322 I;I:I-I:ATKI) STKKSSKS. 



stress on the material was limited to a certain pre- 

 arranged magnitude. Loadings, giving rise to both 

 stresses in one direction only and to reversed stresses, 

 were applied. 



(6) Repeated Tensions. A power-driven machine was 

 used for these tests also, the free end of the specimens 

 being attached to the short end of a rocking lever, whose 

 movement was controlled by springs, so that the stresses 

 could not exceed a certain given amount. 



(c) Repeated Bendings.. A third machine was used 

 for the purpose of imposing a succession of bending 

 stresses on a beam specimen, a stop being provided, so 

 that, in some of the tests, the stress could not be wholly 

 taken off the bar, but kept within previously defined 

 limits. 



(d) Reversed Bending Stresses. The fourth machine 

 was arranged to apply reversed stresses to cylindrical 

 beams. This was effected by slowly rotating the bar to 

 be tested, one end being attached to the shaft of the 

 machine and the other being free and carrying a load at 

 its outer end, so that, as it was turned through one 

 revolution, it became a cantilever, bent first in one 

 direction and then in the other. 



A large number of materials were tested under the 

 various conditions indicated. In all cases the original 

 statical strength of the material was determined in the 

 usual way. 



In the torsion tests, some of the bars were tested 

 under stresses in one direction only, the maximum stress 

 attained and the number of repetitions of this stress 

 required to produce fracture being noted. In the others, 

 where the stress was in two directions alternately, the 

 maximum and minimum, and, therefore, the range of 

 stress was found, along with the number of repetitions. 



In most of the tension tests the stresses were between 

 zero and a maximum stress ; but in some cases the range 

 of stress was between a minimum and a maximum stress. 

 The same is true for the transverse stresses, many of the 

 tests being made with the specimen pressing against a 

 stop on the removal of the load, so that the stress was 

 never entirely removed. 



In the tests of the rotating cantilevers, loaded at the 

 ends, the range of stress was necessarily between a 



