Page 85 - Fundamental Of Design In Mechanical Engineering
P. 85
Example 4
A circular bar of diameter 2.5cm is subjected to an axial tension of 20kN. If
2
the material is elastic with a Young’s Modules E=70GN/m , estimate the
percentage elongation.
Solution:
The cross-section area of the bar is
A= π 0.025 2 = 0.491 10 2
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4
The average tensile stress is then
σ = = 20 103 = 40.7MN/m 2
0.491 10 −3
The longitudinal tensile strain will therefore be
σ
ε = = 40.7 106 = 0.582 x 10 −3
70 109
The percentage elongation will therefor be (ε=δ/L) 85
δ= (0.582 x 10 )100 = 0.058%
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