The influence of juvenile wood content on shear parallel, compression,and tension perpendicular to grain strength and mode I fracture toughness of loblolly pine at various ring orientation

Abstract

Forest products from improved trees grown on managed plantations and harvested in short rotations will contain higher proportions of juvenile wood than in current harvests. More information is needed on the influence of juvenile wood on lumber properties. Most information developed to date has concentrated on ultimate tensile stress, modulus of rupture, and modulus of elasticity. This paper shows for this sample of loblolly pine three-dimensional surfaces fit to test results for shear stress parallel to the grain, compression and tension stress perpendicular to the grain, and mode I fracture toughness for various percentages of juvenile wood content and ring orientations. The properties of more than 340 small specimens for each property tested made from clear wood taken from lumber produced from logs harvested in a 28-year-old fast-grown plantation of loblolly pine in North Carolina were determined. Three-dimensional polynomial surfaces dependant on juvenile wood content and ring orientation ere fit to the data. The average strength of all properties decreased with increasing amounts of juvenile wood in the cross section. Shear strength was insensitive to annual ring orientation and seemed to be strongly dependant on reductions in density caused by increased juvenile wood content. Compression and tension perpendicular to the grain strength and stiffness and mode fracture toughness were very sensitive to juvenile wood content and annual ring orientation.

Citation

Kretschmann, David E. 2008. The influence of juvenile wood content on shear parallel, compression,and tension perpendicular to grain strength and mode I fracture toughness of loblolly pine at various ring orientation. Forest products journal. Vol. 58, nos. 7/8 (July/Aug. 2008): Pages 89-96