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Biomimetic inspiration for designers in plastics

Join Date: 2018-12-11

Low weight garage roof in Montreux using Tensairity self-healing pneumatic supports.

In this feature for Plastics News Europe David Vink looks at how researchers have been imitating structures found in nature and using plastics technologies to try to turn concepts into reality.

The potential of biomimicry to borrow design elements from nature and help drive product innovation has been recognised for a long time. Velcro, the most famous example, was invented in 1948 by Swiss electrical engineer George de Mestral who developed the hook and loop fastener by studying plant burrs that stuck to his clothes during a walk.

But recently there has been growing interest in biomimetic (or bionic) solutions to design and engineering problems as the work of researchers has suggested applications for their concepts.

The plant world is the inspiration behind these German projects: a highly shock-absorbing pallet; branched and straight braided fibre fabric composite parts; self?healing foam-coated pneumatic systems; and “elastic architecture”. These were shown in a presentation at the 2015 VDMA KuG members’ meeting in K?nigstein-Falkenstein, Germany, by Prof. Thomas Speck, director of the PBMG plant bio-mechanics group at the BGF botanical gardens in Freiburg, Germany.

The pallet has been inspired by the highly gradient dampening structure of bamboo tree trunks, supplemented by tension bands in the knots, as well as the shock?absorbing spines found on hedgehogs and porcupines. PBMG worked on the pallet with the ITV textile technology and process engineering institute in Denkendorf, electrical/electronic cabinet & rack producer Rittal, and Offenbach Design University. The modular pallet design consists of a natural fibre reinforced polylactide acid (PLA) composite sheet separated by nine feet in the form of rods (or spines) inserted into foam-filled or silicone rubber balls.

With 1,200 kg load bearing capability, the pallet withstands impact and vibration frequencies of 15?35Hz. PBMG claims it is more ecologically and economically favourable than conventional pallets. Although the pallet received a Materialica innovation award in 2011, Plastics News Europe has found no sign of Rittal or others commercialising it, nor of Rittal’s intended development of bioplastic cabinets and racks.

Speck described giant cane (arundo donax) as interesting for biomimetic design on account of its structural and mechanical properties, which come from the gradual transition between the fibre and matrix in the plant material. Designs based on giant cane enable lightweight structures with high stiffness and strength, combined with “well behaved” breaking performance, he said.

PBMG and ITV Denkendorf have developed a structured technical plastic composite pultrusion profile based on giant cane and rough horsetail (equisetum hyemale). A 3D braided fibre fabric pultrusion line at ITV Denkendorf, using August Herzog Maschinenfabrik braiding machinery, has also produced branched composite profile parts based on the structure of the monocotyledon (parallel veined) rainforest dragon tree (dracaena genus) and columnar cacti (for example, Cereus genus).

This was done within a project involving PBMG with Dresden Technical University and the ILK lightweight construction and plastics institute in Dresden. PBMG researcher Tom Masselter has shown how dragon tree stem notches and grooves reduce critical stress levels.

Both Speck at the 2015 VDMA members’ meeting, and Dr Simon Küppers of ITV Denkendorf in a submission to the 2014 AVK innovation awards jury, have spoken about high load bearing capability of such structures produced in the new braiding process. As this involves fibres running right through the structure, Küppers said this avoids over?dimensioning of the branch junction, and that such structures have potential in automotive B- and C-pillars. Speck talks of good vibration dampening, high load-bearing resistance to continuous dynamic loads and favourable breaking behaviour.

Working with the federal Swiss material science laboratory (EMPA) in Dübendorf, PBMG has developed pneumatic systems with self-healing, closed core polyurethane foam interior coating and outer fibre reinforced membranes. The operating principle is based on the self-healing mechanism of the North American liana or Dutch pipe vine (aristolochia genus).

The technique has been adopted by Tensairity Solutions in Provaglio d’Iseo near Brescia, Italy, which says the pneumatic structures combine lightness and simplicity of an airbeam with load bearing capacity of a truss structure. Tensairity has applied the technology to temporary facilities such as tents, as well as to permanent and temporary bridges and wide-span roof structures. These include an 8 metre span vehicle bridge with 3.5 tonnes load-bearing, a 52 metre span bridge for skiers and a 27 metre span garage roof in Montreux, Switzerland. Speck says the self?healing PU foam is available commercially from Rampf Giessharze in Grafenberg, Germany.

A biomimetic design that made an impact in the architectural world was the Flectofin fa?ade of the One Ocean thematic pavilion at the Expo 2012 world fair in Yeosu, South Korea.

Flectofin is a bio-inspired, self?adapting, hinge-free, sun-blind system developed by PBMG, ITV Denkendorf, the ITKE institute for building structures and structural design in Stuttgart and blind system producer Clauss Markisen Projekt in Leinfelden-Echeterdingen near Stuttgart. Flectofin is an example of “elastic deforming architecture” inspired by opening and closing of a bird-of-paradise flower (estrelitzia reginae) petal as a pollination mechanism.

When a bird lands on the flower, this initiates a complex deformation of multiple structural members consisting of ribs, lamellae and wings, with kinematically stored elastic energy resetting and reversing the system. These aspects have been incorporated in Flectofin lamella design, consisting of a pultruded glass fibre reinforced plastic (GFRP) backbone that is flexed via vertical movement of the lower blind support, or by temperature control. This movement sets off torsional buckling of the attached stepped four-to-eight-layer vacuum assisted process (VAP) moulded GFRP laminate, which has encapsulated glass rovings as “eucalyptus leaf venation patterns” for force distribution.

Speck said Flectofin sun-shading has low maintenance, is more reliable than conventional external and internal blind systems and can be easily applied to curved fa?ades. For the Expo 2012 pavilion, the Flectofin partners worked with Architekturbüro Soma in Vienna, Ingenieurbüro Knippers Helbig in Stuttgart and Clauss Markisen Projekt, to make a kinetic fa?ade system with 108 Flectofin lamellae, 8mm in thickness and ranging 3-17 metres in height, for the 140 metre-long curved fa?ade. A highly flexible epoxide resin was used for the GFRP lamellae, which were produced by Ojoo near Seoul.

PBMG and ITKE researchers described Flectofin in a project review as a “bottom-up bio-mimetics approach”, adding that a “top-down-approach” starting with a technical question and “screening the plant kingdom for promising solutions” has also been followed. For example, having developed Flectofin with bird-of-paradise flower inspiration, a double-wing version has been designed, based on the trapping mechanism of the carnivorous aquatic waterwheel plant (aldrovanda vesiculosa). The researchers say double?wing Flectofins enable fully maintained free-form building geometries in open and closed configurations.

Shading systems account for 6% of the ?12bn worldwide fa?ade market, and the researchers point out that the EU and Germany intend to make fa?ade shading compulsory in order to cut energy consumption – through a reduced need for air conditioning in summer, and less heat loss in winter, in modern highly glazed public buildings. Physibel Institute in Maldegem, Belgium estimates fa?ade shading could save 41m million tonnes equivalent of oil and around 111m tonnes of CO2 each year in Europe.

Concluding his presentation at the VDMA members’ meeting, Speck spoke about the possibilities and limits to biomimetic inspiration for innovative products. There has been progress, he said, moving from the situation in 1980 of “everything is conceivable and hardly anything is realisable” to 2015, when “everything is conceivable and almost everything is realisable”.

Further development of analysis, simulation and production technologies, against a background of society’s interest in sustainability, means it is now possible to exploit a “historical opportunity” with bionic design, Speck suggested. But he warned that, despite all enthusiasm for modern production technologies, it is necessary to take into consideration that bionic design approaches have still to find their way into large series production via conventional production technologies.

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