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Toughness or tenacity describes the resistance of a material to breakage or crack propagation .

The toughness is the ability to absorption of energy in plastic deformation determined. Tough materials usually have a good balance between strength and ductility .

Most metals are tough because they have a high strength and at the same time are able to absorb a lot of deformation energy without breaking. This applies to wrought iron , for example (but not to cast iron ).

The toughness can be estimated on the basis of the load-deformation diagram , but cannot be conclusively determined because, in addition to the nominal stress at break , the parameters deformation at break , energy absorption at break and crack stopping capacity are also used. In addition to improved fracture properties, crack deflection or crack branching can also lead to an increase in toughness.

The opposite of toughness is brittleness . Examples of brittle materials are glass , ceramics , some hard plastics, and hardened steel . These materials are only able to deform plastically to a very limited extent and can therefore absorb significantly less energy than tough materials before they break.

Temperature dependence

Some materials (especially plastics as well as structural steel and all other body-centered cubic materials) show a pronounced temperature dependence of their toughness. The transition between the tough “high position” and the brittle “low position” is described by the transition temperature . The operating temperature should always be above .

Before this effect was known, ships (e.g. the Liberty freighters during World War II) broke apart brittle for no apparent reason in calm seas but low temperatures .

Measurement methods

The toughness parameters are determined with the help of different test procedures or methods of fracture mechanics . Thus, the fracture nominal voltage and the work of fracture are uptake by the Charpy impact test , Kerbzugversuch , penetration test or tensile test , the fracture strain of the bending or folding test and the Charpy impact test determined. The crack stopping power is determined by the notched impact test or the drop weight test.

Toughness classes

Tenacity of minerals

In mineralogy , the tenacity (toughness) of a mineral surface is a degree of hardness tested with a steel needle:

  • In the case of brittle (fragile) mineral, the scratch dust jumps away from the surface. Most of the minerals fall into this category.
  • In the case of mild (tendilem) mineral, the scratching powder does not jump away, but remains on the edge of the scratched track. E.g .: galena , antimonite
  • In the case of cuttable (sectile) mineral, the penetrating needle creates a scratch track, but no scratch powder. E.g .: talc , solid bismuth

The tenacity of the entire mineral is tested by bending:

  • Breaking brittle minerals.
  • Pliable (ductile / malleable) minerals change their shape permanently. The change in shape takes place plastically, i.e. H. without breaking; z. B. A mineral can be hammered into a plate or drawn into a wire. E.g .: many metals ( silver , gold , copper etc.), argentite .
  • Inelastic-pliable (flexible) minerals differ from ductile minerals in that the crystal can only be bent. Hammering or pulling would break it. They also remain in the new shape after bending. Example: plaster of paris .
  • Elastic minerals, on the other hand, return to their original shape after being bent. E.g. biotite , light mica , biotite mica

Toughness of carbon fibers

Carbon fibers are classified according to seven levels of tear resistance:

high tenacity
intermediate (intermediate modulus)
extremely rigid (high modulus)
(Ultra Modulus)
(Ultra High Modulus)
(Ultra Modulus Strength)
high stiff / high strength

See also

Individual evidence

  1. a b c Lothar Issler , Hans Ruoß, Peter Häfele: Strength theory - basics . Springer, 2003, ISBN 978-3-540-40705-8 ( page 311 in the Google book search).
  2. "Toughness" , NDT Education Resource Center , Brian Larson, editor, 2001-2011, The Collaboration for NDT Education, Iowa State University
  3. ^ Hermann Dietrich: Mechanical material testing: Fundamentals, test methods, applications . Expert, 1994, ISBN 978-3-8169-1035-0 ( page 140 in the Google book search).
  4. Manfred Riehle, Elke Simmchen: Fundamentals of material technology . Wiley-VCH, 2000, ISBN 978-3-527-30953-5 ( page 103 in the Google book search).
  5. ^ Gunter Erhard: Constructing with plastics . Carl Hanser, 2008, ISBN 978-3-446-41646-8 ( page 125 in the Google book search).
  6. Günter Schulze: The metallurgy of welding . Springer Berlin Heidelberg, 2009, ISBN 978-3-642-03182-3 ( page 261 in the Google book search).
  7. Determination criteria of mineral tenacity,