Failure & Strength in Timber While it is easy to appreciate the concept of deformation primarily because it is something that can be observed, it is much more difficult to define in simple terms what is meant by the strength of a material. Perhaps one of the simpler definitions of strength is that it is …
Viscoelastic Deformation in Timber Timber is neither truly elastic in its behaviour nor truly viscous, but rather a combination of both states; such behaviour is usually described as viscoelastic and, in addition to timber, materials such as concrete, bitumen and the thermoplastics are also viscoelastic in their response to stress. Viscoelasticity implies that the behaviour …
Creep in Timber Creep Parameters It is possible to quantify creep by a number of time dependent parameters, of which the two most common are creep compliance (known also as specific creep) and relative creep (known also as the creep coefficient); both parameters are a function of temperature. Creep compliance (cc) is the ratio of …
Deformation in Timber Under Load This article is concerned with the type and magnitude of the deformation that results from the application of external load. As in the case of both concrete and polymers, the load–deformation relationship in timber is exceedingly complex, resulting from the facts that: Under service conditions timber often has to withstand …
Deformation in Timber DIMENSIONAL CHANGE IN TIMBER DUE TO MOISTURE In timber it is customary to distinguish between those changes that occur when green timber is dried to very low moisture contents (e.g. 12%), and those that arise in timber of low moisture content due to seasonal or daily changes in the relative humidity of …
Flow in Timber The term flow is synonymous with the passage of liquids through a porous medium such as timber, but the term is also applicable to the passage of gases, thermal energy and electrical energy; it is this wider interpretation of the term that is applied in this article, albeit that the bulk of …
Moisture in Timber Equilibrium Moisture Content Timber is hygroscopic, that is it will absorb moisture from the atmosphere if it is dry and correspondingly yield moisture to the atmosphere when wet, thereby attaining a moisture content that is in equilibrium with the water vapour pressure of the surrounding atmosphere. Thus, for any combination of vapour …
Mass Volume Relationship of Timber Density The density of a piece of timber is a function not only of the amount of wood substance present, but also of the presence of both extractives and moisture. In a few timbers extractives are completely absent, while in many they are present, but only in small amounts and usually …
Appearance of Timber in Relation to Structure Most of you will agree that many timbers are aesthetically pleasing and the various and continuing attempts to simulate the appearance of timber in the surface of synthetic materials bear testament to the very attractive appearance of many timbers. Although a very large proportion of the timber consumed …
MOLECULAR STRUCTURE AND ULTRASTRUCTURE Chemical constituents Chemical analysis reveals the existence of four constituents and provides data on their relative proportions. This information may be summarised as in Table 1 proportions are for timber in general and slight variations in these can occur between timber of different species, or in different parts of a single …