Research On The Plastic Deformation Mechanism For Low Stress Repeated Impact Load Of Metallic Copper

In electrical system, it is too many to count that the contact failure due to disturbance of electric system, and even paralysis. The collision to the contact in the practical work of relay is not traditional collision. The collision force is far less than the yield strength of contact material, it belongs to the low stress repeated impact. Copper and copper alloys are widely used in switch contact, the paper discusses the plastic deformation rule, influencing factors and mechanism of the copper commonly used in contact materials in the condition of 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 were conducted on the copper commonly used in contact materials. The results show that under the low stress repeated impact load, the difference of deformation between two adjacent impact of the copper will reduce firstly, and will increase at about32X103, eventually in the impact number reached512×103, deformation basic tends to0, reach the stable state. Comparison of the plastic deformation of the copper and iron in the low stress repeated impact 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 is larger when closer to the surface. But under the same conditions (shock peak value as4/5of the yield strength), pure copper deformation termination layer is more distance from the surface than the pure iron deformation termination layer.Analyze the changes of the hardness before and after the low stress repeated impact of the copper separately on the impact of lOMPa,15MPa and20MPa impact, shows that after the repeated impact test, hardness has increased to some extent, because the sample produced a hardening phenomenon, and the impact greater the hardening degree higher. But the hardening happen to some extent only, hardening phenomenon is most obvious in the 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 on separate impact, shows that along with the impact stress is larger, more grain number, grain refinement trend appears more obvious. The XRD diffraction patterns before and after the impact of the copper are basically the same, only the grain size has changed, but no new phase formed.With the impact of greater stress, half of the broad diffraction peaks wider, the grain size is small er.Analyze the changes of the hardness of copper in different impact times in20MPa impact stress, shows that the hardness increased with the increased number of impact on the whole, but in the impact number about32×103, 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 the metallographic also has close relationship with impact times. On the whole, the impact number more, the extent of grain refinement is bigger. Until the specimen is no longer occurs, the size and quantity of grain tends to be stable large, no longer change. But in times of shock is32×103, the grain refinement degree also eased.Established the mathematical model of copper on low stress repeated impact load, preliminary analyze the copper in low stress and deformation mechanism of multi touch, with a view to provide references for the research of the hierarchical collision plastic law of the nonferrous metals on the low stress repeated impact load.