Simple Stress and Strain MCQ with answer and solution

Concept

Superposition of combined axial tension and bending stresses

Formula

σ_max = σ_axial + σ_bending

Step-by-step solution

1. When a prismatic bar carries simultaneous axial tension and bending, total normal stress is obtained by superposition. 2. Given axial tensile stress σ_axial = 50 MPa (uniform tension across section). 3. Given maximum bending stress σ_bending = 80 MPa (tensile at extreme tension fiber, compressive at opposite fiber). 4. The maximum normal stress occurs at the extreme tension fiber: σ_max = σ_axial + σ_bending = 50 + 80 = 130 MPa. Answer: D

Explanation

When a structural member is subjected to simultaneous axial tension and bending, the maximum normal stress occurs at the extreme tensile fiber where axial tensile stress and bending tensile stress act in the same direction: σ_max = σ_axial + σ_bending = 50 MPa + 80 MPa = 130 MPa.

Why the other options are wrong

A) 30 MPa is the minimum net stress at the extreme compressive fiber (80 - 50). B) 50 MPa is axial stress alone. C) 80 MPa is bending stress alone.

Shortcut

Combined stress = Axial tension + Bending stress = 50 + 80 = 130 MPa.

Common mistake

Subtracting bending stress from axial tension (80 - 50 = 30 MPa), which gives minimum stress instead of maximum.