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Design of a self-adjusting terminal connector based on shape memory alloys

: Pagel, Kenny; Zimmermann, Philipp; Bucht, Andre; Drossel, Welf-Guntram


Zagrai, Andrei ; American Society of Mechanical Engineers -ASME-:
ASME Conference on Smart Materials, Adaptive Structures and Intelligent Systems, SMASIS 2014. Proceedings : September 8-10, 2014, Newport, Rhode Island, USA
New York/NY.: ASME, 2014
Paper 7429
Conference on Smart Materials, Adaptive Structures, and Intelligent Systems (SMASIS) <7, 2014, Newport/R.I.>
Fraunhofer IWU ()
shape memory alloy; terminal connector; electrical contact; connector; self adjusting; self suficcient actuator; adaptive connector; creep; reset pretension

In electrical engineering terminal connectors are commonly used for connecting and releasing electrical conductors. They are sophisticated mass products sufficient for high- and low power transmission or transmitting information. There are various applications for wiring in cars, control- or house installations and electrical power supply systems. Depending on the electrical current to be transmitted and consequently the wire diameter there are several approaches to realize a durable and safe mechanical connection between the conductors. The electrical contact resistance of such systems is defined by the constriction- and the film resistance. The constriction resistance heavily depends on the contact or load force. If the connection becomes loose, this force decreases or even disappears, which results in an extensive raise of the temperature in the contact area. The current density is locally increasing on certain connection points. The raised temperature may lead to unwanted operational states or even fire. There are a few mechanical solutions to realize a constant or re-adjusting contact force. However, these approaches are mechanically complex and hence cost intensive.
In this paper we present the development and experimental investigation of a self-adjusting terminal connector based on shape-memory alloys (SMA) which is far less complex than currently known mechanical solutions. The compensation of the decreasing contact force is realized by a precompressed SMA cylinder, which is located in a drill hole at the bottom of the terminal connector’s screw. Under normal conditions the terminal works similar to a conventional screw connector. In case of decreasing contact forces, the increasing contact resistance results in a rising temperature. As soon as the austenite start temperature is reached the SMA cylinder starts to expand and resets the contact force. As a result the system cools down and the SMA cylinder keeps a desired contact force. In this paper we present the general design of such a system and ist limitations. Measurement data of the SMA cylinder and the active terminal connector will further show the proof of the concept.