W. J. van Wyk

The Strength, Stiffness and Durability of Glued, Nail-glued and Screw-glued Timber Joints

SYNOPSIS The strength and stiffness of glued, nail-glued and screw-glued joints were compared to establish whether or not the nails or screws contribute to joint strength when used in combination with an adhesive. The durability of the three groups was also tested by exposing the joints to the weather for three months and subjecting them to three successive wetting and drying cycles. It was concluded that the control joints were equally strong with a little difference in stiffness. The nails and screws did not contribute to the ultimate shear strength of the joints and the durability of the joints exposed to the weather was improved by treatment with a water repellent.

Characteristics and Wood Properties of Alnus formosana (Burk.) Makino Successfully Introduced into South Africa

SYNOPSIS Formosan alder (Alnus formosana) was introduced into South Africa in 1982. The species proved to be site specific. On deep, well drained but moist soils it grows fast producing timber in excess of 20 m3/ha per annum at eight years of age. Properties of the juvenile wood indicate a density of 502 kg/m3 at 9% moisture content and pulp strength properties inferior to Eucalyptus grandis, except for burst index. The species increased the soil nitrogen level by 75% in eight years. Its wood is relatively light, easy to work, and gives a good finish. The timber could be used for doors, cupboards, panelling and furniture. Growth models, volume equations and wood properties of young South-African grown trees are presented. The species shows promise for commercial planting in South Africa.

Pulping characteristics of Eucalyptus provenance trials grown in the Western Cape. Part 1: Comparison between species.

SYNOPSIS For the purpose of Part I of this investigation, eight eucalypt species (irrespective of provenance), 12 years of age and grown along the northern slope of Stellenbosch mountain in the Western Cape were chipped, screened and pulped using the Kraft process. The pulps so obtained were compared with E. grandis pulp, cooked under similar conditions, since E. grandis pulp is known to be excellent papermaking fibre. The pulp evaluations revealed excellent strength development during beating in the case of the E. globulus, E. dunnii and E. nitens. These species also produced high screened yields with low percentages of rejects as well as acceptable strength values for burst, tear, and breaking length at a wetness of 38° SR and compared well with corresponding values obtained for E. grandis. In Part II (to follow) data on Kraft pulping characteristics as well as pulp strength properties of E. dunnii (three provenances), E. globulus (three provenances) and E. nitens (10 provenances) will be presented and ...

Physical and Morphological Changes of Wood Fibres During Beating and Recycling

SYNOPSIS To present a clear picture of exactly how the surfaces of recycled fibres were changed during successive beating cycles, scanning electron microscope (SEM) micrographs were taken of unbeaten pulp and afterwards of the same pulp subjected to one, four and 10 beating cycles. The unbeaten fibres appeared to be more round in shape with smaller contact areas between them. The fibrillating damaging and shortening effects of beating, especially after 10 cycles, were clearly demonstrated. Deterioration in pulp strength properties was quite pronounced especially after four and 10 cycles.

The mechanical and physical properties of Gardenia thunbergia (White Gardenia) wood

SYNOPSIS The species Gardenia thunbergia was evaluated for mechanical and physical properties of its timber. As a result of its hardness and toughness it could be used for tools, implement handles, buttons and agricultural implements. The wood has a fine grain and can take a high polish. Flexural properties are unique in the sense that the MOR is high but the stiffness low. It was found that the wood bent quite excessively before failure occurred. The submicroscopic structure of the wood was studied with the aid of a scanning electron microscope. Anatomically the wood revealed extremely thick-walled fibres and solitary vessels.

Pulping characteristics of Eucalyptus provenance trials grown in the Western Cape. Part 2: Pulping properties of E. dunnii grown from seed of three provenances

SYNOPSIS For the purpose of Part 2 of this investigation, 14-year-old E. dunnii trees grown from seed of three different localities in Australia were chipped, screened and pulped using the Kraft process. The trees grown from seedlots 10411 and 11705 yielded high percentages of pulp (approximately 48 to 49 per cent). The pulp strength properties (breaking length, burst index and tear index) of these two E. dunnii provenances were substantially higher than those of provenance 11786. The total chemical demand of provenance 10411 was higher than those of 11705 and 11786. Data on E. globulus and E. nitens are not yet available.

Creep Behaviour of Laminated Pine Beams under Sustained Loading

SYNOPSIS Studies on the creep behaviour of four groups of small defect-free laminated S.A. pine beams kept under varying bending stresses for 45 days at constant environmental conditions were carried out to establish the creep limit in bending. In addition, a computer program based on the equation was employed to calculate the values of d (creep factor), k (rate of creep) for each beam and to fit a theoretical creep deflection curve to the measured data. It was found that a creep limit exists at approximately 50% of the ultimate static bending stress. Contrary to expectations, long duration loading for 45 days did not seem to have a decreasing effect on the strength and stiffness of the defect-free laminated beams.

Protecting wood with a water repellent/ paint combination

Summary The influence of high and/or low solids water repellent on the durability of an alkyd enamel paint on P. radiata was investigated. Apart from increasing the drying time of the first paint coat, a low solids water repellent proved a paintable primer which eventually markedly improved the durability of the paint film.

A Comparison of Two Methods for Determining the Proportional Limit of Wood in Compression Parallel to the Grain

SUMMARY Two methods for determining the proportional limit of compression parallel to the grain were compared. No significant difference was found between results from force-strain and force-d-c-resistance curves.

A Method of Measuring Joint-Slip of Nailed Joints in Shear

SUMMARY The joint-slip in nailed joints in the form of standard block shear specimens was measured with the aid of a small apparatus which can be fixed directly to the specimen. The method of measuring joint-slip of nailed joints as described in this paper yielded very accurate and satisfactory results. The load-displacement curves obtained are very typical for nailed joints. The deformation registered by the Instron testing machine did not represent the true joint-slip, but rather the total deformation which took place in the wood as well as the machine parts.