C.2.1 Parallel length of machined test piece
The parallel length ( ) shall be at least equal to:
- a) in the case of test pieces with circular cross-section;
- b) in the case of prismatic test pieces.
Depending on the type of test piece, the length or shall be used in cases of dispute, unless there is insufficient material.
C.2.2 Length of unmachined test piece
The free length between the grips of the machine shall be adequate for the gauge marks to be at a reasonable distance from these grips.
C.2.3 Original gauge length ( )
C.2.3.1 Proportional test pieces
As a general rule, proportional test pieces are used where the original gauge length ( ) is related to the original cross-sectional area ( ) by the equation
where k is equal to 5,65.
Test pieces of circular cross-section preferably have the dimensions given in table C.1.
The scale given in annex F makes it easier to determine the original gauge length (Lo) corresponding to the dimensions of test pieces of rectangular cross-section.
C.2.3.2 Non-proportional test pieces
Non-proportional test pieces may be used if specified by the product standard.
Table C.1 — Circular cross-section test pieces
| k | Diameter d mm | Original cross- sectional area S0 mm2 | Original gauge length L0 = k√S0 mm | Minimum parallel length Lc mm | Total length Lt |
|---|---|---|---|---|---|
| 5,65 | 20 ± 0,15 | 314 | 100 ± 1 | 110 | Depends on the method of fixing the test piece in the machine grips |
| 10 ± 0,075 | 78,5 | 50 ± 0,5 | 55 | ||
| 5 ± 0,040 | 19,6 | 25 ± 0,25 | 28 | ||
| In principle: Lt > Lc + 2d or 4d |