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Fracture behavior of welded polyolefin pipes
Mikula, Jakub ; Kučera,, Jaroslav (oponent) ; Ševčík, Martin (vedoucí práce)
The purpose of this diploma thesis is to introduce fracture behavior of welded polyolefin pipes. This study is focused on numerical modelling of the quasi-brittle failure which is a direct result of slow creep crack growth. Welding of polyolefin pipes causes material inhomogeneity in the welded region and the weld bead shape introduces geometric stress raisers. The aim of the thesis is to evaluate these influences on the welded pipe lifespan and its assessment. Different experimental tests (mainly CRB and PENT tests) which allow measuring of material properties describing the crack growth kinetics are presented in the thesis. The results of numerical modelling are presented for a polyethylene pipe (PE 100 110 x 6.3 SDR 17.6). Polyethylene is one of the most common material used in the pipeline industry, but the results of the thesis can be used for any other polyolefin material as well. Lifetime prediction of polyolefin pipes is based on the Linear Elastic Fracture Mechanics (LEFM) using the concept of the stress intensity factor. The thesis complements the existing methodology of pipe lifetime assessment, specifically lifetime prediction of welded polyolefin pipes and a possible direction for future related research is given.
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Numerical modeling of crack propagation under conditions of LEFM
Mikula, Jakub ; Hutař, Pavel (oponent) ; Ševčík, Martin (vedoucí práce)
The presented bachelor’s thesis deals with numerical modeling of crack propagation in general planar body. A user macro was created in APDL programming language for estimation of crack propagation direction and collection of data. Macro allows selection one of the four criteria intended to estimate the direction of the crack and the subsequent listing of the data into a text document. The calculation is based on the finite element method (FEM) using a commercial system ANSYS. The conditions of linear elastic fracture mechanics (LEFM) are expected during the calculation. The first part of this thesis describes the basic concepts of LEFM, including a description of mentioned criteria. The second part is devoted to the created macro. It also describes the algorithm and the necessary conditions for correct processing of data. A comparison with available published data or with experimental data gives a summary of the accuracy and utilization of created macro. In conclusion, the example of estimation of the residual life by different criteria is shown, as its other application.
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FRACTURE MECHANICS ASSESSMENT OF CRACKED WELDED POLYOLEFIN PIPES
Mikula, Jakub ; Ševčík, Martin ; Hutař, Pavel ; Náhlík, Luboš
The aim of this paper is to present methodology for estimation of fracture mechanics parameters in polyolefin pipes with an axially oriented crack using three dimensional numerical analyses. Linear elastic fracture mechanics is used for description of fracture behavior. In the paper, three different variants of pipe weld with an internal axial semi-elliptical crack are studied. Numerical models correspond to a cracked pipe containing material nonhomogeneity in the welding area caused by welding process. A critical locations of the crack initiated along the pipe wall is found and the stress intensity factor for such cracks with real crack shape are numerically estimated in these critical locations. The methodology presented here can be used for estimation of residual lifetime of welded polymer pipes containing crack.
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Fracture behavior of welded polyolefin pipes
Mikula, Jakub ; Kučera,, Jaroslav (oponent) ; Ševčík, Martin (vedoucí práce)
The purpose of this diploma thesis is to introduce fracture behavior of welded polyolefin pipes. This study is focused on numerical modelling of the quasi-brittle failure which is a direct result of slow creep crack growth. Welding of polyolefin pipes causes material inhomogeneity in the welded region and the weld bead shape introduces geometric stress raisers. The aim of the thesis is to evaluate these influences on the welded pipe lifespan and its assessment. Different experimental tests (mainly CRB and PENT tests) which allow measuring of material properties describing the crack growth kinetics are presented in the thesis. The results of numerical modelling are presented for a polyethylene pipe (PE 100 110 x 6.3 SDR 17.6). Polyethylene is one of the most common material used in the pipeline industry, but the results of the thesis can be used for any other polyolefin material as well. Lifetime prediction of polyolefin pipes is based on the Linear Elastic Fracture Mechanics (LEFM) using the concept of the stress intensity factor. The thesis complements the existing methodology of pipe lifetime assessment, specifically lifetime prediction of welded polyolefin pipes and a possible direction for future related research is given.
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Numerical modeling of crack propagation under conditions of LEFM
Mikula, Jakub ; Hutař, Pavel (oponent) ; Ševčík, Martin (vedoucí práce)
The presented bachelor’s thesis deals with numerical modeling of crack propagation in general planar body. A user macro was created in APDL programming language for estimation of crack propagation direction and collection of data. Macro allows selection one of the four criteria intended to estimate the direction of the crack and the subsequent listing of the data into a text document. The calculation is based on the finite element method (FEM) using a commercial system ANSYS. The conditions of linear elastic fracture mechanics (LEFM) are expected during the calculation. The first part of this thesis describes the basic concepts of LEFM, including a description of mentioned criteria. The second part is devoted to the created macro. It also describes the algorithm and the necessary conditions for correct processing of data. A comparison with available published data or with experimental data gives a summary of the accuracy and utilization of created macro. In conclusion, the example of estimation of the residual life by different criteria is shown, as its other application.
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