RCAT - Research Center for Architecture and Tectonics

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2010 _ Shaping Wood: The Material is the Mechanism

Diploma Student: Linn Tale Haugen - IDE Institute for Design

Supervisor: Prof. Dr. Michael U. Hensel

Industrial Design master student Linn Tale Haugen examined the seedpod of a Flamboyant Tree (Delonix regia) regarding its material make-up and resulting self-shaping tendencies induced by hygroscopic behaviour. The seedpod is characterised by a layering of material with different fibre directions. The angle of rotation of the fibres in the layers and the thickness of the layers determines the degree of warping of the two parts of the seed pot as a result of moisture-loss induced shrinkage. The warping serves the purpose of separating the two parts of the seed pot and releasing the seeds. Based on this observation Haugen re-examined lamination rules for form-stabile laminates. Timber laminates are generally composed of an odd number of layers since this locks the warping directions of the different layers into a form-stabile configuration. As the warping is determined by the fibre-direction, the specific rotation of the layers is key to accomplishing form-stability. Likewise, however, this offers the opportunity to devise non-form-stabile laminates that exploit the hygroscopic behaviour of the material. In a laminate with an even number of layers, the fibre-direction of the various layers can be utilized to warp the laminate in a controlled way. In addition wood species and cuts with lesser or greater hygroscopic behaviour determines the degree of warping. This then delivers control over the direction and extent of what becomes controlled warping.

 

Specific single or double curvature of laminates can be attained by way of fibre direction in the different layers and the related directions of swelling and shrinkage in

moisturizing and drying the wood. It is then no longer necessary to derive such curved elements by means of machining, such as routing, which results in a large amount of off-cuts or sawdust, or, alternatively, the costly production of moulds. After numerous experiments with different types of wood Haugen decided on using beech veneer due to its elasticity and related ability to warp without cracking. Subsequently she undertook a large number of experiments to arrive at pre-specified curvatures of the laminate. This was initially done with continuous layers, that is to say one fibredirection per layer, and subsequently with layers consisting of rotated patches to gain more surface area and more curvature variation in the laminate. The self-shaping process remains to some extent reversible when the material remains untreated. Alternatively the laminate can be fixed in the warped shape by sealing the surface. In her master dissertation Haugen also demonstrated various product design related uses, including a screen-wall and a lampshade that respond to changes in the ambient humidity.

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