NOTES ON CHAIN CABLES. 173 



DISCUSSION. 



Naval Constructor Otterson : — Mr. Howard is present. He was the inspector of 

 the chain made at the Navy Yard for the Panama Canal Commission. I hope that he 

 will take part in this discussion, and probably state the results obtained from his inspec- 

 tion ; and, if he is in a position to do so, to include in his discussion some of the notes from 

 his report on these tests, which I think were rather interesting. 



The Chairman: — ^Mr. Howard, do you feel hke saying something on this question? 



Mr. James E. Howard, Visitor: — Mr. Otterson has gone over the subject of the man- 

 ufacturing details in the making of chain exceedingly well. My remarks, therefore, had 

 better be along other lines, since he has covered the manufacturing details much better than 

 I could. 



In regard to material, it seems that the best results have commonly been obtained with 

 puddled iron, of not too high a degree of refinement. When iron is refined to the extent 

 of almost reaching a puddled steel there is danger of brittleness in the manufactured chain, 

 and in the subsequent use of the chain such brittleness will manifest itself. 



The fabrication of bar iron into the form of a link necessarily puts it into such shape 

 that there is not a good distribution of stresses in the cross-section of the sides of the links, 

 and probably very little chain is used which under service conditions is not overstrained, at 

 least in some of its parts. Such overstraining may and in many cases does lead to ultimate 

 brittleness. As an illustration of such a tendency in plain bars, there were some single re- 

 fined and extra refined puddled irons tested in the early days of the Watertown machine, 

 which originally had a tough and fibrous character. After an interval of rest, following 

 the original test, the material gradually became brittle in the fracture upon subsequent tests 

 being made. In the course of a few years, the fractures, which were made in retesting 

 from time to time, changed from fibrous to granular. This was accompanied, however, by 

 increased tensile strength, the iron originally having shown a tensile strength of about 51,000 

 to 52,000 pounds per square inch, but which finally rose to some 64,000 pounds per square 

 inch. Annealing restored the iron to its fibrous and tough character, at the same time bring- 

 ing the tensile strength down to about its original value. 



There is a feature of interest in regard to chain cable which should be considered and 

 which pertains to the location of the place of fracture, when a link breaks in service. Many 

 links, after the chain has been in service, break not at the weld, but in other places in the 

 quarter at the opposite end from the weld or elsewhere, and such service fractures are 

 commonly brittle ones. This is thought to result from frequent bending, slight in extent 

 it may be, but occurring in different parts of the link. 



Having a soft and tough fibrous iron at the outset, obtained by proper selection of 

 material, it is desirable to keep it so. Applying a proving stress to a chain, say one and a 

 half times its working load, overstrains it in a degree, and to some extent this is detrimental. 

 After a manner the proof stress has an effect similar to the testing of the puddled iron 

 referred to — it may introduce a tendency in the iron to become brittle. It would be safe prac- 

 tice to anneal chains after proof stresses have been applied, and in order to maintain a 

 state of toughness the annealing should be repeated after there have been overstraining 

 loads on the chain. 



