Sohncke's Law


Quick
The rule which states that cleavage results when the critical normal fracture stress equals (F/A)cos 2ψ is known as Sohncke's law.


Equations
(Eq1)    when   σc =  
F
A
cos 2ψ    cleavage results
Sohncke's Law


Nomenclature
Ftensile force
ψangle defining the normal to the slip plane
Across-sectional area of cylindrical specimen
σccritical normal fracture stress


Details

If a material is so constituted that the normal stress σn reaches a magnitude large enough to cause cleavage of the crystal before the resolved shearing stress reaches critical value, then the crystal will be cleaved into two parts. The magnitude of σn that results in cleavage fracture is called the critical normal fracture stress and has been shown to be a material constant similar to the critical resolved shearing stress. The rule which states that cleavage results when the critical normal fracture stress equals (F/A)cos2ψ is known as Sohncke's law. As in the case of deformation processes, it is found that the most common cleavage planes are those of high atomic density.