164 



BULLETIN 42, UNITED STATES NATIONAL MUSEUM. 



Fifth. Shearing stress. — This is the stress that comes into action on 

 the pins of bridge and roof links, namely, a center link pulling in one 

 direction while the two side links pull iu the opposite direction, thus 

 tending to cut or shear the pin at the two junctions. 



Strength.— intimate shearing stress 61,412, 79,737, 71,648, 45,410 

 pounds per square inch, given according to carbon contents, each being 

 the mean of experiments on three bars. These experiments prove that 

 the strength to resist a shearing is on an average oue-fourth less than 

 the tensile strength. 



Hardness. — As shown by the amount of detrusion before rupture 

 0.193, 0.249, 0.281, 0.323 parts of 1 inch. 



Effects. — The hardest bars, 1.2, were very slightly cut, but broke sud- 

 denly into many small pieces at the junctions; 0.9, more cut and fewer 

 pieces ; 0.6, edges more curved on reverse sides, and cut, only two 

 small pieces; the fractures being all granular, excepting where cut 

 Bars 0.3, or the softest, reverse sides more curved and cut, and remain- 

 ing portions parting with a smooth shining surface. 



Series B. 



Steel ingots cast to 6 inches square were tested by pulling to ascer- 

 tain the mechanical effects produced by their being hammered down to 

 5, 4, 3, and 2 inch square bars. Four ingots, of different degrees of hard- 

 ness, containing 0.8, 0,6, 0.4, and 0.2 of carbon, were operated upon. 



One set was tested as received, the other set as annealed. The dif- 

 ferences between the unannealed and the annealed are more marked in 

 the elastic than iu the ultimate stress borne. 



Deacriptiou. 

 As received. 



Elastic stress. 



0.8 



0.6 



0.4 



0.2 



Total nieau 



Unan- 

 nealed. 



Pounds. 

 53, 457 

 41,743 

 31, 943 

 2", 800 



38, 736 



Annealed. 



Pounds. 



41, 500 

 39, 880 

 29, 671 

 2.5, 514 



34, 143 



Difference. 



Per cent. 



22.3 



4.1 



7.1 



8.2 



Ultimate stress. 



Unan- 

 nealed. 



Pounds. 

 75, 959 

 75, 63!) 

 65, 001 

 56, 401 



11.86 



68, 250 



Annealed. 



Pounds. 

 70, 608 

 74, 481 

 62, 334 

 54, 300 



65, 431 



Difference. 



Per cent. 

 7.1 



1.5 

 4.1 

 3.7 



4.13 



Annealing the bars gives 11.86 per cent, less in the elastic and 4.13 

 per cent, ia the ultimate stress. 



