![]() An increase in force results in a permanent deformation even when the force is removed (Figure 71-1). Above the proportional limit, wood behave plastically. A graphic way to illustrate these characteristics is with a stress-strain diagram (Figure 71-1).īelow the proportional limit, wood behaves elastically. The most important point in wood bending is that wood is both plastic (it can be deformed permanently, without breaking, like a piece of soft wax) and elastic (it can be stretched slightly and when the force is removed it will return to its original shape). This is because of the fact that, although wood bending is an "art," it is solidly backed by engineering theory. Even with a severe bend, rejects should not exceed 10%. Yet, with a knowledge of the basics of wood bending and with suitable raw material and equipment, nearly every bend can be made successfully. The bending room of a furniture plant is often a room of mystique and amazement-a place where, when the bending room foreman retires, defects and rejects show up like dandelions in the spring lawn. BAZAN, Wood Science 13 (1980) 50.Editors note: The following article is an excerpt from the book "The Wood Doctor's Rx," by Gene Wengert, retired Professor and Extension Specialist in Wood Processing, Department of Forestry, University of Wisconsin-Madison. ![]() SCHMIDT, Holz als Roh und Werkstoff 20 (1962), 333. DOBRASZCYK, “An investigation into the fracture and fatigue behaviour of wood”, PhD Thesis, University of Bath, Bath (1983). GILDWALD, Holz als Roh und Werkstoff 19 (1961) 86.ĭ. ROSE, Holz als Roh und Werkstoff 23 (1971) 271. SIEMINSKI, Hols als Roh und Werkstoff 18 (1960) 369. Idem, Holz als Roh und Werkstoff 22 (1964) 264.Ī. STERR, Holz als Roh und Werkstoff, 21 (1963) 47. JENKINS, Bristol Aircraft Ltd, Structures and Materials Laboratory Report No. American Society of Mechanical Engineers (April 1943) 187. LEWIS, Proceedings American Society for Testing Materials 46 (1946) 814. (Proceedings of American Society of Civil Engineers, 1960) 15. Musgrove (Cambridge University Press, 1984) p. MOORE in “Wind Energy Conversion 1983”, edited by P. ZUTECK, in Proceedings of DOE/NASA Horizontal Axis Wind Turbine Workshop (July 1981). MCLEISH, Institute of Electrical Engineers Proc. ![]() LARK, “Construction of Low-Cost MOD O-A Wood Composite Wind Turbine Blades”, in Proceedings 28th Meeting of National Society for the Advancement of Materials and Process Engineering (1983) p. DINWOODIE, “Timber, its Nature and Behaviour”, (Van Nostrand Reinhold Company Inc., New York, 1981). Optical microscopy demonstrates that fatigue damage is progressive commencing on the compression face of flexural samples as fine scale cell wall kinks and developing into macroscopic creases. A constant life diagram for sliced Khaya laminate has been constructed which summarizes the effect of Rratio on fatigue life. Increased moisture content reduces the static strength and fatigue life and reversed loading results in the lowest fatigue life. Fatigue life is largely species independent when normalized by static strength. Tests were conducted in repeated and reversed loading over a range of five Rratios at three moisture contents, and the accumulation of fatigue damage was followed by microtoming fatigued wood and observing the formation of cell wall kinks by polarized light optical microscopy. A laminated hardwood, Khaya ivorensis, a softwood, Sitka spruce, and compressed beech laminates were fatigue tested under load control in four point flexure. A detailed review of the wood fatigue literature is presented and the need for experimental work under load control at a range of moisture contents and Rratios is emphasized.
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