Testing Methods for JIS Steel Materials

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Introduction to Tensile Testing

The tensile test represents the most widely used method to determine the mechanical properties of materials. In this standardized procedure, a specimen is pulled until fracture occurs, while continuously measuring both the applied load and specimen elongation. From these measurements, stress and strain values are calculated and used to construct a stress-strain curve, which reveals critical material properties including elastic modulus and yield strength.

The highest load recorded during testing determines the tensile or ultimate strength of the material. After fracture, measurements of the final length and cross-sectional area allow calculation of percent elongation and percent reduction of area, providing valuable indicators of material ductility. By tracking instantaneous dimensions during testing, true stress and true plastic strain can be derived from load and elongation data.

Further analysis using a logarithmic plot of true stress versus true plastic strain reveals the strain hardening characteristics of the material. This comprehensive approach allows engineers to extract extensive information about mechanical properties from a single test.

International Testing Standards

Numerous organizations worldwide have developed standardized methods for conducting tensile tests. In the United States, ASTM standards are commonly referenced to define tensile test procedures and parameters. Internationally, other prominent standards organizations include:

• Japanese Industrial Standards (JIS)
• Deutsche Institut für Normung (DIN)
• International Organization for Standardization (ISO)

While other technical groups in the United States have developed additional standards, these generally derive from the foundation established by ASTM E.8.

Test Piece Configuration and Testing Equipment

Tensile test specimens are typically manufactured in either circular or flat configurations, with standard circular specimens having a diameter of 12.5mm.

Figure 1: Typical test pieces showing various specimen configurations

The tensile test specimen is secured in the grips of a tensile testing machine. During testing, the grips separate at a constant rate while a load cell measures the applied force and an extensometer records specimen extension.

Figure 2: Unstretched and full stretched specimens

Figure 3: Test pieces after tensile testing

Figure 4: Tensile test machine

It's important to note that tensile testing is generally destructive, as specimens undergo permanent deformation and typically fracture during the procedure.

JIS Classification of Test Pieces

The Japanese Industrial Standard classifies test pieces into proportional and non-proportional categories depending on the form and size of the material. Table 1 provides a comprehensive classification system.

Table 1. Classification of test pieces by form including flat, bar, tubular, arc section, and wire specimens

Form of test piece	Flat form test piece	Bar form test piece	Tubular form test piece	Arc section test piece	Wire form test piece
Proportional test piece	N°14B	N°2; N°14A	N°14C	N°14B
Non-proportional test piece	N°1A; N°1B; N°5; N°13A; N°13B	N°4; N°10; N°8A; N°8B; N°8C; N°8D	N°11	N°12A; N°12B; N°12C	N°9A; N°9B

The selection of appropriate test piece type should follow the requirements specified in the standard for each particular material. Table 2 provides recommended test piece selections based on material type and dimensions.

Table 2. Detailed classification system correlating materials with appropriate test piece selections

Material		Test Piece		Remarks
Form	Dimensions	Proportional	Non-proportional
Sheet, Plate, Shape, Strip	*t > 40	N°14A	N°4; N°10	For bar form test piece
		N°14B	-	For bar form test piece
	20 < t ≤ 40	N°14A	N°4; N°10	For bar form test piece
		N°14B	N°1A	For flat form test piece
	6 < t ≤ 20	N°14B	N°1A; N°5
			N°5; N°13A; N°13B
	3 < t ≤ 6
	t ≤ 3	-
Bar	-	N°2; N°14A	N°4; N°10	-
Wire	-	-	N°9A; N°9B	-
Pipe	Pipe of small outside diameter	N°14C	N°11	For tubular form test piece
	**D ≤ 50	N°14B	N°12A	For arc section test piece
	50 < D ≤170		N°12B
	D >170		N°12C
	D ≥200	N°14B	N°5	For flat form test piece or arc section test piece
	Thick wall pipe	N°14A	N°4	For bar form test piece
Casting	-	N°14A	N°4; N°10	-
	-	-	N°8A; N°8B; N°8C; N°8D	To be used when elongation value is not required. To be taken from test coupon casted for test piece.
Forging	-	N°14A	N°4; N°10	-

*t - thicknesses in mm
**D - outside diameter in mm

For cases where standard test pieces are not suitable, alternative specifications are provided:

• N°1B test piece can be used when standard test pieces from Table 2 are unsuitable
• N°3, N°6, and N°7 test pieces (specified in Annex) are available when Table 2 options cannot be applied
• Materials specified in International Standards may follow the division of use shown in Remarks Table 1

Remarks Table 1. Division of use and dimension specifications for test pieces based on International Standards

Shape of cross section of product	Dimension [mm]	Width W	Gauge length L	Parallel length P	Distance from end of parallel portion to grip
Sheet	t < 3	12.5	50	75	87.5
		20	80	120	140
	t ≥ 3		5.65√***A	L+2√A
Bar	D < 4		200		250
			100		150
	D ≥ 3		5D	L+2D
Wire	D < 4		200		250
			100		150
	D ≥ 4		5D	L+2D
Pipe	t < 3	12.5	50	75	87.5
		20	80	120	140
	t ≥ 3		5.65√A	L+2√A
Shape	t < 4		200		250
			100		150
	t ≥ 4		5D	L+2D

***A- sectional area of parallel portion