Crushing Strength and Modulus of Elasticity of Unmachined Lodgepole Pine Stem Sections Compared to Machined Dowels of the Same Diameter–Kerfed and Kerf-Free, Round and Half-Round

Six-inch-long cylindrical or half-cylindrical stem sections from suppressed stands in two western Montana locations, tested when dry in compression, showed that specific gravity and two mechanical properties–maximum crushing strength parallel to the grain, and modulus of elasticity (MOE) — are positively correlated with average rings per inch. To be equal in mechanical properties with 3- or 4-inch-diameter unmachined specimens having 17 rings per inch, 2-inch-diameter specimens should probably have 35 or more rings per inch; such 2- to 4-inch-diameter unmachined specimens containing small knots typical of stems in suppressed stands can be expected to have mechanical properties equal to, or exceeding, handbook values for clear lodgepole pine wood sawn to square cross section. Drying checks caused by not kerfing rounds before drying them do not appear to diminish compression mechanical properties. Half-rounds–edged or unedged–have mechanical properties in compression about equal to rounds of the same diameter. Unmachined (not doweled) 2-inch-diameter and larger rounds have about one-third higher MOE and one-tenth higher maximum crushing strength than dowels of the same diameter that have had 1/4 to 1/2 inch of radius machined from them in the doweling process. A sub-experiment indicated that MOE of cylindrical stem sections nondestructively measured in compression parallel to the grain did not differ significantly from MOE measured on the sections in tension and bending.

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