Thermally modified (TM) beech wood: compression properties, fracture toughness and cohesive law in mode II obtained from the three-point end-notched flexure (3ENF) test

The fracture properties of thermally modified beech (Fagus sylvatica) wood (TMW) at 180° and 200°C were evaluated in mode II using the three-point end-notched flexure (3ENF) scheme assisted by three-dimensional (3D) stereovision equipment for obtaining displacements and strains. The compliance-based beam method (CBBM) provided the strain energy release rates (GII) of TMW and cohesive laws for both native wood (W) and TMW. Based on the CBBM and equivalent crack length approach (ECLA),GIIwas obtained directly from the force-deflection data. The thermal modification (TM) process reduced the compressive strength by 4.4% and increased the compressive elastic modulus by 38.3%, whereasGIIwas reduced substantially by 40.8% and 67.9% at TM180°Cand TM200°C, respectively. TM also increased wood brittleness that was visible on the displacement slip reduction. The resulting mean cohesive models can be used for numerical analyses. The fracture properties of TMW have to be taken into consideration for constructional wood application, when cyclic loading may lead to microcracking and material fatigue.

An introduction to the Babcock designed super dock blocks

This paper considers the issue of gaining access to the full extent of a vessel’s bottom plating whilst it is dry docked. The current methods of secondary docking positions and block removals are reviewed and a new approach using jacks is presented. The development of an initial version of the new approach is described. This covers the elements of removal and replacement concept, general arrangement, limitations of the existing equipment, removal equipment and wood compression properties. These aspects are then brought together to create the requirements for the jacks. Operational experience on the first three dockings using the initial version at Babcock’s Devonport site is discussed. The limitations of the initial approach are quantified and a fully developed solution which allows 100% block removal is presented. The paper concludes that the new approach of using jack-able super blocks provides benefits to both the shipyard and the ship operator. This project has been achieved through new research and the application of a sound knowledge of engineering and tolerances. The intellectual property of the paper is the subject of a pending patent.

Calculation of wooden beams reinforced with polymeric composites with modification of the wood compression area

Peculiar features of engineering and numerical calculations of wooden beams reinforced with polymeric composites with the local modification of the wood compression area under an insufficient volume of the initial data have been considered in this article. A technique for determining the physical and mechanical properties of materials and a stress-deformation diagram based on experimental investigation has been described. The enlarged algorithm of engineering calculation on the enumerated geometrical characteristics and numerical calculation by the consecutive loading technique and with correcting of the tangent modulus of elasticity at each step instantiated in PC Lira 10.6 has been presented. Analysis of the stress-strain state of wood-composite beams with local modification of wood has been made. Comparative analysis of engineering and numerical calculations has been performed within the limits of the calculated load. Conclusions on the results of theoretical investigations of the proposed beam construction have been formulated and compared with the existing investigations in the field of reinforcement of beam constructions with polymeric composites.

Influence of strain rate, temperature and fatigue on the radial compression behaviour of Norway spruce

A dynamic elastoplastic compression model of Norway spruce for virtual computer optimization of mechanical pulping processes was developed. The empirical wood behaviour was fitted to a Voigt-Kelvin material model, which is based on quasi static compression and high strain rate compression tests (QSCT and HSRT, respectively) of wood at room temperature and at high temperature (80–100°C). The effect of wood fatigue was also included in the model. Wood compression stress-strain curves have an initial linear elastic region, a plateau region and a densification region. The latter was not reached in the HSRT. Earlywood (EW) and latewood (LW) contributions were considered separately. In the radial direction, the wood structure is layered and can well be modelled by serially loaded layers. The EW model was a two part linear model and the LW was modelled by a linear model, both with a strain rate dependent term. The model corresponds well to the measured values and this is the first compression model for EW and LW that is based on experiments under conditions close to those used in mechanical pulping.

Quantitative observation of the foraging tunnels in Sitka spruce and Japanese cypress caused by the drywood termite Incisitermes minor (Hagen) by 2D and 3D X-ray computer tomography (CT)

The cryptic lifestyle of drywood termites makes it difficult to study their foraging behaviour and to detect infestations in hidden regions. In the present research, computer tomography (CT) scanning images were collected over a 1-year observation period of drywood termite Incisitermes minor (Hagen) in order to understand its foraging behaviour and, perhaps, to be able to detect the infestation as early as possible. Sitka spruce and Japanese cypress woods were the test objects. As CT scanning results show, foragers caused distinguished tunnelling patterns based on the physical properties of wood during gallery construction. The foragers primarily excavate along the earlywood in radial direction towards the outer surface of the wood to establish the primary and satellite chambers, followed by mainly superficial (0.3–3.0 cm under the surface) longitudinal expansion with occasional lateral deviations. The development of tunnelling is affected by the physical constraints of knots with their high density, high extractive and lignin contents, reaction wood (compression wood) and wood damage caused by wind.

The variability of wood density and compression strength of Norway spruce (Picea abies/L./Karst.) within the stem

This study relates to the variability of wood density and compression strength parallel to grain within the stem of spruce trees (Picea abies/L./Karst.). The sample tree originated from the Giant Mountains and was an adult autochtonous mountain spruce. The properties were analysed for wood that formed between 1850 and 1990 along (1) the north-south oriented radius and along (2) the stem height on test specimens with the following dimensions: 20×20×30 mm, prepared from logs taken from the stem base at distances of 2, 4, 6, 10, 14, 20, 22, 24 and 26 m. In individual sections, the properties of the samples oriented in the north or south direction did not differ, while the effect of different ages on the properties showed statistically significant differences at each orientation (p < 0.05). Along the radius, the properties showed an increasing trend in tree-rings that developed between 1850 and 1940 with a slight decrease in the following years. The coefficient of variation in various decades was 1–7 % (wood density) and 3–15 % (wood compression strength). Along the stem height, the properties gradually increased to a height of 20 m, while the increase in values ​​was more pronounced in the 22–26 m interval. The variability of the wood properties along the stem height corresponded to the variability of the properties along the stem radius. A linear dependence between wood strength and density was demonstrated. Compared to what had been previously written, wood density showed a greater impact, probably due to the biomechanical optimization of the stem with regard to mechanical wind and snow loads in the mountains.

Parametric study on the capability of three-dimensional finite element analysis (3D-FEA) of compressive behaviour of Douglas fir

This study is aiming at the simulation of wood compression (C) at a macroscopic level by means of a three-dimensional finite element analysis (3D-FEA) of solid wood and evaluation of the capability and limitations of this approach. C-Tests were carried out on Douglas fir according to ASTM D 143. The specimens included the 25×25×100 mm3 cuboid bars for longitudinal (L), radial (R) and tangential (T) directions and the conventional 50×50×150 mm3 blocks for the perpendicular to grain (⊥) direction. Two sets of wood parameters were developed and the 3D-FEA was implemented for the two types of specimens. The 3D-FEA worked successfully provided that the stress state coming from the total wood C was uniform. However, in case of the dominance of local compressive behaviour such as bearing, crushing and fibre shear, a microscopic-level modelling technique is needed for correction of the material parameters. More details on the limitations and difficulties of 3D-FE implementation for wood were discussed.

The significance of compression wood in restoration of the leader in Pinus sihestris L. damaged by moose (Alces alces). II. Structure of growth rings in regenerating stems in relation to juvenile wood formation

The corewood of pine ds very prone to compression wood formation, this changing the whole pattern of the tree ring structure and the siz.es of early and late wood. Compression wood always increases the formation of late wood at the expense of early wood. Tree rings with compression wood are generally wider than those without it, but there occur also tree rings wihout compression wood wider than those in which it is present, formed in the same year and in the same tree.