Elongation at break

The elongation at break is a characteristic value in materials science , which indicates the permanent elongation of the tensile specimen after breakage, based on the initial gauge length. It characterizes the deformability (or ductility ) of a material and can, according to the characteristic mechanical behavior of the material types, be defined in different ways and also be designated with different symbols. The elongation at break is not included in the usual calculation models (e.g. in structural engineering ). ${\displaystyle A}$

metallic materials

definition

The elongation at break is the permanent change in length after a break, based on the initial gauge length of a sample in the tensile test . ${\displaystyle L_{0}}$ ${\displaystyle \Delta L}$

${\displaystyle A={\frac {\Delta L}{L_{0}}}\cdot 100\,\%={\frac {L_{u}-L_{0}}{L_{0}}}\cdot 100\,\%}$

With

${\displaystyle L_{u}=}$ Length after the break

The initial gauge length is determined by measuring marks on the tensile specimen before the tensile test. ${\displaystyle L_{0}}$

The elongation at break is still occasionally denoted today with the symbol that was used in the past . ${\displaystyle \varepsilon _{B}}$

Proportional bars

As a result of the locally limited constriction, the elongation at break depends on the initial measuring length . In order to obtain comparable values ​​for the elongation at break, proportional bars are mostly used for tensile tests, i.e. H. Samples in which the initial gauge length to the exit cross-section is in a fixed ratio. ${\displaystyle A}$ ${\displaystyle L_{0}}$ ${\displaystyle L_{0}}$ ${\displaystyle S_{0}}$

Flat bars:

${\displaystyle L_{0}=k\cdot {\sqrt {S_{0}}}}$

A value of is used internationally for flat specimens . Alternatively, a value of can also be used. ${\displaystyle k=5{,}65}$ ${\displaystyle k=11{,}3}$

Round bars:

${\displaystyle L_{0}=k\cdot d_{0}}$

A value of is normal for round specimens . Alternatively, a value of can also be used. ${\displaystyle k=5}$ ${\displaystyle k=10}$

For round specimens, the elongation at break is usually indicated with or . The index relates to the ratio of the initial gauge length to the initial diameter : ${\displaystyle A_{5}}$ ${\displaystyle A_{10}}$ ${\displaystyle k}$ ${\displaystyle L_{0}}$ ${\displaystyle d_{0}}$

- with a short proportional rod, it applies ${\displaystyle A_{5}}$ ${\displaystyle L_{0}=5\cdot d_{0}}$

- for a long proportional rod, it applies ${\displaystyle {A_{10}}}$ ${\displaystyle L_{0}=10\cdot d_{0}}$

Polymer materials ( plastics )

definition

Elongation at break is the last elongation value recorded before the stress drops to less than or equal to 10% of the strength value. It is specified as a size of dimension 1 or in percent (%). ${\displaystyle \varepsilon _{b}}$

For breaks above the yield point , the nominal elongation at break is given. This is the last nominal elongation value recorded before the stress drops to less than or equal to 10% of the strength value. The nominal elongation is determined from the measured values ​​between the clamping clamps. ${\displaystyle \varepsilon _{tb}}$

Multipurpose specimen

The elongation at break for polymer materials is usually determined using the multipurpose specimen.

literature

• Burkhard Heine: Materials testing - determination of the properties of metallic materials . 3rd edition, Hanser Verlag Munich, 2015. ISBN 978-3-446-44455-3 .
• Wolfgang Grellmann, Sabine Seidler: Plastic testing . 3rd edition, Hanser Verlag Munich, 2015. ISBN 978-3-446-44350-1 .

Individual evidence

1. ↑ Tensile strength, yield point, yield strength, elongation at break (accessed on September 14, 2018)
2. ↑ EN ISO 6892-1: 2016 Metallic materials - Tensile test - Part 1: Test method at room temperature.
3. ^ W. Bickel: The metallic materials of mechanical engineering . Springer Verlag Berlin, 1953.
4. ↑ EN ISO 527-1: 2012 Plastics - Determination of tensile properties - Part 1: General principles.
5. ↑ EN ISO 3167: 2014 Plastics - Multipurpose test specimens.