FED-STD-228A
4.2 Cross-sectional area of specimen.
4.2.1 Dumbbell.
4.2.1.1 Thickness. The thickness of the specimen shall be determined as described in method 1124
except that three measurements shall be made, one at the center and one near each end of the reduced
section of the specimen. If the specimen is narrower than the diameter of the foot, measurements shall
be made with the center of the micrometer foot coinciding with the longitudinal center line of the specimen
so that there will be an equal overlap of the foot on each side. The median of the three measurements
shall be used as the thickness in calculating the cross-sectional area of the specimen except that
specimens for which the difference between maximum and minimum thickness exceeds 0.003 inch shall
be discarded.
4.2.1.2 Width. The width of a specimen shall be the distance, W in the legend for figure 3021, between
the cutting edges of the die in the reduced section.
4.2.1.3 The cross-sectional area of the specimen shall be calculated by multiplying the width of the
specimen by the median thickness of the specimen.
4.2.2 Straight.
4.2.2.1 The weight of the specimen in grams, the length of the specimen in centimeters, and the density
in grams per cubic centimeter shall be determined. The cross-sectional area shall then be calculated
from these measurements in the following manner:
Cross-sectional area, square inches=0.155W
DxL
where:
W=the weight of the specimen in air in grams
D=the density of the specimen in grams per cubic centimeter
L=the length of the specimen in centimeters
4.3 Determination of tensile strength.
4.3.1 The testing machine shall be calibrated as described in method 3016.
4.3.2 The specimen shall be placed in the grips of the machine and adjusted symmetrically in order that
the tension will be distributed uniformly over the cross section. If the tension is greater on one side of the
specimen than on the other, the maximum strength of the specimen will not be developed. The force
shall be applied to the specimen at such a rate that the power actuated grip will travel at a uniform speed
of 20 ± 1 inch per minute. After rupture of the specimen, the breaking force shall be noted from the dial or
scale or by means of an autographic or spark recorder and the value recorded.
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