FED-STD-228A
Method 3021.1
18 APRIL 2014
TENSILE STRENGTH, INSULATION AND SHEATH
1. SCOPE
1.1 This method is intended for use in determining the tensile strength of insulation and sheath
compounds. It is applicable to the usual grades of rubber and thermoplastic compounds used for
insulation and sheaths.
2. SPECIMEN
2.1 The specimen should be a piece of the insulation or sheath taken from the inspection unit as follows:
2.1.1 Dumbbell. Whenever it is practicable to prepare it from the inspection unit, a dumbbell shaped
specimen cut by one of the dies shown on figure 3021 should be used except for varnished cambric
insulation. When the size of the piece of material to be tested will permit, the reduced portion of the
specimen should be ¼ inch wide and either 1-5/16 or 2-5/16 inches long. If the piece of material to be
tested is narrow, a specimen with reduced portion 1/8 inch wide may be used. When the size of the piece
permits, enlarged ends of the specimen should be 1 inch wide. When the piece of material is narrow, the
enlarged ends of the specimen may be 5/8 inch wide. The thickness of the specimen should not exceed
0.125 inch.
2.1.2 Straight specimen. A straight specimen in the form of a tube should be used when it is not
practicable to prepare a dumbbell shaped specimen from the insulation or sheath of the inspection unit.
3. APPARATUS
3.1 The apparatus shall be as follows:
3.1.1 A testing machine which meets the following requirements:
3.1.1.1 A machine shall be power-driven.
3.1.1.2 The applied tension shall be indicated to within ± 1 percent by a dial, scale, or automatic recorder
when calibrated according to method 3016.
3.1.1.3 The indicator shall remain at the point of maximum force after rupture of the specimen.
3.1.1.4 The rate of travel of the power actuated grip shall be 20 ± 1 inch per minute and shall be uniform
at all times.
3.1.1.5 The machine, when used for a given specimen, should be of such capacity that the maximum
load required to break the specimen is not greater than 85 nor less than 15 percent of the rated capacity.
3.1.1.6 If the machine is equipped with a dynamometer head of the compensating type for convenience
in eliminating calculations, the head shall have means for making adjustments for variation in thickness of
specimens.
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