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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 60 (1986), S. 2655-2658 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A statistical consideration based upon a theory of microscopic molecular kinetics is developed to describe the time-dependent fracture process for oriented polymers. The interrelation between the macroscopic fracture strength and the microscopic behaviors is formulated with the aid of a double Fourier series expansion. The microscopic behavior in the vicinity of a point is expressed in the form of a spherical function which can be expanded into a series of symmetric tensorial terms. Subsequently, the fracture strength of polymers is evaluated in terms of both time and molecular orientation. By taking account of the individual values of the directional fraction of integrity, the time to fracture and the most probable direction of fracture within any volume element in a medium are predicted.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4884-4888 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Statistical theories in fracture kinetics constitute a very important role in investigating the fracture strength of solids and their utilization in modern engineering. In this paper, a review of some of the recent concepts and models is provided. The main concern is the effect of the breaking stress on the time-to-break. Based upon the consideration of the fraction of integrity of a medium, a number of models have been evaluated and compared. Two basic considerations used for evaluation and comparison are Zhurkov's empirical kinetic relationship and Hsiao's statistical absolute reaction rate model. Other considerations reducible from these two are also given for comparison. Using a well-known numerical analysis method, it appears that the nonlinear mathematical consideration is more realistic in describing the time-dependent fracture strength behavior of a medium over any linear ones. The computed results seem to fit reasonably well with the general observations.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 58 (1985), S. 2837-2842 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The propagation of a craze as quasifracture under repeated cyclic stressing in polymeric systems has been under intensive investigation recently. Based upon a time-dependent crazing theory, the governing differential equation describing the propagation of a single craze as quasifracture in an infinite viscoelastic plate has been solved for sinusoidal stresses. Numerical methods have been employed to obtain the normalized craze length as a function of time. The computed results indicate that the length of a quasifracture may decelerate and decrease indicating that its velocity can reverse. This behavior may be consistent with the observed and much discussed craze healing and the enclosure model in fatigue and fracture of solids.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 57 (1985), S. 1823-1834 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The time-dependent craze failure process of polymers has been investigated. The process is characterized by several stages: deformation, development of microporosity, craze initiation, craze propagation, craze-crack transition, and propagation of crack to final fracture. Using Laurent's series expansion and convolution integral form of material's constitutive function, a time-, temperature-, and stress-dependent instability criterion for viscoelastic media has been considered. It is found that under a constant load, an incubation time for craze initiation can be obtained. This incubation time goes to zero for sufficiently high values of stress and approaches to infinity for low values of stress. The crazing stress depends linearly on temperature, and decreases as the test temperature increases toward the glass transition temperature. The interrelationship among the applied stress, craze initiation time, and temperature is then established and a fairly general time-dependent theory on craze or quasifracture initiation in viscoelastic media is formulated.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 57 (1985), S. 170-174 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This paper deals with the nonlinear quasi-fracture behavior of polymers. Using the finite element method, the quasi-fracture model composed of an isolated craze opening with a nonlinear boundary envelope forces represented by oriented fibril domains is analyzed in simply-stressed rectangular plate. The stress distribution, the displacement profile, as well as the yield or plastic or flow zone adjacent to the craze tips are obtained. It is found that the variation of the stress distribution near the craze tip is not as sharp as that for an elastic crack. The initial load required for yielding or flowing is greater for the quasifracture as compared with that for a classical fracture. Under the same load the yeild or flow zone is somewhat smaller as compared with that obtained on the basis of linear elastic-plastic fracture mechanics theory.
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  • 6
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 186 (1960), S. 535-537 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] As one special case, if we let : p tb then from (1) : (3) where t b is the time to fracture, s& is the fracture strain and a& the stress maintained until fracture occurs. This agrees well with the current theoretical and experimental developments of the subject4-8. On the basis of ...
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  • 7
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 181 (1958), S. 1527-1528 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The sample prepared for this investigation was a small piece of steel having the following chemical analysis (per cent) : Carbon 0-084 Aluminium 0-036 Manganese 0-27 Nickel 0-019 Phosphorus 0 008 Chromium 0-055 Sulphur 0 008 Vanadium 0-003 Silicon 0-009 Molybdenum 0 009 The sample was ...
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 50 (1996), S. 404-415 
    ISSN: 0006-3592
    Keywords: hepatocyte ; spheroids ; tissue engineering ; bioartificial liver ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Freshly harvested primary rat hepatocytes cultivated as multicellular aggregates, or spheroids, have been observed to exhibit enhanced liver-specific function and differentiated morphology compared to cells cultured as monolayers. An efficient method of forming spheroids in spinner vessels is described. Within 24 h after inoculation, greater than 80% of inoculated cells formed spheroids. This efficiency was significantly greater than that reported previously for formation in stationary petri dishes. With a high specific oxygen uptake rate of 2.0 × 10-9 mmol O2/cell/h, the oxygen supply is critical and should be monitored for successful formation. Throughout a 6-day culture period, spheroids assembled in spinner cultures maintained a high viability and produced albumin and urea at constant rates. Transmission electron microscopy indicated extensive cell-cell contacts and tight junctions between cells within spheroids. Microvilli-lined bile canaliculus-like channels were observed in the interior of spheroids and appeared to access the exterior through pores at the outer surface. Spheroids from spinner cultures exhibited at least the level of liver-specific activity as well as similar morphology and ultrastructure compared to spheroids formed in stationary petri dishes. Hepatocytes cultured as spheroids are potentially useful three-dimensional cell systems for application in a bioartificial liver device and for studying xenobiotic drug metabolism. © 1996 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 26 (1988), S. 967-979 
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: This paper deals with a viscoelastic boundary element method for analyzing a polymer quasifracture usually called a craze in polymers. A time-dependent boundary stiffness is considered on the quasifracture envelope surface. The viscoelastic property of the glassy polymer is represented by a generalized Kelvin model with multiple retardation times. According to the linear viscoelastic correspondence principle, the associated elasticity solution can be solved by applying the general integral boundary element method. Then the viscoelastic solution in the time domain can be obtained by applying a collocation Laplace inversion transformation. Using these methods, the quasifracture problem composed of an isolated craze opening with time-dependent stiffness traction in a stressed rectangular plate is analyzed. The displacement profile and the stress distribution around the craze envelope surface are computed.
    Additional Material: 6 Ill.
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  • 10
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A mathematical analysis is given to describe the effect of prior large flow orientation on the variation of the fracture strength of a model linear hard polymer solid. For the simple state of uniaxial orientation, the fracture strengths in the direction of orientation and that perpendicular to the direction of orientation are evaluated as functions of the strain change and the strength of the unoriented material. The results indicate an increase of strength in the direction of orientation and a decrease of strength perpendicular to the direction of orientation as the degree of orientation increases.
    Additional Material: 4 Ill.
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