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  • 1
    Electronic Resource
    Electronic Resource
    Effect of branch frequency on dynamic fatigue behavior of slowly notched polyethylene polymers (1994)
    Springer
    Journal of polymer research 1 (1994), S. 375-383 
    Details
    ISSN: 1572-8935
    Keywords: Dynamic fatigue properties ; Branch length ; Branch frequency ; Tie molecule density ; Fracture surface morphology ; Failure cycle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Samples with the same weight average molecular weight and molecular weight distribution but different branch frequency were utilized to study the effects of branch frequency and thermal history on tie molecule density and their subsequent influence on the slow crack growth of short chain branched polyethylenes. The dynamic fatigue properties are improved significantly with increasing branch frequency and with samples crystalloid at fast cooling rate. However, at temperatures ranging from -20 to 80 °C. the amount of the failure cycle (Nf) improved due to the slight increase in branch frequency is less than those of samples prepared by crystallization at fast cooling rate. Additionally, it is interesting to note that the drawn fibers observed on the fracture surfaces were larger and longer for samples associated with longer Nf. In fact, it is interesting to note that the average number of tie molecules formed per chain (T(M)) of samples associated with longer Nt is also larger. This increasing in T(M) is suggested to be responsible for the improved fatigue properties of samples associated with larger branch frequency and crystallized at fast cooling rate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01378771
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  • 2
    Electronic Resource
    Electronic Resource
    Fatigue crack-propagation in annealed poly(butylene terephthalate) (1989)
    Springer
    Journal of materials science 24 (1989), S. 2637-2642 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Samples with the same percentage crystallinity, supermolecular structure and lamellar thickness but different average molecular weight were prepared to distinguish the effect of tie chain density on fatigue crack propagation (FCP) behaviour. This alteration in molecular weight was accomplished by “controlled” chain degradation during thermal annealing. A significant decrease in FCP resistance was observed when samples were annealed at different temperatures for various amounts of time. In addition, an examination of the fracture surfaces of these specimens indicates a transition to a more brittle-type behaviour when annealed for longer periods of time at any specific annealing temperature. The decrease in FCP resistance is attributed to a decrease in the tie chain density.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01174538
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  • 3
    Electronic Resource
    Electronic Resource
    Effect of notching speed on dynamic fatigue behaviour of polyethylene terephthalate polymers (1993)
    Springer
    Journal of materials science 28 (1993), S. 3900-3910 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The influence of notching speed on the fatigue behaviour of crystalline and amorphous polyethylene terephthalate (PET) was investigated. A clear precrack adjacent to the notch tip was found after each crystalline sample was notched, and the precrack length increased when the samples were notched at higher speeds. The failure time, t f, decreased significantly for samples with longer precrack lengths, and the decrease in t f due to faster notching speeds was significantly lower for samples of high average molecule weight and calculated tie-molecule density. In contrast, a heart-shaped damaged structure surrounding the notch tip was observed after each amorphous sample was notched, and the size of the damaged zone, adjacent to the notch tip, increased significantly with the notching speed. Furthermore, the time to failure of each amorphous sample increased significantly as the notching speed increased. In fact, most of the increase in t f is due to an increase in the initiation period, t i. This significant increase in t i is attributed to the larger damaged zone caused by higher notching speeds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00353198
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  • 4
    Electronic Resource
    Electronic Resource
    Impact properties of carbon fiber reinforced linear and short-chain branched polyethylenes (1994)
    Springer
    Polymer bulletin 33 (1994), S. 607-614 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary An investigation of the influence of short-chain branched length on impact behavior of linear high density polyethylene (HDPE), short-chain branched polyethylenes (SBPEs) and their fiber reinforced samples is reported. The result shows that the total impact energies (Et) increased with increasing branch length at any given temperature used in this study. Similar trend was found for their fiber reinforced samples. For a given polyethylene resin, Et increased with fiber content up to 5%, and then decreased consistently with further increase of fiber content. The amount of Et improved due to the presence of 5% carbon fibers increased significantly with the branch length at temperatures higher than 25°C. In addition, the fracture surface morphology indicated that the adhesion between carbon fibers and PE resins increased with the branch length. However, the adhesion and the amount of Et improved due to the presence of 5% carbon fibers reduced significantly with decreasing temperature. Finally, it was found that Et decreased slightly with rising temperature until the temperature reached around 40°C, and then increased sharply with increasing temperature. It is suggested that this “transition” behavior is related to the molecular motion accounting for the α transition of PE resins.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00296171
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  • 5
    Electronic Resource
    Electronic Resource
    Fatigue-fracture mechanism of slowly notched poly(ethylene terephthalate) polymers (1994)
    Springer
    Polymer bulletin 33 (1994), S. 361-368 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary Fatigue fracture behavior of slowly notched polyethylene terephathalate (PET) polymers were investigated at temperatures close to their β transition temperatures up to well above their glass transition temperatures. Detailed characterization on the morphology of the notched roots showed that the crack tip during crack propagation became more dull with increasing testing temperature. The failure cycle (Nf) of these samples increased with increasing temperatures until it reached the α transition temperatures of PET polymers, and most of the increase in Nf is due to the increased time consumed in the initiation period. On the other hand, the initial crack growth rate increased significantly and Nf of these samples decreased dramatically as the temperature increased well above the glass transition temperature. This interesting temperature dependence of fatigue behavior is explained due to the change of molecular motion of PET polymers at this temperature range.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00314275
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  • 6
    Electronic Resource
    Electronic Resource
    Effects of compatibilizer precursors on the barrier properties and morphology of polyethylene/polyamide blends (1995)
    Springer
    Polymer bulletin 35 (1995), S. 371-378 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary A systematic investigation on the effects of type of compatibilizer precursors (CP) upon the barrier properties and morphology of PE/PA blends was reported. Three alkyl carboxyl-substituted polyolefins were selected to modify PA in a twin screw extruder by “reactive extrusion” process. The barrier property of the modified PA (MPA) was better than pure PA, and the amount of barrier improvement of the blend of PE and MPA dependended significantly on the barrier property of the MPA prepared. The extent of mixing PE and MPA before blow-molding has a significant effect on its corresponding barrier properties. Further analysis of the fracture surfaces indicated that a more demarcated laminar structure of MPA dispersed in PE matrix is essential for better barrier properties of PE/MPA blends. It is not completely clear how the type of CP added affects the barrier properties of MPAs. However, it is suggested that long PA sequence with shorter grafted CP chain and high normalized grafting efficiency of MPA are essential for preparing a clear laminar structure of MPA, and a good barrier properties of PE/MPA blends.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00963137
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  • 7
    Electronic Resource
    Electronic Resource
    Static fatigue behaviour of linear low-density polyethylenes (1994)
    Springer
    Journal of materials science 29 (1994), S. 4104-4112 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Various thermal histories were utilized to generate samples with the same crystalline microstructure (i.e. degree of crystallinity, supermolecular structure, tie molecule density and lamellar thickness) for linear low-density polyethylenes (LLDPEs) with the same molecular weight, molecular weight distribution and branch frequency but different branch length. The static fatigue properties were found to improve with decreasing applied load for samples with the same type of short-chain branches. The failure time of static fatigue (t f) was found to increase dramatically as the branch length increased. An equation was used to predict t f from the stress, the branch length and other material parameters. In addition, the initial growth rate of the crack opening displacement and the time required to reach the critical opening displacement at the notch roots of the specimens were observed to decrease and increase, respectively, with increasing branch length. This dramatic improvement in static fatigue properties is attributed to the increasing sliding resistance of the polymer chains through the crystal and through entanglements in the amorphous region as the branch length of LLDPEs increases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00355978
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  • 8
    Electronic Resource
    Electronic Resource
    Fatigue crack propagation in high-density polyethylene (1991)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 29 (1991), S. 371-388 
    Details
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: An investigation of the influence of crystalline microstructure on fatigue crack propagation (FCP) in high-density polyethylene (HDPE) is reported. Various thermal histories were used to generate samples with the same crystallinity and supermolecular structure for three different molecular weight HDPEs. Estimation of tie chain densities were obtained from measurements of brittle fracture stress and predicted from the estimated chain dimensions of the polymers using the modified version of the approach originally taken by Huang and Brown. A significant decrease in FCP resistance and a clear transition to a more brittle fracture surface was observed with decreasing molecular weight. Detailed studies of damaged zones preceding the growing crack show a transition to a more highly branched crack structure for those samples associated with a higher FCP resistance. These results strongly suggest that the branched damaged zone structure improves the FCP resistance by enlarging and blunting the crack tip and, therefore, consuming more energy during the fatigue crack propagation. Additional efforts were made to prepare samples with the same crystallinity and tie chain density, but different supermolecular structure. However, in contrast to reports in the literature, no significant difference in FCP resistance was observed for specimens with different average spherulite sizes. This is probably because the propagating crack front is preceded by a significant zone of plastic deformation and is not expected to directly encounter the spherulites.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1991.090290313
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  • 9
    Electronic Resource
    Electronic Resource
    Multiple melting in annealed poly(butlene terephthalate) (1989)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 27 (1989), S. 1543-1550 
    Details
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1989.090270714
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  • 10
    Electronic Resource
    Electronic Resource
    Environmental stress cracking behavior of short-chain branch polyethylenes in Igepal solution under a constant load (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 54 (1994), S. 2171-2186 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: An investigation of the influence of branch length and crystallinity on environmental stress cracking properties of short-chain branch polyethylenes (SBPEs) in Igepal solution is reported. The precise value of Igepal transition time (ITT) and difference between the failure process of SBPEs in air and in Igepal solution were determined by comparing their plots of notch opening displacements vs. time in air and in Igepal solution. Igepal transition time can only be found as the failure time (tfI) is greater than the critical time Igepal required to “accelerate” the fracture of SBPEs in Igepal solution. Prior to ITT, time dependence of notch opening displacements and fracture surfaces of samples in Igepal solution were similar to those in air. In contrast, obvious voids appeared in the base of craze and crazelike structures containing clear voids were found on the fracture remnants of samples with tfI longer than their ITTs. The value of ITT and tfI were found to increase significantly for samples associated with higher crystallinity. However, no significant difference in value of ITT was found for samples with the same crystallinity, tie-molecule density, molecular weight, branch frequency, but different branch length. Finally, environmental stress cracking resistance (ESCR) and tfI of SBPEs in Igepal solution increased dramatically as the short-chain branch length increased. This dramatic improvement in environmental stress cracking properties with short-chain branch length is attributed to the increasing sliding resistance of the polymer chains through the crystal and through the entanglement in amorphous region at time before and after ITT. © 1994 John Wiley & Sons, Inc.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1994.070541320
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