感应热处理工艺对拖拉机轴类零件扭转强度的影响     

马戈  毛长恩  孔春花  白翎 《拖拉机与农用运输车》2014,(1):70-74

对驱动轮工艺轴进行了7种工艺方案的感应热处理表面强化,然后对工艺轴进行扭转破坏试验。通过对驱动轮工艺轴扭转断裂的研究,为驱动轮轴及承受扭力的轴类零件结构设计、工艺流程设计和热处理技术要求提供指导,从而提高其扭转疲劳强度和使用寿命。  相似文献   

Definition and Mechanical Characteristics of True Stress-Strain   总被引：1，自引：0，他引：1  

LI Yu-lan 《保鲜与加工》2001,(3):58-60

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THE STUDY OF CYCLIC SOFTENING AND HARDENING BEHAVIORS IN A LOW ALLOY STEEL CONTAINING VANADIUM     

Sheng Guangmin Gong Sihong 《保鲜与加工》1988,(5)

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A STUDY OF THE CONSTITUTION OF 42CrMo STEEL AFTER ION NITRIDING-PRECIPITATION HARDENING     

Zhao Yuqin Zhou Shangqi Hu Zhenji Ren Qin 《保鲜与加工》1991,(5):48-53

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35CrMo旋转接头激光表面硬化技术的试验研究     

骆有东 《农机化研究》2006,(3):141-142,145

用L9(34)正交试验法研究35CrMo旋转接头激光相变硬化工艺参数优化组合,分析了旋转接头激光相变硬化方法.试验结果表明:激光相变硬化层硬度比渗氮淬火提高了30%,耐磨性提高了1倍,表面残余应力为压应力;满足了旋转接头工作要求,为改进旋转接头表面处理方法提供了依据.  相似文献   

齿轮激光淬火工艺及性能研究   总被引：3，自引：0，他引：3  

周建忠  杨继昌 《农业机械学报》2002,33(5):93-95,104

采用快速轴流CO2激光器的低阶光束模式和轴向分齿扫描方式，可一次扫描整个齿廓，并获得沿齿廓理想分布的硬化带形状，在优化工艺参数的基础上，对20CrMnTi齿轮进行激光淬火，处理结果为：表明为细针状马氏体组织，硬度为HRC61，硬化层深为0.6mm，且硬化层浓度上的硬度分布几乎无变化梯度，可有效地提高齿轮的耐磨性和接触疲劳强度，齿面的激光淬火解决了常规齿轮渗碳工艺中存在的变形难题，可省去后面的磨齿工序，降低生产成本。  相似文献   

Photoperiodic Regulationof Apical Growth Cessation in Northern Tree Species     

《Journal of Crop Improvement》2013,27(1-2):77-112

Summary

Tree species adapted to the climatic conditions of the northern boreal and subarctic vegetation zones have a capacity to develop a very high level of frost hardiness, even to survive the temperature of liquid nitrogen in midwinter. Proper timing of hardening, as well as of dehardening, is crucial for winter survival of these species. In northern tree species, cessation of apical elongation growth and bud set is a prerequisite for developmental and metabolic processes leading to hardening, and this chain of events is induced by photoperiod. The northern tree species are closely adapted to the local light climate and display photoperiodic ecotypes. The critical photoperiod is under genetic control and increases with increasing latitude of origin of the eco-type. The photoperiod is probably perceived by the phytochrome system, but the role of other pigment systems, like cryptochrome, has not been studied in woody plants. Phytochrome genes have been cloned from both conifers and deciduous species, but so far we do not have any information about possible differences between photoperiodic ecotypes at the phytochrome level. Northern and southern ecotypes have different responses to red:far red ratios, which could indicate differences in composition of their phytochrome systems, for example, the proportions of phytochrome A and B. Both phytochrome A and phytochrome B can be involved in photoperiodic responses. Experiments with transgenic hybrid aspen suggest that responses to photoperiod could be affected by the amount of phytochrome A present in plants. In deciduous species, the plant hormone gibberellin A₁ (GA1) can completely substitute for a long photoperiod, and short day induced cessation of growth is preceded by a significant reduction of GA1 levels, particularly in the elongation zone. Photoperiodic control of GA metabolism is supported by several studies, but very little is known about the interaction between phytochrome and GA metabolism and/or responsiveness to GA1. Although our knowledge is still very fragmentary, available results suggest that cessation of growth and initiation of hardening in trees can be controlled both through the phytochrome and the GA mediated systems. Research with tree species is a tedious and slow process, but with the emerging new methods and approaches, we may expect exciting new results in the near future.  相似文献   

Frost hardiness, bud phenology and growth of containerized Picea mariana seedlings grown at three nitrogen levels and three temperature regimes     

F. J. Bigras  A. Gonzalez  A. L. D'Aoust  C. Hébert 《New Forests》1996,12(3):243-259

We studied the influence of temperature and near- and sub- optimal mineral nutrition of black spruce seedlings (Picea mariana [Mill.] B.S.P.) during their second growing period on bud set, bud development, growth, mineral content and cold tolerance. Bud break and growth after bud break were also studied. Seedlings were grown for 106 d in growth chambers under three temperature regimes in combination with three concentrations of a fertilizer. They were then cold hardened for 56 d and dehardened for 66 d.Under these near- and sub-optimal N levels, bud formation occurred during the growing season. Bud formation was accelerated with decreasing fertilization, but was not affected by temperature treatments. Needles from seedlings with 0.64% N (dry mass basis) before hardening did not harden. Those with 0.87% N showed a lesser degree of hardiness than those with 1.28% N. Stem diameter increased at the beginning of the hardening period. During this acclimation period, shoot dry mass decreased with time at a constant rate and at the same rate over time for all treatments whereas root dry mass was more variable. Total number of needle primordia was low and no difference was observed among growing conditions. Bud break was similar in all treatments. Following bud break, shoot height and stem diameter increases were small but their magnitude varied with the nutritional regimes applied during the previous growing period. During hardening, nitrogen concentration of shoot tissues first increased and then decreased; phosphorus concentration first increased and then remained stable; potassium concentration remained stable. Concentration of these three elements generally decreased in the roots during this hardening.  相似文献   

Strain Hardening Properties and Extensibility of Flour and Gluten Doughs in Relation to Breadmaking Performance     

J.J. Kokelaar  T. van Vliet  A. Prins 《Journal of Cereal Science》1996,24(3):199-214

The mechanical properties of flour–water doughs and hydrated gluten of different wheat cultivars were determined. Measurements were performed at small deformations (dynamic measurements) as well as at large deformations (biaxial extension measurements). Results of dynamic measurements of flour doughs related poorly to breadmaking quality. For hydrated gluten doughs, all having the same water content, it was found that glutens from wheat cultivars with good baking quality had higher values for the storage modulus,G, and lower values for the loss tangent. The relevant type of deformation around an expanding gas bubble is biaxial extension. Wheats with a good baking performance exhibited greater strain hardening and greater extensibility. The differences in strain hardening observed at 20 °C were also present at 55 °C. No clear effects of NaCl or emulsifiers on the biaxial extension properties of flour dough were found. Extensograms as well as Alveograms from the flour doughs showed that, in general, good baking flours exhibited stronger resistance to extension and a greater extensibility, but differences found were not directly related to the results of the baking tests. The results indicate that the baking performance of dough is related to a combination of at least three different rheological characteristics.  相似文献   

Cold tolerance in beans (Phaseolus spp.) as analyzed by their exotherms     

R. Holubowicz  M. H. Dickson 《Euphytica》1989,41(1-2):31-37

Summary Cold tolerance of common bean (Phaseolus vulgaris L.), runner bean (P. coccineus L.) and several bean lines was evaluated under artificial conditions. Seedlings were exposed to –6°C gradually, then to –12°C rapidly in the growth chamber with copper-constantan thermocouples attached to various parts of the plant. Seedling freezing curves with exotherms were then analyzed. Three basic parameters were measured: time required for exotherm to appear, temperature of the appearance of the exotherm and temperature rise caused by the exotherm. Exotherm appearance in beans was related to freezing injury and death of the seedlings. Exotherms of the common bean variety Bush Blue Lake 92 seedling recorded at the stem, primary leaf base, tip and petiole and true leaf appeared at the same time, however their shape was different. Exotherms of stem appeared at higher temperature than those of primary leaves. Their shapes always followed the same pattern. Beans with cold tolerance were found to produce exotherms later than susceptible ones. Exposing 3 weeks old bean seedlings to 12°C delayed the time of exotherm appearance in the cold susceptible cultivar Bush Blue Lake 92. Some plants survived 2 hours exposure to –6°C in the growth chamber.  相似文献