Estrogen withdrawal in postmenopausal women increases bone loss and bone fragility in the vertebra. Bone loss with osteoporosis not only reduces bone mineral density (BMD), but actually alters bone quality, which can ...Estrogen withdrawal in postmenopausal women increases bone loss and bone fragility in the vertebra. Bone loss with osteoporosis not only reduces bone mineral density (BMD), but actually alters bone quality, which can be comprehensively represented by bone post-yield behaviors. This study aimed to provide some information as to how osteoporosis induced by estrogen depletion could influence the evolution of post-yield microdamage accumulation and plastic deformation in vertebral bodies. This study also tried to reveal the part of the mechanisms of how estrogen deficiency-induced osteoporosis would increase the bone fracture risk. A rat bilateral ovariectomy (OVX) model was used to induce osteoporosis. Progressive cyclic compression loading was developed for vertebra testing to elucidate the post-yield behaviors. BMD, bone volume fraction, stiffness degradation, and plastic deformation evolution were compared among rats raised for 5 weeks (ovx5w and sham5w groups) and 35 weeks (ovx35w and sham35w groups) after sham surgery and OVX. The results showed that a higher bone loss in vertebral bodies corresponded to lower stiffness and higher plastic deformation. Thus, osteoporosis could increase the vertebral fracture risk probably through microdamage accumulation and plastic deforming degradation.展开更多
The perfect single crystal has ultra-high strength but is often accompanied by catastrophic failures after yielding.This study reveals that nano-lamellar TiAl single crystals alleviate the catastrophic failure due to ...The perfect single crystal has ultra-high strength but is often accompanied by catastrophic failures after yielding.This study reveals that nano-lamellar TiAl single crystals alleviate the catastrophic failure due to a post-yielding dislocation retraction through atomistic simulations and theoretical analyses.This dislocation retraction leads to a retained post-yielding strength of1.03 to 2.33 GPa(about 50%of the yielding strength).It is shown that this dislocation retraction is caused by local stress relaxation and interface-mediated image force.The local stress relaxation is due to successive dislocation nucleation in different slip systems,and the interface-mediated image force is caused by the heterogeneous interface.Based on dislocation theory,this study demonstrates that the size effect also plays a vital role in dislocation retraction.Theoretical modeling shows that the dislocation retraction occurs when the lamellar thickness is less than approximately 12 nm.Additionally,the post-yielding dislocation retraction is more pronounced at higher temperatures,making it more effective in alleviating catastrophic failures.These findings demonstrate a viable option for avoiding catastrophic failure of single crystals through nanoscale-lamellar design.展开更多
具有屈服后硬化刚度减震结构的输入能计算中,等效速度谱一般通过改变结构阻尼比获得,这与实际不符,而不同的反应谱对输入能的计算精度影响较大。本文旨在构建综合考虑结构参数、场地类别和地震类型的等效速度谱,为相关减震结构能量设计...具有屈服后硬化刚度减震结构的输入能计算中,等效速度谱一般通过改变结构阻尼比获得,这与实际不符,而不同的反应谱对输入能的计算精度影响较大。本文旨在构建综合考虑结构参数、场地类别和地震类型的等效速度谱,为相关减震结构能量设计提供参考。基于此,首先,建立了考虑屈服后硬化刚度影响的能量平衡方程及其运动方程,并构建了具有屈服后硬化刚度单自由度(single degree of freedom,SDOF)体系等效速度谱计算程序;其次,选取了不同场地类别和地震类型的120条地震记录,利用上述程序分析了屈服后硬化刚度、阻尼比、延性系数、场地类别和地震类型等五种因素对等效速度的影响规律;最后,利用数据拟合工具提出了综合考虑多因素影响的等效速度谱计算公式并与程序计算结果对比。研究表明:等效速度随硬化刚度系数的增大呈减小趋势,但对等效速度谱的下降段影响较小,同时,等效速度随延性系数和阻尼比增大也有减小趋势,但阻尼比影响更为显著。展开更多
基金supported by the National Natural Science Foundation of China (Grants 11472017, 11002004)
文摘Estrogen withdrawal in postmenopausal women increases bone loss and bone fragility in the vertebra. Bone loss with osteoporosis not only reduces bone mineral density (BMD), but actually alters bone quality, which can be comprehensively represented by bone post-yield behaviors. This study aimed to provide some information as to how osteoporosis induced by estrogen depletion could influence the evolution of post-yield microdamage accumulation and plastic deformation in vertebral bodies. This study also tried to reveal the part of the mechanisms of how estrogen deficiency-induced osteoporosis would increase the bone fracture risk. A rat bilateral ovariectomy (OVX) model was used to induce osteoporosis. Progressive cyclic compression loading was developed for vertebra testing to elucidate the post-yield behaviors. BMD, bone volume fraction, stiffness degradation, and plastic deformation evolution were compared among rats raised for 5 weeks (ovx5w and sham5w groups) and 35 weeks (ovx35w and sham35w groups) after sham surgery and OVX. The results showed that a higher bone loss in vertebral bodies corresponded to lower stiffness and higher plastic deformation. Thus, osteoporosis could increase the vertebral fracture risk probably through microdamage accumulation and plastic deforming degradation.
基金supported by the National Key Research and Development Program of China(Grant No.2019YFA0705400)the National Natural Science Foundation of China(Grant No.51535005)+2 种基金the Research Fund of State Key Laboratory of Mechanics and Control of Mechanical Structures(Grant No.MCMS-I-0419K01)the Fundamental Research Funds for the Central Universities(Grant Nos.NJ2020003,and NZ2020001)a Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions。
文摘The perfect single crystal has ultra-high strength but is often accompanied by catastrophic failures after yielding.This study reveals that nano-lamellar TiAl single crystals alleviate the catastrophic failure due to a post-yielding dislocation retraction through atomistic simulations and theoretical analyses.This dislocation retraction leads to a retained post-yielding strength of1.03 to 2.33 GPa(about 50%of the yielding strength).It is shown that this dislocation retraction is caused by local stress relaxation and interface-mediated image force.The local stress relaxation is due to successive dislocation nucleation in different slip systems,and the interface-mediated image force is caused by the heterogeneous interface.Based on dislocation theory,this study demonstrates that the size effect also plays a vital role in dislocation retraction.Theoretical modeling shows that the dislocation retraction occurs when the lamellar thickness is less than approximately 12 nm.Additionally,the post-yielding dislocation retraction is more pronounced at higher temperatures,making it more effective in alleviating catastrophic failures.These findings demonstrate a viable option for avoiding catastrophic failure of single crystals through nanoscale-lamellar design.
文摘具有屈服后硬化刚度减震结构的输入能计算中,等效速度谱一般通过改变结构阻尼比获得,这与实际不符,而不同的反应谱对输入能的计算精度影响较大。本文旨在构建综合考虑结构参数、场地类别和地震类型的等效速度谱,为相关减震结构能量设计提供参考。基于此,首先,建立了考虑屈服后硬化刚度影响的能量平衡方程及其运动方程,并构建了具有屈服后硬化刚度单自由度(single degree of freedom,SDOF)体系等效速度谱计算程序;其次,选取了不同场地类别和地震类型的120条地震记录,利用上述程序分析了屈服后硬化刚度、阻尼比、延性系数、场地类别和地震类型等五种因素对等效速度的影响规律;最后,利用数据拟合工具提出了综合考虑多因素影响的等效速度谱计算公式并与程序计算结果对比。研究表明:等效速度随硬化刚度系数的增大呈减小趋势,但对等效速度谱的下降段影响较小,同时,等效速度随延性系数和阻尼比增大也有减小趋势,但阻尼比影响更为显著。
