6.1Shape and dimensions

IS 1608:2005, Metallic Materials — Tensile Testing at Ambient Temperature

Last Updated 29 Oct 2026

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6.1.1 General

The shape and dimensions of the test pieces depend on the shape and dimensions of the metallic product from which the test pieces are taken.

The test piece is usually obtained by machining a sample from the product or a pressed blank or casting. However products of constant cross-section (sections, bars, wires, etc.) and also as-cast test pieces (i.e. cast irons and non-ferrous alloys) may be tested without being machined.

The cross-section of the test pieces may be circular, square, rectangular, annular or, in special cases, of some other shape.

Test pieces, the original gauge length of which is related to the original cross-sectional area by the equation $L_{\mathrm{o}}=k \sqrt{S_{\mathrm{o}}}$ are called proportional test pieces. The internationally adopted value for $k$ is 5,65 . The original gauge length shall be not less than 20 mm. When the cross-sectional area of the test piece is too small for this requirement to be met with the coefficient $k$ value of 5,65 , a higher value (preferably 11,3) or a non-proportional test piece may be used.

In the case of non-proportional test pieces, the original gauge length ( $L_{o}$ ) is taken independently of the original cross-sectional area ( $S_{o}$ ).

The dimensional tolerances of the test pieces shall be in accordance with the appropriate annexes (see 6.2).

Table 1Symbols and designations

Reference number ¹)	Symbol	Unit	Designation
			Test piece
1	a²)	mm	Thickness of a flat test piece or wall thickness of a tube
2	b	mm	Width of the parallel length of a flat test piece or average width of a longitudinal strip from a tube or width of flat wire
3	d	mm	Diameter of the parallel length of a circular test piece, or diameter of round wire or internal diameter of a tube
4	D	mm	External diameter of a tube
5	L_o	mm	Original gauge length
—	L'_o	mm	Initial gauge length for determination of A_g
6	L_c	mm	Parallel length
—	L_e	mm	Extensometer gauge length
7	L_t	mm	Total length of test piece
8	L_u	mm	Final gauge length
—	L'_u	mm	Final gauge length after fracture for determination of A_g (see annex H)
9	S_o	mm²	Original cross-sectional area of the parallel length
10	S_u	mm²	Minimum cross-sectional area after fracture
—	k	—	Coefficient of proportionality
11	Z	%	Percentage reduction of area: S_o - S_u S_o × 100
12	—	—	Gripped ends

Table 1(concluded)

Reference number¹⁾	Symbol	Unit	Designation
			Elongation
13	-	mm	Elongation after fracture: L_u - L_o
14	A³⁾	%	Percentage elongation after fracture: L_u - L_o ————— x 100 L_o
15	A_e	%	Percentage yield point extension
—	ΔL_m	mm	Extension at maximum force
16	A_g	%	Percentage non-proportional elongation at maximum force (F_m)
17	A_gt	%	Percentage total elongation at maximum force (F_m)
18	A_t	%	Percentage total elongation at fracture
19	-	%	Specified percentage non-proportional extension
20	-	%	Percentage total extension (see 28)
21	-	%	Specified percentage permanent set extension or elongation
			Force
22	F_m	N	Maximum force
			Yield strength — Proof strength — Tensile strength
23	R_eH	N/mm²	Upper yield strength⁴⁾
24	R_eL	N/mm²	Lower yield strength
25	R_m	N/mm²	Tensile strength
26	R_p	N/mm²	Proof strength, non-proportional extension
27	R_r	N/mm²	Permanent set strength
28	R_t	N/mm²	Proof strength, total extension
—	E	N/mm²	Modulus of elasticity

2019

1)	See figures 1 to 13.
2)	The symbol T is also used in steel tube product standards.
3)	See 4.4.2.
4)	1 N/mm² = 1 MPa

6.1.2 Machined test pieces

Machined test pieces shall incorporate a transition curve between the gripped ends and the parallel length if these have different dimensions. The dimensions of this transition radius may be important and it is recommended that they be defined in the material specification if they are not given in the appropriate annex (see 6.2).

The gripped ends may be of any shape to suit the grips of the testing machine. The axis of the test piece shall coincide with or be parallel to the axis of application of the force.

The parallel length ( $L_{\mathrm{c}}$ ) or, in the case where the test piece has no transition curve, the free length between the grips, shall always be greater than the original gauge length ( $L_{\mathrm{o}}$ ).

6.1.3 Non-machined test pieces

If the test piece consists of an unmachined length of the product or of an unmachined test bar, the free length between the grips shall be sufficient for gauge marks to be at a reasonable distance from the grips (see annexes A and D).

As-cast test pieces shall incorporate a transition radius between the gripped ends and the parallel length. The dimensions of this transition radius are important and it is recommended that they be defined in the product standard. The gripped ends may be of any shape to suit the grips of the testing machine. The parallel length ( $L_{\mathrm{c}}$ ) shall always be greater than the original gauge length $\left(L_{\mathrm{o}}\right)$ .