As has been said before, the ultimate elongation in a test specimen of commercial length 

 measures partly the plasticity of a short length at the "necking-down" portion and partly the 

 plasticity of the bar before this drawing out commenced. It is obvious therefore, that in order 

 to compare the ductility of different qualities of steel by the percentage of elongation, the di'am- 

 eter, thickness and shape of the test specimens ES well as the gauge lengths should be absolutely 

 the same. It is not always possible to fulfill the^e conditions as the length and thickness of a 

 commercial test specimen depends primarily on the size and shape of the finished product from 

 which it is taken. It is possible, however, to compare the ductility of test specimens of different 

 diameters, thicknesses and shapes as well as of different lengths by the percentage of the reduc- 

 tion of area at fracture. 



"The term 'Reduction of Area' refers to a ruptured specimen and means the diminution in 



section area per unit of original area Reduction of area, or contraction of area as it 



is often called, is an index of the ductility of the material and it is generally regarded as a more 

 reliable index than elongation because the ultimate unit elongation is subject to variation with 

 the ratio of the length of the specimen to its diameter, whereas the reduction of area is more 

 constant." Merriman "Mechanics of Materials." (1905), Page 31. 



"The percentage of contraction of area and the quality of the fracture, both very impor- 

 tant factors in determining the quality of the metal, are shown with equal accuracy and distinct- 

 ness with the shorter specimen as with one of greater length." American Society of Testing 

 Materials 1913. 



The percentage of reduction of area is independent of the diameter, thickness, and shape 

 of the test specimen as well as of the length. 



While it would be possible to obtain a test specimen of "Steelcrete" mesh of the same 

 length and thickness as is commonly used in steel bars, (i. e., 8 inches in gauge length and I T 

 inch diameter), such a specimen would be subject to criticism as it does not represent a speci- 

 men of a finished product. In order to avoid all possible criticism, the specimens which have 

 been tested were in every case taken from the center of a commercial sheet of mesh. As the 



170 



