288 



DR E. G. COKER ON 



Table XII. 



Diameter of bar, 0*511". Length, 8'00". 54 - 7 divisions = 1 min. of arc. 



Bending Moment. 



Readings for Torque 

 of 60 inch lbs. 



L. of Bending 

 at Weigh-lever. 



Cos e. 



Corrected 

 Reading 



= Reading 

 x cos 0. 







1091 



0° 



1-000 



1091 



224 



1088 



30' 



•999 



1088 



337 



1086 



48' 



•999 



1086 



529 



1083 



1° 54' 



•999 



1083 



752* 



1084 



2° 24' 



•999 



1084 



922 



1090 



3° 10' 



•998 



1088 



1092 



1095 



3° 20' 



■998 



1092 



1432 



1105 



4° 30' 



■997 



1102 



1772 



1123 



7° 0' 



■993 



1115 



Permanent set due to bending. 



3. Effect of Bending upon the Yield-point. 



The experiment was performed in a similar manner to that in Section IX. Two 

 bars cut from the same rod were turned up to exactly the same size. One of them was 

 tested in the ordinary manner, and the other was subjected to bending moment below 

 the elastic limit, and then twisted beyond the yield-point. Each bar was 0*489 inch 

 in diameter, the length under test being 4 inches, and 12 '8 5 divisions on the scale 

 corresponded to 1 minute of arc. The readings are recorded in Table XIII., in which 

 column I. refers to the first specimen, and the remaining columns to the second 

 specimen. The readings in column II. were made to check the correctness of the 

 setting of the measuring instrument. The readings show a remarkable lowering of the 

 yield-point for a bending moment of 668 inch pounds ; the reason for which was not at 

 first apparent, until it was noticed that the specimen took a permanent set, the ends 

 being bent to a considerable degree. 



At first sight this might appear to be a mere time effect ; but in the author's opinion 

 the probable cause was the increase of stress, due to the torque applied later. Appar- 



