Timber is a type of wood which is processed into beams and planks from any tree that can have a dimensional size. They are cellulose fibres that are held together by a natural resin. Tracheids in a lignin matrix. Can be poured (hardwood) and non-pored (softwood). Hardwood has pores/vessels running through the structure while softwood has a neater, more uniform structure without pores. Timber has excellent strength/weight ratio, can bend, good stiffness. Timber can be used in various ways from building construction, furniture making and has been used in bridge building thus has made timber an important building material. Important properties of timber include colour, moisture content, hardness, strength, elasticity, and density.
The colour of timber varies because of the different species of trees. Although colour can be used to indicate the strength of the wood. For lighter coloured woods it indicates weaker timbers while a darker and sharply coloured timber indicates strength. For example, pine is light weight and pale-yellow wood, and is considered a softwood. Whereas walnut, a dark chocolate brown and dense wood, is considered a hardwood.
The mechanical properties of timber are measured in strength properties these include, hardness, tensile strength, compressive strength, flexural strength, rupture in bending, maximum stress in compression parallel to grain, compressive stress perpendicular to grain, and shear strength parallel to grain.
The hardness of timber also varies from different species of wood. The hardness of wood can be testing using the Janaka hardness test. It measures the resistance of a steel ball and the force embed halfway into a sample of wood. Testing this method perpendicular to the grain is called “side hardness”. Australian Buloke, the strongest timber, can experience 22, 500 Newtons before it deforms. Balsa wood, the softest timber, experiences 98 Newtons before it deforms.
The density of timber is the mass contained in a unit volume of the material, determined by measuring mass and volume. Moisture content is the quantity of water inside of the wood. In a humid environment, the more moisture content in the timber, the more it will expand. And as humidity decreases, the timber shrinks in ratio to its moisture content. Air drying timber reduces the moisture content before use. Because timber absorbs moisture from the air the desirable moisture content will depend on the temperature and humidity of the environment where it will be used.
The Modulus of Elasticity is a measurement of the ratio of stress placed upon the wood compared to the strain that the wood exhibits along its length. Elasticity implies that deformations produced by low stress are completely recoverable after loads are removed. The three moduli of elasticity include longitudinal, radial, and tangential axes of wood. These moduli are usually obtained from compression tests.
Timber is unable to melt, therefore, a melting point cannot be provided, although it does light on fire at a minimum temperature of 180 Celsius. There are also less common properties that are less commonly measured which include torsion, toughness, rolling shear, and fracture toughness. Other properties involving time under load include creep, creep rupture or duration of load, and fatigue strength.