Stress-wave analysis of Douglas-fir logs for veneer properties.

Abstract

Visual characteristics of logs have not been good predictors of the strength and stiffness (modulus of elasticity (MOE)) of lumber and veneer products. However, several studies have shown that stress-wave analysis of logs has successfully predicted the MOE of structural lumber and veneer. The purpose of this study was to determine whether stress-wave analysis of Douglas-fir (Pseudotsuga menziesii [Mirb] (Franco)) logs could also predict the MOE of veneer. Longitudinal stress-wave speed was measured in 25 35-foot (10.7-m) Douglas-fir butt logs. The logs were then cut into 8-foot (2.4-m) bolts plus trim and peeled into veneer. The veneer was dried and scanned using a commercial stress-wave analyzer, and the inverses of log and veneer stress-wave speeds were compared. The inverses of log stress-wave speeds averaged 82.6 μsec./ft. (271.0 μsec./m) and ranged from 71 to 91 μsec./ft. (233.0-298.6 μsec./m). The inverses of veneer stress-wave speeds averaged 63.2 μsec./ft. (207.4 μsec./m) and ranged from 51.6 to 128.9 μsec./ft. (169.3-422.9 μsec./m). Lower inverse stress-wave speeds for veneer indicate higher MOE. One-third of all veneer had inverse speeds lower than 58.3 μsec./ft. (191.3 μsec./m) (high-MOE suitable for laminated-veneer lumber (LVL)). Of this high-MOE veneer, 83 percent came from the bottom two bolts of all logs, indicating that the high-MOE veneer was often located near the base of the study trees. In addition, 43 percent of the veneer produced from logs with the lowest inverse speeds (≤82μsec./ft. (≤269.0 μsec./m)) had high MOE, and only 20 percent of the veneer produced from logs with the highest inverse speeds had high MOE. These findings indicate that stress-wave analysis could be used to sort Douglas-fir logs for the production of high-MOE veneer.