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PROFESSOR OSBORNE REYNOLDS AND MR. J. H. SMITH ON A 
Historical Summary. 
In 1860, Sir W. Fairbairn, using a riveted girder, carried out a series of 
experiments, which seem to be the first recorded experiments on Repeated Stress. 
From I860 to 1870, Wohler carried out his laborious and valuable researches on 
the Fatigue of Wrought Iron and Steel. From his results published in the 
£ Zeitschrift fur Bauwesen,’ Berlin, the following important points may be 
deduced :— 
(1) That these materials (wrought iron and steel) will rupture with stresses 
much below the statical breaking stress, if such stress he repeated a 
sufficient number of times. 
(2) That within certain limits, the range of stress, and not the maximum stress, 
determines the number of reversals necessary for rupture. 
(3) That as the range of stress is diminished, the number of repetitions for 
rupture increases. 
(4) That there is a limiting range of stress for which the number of repetitions 
of stress for rupture becomes infinite. 
(5) That this limiting range of stress diminishes as the maximum stress 
increases. 
Wohler conducted his experiments on bars of wrought iron and steel, subjecting 
them to torsional stress, bending stress, equal and opposite bending stresses, and 
direct tension, with repetitions ranging from 60 to 80 per minute. 
In 1874, Spangenberg repeated Wohler’s experiments, using Wohler’s 
machines, and obtained similar results, also published in the ‘ Zeitschrift fur 
Bauwesen.’ In 1874 also, Gerber, in the ‘Zeitschrift fur Baukunde,’ Miinchen, 
suggested the following formula, as representing the results of Wohler’s 
experiments : 
/(max) = \ A + /(Z 2 - n Ay), 
where / (max) = the maximum stress, 
/(min) = the minimum stress, 
/ = the statical breaking stress, 
A = the range of stress — f (max) ±/ (min), 
and n = a constant. 
Accounts of other experiments and theories bearing on this subject, are given by 
the following :— 
Launhardt (Zeitschrift des Architecten und Ingenieur-Vereins, Hanover, 1873). 
Lippold (Organ fur die Fortschritte des Eisenbahnwesens, Wiesbaden, 1879). 
Professor Mohr (Der Civil-Ingenieur, Leipzig, 1881.) 
