Study On Influence Factors Of Fretting Wear Performance Under Electrical Contact

Electrical connection is a key component in electric power,electronic equipment and electronic system,which is widely used especially in mobile electronics.The reliability of electronic products is the most concerned issue among consumer groups.According to the fault survey and judgment,the failure of the electronic equipment is usually caused by the failure of contact.Consequently,the failure caused by the deterioration of contact service performance has attracted widespread concern about electrical contact problems.This paper,based on independently developed electric contact fretting wear equipment,simulates the actual service condition of the electric contact and analyzes the damaged area through microscopic analysis technology,which showed that the fretting behavior of the contact area can lead to severe contact failure(such as sudden increase of contact resistance,open circuit,and contact welding).A series of experimental studies have shown that the factors affecting the failure of electrical contact have a strong generality and versatility.Therefore,the paper selects the most commonly used "point/plane" contact mode and discusses the influence of basic working conditions on electrical contact reliability based on the micro-analysis of the damaged area,which may contain debris,oxide,pollutants and compounds produced in the interface,as well as the statistics of contact resistance and fretting operation condition.The rubbing wear experimental method also reveals the basic influe nce of different experimental factors(normal load,displacement amplitude and current level)on contact resistance.The evolution of contact resistance in varied conditions and the wear mechanis m are also analyzed in this paper.All mentioned above results can be used to improve the reliability of electrical connection and can be used as scientific design basis and optimizat io n method to prolong the electrical contact performance.The main findings can be summarized as follows:(1)The surface products(debris,corrosion,third body.etc.)generated by interface interaction are the main causes of contact failure under fretting conditions.The effects of different working conditions on the contact performance are summarized as follows:?.A larger load(as pretension force of contact)means a better matched interface.That is to say,a larger effective conductive area carries larger normal load,which means more available current paths and lower electrical contact resistance.In addition,the corrosive gases,pollutants and dust in the air are difficult to enter the conductive interface,so the conductive performance of the contact under large load is better than under the small load.?.Relative large displacement amplitude between the interfaces can produce large amount of debris and finally increase contact resistance.The stability and reliabil it y of the contact resistance seriously decrease due to serious friction and oxidation.?.In the condition of fixed normal load and relative displacement amplitude of the interface,the contact resistance under high current condition is lower than under small current condition.The reason is that it's easy for high current to breakdown oxidation film.(2)Effect of environmental factors on electric contact performance under fretting wear:?.Temperature rise on the interface may accelerate the region's fretting corrosion and oxidation.The rising temperature causes the oxidation and corrosion of the interface,the process of which is also accelerated by the fretting.Oxidation and corrosion products,usually have high insulation resistance,seem easily to adhere to the contact surface to form an insulating film.With the insulation layer gradually accumulat i ng and causing the separation of contact surface,the contact resistance increases sharply and even leads to circuit disconnection.Microscopic analysis helps analyze the composition of surface products so as to analyze the differences of surface products at different temperatures and the effect on electric conductivity.?.It is found that in the nitrogen environment,electrical contact resistance can keep a minimum and stable value and the contact surface suffers a high friction.The rich oxygen environment promotes the formation of cuprous oxide,thereby the electrica l contact resistance increases.In the early stage of fretting motion,a rare circuit disconnection behavior occurs in rich oxygen environment due to generating and accumulating of Cu O/Cu O2 and being discharged by fretting.?.The certain humidity has a positive effect on the contact resistance.With the increase of the humidity,the conductivity also increases.Under relative high humidity,water molecules tend to enter the contact area and changes the mode of debris accumulat io n and connection at the contact area.Water molecules play a role in lubrication which can reduce adhesion and friction of contact surfaces.In other words,relative high humidity reduces the formation of wear debris due to the improved friction properties,which is beneficial to electrical contact properties.?.The physical properties of wear debris can be changed by water molecules,includ i ng stacking mode and composite state.The physical model based on the mathematica l method of electrical contact failure is established.The physical model of the contact surface contaminants simulates the real service process.The theoretical analysis of electrical contact failure model shows that the essential reason of electrical contact failure is the continuous accumulation of surface pollutants.Physical model of the contact surface contaminants for each micro-action is established,which ultimate l y leads to the failure.Thus,the service life of the contact can be predicted reliably.A quantitative study of environmental factors is required to further analyze the contact resistance.(3)The influence of surface roughness on electrical contact performance?.Metal ic wear debris is generated by fretting motion and forms a third body adhered to the rough surfaces which is hardly removed away under stabilized gross slip conditions.Formation of a third body transforms contact surface into metal–debris–metal pattern and eventually causes increases and instability of electrical contact resistance.?.At smoother contactors,wear debris are easily removed with the fretting motion,which decreases the probability of debris' conducting and hence make the electrical contact resistance lower and stable.On the contrary,wear debris difficulty generate under lower displacement amplitude and hence contact resistance gets lower.Whether the wear debris participate in conducting is the essential reason to affect electrical contact resistance.