Material properties of wooden material: scale effect
Treesearch research themes:
The use of wood as a building material because of its efficiency, sustainability, and durability is increasing. Wood is a renewable resource, it has low carbon impact and low embodied energy. The amount of energy needed for producing wood products is much less than comparable products made from other materials.
In spite of its common use, assessing the properties of wood remains a difficult task for many reasons. Firstly, the properties of wood vary depending on the species, age, place, and weather conditions during growth. Secondly, wood is a heterogeneous and anisotropic material, meaning that its properties vary within a single piece of wood and are directionally dependent. In order to use wood as construction material, the material properties of wood need to be known. Using the compression test to get the material properties in a normal direction is well established and commonly used. When it comes to shear properties, there are different techniques such as the Iosipesqcu test, the Arcan test, the rolling shear test, the block shear test (ASTM D 143), and the single cube apparatus test. All of the above-mentioned shear tests share the same problem of multiaxial stress state inside the material. That means that in practice performing a â€œpure shear testâ€ is very difficult. Here a simple method is proposed to obtain all the material properties of wooden samples.
The 17th-century warship Vasa is the largest wooden ship salvaged from the seabed and conserved. The ship sank abruptly in Stockholm harbor on its maiden voyage in 1628. After being salvaged in 1961, the ship underwent a pioneering conservation program for 26 years. Since 1990, the ship has been on display to the public at the Vasa Museum, which has since become the most visited maritime museum in the world. Currently, it suffers from increasing deformation over time, caused by creep in the wood members, time-dependent deformation of joints, and damage accumulation due to chemical degradation and softening effect from polyethylene glycol (PEG) impregnation. Therefore, an objective set by the Vasa museum is to use the mechanical and chemical data of the Vasa oak and create a full-scale three-dimensional (3D) finite element (FE) model of the entire ship as an analytical tool to be used in the design of an improved support structure.
Different sample sizes aiming at different properties of the Vasa oak have been used since 2008. However, the scale effect on material properties of the Vasa oak has not been studied so far. Since the number of samples, as well as the size of the samples from cultural heritage objects, is limited, the scale effect will be very useful material information.
Purpose and aims
The aim of this research is to investigate the scale effect on material properties of wood (in general) as orthotropic material both in terms of stiffness and strength properties. The proposed method is to use only a compression test in combination with image analysis technique to find all the material properties of wooden material.
To find stiffness parameters and strength of wood in the tangential direction and investigate the scale effect on material properties
To investigate the scale effect on material properties