The forming performance of sheet metals in the deep-drawing process with ultrasonic vibrations can be improved by the surface effect between the sheet metal and the die.A sheet metal friction test with ultrasonic vibr...The forming performance of sheet metals in the deep-drawing process with ultrasonic vibrations can be improved by the surface effect between the sheet metal and the die.A sheet metal friction test with ultrasonic vibrations is performed to explore the cause of the surface effect.The frictional characteristics are investigated,and the corresponding friction expressions are established based on the contact mechanics and the elastic–plastic contact model for rough surfaces.Friction is caused by the elastic–plastic deformation of contacting asperities under normal loads.The actual contacting region between two surfaces increases with normal loads,whereas the normal distance decreases.The normal distance between the contacting surfaces is changed,asperities generate a tangential deformation with ultrasonic vibrations,and the friction coefficient is eventually altered.Ultrasonic vibrations are applied on a 40Cr steel punch at the frequency of 20 kHz and the amplitude of 4.2μm.In the friction tests,the punch is perpendicular to the surface of the magnesium alloy AZ31B sheet metals and is sliding with a relative velocity of 1 mm/s.The test results show that the friction coefficient is decreased by approximately 40%and the theoretical values are in accordance with the test values;Ultrasonic vibrations can clearly reduce wear and improve the surface quality of parts.展开更多
苏中地区为稻麦两熟制地区,近年来受气候变化和稻虾综合种养规模扩大的影响,水稻迟播迟栽现象较为普遍,使水稻品种的生长发育等与光、温资源不匹配,成为制约水稻高产稳产的重要因素之一。本研究在迟播迟栽(6月12日播种、6月30日移栽)条...苏中地区为稻麦两熟制地区,近年来受气候变化和稻虾综合种养规模扩大的影响,水稻迟播迟栽现象较为普遍,使水稻品种的生长发育等与光、温资源不匹配,成为制约水稻高产稳产的重要因素之一。本研究在迟播迟栽(6月12日播种、6月30日移栽)条件下,采用毯苗机插方式,设置4个纯氮施氮量(N_(0):0 kg hm^(-2);N_(240):240 kg hm^(-2);N_(300):300 kg hm^(-2);N360:360 kg hm^(-2))、3个穴栽苗株数(D_(3):3株苗、D_(4):4株苗、D_(5):5株苗)处理,以适播适栽期(5月29日)常规施氮量和穴栽苗株数处理(N300D4)为对照(CK),探究氮肥水平与穴栽苗数对迟播迟栽粳稻生长发育和产量形成的影响,为提升苏中地区迟播迟栽粳稻产量潜力和资源利用效率提供依据。结果表明,较CK相比,迟播迟栽条件下各处理产量均下降,主要原因是迟播迟栽处理群体颖花量显著降低,2年最高群体颖花量分别较CK分别降低11.94%和8.12%;迟播迟栽条件下温光资源利用率降低,植株吸氮量和氮肥利用率降低,导致干物质积累量降低。迟播迟栽条件下,除处理N_(360)D_(5)外,随着施氮量和穴栽苗株数的增加,产量增加。主要原因是提高了群体颖花量,抽穗期叶面积指数和高效叶比例,延长了生育期,从而提高了温光资源利用率,进而提高了成熟期干物质积累量,缓解产量下降;另外,氮肥利用率随施氮量增加呈先增加后下降趋势,N_(300)D_(5)处理氮肥利用率最大。因此,迟播迟栽条件下应首先考虑增加穴栽苗数,再适量增加氮肥施用量,可以缓解产量损失,并提高氮肥利用率。展开更多
基金Projects(51775480,51305385)supported by the National Natural Science Foundation of ChinaProject(E2018203143)supported by the Natural Science Foundation of Hebei Province,China
文摘The forming performance of sheet metals in the deep-drawing process with ultrasonic vibrations can be improved by the surface effect between the sheet metal and the die.A sheet metal friction test with ultrasonic vibrations is performed to explore the cause of the surface effect.The frictional characteristics are investigated,and the corresponding friction expressions are established based on the contact mechanics and the elastic–plastic contact model for rough surfaces.Friction is caused by the elastic–plastic deformation of contacting asperities under normal loads.The actual contacting region between two surfaces increases with normal loads,whereas the normal distance decreases.The normal distance between the contacting surfaces is changed,asperities generate a tangential deformation with ultrasonic vibrations,and the friction coefficient is eventually altered.Ultrasonic vibrations are applied on a 40Cr steel punch at the frequency of 20 kHz and the amplitude of 4.2μm.In the friction tests,the punch is perpendicular to the surface of the magnesium alloy AZ31B sheet metals and is sliding with a relative velocity of 1 mm/s.The test results show that the friction coefficient is decreased by approximately 40%and the theoretical values are in accordance with the test values;Ultrasonic vibrations can clearly reduce wear and improve the surface quality of parts.
文摘苏中地区为稻麦两熟制地区,近年来受气候变化和稻虾综合种养规模扩大的影响,水稻迟播迟栽现象较为普遍,使水稻品种的生长发育等与光、温资源不匹配,成为制约水稻高产稳产的重要因素之一。本研究在迟播迟栽(6月12日播种、6月30日移栽)条件下,采用毯苗机插方式,设置4个纯氮施氮量(N_(0):0 kg hm^(-2);N_(240):240 kg hm^(-2);N_(300):300 kg hm^(-2);N360:360 kg hm^(-2))、3个穴栽苗株数(D_(3):3株苗、D_(4):4株苗、D_(5):5株苗)处理,以适播适栽期(5月29日)常规施氮量和穴栽苗株数处理(N300D4)为对照(CK),探究氮肥水平与穴栽苗数对迟播迟栽粳稻生长发育和产量形成的影响,为提升苏中地区迟播迟栽粳稻产量潜力和资源利用效率提供依据。结果表明,较CK相比,迟播迟栽条件下各处理产量均下降,主要原因是迟播迟栽处理群体颖花量显著降低,2年最高群体颖花量分别较CK分别降低11.94%和8.12%;迟播迟栽条件下温光资源利用率降低,植株吸氮量和氮肥利用率降低,导致干物质积累量降低。迟播迟栽条件下,除处理N_(360)D_(5)外,随着施氮量和穴栽苗株数的增加,产量增加。主要原因是提高了群体颖花量,抽穗期叶面积指数和高效叶比例,延长了生育期,从而提高了温光资源利用率,进而提高了成熟期干物质积累量,缓解产量下降;另外,氮肥利用率随施氮量增加呈先增加后下降趋势,N_(300)D_(5)处理氮肥利用率最大。因此,迟播迟栽条件下应首先考虑增加穴栽苗数,再适量增加氮肥施用量,可以缓解产量损失,并提高氮肥利用率。
