烧蚀作用下石墨焊接池与电极接触行为研究

通过测试分析不同石墨焊接池表面形貌、烧蚀率等性能，提出石墨焊接池均匀退化烧蚀特征，建立以线烧蚀系数为表征的烧蚀状态下动态接触电阻模型。且通过实验验证分析了15 N夹持力作用下，石墨表面烧蚀作用对接触电阻的影响。结果表明：石墨焊接池在直径方向的烧蚀速率较大，石墨表面烧蚀作用使得界面接触电阻呈缓慢增加趋势，普通石墨的烧蚀对界面接触电阻的影响相较于精细石墨的作用更加明显，并且模型的计算值与实测值基本一致，误差在合理范围内，保证了模型建立的合理性和准确性。     

直流表面电阻测试系统软件开发与应用

用Visual Basic针对表面直流电阻测试系统进行软件开发,使系统各个部分组成一个可控的整体.该开发软件具有较好的人机界面,实现了表面接触电阻的自动测量和数据处理.测试结果较好地反应材料在不同压强下的表面电阻,符合材料的物理特性,对材料的屏蔽效能评估、工程中材料的选型和应用有较好的参考价值.     

航天电连接器的可靠性设计建模

以库房贮存背景下的J599系列电连接器为研究对象,分析电连接器在贮存环境下的主要失效部位及失效机理,确定了接触失效为最主要的失效模式,而接触对表面氧化物膜层增厚使得膜层电阻增大是造成接触失效最主要的原因;结合氧化物膜层的增长规律、膜层生长的化学反应理论以及接触对的功能与结构,进一步从微观层面对膜层电阻的生长规律进行了描述;基于电连接器接触电阻退化轨迹、接触退化率在温度应力水平下的变化规律以及接触可靠度与接触性能退化量之间的关系,建立电连接器的贮存可靠性统计模型;综合考虑镀层厚度、孔隙率、接触件基体材料、开槽簧片长度以及微观表面形态等尺寸、工艺和材料参数与其可靠性指标之间的关系,建立电连接器可靠性设计的数学模型,提出了电连接器可靠性定量设计的方法。     

镍铬接触对接触电阻失效原因分析

描述了用于K型热电偶回路中的镍铬接触对在电连接器的振动过程中发现接触电阻变大的失效现象,从接触电阻的理论构成和失效接触对的实物状态进行原因分析,通过更换绝缘体材料、固定接触对及更换接触对等方式进行试验验证,确定主要原因。针对分析结果,通过降低表面粗糙度、提高接触压力、涂覆固体膜润滑剂和调整接触对固定机构等方式,解决了镍铬接触对在振动过程中的接触电阻失效问题。通过一系列的试验,总结了避免镍铬接触对失效的关键措施。     

导电滑环滑动摩擦振动机理分析及其影响的研究

滑动摩擦过程中产生的振动会加速材料的磨损,降低材料的使用寿命。通过对导电滑环接触材料摩擦副磨损试验中产生的振动进行研究,分析滑动摩擦过程中振动的形成机理以及振动与表面粗糙度的相互关系,研究振动对于摩擦力和接触电阻的影响。     

半导体放电加工中接触电阻的影响因素研究

从理论上分析了产生接触电阻的原因,建立了切割回路中的导电原理模型。分析了如进电方式、进电材料、接触压力等因素对接触电阻的影响。实验结果表明:选择进电材料时,进电材料的功函数与所要加工的半导体的功函数尽量接近;选择接触形式,两个材料接触时要形成面接触,同时在允许的范围内尽量增大接触压力来减小接触间隙,这样会得到更小的接触电阻。     

不同转速下弹性环滚动载流摩擦性能和损伤分析

采用内滚道、外滚道和弹性环组成滚动载流摩擦副，通过载流摩擦试验研究了其在不同转速下的载流摩擦学性能和材料损伤。结果表明：随着转速从240 r/min增加到600 r/min,摩擦副稳态运行期间的摩擦力升高，接触电阻下降；摩擦前期材料损伤形式主要以接触表面金属塑性变形为主，摩擦平稳期以材料剥落为主；在相同的初始接触条件下，高转速促进表面疲劳和材料磨损，试验后弹性环磨痕宽度明显变宽，磨损量逐渐增大，表面氧化程度下降，O和Cu原子个数比降低；磨痕宽度增幅相近的条件下，同等转速下的摩擦力增幅小于变速条件下的摩擦力增幅；转速增加引起的摩擦力增大与高转速下弹性环滑滚增加也有关系。     

腐蚀性气体对金属镀层的影响

金属镀层耐腐蚀能力一般通过盐雾试验进行验证,大多数情况下忽略了腐蚀性气体的影响。随着产品使用时间的增加,镀层表面光泽会变暗,甚至出现深色斑点。电接触元器件表面长时间腐蚀后形成的腐蚀产物厚度不均匀,接触电阻发生变化,最终造成电接触故障,影响产品使用寿命。显然,气体腐蚀在产品外观以及电气性能上都造成了一定的影响。通过模拟气体腐蚀环境,验证铜镀银、铜镀锡、铜镀镍材料在一定浓度的NO2、SO2、Cl2、H2S气体环境下外观、镀层厚度和接触电阻的变化。试验结果表明,腐蚀性气体对外观影响从大到小为铜镀银、铜镀锡、铜镀镍,对接触电阻影响最大的是铜镀镍,铜镀银和铜镀锡无明显变化。     

渗氮钢粗糙表面的弹塑性接触研究

利用弹塑性有限元和单纯形法求解弹塑性接触模型，分别模拟了屈服强度呈梯度变化的渗氮钢、未经处理的匀质材料和硬涂层材料粗糙表面的弹塑性接触行为。与未经处理的匀质材料相比，渗氮钢可承受更大接触载荷。在相同载荷作用下，渗氮钢表面粗糙峰接触面积较小，平均间距较大，接触体内材料不易发生屈服，从而显著提高接触性能。和硬涂层材料相比，渗氮钢接触体内等效von Mises应力分布平缓，没有应力突变。最后讨论了渗氮层和硬涂层的厚度对粗糙表面接触特性的影响。     

烟炱对电接触磨损的影响

选用常见的铜作为电接触材料,将烟炱溶液喷洒于试样表面,进行不同载荷下的电接触微动试验,用3D形貌仪和SEM对磨痕形貌进行分析。结果表明:载荷对材料的电接触性能影响显著,接触电阻与法向载荷成反比,即增加载荷可改善摩擦副的电接触性能;接触区域的有效导电面积是有限的,故载荷达到某一值后,随着载荷的增加,接触电阻不再有明显的下降趋势;小载荷下,烟炱的加入恶化了摩擦副的电接触性能,随着载荷的增加,这种恶化作用逐渐减小;摩擦因数随着载荷的增加而降低,载荷较低时(2～6 N),摩擦因数曲线可见明显的上升期、跑合期、下降期、稳定期;而载荷较高时(8～10 N),只有上升期和稳定期;大载荷下,触头接触区域匹配良好,摩擦副表面迅速达到了平衡点,摩擦因数较稳定。在电化学的作用下烟炱颗粒在摩擦副表面形成固体膜,起到减摩抗磨的作用。     

Correlation analysis of brush temperature in brush-type DC motor for predicting motor life

Some critical components of motors and generators have sliding electrical contacts. Electrical brushes are usually used in these contact points to conduct current between the stationary part and the moving part of the motor. In this paper, studies on brush wear against copper commutators are briefly reviewed. The main influential factors in brush wear are associated with both mechanical wear and electrical wear. Brush wear is affected by various factors, including temperature, material properties, sliding speed, contact force, and interfacial as well as environmental conditions. The mechanical wear of brushes is proportional to brush spring pressure and sliding speed, and the electrical wear of brushes is associated with current and contact voltage drop. For characterization, a brush wear test machine is designed, and influential factors, such as electrical contact resistance, temperature, wear mass loss, and so on, are measured. The wear tests are processed using a small brush-type automotive DC motor. The study primarily aims to investigate the effects of the wear behavior of copper-graphite brushes on small brush-typed DC motors. The variable conditions of electrical current are obtained by changing the brush spring pressure and the sliding speed. The results are electrical contact resistance, voltage drop, brush surface temperature rise, and so on. Brush wear is greatly changed by electrical current, which indicates that high current itself not only produces more Joule heating but also causes an increase in voltage drop that will result in additional Joule heating.     

粘弹性流体动力润滑与润滑磨损

分析了等效微弹流接触表面形状与真实情况之间的差异。讨论了材料粘性对弹性变形的影响。将材料粘性引入微弹流模型中,给出了润滑条件下磨粒磨损计算模型以及发生润滑磨损的条件准则。利用所给模型对接触弹流润滑磨损问题进行了数值计算并给出了与试验结果的对比。     

大型易磨损件的等磨损面设计

为了解决大型易磨损件的非均匀磨损问题,提出了一种等磨损面设计方法,该方法有效地利用了磨损失效分析、磨损模拟试验及材料的表面处理技术。文中在论述设计方法的同时,举例说明了一个大型薄壳零件——机耕船舶体的等磨损面设计;田间试验的结果表明：经过等磨损面设计的船体不仅消除了非均匀磨损现象,而且其使用寿命提高了一倍以上。     

Conduction degradation by fretting corrosion phenomena for contact samples made of high-copper alloys

The main cause of electrical contact resistance degradation by corrosion is the vibration of contact interfaces. The purpose of this paper is to analyse the change of contact resistance by means of a vibration test for uncoated sphere/plane contact made of new high-copper alloys.The influence of electrical and mechanical properties of materials, and mainly hardness, on contact resistance has been studied in this work. During the fretting test, a contact point was submitted to 16,000 vibration cycles under fretting amplitude of 50 μm and 1 Hz frequency. The sphere part was fixed, while the plane part was submitted to relative motion. At the end of the test, the fretted surfaces and the wear debris were analyzed by scanning electron microscope and energy dispersive X-ray spectroscopy to evaluate damage, oxidation and elemental composition present in the wear surfaces. In addition, the measurement of the wear track profile using a 3D surface scanning system was introduced. Increases in contact resistance and contact temperature were examined during the fretting test.The results showed that the contact resistance for the harder alloy was higher than that obtained for the other materials. In addition, topographic measurements showed that the small wear track corresponds to the harder material.     

QT500的冲蚀磨损试验研究

在自制的转盘式冲蚀磨损试验台上以灰口铸铁（HT200）为对比材料，对球墨铸铁（QT500）的冲蚀磨损性能进行了试验研究，结果显示QTS00的冲蚀磨损规律与HT200基本相似，而耐冲蚀磨损性能比HT200稍强。在电子显微镜（SEM）下对QTS00和HT200冲蚀磨损表面形貌进行观察，分析表明：QTS00的冲蚀磨损机制是硬质砂粒对材料表面的微切削作用，而HT200的冲蚀磨损机制是因赫兹裂纹导致的脆性脱落。     

Effect of laser irradiation on abrasive wear of glass fibre polyester composite

Low power laser irradiation improves the wear resistance of glass-fibre-reinforced polyester composites, if irradiation time is restricted to short periods. Laser irradiation (i) enhances crosslinking in unsaturated polyester, (ii) modifies surface microstructure and (iii) increases the hardness of the composite material. Improved mechanical properties, in turn, increase the material's resistance to wear.     

薄膜型金属网栅的电磁屏蔽特性

为寻求准确评估薄膜型金属网栅电磁屏蔽效能的方法,探索了薄膜型金属网栅在某频段可达到的电磁屏蔽效能。首先,分析了金属网栅膜光电特性常用的计算公式,指出电特性公式中材料无限导电的假定条件与客观事实不符,故其无法准确预估薄膜型金属网栅的电磁屏蔽效能。然后,根据屏蔽效能受感应电压和电阻比控制的理论,借鉴连续导电膜用方块电阻计算屏蔽效能的方法,提出了预估薄膜型金属网栅屏蔽效能的方法并给出了具体步骤。最后,采用激光直写工艺流程制备了薄膜型金属网栅,验证了理论计算结果与实验检测结果的一致性。检测结果显示:薄膜型金属网栅试片在30~1 500MHz的屏蔽效能最高为30dB;用检测方块电阻并代入连续膜经验公式计算得到的屏蔽效能为31.2dB,用金属网栅膜常用公式计算得到的屏蔽效能为75dB。数据显示用金属网栅膜常用电特性公式无法准确评估薄膜型金属网栅的电磁屏蔽效能,而本文所提方法便捷、准确、可行。     

Effect of temperature on the fretting corrosion of tin plated copper alloy contacts

The effect of temperature on the fretting corrosion behaviour of tin plated copper alloy contacts in the temperature range of 25–185 °C, is addressed in this paper. The change in contact resistance with fretting cycles at various temperatures was determined. The contact zone after fretting corrosion test was analyzed using laser scanning microscope, X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray spectrometry (EDX), to assess the surface profile, phase content, morphology and compositional changes across the interface. The study reveals that temperature has a greater influence on the extent of fretting corrosion of tin plated copper alloy contacts. The softening of tin is responsible for the extended region of low contact resistance observed at 85 °C. The increase in thickness and the resistance of Cu–Sn intermetallic compounds (IMCs) is responsible for the decrease in surface roughness and the drastic increase in the contact resistance at higher temperatures. The study suggests that the tin plated copper alloy contact system should be considered as copper alloy/IMC/Sn/SnO₂ instead tin plated copper alloy. During fretting corrosion test at elevated temperatures, once the top surface layers are worn out, the contact interface is transformed from tin versus tin-to-tin-intermetallic versus tin-intermetallic. The study concludes that tin plated copper alloy contacts are not suitable for high temperature applications.     

高性能肌电检测前置放大器的设计

介绍了一种为消除50Hz干扰而设计的肌电(EMG)前置放大器，通过对前置放大器采取电磁屏蔽处理、DC-DC隔离变换器供电和浮地共模自举等措施。获得了满意的抗50Hz干扰性能。