TENSION TESTING. 141 



little time is required for equilibrium to be attained. 

 When the measurements are taken the beam should be 

 floating freely in a horizontal position, and have no 

 tendency to fall owing to a further stretching of the bar. 



When the point of fracture has been reached and the 

 bar broken in two pieces, the first thing to be done is to 

 make sure that both the maximum and breaking loads 

 have been properly noted. The broken bar can now be 

 taken out of the machine, the load run back to its zero 

 position, and the hydraulic rani allowed to return to its 

 initial position by letting out the water which has been 

 used to actuate it. The bar, having been taken out of the 

 machine, can now be measured. The measurements 

 required are : the diameter of the bar at the point of 

 fracture, the distance between the two 10 in. marks on 

 which the extensions have been measured, and also the 

 distance between the pair of marks on each side of the 

 actual fracture, which were originally two inches apart. 

 These measurements can be made with an ordinary steel 

 rule to the nearest hundredth of an inch. In some cases 

 the fracture is found to have taken place outside the 10 in. 

 gauge marks, and when this is so, another pair of marks 

 must be selected so as to include the point of fracture. 

 In measuring the diameter of the bar at the fracture, a 

 vernier caliper may be used, but it is generally found that 

 this diameter is not uniform and an average must be taken, 

 depending upon the judgment of the experimenter him- 

 self. A note should be made in the book as to the nature 

 and appearance of the fracture itself; thus, it may be 

 defined as " silky," " crystalline," or " fibrous," as the case 

 may be. 



Having completed the test and obtained the above 

 measurements, all the results can now be worked out and 

 a diagram plotted. The following is an example of the 

 record of such a test, the results of which are fully worked 

 out in detail : 



TEST RECORD. 



Date : January 20th, 1899. 



Specimen of: Mild steel. Tested in : Tension. 



Original dimensions: 1 '002 in. diameter. Length: 

 loin. Area : 0788 sq. in. 



Final dimensions : 0'G59 in. diameter. Length : 

 13-06 in. Area : 0'341 sq. in. 



