Timothy L. Norman

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Increased bone fragility and osteoporotic fracture in human bone has been attributed to the accumulation of microdamage. According to Martin and Burr (J Biomech 15:137-139; 1982), microcracks from interstitial bone propagate to the cement line or concentric lamellae and debond or separate the Haversian canal from the surrounding bone which leads to repair(More)
The fracture toughness of the right femoral neck, femoral shaft, and tibial shaft of matched cadaveric bones, ages 50 to 90 years, was compared. Results of this study indicate that tensile (G(Ic)) and shear (G(IIc)) fracture toughness vary depending on bone location. The femoral neck has the greatest resistance to crack initiation for both tension and shear(More)
It has been proposed that longitudinal shear stresses create bone microdamage, which suggests that bone is weak in shear and may not be adapted to prevent crack growth under shear loading. However, based on the similarities between bone and other fiber-reinforced composites that are tough, i.e. resistant to crack growth, we hypothesized that resistance of(More)
The effects of porosity and pore size; osteonal area, size, and density; mineral content; water content; wet and dry apparent densities; and age on mode I (tensile) and mode II (shear) strain energy release rate were investigated for femoral neck cortical bone from human cadavers aged >/=50 years. The results suggest that porosity- and density-based(More)
Sixteen paired human cadaver femora were prepared using conventional broaches. Cancellous bone was irrigated with 1 L pulsed lavage in one femur and 1 L syringe lavage in the contralateral femur. The specimens were embedded in specially designed pots, and vacuum-mixed bone-cements were applied in a retrograde manner. After application of a standard pressure(More)
This study was concerned with the mechanics and micromechanisms of diffuse (ultrastructural) damage occurrence in human tibial cortical bone specimens subjected to tension-tension fatigue. A nondestructive technique was developed for damage assessment on the surfaces of intact compact tension specimens using laser scanning confocal microscopy. Results(More)
The seroconversion by indirect ELISA to Cowdria ruminantium over the first year of life of sixty-six Malawi zebu calves born into groups which were dipped 17 times per year was compared to seroconversion of 32 calves born into non-dipped groups. Amblyomma variegatum tick counts and clinical disease in each group of cattle were monitored throughout the study(More)
BACKGROUND Loss of bone and skeletal muscle atrophy resulting from non-weight-bearing are major concerns associated with microgravity environment and spaceflight deconditioning. The objective of this research was to address the fundamental issue of whether bone loss and muscle atrophy could be attenuated using weight-bearing aerobic exercise on a treadmill(More)
The longitudinal fracture toughnesses of human cortical bone were compared to those of bovine cortical bone to test the hypothesis that although human osteonal bone is significantly weaker and more compliant than primary (plexiform) bone, it is not less tough than primary bone. The fracture toughness indices, critical strain energy release rate (Gc) and(More)
The influence of porosity, osteon density, osteonal area, osteonal lamellar area, osteon size, and haversian canal size on the tension and shear fracture toughness, that is, the mode I and mode II strain energy release rate (GIc and GIIc), respectively, were investigated for the human femur and the tibia. The results suggest that porosity and osteon density(More)