FED-STD-791 Lubricants, Liquid Fuels, And Related Products, Testing Method OfThis test method standard is composed of standard test methods for sampling, inspecting and testing lubricants, liquid fuels and related products. It is issued pursuant to the Federal Property and Administration Services Act of 1949, as amended and its application to the purchase of commodities referred to herein is mandatory on all Federal agencies.

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'�NOTE:This draft dated 15 April 2006' by DasH - Page 165 of 460

FED-STD-791D

6.6.4.1 The hardness of the rubber specimen shall be determined in accordance with

ASTM Method D 2240, Type A durometer.

6.6.4.2 The thickness of the rubber specimen for the hardness test should be at least 0.3

cm. Therefore, a single-ply thickness of silicone rubber may be used as a cushion.

6.6.4.3 After swell testing, hardness readings shall be conducted on the end of each test

specimen outside of the area to be used for tensile testing.

6.6.4.4 Apply the pressure foot to the specimen. Read the scale 15 s after the pressure

foot is in firm contact with the specimen.

6.6.4.5 The hardness value of the test specimen shall be the average value obtained for

the three test specimens.

6.6.5 Tensile strength.

6.6.5.1 Determine the loss in tensile strength by use of Method D 412, Standard Method

of Tensile Testing of Vulcanized Rubber.

6.6.5.2 Three measurements shall be made for thickness; one at the center and one at

each end of the specimen. The median of the three measurements shall be used as the thickness

in calculating the cross sectional area.

6.6.5.3 When rubber specimens of standard thickness are used as per section 5.2 of this

test method and the difference between the maximum and minimum thickness does not exceed

0.0762 cm (0.003 in), it is not necessary to calculate the cross-sectional area for each piece.

6.6.5.4 Place a specimen in the grips of the testing machine, using care to adjust it

symmetrically in order that the tension will be distributed uniformly over the cross section. If

tension is greater on one side of the specimen than the other, maximum strength of the rubber

will not be developed. Start the machine and record the stress at the time of the rupture.

7 CALCULATIONS

7.1 Calculate the percentage change in volume (V) of each rubber sample as follows:

(A - B) 100

where:

V = change in volume, percent.

A = displacement weight at conclusion of test, mg.

B = displacement weight before immersion in sample, mg.

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