Constriction of the fracture

In the tensile test , after the tensile strength has been reached, a local constriction occurs in ductile materials, in the area of ​​which the break then also occurs. ${\displaystyle R_{m}}$

The largest relative change in cross-section that occurs is referred to as the fracture necking ; it is a measure of the ductility of the material: ${\displaystyle Z}$

${\displaystyle {\begin{aligned}Z&={\frac {\Delta S}{S_{0}}}\cdot 100\,\%\\&={\frac {S_{0}-S_{u}}{S_{0}}}\cdot 100\,\%\\&=(1-{\frac {S_{u}}{S_{0}}})\cdot 100\,\%\end{aligned}}}$

With

• the initial cross- sectional area of the unloaded test rod ${\displaystyle S_{0}}$
• the smallest cross-sectional area of the broken rod, i.e. the remaining cross-sectional area at the constricted point. ${\displaystyle S_{u}}$

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  Course of the constriction of a sample in the tensile test up to ductile fracture

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  Photo of a ductile fractured tensile specimen

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  End view of a round sample ( AlMgSi alloy) after ductile fracture

literature

• Elsbeth Wendler-Kalsch, Hubert Graefen: Corrosion damage theory. 1st edition, Springer Verlag, Berlin / Heidelberg 1998, ISBN 978-3-662-22074-0 .
• Volker Läpple: Introduction to strength theory. Text and exercise book, 2nd edition, Vieweg + Teubner Verlag, Wiesbaden 2008, ISBN 978-3-8348-0426-6 .

Web links

• Tensile test on metallic materials (accessed December 6, 2019)
• Fracture behavior of light metals under impact stress (accessed on December 6, 2019)
• To determine cyclical material parameters and damage parameter Wöhler curves (accessed on December 6, 2019)
• Deformation and fracture of modern, high-strength multiphase steels (accessed December 6, 2019)
• Strength and deformation of weldable, heat-treated reinforcing steel in the range of low temperatures (accessed December 6, 2019)