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Description of the residual stresses in polymer pipes
Poduška, Jan ; Majer, Zdeněk (referee) ; Hutař, Pavel (advisor)
This thesis is dealing with the issue of residual stress present in the wall of a polymer pipe and the influence on its lifetime. Experimental data obtained by the ring slitting method are evaluated and the tangential residual stress in the wall of polypropylene pipe is determined. The evaluation is carried out using a new methodology based on the curved beam theory. The method is verified using numerical simulation. 3D numerical model is used to verify the behavior of the pipe, when there are both tangential and axial residual stresses present in the pipe wall, because the presence of axial stress causes a rise in the magnitude of tangential residual stress. A correction of the tangential stress values corresponding to the pipe length is then proposed. It is shown, that the distribution of the tangential residual stress does not depend significantly on the dimensions or ma-terial of the extruded pipe and a general equation is proposed to describe the distribution. This general distribution is then involved in the calculations of the pipe lifetime that are carried out using a method based on the linear elastic fracture mechanics. A significantly lower lifetimes are obtained when taking the residual stress into account.
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Prediction of slow crack growth in polymer pressure pipes
Luky, Robin ; Knésl, Zdeněk (referee) ; Hutař, Pavel (advisor)
A new methodology of polymer pipe lifetime estimation taking into account residual stresses is described in this thesis. Engineering equations derived based on numerical simulations of a hydrostatic pressure test are proposed. Residual lifetime calculations were performed for different loading conditions using experimental data of a creep crack propagation in studied material and stress distribution in the pipe wall. The effects which significantly influence lifetime estimation were quantified with special focus on residual stresses.
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Description of the residual stresses in polymer pipes
Poduška, Jan ; Majer, Zdeněk (referee) ; Hutař, Pavel (advisor)
This thesis is dealing with the issue of residual stress present in the wall of a polymer pipe and the influence on its lifetime. Experimental data obtained by the ring slitting method are evaluated and the tangential residual stress in the wall of polypropylene pipe is determined. The evaluation is carried out using a new methodology based on the curved beam theory. The method is verified using numerical simulation. 3D numerical model is used to verify the behavior of the pipe, when there are both tangential and axial residual stresses present in the pipe wall, because the presence of axial stress causes a rise in the magnitude of tangential residual stress. A correction of the tangential stress values corresponding to the pipe length is then proposed. It is shown, that the distribution of the tangential residual stress does not depend significantly on the dimensions or ma-terial of the extruded pipe and a general equation is proposed to describe the distribution. This general distribution is then involved in the calculations of the pipe lifetime that are carried out using a method based on the linear elastic fracture mechanics. A significantly lower lifetimes are obtained when taking the residual stress into account.
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|
|
Prediction of slow crack growth in polymer pressure pipes
Luky, Robin ; Knésl, Zdeněk (referee) ; Hutař, Pavel (advisor)
A new methodology of polymer pipe lifetime estimation taking into account residual stresses is described in this thesis. Engineering equations derived based on numerical simulations of a hydrostatic pressure test are proposed. Residual lifetime calculations were performed for different loading conditions using experimental data of a creep crack propagation in studied material and stress distribution in the pipe wall. The effects which significantly influence lifetime estimation were quantified with special focus on residual stresses.
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