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  • 1
    Electronic Resource
    Electronic Resource
    Insulin Binding to the Blood-Brain Barrier in the Streptozotocin Diabetic Rat (1986)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 47 (1986), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: 125I-Insulin binding to isolated brain microvessels from control, streptozotocin diabetic, and insulin-treated diabetic rats was measured. The binding was highest in the control (21.1 ± 1.8%/mg capillary protein) and lowest in the diabetic (14.8 ± 1.9%, p 〈 0.01) animals. Administration of 2 U of protamine zinc insulin per day increased the maximum binding in the diabetic rats to 17.2 ± 2.1%. Scatchard analyses of the binding showed that the major difference between the diabetic and the control animals was a decrease in the number of both high- and low-affinity sites in the diabetic animals. To test whether the failure of up-regulation in the hypoinsulinemic diabetic animal was related to an inherent defect in the endothelial cell or resulted from the diabetic milieu, cultured brain endothelial cells were tested for their capacity to up- and down-regulate their insulin receptors in vitro. In response to 100 ng/ml insulin for 12 h, these cells down-regulated their insulin receptors. When the insulin was removed, the insulin receptors returned to control levels. These studies showed that in vitro brain capillary endothelial cells have the capacity to increase their insulin receptors in response to a low-insulin environment, whereas in vivo the microvessels decrease their insulin receptors in response to diabetes. Furthermore, insulin levels in both plasma (33.4 ± 3.5 μU/ml in controls versus 21.9 ± 2.1 in diabetic, p 〈 0.02) and brain 2.6 ± 0.4 μU/g wet weight in control versus 0.32 ± 0.30 in diabetic, p 〈 0.02) were lower in the diabetic animals. However, the ratio of brain to plasma insulin levels was lower in the diabetic (0.029 ± 0.011) than in the control animals (0.092 ± 0.024, p 〈 0.02), implying that there is a selective decrease in the brain insulin relative to the plasma insulin in diabetes. These findings suggest that the brain capillaries may be involved in transport of insulin from the blood to the underlying brain cells and that a specific defect occurs in the diabetic brain capillary that can cause a further deficiency in brain insulin in poorly controlled diabetes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1986.tb04516.x
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  • 2
    Electronic Resource
    Electronic Resource
    A STATISTICAL MODEL OF INTERMITTENT SHORT FATIGUE CRACK GROWTH (1987)
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 9 (1987), S. 0 
    Details
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The stochastic nature of the growth of short surface fatigue cracks under uniform cyclic loading can be attributed to their interaction with a stochastic microstructure. In this paper, a computational scheme is proposed to describe the statistical effects of the temporary arrest of short cracks by grain boundaries, and the modification of rates of propagation across grains by various effects of grain boundary constraint. The fact that a crack tip may be in one of two states, either temporarily arrested at a grain boundary or actively propagating, is treated explicitly by considering probability densities evolving in complementary state spaces corresponding to each case. The evolution of the densities during fatigue is described by conservation equations, which are solved numerically. It is shown how engineering quantities, such as the time to initiation of a macroscopic crack, can be derived from the calculated densities. The explicitness with which the characteristics of short crack growth are treated greatly enhances the potential accuracy of predictions based on this approach.The theory is constructed to allow considerable flexibility in the microstructure-related mechanisms assumed to control growth rates in any given material. However, as it is stated here, the theory is restricted to Mode I (tensile opening) transgranular crack growth under constant amplitude cyclic loading. Examples are given of the various effects that can be treated, as well as those that would require modification of the structure of the computational procedure. The theory is illustrated by an application to data for Al 2219-T851.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1460-2695.1987.tb00470.x
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  • 3
    Electronic Resource
    Electronic Resource
    A STUDY OF FATIGUE AND CREEP BEHAVIOUR OF FOUR HIGH TEMPERATURE SOLDERS (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 19 (1996), S. 0 
    Details
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Creep and cyclic deformation behavior of two lead-free high temperature solder alloys, 95Sn-5Ag and 99Sn-1.0Cu, a high lead alloy 97.SPb-1.SAg-1.0Sn, and an Ag-modified eutectic alloy 62.SSn-36.1Pb-1.4Ag, were studied. Room temperature and high (100°C and 150°C) temperature fatigue tests (with cyclic strain amplitude up to 6.0%) for the four solders were conducted, with the fatigue lives ranging from a few cycles to more than 100,000 cycles. It is shown that among the alloys studied, 62.SSn-36.1Pb-1.4Ag (the modified Sn-Pb eutectic alloy) has the lowest fatigue resistance in term of low cycle fatigue life (strain controlled). The high lead alloy, 97.SPb-1.5Ag-1.0Sn, has the highest strain fatigue resistance in the large strain region (Δ 〉 2.0%). Temperature has a significant effect on alloys 95Sn-5Ag and 99Sn-1.0Cu, but has a negligible effect on the Ag modified Sn-Pb eutectic alloy 62.5Sn-36.1Pb-1.4Ag and 97.5Pb-1.5Ag-1.0Sn. Creep studies show that these alloys generally have a very significant primary creep regime (up to 20%); thus, any realistic constitutive relation has to take such a primary creep phase into consideration. Cyclic deformation of alloy 95Sn-SAg was simulated by using a constitutive relation built upon a 2-cell model, which covers both primary and secondary creep. This model provides a good estimate of the peak stresses (the minimum stress and the maximum stress in each cycle); it agrees with experimental results when the applied cyclic strain is small and/or the applied strain rate is very low.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1460-2695.1996.tb00175.x
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  • 4
    Electronic Resource
    Electronic Resource
    MODEL-BASED STATISTICAL ANALYSIS OF SHORT FATIGUE CRACK GROWTH IN Ti 6Al-2Sn-4Zr-6Mo (1987)
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 10 (1987), S. 0 
    Details
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— The framework of a new probabilistic model of short fatigue crack growth was laid down in the preceding paper. In this paper, the model is used to analyze growth rate statistics for surface fatigue cracks in Ti 6Al-2Sn-4Zr-6Mo. Specific models are proposed for the evolution of the stochastic growth control variable, which appears subsequently as an independent variable in a parametric law for the growth rate. Comparison with data shows that for cracks of length 10–250 μm in Ti 6–2-4–6, fluctuations in the instantaneous rate of propagation of each surface crack tip depend only on the visible surface microstructure in the tip's immediate neighborhood. They are not influenced by the microstructural environment of the subsurface crack front. Furthermore, they probably depend only on the sizes of at most the three grains nearest the crack tip, i.e. those within about 30 μm of it.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1460-2695.1987.tb00494.x
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  • 5
    Electronic Resource
    Electronic Resource
    A PROBABILISTIC MODEL OF SHORT FATIGUE CRACK GROWTH (1987)
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 10 (1987), S. 0 
    Details
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— A probabilistic model is presented that draws a direct link between stochastic microstructure and the statistics of measured growth rates. The model is formulated as a semi-Markov process. The underlying Markov process describes the evolution of a growth control variable as an explicit function of crack length. The growth control variable is open to a variety of interpretations, depending on the mechanisms known to control growth in any given application. Elapsed fatigue cycles and the distribution of times to failure are calculated by invoking an empirical or postulated law of growth rate. This law is either a deterministic or probabilistic relationship between the growth control variable and the crack velocity. It may, and usually does, contain parameters that are evaluated by calibration against available statistical data. This process guarantees a high level of robustness of the model's predictions. The computational generality of the formulation facilitates the treatment of spectral loading.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1460-2695.1987.tb00490.x
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  • 6
    Electronic Resource
    Electronic Resource
    ON THE TRANSITION FROM NEAR-THRESHOLD TO INTERMEDIATE GROWTH RATES IN FATIGUE (1983)
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 6 (1983), S. 0 
    Details
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— Evidence is presented that the cyclic stress intensity threshold for fatigue crack growth in A1 2219-T851 is associated with a critical maximum value of stress intensity, Kc. This relationship is discovered by measuring the local value of stress intensity at the crack tip which is less than the applied stress intensity because of fatigue induced compressive residual stresses in the plastic zone. Crack growth rates and values of the crack tip residual stress are measured as functions of load ratio. For local stress intensities greater than Kc, the growth rate follows a power-law relationship, increasing monotonically with δK. For local stress intensities below Kc, growth rates are also sensitive to the cyclic stress range, δσ. If the stress range is small, a threshold to growth, typical of long cracks, is seen. When the cracks are short and δσ exceeds a critical value, growth rates are a complex function of both δσ and δK. This behavior is attributed to the effect of δσ on the propagation of the crack front past obstacles such as grain boundaries.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1460-2695.1983.tb00344.x
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  • 7
    Electronic Resource
    Electronic Resource
    Remaining fatigue life prediction in the initiation regime using SAW NDE (1980)
    Springer
    Journal of nondestructive evaluation 1 (1980), S. 3-9 
    Details
    ISSN: 1573-4862
    Keywords: harmonic generation ; fatigue ; microcracks ; aluminum ; surface acoustic waves ; NDE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract Harmonic generation of surface acoustic waves (SAW) is shown to be a useful tool for the detection of the initiation of surface cracks during fatigue of high strength aluminum alloys. A model that relates the length and density of microcracks to the amplitude of a SAW harmonic signal is described, and an associated coefficient of generation efficiency for the second harmonic amplitude is derived. A correlation between experimentally measured harmonic amplitude and remaining fatigue life is then demonstrated, which allows the mean remaining fatigue lifetime to be estimated to within 5% over the last 50% of the fatigue life for an Al 7075 alloy if the cyclic stress amplitude, but not the duration of fatigue, is known.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00566227
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  • 8
    Electronic Resource
    Electronic Resource
    Relationships between crack opening displacement, alloy variables, and crack detection sensitivity (1982)
    Springer
    Journal of nondestructive evaluation 3 (1982), S. 189-200 
    Details
    ISSN: 1573-4862
    Keywords: Acoustic harmonic generation ; critical angle acoustics ; fatigue crack detection ; alloy microstructure ; load amplitude ; NDE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract Alloy grain size is known to influence both the propagation path and the closure stress of surface fatigue cracks in many alloys. The general trend is for the path to be more tortuous and the closure stress to be larger, the larger the grain size. By use of Ti Al-4V and Al 7075-T6, the effects of grain size on the nondestructive detection of surface cracks which might arise from closure stress and path irregularity variables were evaluated. Titanium specimens were inspected using an acoustic harmonic generation technique, and it was discovered that the major source of harmonic signals was grain sized crystallographic cracks. Harmonic signals were larger during fatigue in an 8-µm compared to a 4-µm grain sized alloy, as there were more grain sized cracks in the large grain material. Crack closure was found to be extremely important in determining the reflected acoustic amplitude obtained in inspecting small (100–1000 µm) cracks in Al 7075-T6 using a critical angle technique. Average received amplitudes were an order of magnitude smaller for cracks at zero load than for those opened by a tensile stress. The scatter in the reflected amplitude was also large, apparently as the result of variations in the degree of the closure from crack to crack. For the 7075 material, the important effect of larger grain size was to increase the irregularity of the crack path, making the small cracks more visible acoustically at azimuthal angles not normal to the crack plane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00565864
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  • 9
    Electronic Resource
    Electronic Resource
    The micromechanics of fatigue-induced delamination of a graphite/epoxy composite (1987)
    Springer
    Journal of materials science 22 (1987), S. 4426-4433 
    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 Fatigue crack growth in the resin layer between 0 and 90 plies of an AS/3501-5A graphite fibre/epoxy composite is discontinuous. Regularly spaced extensions of the crack front occur after periods of arrest. Crack compliance and tip strain fields have been measured to determine how the local minimum (K min l) and maximum (K max l) crack tip stress intensities affect growth. Contact of the fracture surfaces and swelling of the 90° ply modify these local stress intensities by an amount sensitive to load ratio (R), and the resulting propagation rate depends strongly onR. A model capable of describing thisR effect relates the distance of each individual crack advance to Kmax l and the duration of each arrest toK mnax l -K min l, i.e., to ΔK eff. We discuss the genesis of this model, and its explanation of the large Paris law coefficient which results if growth rates are instead expressed against the applied cyclic stress intensity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01132042
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  • 10
    Electronic Resource
    Electronic Resource
    Microscopic deformation in a heated unidirectional graphite-epoxy composite (1989)
    Springer
    Journal of materials science 24 (1989), S. 199-204 
    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 Out-of-plane displacements caused by heating of a unidirectional P75S/1962-ERLX graphite-epoxy composite were measured on a surface cut normal to the fibres after thermal cycling. On heating to 44° C from room temperature, the epoxy confined within clusters of three fibres sank in a trough beneath the plane of the fibre ends by 50–120 nm. The sense of the deformation was the opposite of what one would expect from differential thermal expansion. The role of residual stresses in this deformation was studied by measuring the depth of the trough for several different thermal histories applied before the free surface was cut. When the maximum temperature achieved in the prior thermal cycles exceeded 100° C, the depth of the trough increased. However, if cycles exceeding 100° C were followed by thermal cycles of decreasing amplitude, chosen to induce interfacial stress relaxation, the depth of the trough decreased, as expected. The experiments illustrate the feasibility of deducing quantitative information about local deformation in the interior of a specimen from high spatial resolution strain measurements on cut surfaces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00660954
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