The effect of knots on the passage of ultrasound in wood

The possibility of using ultrasound to detect the presence and assess the condition of knots in wood is considered. Sorting lumber for defects or flaws is primarily done visually, which does not always allow for an accurate determination of the intended use of these semi-finished products with the required performance characteristics. Furthermore, visual assessment of the grade and condition of lumber is highly prone to making erroneous decisions, as some defects are hidden. The presence of hidden internal defects or flaws, including knots and cracks in the areas where they are located, can lead to further failure of either a single element or the entire structure. Ultrasonic diagnostics can be used to assess the presence and condition of these materials. The shadow method of acoustic testing demonstrates a high degree of reliability in the diagnostics of solid wood. A frequency of 2.5 MHz was used in the studies. Due to the anatomical structure of wood, several diagnostic features arise during the sounding process, which expand the scope of this method. These characteristics include the need to amplify the signal amplitude to pass through the wood, which indicates the presence or absence of defects and flaws, and allows for an assessment of their condition and the determination of their functional purpose. A defect-free zone, as well as a zone with healthy intergrown knots, requires signal amplification to 70 dB. Increasing the signal amplitude above 70 dB indicates the presence of a zone of internal stress concentration, as well as defects and flaws that significantly reduce the quality of the lumber.

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