Stepwise fatigue crack propagation in polyethylene resins of different molecular structure

Shah, A.; Stepanov, E. V.; Capaccio, G.; Hiltner, A.; Baer, E.

doi:10.1002/(sici)1099-0488(19980930)36:13<2355::aid-polb11>3.0.co;2-2

Cited by 39 publications

(12 citation statements)

References 15 publications

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“…The presence of these flexible interlamellar tie chains contribute to energy absorption of the material during flexing and hinders crack initiation and propagation. The effect of SCB distribution on crack propagation and fracture toughness of polyethylene has been also investigated by Shah et al They reported that superior fracture toughness can be achieved by distributing the short chain branches on high molecular weight chains. They confirmed the results by performing fatigue tests.…”

Section: Resultsmentioning

confidence: 99%

Application of single site catalyst metallocene polyethylenes in extruded films: Effect of molecular structure on sealability, flexural cracking and mechanical properties

Sadeghi

Ajji

2014

Can J Chem Eng

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Three single site catalysts metallocene polyethylenes (mPE) different in molecular structure were selected and films from them were produced using a semi‐industrial cast film extrusion line. Rheological and gel permeation chromatography tests were performed on the mPE resins to assess their molecular structure. Mechanical, physical and sealability properties of the films were evaluated as well as flexural cracking and particles encapsulation (caulkability) and the results are discussed in relation to the molecular structures of the resins. It was found that molecular weight and distribution of short chain branching (comonomer) on the backbone of the polyethylene chains are the main factors that control sealability, flexural cracking and mechanical properties. The placement of comomoner on medium length chains generated crystals with smaller size that show a lower melting peak. Sealing was controlled by crystal distribution, chain diffusion and entanglement formation at the interface. mPE with lower melting point and linear molecular structure showed greater hot tack and seal strength. Polydispersity along with molecular weight contributed to toughness and puncture resistance. Flexural cracking resistance was revealed to be related to crystallinity, tie chain density and more importantly to fraction of amorphous phase. The amorphous part could absorb flexural energy and hinders crack initiation and propagation. Seal through contamination (caulkability) was found to be related to flowability of the melt. The resin with stronger shear thinning in melt state and lower heat seal initiation temperature showed an improved caulkability.

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Section: Resultsmentioning

confidence: 99%

Application of single site catalyst metallocene polyethylenes in extruded films: Effect of molecular structure on sealability, flexural cracking and mechanical properties

Sadeghi

Ajji

2014

Can J Chem Eng

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“…This test carried out at 808C was finally standardized in ASTM F1473 [15]. Shah and Parsons have also studied this phenomenon at ambient temperature in medium and high density polyethylenes through a fatigue test that improves the PENT failure time having both tests a good correlation [16][17][18][19]. Plummer and co-workers have deeply studied the micromechanisms of SCG process in polyethylenes exposed to a constant and cycling loads at 808C in air and Igepal (nonylphenoxypoly (ethyleneoxy) ethanol) [20][21][22].…”

Section: Introductionmentioning

confidence: 99%

Slow crack growth resistance in resin blends of chromium and metallocene catalyzed ethylene‐hexene copolymers for pipe applications

García

Carrero

Aroca

et al. 2008

Polymer Engineering & Sci

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A bimodal system has been developed by blending a high density and linear medium density ethylene‐hexene copolymers synthesized with chromium and metallocene catalysts, respectively. The resistance to slow crack growth examined by the Pennsylvania Edge‐Notch Tensile test (PENT test‐ASTM F1473) and the crack opening displacement was determined at 80°C and 2.4 MPa. The effects of molecular and morphological structure on the slow crack growth (SCG) resistance were evaluated, the molecular weight and lamellar thickness being the most critical parameters for this system. The great importance of the short chain branching content and distribution was determined and discussed by SEC‐FTIR. Therefore, two main factors were found determinant in the SCG resistance. On the one hand, the increase of tie molecule density and therefore the continuity in the network formed by crystals and tie molecules and, on the other hand, the short chain branching density increase as the linear medium density ethylene‐hexene copolymer fraction does so. In addition, a morphological analysis of the fracture surface was performed in order to analyze the fracture mechanisms that took place. Differences observed in the fracture surface morphology were related to the molecular and morphological structure. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

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“…Basic requirements for the application of LEFM in plastics are that the global loading situation of the specimen or component is within the range of linear viscoelasticity, and that the formation of plastic deformations at the crack tip is limited to a small area 24. Different studies suggested that within the boundaries of LEFM frequently the same failure mechanisms may be responsible for SCG in cyclic tests as well as in static tests 5, 21–34. Furthermore, those studies proposed that the results of fatigue tests are in good accordance to internal pressure tests regarding the purpose of material ranking which makes such methods useful for a material ranking by SCG resistance.…”

Section: Introductionmentioning

confidence: 99%

Numerical Assessment of PE 80 and PE 100 Pipe Lifetime Based on Paris‐Erdogan Equation

Frank

Hutař

Pinter

2012

Macromolecular Symposia

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Summary: A novel accelerated fracture mechanics extrapolation procedure based on cyclic test with cracked round bar (CRB) specimens was verified by a correlation of real pipe failure time to simulated failure times at a temperature of 60 °C. The procedure was applied to predict the long‐term failure of modern PE 80 and PE 100 pipes 23 °C. Moreover, the used stress intensity factor concept also allows to consider the impact of arbitrary additional loading situations like soil loads or point loads and to assess pipe lifetime under complex loading situations.

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Stepwise fatigue crack propagation in polyethylene resins of different molecular structure

Cited by 39 publications

References 15 publications

Application of single site catalyst metallocene polyethylenes in extruded films: Effect of molecular structure on sealability, flexural cracking and mechanical properties

Application of single site catalyst metallocene polyethylenes in extruded films: Effect of molecular structure on sealability, flexural cracking and mechanical properties

Slow crack growth resistance in resin blends of chromium and metallocene catalyzed ethylene‐hexene copolymers for pipe applications

Numerical Assessment of PE 80 and PE 100 Pipe Lifetime Based on Paris‐Erdogan Equation

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