IKON AND STEEL 



227 



For measuring deflections in transverse tests various methods are 

 used. A simple instrument for this purpose is shown in Fig. 149. 

 This instrument is placed under the beam and the deflections meas- 

 ured to .001 of an inch. The strain diagram for flexure is thus a 

 load-deflection curve. 



Problem 171. A rod of nickel steel .854 in. in diameter, and with a gauged 

 length of 8 in., when tested in tension gave the data tabulated below. From this 

 data draw the strain diagram and locate the elastic limit; also compute the mod- 

 ulus of elasticity and the modulus of elastic resilience. 



177. Torsion tests. The determination of the resistance of a material 

 to shear or torsion is usually made by means of a machine designed 

 to read twisting moment in inch-pounds on the scalebeam. The 

 Kiehle machine shown in Fig. 150 may be taken as a type of torsion 

 machines. 



In making the test one end of the specimen is attached to the 

 twisting head of the machine and the other end to the stationary 

 head, which is connected by a system of levers to a scalebeam read- 

 ing inch-pounds of moment. The machine shown in Fig. 150 has 

 the stationary head suspended by stirrups, thus leaving it free to move 

 slightly when the specimen shortens in twisting. The older types of 

 torsion machine are not made to accommodate themselves in this way 

 to the shortening of the test piece. 



The angular distortion of the test bar is measured by an instrument 

 called a troptometer. This consists of two arms attached to the bar at 

 the extreme points of the part that is being tested. One of these 

 arms carries a scale bent into the arc of a circle of which the arm is 



