196 MR W. GORDON AND MR G. H. GULLIVER ON 
cross-sectional dimensions of all test-bars shall be the same also. This rule is observed 
generally in important work, but there are different standard gauge-lengths to suit 
different classes of material. The most common lengths in use in this country are 
8 inches and 2 inches (1), corresponding closely with the Continental leneths of 200 
millimetres and 50 millimetres. 
There is one remaining difficulty, namely, that of securing comparable measute- 
ments with bars of different sectional form. The importance of this point is such that 
the proportions of the test-bar may make all the difference between an apparently 
satisfactory and an apparently unsatisfactory material. The great majority of bars 
submitted to the tensile test are either of circular or of rectangular section, and the 
difficulty consists in comparing among themselves the values obtained from rectangular 
bars having varying widths and thicknesses, and in turn comparing these with the 
values obtained from round bars. The object of the experiments to be described was 
to determine the variation of apparent strength and ductility caused by variation in 
the width of soft steel test-bars of constant thickness. 
2. EARLIER INVESTIGATIONS. 
The earliest experiments which bear upon the point under discussion appear to be 
those of Barpa (2). This investigator cut from a steel plate, 10 mm. (0°39 inch) 
thick, a number of test-bars with widths of 10 to 80 mm., and obtained the results 
set forth in Table I. 
TABLE I. 
Tensite Tests or Sorr Stee, Bars 10 mm. Tuck (BarBa). 
© Yield-point. Tenacity. | Extension per cent. on 
‘ Ratio, 
eaten ane 
; thickness’ | Kg. per sq. Tons per sq.) Kg. per sq. | Tons per sq. Bode 100 mm. 
mm. inch. mm. inch, 
10 1 24°8 15°8 38°4 24°4 37°6 31:0 
20 2 | 24°6 15°6 40°1 25°5 45:0 34:0 
| 30 3 | 25°4 16:1 39°4 25°0 48-0 35°0 
| 40 4 25-0 Ib9\ | 29°8 25°3 52-0 37-0 
50 5 24°6 156 381 24°2 560 39°0 
60 6 24°9 Los || 37°7 23°9 61-0 40°8 
70 7 24°8 15:8 37°8 24:0 57°0 385 
80 8 23°5 14:9 384 24°4 52:0 34:5 
The yield-point and the tenacity of the metal remain sensibly constant, but the 
extension, measured on two different gauge-lengths of 50 and 100 mm. respectively, 
shows considerable variation. In fig. 1 the extension is plotted against the ratio. 
width/thickness, and both curves exhibit a well-marked maximum when the width is 
about six times the thickness. 
f 
