Table 73. 



ELASTICITY AND STRENGTH OF IRON.* 



Table 74. 



APPROXIMATE VARIATION OF THE STRENGTH OF BAR IRON, WITH 



VARIATION OF SECTION. t 



* This table was computed from the results published in the Report of the U. S. Board on Testing Iron and Steel, 

 Washington, iS8i, and shows approximately by the relative effect of different amounts of reduction of section from the 

 pile to the rolled bar. A reduction of the pile to lo per cent of its original volume is taken as giving a strength of 

 100, and the others are expressed in the same units. 



t The strength of bar iron may be taken as ranging from 15 per cent above to is per cent below the numbers here 

 given, which represent the average of a large number of tests taken from various sources. 



Notes. —The stress at the yield point averages about f>o per cent of the ultimate strength, and generally lies be- 

 tween 50 and 70 per cent. The variation depends largely on the temperature of rolling if the iron be otherwise fairly 



I pure. 



\ According to the experiments of the U. S. Board for Testing Iron and Steel, above referred to, a bar of iron which 

 Jjias been subject to tensile stress up to its limit of strength gains from 10 to 20 per cent in strength if allowed to rest 

 Aree from stress for eight days or more before breaking. The effect of stretching and subsequent rest in raising the 

 Elastic limit and tensile strength was discovered by Wohler, and has been investigated by Bauschinger, who shows 

 *jiat the modulus of elasticity is also raised after rest. The strengthening effect of stretching with rest, or continuous 

 y ery slowly increased loading, has been rediscovered by a number of experimenters. 



"Smithsonian Tables. 



72 



