120 Mr. "W. A. Scoble on Ductile 



In these tests there are stresses in one plane only, and the 

 expression becomes 



If the maximum strain be constant, then F 1 ^rfP 9 must be 

 constant, so that this hypothesis comes between the maximum 

 stress law, that P 1 is constant, and the stress difference or 

 shear-stress theory, that P 1 — F 3 is constant, but it is nearer 

 the former. 



The Results from Steel Bars. 

 Table A.— Original Tests of Solid Steel Bars. 



Number 



of 



Bar. 



Tensile 

 Bending I Twisting Stress 

 Moment. Moment, due to 



Shear 



Stress 



Maximum 



Principal 

 due to | s * 



lbs. ins. lbs. ins. Bendins;. Torque, i „ , ." 

 Hi,. !, i • ' lbs./s. m. 

 lbs./s. m. lbs./s. in. 



Stress 

 Minimum ; Difference 

 Principal ! =2ce 



Stress. | Maximum | 

 lbs.s. in. | Shear 

 Stress. 



III. ... 







IV. ... 



667-5 



XL... 



1160 



V. ... 



1331 



XII.... 



2000 



VI.... 



2000 



IX.... 



2020 



VIII. ... 



2320 



VII.... 



2420 



2190 

 2130 

 2033 

 1985 

 1360 

 1630 

 1335 

 645 

 980 





 16220 



28200 

 32350 

 48600 

 48600 

 49000 

 56300 

 58750 



26600 

 25880 

 24700 

 24100 

 16520 

 19800 

 16220 

 7840 

 11900 



26600 

 35260 

 42520 

 45210 

 53700 

 55650 

 53900 

 57350 

 61075 



-26600 

 -19040 

 -14320 

 -12860 



- 5100 



- 7050 



- 4900 



- 1050 



- 2325 



53200 

 54300 

 56840 

 58070 

 58800 

 62700 

 58800 

 58400 

 63400 



Only one test was made on each bar. The bending and 

 twisting moments at yield are plotted in fig. 1 (PI. I.). If the 

 maximum principal stress were constant at the yield-point, 

 the twisting moment under "pure torque would be double the 

 bending moment required to cause the bar to yield. If the 

 maximum shearing stress were constant, the plotted points 

 would lie on a circle described with the origin as centre. 

 Fig. 1 confirms the writer's original conclusion that the 

 maximum shear stress is approximately constant at failure, 

 but that an ellipse lies between the points better than a circle, 

 and that the bending moment is greater than the torque. 



The maximum stress varies between 26,600 and 61,075 

 lbs./s. in., it certainly is not constant. The stress difference 

 is not exactly constant ; it varies from 53,200 to 63,400 

 lbs./s. in., but it increases steadily with the bending moment, 

 consequently the deviation from the stress difference, or shear 

 stress law, is still further away from a constant maximum 

 stress, so that the maximum strain also varies considerably. 



