EVALUATION OF LAMINATED VENEER LUMBER TENSILE STRENGTH USING OPTICAL SCANNING AND COMBINED OPTICAL-ULTRASONIC TECHNIQUES

Author 

David B. DeVallance, James W. Funck, James E. Reeb

Abstract 

Nondestructive commercial ultrasonic grading provides laminated veneer lumber (LVL) manufacturers a means for sorting veneer based on average ultrasonic propagation time (UPT) and/or average dynamic modulus of elasticity (MOE_d). However, little is known about the influence of veneer defects on strength properties of veneer and LVL. Including veneer defect and growth ring pattern measurements, obtained via optical scanning, was hypothesized to improve LVL static tensile strength (F_t) property predictions. Nondestructive and destructive testing of Douglas-fir (Pseudotsuga menziesii) veneer and LVL was performed to evaluate improvements in LVL F_t property predictions. Various models based solely on density, optical, ultrasonic, and combined system measurements were developed for LVL property predictions. LVL static F_t was best predicted (R² 1/4 0.65) with integrated optical and ultrasonic measurements (ie combined system model), which included average defect, growth ring pattern, and MOE_d measurements from the LVL material. Results suggested improved LVL F_t predictions could be achieved by integrating ultrasonic and optical systems. Additionally, the optical model, which included average defect, growth ring, and density measurements, better explained the variation in LVL static F_t values (R² = 0.58) compared with the MOE_d (R² = 0.51) and UPT (R² = 0.31) models.

KEYWORDS

Optical scanning;laminated veneer lumber tensile strength;veneer;veneer defects;ultrasonic NDE;Douglas-fir veneer;nondestructive evaluation

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