Maximum principal strain theory :
This theory states that “ Yielding in a member subjected to complex/compound stress system commences when maximum principal strain of the system becomes equal to the strain corresponding to the yield point under simple tension test of the same material.”
For a 3 – dimensional state of stress system
For a 2 – dimensional state of stress system
- є1 = maximum principal strain.
- υ = Poisson’s ratio.
- σ1= Major principal stress in x direction.
- σ2 = Minor principal stress in y direction.
- σ3 = Minor principal stress in z direction.
- σyt= Maximum Tensile strength in yielding.
- σyc =Maximum Compressive strength in yielding.
- It computes the failure load based on all 3 values of principal stresses.
De merits :
- This theory gives unsatisfactory results for various materials.
- This theory is not much used for design purposes.
- This is not a very popular theory.