278 



STRENGTH OF MATERIALS 



AVERAGE ULTIMATE STRENGTH OF WOODS, IN 

 POUNDS PER SQUARE INCH 



elasticity for tension, compression, and shear. If k is the 

 increase per unit of length of a material subjected to tensile 

 stress and s the unit stress producing this elongation, the 

 modulus of elasticity of the material for tension is 



5 

 "~ k 



For example, if a wrought-iron bar subjected to a unit 

 tensile stress of 10,000 Ib. per sq. in. is stretched .0003625 in. 

 per inch of length, the modulus of elasticity of the wrought 

 iron for tension is 



It should be observed that E must be expressed in the same 

 units as the unit stress s; in this example, in pounds per square 

 inch. 



If the total length of a bar is L, its sectional area A, the 

 total stress to which the bar is subjected P, and the total 

 deflection produced K, then the modulus of elasticity of the 

 material of the bar will be 



PL 



E = 



AK 



