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Computational analysis of the influence of initial defects on the ceramic foam failure upon mechanical loading
Papšík, Roman ; Majer, Zdeněk (referee) ; Ševeček, Oldřich (advisor)
The thesis deals with computational modelling of ceramic foams and analysis of influence of structural manufacturing defects (like broken struts, closed pores and material clumps) have on foam strength. Model of foam geometry was discretized using beam elements in order to decrease computational cost. In place where several struct join, rigid beam element was used so that the increased stiffness is better modelled. Closed walls of pores were modelled and discretised by shell elements. Influence of loading direction was analysed on foams containing no defects and then influence of amount of defects in foam on strength was further analysed. Highest strength show foams created by cells whose structs are oriented in direction of loading. These were losing strength most rapidly. Foam with structure of rhombic dodecahedral cell was least influenced by presence of closed pore defects but it also showed lowest strength even without defects. Cells with struts oriented in direction of loading experienced biggest drop in strength. Kelvin cell is a compromise. It was shown that difference in strength of strut with constant and varying cross-section is tenths of percent.
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Numerical simulation of failure of ceramic foams upon mechanical loading
Hanák, Jiří ; Skalka, Petr (referee) ; Ševeček, Oldřich (advisor)
The master’s thesis deals with a numerical simulation of failure of ceramic foams with open-cell structure and with understanding of conditions required for the failure of the structure under various mechanical loading conditions. To this purpose, the so-called stress-energy coupled criterion was utilized. The motivation for this thesis was to create a model able of the most accurate prediction of the ceramic foam strength in comparison with experimental observations. First part of the thesis is focused on the theoretical background required for solving the problem. More specifically there are mentioned methods of the foam material modelling, Linear Elastic Fracture Mechanic (LEFM) and coupled stress-energy criterion used for definition of the crack initiation. In the second part of the thesis, numerical Finite Element Analyses (FEA) whose main purpose was to determine critical conditions necessary for the initiation of strut failure within the foam structure, were performed. These pieces of knowledge were then used for creation of the numerical simulation algorithm of the mechanical test of foam material with regular cell pattern. Outputs of numerical simulations were at the end of this work compared with experimental results (of the compression test) made on the real Al_2 O_3 foams prepared by 3D printing technology and provided by the Institute of Physics of Materials Czech Academy of Science. It can be concluded that a good agreement between results of both approaches was reached and the prediction of the ceramic foam mechanical strength using the developed model is in the meanwhile the most accurate estimation from recently published approaches.
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Numerical simulation of failure of ceramic foams upon mechanical loading
Hanák, Jiří ; Skalka, Petr (referee) ; Ševeček, Oldřich (advisor)
The master’s thesis deals with a numerical simulation of failure of ceramic foams with open-cell structure and with understanding of conditions required for the failure of the structure under various mechanical loading conditions. To this purpose, the so-called stress-energy coupled criterion was utilized. The motivation for this thesis was to create a model able of the most accurate prediction of the ceramic foam strength in comparison with experimental observations. First part of the thesis is focused on the theoretical background required for solving the problem. More specifically there are mentioned methods of the foam material modelling, Linear Elastic Fracture Mechanic (LEFM) and coupled stress-energy criterion used for definition of the crack initiation. In the second part of the thesis, numerical Finite Element Analyses (FEA) whose main purpose was to determine critical conditions necessary for the initiation of strut failure within the foam structure, were performed. These pieces of knowledge were then used for creation of the numerical simulation algorithm of the mechanical test of foam material with regular cell pattern. Outputs of numerical simulations were at the end of this work compared with experimental results (of the compression test) made on the real Al_2 O_3 foams prepared by 3D printing technology and provided by the Institute of Physics of Materials Czech Academy of Science. It can be concluded that a good agreement between results of both approaches was reached and the prediction of the ceramic foam mechanical strength using the developed model is in the meanwhile the most accurate estimation from recently published approaches.
|
|
|
Computational analysis of the influence of initial defects on the ceramic foam failure upon mechanical loading
Papšík, Roman ; Majer, Zdeněk (referee) ; Ševeček, Oldřich (advisor)
The thesis deals with computational modelling of ceramic foams and analysis of influence of structural manufacturing defects (like broken struts, closed pores and material clumps) have on foam strength. Model of foam geometry was discretized using beam elements in order to decrease computational cost. In place where several struct join, rigid beam element was used so that the increased stiffness is better modelled. Closed walls of pores were modelled and discretised by shell elements. Influence of loading direction was analysed on foams containing no defects and then influence of amount of defects in foam on strength was further analysed. Highest strength show foams created by cells whose structs are oriented in direction of loading. These were losing strength most rapidly. Foam with structure of rhombic dodecahedral cell was least influenced by presence of closed pore defects but it also showed lowest strength even without defects. Cells with struts oriented in direction of loading experienced biggest drop in strength. Kelvin cell is a compromise. It was shown that difference in strength of strut with constant and varying cross-section is tenths of percent.
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