CAST IRON. 



389 



207. Modulus of Elasticity for Cast Iron. The elastic 

 modulus for cast iron, as well as for most of the alloys, is 

 a somewhat variable quantity. It has been pointed out 

 that the deflections of cast-iron beams vary according to 

 the number of times the loads have been applied ; and, 

 therefore, it is to be assumed that the value of the modulus 

 calculated from the first loading, will be different from the 

 value obtained after the bar has been half-a-dozen times 

 under the load, because the metal will have taken up the 

 greater part of its permanent set. The modulus also 

 varies with the grade of metal and the conditions of casting. 

 Unwin asserts that there is no true modulus for cast iron, 

 as the set can never be quite eliminated. 



Johnson states that the modulus for cast iron varies 

 from 12 to 15,000,0001bs. per square inch. 



The following figures give the values as obtained by 

 different experimenters : 



TABLE OF MODULUS OF ELASTICITY FOR CAST IRON. 



208. The Effect of Temperature on the Strength of 

 Cast Iron. No great difference is observable in the tensile 

 strength of cast iron as the temperature is increased, until 

 a temperature of about 900 Fah. is reached. Up to this 



