NONDESTRUCTIVE TESTING TECHNIQUES AND PIEZOELECTRIC ULTRASONICS TRANSDUCERS FOR WOOD AND BUILT IN WOODEN STRUCTURES

Abstract

A survey of the main NDT methods used to evaluate the quality and properties of wood and wooden structures is given. Among the most important ones there are visual inspection, sonic and ultrasonic stress wave. Some other methods include: deflection, electrical, isotope and X-ray methods. The ultrasonic methods seem to be the most suitable ones in many cases especially for quality control purposes, but these methods depend on the quality of the piezoelectric transducers. Consequently, the construction and characteristics of a new type of piezoelectric transducer are reported. The new transducer is a composite type transducer, consisting of a sandwich type piezoactive element and a steel cylinder glued together. The sandwich piezoactive element was made of five thinner discs of 20 mm diameter and 2 mm thickness. The whole construction has the resonant frequency at 60 kHz, proper to wood investigation. The transducer can be successfully used for NDT of wood, either in the trough transmission or pulse-echo arrangements. The transducers were tested for sound velocity measurements in different wood samples.