argin for
notes. (See Fig. 32.) The load in some convenient unit (1,000 to
10,000 pounds, depending upon the dimensions of the specimen) is
entered on the ordinates, the deflection in tenths of an inch on
the abscissae. The increments of load should be chosen so as to
furnish about ten points on the stress-strain diagram below the
elastic limit.

As the readings of the wire on the scale are made they are
entered directly in their proper place on the cross-section
paper. In many cases a test should be continued until complete
failure results. The points where the various failures occur are
indicated on the stress-strain diagram. A brief description of
the failure is made on the margin of the log sheet, and the form
traced on the sketches.

_Disposal of the specimen_: Two one-inch sections are cut from
the region of failure to be used in determining the moisture
content. (See MOISTURE DETERMINATION, above.) A two-inch section
may be cut for subsequent reference and identification, and
possible microscopic study. The remainder of the beam may be cut
into small beams and compression pieces.

_Calculating the results_: The formulae used in calculating the
results of tests on large rectangular simple beams loaded at
third points of the span are as follows:

0.75 P
(1) J = --------
b h

l (P_{1} + 0.75 W)
(2) r = --------------------
b h^{2}

l (P + 0.75 W)
(3) R = ----------------
b h^{2}

P_{1} l^{3}
(4) E = ---------------
4.7 D b h^{3}

0.87 P_{1} D
(5) S = --------------
2 V

b, h, l = breadth, height, and span of specimen, inches.
D = total deflection at elastic limit, inches.
P = maximum load, pounds.
P_{1} = load at elastic limit, pounds.
E = modulus of elasticity, pounds per square inch.
r = fibre stress at elastic limit, pounds per sq. inch.
R = modulus of rupture, pounds per square inch.
S = elastic resilience or work to elastic limit, inch-pounds
per cu. in.
J = greatest calculated longitudinal shear, pounds per square
inch.
V = volume of beam, cubic inches.
W = weight of the beam.

In large beams the weight should be taken into account in
calculating the fibre stress. In (2) and (3) three-fourths of
the weight of the beam is added to the load for this reason.

BENDING S