’ COMPLEX STRESS DISTRIBUTIONS IN ENGINEERING MATERIALS. 381 
stress concentrations and alter the elastic properties, and the modulus of elasticity 
applicable to an unperforated plate cannot be used to get the stresses accurately ; 
a corrected modulus is necessary. 
The writers have found no records of experiments on the effect of the perforation 
on the modulus, and made the experiments of which details are given in fig. 12. The 
two test-pieces measured 14 in. wide by about ;'; in. thick and 12 in. long; one was 
plain and one had holes drilled along its length, so that it formed the model of a plate 
15 in. wide, jin. thick, with holes jin. diameter at 3in. pitch. Both were of the same 
mild steel. The strains measured with a Ewing extensometer are plotted in fig. 12 
as parts in 10,000. The full lines represent the first measurements on an increasing 
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stress, and the dotted ones represent the elastic lines up and down which the strains 
lay after the stress had been carried up to about 8 tons on the net area in each case. 
The modulus corresponding to the dotted line of the plain test is 12,150 tons per sq. 
in., and to that of the perforated plate 10,150 tons per sq. in.* 
In applying the corrected modulus it saves confusion to apply it to the gross area. 
Thus in the experiment, assuming the area to be 1 sq. in., the change in load to produce 
a strain of 4 in 10,000 was 4-86 tons, and on the perforated plate the change in load 
for the same strain was 4-06 tons total. This load converted into stress on the net 
area (0-741 of gross) would equal 5-48 tons. 
_ + The ratio of the two moduli a = 0-835. 
In comparison 
2 
tr tio ae of perforated ue) ~ 0-870, 
volume of plain plate 
Sad a/ net length along perforations ae ae, 
gross length of plate 
