144 TENSION TESTING. 



; ,t ,-lastir limit 



Stress at Elastic Limit = . 



original area ol the bar. 



13 



0788 



= 16-50 tons per sq. in. 

 83. flaximum Stress. 



The maximum stress = - maximum load 



original area of the bar. 



21-90 

 = = 27 '80 tons per sq. m. 



84. Percentage Extension on 10 Inches. After the 

 completion of the test, the broken bar is taken out of the 

 machine, the two halves placed together just as they have 

 broken, and the distance between the two 10 in. gauge 

 points measured. If the fracture has occurred outside 

 these points, another pair of points, including the fracture, 

 and which were originally 10 in., apart, must be selected. 



In the present case this measured length is 



13-06 in. 

 Therefore the extension is 



13-06 - 10-00 = 3-06. in., 

 and the percentage elongation on the 10-in. length is : 



Percentage Elongation on 10 Inches 



, _ 



original length 



3 ' 06 x 100 



10 



= 30-6 per cent. 



85. Percentage Extension on 2 Inches. This extension 

 must be measured on a pair of gauge points originally 

 2 in. apart, and including the point of fracture. In the 

 present case this was found to be 3'1 in ; so that the 

 actual extension on this length was 



3-1 - 2 = 1-1 in., 



and 



The Percentage Elongation on 2 Inches 



stretch 



= -.--. -f- x 100 



original length 



- -f x 10 



= 55 per cent. . 



On Fig. 66 are shown views of the bars both before and 

 after testing. The measurements for obtaining the elonga- 

 tion are indicated. 



