In initial low frequency ultrasonic laboratory tests signals from a 

 solid specimen were compared to signals from a specimen with a known 

 amount of cross-sectional wood loss. The laboratory test procedures, 

 data analysis and test results are explained in detail in Reference 7. 

 The laboratory evaluation of direct and indirect ultrasonic inspection 

 indicated the following: 



1. Ultrasonic tirae-of-f light and attenuation measurements do not 

 consistently correlate with voids smaller than 25% of the wood cross- 

 section. 



2. Direct time-of-f light measurements cannot detect water-filled 

 voids (marine borer tunnels) because the acoustic velocity of wood across 

 the grain is very close to that of the acoustic velocity of seawater 

 (Figure 2) . 



3. A digital readout of the time-of-f light or transit time alone 

 is not an accurate or reliable measure of cross-sectional wood loss with 

 either direct or indirect transmission modes. 



w = 5000 fps 



WOOD 



(a) SOLID WOOD PATH 



TIME = 12"/12 



5000 FT/SEC 



= 200^XSEC 



= 4860 fps 



(b) 2 WATER FILLED VOID 

 TIME = 10V12 + 2/12 



5000 FT/SEC 4860 FT/SEC 

 = 201/XSEC 



• =800 fps 



'air 



(c) 2" AIR FILLED VOID 

 = 10"/12 + 2"/12 



5000 FT/SEC 800 FT/SEC 

 = 188/XSEC 



Figure 2. Direct transmission time-of-f light measurements through 



(a) solid wood, (b) solid wood with a 2-inch water filled 

 void, and (c) solid wood with a 2-inch air filled void. 



Although consistent correlation between the ultrasonic signal and 

 the timber specimen had not been identified, further testing was required 

 to determine what, if any, inspection capability existed. In particular, 

 the accuracy and reliability of using ultrasonics for the inspection of 

 timber waterfront structures must be determined. Based upon the labora- 

 tory test results the following recommendations were made: 



