1. Utilization of timber specimens with increasing known amounts 

 of damage or wood loss to identify the minimum amount of damage detec- 

 table. 



2. Incorporation of appropriate state-of-the-art data processing 

 techniques to correlate digitized acoustic data to the condition of the 

 timber. 



3. Evaluation of ultrasonic parameters besides time-of-f light and 

 peak-to-peak values. 



4. Utilization of multiple transducers to show relative changes in 

 the acoustic signal at adjacent locations. 



ASSESSMENT OF POTENTIAL TIMBER NDT TECHNIQUES 



In light of the problems encountered during the initial laboratory 

 evaluation of ultrasonic inspection of timber piling, a study was con- 

 ducted to identify new alternative techniques. A contract was awarded 

 to Southwest Research Institute (SWRI) , San Antonio, Tex., to evaluate 

 existing and assess new NDT techniques for use by Navy divers (Ref 8). 

 Potential NDT techniques were analyzed to determine feasibility and to 

 predict performance capabilities and characteristics. The most promising 

 techniques were then tested in the laboratory to demonstrate their feasi- 

 bility. 



From the results of the laboratory experiments and feasibility study 

 conducted in seawater on small-scale wooden models with simulated marine 

 borer damage along the grain, the contractor determined that the following 

 six techniques were technically feasible: 



• indirect ultrasonic testing 



• impact testing 



• X-ray tomography 



• real time X-ray imaging 



• acoustic emission 



• dielectric measurement 



Each of the six potential timber inspection techniques are discussed 

 below. 



Indirect Ultrasonic Analysis 



SWRI evaluated this technique using essentially the same equipment 

 as during the laboratory tests at NCEL. Two 50-kHz transducers, separated 

 a distance of 18 inches in the axial direction, generated compressional 



