Paul Gümpel

Phase Change Behavior of Nitinol Shape Memory Alloys

Among other special characteristics Shape Memory Alloys (SMAs) have the ability to return to a predetermined shape when heated. In fact, the phase change of an existing element can strongly be influenced by thermal and thermo-mechanical treatments. Up to now, SMEs have been discovered in various materials, which can generally be classified into noble-metal based, Cu-based, Fe-based, Ni-Ti-based alloy systems and non-metallic SMAs. In this paper a general overview of the Ni-Ti system and a detailed review over the Ni-Ti-Cu system will be given with special regard to the influence of heat treatments upon the phase change behavior.

Using Shape Memory Alloys in Automotive Safety Systems

In modern automobiles a lot of actuators are used to run safety systems. Nowadays these are mechanical, electromechanical, pneumatic, pyrotechnic or electromagnetic actuators. For releasing them electrical or mechanical energy is used. This paper presents a new class of actuators in safety systems using shape memory wires. They are able to replace the conventional actuators. The goal for this research work is to use shape memory elements in a clamping system of a steering column as well in safety as in comfort area. The shape memory elements control the opening and closing function that presses with maximum 5,000 N against the steering jacket. For the first prototype, called drum type, shape memory wires are used to open the system and disc springs are used for closing. The second prototype is a so-called lateral actuator, where shape memory elements are used for the opening and closing function. Tests with the drum prototype are carried out with up to 16 wires up to date. Each wire is preloaded with 50 N that corresponds to a compression of the disc springs of 800 N. When the wires are electrically activated they contract the disc springs until 1,200 N over a stroke of 1 mm. In this configuration an electrical power of 16 V and 56 A is used. The second prototype is designed with four wires of 0.5 mm diameter for closing and two wires for opening the clamping system. To open the clamping system in less than one second an electrical power of 7 A and 12 V is necessary, while 14 A and 12 V is needed to close it within 1.5 s. At the moment the application of the first prototype is restrained through an energy limitation, because the battery of modern automobiles would not be sufficiently adequate. Anyway, in the near future more electrical cars will be on the market and therefore this prototype can successfully be implemented. One of the advantages using shape memory alloys in the design of a steering column is its lightweight. Moreover it is possible to control the energy in any time because of the electrical activation and the control of the electrical resistance of the shape memory actuators. Thereby this actuator can be activated and the steering column can even be released in special crash situations in order to create enough space for the airbag and to avoid a possible touch of the body of the driver with the steering wheel.

Harte und Verschleissfeste Randschicht auf Korrosionsbeständigen Stählen

Im Fahrzeug- und Motorenbereich werden immer haufiger nichtrostende Stahle eingesetzt. Diese hochkorrosionsbestandigen austenitischen oder ferritischen Werkstoffe sind nicht hartbar und neigen daher bei mechanischen / tribologischen Beanspruchungen an der Oberflache zu Verschleiserscheinungen. Hier kann mit einem neuartigen Oberflachenhartungsprozess Abhilfe geschaffen werden, ohne dass dabei die Korrosionsbestandigkeit eingeschrankt wird. In Zusammenarbeit zwischen der Hochschule Konstanz und Bodycote wird kontinuierlich die Entwicklung vorangetrieben, um neue Anwendungsfelder zu eroffnen.

Smart Materials: Opportunities and Applications in Some Fields

Abstract In the first part of this paper, a short introduction to the mechanism of shape memory alloys (SMAs) is given and especially the NiTi alloys are described. Some examples for the application of these materials are presented. One is a quick changing actuator in a car safety system. Some examples of different safety systems in modern cars are described and the material development of an adaptive safety system with SMAs is explained. Through the spontaneous conversion of the SMA when exceeding a critical temperature, a very fast and functional secure linear movement can be performed. It should be possible to implement SMAs with long time stability. Quick heating systems have been developed for this purpose to enable a quick and safe heating of the SM elements by using the actual current network system on board. In the second part, a newly-developed intramedullary nail with a device made of SMAs used for limb lengthening is presented. The benefit of such an alternative device is described, together with the details of the design. The use of smart materials in mechanical design offers benefits such as lower complexity of the device and closeness to bionic structures.

Potential Capabilities of Shape Memory Driven Automotive Devices

In the automotive industry a strong effort has been undertaken to reduce the weight of modern vehicles. In order to reduce the energy consumption and to improve the environmental sustainability, the importance of weight reduction activities is even growing faster. As lightweight designing is becoming more and more expensive and show less potential savings, new approaches are needed. One promising technology could be the use of shape memory elements. In the last years a lot of potential application possibilities were presented, demonstrating the benefit of these functional elements in automotive design solutions: they often reduce complexity, weight and design space of an actuation device and enable new functions. In addition they work silently and are therefore ideally suitable for comfort applications in the passenger cabin. Because of the current trend to electric vehicle the hitherto existing drawback of a high electrical energy consumption of shape memory actuators in some design proposals is not given any more.

Improving hardness and wear resistance of austenitic stainless steel

Nowadays more stainless steels are used in the field of automotive technology. These austenitic or ferritic steels have a high corrosion resistance but they are not hardenable and therefore they are susceptible to gallig/fretting during mechanical/tribological loading, for example in connecting rods. With a new surface hardening treatment these detrimental effects can be avoided. Hochschule Konstanz and Bodycote jointly develop this process further to open up new market areas.