A hollow alloy tube 5m withexternal and internal diametersequal to 40m...
Given data:
Length of the alloy tube (L) = 5 m
External diameter (D) = 40 mm
Internal diameter (d) = 25 mm
Extension under load (ΔL) = 6.4 mm
Tensile load (P) = 60 kN
Factor of safety (FOS) = 4
To find: Safe compressive load for the tube
Formula used:
Stress in the tube under tensile load, σ = P/A
where A is the cross-sectional area of the tube.
Area of the hollow tube, A = π/4[(D^2 - d^2)]
Strain in the tube, ε = ΔL/L
Modulus of elasticity, E = σ/ε
The compressive stress can be found using Euler's formula:
Pcr = (π^2EI)/(KL)^2
where Pcr is the critical buckling load, E is the modulus of elasticity, I is the moment of inertia of the tube, K is the effective length factor, and L is the length of the tube.
Calculation:
External radius, r = D/2 = 40/2 = 20 mm = 0.02 m
Internal radius, r1 = d/2 = 25/2 = 12.5 mm = 0.0125 m
Cross-sectional area, A = π/4[(D^2 - d^2)] = π/4[(0.04^2 - 0.025^2)] = 0.00123 m^2
Stress, σ = P/A = 60 × 10^3 / 0.00123 = 48780.5 Pa
Strain, ε = ΔL/L = 6.4 × 10^-3 / 5 = 0.00128
Modulus of elasticity, E = σ/ε = 48780.5 / 0.00128 = 38126.6 MPa
Moment of inertia of the tube, I = π/64[(D^4 - d^4)] = π/64[(0.04^4 - 0.025^4)] = 3.416 × 10^-8 m^4
Effective length factor for both ends pinned, K = 1.0
Critical buckling load, Pcr = (π^2EI)/(KL)^2 = (π^2 × 38126.6 × 3.416 × 10^-8)/(1.0 × 5)^2 = 642.5 N
Safe compressive load, Psafe = Pcr/FOS = 642.5 / 4 = 160.6 N ≈ 161 N
Therefore, the safe compressive load for the tube is 161 N (approx). Hence, option (b) is the correct answer.
A hollow alloy tube 5m withexternal and internal diametersequal to 40m...