Which of the following statements is true?
Try it first: pick an option, then read the explanation.
Correct answer: A. Shear stress on principal planes is zero
Asked in SSC JE 27/01/2018 (Evening)
Detailed Explanation
At any point of a stressed body there are three mutually perpendicular planes on which no shear stress acts. These are the principal planes, and the normal stresses on them are the principal stresses.
Why “Shear stress on principal planes is zero” Is Correct
By definition, the shear stress on principal planes is zero. The maximum shear stress occurs on planes at 45° to them.
Why the Other Options Are Wrong
- B. Shear stress on principal planes is maximum: Maximum shear acts on planes at 45° to the principal planes.
- C. Shear stress on principal planes is minimum: Shear on principal planes is exactly zero, which is more specific than 'minimum'.
- D. None of these: Option (a) is true.
Key Point
Principal planes: τ = 0; σ = principal stress (max/min).
Key Concepts for Students
- tan 2θp = 2τxy/(σx − σy).
- Principal planes are mutually perpendicular.
- Normal stress on max-shear planes = (σ₁ + σ₂)/2.
Practice more: this is question 6 in Principal Stress and Principal Planes MCQs – Part 1. Try the whole set and check every answer instantly.