353 
1911-12.] The Elastic Strength of Flat Plates. 
for most of them. Accordingly, with this object in view, a modification of 
the original apparatus was constructed which is shown on the accompanying 
drawing No. 1, and which was found on trial to give satisfactory results. 
M is a mild-steel block, over an inch thick. A rectangular recess, about 
11 in. by 8 in., is machined into the centre of it. Two duplicate cast-iron 
pieces X X, externally fitting the recess and internally shaped to the form 
of the flat plates to be tested, are accurately machined and scraped flat. 
The flat plate rests between these duplicate blocks, and is clamped hard 
down by means of rigid clamps S, bars R, studs, and distance pieces. 
Underneath the bottom forming-piece X is placed a shaped piece of 
Jenkins K packing, and between the flat plate and the top of the 
lower piece X is placed another piece of the same packing, thus ensur- 
ing an even seating and preventing leakage. The oil is led to the 
under surface of the plate by the duct K. The drawing shows a square 
plate in position for testing. 
Determination of the Elastic Constants. 
Youngs Modulus . — The direct method was used. A strip of plate 
8 in. long and in. wide, having enlarged ends for gripping in the chucks, 
was prepared, placed in the testing machine, and extensometer readings 
taken for small increments of load. In view of the importance of this 
curve, from the point of view not only of Young’s modulus, but of the 
elastic limit and yield points, an example is given herewith (Diagram 1). 
The elastic limit occurs at K and the yield point at Y. Young’s modulus is 
about 29,500,000 lbs. per sq. in. The elastic limit corresponds to 10 tons 
per sq. in. The yield point is at about 27,000 lbs. per sq. in. About 
one hundred readings were taken, to ensure accuracy, as the determination 
of an accurate yield point was of the first importance. 
In the experiments made, the elastic limit was fairly constant, averaging 
10 tons per sq. in. ; the breaking stress was low, averaging 20 tons. On 
the diagram the curve has been drawn to two scales. In determining 
values for the yield point, the point of intersection M has been taken. 
Although the elastic limit appears low at 10 tons, yet Dr J. H. Smith 
assures the author that in some steels he has obtained it down to 8 tons. 
Moreover, it is well known that the elastic limit is a fickle point, and is 
ready to jump about on the least provocation. 
The average of three results gave 27,800 lbs. per sq. in. as the yield 
point. 
The average of three results gave 29,530,000 lbs. per sq. in. as Young’s 
modulus. 
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