Experimental Study on Arcing Effects to Contact Materials in 270V dc

As supply DC voltage levels in automobiles, aviation and aerospace are becoming higher, high voltage and large capacity compact DC electromagnetic relays or contactors are becoming more important. In this paper, experiments were conducted at DC 270V/100 A in air and nitrogen, respectively, with CuCr40, CuCr45, CuCr50, CuW60, CuW70 and CuW90 as contact materials. Welding resistance (corresponding to electrical contact life), contact erosion and breaking arc durations were measured, and the obtained results were discussed.

Radar Non-Contact Life Parameter Detection System

The main principle of radar non - contact life detection technology is the use of electromagnetic wave by the human body, the echo signal is modulated by the surface movement caused the life activities of the human body, so that some parameters of the return signal change. The research on the non contact detection technology, completed the construction of life monitoring system module of hardware, design of software algorithm, real-time data acquisition, and the use of special software algorithms, to detect these changes, and then extracting parameters of human life.

Fatigue Failure of Silicon Nitride Ceramic Balls

Silicon nitride ceramic ball surface is examined after failure with scanning electron microscopy. The profile of the fatigue spalling takes the shape of an ellipse. The failure cause, fatigue phenomenon and mechanics are analyzed. The research shows that subsurface cracks play a dominant role in the formation of spalling failure. These cracks originated from volume defects of the material, and propagate, to form fatigue spalls under the action of principal tensile stresses. The contours of equal tensile stress of Oxy plane underneath surface are elliptical. Subsurface cracks are shape of ellipses and spall is also of the elliptic shape. The principal tensile stress increases with increasing contact load, causing spall formation and reduction of rolling contact life.

The Effects of One Sided Gold Finish on the Reliability of Electrical Contacts under Fretting Conditions

The electric contact is one of the most primary elements to affect the reliability of the electric systems. Gold finish can maintain high contact reliability but increase the manufacture cost. In this paper, the effects of one sided gold plated contacts with various thickness of gold finish on the contact reliability were investigated. The failure mechanism of the one sided gold plated contacts under fretting conditions was analyzed. The contact life and the optimum thickness of the one sided gold finish under fretting conditions was achieved and compared. The effect of the curvature of the probes on the contact life was also discussed.