Research On Thermal Stress And Interface Crack Mechanical Characteristics Of Relay Composite Contact In Life Test

The AgMeO/Cu composite contact is widely used in the low voltageelectrical apparatus because of its excellent performance. The composite contactfailed because of the AgMeO layer of the moving contact peeling from the Culayer and spiced with the fixed contact in the life test. In this paper, the typicalAgMeO/Cu composite contacts were regarded as the research object. The failure ofcomposite contact repeat process was analyzed. A complete simulation wasestablished to calculate the temperature and thermal stress of the relay in the lifetest. It was investigated the effect of the AgMeO layer’s thickness on the movingcontact interface crack parameters under different load conditions from thetemperature and thermal stress angle.Firstly, A complete simulation model, considering the making, arcing andbreaking, was established to calculate the contact temperature and thermal stressafter any operation cycle in the life test based on3D finite element method. Theheating and heat-transfer mechanism of the composite contact was analyzed in therepetitive movement. The transient thermal field mathematical model of the relay’slife test was established.Specifically, the equivalent model of contact resistance andair was established and the heat source of the relay was calculated in differentstages. Then, the heat generation of contact resistant and the heat flux of the arcenergy pouring into the contact were loaded on the equivalent model respectively,according to the stage of the relay’s repeat operations. Finally, the transient thermaldistribution of the relay was obtained in the way of cyclic solving. The correctnessof the simulation was verified by the temperature measurement of the relay in thelife test.Secondly, it is achieved the calculation of multi-physics field in the way ofindirect coupling analysis pattern. It is obtained the stress contribution of thecomposite contact while the temperature achieved dynamic balance in the life test ofthe relay. It was simulated the stress distribution of the moving composite contactwith different thickness of the AgMeO layer under different load conditions by theabove analysis method. And the relationship between the AgMeO layer’s thicknessand the stress distribution was obtained.Finally, A crack position was assumed in the interface of the moving compositecontact according to the analytic result of the stress. The complex stress intensityfactor was introduced to describe the stress intensity of the near crack tip region. A2D finite element model with cracks in the composite contact was established. By reanalyzing the thermal and stress contribution of the moving composite contact, itwas obtained the complex stress intensity factor of contacts. And the influence ofthe AgMeO layer’s thickness on the complex stress intensity factor under differentload conditions was analyzed.The analysis method and conclusions in this paper provide the basis forfurther analysis of the optimization of composite contact and the mechanism ofcrack initiation and propagation.