The effect of temperature on the strength of wood, plywood and glued joints

This publication covers experimental investigations made at the Division of Forest Products, Council for Scientific and Industrial Research, Melbourne, during the period December, 1940, to January, 1946, to determine the effect of temperature on the strength of wood, plywood and glued joints. The investigations deal with reversible changes in_ strength, elasticity, and the like which may accompany variations in the temperature of the material. Results show that all properties investigated are affected by temperature at some moisture content, in many instances to such an extent that serious error is introduced in mechanical testing and in design where this factor is not taken into account. Temperature coefficients may exceed one per cent of the value at 20° C. per degree centigrade. Relations are given from which the effect of temperature on certain properties of a species can be estimated quantitatively with considerable confidence for a wide range of temperatures and moisture contents. PART I. deals with compression, bending, and toughness tests on Sitka spruce and five Australian species at nominal moisture contents of 8, 12, and 20 per cent. in the range - 20 to + 60° C. Compression tests on these species were extended to zero moisture content and near saturation, in respective ranges of - 20 to + 90° C. and - 20 to + 60° C. In addition, two low density species were included in the compression tests. Two species were also examined in bending at zero moisture content from - 20 to + 80° C. PART II. covers tests made at 15 per cent. nominal moisture content on standard size hoop pine specimens in compression and shear from zero to 40° C. and in bending at 20 and 40° C., also on 2 in. X 3/4 in. X 3/4 in. specimens of the same species in compression from - 20 to + 60° C. PART III. describes tests on hoop pine plywood. At nominal moisture contents of 8, 12, and 20 per cent., tensile and crushing strengths were examined from - 20 to + 80° C. Investigation of crushing strength was extended to include zero moisture content. Modulus of elasticity was examined at all the above moisture contents, but only from - 20 to + 60° C. PART IV. discusses tests on casein, pheno-formaldehyde and urea-formaldehyde glued joints at temperatures from - 15 to + 60° C. in the range 8 to 20 per cent moisture content. PART V. summarizes the more important features of the investigations in general terms and gives results of independent confirmatory tests.