Stress intensity factor

The stress intensity factor (SIF or K factor for short) is a measure of the intensity of the stress field near a crack tip. It is a scalar quantity that depends on the external load as well as on the geometry of the crack and the component. The further crack growth depends on the value of the stress intensity factor . ${\displaystyle K}$

The one stress intensity factor, which is to crack initiation and eventually to violent rupture occurs, the critical stress intensity factor ${\displaystyle K_{\mathrm {C} }}$ . This material characteristic is also referred to as crack or fracture toughness .

Crack opening types

In general, a distinction is made between three types of crack opening (crack opening modes), each of which is assigned a stress intensity factor:

• The index characterizes the crack opening perpendicular to the crack surface ( opening mode ). This crack opening mode has the greatest importance in practice. ${\displaystyle \mathrm {I} }$

The parameter can be used to characterize the complete stress field at the tip of the crack stressed by Modus : ${\displaystyle K_{\mathrm {I} }}$ ${\displaystyle \mathrm {I} }$

${\displaystyle K_{\mathrm {I} }=\sigma \cdot {\sqrt {\pi \cdot a}}\cdot f.}$

Describes therein

• ${\displaystyle \sigma }$the stress in the component cross-section without cracks (nominal stress)
• a is the crack length
• f or Y is a correction factor that depends on the crack length, the component geometry and the load situation.

For that is unit or used. ${\displaystyle K_{\mathrm {I} }}$ ${\displaystyle {\frac {\mathrm {N} }{\sqrt {\mathrm {mm} ^{3}}}}}$ ${\displaystyle \mathrm {MPa} \cdot {\sqrt {\mathrm {m} }}}$

• The opening types and describe longitudinal ( sliding mode ) and transverse shear ( tearing mode ). ${\displaystyle \mathrm {II} }$ ${\displaystyle \mathrm {III} }$

literature

• Hans Albert Richard, Manuela Sander: Recognize fatigue cracks, assess reliably, avoid. Vieweg + Teubner Verlag, Wiesbaden 2009, ISBN 978-3-8348-0292-7 .
• Hans-Jürgen Bargel, Hermann Hilbrans, Günter Schulze, Karl-Heinz Hübner, Oswald Krüger: Materials science. 9th edited edition, Springer Verlag, Berlin / Heidelberg 2005, ISBN 978-3-540-29250-0 .
• H.-P. Rossmanith (ed.): Fundamentals of fracture mechanics. Springer Verlag, Vienna / New York 1982, ISBN 978-3-7091-8648-0 .

Web links

• Fundamentals and applications of fracture mechanics, University of Magdeburg
• Fundamentals of fracture mechanics, University of Siegen
• Fracture mechanical characterization of aviation alloys under realistic loads, RWTH Aachen
• Plasticity and fracture mechanics, University of Kiel
• Microstructural aspects of crack initiation and propagation in metallic materials
• Load deformation behavior and crack formation on panes, ETH Zurich

Individual evidence

1. ^ HA Richard: cause of damage. Uni Magdeburg, 1990, accessed in 2020 .