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ASTM E646-2015
金属薄板材拉伸应变硬化指数 (n值) 的标准试验方法

Standard Test Method for Tensile Strain-Hardening Exponents (n -Values) of Metallic Sheet Materials



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ASTM E646-2015

5.1x00a0;This test method is useful for estimating the strain at the onset of necking in a uniaxial tension test (1). Practically, it provides an empirical parameter for appraising the relative stretch formability of similar metallic systems. The strain-hardening exponent is also a measure of the increase in strength of a material due to plastic deformation.

5.2x00a0;The strain-hardening exponent may be determined over the entire plastic stress-strain curve or any portion(s) of the stress-strain curve specified in a product specification.

Note 4:x00a0;The engineering strain interval 10x2013;20% is commonly used for determining the strain-hardening exponent, n, of formable low-carbon steel products

5.3x00a0;This test method is not intended to apply to any portion of the true -stress versus true -strain curve that exhibits discontinuous behavior; however, the method may be applied by curve-smoothing techniques as agreed upon.

Note 5:x00a0;For example, those portions of the stress-strain curves for mild steel, aluminum, or other alloys that exhibit yield point and Lx00fc;ders band elongation, twinning, or Portevinx2013;Le Chatelier effect (PLC) may be characterized as behaving discontinuously.

Note 6:x00a0;Caution should be observed in the use of curve-smoothing techniques as they may affect the n-value.

5.4x00a0;This test method is suitable for determining the tensile stress-strain response of metallic sheet materials in the plastic region prior to the onset of necking.

5.5x00a0;The n-value may vary with the displacement rate or strain rate used, depending on the metal and test temperature.

1.1x00a0;This test method covers the determination of a strain-hardening exponent by tension testing of metallic sheet materials for which plastic-flow behavior obeys the power curve given in the Introduction.

Note 1:x00a0;A single power curve may not be a satisfactory fit to the entire stress-strain curve between yield and necking. If such is the case, more than one value of the strain-hardening exponent may be obtained (2) by agreement using this test method.

1.2x00a0;This test method is specifically for metallic sheet materials with thicknesses of at least 0.005 in. (0.13 mm) but not greater than......

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