COMPLEX STRESS DISTRIBUTION IN ENGINEERING MATERIALS. 323 
length defined on one specimen with dots and on a second specimen with flanges 
is the same within experimental error. 
When stretching is carried to the point at which the elastic limit is passed and the 
metal begins to flow, the influence of the flanges begins to be felt. The total effect of 
flanges is to reduce the total extension of the gauge length about 3 per cent. in soft 
materials. This may appear a disadvantage, but it is no disadvantage if test-pieces 
are made of similar form. Then, whatever the form chosen, the end effects are 
included in all the tests in the same way and the results are strictly comparative. 
| INN aa 
: 4) a 
ss a ee 
——-—--—— 7()" OG VCMT LA, 
DIMENSIONS OF PLANE MODEL OF NITRO- 
CELLULOSE. THICKNESS 0-/2/ INCH. 
Having decided to adopt as a standard the test-piece shown in fig. 8, I carried out 
two experimental researches to investigate :— 
(a) The effect of the flanges on the value of E and on the final extension of the 
gauge length, and 
(6) The validity of the law of similarity when applied to test-pieces of this kind. 
2. Comparative Experiments, 
(a) The test-pieces were cut from the same bar of mild steel of which the chemical 
analysis is :— 
Carbon ; : . 0-15 per cent. 
Silicon § 3 cay OODT 0 ths 
Sulphur. F . 0064 ,, 
Phosphorus : 280052) ee 
Manganese . e . 0:99 7. 
Two test-pieces were prepared, one with flanges and one plain, and both were 
turned accurately to § in. diameter along the gauge length, like fig. 1. A Ewing 
extensometer was used to find the modulus of elasticity of the plain bar, and an 
automatic record was taken with the Dalby Elastic Recorder from the flanged bar. 
_ The modulus of elasticity was calculated from the record. 
The results are :-— 
With the Ewing Extensometer on a plain bar $ in. diameter, 
5in. gauge length . 5 f ; : : . E=13300 
With the Dalby Elastic Recorder on a flanged bar § in. 
diameter, 5 in. gauge length : : : ; E=13320 
‘These figures are within experimental error. 
Repeated experiments led to the conclusion that the elastic extensions and the 
small quasi-elastic extensions leading to the plastic extensions are not materially 
affected by the flanges. 
The test-pieces were afterwards broken, so as to investigate the effect on the final 
extension. It was found that the final extension of the flanged bar was about 
3 per cent. less than the final extension of the plain bar. 
The conclusion may therefore be stated as follows — 
1. Flanges have no material effect on the elastic extension of the length between 
¥ 2 
