MECHAXH'S AXD USKI-TL AKT>. 57 



lime to ferruginous clays, or mixtures of clay with hydrated peroxide of 

 iron, or even mixtures of clay and substances capable of generating oxide 

 of iron, \vill not be attacked by sea-water. But these experiments require 

 a considerable time, and in the meantime, it may do good to give publicity 

 to the results which they have obtained, as they may be useful to those 

 engaged in the construction of hydraulic works, and because it is of the 

 greatest importance that they should be verified by experience. 



ON THE FATIGUE OR CONSEQUENT FRACTURE OF METALS. 



At a recent meeting of the Institution of Civil Engineers, a paper was 

 read on the above subject, by Mr. Braithwaite, C. E. 



Many accidents, the causes of which have been pronounced "mysteri- 

 ous," having professionally engaged the author's attention, he had care- 

 fully examined the circumstances of each, and the condition of the 

 fractured metal, in all cases, and at length arrived at the conclusion, that 

 almost all the accidents might be ascribed to a progressive deteriorating 

 action, which might be termed the "fatigue of metals" 



Metal in a state of rest, although sustaining a heavy pressure or strain, 

 as in a beam, or girder, and exhibiting only the deflexion due to the super- 

 posed weight, would continue to bear that pressure without fracture, so 

 long as its rest was not disturbed, and the same strain was not too fre- 

 quently repeated. But if either of these cases occurred, a certain disturb- 

 ance of the particles took place ; the metal was deteriorated, and that 

 portion subject to the reiterated strain was so far destroyed that it ulti- 

 mately broke down. This might also arise from, sudden concussions, 

 when the metal was under. a certain strain, and those concussions might 

 be caused by the girder being suddenly unloaded. Several examples were 

 given of accidents of the kind that had been alluded to ; for instance that 

 of a vat in a London brewery, carried on cast-iron girders, by which it 

 had been supported for some years ; but suddenly, without any apparent 

 cause, they broke, and killed and wounded some workmen. In this' case 

 it was shown that the girders were not sufficiently strong for the load, and 

 therefore, the intermittent load of the vat, which was sometimes full, and 

 sometimes empty, caused a constantly recurring deflexion, and a subse- 

 quent corresponding effort to regain its natural position, by which the 

 composition of the metal was disturbed, and fracture ensued. Other 

 examples of the same nature were given, and it was shown that the 

 repeated buckling of the tube-plate of a locomotive, arising from the 

 action of the pistons, had a tendency to cause fracture mechanically, and 

 also that the side strains and vibrations to which suspension- rods of the 

 ash-pans of locomotives were subjected, had produced very serious 

 results, which it sufficed to point out forcibly to guard against the recur- 

 rence of. 



The author contended, that presuming adequate dimensions to have 

 been given to girders, and the stipulated weight not to have been exceeded, 

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