Polyethylene Resins Slow Crack Growth Testing based on Strain Hardening Modulus and Crystallinity

AbstractEnvironmental stress cracking is a serious problem for polyethylene because it can cause failure without any visible warning due to the slow crack growth accelerated by aggressive agents. Tie molecules and entanglements are the main macromolecular characteristic increasing environmental stress cracking resistance, thus in this work mechanical and thermal properties governed by those macromolecular characteristics are determined by performing simple tests executable in the industrial laboratories for quality control on recycled high-density polyethylene. The mutual relation between the determined properties confirms their dependence on the investigated macromolecular characteristics and allows to predict in a comparative way the expected environmental stress cracking. The mechanical properties related to the environmental stress cracking resistance are the strain hardening modulus and the natural draw ratio. The strain hardening modulus is an intrinsic property that measure the disentanglement capability of the inter-lamellar links and the natural draw ratio is a highly sensitive parameter to the macromolecular network strength via the intercrystalline tie molecules. Since the measurement of these properties according to the standard ISO 18,488 requires a temperature chamber not often available in the industrial laboratories, the tensile test was performed also at room temperature and displacement rate 0.5 mm/min; a proportionality between the data obtained at different test condition emerged. The thermal property related to the environmental stress cracking resistance is the stepwise isothermal segregation ratio that state the chain fraction that generates a high rate of tie molecules responsible of environmental stress cracking resistance.

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Slow crack growth resistance of modern PA-U12 grades measured by cyclic cracked round bar tests and strain hardening tests

Polymer Testing ◽

10.1016/j.polymertesting.2020.106468 ◽

2020 ◽

Vol 86 ◽

pp. 106468

Author(s):

Mario Messiha ◽

Britta Gerets ◽

Jan Heimink ◽

Andreas Frank ◽

Florian Arbeiter ◽

...

Keyword(s):

Strain Hardening ◽

Crack Growth ◽

Slow Crack Growth ◽

Crack Growth Resistance ◽

Round Bar

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Strain hardening test on the limits of Slow Crack Growth evaluation in high resistance polyethylene resins: Effect of comonomer type

Polymer Testing ◽

10.1016/j.polymertesting.2019.106155 ◽

2020 ◽

Vol 81 ◽

pp. 106155 ◽

Cited By ~ 2

Author(s):

Carlos Domínguez ◽

Nuria Robledo ◽

Beatriz Paredes ◽

Rafael A. García-Muñoz

Keyword(s):

Strain Hardening ◽

Crack Growth ◽

High Resistance ◽

Slow Crack Growth ◽

Growth Evaluation

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Examination of Fracture Interfaces in Silicon Nitride

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100113925 ◽

1975 ◽

Vol 33 ◽

pp. 60-61

Author(s):

Nancy J. Tighe

Keyword(s):

Silicon Nitride ◽

Grain Boundary ◽

Crack Growth ◽

Subcritical Crack Growth ◽

Slow Crack Growth ◽

Ceramic Materials ◽

Grain Boundary Sliding ◽

Boundary Phase ◽

Turbine Engines ◽

Boundary Sliding

Silicon nitride is one of the ceramic materials being considered for the components in gas turbine engines which will be exposed to temperatures of 1000 to 1400°C. Test specimens from hot-pressed billets exhibit flexural strengths of approximately 50 MN/m2 at 1000°C. However, the strength degrades rapidly to less than 20 MN/m2 at 1400°C. The strength degradition is attributed to subcritical crack growth phenomena evidenced by a stress rate dependence of the flexural strength and the stress intensity factor. This phenomena is termed slow crack growth and is associated with the onset of plastic deformation at the crack tip. Lange attributed the subcritical crack growth tb a glassy silicate grain boundary phase which decreased in viscosity with increased temperature and permitted a form of grain boundary sliding to occur.

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Polyolefin pipes for the conveyance of fluids. Determination of resistance to crack propagation. Test method for slow crack growth on notched pipes (notch test)

10.3403/01126392u ◽

2015 ◽

Keyword(s):

Crack Propagation ◽

Crack Growth ◽

Slow Crack Growth ◽

Test Method

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Unique Slow Crack Growth Behavior of Isotactic Polypropylene: The Role of Shear Layer-Spherulites Layer Alternated Structure

Polymers ◽

10.3390/polym12112746 ◽

2020 ◽

Vol 12 (11) ◽

pp. 2746

Author(s):

Mingjin Liu ◽

Jiaxu Luo ◽

Jin Chen ◽

Xueqin Gao ◽

Qiang Fu ◽

...

Keyword(s):

Shear Layer ◽

Crack Growth ◽

Isotactic Polypropylene ◽

Slow Crack Growth ◽

Crack Growth Behavior ◽

Polymer Science ◽

The Past ◽

Propagation Behavior ◽

Crack Propagation Behavior

With the development of polymer science, more attention is being paid to the longevity of polymer products. Slow crack growth (SCG), one of the most important factors that reveal the service life of the products, has been investigated widely in the past decades. Here, we manufactured an isotactic polypropylene (iPP) sample with a novel shear layer–spherulites layer alternated structure using multiflow vibration injection molding (MFVIM). However, the effect of the alternated structure on the SCG behavior has never been reported before. Surprisingly, the results showed that the resistivity of polymer to SCG can be enhanced remarkably due to the special alternated structure. Moreover, this sample shows unique slow crack propagation behavior in contrast to the sample with the same thickness of shear layer, presenting multiple microcracks in the spherulites layer, which can explain the reason of the resistivity improvement of polymer to SCG.

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