Wanbin Ren

Fretting Behavior of Au Plated Copper Contacts Induced by High Frequency Vibration

Fretting, which induced by high frequency vibration, remains a major cause of connector failure and can impair reliability in aerospace electrical and electronic systems. The test system was developed for high frequency fretting conditions (Maximum vibration frequency 2000Hz) by using electro dynamic shaker in this paper. The fretting behavior of gold plated copper contacts was studied by controlling the fretting frequency and the fretting amplitude. Contact resistance, friction force, and dynamic fretting displacement were recorded explicitly. Surface characteristics of fretted area are also analyzed by SEM/EDX. It is clearly revealed that the contact micro morphology feature, fretting amplitude and frequency are important factors for electrical contact degradation and the failure mechanisms of contacts.

Mechanical and Electrical Characteristics of the Electromagnetic Relay under Vibration and Shock Environment

The electromagnetic relay, which has mechanical structure and break/make contacts, is affected by vibration and shock environment greatly. Contact wear and failure will be result from serious mechanical conditions. The samples used in this study were relays consisting two spring sets connected with armature component. Simulation results for a variety of vibration levels, frequencies, and shock levels are presented. Thereafter main factors and threshold conditions which influencing contact reliability were determined by the modal analysis and the harmonic response analysis and transient response analysis. The vibration and shock characteristics of movable parts within relay were also obtained by using high speed camera PhantomV7.3�ƒ 10000fps�≈ , thus the mechanism of contact failure is revealed clearly. In addition, the characteristics of contact resistance were investigated when relay working in the mechanical environment. The results are valuable in modeling characteristics degradation and contact failure evaluation caused by mechanical environment for electromagnetic relay. structure. Zhai (3) studied the natural frequency and vibration reaction force of reed by using the analytical method and the finite element program ANSYS/LS-DYNA individually. In his research, the limit vibration acceleration of spring system, referring to the maximum of vibration acceleration which can keep the spring contact reliable, is presented. The results are valuable in determining the thresholds of vibration condition for electromagnetic relay. The other relative research on testing and analyzing performance for relay that working in the mechanical vibration environment were so few, except Flowers (4-7) investigated the electrical connector fretting behavior induced by vibration. We have ever designed the vibration characteristics testing and analyzing system specialized for electromagnetic relay (8). In this paper, simulation model of some commercial electromagnetic relay was built by using FEA software MSC.Patran/Nastran, subsequently modal analysis and harmonic analysis and transient analysis induced by vibration and shock were completed. Experiment results agreed with simulation results well, so the threshold conditions that keep the spring contact reliable was determined. At last the effect of vibration and shock condition on contact resistance of relay is also investigated.

A novel test rig for in situ and real time measurement of welding force and impact force of contacts within electromagnetic relay

Bounce and welding phenomena during contact make and break causes contact resistance degradation and contact material transfer. The correlative failure modes affect electromagnetic relay life greatly. An experimental rig is developed in order to measure the welding force and the impact force of contacts within electromagnetic relay. Furthermore, time parameters (pick-up time, arcing time and bounce time etc.) are also measured synchronously. This is achieved by using a piezoelectric force sensor connected with the stationary contact in addition to synchronization with data acquisition and processing circuit to obtain in situ and real time measurement. And this novel apparatus is designed with five Liner Translation Stages (LTS) to modify the tested-relays structure parameters, including magnetic gap, contact gap, contact position and spring force. The various features and capabilities of the test rig are presented along with some preliminary experimental results of welding force and impact force behavior to assess relays failure mechanism.

Research on storage degradation testing and life prediction based on ARMA and wavelet transform model for aerospace electromagnetic relay

Aerospace electromagnetic relay (EMR) is one of the key electromechanical components used for signal transmission, load switching, circuit protection and control and system isolation. At present, concern for the storage reliability of Aerospace EMR is respectively light although it comes to the highly-dependable and long-life electrical components. And the corresponding research still faces a series of problems, such as low level experiment and test detection, unclear law of performance parameters changing, ambiguous about failure mode and failure mechanism, and lack of effective evaluating and predicting means. Therefore, how to evaluate the storage reliability of aerospace EMR has become the important subject that demanding prompt solution at present. This study used aerospace EMR as research object. A new method for testing storage reliability is proposed by performance parameters degradation. The test and analysis system of aerospace electromagnetic relay storage parameters under temperature-accelerated stress was designed and developed. Based on the analysis of parameters changing in storage degradation testing, the modeling storage reliability method of aerospace EMR is extensively investigated. Prediction parameters preprocessing method is proposed which combines time series analysis with one-dimensional wavelet transform method. This reduces the random signals influence on the prediction precision in prediction parameters. Parameters of the storage degradation model are estimated through regression theory. And the storage life of aerospace EMR under normal stress is predicted. These studies provide the necessary theoretical method and basis for studying storage reliability of the aerospace EMR. Its key techniques and methods could be also applied to other electromechanical components storage reliability studies.

A New Automated Test Equipment for Measuring Electrical Contact Resistance of Real Size Rivets

It is well known that electrical contact resistance influencing factors include not only the contact material physical characteristics, contact type (sphere-flat, flat-flat), the contact surface status (clean, contaminated), but also contact current and mechanical load during measuring. Electrical contact material industry has considerable trouble with batch consistency check of rivet contacts. An automated test equipment and a test method have been described that make it possible to measure the electrical contact resistance of many real size rivet-type contacts with shank diameters 1~4mm at small contact loads with high efficiency. A stainless steel hemisphere with gold coating is designed as standard indenter; meanwhile the alternative choice would be the sphere-flat, flat-flat and sphere-sphere rivet contact pairs. Firstly, the voltage vs. current characteristics of AgCdO rivets is tested under different constant contact force. Secondly, the relationship between contact load and contact resistance during loading and unloading is investigated explicitly with different current. Furthermore, the effect of surface roughness and cleanness on the contact resistance is analyzed by comparison with normal and polished rivets, and those of long term exposure to the air. This equipment can be used for finding out the contact resistance consistency of batch contacts effectively for statistics analysis. But it also helps for the research work on the affecting factors of electrical contact resistance of stationary contacts.

Research on Accelerated Storage Degradation Testing for Aerospace Electromagnetic Relay

It is difficult to obtain the failure data of high-reliability and long-lifetime aerospace electromagnetic relay, even if based on the traditional accelerated storage life testing method. Aiming at this issue Based on the reliability test technique, the scheme of accelerated degradation testing for aerospace relay was designed. The test system of aerospace electromagnetic relay storage parameters under temperature-accelerated stress was designed and developed. Taking a certain aerospace electromagnetic relay as the research object, the accelerated storage degradation testing was carried out. The most past research on storage reliability of relay only focuses on the measurement of relay contact resistance. And, the relay time parameters (closing time, opening time, overtravel time, rebound duration time.) which reflect main performance function was not monitored. So, in this paper the relay time parameters and relay contact resistance were detected simultaneously. The test system of relay storage parameters could be implemented the function that the contact resistances and time parameters of 40 aerospace relays under several temperatures were monitored automatically at the same time. And, the test system transmitted the test data to the host computer for processing. According to the analysis on experiment results of contact resistance, relay time parameters, the degradation phenomena and degradation mechanism of aerospace electromagnetic relay in long-term storage are investigated. These studies provide the basis and reference for latter aerospace electromagnetic relay storage life prediction and using the method of prognostics and health management.

Understanding the fretting failure mechanisms in gold-plated contact materials

Using an electro-dynamic-shaker-based test setup, experiments were performed on gold-plated contacts under a variety of fretting conditions, including different vibration frequencies, vibration amplitudes and different environment temperatures. The variations in contact resistance with fretting cycles are recorded explicitly. The fretted surface is examined using a scanning electron microscope, energy-dispersive X-ray spectroscopy, and a con-focal laser scanning microscope to assess the surface morphology, extent of oxidation and elemental distribution across the fretted zone. It was found that fretting damage is a complex phenomenon for electrical contact applications. Different fretting regimes, including the infinite electrical contact life, the oxidation-dominated failure, and the transient unstable conductivity failure are determined. Finally, the degradation mechanisms of gold-plated contacts are proposed.

Modeling and Simulation of Hermetically Sealed Electromagnetic Relay under Mechanical Environment

Hermetically sealed electromagnetic relays (EMR) are widely used for high reliability control and executive systems as a device mechanically transferring signals. Now they are more indispensable in space engineering, such as rockets, satellites and other ground attachment, but which mechanical atmosphere is too harsh. So dynamics response of EMR is needed to satisfy particularity of such mechanical atmosphere. In this paper, a typical hermetically sealed EMR structure is modeled by using finite element analysis software-Nastran. In the meantime the equivalent spring elements are introduced to simulate the contact of normally closed contacts, and the contact between armature and iron stopper. Therefore dynamic performance of EMR under different mechanical environment, including sinusoid vibration and shock condition is investigated completely. The factors affecting normal modes and dynamic response of EMR are analyzed. Comparisons show good correlation between experimental and numerical results.

Preliminary study on switching characteristics of silver tin oxide type contacts for capacitive load

Electrical lifetime and relative dynamic welding failure mechanisms of electromechanical relay for capacitive load are hot topics in the area of switching devices and electrical contact materials. In this work, the silver tin oxide contact material has been tested with a capacitive load by using our designed novel model switch. The typical waveforms of contact current and contact voltage at making and breaking are presented. Further, the variations in contact resistance and contact force as a function of operation cycles are plotted and analyzed explicitly. Particularly, an intermittent long-duration arcing phenomena during breaking is observed and explained with the change of arcing duration and obtained SEM image. Finally, the associated physical degradation mechanism of contact material is proposed.

The effect of mechanical parameters of switch-type contact on relay operation characteristics

Electric arc erosion during contact break/make cause contact resistance degradation, material transfer, non-closing and non-opening, above failure modes affect relay operation characteristics greatly. A relay model testing device which could simulate relay parameters of: initial contact force between N.C. contacts, contact gap and N.O. over-travel mechanical parameters assembly was used to study arc erosion. During breaking and closing operation, contact resistance, pick-up/release voltage, pick-up/release/arc duration were recorded explicitly during test. The optimal matching mechanical parameters assembly of switch-type contact was determined by test results comprehensively. Therefore the contradiction between reducing arc duration and lower bouncing time was solved in maximum extent. The conclusions drawn in this paper are meaningful for optimization of mechanical parameters of switch-type contact in relay.