In Haigh Westergaard stress space linear combination of twin shear stress and Tresca yield functions is called the mean yield （MY） criterion. The mathematical relationship of the criterion and its plastic work rate ...In Haigh Westergaard stress space linear combination of twin shear stress and Tresca yield functions is called the mean yield （MY） criterion. The mathematical relationship of the criterion and its plastic work rate done per unit volume were derived. A generalized worked example of slab forging was analyzed by the criterion and its corresponding plastic work rate done per unit volume. Then, the precision of the solution was compared with those by Mises and Twin shear stress yield criterions, respectively. It turned out that the calculated results by MY criterion were in good agreement with those by Mises criterion.展开更多
Currently, for some complex plastic deformations, the analytical solution can not be obtained by using Mises yield criterion, because Mises yield criterion is nine dimensions, the velocity field is complex, and the so...Currently, for some complex plastic deformations, the analytical solution can not be obtained by using Mises yield criterion, because Mises yield criterion is nine dimensions, the velocity field is complex, and the solving methods are not innovative. Corresponding solutions of these problems are that yield criterion is linearized to reduce the variable numbers, and the velocity field and the solving methods are reasonably simplified, respectively. In this paper, a new linear yield criterion--mean yield（MY） criterion and inner-product of strain rate vector are used to analytically solve 3D forging taking into account bugling of sides. The velocity field is expressed as a vector in three dimensions, and rotation and divergence are applied to confirm that the velocity field is kinematically admissible. Then, the corresponding strain rate tensor of the velocity field is transformed into principal one by making the determinant of coefficients of the tensor cubic equation be zero. By using MY criterion, the plastic power is term by term integrated and summed according to inner-product of strain rate vector. An upper bound analytical solution is obtained for the forging, and verified by a pure lead press test. The test result turns out that the total pressure calculated by MY criterion is higher by 2.5%-15% than measuring value. In addition, a measuring formula of bulging parameter （a） is proposed, but the values of a measured by the formula are lower than those optimized by the golden section search. The total pressure calculated by MY criterion is compared with the ones by twin shear, Trasca yield, and Mises yield criterion. The comparing result shows that the total pressure calculated by MY criterion is slightly higher than the mean value of that by twin shear and Trasca yield criterion, and lower than that by Mises yield criterion, but more close to that by Mises yield criterion compared with that by other two. The proposed analytical solving methods can be effectively used to other complex plastic deformation, simplifying the solving process and obtaining the reasonable results.展开更多
冬虫夏草是我国特有的名贵中药材,其道地产区是青藏高原那曲、昌都,青海玉树等地区。最近10年,虫草资源在盲目和过度的采挖中已经到达临界点,如何加快保护、发展和合理利用冬虫夏草这一宝贵资源,已提到了冬虫夏草研究和利用的重要议事...冬虫夏草是我国特有的名贵中药材,其道地产区是青藏高原那曲、昌都,青海玉树等地区。最近10年,虫草资源在盲目和过度的采挖中已经到达临界点,如何加快保护、发展和合理利用冬虫夏草这一宝贵资源,已提到了冬虫夏草研究和利用的重要议事日程。青藏高原生态环境和气候变化比其他地区具有超前变化趋势,这意味着冬虫夏草种群的分布和演化与其他种群比起来更明显和剧烈,该文基于RS(remote sensing,遥感)/GIS(geographic information system,地理信息系统)技术,利用雪线高程,采收期(4,5月)的平均气温,降水量和日照时长等环境因子和虫草产量之间的关系,建立加权几何平均模型,在每年的6月上旬预测当年的虫草产量,经过检验,该模型的精度可达82.16%以上。该研究可为虫草产业的健康、可持续发展提供基础数据和信息。展开更多
1975～1985年,在辽宁西部前所果树农场进行红星苹果矮化中间砧试验研究。中间砧有 M 系的2,4,5,6,7,9,11、16,还有丹麦道生、保加利亚18号及甜黄魁。以山定砧嫁接苗作对照。经过10年试验,对其抗寒性、抗风、嫁接亲和力、开花株率、花序...1975～1985年,在辽宁西部前所果树农场进行红星苹果矮化中间砧试验研究。中间砧有 M 系的2,4,5,6,7,9,11、16,还有丹麦道生、保加利亚18号及甜黄魁。以山定砧嫁接苗作对照。经过10年试验,对其抗寒性、抗风、嫁接亲和力、开花株率、花序座果率,平均株产、树高、树冠体积、根系生长状况及分布、各砧穗组合的丰产相关指标进行了调查研究,并对各组合在前所果树农场自然条件及管理水平情况下的表现特点作出评价。展开更多
基金This research was supported by the National Natural Sci—ence Foundation of China(Grant No.50474015)
文摘In Haigh Westergaard stress space linear combination of twin shear stress and Tresca yield functions is called the mean yield （MY） criterion. The mathematical relationship of the criterion and its plastic work rate done per unit volume were derived. A generalized worked example of slab forging was analyzed by the criterion and its corresponding plastic work rate done per unit volume. Then, the precision of the solution was compared with those by Mises and Twin shear stress yield criterions, respectively. It turned out that the calculated results by MY criterion were in good agreement with those by Mises criterion.
基金supported by National Natural Science Foundation of China (Grant No. 50474015)State Key Laboratory of Rolling and Automation(RAL) Self-determination Science Foundation of UK (Grant No. RAL_SD_2008_2)
文摘Currently, for some complex plastic deformations, the analytical solution can not be obtained by using Mises yield criterion, because Mises yield criterion is nine dimensions, the velocity field is complex, and the solving methods are not innovative. Corresponding solutions of these problems are that yield criterion is linearized to reduce the variable numbers, and the velocity field and the solving methods are reasonably simplified, respectively. In this paper, a new linear yield criterion--mean yield（MY） criterion and inner-product of strain rate vector are used to analytically solve 3D forging taking into account bugling of sides. The velocity field is expressed as a vector in three dimensions, and rotation and divergence are applied to confirm that the velocity field is kinematically admissible. Then, the corresponding strain rate tensor of the velocity field is transformed into principal one by making the determinant of coefficients of the tensor cubic equation be zero. By using MY criterion, the plastic power is term by term integrated and summed according to inner-product of strain rate vector. An upper bound analytical solution is obtained for the forging, and verified by a pure lead press test. The test result turns out that the total pressure calculated by MY criterion is higher by 2.5%-15% than measuring value. In addition, a measuring formula of bulging parameter （a） is proposed, but the values of a measured by the formula are lower than those optimized by the golden section search. The total pressure calculated by MY criterion is compared with the ones by twin shear, Trasca yield, and Mises yield criterion. The comparing result shows that the total pressure calculated by MY criterion is slightly higher than the mean value of that by twin shear and Trasca yield criterion, and lower than that by Mises yield criterion, but more close to that by Mises yield criterion compared with that by other two. The proposed analytical solving methods can be effectively used to other complex plastic deformation, simplifying the solving process and obtaining the reasonable results.
文摘冬虫夏草是我国特有的名贵中药材,其道地产区是青藏高原那曲、昌都,青海玉树等地区。最近10年,虫草资源在盲目和过度的采挖中已经到达临界点,如何加快保护、发展和合理利用冬虫夏草这一宝贵资源,已提到了冬虫夏草研究和利用的重要议事日程。青藏高原生态环境和气候变化比其他地区具有超前变化趋势,这意味着冬虫夏草种群的分布和演化与其他种群比起来更明显和剧烈,该文基于RS(remote sensing,遥感)/GIS(geographic information system,地理信息系统)技术,利用雪线高程,采收期(4,5月)的平均气温,降水量和日照时长等环境因子和虫草产量之间的关系,建立加权几何平均模型,在每年的6月上旬预测当年的虫草产量,经过检验,该模型的精度可达82.16%以上。该研究可为虫草产业的健康、可持续发展提供基础数据和信息。
文摘1975～1985年,在辽宁西部前所果树农场进行红星苹果矮化中间砧试验研究。中间砧有 M 系的2,4,5,6,7,9,11、16,还有丹麦道生、保加利亚18号及甜黄魁。以山定砧嫁接苗作对照。经过10年试验,对其抗寒性、抗风、嫁接亲和力、开花株率、花序座果率,平均株产、树高、树冠体积、根系生长状况及分布、各砧穗组合的丰产相关指标进行了调查研究,并对各组合在前所果树农场自然条件及管理水平情况下的表现特点作出评价。
