**5.3. Structural modeling of flexible fluidic actuators**

Structural and material nonlinearities as well as large strains make it very hard to predict the behavior and characteristics of flexible fluidic actuators. Thus implementing a structural model of FFAs is a challenging task. The FEM-model was developed with ANSYS in order to provide a design tool for FFAs. The configuration of the model is illustrated in figure 20. The different layers of the actuator shell are modeled using different elements. The inner and outer rubber shell is modeled with 941, 902 SOLID285-elements using a hyperelastic material model according to YEOH 2. The fiber reinforcement is represented by 13, 428 SHELL181-elements which are connected to REINF265-elements respectively 3. The structural integrity of the corresponding joint is modeled using 1, 502 MPC184-Link/Beam-elements. The metal brackets are implemented using 14.042 SOLID185-elements 4. Including the contact elements, the model consists of 1, 235, 804 elements.

**Figure 20.** Set-up of the FEM-Model for a Flexible Fluidic Actuator


In order to compare the structural model with the behavior of the real actuator at first a strain analysis is conducted. Figure 21(a) compares the strain behavior of the model and the real actuator for joint motions of 0◦ − 90◦. The comparison shows good compliance of model and actuator.

18 Will-be-set-by-IN-TECH

The requirements to operate FFAs are pressure supply, control members, and sensory infrastructure. Depending on the complexity of control that is desired, control members and sensors can include valves, position sensors, pressure sensors, and micro controllers. A detailed overview for highly integrated FFAs is given in [1]. Using hydraulics for mobile

Structural and material nonlinearities as well as large strains make it very hard to predict the behavior and characteristics of flexible fluidic actuators. Thus implementing a structural model of FFAs is a challenging task. The FEM-model was developed with ANSYS in order to provide a design tool for FFAs. The configuration of the model is illustrated in figure 20. The different layers of the actuator shell are modeled using different elements. The inner and outer rubber shell is modeled with 941, 902 SOLID285-elements using a hyperelastic material model according to YEOH 2. The fiber reinforcement is represented by 13, 428 SHELL181-elements which are connected to REINF265-elements respectively 3. The structural integrity of the corresponding joint is modeled using 1, 502 MPC184-Link/Beam-elements. The metal brackets are implemented using 14.042 SOLID185-elements 4. Including the contact

applications instead of pneumatics can help to avoid bulky pressure supplies.

**5.3. Structural modeling of flexible fluidic actuators**

elements, the model consists of 1, 235, 804 elements.

**Figure 20.** Set-up of the FEM-Model for a Flexible Fluidic Actuator

<sup>2</sup> *<sup>C</sup>*<sup>10</sup> <sup>=</sup> 0.477330421717; *<sup>C</sup>*<sup>20</sup> <sup>=</sup> <sup>−</sup>0.148261658100; *<sup>C</sup>*<sup>30</sup> <sup>=</sup> 0.225732915194 <sup>3</sup> Young's Modulus *<sup>E</sup>*� <sup>=</sup> <sup>124</sup> *kN mm*<sup>2</sup> ; *<sup>E</sup>*<sup>⊥</sup> <sup>=</sup> <sup>8</sup> *kN*

*mm*<sup>2</sup> ; Poisson's Ratio *<sup>ν</sup>* = 0.32

<sup>4</sup> Young's Modulus *E* = 210 *kN*

*mm*<sup>2</sup> ; Poisson's Ratio *<sup>ν</sup>* = 0.32

**5.2. Operating flexible fluidic actuators**

(b) Stress Analysis of the Fiber Reinforcement of a Flexible Fluidic Actuator (∅18 *mm*)

#### **Figure 21.** Structural Analysis of the Actuator Model

The stress analysis of the fiber reinforcement in the actuator shell is shown in figure 21(b). The regions of high stress correspond with the areas where fatigue failure occurs.
