Mohr’s circle – scope of application: Mohr’s circle can be used to find stresses on an oblique plane of a body subjected to which of the following loading combinations?
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ADirect tensile (or compressive) stress in one plane with shear stress
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BDirect stresses in two mutually perpendicular directions
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CDirect stresses in two perpendicular directions with a shear stress
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DAll of the above
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ENone of the above
Answer
Correct Answer: All of the above
Explanation
Introduction / Context:Mohr’s circle is a powerful graphical tool for 2D stress transformation. It provides principal stresses, maximum shear stress, and normal and shear stresses on any oblique plane from a single diagram, unifying different combined-stress scenarios.
Given Data / Assumptions:
- Plane stress condition (sigma_x, sigma_y, tau_xy) acting on a differential element.
- Linear elastic continuum; sign conventions consistent.
- Interest is in stresses on a plane at angle theta from the reference axis.
Concept / Approach:Mohr’s circle plots normal stress on the abscissa and shear stress on the ordinate. For any given 2D state, the center C is at ( (sigma_x + sigma_y)/2, 0 ) and the radius R = sqrt( ((sigma_x − sigma_y)/2)^2 + tau_xy^2 ). Rotating 2 * theta around the circle yields the transformed stresses on a plane at angle theta.
Step-by-Step Solution:
Construct circle with center and radius from the given sigma_x, sigma_y, tau_xy.A pure uniaxial case with shear (option a) maps to a circle offset from zero with nonzero tau.Two perpendicular direct stresses without shear (option b) map to a circle with tau_xy = 0.The most general 2D case (option c) is directly represented and solved.Verification / Alternative check:The analytical transformation equations sigma_theta = (sigma_x + sigma_y)/2 + ((sigma_x − sigma_y)/2) * cos(2theta) + tau_xy * sin(2theta) and tau_theta = −((sigma_x − sigma_y)/2) * sin(2theta) + tau_xy * cos(2theta) yield identical results to the circle construction, confirming its universality in plane stress.
Why Other Options Are Wrong:
- Each individual option (a), (b), or (c) is a subset; the comprehensive answer is that Mohr’s circle handles all of them.
- “None” contradicts standard strength-of-materials practice.
Common Pitfalls:Misinterpreting the 2*theta rotation rule; forgetting sign conventions for shear; or applying plane-stress Mohr’s circle to 3D states without modification.
Final Answer:All of the above