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《真空科学与技术学报》2015,(12)
真空绝缘子表面电荷的积聚会改变电场分布,影响绝缘子的闪络电压。为了量化研究表面电荷积聚对表面电场的影响程度,本文采用静电探头法测量了真空中纳秒脉冲作用下多种陶瓷绝缘子表面电荷的二维分布,并结合扫描电子显微镜获得的绝缘子表面微观形貌特征分析了不同试品表面电荷积聚存在差异的原因。提出了一种由表面电荷测量结果求得表面电荷引起的电场的计算方法,与软件仿真得到的脉冲电压产生的电场相结合,量化了表面电荷积聚对表面电场的影响程度。研究结果显示,表面电荷对绝缘子表面电场有增强或削弱作用,大部分情况会增强电场,最大增强程度可达近2倍。闪络试验结果证实表面电荷的积聚会降低绝缘子的闪络电压。因此要尽量选择表面电荷积聚少的真空绝缘材料,以提高绝缘强度。 相似文献
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强电场对摩擦焊接头组织与性能的影响 总被引:1,自引:1,他引:0
为提高摩擦焊缝金属的变形能力,采用外加电场考察了摩擦焊缝金属的电塑性效应,利用金属组织观察、显微硬度测试及抗拉试验,定量分析了外加强电场对LY12铝合金摩擦焊缝组织与力学性能的影响,结果表明:外加强电场使焊缝金属组织轴向分布梯度减小,等轴性提高;不同焊接压力时,强电场使焊接接头的动态再结晶区宽度有不同程度的增大;在中等摩擦压力作用下,使近轴心线处的动态再结晶区宽度趋干均匀;此外,外加电场使接头焊合区硬度增加,并使焊接接头的硬度分布趋干均匀;采用强规范施焊时,外加电场提高了焊接接头的抗拉强度。 相似文献
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目的 解决新一代轻质镁锂合金微型热管加工难度大、尺寸精度差、性能不稳定的难题。方法 对镁锂合金坯料施加脉冲电流,利用脉冲电流产生的电致超塑性效应提高塑性变形能力,降低镁锂合金微型热管的加工难度。利用有限元仿真和实验相结合的方法,分析微型热管电场辅助超塑挤压过程中微型热管的变形行为与缺陷演变。结果 电场辅助超塑成形的挤压力远低于相同温度下纯加热成形的变形力,能够单道次挤压出Φ2 mm的微细热管。结论 与相同温度下的纯加热成形相比,电场辅助微型热管超塑挤压成形的变形抗力降低了50%,证明电致超塑性可有效降低镁锂合金微型热管的加工难度。随着超塑挤压速度的增加,变形不均匀性加剧。当挤压速度为0.006~0.02 mm/s时,能够获得尺寸精度和表面质量较好的微型齿槽。当挤压速度超过0.02 mm/s时,容易导致微型齿与管壁区域之间的材料流动不均匀,甚至诱发断裂。当挤压温度为200~280 ℃时,可以软化材料,降低挤压力,避免了温度过高产生的“焊接”现象。镁锂合金微型热管成形过程受尺寸效应影响,在挤压杆微型齿槽表面,亚毫米尺寸导致镁锂合金与模具间的界面摩擦增大、材料流动变慢,进而影响了微型齿槽的填充质量。 相似文献
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本文用定量金相测量了球化20钢制光滑与缺口试样在拉伸变形不同阶段中微空洞的体积分数fr和单位面积上的做空洞个数NA,分析了三轴应力和有效塑性变形对微空洞萌生和长大的影响.作者认为,用一组原始形状不同的试样进行变形,在每个试样上取一个区域测量空洞数量并计算相应的应力应变.用这种方法验证Rice-Tracey关于空洞长大速率的公式是不合适的。 相似文献
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本文对几种稀土Al-Zn-Mg-Cu合金的小角X射线散射强度进行了分析,试验结果表明,在超塑变形过程中,合金中的微空洞产生的越多,材料的延伸率越好,稀土的含量对合金的超塑性也有一定的影响。 相似文献
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本文对铍青铜(QBe2)超塑变形中的空洞形成过程和晶粒重排进行了研究。结果表明,空洞的形成直接影响着晶粒重排过程。晶粒重排以多重方式进行,而不是单一方式,形成空洞是其中的一个步骤。对于含有第二相粒子的 QBe2合金,其超塑变形中所产生的位错与第二相粒子的交互作用是导致空洞形成的重要原因。空洞的形成并不直接导致材料的断裂,而断裂的真正原因是空洞的连结。文中给出了描述晶粒重排和空洞形成与连结的示意图。 相似文献
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The dynamic compression behavior of AZ31B magnesium alloy with hat shaped specimen was investigated at high strain rate in this paper. Based on the Johnson‐cook constitutive model and fracture model, the interaction of temperature, stress and strain fields of AZ31B magnesium alloy with hat shaped specimen were numerically simulated by using ANSYS/LS‐DYNA software under different strain rates, which was validated by experiment. It is found that the plastic strain is highly concentrated on the corner of the hat shaped specimen, which leads to large localized deformation. The voids are nucleated and extended by compression stress. Work harden effect is caused by remained plastic strain, which is located around adiabatic shear band. The stress collapse is discovered in gauge section, which is also discovered in experiment. Thermal soften effect is suppressed with the strain rate increased. 相似文献
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The objective of the paper is to study the effect of ageing, inclusions and voids on the mechanism of fracture and resultant
toughness. It has been found that the voids are initiated at only a fraction of the larger inclusions present. The initiation
of voids at small particles in the ductile fracture process appears to have little effect on fracture toughness. The strain
hardening capacity has a marked effect on void size, and is an indicator of fracture toughness in the commercial Al alloy. 相似文献
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对网篮组织TC21钛合金进行了0.001 s-1~50 s-1的中应变速率室温拉伸试验。试验结果表明,TC21拉伸力学行为在试验应变速率范围内具有明显的应变速率强化效应、应变硬化效应和随应变速率升高而逐渐增大的温升软化效应;屈服应力的应变速率相关性在6 s-1时发生转折;随应变率的升高,应变硬化效应减小,断裂应变和失稳应变增大;试验应变速率范围内TC21的变形机制为位错的热激活机制。SEM和金相观察结果表明,TC21的断裂方式均为韧性断裂,断裂机理为微孔洞的聚集和长大。 相似文献
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建立了Fe-Ga合金弓张结构发音振子换能器电场、磁场和固体力学场的多场耦合模型,研究了发音振子换能器磁场强度、磁感应强度和应变分布情况,并进行了换能器在不同频率下的磁场强度分析和模态分析。分析发现,随着频率的增高,Fe-Ga合金发音振子换能器的磁场强度逐渐减小,计算得到换能器的共振频率为984 Hz。测试了Fe-Ga合金换能器中的核心元件Fe-Ga合金的磁场强度与应变的关系,当磁场强度饱和值为40 k A·m-1时,应变为70×10-6。搭建了磁致伸缩材料磁特性测试系统,测试了Fe-Ga合金磁场频率为5、20、50 Hz的磁滞曲线,并测试了Fe-Ga合金的应变随频率的变化曲线,实验结果与换能器中Fe-Ga合金的应变仿真结果一致。 相似文献
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Dong Chen Xianglin Chen Rong Ma Qingfu Tang Bin Su Zhenhong Wang 《Materials Science & Technology》2018,34(1):12-19
The microstructure and tensile properties of an aged U-5.5?wt-% Nb alloy have been experimentally investigated with the aim of obtaining the influence of strain rates on fracture behaviour. The result shows that strain to failure is sensitive to strain rate and decreases with an increase in the strain rate. Fracture surface analysis indicates that the alloy exhibits a typical ductile fracture. Two types of carbides (niobium carbide and uranium carbide), mainly distributed at the grain boundary, are confirmed, which participate in the process of fracture and are involved in different void nucleation mechanisms during the final ductility fracture. Namely, niobium carbide tends to generate voids by debonding with the matrix, while uranium carbide is more likely to experience cracking. 相似文献
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研究了初始应变速率在1.39×10^4 ̄6.95×10^-1s^-1范围内Fe-40Al的室温拉伸性能。结果发现,应变速率对FeAl合金室温下的断裂延伸率屈服强度和抗拉强度均有不同程度的影响,其中对断裂延伸率的影响最为显著。应变速率对FeAl合金力学性能的影响程度还与Al含量有关,Fe-36.5Al较Fe-40Al合金受应变速率的影响更大,研究结果还表明,Al含量还影响着FeAl合金拉伸断口中穿晶 相似文献
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On the effects of an electric field on the fracture toughness of poled piezoelectric ceramics 总被引:1,自引:0,他引:1
Central crack specimens have been used to study the effects of an applied electric field on the fracture toughness of poled soft lead zirconate titanate ceramics (PZT-5). The ultrasonic lapping technique was used to machine the central crack of the specimens used. The present experimental study illustrated that changing the field from negative to positive reduced the fracture toughness of a specimen subjected to an applied electric field. These experimental results were in agreement with the observations made by Park and Sun (J. Am. Ceram. Soc. 78 (1995) 1475) and Heyer et al. (Acta Mater. 46 (1998) 6615). Finite element results were employed to compare with the experimental data. Four fracture criteria, i.e. total energy release rate, mechanical energy release rate, local energy release rate and strain energy release rate, were compared with the experimental results. It was found the local energy release rate, which was defined based on a strip electric saturation model, was in broad agreement with the experimental observations. Moreover, it was found that the strain energy density criterion was unable to describe the effect of electric field on fracture toughness when a large electric field was applied. 相似文献