IRON AND STEEL UNDER CYCLICAL VARIATIONS OF STRESS. 



51 



At 800 r.p.m. the Swedish iron gave a safe range of 19'0 tons per sq. inch and at 

 1200 r.p.m. of 18'2 tons per sq. inch. The elastic range now found at 2 r.p.m. is 

 19 tons per sq. inch, which is in close agreement. 



The Bessemer steel was not tested at 800 r.p.m., but gave a range of 26'5 tons per 

 sq. inch at 1200 r.p.m. A similar material at 800 r.p.m. gave a range of 30'5 tons 

 per sq. inch. The elastic range now found at 2 r.p.m. is 33 tons per sq. inch. Here 

 the effect of speed would appear to agree with that found by REYNOLDS and SMITH, 

 the differences being too great for errors of observation. 



(N.P.U) 

 ELASTIC RANGES 



SWEDISH IRON 



SAFE: RANGES ( 



WROUGHT IRON 



O 10 to to 



AXLE STEEL 



UNTEMPEREO SPRING. STEEL 



AXLE STEEL 



y-'j so -40 ~ -10 a >o 



MINIMUM STRESS TONS. SO. IN. 



Fig. 7. 



The abscissa for each curve of fig. 7 is the stress at the inferior limit of elasticity, 

 compressive stresses being counted as negative. The ordinate is the elastic range of 

 stress, corresponding to the minimum stress represented by the abscissa. 



The value of the abscissa for the point where the ordinate is zero is the ordinary 

 tensile maximum stress, as has been pointed out by GERBEK. A line inclined at 45 

 to both axes and passing through this point forms an upper limit to the possible 

 curve obtainable, for at any point on this line the superior limit of stress is equal to 

 the tensile maximum stress. This line, AB, is shown dotted in all the curves. 



For the reason given above the portion of the curve CB cannot cross the line AB, 

 and, after the points have been carried close to the latter limit, the whole series of 

 observations is completed by taking the maximum stress as the upper limit of 

 elasticity. This, of course, is not strictly true, but the degree of approximation is 



H 2 



