Critical Resolved Shear Stress (CRSS)

Critical resolved shear stress is the component of SHEAR STRESS, resolved in the direction of slip, necessary to initiate slip in a grain. It is a constant for a given CRYSTAL.Tests have been conducted on single crystals of metals to measure the shear stress required to initiate plastic deformation, or cause atomic planes to slip. Since this is a threshold value, it is referred to as critical; and since it is a component of the applied force or stress, it is said to be resolved; that is, the critical resolved shear stress.

Load

Area

P cosA

cos

, since =P

A tensile stress

=cos cos , and =2

is max when cos cos is max(45 )

max .707 .707 y

2 y yield strength

max y

2 critical observed critical calculated

Reason : Slip is aided by dislocation movement

FCC crystal with 12 slip systems

Resolved shear stress is given by

ζ = σ cos Φ cos λ

where σ is the magnitude of the applied tensile stress,

Φ is the angle between the slip plane direction and the direction of the applied force and

λ is the angle between the normal of the slip plane and the direction of the applied force.

• Critical Resolved Shear Stress (CRSS):

• - minimum stress to initiate slip, or stress required to initiate slip on a given slip plane and in a given direction

[most favorably oriented slip system].