Log of the test:  The proper log sheet for this test consists of a piece of cross-section paper with space at the margin 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 SMALL BEAMS

Apparatus:  An ordinary static bending machine, a steel I-beam bearing two adjustable knife-edge supports to rest on the platform, and a special deflectometer, are required. (See Fig. 31.)

[Illustration:  FIG. 31.—­Static bending test on small beam.  Note the use of the deflectometer with indicator and dial for measuring the deflection; also roller bearings between beam and supports.]