ULTRASONIC VELOCITY IN WOOD AND ITS MOISTURE-CONTENT .1. EFFECTS OF MOISTURE GRADIENTS ON ULTRASONIC VELOCITY IN WOOD

The effects of moisture gradients in woods on ultrasonic velocity were examined on model specimens which were assembled from woods which had been equilibrated to known moisture contents, to simulate specimens w ith moisture gradients. The specimens with different moisture contents (water-saturated, vapor-saturated, and air-dried conditions) were ass embled initially in a series of horizontal layers and then parallel in an upright series in the forward direction of ultrasound. Ultrasonic velocity was measured in a radial direction in a room maintained at 20 degrees C and 65% relative humidity. When the specimens with differen t moisture contents were assembled in a series (that is, moisture grad ient parallel to the forward direction of the ultrasound), those which were calculated from the law of composites agreed well with the measu red values. When the specimens were assembled in parallel (that is, mo isture gradient against the forward direction of the ultrasound), ultr asonic velocity was more dependent on the specimens with the faster ve locities.