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Research Papers

# Lightweight Actuator Structure With SMA Honeycomb Core and CFRP Skins

[+] Author and Article Information
Yoji Okabe

Department of Mechanical and Biofunctional Systems, Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japanokabey@iis.u-tokyo.ac.jp

Hiroshi Sugiyama

Department of Mechanical and Biofunctional Systems, Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japansugiyama@smart.k.u-tokyo.ac.jp

Toru Inayoshi

Department of Mechanical and Biofunctional Systems, Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japaninayoshi@iis.u-tokyo.ac.jp

J. Mech. Des 133(1), 011006 (Jan 03, 2011) (8 pages) doi:10.1115/1.4003139 History: Received September 29, 2009; Revised November 10, 2010; Published January 03, 2011; Online January 03, 2011

## Abstract

The authors proposed a sandwich structure that consists of a shape memory alloy (SMA) honeycomb core and carbon fiber reinforced plastic (CFRP) skins as a shape-controllable structure. The proposed lightweight actuator structure can be bent by heating even though it has a moderate bending stiffness. First, unidirectional CFRP skins were bonded to the SMA honeycomb core made of thin SMA foils, and residual shear strain was applied to the SMA core. Then, the ends of the upper and lower skins were fixed to other cores. The length, thickness, and width of the sandwich beam specimen were 180 mm, 16 mm, and 13 mm, respectively, and its weight was 9.6 g. Hence, the effective density of the entire beam was only $0.26 g/cm3$. When the specimen was heated, the beam either bent upward, taking the form of a sigmoid curve, or generated a moderate blocking force. When the specimen was cooled to room temperature, the beam regained its initial straight shape. Therefore, a two-way actuation is possible. This method has a better ability to bend skins with high in-plane stiffness because the recovery shear force has an out-of-plane stress component and is applied uniformly to all the skins from the inner core. In addition, the microscopic mechanism of this bending deformation can be clarified by a numerical simulation with a finite element method. Furthermore, the proposed actuator structure can possibly be used as a member that suppresses resonance since the natural frequency of the beam can be controlled by increasing the elastic moduli of SMA on heating.

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## Figures

Figure 1

Honeycomb core made of 50-μm SMA foils

Figure 2

SMA honeycomb sandwich panel with self-repair property for impact damages (1): (a) intact panel, (b) impact load was applied, and (c) impact damage was repaired by heating

Figure 3

Principle of bending deformation actuated by recovery shear stress of SMA honeycomb core: (a) adhesive bonding of CFRP skins and SMA honeycomb core, (b) application of residual shear strain to the SMA core, (c) fixing both ends of the skins and heating the core, and (d) bending deformation

Figure 4

SMA foils are held in paired metal molds for memorization of the honeycomb shape

Figure 5

Manufacturing process of the SMA honeycomb core: (a) SMA foil having memorized the half-hexagonal shape and (b) SMA foils bonded to each other to form the honeycomb shape

Figure 6

Manufacturing process of the sandwich beam: (a) after application of residual shear strain and (b) fixing the ends of both skins

Figure 7

Dimensions of the specimen

Figure 8

Experimental setup to measure the shape of the sandwich beam in a thermostatic chamber

Figure 9

Deformation of the upper skin measured at various temperatures

Figure 10

Photographs of the specimen in the thermostatic chamber: (a) at 25°C and (b) at 90°C

Figure 11

Deformation of the honeycomb cell: (a) at 25°C and (b) at 90°C

Figure 12

A weight being lifted due to the bending actuation of the sandwich beam: (a) at 25°C and (b) at 90°C

Figure 13

Illustration of blocking force measurement in a thermostatic chamber

Figure 14

Blocking force measured at various temperatures

Figure 15

Stress-strain curves of SMA foils plotted at 25°C and 90°C for determination of the properties used in FEM analysis: (a) at 25°C and (b) at 90°C

Figure 16

Calculation of shear deformation

Figure 17

Longitudinal strain in SMA foils along the inner surface of the honeycomb cell at 25°C: (a) initial state and (b) after the shear deformation (step 2)

Figure 19

Calculated deformation of SMA sandwich beam at high temperature

Figure 20

Comparison of bending deformation of the upper skin obtained from the experiments and by numerical simulation at 90°C

Figure 21

Longitudinal strain in SMA foils along the inner surface of the honeycomb cell at 90°C: (a) upper and lower surfaces are constrained and (b) upper and lower surfaces are free

Figure 22

Free oscillations of the SMA sandwich beam without residual shear strain in the SMA honeycomb: (a) at 25°C and (b) at 90°C

Figure 23

Frequency characteristics of free oscillations

Figure 18

Constraint conditions for calculation of bending deformation

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