Transcript Critical Resolved Shear Stress (CRSS)

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.
FCC crystal with 12 slip systems
Load

Area
P cos 
P

, since  =  t ensile st ress
 A 
A




cos  
 = cos cos  , and  =


2
 is max when coscos  is max(45)
 max   .707.707 
 max 
y
2
y
2
 y  yield strengt h
 critic alobserve d    critic alcalculated
Reason : Slip is aided by dislocation movement
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].