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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 after step-wise change of relative humidity from 85% to 35%.Color code: red: 0.2mm spruce layer (thickness ratio m = 0.05); blue: 0.8mm (0.2), green: 1mm (0.25), orange: 2mm (0.5), purple: 3mm (0.75), brown: 4mm (1). a) Wood moisture content, b) curvature, c) curvature of bilayers with different m (note that the overall thickness h also changes), d) curvature of a bilayer 1,2,4,8, and 24 hours after transfer. The actuation is also made visible in a movie (S1 Movie). e) Comparison of experimentally derived and calculated specific curvature k 24 hours after transfer. Calculations are shown for values of n = E1/E2 of 10 (dotted line), 20 (solid line), and 30 (patched line). f) Relative amplitude of k as a function of n and m.
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pone.0120718.g002: Actuation of bilayers after step-wise change of relative humidity from 85% to 35%.Color code: red: 0.2mm spruce layer (thickness ratio m = 0.05); blue: 0.8mm (0.2), green: 1mm (0.25), orange: 2mm (0.5), purple: 3mm (0.75), brown: 4mm (1). a) Wood moisture content, b) curvature, c) curvature of bilayers with different m (note that the overall thickness h also changes), d) curvature of a bilayer 1,2,4,8, and 24 hours after transfer. The actuation is also made visible in a movie (S1 Movie). e) Comparison of experimentally derived and calculated specific curvature k 24 hours after transfer. Calculations are shown for values of n = E1/E2 of 10 (dotted line), 20 (solid line), and 30 (patched line). f) Relative amplitude of k as a function of n and m.

Mentions: In analogy to the biological role models (pine cone, wheat awn) wooden bilayers were exposed to a step wise change of relative humidity from 85% to 35%. Samples with different bilayer constitutions were tested with the thickness of the resistive spruce layer being varied in the range of 0.2 to 4mm, whereas in all cases the beech layerwas 4mm thick. After the step-wise change of relative humidity, wood moisture content strives towards a new equilibrium moisture content. A decrease of the wood moisture content from around 18% to around 10% within 24 hours was observed (Fig. 2a) and the initially straight bilayers became increasingly curved (Figs. 1b and 2b). While the amplitude of wood moisture change was very similar for all bilayers, the amplitude of curvature was negatively correlated with the thickness of the spruce layer for thicknesses greater than 1mm. For bilayers with a thickness of the spruce layer up to 1mm, curvatures up to 8.7*10-3mm-1 were reached, whereas bilayers with a spruce layer of 4mm thickness reached a curvature of 1.5*10-3 mm-1 after 24 hours only. Fig. 2c presents the curved bilayers with the different ratios of layer thickness after 24 hours. The actuation over time is made visible as composite image in Fig. 2d and in a movie (S1 Movie). With the length of the bilayers being 120mm, the change in curvature of 8.7*10-3mm-1 results in an angular change of 59° (Equation 4), which is close to the measured change of 55° (Fig. 2d).


Bio-inspired wooden actuators for large scale applications.

Rüggeberg M, Burgert I - PLoS ONE (2015)

Actuation of bilayers after step-wise change of relative humidity from 85% to 35%.Color code: red: 0.2mm spruce layer (thickness ratio m = 0.05); blue: 0.8mm (0.2), green: 1mm (0.25), orange: 2mm (0.5), purple: 3mm (0.75), brown: 4mm (1). a) Wood moisture content, b) curvature, c) curvature of bilayers with different m (note that the overall thickness h also changes), d) curvature of a bilayer 1,2,4,8, and 24 hours after transfer. The actuation is also made visible in a movie (S1 Movie). e) Comparison of experimentally derived and calculated specific curvature k 24 hours after transfer. Calculations are shown for values of n = E1/E2 of 10 (dotted line), 20 (solid line), and 30 (patched line). f) Relative amplitude of k as a function of n and m.
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Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4383548&req=5

pone.0120718.g002: Actuation of bilayers after step-wise change of relative humidity from 85% to 35%.Color code: red: 0.2mm spruce layer (thickness ratio m = 0.05); blue: 0.8mm (0.2), green: 1mm (0.25), orange: 2mm (0.5), purple: 3mm (0.75), brown: 4mm (1). a) Wood moisture content, b) curvature, c) curvature of bilayers with different m (note that the overall thickness h also changes), d) curvature of a bilayer 1,2,4,8, and 24 hours after transfer. The actuation is also made visible in a movie (S1 Movie). e) Comparison of experimentally derived and calculated specific curvature k 24 hours after transfer. Calculations are shown for values of n = E1/E2 of 10 (dotted line), 20 (solid line), and 30 (patched line). f) Relative amplitude of k as a function of n and m.
Mentions: In analogy to the biological role models (pine cone, wheat awn) wooden bilayers were exposed to a step wise change of relative humidity from 85% to 35%. Samples with different bilayer constitutions were tested with the thickness of the resistive spruce layer being varied in the range of 0.2 to 4mm, whereas in all cases the beech layerwas 4mm thick. After the step-wise change of relative humidity, wood moisture content strives towards a new equilibrium moisture content. A decrease of the wood moisture content from around 18% to around 10% within 24 hours was observed (Fig. 2a) and the initially straight bilayers became increasingly curved (Figs. 1b and 2b). While the amplitude of wood moisture change was very similar for all bilayers, the amplitude of curvature was negatively correlated with the thickness of the spruce layer for thicknesses greater than 1mm. For bilayers with a thickness of the spruce layer up to 1mm, curvatures up to 8.7*10-3mm-1 were reached, whereas bilayers with a spruce layer of 4mm thickness reached a curvature of 1.5*10-3 mm-1 after 24 hours only. Fig. 2c presents the curved bilayers with the different ratios of layer thickness after 24 hours. The actuation over time is made visible as composite image in Fig. 2d and in a movie (S1 Movie). With the length of the bilayers being 120mm, the change in curvature of 8.7*10-3mm-1 results in an angular change of 59° (Equation 4), which is close to the measured change of 55° (Fig. 2d).

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