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  • 1
    Electronic Resource
    Electronic Resource
    Effect of deformation ratio on fibril deformation in fatigue of polystyrene (1988)
    Springer
    Journal of materials science 23 (1988), S. 248-252 
    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 Small-angle X-ray scattering has been used to measure the deformation of craze fibrils during mechanical fatigue of polystyrene. The maximum deformation of the sample in the fatigue cycle was kept constant while the minimum deformation was varied. When the minimum deformation was 50% or more of the maximum, the load on the craze fibrils remained tensile. When the minimum deformation was reduced below this, the load on the fibrils became compressive and they buckled. The main effect of minimum sample deformation on fatigue life occurred in the regime where the fibrils remained straight. In this regime a decrease in minimum sample deformation caused a considerable decrease in fatigue life. At low minimum sample deformations the effects of minimum deformation on fatigue life were not large. These effects probably stem from the fibril strains involved in the deformation processes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01174061
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  • 2
    Electronic Resource
    Electronic Resource
    Studies of craze fibril deformation during fatigue in polystyrene (1987)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 25 (1987), S. 1765-1778 
    Details
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Small-angle scattering of synchrotron x-ray radiation has been used to study the effects of fatigue on craze fibril microstructure. The results obtained during unloading and reloading during a single cycle have been compared with those predicted by a model of sinusoidally bent fibrils. In addition the total displacement of the craze boundaries was found from the change in the invariant on unloading. The mean fibril diameter D was measured at the maximum tensile strain in each cycle. Over 250 cycles, D increased by at least a factor of 2 from an initial value of 6.5 nm, with most of this change happening in the first few cycles. The increase in D must occur by fibril coalescence, a mechanism that requires that the material in craze fibrils have considerable molecular mobility, even at room temperature, 70°C below the glass transition temperature.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1987.090250816
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  • 3
    Electronic Resource
    Electronic Resource
    Relative molecular weight distributions of cis-polybenzoxazole/polyphosphoric acid rodlike liquid crystalline polymer solutions from dilute solution rheometry (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 30 (1992), S. 259-264 
    Details
    ISSN: 0887-6266
    Keywords: liquid crystalline polymer solutions, MWD from viscometry in ; cis-Polybenzoxazole/polyphosphoric acid, MWD from viscometry liquid of, crystalline solutions of ; intrinsic viscosity and MWD in dilute solutions of rodlike liquid crystalline polymer ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The molecular weight for a dilute solution of cis-polybenzoxazole (PBO) in polyphosphoric acid (PPA) was determined by fitting the rheological data with a semiempirical polydisperse hybrid theory. The hybrid theory models a semiflexible rigid rod as an elastic cylinder. The cylinder has both a rotational relaxation spectrum given by an ideal rigid rod and an internal bending relaxation spectrum spaced in accord with the relaxation time spectra of a flexible coil with fully developed hydrodynamic interactions. The model was fitted to rheological data collected for a 0.05 weight percent solution with intrinsic velocity (one-point determination) of 320 ± 10 cc/g. The model predicts a number-average molecular weight near 12800 ± 400 g/mol with a polydispersity index of 2.5 ± 0.1. By using the Yamakawa-Yoshizaki equation the intrinsic viscosity is calculated for the model molecular weight distribution as 310 cc/g.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1992.090300305
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  • 4
    Electronic Resource
    Electronic Resource
    Low-angle electron diffraction from high temperature polystyrene crazes (1987)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 25 (1987), S. 1679-1697 
    Details
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Low-angle electron diffraction (LAED) was used to study the microstructure of crazes produced at different temperatures T and strain rates in thin films of monodisperse polystyrene (PS). At a slow strain rate of 4.1 × 10-6 s-1 both the fibril diameter D and the fibril spacing D0 of crazes in 1800k molecular weight PS remained constant with temperature up to T ≈ 70°C and then sharply increased as T approaches Tg. At a higher strain rate of ∼ 10-2 s-1, both D and D0 increase only slightly with T. The values of D and D0 over a range of temperature are in very good agreement with those values obtained in bulk samples using small-angle x-ray scattering. The crazing stress was measured as a function of temperature in the thin films of the 1800k molecular weight PS strained at the same slow strain rate used for the LAED measurements. These measurements were analyzed using a simple model of craze growth to reveal the temperature and strain rate dependence of the craze surface energy Γ. At room temperature Γ ≈ 0.076 J/m2 (versus Γ ≈ 0.087 J/m2 predicted) and was observed to remain constant up to T ≈ 70°C and then decrease by approximately a factor of two at T = 90°C. This decrease in Γ is believed to result from chain disentanglement to form fibril surfaces at sufficiently high temperatures and occurs in the same temperature range in which the craze fibril extension ratio λ was observed to increase.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1987.090250810
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  • 5
    Electronic Resource
    Electronic Resource
    Growth kinetics of solvent crazes in glassy polymers (1978)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 16 (1978), S. 1195-1217 
    Details
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The kinetics of craze growth from sharp cracks in polystyrene (PS) and poly(methyl methacrylate) (PMMA) in contact with liquid methanol were measured with time-lapse photography as a function of the stress intensity factor KI. At high KI the craze length in both systems increases as √t if the sides of the craze are protected from methanol and as t if they are not, where t is the elapsed time after loading. If such a side-protected craze is dried under load and then methanol is reintroduced to the crack tip, the methanol front advances with the same kinetics as the original craze growth. This experiment Proves that solvent crazing velocities are limited by the hydrodynamic transport of solvent through the porous craze structure under a capillary pressure driving force (which can be as high as 100 atm). An improved model of fluid flow through the craze is developed and shown to predict craze growth kinetics in good agreement with those observed. The hydraulic permeability of methanol crazes in PS was found to be independent of craze length at small craze length and to be independent of KI except at very low KI. Although increases in molecular weight in the range Mw = 200,000 to Mw = 670,000 do not markedly affect the crazing kinetics, they greatly increase the time to fracture of the craze.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1978.180160705
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  • 6
    Electronic Resource
    Electronic Resource
    The entanglement network and craze micromechanics in glassy polymers (1982)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 20 (1982), S. 1129-1141 
    Details
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Crazes have been grown from crack tips in thin films of the following five polymers: polytertbutylstyrene (PTBS), polystyrene (PS), poly(styrene-acrylonitrile) (PSAN), poly(phenylene oxide) (PPO), and poly(styrene-methyl methacrylate) (PSMMA). These polymers represent a wide range of le values, where le is the chain contour length between entanglements. Quantitative transmission electron microscopy has been used to analyze the extension ratio λcraze and displacement profiles for these crazes. From these measurements the craze surface stresses have been computed by using the method of distributed dislocations. This analysis also permits an accurate measure of the level of the applied stress σ∞. These measurements show that the stress necessary for crazing increases as le decreases and that the higher surface stresses present at crack tips generate crazes that have higher λs than isolated crazes in the same polymers. Surface drawing is shown to be the dominant mechanism for craze thickening in all five polymers.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1982.180200703
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