Toughness of Selected Wood Composites

Standard toughness tests were conducted on 560 specimens from 14 commercial lumber, plywood, particleboard, and hardboard products of selected species using, a Forest Products Laboratory toughness testing machine. Whereas maximum values were obtained from three softwood lumber specimens with grain parallel to span, minimum values-were obtained from the three softwood lumber specimens with grain perpendicular to the span. Comparable average toughness values were shown from ponderosa pine plywood in parallel grained face veneers, southern pine plywood in vertical grained face veneers; standard hardboard, and a medium density fiber-type particleboard of mixed hardwood species. Average toughness values of specimens parallel to the grain compared to those of specimens at right angle to the grain were 16, 17, and 48 to l, respectively, for Douglas fir, ponderosa pine, and southern pine lumber. The average toughness values between two face grain directions for plywood of the same three softwood species was only 1.6 to 1. Differences in average impact resistance between two machine directions of the eight commercial particleboard and hardboard tested were insignificant. Within each face grain or machine direction of each materials, all tangentially loaded lumber with grain parallel to span had better impact resistance than radially loaded lumber except the lumber with grain perpendicular to span. Specimens of plywood, particleboard, and hardboard loaded on width possessed higher-toughness values than specimens loaded on thickness. On the average, the variation in toughness value within a material was three times higher in three softwood lumber and plywood specimens than in the particleboard and the hardboard specimens tested.

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