Sliding tape

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TEM image of PSB structures in a metal alloy

Slip bands (according to the English name persistent slip bands , PSBs as persistent slip bands designated; persistent : persisting, ongoing) play in the materials science an important role in fatigue . They are structures in metals in which deformation is concentrated under external loads .

When dislocations migrate along slip planes to the material surface, they create surface steps there. These steps, about 1000  atomic diameter high, are also called slip lines. They are grouped closely together (approx. 100 atomic diameter) and thereby form sliding bands. These are visible as extrusions and intrusions (shear lips) on the polished surfaces of a material sample. Shear lips, as notches, can lead to premature breakage under vibrating loads .

Depending on the metal and alloy , wall-like or even labyrinth-like structures can be formed in addition to straight lines (PSBs). What all forms have in common is that they have an increased activity of dislocations and that they generate explosions and intrusions when they emerge on the metal surface.

Investigation procedure

In the laboratory, the symmetrical tension - compression test is often used on the model: the clamped material sample is stretched at a constant speed and compressed by the same amount, or moved with a constant stretch or with a constant stress amplitude . The results of the experiment are often transferred to a double logarithmic diagram , the Wöhler diagram .

Using a transmission electron microscope (TEM), the dislocation structure of the PSBs was initially explored. In order to map dislocations, a new observation method has been used in recent years, Electron Channeling Contrast Imaging (ECCI). This method has the advantage that the dislocations lying close to the crystal surface can be detected non-destructively using a scanning electron microscope (SEM).

See also

literature

  • Henning M., Schäfer R .: Anisotropic material data of individual grains in polycrystals, In: Meyer LW: Working group meeting "Material and Simulation" on May 23, 2007 in Erlangen as part of the DFG SPP 1138 "Modeling of Size Influences in Manufacturing Processes" - Lectures. Chemnitz: self-published, ISSN  1860-8698 , 2007
  • H.-J. Christ, H. Mughrabi, C. Wittig-Link: Cyclic deformation behavior, microstructure and fatigue crack initiation of copper polycrystals fatigued in air and in vacuum . In: Basic Mechanisms in Fatigue of Metals. Proceedings of the International Colloquium . 1988, p. 83-92 .
  • Macherauch E. Internship in materials science Vieweg Verlag, Braunschweig, 6th edition (1985) 252–291
  • Munz D., Schwalbe K., Mayr P. Fatigue behavior of metallic materials Vieweg-Verlag, Braunschweig (1971)
  • Materials science and methodology by Prof. Dr. Horst Vehoff, UNI - Saarland, 2004

Web links