14 Foster, Phenomena due to Repetitions of Stress 



A Neiv Testing Machine. Most experimentalists on 

 repetitions of stress have adopted the simple method of 

 rotating a bent bar. Unfortunately simple stresses cannot 

 be obtained by this method. Professor Reynolds obtained 

 simple alternating stresses by causing the specimen under 

 test to reciprocate a dead weight in a straight path. The 

 motion was obtained from a rotating crank shaft and was 

 very nearly simple periodic. The stress producing 

 mechanism was indeed essentially that of the ordinary 

 steam engine. *The machine is illustrated diagrammatically 



Fig. 7. 

 in Fig. 7. Two equal sets of parts at right angles to each 

 other are driven from a single crank pin. The specimen 

 is at S^ and must transmit the forces required to accelerate 

 and retard the weight W. In this way it is subject to 



*"On a throw-testing machine for reversals of mean stress:" by 

 Osborne Reynolds and J. H. Smith. Trans. Roy. Soc. Vol. 199, Series A. 



