ON THE MECHANICAL PROPERTIES OF STEEL. 



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mental data tlie engineer and architect may select the steel possessing the 

 actual quality required for any particiUar structure. This wiU be found 

 especially reqxusite in the construction of boilers, ships, bridges, and other 

 structures subjected to severe strains, where safety, strength, and economy 

 should be kept in view. 



In the case of transverse strain some difficulties presented themselves in 

 the course of the experiments, arising from the ductile natui-e of some part 

 of the material, and from its tendency to bend or deflect to a considerable 

 depth without fracture. 



But this is always the case with tough bars whether of iron or steel, 

 and hence the necessity of fixing upon some unit of measure of the deflections, 

 in order to compare the flexibility of the bars with one another, and, from 

 the mean value of this unit of deflection, to obtain a mean value of the 

 modiilus of elasticity (E) for the different bars. This unit or measure of 

 flexibility given in the Table is the mean value of aU the deflections corre- 

 sponding to unity of pressure and section. The modulus of elasticity has 

 also been calculated from the deflection produced by 112 lbs., in order that 

 it may be compared with the results of experiments on cast iron, given at 

 pages 73 and 74 in my work ' On the Application of Iron to BuUding Pur- 

 poses.' In order to determiae the resistance of the bars to a force analogous 

 to that of impact, the ivorl- in deflecting each bar up to its Emit of elasticity 

 has been calculated. These results differ considerably from each other, 

 showing the different degrees of hardness, ductility, &c. of the material of 

 which the bars are composed. The transverse strength of the different bars 

 up to their limit of elasticity is shown by the amount of the modulus of 

 strength or the unit of strenfjth calculated for each bar. 



Table II., on tensile strain, gives the breaking strain of each bar per 

 square inch of section, and the corresponding elongation of the bar per unit 

 of length, together with the ultimate resistance of each bar to a force analo- 

 gous to that of impact. 



Table III., on compression, gives the force per square inch of section 

 requisite to crush short columns of the different specimens, with the corre- 

 sponding compression of the column per unit of length, together with the work 

 expended in producing this compression. 



Having selected the requisite number of specimens from different works, 

 the experiments commenced with the transverse strains, which were con- 

 ducted as on former occasions, by suspending dead weights from the middle 

 of the bar, which was supported at its extremities, the supports being 4 feet 

 6 inches apart. The apparatus for this class of experiments consisted of the 



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