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异径弯管的无力矩环向应力解析解 被引量:3
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作者 陈孙艺 柳曾典 +1 位作者 陈进 何录武 《压力容器》 北大核心 2007年第2期35-39,共5页
提出以异径管单位高度(长度)的直径变化程度作为反映异径管结构特征的无因次量,并定义为异径系数。根据异径弯管横截面管径随经向弯角而变化及其锥形结构的两个特点,推导了内压作用下异径弯管无力矩环向应力式,最大环向应力位于大端内... 提出以异径管单位高度(长度)的直径变化程度作为反映异径管结构特征的无因次量,并定义为异径系数。根据异径弯管横截面管径随经向弯角而变化及其锥形结构的两个特点,推导了内压作用下异径弯管无力矩环向应力式,最大环向应力位于大端内侧。该式可以作为工程中常见回转壳无力矩环向应力式的任意条件式,等径弯管、直管及异径直管的环向应力公式均是异径弯管环向应力式的一个特定条件的特例,本质上这些公式均是环向应力的薄膜解。计算环向薄膜应力时,一般来说,工程中各种异径管与连接直管之间的边缘应力可以忽略。 展开更多
关键词 环向应力 异径度 弯头 径弯管
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Interclonal and within-tree variation in wood properties of poplar clones 被引量:5
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作者 方升佐 杨文忠 《Journal of Forestry Research》 SCIE CAS CSCD 2003年第4期263-268,共6页
The wood basic density, cellulose content and fiber form were investigated for all sample trees at breast height (1.3 m) in seven poplar clones, and at 0 (butt), 5.6, 9.6, 13.6, 17.6, 19.6 and 21.6 m for clone Nanlin-... The wood basic density, cellulose content and fiber form were investigated for all sample trees at breast height (1.3 m) in seven poplar clones, and at 0 (butt), 5.6, 9.6, 13.6, 17.6, 19.6 and 21.6 m for clone Nanlin-95 and Nanlin-895, respectively, for providing information on variation patterns of wood density, fiber characteristics and holocellulose content within trees and among clones. The results showed that significant variations about wood density, cellulose content, fiber diameter and the ratio of fiber length to diameter existed among poplar clones examined. Variance analysis indicated that there were significant differences in wood basic density, fiber length, fiber diameter and cellulose content among the growth rings, which had an increasing tendency along the direction from pith to bark. The significant differences also existed in wood basic density, fiber length and fiber diameter at different tree height. The mean wood basic density had a general increase trend with increasing height of trees and the lowest was found at the base, while fiber length and fiber diameter had a general decline pattern with increasing height of trees and the biggest value was observed at the height of 5.6 m. Regression analysis indicated that the relationship between examined wood properties and growth ring number (cambial age), and the relationship between examined wood properties and tree height can be described by polynomial functions. 展开更多
关键词 Poplar clone Wood basic density Fiber characteristics Cellulose content Clonal variation Within-tree variation
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