FED-STD-228A
Method 3001.1
18 APRIL 2014
TENSION TESTS, INSULATION AND SHEATH; GENERAL
1. SCOPE
1.1 This group of tests is intended for use in determining the effect of application of a tension load to the
insulation and sheaths of insulated wire and cable. Methods of test for tensile strength, ultimate
elongation, tensile stress, tearing strength, and set of rubber and thermoplastic compounds, and tensile
strength of varnished cambric insulation are described.
2. DEFINITIONS
2.1 Tensile strength. Tensile strength is the force per unit of the original cross-sectional area of the
unstretched specimen which is applied at the time of rupture of the specimen. It is calculated by dividing
the breaking force in pounds by the cross section of the unstretched specimen in square inches. For
example, if a specimen of cross section 0.25 inch by 0.10 inch broke at a force of 50 pounds, the tensile
strength would be 50 divided by (0.25 x 0.10) which is equal to 2,000 pounds per square inch. When a
stress is applied to the specimen of rubber and thermoplastic compounds, the material stretches with an
accompanying reduction in cross-sectional area. Since precise measurements of the specimen cannot
be made at the moment the specimen breaks, calculation of the tensile strength at break is based on the
cross-sectional area of the specimen before application of any load.
2.2 Elongation. Elongation is the extension between bench marks produced by a tension force applied to
a specimen and is expressed as a percentage or original distance between the marks on the unstretched
specimen. Ultimate elongation is the elongation at the moment of rupture. For example, if a 1-inch bench
length if marked on an unstretched specimen and the specimen is stretched until the bench marks are 7
inches apart, elongation is 7 inches-1 inch = 6 inches or 600 percent.
2.3 Tensile stress. Tensile stress is the force per unit of original cross-sectional area of the unstretched
specimen required to stretch the specimen to a stated elongation. It is expressed in pounds of tension
load per square inch at the stated elongation. For example, 1,000 pounds per square inch at 500 percent
elongation. It is often designated in rubber technology by the term "modulus".
2.4 Tension set. Set is the elongation remaining after a specimen has been stretched and held at a
specified elongation for a given period of time, then relieved of the force and allowed to rest for a definite
period of time. It is expressed as a percentage of the original distance between bench marks on the
unstretched specimen. For example, a specimen is stretched from 1 to 5 inches for a period of 10
minutes and then released. Its length after the 10 minute rest is 1.2 inches, so that the set under these
conditions is 0.20 inch or 20 percent.
2.5 Tearing strength. Tearing strength is the ratio of the maximum force applied during tear of a
specimen to the thickness of the unstretched specimen. For example, if a force of 36 pounds is
necessary to tear a specimen 0.082 inch thick, the tearing strength would be 36 divided by 0.082, or 439
pounds per inch.
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