Shear strength
The shear strength is the resistance which opposes to a solid tangential shear forces. It is the maximum shear stress to which a body can be loaded in front of the shearing, i.e., related to the tangential fracture surface.
Basics
The shear strength is a function of the acting axial force and measures the cohesive forces, in contrast to the pressure acting on surfaces of friction forces. The shear strength is mostly in N / mm ² or MN / m² specified ( force per area ), so the unit has a voltage.
The known test equipment to realize the ratio of normal to shear force differently. It may be constant, variable or undefined. To describe the deformation behavior of techn. Materials or rocks is most commonly used elasticity theory. Hooke's law describes the proportional stress-strain behavior of homogeneous, isotropic, elastic materials.
Materials Science
In materials science, the shear strength is an important parameter for the mechanical characterization of materials, it pushes the load capacity of the material to shear off. The shear strength is determined in a standardized measurement method, the appropriately named shear test. Here, a circular cylindrical test rod is inserted into a U-shaped cutter and loaded with a precisely fitting into the recess shearing die perpendicular to longitudinal axis until it shears off.
The shear strength is calculated from the following relationship between the maximum force and the shear area:
Soil Mechanics
In Soil Mechanics shear strength plays an important role in the discussion of the mechanical properties of the soil and rock formations. To determine the shear strength of rock or soil samples in the laboratory using the following test equipment:
- Triaxial ( see DIN 18137-2, as opposed to 1 - or 2- axial compression tests of materials testing )
- Direct shear tests in accordance with DIN 18137-3: Box or direct shear device
- Circular ring shear tester
The shear strength can be determined or inferred in situ (on site ), eg with the following test methods:
- Field vane tests according to DIN 4094-4
- CPTs according to DIN 4094-1
- Large appliances like the Phicometer shear tester
The soil mechanics quantifies the shear strength with the failure criterion Mohr / Coulomb, which contains as soil parameters, cohesion (fracture strength of the blend particles ) and the friction angle as well as external influence the normal stress.
The shear strength of jointed rock also affects its compressive strength.
Structural Engineering
Of importance is the shear strength, inter alia, when the permitted capacity of foundations on soils and structures in rock, tunneling and in the capacity of construction materials (steel, aluminum, plastic), eg welds, screws and rivets.
Also recently introduced calculations for the design of steel fiber reinforced concrete are based on the shear strength of Mohr -Coulomb.