低应力多碰载荷下紫铜的塑性变形及其机理研究（学位论文-工学）.docx

硕士学位论文论文题目 低应力多碰载荷下紫铜的塑性变形及其机理研究研究生姓名 郁佳莉指导教师姓名 傅戈雁专 业 名 称 机械电子工程研 究 方 向 金属材料失效分析论文提交日期 2013 年 4 月低应力多碰载荷下紫铜的塑性变形及其机理研究 中文摘要低应力多碰载荷下紫铜的塑性变形及其机理研究中文摘要在电气系统中，由于触头失效造成电气系统工作紊乱，甚至瘫痪的情况不计其数继电器在实际工作中对触点的碰撞并不是传统意义上的碰撞，碰撞力远远低于触点材料的屈服强度，属于超低应力多碰铜及铜合金广泛应用于开关触头，本文即探讨了常用于触头材料的紫铜在低应力多碰条件下的累积塑性变形的规律、影响因素及其机理，对提高其使用寿命、降低成本、提高系统的可靠性和安全性有着重要的意义本文利用自制多碰试验机，对常用于触头材料的紫铜进行了低应力多碰试验，研究了低应力冲击次数对变形量的影响规律结果表明：紫铜在低应力多碰冲击载荷下，紫铜的相邻两次冲击次数下的变形量的差值会出现先减少，在冲击次数大约为 32×103时又会增加，最终在冲击次数达到 512×103 时，变形量基本趋向于 0，达到安定状态；对比纯铜和纯铁在低应力多碰载荷下的塑性变形规律可以得出，在低应力多碰载荷下，纯铜和纯铁的变形规律都很明显地符合“趋表效应” ，即变形都是从表层开始，且距表层越近变形量越大，但在同样条件（冲击峰值均为屈服强度的 4/5）下，纯铜的变形终止层比纯铁变形终止层距表面距离远。

分别对 10MPa、15MPa 、20MPa 冲击力下的紫铜多碰前后的硬度变化分析，研究了碰撞应力值大小对碰撞前后硬度的影响规律，结论如下：紫铜在经过多冲碰撞试验之后，硬度都出现了不同程度的升高现象，这是由于试样产生了硬化现象，且冲击力越大硬化程度越大，但是硬化也只是在一定程度上发生，硬化现象在表层最明显，由冲击层向内逐渐减小，同样符合 “趋表效应”对在 20MPa 冲击应力下不同冲击次数下的紫铜硬度变化分析得，随冲击次数也会发生变化，从整体上来说，硬度随冲击次数的增加而有所增加，但在冲击次数大约为 32×103 时，由于金属的循环软化速率大于了循环硬化速率，硬度的增加趋势出现了缓和观察各冲击力下多碰前后的金相显微组织，研究了不同碰撞力值大小对微观组织的影响规律，解释了微观组织与力学性能之间的本质关系可得，随着冲击应力越大，I中文摘要 低应力多碰载荷下紫铜的塑性变形及其机理研究晶粒的数量越多，晶粒出现细化趋势越明显；紫铜在冲击前后的 XRD 衍射图谱物相基本相同，只是晶粒尺寸发生了变化，并没有新的物相生成，但随着冲击应力越大，衍射峰的半高宽宽化，晶粒尺寸越小对各冲击次数下紫铜金相组织可得，金相的变化趋势和冲击次数也有密不可分的关系，从整体上而言，冲击次数越多，晶粒细化的程度越大，直到试样不再发生变形时，晶粒的尺寸与数量也趋于稳定，不再发生较大变化，但在冲击次数为 32×103 时，晶粒的细化程度也有所缓和。

建立了紫铜在低应力多冲碰撞下的数学模型，初步分析了紫铜在低应力多碰下的变形机理，以期能为有色金属多冲碰撞下的分层塑性规律的研究提供参考关键字：紫铜；低应力多碰；分层塑性响应；数学模型作 者：郁佳莉指导老师：傅戈雁IIResearch on the plastic deformation mechanism for low stress repeated impact load of metallic copper AbstractResearch on the plastic deformation mechanism for lowstress repeated impact load of metallic copperAbstractIn electrical system, it is too many to count that the contact failure due to disturbanceof electric system, and even paralysis. The collision to the contact in the practical work ofrelay is not traditional collision. The collision force is far less than the yield strength ofcontact material, it belongs to the low stress repeated impact. Copper and copper alloys arewidely used in switch contact, the paper discusses the plastic deformation rule, influencingfactors and mechanism of the copper commonly used in contact materials in the conditionof low stress repeated impact. It has an important significance to improve its service life,reduce the cost and improve the reliability and safety of the system.Using a self-made impact testing machine, low stress repeated impact tests wereconducted on the copper commonly used in contact materials . The results show that underthe low stress repeated impact load, the difference of deformation between two adjacentimpact of the copper will reduce firstly, and will increase at about 32×10³, eventually inthe impact number reached 512 ×10³, deformation basic tends to 0, reach the stable state.Comparison of the plastic deformation of the copper and iron in the low stress repeatedimpact can obtain that the deformation of the copper and iron are clearly conform to the"skin effect", namely the deformation are from the surface, and the deformation amount islarger when closer to the surface. But under the same conditions (shock peak value as 4/5ofthe yield strength), pure copper deformation termination layer is more distance from thesurface than the pure iron deformation termination layer.Analyze the changes of the hardness before and after the low stress repeated impact ofthe copper separately on the impact of 10MPa, 15MPa and 20MPa impact, shows that afterthe repeated impact test, hardness has increased to some extent, because the sampleproduced a hardening phenomenon, and the impact greater the hardening degree higher.But the hardening happen to some extent only, hardening phenomenon is most obvious inIIIAbstract Research on the plastic deformation mechanism for low stress repeated impact load of metallic copperthe surface layer, decreases gradually as the inward of the impact layer, also conform to the"skin effect". Observe the microstructure before and after the low stress repeated impact onseparate impact, shows that along with the impact stress is larger, more grain number,grain refinement trend appears more obvious. The XRD diffraction patterns before andafter the impact of the copper are basically the same, only the grain size has changed, butno new phase formed. With the impact of greater stress, half of the broad diffraction peakswider, the grain size is smaller.Analyze the changes of the hardness of copper in different impact times in 20MPaimpact stress, shows that the hardness increased with the increased number of impact onthe whole, but in the impact number about 32×10³, the increase of hardness trend to ease,because the rate of metal cyclic softening is higher than the rate of cyclic hardening.Observe the metallographic structure in different impact times shows that the change of themetallographic also has close relationship with impact times. On the whole, the impactnumber more, the extent of grain refinement is bigger. Until the specimen is no longeroccurs, the size and quantity of grain tends to b。