Drying Stresses in Red Oak: Effect of Temperature

The effects of kiln-drying at 80 to 140?F. and controlled room drying at 35 and 80?F. on tensile and compressive stresses, perpendicular to grain, in 2-inch red oak are reported. Increasing temperature tended to increase maximum tensile strain in the outside layers at the start of drying and maximum tensile strain in the center layers after stress reversal. Maximum compressive strain in the center layers was about the same at most temperatures but considerably lower at 140?F. Temperature had little effect on tension set in the outside layers. The greater compression set in the interior layers at higher temperatures resulted in significantly greater board shrinkage. The specimens were from the second log of northern red oak on a good site. The trees were about 110 years old and 82 to 100 feet high. The number of rings per inch was 7 to 10. The material was green, clear, flat-sawed heartwood. Kiln runs were made at 80, 95, 110, 125, and 140?F. in small drying chambers. A mild relative reduction schedule was used. Curves showing strain, set, and moisture content of 2- by 7-inch slices of red oak are given for each of the foregoing kiln temperatures.

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