878 DEPORT — 1892. 



9. The Strength of Small Chains. 

 Bij Professor H. Hele-Shaw, M.Inst.C.E. 



The autlior has frequently found the result of using small chaiu most unsatis- 

 factory. 



In the tirst place, no small chain which he has been able to procure seemed to 

 give a reasonable amount of strength in proportion to its weight and the tensile 

 strength of the material. 



In the second place, no maker will usually give any guarantee of strength 

 below a certain size — generally f ths of an inch — although in some special cases 

 makers will guarantee the strength as low as \ inch. 



Below xijflis of an inch no strengths are ever quoted in textbooks, engineering 

 pocket-books, or books of engineering reference. 



The results are then given of an examination of various well-known books 

 concerning this subject. 



From these data, which are not very satisfactory in themselves, it is seen that 

 there are no results for chain of less than ^\, inch diameter ; whereas enormous 

 quantities of chain under this size are made and sold. 



Recently a numerous series of tests on the strength of small chaiu have been 

 made in the Walker Engineering Laboratory. Tbese tests include all sizes of 

 chain up to \ inch diameter that could be obtained either in shops or from whole- 

 sale makers. 



The result of these tests is given in five table-, under the following heads : — 



Table I., Single Jack ; Table II., Double .Tack : Table III., Ordinary Welded ; 

 Table IV., Triumph (American) ; Table V., Miscellaneous (Brazed and Odd-size 

 Welded). 



In every size three tests of ultimate strength were made, the results of which, 

 in lbs., have been recorded, the average being given in another column, These 

 tables of results have been plotted in a diagram exhibited, giving the areas in 

 square inches as absciss.T and the strength in lbs. as ordinates. It will be seen 

 that the want of uniformity in results is sufficient to explain why no values for 

 strength are given b)' the makers, and why the recorded results in books difler so 

 much. Nevertheless there is sufficient agreement to justify the following rules 

 being used to give an approximate idea of strength, tliougb, of course, for working 

 purposes a large factor of saft^ty must be employed : — 



Let P = Working strength in lbs. 



A = Area in square inches. 



C = Constant. 



Then V = C A. 



The constants are as follows: — 



Kind of Chain C 



(I) Single Jack. . . .1x10^ 



(L') Double Jack . . . :i x 10< 



(H) Welded . . . . .5 x 10< 



(4) Triumph . . . . 10 x 10* 



These results are easily remembered, and, as was seen from the lines drawn 

 on the diagram representing the formula!, give values well below the average 

 strength, and may fairly be taken with the proper factor of safety' — say 4 — as the 

 working strength of the chain. 



The chief elTect to be noticed is the extraordinary strength of the new Ameri- 

 can chain, which, on an average, is twice as strong lor every corresponding tize as 

 the English Welded Chain ; five times as strong as the Double Jack Chain ; and 

 nearl)' eleven times as strong as the Single Jack Chain; and, in most cases, gave 

 way, not as in the case of the Jack Chain and Welded Chain at the joints, but 

 in the material itself. 



A further experiment was made of twisting a piece of iron wire into the form 

 of the American link, and then testing the link and afterwards the wire itself, 



