302 Kl I K<T OK Tl.MH. 



that the extensions for given loads will be less in the 

 former case than in the latter. That this is so Is shown 

 by autographic diagrams taken under the two conditions. 



On Fig. 153 are shown two load-strain diagrams given 

 by Professor Barr,* 'the curve marked A being for a piece 

 of charcoal iron wire, with the load applied at 5'4 tons 

 per minute per square inch; that marked B, for a piece 

 of precisely similar wire, loaded at the rate of 1*8 tons 

 per square inch per minute, and C is for the same wire, 

 loaded at 0'66 tons per square inch per minute. It will 

 be seen that there is a considerable difference in the form 

 of the curves. 



On the other hand, Col. Maitlandf has shown that 

 the ultimate total elongation may be increased after 

 extremely rapid loading, such as is effected by the explo- 

 sion of gunpowder. The explanation of this, given by 

 Unwin, is that the very rapid loading does not allow of 

 the formation of the local "waist" and the general 

 extension continues up to the point of fracture. 



Colonel Maitland, in applying his sudden loads to 

 specimens of gun steel, first attached the lower end of the 

 specimen to a dead load which was supported in position. 

 By removing the support, the load was allowed to come 

 upon the specimen suddenly, and the elongation- was 

 increased from 27 per cent, with a gradually applied 

 load to 47 per cent. 



In order to make the application still more rapid, two 

 closely-fitting plugs or pistons were fitted into a strong 

 accurately-bored cylinder, and the two ends of the 

 specimen to be tested were attached to these. The 

 annular space between the specimen and the cylinders 

 was filled with guncotton or gunpowder and exploded. 

 The effect of this was to give an elongation of from 47 to 

 62 per cent. In some cases the specimen fractured in 

 two places, leaving a cigar-shaped piece between. 



These results appear to show that a rapidly-applied 

 load in a testing machine gives a smaller elongation 

 than when the load is very gradually applied, owing to 

 the shorter time allowed for the metal to flow into its 

 position of equilibrium ; but that, when the suddenness 

 of application is greatly increased, the conditions are 

 again altered, there being little time for the local effects, 



* Min. Proc. lust. C.E., Vol. Ixxxviii. 

 t Min. Proc. lust. C.E., Vol. Ixxxix. 



