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UPSC Civil Service Exam Questions - Engineering

Q1:

A mild steel bar of square cross-section 40 mm x 40 mm is 400 mm long. It is subjected to a longitudinal tensile stress of 440 N/mm2 and lateral compressive stress is 200 N/mm2 in perpendicular directions. E = 2 x 10-5 N/mm2, μ = 0.3. What is the approximate elongation of tht bar in the longitudinal direction ?

A 0.44 mm

B 088 mm

C 0.22 mm

D 1 mm

ANS:D - 1 mm

longitudinal tensile stress, fx = 440 MPa. Lateral Stress, fy = fz = -200 MPa (negative because compressive).

Longitudinal strain, ex = (fx/E)-(m*fy/E)-(m*fz/E) = (440/2*10^5)+(2*0.3*200/2*10^5) =0.0028.

Elongation= 0.0028*400 = 1.12 mm.