Various proportional and nonproportional tension-torsion fatigue tests are conducted on aeronautical material-LY12CZ aluminum alloy. The stress and strain states under tension-torsion loading are analyzed by an elasti...Various proportional and nonproportional tension-torsion fatigue tests are conducted on aeronautical material-LY12CZ aluminum alloy. The stress and strain states under tension-torsion loading are analyzed by an elastic-plastic finite element method. The relation between the orientation of crack propagation and each stress and strain component is investigated. Analytical results are compared with experimental data. Results demonstrate that the fatigue cracks tend to be propagated perpendicular to the direction of the largest principle strains under proportional loading, and grow alone one of the maximum shear strain planes under 45° and 90° out-of-phase loadings.展开更多
Objective： To validate the hypothesis that there exists an optimal axial compression stress range to enhance tibial fracture healing.Methods： Rabbits with a surgically induced V-shaped tibial fracture were separated...Objective： To validate the hypothesis that there exists an optimal axial compression stress range to enhance tibial fracture healing.Methods： Rabbits with a surgically induced V-shaped tibial fracture were separated into 2 main groups： the control group （C Group, n=6） without application of any axial compression stress stimulation postoperatively and the stimulation group （ S Group, n=90）. The S Group was further divided into 20 subgroups （S11 to S54） in terms of 5 axial compression stress stimulation levels （112.8 kPa, 289.8kPa, 396.5 kPa, 472.7 kPa, and 602.3 kPa） and 4 experimental endpoints （1, 3, 5 and 8 weeks after operation）. A custom made circular external fixator was used to provide the axial compression stress of the fracture sites. Based on X-ray observation, a fracture healing scoring system was created to evaluate the fracture healing process.Results： At 8 weeks after operation, there existed a ＂⌒-shape＂ relationship between healing score and axial compression stress stimulation level of fracture site. The optimal axial compression stress stimulation ranged from 289.8 kPa to 472.7 kPa, accompanying the best fracture healing, i.e. the fracture line became indistinct or almost disappeared, and a lot of callus jointed the two fracture ends. Meanwhile, at 5 weeks after operation, corresponding to the relatively low healing scores, there was a fracture healing performance similar to that at 8 weeks. Besides, at 1 or 3 weeks after operation, for all the axial compression stress levels （0-602.3 kPa）, no obvious healing effect was found.Conclusions： It is implied from the stated X-ray observation results in this study that the potential optimal axial compression stress stimulation and optimal fracture healing time are available. The axial compression stress level of 289.8-472.7 kPa and fracture healing time of more than 8 weeks jointly comprise the optimal axial compression stress stimulation conditions to enhance tibial fracture healing.展开更多
文摘Various proportional and nonproportional tension-torsion fatigue tests are conducted on aeronautical material-LY12CZ aluminum alloy. The stress and strain states under tension-torsion loading are analyzed by an elastic-plastic finite element method. The relation between the orientation of crack propagation and each stress and strain component is investigated. Analytical results are compared with experimental data. Results demonstrate that the fatigue cracks tend to be propagated perpendicular to the direction of the largest principle strains under proportional loading, and grow alone one of the maximum shear strain planes under 45° and 90° out-of-phase loadings.
基金This work was supported by grants from the Chongqing Academician Foundation （No. 1998-93）, the National Natural Science Foundation of China （No. 30122202 and No. 30928005） and the Third Military Medical University Research Foundation （No. 2009 XHG16）,
文摘Objective： To validate the hypothesis that there exists an optimal axial compression stress range to enhance tibial fracture healing.Methods： Rabbits with a surgically induced V-shaped tibial fracture were separated into 2 main groups： the control group （C Group, n=6） without application of any axial compression stress stimulation postoperatively and the stimulation group （ S Group, n=90）. The S Group was further divided into 20 subgroups （S11 to S54） in terms of 5 axial compression stress stimulation levels （112.8 kPa, 289.8kPa, 396.5 kPa, 472.7 kPa, and 602.3 kPa） and 4 experimental endpoints （1, 3, 5 and 8 weeks after operation）. A custom made circular external fixator was used to provide the axial compression stress of the fracture sites. Based on X-ray observation, a fracture healing scoring system was created to evaluate the fracture healing process.Results： At 8 weeks after operation, there existed a ＂⌒-shape＂ relationship between healing score and axial compression stress stimulation level of fracture site. The optimal axial compression stress stimulation ranged from 289.8 kPa to 472.7 kPa, accompanying the best fracture healing, i.e. the fracture line became indistinct or almost disappeared, and a lot of callus jointed the two fracture ends. Meanwhile, at 5 weeks after operation, corresponding to the relatively low healing scores, there was a fracture healing performance similar to that at 8 weeks. Besides, at 1 or 3 weeks after operation, for all the axial compression stress levels （0-602.3 kPa）, no obvious healing effect was found.Conclusions： It is implied from the stated X-ray observation results in this study that the potential optimal axial compression stress stimulation and optimal fracture healing time are available. The axial compression stress level of 289.8-472.7 kPa and fracture healing time of more than 8 weeks jointly comprise the optimal axial compression stress stimulation conditions to enhance tibial fracture healing.
