Smart Materials and Structures

Grazvydas Kazokaitis has experience in design and R&D fields developing small and precise mechanisms for ultra-fast laser beam control and machining apparatus. This experience allows provide solid foundation and knowledge creating possible solutions for laser beam orientation mechanisms between small units in space, attitude control and other control tasks. \r\n \r\nVytautas Jurenas is senior researcher in Kaunas University of Technology. The main areas of R&D are dynamics and diagnostics of mechanical systems. His research interests include piezomechanics and its application in hi-tech mechatronics. Research interest: Mechanical engineering; piezoelectric drives and actuators, spaces technologies.\r\n

Piezoelectric magnetic drive is a device which uses two piezoelectric actuators for precise 3 degrees of freedom (DOF) rotation of sphere-shaped rotor. Mechanical part of this drive described further: sphere-shaped rotor inserted between two piezoelectric actuators. These ring-shaped piezoelectric actuators have polarization in axial direction and one of the electrodes is devided into three equal sectors. Each segmented electrode is excited by separate harmonic signal. All three electrodes can be excited independently i.e. three channels generator is used to drive actuator. Amplitude and duration of the applied signal depends on rotation velocity and motion trajectory of the sphere. The out-of-plane bending and radial vibrations of the piezoelectric rings are excited to obtain elliptical motion of the contacting points and to rotate magnetic sphere in desired direction. In addition, it must be mentioned that actuator can be driven by burst type signal in order to achieve positioning of the sphere with very high resolution. Described system could be used for applications, where precise 3 DOF rotational control of the sphere-shaped rotor is needed. Few examples of such applications: space and attitude control of the satellites, laser beam control, precise mirror deflectors and etc.

Miss S. Norouzi Esfahany has just completed her MSc from Tarbiat Modares University. This article is a portion of her MSc thesis.

In this work, chemically cross-linked polyacrylamide (PAAm) hydrogel prepared by free radical polymeriztion. The effect of water content on glass tarnsition temperature (Tg) of hydrogel, as switch temperature of shape memory system, was investigated using dynamic mechanical analysis (DMA). The transition temperature, i.e. the desired switch temperature for our work, was chosen around ~ 30 oC by tunning the water content of hydrogel at 25%, Fig. 1. Shape memory behaviour of chosen hydrogel was investigated for a full cycle, i.e. four steps, by DMA. The four steps procedure performed at a constant heating/cooling rate of 5oC.min-1. First, the sample was heated to 50 oC (above the switch temperature) and stretched to a certain strain (ε) under a constant force (Step 1). Then, the deformed sample was cooled to -50oC under the fixed force (Step 2). The force then removed and the temporary strain was measured (Step 3). Finally, the sample was reheated to 50 oC and kept for 50 min in this temperature, then the recovery strain recorded (Step 4). The shape fixing ratio and shape recovery ratio as the main characteristics of shape memory polymeric system calculated from Fig. 2. The results indicated that the shape fixing ratio and shape recovery ratio of the system were 96% and 78%, respectively. Recovering to orginal shape was started around 10 oC. The sample showed good shape fixity because of existence the hydrogen bonds between PAAm and water. Hydrogen bonds as physical cross linkers could improve structural strength of the sample.