A continuous ultrasonic scanner for lumber grading

Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to digital@library.tamu.edu, referencing the URI of the item.Includes bibliographical references.Issued also on microfiche from Lange Micrographics.The goal of this research was to improve mechanical stress grading technology through more accurate lumber strength and stiffness predictions. Specific objectives are: 1) develop a prototype ultrasonic lumber scanning system to measure localized stress wave characteristics in lumber, 2) verify the use of ultrasonics for predicting the long-span tensile strength and modulus of elasticity of Southern Pine lumber. The lumber sample contained 225 pieces of nominal 51 mm (2 in.) x 152 mm (6 in.) x 5.49 m (18 ft) long No. 1, No. 2, and No. 3 grade Southern Pine lumber. After the lumber had reached its equilibrium moisture content, the gross density and transverse vibration MOE were measured. Utrasonic stress wave travel times were automatically collected along the length of each sample with a prototype ultrasonic lumber scanner. This scanner used a configuration of four 200 kHz transducers which were sensitive to slope of grain and edge knots, two growth characteristics which greatly affect tensile strength. The lumber was then destructively tested in tension at a span of 3.35 m (11 ft). Multivariate regression techniques were used to develop several statistical models to predict ultimate tensile stress (UTS) and MOE. The coefficient of determination (R) between the predicted and actual UTS using the MOE and density data was 0.590 and 0.398 respectively. These two nondestructive testing (NDT) variables form the basis for current state of the art grading systems. The ultrasonic predictor variables provided a higher R2 of 0.658. The correlation was further improved by combining the ultrasonic variables with MOE and density to provide R2 values of 0.760 and 0.725 respectively. The model combining the ultrasonics, density, and MOE information provided the highest R2 of 0.777. The average weighted longitudinal velocity and density were used to predict MOE. The W between the predicted and transverse vibration MOE was 0.839. In conclusion, the ultrasonic variables were shown to be better predictors of lumber strength than MOE and density. Utrasonics show great potential for accurate prediction of lumber strength and stiffness, and information obtained from this research can be used for future development of an ultrasonic grading system