The angle made by the resultant stress with the normal of the oblique plane is known as obliquity (φ) and is expressed as :
- Atan φ = Shear Stress / Normal StressCorrect
- Bcos φ = Shear Stress / Normal Stress
- Ctan φ = Normal Stress / Tangential Stress
- Dcos φ = Normal Stress / Tangential Stress
Solution
Concept
Obliquity
Formula
tan φ = τ / σn
Step-by-step solution
1. Resultant stress has normal component σn and tangential component τ. 2. The angle φ between the resultant and the normal satisfies tan φ = τ / σn.
Explanation
Obliquity is the inclination of the resultant stress with the normal to the plane. The tangent of the angle is the ratio of shear to normal stress.
Why the other options are wrong
Cosine relations and the inverted ratio do not describe the angle between the resultant and the normal.
Shortcut
tan φ = shear ÷ normal.
Common mistake
Using sine or cosine of the angle.
Correct answer: A) tan φ = Shear Stress / Normal Stress