Mohr's strength theory is based on which of the following facts?
Try it first: pick an option, then read the explanation.
Asked in SSC JE 04/03/2017 (Evening)
Detailed Explanation
Mohr's theory of failure (the word "straight" in the original is a misprint for "strength") draws an envelope tangent to the Mohr circles of stress states at failure. A state is safe if its circle lies inside the envelope.
Why “All options are correct” Is Correct
All three statements are assumptions of the theory: failure is by shear on a slip plane; the strength depends on the normal and shear stresses on that plane; and only the largest circle (σ₁ and σ₃) matters, so the intermediate principal stress has no influence. Hence all options are correct.
Why the Other Options Are Wrong
- A. The material fails essentially by shear: True, but only one of the bases.
- B. The ultimate strength of the material is determined by the stress on the plane of slip: True, but only one of the bases.
- C. The failure criterion is independent of the intermediate principal stress: True, but only one of the bases.
Key Point
Mohr's strength theory: shear failure on a slip plane, governed by σ and τ there, independent of σ₂.
Key Concepts for Students
- Mohr–Coulomb (τ = c + σ tanφ) is its straight-line form used for soils.
- Suits materials with different tensile and compressive strengths.
- Tresca is a special case with a horizontal envelope.
Practice more: this is question 17 in Principal Stress and Principal Planes MCQs – Part 2. Try the whole set and check every answer instantly.