The Mechanical properties and availability of wood have made it a natural material for building structures, furniture, tools, vehicles, and decorative objects. Worldwide it is used more than metal or plastic.
Wood is a natural product and when used responsibly is a sustainable resource which need not result in damage to the environment. Forests can be protected by recycling and reusing the wood, using less wood and by supporting sustainable forest management
All wood is composed of cellulose,lignin, hemicelluloses, and minor amounts (5% to 10%) of extraneous materials contained in a cellular structure.
Wood comprises about 50% of cellulose which responsible for most of its mechanical properties.
Natural wood is generally composed of bundles of long fibres which are effectively water carrying tubes. These fibres are laid in the direction of the tree trunk or branch from which the wood is removed.
The strength of wood is highly dependent on the loading direction. Wood is strongest in tension along the fibres and is weakest in the radial and tangential direction. When loaded in its strongest direction (longitudinal along the grain - see figure below) wood can have a strength to weight ratio advantage relative to steel of 2:1. However when wood is loaded in other directions (radial and tangential to the grain- see figure below) this advantage disappears
To use wood to its best advantage and most effectively in engineering applications, specific characteristics or physical properties must be considered.
It is customary to describe wood using the following terms. Of course there is some degree of overlapping in practice.
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Hardwood trees are generally broadleaved trees. These tree species are deciduous, retaining their leaves only one growing season. The designation Hardwood trees does not necessarily relate to the hardness of the wood.. Hardwood trees are also called broad leaf trees or deciduous trees.
Typical hardwood trees include ash, elms, oak, maple, walnut, hickory, mahogany, and walnut. Woods grown in tropical climates are generally hardwoods. Hardwood have shorter fibers compared to softwood. some hardwoods are evergreen.
Softwoods are one of the botanical groups of trees that has persistent needle-like or scale-like leaves; softwoods are evergreen and have longer-length fibers than hardwoods.
Softwood trees include pines, spruces, firs , cedars. The yew is one of the few softwoods that is native to the UK. There are a number of softwoods (yew)that are harder and tougher than many hardwoods
Larches, including tamarack, are exceptions, being deciduous "softwoods".
This is a product made from an odd number (three, five ...) of thin layers (veneers) of wood (generally hardwoods) bonded together by an adhesive. The alternate plies are at right angles thus ensuring that the resulting material has a high uniform strength in all directions.
Plywood does not split as easily as conventional wood and has a good dimensional stability under conditions of varying moisture conditions. Plywood will not easily split if a nail is close to any edges. Plywood can be considered as a high strength construction material used for internal and external load bearing panels.
Plywood is normally supplied as 1,2m x 2,4m sheets in thickness from 3 to 25mm thickness. It can however be supplied in lengths of up to 40m and in thickness of up to 50mm.
Chipboard is made from particles of wood bonded together with a synthetic resin and sometimes other binders. The panels are generally 2,4m x 1,2m with thicknesses from 3mm to 40mm. Larger sizes are available up to 5m x 1,5m. The particles are obtained from forrest thinnings sawdust and small pieces of wood unsuitable for other uses are granulated to chips. The resin used is generally urea formalehyde. Chipboard is normally only suitable for interior use in the manufacture of low cost furniture, wall panels and floor panels.
There are different types fibreboard which differentiated by
..the size and type of wood fibres used
..the method of heating
..what type of bonding agent is used
..the method by which it is pressed into shape
Medium Density Fibreboard (MDF) is a wood substitute form which is made from fine wood fibres in a resin which is bonded under heat and pressure. It is manufactured by a dry process at a lower temperature than other fibreboards e.g hardboard. The natural glues and resins contained within the wood are not effective. MDF therefore uses artificial bonding agents / resins. The resin used is usually urea formaldehyde, but some fibreboard including exterior or marine quality board will use stronger glues such as phenol formaldehyde. MDF may be used instead of plywood or chipboard. It is dense, flat, stiff, has no knots and is easily machined. It is made up of fine particles and therefore does not have an easily recognisable surface grain
MDF can be painted to produce a smooth quality surface. Because MDF has no grain it can be cut, drilled, machined and filed without damaging the surface. MDF may be dowelled together and traditional woodwork joints may even be cut. MDF may be glued together with PVA wood glue. Oil, water-based paints and varnishes may be used on MDF. Veneers and laminates may also be used to finish MDF
Safety: It should be noted by anyone involved with MDF that there is an accepted risk that wood dust inhaled at certain level, is a carcinogen (cancer causing) and that formaldehyde is possibly carcinogenic to humans'. Exposure to formaldehyde by inhalation can cause irritation to the eyes, nose, throat and mucus membrane.formaldehyde can also cause dermatitis. A number of countries have but legal limitations on the use of MDF
Note: Density relates to wood in seasoned condition and is really only useful for relative comparisons
| Type of wood | Description/Uses | Density kg/m3 |
| Alder - Common | From Europe and UK. A soft timber similar to poplar. Imported as plywood and used for turning. Light reddish brown colour. Not very durable. | 530 |
| Balsa | From Euador. A low density wood used for modelmaking and insulation | 40-320 |
| Beech | From UK, Europe and America. Used for furniture, flooring, musical instruments. Often used for woodstrip and woodblockflooring. | 720 |
| Birch | From UK, Europe and America.General purpose timber, plywood. | 660 |
| European Boxwood, | Turnery, craftwork, sports goods, musical instruments | 910 |
| American Cedar, | From South and Central America. This wood is used for Cabinet making, boatbuilding, and light construction | 480 |
| Cedar,Western Red | From North America. Reddish brown - non-resinous lightweight softwood with good durability under all conditions. Used for roofing shingles, greenhouse construction and for interior furniture. Can cause corrosion of contact metal. | 370 |
| Sweet Chestnut | A European tree used for furniture joiner and fencing and often used for beams. Stains when in contact with damp iron | 560 |
| European Cherry | European/ America tree. Used for specialised crafted furniture, decorative work, musical instruments | 430 |
| Ebony | An african /Asian tree. Dark wood used for cutlery handles, musical instruments, craftwork. This is an endangered wood | 1000 |
| Elm | English. Cross grained with high tendency to warp. High temperature steaming reduces this tendency Used for furniture, joinery, flooring, external cladding. Durable under water and excellent for piles and dock construction | 550 |
| Elm rock | North American. Tough dense and resisant to abrasion. Durable under water and mainly used for piles and dock construction. | 700 |
| Fir, Douglas (softwood) | From UK , Europe and North America. Straight grained softwood. Higher than average strength. Used extensively for plywood, heavy construction work, sea defences | 530 |
| Silver Fir (softwood) | Cultivated in Eurpoean Plantations. Marketed as whitewood. Used for building, joinery, packaging | 480 |
| Hemlock | UK, European and N. America. Non resinous softwood with strainght even grain. Not very durable. Used in construction industry for interior work generally. Used for crates and boxes | 480 |
| Hickory | North American. tough, hard smooth and straight grained. Used for spokes and rims of wheels, tool handles and machine parts | 820 |
| Horse Chestnut | A European tree sometimes used for minor goods, turnery and utensils and often used beams | 510 |
| Holly | Grown in UK and Europe. Difficult to dry and will easily distort and split. Used for Craft work, inlays | 800 |
| Larch | Grown in UK softwood plantation and Europe. Good strength and durability. A general purpose timber for outdoor use used for gates and fencing and mining timbers. | 590 |
| Lime | Europe. Fine textured soft and compact and cuts cleanly. Not durable. Excellent for carving and is used for musical instrument construction. Brush backs, turning, minor goods | 550 |
| Mahogany | From West Africa Courser texture than other types of Mahogany Dark wood and not as stable. used for utility and decorative work, indoors and outdoors, from boatbuilding to furniture and joinery. | 530 |
| Spanish /Cuban Mahogany | Used in joinery, high quality furniture, plywood. | 720 |
| Maple | From N. America. Even texture hard and strong. Very good timber for flooring. Used for interior timbers and a wide range of industrial applications. | 740 |
| Oak | Found UK, Europe and North America. Best wood for construction purposes demanding strength and durability. Wide range of applications, including joinery, furniture, fittings, flooring wood strip and woodblock flooring | 720 |
| Pine (Redwood) | Found UK, Europe and North America. Wide range of applications, including, furniture, flooring and utility applcations. | 510 |
| Rubberwood | Grown in plantations in Malasia. Major use in furniture production | 600 |
| Rosewood | Africa, South America, India. Minor use for furniture and musical Instruments | 850 |
| Sapele | From West Africa. Major use in furniture, joinery, decorative applications | 620 |
| Spruce White Wood | From UK, Europe ,North America. Near white straight grained softwood. Not durable in exposed locations.General used for boxes packing cases and construction work.. | 420 |
| Sycamore | UK , Europe. Turned wood and veneers.. | 610 |
| Teak | Mainly from S.E Asia. High quality furniture, joinery, garden furniture ..Sometimes used for beams | 900 |
| Walnut, European | Native to UK and Europe. Greyish brown finely figured. Used for furniture cabinets and gun handles and rifle stocks. | 640 |
| Willow | Native to UK and Europe. Lightweight soft perishable wood. Used to make cricket bats, basket work, toys and other items | 440 |
| Yew | Native to UK and Europe. Used for decorative veneers ornaments. -Historical use for bows | 670 |
Density of wood
The density of wood varies widely for different woods, and for the same wood. The density is significantly affected by the moisture content which varies through its life from initial cutting to final use. The normal range of wood densities varies form about 320 kg/m3 to 720 kg/m3. Imported woods can be obtained with densities as low as 160 kg/m3 and as high as 1020 kg/m3.
Strength of wood
Wood is a natural product and its properties vary continuously throughout processing from when the tree is cut down. Green wood has high moisture content (generally) and this results in reduced strength. As it is dried it loses the moisture content and becomes stronger.
Wood may be described as an orthotropic material; that is, it has unique and independent mechanical properties in the directions of three mutually perpendicular axes: longitudinal, radial, and tangential. The longitudinal axis is assumed parallel to the fiber (grain); the radial axis is normal to the growth rings (perpendicular to the grain in the radial direction); and the tangential axis is perpendicular to the grain but tangent to the growth rings. (Think of the grain as the tree rings running up the trunk /branch - planks of wood are simply sections of the tree trunk (or branch)
There are a massive number of values for mechanical properties of woods available mostly form american sources (see links below). This page will simply identify a range for Modulus of rupture for two woods Oak and white wood. The rupture modulus is the longitudinal stress in the extreme fibre at failure due to bending.
Please note that these are maximum strength values.. If the wood is subject to bending in any other direction the wood will fail at much lower values. The stress at failure of wood is shear or compression (in any direction) is lower
Note: BS 5268: Part 2 2002 includes guidance on the permissible stresses in timber. The standard relates permissible stressess to the strength grade of wood. An example extracted from the standard is a wood with a strength class of D30 ( a low strength oak) has a permissible bending stress of 9 N/mm2. Please note that this is a permissible stress as opposed to actual rupture (ultimate values) in the table below.
| Wood Name | Moisture % | Modulus of Rupture | Modulus of Elasticity |
| Softwoods | |||
| MPa | MPa | ||
| Fir Douglas | 41 | 54 | 10400 |
| 12 | 93 | 12700 | |
| Hemlock | 51 | 49 | 8700 |
| 13 | 83 | 10400 | |
| Larch | 66 | 53 | 7900 |
| 13 | 92 | 9900 | |
| Pine (Scots) | 89 | 46 | 7300 |
| 12 | 89 | 10000 | |
| Redwood (Baltic) | 51 | 44 | 7700 |
| 13 | 83 | 10000 | |
| Spruce (European) | 53 | 39 | 7400 |
| 14 | 72 | 10200 | |
| Spruce(Canadian | 43 | 39 | 8800 |
| 12 | 74 | 10500 | |
| Hardwoods | |||
| Ash (European) | 48 | 66 | 9500 |
| 12 | 116 | 11900 | |
| Balsa | 11 | 23 | 3200 |
| Beech (European) | 88 | 65 | 9800 |
| 12 | 118 | 12600 | |
| Birch (European) | 76 | 63 | 9900 |
| 12 | 123 | 13300 | |
| Elm (English) | 140 | 40 | 5200 |
| 12 | 68 | 7000 | |
| Elm Wych | 75 | 68 | 9400 |
| 12 | 105 | 10600 | |
| Greenheart | 34 | 140 | 15900 |
| 14 | 181 | 21000 | |
| Kari | 64 | 77 | 13400 |
| 12 | 139 | 17900 | |
| Mahogany | 64 | 54 | 7400 |
| 12 | 78 | 9000 | |
| Oak Europe | 89 | 59 | 8300 |
| 12 | 97 | 10100 | |
| Obeche | 76 | 37 | 4600 |
| 12 | 54 | 5500 | |
| Polpar Black | 154 | 41 | 6800 |
| 12 | 12 | 8600 | |
| Saraya White | 55 | 60 | 9100 |
| 12 | 80 | 10100 | |
| Teak Burma | 48 | 84 | 8800 |
| 10.6 | 106 | 10000 | |
Wood is generally machined by Sawing, Planing, Turning, Sanding etc..Below is a crude table identifying the machinability of various wood types.
From a number of samples machined the proportion of good quality results. * Very low. ** Low *** Medium, **** High , *****Over 90%
| Wood | Planing | Shaping | Turning | Boring | Mortising | Sanding |
| Alder | *** | * | **** | *** | *** | |
| Ash | **** | *** | **** | ***** | *** | **** |
| Beech | **** | * | ***** | ***** | ***** | ** |
| Birch | *** | *** | **** | ***** | ***** | ** |
| Cherry | **** | **** | **** | ***** | ***** | |
| Chestnut | **** | * | **** | ***** | **** | *** |
| Elm | * | * | *** | ***** | **** | *** |
| Hickory | **** | * | **** | ***** | ***** | **** |
| Maple | *** | *** | **** | ***** | ***** | ** |
| Maple(soft) | ** | * | *** | **** | ** | ** |
| Oak | ***** | * | **** | ***** | ***** | **** |
| Sycamore | * | * | **** | ****** | ****** | * |
| Walnut | *** | ** | **** | ****** | ****** | |
| Willow | ** | * | *** | *** | * | * |
| Poplar | *** | * | **** | **** | *** | * |
