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采用干冰急冷、自然冷却和250℃×2 h低温回火三种方式对焊接接头进行焊后处理。通过光学显微镜、显微硬度试验,研究三种焊后处理对Q690钢焊接热影响区粗晶区(CGHAZ)组织及硬度的影响。结果表明:当焊后处理由干冰急冷向自然冷却、250℃×2 h回火改变时,CGHAZ显微组织由以板条马氏体为主改变为板条贝氏体为主,并有少量粒状贝氏体产生。焊后处理对焊缝显微硬度影响较大,对CGHAZ的显微硬度影响程度较小,自然冷却和250℃×2 h回火,可避免焊缝形成淬硬组织,缓解焊缝区的应力状态。 相似文献
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齿轮激光淬火工艺及性能研究 总被引:3,自引:0,他引:3
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
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稀土元素对渗硼层显微硬度、耐磨性能的影响 总被引:3,自引:0,他引:3
渗硼层本身具有较高的硬度及耐磨性,但其脆性大,易剥落,又影响其使用效果。稀土元素对渗硼层的显微组织具有明显影响,如硼化物组织致密、晶粒细化、硬度梯度变缓等,同时由于其独特的微合金化作用、固溶强化作用和对晶界的净化作用,使得硼化物的硬度提高而脆性下降,从而使得硼化物层的耐磨性能明显提高。 相似文献
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为了探究水射流空化对NiTi形状记忆合金的显微组织和性能的影响机制,采用水射流空化发生装置在自来水介质中对NiTi形状记忆合金进行不同时间的射流空化试验,并借助SEM,XRD,TEM、显微维氏硬度计、纳米压痕仪、激光共聚焦显微镜对样品的显微组织、物相和性能进行表征.结果表明:在射流空化20 min内,NiTi形状记忆合金表面显微硬度和超弹性均随射流时间的延长而增加;当射流时间为15 min时,NiTi形状记忆合金中出现大量位错,表面显微硬度HV达到最大值340.35(载荷约为0.245 N),与原样相比提高约34%;水射流空化对NiTi合金的影响层深度约为300μm;以纳米压痕能量恢复率来衡量合金的超弹性,在水射流空化15 min内,合金的弹性能量恢复率从38.25%提升至45.70%,表明水射流空化处理可有效提升试样的超弹性;NiTi形状记忆合金中显微硬度和超弹性的提升可归因于合金中的位错增殖. 相似文献
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《拖拉机与农用运输车》2015,(3):58-59
针对某农机主要轴类零件,经感应淬火后,对淬火层深度的测量,一般采用硬度法测量感应淬火层深度,即有效硬化层法来作为仲裁的方法。通过大量试验发现,有效硬化层法在测量感应淬火层深度时存在一定程度的测量盲区,采用金相法时可避免盲区出现,使用不同种类的硬度计会出现不同结果,极限硬度值越高,偏差越大;对于带状组织感应淬火层深度的测量,两种方法仍存在不足。 相似文献
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渗硼层本身具有较高的硬度及耐磨性 ,但其脆性大 ,易剥落 ,又影响其使用效果。稀土元素对渗硼层的显微组织具有明显影响 ,如硼化物组织致密、晶粒细化、硬度梯度变缓等 ,同时由于其独特的微合金化作用、固溶强化作用和对晶界的净化作用 ,使得硼化物的硬度提高而脆性下降 ,从而使得硼化物层的耐磨性能明显提高。 相似文献
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Selection of the time period when liquid N fertilizer is introduced during an irrigation (timing), can potentially lead to more accurate placement of N in the root zone of perennial crops. The effect of four timing treatments, T1, T2, T3 and T4 the four quarters of a water application on in situ redistribution of ammonium nitrate at two water application rates (23 and 58 mm) was investigated. Irrespective of applied water quantity, soil ammonium-N content decreased with depth from the soil surface. Retarding the timing from T1 to T4 resulted in a significant increase in ammonium-N content in the uppermost 50 mm depth increment at both water application rates. In all timing treatments, the negatively charged nitrate ion moved to greater depths than its positively charged counterpart. These differences were greater where 58 vs. 23 mm of water was applied. Except for the T3 and T4 treatments at the 23 mm level, peak soil nitrate concentrations appeared below the soil surface. Retarding the timing at the 58 mm level gave rise to consecutive nitrate peaks between the surface and the 500 mm depth. A less distinct trend was also apparent where 23 mm was applied. Evidence for preferential movement of N in a uniform course sandy profile is also presented. 相似文献
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An artificial capillary barrier to improve root zone conditions for horticultural crops: physical effects on water content 总被引:1,自引:1,他引:0
Eviatar Ityel Naftali Lazarovitch Moshe Silberbush Alon Ben-Gal 《Irrigation Science》2011,29(2):171-180
Capillary barriers (CBs) occur at the interface of two soil layers having distinct differences in textural and hydraulic characteristics.
The objective of this study was to introduce an artificial CB, created by a layer of gravel below the root zone substrate,
in order to optimize conditions for the cultivation of horticultural crops. Potential root zone formats were analyzed with
and without the gravel CBs for variables including the following: depth of CB; barrier separating the root zone from the surrounding
soil; and root zone soil texture. Field and simulated results revealed that artificial CBs increased root zone water content
and changed water flow dynamics. Volumetric soil water content was increased by 20–70%, depending on the soil texture and
depth of the barrier. Sandy soil texture and shallower placement resulted in relatively higher water content. For sandy soil
without plants, a shallow (0.2 m depth) CB increased water content of the overlaying soil by 50% compared to the control.
The introduction of a gravel CB below the root zone of pepper plants (Capsicum Annum L.) lead to 34% higher matric head, 50% lower diurnal fluctuations in matric head and 40% increase in pepper fruit yield.
Increasing water content by way of artificial CBs appeared to improve the water use efficiency of pepper plants. Such an improvement
could lead to reduced water and fertilizer application rates and subsequent reduction in contamination below the root zone.
This is especially relevant for substrates of low water-holding capacity typically used in horticulture crop production. 相似文献
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黄土高原土石山区碎石分布特征及其导水性质分析 总被引:2,自引:0,他引:2
天水凤凰山中等风化变质岩碎块含量随土层增加含量增大;各层土体中粒级为2~5 mm碎石含量在各坡位变异小,坡中、坡下处粒径大于25 mm碎石含量相对高;铜川崾崄梁坡上土体的风化沉积岩碎石含量有随着土层加深有增大的趋势,其他坡位该趋势不明显,含量最高的为10~30 mm碎石;泾阳张家山卵石含量在坡位和土层上分布差异较小,粒径10~30 mm碎石含量最高。中等风化的块状碎石构成的土石介质的饱和导水率(ks)与土石比(土壤和碎石的质量比)关系呈对数关系,而片块状沉积岩碎屑构成的土石介质的ks与土石比关系呈正比线性关系;而椭圆卵石构成的碎石构成的土石介质ks与土石比无明显关系。 相似文献
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《Journal of Agricultural Engineering Research》1988,39(1):39-48
A curved, rigid tine with a 50 mm wide point was used to deep rip a texture-contrast soil at different depths of working. The soil had a sandy clay loam A horizon, about 90 mm deep, over a dense clay B horizon; both horizons were drier than their lower plastic limit when ripped. The depth of working varied from 100 to 500 mm and the analysis was done on the loose soil from the lower part of the trough formed by the tine, below the lower boundary of the A horizon. The size and horizon-of-origin of the fragments were measured and their volume recorded as a proportion of the total volume at the water content when ripped. The smaller (0·5 to 2 mm) fragments from the A horizon moved more easily towards the bottom of the trough, but their proportion declined as working depth increased. Fragments from the B horizon with diameter less than a tenth of the point width declined with working depth, whereas soil from the same horizon with more than a tenth of the point width increased with working depth. These different size classes of fragments may have been produced by different soil failure processes induced by the tine. Below a depth of 300 mm the mixture had a relatively constant composition; this depth seemed to correspond to the “critical depth” of working of the tine. The amount of mixing of soil from the two horizons was more than was anticipated from initial visual inspection of the contents of the trough. 相似文献
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为探求循环曝气地下滴灌对温室番茄土壤水分及耗水特性的影响规律,采用正交试验,研究了不同滴灌带埋深、曝气水平及灌水量对温室番茄土壤含水率、耗水量、产量及水分利用效率的影响.整个生育期内番茄耗水量呈先增大后减小的趋势,曝气处理番茄耗水量显著高于不曝气处理.相比于不曝气处理,曝气滴灌处理番茄产量提高10%.15 cm滴灌带埋深、溶氧值30 mg/L以及KP为0.75灌水量处理的番茄产量和水分利用效率达到最大值,分别为64 951.3 kg/hm2和23.26 kg/(hm2·mm).结果表明,曝气处理对番茄产量、水分利用效率的影响具有统计学意义(P<0.05).曝气对于土壤含水率有一定影响,且曝气处理有助于番茄对水分的吸收.滴灌带埋深和灌水量交互作用对番茄产量的影响具有统计学意义(P<0.05),滴灌带埋深和曝气量交互作用对番茄产量的影响具有统计学意义(P<0.01),灌水量与滴灌带埋深、灌水量与曝气水平交互作用分别对番茄水分利用效率的影响具有统计学意义(P<0.01). 相似文献
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《灌溉排水学报》2019,(Z2)
【目的】研究农田作物生长过程中,覆膜和降雨特征等因素对玉米耗水过程和土壤入渗产生影响。【方法】根据北京地区典型年降雨量设计和模拟春玉米生育期降雨过程,利用群集式测坑和挡雨棚及附设人工降雨装置,开展了不同地表覆盖条件下降雨强度对玉米耗水及水分利用效率的影响研究。降雨强度包括小雨强0.5 mm/min和大雨强1.5 mm/min,覆盖和种植条件包括膜下滴灌(MDI)、地面滴灌(SDI)和对照无作物种植(NP)。【结果】①MDI处理水分利用效率较SDI处理高13.5%。与SDI处理相比,MDI处理作物耗水量减小了40.6 mm,覆膜主要提高20~60 cm土层储水量。②大雨强条件下土壤深层渗漏量增多了3.4%~15.6%;降雨和灌溉对土壤水分影响深度主要为0~150 cm土层,相对于SDI处理,MDI和NP处理土壤储水量大大增加。③小雨强时表层0~20cm土壤入渗NP处理最快,大雨强时MDI处理入渗最快。作物根区40 cm深度处,小雨强时MDI处理的土壤水分最快达到峰值,而大雨强时NP处理最快达到峰值。60 cm深度处不同覆盖条件下在2种雨强时土壤水分变化速率一致,达到峰值速率表现为NP处理>MDI处理>SDI处理。【结论】覆膜具有较好的节水增产效应;降雨强度越大,土壤水分下渗越快;相同降雨量时小雨强降雨更有利于土壤水存储。不同的降雨强度对土壤水分入渗和再分布影响不同。研究结果可为雨水资源的合理利用从而提高农田水分利用效率提供理论依据。 相似文献
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【目的】探究冬小麦适宜的计划湿润层深度和土壤含水率控制下限的组合模式,为冬小麦田间用水管理及自动灌溉控制决策提供理论依据。【方法】以冬小麦为研究对象,采用大田试验,设置3个土壤含水率控制下限(L:40%,M:50%,H:60%)和3个计划湿润层深度(60、80、100 cm),共9个处理(T60L、T60M、T60H、T80L、T80M、T80H、T100L、T100M、T100H),研究了不同计划湿润层深度与土壤含水率控制下限对华北地区冬小麦生长发育和水分利用的影响。【结果】计划湿润层深度及土壤含水率控制下限的不同改变了处理间灌水定额及灌水次数,计划湿润层深度过高或土壤含水率控制下限过低均不利于冬小麦植株的生长发育。随着计划湿润层深度(60~100 cm)和土壤含水率控制下限(40%~60%)的增大,冬小麦花前及花后的干物质累积量呈先增大后减小的趋势。产量随土壤含水率控制下限增高呈增加趋势,当计划湿润层深度为80 cm时,产量相对最高,同时耗水量也越多,而计划湿润层深度为60 cm时耗水量最少。计划湿润层深度越低,土壤含水率控制下限越高,冬小麦水分利用效率则越高。T60H处理的水分利用效率最大,为19.96 kg/(hm2·mm),比最小值T100L大21.0%。【结论】本试验条件下,计划湿润层深度为60 cm,土壤含水率控制下限设置为土壤有效含水率的60%时,冬小麦节水高产效果相对最优。 相似文献
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玉米根土复合体剪切性能试验 总被引:2,自引:0,他引:2
以玉米品种沈农46自然状态的根土复合体为试验材料,在电子万能试验机和自制的试样周围压力系统上进行剪切力学性能试验。试验结果表明:含水率是影响极限剪切应力的最显著自然因素,极限剪切应力基本随着含水率增加而增大;距离根茎中心约20 mm的竖直剖面极限剪切应力最大,通过根茎中心的剖面次之,对于大于20 mm的其他剖面,距离根茎中心越远,极限剪切应力越小,结合垄作规格,破茬刀在距离垄台中心40 cm左右的剖面进行作业是合理的;在该剖面地表下20~60 mm位置,玉米须根最发达,抗剪切应力最大,约为5.20~7.15 MPa,是破茬装置功率损耗最大的工作段。 相似文献