Two new size factors of cross-section hollow coefficient and bending degree are introduced to reveal the size effect of bending forming of bimetallic composite tube.Hollow coefficient and bending degree can limit the ...Two new size factors of cross-section hollow coefficient and bending degree are introduced to reveal the size effect of bending forming of bimetallic composite tube.Hollow coefficient and bending degree can limit the commonly used bent tube to the size description range of(0,2.00).The evolution laws of the cross-section distortion forms in the hollow coefficient-bending degree interval are revealed as well as the action of the mandrel-cores on the size effect.Results show the mandrel-cores filling can expand the forming limit of the bent tube,but also bring two other forming defects of wrinkle and rupture.The identification factor(hollow coefficient multiply bending degree)provides a method for querying the cross-section distortion forms of all composite bending tubes.In the identification factor interval(0,1.00),the distribution area of bending forming defects of the composite tube is continuous.The thin-walled composite bending tube collapses when identification factor in(0,0.39),wrinkles when identification factor in[0.39,0.50),and ruptures when identification factor in[0.50,1.00).The mathematical model of size effect is derived,by which the average cross-section distortion rate is found to distribute like a radial leaf in the hollow coefficient-bending degree qualified forming space.The best forming zone is hollow coefficient 0.46-0.68,and bending degree 0.25-0.47.展开更多
The article presents results of the computer simulation of quenching large-size parts in water and aqueous solutions. It has been shown that the main attention should be paid to eliminating film boiling and providing ...The article presents results of the computer simulation of quenching large-size parts in water and aqueous solutions. It has been shown that the main attention should be paid to eliminating film boiling and providing uniform cooling at the surface of the part to be quenched. Simplified formulas for calculating the optimal time of cooling large-size steel parts are presented.展开更多
随着城市化进程中地下空间开发及抗浮问题的凸显,抗拔桩在东南沿海等高水位黏性土地区的应用日益广泛,然而常规钻孔施工工艺面临诸多挑战,如泥皮效应导致桩侧阻力难以达标、扩底成孔困难等。为此,提出考虑扰动效应的束浆挤扩桩抗拔承载...随着城市化进程中地下空间开发及抗浮问题的凸显,抗拔桩在东南沿海等高水位黏性土地区的应用日益广泛,然而常规钻孔施工工艺面临诸多挑战,如泥皮效应导致桩侧阻力难以达标、扩底成孔困难等。为此,提出考虑扰动效应的束浆挤扩桩抗拔承载力计算方法。以上海第(5)1层灰色黏土为对象,建立黏土和砂的弹塑性扰动状态(clay and sand elastic-plastic-disturbed state concept,简称CASM-DSC)模型,精确模拟桩周地基土力学特性。通过用户自定义材料本构(user-defined material mechanical behavior,简称UMAT)子程序,开展数值模拟,分析桩周地基土及挤扩尺寸的扰动效应。修正前期研究的束浆挤扩钢管桩抗拔简化计算方法。结果表明,钻孔开挖显著削弱黏性土的侧阻力,影响桩-土界面的力学性能,扰动系数和范围对地基土应力状态呈二次曲线和线性折减关系。在不同的挤扩长度下,模型桩的极限抗拔承载力随长度增加呈“V”字型特点,且挤扩工艺可改变桩侧受力面积与轴力分布。通过上海徐汇滨江地块的现场试验,验证了简化计算方法的有效性与适用性,其计算误差控制在15%以内,为桩基础工程设计提供了可靠的理论支持与实用计算方法。展开更多
Purpose:We aimed to perform a systematic review and meta-analysis of the effects of training to muscle failure or non-failure on muscular strength and hypertrophy.Methods:Meta-analyses of effect sizes(ESs)explored the...Purpose:We aimed to perform a systematic review and meta-analysis of the effects of training to muscle failure or non-failure on muscular strength and hypertrophy.Methods:Meta-analyses of effect sizes(ESs)explored the effects of training to failure vs.non-failure on strength and hypertrophy.Subgroup meta-analyses explored potential moderating effects of variables such as training status(trained vs.untrained),training volume(volume equated vs.volume non-equated),body region(upper vs.lower),exercise selection(multi-vs.single-joint exercises(only for strength)),and study design(independent vs.dependent groups).Results:Fifteen studies were included in the review.All studies included young adults as participants.Meta-analysis indicated no significant difference between the training conditions for muscular strength(ES=-0.09,95%confidence interval(95%CI):-0.22 to 0.05)and for hypertrophy(ES=0.22,95%CI:-0.11 to 0.55).Subgroup analyses that stratified the studies according to body region,exercise selection,or study design showed no significant differences between training conditions.In studies that did not equate training volume between the groups,the analysis showed significant favoring of non-failure training on strength gains(ES=-0.32,95%CI:-0.57 to-0.07).In the subgroup analysis for resistance-trained individuals,the analysis showed a significant effect of training to failure for muscle hypertrophy(ES=0.15,95%CI:0.03-0.26).Conclusion:Training to muscle failure does not seem to be required for gains in strength and muscle size.However,training in this manner does not seem to have detrimental effects on these adaptations,either.More studies should be conducted among older adults and highly trained individuals to improve the generalizability of these findings.展开更多
Single-crystal rods with different diameters and deviation angles with respect to the solidification direction were produced by Bridgman rapid solidification method at withdrawal rates of 3 and 6 mm·min^(-1) and ...Single-crystal rods with different diameters and deviation angles with respect to the solidification direction were produced by Bridgman rapid solidification method at withdrawal rates of 3 and 6 mm·min^(-1) and used as grain continuators.The crystallographic orientation of the rods,which cross-sections were perpendicular to the solidification direction at different solidification heights,was measured by electron backscattered diffraction,while the corresponding microstructures were observed by optical microscopy.The mushy zone morphology and the distribution of the temperature gradient were simulated by the finite element analysis software ProCAST.The experimental results indicate that the crystallographic orientation of the single-crystal rods corresponds to the statistical average value of all the dendrite orientations in cross-section.The crystallographic orientation of the primary and secondary dendrites of each single-crystal rod at different cross-sections fluctuates irregularly within a small range(less than 4°).The crystallographic orientation of the dendrite in each single-crystal rod is not exactly consistent with each other and is affected by their branching mode of dendrites in the solidification space.In addition,the simulation results show that the mushy zone shapes and the temperature gradient of single-crystal rods change with the increase of solidification height during the solidification process.Finally,the evolution mechanism of the crystallographic orientations and the corresponding influence factors were analyzed and discussed.展开更多
基金co-supported by the National Natural Science Foundation of China(Nos.51601070 and 51875263)the Open Project of Guangdong Key Laboratory of Precision Equipment and Manufacturing Technology,China(No.PEMT202102)the Natural Science Foundation of Jiangsu Province,China(No.BK20181447)。
文摘Two new size factors of cross-section hollow coefficient and bending degree are introduced to reveal the size effect of bending forming of bimetallic composite tube.Hollow coefficient and bending degree can limit the commonly used bent tube to the size description range of(0,2.00).The evolution laws of the cross-section distortion forms in the hollow coefficient-bending degree interval are revealed as well as the action of the mandrel-cores on the size effect.Results show the mandrel-cores filling can expand the forming limit of the bent tube,but also bring two other forming defects of wrinkle and rupture.The identification factor(hollow coefficient multiply bending degree)provides a method for querying the cross-section distortion forms of all composite bending tubes.In the identification factor interval(0,1.00),the distribution area of bending forming defects of the composite tube is continuous.The thin-walled composite bending tube collapses when identification factor in(0,0.39),wrinkles when identification factor in[0.39,0.50),and ruptures when identification factor in[0.50,1.00).The mathematical model of size effect is derived,by which the average cross-section distortion rate is found to distribute like a radial leaf in the hollow coefficient-bending degree qualified forming space.The best forming zone is hollow coefficient 0.46-0.68,and bending degree 0.25-0.47.
文摘The article presents results of the computer simulation of quenching large-size parts in water and aqueous solutions. It has been shown that the main attention should be paid to eliminating film boiling and providing uniform cooling at the surface of the part to be quenched. Simplified formulas for calculating the optimal time of cooling large-size steel parts are presented.
文摘随着城市化进程中地下空间开发及抗浮问题的凸显,抗拔桩在东南沿海等高水位黏性土地区的应用日益广泛,然而常规钻孔施工工艺面临诸多挑战,如泥皮效应导致桩侧阻力难以达标、扩底成孔困难等。为此,提出考虑扰动效应的束浆挤扩桩抗拔承载力计算方法。以上海第(5)1层灰色黏土为对象,建立黏土和砂的弹塑性扰动状态(clay and sand elastic-plastic-disturbed state concept,简称CASM-DSC)模型,精确模拟桩周地基土力学特性。通过用户自定义材料本构(user-defined material mechanical behavior,简称UMAT)子程序,开展数值模拟,分析桩周地基土及挤扩尺寸的扰动效应。修正前期研究的束浆挤扩钢管桩抗拔简化计算方法。结果表明,钻孔开挖显著削弱黏性土的侧阻力,影响桩-土界面的力学性能,扰动系数和范围对地基土应力状态呈二次曲线和线性折减关系。在不同的挤扩长度下,模型桩的极限抗拔承载力随长度增加呈“V”字型特点,且挤扩工艺可改变桩侧受力面积与轴力分布。通过上海徐汇滨江地块的现场试验,验证了简化计算方法的有效性与适用性,其计算误差控制在15%以内,为桩基础工程设计提供了可靠的理论支持与实用计算方法。
文摘Purpose:We aimed to perform a systematic review and meta-analysis of the effects of training to muscle failure or non-failure on muscular strength and hypertrophy.Methods:Meta-analyses of effect sizes(ESs)explored the effects of training to failure vs.non-failure on strength and hypertrophy.Subgroup meta-analyses explored potential moderating effects of variables such as training status(trained vs.untrained),training volume(volume equated vs.volume non-equated),body region(upper vs.lower),exercise selection(multi-vs.single-joint exercises(only for strength)),and study design(independent vs.dependent groups).Results:Fifteen studies were included in the review.All studies included young adults as participants.Meta-analysis indicated no significant difference between the training conditions for muscular strength(ES=-0.09,95%confidence interval(95%CI):-0.22 to 0.05)and for hypertrophy(ES=0.22,95%CI:-0.11 to 0.55).Subgroup analyses that stratified the studies according to body region,exercise selection,or study design showed no significant differences between training conditions.In studies that did not equate training volume between the groups,the analysis showed significant favoring of non-failure training on strength gains(ES=-0.32,95%CI:-0.57 to-0.07).In the subgroup analysis for resistance-trained individuals,the analysis showed a significant effect of training to failure for muscle hypertrophy(ES=0.15,95%CI:0.03-0.26).Conclusion:Training to muscle failure does not seem to be required for gains in strength and muscle size.However,training in this manner does not seem to have detrimental effects on these adaptations,either.More studies should be conducted among older adults and highly trained individuals to improve the generalizability of these findings.
基金supported by the National Natural Science Foundation of China(No.51674235)the National Key Research and Development Program of China(Nos.2017-VI0001-0070 and 2017-VI-0019-0091)。
文摘Single-crystal rods with different diameters and deviation angles with respect to the solidification direction were produced by Bridgman rapid solidification method at withdrawal rates of 3 and 6 mm·min^(-1) and used as grain continuators.The crystallographic orientation of the rods,which cross-sections were perpendicular to the solidification direction at different solidification heights,was measured by electron backscattered diffraction,while the corresponding microstructures were observed by optical microscopy.The mushy zone morphology and the distribution of the temperature gradient were simulated by the finite element analysis software ProCAST.The experimental results indicate that the crystallographic orientation of the single-crystal rods corresponds to the statistical average value of all the dendrite orientations in cross-section.The crystallographic orientation of the primary and secondary dendrites of each single-crystal rod at different cross-sections fluctuates irregularly within a small range(less than 4°).The crystallographic orientation of the dendrite in each single-crystal rod is not exactly consistent with each other and is affected by their branching mode of dendrites in the solidification space.In addition,the simulation results show that the mushy zone shapes and the temperature gradient of single-crystal rods change with the increase of solidification height during the solidification process.Finally,the evolution mechanism of the crystallographic orientations and the corresponding influence factors were analyzed and discussed.
