FED-STD-228A
Method 3031.1
18 APRIL 2014
ELONGATION, INSULATION AND SHEATH
1. SCOPE
1.1 This method is intended for use in determining the elongation of insulation and sheath compounds at
break. It is applicable to the usual grades of rubber and thermoplastic compounds used for insulation and
sheath.
2. SPECIMEN
2.1 The specimen should be as described in method 3021.
3. APPARATUS
3.1 The apparatus shall be as follows:
3.1.1 The apparatus described in method 3021.
3.1.2 Bench marker having two parallel knife edges ground smooth and true and which are between
0.002 and 0.003 inch in width at the edge and beveled at an angle of not more than 15° to the
perpendicular. The distance between the centers of the knife edges shall be 1.000 ± 0.003 inch or 2.000
inches ± 0.003 inch as required.
3.1.3 Stamp pad having a plane unyielding surface (hardwood, plate glass, or plastic) containing ink of
the desired color and quality for marking the specimen. The ink shall have no deteriorating effect on
rubber or plastic compounds, and shall be of contrasting color to that of the specimen.
3.1.4 Measuring scale or other device graduated in 0.1 inch for indicating elongation.
4. PROCEDURE
4.1 Unless otherwise specified in the detail specification, the elongation shall be determined on the same
specimen and at the same time as the tensile strength.
4.2 Preparation of specimen. The specimen shall be prepared as described in method 3021. Two
parallel bench marks shall be placed symmetrically on the straight specimen and on the reduced section
of the dumbbell specimen perpendicular to the longitudinal axis of the specimen by means of the bench
marker and ink. The marks shall be not more than 0.010 inch wide. Care shall be taken not to injure the
specimen.
4.3 Determination of elongation. The specimen shall be placed in the grips of the testing machine and
the force applied as described for tensile strength, method 3021. The distance between the two bench
marks on the dumbbell or straight specimen shall be noted continuously to the nearest 0.1 inch by means
of the scale or other device which shall be used in such a manner as not to touch the specimen or only
very lightly touch it on the front or back. Two operators may be required to conduct this test. The
distance between the bench marks when the specimen ruptures together with the original distance
between the bench marks shall be recorded.
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