Teak (Tectona Grandis)
Teak originates from Burma and grows widespread in India, Thailand, Indonesia and Java.
Cultivated in Malaysia, Borneo, on the Philippines, in the tropical Africa and central America. The teak tree belongs to the iron herb plants and grows up to a height of 40 m and up to 1 m in diameters. In the tropical forest of Burma (today Myanmar) the felling is strictly controlled. Work elephants get the trunks from the jungle, a simple way to be careful with the environment.
Teak is composed of thin yellow-brown sapwood and dark gold-brown heartwood, which darkens in open air.
Java- and Plantation-Teak has mostly more brightness than Burma-Teak. Has usually a straight fibre direction with rough and unequal texture.
Teakwood is water-resistant, from nature decoratively touched, extraordinary hard, and a long-lived material. The density is about 440 - 720 kg/m³ with an average of 630 kg/m³. The wood dries quite slowly and moves at a minimum, has middle bending strength, load capacity and impact strength, high pressure strength and moderate steam bending characteristics.
Sun, wetness, rain - no wind and no weather can harm teakwood !
Only if you don't like the silver grey patina, you have to treat Teak regular with Teak-oil - besides this no care is necessary.
Environmentally and consciously working manufacturers offer only wood from plantation or high quality Teak form "selective felling", which means the number of the regenerating trees exceed those of the trees felled.
The supplier of our teak-veneer - Sommerfeld + Thiele GmbH - do have appropriate certificates present.
spec. density: 0,44 - 0,63g/cm3
tensile strength: 95 - 155 N/mm2
pressure strength: 42 - 59 N/mm2
bending strength: 58 - 109 N/mm2
hardness (brinell): 63 - 71 N/mm2
Obeche (Triplochito scleroxylon)
West African equatorial forest of all coastal states from Liberia to Gabon. The trees come up to a height of 50m and up to 2m in diameters.
The sapwood is hardly distinguishable from the crème-yellow to straw-coloured heartwood. The fibre has a radial growth and so the sectional plane has a strip design.
Pores are scattered, large, have refined cross fibre, due to storeyed growth. Irregular radial growth. The density is about 350 kg/m³ . Wood dries very fast without fragmentation and with insignificant warp. Moves moderately and has small bending, pressure and impact strength, very small load capacity and moderate steam bending characteristics.
The wood is soft, elastic, flexible and very light-weighted. Shrinks and warps very little and can be well processed. Gluing without difficulties and stains very well. Although tools are long lasting sharp blades with reduced angle are recommended. Can be nailed easily, however very little firmness. Surface has to be filled before treatment.
spec. density: 0,35 - 0,50g/cm3
tensile strength: 45 - 52 N/mm2
pressure strength: 26 - 42 N/mm2
bending strength: 51 - 72 N/mm2
hardness (brinell 12% humidity): (HB I) 17 - 21 N/mm2 | (HB II) 37 - 41 N/mm2
What is Composite?
The selection of the appropriate material for a part or component depends on the following properties:
Classic materials are metals, such as steel or aluminium.
The atoms of metals form regular structures, the crystals. The internal forces in the crystals, which counteract a separation of the atoms, are high. But regarding the microstructure of a metal, the extent of the crystals is limited. The crystals form small pieces, which are bound together by rather weak forces. Thus, the strength of the material remains on a comparatively low level. Of course, the strength of a high quality steel is good anyhow, but its specific properties are not acceptable for many applications because of its high specific weight.
Such materials with very high strength in the longitudinal direction (but, for certain materials, nearly none under lateral loads), produced as a sort of "threads", are called "fibres".
Everybody knows the excellent properties of wood, a natural fibre material.
Technical fibres are i.e.: Glass, KEVLAR and carbon (or graphite). As the high internal forces between the atoms of graphite crystals are well known, the strength of carbon fibres should be very good. In fact, you can "breed" long graphite crystals in a laboratory, the so-called "whiskers", with enormous strength.
For technical applications, this procedure is too expensive. To produce carbon fibres, a synthetic fibre, the PAN (polyarcrylnitril) is carbonized at high pressure and temperature; only its carbon skeleton remains. The rather short and thin carbon fibres produced in this way are put together as "rovings". By means of a carbon roving of only 10 mm2 cross section you can lift a car that weighs more than a metric ton! And the specific weight of carbon fibres is only one fifth compared with steel!
The fibres themselves can only take tensile loads (even if the strength of the material itself is the same under compression), as they will be deflected laterally under compressive loads.
So, in order to manufacture a component using fibres, these fibres have to be impregnated with a second material, which bonds them together and supports them laterally, This second material, the "matrix", is usually an epoxy resin. Fibres and matrix form together the "composite", for example "CFRP" (Carbon fibre reinforced plastic).
In a composite, the resin must have a good adhesion to the fibres, and must be tolerant against the maximum (ultimate) fibre elongation. The properties of a composite depend mainly on those of the fibres and not on those of the resin - as long as the resin is not destroyed by high temperatures.
The permissible temperatures for epoxy resins range between 60°C and 200°C - the higher they shall be, the higher must be the temperatures and pressure applied during the curing process of the resin.
Complex parts are made of rovings, tapes or woven fibre cloth. The dry fibres are laid up in negative moulds and impregnated with the liquid resin (freshly mixed with hardener). Or, for even better results, preimpregnated "prepregs" are used (which do not cure as long as they are kept cool). During the curing process, the parts (in their moulds) are usually heated in an oven under vacuum, or under pressure in an auto-clave.
Before curing, the composite material fits easily into any negative mould. So, the designer is free in selecting even a very complex shape of a component, an important advantage compared with classic materials. And, compared with tools for sheet metal forming, the negative moulds for the manufacture of composite parts are much less expensive.
The orientation of the fibres can be selected freely according to the requirements.
If the designer wants a part with equal properties in every direction (similar to the isotropic metals), he combines longitudinal and diagonal layers in a "quasi-isotropic" layup. Or, he designs a part with high flexural, but low torsional stiffness –composites make it possible.
The composite parts, manufactured layer by layer in a mould, are usually called "laminates". A laminate can also incorporate local stiffeners - all as an integral part.
As mentioned above, the specific material properties of CRP can be 5 times higher than those of steel. Obviously, composite materials find already many applications in the aeronautical and space industries. In the future, composite materials will be more and more used in all other fields.
Mahogany (Swietenia macrophylla)
The mahogany plants (Meliaceae), also called cedar plants, are a plant family in the order of the soap-tree species (Sapindales).
Genuine (American) mahogany comes exclusively from Central and South America. The wood species is common in almost every country in South America.
Real mahogany has medium to large pores and a very fine, well-recognizable flare. The wood beams are very fine. Clear gold luster is possible (depending on the course of the wood fibers, and only after drying).
The color of the heartwood is bright at first, often reddish, later darkening to a very dark brown tone. The sapwood retains its yellowish gray or light gray color.
Mahogany has an average hardness, but very good shading properties and allows very good workability. Weight and strength characteristics can vary partly depending on the origin. In general, the southern woods are somewhat heavier and stronger.
Mahogany is mainly a wood for high-quality interior furnishing - both as solid wood and as plywood. It is also highly appreciated in high-quality boatbuilding (yacht construction) as high-quality equipment. Used occasionally also in the door construction.
As a rule, drying takes place without problems, the shrinkage behavior is very low in mahogany. This makes it among other things to an excellently workable wood with outstanding characteristics.
room weight: 0,48-0,54 g/cm3
tensile strength: 100-110 N/mm2
compressive strength: 51-60 N/mm2
flexural strength: 90-104 N/mm2
hardness (Brinell ,12% humidity): (HB I) 14-17 N/mm2 | (HB II) 45 N/mm2
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