[LUM#7] From the wood of tomorrow
The oldest material in the world is now considered one of the most modern. A renewable natural resource, wood offers extraordinary mechanical qualities. And it's by far the most eco-friendly of all materials...
Furniture, transport, construction, aeronautics and robotics: visible or hidden, rustic or techno, solid or transformed, it's everywhere! Is wood making a comeback? It's only just begun, promises Bernard Thibaut, a researcher at the Mechanics and Civil Engineering Laboratory(LMGC). And with good reason: "like metal and polymers, it's one of those universal materials with which we can make just about anything we want ", believes this researcher who has been studying tree biomechanics and wood properties for 40 years(Usinage du bois avec un focus sur la recherche française depuis 50 ans, in Annales des sciences forestières, 2016).
Reference material
This material is as old as mankind, yet it has undergone a recent eclipse. Since its appearance on Earth, almost everything around us has come from the bounty of trees. Until the golden age of the 18th century, when wood became a universal material, invading the human sphere more than ever.
Then came the Industrial Revolution, and the triumph of competitors: the 19th century was the age of steel, the 20th of concrete and plastic. And the 21st century? It's time for a wood renaissance, says Bernard Thibaut. " Wood took a long time, but it has finally made the transition to modernity. This eternal reference material is now being rediscovered thanks to the technological advances it is benefiting from.
New industrial uses
If wood is making a comeback, it's in new forms, confirms Cédric Montero. Historically, we've used untreated wood for a very long time," sums up this researcher specializing in structural wood at LMGC. The current boom in the use of wood, particularly in construction, is largely due to new transformation processes: plywood, glued laminated timber, cross-laminated timber, products using chips or sawdust such as particleboard or fiberboard..." (Feasibility of glulam beams using tropical hardwoodsB.Thibaud, 2013)
A revolution. By freeing itself from the limitations of its original form, wood has moved from the handicraft to the industrial age. And it can now be used for a wide range of applications. This reconstituted wood is in fact " comparable to a fiber composite ", continues the researcher: a standardized, reproducible material. Today, it is used even in high-tech applications, and offers excellent mechanical performance: it has nothing to envy its artificial cousins, glass fibre, carbon fibre or even Kevlar... over which it has a major advantage: its lightness, due to its honeycomb structure on a microscopic scale.
The trend today is to combine wood with these same materials or with others - steel, for example - in composites whose structure depends on the desired results. The result is performance far superior to that of the individual components. " It's a field that opens up vast horizons: we're only at the beginning, with many technological innovations still to come.
Strong, light... and fire-resistant!
Man's oldest ally is proving to be a promising material, capable of turning any industrialist into a convinced xylophile. " Recent innovations have brought about a real revolution in thinking," notes Bernard Thibaut. Building quickly, using prefabricated modular structures? The lightness of wood makes it possible. Building huge towers? It's possible! The race for height is on: new industrial materials derived from wood can support buildings of over 20 storeys. And their behavior is ideally suited to seismic constraints...
Wooden construction, hitherto uncommon in France for cultural reasons, is now gaining ground. "Just a few decades ago, it was unimaginable to build large-scale projects in wood. Today, its fire resistance is being reassessed. Less a conductor of heat than steel or concrete, wood burns slowly, without deforming or releasing toxic substances.
Green fiber
Wood's greatest asset lies elsewhere: for this son of the forest has a resolutely ecological bent. Abundant and little exploited - particularly in France, which has the4th largest forest area in the European Union - wood is a renewable and inexpensive resource, requiring little energy to transform. And while the manufacture of steel, concrete, aluminium or plastic produces greenhouse gases, wood can help reduce them: trees naturally capture and trap carbon dioxide (CO2), a gas responsible for global warming, at a rate of one tonne per cubic metre. This CO2 is directly removed from the atmosphere... and all that's left to do is store it, in the form of wooden furniture or buildings. If wood is making a comeback, it's against a backdrop of sustainable development: using it as a material means fighting the greenhouse effect. Not to be missed.
30,000 different species
" There are at least as many woods as there are tree species - over 30,000 species worldwide! Each has its own properties, which can vary by a factor of 1 to 100, depending on the variety," explains Bernard Thibaut. The good idea is to combine different species for better results. This is particularly relevant to the construction industry. Even in its raw form, wood, a protean material, offers an extraordinary range of possibilities. As for its mechanical properties, they are "necessarily" of great interest (Physical and mechanical properties of reaction woodin The biology of reaction wood, 2013): "Let' s not forget that wood has made a tree, i.e., a particularly audacious structure: few architects would dare attempt this kind of achievement! "
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