2016 Berlin : Residual stress distribution in the extruded polyolefin pipes
Author(s) : Pavel Hutař, Jan Poduška, Jaroslav Kučera, Eva Nezbedová, Andreas Frank, Jiří Sadílek, Gerald Pinter
Residual stresses can significantly influence the lifetime of polymer pipes. Therefore, realistic estimation of residual hoop stress can contribute to accurate lifetime estimations. The previously used “accurate method” is quite time consuming and needs a lot of specimens to be prepared and treated. A simplified...
2012 Barcelona : Comparison of accelerated tests for PE grades lifetime assessment
Author(s) : Andreas Frank, Gerald Pinter, Mridula Kapur, E. Nezbedová
Results from cracked round bar tests (CRB) and pennsylvania notch tests (PENT) for several polyethylene (PE) pipe grades are compared. The CRB tests were conducted at 23 °C and 80 °C, the PENT tests only at 80 °C. A material ranking based on the CRB tests was in good accordance to PENT failure times, although a slight...
2006 Washington DC : Analysis of the Fracture Behaviour of Multi-Layer Pipes
Author(s) : Nezbedova, Vlach, Knesl
A multilayer pipe consisting of two different layers, namely of PE and PPH, was analysed.
The relevant numerical model based on the Finite Element Method (FEM) was used to
calculate the stress and strain distribution and to estimate the fracture characteristics. As
variables the thickness of the material layers and...
2006 Washington DC : Effect of Processing on the Lifetime of Pipe HDPE Grade
Author(s) : Sindelar, Nezbedova, Buran
The influence of processing conditions on molecular structure and microstructure of highdensity polyethylene pipe material has been studied. By modifying the segment arrangement
and package of additives, conditions during pelletising in the extruder have been changed.
Structural analyses obtained by gel permeation...
2006 Washington DC : Full Notch Creep Test - ISO Round Robin Test
Author(s) : Niebergall, Mertlova, Nezbedova
Full Notch Creep Test (FNCT) is widely used to characterize the slow crack growth behavior of particularly pipe and blow moulding PE materials, especially in Europe. However, the validity of the FNCT data is not satisfactory, as the results show large variability so far. Among other SCG tests, which exist and are used...
2004 Milan : Effect of structural parameters on RCP in polyethylene
Author(s) : Eva Nezbedová, Pavel Šindelář and Petr Bohatý
Changing the catalyst composition, it allowed us to alter placement of comonomer from lower
to higher polymer molecular weight fractions together with a certain reduction of molecular
weight distribution (MWD). Using this catalyst several polymer samples differing in level of
branching, in comonomer unit placement and...
1998 Gothenburg : Relationship between Toughness and Structural Parameter of PE-Copolymers
Author(s) : Nezbedova, Salajka, Kucera
Structural and morphological parameters together with processing conditions determine the type of fracture behaviour of polyethylenes. Long time brittle failure which occurs under low stresses and at room temperature limits the lifetime of polyethylens used as pipes for water and gas distribution. In order to optimise...
Fracture Mechanics - Analysis of Multiplayer
Author(s) : Nezbedova, Knesl, Sestakova, Vlach