Shear strength

The shear strength is the resistance that a solid opposes tangential shear forces . It indicates the maximum shear stress with which a body can be loaded before shearing, i.e. H. the maximum tangential force related to the fracture surface : ${\displaystyle \tau _{\mathrm {aB} }}$ ${\displaystyle S_{\mathrm {0} }}$ ${\displaystyle F_{\mathrm {max} }}$

${\displaystyle \tau _{\mathrm {aB} }={\frac {F_{\mathrm {max} }}{S_{\mathrm {0} }}}}$

Basics

The shear strength depends on the normal force acting and measures the cohesive forces, in contrast to the frictional forces acting on surfaces . The test facilities realize the relationship between normal and shear force in different ways: it can be constant, variable or indefinite.

The shear strength has the unit of tension (force per area) and is usually given in N / mm² or MN / m².

The theory of elasticity is most often used to describe the deformation behavior of technical materials or rocks . The Hooke's law describes the proportional voltage elongation s behavior homogeneous , isotropic , elastic materials.

Materials science

In materials science , the shear strength is an important parameter for the mechanical characterization of materials; it expresses the load capacity of a material on shear.

The shear strength is determined in a standardized measuring method , the shear test . A circular cylindrical test rod is inserted into a U-shaped shear device and loaded perpendicular to the longitudinal axis with a shear punch that fits exactly into the recess until it shears.

Soil mechanics

In soil mechanics , shear strength plays an important role in the discussion of the mechanical properties of soils and rock formations.

The following experimental devices ( shear devices ) are also used to determine the shear strength of rock or soil samples in the laboratory :

• Triaxial (cf. DIN 18137-2;., In contrast to 1- or 2-axial compression tests of the material testing )
• direct shear tests according to DIN 18137-3:
  • Box or frame shear device
  • Circular shear device
• Wing shear device

The shear strength can also be determined or derived in situ (on site), e.g. B. with the following examination procedures:

• Wing shear tests according to DIN 4094-4
• CPT according to DIN 4094-1
• Large devices such as the Phicometer shear device
• Small devices like the shear pressure cylinder

The soil mechanics quantified the shear strength with the failure criterion Mohr / Coulomb that as soil properties , the cohesion (adhesive strength of the mixture particles) and the friction angle , as well as an external influence includes the normal voltage.

The shear strength of fissured rock also influences its compressive strength .

In the field of soil mechanics, a distinction is also made between drained and undrained shear strength for loose rock . With the help of the undrained shear strength, approximate information on consistency and sensitivity can be made.

Construction engineering

In civil engineering , the shear strength is important u. a. in the permissible load-bearing capacity of foundations on floors and structures in rock, in tunnel construction and in the load-bearing capacity of construction materials ( steel , aluminum , plastic ), e.g. B. in welds , screws and rivets .

Recently introduced calculations for the dimensioning of steel fiber concrete are based on the shear strength of Mohr-Coulomb.

See also

• Strength , breaking strength , flow resistance , edge strength
• Tensile strength , splitting strength , flexural strength

Individual evidence

1. ↑ Helmut Prinz, Roland Strauss: Engineering Geology . 5th edition. Spectrum, Heidelberg, ISBN 978-3-8274-2472-3 , p. 73 .
2. ↑ Bernhard Wietek : Stahlfaserbeton ( Memento of the original of September 13, 2011 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. Publisher: Vieweg + Teubner 2nd edition 2010. 

Web links

• Shear strength. Basics of soil physics and measuring devices. Society for Geotechnics GmbH, Vienna