1911 - 12 .] Effect of Vibration upon the Structure of Alloys. 315 
XXII. — Preliminary Note on the Effect of Vibration upon the 
Structure of Alloys. By G. H. Gulliver, B.Sc., A.M.I.Mech.E., 
Lecturer in Engineering in the University of Edinburgh. (With 
Two Plates.) 
(Read May 6, 1912. MS. received July 5, 1912.) 
Of late years a great deal of experimental work has been carried out with 
the object of determining the effect upon various metals of a load applied 
and removed many times in quick succession. The chief object of such 
researches is to determine the maximum stress which can be applied and 
removed indefinitely without causing fracture of the piece. Little attention 
has been given to any change in the structure of the metal, except in cases 
where there has been well-marked permanent distortion. The writer 
accordingly undertook some simple preliminary experiments in order to 
ascertain the effect upon the structure of a few alloys of numerous small 
blows, each of insufficient force to cause a permanent deformation of the 
specimens. 
Before the internal structure of metals and alloys had been investigated 
there was a strong belief among engineers that shock and vibration caused 
crystallisation of a metal, and that belief is widely held even at present. 
A piece of metal, after long service in a situation where it has been exposed 
to much vibration, may fail in one of two ways — abruptly or gradually. 
In the latter case a crack starts at some point of weakness or defect, and 
spreads gradually through the piece, until the section is so much reduced 
that the rest breaks abruptly ; the earlier developed part of the broken 
surface is smooth and shows little or no structural detail, whereas the later 
part is rough and often crystalline in appearance. When the complete 
fracture has occurred suddenly, due probably to an excessive shock, the 
whole of the broken surface may have a coarsely crystalline appearance ; 
this is especially true of wrought iron. It is a common observation that 
shock fractures of wrought iron are apt to be crystalline ; the apparent 
degree of coarseness of the broken surface, though not an accurate measure, 
gives a rough indication of the scale of structure of the metal. There is 
always the possibility that the coarse structure existed before the piece 
was subjected to shock, though the apparent degree of coarseness is not 
infrequently such as to make this doubtful ; in days when metals under 
ordinary conditions were not regarded as crystalline the possibility was not 
admitted. 
