strength may well be a factor. Alternating 

 stresses of moderate magnitudes superimposed on 

 high mean-stress levels do reduce the strength of a 

 structure subjected to repeated loading; further- 

 more, in places where cold-working is involved as 

 a result of such stress combinations (as appears 

 likely near welds) the notch sensitivity and transi- 

 tion temperature of the affected material are 

 generally raised. In the design of structures for 

 endurance strength, the frequency distributions 

 here should be directly applicable. 



Acknowledgments 

 The data presented in this paper have been ob- 

 tained as the result of the co-operative effort of 

 many people, only a few of whom can be men- 

 tioned here. The excellent co-operation of the 

 Esso Company, especially of Mr. Stewart and 

 Captain Stober, made possible the collection of 

 service data on a tanker, the £550 A sheville, under 

 service conditions. The financial and technical 

 contributions of the SNAME panel on "Strain 

 Measurements in FuU-Scale Structures" were es- 

 sential to the planning and execution of the Esso 

 A sheville and Gopher Mariner tests. The pleas- 

 ant co-operation of Mr. H. M. Tiedemann (at the 

 time connected with the SNAME office) was par- 

 ticularly helpful. Credit for the extensive data on 

 the weatherships is due to both the U.S. Coast 

 Guard and the Weather Bureau. The success of 

 the sea tests on the carrier and destroyer is to a 

 large measure the result of the tireless efforts of 

 Cdr. R. Brooks, USN, and Mr. J. Birmingham of 

 the TMB staff. The data could not have been 

 secured without the extensive assistance of the 

 ship's officers and personnel. The development 

 of the automatic recording and counting instru- 

 mentation has been greatly expedited by the sup- 

 port given it by Mr. R. T. McGoldrick of TMB 

 and Mr. J. Vasta of the Bureau of Ships. The 

 advice and opinions of statisticians from various 

 government and private activities have been 

 solicited and used freely. In particular the ad- 

 vice of Mr. I. R. Savage and Dr. Lieblein of the 

 National Bureau of Standards has been quite help- 

 ful. 



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40 



