, simply-simply supported and fixed-fixed. Due to the huge amount of computed data, only outcomes of eigenfrequency computations for the nanobeams of armchair type with fixed and simply supported ends, and different nonlocal parameters are represented in the form of graphs at the end of the article. The study shows how the nanotube eigenfrequencies depend on nonlocal parameters as well as on the length and diameter of CNTs. The obtained results are in good agreement with the results published in papers which were gained by different procedures.

Engineering Failure Analysis

Materials

Isogeometric analysis (IGA) represents a relatively new method of problem-solving in engineering ... more Isogeometric analysis (IGA) represents a relatively new method of problem-solving in engineering practice. A huge advantage of this method over the finite element method (FEM), is the reduction of the simulation execution time. Non-uniform rational B-splines (NURBS) allow the use of higher-order basis functions, thus increasing the accuracy of the solution. This paper deals with the comparison of structural analysis of thin-walled structural elements using isogeometric analysis and the finite element method. The investigated objects are modelled using a single patch in MATLAB. The basic functions are created from NURBS, which were previously used in the creation of an accurate geometric model. The paper contains a comparison of the results obtained by the above-mentioned methods. All computations are performed in the elastic domain.

International Journal of Applied Mechanics and Engineering

When designing structures, it is often necessary to re-analyse a structure that is different in s... more When designing structures, it is often necessary to re-analyse a structure that is different in some parts from the original one. As real structures are often complex, their analysis is therefore very challenging. In such cases, reanalysis methods are advantageously used. The aim of this paper is to approach the problem of solving the constructions using reanalysis method in which the time taken in solving algebraic equations is reduced. In particular, the purpose of this work is to demonstrate on a chosen system the time savings and the advantages of the chosen direct efficient reanalysis method for a given design problem. A basic condition for meeting these criteria is the modernization of computational procedures in the mechanics of compliant solids.

Materials

The present paper discusses a new approach for the experimental determination of modal parameters... more The present paper discusses a new approach for the experimental determination of modal parameters (resonant frequencies, modal shapes and damping coefficients) based on measured displacement values, using the non-contact optical method of digital image correlation (DIC). The output is a newly developed application module that, based on a three-dimensional displacement matrix from the experimental measurement results, can construct a frequency response function (FRF) for the purpose of experimental and operational modal analysis. From this frequency response function, the modal parameters of interest are able to be determined. The application module has been designed for practical use in Scilab 6.1.0, and its code interfaces directly with the ISTRA4D high-speed camera software. The module was built on measurements of a steel plate excited by an impact hammer to simulate experimental modal analysis. Verification of the correctness of the computational algorithm or the obtained modal p...

IOP Conference Series: Materials Science and Engineering, 2021

In this paper, the elastic modulus of single-layered graphene sheets (SLGSs) with and without def... more In this paper, the elastic modulus of single-layered graphene sheets (SLGSs) with and without defects is investigated using the finite element method. The SLGSs with two chiralities (armchair and zigzag) are modeled by beam elements. At first, the SLGSs without defects are investigated then the carbon atoms and corresponding beam elements are removed and the elastic modulus of SLGSs is determined. The increasing number of defects apparently decreased the elastic modulus of graphene sheets.

American journal of mechanical engineering, 2017

The paper deals with geometric imperfections, which are defined as the deviation of the mid-surfa... more The paper deals with geometric imperfections, which are defined as the deviation of the mid-surface of the shell. A parametric model of the axially symmetrical shell was created which was loaded with axial compressive load. The task was to determine the decrease in critical force causing loss of stability. The finite element method was used in order to find solution.

American journal of mechanical engineering, 2016

The paper deals with the description of methodology for performing of drop test of smartphones us... more The paper deals with the description of methodology for performing of drop test of smartphones using high-speed digital image correlation method. This method allows capturing the impact of the phone at high sampling frequencies and thus the stresses in each surface point can be computed. The measurement was realized in laboratory conditions, in which the phone was fallen down from the height of one meter, which is a distance, which the mobile phones are dropped out from the being’s hand. Five different possibilities of the phone impact were investigated. The acquired results are in a form of deformation as well as von Mises stress computed in chosen locations of the touchscreen area.

American journal of mechanical engineering, 2015

Nonlinear analysis of the enclosure of the pulley is described in this paper. Three different mat... more Nonlinear analysis of the enclosure of the pulley is described in this paper. Three different materials were used for the enclosure. Polyethylene, aluminium alloy and titanium alloy were used for model of the enclosure. The enclosure was pressed on the pulley and this frictional contact with friction coefficient was used in nonlinear finite element analysis. The maximal von Misses stress of the enclosure was higher than tensile strength of the materials used for the enclosure so three different variants were proposed. The maximal stress level of the three new variants was smaller than the yield point of the materials.

During the operation of the tank its shell was deformed in plastic area. In order to assess its f... more During the operation of the tank its shell was deformed in plastic area. In order to assess its further operation there were determined residual stresses in the shell and by the finite element method as well as by the experimental methods the analysis of stresses was performed. On the base of these results were suggested simple improvements of design that allow further operation of tank.

American journal of mechanical engineering, 2016

This paper deals with the description of methodology for experimental non-contact investigation o... more This paper deals with the description of methodology for experimental non-contact investigation of stress fields in the area of contact mechanics using digital image correlation method. The measurement was realized in laboratory conditions via low-speed digital image correlation system. As the control software of mentioned digital image correlation system does not allow investigate and visualize stress fields, the authors used an additional application called Q-STRESS v.1.0 allowing compute several types of stress. The paper also briefly described the creation of numerical model in Ansys software. The Von Mises stress levels were in chosen location compared, whereby the results show agreement adequate for comparison of experimental and numerical modeling.

American journal of mechanical engineering, 2017

The contribution deals with describing of two experimental approaches leading to assumption of mo... more The contribution deals with describing of two experimental approaches leading to assumption of modal parameters in a form of natural frequencies, mode shapes and damping of freely supported steel pipe. In the first approach, the model of the pipe was created in common way using planar elements. In the second one, the model of the pipe was simplified using line elements, which should lead to the increasing of time needed for realization of experimental investigation. The results obtained by both approaches as well as their pros and cons are described in the paper.

American journal of mechanical engineering, 2015

The paper deals with application of Bodner-Partom material model for description of material beha... more The paper deals with application of Bodner-Partom material model for description of material behavior. The results from experimental measurements of test specimens of given material were used for identification of parameter of Bodner-Partom model by using procedures based on genetic algorithms. The parameters of material were then used in computations by procedure UMAT of finite element program ABAQUS. The results of computations demonstrate ability of model to simulate material behavior with satisfied accuracy.

American journal of mechanical engineering, 2016

This paper deals about a buckling analysis of composite plates with four different layers orienta... more This paper deals about a buckling analysis of composite plates with four different layers orientations and with three, six and twelve layers. Composite plate was modeled by the finite element method. Compression load, shear load and combination of both loads were applied to the composite plate. Then the computational buckling analysis for the all combinations of load was performed for four different orientations of layers and for plates with different numbers of layers. The computed critical buckling loads for the applied loads were compared for all orientations of layers. From the results the inappropriate orientations of layers for different loads were obtained. The critical buckling load increased almost ten times for the composite plates with two times higher thickness.

American journal of mechanical engineering, 2016

The paper deals with the analysis of stress and deformation conditions that occur in bolted joint... more The paper deals with the analysis of stress and deformation conditions that occur in bolted joints with prestress. The stress and deformation states are significantly influenced by the grooves made in nuts. The grooves affect stress distribution in the nut – bolt connection and accordingly the shape of groove is very important for the knowledge of stress conditions in threads as well as in the whole bolted joint. In the paper is described a parametric study of grooves and corresponding stress states in bolted connections. Several types of grooves of different dimensions are studied. The grooves and corresponding results of computations can serve as material for better understanding of stress states inside joint assembly and consequently for better design of bolted joints. The computations of parametric studies were accomplished by the finite element method.

Applied Optics, 2020

This paper deals with the visualization and analysis of interaction of a cutting wedge disintegra... more This paper deals with the visualization and analysis of interaction of a cutting wedge disintegrator with plastic at low loads. For exploratory research, a contactless optical holographic interferometry method was used, allowing a comprehensive picture of the stress state when opening microcracks. An experimental model was set up for the purposes of the research. The structure of the model as well as its geometric parameters had to comply with the applied optical method. The method of holographic interferometry enabled us to record even the initial stages of the crack. Pictures of holographic interferograms allowed us to observe stress fields on the cutting wedge as well as on the loaded body in the form of interference fringes. In order to record the interferograms, we used the method of two exposures so that we gained double-exposure interferograms, which represent the state of the object during the second exposure. The first exposure was caused by superposition of object-related ...

IOP Conference Series: Materials Science and Engineering, 2020

In this paper, the techniques of modelling bolts in program ANSYS are investigated. Several types... more In this paper, the techniques of modelling bolts in program ANSYS are investigated. Several types of the bolt models are proposed and compared. The finite element models with solid bolt with and without thread, and no-solid model. The pretension effect is applied for all types of bolts. Different types of connections and finite elements are used for modelling. In addition, the assembled mechanical structure is loaded by pretension effect and the field of stress and displacement of points around holes for bolts are investigated. Moreover, the stresses in the bolts computed by three-dimensional finite elements are investigated.

Journal of Engineering Sciences, 2019

The article dials with studying of the gas-dispersed systems classification process in gravitatio... more The article dials with studying of the gas-dispersed systems classification process in gravitation pneumoclassifiers of prismatic shape. The aim of the research is to determine operating parameters of the investigated process. Recent research is based on the previously developed mathematical model of hydrodynamics for a gasdispersed flow in a vertical channel with variable cross-section. As a development of this study, a physical model based on the process of kinetic removal from the mixture was used. This process is caused by the removal of fine particles from the weighed layer in the case of theirs low velocities in comparison with the average gas flow velocity. This model also considers the inertial effect due to the kinetic energy of fine particles removed from the surface of the weighted later. The first order linear nonhomogeneous partial differential equation describing the unsteady process of changing the dispersed phase concentration in the gas-mechanical mixture by channel height was solved by mathematical modeling using the combination of direct and inverse Laplace transforms. As a result, for the first time the general solution was obtained for for non-trivial boundary and initial conditions. This fact allowed developing the mathematical model of the nonstationary problem for the disperse phase concentration during the pneumoclassification process of mechanical mixtures in pneumoclassifiers. The model allows determining the concentration of fine fraction of the gas-dispersed mixture by channel height in operating volume of the device, as well as evaluating time of the pneumoclassification process. Particularly, it was found that the dispersed phase concentration decreases by the height of the apparatus with respect to time. This fact proves the possibility of effective separation of components in gas-mechanical mixtures. Finally, the achieved results allow proposing the engineering technique for calculations of vertial-type gravitation pneumoclassifiers.

Acta Mechatronica, 2018

The paper deals with a description of the aspects of stress analysis performed by 2D or 3D digita... more The paper deals with a description of the aspects of stress analysis performed by 2D or 3D digital image correlation system. It describes the differences between the types of smoothing used in Istra4D that is a software commercially delivered with correlation systems Dantec Dynamics. The analysis was performed on flat specimen made from PSM-1 material used in photoelasticity method. By loading of the specimen in form of three-point bending, a proper dependence between the facet size set for correlation of the images and level of local regression filter (characterized by a kernel size) was found. The finding for mentioned dependence was realised by comparison of the results with the results obtained numerically in Ansys Workbench 17.0.

Mechanical Sciences, 2018

In this work, a recently proposed nonlocal theory of bending is used in the analysis of eigenfreq... more In this work, a recently proposed nonlocal theory of bending is used in the analysis of eigenfrequencies of single-walled carbon nanotubes (SWCNTs). The nanotube vibration is analyzed in the form of a homogenized continuum. Classical treatment where a nanotube is approximated by standard beam theory, is replaced by the more sophisticated nonlocal method of material interactions where a nonlocal parameter is used. The eigenfrequencies are computed by the combination of analytical as well as numerical methods for four different carbon nanotube (CNT) supports. Various types of supports are considered for the analysis: fixed-simply supported, fixed-free, simply-simply supported and fixed-fixed. Due to the huge amount of computed data, only outcomes of eigenfrequency computations for the nanobeams of armchair type with fixed and simply supported ends, and different nonlocal parameters are represented in the form of graphs at the end of the article. The study shows how the nanotube eigenfrequencies depend on nonlocal parameters as well as on the length and diameter of CNTs. The obtained results are in good agreement with the results published in papers which were gained by different procedures.