wood, a building material of the future

This Tuesday, November 5, the very first wooden satellite was launched into space. It was developed by scientists at Kyoto University. Proof that wood can be considered as a construction material of the future.

Since the invention of the wheel, estimated at 4,000 BC. BC, wood was used by humanity for land travel. Except in boating, it is little known that its use was still frequent at the end of the 20th century.^e century. Among the many examples documented in our articles, one of the best aircraft of the Second World War was the Mosquito, produced by De Havilland in 7,781 copies, capable of flying at 680 km/h and whose structure was made of birch, Douglas fir. and balsa.

Until today, the Robin Aircraft company, established in Dijon, has produced the DR 400 in wood and canvas construction in 2,700 units. On the automotive side, the English company Morgan still uses ash for part of its chassis. But one of the finest examples was the Costin Nathan Le Mans 1967 whose structure was made of plywood and weighed only 400 kg, which is half the size of the Ferrari P4 of the same year.

These examples show both the lightness and resistance of wood but also a partly lost know-how. In fact, only the English brand Morgan still uses wood for its small series cars today.

The question of its use is closely linked to the available resource. If in the Southern Hemisphere, forest cover is disappearing mainly due to its use as firewood, in the Northern Hemisphere it continues to increase. For the European Union, the increase in the stock of standing wood was 30% over the period 2000-2020 and forest cover represents 39% of the surface area of ​​the member states. In France, forest cover has doubled in 100 years. Unfortunately, it is mainly softwoods that are exploited while structural use for vehicles would require hardwoods such as poplar or birch which are local and abundant species.

Wood, a resistant but complex material

Our research first focused on the mechanical characterization of plywood alone or sandwiched with other materials such as aluminum; carbon fibers, glass fibers and also flax fibers. Although the resistances found are satisfactory, plywood turns out to be a very complex material due to the way it is obtained. We will find different characteristics depending on the position of the wood in the tree (juvenile or adult, spring or summer wood). Added to this complexity is also a strong sensitivity of wood to its environment in terms of humidity and heat.

All these complexities influence the mechanical characteristics of the plies which constitute the plywood and to remedy this we have developed identification methods thanks to the theses of John Susainathan and Axel Peignon, the postdoctoral work of Hajer Hadiji and the ANR BOOST .

Concrete applications in the automobile

Today’s vehicles must be able to absorb shock during accidents. These are most often steel or aluminum tubes which serve as energy absorbers. It was therefore important to know the response of wood to crashes. During Romain Guélou’s thesis, we tested tubes made with several species (poplar, birch and oak) with or without interior or exterior skins, made of glass or carbon fiber fabrics. The crash behavior of the wood is very good. A tube with carbon skins and a birch ply core was able to absorb the energy of a 170 kg mass dropped from a height of 4.2 m. We were also able to show the significant contribution of wood since by going from 2 to 6 layers of birch, the energy absorbed is multiplied by 2.

Recently a group of students from the mechanical engineering department of INSA Toulouse showed that on a light vehicle, loosely inspired by the Africar (a car with an extremely robust wooden chassis designed in the 1980s for Africa), the constraints are low and perfectly bearable by birch or poplar plywood.

Studies carried out at INSA Toulouse and the Clément Ader Institute over the past 12 years show the possibilities of this historic material that nature has made very advanced for sustainable mobility. These studies are part of a movement of rediscovery and reuse. In France, the company Aura Aéro, based in Toulouse, has developed the Integral R, a wood-carbon aerobatic aircraft currently undergoing certification. In Belfort, Mauboussin aircraft, with whom we are collaborating, are developing an aircraft with a wooden structure, inspired by the Mosquito.

Through several research programs, Professor Ulrich Müller and his Austrian team have demonstrated that the replacement and calculation of vehicle parts with wood was economically advantageous and made it possible to make structures lighter.

Wood in space

But the most surprising is the use of wood in the space. Two studies are currently underway, in Japan and in Europe (Finland), to use wood as a structural material for small satellites.

The Japanese study LignoSat Space Wood has just launched a magnolia wood satellite into low Earth orbit. In addition to being environmentally friendly during manufacture and burning up completely in Earth’s atmosphere once deorbited, a wooden satellite will be largely transparent to radio waves. The communication and research antennas could thus be internal because the wood is transparent to radio waves, thus avoiding hazardous deployment operations. Tests carried out on wood samples on the International Space Station (ISS) by researchers from Kyoto University confirmed minimal deterioration and good stability of the wood in space. The European satellite is made from Finnish birch plywood, but doped to help it withstand space conditions.

There is therefore a growing interest in wood in the most varied areas of transport. Although much research has been carried out on wood for civil engineering use, it remains an almost virgin area for plywood in the transport sector despite enormous potential in terms of sustainable development. Aeronautical and space applications have already seen the light of day but for transport, apart from a few creations by enlightened amateurs, there is currently no industrial application.