Some Non-Destructive Tests for Wood

Non-destructive methods of testing wood were reviewed. Non-destructive testing was defined as the evaluation of materials without damage. One of the first and most limited tests of this type to be developed was visual inspection to evaluate the appearance of wood products. This included grading logs and lumber, visual inspection in wood products manufacture, inspection of kiln loads, decay determination, insect infestation assessment and abnormal wood recognition. Radiography has been employed in testing wood. X-rays have been used in determining the proportion of unsound wood in poles, in detecting the presence of insects in timbers, in differentiating termite cavities from decay pockets, and for locating pitch pockets, stones and metal objects in logs. Magnetic detectors offer another approach to locating metal in timber. Numerous devices, some based on surplus mine detectors, have been adapted for locating ferrous metals in wood. Limits of detection range from 5 to 12 inches. A number of non-destructive tests have been developed for determining wood surface qualities. Surface roughness has been determined using profile measuring equipment, incident lighting, and straight-line shadow sectioning. Surface stresses have been evaluated using dial and optical gauges, brittle lacquers, and electrical strain gauges. Surface color reactions to certain chemicals have been used in wood identification. Several methods have been developed for measuring slope of grain on wood surfaces including the FPL scribe procedure. Non-destructive devices have been developed which utilize atomic, electrical or sonic energy. Radioisotopes have been used to measure density and thickness of wood and paper. Direct current sensitivity and dielectric capacity have been used as the basis for electric moisture meters. Resonance techniques have been adopted for vibration testing of standard beams, and plywood plates and panels, and pulsed ultrasonic energy has been used in dynamic testing of wood.

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