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The influence of residual stresses on the polymer pipe lifetime
Luky, R. ; Zouhar, Michal ; Hutař, Pavel
The aim of this article is study the influence of residual stresses on the pipe lifetime. The two dimensional numerical model of the pipe with inner crack was created and the creep crack growth in the pipe with and without residual stress is modelled. The results of K-kalibration curves are presented. After that the Paris law is used for solving the lifetime. The results of time to failure in dependency on the hoop stress for pipe with and without residual stress were compared. The existence of residual stresses decrease the lifetime of the pipe. Combination of the creep crack growth tests and numerical simulations can be a very powerful tool for lifetime estimation of plastic pipes under different loading conditions.
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Influence of point load on crack shape in polymeric pipe
Ševčík, Martin ; Hutař, Pavel ; Náhlík, Luboš ; Pinter, G. ; Frank, A.
The aim of this work was to develop an easy applicable algorithm of numerical model creation simulating a cracked polymeric pipe under various combination of loading. Proposed algorithm is able to find a real crack front shape using iterative procedure. The main aim was to study the effect of the point load and its consequences on the crack front shape. It was numerically confirmed that point loading causes grater crack extension in axial direction than in the case of pipe loaded by pure inner pressure. This results leads to higher stress intensity factor and lower residual life-time of the pipe system.
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Dimensioning of thick-walled pipe in creep
Zouhar, Michal ; Hutař, Pavel ; Náhlík, Luboš ; Hlavoň, P.
The numerical simulations of the creep in the case of X10CrMoVNb91 steel were performed. Geometry of the objects studied well-fit usual parts of the pipe system. The discrepancies between numerical simulations and usual standard Design By Formula (DBF) used for the pipe system lifetime prediction were found. Therefore, accurate numerical simulations based on creep description of the material behaviour is necessary for the accurate estimation of the service conditions.
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Simulation of the crack growth in the weld of the polyolefin pipes
Ševčík, Martin ; Hutař, Pavel ; Náhlík, Luboš
The aim of this work was to study the effect of the material properties change due to the butt welding on the stress intensity factor in polyolefin pipe. The gradient change of the Young’s modulus was assumed. The crack was located in the middle of the affected zone. The stress intensity factors estimated in both graded region and basic material (homogenous case) were compared. Strong influence of the graded region on the value of the stress intensity factor was observed. Therefore, for realistic estimation of the welded pipe lifetime the change of the material properties inside the polymer weld should be taken into account.
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