- #1
DevonZA
- 181
- 6
Homework Statement
Homework Equations
Stress = force/ cross sectional area
elongation = force x length / modulus of elasticity x cross sectional area
The Attempt at a Solution
The given solution is 0.149mm
I assumed that the bar needs to be solved in two sections because of the hole of diameter 20mm in the first 70mm of the bar. I will call this part A and the 90mm section part B.
Part A:
Stress = force/ cross sectional area
Force = stress x cross sectional area
= 125x10^6 x pi/4(.03-.02)^2
= 9.8kN
elongation = force x length / modulus of elasticity x cross sectional area
= 9.8x10^3 x 0.07 / 100x10^9 x pi/4(.03-.02)^2
= 8.73x10^-5mm
Part B:
Force = stress x cross sectional area
= 125x10^6 x pi/4(.03)^2
= 88.4kN
elongation = force x length / modulus of elasticity x cross sectional area
= 88.4x10^3 x 0.09 / 100x10^9 x pi/4(.03)^2
= 1.126x10^-4mm
now if I add the elongation from part A & B together I do not get 0.149mm.
Please show me where I am going wrong.