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Shape memory actuators - potentials and specifics of their technical use and electrical activation

Strittmatter J., Gümpel P., Gheorghita V.

Journal of Achievements in Materials and Manufacturing Engineering

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2012

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Vol. 55, nr 2

368--377

EN

Due to a martensitic phase change shape memory alloys can revert to their original shape by heating when they undergo an appropriate treatment. Actuator elements with this shape memory effect can show a significant design change combined with a considerable force. Therefore they can be used to solve many technical tasks in the field of actuating elements and mechatronics. These intelligent materials will play an increasing role in the next years, especially within the automotive technology, energy management, power and mechanical engineering as well as medical technology. In order to use the potential of these materials in an optimal way it is necessary to know and understand the extraordinary and unconventional properties of shape memory alloys. This paper will present the commonly used systems of shape memory alloys of today including their performance characteristics and will explain the basics of the shape memory effect in a vivid way. A multitude of application possibilities of shape memory actuators will be presented, in particular the research and development projects that have been carried out at the Konstanz University of Applied Sciences during the last years. In this way a solid state heat engine and an intramedullary nail for bone elongation will be presented as well as various adaptive systems for automotive safety and comfort systems, driven by shape memory elements. Regarding the applications in the automotive field a special focus will be given to different electrical activations to enable very fast contraction times of the shape memory components.

2

Pitting corrosion in the wet section of the automotive exhaust systems

Hoffmann C., Gümpel P.

Journal of Achievements in Materials and Manufacturing Engineering

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2009

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Vol. 34, nr 2

115-121

EN

Purpose: In the rear section of the automotive exhaust systems condensates bearing appreciable chloride ion concentrations and often low pH-values together with particles of electrochemical active soot can lead to pronounced pitting corrosion on the inner surfaces. For selection of an appropriate material that can enable cost-effective construction, the corrosion resistance of different candidate grades has to be rated. Design/methodology/approach: The different types of occurring corrosion, both general attack and pitting corrosion demands a combination of evaluation methods of the corrosion attack: mass loss measurements and the measure of the average depth of a certain number of pits with an optical 3D-Measuring System MicroCAD were used. Findings: The two methods for the evaluation of the corrosion attack provide the same ranking of the materials. Both methods are complementary to each other and together they provide a noticeable differentiation between some of the investigated materials. Research limitations/implications: The average depth of the pits gives no information about the entire rate of the corrosion attack, about the total number of the pits and their depth. In the future, research with the same optical 3D-Measuring System MicroCAD and new software will be carried out. This will form a structured analysis of the entire pits for the quantification of the corrosion. Practical implications: A higher quantification of the pitting corrosion leads to a better rating of the different stainless steel grades for using them in the wet section of the automotive exhaust systems. Originality/value: The evaluation of the pitting corrosion by means of the new measurement methods with the optical 3D-Measuring System MicroCAD is more accurate, work fast and is an obligatory complement of the previous methods of evaluation of the pitting corrosion: mass loss and the depth of the deepest pit.

3

Long-time stability of shape memory actuators for pedestrian safety system

Strittmatter J., Gümpel P., Zhigang H.

Journal of Achievements in Materials and Manufacturing Engineering

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2009

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Vol. 34, nr 1

23-30

EN

Purpose: Pedestrian safety systems play an increasing significant role to reduce injuries and fatal casualties caused by accidents. One automotive safety system for pedestrian protection is the bonnet lifting system. Using shape memory alloys (SMA) the existing systems could be simplified, performing the same function through new mechanisms with reduced size, weight and costs. A drawback for the use of SMA in such safety systems is the lack of material knowledge concerning the durability of the switching function. This paper gives an introduction to existing bonnet lifting systems for pedestrian protection, describes the use of quick changing SM actuators and presents the testing facilities and some results of the study concerning the long-time stability of the tested NiTi-wires. Design/methodology/approach: A large number of NiTi-wires was trained, exposed up to four years at elevated temperatures and tested regarding their phase change temperatures, times and strokes. Findings: It was found out that Ap-temperature is shifted towards higher temperatures with longer exposing periods and higher temperatures. However, in the functional testing plant a delay in the switching time could not be detected. Research limitations/implications: For future works it is suggested that more NiTi-specimens at longer ageing periods should be tested, stress should also be applied by a constant load and the functional testing plant should be further optimized. Practical implications: It can be concluded, that the use of quick changing SM actuators in safety systems could simplify the mechanism, reduce maintenance and manufacture cost and should be insertable also for other automotive applications. Originality/value: This paper gives some answers concerning the long-time stability of NiTi-wires that were missing till now. With this knowledge the number of future automotive applications using SMA can be increased.