The isothermal local loading forming technology provides a feasible way to form Ti-alloy large-scale rib-web components in aerospace and aviation fields.However,the local loading process forming limit is restricted by...The isothermal local loading forming technology provides a feasible way to form Ti-alloy large-scale rib-web components in aerospace and aviation fields.However,the local loading process forming limit is restricted by forming defects in the transitional region.In this work,the feasibility of controlling forming defects and improving the process forming limit by adjusting die parameters is explored through finite element（FE） simulation.It is found that the common cavum and folding defects in the transitional region are significantly influenced by the fillet radii of left rib and middle rib,respectively.The cavum and folding defects can be effectively controlled by increasing the fillet radii of left rib and middle rib,respectively.The process forming limits considering forming defects in the transitional region are determined by the stepwise searching method under various die parameters.Moreover,the relationship between the process forming limit and die parameters is developed through the response surface methodology（RSM）.The developed RSM models suggest that increasing the fillet radii of left and middle ribs is effective to improve the process forming limit during local loading forming of rib-web components.The results will provide technical basis for the design of die parameters and the reduction amount,which is of great importance to control forming defects and improve the process forming limit in local loading forming of Ti-alloy large-scale rib-web components.展开更多
解释群落的物种多样性大小是生态学研究的一个重要的理论和实践问题。人们提出了群落物种多样性的多种假说,Zobel等人提出的种库假说(species pool hypothesis)是生物多样性理论研究的重要发展。该假说认为,一个群落的物种多样性不仅与...解释群落的物种多样性大小是生态学研究的一个重要的理论和实践问题。人们提出了群落物种多样性的多种假说,Zobel等人提出的种库假说(species pool hypothesis)是生物多样性理论研究的重要发展。该假说认为,一个群落的物种多样性不仅与环境条件和生态过程(ecological process)(如竞争、捕食)有关,也受区域种库(regional species pool)的限制。区域种库是指一个地区可进入某一群落的潜在物种数量,它由地史过程(如冰期、地质年代)和区域过程(物种形成、迁移扩散以及消亡)所决定。按照种库假说,某一生境类型的面积越大,地质年代越古老,物种形成的机会也就越多,因而能适应和分布于该生境的物种也就越多,实际群落中的物种丰富度也就越高。种库在空间上主要有两个层次:区域种库和实际种库,前者指某一生境所拥有的潜在物种数量,主要由生物地理过程(biogeographic processes)所决定;后者则为调查的群落中实际出现的物种数量,主要由竞争等生态过程和区域种库共同决定。本文对种库假说的基本概念、主要内容、种库确定方法等作了介绍,并阐述了作者对这些问题的理解和认识。展开更多
干热河谷植被是我国极为特殊的一种干旱植被类型。种库假说(species pool hypothesis)是生物多样性理论的重要发展,对揭示干热河谷植物群落构建、物种组成和多样性维持机理具有重要的理论和实践意义。本文利用种库假说的理论和方法,对...干热河谷植被是我国极为特殊的一种干旱植被类型。种库假说(species pool hypothesis)是生物多样性理论的重要发展,对揭示干热河谷植物群落构建、物种组成和多样性维持机理具有重要的理论和实践意义。本文利用种库假说的理论和方法,对金沙江干热河谷典型地段——元谋坝区不同类型植物群落实际种库和局域种库的组成特征进行了比较研究。结果显示:在局域种库中,种子植物属和种的数目最多的3个科均为禾本科、蝶形花科和菊科,热带分布的属占绝对优势;在实际种库中,大多数人工恢复植物群落在属和种的组成特征上均以单个科的植物(禾本科或蝶形花科)占绝对优势,受到局域过程,如竞争、捕食和环境变动(干扰)等因素的影响更加明显;天然次生植物群落和极少量人工恢复植物群落,在属和种的组成特征上呈现更加多元化的特点,除禾本科、蝶形花科和大戟科等植物占明显优势以外,唇形科、菊科和莎草科等植物也较为丰富,受到局域种库的显著影响;所有植物群落的实际种库在植物区系特征上均与局域种库呈显著相关。研究结果表明:尽管不同立地条件下植物群落的实际种库与局域种库之间的相关性存在差异,但实际种库的大小主要还是由局域种库决定的;因此,实现区域内退化植物群落的生态恢复和生物多样性保护需要准确估算局域种库的大小。展开更多
基金the support of the National Natural Science Foundation of China(Nos.51605388,51675433)111 Project(B08040)+2 种基金the Research Fund of the State Key Laboratory of Solidification Processing(NWPU)in China(Grant No.131-QP-2015)the Fundamental Research Funds for the Central Universitiesthe Open Research Fund of State Key Laboratory of Materials Processing and Die&Mold Technology at Huazhong University of Science and Technology
文摘The isothermal local loading forming technology provides a feasible way to form Ti-alloy large-scale rib-web components in aerospace and aviation fields.However,the local loading process forming limit is restricted by forming defects in the transitional region.In this work,the feasibility of controlling forming defects and improving the process forming limit by adjusting die parameters is explored through finite element（FE） simulation.It is found that the common cavum and folding defects in the transitional region are significantly influenced by the fillet radii of left rib and middle rib,respectively.The cavum and folding defects can be effectively controlled by increasing the fillet radii of left rib and middle rib,respectively.The process forming limits considering forming defects in the transitional region are determined by the stepwise searching method under various die parameters.Moreover,the relationship between the process forming limit and die parameters is developed through the response surface methodology（RSM）.The developed RSM models suggest that increasing the fillet radii of left and middle ribs is effective to improve the process forming limit during local loading forming of rib-web components.The results will provide technical basis for the design of die parameters and the reduction amount,which is of great importance to control forming defects and improve the process forming limit in local loading forming of Ti-alloy large-scale rib-web components.
文摘解释群落的物种多样性大小是生态学研究的一个重要的理论和实践问题。人们提出了群落物种多样性的多种假说,Zobel等人提出的种库假说(species pool hypothesis)是生物多样性理论研究的重要发展。该假说认为,一个群落的物种多样性不仅与环境条件和生态过程(ecological process)(如竞争、捕食)有关,也受区域种库(regional species pool)的限制。区域种库是指一个地区可进入某一群落的潜在物种数量,它由地史过程(如冰期、地质年代)和区域过程(物种形成、迁移扩散以及消亡)所决定。按照种库假说,某一生境类型的面积越大,地质年代越古老,物种形成的机会也就越多,因而能适应和分布于该生境的物种也就越多,实际群落中的物种丰富度也就越高。种库在空间上主要有两个层次:区域种库和实际种库,前者指某一生境所拥有的潜在物种数量,主要由生物地理过程(biogeographic processes)所决定;后者则为调查的群落中实际出现的物种数量,主要由竞争等生态过程和区域种库共同决定。本文对种库假说的基本概念、主要内容、种库确定方法等作了介绍,并阐述了作者对这些问题的理解和认识。
文摘干热河谷植被是我国极为特殊的一种干旱植被类型。种库假说(species pool hypothesis)是生物多样性理论的重要发展,对揭示干热河谷植物群落构建、物种组成和多样性维持机理具有重要的理论和实践意义。本文利用种库假说的理论和方法,对金沙江干热河谷典型地段——元谋坝区不同类型植物群落实际种库和局域种库的组成特征进行了比较研究。结果显示:在局域种库中,种子植物属和种的数目最多的3个科均为禾本科、蝶形花科和菊科,热带分布的属占绝对优势;在实际种库中,大多数人工恢复植物群落在属和种的组成特征上均以单个科的植物(禾本科或蝶形花科)占绝对优势,受到局域过程,如竞争、捕食和环境变动(干扰)等因素的影响更加明显;天然次生植物群落和极少量人工恢复植物群落,在属和种的组成特征上呈现更加多元化的特点,除禾本科、蝶形花科和大戟科等植物占明显优势以外,唇形科、菊科和莎草科等植物也较为丰富,受到局域种库的显著影响;所有植物群落的实际种库在植物区系特征上均与局域种库呈显著相关。研究结果表明:尽管不同立地条件下植物群落的实际种库与局域种库之间的相关性存在差异,但实际种库的大小主要还是由局域种库决定的;因此,实现区域内退化植物群落的生态恢复和生物多样性保护需要准确估算局域种库的大小。
