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Tensile Properties - ASTM D638 Plastic Test Standard

Tensile Properties - ASTM D638

Tensile testing is performed by elongating a specimen and measuring the load carried by the specimen. From a knowledge of the specimen dimensions, the load and deflection data can be translated into a stress-strain curve. A variety of tensile properties can be extracted from the stress-strain curve.

Tensile Test

Property Definition
Tensile Elongation at Break Tensile elongation corresponding to the point of rupture.
Tensile Elongation at Yield Tensile elongation corresponding to the yield (an increase in strain does not result in an increase in stress).
Tensile Strength at Break Tensile stress corresponding to the point of rupture.
Tensile Strength at Yield Tensile stress corresponding to the yield point (an increase in strain does not result in an increase in stress).
Tensile Strength Tensile stress at a specified elongation.
Tensile Strength, Ultimate The highest tensile stress a material can support before failing.
Tensile Modulus The ratio of tensile stress to tensile strain of a material in the elastic region of a stress-strain curve. A "Tangent" tensile modulus value is the slope of the elastic region of the stress-strain curve and is also known as Young's Modulus, or the Modulus of Elasticity. A "Secant" tensile modulus value is the slope of a line connecting the point of zero strain to a point on the stress-strain curve at a specified strain. This is used for materials that exhibit little or no linear behavior.

Illustration of Tangent and Secant Tensile Moduli

Test Specimen Summary
Specimen Rigidity Case Note Thickness
Type I Rigid Preferred specimen. <7 mm (0.28 in)
Type II Rigid Use when Type I specimen does not break in the narrow section. <7 mm (0.28 in)
Type III Rigid/Nonrigid   >7 mm (0.28 in)
<14 mm (0.55 in)
Type IV Rigid/Nonrigid Should be used for comparison between materials in different rigidity cases. Essentially the same as Die C specimen from ASTM D412. <4 mm (0.16 in)
Type V Rigid Used when limited material is available or laboratory space is a concern (for environmental testing) <4 mm (0.16 in)

Type I, II, III, and V Specimen

Type IV Specimen

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