200 MR W. GORDON AND MR G. H. GULLIVER ON 
the bars were tested, are made with slightly convex faces to assist in this respect. 
The rate of straining was kept constant throughout the tests at about 0°12 inch per 
minute, that is, | per cent. per minute on the 12-inch length between the grips. 
The loads noted during the test were the yield load, at which permanent stretch 
becomes well marked, the maximum load carried, and the load sustained by the bar at 
the moment before rupture; the last is difficult to determine with great accuracy. 
After fracture the various dimensions of each bar were re-measured for comparison with 
the original dimensions. From these measurements the variations in mechanical 
properties, corresponding with change in the ratio of original width/original thickness 
of the bars, have been deduced. ‘The more important quantities dealt with are :— 
(1) The yield point, the tenacity, and the mean breaking stress. 
(2) The extension on various constant gauge-leneths, on gauge-lengths proportional 
to the ratio width/thickness, and on gauge-lengths proportional to the square root of 
the cross-sectional area. 
(3) The reduction of area at fracture. 
4. YieELD PoinT and TENACITY. 
The yield point is the stress at which there is marked evidence of permanent 
distortion of the metal; it is found by dividing the yield load by the original area of 
cross-section of the bar. From the figures given in Table III. it is evident that the 
yield point is not affected sensibly by a change in the ratio width/thickness. The 
average yield point is at 18°14 tons per square inch. 
TABLE III. 
VARIATION OF YIELD Point, Tenacity, AnD Mean Breakine STRESS, WITH THE Ratio 
WiptH/THICKNESS. 
, 5 Widtl : F é Mean Breaking 
Nominal Width. 1ath Yield Point. Tenacity. 
Inches Thickness" Tons per sq. inch. | Tons per sq. inch ues 
ies gu . ae ‘| Tons per sq. inch. 
$ 1:76 18:17 25°26 54:29 
1 3°81 18°28 25°32 . 50°64 
13 5°64 18-29 25°45 48°77 
2 757 18°10 25°45 46:00 
24 9°57 18-08 25°47 49°87 
3 11°14 18:00 25°40 47°91 
34 13°32 18°05 25°66 50-03 
4 15°39 18°16 25°87 50-75 
The tenacity is the maximum load carried by the bar divided by the original cross- 
sectional area. This quantity also remains almost constant throughout the series of 
bars, though there is a slight tendency to rise as the width is increased; the figures 
are given in Table III. The average tenacity is 25:49 tons per square inch. 
The tenacity, as defined above, though a useful quantity to the engineer, furnishes” 
no information as to the maximum stress sustained by the metal. A near approxima- 
