Moisture content and temperature effect on ultrasound timber grading

Summary Because wood is a natural material, the variability of its properties is very large. In order to use wood efficiently in building, it has to be stress graded. The ultrasonic stress grading was developped as an improved alternative to visual grading. This non destructive evaluative technique allows reliable higher strength values while working with new products. Corrected models were studied to reference the ultrasonic propagation speed at constant moisture content and temperature. Using a referential ultrasonic wave velocity, stress grading can be carried out on trees or logs before cutting, or on fresh beams. The correlation between conditioned beams and test specimens is very high, especially for the strongest material.The author wishes to thank the Swiss Federal Institute of Technology Lausanne for acceptance of his doctoral thesis work, June 1990