Ductile Materials under Combined Stress. 129 



Fig. 22 represents a combined^tension and internal pressure 

 test ; the tension load was applied first, the actual loads being 

 marked along the central line and the corresponding stresses 

 along the right-hand side line of the figure. The axial strains 

 are positive and are set off to the right of the central line ; the 

 circumferential strains (diametral extensometer) are set off 

 positively to the left of the central line, but during the appli- 

 cation of the tension loads this strain is negative, and the 

 stress-strain line therefore bears to the right. After a load of 

 900 lbs., actual, was reached, the tension load was kept con- 

 stant and the internal pressure applied; the values are marked 

 off along the central line, the resulting circumferential stresses 

 are given on the left-hand, and the total axial stresses on the 

 right-hand of the diagram. Along the line of no internal 

 pressure are given the actual extensometer readings, the 

 corresponding strains being placed at the top. 



Fig. 23 represents a combined tension and torsion test ; 

 the torque was applied first, and the values of W are set oft' 

 along the central line and the corresponding stresses on the 

 right-hand side of the diagram. The shearing-strains or 

 slides are set off to the right of the central line. After W 

 had reached the value of 25 lbs., it was kept constant 

 and the tension-loads applied ; it will be noticed that the 

 initial tension- load was 150 lbs. The actual tension loads 

 are recorded along the central line, and the corresponding 

 stresses on the left-hand side ; the resulting axial strains are 

 positive to the left of the central line. The principal strains 

 at any point cannot be determined at once from the diagram 

 without a construction or calculation. The addition of a 

 tension load should not change the twist (slide) reading, unless 

 the elastic limit has been passed ; the slight inclination of 

 this part of the line may be due to a bending-moment, or to a 

 slight want of isotropy introduced by the previous tests. 



Fig. 24 is a similar diagram for a torque and internal- 

 pressure test, and can be readily understood from its similarity 

 to the preceding figures. 



All these figures, and the corresponding ones for simple 

 tension and torsion, show the stress-strain line as bending 

 gradually over, the strongly-marked yield-point of iron and 

 steel being absent ; they also show how unsatisfactory, in 

 such cases, any tabulation of elastic-limit or yield-point 

 stresses and strains must be. The selection of apparently 

 similar points on the curves, however, leads to the discovery 

 at them of the same amount of shearing-stress. 



Phil. Mag. S. 5. Vol. 50. No. 302. July 1900. K 



