Treesearch

Mathematical modeling computer programs for several hardwood sawing systems have been developed and are described. One has judgment capabilities. Several of the subroutines are common to all of the models. These models are the basis for further research which examines the question of best-grade sawing method in terms of lumber value yield.

It is often difficult to kiln dry California black oak lumber green from the saw without developing excessive degrade from honeycomb, ring failure, and collapse. Results from this study indicate that defect-prone lumber contains heartwood that was infected and weakened by anaerobic bacteria in the living tree. Green, bacterially infected boards should be segregated and dried to 20 percent moisture content (MC) under mild air-drying conditions or by low temperature, forced air-drying schedules. The percent MC lumber can then be kiln dried to end-use MC without additional defect. Boards with...

Circular plates of reconstituted wood were fabricated and destructively tested to appraise the potential of such material for cable reel flanges. The reconstituted wood consisted of flakeboard from quality-cut flakes and also from factory residue. The high quality flakeboard used 0.020- by 1/2-by 2-inch southern pine flakes cut on a disk flaker, whereas the flakeboard from residues was of 2 degrees of refinement, and consisted of 50 percent lumber residue and 50 percent hogged plywood scrap. Flake alignment variations in the plates included all random, all radial, all concentric, radial...

This paper surveys research leading to allowable shear stress parallel to grain for lumber. In early flexure tests of lumber, some pieces failed in shear. The estimated shear stress at time of failure was generally lower than shear strength measured on small, clear, straight-grained specimens. This and other engineering observations gave rise to adjustments that underwent some evolution not well described in the literature. Some anomalies which developed are discussed; an error is shown to have prevailed in the concept of a split beam for about 20 years. Some recent research done in Canada...

Until approximately 1965, allowable design stresses for lumber in tension were taken as equal to those assigned for bending. As interest in tensile properties increased, testing machines were designed specifically to stress lumber in tension. Research results that accumulated on tensile tests of full-size lumber suggested lower design stresses for tension than for bending for both machine stress rated and visually graded lumber. The latest change for visual grades, based on a review of research data available up to 1977, was a reduction in design tensile stresses that varied by size and grade.

A plane-stress analysis of orthotropic or isotropic beams is presented. The loading conditions considered are: (1) a concentrated normal load arbitrarily located on the beam, and (2) a distributed normal load covering an arbitrary length of the beam. exhibit close agreement with existing experimental data from Sitka spruce beams. Other loading conditions can similarly be considered. Numerical results based on the present analysis exhibit close agreement with existing experimental data from Sitka spruce beams.

A study was conducted to compare stress wave devices and determine the information available from stress waves in veneer sheets. The distortion of the stress wave as it passed a defect indicated that an estimate of the location and size of the defect can be obtained but information regarding wood quality is lost in the areas immediately behind a knot.

This paper describes increment cores (a useful tool in forestry and wood technology) and their uses which include age determination, growth increment, specific gravity determination, fiber length measurements, fibril angle measurements, cell measurements, and pathological investigations. Also described is the use and care of the increment borer which is essential in obtaining good cores. A caution is also given as to the tree damage that boring can cause, with suggestions for minimizing damage.

Flakeboards made with uniform densities throughout their thickness and different degrees of flake alignment were used to establish relationships between bending, tension, and compression values of modulus of elasticity or modulus of rupture (or stress to maximum load) and the variables of specific gravity and flake alignment. An equation using sonic velocity as an indicator of alignment was developed that describes the relations over a broad range with a high degree of confidence. Bending stiffness of boards having a density gradient were predicted within approximately ± 20% using the...

A simple and durable exterior natural finish developed at the Forest Products Laboratory is described. The finish is classified as a semi-transparent oil-base penetrating stain that effectively retains much of the natural grain and texture of wood when exposed to the weather. The directions for preparation are included as are the recommendations for application to both smooth and rough wood surfaces.