Problem definition and objectives: Today, in the product quality control process, the use of destructive tests is being replaced by non-destructive evaluations. Ultrasonic technique is one of the non-destructive testing methods. By means of this technique, if a relationship can be found between the velocity of ultrasonic waves and various physical and mechanical properties of wood and other wood products, then this technique can be used in the quality control of that material. The aim of this research was to investigate the correlation between the velocity of ultrasonic waves in different directions (longitudinal, transverse and thickness) of particleboards made with small and large poplar wood chips and modulus of elasticity, modulus of rupture and internal bonding of the particleboards, so that if there is a correlation, this technique can be used in industry instead of destructive evaluations quality control.
Methodology: In this research, at first, using poplar logs and urea formaldehyde resin, two types of particleboard were produced from small and large wood chips, with a density of 0.7 g/cm3 and a thickness of 16 mm. Press temperature was 170 degrees Celsius, press pressure was 200 bar, and pressing time was 5 minutes. After conditioning and cutting test samples from the manufactured particleboards, the velocity of ultrasonic waves in different directions (longitudinal, transverse and thickness) of the test samples was calculated by the ultrasound technique. Afterward, modulus of elasticity, modulus of rupture and internal bonding were measured in the same test samples by destructive testing. Then, the correlation between the ultrasonic waves velocity and the measured mechanical properties was determined by means of statistical analysis.
Results: Based on the results, the effect of sample direction on ultrasonic waves velocity in static bending and internal bonding samples, also the effect of wood chip dimensions on ultrasonic waves velocity in internal bonding samples were significant. The maximum average ultrasonic wave velocity was measured in longitudinal direction and the minimum in thickness direction of the samples. In addition, the correlation between the ultrasonic waves velocity and the modulus of rupture in the longitudinal direction of samples made of small and large chips was significant. Meanwhile, the correlation between ultrasonic waves velocity and internal bonding in the thickness direction of samples made of small and large chips was significant.
Conclusion: According to significant correlation between ultrasonic waves velocity in longitudinal direction of boards made of small and large chips and their modulus of rupture, the ultrasonic technique can be used to monitor the modulus of rupture of particleboard in the production line. Also, according to significant correlation between ultrasonic waves velocity in the thickness direction of boards made from small and large chips and their internal bonding, the ultrasonic technique can be used to quality control of the internal bonding of particleboard in industry. Finally, it is concluded that by measuring ultrasonic waves velocity in the longitudinal and thickness directions of particleboard in the production line, its mechanical properties can be controlled in a non-destructive way.