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Bio-inspired wooden actuators for large scale applications.

Rüggeberg M, Burgert I - PLoS ONE (2015)

Bottom Line: Field tests in full weathering conditions revealed long-term stability of the actuation.The potential of the concept is shown by a first demonstrator.With the sensor and actuator intrinsically incorporated in the wooden bilayers, the daily change in relative humidity is exploited for an autonomous and solar powered movement of a tracker for solar modules.

View Article: PubMed Central - PubMed

Affiliation: Institute for Building Materials, Swiss Federal Institute of Technology Zürich (ETH Zürich), Zürich, Switzerland; Applied Wood Materials, Swiss Federal Laoratories of Materials Science and Technology (EMPA), Dübendorf, Switzerland.

ABSTRACT
Implementing programmable actuation into materials and structures is a major topic in the field of smart materials. In particular the bilayer principle has been employed to develop actuators that respond to various kinds of stimuli. A multitude of small scale applications down to micrometer size have been developed, but up-scaling remains challenging due to either limitations in mechanical stiffness of the material or in the manufacturing processes. Here, we demonstrate the actuation of wooden bilayers in response to changes in relative humidity, making use of the high material stiffness and a good machinability to reach large scale actuation and application. Amplitude and response time of the actuation were measured and can be predicted and controlled by adapting the geometry and the constitution of the bilayers. Field tests in full weathering conditions revealed long-term stability of the actuation. The potential of the concept is shown by a first demonstrator. With the sensor and actuator intrinsically incorporated in the wooden bilayers, the daily change in relative humidity is exploited for an autonomous and solar powered movement of a tracker for solar modules.

No MeSH data available.


Related in: MedlinePlus

Actuation of bilayers during cyclic change of relative humidity.a) Relative humidity and wood moisture content, b) curvature of bilayers (color code as in Fig. 2). c) Specific curvature k*Δα: experimentally derived (small dots), average of each loop (squares), and calculated using Equation 3 (lines).
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pone.0120718.g003: Actuation of bilayers during cyclic change of relative humidity.a) Relative humidity and wood moisture content, b) curvature of bilayers (color code as in Fig. 2). c) Specific curvature k*Δα: experimentally derived (small dots), average of each loop (squares), and calculated using Equation 3 (lines).

Mentions: Since the water exchange in wood via sorption and diffusion takes time, the new equilibrium state in the step wise changes was reached after approximately 24 hours. In practical applications the bilayers will be subjected to gradual and cyclic changes and, thus, will be operated in non-equilibrium state which results in a more complex behaviour. Hence, the actuation pattern in cyclic conditions was investigated for four bilayers made of beech and spruce with varying spruce layer thicknesses. These bilayers were subjected to a cyclic change of relative humidity between 85% and 35% with cyclic periods of 24, 12, and 6 hours, respectively (Fig. 3a). For each period four loops were programmed. The cyclic change in relative humidity resulted in changes of wood moisture content of 3.3±0.2% for a cycle of 24 hours, 2.1% for 12 hours and 1.3% for 6 hours. For a bilayer with 0.2mm thick spruce layer this change in wood moisture content resulted in amplitudes of curvature of 4.1±0.4*10-3mm-1, 2.9±0.2*10-3mm-1, and 2.0±0.05*10-3mm-1, respectively (Fig. 3a-b). Table 1 gives an overview of the curvatures achieved with the other three bilayers. The amplitudes stayed almost constant during the four loops of one specific cycle. The wood moisture content could not be measured on the bilayers themselves, but was measured on additional beech strips on a scale within the climate chamber.


Bio-inspired wooden actuators for large scale applications.

Rüggeberg M, Burgert I - PLoS ONE (2015)

Actuation of bilayers during cyclic change of relative humidity.a) Relative humidity and wood moisture content, b) curvature of bilayers (color code as in Fig. 2). c) Specific curvature k*Δα: experimentally derived (small dots), average of each loop (squares), and calculated using Equation 3 (lines).
© Copyright Policy
Related In: Results  -  Collection

License
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getmorefigures.php?uid=PMC4383548&req=5

pone.0120718.g003: Actuation of bilayers during cyclic change of relative humidity.a) Relative humidity and wood moisture content, b) curvature of bilayers (color code as in Fig. 2). c) Specific curvature k*Δα: experimentally derived (small dots), average of each loop (squares), and calculated using Equation 3 (lines).
Mentions: Since the water exchange in wood via sorption and diffusion takes time, the new equilibrium state in the step wise changes was reached after approximately 24 hours. In practical applications the bilayers will be subjected to gradual and cyclic changes and, thus, will be operated in non-equilibrium state which results in a more complex behaviour. Hence, the actuation pattern in cyclic conditions was investigated for four bilayers made of beech and spruce with varying spruce layer thicknesses. These bilayers were subjected to a cyclic change of relative humidity between 85% and 35% with cyclic periods of 24, 12, and 6 hours, respectively (Fig. 3a). For each period four loops were programmed. The cyclic change in relative humidity resulted in changes of wood moisture content of 3.3±0.2% for a cycle of 24 hours, 2.1% for 12 hours and 1.3% for 6 hours. For a bilayer with 0.2mm thick spruce layer this change in wood moisture content resulted in amplitudes of curvature of 4.1±0.4*10-3mm-1, 2.9±0.2*10-3mm-1, and 2.0±0.05*10-3mm-1, respectively (Fig. 3a-b). Table 1 gives an overview of the curvatures achieved with the other three bilayers. The amplitudes stayed almost constant during the four loops of one specific cycle. The wood moisture content could not be measured on the bilayers themselves, but was measured on additional beech strips on a scale within the climate chamber.

Bottom Line: Field tests in full weathering conditions revealed long-term stability of the actuation.The potential of the concept is shown by a first demonstrator.With the sensor and actuator intrinsically incorporated in the wooden bilayers, the daily change in relative humidity is exploited for an autonomous and solar powered movement of a tracker for solar modules.

View Article: PubMed Central - PubMed

Affiliation: Institute for Building Materials, Swiss Federal Institute of Technology Zürich (ETH Zürich), Zürich, Switzerland; Applied Wood Materials, Swiss Federal Laoratories of Materials Science and Technology (EMPA), Dübendorf, Switzerland.

ABSTRACT
Implementing programmable actuation into materials and structures is a major topic in the field of smart materials. In particular the bilayer principle has been employed to develop actuators that respond to various kinds of stimuli. A multitude of small scale applications down to micrometer size have been developed, but up-scaling remains challenging due to either limitations in mechanical stiffness of the material or in the manufacturing processes. Here, we demonstrate the actuation of wooden bilayers in response to changes in relative humidity, making use of the high material stiffness and a good machinability to reach large scale actuation and application. Amplitude and response time of the actuation were measured and can be predicted and controlled by adapting the geometry and the constitution of the bilayers. Field tests in full weathering conditions revealed long-term stability of the actuation. The potential of the concept is shown by a first demonstrator. With the sensor and actuator intrinsically incorporated in the wooden bilayers, the daily change in relative humidity is exploited for an autonomous and solar powered movement of a tracker for solar modules.

No MeSH data available.


Related in: MedlinePlus