126 
PROF. W. E. DALBY: RESEARCHES ON THE ELASTIC 
The limit of proportionality occurs now at about 3 tons and there is no definite 
yield point. The loop areas and their rates of increase are about equal in the two 
plates. 
The explanation of the difference in quality shown by comparing the two diagrams 
may be found in the fact that the test piece of fig. 8 was cut from a bar delivered 
before the war. The test piece of fig. 9 was cut from a bar delivered towards 
the end of the war. There has clearly been some change in the manufacturing 
process. 
Nickel Chrome Steel. —Fig. 10. The ultimate strength of this steel found from a 
Fig. 10 (nickel chrome steel). 
bar 1 inch diameter is 54 tons per sq. inch, with an extension of 14 per cent, on 
8 inches and 55 per cent, reduction of area. The limit of proportionality is at a load 
of 10 tons on the standard test piece 0'625 inch diameter, corresponding to 32'5 tons 
per sq. inch, \ield sets in at 11 tons, that is, 36 tons per sq. inch. 
The first loop of the diagram is small, but the area increases rapidly, as will be 
seen from the three loops visible in the record. 
Nickel Steel. Carbon 0'33 per cent., Ni 3'52 per cent.—Fig. 11. The ultimate 
strength of this material is about 48 tons per sq. inch, with an elongation of 20 per 
cent, on 5 inches and a reduction of area of 47 per cent. Limit of proportionality 
occurs at about 30 tons per sq. inch and yield at 32 tons per sq. inch. The limit of 
proportionality here approaches quite near to the yield point. 
