Shape memory actuators - potentials and specifics of their technical use and electrical activation
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.
The electro-mechanical control of element NiTi shape memory alloy strip while bending, based on thermal analysis evidence
This paper presents an experimental investigation of a commercial shape memory alloy strip consisting of nickel and titanium (NiTi SMA), which correlates the thermal properties (phase transitions) with the electrical and mechanical properties of the material, allowing to be used for control applications in engineering. The bending performances of the SMA strip at different values of the activation electric current, during heating process, are also investigated. By using the differential scanning calorimetry (DSC) experiments, the thermal characteristics of the SMA strip were identified. The results of this thermal analysis were the basis for determining the equilibrium temperature, entropy and force developed by the SMA strip during the phase transformation. For the study of the SMA strip, the authors have developed an experimental platform, which uses a portable reconfigurable I/O (RIO) device and LabVIEW graphical programming environment for the measurement, testing and rapid control of parameters, and a piezo-film sensor for controlling of SMA strip movement. The real-time measurements and acquired waveforms are displayed on a PC screen, and the data associated with these waveforms are stored for later use, i.e. for applications in safety engineering like the fire extinguishing control, where very short response/activation times are required.
Development and full-scale dummy tests of a pop-up hood system for pedestrian protection
A pop-up hood system has been developed to reduce the severity of head injuries to pedestrians in pedestrian-to-automobile accidents. The system employs sensors located on the bumper to detect impact with a pedestrian. If an impact occurs, a signal is sent to an actuator to raise the rear portion of the engine hood approximately 100mm. This provides a space between the engine and other hard components and the hood, resulting in reduced pedestrian head injuries. Previous studies have mainly employed headform impactors to evaluate the head injury criteria (HIC) values for pop-up hoods. This report describes studies of the effect of the pop-up hood on injury parameters and kinematics using the POLAR pedestrian dummy. The effectiveness of the pop-up hood system was confirmed by the significant reduction of HIC values in impact tests using the POLAR dummy.