Mechanically adaptive shape memory

Fig. 21 (a) Stress-strain curves for polymer P3-4 and control P3-5 shown in Fig. 20. (b) Proposed molecular mechanism for shape-memory behavior. Adapted with permission from [72]. Copyright 2009 American Chemical Society... 

To date, heat-triggered shape memory polymers have had the greatest share of research and application adaptation. However, trigger mechanisms could also be chemo-responsive, e.g., water, ethanol, and pH change photo-responsive, e.g., UV or IR, including radio waves and/or mechano-responsive, e.g., stretching, impact, etc. 

Molecular mechanism of thermally triggered shape memory effect of polymers. T, 5 = thermal transition temperature related to the switching phase. (Adapted from Lendlein, A., and Kelch, S. 2002. Shape-memory polymers. Angewandte Chemie, International Edition 41 2034-2057. Copyright Wiley-VCH Verlag GmbH Co. KGaA. Reproduced with permission.)... 

Schematic figures of the shape memory mechanism of the styrene-butadiene-styrene (SBS) triblock copolymer/poly(e-caprolactone) (PCL) blend in (a)-(d). (Adapted from Zhang, H., Wang, H., Zhong, W, and Du, Q. 2009. A novel type of shape memory polymer blend and the shape memory mechanism. Polymer 50 1596-1601. Copyright Elsevier Ltd. Reproduced with permission.)...

Materials that allow an intelligent or smart structure to adapt to its environment are known as actuators. These materials have the ability to change the shape, stiffness, position, natural frequency, damping, friction, fluid flow rate, and other mechanical characteristics of adaptronic structures in response to changes in temperature, electric field, or magnetic field. The most common actuator materials are shape memory alloys, piezoelectric materials, mag-netostrictive materials, electrorheological fluids, and magnetorheological fluids [2]. Actuators with these materials will be described in detail in Sects. 6.2 to 6.6 therefore you will find only a brief overview below. 

SM actuators may have very many different shapes and offer a variety of shape changes (i. e. actuator strokes). This property can be exploited so as to adapt the SM elements shape to the actuating task. As an application example, a miniature parallel gripper with electrically heated SM wires integrated into its mechanical structure was presented. Further on the performance of pseudo-elastic shape memory flexure hinges in parallel robots for micro-assembly tasks was shown. The future opportunity for thin-fllm SM actuators to drive micromechanical systems and devices was demonstrated by a miniature silicon gripper. 

Water-activated shape-memory materials are a particularly attractive subset of shape-memory polymers, as they can be considered for applications where temperature activation is not desirable. Combining the mechanically adaptive properties of CNC-containing composites and the shape-shifting abilities of shape-memory materials, Mendez et... 

J. Mendez, P. K. Annamalai, S. J. Eichhorn, R. Rush, S. J. Rowan, J. E. Foster, and C. Weder, Bioinspired Mechanically Adaptive Polymer Nanocomposites with Water-Activated Shape-Memory Effect. Macromolecules 44, 6827-6835 (2001). 

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