Tensile Strength

What is the Tensile Strength?

The tensile strength Rm (also tearing strength) is a material characteristic value for the evaluation of strength and deformation behavior. The tensile strength is the maximum mechanical tensile stress with which a specimen can be stressed relative to the cross-section. If the tensile strength is exceeded the material fails: a material specimen tears during the tensile test. The material however undergoes plastic deformation (residual) before reaching the actual tensile strength value.

The tensile strength is calculated from the results of the tensile test (e.g. to ISO 6892 (metals) or ISO 527 (plastics): Tensile strength Rm = maximum tensile force Fm / stress cross section

The tensile strength is measured in N/mm².

Tensile strength Rm in tensile test

In the stress-strain diagram (also stress-strain curve), the tensile stress of the specimen is plotted over its relative change in length in the tensile test.

This curve can be used to read off different parameters of the elastic behavior of the specimen. In the stress-strain diagram the tensile strength is the maximum value of the stress reached in the tensile test.

Tensile strength Rm for different material behaviors

Tensile Strength for Different Materials

In the image on the left, the stress-strain diagram shows examples of various curves and their tensile strength Rm.

Tensile strength with a high level of work-hardening (1) and with a low level of work-hardening (2) after the yield point

The Tensile Strength with Different Levels of Material Hardening

For materials with a pronounced yield point the maximum tensile force is defined as the highest endured force after the upper yield strength. The maximum tensile force after exceeding the yield strength can also lie below the yield point for weakly work-hardened materials, therefore the tensile strength in this case is lower than the value for the upper yield strength.

The stress strain curve image to the left shows a curve with a high level of work-hardening (1) and with a low level of work-hardening (2) after the yield point.

For plastics with yield point and subsequent stress, on the other hand, the tensile strength corresponds to the stress at the yield point.

Additional Characteristic Values for the Evaluation of Strength Properties

For the evaluation of strength properties yield points, the tensile strength or also breaking strength or tear strength are determined.

Yield point is generally used to describe the stress at the transition from elastic to plastic deformation. It is the generic term for elastic limit, yield strength (tensile test), compressive yield strength (compression test), flexural yield strength (flexure test) or torsional yield strength (torsion test).

Offset yield points are stresses that cause a certain residual or total elongation. They are preferred with metallic materials to mark the continuous transition from the elastic to the plastic range.

Flow stress, on the other hand, is the stress required to carry out the plastic deformation of metallic materials. It increases as the material resistance increases due to hardening and is also referred to as deformation resistance kf (flow curve) and must not be confused with the yield point.

After the maximum force Fm has been reached, the stress in many materials decreases with increasing elongation, until the specimen tears. The breaking force related to the initial cross section is also called breaking strength or tear strength. It is determined more for plastics and less for metallic materials. In the case of brittle metallic materials, elastomers and tough plastics without yield point, the tear strength generally corresponds to the tensile strength.

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