Bent Wood Research Articles

Shearing Stress in Plastic Bending of Wood Beams

The shearing stress analysis of glue‐laminated wood beams in the elastic‐plastic range is presented, and the theoretical method for calculating the ultimate shearing stresses is developed. The validity of the theoretical method was verified by a test program using 16 models. The test results support the theoretical prediction. It is proved that the elastic theory on which the present design criteria of bending wood beams are based does not explain adequately the true structural behavior of wood beams in the elastic‐plastic range. This theory is verified through tests of glue‐laminated wood beams of defect‐free material and of commercial quality. The theory is proved for beams of defectfree material, and it is of significant value since it makes it possible to compute the shearing stress for a fully plastic case under ultimate load.

The analysis of life data for wood in the bending mode

The applicability of a proposed procedure based on accepted, reliable, statistics was evaluated for characterizing the duration of load properties of wood in bending. By subjecting small, clear, wood specimens to several constant stress levels, it was experimentally demonstrated that the proposed procedure is capable of estimating, at an acceptable level of confidence δ the maximum service life beyond which a specified proportion γ of the nominal population will survive. The extension of this procedure to structural sized members seems plausible, since an estimate of the short term ultimate strength for each specimen is not required. Another attribute of the procedure is that parametric estimates can be computed without failing all of the specimens; thus this should significantly reduce the duration of load test time.

Sculpture: The Ammonia Plasticization Process for Bending Pieces of Wood

Bending wood by the steam process is common enough in furniture manufacture, but it is rarely used for making sculpture in the U.S.A. Instead, the slow, timeconsuming and expensive technique of lamination generally has been adopted for sculpture with curved elements of wood. The troublesome features of working with steam-softened wood have been the difficulty of holding a piece of it with jigs or clamps, the tendency, especially pronounced when complex curved surfaces are involved, for it to retain a degree of 'memory' of its original shape upon drying and, not infrequently, for it to crack during drying. In the process described here ammonia gas is employed in a manner similar to that used in a small steam-bending plant and several advantages are realized. Since ammonia gas (NH3) under pressure at temperatures of about 70?F (21?C) is a plasticizing agent, a costly source of heat for the production of steam is avoided. Wood softened by ammonia gas instead of steam is more pliable and can be worked into fairly intricate shapes, depending on the dimensions of the piece, without the use of clamps. Simple bracing or tying of a piece for little more than an hour is sufficient to give it permanently the desired shape and there is no problem of 'memory' retention. The information that follows and the construction of the treatment setup were the result of a research program that was, in part, made possible by the support of Collaboration in Art, Science and Technology Inc., under a grant from the New York State Council in the Arts, and of Syracuse University. Alternative methods for plasticizing wood have been investigated in the U.S.A. since the late 1950's. R. W. Davidson and W. G. Baumgardt have indicated the

Some aspects of the rheological behaviour of wood part IV: Non-linear behaviour at high stresses in bending and compression

The incidence of non-linearity with stress in the rheological behaviour of wood in bending was shown earlier to occur at an unexpectedly low stress. This has been further confirmed by the study of an additional species, alpine ash.

NOTICES

Journal Article NOTICES Get access Methods of Bending Wood by Hand . Forest Products Research Bulletin No. 17. H.M. Stationery Office . 1937 . Price 1 s . Forestry: An International Journal of Forest Research, Volume 11, Issue 2, 1937, Page 146, https://doi.org/10.1093/oxfordjournals.forestry.a062717 Published: 01 October 1937