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STRENGTH OF MATERIALS 



The first formula serves to compute the thickness when 

 p, d, and 5 (working stress) are given; and the second one is 

 used to compute the intensity of stress when the intensity of 

 pressure p and the dimensions of the cylinder are given. 



EXAMPLE. What should be the thickness of walls of a cast- 

 iron water pipe, inside diameter 24 in., to resist a water pres- 

 sure of 200 Ib. per sq. in., using a unrt working stress of 2,000 Ib. 



SOLUTION. Here, d = 24, = 200, and 5 = 2,000. Substi- 

 tuting in the formula for t, 



200X24" 



/ = =1.2 in. 

 2X2000 



4. Temperature Stresses. If a bar subjected to change of 

 temperature is constrained so that it can neither expand nor 

 contract, the constraint exerts on it a force sufficient to pre- 

 vent the deformation. This causes in the bar a corresponding 

 stress called temperature stress. It is compressive when the 

 change of temperature is a rise, and tensile when a fall. 



COEFFICIENT OF EXPANSION FOR A NUMBER OF 

 SUBSTANCES 



Let T be the stress induced in a bar, whose area is a, by a 

 rise or fall of /; let, also, c be the coefficient of expansion and E 

 the modulus of elasticity of the material. Then, 



