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  • 1
    Publication Date: 1999-09-01
    Print ISSN: 0014-4851
    Electronic ISSN: 1741-2765
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Springer
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Annals of biomedical engineering 28 (2000), S. 1194-1199 
    ISSN: 1573-9686
    Keywords: Cancellous bone ; stress ; strain ; strength ; adaptation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The statistical distribution of von Mises stress in the trabeculae of human vertebral cancellous bone was estimated using large-scale finite element models. The goal was to test the hypothesis that average trabecular von Mises stress is correlated to the maximum trabecular level von Mises stress. The hypothesis was proposed to explain the close experimental correlation between apparent strength and stiffness of human cancellous bone tissue. A three-parameter Weibull function described the probability distribution of the estimated von Mises stress (r2) 〉 0.99 for each of 23 cases). The mean von Mises stress was linearly related to the standard deviation (r2=0.63) supporting the hypothesis that average and maximum magnitude stress would be correlated. The coefficient of variation (COV) of the von Mises stress was nonlinearly related to apparent compressive strength, apparent stiffness, and bone volume fraction (adjusted r2=0.66, 0.56, 0.54, respectively) by a saturating exponential function [COV=A+B exp(−x/C)]. The COV of the stress was higher for low volume fraction tissue (〈0.12) consistent with the weakness of low volume fraction tissue and suggesting that stress variation is better controlled in higher volume fraction tissue. We propose that the average stress and standard deviation of the stress are both controlled by bone remodeling in response to applied loading. © 2000 Biomedical Engineering Society. PAC00: 8719Rr
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Experimental mechanics 39 (1999), S. 217-226 
    ISSN: 1741-2765
    Keywords: Strain measurement ; X-ray tomography ; image correlation ; trabecular bone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A three-dimensional extension of two-dimensional digital image correlation has been developed. The technique uses digital image volumes generated through high-resolution X-ray tomography of samples with microarchitectural detail, such as the trabecular bone tissue found within the skeleton. Image texture within the material is used for displacement field measurement by subvolume tracking. Strain fields are calculated from the displacement fields by gradient estimation techniques. Estimates of measurement precision were developed through correlation of repeat unloaded data sets for a simple sum-of-squares displacement-only correlation formulation. Displacement vector component errors were normally distributed, with a standard deviation of 0.035 voxels (1.22 μm). Strain tensor component errors were also normally distributed, with a standard deviation of approximately 0.0003. The method was applied to two samples taken from the thigh bone near the knee. Strains were effectively measured in both the elastic and postyield regimes of material behavior, and the spatial patterns showed clear relationships to the sample microarchitectures.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1573-9686
    Keywords: Stress fracture ; Bone strain ; Fatigue ; Aging ; Exercise
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Muscular fatigue in the training athlete or military recruit has been hypothesized to cause increased bone strain that may contribute to the development of a stress fracture. Under normal circumstances, muscles exert a protective effect by contracting to reduce bending strains on cortical bone surfaces. In vivo strain studies in dogs show that muscle fatigue following strenuous exercise elevates bone strain and changes strain distribution. However, a similar experiment has yet to be performed in humans. The purpose of this work was to test the hypothesis in humans that strenuous fatiguing exercise causes an elevation in bone strain. It was also hypothesized that this elevation is greater in younger people than in older people due to the decline in muscle strength and endurance that normally occurs with age. To test these hypotheses, strain in the tibiae of seven human volunteers was measured during walking before and after a period of fatiguing exercise. Neither hypothesis was sustained. Post-hoc analysis of the strain data suggests that strain rate increases after fatigue with a greater increase in younger as opposed to older persons. Although not conclusive, this suggests that it is strain rate, rather than strain magnitude, that may be causal for stress fracture. © 1998 Biomedical Engineering Society. PAC98: 8745Dr, 8745Bp, 0180+b
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