ON THR ENDURANCE OF METALS. 



429 



fracture, bat that a similar bar broke with only 480,852 applications of 

 38,520 lbs., being an addition of 12^ per cent, to the stress ; similarly the 

 steel bar withstood 13,600,000 applications of 51,360 lbs. without fracture, 

 while a similar bar broke with 473,766 applications of 53,500 lbs., being 

 an addition of 4 per cent, to the stress. 



The preceding table — No. IV. — shows the effects of subjecting test- 

 bars of iron and steel to tensile stresses where the load is completely 

 taken off between each application as compared with the cases where the 

 load varies from a certain minimum to a certain maximum at each appli- 

 cation. Thus with a load of 47,080 lbs. per square inch, taken off' com- 

 pletely between each application, the iron bar broke with 106,910 

 applications ; but with the same load as a maximum, reduced to 21,400 lbs. 

 as a minimum between each application, the bar failed only with 2,373,424 

 applications ; and it withstood 4,000,000 applications when the minimum 

 load was further raised to 25,680 lbs. 



General Deductions of Herr WoJiler, 



Material 



Maximum Stress on 



Fibres in lbs. per 



square inch 



Minimum Stress on 



Fibres in lbs. per 



square inch 



JBars subjected to tensional or transverse stress. 



Iron 



Cast steel for axles 



Untempered cast steel for springs 



+ 17,120 

 + 3.5,310 

 + 47,080 

 + 29,960 

 + 51,360 

 + 85,600 

 + 53,500 

 + 74,900 

 + 85,600 

 + 96,300 



Cast steel for axles 



Bars subjected to shearin/j stress. 



. I +23,540 



+ 40,660 



-17,120 





 + 25,680 

 -29,960 





 + 37,450 





 + 26,750 

 + 42,800 

 + 64,200 



+ 23,540 

 



In 1881 and succeeding years. Professor Bauschinger, of Munich, 

 published the results of his experiments on the behaviour of metals when 

 subjected to stresses exceeding their elastic limit.' 



The most important of these is a paper, * Ueber die Veranderung der 

 Elasticitatsgrenze,' in the Mitth. desk, techn. Laboratorium in Miinchen. 

 An abstract of some of these results, and a comparison of them with the 

 corresponding results of Wohler, is given in a paper by Prof. Unwin in 

 the ' Engineer ' for Dec. 10, 1886, and Jan. 7, 1887. 



First of all, to show the effect of stretching a bar just beyond its 

 yielding point on the position of the elastic limit. The following table 

 is taken from an earlier paper of Bauschinger's, 1881. It will be seen 

 that if the loading of a bar is repeated, immediately after straining it to 

 the yielding point, the elastic limit is lowered. If a period of rest is 

 allowed, the elastic after-effect comes into play and the elastic limit rises, 

 sometimes above the load previously imposed. 



' See the Engineer, Jan. 7, 18S7. 



