134 
PROF. W. E. DALBY: RESEARCHES ON THE ELASTIC 
Processions of loops were similarly taken from a nickel steel test piece, from a 
mild steel test piece, and from an iron test piece. 
§ 9. Looping under Constant Load. 
The diagram in fig. 24 shows the effect of looping under constant load. 
Time i . 43./7 Toms 
^/ 2.10 PM 
Loading, stopped 
AT EACH TON 
TP TAKE READING 
of Extension 
LOOP 
Areas ■ 
1 
0-25 sq.in. 
2 
0-18 • " 
3 
0155 ' • 
4 
O- ISS . - 
5 
O' 17 . • 
PL.562 A 
PL. 56£ B 
— Looping under Constant Load 
Fic. 24 
— o-8 Carbon Steel — 
The test piece was placed in a Buckton testing machine and loaded gradually until 
yield began at 7'86 tons, and then loading was stopped. The extension was allowed 
to proceed under this load for 4 minutes. Then the load was removed and re-applied 
and the spot of light traced out loop 1. 
Extension continued slowly under the load, still maintained at 7'86 tons, and loops 
2, 3 and 4 were taken at intervals of 20, 30 and 60 minutes respectively. 
The next interval was 17 hours 20 minutes, during which time the gauge length 
extended 10 V 0 i n(J h approximately. Loop 5 was then taken. Comparing these 
loops it will be seen that there is no recovery of proportional elasticity although the 
piece was allowed to stretch under the yield load of 7'86 tons for about 20 hours. 
This shows that if the yield load is kept on until the test piece has stopped 
extending, a process which may take a long time, at the end of the experiment the 
test piece will not have gained proportional elasticity. It is still in a state of 
imperfect, or unproportional elasticity. 
§ 10. The Practical Utility of the Load Elastic Extension Looped Diagram. 
A diagram showing the elastic line and a few loops is of great practical utility in 
industrial applications. The data, immediately measurable from the diagram are 
(l) the load at the limit of proportionality ; 
